Cocaine- and amphetamine-regulated transcript is expressed in adipocytes and regulate lipid- and glucose homeostasis.

Cocaine- and amphetamine-regulated transcript (CART) is a regulatory peptide expressed in the nervous system and in endocrine cells, e.g. in pancreatic islets. CART deficient mice exhibit islet dysfunction, impaired insulin secretion and increased body weight. A mutation in the CART gene in humans is associated with reduced metabolic rate, obesity and diabetes. Furthermore, CART is upregulated in islets of type-2 diabetic rats and regulates islet hormone secretion in vitro. While the function of CART in the nervous system has been extensively studied, there is no information on its expression or function in white adipose tissue. CART mRNA and protein were found to be expressed in both subcutaneous and visceral white adipose tissues from rat and man. Stimulating rat primary adipocytes with CART significantly potentiated isoprenaline-induced lipolysis, and hormone sensitive lipase activation (phosphorylation of Ser 563). On the other hand, CART significantly potentiated the inhibitory effect of insulin on isoprenaline-induced lipolysis. CART inhibited insulin-induced glucose uptake, which was associated with inhibition of PKB phosphorylation. In conclusion, CART is a novel constituent of human and rat adipocytes and affects several biological processes central in both lipid- and glucose homeostasis. Depending on the surrounding conditions, the effects of CART are insulin-like or insulin-antagonistic

TCF7L2 is a master regulator of insulin production and processing

Genome-wide association studies have revealed >60 loci associated with type 2 diabetes (T2D), but the underlying causal variants and functional mechanisms remain largely elusive. Although variants in TCF7L2 confer the strongest risk of T2D among common variants by presumed effects on islet function, the molecular mechanisms are not yet well understood. Using RNA-sequencing, we have identified a TCF7L2-regulated transcriptional network responsible for its effect on insulin secretion in rodent and human pancreatic islets. ISL1 is a primary target of TCF7L2 and regulates proinsulin production and processing via MAFA, PDX1, NKX6.1, PCSK1, PCSK2 and SLC30A8, thereby providing evidence for a coordinated regulation of insulin production and processing. The risk T-allele of rs7903146 was associated with increased TCF7L2 expression, and decreased insulin content and secretion. Using gene expression profiles of 66 human pancreatic islets donors', we also show that the identified TCF7L2-ISL1 transcriptional network is regulated in a genotype-dependent manner. Taken together, these results demonstrate that not only synthesis of proinsulin is regulated by TCF7L2 but also processing and possibly clearance of proinsulin and insulin. These multiple targets in key pathways may explain why TCF7L2 has emerged as the gene showing one of the strongest associations with T2

The role of cocaine- and amphetamine-regulated transcript in endocrine cells

Type 2 diabetes (T2D) is a metabolic disease characterized by insufficient insulin secretion and insulin resistance. Disturbed beta-cell function is the final culprit that leads to the development of T2D. In addition, impaired incretin effect is likely a part of the pathogenesis of T2D. The aim of this thesis was to study the role of CART in beta-cells and incretin producing L- and K-cells.Endogenous beta-cell CART was found to regulate insulin secretion and production, ATP levels and beta-cell exocytosis in INS-1 (832/13) cells. CART silencing (KD) decreased expression of genes important for exocytosis, glucose sensing, and insulin processing, likely as a consequence of reduced expression of beta-cell transcription factors Mafa, Pdx-1, Isl1, NeuroD1, Nkx2.2 and Nkx6.1. Moreover, in human islets, CARTPT expression correlated with insulin, exocytosis genes and beta-cell transcription factors. To increase our understanding of the function of CART in beta-cells, we performed RNAseq on CART-silenced INS-1 (832/13) cells. Differential expression analysis revealed that CART KD affected expression of 25.5% of all detected genes, including genes with important roles for insulin secretion and exocytosis. The most strongly upregulated and downregulated genes after CART KD were AABR07068253.1, Jun, Srp14 and Adam11, Pak3, Ppp1r17 respectively. Stxa1, Gnas and Stxbp1 were the top differentially expressed genes related to insulin secretion. In a follow-up study, we established the role of one of the strongest CART-regulated genes, SCRT1 in beta-cell function. SCRT1 expression was found in rodent and human beta-cells. SCRT1 was translocated from the nucleus to the cytosol in diabetic DEX rats and SCRT1 mRNA expression was reduced by increasing glucose concentrations in vitro. SCRT1 KD in INS-1 (832/13) cells resulted in decreased insulin expression and secretion, as well as reduced expression of Tcf7l2, Pdx-1, Isl1, Neurod1 and Mafa. In human islets, SCRT1 expression correlated with insulin, glucagon, beta-cell transcription factors and exocytotic genes. Finally, we established CART expression in K- and L-cells in the human duodenum and jejunum and CART plasma levels were increased after a meal in humans. In incretin-producing GLUTag and STC-1 cells, CART mRNA was increased by fatty acids and GIP. In addition, CART KD in GLUTag cells reduced GLP-1 expression and secretion. CART also increased GLP-1 and GIP secretion during an oral glucose-tolerance test in vivo in mice. Collectively, our data imply that CART is an important regulator of insulin and incretin-producing cell function and glucose homeostasis. Thus, the therapeutic potential of CART-based therapy for treatment of T2D should be evaluated

