Absence of cannabinoid 1 receptor in beta cells protects against high-fat/high-sugar diet-induced beta cell dysfunction and inflammation in murine islets.

AIMS/HYPOTHESIS: The cannabinoid 1 receptor (CB1R) regulates insulin sensitivity and glucose metabolism in peripheral tissues. CB1R is expressed on pancreatic beta cells and is coupled to the G protein Gαi, suggesting a negative regulation of endogenous signalling in the beta cell. Deciphering the exact function of CB1R in beta cells has been confounded by the expression of this receptor on multiple tissues involved in regulating metabolism. Thus, in models of global genetic or pharmacological CB1R blockade, it is difficult to distinguish the indirect effects of improved insulin sensitivity in peripheral tissues from the direct effects of inhibiting CB1R in beta cells per se. To assess the direct contribution of beta cell CB1R to metabolism, we designed a mouse model that allows us to determine the role of CB1R specifically in beta cells in the context of whole-body metabolism. METHODS: We generated a beta cell specific Cnr1 (CB1R) knockout mouse (ß-CB1R-/-) to study the long-term consequences of CB1R ablation on beta cell function in adult mice. We measured beta cell function, proliferation and viability in these mice in response to a high-fat/high-sugar diet and induction of acute insulin resistance with the insulin receptor antagonist S961. RESULTS: ß-CB1R-/- mice had increased fasting (153 ± 23% increase at 10 weeks of age) and stimulated insulin secretion and increased intra-islet cAMP levels (217 ± 33% increase at 10 weeks of age), resulting in primary hyperinsulinaemia, as well as increased beta cell viability, proliferation and islet area (1.9-fold increase at 10 weeks of age). Hyperinsulinaemia led to insulin resistance, which was aggravated by a high-fat/high-sugar diet and weight gain, although beta cells maintained their insulin secretory capacity in response to glucose. Strikingly, islets from ß-CB1R-/- mice were protected from diet-induced inflammation. Mechanistically, we show that this is a consequence of curtailment of oxidative stress and reduced activation of the NLRP3 inflammasome in beta cells. CONCLUSIONS/INTERPRETATION: Our data demonstrate CB1R to be a negative regulator of beta cell function and a mediator of islet inflammation under conditions of metabolic stress. Our findings point to beta cell CB1R as a therapeutic target, and broaden its potential to include anti-inflammatory effects in both major forms of diabetes. DATA AVAILABILITY: Microarray data have been deposited at GEO (GSE102027).

Human CB1 Receptor Isoforms, present in Hepatocytes and ß-cells, are Involved in Regulating Metabolism.

Therapeutics aimed at blocking the cannabinoid 1 (CB1) receptor for treatment of obesity resulted in significant improvements in liver function, glucose uptake and pancreatic ß-cell function independent of weight loss or CB1 receptor blockade in the brain, suggesting that peripherally-acting only CB1 receptor blockers may be useful therapeutic agents. Neuropsychiatric side effects and lack of tissue specificity precluded clinical use of first-generation, centrally acting CB1 receptor blockers. In this study we specifically analyzed the potential relevance to diabetes of human CB1 receptor isoforms in extraneural tissues involved in glucose metabolism. We identified an isoform of the human CB1 receptor (CB1b) that is highly expressed in ß-cells and hepatocytes but not in the brain. Importantly, CB1b shows stronger affinity for the inverse agonist JD-5037 than for rimonabant compared to CB1 full length. Most relevant to the field, CB1b is a potent regulator of adenylyl cyclase activity in peripheral metabolic tissues. CB1b blockade by JD-5037 results in stronger adenylyl cyclase activation compared to rimonabant and it is a better enhancer of insulin secretion in ß-cells. We propose this isoform as a principal pharmacological target for the treatment of metabolic disorders involving glucose metabolism.

Blockade of cannabinoid 1 receptor improves GLP-1R mediated insulin secretion in mice.

The cannabinoid 1 receptor (CB1) is an important regulator of energy metabolism. Reports of in vivo and in vitro studies give conflicting results regarding its role in insulin secretion, possibly due to circulatory factors, such as incretins. We hypothesized that this receptor may be a regulator of the entero-insular axis. We found that despite lower food consumption and lower body weight postprandial GLP-1 plasma concentrations were increased in CB1(-/-) mice compared to CB1(+/+) mice administered a standard diet or high fat/sugar diet. Upon exogenous GLP-1 treatment, CB1(-/-) mice had increased glucose-stimulated insulin secretion. In mouse insulinoma cells, cannabinoids reduced GLP-1R-mediated intracellular cAMP accumulation and subsequent insulin secretion. Importantly, such effects were also evident in human islets, and were prevented by pharmacologic blockade of CB1. Collectively, these findings suggest a novel mechanism in which endocannabinoids are negative modulators of incretin-mediated insulin secretion.

