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1.  Evaluation of Genetic Association and Expression Reduction of TRPC1 in the Development of Diabetic Nephropathy 
American journal of nephrology  2008;29(3):244-251.
The TRPC1 gene on chromosome 3q22–24 resides within the linkage region for diabetic nephropa-thy (DN) in type 1 (T1D) and type 2 diabetes mellitus (T2D). A recent study has demonstrated that TRPC1 expression is reduced in the kidney of diabetic ZDF- and STZ-treated rats. The present study aimed to evaluate the genetic and functional role of TRPC1 in the development of DN.
Genetic association study was performed with two independent cohorts, including 1,177 T1D European Americans with or without DN from GoKinD population and 850 African-American subjects with T2D-associated end-stage renal disease (ESRD), or with hypertensive (non-diabetic) ESRD, and nondiabetic controls. Seven tag SNP markers derived from HapMap data (phase II) were genotyped. TRPC1 gene expression was examined using real time RT-PCR.
No significant association of TRPC1 DNA polymorphisms with DN or ERSD was found in GoKinD and African-American populations. TRPC1 gene mRNA expression in kidney was found to be trendily reduced in 12-week and significantly in 26-week-old db/db mice.
TRPC1 genetic polymorphism may not fundamentally contribute to the development of DN, while reduction of the gene expression in kidney may be a late phenomenon of DN as seen in diabetic animal models.
PMCID: PMC2698220  PMID: 18802326
TRPC1 gene; Single-nucleotide polymorphism; Diabetic nephropathy; End-stage renal disease; Diabetes types 1 and 2
2.  Association of TRPC1 Gene Polymorphisms with Type 2 Diabetes and Diabetic Nephropathy in Han Chinese Population 
Endocrine Research  2013;38(2):59-68.
The recent genome-wide association studies reveal that chromosome 3q resides within the linkage region for diabetic nephropathy (DN) in type 1 and type 2 diabetes mellitus (T1D and T2D). The TRPC1 gene is on chromosome 3q22-24, and it has been demonstrated that TRPC1 expression is reduced in the kidney of diabetic animal models. Genetic association of TRPC1 polymorphism with T1D and DN has been reported in European Americans. However, there are no studies reporting the association of TRPC1 genetic polymorphism with T2D with and without DN in Chinese population. This study aimed to demonstrate the genetic role of TRPC1 in the development of T2D with and without DN in Chinese Han population. A genetic association study of TRPC1 was performed in T2D cases and in nondiabetic controls from Han population located in Northern Chinese areas. Six tag single nucleotide polymorphism (SNP) markers derived from HapMap data were genotyped. Among the six SNPs, only rs7638459 was suspected as risk factor of T2D without DN, fitting the log-additive model. The adjusted odds ratio (OR) for the CC genotyping was 2.39 (95% confidence interval (CI) = 1.00–5.68), compared with the TT genotyping. In addition, rs953239 was found to be a protective factor of getting DN in T2D, also fitting the log-additive model. When compared with the AA genotyping for SNP rs953239, the adjusted OR for CC genotyping was 0.63 (95% CI = 0.44–0.99). To summarize, this study shows that TRPC1 genetic polymorphisms are associated with T2D and DN in T2D in the Han Chinese population.
PMCID: PMC3619450  PMID: 23544998
TRPC1; Single nucleotide polymorphism; Type 2 diabetes mellitus; Diabetic nephropathy
3.  Corticolimbic Expression of TRPC4 and TRPC5 Channels in the Rodent Brain 
PLoS ONE  2007;2(6):e573.
The canonical transient receptor potential (TRPC) channels are a family of non-selective cation channels that are activated by increases in intracellular Ca2+ and Gq/phospholipase C-coupled receptors. We used quantitative real-time PCR, in situ hybridization, immunoblots and patch-clamp recording from several brain regions to examine the expression of the predominant TRPC channels in the rodent brain. Quantitative real-time PCR of the seven TRPC channels in the rodent brain revealed that TRPC4 and TRPC5 channels were the predominant TRPC subtypes in the adult rat brain. In situ hybridization histochemistry and immunoblotting further resolved a dense corticolimbic expression of the TRPC4 and TRPC5 channels. Total protein expression of HIP TRPC4 and 5 proteins increased throughout development and peaked late in adulthood (6–9 weeks). In adults, TRPC4 expression was high throughout the frontal cortex, lateral septum (LS), pyramidal cell layer of the hippocampus (HIP), dentate gyrus (DG), and ventral subiculum (vSUB). TRPC5 was highly expressed in the frontal cortex, pyramidal cell layer of the HIP, DG, and hypothalamus. Detailed examination of frontal cortical layer mRNA expression indicated TRPC4 mRNA is distributed throughout layers 2–6 of the prefrontal cortex (PFC), motor cortex (MCx), and somatosensory cortex (SCx). TRPC5 mRNA expression was concentrated specifically in the deep layers 5/6 and superficial layers 2/3 of the PFC and anterior cingulate. Patch-clamp recording indicated a strong metabotropic glutamate-activated cation current-mediated depolarization that was dependent on intracellular Ca2+and inhibited by protein kinase C in brain regions associated with dense TRPC4 or 5 expression and absent in regions lacking TRPC4 and 5 expression. Overall, the dense corticolimbic expression pattern suggests that these Gq/PLC coupled nonselective cation channels may be involved in learning, memory, and goal-directed behaviors.
PMCID: PMC1892805  PMID: 17593972
4.  An intergenic region on chromosome 13q33.3 is associated with the susceptibility to kidney disease in type 1 and 2 diabetes 
Kidney international  2011;80(1):105-111.
