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1.  Mechanistic population modeling of diabetes disease progression in Goto-Kakizaki rat muscle 
Pyruvate dehydrogenase kinase 4 (PDK4) is a lipid status responsive gene involved in muscle fuel selection. Evidence is mounting in support of the therapeutic potential of PDK4 inhibitors to treat diabetes. Factors that regulate PDK4 mRNA expression include plasma corticosterone, insulin and free fatty acids. Our objective was to determine the impact of those plasma factors on PDK4 mRNA and to develop and validate a population mathematical model to differentiate aging, diet and disease effects on muscle PDK4 expression. The Goto-Kakizaki (GK) rat, a polygenic non-obese model of type 2 diabetes, was used as the diabetic animal model. We examined muscle PDK4 mRNA expression by real-time QRTPCR. Groups of GK rats along with controls fed with either a normal or high fat diet were sacrificed at 4, 8, 12, 16, and 20 weeks of age. Plasma corticosterone, insulin and free fatty acid were measured. The proposed mechanism-based model successfully described the age, disease and diet effects and the relative contribution of these plasma regulators on PDK4 mRNA expression. Muscle growth reduced the PDK4 mRNA production rate by 14% per gram increase. High fat diet increased the initial production rate constant in GK rats by 2.19-fold. The model indicated that corticosterone had a moderate effect and PDK4 was more sensitive to free fatty acid than insulin fluxes, which was in good agreement with the literature data.
doi:10.1002/bdd.738
PMCID: PMC3080028  PMID: 21162119
population model; type 2 diabetes; disease progression; PDK4; Goto-Kakizaki rats
2.  Adipose Tissue Deficiency and Chronic Inflammation in Diabetic Goto-Kakizaki Rats 
PLoS ONE  2011;6(2):e17386.
Type 2 diabetes (T2DM) is a heterogeneous group of diseases that is progressive and involves multiple tissues. Goto-Kakizaki (GK) rats are a polygenic model with elevated blood glucose, peripheral insulin resistance, a non-obese phenotype, and exhibit many degenerative changes observed in human T2DM. As part of a systems analysis of disease progression in this animal model, this study characterized the contribution of adipose tissue to pathophysiology of the disease. We sacrificed subgroups of GK rats and appropriate controls at 4, 8, 12, 16 and 20 weeks of age and carried out a gene array analysis of white adipose tissue. We expanded our physiological analysis of the animals that accompanied our initial gene array study on the livers from these animals. The expanded analysis included adipose tissue weights, HbA1c, additional hormonal profiles, lipid profiles, differential blood cell counts, and food consumption. HbA1c progressively increased in the GK animals. Altered corticosterone, leptin, and adiponectin profiles were also documented in GK animals. Gene array analysis identified 412 genes that were differentially expressed in adipose tissue of GKs relative to controls. The GK animals exhibited an age-specific failure to accumulate body fat despite their relatively higher calorie consumption which was well supported by the altered expression of genes involved in adipogenesis and lipogenesis in the white adipose tissue of these animals, including Fasn, Acly, Kklf9, and Stat3. Systemic inflammation was reflected by chronically elevated white blood cell counts. Furthermore, chronic inflammation in adipose tissue was evident from the differential expression of genes involved in inflammatory responses and activation of natural immunity, including two interferon regulated genes, Ifit and Iipg, as well as MHC class II genes. This study demonstrates an age specific failure to accumulate adipose tissue in the GK rat and the presence of chronic inflammation in adipose tissue from these animals.
doi:10.1371/journal.pone.0017386
PMCID: PMC3045458  PMID: 21364767
3.  Effects of High Fat Feeding on Liver Gene Expression in Diabetic Goto-Kakizaki Rats 
Effects of high fat diet (HFD) on obesity and, subsequently, on diabetes are highly variable and modulated by genetics in both humans and rodents. In this report, we characterized the response of Goto-Kakizaki (GK) rats, a spontaneous polygenic model for lean diabetes and healthy Wistar-Kyoto (WKY) controls, to high fat feeding from weaning to 20 weeks of age. Animals fed either normal diet or HFD were sacrificed at 4, 8, 12, 16 and 20 weeks of age and a wide array of physiological measurements were made along with gene expression profiling using Affymetrix gene array chips. Mining of the microarray data identified differentially regulated genes (involved in inflammation, metabolism, transcription regulation, and signaling) in diabetic animals, as well as the response of both strains to HFD. Functional annotation suggested that HFD increased inflammatory differences between the two strains. Chronic inflammation driven by heightened innate immune response was identified to be present in GK animals regardless of diet. In addition, compensatory mechanisms by which WKY animals on HFD resisted the development of diabetes were identified, thus illustrating the complexity of diabetes disease progression.
doi:10.4137/GRSB.S10371
PMCID: PMC3516129  PMID: 23236253
diabetes; high fat diet; gene expression; microarray
4.  MicroRNA-125a is over-expressed in insulin target tissues in a spontaneous rat model of Type 2 Diabetes 
BMC Medical Genomics  2009;2:54.
Background
MicroRNAs (miRNAs) are non-coding RNA molecules involved in post-transcriptional control of gene expression of a wide number of genes, including those involved in glucose homeostasis. Type 2 diabetes (T2D) is characterized by hyperglycaemia and defects in insulin secretion and action at target tissues. We sought to establish differences in global miRNA expression in two insulin-target tissues from inbred rats of spontaneously diabetic and normoglycaemic strains.
Methods
We used a miRNA microarray platform to measure global miRNA expression in two insulin-target tissues: liver and adipose tissue from inbred rats of spontaneously diabetic (Goto-Kakizaki [GK]) and normoglycaemic (Brown-Norway [BN]) strains which are extensively used in genetic studies of T2D. MiRNA data were integrated with gene expression data from the same rats to investigate how differentially expressed miRNAs affect the expression of predicted target gene transcripts.
Results
The expression of 170 miRNAs was measured in liver and adipose tissue of GK and BN rats. Based on a p-value for differential expression between GK and BN, the most significant change in expression was observed for miR-125a in liver (FC = 5.61, P = 0.001, Padjusted = 0.10); this overexpression was validated using quantitative RT-PCR (FC = 13.15, P = 0.0005). MiR-125a also showed over-expression in the GK vs. BN analysis within adipose tissue (FC = 1.97, P = 0.078, Padjusted = 0.99), as did the previously reported miR-29a (FC = 1.51, P = 0.05, Padjusted = 0.99). In-silico tools assessing the biological role of predicted miR-125a target genes suggest an over-representation of genes involved in the MAPK signaling pathway. Gene expression analysis identified 1308 genes with significantly different expression between GK and BN rats (Padjusted < 0.05): 233 in liver and 1075 in adipose tissue. Pathways related to glucose and lipid metabolism were significantly over-represented among these genes. Enrichment analysis suggested that differentially expressed genes in GK compared to BN included more predicted miR-125a target genes than would be expected by chance in adipose tissue (FDR = 0.006 for up-regulated genes; FDR = 0.036 for down-regulated genes) but not in liver (FDR = 0.074 for up-regulated genes; FDR = 0.248 for down-regulated genes).
