HERC1 E3 Ubiquitin Ligase Is Necessary for Autophagy Processes and for the Maintenance and Homeostasis of Vesicles in Motor Nerve Terminals, but Not for Proteasomal Activity.

The ubiquitin proteasome system (UPS) is implicated in protein homeostasis. One of the proteins involved in this system is HERC1 E3 ubiquitin ligase, which was associated with several processes including the normal development and neurotransmission at the neuromuscular junction (NMJ), autophagy in projection neurons, myelination of the peripheral nervous system, among others. The tambaleante (tbl) mouse model carries the spontaneous mutation Gly483Glu substitution in the HERC1 E3 protein. Using this model, we analyzed the implication of HERC1 E3 ubiquitin ligase in the activity of UPS, autophagy, and synaptic homeostasis in brain and muscle tissues. Regarding UPS, no differences were found in its activity nor in the specific gene expression in both brain and muscle tissues from tbl compared with the control littermates. Furthermore, the use of the specific UPS inhibitor (MG-132), did not alter the evoked neurotransmitter release in the levator auris longus (LAL) muscle. Interestingly, the expression of the autophagy-related gene p62 was significantly increased in the muscle of tbl compared to the control littermates. Indeed, impaired evoked neurotransmitter release was observed with the autophagy inhibitor Wortmannin. Finally, altered levels of Clathrin and Synaptophysin were detected in muscle tissues. Altogether, our findings show that HERC1 E3 ubiquitin ligase mutation found in tbl mice alters autophagy and vesicular recycling without affecting proteasomal function.