Children from diabetic pregnancies have a greater incidence of Type 2 diabetes. Our objective was to determine if exposure to mild-moderate hyperglycemia, modeling managed diabetic pregnancies, affects fetal β-cell function. In sheep fetuses β-cell responsiveness was examined after two weeks of sustained hyperglycemia with 3 pulses/day, mimicking postprandial excursions, and compared to saline-infused controls (n=10). Two pulsatile hyperglycemia treatments were studied: mild (mPHG, n=5) with +15% sustained and +55% pulse; and moderate (PHG, n=10) with +20% sustained and +100% pulse. Fetal glucose-stimulated insulin secretion and glucose potentiated arginine insulin secretion were lower (P<0.05) in PHG (0.86±0.13 and 2.91±0.39 ng/ml plasma insulin) but not mPHG fetuses (1.21±0.08 and 4.25±0.56 ng/ml) compared to controls (1.58±0.25 and 4.51±0.56 ng/ml). Islet insulin content was 35% lower in PHG and 35% higher in mPHG versus controls (P<0.01). Insulin secretion and maximally stimulated insulin release were also reduced (P<0.05) in PHG islets due to lower islet insulin content. Isolated PHG islets also had 63% greater (P<0.01) ROS accumulation at 11.1 mmol/L glucose than controls (P<0.01), but oxidative damage was not detected in islet proteins. PHG fetuses showed evidence of oxidative damage to skeletal muscle proteins (P<0.05) but not insulin resistance. Our findings show that PHG induced dysregulation of islet ROS handling and decreased islet insulin content, but these outcomes are independent. The β-cell outcomes were dependent on the severity of hyperglycemia because mPHG fetuses had no distinguishable impairments in ROS handling or insulin secretion but greater insulin content.
Gestational diabetes; GSIS; islets of Langerhans; oxidative stress; ROS
During normal pregnancy, dramatically increased placental blood flow is critical for fetal growth and survival as well as neonatal birth weights and survivability. This increased blood flow results from angiogenesis, vasodilatation, and vascular remodeling. Locally produced growth factors including fibroblast growth factor2 (FGF2) and vascular endothelial growth factor (VEGFA) are key regulators of placental endothelial functions including cell proliferation, migration, and vasodilatation. However, the precise signaling mechanisms underlying such regulation in fetoplacental endothelium are less well defined, specifically with regard to the interactions amongst protein kinases, protein phosphatase, and nitric oxide (NO). Recently we and others researchers have obtained solid evidence showing that different signaling mechanisms participate in FGF2- and VEGFA-regulated fetoplacental endothelial cell proliferation and migration as well as NO production. This review will briefly summarize currently available data on signaling mediating fetoplacental angiogenesis with a specific emphasis on protein kinases, ERK1/2, AKT1, and p38 MAPK and protein phosphatases, PPP2 and PPP3.
The adipokine leptin is primarily produced by white adipose tissue (AT) and is a potent monocyte/macrophage chemoattractant in vitro. The long form of the leptin receptor (LepR) is required for monocyte/macrophage chemotaxis towards leptin. In this study, we examined the effects of haematopoietic LepR as well as LepR with C-C Chemokine Receptor 2 (CCR2) deficiency (double knockout; DKO) on macrophage recruitment to AT after two different periods of high fat diet (HFD) feeding. Briefly, 8 week old C57BL/6 mice were transplanted with bone marrow from LepR+/+, LepR-/- or DKO donors (groups named BM-LepR+/+, BMLepR-/- and BM-DKO, respectively), and were placed on a HFD for 6 or 12 weeks. At the end of the study, macrophage infiltration and the inflammatory state of AT were evaluated by real-time RT-PCR, histology, and flow cytometry. In addition, glucose and insulin tolerance were assessed at both time points. Our results showed no differences in macrophage accumulation or AT inflammatory state between the BM-LepR+/+ and BM-LepR-/- mice after 6 or 12 weeks of HFD feeding; any effects observed in the BM-DKO were attributed to the haematopoietic deficiency of CCR2. In addition, no changes in glucose or insulin tolerance were observed between groups after either period of HFD feeding. Our findings suggest that although leptin is a potent chemoattractant in vitro, haematopoietic LepR deficiency does not affect macrophage accumulation in AT in early to moderate stages of diet induced obesity.