A genome-wide association (GWA) scan of the Genetics of Kidneys in Diabetes (GoKinD) collections identified four novel susceptibility loci, located on chromosomes 7p14.3, 9q21.32, 11p15.4, and 13q33.3 that were associated with nephropathy in type 1 diabetes. The recent examination of these loci in Japanese patients with type 2 diabetes further supported associations at the chromosome 13q33.3 locus. To follow up these findings, we focused on these same four loci and examined whether single nucleotide polymorphisms (SNPs) at these susceptibility loci were associated with diabetic nephropathy in the Joslin Study of Genetics of Nephropathy in Type 2 Diabetes collection. A total of six SNPs across these loci were genotyped in 646 normoalbuminuric controls and 743 nephropathy cases of European ancestry. A significant association was identified at the 13q33.3 locus (rs9521445: OR=1.25, P=4.4×10−3). At this same locus, rs1411766 was also associated with type 2 diabetic nephropathy in this collection (OR=1.19, P=0.03). A meta-analysis combining this data with that from the Japanese and GoKinD collections significantly improved the strength of this association (OR=1.29 P=9.7×10−9). Additionally, we also observed an association at the 11p15.4 locus (rs451041: OR=1.21, P=0.02). Our analysis increases support that associations identified in the GoKinD collections on chromosomes 11p15.4 (near the CARS gene) and 13q33.3 (within an intergenic region between MYO16 and IRS2) are true diabetic nephropathy susceptibility loci common to both type 1 and type 2 diabetes.
PMCID: PMC3774030  PMID: 21412220
5.  Trpc2 Depletion Protects RBC from Oxidative Stress-Induced Hemolysis 
Experimental hematology  2011;40(1):71-83.
Transient receptor potential channels Trpc2 and Trpc3 are expressed on normal murine erythroid precursors, and erythropoietin stimulates an increase in intracellular calcium ([Ca2+]i) through TRPC2 and TRPC3. Because modulation of [Ca2+]i is an important signaling pathway in erythroid proliferation and differentiation, Trpc2, Trpc3, and Trpc2/Trpc3 double knockout mice were utilized to explore the roles of these channels in erythropoiesis. Trpc2, Trpc3, and Trpc2/Trpc3 double knockout mice were not anemic, and had similar red blood cell counts, hemoglobins, and reticulocyte counts as wild type littermate controls. Although the erythropoietin induced increase in [Ca2+]i was reduced, these knockout mice showed no defects in red cell production. The major phenotypic difference at steady state was that the mean corpuscular volume, mean corpuscular hemoglobin, and hematocrit of red cells were significantly greater in Trpc2 and Trpc2/Trpc3 double knockout mice, and mean corpuscular hemoglobin concentration was significantly reduced. All hematological parameters in Trpc3 knockout mice were similar to controls. When exposed to phenyhydrazine, unlike the Trpc3 knockouts, Trpc2 and Trpc2/Trpc3 double knockout mice showed significant resistance to hemolysis. This was associated with significant reduction in hydrogen peroxide-induced calcium influx in erythroblasts. While erythropoietin induced calcium influx through TRPC2 or TRPC3 is not critical for erythroid production, these data demonstrate that TRPC2 plays an important role in oxidative stress-induced hemolysis which may be related to reduced calcium entry in red cells in the presence of Trpc2 depletion.
PMCID: PMC3237850  PMID: 21924222
TRP Channels; Trpc2; Trpc3; erythropoietin; oxidative stress
6.  Expression of trpC1 and trpC6 orthologs in zebrafish 
Gene expression patterns : GEP  2008;8(5):291-296.
Transient receptor potential (TRP) genes encode subunits that form cation-selective ion channels in a variety of organisms and cell types. TRP channels serve diverse functions ranging from thermal, tactile, taste, and osmolar sensing to fluid flow sensing. TRPC1 and TRPC6 belong to the TRPC subfamily, members of which are thought to contribute to several cellular events such as regulated migration of neuronal dendrites, contractile responses of smooth muscle cells and maintenance of the structural integrity of kidney podocytes. Pathogenic roles have been suggested for TRPC1 in asthma and chronic obstructive pulmonary disease, and TRPC6 dysfunction was recently linked to proteinuric kidney disease. To explore the potential roles for TRPC channels in zebrafish organ function, we cloned zebrafish trpC1 and trpC6 cDNAs, and investigated their expression during zebrafish development. We detected trpC1 expression in the head, in cells surrounding the outflow tract of the heart, and in the ganglion cells as well as the inner nuclear layer of the eye. trpC6 expression was detected in the head, pectoral fins, aortic endothelial cells, and gastrointestinal smooth muscle cells. Our results point to roles of TRPC channels in several tissues during zebrafish development, and suggest that the zebrafish may be a suitable model system to study the pathophysiology of TRPC1 and TRPC6 in specific cell types.
PMCID: PMC2431112  PMID: 18378501
Transient receptor potential; ion channel; smooth muscle; in situ hybridization
7.  Genetic Examination of SETD7 and SUV39H1/H2 Methyltransferases and the Risk of Diabetes Complications in Patients With Type 1 Diabetes 
Diabetes  2011;60(11):3073-3080.
Hyperglycemia plays a pivotal role in the development and progression of vascular complications, which are the major sources of morbidity and mortality in diabetes. Furthermore, these vascular complications often persist and progress despite improved glucose control, possibly as a result of prior episodes of hyperglycemia. Epigenetic modifications mediated by histone methyltransferases are associated with gene-activating events that promote enhanced expression of key proinflammatory molecules implicated in vascular injury. In this study, we investigated genetic polymorphisms of the SETD7, SUV39H1, and SUV39H2 methyltransferases as predictors of risk for micro- and macrovascular complications in type 1 diabetes.
In the Finnish Diabetic Nephropathy Study (FinnDiane) cohort, 37 tagging single nucleotide polymorphisms (SNPs) were genotyped in 2,991 individuals with type 1 diabetes and diabetic retinopathy, diabetic nephropathy, and cardiovascular disease. Seven SNPs were genotyped in the replication cohorts from the Steno Diabetes Center and All Ireland/Warren 3/Genetics of Kidneys in Diabetes (GoKinD) U.K. study.