Resveratrol prevents ß-cell dedifferentiation in nonhuman primates given a high-fat/high-sugar diet.

Eating a "Westernized" diet high in fat and sugar leads to weight gain and numerous health problems, including the development of type 2 diabetes mellitus (T2DM). Rodent studies have shown that resveratrol supplementation reduces blood glucose levels, preserves ß-cells in islets of Langerhans, and improves insulin action. Although rodent models are helpful for understanding ß-cell biology and certain aspects of T2DM pathology, they fail to reproduce the complexity of the human disease as well as that of nonhuman primates. Rhesus monkeys were fed a standard diet (SD), or a high-fat/high-sugar diet in combination with either placebo (HFS) or resveratrol (HFS+Resv) for 24 months, and pancreata were examined before overt dysglycemia occurred. Increased glucose-stimulated insulin secretion and insulin resistance occurred in both HFS and HFS+Resv diets compared with SD. Although islet size was unaffected, there was a significant decrease in ß-cells and an increase in α-cells containing glucagon and glucagon-like peptide 1 with HFS diets. Islets from HFS+Resv monkeys were morphologically similar to SD. HFS diets also resulted in decreased expression of essential ß-cell transcription factors forkhead box O1 (FOXO1), NKX6-1, NKX2-2, and PDX1, which did not occur with resveratrol supplementation. Similar changes were observed in human islets where the effects of resveratrol were mediated through Sirtuin 1. These findings have implications for the management of humans with insulin resistance, prediabetes, and diabetes.

The biarylpyrazole compound AM251 alters mitochondrial physiology via proteolytic degradation of ERRα.

The orphan nuclear receptor estrogen-related receptor alpha (ERRα) directs the transcription of nuclear genes involved in energy homeostasis control and the regulation of mitochondrial mass and function. A crucial role for controlling ERRα-mediated target gene expression has been ascribed to the biarylpyrazole compound 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide (AM251) through direct binding to and destabilization of ERRα protein. Here, we provide evidence that structurally related AM251 analogs also have negative impacts on ERRα protein levels in a cell-type-dependent manner while having no deleterious actions on ERRγ. We show that these off-target cellular effects of AM251 are mediated by proteasomal degradation of nuclear ERRα. Cell treatment with the nuclear export inhibitor leptomycin B did not prevent AM251-induced destabilization of ERRα protein, whereas proteasome inhibition with MG132 stabilized and maintained its DNA-binding function, indicative of ERRα being a target of nuclear proteasomal complexes. NativePAGE analysis revealed that ERRα formed a ∼220-kDa multiprotein nuclear complex that was devoid of ERRγ and the coregulator peroxisome proliferator-activated receptor γ coactivator-1. AM251 induced SUMO-2,3 incorporation in ERRα in conjunction with increased protein kinase C activity, whose activation by phorbol ester also promoted ERRα protein loss. Down-regulation of ERRα by AM251 or small interfering RNA led to increased mitochondria biogenesis while negatively impacting mitochondrial membrane potential. These results reveal a novel molecular mechanism by which AM251 and related compounds alter mitochondrial physiology through destabilization of ERRα.

Of mice and men: the benefits of caloric restriction, exercise, and mimetics.

During aging there is an increasing imbalance of energy intake and expenditure resulting in obesity, frailty, and metabolic disorders. For decades, research has shown that caloric restriction (CR) and exercise can postpone detrimental aspects of aging. These two interventions invoke a similar physiological signature involving pathways associated with stress responses and mitochondrial homeostasis. Nonetheless, CR is able to delay aging processes that result in an increase of both mean and maximum lifespan, whereas exercise primarily increases healthspan. Due to the strict dietary regime necessary to achieve the beneficial effects of CR, most studies to date have focused on rodents and non-human primates. As a consequence, there is vast interest in the development of compounds such as resveratrol, metformin and rapamycin that would activate the same metabolic- and stress-response pathways induced by these interventions without actually restricting caloric intake. Therefore the scope of this review is to (i) describe the benefits of CR and exercise in healthy individuals, (ii) discuss the role of these interventions in the diseased state, and (iii) examine some of the promising pharmacological alternatives such as CR- and exercise-mimetics.

Nampt/visfatin/PBEF affects expression of myogenic regulatory factors and is regulated by interleukin-6 in chicken skeletal muscle cells.

