Renal tubule-specific Atgl deletion links kidney lipid metabolism to glucagon-like peptide 1 and insulin secretion independent of renal inflammation or lipotoxicity.

OBJECTIVE: Lipotoxic injury from renal lipid accumulation in obesity and type 2 diabetes (T2D) is implicated in associated kidney damage. However, models examining effects of renal ectopic lipid accumulation independent of obesity or T2D are lacking. We generated renal tubule-specific adipose triglyceride lipase knockout (RT-SAKO) mice to determine if this targeted triacylglycerol (TAG) over-storage affects glycemic control and kidney health. METHODS: Male and female RT-SAKO mice and their control littermates were tested for changes in glycemic control at 10-12 and 16-18 weeks of age. Markers of kidney health and blood lipid and hormone concentrations were analyzed. Kidney and blood lysophosphatidic acid (LPA) levels were measured, and a role for LPA in mediating impaired glycemic control was evaluated using the LPA receptor 1/3 inhibitor Ki-16425. RESULTS: All groups remained insulin sensitive, but 16- to 18-week-old male RT-SAKO mice became glucose intolerant, without developing kidney inflammation or fibrosis. Rather, these mice displayed lower circulating insulin and glucagon-like peptide 1 (GLP-1) levels. Impaired first-phase glucose-stimulated insulin secretion was detected and restored by Exendin-4. Kidney and blood LPA levels were elevated in older male but not female RT-SAKO mice, associated with increased kidney diacylglycerol kinase epsilon. Inhibition of LPA-mediated signaling restored serum GLP-1 levels, first-phase insulin secretion, and glucose tolerance. CONCLUSIONS: TAG over-storage alone is insufficient to cause renal tubule lipotoxicity. This work is the first to show that endogenously derived LPA modulates GLP-1 levels in vivo, demonstrating a new mechanism of kidney-gut-pancreas crosstalk to regulate insulin secretion and glucose homeostasis.

More than meets the islet: aligning nutrient and paracrine inputs with hormone secretion in health and disease.

The pancreatic islet is responsive to an array of endocrine, paracrine, and nutritional inputs that adjust hormone secretion to ensure accurate control of glucose homeostasis. Although the mechanisms governing glucose-coupled insulin secretion have received the most attention, there is emerging evidence for a multitude of physiological signaling pathways and paracrine networks that collectively regulate insulin, glucagon, and somatostatin release. Moreover, the modulation of these pathways in conditions of glucotoxicity or lipotoxicity are areas of both growing interest and controversy. In this review, the contributions of external, intrinsic, and paracrine factors in pancreatic ß-, α-, and δ-cell secretion across the full spectrum of physiological (i.e., fasting and fed) and pathophysiological (gluco- and lipotoxicity; diabetes) environments will be critically discussed.

Adiponectin deficiency induces hepatic steatosis during pregnancy and gestational diabetes in mice.

AIMS/HYPOTHESIS: Obesity and hepatic steatosis are risk factors for gestational diabetes mellitus (GDM), a common complication of pregnancy. Adiponectin is a fat-derived hormone that improves hepatic steatosis and insulin sensitivity. Low levels of circulating adiponectin are associated with GDM development. We hypothesised that adiponectin deficiency causes fatty liver during pregnancy, contributing to the development of GDM. METHODS: To determine the role of adiponectin in fatty liver development during pregnancy, we compared pregnant (third week of pregnancy) adiponectin knockout (KO) mice (strain B6;129-Adipoqtm1Chan/J) with wild-type mice and assessed several variables of hepatic lipid metabolism and glucose homeostasis. The impact of adiponectin supplementation was measured by administering adenovirus-mediated full-length adiponectin at the end of the second week of pregnancy and comparing with green fluorescent protein control. RESULTS: In the third week of pregnancy, fasted pregnant adiponectin KO mice were hyperglycaemic on a low-fat diet (9.2 mmol/l vs 7.7 mmol/l in controls, p<0.05) and were glucose and pyruvate intolerant relative to wild-type mice. Pregnant adiponectin KO mice developed hepatic steatosis and a threefold elevation in hepatic triacylglycerols (p<0.05) relative to wild-type mice. Gestational weight gain and food consumption were similar in KO and wild-type mice. Adenoviral-mediated adiponectin supplementation to pregnant adiponectin KO mice improved glucose tolerance, prevented fasting hyperglycaemia and attenuated fatty liver development. CONCLUSIONS/INTERPRETATION: Adiponectin deficiency increased hepatic lipid accumulation during the period of pregnancy associated with increased fat utilisation. Consequently, adiponectin deficiency contributed to glucose intolerance, dysregulated gluconeogenesis and hyperglycaemia, all of which are characteristic of GDM. Increasing adiponectin in the last week of pregnancy alleviated hepatic steatosis and restored normal glucose homeostasis during pregnancy.

