Acetyl-CoA-carboxylase 1 (ACC1) plays a critical role in glucagon secretion.

Dysregulated glucagon secretion from pancreatic alpha-cells is a key feature of type-1 and type-2 diabetes (T1D and T2D), yet our mechanistic understanding of alpha-cell function is underdeveloped relative to insulin-secreting beta-cells. Here we show that the enzyme acetyl-CoA-carboxylase 1 (ACC1), which couples glucose metabolism to lipogenesis, plays a key role in the regulation of glucagon secretion. Pharmacological inhibition of ACC1 in mouse islets or αTC9 cells impaired glucagon secretion at low glucose (1 mmol/l). Likewise, deletion of ACC1 in alpha-cells in mice reduced glucagon secretion at low glucose in isolated islets, and in response to fasting or insulin-induced hypoglycaemia in vivo. Electrophysiological recordings identified impaired KATP channel activity and P/Q- and L-type calcium currents in alpha-cells lacking ACC1, explaining the loss of glucose-sensing. ACC-dependent alterations in S-acylation of the KATP channel subunit, Kir6.2, were identified by acyl-biotin exchange assays. Histological analysis identified that loss of ACC1 caused a reduction in alpha-cell area of the pancreas, glucagon content and individual alpha-cell size, further impairing secretory capacity. Loss of ACC1 also reduced the release of glucagon-like peptide 1 (GLP-1) in primary gastrointestinal crypts. Together, these data reveal a role for the ACC1-coupled pathway in proglucagon-expressing nutrient-responsive endocrine cell function and systemic glucose homeostasis.

Abcc5 Knockout Mice Have Lower Fat Mass and Increased Levels of Circulating GLP-1.

OBJECTIVE: A previous genome-wide association study linked overexpression of an ATP-binding cassette transporter, ABCC5, in humans with a susceptibility to developing type 2 diabetes with age. Specifically, ABCC5 gene overexpression was shown to be strongly associated with increased visceral fat mass and reduced peripheral insulin sensitivity. Currently, the role of ABCC5 in diabetes and obesity is unknown. This study reports the metabolic phenotyping of a global Abcc5 knockout mouse. METHODS: A global Abcc5-/- mouse was generated by CRISPR/Cas9. Fat mass was determined by weekly EchoMRI and fat pads were dissected and weighed at week 18. Glucose homeostasis was ascertained by an oral glucose tolerance test, intraperitoneal glucose tolerance test, and intraperitoneal insulin tolerance test. Energy expenditure and locomotor activity were measured using PhenoMaster cages. Glucagon-like peptide 1 (GLP-1) levels in plasma, primary gut cell cultures, and GLUTag cells were determined by enzyme-linked immunosorbent assay. RESULTS: Abcc5-/- mice had decreased fat mass and increased plasma levels of GLP-1, and they were more insulin sensitive and more active. Recombinant overexpression of ABCC5 protein in GLUTag cells decreased GLP-1 release. CONCLUSIONS: ABCC5 protein expression levels are inversely related to fat mass and appear to play a role in the regulation of GLP-1 secretion from enteroendocrine cells.

GPR41 modulates insulin secretion and gene expression in pancreatic ß-cells and modifies metabolic homeostasis in fed and fasting states.

Insulin secretion by pancreatic ß-cells is primarily regulated by glucose; however, hormones and additional nutrients, such as long-chain fatty acids, also play an important role in adjusting insulin output to physiologic needs. To examine the role of short-chain fatty acids (SCFAs) in ß-cell function, we analyzed mouse models of gain and loss of function of GPR41 (FFAR3), a receptor for SCFAs, vs. wild-type control mice. GPR41 gain of function [GPR41-overexpressing transgenic (41 Tg) model] and GPR41 loss of function [GPR41-knockout (KO 41) model] resulted in complementary changes in glucose tolerance, without significant effects on insulin sensitivity. KO 41 mice showed fasting hypoglycemia, which was consistent with increased basal and glucose-induced insulin secretion by islets in vitro Mirroring this, 41 Tg islets showed impaired glucose responsiveness in vitro Microarray analysis of islets from 41 Tg mice indicated significant alterations in gene expression patterns; several of the altered genes were chosen for further analysis and were also observed to change upon incubation of islets and cultured ß-cells with SCFAs in a GPR41-dependent manner. Taken together, our results indicate that GPR41 and its ligands, SCFAs, may play an important role in the fine-tuning of insulin secretion in fed and fasting states.-Veprik, A., Laufer, D., Weiss, S., Rubins, N., Walker, M. D. GPR41 modulates insulin secretion and gene expression in pancreatic ß-cells and modifies metabolic homeostasis in fed and fasting states.

The role of lycopene and its derivatives in the regulation of transcription systems: implications for cancer prevention.

