FNDC5/Irisin protects neurons through Caspase3 and Bax pathways

Irisin is a glycosylated protein formed from the hydrolysis of fibronectin type III domain-containing protein 5 (FNDC5). Recent studies have demonstrated that FNDC5/Irisin is involved in the regulation of glucose and lipid metabolism, it can inhibit inflammation and have neuroprotective effects. However, the effect and mechanism of FNDC5/Irisin on motor neuron-like cell lines (NSC-34) have not been reported. In this study, we used lipopolysaccharide to construct cellular oxidative stress injury models and investigated the potential roles of FNDC5/Irisin on neurons by different cellular and molecular pathways. Taken together, our findings showed that FNDC5/Irisin can protect neurons, and this effect might be associated with Caspase3 and Bax pathways. These results laid the foundation for neuronal protection and clinical translation of FNDC5/Irisin therapy.     

The AMPK-SIRT signaling network regulates glucose tolerance under calorie restriction conditions

Aims

SIRT1 and AMP-activated protein kinase (AMPK) share common activators, actions and target molecules. Previous studies have suggested that a putative SIRT1-AMPK regulatory network could act as the prime initial sensor for calorie restriction-induced adaptations in skeletal muscle—the major site of insulin-stimulated glucose disposal. Our study aimed to investigate whether a feedback loop exists between AMPK and SIRT1 in skeletal muscle and how this may be involved glucose tolerance.

Main methods

To investigate this, we used skeletal muscle-specific AMPKα1/2 knockout mice (AMPKα1/2^−/−) fed ad libitum (AL) or a 30% calorie restricted (CR) diet and L6 rat myoblasts incubated with SIRT1 inhibitor (EX527).

Key findings

CR-AMPKα1/2^−/− displayed impaired glucose tolerance (*p < 0.05), in association with down-regulated SIRT1 and PGC-1α expression (< 300% vs. CR-WT, ^±±p < 0.01). Moreover, AMPK activity was decreased following SIRT1 inhibition in L6 cells (~ 0.5-fold vs. control, *p < 0.05).

Significance

This study demonstrates that skeletal muscle-specific AMPK deficiency impairs the beneficial effects of CR on glucose tolerance and that these effects may be dependent on reduced SIRT1 levels.     

Bone and glucose metabolism: A two-way street

Evidence from rodent models indicates that undercarboxylated osteocalcin (ucOC), a product of osteoblasts, is a hormone affecting insulin production by the pancreas and insulin sensitivity in peripheral tissues, at least in part through enhanced secretion of adiponectin from adipocytes. Clinical research to test whether this relationship is found in humans is just beginning to emerge. Cross-sectional studies confirm associations between total osteocalcin (OC), ucOC and glucose metabolism but cannot distinguish causality. To date, longitudinal studies have not provided a consistent picture of the effects of ucOC or OC on fasting glucose and insulin sensitivity. Further exploration into the physiological and mechanistic effects of ucOC and OC, in rodent models and clinical studies, is necessary to determine to what extent the skeleton regulates energy metabolism in humans.     

Studies on the role of β-cell metabolism in the insulinotropic effect of α-ketoisocaproic acid

α-Ketoisocaproic acid has been shown to be apotent insulin secretagogue but the mechanism has not been elucidated. To define the role of β-cell metabolism in the insulinotropic activity of α-ketoisocaproic acid the utilization of glucose and the oxidation of α-ketoisocaproic and isovaleric acid by incubated islets of obese hyperglycemic mice were measured.Glucose metabolism was never enhanced by α-ketoisocaproic acid. The same ¹⁴CO₂ amounts were released from the non-secretagogue [1-¹⁴C]isovaleric acid (10 mM) or from α-keto [2-¹⁴C]isocaproic acid (5–20 mM). Pyruvate (20 mM) did not inhibit α-ketoisocaproic acid-induced insulin secretion in spite of reduction of decarboxylation of α-ketoisocaproic acid by more than 40%.The results indicate that stimulated insulin release in response to α-ketoisocaproic acid is not mediated by an indirect increase in glucose metabolism and further suggest that isovaleryl-CoA and following CoA-esters in α-ketoisocaproic acid degradation are not likely recognized as signals. The possibility, however, remains that enhanced intramitochondrial production of reducing equivalents elicits insulin secretion.     