Intermittent cold exposure improves glucose homeostasis despite exacerbating diet-induced obesity in mice housed at thermoneutrality.

KEY POINTS: Ambient cold exposure is often regarded as a promising anti-obesity treatment in mice. However, most preclinical studies aimed at treating obesity via cold-induced thermogenesis have been confounded by subthermoneutral housing temperatures. Therefore, the ability of ambient cold to combat diet-induced obesity in mice housed under humanized thermoneutral conditions is currently unknown. Moreover, mammals such as mice are rarely exposed to chronic ambient cold without reprieve, yet mice are often subjected to experimental conditions of chronic rather than intermittent cold exposure (ICE), despite ICE being more physiologically relevant. In the present study, we provide novel evidence that thermoneutral housing uncouples the effects of ICE on glucose and energy homeostasis suggesting that ICE, despite improving glucose tolerance, is not an effective obesity treatment when mice are housed under humanized thermoneutral conditions. ABSTRACT: The present study examines whether a physiologically relevant model of ambient cold exposure, intermittent cold exposure (ICE), could ameliorate the metabolic impairments of diet-induced obesity in male and female mice housed under humanized thermoneutral conditions. Male and female C57BL/6J mice housed at thermoneutrality (29°C) were fed a low-fat diet or high-fat diet for 6 weeks before being weight matched into groups that remained unperturbed or underwent ICE for 4 weeks (4°C for 60 min day-1 ; 5 days week-1 ) when being maintained on their respective diets. ICE induced rapid and persistent hyperphagia exacerbating rather than attenuating high-fat diet-induced obesity over time. These ICE-induced increases in adiposity were found to be energy intake-dependent via pair-feeding. Despite exacerbating high-fat diet-induced obesity, ICE improved glucose tolerance, independent of diet, in a sex-specific manner. The effects of ICE on glucose tolerance were not attributed to improvements in whole-body insulin tolerance, tissue specific insulin action, nor differences in markers of hepatic insulin clearance or pancreatic beta cell proliferation. Instead, ICE increased serum concentrations of insulin and C-peptide in response to glucose, suggesting that ICE may improve glucose tolerance by potentiating pancreatic glucose-stimulated insulin secretion. These data suggest that ICE, despite improving glucose tolerance, is not an effective obesity treatment in mice housed under humanized conditions.

Misoprostol treatment prevents hypoxia-induced cardiac dysfunction through a 14-3-3 and PKA regulatory motif on Bnip3.

Systemic hypoxia is a common element in most perinatal emergencies and is a known driver of Bnip3 expression in the neonatal heart. Bnip3 plays a prominent role in the evolution of necrotic cell death, disrupting ER calcium homeostasis and initiating mitochondrial permeability transition (MPT). Emerging evidence suggests a cardioprotective role for the prostaglandin E1 analog misoprostol during periods of hypoxia, but the mechanisms for this protection are not completely understood. Using a combination of mouse and cell models, we tested if misoprostol is cardioprotective during neonatal hypoxic injury by altering Bnip3 function. Here we report that hypoxia elicits mitochondrial-fragmentation, MPT, reduced ejection fraction, and evidence of necroinflammation, which were abrogated with misoprostol treatment or Bnip3 knockout. Through molecular studies we show that misoprostol leads to PKA-dependent Bnip3 phosphorylation at threonine-181, and subsequent redistribution of Bnip3 from mitochondrial Opa1 and the ER through an interaction with 14-3-3 proteins. Taken together, our results demonstrate a role for Bnip3 phosphorylation in the regulation of cardiomyocyte contractile/metabolic dysfunction, and necroinflammation. Furthermore, we identify a potential pharmacological mechanism to prevent neonatal hypoxic injury.