Conclusion
MiR-125a is over-expressed in liver in hyperglycaemic GK rats relative to normoglycaemic BN rats, and our array data also suggest miR-125a is over-expressed in adipose tissue. We demonstrate the use of in-silico tools to provide the basis for further investigation of the potential role of miR-125a in T2D. In particular, the enrichment of predicted miR-125a target genes among differentially expressed genes has identified likely target genes and indicates that integrating global miRNA and mRNA expression data may give further insights into miRNA-mediated regulation of gene expression.
doi:10.1186/1755-8794-2-54
PMCID: PMC2754496  PMID: 19689793
5.  Global microRNA expression profiles in insulin target tissues in a spontaneous rat model of type 2 diabetes 
Diabetologia  2010;53(6):1099-1109.
Aims/hypothesis
MicroRNAs regulate a broad range of biological mechanisms. To investigate the relationship between microRNA expression and type 2 diabetes, we compared global microRNA expression in insulin target tissues from three inbred rat strains that differ in diabetes susceptibility.
Methods
Using microarrays, we measured the expression of 283 microRNAs in adipose, liver and muscle tissue from hyperglycaemic (Goto–Kakizaki), intermediate glycaemic (Wistar Kyoto) and normoglycaemic (Brown Norway) rats (n = 5 for each strain). Expression was compared across strains and validated using quantitative RT-PCR. Furthermore, microRNA expression variation in adipose tissue was investigated in 3T3-L1 adipocytes exposed to hyperglycaemic conditions.
Results
We found 29 significantly differentiated microRNAs (padjusted < 0.05): nine in adipose tissue, 18 in liver and two in muscle. Of these, five microRNAs had expression patterns that correlated with the strain-specific glycaemic phenotype. MiR-222 (padjusted = 0.0005) and miR-27a (padjusted = 0.006) were upregulated in adipose tissue; miR-195 (padjusted = 0.006) and miR-103 (padjusted = 0.04) were upregulated in liver; and miR-10b (padjusted = 0.004) was downregulated in muscle. Exposure of 3T3-L1 adipocytes to increased glucose concentration upregulated the expression of miR-222 (p = 0.008), miR-27a (p = 0.02) and the previously reported miR-29a (p = 0.02). Predicted target genes of these differentially expressed microRNAs are involved in pathways relevant to type 2 diabetes.
Conclusion
The expression patterns of miR-222, miR-27a, miR-195, miR-103 and miR-10b varied with hyperglycaemia, suggesting a role for these microRNAs in the pathophysiology of type 2 diabetes, as modelled by the Gyoto–Kakizaki rat. We observed similar patterns of expression of miR-222, miR-27a and miR-29a in adipocytes as a response to increased glucose levels, which supports our hypothesis that altered expression of microRNAs accompanies primary events related to the pathogenesis of type 2 diabetes.
Electronic supplementary material
The online version of this article (doi:10.1007/s00125-010-1667-2) contains supplementary material, which is available to authorised users.
doi:10.1007/s00125-010-1667-2
PMCID: PMC2860560  PMID: 20198361
Expression; MicroRNA; Murine diabetes model
6.  Pathophysiological, Genetic and Gene Expression Features of a Novel Rodent Model of the Cardio-Metabolic Syndrome 
PLoS ONE  2008;3(8):e2962.
Background
Complex etiology and pathogenesis of pathophysiological components of the cardio-metabolic syndrome have been demonstrated in humans and animal models.
Methodology/Principal Findings
We have generated extensive physiological, genetic and genome-wide gene expression profiles in a congenic strain of the spontaneously diabetic Goto-Kakizaki (GK) rat containing a large region (110 cM, 170 Mb) of rat chromosome 1 (RNO1), which covers diabetes and obesity quantitative trait loci (QTL), introgressed onto the genetic background of the normoglycaemic Brown Norway (BN) strain. This novel disease model, which by the length of the congenic region closely mirrors the situation of a chromosome substitution strain, exhibits a wide range of abnormalities directly relevant to components of the cardio-metabolic syndrome and diabetes complications, including hyperglycaemia, hyperinsulinaemia, enhanced insulin secretion both in vivo and in vitro, insulin resistance, hypertriglyceridemia and altered pancreatic and renal histological structures. Gene transcription data in kidney, liver, skeletal muscle and white adipose tissue indicate that a disproportionately high number (43–83%) of genes differentially expressed between congenic and BN rats map to the GK genomic interval targeted in the congenic strain, which represents less than 5% of the total length of the rat genome. Genotype analysis of single nucleotide polymorphisms (SNPs) in strains genetically related to the GK highlights clusters of conserved and strain-specific variants in RNO1 that can assist the identification of naturally occurring variants isolated in diabetic and hypertensive strains when different phenotype selection procedures were applied.
Conclusions
Our results emphasize the importance of rat congenic models for defining the impact of genetic variants in well-characterised QTL regions on in vivo pathophysiological features and cis-/trans- regulation of gene expression. The congenic strain reported here provides a novel and sustainable model for investigating the pathogenesis and genetic basis of risks factors for the cardio-metabolic syndrome.
doi:10.1371/journal.pone.0002962
PMCID: PMC2500170  PMID: 18698428
7.  Regressed three-dimensional capillary network and inhibited angiogenic factors in the soleus muscle of non-obese rats with type 2 diabetes 
Based on findings obtained using two-dimensional capillary analyses on tissue cross-sections, diabetes has been shown to be associated with a high risk for microangiopathy and capillary regression in skeletal muscles. We visualized the three-dimensional architecture of the capillary networks in the soleus muscle of non-obese Goto-Kakizaki (GK) rats with type 2 diabetes and compared them with those of control Wistar rats to provide novel information, e.g., capillary volume, on the capillary networks. In addition, we examined pro- and anti-angiogenic gene expression levels in the soleus muscle of GK rats using TaqMan probe-based real-time PCR. As expected, plasma glucose levels were higher and insulin levels lower in GK than control rats. The three-dimensional architecture of the capillary networks was regressed and capillary volume was smaller in the soleus muscle of GK compared to control rats. The mRNA expression levels of the pro-angiogenic factors HIF-1α, KDR, Flt-1, ANG-1, and Tie-2 were lower, whereas the level of the anti-angiogenic factor TSP-1 was higher in GK than control rats. These data suggest that a decrease in pro-angiogenic and increase in anti-angiogenic factors may play an important role in type 2 diabetes-induced muscle circulatory complications.
doi:10.1186/1743-7075-8-77
PMCID: PMC3229446  PMID: 22050781
angiogenic factors; capillary network; skeletal muscle; three-dimensional imaging; type 2 diabetes
8.  Differential Glucose-Regulation of MicroRNAs in Pancreatic Islets of Non-Obese Type 2 Diabetes Model Goto-Kakizaki Rat 
PLoS ONE  2011;6(4):e18613.