In a meta-analysis, the minor T allele of the exonic SNP rs17353856 in the SUV39H2 was associated with diabetic retinopathy (genotypic odds ratio 0.75, P = 1.2 × 10−4). The same SNP showed a trend toward an association with diabetic nephropathy as well as cardiovascular disease in the FinnDiane cohort.
Our findings propose that a genetic variation in a gene coding for a histone methyltransferase is protective for a diabetic microvascular complication. The pathophysiological implications of this polymorphism or other genetic variation nearby for the vascular complications of type 1 diabetes remain to be investigated.
PMCID: PMC3198095  PMID: 21896933
8.  Regulation of TRPC6 Channels by Non-Steroidal Anti-Inflammatory Drugs1 
Family focal segmental glomerulosclerosis (FSGS) is characterized by sclerosis and hyalinosis of particular loops of glomeruli and is one of the causes of the nephrotic syndrome. Certain mutations in the structure of TRPC6 channels are the genetic impetus for FSGS development resulting in podocytes functional abnormalities and various nephropathies. We have recently demonstrated that non-steroid anti-inflammatory drugs (NSAID) ibuprofen and diclofenac decrease the activity of endogenous TRPC like cal cium channels in the podocytes of the freshly isolated rat glomeruli. It has also been shown that TRPC6 chan nels are expressed in the podocytes. In the current study we have functionally reconstituted TRPC6 channels in mammalian cells to investigate the effects of diclofenac on the activity of wild type TRPC6 channel and TRPC6P112Q channel containing a mutation in the N-terminus that was described in FSGS patients. Intracellular calcium level measurements in transfected cells revealed a more intensive carbachol induced increase of calcium concentration in HEK 293 cells expressing TRPC6P112Q versus the cells expressing wild-type TRPC6. We also performed patch-clamp experiments to study TRPC6 channels reconstituted in Chinese hamster ovary (CHO) cell line and found that application of diclofenac (500 μM) acutely reduced single channel activity. Preincubation with diclofenac (100 μM) also decreased the whole cell current in CHO cells overexpressing TRPC6P112Q. Therefore, our previously published data on the effects of NSAID on TRPC-like channels in the isolated rat glomeruli, along with this current investigation on the cultured overexpressed mammalian cells, allows hypothesizing that TRPC6 channels may be a target for NSAID that can be impor tant in the treatment of FSGS.
PMCID: PMC4180105  PMID: 25279100
TRPC6; non-steroid anti-inflammatory drugs; calcium; ion channels; focal segmental glomerulosclerosis
9.  TRPC6 Single Nucleotide Polymorphisms and Progression of Idiopathic Membranous Nephropathy 
PLoS ONE  2014;9(7):e102065.
Activating mutations in the Transient Receptor Potential channel C6 (TRPC6) cause autosomal dominant focal segmental glomerular sclerosis (FSGS). TRPC6 expression is upregulated in renal biopsies of patients with idiopathic membranous glomerulopathy (iMN) and animal models thereof. In iMN, disease progression is characterized by glomerulosclerosis. In addition, a context-dependent TRPC6 overexpression was recently suggested in complement-mediated podocyte injury in e.g. iMN. Hence, we hypothesized that genetic variants in TRPC6 might affect susceptibility to development or progression of iMN.
Methods & Results
Genomic DNA was isolated from blood samples of 101 iMN patients and 292 controls. By direct sequencing of the entire TRPC6 gene, 13 single nucleotide polymorphisms (SNPs) were identified in the iMN cohort, two of which were causing an amino acid substitution (rs3802829; Pro15Ser and rs36111323, Ala404Val). No statistically significant differences in genotypes or allele frequencies between patients and controls were observed. Clinical outcome in patients was determined (remission n = 26, renal failure n = 46, persistent proteinuria n = 29, follow-up median 80 months {range 51–166}). The 13 identified SNPs showed no association with remission or renal failure. There were no differences in genotypes or allele frequencies between patients in remission and progressors.
Our data suggest that TRPC6 polymorphisms do not affect susceptibility to iMN, or clinical outcome in iMN.
PMCID: PMC4096511  PMID: 25019165
10.  Nephropathy in Type 1 Diabetes Is Diminished in Carriers of HLA-DRB1*04: The Genetics of Kidneys in Diabetes (GoKinD) Study 
Diabetes  2007;57(2):518-522.
The purpose of this study was to examine whether known genetic risk factors for type 1 diabetes (HLA-DRB1, -DQA1, and -DQB1 and insulin locus) play a role in the etiology of diabetic nephropathy.
Genetic analysis of HLA-DRB1, -DQA1, -DQB1 and the insulin gene (INS) was performed in the Genetics of Kidneys in Diabetes (GoKinD) collection of DNA (European ancestry subset), which includes case patients with type 1 diabetes and nephropathy (n = 829) and control patients with type 1 diabetes but not nephropathy (n = 904). The availability of phenotypic and genotypic data on GoKinD participants allowed a detailed analysis of the association of these genes with diabetic nephropathy.
Diabetic probands who were homozygous for HLA-DRB1*04 were 50% less likely to have nephropathy than probands without any DRB1*04 alleles. In heterozygous carriers, a protective effect of this allele was not as clearly evident; the mode of inheritance therefore remains unclear. This association was seen in probands with both short (<28 years, P = 0.02) and long (≥28 years, P = 0.0001) duration of diabetes. A1C, a marker of sustained hyperglycemia, was increased in control probands with normoalbuminuira, despite long-duration diabetes, from 7.2 to 7.3 to 7.7% with 0, 1, and 2 copies of the DRB1*04 allele, respectively. This result is consistent with a protective effect of DRB1*04 that may allow individuals to tolerate higher levels of hyperglycemia, as measured by A1C, without developing nephropathy.
These data suggest that carriers of DRB1*04 are protected from some of the injurious hyperglycemic effects related to nephropathy. Interestingly, DRB1*04 appears to be both a risk allele for type 1 diabetes and a protective allele for nephropathy.