Tafazzin Deficiency Reduces Basal Insulin Secretion and Mitochondrial Function in Pancreatic Islets From Male Mice.

Tafazzin (TAZ) is a cardiolipin (CL) biosynthetic enzyme important for maintaining mitochondrial function. TAZ affects both the species and content of CL in the inner mitochondrial membrane, which are essential for normal cellular respiration. In pancreatic ß cells, mitochondrial function is closely associated with insulin secretion. However, the role of TAZ and CL in the secretion of insulin from pancreatic islets remains unknown. Male 4-month-old doxycycline-inducible TAZ knock-down (KD) mice and wild-type littermate controls were used. Immunohistochemistry was used to assess ß-cell morphology in whole pancreas sections, whereas ex vivo insulin secretion, CL content, RNA-sequencing analysis, and mitochondrial oxygen consumption were measured from isolated islet preparations. Ex vivo insulin secretion under nonstimulatory low-glucose concentrations was reduced ~52% from islets isolated from TAZ KD mice. Mitochondrial oxygen consumption under low-glucose conditions was also reduced ~58% in islets from TAZ KD animals. TAZ deficiency in pancreatic islets was associated with significant alteration in CL molecular species and elevated polyunsaturated fatty acid CL content. In addition, RNA-sequencing of isolated islets showed that TAZ KD increased expression of extracellular matrix genes, which are linked to pancreatic fibrosis, activated stellate cells, and impaired ß-cell function. These data indicate a novel role for TAZ in regulating pancreatic islet function, particularly under low-glucose conditions.

Circadian Regulation of the Pancreatic Beta Cell.

Beta cell dysfunction is central to the development of type 2 diabetes (T2D). In T2D, environmental and genetic influences can manifest beta cell dysfunction in many ways, including impaired glucose-sensing and secretion coupling mechanisms, insufficient adaptative responses to stress, and aberrant beta cell loss through increased cell death and/or beta cell de-differentiation. In recent years, circadian disruption has emerged as an important environmental risk factor for T2D. In support of this, genetic disruption of the circadian timing system in rodents impairs insulin secretion and triggers diabetes development, lending important evidence that the circadian timing system is intimately connected to, and essential for the regulation of pancreatic beta cell function; however, the role of the circadian timing system in the regulation of beta cell biology is only beginning to be unraveled. Here, we review the recent literature that explores the importance of the pancreatic islet/beta cell circadian clock in the regulation of various aspects of beta cell biology, including transcriptional and functional control of daily cycles of insulin secretion capacity, regulation of postnatal beta cell maturation, and control of the adaptive responses of the beta cell to metabolic stress and acute injury.

Misoprostol attenuates neonatal cardiomyocyte proliferation through Bnip3, perinuclear calcium signaling, and inhibition of glycolysis.

Systemic hypoxia resulting from preterm birth, altered lung development, and cyanotic congenital heart disease is known to impede the regulatory and developmental pathways in the neonatal heart. While the molecular mechanisms are still unknown, hypoxia induces aberrant cardiomyocyte proliferation, which may be initially adaptive, but can ultimately program the heart to fail in early life. Recent evidence suggests that the prostaglandin E1 analogue, misoprostol, is cytoprotective in the hypoxia-exposed neonatal heart by impacting alternative splicing of the Bcl-2 family member Bnip3, resulting in the generation of a variant lacking the third exon (Bnip3ΔExon3 or small Nip; sNip). Using a rodent model of neonatal hypoxia, in combination with rat primary neonatal cardiomyocytes (PVNCs) and H9c2 cells, we sought to determine if misoprostol can prevent cardiomyocyte proliferation and what the key molecular mechanisms might be in this pathway. In PVNCs, exposure to 10% oxygen induced myocyte proliferation concurrent with molecular markers of cell-cycle progression, such as Cyclin-D1, which were prevented by misoprostol treatment. Furthermore, we describe a critical role for sNip in opposing cardiomyocyte proliferation through several mechanisms, including reduced expression of the proliferative MEF2C-myocardin-BMP10 pathway, accumulation of nuclear calcium leading to NFATc3 activation, and increased expression of the cardiac maturation factor BMP2. Intriguingly, misoprostol and sNip inhibited hypoxia-induced glycolytic flux, which directly influenced myocyte proliferation. These observations were further supported by knockdown studies, where hypoxia-induced cardiomyocyte proliferation is restored in misoprostol-treated cells by an siRNA targeting sNip. Finally, in postnatal day (PND)-10 rat pups exposed to hypoxia, we observed histological evidence of increased nuclei number and increased PPH3 staining, which were completely attenuated by misoprostol treatment. Collectively, this data demonstrates how neonatal cardiomyocyte proliferation can be pharmacologically modulated by misoprostol treatment, which may have important implications for both neonatal and regenerative medicine.

