FIGURE 6.

Proposed model depicting the regulation of small EV secretion by p62-mediated autophagy and cofilin-mediated actin dynamics through the SSH1 pathway. Note that blue lines/arrows favor lysosomal degradation, whereas red lines/arrows favor secretory clearance. (A) Accumulation of misfolded proteins or dysfunctional mitochondria activates autophagy through ULK1 and TBK1, which phosphorylate p62 at Ser403, resulting in p62 binding to ubiquitinated cargo and activation of LC3 to drive autophagosome maturation. This promotes autophagy flux and fusion of autophagosomes and amphisomes with lysosomes, resulting in the degradation of ubiquitinated cargo together with intraluminal vesicles from amphisomes, thereby reducing small EV secretion. (B) Oxidative stress (ROS) or calcium elevation induced by Aβ oligomers or otherwise activates SSH1, which dephosphorylates p62 at pSer403 and inhibits p62 autophagy flux. Dephosphorylated p62 is less able to bind ubiquitinated cargo and activate LC3, which slows autophagy flux and fusion of autophagosomes and amphisomes with lysosomes. This process diverts amphisomes toward the secretory fusion pathway and increases small EV secretion. Like SSH1, inhibition of p62 autophagy flux by misfolded tau (Fang et al., 2021) also likely contributes to increased small EV secretion. (C) Actin filaments serve to recruit vesicles and create a diffusion barrier for vesicles to gain access to the plasma membrane. SSH1 activation by ROS or calcium also activates cofilin, which severs and depolymerizes the F-actin network near the plasma membrane. This process allows large secretory amphisomes to access membrane docking sites, facilitating small EV secretion. This illustration was generated at Biorender.com.