Nicotinamide phosphoribosyltransferase (Nampt/visfatin/PBEF) has been identified as a rate-limiting NAD(+) biosynthetic enzyme and an adipokine found in the circulation. Human and chicken skeletal muscles are reported to have the highest level of Nampt expression among various tissues whose functional significance remains undetermined. Expression of Nampt is regulated by interleukin-6 (IL-6), an essential cytokine for postnatal muscle growth in mammals. The objective of the current study was to characterize expression of Nampt in chicken (Gallus gallus) myogenic cells and to determine the effect of Nampt on expression of IL-6, myogenic transcription factors, and glucose uptake. We also sought to determine the effect of IL-6 on Nampt expression in chicken myogenic cells. Nampt mRNA and protein were identified in both myoblasts and myocytes, although expression did not differ between the two cell types. Treatment with recombinant human Nampt was found to decrease myoD and mrf4 expression but to increase myf5 expression in myocytes, while glucose uptake was unaffected. In response to treatment with recombinant Nampt, IL-6 expression in myocytes was increased at 24h but decreased when treated for 48 or 72 h. Forced over-expression of chicken Nampt cDNA significantly decreased myf5 expression in myoblasts. Treatment of myogenic cells with lower levels (1 ng.mL(-1)) of recombinant IL-6 increased Nampt expression, whereas a higher IL-6 concentration (100 ng.mL(-1)) decreased Nampt mRNA abundance. Collectively, these results demonstrate that Nampt, regulated in part by IL-6, alters the expression of key myogenic transcription factors and thereby may influence postnatal myogenesis.

NAMPT (visfatin) in the chicken testis: influence of sexual maturation on cellular localization, plasma levels and gene and protein expression.

Nicotinamide phosphoribosyltransferase (NAMPT) is a cytokine hormone and rate-limiting enzyme involved in production of NAD and therefore affects a variety of cellular functions requiring NAD. Spermatogenesis and testicular steroidogenesis are likely to depend on NAD-dependent reactions and may therefore be affected by changes in testicular NAMPT expression. The objectives of the present study are to investigate testicular NAMPT expression as well as plasma NAMPT levels in prepubertal and adult chickens. By RT-PCR, NAMPT cDNA expression was detected in prepubertal and adult chicken testes. Using immunohistochemistry, NAMPT was predominantly localized in the nucleus of myoid cells, Sertoli cells, and Leydig cells in the prepubertal chicken testis. In adult chickens, however, NAMPT-immunostaining was observed in the cytoplasm of Leydig cells, Sertoli cells, primary spermatocytes, secondary spermatocytes, round spermatids, and elongated spermatids, but not in the spermatogonial cells. Using real-time quantitative PCR, adult chicken testis was found to contain fourfold greater NAMPT mRNA quantity compared with prepubertal chickens. Testicular NAMPT protein quantities determined by western blotting were not significantly different between adult and prepubertal chicken testes. Using immunoblotting, NAMPT was detected in the seminal plasma and sperm protein extracts obtained from chicken semen. Plasma NAMPT levels, determined by enzyme immunoassay, were at least 28-fold higher in the adult chickens compared with prepubertal male chickens. Taken together, sexual maturation is associated with several changes in testicular NAMPT expression indicating that NAMPT is likely to play a significant role in testicular functions such as spermatogenesis and steroidogenesis.

Unique profile of chicken adiponectin, a predominantly heavy molecular weight multimer, and relationship to visceral adiposity.

Adiponectin, a 30-kDa adipokine hormone, circulates as heavy, medium, and light molecular weight isoforms in mammals. Plasma heavy molecular weight (HMW) adiponectin isoform levels are inversely correlated with the incidence of type 2 diabetes in humans. The objectives of the present study were to characterize adiponectin protein and quantify plasma adiponectin levels in chickens, which are naturally hyperglycemic relative to mammals. Using gel filtration column chromatography and Western blot analysis under nonreducing and non-heat-denaturing native conditions, adiponectin in chicken plasma, and adipose tissue is predominantly a multimeric HMW isoform that is larger than 669 kDa mass. Under reducing conditions and heating to 70-100 C, however, a majority of the multimeric adiponectin in chicken plasma and adipose tissue was reduced to oligomeric and/or monomeric forms. Immunoprecipitation and elution under neutral pH preserved the HMW adiponectin multimer, whereas brief exposure to acidic pH led to dissociation of HMW multimer into multiple oligomers. Mass spectrometric analysis of chicken adiponectin revealed the presence of hydroxyproline and differential glycosylation of hydroxylysine residues in the collagenous domain. An enzyme immunoassay was developed and validated for quantifying plasma adiponectin in chickens. Plasma adiponectin levels were found to be significantly lower in 8- compared with 4-wk-old male chickens and inversely related to abdominal fat pad mass. Collectively, our results provide novel evidence that adiponectin in chicken plasma and tissues is predominantly a HMW multimer, suggesting the presence of unique multimerization and stabilization mechanisms in the chicken that favors preponderance of HMW adiponectin over other oligomers.