Maternal resveratrol administration protects against gestational diabetes-induced glucose intolerance and islet dysfunction in the rat offspring.

KEY POINTS: Maternal resveratrol (RESV) administration in gestational diabetes (GDM) restored normoglycaemia and insulin secretion. GDM-induced obesity was prevented in male GDM+RESV offspring but not in females. GDM+RESV offspring exhibited improved glucose tolerance and insulin sensitivity. GDM+RESV restored hepatic glucose homeostasis in offspring. Glucose-stimulated insulin secretion was enhanced in GDM+RESV offspring. ABSTRACT: Gestational diabetes (GDM), the most common complication of pregnancy, is associated with adverse metabolic health outcomes in offspring. Using a rat model of diet-induced GDM, we investigated whether maternal resveratrol (RESV) supplementation (147 mg kg-1  day-1 ) in the third week of pregnancy could improve maternal glycaemia and protect the offspring from developing metabolic dysfunction. Female Sprague-Dawley rats consumed a high-fat and sucrose (HFS) diet to induce GDM. Lean controls consumed a low-fat (LF) diet. In the third trimester, when maternal hyperglycaemia was observed, the HFS diet was supplemented with RESV. At weaning, offspring were randomly assigned a LF or HFS diet until 15 weeks of age. In pregnant dams, RESV restored glucose tolerance, normoglycaemia and improved insulin secretion. At 15 weeks of age, GDM+RESV-HFS male offspring were less obese than the GDM-HFS offspring. By contrast, the female GDM+RESV-HFS offspring were similarly as obese as the GDM-HFS group. Hepatic steatosis, insulin resistance, glucose intolerance and dysregulated gluconeogenesis were observed in the male GDM offspring and were attenuated in the offspring of GDM+RESV dams. The dysregulation of several metabolic genes (e.g. ppara, lpl, pepck and g6p) in the livers of GDM offspring was attenuated in the GDM+RESV offspring group. Glucose stimulated insulin secretion was also improved in the islets from offspring of GDM+RESV dams. Thus, maternal RESV supplementation during the third trimester of pregnancy and lactation induced several beneficial metabolic health outcomes for both mothers and offspring. Therefore, RESV could be an alternative to current GDM treatments.

Gestational Diabetes Adversely Affects Pancreatic Islet Architecture and Function in the Male Rat Offspring.

Fetal exposure to gestational diabetes mellitus (GDM) and poor postnatal diet are strong risk factors for type 2 diabetes development later in life, but the mechanisms connecting GDM exposure to offspring metabolic health remains unclear. In this study, we aimed to determine how GDM interacts with the postnatal diet to affect islet function in the offspring as well as characterize the gene expression changes in the islets. GDM was induced in female rats using a high-fat, high-sucrose (HFS) diet, and litters from lean or GDM dams were weaned onto a low-fat (LF) or HFS diet. Compared with the lean control offspring, GDM exposure reduced glucose-stimulated insulin secretion in islets isolated from 15-week-old offspring, which was additively worsened when GDM exposure was combined with postnatal HFS diet consumption. In the HFS diet-fed offspring of lean dams, islet size and number increased, an adaptation that was not observed in the HFS diet-fed offspring of GDM dams. Islet gene expression in the offspring of GDM dams was altered in such categories as inflammation (e.g., Il1b, Ccl2), mitochondrial function/oxidative stress resistance (e.g., Atp5f1, Sod2), and ribosomal proteins (e.g., Rps6, Rps14). These results demonstrate that GDM exposure induced marked changes in gene expression in the male young adult rat offspring that cumulatively interact to worsen islet function, whole-body glucose homeostasis, and adaptations to HFS diets.