Leptin; leptin receptor; macrophage; adipose tissue; obesity
Suppression of TSH release from the hypothyroid thyrotrophs is one of the most rapid effects of T3 or T4. It is initiated within an hour, and precedes the decrease in TSHβ mRNA inhibition and is blocked by inhibitors of mRNA or protein synthesis. TSH elevation in primary hypothyroidism requires both the loss of feedback inhibition by thyroid hormone in the thyrotrophs and the positive effects of TRH. Another event in this feed back regulation may be the thyroid hormone induction of the TRH-inactivating pyroglutamyl peptidase II (PPII) in the hypothalamic tanycytes. This study compared the chronology of the acute effects of T3 or T4 on TSH suppression, TRH mRNA in the hypothalamic paraventricular nucleus (PVN), and the induction of tanycyte PPII. In wild type mice, T3 or T4 caused a 50% decrease in serum TSH in hypothyroid mice by 5 hours. There was no change in TRH mRNA in PVN over this interval, but there was a significant increase in PPII mRNA in the tanycytes. In mice with genetic inactivation of the type 2 iodothyronine deiodinase, T3 decreased serum TSH and increased PPII mRNA levels, while T4-treatment was ineffective. We conclude that the rapid suppression of TSH in the hypothyroid mouse by T3 occurs prior to a decrease in TRH mRNA though TRH inactivation may be occurring in the median eminence through the rapid induction of tanycyte PPII. The effect of T4, but not T3, requires the type 2 iodothyronine deiodinase.
type 2 deiodinase; feed-back; thyrotroph; TSH; hypothalamus; TRH; PPII; hypothyroid; thyroxine; triiodothyronine
Excessive fat accumulation in liver (hepatic steatosis) predisposes to hepatic functional and structural impairment and overall metabolic risk. Previous studies noted an association between hepatic steatosis and age in humans and rodents. However, the mechanisms leading to age-associated hepatic fat accumulation remain unknown. Earlier work from our group showed that β-adrenergic receptor (β-AR) levels and β-AR-stimulated adenylyl cyclase activity increase in rat liver during aging. Here we investigated whether age-associated increases in β-AR signaling play a role in augmenting hepatic lipid accumulation. We demonstrate an increase in hepatic lipid content during senescence and a significant correlation between hepatic fat content and stimulation of adenylyl cyclase activity by the β-AR agonist isoproterenol in rat liver. Isoproterenol administration to young and old rodents in vivo increased hepatic lipid accumulation. Furthermore, in vitro overexpression of β1- and β2-AR subtypes in hepatocytes from young rodents increased cellular lipid content, whereas inhibition of β-ARs by receptor subtype-specific inhibitors reduced lipid levels in hepatocytes from senescent animals. Isoproterenol-induced hepatic lipid accumulation in vivo was prevented by the β-AR nonselective blocker propranolol, suggesting a novel therapeutic effect of this class of drugs in hepatic steatosis. Acipimox, which inhibits adipose tissue lipolysis, did not alter isoproterenol-mediated hepatic fat accumulation; thus β-AR responsive hepatic lipid accumulation does not appear to be related primarily to altered lipolysis. These findings suggest that augmented hepatic β-AR signaling during aging may increase lipid accumulation in liver and advocate a possible role for β-adrenergic blockers in preventing or retarding the development of hepatic steatosis.
Elevation of dietary or brain leucine appears to suppress food intake via a mechanism involving mTOR, AMPK and/or branched chain amino acid (BCAA) metabolism. Mice bearing a deletion of mitochondrial branched chain amino transferase (BCATm), which is expressed in peripheral tissues (muscle) and brain glia, exhibit marked increases in circulating BCAAs. Here we test whether this increase in circulating BCAAs alters feeding behavior and brain neuropeptide expression. Circulating and brain levels of BCAAs were increased 2-4 fold in BCATm-deficient mice (KO). KO mice weighed less than controls (25.9 vs. 20.4g, P < 0.01), but absolute food intake was relatively unchanged. In contrast to wildtype mice, KO mice preferred a low BCAA diet to a control diet (P < 0.05), but exhibited no change in preference for low vs. high protein diets. KO mice also exhibited low leptin levels and increased hypothalamic NPY and AgRP mRNA. Normalization of circulating leptin levels had no effect on either food preference or the increased NPY and AgRP mRNA expression. If BCAAs act as signals of protein status, one would expect reduced food intake, an avoidance of dietary protein, and a reduction in neuropeptide expression in BCATm-KO mice. Instead, these mice exhibit increased expression of orexigenic neuropeptides and an avoidance of BCAAs but not high protein. These data thus suggest either that BCAAs do not act as physiological signals of protein status, or that the loss of BCAA metabolism within brain glia impairs the detection of protein balance.
