DRAK2 suppresses autophagy by phosphorylating ULK1 at Ser56 to diminish pancreatic ß cell function upon overnutrition.

Impeded autophagy can impair pancreatic ß cell function by causing apoptosis, of which DAP-related apoptosis-inducing kinase-2 (DRAK2) is a critical regulator. Here, we identified a marked up-regulation of DRAK2 in pancreatic tissue across humans, macaques, and mice with type 2 diabetes (T2D). Further studies in mice showed that conditional knockout (cKO) of DRAK2 in pancreatic ß cells protected ß cell function against high-fat diet feeding along with sustained autophagy and mitochondrial function. Phosphoproteome analysis in isolated mouse primary islets revealed that DRAK2 directly phosphorylated unc-51-like autophagy activating kinase 1 (ULK1) at Ser56, which was subsequently found to induce ULK1 ubiquitylation and suppress autophagy. ULK1-S56A mutation or pharmacological inhibition of DRAK2 preserved mitochondrial function and insulin secretion against lipotoxicity in mouse primary islets, Min6 cells, or INS-1E cells. In conclusion, these findings together indicate an indispensable role of the DRAK2-ULK1 axis in pancreatic ß cells upon metabolic challenge, which offers a potential target to protect ß cell function in T2D.

Myofiber Baf60c controls muscle regeneration by modulating Dkk3-mediated paracrine signaling.

Obesity and type 2 diabetes (T2D) are the leading causes of the progressive decline in muscle regeneration and fitness in adults. The muscle microenvironment is known to play a key role in controlling muscle stem cell regenerative capacity, yet the underlying mechanism remains elusive. Here, we found that Baf60c expression in skeletal muscle is significantly downregulated in obese and T2D mice and humans. Myofiber-specific ablation of Baf60c in mice impairs muscle regeneration and contraction, accompanied by a robust upregulation of Dkk3, a muscle-enriched secreted protein. Dkk3 inhibits muscle stem cell differentiation and attenuates muscle regeneration in vivo. Conversely, Dkk3 blockade by myofiber-specific Baf60c transgene promotes muscle regeneration and contraction. Baf60c interacts with Six4 to synergistically suppress myocyte Dkk3 expression. While muscle expression and circulation levels of Dkk3 are markedly elevated in obese mice and humans, Dkk3 knockdown improves muscle regeneration in obese mice. This work defines Baf60c in myofiber as a critical regulator of muscle regeneration through Dkk3-mediated paracrine signaling.

An integrative profiling of metabolome and transcriptome in the plasma and skeletal muscle following an exercise intervention in diet-induced obese mice.

Exercise intervention at the early stage of type 2 diabetes mellitus (T2DM) can aid in the maintenance of blood glucose homeostasis and prevent the development of macrovascular and microvascular complications. However, the exercise-regulated pathways that prevent the development of T2DM remain largely unclear. In this study, two forms of exercise intervention, treadmill training and voluntary wheel running, were conducted for high-fat diet (HFD)-induced obese mice. We observed that both forms of exercise intervention alleviated HFD-induced insulin resistance and glucose intolerance. Skeletal muscle is recognized as the primary site for postprandial glucose uptake and for responsive alteration beyond exercise training. Metabolomic profiling of the plasma and skeletal muscle in Chow, HFD, and HFD-exercise groups revealed robust alterations in metabolic pathways by exercise intervention in both cases. Overlapping analysis identified nine metabolites, including beta-alanine, leucine, valine, and tryptophan, which were reversed by exercise treatment in both the plasma and skeletal muscle. Transcriptomic analysis of gene expression profiles in the skeletal muscle revealed several key pathways involved in the beneficial effects of exercise on metabolic homeostasis. In addition, integrative transcriptomic and metabolomic analyses uncovered strong correlations between the concentrations of bioactive metabolites and the expression levels of genes involved in energy metabolism, insulin sensitivity, and immune response in the skeletal muscle. This work established two models of exercise intervention in obese mice and provided mechanistic insights into the beneficial effects of exercise intervention on systemic energy homeostasis.

Dietary intervention preserves ß cell function in mice through CTCF-mediated transcriptional reprogramming.

Pancreatic ß cell plasticity is the primary determinant of disease progression and remission of type 2 diabetes (T2D). However, the dynamic nature of ß cell adaptation remains elusive. Here, we establish a mouse model exhibiting the compensation-to-decompensation adaptation of ß cell function in response to increasing duration of high-fat diet (HFD) feeding. Comprehensive islet functional and transcriptome analyses reveal a dynamic orchestration of transcriptional networks featuring temporal alteration of chromatin remodeling. Interestingly, prediabetic dietary intervention completely rescues ß cell dysfunction, accompanied by a remarkable reversal of HFD-induced reprogramming of islet chromatin accessibility and transcriptome. Mechanistically, ATAC-based motif analysis identifies CTCF as the top candidate driving dietary intervention-induced preservation of ß cell function. CTCF expression is markedly decreased in ß cells from obese and diabetic mice and humans. Both dietary intervention and AAV-mediated restoration of CTCF expression ameliorate ß cell dysfunction ex vivo and in vivo, through transducing the lipid toxicity and inflammatory signals to transcriptional reprogramming of genes critical for ß cell glucose metabolism and stress response.