Background
The Goto-Kakizaki (GK) rat is a well-studied non-obese spontaneous type 2 diabetes (T2D) animal model characterized by impaired glucose-stimulated insulin secretion (GSIS) in the pancreatic beta cells. MicroRNAs (miRNAs) are short regulatory RNAs involved in many fundamental biological processes. We aim to identify miRNAs that are differentially-expressed in the pancreatic islets of the GK rats and investigate both their short- and long term glucose-dependence during glucose-stimulatory conditions.
Methodology/Principal Findings
Global profiling of 348 miRNAs in the islets of GK rats and Wistar controls (females, 60 days, N = 6 for both sets) using locked nucleic acid (LNA)-based microarrays allowed for the clear separation of the two groups. Significant analysis of microarrays (SAM) identified 30 differentially-expressed miRNAs, 24 of which are predominantly upregulated in the GK rat islets. Monitoring of qPCR-validated miRNAs during GSIS experiments on isolated islets showed disparate expression trajectories between GK and controls indicating distinct short- and long-term glucose dependence. We specifically found expression of rno-miR-130a, rno-miR-132, rno-miR-212 and rno-miR-335 to be regulated by hyperglycaemia. The putative targets of upregulated miRNAs in the GK, filtered with glucose-regulated mRNAs, were found to be enriched for insulin-secretion genes known to be downregulated in T2D patients. Finally, the binding of rno-miR-335 to a fragment of the 3′UTR of one of known down-regulated exocytotic genes in GK islets, Stxbp1 was shown by luciferase assay.
Conclusions/Significance
The perturbed miRNA network found in the GK rat islets is indicative of a system-wide impairment in the regulation of genes important for the normal functions of pancreatic islets, particularly in processes involving insulin secretion during glucose stimulatory conditions. Our findings suggest that the reduced insulin secretion observed in the GK rat may be partly due to upregulated miRNA expression leading to decreased production of key proteins of the insulin exocytotic machinery.
doi:10.1371/journal.pone.0018613
PMCID: PMC3072418  PMID: 21490936
9.  Effect of a Low-Protein Diet Supplemented with Ketoacids on Skeletal Muscle Atrophy and Autophagy in Rats with Type 2 Diabetic Nephropathy 
PLoS ONE  2013;8(11):e81464.
A low-protein diet supplemented with ketoacids maintains nutritional status in patients with diabetic nephropathy. The activation of autophagy has been shown in the skeletal muscle of diabetic and uremic rats. This study aimed to determine whether a low-protein diet supplemented with ketoacids improves muscle atrophy and decreases the increased autophagy observed in rats with type 2 diabetic nephropathy. In this study, 24-week-old Goto-Kakizaki male rats were randomly divided into groups that received either a normal protein diet (NPD group), a low-protein diet (LPD group) or a low-protein diet supplemented with ketoacids (LPD+KA group) for 24 weeks. Age- and weight-matched Wistar rats served as control animals and received a normal protein diet (control group). We found that protein restriction attenuated proteinuria and decreased blood urea nitrogen and serum creatinine levels. Compared with the NPD and LPD groups, the LPD+KA group showed a delay in body weight loss, an attenuation in soleus muscle mass loss and a decrease of the mean cross-sectional area of soleus muscle fibers. The mRNA and protein expression of autophagy-related genes, such as Beclin-1, LC3B, Bnip3, p62 and Cathepsin L, were increased in the soleus muscle of GK rats fed with NPD compared to Wistar rats. Importantly, LPD resulted in a slight reduction in the expression of autophagy-related genes; however, these differences were not statistically significant. In addition, LPD+KA abolished the upregulation of autophagy-related gene expression. Furthermore, the activation of autophagy in the NPD and LPD groups was confirmed by the appearance of autophagosomes or autolysosomes using electron microscopy, when compared with the Control and LPD+KA groups. Our results showed that LPD+KA abolished the activation of autophagy in skeletal muscle and decreased muscle loss in rats with type 2 diabetic nephropathy.
doi:10.1371/journal.pone.0081464
PMCID: PMC3841136  PMID: 24303049
10.  Genomic and Metabolic Disposition of Non-Obese Type 2 Diabetic Rats to Increased Myocardial Fatty Acid Metabolism 
PLoS ONE  2013;8(10):e78477.
Lipotoxicity of the heart has been implicated as a leading cause of morbidity in Type 2 Diabetes Mellitus (T2DM). While numerous reports have demonstrated increased myocardial fatty acid (FA) utilization in obese T2DM animal models, this diabetic phenotype has yet to be demonstrated in non-obese animal models of T2DM. Therefore, the present study investigates functional, metabolic, and genomic differences in myocardial FA metabolism in non-obese type 2 diabetic rats. The study utilized Goto-Kakizaki (GK) rats at the age of 24 weeks. Each rat was imaged with small animal positron emission tomography (PET) to estimate myocardial blood flow (MBF) and myocardial FA metabolism. Echocardiograms (ECHOs) were performed to assess cardiac function. Levels of triglycerides (TG) and non-esterified fatty acids (NEFA) were measured in both plasma and cardiac tissues. Finally, expression profiles for 168 genes that have been implicated in diabetes and FA metabolism were measured using quantitative PCR (qPCR) arrays. GK rats exhibited increased NEFA and TG in both plasma and cardiac tissue. Quantitative PET imaging suggests that GK rats have increased FA metabolism. ECHO data indicates that GK rats have a significant increase in left ventricle mass index (LVMI) and decrease in peak early diastolic mitral annular velocity (E’) compared to Wistar rats, suggesting structural remodeling and impaired diastolic function. Of the 84 genes in each the diabetes and FA metabolism arrays, 17 genes in the diabetes array and 41 genes in the FA metabolism array were significantly up-regulated in GK rats. Our data suggest that GK rats’ exhibit increased genomic disposition to FA and TG metabolism independent of obesity.
doi:10.1371/journal.pone.0078477
PMCID: PMC3804536  PMID: 24205240
11.  Postprandial hypoglycemic effect of mulberry leaf in Goto-Kakizaki rats and counterpart control Wistar rats 
Nutrition Research and Practice  2009;3(4):272-278.