protein intake; amino acid metabolism; hypothalamus; leucine
The neuropeptide apelin is expressed in hypothalamic paraventricular and supraoptic nuclei and mediates its effects via activation of the apelin receptor (APJ). Evidence suggests a role for apelin and APJ in mediating the neuroendocrine response to stress. To understand the physiological role of APJ in regulation of the hypothalamic–pituitary–adrenal (HPA) axis, we measured ACTH and corticosterone (CORT) plasma levels in male and female mice lacking APJ (APJ knockout, APJ KO) and in wild-type controls, in response to a variety of acute stressors. Exposure to mild restraint, systemic injection of lipopolysaccharide (LPS), insulin-induced hypoglycaemia and forced swim (FS) stressors, elevated plasma ACTH and CORT levels in wild-type mice. Acute mild restraint significantly increased plasma ACTH and CORT to a similar level in APJ KO mice as in wild-type mice. However, an intact APJ was required for a conventional ACTH, but not CORT, response to LPS administration in male mice and to insulin-induced hypoglycaemia in male and female mice. In contrast, APJ KO mice displayed an impaired CORT response to acute FS stress, regardless of gender. These data indicate that APJ has a role in regulation of the HPA axis response to some acute stressors and has a gender-specific function in peripheral immune activation of the HPA axis.
In this study, we investigated the role of intercellular adhesion molecule-2 (ICAM2) in the testis. ICAM2 is a cell adhesion protein having important roles in cell migration, especially during inflammation when leukocytes cross the endothelium. Herein, we showed ICAM2 to be expressed by germ and Sertoli cells in the rat testis. When a monospecific antibody was used for immunolocalization experiments, ICAM2 was found to surround the heads of elongating/elongated spermatids in all stages of the seminiferous epithelial cycle. To determine whether ICAM2 is a constituent of apical ectoplasmic specialization (ES), co-immunoprecipitation and dual immunofluorescence staining were performed. Interestingly, ICAM2 was found to associate with β1-integrin, nectin-3, afadin, Src, proline-rich tyrosine kinase 2, annexin II, and actin. Following CdCl2 treatment, ICAM2 was found to be upregulated during restructuring of the seminiferous epithelium, with round spermatids becoming increasingly immunoreactive for ICAM2 by 6–16 h. Interestingly, there was a loss in the binding of ICAM2 to actin during CdCl2-induced germ cell loss, suggesting that a loss of ICAM2–actin interactions might have facilitated junction restructuring. Taken collectively, these results illustrate that ICAM2 plays an important role in apical ES dynamics during spermatogenesis.
ICAM2; testis; cadmium chloride; cell junction
Low birth weight is an important risk factor for impaired glucose tolerance and diabetes later in life. One hypothesis is that fetal β-cells inherit a persistent defect as a developmental response to fetal malnutrition, a primary cause of intrauterine growth restriction (IUGR). Our understanding of fetal programming events in the human endocrine pancreas is limited, but several animal models of IUGR extend our knowledge of developmental programming in β-cells. Pathological outcomes such as β-cell dysfunction, impaired glucose tolerance, and diabetes are often observed in adult offspring from these animal models, similar to the associations of low birth weight and metabolic diseases in humans. However, the identified mechanisms underlying β-cell dysfunction across models and species are varied, likely resulting from the different methodologies used to induce experimental IUGR, as well as intraspecies differences in pancreas development. In this review, we first present the evidence for human β-cell dysfunction being associated with low birth weight or IUGR. We then evaluate relevant animal models of IUGR, focusing on the strengths of each, in order to define critical periods and types of nutrient deficiencies that can lead to impaired β-cell function. These findings frame our current knowledge of β-cell developmental programming and highlight future research directions to clarify the mechanisms of β-cell dysfunction for human IUGR.
Insulin Secretion; Pancreas; Pregnancy; Diabetes; Fetus
Circulating IGFBP-1 levels vary in response to nutritional status, and preclinical studies suggest that elevated IGFBP-1 may be protective against the development and progression of prostate cancer. We hypothesized that global deletion of IGFBP-1 would accelerate the development of prostate cancer in a c-Myc transgenic mouse model. To test our hypothesis, c-Myc transgenic mice (Myc/BP-1 WT) were crossed and interbred with the IGFBP-1 knockout mice (Myc/BP-1 KO). The animals were placed on a high protein diet at weaning, weighed every two weeks, and euthanized at 16 weeks of age. Prostate histopathology was assessed and proliferation status was determined by Ki 67 and PCNA analyses. IGF-related serum biomarkers and body composition were measured. No significant difference in the incidence of prostate cancer was observed between the Myc/BP-1 KO and Myc/BP-1 WT mice (65% and 80% respectively, p= 0.48). Proliferation was significantly decreased by 71% in prostate tissue of Myc/BP-1 KO mice compared to Myc/BP-1 WT mice. Myc/BP-1 KO mice exhibited a significant 6.7% increase in body weight relative to the Myc/BP-1 WT mice attributed to an increase in fat mass. Fasting insulin levels were higher in the Myc/BP-1 KO mice without any difference between the groups in fasting glucose concentrations. Thus, contrary to our hypothesis, global deletion of IGFBP-1 in a c-Myc transgenic mouse model did not accelerate the development of prostate cancer. Global IGFBP-1 deletion did result in a significant increase in body weight and body fat mass. Further studies are required to understand the underlying mechanisms for these metabolic effects.