Adiponectin and its receptors are expressed in the chicken testis: influence of sexual maturation on testicular ADIPOR1 and ADIPOR2 mRNA abundance.

Adiponectin is an adipokine hormone that influences glucose utilization, insulin sensitivity, and energy homeostasis by signaling through two distinct receptors, ADIPOR1 and ADIPOR2. While adipose tissue is the primary site of adiponectin expression in the chicken, we previously reported that adiponectin and its receptors are expressed in several other tissues. The objectives of the present study are to characterize adiponectin, ADIPOR1, and ADIPOR2 expressions in the chicken testis and to determine whether sexual maturation affects the abundance of testicular adiponectin, ADIPOR1, and ADIPOR2 mRNAs. By RT-PCR and nucleotide sequencing, testicular adiponectin, ADIPOR1, and ADIPOR2 mRNAs were found to be identical to that expressed in the abdominal fat pad. Using anti-chicken adiponectin, ADIPOR1, or ADIPOR2 antibodies and immunohistochemistry, adiponectin-immunoreactive (ir) and ADIPOR1-ir cells were found exclusively in the peritubular cells as well as in Leydig cells. However, ADIPOR2-ir cells were found in the adluminal and luminal compartments of the seminiferous tubules as well as in interstitial cells. In particular, Sertoli cell syncytia, round spermatids, elongating spermatids, spermatozoa, and Leydig cells showed strong ADIPOR2 immunoreactivity. Using quantitative real-time PCR analyses, testicular ADIPOR1 and ADIPOR2 mRNA abundance were found to be 8.3- and 9-fold higher (P<0.01) in adult chickens compared with prepubertal chickens respectively, suggesting that sexual maturation is likely to be associated with an up-regulation of testicular ADIPOR1 and ADIPOR2 gene expressions. Collectively, our results indicate that adiponectin and its receptors are expressed in the chicken testis, where they are likely to influence steroidogenesis, spermatogenesis, Sertoli cell function as well as spermatozoa motility.

Gonadotropin-inhibitory hormone (GnIH) receptor gene is expressed in the chicken ovary: potential role of GnIH in follicular maturation.

Gonadotropin-inhibitory hormone (GnIH), an RFamide peptide, has been found to inhibit pituitary LH secretion in avian and mammalian species. The gene encoding a putative receptor for GnIH (GnIHR) was recently identified in the chicken and Japanese quail brain and pituitary gland. GnIHR appears to be a seven-transmembrane protein belonging to a family of G-protein-coupled receptors. In the present study, we have characterized the expression of GnIHR mRNA in the chicken ovary and demonstrate that GnIHR may exert an inhibitory effect on ovarian follicular development. By RT-PCR, we detected GnIHR mRNA in the chicken testis and in the ovary, specifically both thecal and granulosa cell layers. Real-time quantitative PCR analysis revealed greater GnIHR mRNA quantity in theca cells of prehierarchial follicles compared with that of preovulatory follicles. GnIHR mRNA quantity was significantly decreased in sexually mature chicken ovaries versus ovaries of sexually immature chickens. Estradiol (E(2)) and/or progesterone (P(4)) treatment of sexually immature chickens significantly decreased ovarian GnIHR mRNA abundance. Treatment of prehierarchial follicular granulosa cells in vitro with chicken GnIH peptide significantly decreased basal but not FSH-stimulated cellular viability. Collectively, our results indicate that the ovarian GnIHR is likely to be involved in ovarian follicular development. A decrease in ovarian GnIHR mRNA abundance due to sexual maturation or by E(2) and/or P(4) treatment would implicate an inhibitory role for GnIHR in ovarian follicular development. Furthermore, GnIH may affect follicular maturation by decreasing the viability of prehierarchial follicular granulosa cells through binding to GnIHR.

Is visfatin an adipokine or myokine? Evidence for greater visfatin expression in skeletal muscle than visceral fat in chickens.