Postprandial hypoglycemic effect of mulberry leaf (Morus alba L.) was compared in two animal models: Goto-Kakizaki (GK) rats, a spontaneous non-obese animal model for type II diabetes, and their counterpart control Wistar rats. First, the effect of a single oral administration of mulberry leaf aqueous extract (MLE) on postprandial glucose responses was determined using maltose or glucose as substrate. With maltose-loading, MLE reduced peak responses of blood glucose significantly in both GK and Wistar rats (P < 0.05), supporting the inhibition of α-glucosidase by MLE in the small intestine. With glucose-loading, MLE also significantly reduced blood glucose concentrations, measured at 30 min, in both animal models (P < 0.01), proposing the inhibition of glucose transport by MLE. Next, dried mulberry leaf powder (MLP) was administered for 8 weeks by inclusion in the diet. By MLP administration, fasting blood glucose was significantly reduced at weeks 4 and 5 (P < 0.05), but then returned to values that were similar to those of the control at the end of experimental period in GK rats. Insulin, HOMA-IR, C-reactive protein, and triglycerides tended to be decreased by MLP treatment in GK rats. All other biochemical parameters were not changed by MLP administration in GK rats. Collectively, these findings support that MLE has significant postprandial hypoglycemic effect in both non-obese diabetic and healthy animals, which may be beneficial as food supplement to manage postprandial blood glucose. Inhibitions of glucose transport as well as α-glucosidase in the small intestine were suggested as possible mechanisms related with the postprandial hypoglycemic effect of MLE.
doi:10.4162/nrp.2009.3.4.272
PMCID: PMC2809233  PMID: 20098579
Aqueous mulberry leaf extract; Goto-Kakizaki rats; postprandial hypoglycemic effect
12.  Overexpression of Insulin Degrading Enzyme could Greatly Contribute to Insulin Down-regulation Induced by Short-Term Swimming Exercise 
Laboratory Animal Research  2011;27(1):29-36.
Exercise training is highly correlated with the reduced glucose-stimulated insulin secretion (GSIS), although it enhanced insulin sensitivity, glucose uptake and glucose transporter expression to reduce severity of diabetic symptoms. This study investigated the impact of short-term swimming exercise on insulin regulation in the Goto-Kakizaki (GK) rat as a non-obese model of non-insulin-dependent diabetes mellitus. Wistar (W/S) and GK rats were trained 2 hours daily with the swimming exercise for 4 weeks, and then the changes in the metabolism of insulin and glucose were assessed. Body weight was markedly decreased in the exercised GK rats compare to their non-exercised counterpart, while W/S rats did not show any exercise-related changes. Glucose concentration was not changed by exercise, although impaired glucose tolerance was improved in GK rats 120 min after glucose injection. However, insulin concentration was decreased by swimming exercise as in the decrease of GSIS after running exercise. To identify the other cause for exercise-induced insulin down-regulation, the changes in the levels of key factors involved in insulin production (C-peptide) and clearance (insulin-degrading enzyme; IDE) were measured in W/S and GK rats. The C-peptide level was maintained while IDE expression increased markedly. Therefore, these results showed that insulin down-regulation induced by short-term swimming exercise likely attributes to enhanced insulin clearance via IDE over-expression than by altered insulin production.
doi:10.5625/lar.2011.27.1.29
PMCID: PMC3145980  PMID: 21826157
Exercise; insulin; glucose; insulin-degrading enzyme; C-peptide
13.  Transmembrane Emp24 Protein Transport Domain 6 is Selectively Expressed in Pancreatic Islets and Implicated in Insulin Secretion and Diabetes 
Pancreas  2012;41(1):10.1097/MPA.0b013e318223c7e4.
Objectives
The objective of the study was to identify pancreatic islet-selective gene(s) that may play a functional role in islet biology and diabetes development.
Methods
Through bioinformatics, we identified and cloned a pancreas-enriched complementary DNA encoding transmembrane emp24 protein transport domain 6 (TMED6) and examined its mRNA and protein expression in tissues and islet cell lines by Northern analysis and immunofluorescence histochemistry. We also studied die role of TMED6 in insulin secretion using a knockdown approach and its gene expression changes during the development of diabetes in Goto-Kakizaki rats.
Results
TMED6 is selectively expressed in pancreatic islets and belongs to the EMP24_GP25L superfamily, which is known to be involved in protein trafficking and secretion. Northern analysis revealed that TMED6 mRNA is highly and selectively expressed in pancreas. Immunofluorescence histochemistry of mouse pancreas showed that TMED6 expression is restricted to pancreatic islets with higher levels in α cells than β cells. Knockdown of TMED6 gene expression in Min6 β cells decreased insulin secretion. Moreover, TMED6 gene expression was significantly lower in diabetic Goto-Kakizaki rats.
Conclusions
TMED6 may play a functional role in islet biology, particularly in hormone production or secretion, and its dysregulation may be implicated in the development of diabetes.
doi:10.1097/MPA.0b013e318223c7e4
PMCID: PMC3870856  PMID: 22129529
TMED6; expression; islets; insulin; diabetes; Goto-Kakizaki rats
14.  Altered gene expression profiles in the hippocampus and prefrontal cortex of type 2 diabetic rats 
BMC Genomics  2012;13:81.
Background
There has been an increasing body of epidemiologic and biochemical evidence implying the role of cerebral insulin resistance in Alzheimer-type dementia. For a better understanding of the insulin effect on the central nervous system, we performed microarray-based global gene expression profiling in the hippocampus, striatum and prefrontal cortex of streptozotocin-induced and spontaneously diabetic Goto-Kakizaki rats as model animals for type 1 and type 2 diabetes, respectively.
Results
Following pathway analysis and validation of gene lists by real-time polymerase chain reaction, 30 genes from the hippocampus, such as the inhibitory neuropeptide galanin, synuclein gamma and uncoupling protein 2, and 22 genes from the prefrontal cortex, e.g. galanin receptor 2, protein kinase C gamma and epsilon, ABCA1 (ATP-Binding Cassette A1), CD47 (Cluster of Differentiation 47) and the RET (Rearranged During Transfection) protooncogene, were found to exhibit altered expression levels in type 2 diabetic model animals in comparison to non-diabetic control animals. These gene lists proved to be partly overlapping and encompassed genes related to neurotransmission, lipid metabolism, neuronal development, insulin secretion, oxidative damage and DNA repair. On the other hand, no significant alterations were found in the transcriptomes of the corpus striatum in the same animals. Changes in the cerebral gene expression profiles seemed to be specific for the type 2 diabetic model, as no such alterations were found in streptozotocin-treated animals.