Effect of moderate physical activity on plasma leptin concentration in humans

In subjects who maintain a constant body mass, the increased energy expenditure induced by exercise must be compensated by a similar increase in energy intake. Since leptin has been shown to decrease food intake in animals, it can be expected that physical exercise would increase energy intake by lowering plasma leptin concentrations. This effect may be secondary either to exercise-induced negative energy balance or to other effects of exercise. To delineate the effects of moderate physical activity on plasma leptin concentrations, 11 healthy lean subjects (4 men, 7 women) were studied on three occasions over 3 days; in study 1 they consumed an isoenergetic diet (1.3 times resting energy expenditure) over 3 days with no physical activity; in study 2 the subjects received the same diet as in study 1, but they exercised twice daily during the 3 days (cycling at 60 W for 30 min); in study 3 the subjects exercised twice daily during the 3 days, and their energy intake was increased by 18% to cover the extra energy expenditure induced by the physical activity. Fasting plasma leptin concentration (measured on the morning of day 4) was unaltered by exercise [8.64 (SEM 2.22) 7.17 (SEM 1.66), 7.33 (SEM 1.72) 1 microg x l(-1) in studies 1, 2 and 3, respectively]. It was concluded that a moderate physical activity performed over a 3-day period does not alter plasma leptin concentrations, even when energy balance is slightly negative. This argues against a direct effect of physical exercise on plasma leptin concentrations, when body composition is unaltered.     

Circular RNA AFF4 modulates osteogenic differentiation in BM-MSCs by activating SMAD1/5 pathway through miR-135a-5p/FNDC5/Irisin axis

Bone marrow-derived mesenchymal stem cells (BM-MSCs), the common progenitor cells of adipocytes and osteoblasts, have been recognized as the key mediator during bone formation. Herein, our study aim to investigate molecular mechanisms underlying circular RNA (circRNA) AFF4 (circ_AFF4)-regulated BM-MSCs osteogenesis. BM-MSCs were characterized by FACS, ARS, and ALP staining. Expression patterns of circ_AFF4, miR-135a-5p, FNDC5/Irisin, SMAD1/5, and osteogenesis markers, including ALP, BMP4, RUNX2, Spp1, and Colla1 were detected by qRT-PCR, western blot, or immunofluorescence staining, respectively. Interactions between circ_AFF4 and miR-135a-5p, FNDC5, and miR-135a-5p were analyzed using web tools including TargetScan, miRanda, and miRDB, and further confirmed by luciferase reporter assay and RNA pull-down. Complex formation between Irisin and Integrin αV was verified by Co-immunoprecipitation. To further verify the functional role of circ_AFF4 in vivo during bone formation, we conducted animal experiments harboring circ_AFF4 knockdown, and born samples were evaluated by immunohistochemistry, hematoxylin and eosin, and Masson staining. Circ_AFF4 was upregulated upon osteogenic differentiation induction in BM-MSCs, and miR-135a-5p expression declined as differentiation proceeds. Circ_AFF4 knockdown significantly inhibited osteogenesis potential in BM-MSCs. Circ_AFF4 stimulated FNDC5/Irisin expression through complementary binding to its downstream target molecule miR-135a-5p. Irisin formed an intermolecular complex with Integrin αV and activated the SMAD1/5 pathway during osteogenic differentiation. Our work revealed that circ_AFF4, acting as a sponge of miR-135a-5p, triggers the promotion of FNDC5/Irisin via activating the SMAD1/5 pathway to induce osteogenic differentiation in BM-MSCs. These findings gained a deeper insight into the circRNA-miRNA regulatory system in the bone marrow microenvironment and may improve our understanding of bone formation-related diseases at physiological and pathological levels.Subject terms: Stem cells, Diseases     

Atypical protein kinase C in glucose metabolism

Type 2 diabetes mellitus is a multigenic disease with evident genetic predisposition, and complex pathogenesis in which environmental and genetic factors interact. The disorder of body utilization glucose is a crucial reason for causing diabetes. Atypical PKCs, belonging to Ser/Thr protein kinase, have many important biological functions in vivo, and may be involved in the pathogenesis of diabetes mellitus. APKCs participate in glucose metabolism by regulating glucose transport and absorption, glycogen synthesis, and insulin secretion. The exact mechanism by which aPKCs participate in glucose metabolism remains unclear. So far, the clarification of which will be helpful for the prevention and cure of type 2 diabetes.     