PMCID: PMC2679388  PMID: 18039812
11.  Confirmation of Genetic Associations at ELMO1 in the GoKinD Collection Supports Its Role as a Susceptibility Gene in Diabetic Nephropathy 
Diabetes  2009;58(11):2698-2702.
To examine the association between single nucleotide polymorphisms (SNPs) in the engulfment and cell motility 1 (ELMO1) gene, a locus previously shown to be associated with diabetic nephropathy in two ethnically distinct type 2 diabetic populations, and the risk of nephropathy in type 1 diabetes.
Genotypic data from a genome-wide association scan (GWAS) of the Genetics of Kidneys in Diabetes (GoKinD) study collection were analyzed for associations across the ELMO1 locus. In total, genetic associations were assessed using 118 SNPs and 1,705 individuals of European ancestry with type 1 diabetes (885 normoalbuminuric control subjects and 820 advanced diabetic nephropathy case subjects).
The strongest associations in ELMO1 occurred at rs11769038 (odds ratio [OR] 1.24; P = 1.7 × 10−3) and rs1882080 (OR 1.23; P = 3.2 × 10−3) located in intron 16. Two additional SNPs, located in introns 18 and 20, respectively, were also associated with diabetic nephropathy. No evidence of association for variants previously reported in type 2 diabetes was observed in our collection.
Using GWAS data from the GoKinD collection, we comprehensively examined evidence of association across the ELMO1 locus. Our investigation marks the third report of associations in ELMO1 with diabetic nephropathy, further establishing its role in the susceptibility of this disease. There is evidence of allelic heterogeneity, contributed by the diverse genetic backgrounds of the different ethnic groups examined. Further investigation of SNPs at this locus is necessary to fully understand the commonality of these associations and the mechanism(s) underlying their role in diabetic nephropathy.
PMCID: PMC2768169  PMID: 19651817
12.  Transient Receptor Potential Canonical-3 Channel–Dependent Fibroblast Regulation in Atrial Fibrillation 
Circulation  2012;126(17):2051-2064.
Fibroblast proliferation and differentiation are central in atrial fibrillation (AF)–promoting remodeling. Here, we investigated fibroblast regulation by Ca2+-permeable transient receptor potential canonical-3 (TRPC3) channels.
Methods and Results
Freshly isolated rat cardiac fibroblasts abundantly expressed TRPC3 and had appreciable nonselective cation currents (INSC) sensitive to a selective TPRC3 channel blocker, pyrazole-3 (3 μmol/L). Pyrazole-3 suppressed angiotensin II-induced Ca2+ influx, proliferation, and α-smooth muscle actin protein expression in fibroblasts. Ca2+ removal and TRPC3 blockade suppressed extracellular signal-regulated kinase phosphorylation, and extracellular signal-regulated kinase phosphorylation inhibition reduced fibroblast proliferation. TRPC3 expression was upregulated in atria from AF patients, goats with electrically maintained AF, and dogs with tachypacing-induced heart failure. TRPC3 knockdown (based on short hairpin RNA [shRNA]) decreased canine atrial fibroblast proliferation. In left atrial fibroblasts freshly isolated from dogs kept in AF for 1 week by atrial tachypacing, TRPC3 protein expression, currents, extracellular signal-regulated kinase phosphorylation, and extracellular matrix gene expression were all significantly increased. In cultured left atrial fibroblasts from AF dogs, proliferation rates, α-smooth muscle actin expression, and extracellular signal-regulated kinase phosphorylation were increased and were suppressed by pyrazole-3. MicroRNA-26 was downregulated in canine AF atria; experimental microRNA-26 knockdown reproduced AF-induced TRPC3 upregulation and fibroblast activation. MicroRNA-26 has NFAT (nuclear factor of activated T cells) binding sites in the 5′ promoter region. NFAT activation increased in AF fibroblasts, and NFAT negatively regulated microRNA-26 transcription. In vivo pyrazole-3 administration suppressed AF while decreasing fibroblast proliferation and extracellular matrix gene expression.
TRPC3 channels regulate cardiac fibroblast proliferation and differentiation, likely by controlling the Ca2+ influx that activates extracellular signal-regulated kinase signaling. AF increases TRPC3 channel expression by causing NFAT-mediated downregulation of microRNA-26 and causes TRPC3-dependent enhancement of fibroblast proliferation and differentiation. In vivo, TRPC3 blockade prevents AF substrate development in a dog model of electrically maintained AF. TRPC3 likely plays an important role in AF by promoting fibroblast pathophysiology and is a novel potential therapeutic target.
PMCID: PMC3675169  PMID: 22992321
arrhythmia; calcium; ion channels; fibrillation; remodeling
13.  Differential Effects of MYH9 and APOL1 Risk Variants on FRMD3 Association with Diabetic ESRD in African Americans 
PLoS Genetics  2011;7(6):e1002150.
Single nucleotide polymorphisms (SNPs) in MYH9 and APOL1 on chromosome 22 (c22) are powerfully associated with non-diabetic end-stage renal disease (ESRD) in African Americans (AAs). Many AAs diagnosed with type 2 diabetic nephropathy (T2DN) have non-diabetic kidney disease, potentially masking detection of DN genes. Therefore, genome-wide association analyses were performed using the Affymetrix SNP Array 6.0 in 966 AA with T2DN and 1,032 non-diabetic, non-nephropathy (NDNN) controls, with and without adjustment for c22 nephropathy risk variants. No associations were seen between FRMD3 SNPs and T2DN before adjusting for c22 variants. However, logistic regression analysis revealed seven FRMD3 SNPs significantly interacting with MYH9—a finding replicated in 640 additional AA T2DN cases and 683 NDNN controls. Contrasting all 1,592 T2DN cases with all 1,671 NDNN controls, FRMD3 SNPs appeared to interact with the MYH9 E1 haplotype (e.g., rs942280 interaction p-value = 9.3E−7 additive; odds ratio [OR] 0.67). FRMD3 alleles were associated with increased risk of T2DN only in subjects lacking two MYH9 E1 risk haplotypes (rs942280 OR = 1.28), not in MYH9 E1 risk allele homozygotes (rs942280 OR = 0.80; homogeneity p-value = 4.3E−4). Effects were weaker stratifying on APOL1. FRMD3 SNPS were associated with T2DN, not type 2 diabetes per se, comparing AAs with T2DN to those with diabetes lacking nephropathy. T2DN-associated FRMD3 SNPs were detectable in AAs only after accounting for MYH9, with differential effects for APOL1. These analyses reveal a role for FRMD3 in AA T2DN susceptibility and accounting for c22 nephropathy risk variants can assist in detecting DN susceptibility genes.
