Extracellular vesicle secretion is tissue-dependent ex vivo and skeletal muscle myofiber extracellular vesicles reach the circulation in vivo.

Extracellular vesicles (EVs) are biomarkers and modifiers of human disease. EVs secreted by insulin-responsive tissues like skeletal muscle (SkM) and white adipose tissue (WAT) contribute to metabolic health and disease but the relative abundance of EVs from these tissues has not been directly examined. Human Protein Atlas data and directly measuring EV secretion in mouse SkM and WAT using an ex vivo tissue explant model confirmed that SkM tissue secretes more EVs than WAT. Differences in EV secretion between SkM and WAT were not due to SkM contraction but may be explained by differences in tissue metabolic capacity. We next examined how many EVs secreted from SkM tissue ex vivo and in vivo are myofiber-derived. To do this, a SkM myofiber-specific dual fluorescent reporter mouse was created. Spectral flow cytometry revealed that SkM myofibers are a major source of SkM tissue-derived EVs ex vivo and EV immunocapture indicates that ∼5% of circulating tetraspanin-positive EVs are derived from SkM myofibers in vivo. Our findings demonstrate that 1) SkM secretes more EVs than WAT, 2) many SkM tissue EVs are derived from SkM myofibers, and 3) SkM myofiber-derived EVs reach the circulation in vivo. These findings advance our understanding of EV secretion between metabolically active tissues and provide direct evidence that SkM myofibers secrete EVs that can reach the circulation in vivo.

Trehalose supplementation reduces hepatic endoplasmic reticulum stress and inflammatory signaling in old mice.

The accumulation of damaged proteins can perturb cellular homeostasis and provoke aging and cellular damage. Quality control systems, such as the unfolded protein response (UPR), inflammatory signaling and protein degradation, mitigate the residence time of damaged proteins. In the present study, we have examined the UPR and inflammatory signaling in the liver of young (~6 months) and old (~28 months) mice (n=8/group), and the ability of trehalose, a compound linked to increased protein stability and autophagy, to counteract age-induced effects on these systems. When used, trehalose was provided for 4 weeks in the drinking water immediately prior to sacrifice (n=7/group). Livers from old mice were characterized by activation of the UPR, increased inflammatory signaling and indices of liver injury. Trehalose treatment reduced the activation of the UPR and inflammatory signaling, and reduced liver injury. Reductions in proteins involved in autophagy and proteasome activity observed in old mice were restored following trehalose treatment. The autophagy marker, LC3B-II, was increased in old mice treated with trehalose. Metabolomics analyses demonstrated that reductions in hexosamine biosynthetic pathway metabolites and nicotinamide in old mice were restored following trehalose treatment. Trehalose appears to be an effective intervention to reduce age-associated liver injury and mitigate the need for activation of quality control systems that respond to disruption of proteostasis.

Endoplasmic reticulum stress in obesity and obesity-related disorders: An expanded view.

The endoplasmic reticulum (ER) is most notable for its central roles in calcium ion storage, lipid biosynthesis, and protein sorting and processing. By virtue of its extensive membrane contact sites that connect the ER to most other organelles and to the plasma membrane, the ER can also regulate diverse cellular processes including inflammatory and insulin signaling, nutrient metabolism, and cell proliferation and death via a signaling pathway called the unfolded protein response (UPR). Chronic UPR activation has been observed in liver and/or adipose tissue of dietary and genetic murine models of obesity, and in human obesity and non-alcoholic fatty liver disease (NAFLD). Activation of the UPR in obesity and obesity-related disorders likely has two origins. One linked to classic ER stress involving the ER lumen and one linked to alterations to the ER membrane environment. This review discusses both of these origins and also considers the role of post-translational protein modifications, such as acetylation and palmitoylation, and ER-mitochondrial interactions to obesity-mediated impairments in the ER and activation of the UPR.

Fuzhuan tea consumption imparts hepatoprotective effects and alters intestinal microbiota in high saturated fat diet-fed rats.

SCOPE: Nonalcoholic fatty liver disease is an obesity-related disorder characterized by lipid infiltration of the liver. Management is limited to lifestyle modifications, highlighting the need for alternative therapeutic options. The objective of this study was to examine if fermented Fuzhuan tea prevents metabolic impairments associated with development of hepatic steatosis. METHODS AND RESULTS: Rats consumed control (CON) or high saturated fat (SAT) diets with or without Fuzhuan tea for 8 weeks. Outcomes included enzymatic and gene expression measures of metabolic dysregulation in liver and adipose tissue. Pyrosequencing was used to assess intestinal microbiota adaptations. Fuzhuan tea prevented diet-induced inflammation in the liver. Liver triglycerides of ∼18 mg/g were observed in SAT-fed animals, but remained similar to CON diet levels (∼12 mg/g) when supplemented with Fuzhuan tea. In adipose tissue, tea treatment prevented SAT-induced inflammation and reduced plasma leptin approximately twofold. Fuzhuan tea also altered intestinal function and was associated with a threefold increase in two Lactobacillus spp. CONCLUSIONS: These data suggest that Fuzhuan tea protects against liver and adipose tissue stress induced by a high SAT diet and positively influences intestinal function. Further investigation of the molecular targets of Fuzhuan tea is warranted.