Autophagy regulates exosome secretion in rat nucleus pulposus cells via the RhoC/ROCK2 pathway

Our present study investigated whether exosome secretion of nucleus pulposus cells (NPCs) is regulated by autophagy. Different autophagic states of NPCs were induced by rapamycin (Rap), bafilomycin A1 (Baf) and other agents, and it was found that exosomes were secreted in an autophagy-dependent manner. Activation or inhibition of autophagy increased or decreased, respectively, the amount of exosomes that were released into the extracellular space. In addition, in order to confirm that Rap-promoted release of exosomes was mediated by autophagy rather than other pathways, we used autophagy associated gene 5 (ATG5) small-interfering RNA (siRNA) to silence the expression of ATG5 gene, which is indispensable for autophagy. The results showed that siRNA against ATG5 (siATG5) induced an accumulation of intraluminal vesicles (ILVs) in NPCs and a concomitant decrease in the amount of exosomes isolated from supernatant. Ras homolog gene (Rho) and Rho-associated coiled-coil forming protein kinase (ROCK) family molecules are capable of cytoskeletal remodeling and affecting vesicle transport. Therefore, we carried out targeted interventions and evaluated the effects of the RhoC/ROCK2 pathway on the secretion of exosomes within autophagic environment. Knockdown of RhoC and ROCK2 with corresponding siRNA significantly inhibited the secretion of exosomes originating from ILVs in NPCs, even when NPCs were subsequently treated with Rap. Taken together, our findings suggest that autophagy positively regulates expression levels of RhoC and ROCK2, and that the RhoC/ROCK2 pathway exerts a key function on NPCs-derived exosome secretion.