The role of muscle-derived extracellular vesicles in adipocyte metabolism

细胞外囊泡（EVs）是几乎所有细胞类型都可能释放的膜结合囊泡

Extracellular vesicles (EVs) are membrane-bound vesicles released by virtually all cell types, potentially mediating intercellular communication and thereby play essential roles in many physiological and pathological processes. This capacity relies on EVs’ ability to serve as delivery vehicles for a wide range of endogenous cargo molecules, such as RNAs, proteins, and lipids. EVs have also been found to display tissue-specific recognition mediated by surface molecules (such as integrins and glycans), making them promising for drug delivery applications. However, a better understanding of EV composition and cargo is necessary to enable the use of EVs as delivery vehicles. Preliminary data demonstrate that after a hypertrophic stimulus, muscle-derived EVs (mEVs) are specifically delivered to adipose tissue. Interestingly, the delivery of mEVs to adipose tissue induced lipolysis and fat loss in high-fat-diet-fed mice. This exciting preliminary data could represent the first steps into the development of therapy for obesity. Additionally, our preliminary data indicate high levels of diacylglycerol (DAG) within mEVs, which could, upon delivery, mediate protein kinase C (PKC) activation and induce changes in adipocyte metabolism. The proposed project expands upon our preliminary data and is based on the overarching hypothesis that a hypertrophic stimulus would change the lipid makeup of mEVs, leading to adipocyte metabolism changes. More specifically, it is hypothesized that a hypertrophic stimulus will increase DAG concentration within mEVs that will induce adipocyte lipolysis through PKC activation, resulting in wholebody metabolic benefits. In order to confirm our preliminary data, we will use muscle cells (C2C12 cells) to isolate mEVs with or without a hypertrophic stimulus (treatment with insulin-like growth factor 1) and perform a lipid profile of these vesicles. After establishing the lipid profile, mEVs will be transferred to adipocyte cells (3T3L1 cells) or will be tail vein injected into obese mice. The purpose of this project is to test this working hypothesis by pursuing three specific aims. Specific Aim 1 is to determine whether the lipid composition of skeletal muscle extracellular vesicles is altered in response to a hypertrophic stimulus; Specific Aim 2 is to determine whether mEVs stimulate adipocyte lipolysis through PKC activation; and Specific Aim 3 is to determine whether extracellular vesicles in response to a hypertrophic stimulus can induce fat loss through enhanced lipolysis in obese mice. Preliminary data suggest that mEVs provide beneficial effects on adipocyte metabolism and induce fat loss in obese mice. If the results of the proposed experiments provide evidence to support the hypothesis, a future R01 application will seek to rigorously test which class/classes of lipids can specifically mediate changes in adipocyte metabolism.