Myc; IGFBP-1 knockout; IGF-1; IGFBP; prostate cancer; proliferation; body composition; insulin
Oxyntomodulin (OXM) is a peptide secreted from the L cells of the gut following nutrient ingestion. OXM is a dual agonist of the glucagon-like peptide-1 receptor (GLP1R) and the glucagon receptor (GCGR) combining the effects of GLP1 and glucagon to act as a potentially more effective treatment for obesity than GLP1R agonists. Injections of OXM in humans cause a significant reduction in weight and appetite, as well as an increase in energy expenditure. Activation of GCGR is classically associated with an elevation in glucose levels, which would be deleterious in patients with T2DM, but the antidiabetic properties of GLP1R agonism would be expected to counteract this effect. Indeed, OXM administration improved glucose tolerance in diet-induced obese mice. Thus, dual agonists of the GCGR and GLP1R represent a new therapeutic approach for diabetes and obesity with the potential for enhanced weight loss and improvement in glycemic control beyond those of GLP1R agonists.
The mechanisms underlying menopausal hot flushes are poorly understood, although it is generally assumed they result from disturbances of thermoregulatory centres in the hypothalamus. 8-prenylnaringenin (8-PN) has been identified as a potent phytoestrogen in hops (Humulus lupulus) and there are claims that hop-containing preparations can reduce hot flushes. We have investigated the site of action of 8-PN in a rat model of menopausal hot flushes, in which the tail skin temperature (TST) is increased after oestrogen withdrawal induced by ovariectomy. Daily subcutaneous administration of either 17β-oestradiol (E2; 4 μg/kg) or 8-PN (400 μg/kg) significantly reduced the elevated TST after 2 days of treatment. Subcutaneous co-administration of either E2 or 8-PN with the oestrogen receptor (ER) antagonist, ICI 182,780 (200 μg/kg), which is thought not to cross the blood-brain-barrier, completely blocked the effect of E2 and 8-PN on TST. The ERα and ERβ specific agonists, PPT (100 μg/kg) and DPN (60 μg/kg) respectively, both significantly reversed the raised TST in ovariectomised rats. These observations suggest that the regulation of the vasomotor response by oestrogens and phytoestrogens is mediated, at least in part, by peripheral mechanisms involving both ERα and ERβ.
Oestrogen; Phytoestrogen; Menopause; 8-prenylnaringenin; Rat
Studies on bone development, formation and turnover have grown exponentially over the last decade in part because of the utility of genetic models. One area that has received considerable attention has been the PI3K signaling pathway, which has emerged as a major survival network for osteoblasts. Genetic engineering has enabled investigators to study downstream effectors of PI3K by directly over-expressing activated forms of AKT in cells of the skeletal lineage or deleting Pten which leads to a constitutively active AKT. The results from these studies have provided novel insights into bone development and remodeling, critical processes in the lifelong maintenance of skeletal health. This paper reviews those data in relation to recent advances in osteoblast biology and their potential relevance to chronic disorders of the skeleton and their treatment.
In mammals, parathyroid hormone (PTH), secreted by parathyroid glands, increases calcium levels in the blood from reservoirs in bone. While mammals have two PTH receptor genes, PTH1R and PTH2R, zebrafish has three, pth1r, pth2r and pth3r. PTH can activate all three zebrafish Pthrs while PTH2 (alias tuberoinfundibular peptide 39, TIP39) preferentially activates zebrafish and mammalian PTH2Rs. We know little about the roles of the PTH2/PTH2R system in the development of any animal. To determine the roles of PTH2 and PTH2R during vertebrate development, we evaluated their expression patterns in developing zebrafish, observed their phylogenetic and conserved synteny relationships with humans, and described the genomic organization of pth2, pth2r, and pth2r splice variants. Expression studies showed that pth2 is expressed in cells adjacent to the ventral part of the posterior tuberculum in the diencephalon, whereas pth2r is robustly expressed throughout the CNS. Otic vesicles express both pth2 and pth2r, but heart expresses only pth2. Analysis of mutants showed that Hedgehog (Hh) signaling regulates the expression of pth2 transcripts more than that of nearby gnrh2-expressing cells. Genomic analysis showed that a lizard, chicken, and zebra finch lack a PTH2 gene, which is associated with an inversion breakpoint. Likewise, chickens lack PTH2R, while humans lack PTH3R, a case of reciprocally missing ohnologs (paralogs derived from a genome duplication). The considerable evolutionary conservation in genomic structure, synteny relationships, and expression of zebrafish pth2 and pth2r provides a foundation for exploring the endocrine roles of this system in developing vertebrate embryos.