Maternal obesity, diabetes during pregnancy and epigenetic mechanisms that influence the developmental origins of cardiometabolic disease in the offspring.

Since 1980, global obesity has doubled, and the incidence of cardiometabolic diseases such as type 2 diabetes and heart disease is also increasing. While genetic susceptibility and adult lifestyle are implicated in these trends, evidence from clinical cohorts, epidemiological studies and animal model experiments support a role for early-life environmental exposures in determining the long-term health of an individual, which has led to the formulation of the Developmental Origins of Health and Disease (DOHaD) theory. In fact, maternal obesity and diabetes during pregnancy, which are on the rise, are strongly associated with altered fetal growth and development as well as with lifelong perturbations in metabolic tissues. A mounting body of evidence implicates epigenetic mechanisms (e.g. DNA methylation and histone modifications) in the regulation of these effects and their transmission to future generations. This review critically discusses the current evidence (in animal model systems and humans) that implicates maternal obesity and diabetes during pregnancy in perturbing the epigenome of the next generation, and the consequential impact on growth, organ development and ultimately cardiometabolic disease progression. Additionally, this review will address some of the limitations of the DOHaD approach and areas that require further study. For example, future research requires verification of the mechanistic impact of the epigenetic marks and their persistence over the life course. Ultimately, this knowledge is needed to establish optimal screening, prevention and therapeutic approaches for children at risk of cardiometabolic disease development.

Uncoupling protein 2 regulates daily rhythms of insulin secretion capacity in MIN6 cells and isolated islets from male mice.

OBJECTIVE: Upregulation of uncoupling protein 2 (UCP2) is associated with impaired glucose-stimulated insulin secretion (GSIS), which is thought to be an important contributor to pathological ß cell failure in obesity and type 2 diabetes (T2D); however, the physiological function of UCP2 in the ß cell remains undefined. It has been suggested, but not yet tested, that UCP2 plays a physiological role in ß cells by coordinating insulin secretion capacity with anticipated fluctuating nutrient supply, such that upregulation of UCP2 in the inactive/fasted state inhibits GSIS as a mechanism to prevent hypoglycemia. Therefore, we hypothesized that daily cycles of GSIS capacity are dependent on rhythmic and predictable patterns of Ucp2 gene expression such that low Ucp2 in the active/fed phase promotes maximal GSIS capacity, whereas elevated Ucp2 expression in the inactive/fasted phase supresses GSIS capacity. We further hypothesized that rhythmic Ucp2 expression is required for the maintenance of glucose tolerance over the 24 h cycle. METHODS: We used synchronized MIN6 clonal ß cells and isolated mouse islets from wild type (C57BL6) and mice with ß cell knockout of Ucp2 (Ucp2-ßKO; and respective Ins2-cre controls) to determine the endogenous expression pattern of Ucp2 over 24 h and its impact on GSIS capacity and glucose tolerance over 24 h. RESULTS: A dynamic pattern of Ucp2 mRNA expression was observed in synchronized MIN6 cells, which showed a reciprocal relationship with GSIS capacity in a time-of-day-specific manner. GSIS capacity was suppressed in islets isolated from wild type and control mice during the light/inactive phase of the daily cycle; a suppression that was dependent on Ucp2 in the ß cell and was lost in islets isolated from Ucp2-ßKO mice or wild type islets treated with a UCP2 inhibitor. Finally, suppression of GSIS capacity by UCP2 in the light phase was required for the maintenance of normal patterns of glucose tolerance. CONCLUSIONS: Our study suggests that Ucp2/UCP2 in the ß cell is part of an important, endogenous, metabolic regulator that controls the temporal capacity of GSIS over the course of the day/night cycle, which, in turn, regulates time-of-day glucose tolerance. Targeting Ucp2/UCP2 as a therapeutic in type 2 diabetes or any other metabolic condition must take into account the rhythmic nature of its expression and its impact on glucose tolerance over 24 h, specifically during the inactive/fasted phase.

