Study On The Effects And Mechanisms Of STAT3 Pathway And Atractylenolide ? In Regulating Exosome Biogenesis And Cancer Cachexia

Up to now,cancer has become one of the most serious global health threats,and the morbidity is rising.More than 30% of the patients with cancer die due to cachexia,which is associated with adverse prognosis and shorter survival times.In recent decades,proinflammatory cytokines,such as IL-6,have received attention as potential key molecules in cancer cachexia.In recent years,increasing studies indicated that exosomes secreted by tumor cells can travel through the body fluids to deliver their contents to the distant target organs without degradation,thus inducing cancer cachexia.Clarifying the regulation of exosome biogenesis and finding possible targets for cancer cachexia therapy are important and necessary.The regulation of STAT3 on production of inflammatory cytokines such as IL-6,which is involved in cancer cachexia development,has been well known.Several previous studies suggested that STAT3 might play roles in the regulation of exosome biogenesis.However,the mechanisms of STAT3 in regulation of exosome biogenesis have not been fully clarified and the contribution of STAT3-controlled exosome release to cancer cachexia needs to be confirmed.In the present study,systemic analysis of the roles of STAT3 in controlling exosome biogenesis of murine C26 colon tumor cells and its contribution to the development of cancer cachexia is conducted.STAT3 knockout significantly inhibited the exosome biogenesis and also the potency of C26 conditioned medium in inducing muscle atrophy and lipolysis in vitro.STAT3 knockout inhibited the phosphorylation of PKM2 and glycolysis.STAT3 knockout and STAT3 inhibitors inhibited the activation of PKM2/SNAP23 pathway,which was involved in regulation of exosome biogenesis,hence the exosome secretion of C26 cells was inhibited.In contrast,STAT3 overexpression showed opposite effects.Mice inoculated with STAT3 knockout or overexpression C26 cells exhibited ameliorated or aggravated cancer cachexia symptoms,with a positive correlation with the serum exosome and IL-6levels.The activation of STAT3/PKM2/SNAP23 pathway was inhibited in C26 tumor tissues with STAT3 knockout,STAT3 overexpression showed opposite effects.The capacity of exosome biogenesis of different human cancer cells also exhibited a positive correlation with the activation of STAT3/PKM2/SNAP23 pathway.The research presented here confirms that STAT3 plays a critical role in regulating biogenesis of tumor-derived exosomes which could contribute to cancer cachexia development.Atractylenolide I(AI)is a natural sesquiterpene lactone isolated from Atractylodes macrocephala Koidz,known as Baizhu in traditional Chinese medicine.AI has been found to ameliorate cancer cachexia in clinic cancer patients and in tumor-bearing mice.Here,we checked the influence of AI on biogenesis of IL-6 and exosomes in cancer cachexia mice and then focused on studying the mechanisms of AI in inhibiting the production of tumor-derived exosomes which contribute to the ameliorating effects of AI on cancer cachexia.Our results show that AI ameliorated cancer cachexia symptoms,improved grip strength,decreased serum exosome and IL-6 levels of C26 tumor-bearing mice.AI directly inhibited exosome biogenesis and IL-6 secretion of cultured C26 cells.The potency of C26-medium in inducing C2C12 myotube atrophy and 3T3-L1 adipocyte lipolysis was significantly attenuated when C26 cells were treated with AI.AI treatment inhibited aerobic glycolysis and the pathway of STAT3/PKM2/SNAP23 in C26 cells.Furthermore,overexpression of STAT3 partly antagonized the effects of AI in suppressing STAT3/PKM2/SNAP23 pathway,exosome secretion,glycolysis and the potency of C26-medium in inducing muscle atrophy and lipolysis,whereas knockout of STAT3 enhanced the inhibitory effect of AI on these values.The inhibition of AI on STAT3/PKM2/SNAP23 pathway was also observed in C26 tumor tissues.In general,AI ameliorates cancer cachexia by decreasing the production of IL-6 and exosomes of tumor cells.The decreasing effects of AI on exosome biogenesis are based on its inhibition on STAT3/PKM2/SNAP23 pathway.Our study provides scientific evidence for inhibiting production of cachexic factors of tumor cells in the treatment of cancer cachexia as well as developing AI as a potential agent for cancer cachexia therapy.