pth; pth receptor; pth2 evolution; pth2 development; pthr gene duplication
While the Renin-Angiotensin System is important for adrenomedullary responses to stress, the involvement of specific angiotensin II receptor subtypes is unclear. We examined gene expression changes of angiotensin II type 1A (AT1A) and type 2 (AT2) receptors in rat adrenal medulla in response to immobilization stress (IMO). AT2 receptor mRNA levels decreased immediately after a single 2 h IMO. Repeated IMO also decreased AT2 receptor mRNA levels, but the decline was more transient. AT1A receptor mRNA levels were unaltered with either single or repeated IMO, although binding was increased following repeated IMO. These effects of stress on angiotensin II receptor expression may alter catecholamine biosynthesis, as tyrosine hydroxylase and dopamine beta-hydroxylase mRNA levels in PC12 cells are decreased with angiotensin II treatment in the presence of ZD7155 (AT1 receptor antagonist), or with CGP42112 (AT2 receptor agonist) treatment. Involvement of stress-triggered activation of the hypothalamic-pituitary-adrenocortical (HPA) or sympatho-adrenal axis in AT2 receptor downregulation was examined. Cultured cells treated with the synthetic glucocorticoid dexamethasone displayed a transcriptionally-mediated decrease in AT2 receptor mRNA levels. However, glucocorticoids are not required for the immediate stress-triggered decrease in AT2 receptor gene expression, as demonstrated in corticotropin-releasing hormone knockout (CRH KO) mice and hypophysectomized rats, although they can regulate basal gene expression. cAMP and pituitary adenylate cyclase-activating polypeptide (PACAP) also reduced AT2 receptor gene expression and may mediate this response. Overall, the effects of stress on adrenomedullary AT1A and AT2 receptor expression may contribute to allostatic changes, such as regulation of catecholamine biosynthesis.
Stress; renin-angiotensin system; angiotensin II receptors; glucocorticoids; dexamethasone; tyrosine hydroxylase; dopamine beta-hydroxylase; cAMP; pituitary adenylate cyclase-activating polypeptide
GH and its anabolic mediator, IGF1, are important not only in somatic growth but also in the regulation of brain function. Even though GH treatment has been used clinically to improve body composition and exercise capacity in adults, its influence on central nervous system function has only recently been recognized. This is also the case for children with childhood-onset GH deficiency (GHD) where GH has been used to stimulate bone growth and enhance final adult height. Circulating IGF1 is transported across the blood–brain barrier and IGF1 and its receptors are also synthesized in the brain by neurons and glial and endothelial cells. Nevertheless, the relationship between circulating IGF1 and brain IGF1 remains unclear. This study, using a GH-deficient dwarf rat model and peripheral GH replacement, investigated the effects of circulating IGF1 during adolescence on IGF1 levels in the brain. Our results demonstrated that hippocampal IGF1 protein concentrations during adolescence are highly regulated by circulating IGF1, which were reduced by GHD and restored by systematic GH replacement. Importantly, IGF1 levels in the cerebrospinal fluid were decreased by GHD but not restored by GH replacement. Furthermore, analysis of gene expression using microarrays and RT-PCR indicated that circulating IGF1 levels did not modify the transcription of Igf1 or its receptor in the hippocampus but did regulate genes that are involved in microvascular structure and function, brain development, and synaptic plasticity, which potentially support brain structures involved in cognitive function during this important developmental period.