Author Summary
African Americans have high rates of kidney disease attributed to type 2 diabetes mellitus. However, approximately 25% of patients are misclassified and have non-diabetic kidney disease on renal biopsy. The APOL1-MYH9 gene region on chromosome 22 is powerfully associated with non-diabetic kidney diseases in African Americans. Therefore, we tested for interactions between single nucleotide polymorphisms across the genome with APOL1 and MYH9 non-diabetic nephropathy risk variants in African Americans with presumed diabetic nephropathy. Markers in FRMD3, a gene associated with type 1 diabetic nephropathy in Caucasians, appeared to interact with MYH9; however, increased nephropathy risk was seen in diabetic cases lacking two MYH9 risk haplotypes, and protective effects were seen in those with two MYH9 risk haplotypes. Stratified analyses based on the chromosome 22 nephropathy risk haplotypes demonstrated that FRMD3 variants were associated with diabetic nephropathy risk in cases without two MYH9 (or APOL1) risk haplotypes. It appears that African Americans with diabetes and kidney disease who are not chromosome 22 nephropathy risk variant homozygotes are enriched for the presence of diabetic nephropathy and FRMD3 risk alleles. This genetic dissection ultimately allowed for detection of the FRMD3 diabetic nephropathy gene association in a subset of cases enriched for this disorder.
PMCID: PMC3116917  PMID: 21698141
14.  Abnormal expression, localization and interaction of canonical transient receptor potential ion channels in human breast cancer cell lines and tissues: a potential target for breast cancer diagnosis and therapy 
Ca2+ is known to be involved in a number of metastatic processes including motility and proliferation which can result in store-depletion of Ca2+. Up regulation of genes which contribute to store operated channel (SOC) activity may plausibly be necessary for these processes to take place efficiently. TRPC proteins constitute a family of conserved Ca2+-permeable channels that have been shown to contribute to SOC activity.
In breast cancer biopsy tissues, TRPC3 and TRPC6 were the predominant TRPC genes expressed with TRPC3 and TRPC6 being significantly up regulated compared to normal breast tissue. In the lowly metastatic breast cancer cell line MCF-7, TRPC6 was the chief TRPC gene expressed while in the highly metastatic breast cancer cell line MDA-MB-231 both TRPC3 and TRPC6 were the predominant TRPC genes expressed. Western blotting, immunoconfocal analysis and immunoprecipitation experiments confirmed that the MDA-MB-231 cell line expressed both TRPC3 and TRPC6 protein with the majority of protein being intracellular. TRPC3 and TRPC6 were found to be in an immunoprecipitatble complex and co-localize within the cell. To demonstrate the potential of targeting TRP channels in breast cancer, hyperforin reportably a specific activator of TRPC6 significantly reduced the growth and viability of the breast cancer cell lines but had no effect on the non-cancerous breast cell line. Silencing of TRPC6 in MDA-MB-231 cells resulted in a significant reduction in cell growth but not viability.
TRPC channels may be potential future targets for breast cancer diagnosis and therapy and deserve further investigation to evaluate their role in cancer cell physiology.
PMCID: PMC2737535  PMID: 19689790
15.  TRPC1 and TRPC6 Contribute to Hypoxic Pulmonary Hypertension through Differential Regulation of Pulmonary Vascular Functions RR 
Hypertension  2013;63(1):173-180.
Hypoxic pulmonary hypertension is characterized by increased vascular tone, altered vasoreactivity and vascular remodeling, which are associated with alterations in Ca2+ homeostasis in pulmonary arterial smooth muscle cells. We have previously shown that classical transient receptor potential 1 and 6 (TRPC1 and TRPC6) are upregulated in pulmonary arteries of chronic hypoxic rats, but it is unclear whether these channels are essential for the development of pulmonary hypertension. Here we found that pulmonary hypertension was suppressed in TRPC1 and TRPC6 knockout (Trpc1−/− and Trpc6−/−) mice compared to wildtype after exposure to 10% O2 for 1 and 3 weeks. Muscularization of pulmonary microvessels was inhibited, but rarefaction was unaltered in hypoxic Trpc1−/− and Trpc6−/− mice. Small pulmonary arteries of normoxic wildtype mice exhibited vasomotor tone, which was significantly enhanced by chronic hypoxia. Similar vasomotor tone was found in normoxic Trpc1−/− pulmonary arteries, but the hypoxia-induced enhancement was blunted. In contrast, there was minimal vascular tone in normoxic Trpc6−/− pulmonary arteries, but the hypoxia-enhanced tone was preserved. Chronic hypoxia caused significant increase in serotonin-induced vasoconstriction; the enhanced vasoreactivity was attenuated in Trpc1−/− and eliminated in Trpc6−/− pulmonary arteries. Moreover, the effects of 3-week hypoxia on pulmonary arterial pressure, right ventricular hypertrophy and muscularization of microvessels were further suppressed in Trpc1−/−Trpc6−/− double-knockout mice. Our results therefore provide clear evidence that TRPC1 and TRPC6 participate differentially in various pathophysiological processes; and the presence of TRPC1 and TRPC6 are essential for the full development of hypoxic pulmonary hypertension in the mouse model.
