Muscarinic Toxin 7 Signals Via Ca2+/Calmodulin-Dependent Protein Kinase Kinase β to Augment Mitochondrial Function and Prevent Neurodegeneration

Abstract

Mitochondrial dysfunction is implicated in a variety of neurodegenerative diseases of the nervous system. Peroxisome proliferator–activated receptor-γ coactivator-1α (PGC-1α) is a regulator of mitochondrial function in multiple cell types. In sensory neurons, AMP-activated protein kinase (AMPK) augments PGC-1α activity and this pathway is depressed in diabetes leading to mitochondrial dysfunction and neurodegeneration. Antimuscarinic drugs targeting the muscarinic acetylcholine type 1 receptor (M1R) prevent/reverse neurodegeneration by inducing nerve regeneration in rodent models of diabetes and chemotherapy-induced peripheral neuropathy (CIPN). Ca2+/calmodulin-dependent protein kinase kinase β (CaMKKβ) is an upstream regulator of AMPK activity. We hypothesized that antimuscarinic drugs modulate CaMKKβ to enhance activity of AMPK, and PGC-1α, increase mitochondrial function and thus protect from neurodegeneration. We used the specific M1R antagonist muscarinic toxin 7 (MT7) to manipulate muscarinic signaling in the dorsal root ganglia (DRG) neurons of normal rats or rats with streptozotocin-induced diabetes. DRG neurons treated with MT7 (100 nM) or a selective muscarinic antagonist, pirenzepine (1 μM), for 24 h showed increased neurite outgrowth that was blocked by the CaMKK inhibitor STO-609 (1 μM) or short hairpin RNA to CaMKKβ. MT7 enhanced AMPK phosphorylation which was blocked by STO-609 (1 μM). PGC-1α reporter activity was augmented up to 2-fold (p < 0.05) by MT7 and blocked by STO-609. Mitochondrial maximal respiration and spare respiratory capacity were elevated after 3 h of exposure to MT7 (p < 0.05). Diabetes and CIPN induced a significant (p < 0.05) decrease in corneal nerve density which was corrected by topical delivery of MT7. We reveal a novel M1R-modulated, CaMKKβ-dependent pathway in neurons that represents a therapeutic target to enhance nerve repair in two of the most common forms of peripheral neuropathy.

Prevention of HIV-1 TAT Protein-Induced Peripheral Neuropathy and Mitochondrial Disruption by the Antimuscarinic Pirenzepine

“…Pharmacologically inhibiting M 1 R with the selective antagonist pirenzepine (PZ) activates the AMPK/PGC-1α pathway, enhances mitochondrial function and promotes neurite outgrowth in vitro . PZ treatment also prevented and/or reversed multiple indices of diabetic and chemotherapy-induced peripheral neuropathies in rodent models of these conditions ( 7 , 33 , 34 ). Most pertinent to our present studies, topical administration of the specific M 1 R antagonist MT7 to the eye both prevented and reversed corneal sensory nerve loss caused by topical delivery of the neurotoxic HIV envelope protein gp120 ( 32 ).…”

Diabetic Corneal Neuropathy: Pathogenic Mechanisms and Therapeutic Strategies

“…In addition, using plasmid with PGC-1α promoter, using gene silencing and nanotechnology to knockdown CaMKKβ, the authors revealed that muscarinic toxin 7 augmented elevated mitochondrial function, neurite outgrowth in dorsal root ganglia neurons, and increased corneal nerve density through Ca 2+ /Calmodulin-Dependent Protein kinase ß ( Saleh et al, 2020 ).…”

Structural and Functional Diversity of Animal Toxins Interacting With GPCRs

“…Finally, the group of Fernyhough has shown that, via ERK-CREB signaling activation, MT7 elevates neurite outgrowth and protects from small and large fiber neuropathy in adult sensory neurons (Sabbir and Fernyhough, 2018). This effect is mediated via the enhancement of mitochondrial function and MT7 seems able to prevent neurodegeneration and drive nerve fiber repair in two of the most common forms of peripheral neuropathy, type 1 diabetes and chemotherapy-induced peripheral neuropathy (Saleh et al, 2020).…”