Visfatin, an adipokine hormone produced primarily by visceral adipose tissue in mammals, has been implicated in the immune system, cellular aging, and glucose metabolism. Increased visceral adiposity and hyperglycemia have been correlated with elevated plasma visfatin levels in humans. The present study investigated visfatin cDNA and protein expression as well as plasma visfatin levels in chickens that are selected for rapid growth and are naturally hyperglycemic relative to mammals. By RT-PCR, we detected visfatin cDNA in multiple tissues in the chicken. The deduced amino acid sequence of full-length chicken visfatin was 92-93% homologous to mammalian visfatin. Using real-time quantitative PCR and Western blotting, chicken skeletal muscle was found to contain 5- and 3-fold greater quantities of visfatin mRNA and protein than abdominal fat pad, respectively. Visfatin mRNA and protein quantities were not significantly different among sc and visceral adipose tissue depots. Skeletal muscle visfatin mRNA and protein quantities as well as plasma visfatin levels determined by enzyme immunoassay were significantly higher in 8-wk-old compared with 4-wk-old chickens, possibly due to rapid skeletal muscle growth and visceral fat accretion occurring in broiler chickens during this period. However, fasting and refeeding did not affect plasma visfatin levels in the chicken. Collectively, our results provide novel evidence that skeletal muscle, not the visceral adipose tissue, is the primary source of visfatin in chickens, thereby raising the possibility that visfatin may be acting as a myokine affecting skeletal muscle growth and metabolism.

Identification of calcitonin expression in the chicken ovary: influence of follicular maturation and ovarian steroids.

Calcitonin (CALCA), a hormone primarily known for its role in calcium homeostasis, has recently been linked to reproduction, specifically as a marker for embryo implantation in the uterus. Although CALCA expression has been documented in several tissues, there has been no report of production of CALCA in the ovary of any vertebrate species. We hypothesized that the Calca gene is expressed in the chicken ovary, and its expression will be altered by follicular maturation or gonadal steroid administration. Using RT-PCR, we detected Calca mRNA and the calcitonin receptor (Calcr) mRNA in the granulosa and theca layers of preovulatory and prehierarchial follicles. Both CALCA and Calca mRNA were localized in granulosa and thecal cells by confocal microscopy. Using quantitative PCR analysis, F1 follicle granulosa layer was found to contain significantly greater Calca mRNA and Calcr mRNA levels compared with those of any other preovulatory or prehierarchial follicle. The granulosa layer contained relatively greater Calca and Calcr mRNA levels compared with the thecal layer in both prehierarchial and preovulatory follicles. Progesterone (P(4)) treatment of sexually immature chickens resulted in a significantly greater abundance of ovarian Calca mRNA, whereas estradiol (E(2)) or P(4) + E(2) treatment significantly reduced ovarian Calca mRNA quantity. Treatment of prehierarchial follicular granulosa cells in vitro with CALCA significantly decreased FSH-stimulated cellular viability. Collectively, our results indicate that follicular maturation and gonadal steroids influence Calca and Calcr gene expression in the chicken ovary. We conclude that ovarian CALCA is possibly involved in regulating follicular maturation in the chicken ovary.

Calcitonin is expressed in the chicken pituitary gland: influence of gonadal steroids and sexual maturation.

Calcitonin (CT) is primarily produced by the thyroid C cells in mammals or by the ultimobranchial gland in chickens. CT is also expressed by the pituitary gland in rats in which it functions as a paracrine factor causing decreased lactotroph proliferation and prolactin (PRL) secretion. Gonadal steroids influence CT expression in the rat pituitary gland. However, the expression of the CT gene in the pituitary gland of chickens or of any other avian species has not previously been reported. We have tested the hypotheses that CT is expressed in the chicken pituitary gland, and that its expression is influenced by sexual maturation or in response to ovarian steroid administration. We have detected robust expression of CT cDNA in the chicken pituitary gland by reverse transcription/polymerase chain reaction (PCR). The sequence of the pituitary-derived CT cDNA is identical to that of the ultimobranchial gland. CT-immunoreactive (ir) cells have been observed throughout the anterior pituitary gland by confocal microscopy. Many of the PRL-ir cells show co-localization with CT-ir cells. Quantitative real-time PCR analysis has revealed an inverse relationship between the quantities of PRL mRNA and CT mRNA in the pituitary gland: sexually mature hens contain lower amounts of CT mRNA but larger quantities of PRL mRNA compared with sexually immature chickens. Estradiol and/or progesterone treatment of sexually immature chickens leads to a significant decrease in the quantity of pituitary CT mRNA relative to that in the vehicle-treated chickens. We conclude that pituitary CT plays an important paracrine/autocrine role in the control of lactotroph function and PRL secretion in the chicken.