PMCID: PMC4102175  PMID: 24144647
Chronic hypoxia; pulmonary hypertension; vasoreactivity; vascular remodeling; vasomotor tone
16.  Molecular and clinical analysis of TRPC6 and AGTR1 genes in patients with pulmonary arterial hypertension 
Pulmonary arterial hypertension (PAH) is a rare and progressive vascular disorder characterized by increased pulmonary vascular resistance and right heart failure. The aim of this study was to analyze 5′UTR region in canonical transient receptor potential isoform 6 (TRPC6) and 3′UTR region in Angiotensin II type I receptor (AGTR1) genes in patients with idiopathic and associated PAH. Correlation among mutations and clinical and functional parameters was further analyzed.
Analysis of TRPC6 and AGTR1 genes was performed by polymerase chain reaction (PCR) and direct sequencing. We used a non-parametric test to determine if significant differences were found between the groups studied and chi-square test to compare clinical and hemodynamic variables among genotypes.
Fifty five patients and fifty two controls were included in this study. We found statistically significant differences for c.1-361A > T (p = 0.0077), c.1-254C > G (p < 0.0001) and c.1-218C > T (p = 0.0021) in TRPC6 gene and c.1166A > C (p < 0.001) in AGTR1 gene, between patients and controls. Idiopathic PAH patients (IPAH) and controls presented significant differences for all 3 TRPC6 polymorphisms (p = 0.020), (p = 0.002) and (p = 0.008) respectively, and also showed differences for AGTR1 gene (p < 0.001). In associated PAH (APAH) patients we found statistical differences for c.1-254C > G (p < 0.001) and c.1-218C > T (p = 0.001) in TRPC6 gene and c.1166A > C (p = 0.001) in AGTR1 gene. Several clinical and hemodynamic parameters showed significant differences between carriers and non-carriers of these single nucleotide polymorphisms (SNPs). Nineteen patients were carriers of all 3 SNPs in TRPC6 gene and presented a more severe phenotype with differences in mean pulmonary arterial pressure (p = 0.016), systolic pulmonary arterial pressure (p = 0.040), cardiac index (p < 0.001) and 6 minute walking test (p = 0.049). 16 of these patients harbored the SNP in AGTR1 gene. These patients showed differences in age at diagnosis (p = 0.049), mean pulmonary arterial pressure (p = 0.033), cardiac index (p = 0.002) and 6 minute walking test (p = 0.039).
PAH is a rare disease with pulmonary vascular remodeling caused in part by a heterogeneous constellation of genetic arrangements. This study seems to suggest that c.1-361A > T, c.1-254C > G and c.1-218C > T polymorphisms in TRPC6 gene and c.1166A > C polymorphism in AGTR1 could have a role in the development of this disease.
PMCID: PMC4307182  PMID: 25603901
Pulmonary Arterial Hypertension; TRPC6; AGTR1; Polymorphism; Correlation genotype/phenotype
17.  Evaluation of Candidate Nephropathy Susceptibility Genes in a Genome-Wide Association Study of African American Diabetic Kidney Disease 
PLoS ONE  2014;9(2):e88273.
Type 2 diabetes (T2D)-associated end-stage kidney disease (ESKD) is a complex disorder resulting from the combined influence of genetic and environmental factors. This study contains a comprehensive genetic analysis of putative nephropathy loci in 965 African American (AA) cases with T2D-ESKD and 1029 AA population-based controls extending prior findings. Analysis was based on 4,341 directly genotyped and imputed single nucleotide polymorphisms (SNPs) in 22 nephropathy candidate genes. After admixture adjustment and correction for multiple comparisons, 37 SNPs across eight loci were significantly associated (1.6E-05
PMCID: PMC3923777  PMID: 24551085
The Journal of General Physiology  2014;143(2):183-201.
Phosphatidylinositol 4,5-bisphosphate has a direct role in regulating receptor-operated TRPC channel activation and inactivation.
Transient receptor potential classical (or canonical) (TRPC)3, TRPC6, and TRPC7 are a subfamily of TRPC channels activated by diacylglycerol (DAG) produced through the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) by phospholipase C (PLC). PI(4,5)P2 depletion by a heterologously expressed phosphatase inhibits TRPC3, TRPC6, and TRPC7 activity independently of DAG; however, the physiological role of PI(4,5)P2 reduction on channel activity remains unclear. We used Förster resonance energy transfer (FRET) to measure PI(4,5)P2 or DAG dynamics concurrently with TRPC6 or TRPC7 currents after agonist stimulation of receptors that couple to Gq and thereby activate PLC. Measurements made at different levels of receptor activation revealed a correlation between the kinetics of PI(4,5)P2 reduction and those of receptor-operated TRPC6 and TRPC7 current activation and inactivation. In contrast, DAG production correlated with channel activation but not inactivation; moreover, the time course of channel inactivation was unchanged in protein kinase C–insensitive mutants. These results suggest that inactivation of receptor-operated TRPC currents is primarily mediated by the dissociation of PI(4,5)P2. We determined the functional dissociation constant of PI(4,5)P2 to TRPC channels using FRET of the PLCδ Pleckstrin homology domain (PHd), which binds PI(4,5)P2, and used this constant to fit our experimental data to a model in which channel gating is controlled by PI(4,5)P2 and DAG. This model predicted similar FRET dynamics of the PHd to measured FRET in either human embryonic kidney cells or smooth muscle cells, whereas a model lacking PI(4,5)P2 regulation failed to reproduce the experimental data, confirming the inhibitory role of PI(4,5)P2 depletion on TRPC currents. Our model also explains various PLC-dependent characteristics of channel activity, including limitation of maximum open probability, shortening of the peak time, and the bell-shaped response of total current. In conclusion, our studies demonstrate a fundamental role for PI(4,5)P2 in regulating TRPC6 and TRPC7 activity triggered by PLC-coupled receptor stimulation.
