Lung cancer-derived extracellular vesicles induced myotube atrophy and adipocyte lipolysis via the extracellular IL-6-mediated STAT3 pathway

Abstract

Cancer-associated cachexia (CAC) constitutes a metabolic dysfunction characterized by systemic inflammation and body weight loss. Muscle atrophy and adipose tissue lipolysis might explain weight loss in CAC. Specific functions of numerous hormones and cytokines derived from tumours can provoke cachexia. Extracellular vesicles (EVs) can be involved in intercellular communication. However, whether EVs participate in this process has not been investigated thoroughly. Using Lewis lung carcinoma (LLC) cell cultures, we tested whether LLC-derived EVs induced C2C12 myotube atrophy and 3T3-L1 adipocyte lipolysis. EVs derived from LLC cells and serum from patients with lung cancer, non-lung cancer controls, tumour-bearing mice, and non-tumour-bearing control mice were isolated and characterized biochemically and biophysically. LLC cell-derived EVs induced dose-dependent effects of atrophy in C2C12 myotubes and lipolysis in 3T3-L1 adipocytes. Mechanistically, EVs directly fused with target C2C12 myotubes and 3T3-L1 adipocytes, and transferred interleukin-6 (IL-6) activates the STAT3 signalling pathway in C2C12 myotubes and 3T3-L1 adipocytes. Neutralization of extracellular IL-6 prevented the atrophy and lipolysis effects of EVs. Inhibiting the STAT3 signalling pathway also prevented the atrophy and lipolysis effects of EVs. PKH67-labelled (PKH 67 is a lipid dye that can be used to label extracellular vesicles) LLC-EVs were readily internalized into myotubes and adipocytes. Our data showed that LLC cell-derived EVs induced myotube atrophy and adipocyte lipolysis via the extracellular IL-6-mediated STAT3 pathway in target cells. These findings represent a potentially novel basis for further research in this field towards identifying targets and developing strategies for maintaining weight in CAC.

Keywords: Adipocyte lipolysis; Cachexia; Extracellular vesicles; IL-6; Myotube atrophy; STAT3.