Conclusions
According to our knowledge this is the first characterization of the whole-genome expression changes of specific brain regions in a diabetic model. Our findings shed light on the complex role of insulin signaling in fine-tuning brain functions, and provide further experimental evidence in support of the recently elaborated theory of type 3 diabetes.
doi:10.1186/1471-2164-13-81
PMCID: PMC3299604  PMID: 22369239
15.  Activities of asymmetric dimethylarginine-related enzymes in white adipose tissue are associated with circulating lipid biomarkers 
Background
Asymmetric NG,NG-dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is regulated by the enzymatic participants of synthetic and metabolic processes, i.e., type I protein N-arginine methyltransferase (PRMT) and dimethylarginine dimethylaminohydrolase (DDAH). Previous reports have demonstrated that circulating ADMA levels can vary in patients with type 1 and type 2 diabetes mellitus (T2DM). White adipose tissue expresses the full enzymatic machinery necessary for ADMA production and metabolism; however, modulation of the activities of adipose ADMA-related enzymes in T2DM remains to be determined.
Methods
A rodent model of T2DM using 11- and 20-week old Goto-Kakizaki (GK) rats was used. The expression and catalytic activity of PRMT1 and DDAH1 and 2 in the white adipose tissues (periepididymal, visceral and subcutaneous fats) and femur skeletal muscle tissue were determined by immunoblotting, in vitro methyltransferase and in vitro citrulline assays.
Results
Non-obese diabetic GK rats showed low expression and activity of adipose PRMT1 compared to age-matched Wistar controls. Adipose tissues from the periepididymal, visceral and subcutaneous fats of GK rats had high DDAH1 expression and total DDAH activity, whereas the DDAH2 expression was lowered below the control value. This dynamic of ADMA-related enzymes in white adipose tissues was distinct from that of skeletal muscle tissue. GK rats had lower levels of serum non-esterified fatty acids (NEFA) and triglycerides (TG) than the control rats. In all subjects the adipose PRMT1 and DDAH activities were statistically correlated with the levels of serum NEFA and TG.
Conclusion
Activities of PRMT1 and DDAH in white adipose tissues were altered in diabetic GK rats in an organ-specific manner, which was reflected in the serum levels of NEFA and TG. Changes in adipose ADMA-related enzymes might play a part in the function of white adipose tissue.
doi:10.1186/1758-5996-4-17
PMCID: PMC3472189  PMID: 22546019
Protein N-arginine methyltransferase 1; Dimethylarginine dimethylaminohydrolase 1 and 2; Non-esterified fatty acids; Triglycerides; Type 2 diabetes mellitus
16.  GALNT2 Expression Is Reduced in Patients with Type 2 Diabetes: Possible Role of Hyperglycemia 
PLoS ONE  2013;8(7):e70159.
Impaired insulin action plays a major role in the pathogenesis of type 2 diabetes, a chronic metabolic disorder which imposes a tremendous burden to morbidity and mortality worldwide. Unraveling the molecular mechanisms underlying insulin resistance would improve setting up preventive and treatment strategies of type 2 diabetes. Down-regulation of GALNT2, an UDPN-acetyl-alpha-D-galactosamine polypeptideN-acetylgalactosaminyltransferase-2 (ppGalNAc-T2), causes impaired insulin signaling and action in cultured human liver cells. In addition, GALNT2 mRNA levels are down-regulated in liver of spontaneously insulin resistant, diabetic Goto-Kakizaki rats. To investigate the role of GALNT2 in human hyperglycemia, we measured GALNT2 mRNA expression levels in peripheral whole blood cells of 84 non-obese and 46 obese non-diabetic individuals as well as of 98 obese patients with type 2 diabetes. We also measured GALNT2 mRNA expression in human U937 cells cultured under different glucose concentrations. In vivo studies indicated that GALNT2 mRNA levels were significantly reduced from non obese control to obese non diabetic and to obese diabetic individuals (p<0.001). In vitro studies showed that GALNT2 mRNA levels was reduced in U937 cells exposed to high glucose concentrations (i.e. 25 mmol/l glucose) as compared to cells exposed to low glucose concentration (i.e. 5.5 mmol/l glucose +19.5 mmol/l mannitol). In conclusion, our data indicate that GALNT2 is down-regulated in patients with type 2 diabetes and suggest that this association is, at least partly, secondary to hyperglycemia. Further studies are needed to understand whether GALNT2 down-regulation plays a pathogenic role in maintaining and/or aggravating the metabolic abnormalities of diabetic milieu.
doi:10.1371/journal.pone.0070159
PMCID: PMC3718685  PMID: 23894607
17.  Administration of a Substituted Adamantly-urea Inhibitor of Soluble Epoxide Hydrolase Protects the Kidney from Damage in Hypertensive Goto-Kakizaki Rats 
Hypertension and type II diabetes are co-morbid diseases that lead to the development of nephropathy. Soluble epoxide hydrolase (sEH) inhibitors are reported to provide protection from renal injury. We hypothesized that the sEH inhibitor 12-(3-adamantan-1-yl-ureido) dodecanoic acid (AUDA) protects the kidney from the development of nephropathy associated with hypertension and type II diabetes. Hypertension was induced in spontaneously diabetic Goto-Kakizaki rats using angiotensin II and a high salt diet. Hypertensive Goto-Kakizaki rats were treated for two weeks with either AUDA or its vehicle added to drinking water. Mean arterial pressure increased from 118 ± 2 mmHg to 182 ± 20 and 187 ± 6 mmHg for vehicle and AUDA treated hypertensive Goto-Kakizaki rats, respectively. AUDA treatment did not alter blood glucose. Hypertension in Goto-Kakizaki rats resulted in a 17-fold increase in urinary albumin excretion that was decreased with AUDA treatment. Renal histological evaluation determined that AUDA treatment decreased glomerular and tubular damage. In addition, AUDA treatment attenuated macrophage infiltration and inhibited urinary excretion of MCP-1 and kidney cortex MCP-1 gene expression. Taken together, these data provide evidence that sEH inhibition with AUDA attenuates the progression of renal damage associated with hypertension and type II diabetes.
doi:10.1042/CS20080039
PMCID: PMC2590620  PMID: 18459944
diabetes; inflammation; eicosanoids; nephropathy; blood pressure
18.  A Combination of Nutriments Improves Mitochondrial Biogenesis and Function in Skeletal Muscle of Type 2 Diabetic Goto–Kakizaki Rats 
PLoS ONE  2008;3(6):e2328.