PMCID: PMC4001779  PMID: 24470487
Nephrology Dialysis Transplantation  2010;25(10):3348-3355.
Background. Non-diabetic forms of nephropathy commonly lead to end-stage renal disease (non-DM ESRD). Previous studies have demonstrated that African Americans are more susceptible to non-DM ESRD compared to other ethnic groups, and this risk has a strong genetic component. A genome-wide scan for ESRD in African American families enriched for non-DM ESRD showed evidence for linkage in chromosome 13q33.3, and a candidate gene in this region, klotho, was selected for a detailed analysis in a follow-up case-control association study.
Methods. Thirty-four single-nucleotide polymorphisms (SNPs) in the klotho gene were genotyped in 317 unrelated African American non-DM ESRD cases and 354 non-nephropathy controls, including 12 SNPs identified by re-sequencing a region around exon 4.
Results. Two SNPs demonstrated modest admixture-adjusted evidence of association with non-DM ESRD, rs650439 (P = 0.013, recessive model) and rs643780 (P = 0.017, recessive model), while rs17643698 approached significance (P = 0.0953, two degrees of freedom test). Eight of the most significant SNPs were tested for replication in a second case-control collection (557 African American non-DM ESRD cases and 187 controls), and there was no evidence of association in replicate cases and controls; nor when the samples were combined for a total of 874 non-DM cases and 541 controls. Cox proportional hazards models were computed to test for association between polymorphisms in klotho and age at onset of ESRD. A three-SNP haplotype, rs526906, rs525014 and rs571118 (T/T/A), was associated with age of onset of ESRD [P = 0.007, recessive model; hazard ratio (HR) = 0.70]. Subjects homozygous for this haplotype had a mean 4 years later onset of ESRD, suggesting a slower disease progression. HapMap subjects homozygous for this haplotype had increased expression of klotho, further supporting a protective role of this variant in ESRD.
Conclusion. We conclude that three SNPs in intron 1 of the klotho gene are associated with delayed age at onset of non-DM ESRD in African Americans.
PMCID: PMC2948839  PMID: 20466664
genetics; klotho; non-diabetic ESRD
Biomarker Insights  2010;5:29-32.
The fat mass and obesity associated (FTO) gene has an important genetic effect on body mass index (BMI) and risk of obesity, and obesity contributes to the progression of renal diseases, including diabetic nephropathy. We thus conducted a genetic association study to evaluate whether the FTO gene confers the risk susceptibility to the development of diabetic nephropathy. Genotyping experiments of the common FTO polymorphism, rs9939609, in 1170 type 1 diabetes patients with (n = 597) or without diabetic nephropathy (n = 573) were performed with TaqMan allelic discrimination. All subjects are of European descent and selected from the Genetics of Kidney Diseases in Diabetes (GoKinD) study. The frequency of T allele of this polymorphism was 0.414 in the studied population. There was no allelic association of this polymorphism with diabetic nephropathy. But, the risk susceptibility of A allele conferring to the increased BMI among type 1 diabetes patients was observed. The subjects carrying with AA genotype had higher BMI compared to the carriers with TA and/or TT genotype(s) (P ≤ 0.019). The present study provides evidence that the common FTO genetic polymorphism, rs9939609, is associated with increased BMI in type 1 diabetes but not with diabetic nephropathy.
PMCID: PMC2867633  PMID: 20467478
diabetic nephropathy; fat mass and obesity associated; genetic association; single nucleotide polymorphism
The Journal of Neuroscience  2014;34(10):3653-3667.
Transient receptor potential (TRP) channels are abundant in the brain where they regulate transmission of sensory signals. The expression patterns of different TRPC subunits (TRPC1, 4, and 5) are consistent with their potential role in fear-related behaviors. Accordingly, we found recently that mutant mice lacking a specific TRP channel subunit, TRPC5, exhibited decreased innate fear responses. Both TRPC5 and another member of the same subfamily, TRPC4, form heteromeric complexes with the TRPC1 subunit (TRPC1/5 and TRPC1/4, respectively). As TRP channels with specific subunit compositions may have different functional properties, we hypothesized that fear-related behaviors could be differentially controlled by TRPCs with distinct subunit arrangements. In this study, we focused on the analysis of mutant mice lacking the TRPC4 subunit, which, as we confirmed in experiments on control mice, is expressed in brain areas implicated in the control of fear and anxiety. In behavioral experiments, we found that constitutive ablation of TRPC4 was associated with diminished anxiety levels (innate fear). Furthermore, knockdown of TRPC4 protein in the lateral amygdala via lentiviral-mediated gene delivery of RNAi mimicked the behavioral phenotype of constitutive TRPC4-null (TRPC4−/−) mouse. Recordings in brain slices demonstrated that these behavioral modifications could stem from the lack of TRPC4 potentiation in neurons in the lateral nucleus of the amygdala through two Gαq/11 protein-coupled signaling pathways, activated via Group I metabotropic glutamate receptors and cholecystokinin 2 receptors, respectively. Thus, TRPC4 and the structurally and functionally related subunit, TRPC5, may both contribute to the mechanisms underlying regulation of innate fear responses.
PMCID: PMC3942581  PMID: 24599464
amygdala; anxiety; cholecystokinin 4; fear; TRP channel; TRPC4
Seminars in nephrology  2010;30(2):126-140.
The Genetics of Kidneys in Diabetes (GoKinD) study was initiated to facilitate research aimed at identifying genes involved in diabetic nephropathy (DN) in type 1 diabetes (T1D). In this review, we present on overview of this study and the various reports that have utilized its collection. At the forefront of these efforts is the recent genome-wide association (GWA) scan implemented on the GoKinD collection. We highlight the results from our analysis of these data and describe compelling evidence from animal models that further support the potential role of associated loci in the susceptibility of DN. To enhance our analysis of genetic associations in GoKinD, using genome-wide imputation (GWI), we expanded our analysis of this collection to include genotype data from more than 2.4 million common SNPs. We illustrate the added utility of this enhanced dataset through the comprehensive fine-mapping of candidate genomic regions previously linked with DN and the targeted investigation of genes involved in candidate pathway implicated in its pathogenesis. Collectively, GWA and GWI data from the GoKinD collection will serve as a springboard for future investigations into the genetic basis of DN in T1D.