In utero exposure to gestational diabetes mellitus conditions TLR4 and TLR2 activated IL-1beta responses in spleen cells from rat offspring.

Fetal exposure to gestational diabetes mellitus (GDM) is associated with a higher risk of youth-onset insulin resistance and type 2 diabetes. We have previously shown that the rat offspring of GDM dams are insulin resistant when compared to the offspring of lean dams. Since inflammation influences insulin sensitivity, we examined the impact of fetal exposure to GDM on inflammatory responses in the offspring. In rats, we compared inflammatory activity in newborn pups as well as 16week-old young-adult offspring from lean control dams with offspring from high fat and sucrose diet (HFS)-induced GDM dams. To determine whether there are additive effects of exposure to GDM and post-weaning diets, offspring of lean and GDM dams were fed either low fat or HFS diets until 16weeks of age. Plasma levels of interleukin(IL)-1ß were elevated in the offspring of GDM dams. To determine whether this was related to immune reactivity, spleen cells from both the newborn and 16week-old offspring were isolated and reactivity to the toll-like receptor activators, pam3CSK4 and lipopolysaccharides were measured over a 72h timeframe. Spleen cells of GDM dams exhibited sustained stimulation of interleukin(IL)-1ß and IL-10 production, whereas IL-1ß and IL-10 synthesis diminished over time in spleen cells from the offspring of lean dams. Additive effects of GDM exposure and post-weaning HFS diet were not observed, suggesting the effects of GDM on cytokine production are independent of the post-weaning diet. Thus, we conclude that exposure to GDM in utero may condition the immune reactivity of spleen cells.

Bcl-2 Regulates Reactive Oxygen Species Signaling and a Redox-Sensitive Mitochondrial Proton Leak in Mouse Pancreatic ß-Cells.

In pancreatic ß-cells, controlling the levels of reactive oxygen species (ROS) is critical to counter oxidative stress, dysfunction and death under nutrient excess. Moreover, the fine-tuning of ROS and redox balance is important in the regulation of normal ß-cell physiology. We recently demonstrated that Bcl-2 and Bcl-xL, in addition to promoting survival, suppress ß-cell glucose metabolism and insulin secretion. Here, we tested the hypothesis that the nonapoptotic roles of endogenous Bcl-2 extend to the regulation of ß-cell ROS and redox balance. We exposed mouse islet cells and MIN6 cells to the Bcl-2/Bcl-xL antagonist Compound 6 and the Bcl-2-specific antagonist ABT-199 and evaluated ROS levels, Ca(2+) responses, respiratory control, superoxide dismutase activity and cell death. Both acute glucose stimulation and the inhibition of endogenous Bcl-2 progressively increased peroxides and stimulated superoxide dismutase activity in mouse islets. Importantly, conditional ß-cell knockout of Bcl-2 amplified glucose-induced formation of peroxides. Bcl-2 antagonism also induced a mitochondrial proton leak that was prevented by the antioxidant N-acetyl-L-cysteine and, therefore, secondary to redox changes. We further established that the proton leak was independent of uncoupling protein 2 but partly mediated by the mitochondrial permeability transition pore. Acutely, inhibitor-induced peroxides promoted Ca(2+) influx, whereas under prolonged Bcl inhibition, the elevated ROS was required for induction of ß-cell apoptosis. In conclusion, our data reveal that endogenous Bcl-2 modulates moment-to-moment ROS signaling and suppresses a redox-regulated mitochondrial proton leak in ß-cells. These noncanonical roles of Bcl-2 may be important for ß-cell function and survival under conditions of high metabolic demand.

Exploring the role of the HNF-1αG319S polymorphism in ß cell failure and youth-onset type 2 diabetes: Lessons from MODY and Hnf-1α-deficient animal models.