The role of CART in islet biology

Cocaine- and amphetamine-regulated transcript (CART) is mostly known for its appetite regulating effects in the central nervous system. However, CART is also highly expressed in the peripheral nervous system as well as in certain endocrine cells. Our group has dedicated more than 20 years to understand the role of CART in the pancreatic islets and in this review we summarize what is known to date about CART expression and function in the islets. CART is expressed in both islet cells and nerve fibers innervating the islets. Large species differences are at hand and CART expression is highly dynamic and increased during development, as well as in Type 2 Diabetes and certain endocrine tumors. In the human islets CART is expressed in alpha cells and beta cells and the expression is increased in T2D patients. CART increases insulin secretion, reduces glucagon secretion, and protects against beta cell death by reducing apoptosis and increasing proliferation. It is still not fully understood how CART mediates its effects or which receptors that are involved. Nevertheless, CART is endowed with several properties that are beneficial in a T2D perspective. Many of the described effects of CART resemble those of GLP-1, and interestingly CART has been found to potentiate some of the effects of GLP-1, paving the way for CART-based treatments in combination with GLP-1-based drugs

Ghrelin is a regulator of glucagon-like peptide 1 secretion and transcription in mice

The gut hormones ghrelin, glucagon-like peptide 1 (GLP-1), and glucose-dependent insulinotropic peptide (GIP) have been intensively studied for their role in metabolism. It is, however, not well known whether the hormones interplay and regulate the secretion of each other. In this study, we studied the effect of ghrelin on GLP-1, GIP, and insulin secretion during an oral glucose tolerance test (OGTT) in mice. Intravenous administration of ghrelin caused increased GLP-1 secretion during the OGTT. On the other hand, ghrelin had no effect on circulating levels of glucose, insulin, and GIP. Furthermore, ghrelin treatment reduced proglucagon mRNA expression in GLUTag cells. The effect of ghrelin on GLP-1 secretion and proglucagon transcription was reinforced by the presence of GHS-R1a in human and mouse ileal L-cells, as well as in GLUTag cells. In summary, ghrelin is a regulator of GLP-1 secretion and transcription, and interfering with GHS-R1a signaling may be a way forward to enhance endogenous GLP-1 secretion in subjects with type 2 diabetes

Expression of Cocaine- and Amphetamine-Regulated Transcript Is Associated with Worse Survival in Small Bowel Carcinoid Tumors