Cadmium exposure impairs pancreatic ß-cell function and exaggerates diabetes by disrupting lipid metabolism.

Cadmium is known as an environmental pollutant that contributes to pancreatic damage and the pathogenesis of diabetes. However, less attention has been devoted to elucidating the mechanisms underlying Cd-induced pancreatic ß-cell dysfunction and the role of Cd toxicity in the development of diabetes. In this study, we demonstrated that exposure to Cd caused remarkable pancreatic ß-cell dysfunction and death, both in vitro and in vivo. Lipidomic analysis of Cd-exposed pancreatic ß-cells using high-resolution mass spectrometry revealed that Cd exposure altered the profile and abundance of lipids. Cd exposure induced intracellular lipid accumulation, promoted lipid biogenesis, elevated pro-inflammatory lipid contents and inhibited lipid degradation. Furthermore, Cd exposure upregulated the expression levels of TNF-α, IL-1ß and IL-6 in pancreatic ß-cells and elevated the TNF-α, IL1-ß and IL-6 levels in the serum and pancreas. Taken together, the results of our study demonstrated that environmental relevant Cd exposure causes pro-inflammatory lipids elevation and insulin secretion dysfunction in ß-cells and hence exaggerates diabetes development. Combined exposure to environmental hazardous chemicals might markedly increase the probability of developing diabetes in humans. This study provides new metabolic and pharmacological targets for antagonizing Cd toxicity.

Human induced pluripotent stem cell-derived cardiomyocytes reveal abnormal TGFß signaling in type 2 diabetes mellitus.

Diabetes mellitus is a serious metabolic condition associated with a multitude of cardiovascular complications. Moreover, the prevalence of diabetes in heart failure populations is higher than that in control populations. However, the role of cardiomyocyte alterations in type 2 diabetes mellitus (T2DM) has not been well characterized and the underlying mechanisms remain elusive. In this study, two patients who were diagnosed as T2DM were recruited and patient-specific induced pluripotent stem cells (iPSCs) were generated from urine epithelial cells using nonintegrated Sendai virus. The iPSC lines derived from five healthy subjects were used as controls. All iPSCs were differentiated into cardiomyocytes (iPSC-CMs) using the monolayer-based differentiation protocol. T2DM iPSC-CMs exhibited various disease phenotypes, including cellular hypertrophy and lipid accumulation. Moreover, T2DM iPSC-CMs exhibited higher susceptibility to high-glucose/high-lipid challenge than control iPSC-CMs, manifesting an increase in apoptosis. RNA-Sequencing analysis revealed a differential transcriptome profile and abnormal activation of TGFß signaling pathway in T2DM iPSC-CMs. We went on to show that inhibition of TGFß significantly rescued the hypertrophic phenotype in T2DM iPSC-CMs. In conclusion, we demonstrate that the iPSC-CM model is able to recapitulate cellular phenotype of T2DM. Our results indicate that iPSC-CMs can therefore serve as a suitable model for investigating molecular mechanisms underlying diabetic cardiomyopathies and for screening therapeutic drugs.

Polysaccharides derived from natural sources regulate triglyceride and cholesterol metabolism: a review of the mechanisms.

With great changes in people's lifestyles, the incidence of hyperlipidaemia has dramatically increased in recent years. Numerous studies have demonstrated that natural polysaccharides have lipid lowering effects. In this review, the causes and mechanisms of hyperlipidaemia are discussed in order to better understand how polysaccharides alleviate hyperlipidaemia. Natural polysaccharides reduce triglyceride levels through ATGL-(PPAR-α)/(PGC-1α), (SREBP-1c)-ACC/FAS and ACC-CPT1 signal pathways, and exert cholesterol lowering effects via (SREBP-2)-HMGCR and bile acid biosynthesis pathways. Activation of adenosine monophosphate-activated protein kinase (AMPK) is the key factor that mediated the simultaneous regulation of both glucose and lipid metabolism by polysaccharides. The new discovery of polysaccharides increasing the production of endogenous H2S, an important physiological gaseous signaling molecule, is also discussed. Collectively, the current available data suggest that natural polysaccharides could be potentially developed as new and safe lipid-lowering drugs; yet further mechanistic and clinical studies are required during this long-term process.