丙型肝炎病毒核心蛋白通过FOXO1/PGC-1α途径上调磷酸烯醇式丙酮酸羧基酶的转录

【目的】分析丙型肝炎病毒(HCV)核心蛋白(CORE)稳定表达对磷酸烯醇式丙酮酸羧基酶(PCK1)转录水平的影响,并分析HCV CORE调控PCK1转录的分子机制,为进一步阐明HCV感染致2型糖尿病机理的探讨提供新的思路。【方法】利用反转录病毒表达系统构建稳定表达HCV CORE的Huh7-lunet-core细胞系。采用Real-time PCR和萤光素酶报告基因技术检测Huh7-lunet-core细胞系中PCK1、FOXO1以及PGC-1α转录水平变化,并结合Western blot分析FOXO1的活性变化。【结果】HCV CORE的稳定表达显著增强PCK1的转录水平,HCV CORE不影响FOXO1的转录和表达水平,但降低FOXO1的磷酸化水平,激活了FOXO1的转录活性,并增强PGC-1α的mRNA表达水平。【结论】HCV CORE在Huh7-lunet细胞中的稳定表达激活FOXO1的转录活性,并与PGC-1α协同作用,上调PCK1的转录,从而导致肝糖异生过度发生,对HCV CORE调控PCK1转录的分子机制的揭示可能为HCV感染相关的糖尿病的治疗提供新的靶点。     

A PPAR agonist improves TNF-alpha-induced insulin resistance of adipose tissue in mice

Thiazolidinediones (TZDs), agonists for PPARs, have been shown to block the inhibitory effects of TNF-alpha on insulin action using cultured cells. In order to clarify the in vivo effects of TZDs on the inhibition of insulin sensitivity by TNF-alpha, insulin action in muscles and adipose tissues was assessed in the TNF-alpha-overexpression mice model using transplantation of cells secreting the TNF-alpha protein. After the pioglitazone treatment for 4 weeks, glucose uptake, insulin-induced IRS-1 phosphorylation, and lipoprotein lipase mRNA levels were analyzed. Pioglitazone did not ameliorate TNF-alpha-induced hyperinsulinemia in this model, as assessed by the OGTT. Glucose uptake and lipoprotein lipase mRNA levels were decreased by TNF-alpha in adipose tissues from the TNF-alpha-overexpressing mice, and pioglitazone blocked these inhibitions by TNF-alpha. On the other hand, in muscles, pioglitazone did not reverse the effects of TNF-alpha on insulin-induced phosphorylation of IRS-1, glucose uptake, and lipoprotein lipase mRNA levels. Present study revealed the different sensitivities of pioglitazone for the recovery of decreased insulin action in a TNF-alpha-overexpressing model using cell transplantation. These results suggest that the effect of TZDs is dependent on the fat distribution and accumulation in humans.     

Free fatty acids increase PGC-1alpha expression in isolated rat islets

PGC-1alpha mRNA and protein are elevated in islets from multiple animal models of diabetes. Overexpression of PGC-1alpha impairs glucose-stimulated insulin secretion (GSIS). However, it is not well known which metabolic events lead to upregulation of PGC-1alpha in the beta-cells under pathophysiological condition. In present study, we have investigated effects of chronic hyperlipidemia and hyperglycemia on PGC-1alpha mRNA expression in isolated rat islets. Isolated rat islets are chronically incubated with 0, 0.2 and 0.4 mM oleic acid/palmitic acid (free fatty acids, FFA) or 5.5 and 25 mM glucose for 72 h. FFA dose-dependently increases PGC-1alpha mRNA expression level in isolated islets. FFA also increases PGC-1alpha expression in mouse beta-cell-derived beta TC3 cell line. In contrast, 25 mM glucose decreases expression level of PGC-1alpha. Inhibition of PGC-1alpha by siRNA improves FFA-induced impairment of GSIS in islets. These data suggest that hyperlipidemia and hyperglycemia regulate PGC-1alpha expression in islets differently, and elevated PGC-1alpha by FFA plays an important role in chronic hyperlipidemia-induced beta-cell dysfunction.