Purpose: Cocaine-and amphetamine-regulated transcript (CART) peptide exerts several regulatory functions acting both as neurotransmitter and hormone. We recently showed that CART is expressed in various neuroendocrine tumors, including small bowel carcinoids. The main objective of the present study was to examine whether CART expression is associated with survival in patients with small bowel carcinoid. Secondary aims were to assess whether CART expression is associated with other tumor characteristics or clinical symptoms. Experimental Design: Specimens from 97 patients with small bowel carcinoids were examined for CART expression using immunohistochemistry. A CART score was introduced on the basis of the proportion of CART immunoreactive cells. On inclusion, specimens were examined by routine histopathologic methods and detailed clinical patient data were retrieved. The effect of CART on cell viability was assessed in vitro using two intestinal tumor cell lines. Results: Expression of CART (P = 0.011) and increasing CART score (P = 0.033) were associated with worse disease-specific survival. Adjusting for age, disease stage, and tumor grade in multivariable analysis, CART expression was still associated with worse survival [Low CART HR, 5.47; 95% confidence interval (CI), 0.71-42.46; and High CART HR, 9.44; 95% CI, 1.14-78.14]. CART expression was not associated with patient age, disease stage, tumor grade, or any presenting symptom. Supporting our clinical data, we found that CART promoted tumor cell viability in vitro in two different tumor cell lines. Conclusion: Expression of CART in small bowel carcinoid tumors is associated with worse survival. Clin Cancer Res; 18(13); 3668-76. (C)2012 AACR

Ghrelin rescues skeletal muscle catabolic profile in the R6/2 mouse model of Huntington’s disease

Abstract Accumulating evidence suggests altered energy metabolism as a key feature in Huntington’s disease (HD) pathology. Hyper-catabolism, including weight loss and muscle atrophy, is seen in HD patients and HD mouse models. Metabolic hormones are key players, not only in energy metabolism, but also in neurodegenerative processes. Ghrelin, a gut peptide-hormone, plays an important role in regulating energy metabolism, stimulating appetite, and affects brain function and increases neuronal survival. The R6/2 mouse model of HD has previously been shown to exhibit progressive weight loss, dysregulated glucose metabolism, skeletal muscle atrophy and altered body composition. In this study, we targeted energy metabolism in R6/2 mice using ghrelin administration, with the primary aim to delay weight loss and reduce muscle atrophy. We also evaluated glucose metabolism and behaviour. We here demonstrate that ghrelin administration (subcutaneous 150 μg/kg daily injections) for 4 weeks, reversed the catabolic gene expression profile (increased expression of Caspase 8, Traf-5 and Creb1) seen in R6/2 mouse skeletal muscle. Skeletal muscle morphology was also improved with ghrelin, and importantly, ghrelin administration normalized behavioural deficits in R6/2 mice. Taken together, our findings encourage further studies targeting metabolism in HD

GK-rats respond to gastric bypass surgery with improved glycemia despite unaffected insulin secretion and beta cell mass

Roux-en-Y gastric bypass (RYGB) is the most effective treatment for morbid obesity and results in rapid remission of type 2 diabetes (T2D), before significant weight loss occurs. The underlying mechanisms for T2D remission are not fully understood. To gain insight into these mechanisms we used RYGB-operated diabetic GK-rats and Wistar control rats. Twelve adult male Wistar- and twelve adult male GK-rats were subjected to RYGB- or sham-operation. Oral glucose tolerance tests (OGTT) were performed six weeks after surgery. RYGB normalized fasting glucose levels in GK-rats, without affecting fasting insulin levels. In both rat strains, RYGB caused increased postprandial responses in glucose, GLP-1, and GIP. RYGB caused elevated postprandial insulin secretion in Wistar-rats, but had no effect on insulin secretion in GK-rats. In agreement with this, RYGB improved HOMA-IR in GK-rats, but had no effect on HOMA-β. RYGB-operated GK-rats had an increased number of GIP receptor and GLP-1 receptor immunoreactive islet cells, but RYGB had no major effect on beta or alpha cell mass. Furthermore, in RYGB-operated GK-rats, increased Slc5a1, Pck2 and Pfkfb1 and reduced Fasn hepatic mRNA expression was observed. In summary, our data shows that RYGB induces T2D remission and enhanced postprandial incretin hormone secretion in GK-rats, without affecting insulin secretion or beta cell mass. Thus our data question the dogmatic view of how T2D remission is achieved and instead point at improved insulin sensitivity as the main mechanism of remission