Reduction of matrix metalloproteinase 9 (MMP-9) protects motor neurons from TDP-43-triggered death in rNLS8 mice

Abstract

Therapeutic strategies are needed for the treatment of amyotrophic lateral sclerosis (ALS). One potential target is matrix metalloproteinase-9 (MMP-9), which is expressed only by fast motor neurons (MNs) that are selectively vulnerable to various ALS-relevant triggers. Previous studies have shown that reduction of MMP-9 function delayed motor dysfunction in a mouse model of familial ALS. However, given that the majority of ALS cases are sporadic, we propose preclinical testing in a mouse model which may be more clinically translatable: rNLS8 mice. In rNLS8 mice, neurodegeneration is triggered by the major pathological hallmark of ALS, TDP-43 mislocalization and aggregation. MMP-9 was targeted in 3 different ways in rNLS8 mice: by AAV9-mediated knockdown, using antisense oligonucleotide (ASO) technology, and by genetic modification. All 3 strategies preserved the motor unit during disease, as measured by MN counts, tibialis anterior (TA) muscle innervation, and physiological recordings from muscle. However, the strategies that reduced MMP-9 beyond the motor unit lead to premature deaths in a subset of rNLS8 mice. Therefore, selective targeting of MMP-9 in MNs could be beneficial in ALS, but side effects outside of the motor circuit may limit the most commonly used clinical targeting strategies.

Motor Neuron Susceptibility in ALS/FTD

“…Delivery of MMP-9 into FF-MNs, but not in oculomotor neurons, accelerates denervation in SOD1 G93A mice (Kaplan et al, 2014). Similarly, another study demonstrated that reduction of MMP-9 expression attenuated neuromuscular defects in rNLS8 mice expressing cytoplasmic hTDP43 ΔNLS in neurons (Spiller et al, 2019). Edaravone, a free radical scavenger which inhibits MMP-9 expression, was recently approved for the treatment of ALS in Japan, South Korea, United States and Canada (Yoshino and Kimura, 2006; Ito et al, 2008; Yagi et al, 2009).…”

rAAV2-Retro Enables Extensive and High-Efficient Transduction of Lower Motor Neurons following Intramuscular Injection

“…Although the neuronal transduction of rAAV2-retro was more extensive than that of the other tested rAAVs, its efficiency needs to be further determined. As a retrograde transduction efficiency indicator, cholera toxin subunit B (CTB), is a widely used as a retrograde tracer to efficiently label lower motor neurons that correspond to specific muscles following intramuscular injection 11 , 24 , 25 . To comprehensively profile the transduction efficiency of rAAV2-retro in the spinal cord, mice were injected with a mixture of rAAV2-retro-GFP and the retrograde tracer CTB-647 at a single site of the extensor carpi radialis in the right forelimb.…”

Key Molecules and Pathways Underlying Sporadic Amyotrophic Lateral Sclerosis: Integrated Analysis on Gene Expression Profiles of Motor Neurons

“…MMPs are crucial in the development of CNS and many physiological processes of the adult brain by degrading ECM, but the overactivation of MMPs associated with inflammatory response was discovered in multiple neurologic disorders ( Singh et al, 2015 ; De Stefano and Herrero, 2017 ). As the most studied member, MMP9 was involved in the muscle degeneration process by enhancing ER stress, and its reduction rescued TDP-43 triggered death of motor neurons ( Kaplan et al, 2014 ; Spiller et al, 2019 ). The upregulation of MMP9 resulted in the destruction of neurovascular unit in the presymptomatic period in ALS-G93A mice, even prior to the degeneration of motor neurons ( Miyazaki et al, 2011 ).…”