Background
Recent evidence indicates that insulin resistance in skeletal muscle may be related to reduce mitochondrial number and oxidation capacity. However, it is not known whether increasing mitochondrial number and function improves insulin resistance. In the present study, we investigated the effects of a combination of nutrients on insulin resistance and mitochondrial biogenesis/function in skeletal muscle of type 2 diabetic Goto–Kakizaki rats.
Methodology/Principal Findings
We demonstrated that defect of glucose and lipid metabolism is associated with low mitochondrial content and reduced mitochondrial enzyme activity in skeletal muscle of the diabetic Goto-Kakizaki rats. The treatment of combination of R-α-lipoic acid, acetyl-L-carnitine, nicotinamide, and biotin effectively improved glucose tolerance, decreased the basal insulin secretion and the level of circulating free fatty acid (FFA), and prevented the reduction of mitochondrial biogenesis in skeletal muscle. The nutrients treatment also significantly increased mRNA levels of genes involved in lipid metabolism, including peroxisome proliferator–activated receptor-α (Pparα), peroxisome proliferator–activated receptor-δ (Pparδ), and carnitine palmitoyl transferase-1 (Mcpt-1) and activity of mitochondrial complex I and II in skeletal muscle. All of these effects of mitochondrial nutrients are comparable to that of the antidiabetic drug, pioglitazone. In addition, the treatment with nutrients, unlike pioglitazone, did not cause body weight gain.
Conclusions/Significance
These data suggest that a combination of mitochondrial targeting nutrients may improve skeletal mitochondrial dysfunction and exert hypoglycemic effects, without causing weight gain.
doi:10.1371/journal.pone.0002328
PMCID: PMC2391295  PMID: 18523557
19.  Increased expression of adenylyl cyclase 3 in pancreatic islets and central nervous system of diabetic Goto-Kakizaki rats 
Islets  2012;4(5):343-348.
Adenylyl cyclase 3 (AC3) is expressed in pancreatic islets of the Goto-Kakizaki (GK) rat, a spontaneous animal model of type 2 diabetes (T2D), and also exerts genetic effects on the regulation of body weight in man. In addition to pancreatic islets, the central nervous system (CNS) plays an important role in the pathogenesis of T2D and obesity by regulating feeding behavior, body weight and glucose metabolism. In the present study, we have investigated AC3 expression in pancreatic islets, striatum and hypothalamus of GK rats to evaluate its role in the regulation of glucose homeostasis. GK and Wistar rats at the age of 2.5 mo were used. A group of GK rats were implanted with sustained insulin release chips for 15 d. Plasma glucose and serum insulin levels were measured. AC3 gene expression levels in pancreatic islets, striatum and hypothalamus were determined by using real-time RT-PCR. Results indicated that plasma glucose levels in Wistar rats were found to be similar to insulin-treated GK rats, and significantly lower compared with non-treated GK rats. AC3 expression levels in pancreatic islets, striatum and hypothalamus of GK rats were higher compared with Wistar rats, while the levels were intermediate in insulin-treated GK rats. The AC3 expression display patterns between pancreatic islets and striatum-hypothalamus were similar. The present study thus provides the first evidence that AC3 is overexpressed in the regions of striatum and hypothalamus of brain, and similarly in pancreatic islets of GK rats suggesting that AC3 plays a role in regulation of glucose homeostasis via CNS and insulin secretion.
doi:10.4161/isl.22283
PMCID: PMC3524141  PMID: 23018249
Adenylyl cyclase 3; body weight; central nervous system; glucose; pancreatic islets; type 2 diabetes
20.  Gingival vascular functions are altered in type 2 diabetes mellitus model and/or periodontitis model 
The association of vascular reactivity between diabetes and periodontal disease has not been clarified. Gingival blood flow was measured by laser Doppler flowmetry for 31 weeks in Wistar rats, Wistar rats orally challenged with Porphyromonas gingivalis (Wistar rats + Porphyromonas gingivalis), Goto-Kakizaki rats, and Goto-Kakizaki rats orally challenged with Porphyromonas gingivalis (Goto-Kakizaki rats + Porphyromonas gingivalis). Effects of alveolar bone resorption on periodontal tissue was enhanced in Wistar rats + Porphyromonas gingivalis, and Goto-Kakizaki rats, with this effect being significantly enhanced by Goto-Kakizaki rats + Porphyromonas gingivalis. Using the L-band electron spin resonance technique, we succeeded in measuring oxidative stress as decay rate constant (K1 and K2) of 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-yloxy in the oral and maxillofacial region of the animal models. The decay rate constant (K1) of 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-yloxy was significantly greater in the oral and maxillofacial region of Goto-Kakizaki rats + Porphyromonas gingivalis compared to Wistar rats, Wistar rats + Porphyromonas gingivalis and Goto-Kakizaki rats groups. Gingival reactive hyperemia was attenuated by periodontal disease, and this effect was also remarkable in the diabetes mellitus model. Taken together, we found that vascular endothelial function was decreased in diabetes mellitus and/or periodontal disease animal models due to increasing oxidative stress in the gingival circulation.
doi:10.3164/jcbn.11-103
PMCID: PMC3432819  PMID: 22962527
gingival circulation; oxidative stress; L-band ESR; diabetes mellitus; periodontitis
21.  Mechanism-based disease progression modeling of type 2 diabetes in Goto-Kakizaki rats 
The dynamics of aging and type 2 diabetes (T2D) disease progression were investigated in normal [Wistar-Kyoto (WKY)] and diabetic [Goto-Kakizaki (GK)] rats and a mechanistic disease progression model was developed for glucose, insulin, and glycosylated hemoglobin (HbA1c) changes over time. The study included 30 WKY and 30 GK rats. Plasma glucose and insulin, blood glucose and HbA1c concentrations and hematological measurements were taken at ages 4, 8, 12, 16 and 20 weeks. A mathematical model described the development of insulin resistance (IR) and β-cell function with age/growth and diabetes progression. The model utilized transit compartments and an indirect response model to quantitate biomarker changes over time. Glucose, insulin and HbA1c concentrations in WKY rats increased to a steady-state at 8 weeks due to developmental changes. Glucose concentrations at 4 weeks in GK rats were almost twice those of controls, and increased to a steady-state after 8 weeks. Insulin concentrations at 4 weeks in GK rats were similar to controls, and then hyperinsulinemia occurred until 12–16 weeks of age indicating IR. Subsequently, insulin concentrations in GK rats declined to slightly below WKY controls due to β-cell failure. HbA1c showed a delayed increase relative to glucose. Modeling of HbA1c was complicated by age-related changes in hematology in rats. The diabetes model quantitatively described the glucose/insulin inter-regulation and HbA1c production and reflected the underlying pathogenic factors of T2D—IR and β-cell dysfunction. The model could be extended to incorporate other biomarkers and effects of various anti-diabetic drugs.
doi:10.1007/s10928-010-9182-0
PMCID: PMC3727409  PMID: 21127951
Type 2 diabetes; Disease progression modeling; Insulin resistance; β-cell function
22.  Regenerating 1 and 3b Gene Expression in the Pancreas of Type 2 Diabetic Goto-Kakizaki (GK) Rats 
PLoS ONE  2014;9(2):e90045.
