Adverse events in utero, such as intrauterine growth restriction (IUGR), can permanently alter epigenetic mechanisms leading to the metabolic syndrome, which encompasses a variety of symptoms including augmented cholesterol. The major site for cholesterol homeostasis occurs via the actions of hepatic cholesterol 7α-hydroxylase (Cyp7a1), which catabolizes cholesterol to bile acids. To determine whether posttranslational histone modifications influence the long-term expression of Cyp7a1 in IUGR, we used a protein restriction model in rats. This diet during pregnancy and lactation led to IUGR offspring with decreased liver to body weight ratios, followed by increased circulating and hepatic cholesterol levels in both sexes at d 21 and exclusively in the male offspring at d 130. The augmented cholesterol was associated with decreases in the expression of Cyp7a1. Chromatin immunoprecipitation revealed that this was concomitant with diminished acetylation and enhanced methylation of histone H3 lysine 9 [K9,14], markers of chromatin silencing, surrounding the promoter region of Cyp7a1. These epigenetic modifications originate in part due to dietary-induced decreases in fetal hepatic Jmjd2a expression, a histone H3 [K9] demethylase. Collectively, these findings suggest that the augmented cholesterol observed in low-protein diet-derived offspring is due to permanent repressive posttranslational histone modifications at the promoter of Cyp7a1. Moreover, this is the first study to demonstrate that maternal undernutrition leads to long-term cholesterol dysregulation in the offspring via epigenetic mechanisms.

Neuropeptide Y (NPY) is synthesized in neural tissue of the central and peripheral nervous systems and has a number of important functions besides regulating appetite and energy homeostasis. Here we identify a novel site of NPY biosynthesis and a role for NPY in promoting proliferation of adipocyte precursor cells. We show that NPY mRNA is not only expressed in visceral adipose tissue (VAT) but that its levels are up‐regulated 6‐fold in our early‐life programmed rat model of increased visceral adiposity. This is accompanied by a parallel rise in NPY protein, demonstrating that VAT is a novel peripheral site of NPY biosynthesis. Furthermore, NPY mRNA expression is also elevated > 2‐fold in VAT of obese Zucker rats. Importantly, NPY stimulates proliferation of primary rat preadipocytes as well as 3T3‐L1 preadipocytes in vitro . This mitogenic effect appears to be mediated by the Y1 receptor and involves the activation of extracellular related kinase 1/2. In addition, insulin and glucocorticoid up‐regulate VAT NPY expression in lean but not obese Zucker rats. Taken together, these results suggest that an enhanced local expression of NPY within VAT may be a common feature of and contribute to the molecular mechanisms underlying increased visceral adiposity.—Yang, K., Guan, H., Arany, E., Hill, D. J., Cao, X. Neuropeptide Y is produced in visceral adipose tissue and promotes proliferation of adipocyte precursor cells via the Y1 receptor. FASEB J. 22, 2452–2464 (2008)

The relationship between antidopaminergic drugs and glucose has not been extensively studied, even though chronic neuroleptic treatment causes hyperinsulinemia in normal subjects or is associated with diabetes in psychiatric patients. We sought to evaluate dopamine D2 receptor (D2R) participation in pancreatic function. Glucose homeostasis was studied in D2R knockout mice (Drd2−/−) mice and in isolated islets from wild-type and Drd2−/− mice, using different pharmacological tools. Pancreas immunohistochemistry was performed. Drd2−/− male mice exhibited an impairment of insulin response to glucose and high fasting glucose levels and were glucose intolerant. Glucose intolerance resulted from a blunted insulin secretory response, rather than insulin resistance, as shown by glucose-stimulated insulin secretion tests (GSIS) in vivo and in vitro and by a conserved insulin tolerance test in vivo. On the other hand, short-term treatment with cabergoline, a dopamine agonist, resulted in glucose intolerance and decreased insulin response to glucose in wild-type but not in Drd2−/− mice; this effect was partially prevented by haloperidol, a D2R antagonist. In vitro results indicated that GSIS was impaired in islets from Drd2−/− mice and that only in wild-type islets did dopamine inhibit GSIS, an effect that was blocked by a D2R but not a D1R antagonist. Finally, immunohistochemistry showed a diminished pancreatic β-cell mass in Drd2−/− mice and decreased β-cell replication in 2-month-old Drd2−/− mice. Pancreatic D2Rs inhibit glucose-stimulated insulin release. Lack of dopaminergic inhibition throughout development may exert a gradual deteriorating effect on insulin homeostasis, so that eventually glucose intolerance develops.

