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.

Generation of an Rtel1-CreERT2 knock-in mouse model for lineage tracing RTEL1+ stem cells during development.

Regulator of telomere length 1 (RTEL1) DNA helicase has been demonstrated to be essential for the maintenance of telomeres and genomic stability. This function of RTEL1 could be required for protecting stem cells from genomic mutations as suggested by its selective expression in stem cell-zones, as well as by RTEL1 mutations identified in Hoyeraal-Hreidarsson syndrome, a severe dyskeratosis congenita that targets primarily stem cell compartments. As a first step to establish a role of RTEL1 in stem cells, we generated an Rtel1CreERT2 mouse allele in which a tamoxifen-inducible Cre (CreERT2) cDNA was specifically knocked into the Rtel1 genomic locus and controlled by the endogenous Rtel1 regulatory elements. By crossing with a Cre-dependent LacZ reporter mouse strain (R26RLacZ), we further demonstrated that Cre activity in Rtel1CreERT2 mice could be specifically induced by tamoxifen, which allowed the fate of RTEL1+ cells to be traced at various stages of development. Using this tracing assay, we showed for the first time that RTEL1+ cells in the intestine and the testis can act as stem cells that have the capacity to self-renew and differentiate into progeny cells. Therefore, the Rtel1CreERT2 mice generated in this study will be a valuable transgenic tool to explore the function of RTEL1 in stem cells.

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.