The prevalence of youth-onset type 2 diabetes (T2D) is rapidly increasing worldwide, disproportionately affecting Indigenous youth with Oji-Cree heritage from central Canada. Candidate gene screening has uncovered a novel and private polymorphism in the Oji-Cree population in the hepatocyte nuclear factor-1 alpha (HNF-1α) gene, where a highly conserved glycine residue at position 319 is changed to a serine (termed HNF-1αG319S or simply G319S). Oji-Cree youth who carry one or two copies of the "S-allele" present at diagnosis with less obesity, reduced indicators of insulin resistance, and lower plasma insulin levels at diagnosis, suggestive of a primary defect in the insulin-secreting ß cells. Few studies on the impact of the HNF-1αG319S variant on ß cell function have been performed to date; however, much can be learned from other clinical phenotypes of HNF-1α-deficiency, including HNF-1α mutations that cause maturity-onset diabetes of the young 3 (MODY3). In addition, evaluation of Hnf-1α-deficient murine models reveals that HNF-1α plays a central role in the regulation of insulin secretion by regulating the expression of key genes involved in ß cell glucose-sensing, mitochondrial function, and the maintenance of the ß cell phenotype in differentiated ß cells. The overall goal of this minireview is to explore the impact of HNF-1α-deficiency on the ß cell to better inform future research into the mechanisms of ß cell dysfunction in Oji-Cree youth with T2D.

Maternal obesity characterized by gestational diabetes increases the susceptibility of rat offspring to hepatic steatosis via a disrupted liver metabolome.

Maternal obesity is associated with a high risk for gestational diabetes mellitus (GDM), which is a common complication of pregnancy. The influence of maternal obesity and GDM on the metabolic health of the offspring is poorly understood. We hypothesize that GDM associated with maternal obesity will cause obesity, insulin resistance and hepatic steatosis in the offspring. Female Sprague-Dawley rats were fed a high-fat (45%) and sucrose (HFS) diet to cause maternal obesity and GDM. Lean control pregnant rats received low-fat (LF; 10%) diets. To investigate the interaction between the prenatal environment and postnatal diets, rat offspring were assigned to LF or HFS diets for 12 weeks, and insulin sensitivity and hepatic steatosis were evaluated. Pregnant GDM dams exhibited excessive gestational weight gain, hyperinsulinaemia and hyperglycaemia. Offspring of GDM dams gained more weight than the offspring of lean dams due to excess adiposity. The offspring of GDM dams also developed hepatic steatosis and insulin resistance. The postnatal consumption of a LF diet did not protect offspring of GDM dams against these metabolic disorders. Analysis of the hepatic metabolome revealed increased diacylglycerol and reduced phosphatidylethanolamine in the offspring of GDM dams compared to offspring of lean dams. Consistent with altered lipid metabolism, the expression of CTP:phosphoethanolamine cytidylyltransferase, and peroxisomal proliferator activated receptor-α mRNA was reduced in the livers of GDM offspring. GDM exposure programs gene expression and hepatic metabolite levels and drives the development of hepatic steatosis and insulin resistance in young adult rat offspring.

UCP2 regulates the glucagon response to fasting and starvation.

Glucagon is important for maintaining euglycemia during fasting/starvation, and abnormal glucagon secretion is associated with type 1 and type 2 diabetes; however, the mechanisms of hypoglycemia-induced glucagon secretion are poorly understood. We previously demonstrated that global deletion of mitochondrial uncoupling protein 2 (UCP2(-/-)) in mice impaired glucagon secretion from isolated islets. Therefore, UCP2 may contribute to the regulation of hypoglycemia-induced glucagon secretion, which is supported by our current finding that UCP2 expression is increased in nutrient-deprived murine and human islets. Further to this, we created α-cell-specific UCP2 knockout (UCP2AKO) mice, which we used to demonstrate that blood glucose recovery in response to hypoglycemia is impaired owing to attenuated glucagon secretion. UCP2-deleted α-cells have higher levels of intracellular reactive oxygen species (ROS) due to enhanced mitochondrial coupling, which translated into defective stimulus/secretion coupling. The effects of UCP2 deletion were mimicked by the UCP2 inhibitor genipin on both murine and human islets and also by application of exogenous ROS, confirming that changes in oxidative status and electrical activity directly reduce glucagon secretion. Therefore, α-cell UCP2 deletion perturbs the fasting/hypoglycemic glucagon response and shows that UCP2 is necessary for normal α-cell glucose sensing and the maintenance of euglycemia.