Nicotine induces weight loss in both humans and rodents consuming a regular diet; however, the effect of nicotine on body weight and fat composition in rodents consuming a high-fat diet (HFD) has not been well studied. Thus, this study examined the effect of nicotine vs saline on body weight and fat composition in mice fed with either an HFD (62% of kcal from fat) or a standard normal chow diet (NCD) for 7 weeks. Nicotine dose dependently reduced body weight gain in mice that consumed both diets, but this effect was significantly greater in mice on the HFD. Caloric intake was decreased in nicotine-treated mice. Estimates of energy intake suggested that decreased caloric intake accounted for all the reduced weight gain in mice on an NCD and 66% of the reduced weight gain on an HFD. Computed tomography analysis for fat distribution demonstrated that nicotine was effective in reducing abdominal fat in mice that consumed the HFD, with nicotine treatment leading to lower visceral fat. The effect of nicotine on weight loss in mice on an HFD was completely blocked by mecamylamine, a nonselective nicotinic acetylcholine receptor (nAChR) antagonist, but only partially blocked by the α4β2 nAChR partial agonist/antagonist, varenicline. We conclude that nicotine is effective in preventing HFD-induced weight gain and abdominal fat accumulation.
Glucocorticoid concentrations are a balance between production under the negative feedback control and diurnal rhythm of the hypothalamic–pituitary–adrenal (HPA) axis and peripheral metabolism, for example by the enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1), which catalyses the reduction of inactive cortisone (11-dehydrocorticosterone (11-DHC) in mice) to cortisol (corticosterone in mice). Reductase activity is conferred upon 11β-HSD1 by hexose-6-phosphate dehydrogenase (H6PDH). 11β-HSD1 is implicated in the development of obesity, and selective 11β-HSD1 inhibitors are currently under development. We sought to address the concern regarding potential up-regulation of the HPA axis associated with inhibition of 11β-HSD1. We assessed biomarkers for allele combinations of 11β-HSD1 and H6PDH derived from double heterozygous mouse crosses. H6PDH knock out (KO) adrenals were 69% larger than WT while 11β-HSD1 KO and double KO (DKO) adrenals were ∼30% larger than WT – indicative of increased HPA axis drive in KO animals. ACTH-stimulated circulating corticosterone concentrations were 2·2-fold higher in H6PDH KO animals and ∼1·5-fold higher in 11β-HSD1 KO and DKO animals compared with WT, proportional to the observed adrenal hypertrophy. KO of H6PDH resulted in a substantial increase in urinary DHC metabolites in males (65%) and females (61%). KO of 11β-HSD1 alone or in combination with H6PDH led to significant increases (36 and 42% respectively) in urinary DHC metabolites in females only. Intermediate 11β-HSD1/H6PDH heterozygotes maintained a normal HPA axis. Urinary steroid metabolite profile by gas chromatography/mass spectrometry as a biomarker assay may be beneficial in assaying HPA axis status clinically in cases of congenital and acquired 11β-HSD1/H6PDH deficiency.
AMP-activated protein kinase (AMPK) is a key regulator of cellular and body energy homeostasis. We previously demonstrated that AMPK activation in osteoblasts increases in vitro bone formation while deletion of the Ampkα1 (Prkaa1) subunit, the dominant catalytic subunit expressed in bone, leads to decreased bone mass in vivo. To investigate the cause of low bone mass in the Ampkα1−/− mice, we analysed bone formation and resorption in the tibia of these mice by dynamic histomorphometry and determined whether bone turnover can be stimulated in the absence of the Ampkα1 subunit. We subjected 12-week-old Ampkα1+/+ and Ampkα1−/− mice to ovariectomy (OVX), intermittent PTH (iPTH) administration (80 μg/kg per day, 5 days/week) or both OVX and iPTH hormonal challenges. Tibiae were harvested from these mice and bone micro-architecture was determined by micro-computed tomography. We show for the first time that Ampkα1−/− mice have a high bone turnover at the basal level in favour of bone resorption. While both Ampkα1+/+ and Ampkα1−/− mice lost bone mass after OVX, the bone loss in Ampkα1−/− mice was lower compared with controls. iPTH increased trabecular and cortical bone indexes in both ovariectomised Ampkα1+/+ and Ampkα1−/− mice. However, ovariectomised Ampkα1−/− mice showed a smaller increase in bone parameters in response to iPTH compared with Ampkα1+/+ mice. By contrast, non-ovariectomised Ampkα1−/− mice responded better to iPTH treatment than non-ovariectomised Ampkα1+/+ mice. Overall, these data demonstrate that Ampkα1−/− mice are less affected by changes in bone turnover induced by OVX but respond better to the anabolic challenge induced by iPTH. These results suggest that AMPKα1 activation may play a role in the hormonal regulation of bone remodelling.