Evidence from epidemiologic studies has suggested that carotenoids, and lycopene in particular, decrease the risk of cancer: however, not all studies support this view. To gain insight into the molecular mechanisms whereby lycopene and other carotenoids may exert their chemoprotective effects, we and others performed a series of studies that used a large panel of cancer cell lines of different lineages and animal models of human cancer. In this review we address some of the mechanisms proposed for the cancer-preventive activity of tomato lycopene, focusing on the induction of the antioxidant response element transcription system and the inhibition of the transcriptional activity of sex hormones, such as estrogens and androgens, and the activity of growth factors, such as insulin-like growth factor. We also considered the modulation by lycopene of the transcription factors peroxisome proliferator-activated receptor, retinoid X receptor, liver X receptor, and activating protein-1. The ligands and the phytonutrient regulators of these transcription systems contain electrophilic active groups, whereas lycopene and nonxanthophylic carotenoids are devoid of them. Thus, we suggest that at least some of the cellular effects of carotenoids are mediated through their derivatives formed either by chemical oxidation or by enzymatic cleavage inside the cells. This review highlights findings that pertain to this exciting avenue of research, which is currently under intense scrutiny in several laboratories worldwide.

GPR41 gene expression is mediated by internal ribosome entry site (IRES)-dependent translation of bicistronic mRNA encoding GPR40 and GPR41 proteins.

GPR41 is a G protein-coupled receptor activated by short chain fatty acids. The gene encoding GPR41 is located immediately downstream of a related gene encoding GPR40, a receptor for long chain fatty acids. Expression of GPR41 has been reported in a small number of cell types, including gut enteroendocrine cells and sympathetic ganglia, where it may play a role in the maintenance of metabolic homeostasis. We now demonstrate that GPR41, like GPR40, is expressed in pancreatic beta cells. Surprisingly, we found no evidence for transcriptional control elements or transcriptional initiation in the intergenic GPR40-GPR41 region. Rather, using 5'-rapid amplification of cDNA ends analysis, we demonstrated that GPR41 is transcribed from the promoter of the GPR40 gene. We confirmed this finding by generating bicistronic luciferase reporter plasmids, and we were able to map a potential internal ribosome entry site-containing region to a 2474-nucleotide region of the intergenic sequence. Consistent with this, we observed m(7)G cap-independent reporter gene expression upon transfection of RNA containing this region. Thus, GPR41 expression is mediated via an internal ribosome entry site located in the intergenic region of a bicistronic mRNA. This novel sequence organization may be utilized to permit coordinated regulation of the fatty acid receptors GPR40 and GPR41.

Polyphenols, isothiocyanates, and carotenoid derivatives enhance estrogenic activity in bone cells but inhibit it in breast cancer cells.

While exposure to estrogens is a major risk factor of breast and endometrial cancer, it well established that estrogens are beneficial for bone health. We have previously shown that carotenoids inhibit estrogen signaling in breast and endometrial cancer cells. The aim of this study was to compare the effects of various phytonutrients, (carotenoid derivatives, polyphenols, isothiocyanates) on estrogenic activity in breast cancer cells and osteoblast-like cells. All the tested phytonutrients inhibited estrogen response element (ERE) transactivation in breast cancer cells. In contrast, these compounds either did not affect or enhanced ERE activity and the expression of several bone-forming genes. These results were obtained using two osteoblast-like cell lines, MG-63 human osteosarcoma cells stably transfected with estrogen receptor-α (ERα) and MC3T3-E1 mouse calvaria-derived cells expressing endogenous ER. Phytonutrients-induced ERE inhibition in breast cancer cells, and its potentiation in osteoblast-like cells were associated both with a decrease and a rise in total and nuclear ERα levels, respectively. Phytonutrients activated the electrophile/antioxidant response element (EpRE/ARE) transcription system to various extents in both cancer and bone cell lines. Overexpression of Nrf2, the major EpRE/ARE activating transcription factor, mimicked the effects of phytonutrients, causing inhibition and enhancement of ERE transactivation in breast cancer cells and in osteoblast-like cells, respectively. Moreover, reduction in Nrf2 levels by RNAi led to a decrease in the phytonutrient potentiation of ERE activity transactivation in osteoblast-like cells. These findings suggest that the enhancement and inhibition of estrogen signaling by phytonutrients in bone-derived cells and breast cancer cells, respectively, is partially mediated by the activation of the Nrf2/ARE system.

Carotenoids and apocarotenoids in cellular signaling related to cancer: a review.

The basis for the vivid color of carotenoids and their antioxidant activity is the multiple conjugated double bonds, which are characteristic for these phytonutrients. Moreover, the cleavage of these oxidation-prone double bonds leads to the formation of apocarotenoids. A large number of carbonyl-containing oxidation products are expected to be produced as a result of carotenoid oxidation and these can be further metabolized into the corresponding acids and alcohols. As discussed in this review, many, but not all, of these potential products have been detected and identified in plants as well as in human and animal plasma and tissues. Some of these compounds were found to be biologically active as anticancer agents. In addition to the inhibition of cancer cell proliferation, several carotenoid metabolites were shown to modulate the activity of various transcription systems. These include ligand-activated nuclear receptors, such as the retinoic acid receptor, retinoid X receptor, peroxisome proliferator-activated receptor and estrogen receptor, as well as other transcription systems that have an important role in cancer, such as the electrophile/antioxidant response element pathway and nuclear factor-κB. Therefore, apocarotenoids can be considered as natural compounds with multifunctional, rather than monofunctional, activity and, thus, can be useful in the prevention of cancer and other degenerative diseases.