Beta-cell uncoupling protein 2 regulates reactive oxygen species production, which influences both insulin and glucagon secretion.

OBJECTIVE: The role of uncoupling protein 2 (UCP2) in pancreatic ß-cells is highly debated, partly because of the broad tissue distribution of UCP2 and thus limitations of whole-body UCP2 knockout mouse models. To investigate the function of UCP2 in the ß-cell, ß-cell-specific UCP2 knockout mice (UCP2BKO) were generated and characterized. RESEARCH DESIGN AND METHODS: UCP2BKO mice were generated by crossing loxUCP2 mice with mice expressing rat insulin promoter-driven Cre recombinase. Several in vitro and in vivo parameters were measured, including respiration rate, mitochondrial membrane potential, islet ATP content, reactive oxygen species (ROS) levels, glucose-stimulated insulin secretion (GSIS), glucagon secretion, glucose and insulin tolerance, and plasma hormone levels. RESULTS: UCP2BKO ß-cells displayed mildly increased glucose-induced mitochondrial membrane hyperpolarization but unchanged rates of uncoupled respiration and islet ATP content. UCP2BKO islets had elevated intracellular ROS levels that associated with enhanced GSIS. Surprisingly, UCP2BKO mice were glucose-intolerant, showing greater α-cell area, higher islet glucagon content, and aberrant ROS-dependent glucagon secretion under high glucose conditions. CONCLUSIONS: Using a novel ß-cell-specific UCP2KO mouse model, we have shed light on UCP2 function in primary ß-cells. UCP2 does not behave as a classical metabolic uncoupler in the ß-cell, but has a more prominent role in the regulation of intracellular ROS levels that contribute to GSIS amplification. In addition, ß-cell UCP2 contributes to the regulation of intraislet ROS signals that mediate changes in α-cell morphology and glucagon secretion.

Insulin mimetics in Urtica dioica: structural and computational analyses of Urtica dioica extracts.

Urtica Dioica (UD) is a plant shown to reduce blood glucose levels upon oral ingestion; however, neither its active component nor its mechanism of action has been identified. One active fraction of this extract, termed UD-1, was separated by molecular sieve column chromatography and purified by high performance liquid chromatography (HPLC). While UD-1 did not stimulate insulin secretion in glucose-responsive MIN6 clonal beta-cells, chronic exposure (24 h) significantly enhanced glucose uptake (approximately 1.5-fold) in L6-GLUT4myc myoblast cells. Using HPLC and MALDI-TOF, we further purified the UD-1 fraction into two fractions termed UD-1A and UD-1B. Computational and structural analyses strongly suggested that the antidiabetic component of UD-1 was due to one or more structurally related cyclical peptides that facilitate glucose uptake by forming unique glucose permeable pores. The structure and function of these glucose-conducting pores are discussed herein.

Uncoupling protein 2 regulates reactive oxygen species formation in islets and influences susceptibility to diabetogenic action of streptozotocin.

Currently, the physiological function of uncoupling protein-2 (UCP2) in pancreatic islets and its role in the development of diabetes is a matter of great debate. To further investigate the impact of UCP2 on diabetes development, we used streptozotocin (STZ) to experimentally generate diabetes in both wild-type (WT) and UCP2-knockout (UCP2KO) mice. While multiple low-dose STZ injections led to hyperglycemia development over a 14-day period in both WT and UCP2KO mice, we found the development of hyperglycemia to be significantly less severe in the UCP2KO mice. Measurement of insulin and glucagon secretion (in vitro), as well as their plasma concentrations (in vivo), indicated that UCP2-deficiency showed enhanced insulin secretion but impaired alpha-cell function. Glucagon secretion was attenuated, despite reduced insulin secretion after exposure to STZ, which together contributed to less severe hyperglycemia development in UCP2KO mice. Further experimentation revealed that UCP2-deficient alpha- and beta-cells had chronically higher cellular reactive oxygen species (ROS) levels than the WT prior to STZ application, which correlated with increased basal beta- and alpha-cell mass. Overall, we suggest that increased chronic ROS signaling as a result of UCP2-deficiency contributes to enhanced beta-cell function and impairment of alpha-cell function, leading to an attenuation of STZ-induced hyperglycemia development.