The inositol 1,4,5-trisphosphate receptors (IP3Rs) as ligand-gated Ca2+ channels are key modulators of cellular processes. Despite advances in understanding their critical role in regulating neuronal function and cell death, how this family of proteins impact cell metabolism is just emerging. Unexpectedly, a transgenic mouse line (D2D) exhibited progressive glucose intolerance as a result of transgene insertion. Inverse PCR was utilized to identify the gene disruption in the D2D mice. This led to the discovery that Itpr1 is among the 10 loci disrupted in chromosome 6. Itpr1 encodes for IP3R1, the most abundant IP3R isoform in mouse brain and also highly expressed in pancreatic β-cells. To study IP3R1 function in glucose metabolism, we utilized the Itpr1 heterozygous mutant mice, opt/+. Glucose homeostasis in male mice cohorts was examined by multiple approaches of metabolic phenotyping. Under regular diet, the opt/+ mice developed glucose intolerance but no insulin resistance. Decrease in second phase glucose-stimulated blood insulin level was observed in opt/+ mice, accompanied by reduced β-cell mass and insulin content. Strikingly, when fed with high-fat diet, the opt/+ mice were more susceptible to the development of hyperglycemia, glucose intolerance and insulin resistance. Collectively, our studies identify the gene Itpr1 being interrupted in the D2D mice, and uncover a novel role of IP3R1 in regulation of in vivo glucose homeostasis and development of diet-induced diabetes.
IP3R1; mouse models; gene disruption; glucose intolerance; diet-induced diabetes
Kisspeptin, originally identified as metastatin, important in preventing cancer metastasis, has more recently been shown to be important in pregnancy. Roles indicated for kisspeptin in pregnancy include regulating trophoblast invasion and migration during placentation. The pregnancy-specific disorder pre-eclampsia (PE) is now accepted to begin with inadequate trophoblast invasion and the current study therefore sets out to characterise placental expression of both kisspeptin (KISS1) and its receptor (KISS1R) throughout pregnancy and in PE. Placental tissue was obtained from women undergoing elective surgical termination of early pregnancy (n=10) and from women following Caesarean section at term in normal pregnancy (n=10) and with PE (n=10). Immunohistochemistry of paraffin embedded sections and western immunoblotting were performed to assess protein localisation and expression. Quantitative real-time PCR was carried out to evaluate mRNA expression of both KISS1 and KISS1R. Protein and mRNA expression was found to mirror each other with KISS1 expression found to be reduced in PE compared with that in normal term pregnancy. Interestingly, KISS1R expression at both the mRNA and protein levels was found to be increased in PE compared with that in normal term pregnancy. The current findings of increased KISS1R expression may represent a mechanism by which functional activity of KISS1 is higher in PE than in normal pregnancy. Higher levels of activity of KISS1R may be involved in inhibition of trophoblast invasion and angiogenesis, which are associated with PE.
Northern elephant seals endure a 2–3 month fast characterized by sustained hyperglycemia, hypoinsulinemia and increased plasma cortisol and free fatty acids, conditions often seen in insulin resistant humans. We previously showed that adipose Glut4 expression and AMP kinase (AMPK) activity increase and plasma glucose decreases in fasting seals suggesting that AMPK activity contributes to glucose regulation during insulin resistant conditions. To address the hypothesis that AMPK activity increases during fasting-induced insulin resistance, we performed glucose tolerance tests (GTT) on early (n=5) and late (n=8) fasted seal pups and compared adipose tissue expression of insulin signaling proteins, PPARγ, and AMPK, in addition to plasma adiponectin, leptin, cortisol, insulin and non-esterified fatty acids (NEFA) levels. Fasting was associated with decreased glucose clearance, plasma insulin and adiponectin, and intracellular insulin signaling, as well as increased plasma cortisol and NEFAs, supporting the suggestion that seals develop insulin resistance late in the fast. Expression of Glut4 and VAMP2 increased (52% and 63%, respectively) with fasting but did not change significantly during the GTT. PPARγ and phosphorylated AMPK did not change in early fasted seals, but increased significantly (73% and 50%, respectively) in late fasted seals during the GTT. Increased AMPK activity along with the reduction in the activity of insulin-signaling proteins supports our hypothesis that AMPK activity is increased following the onset of insulin resistance. The association between increased AMPK activity and Glut4 expression suggests that AMPK plays a greater role in regulating glucose metabolism in mammals adapted to prolonged fasting than in non-fasting mammals.