Regenerating (REG) proteins are associated with islet development, β-cell damage, diabetes and pancreatitis. Particularly, REG-1 and REG-3-beta are involved in cell growth/survival and/or inflammation and the Reg1 promoter contains interleukin-6 (IL-6)-responsive elements. We showed by transcriptome analysis that islets of Goto-Kakizaki (GK) rats, a model of spontaneous type 2 diabetes, overexpress Reg1, 3α, 3β and 3γ, vs Wistar islets. Goto-Kakizaki rat islets also exhibit increased cytokine/chemokine expression/release, particularly IL-6. Here we analyzed Reg1 and Reg3β expression and REG-1 immuno-localization in the GK rat pancreas in relationship with inflammation. Isolated pancreatic islets and acinar tissue from male adult Wistar and diabetic GK rats were used for quantitative RT-PCR analysis. REG-1 immunohistochemistry was performed on paraffin sections with a monoclonal anti-rat REG-1 antibody. Islet cytokine/chemokine release was measured after 48 h-culture. Islet macrophage-positive area was quantified on cryostat sections using anti-CD68 and major histocompatibility complex (MHC) class II antibodies. Pancreatic exocrine-to-endocrine Reg1 and Reg3β mRNA ratios were markedly increased in Wistar vs GK rats. Conversely, both genes were upregulated in isolated GK rat islets. These findings were unexpected, because Reg genes are expressed in the pancreatic acinar tissue. However, we observed REG-1 protein labeling in acinar peri-ductal tissue close to islets and around large, often disorganized, GK rat islets, which may retain acinar cells due to their irregular shape. These large islets also showed peri-islet macrophage infiltration and increased release of various cytokines/chemokines, particularly IL-6. Thus, IL-6 might potentially trigger acinar REG-1 expression and secretion in the vicinity of large diabetic GK rat islets. This increased acinar REG-1 expression might reflect an adaptive though unsuccessful response to deleterious microenvironment.
doi:10.1371/journal.pone.0090045
PMCID: PMC3936001  PMID: 24587207
23.  Abnormalities in the Fiber Composition and Capillary Architecture in the Soleus Muscle of Type 2 Diabetic Goto-Kakizaki Rats 
The Scientific World Journal  2012;2012:680189.
Type 2 diabetes mellitus is linked to impaired skeletal muscle glucose uptake and storage. This study aimed to investigate the fiber type distributions and the three-dimensional (3D) architecture of the capillary network in the skeletal muscles of type 2 diabetic rats. Muscle fiber type transformation, succinate dehydrogenase (SDH) activity, capillary density, and 3D architecture of the capillary network in the soleus muscle were determined in 36-week-old Goto-Kakizaki (GK) rats as an animal model of nonobese type 2 diabetes and age-matched Wistar (Cont) rats. Although the soleus muscle of Cont rats comprised both type I and type IIA fibers, the soleus muscle of GK rats had only type I fibers. In addition, total SDH activity in the soleus muscle of GK rats was significantly lower than that in Cont rats because GK rats had no high-SDH activity type IIA fiber in the soleus muscle. Furthermore, the capillary diameter, capillary tortuosity, and microvessel volume in GK rats were significantly lower than those in Cont rats. These results indicate that non-obese diabetic GK rats have muscle fiber type transformation, low SDH activity, and reduced skeletal muscle capillary content, which may be related to the impaired glucose metabolism characteristic of type 2 diabetes.
doi:10.1100/2012/680189
PMCID: PMC3504414  PMID: 23213294
24.  Protein kinase B/Akt activity is involved in renal TGF-β1-driven epithelial-mesenchymal transition in vitro and in vivo 
The molecular pathogenesis of diabetic nephropathy (DN), the leading cause of end-stage renal disease worldwide, is complex and not fully understood. Transforming growth factor-β (TGF-β1) plays a critical role in many fibrotic disorders, including DN. In this study, we report protein kinase B (PKB/Akt) activation as a downstream event contributing to the pathophysiology of DN. We investigated the potential of PKB/Akt to mediate the profibrotic bioactions of TGF-β1 in kidney. Treatment of normal rat kidney epithelial cells (NRK52E) with TGF-β1 resulted in activation of phosphatidylinositol 3-kinase (PI3K) and PKB/Akt as evidenced by increased Ser473 phosphorylation and GSK-3β phosphorylation. TGF-β1 also stimulated increased Smad3 phosphorylation in these cells, a response that was insensitive to inhibition of PI3K or PKB/Akt. NRK52E cells displayed a loss of zona occludins 1 and E-cadherin and a gain in vimentin and α-smooth muscle actin expression, consistent with the fibrotic actions of TGF-β1. These effects were blocked with inhibitors of PI3K and PKB/Akt. Furthermore, overexpression of PTEN, the lipid phosphatase regulator of PKB/Akt activation, inhibited TGF-β1-induced PKB/Akt activation. Interestingly, in the Goto-Kakizaki rat model of type 2 diabetes, we also detected increased phosphorylation of PKB/Akt and its downstream target, GSK-3β, in the tubules, relative to that in control Wistar rats. Elevated Smad3 phosphorylation was also detected in kidney extracts from Goto-Kakizaki rats with chronic diabetes. Together, these data suggest that TGF-β1-mediated PKB/Akt activation may be important in renal fibrosis during diabetic nephropathy.
doi:10.1152/ajprenal.00548.2007
PMCID: PMC2494512  PMID: 18495798
diabetic nephropathy; transforming growth factor-β1
25.  Inflammation, Insulin Resistance, and Diabetes—Mendelian Randomization Using CRP Haplotypes Points Upstream 
PLoS Medicine  2008;5(8):e155.
Background
Raised C-reactive protein (CRP) is a risk factor for type 2 diabetes. According to the Mendelian randomization method, the association is likely to be causal if genetic variants that affect CRP level are associated with markers of diabetes development and diabetes. Our objective was to examine the nature of the association between CRP phenotype and diabetes development using CRP haplotypes as instrumental variables.