We induced partial beta-cell loss within the pancreas of neonatal rats using streptozotocin (STZ) to better characterize the mechanisms leading to beta-cell regeneration postnatally. Rats were administered either STZ (70 mg/kg) or buffer alone on postnatal d 4, and the endocrine pancreas was examined between 4 and 40 d later. STZ-treated rats showed an approximately 60% loss of existing beta-cells and a moderate hyperglycemia (<15 mm glucose), with levels returning to near-control values after 20 d. Within preexisting islets, there was increased cell proliferation in both insulin- and glucagon-positive cells at 8 d as well as alpha-cell hyperplasia. These were associated with increased pancreatic content and circulating levels of glucagon. Pancreatic levels of glucagon-like polypeptide-1 (GLP-1) were increased 8 d after STZ compared with control values, and the GLP-1/glucagon ratio changed in favor of GLP-1. Administration of a GLP-1 receptor antagonist, GLP-1-(9-39), resulted in decreased recovery of beta-cells after STZ and worse glucose tolerance. Atypical glucagon-positive cells were found within islets that colocalized pancreatic duodenal homeobox-1 or glucose transporter-2. Pancreatic levels of insulin mRNA did not return to control values until 40 d after STZ. Insulin-positive cells were found after 8 d that colocalized glucagon and GLP-1. The model shows that the pancreas of the young rat can rapidly regenerate a loss of beta-cells, and this is associated with hyperplasia of alpha-cells with an altered phenotype of increased GLP-1 synthesis. The target cells of GLP-1 probably include immature beta-cells that coexpress proglucagon.

In rats, an isoenergetic low protein diet (LP) given throughout gestation perturbs the development of the endocrine pancreas by reducing β-cell mass and islet vascularization at birth. Taurine, an important amino acid during development, has been found to be low in fetal and maternal plasma. When added to a LP diet, taurine normalizes β-cell mass. Therefore, we investigated the ability of taurine to correct altered islet vascularization. Rats were given 20% [control (C)] or 8% (LP) protein in the diet with or without supplementation with 25 g/L taurine (T) in drinking water (C+T and LP+T) during gestation and lactation. Immunostaining for vascular endothelial growth factor (VEGF) and fetal liver kinase-1 (Flk-1), a VEGF receptor, was performed on fetal and neonatal pancreatic sections. Blood vessel density and blood vessel number were analyzed morphometrically on semi-thin sections. Taurine supplementation restored a normal volume and numerical density of vessels in fetal islets. The number of cells showing immunoreactivity for VEGF and Flk-1 was reduced by 33 and 45%, respectively, in islet cells from LP fetuses. In 1-mo-old pups, VEGF-positive cells remained decreased by nearly 22%. Both VEGF and Flk-1 were restored in pancreatic endocrine cells of fetuses and pups given taurine. The LP diet induced a threefold overexpression of Flk-1 in ductal cells, which contain precursors of β cells. However, taurine supplementation was without effect. In conclusion, underexpression of VEGF and Flk-1 is associated with the lower fetal islet vascularization induced by the maternal malnutrition. The addition of taurine to the maternal diet prevents such damage and has a potential role in islet vasculogenesis.

The understanding of the mechanisms by which gender dimorphisms are involved in the modulation of insulin sensitivity and glucose tolerance can be crucial to unravel the development of type 2 diabetes. Rats treated with a low protein diet (LP, 8% protein content) during pregnancy and lactation have a reduced β-cell mass at birth and a reduced insulin secretion at weaning. In this study we examined the effect of LP diet on glucose homeostasis from birth to adulthood when offspring previously exposed to LP were subsequently switched to control diet (C, 20% protein content) at weaning. The LP group had a reduced body weight after weaning compared to the C-fed rats, although their food intake was not significantly different. Furthermore, LP males had a significant increase in visceral adiposity relative to their body weight ( P < 0.05). Intraperitoneal glucose tolerance test (IGTT) showed that glucose clearance was unchanged until 130 days of age when LP-fed females showed elevated blood glucose compared to C, despite similar plasma insulin levels. Females also demonstrated a significant reduction in mean pancreatic islet number, individual islet size and beta cell mass. However, no differences in IGTT or islet morphometry were observed in LP males, although basal insulin levels were twofold higher. Akt phosphorylation in response to insulin was reduced in adipose and skeletal muscle of adult rats following exposure to LP diet in early life when compared to control-fed animals, but this was only apparent in males. Plasma testosterone levels were also reduced in males at 130 days age. These data suggest that the development of impaired glucose homeostasis in offspring of LP-fed rats is likely to occur by different mechanisms in males and females.