Northern Elephant Seal; Insulin Resistance; Glucocorticoids; Fatty Acids; Prolonged Fasting
MEPE (Matrix Extracellular PhosphoglycoprotEin) expression is markedly elevated in X-linked-hypophosphatemic-rickets (HYP) and tumor-induced osteomalacia (TIO). In normal individuals, circulating serum-levels of MEPE are tightly correlated with serum-phosphorus, parathyroid hormone (PTH) and bone mineral density (BMD). Also, MEPE derived, C-terminal ASARM-peptides are candidate minhibins and/or phosphatonins. Our aims were to determine: 1. whether MEPE-ASARM-peptide(s) are abnormally elevated in HYP/hyp serum, and, 2. whether the ASARM-peptide(s) accumulate in hyp mice kidney renal-tubules. Using a specific competitive ELISA we measured a five fold increase (P=0·007) of serum ASARM-peptide(s) in human HYP patients (normal subjects 3·25 μM n=9; S.E.M.=0·51 and HYP-patients 15·74 μM, n=9; S.E.M.=3·32). A 6·23 fold increase (P=0·008) was measured in hyp male mice compared with their normal male siblings (normal-siblings, 3·73 μM, S.E.M.=0·57, n=3; and hyp-mice 23·4 μM, n=3, S.E.M.=4·01). Renal immuno-histological screening also revealed a dramatic increase of ASARM-peptides in regions anatomically consistent with the proximal convoluted tubules. This study demonstrates for the first time that markedly elevated serum levels of protease-resistant ASARM-peptide(s) occur in HYP/hyp and they accumulate in murine hyp kidneys. These peptides are thus likely responsible for the phosphaturia and defective mineralization in HYP/hyp and TIO.
Inactivating PHEX (phosphate regulating gene with homologies to endopeptidases on the X chromosome) mutations cause X-linked hypophosphatemia in humans and mice (Hyp) through overproduction of fibroblast growth factor 23 (FGF23) a phosphaturic factor, by osteocytes. Matrix extracellular phosphoglycoprotein (MEPE) is also elevated in Hyp and other hypophosphatemic disorders. In addition, the administration of an ASARM (acidic serine–aspartate rich MEPE-associated motif) peptide derived from MEPE causes phosphaturia and inhibits bone mineralization in mice, suggesting that MEPE also plays a role in phosphate homeostasis. Since recent studies found that MEPE binds specifically to PHEX in vitro, we tested the effect of recombinant-MEPE and its ASARM peptide on PHEX enzyme activity in vitro and FGF23 expression in bone marrow stromal cell cultures ex vivo. We found that both recombinant MEPE and synthetic phosphorylated ASARM peptide (ASARM-PO4) inhibit PHEX enzyme activities in an in vitro fluorescent-quenched PHEX enzyme activity assay. The ASARM-PO4 peptide inhibits PHEX enzyme activity in a dose-dependent manner with a Ki of 128 nM and Vmax–i of 100%. Recombinant MEPE also inhibits PHEX activity (Ki=2 nM and Vmax–i=26%). Long-term bone marrow stromal cell cultures supplemented with 10 μM ASARM-PO4 peptide resulted in significant elevation of FGF23 transcripts and inhibition of mineralization. These findings suggest that MEPE inhibits mineralization and PHEX activity and leads to increased FGF23 production. The resulting coordination of mineralization and release of a phosphaturic factor by MEPE may serve a physiological role in regulating systemic phosphate homeostasis to meet the needs for bone mineralization.
Glucocorticoid regulation of the hypothalamic-pituitary-adrenal (HPA) axis is believed to depend on multiple actions operative within discrete time domains. However, the underlying cellular and molecular mechanism for those glucocorticoid actions remain undetermined. Moreover, there is an absence of in vivo studies examining whether there are multiple glucocorticoid effects on HPA axis related function within an intermediate feedback time-frame (1–3 h after glucocorticoid elevation), and whether those effects depend on de novo protein synthesis. We examined in rats the effects of protein synthesis inhibition on HPA axis response to restraint (15min) after 1 and 3 h phasic corticosterone (CORT) pretreatment. We measured HPA axis hormones (ACTH and CORT) and gene expression in the paraventricular nucleus (c-fos and crh genes), as well as gene expression in the anterior and intermediate pituitary (c-fos and pomc genes). Both CORT pretreatment intervals produced inhibition of stress-induced ACTH secretion, but no inhibition was seen in the presence of protein synthesis inhibition. CORT pretreatment produced inhibitory effects on stress-induced gene expression that varied for each gene depending on the anatomical site, pretreatment time and protein synthesis dependency. Taken together, the ACTH and gene expression patterns support the presence of multiple independent glucocorticoid actions initiated during the intermediate glucocorticoid negative feedback phase. Moreover, we conclude that those effects are exerted predominantly on the intrinsic anatomical elements of the HPA axis, and some of those effects depend on CORT induction of the expression of one or more regulatory gene products.
ACTH; CRH; POMC; cfos; HPA-axis