Methods and Findings
We genotyped three tagging SNPs (CRP + 2302G > A; CRP + 1444T > C; CRP + 4899T > G) in the CRP gene and measured serum CRP in 5,274 men and women at mean ages 49 and 61 y (Whitehall II Study). Homeostasis model assessment-insulin resistance (HOMA-IR) and hemoglobin A1c (HbA1c) were measured at age 61 y. Diabetes was ascertained by glucose tolerance test and self-report. Common major haplotypes were strongly associated with serum CRP levels, but unrelated to obesity, blood pressure, and socioeconomic position, which may confound the association between CRP and diabetes risk. Serum CRP was associated with these potential confounding factors. After adjustment for age and sex, baseline serum CRP was associated with incident diabetes (hazard ratio = 1.39 [95% confidence interval 1.29–1.51], HOMA-IR, and HbA1c, but the associations were considerably attenuated on adjustment for potential confounding factors. In contrast, CRP haplotypes were not associated with HOMA-IR or HbA1c (p = 0.52–0.92). The associations of CRP with HOMA-IR and HbA1c were all null when examined using instrumental variables analysis, with genetic variants as the instrument for serum CRP. Instrumental variables estimates differed from the directly observed associations (p = 0.007–0.11). Pooled analysis of CRP haplotypes and diabetes in Whitehall II and Northwick Park Heart Study II produced null findings (p = 0.25–0.88). Analyses based on the Wellcome Trust Case Control Consortium (1,923 diabetes cases, 2,932 controls) using three SNPs in tight linkage disequilibrium with our tagging SNPs also demonstrated null associations.
Conclusions
Observed associations between serum CRP and insulin resistance, glycemia, and diabetes are likely to be noncausal. Inflammation may play a causal role via upstream effectors rather than the downstream marker CRP.
Using a Mendelian randomization approach, Eric Brunner and colleagues show that the associations between serum C-reactive protein and insulin resistance, glycemia, and diabetes are likely to be noncausal.
Editors' Summary
Background.
Diabetes—a common, long-term (chronic) disease that causes heart, kidney, nerve, and eye problems and shortens life expectancy—is characterized by high levels of sugar (glucose) in the blood. In people without diabetes, blood sugar levels are controlled by the hormone insulin. Insulin is released by the pancreas after eating and “instructs” insulin-responsive muscle and fat cells to take up the glucose from the bloodstream that is produced by the digestion of food. In the early stages of type 2 diabetes (the commonest type of diabetes), the muscle and fat cells become nonresponsive to insulin (a condition called insulin resistance), and blood sugar levels increase. The pancreas responds by making more insulin—people with insulin resistance have high blood levels of both insulin and glucose. Eventually, however, the insulin-producing cells in the pancreas start to malfunction, insulin secretion decreases, and frank diabetes develops.
Why Was This Study Done?
Globally, about 200 million people have diabetes, but experts believe this number will double by 2030. Ways to prevent or delay the onset of diabetes are, therefore, urgently needed. One major risk factor for insulin resistance and diabetes is being overweight. According to one theory, increased body fat causes mild, chronic tissue inflammation, which leads to insulin resistance. Consistent with this idea, people with higher than normal amounts of the inflammatory protein C-reactive protein (CRP) in their blood have a high risk of developing diabetes. If inflammation does cause diabetes, then drugs that inhibit CRP might prevent diabetes. However, simply measuring CRP and determining whether the people with high levels develop diabetes cannot prove that CRP causes diabetes. Those people with high blood levels of CRP might have other unknown factors in common (confounding factors) that are the real causes of diabetes. In this study, the researchers use “Mendelian randomization” to examine whether increased blood CRP causes diabetes. Some variants of CRP (the gene that encodes CRP) increase the amount of CRP in the blood. Because these variants are inherited randomly, there is no likelihood of confounding factors, and an association between these variants and the development of insulin resistance and diabetes indicates, therefore, that increased CRP levels cause diabetes.
What Did the Researchers Do and Find?
The researchers measured blood CRP levels in more than 5,000 people enrolled in the Whitehall II study, which is investigating factors that affect disease development. They also used the “homeostasis model assessment-insulin resistance” (HOMA-IR) method to estimate insulin sensitivity from blood glucose and insulin measurements, and measured levels of hemoglobin A1c (HbA1c, hemoglobin with sugar attached—a measure of long-term blood sugar control) in these people. Finally, they looked at three “single polynucleotide polymorphisms” (SNPs, single nucleotide changes in a gene's DNA sequence; combinations of SNPs that are inherited as a block are called haplotypes) in CRP in each study participant. Common haplotypes of CRP were related to blood serum CRP levels and, as previously reported, increased blood CRP levels were associated with diabetes and with HOMA-IR and HbA1c values indicative of insulin resistance and poor blood sugar control, respectively. By contrast, CRP haplotypes were not related to HOMA-IR or HbA1c values. Similarly, pooled analysis of CRP haplotypes and diabetes in Whitehall II and another large study on health determinants (the Northwick Park Heart Study II) showed no association between CRP variants and diabetes risk. Finally, data from the Wellcome Trust Case Control Consortium also showed no association between CRP haplotypes and diabetes risk.
What Do These Findings Mean?
Together, these findings suggest that increased blood CRP levels are not responsible for the development of insulin resistance or diabetes, at least in European populations. It may be that there is a causal relationship between CRP levels and diabetes risk in other ethnic populations—further Mendelian randomization studies are needed to discover whether this is the case. For now, though, these findings suggest that drugs targeted against CRP are unlikely to prevent or delay the onset of diabetes. However, they do not discount the possibility that proteins involved earlier in the inflammatory process might cause diabetes and might thus represent good drug targets for diabetes prevention.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0050155.
This study is further discussed in a PLoS Medicine Perspective by Bernard Keavney
The MedlinePlus encyclopedia provides information about diabetes and about C-reactive protein (in English and Spanish)
US National Institute of Diabetes and Digestive and Kidney Diseases provides patient information on all aspects of diabetes, including information on insulin resistance (in English and Spanish)
The International Diabetes Federation provides information about diabetes, including information on the global diabetes epidemic
The US Centers for Disease Control and Prevention provides information for the public and professionals on all aspects of diabetes (in English and Spanish)
Wikipedia has a page on Mendelian randomization (note: Wikipedia is a free online encyclopedia that anyone can edit; available in several languages)
doi:10.1371/journal.pmed.0050155
PMCID: PMC2504484  PMID: 18700811

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