ATG5 overexpression is neuroprotective and attenuates cytoskeletal and vesicle-trafficking alterations in axotomized motoneurons

Abstract

Injured neurons should engage endogenous mechanisms of self-protection to limit neurodegeneration. Enhancing efficacy of these mechanisms or correcting dysfunctional pathways may be a successful strategy for inducing neuroprotection. Spinal motoneurons retrogradely degenerate after proximal axotomy due to mechanical detachment (avulsion) of the nerve roots, and this limits recovery of nervous system function in patients after this type of trauma. In a previously reported proteomic analysis, we demonstrated that autophagy is a key endogenous mechanism that may allow motoneuron survival and regeneration after distal axotomy and suture of the nerve. Herein, we show that autophagy flux is dysfunctional or blocked in degenerated motoneurons after root avulsion. We also found that there were abnormalities in anterograde/retrograde motor proteins, key secretory pathway factors, and lysosome function. Further, LAMP1 protein was missorted and underglycosylated as well as the proton pump v-ATPase. In vitro modeling revealed how sequential disruptions in these systems likely lead to neurodegeneration. In vivo, we observed that cytoskeletal alterations, induced by a single injection of nocodazole, were sufficient to promote neurodegeneration of avulsed motoneurons. Besides, only pre-treatment with rapamycin, but not post-treatment, neuroprotected after nerve root avulsion. In agreement, overexpressing ATG5 in injured motoneurons led to neuroprotection and attenuation of cytoskeletal and trafficking-related abnormalities. These discoveries serve as proof of concept for autophagy-target therapy to halting the progression of neurodegenerative processes.

Improved Motor Nerve Regeneration by SIRT1/Hif1a-Mediated Autophagy

“…Our study is in agreement with He and collaborators (2016), who reported induced autophagy promotes central nervous system axonal regeneration after injury by increasing microtubule (MT) stability [16]. In addition, we previously observed that ATG5 overexpression in MNs induced autophagy but also corrected cytoskeletal alterations [25]. The fact that plantar CMAP amplitudes are significantly greater within 60 days when overexpressing SIRT1 than when overexpressing ATG5, suggests that other pathways triggered by SIRT1 might be synergistically contributing to a better recovery.…”

“…In order to ascertain whether autophagy induction was important in motor nerve regeneration, we aimed to investigate the potential to shift MNs to a growth-competent state by ATG5 overexpression, previously shown to induce autophagy [25]. For this purpose, a nerve conduction test was performed to rats injured with sciatic nerve transection and suture that received previously intrathecal injections of AAV vectors (AAVrh10) to overexpress either ATG5 (AAVrh10-ATG5) or the non-related protein GFP (green fluorescence protein) (AAVrh10-GFP), specifically within the spinal MNs [26].…”

NeuroHeal Treatment Alleviates Neuropathic Pain and Enhances Sensory Axon Regeneration

“…Autophagy is a cell-protective mechanism whenever it is appropriately induced and resolved. This concept is elegantly reflected in neurodegenerative diseases or motoneuron death after PNI [26,42,43]. Besides, some articles reported that autophagy flux is blocked within the dorsal horn neurons after chronic constriction injury (CCI) or SNI, which may trigger neuropathic pain [24].…”

Endogenous Mechanisms of Neuroprotection: To Boost or Not to Be

“…Axotomized MNs 2 [5] ATG7 PD ATG7 induces autophagy by facilitating the conjugation of the complexes ATG12-ATG5 and ATG5 -ATG16L1-ATG12, which facilitates autophagosome formation. ATG7 overexpression protects by increasing the autophagy flux.…”