PMCID: PMC2847588  PMID: 20347642
genome-wide association; diabetic nephropathy; type 1 diabetes; imputation
Circulation  2009;119(17):2313-2322.
Excessive proliferation of pulmonary artery smooth muscle cells (PASMCs) plays an important role in the development of idiopathic pulmonary arterial hypertension (IPAH), whereas a rise in cytosolic Ca2+ concentration triggers PASMC contraction and stimulates PASMC proliferation. Recently, we demonstrated that upregulation of the TRPC6 channel contributes to proliferation of PASMCs isolated from IPAH patients. This study sought to identify single-nucleotide polymorphisms (SNPs) in the TRPC6 gene promoter that are associated with IPAH and have functional significance in regulating TRPC6 activity in PASMCs.
Methods and Results
Genomic DNA was isolated from blood samples of 237 normal subjects and 268 IPAH patients. Three biallelic SNPs, −361 (A/T), −254(C/G), and −218 (C/T), were identified in the 2000-bp sequence upstream of the transcriptional start site of TRPC6. Although the allele frequencies of the −361 and −218 SNPs were not different between the groups, the allele frequency of the −254(C→G) SNP in IPAH patients (12%) was significantly higher than in normal subjects (6%; P<0.01). Genotype data showed that the percentage of −254G/G homozygotes in IPAH patients was 2.85 times that of normal subjects. Moreover, the −254(C→G) SNP creates a binding sequence for nuclear factor-κB. Functional analyses revealed that the −254(C→G) SNP enhanced nuclear factor-κB–mediated promoter activity and stimulated TRPC6 expression in PASMCs. Inhibition of nuclear factor-κB activity attenuated TRPC6 expression and decreased agonist-activated Ca2+ influx in PASMCs of IPAH patients harboring the −254G allele.
These results suggest that the −254(C→G) SNP may predispose individuals to an increased risk of IPAH by linking abnormal TRPC6 transcription to nuclear factor-κB, an inflammatory transcription factor.
PMCID: PMC2749566  PMID: 19380626
calcium; hypertension; pulmonary; ion channels; muscle, smooth; NF-kappa B
Journal of cellular physiology  2012;227(4):1408-1419.
Transient Receptor Potential Canonical (TRPC) channels are implicated in modulating neurite outgrowth. The expression pattern of TRPC changes significantly during brain development, suggesting that fine-tuning TRPC expression may be important for orchestrating neuritogenesis. To study how alterations in the TRPC expression pattern affect neurite outgrowth, we used nerve growth factor (NGF)-differentiated rat pheochromocytoma 12 (PC12) cells, a model system for neuritogenesis. In PC12 cells, NGF markedly up-regulated TRPC1 and TRPC6 expression, but down-regulated TRPC5 expression while promoting neurite outgrowth. Overexpression of TRPC1 augmented, whereas TRPC5 overexpression decelerated NGF-induced neurite outgrowth. Conversely, shRNA-mediated knockdown of TRPC1 decreased, whereas shRNA-mediated knockdown of TRPC5 increased NGF-induced neurite extension. Endogenous TRPC1 attenuated the anti-neuritogenic effect of overexpressed TRPC5 in part by forming the heteromeric TRPC1–TRPC5 channels. Previous reports suggested that TRPC6 may facilitate neurite outgrowth. However, we found that TRPC6 overexpression slowed down neuritogenesis, whereas dominant negative TRPC6 (DN-TRPC6) facilitated neurite outgrowth in NGF-differentiated PC12 cells. Consistent with these findings, hyperforin, a neurite outgrowth promoting factor, decreased TRPC6 expression in NGF-differentiated PC12 cells. Using pharmacological and molecular biological approaches, we determined that NGF up-regulated TRPC1 and TRPC6 expression via a p75NTR-IKK2-dependent pathway that did not involve TrkA receptor signaling in PC12 cells. Similarly, NGF up-regulated TRPC1 and TRPC6 via an IKK2 dependent pathway in primary cultured hippocampal neurons. Thus, our data suggest that a balance of TRPC1, TRPC5, and TRPC6 expression determines neurite extension rate in neural cells, with TRPC6 emerging as an NGF-dependent “molecular damper” maintaining a submaximal velocity of neurite extension.
PMCID: PMC4035231  PMID: 21618530
TRPC channels; NF-κB; IKK2; neurite outgrowth; PC12 cells; hippocampal neurons
Canonical Transient Receptor Potential (TRPC) channel proteins have been identified as downstream molecules in a G protein coupled receptor signaling pathway and are involved in a variety of cell functions due to their ability to regulate intracellular calcium signaling. TRPC channel physiology has been an increasingly interesting and relevant topic over the past decade, and the outcomes from various studies have advanced our understanding of TRPC function in the normal state. Recently, attention has turned to whether or not TRPC proteins are implicated in diseases. Emerging evidence suggests a significant contribution of several isoforms of TRPC proteins to cardiovascular as well as renal diseases. This review focuses on the implication of TRPC proteins as they pertain to diabetes. We summarize the recent findings by other investigators as well as ourselves and additionally discuss the important role of TRPC proteins in the development of various diabetic complications, such as diabetic nephropathy and diabetic vasculopathy. The underlying mechanisms which contribute to these complications are also outlined. Lastly, we elaborate on the role of TRPC proteins as a potential therapeutic target for treating diabetes-associated diseases.
PMCID: PMC3307128  PMID: 22282397
TRPC; Diabetes; Diabetic complications; Calcium

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