Distinct roles for motor neuron autophagy early and late in the SOD1 ^G93A mouse model of ALS

Abstract

Mutations in autophagy genes can cause familial and sporadic amyotrophic lateral sclerosis (ALS). However, the role of autophagy in ALS pathogenesis is poorly understood, in part due to the lack of cell type-specific manipulations of this pathway in animal models. Using a mouse model of ALS expressing mutant superoxide dismutase 1 (SOD1), we show that motor neurons form large autophagosomes containing ubiquitinated aggregates early in disease progression. To investigate whether this response is protective or detrimental, we generated mice in which the critical autophagy gene was specifically disrupted in motor neurons (Atg7 cKO). Atg7 cKO mice were viable but exhibited structural and functional defects at a subset of vulnerable neuromuscular junctions. By crossing Atg7 cKO mice to the SOD1 mouse model, we found that autophagy inhibition accelerated early neuromuscular denervation of the tibialis anterior muscle and the onset of hindlimb tremor. Surprisingly, however, lifespan was extended in Atg7 cKO; SOD1 double-mutant mice. Autophagy inhibition did not prevent motor neuron cell death, but it reduced glial inflammation and blocked activation of the stress-related transcription factor c-Jun in spinal interneurons. We conclude that motor neuron autophagy is required to maintain neuromuscular innervation early in disease but eventually acts in a non-cell-autonomous manner to promote disease progression.

A Combination of Intrathecal and Intramuscular Application of Human Mesenchymal Stem Cells Partly Reduces the Activation of Necroptosis in the Spinal Cord of SOD1G93A Rats

“…Autophagy is an important cellular homeostatic pathway responsible for the clearance of misfolded or aggregated proteins. The inhibition of autophagy in MN of the SOD1 mice leads to the acceleration of the disease onset , and in contrast, autophagy inhibition in symptomatic animals resulted in the suppression of glial activation and prolonged survival . Its role in ALS might therefore be positive at the earlier stage, however, at later stages the effect could be negative.…”

Spatiotemporal Dynamics of Molecular Pathology in Amyotrophic Lateral Sclerosis

“…Interactions between motor neurons and glia contribute to motor neuron loss, but the spatiotemporal ordering of molecular events that drive these processes in intact spinal tissue remains poorly understood. Here, we use spatial transcriptomics to obtain gene expression measurements of mouse spinal cords over the 5 course of disease, as well as of postmortem tissue from ALS patients, to characterize the underlying molecular mechanisms in ALS. We identify novel pathway dynamics, regional differences between microglia and astrocyte populations at early time-points, and discern perturbations in several transcriptional pathways shared between murine models of ALS and human postmortem spinal cords.…”

“…However, the events that initiate disease pathology, and the mechanisms through which pathology spreads remain poorly understood (1)(2)(3)(4). Mounting evidence indicates that dysfunction in signaling between motor neurons and glia is a key component of the disease (1,5,6). Inherent limitations of widely available gene expression profiling technologies, such as low throughput or lack of spatial 20 resolution have thus far frustrated efforts to understand how such dysfunction participates in the onset and spread of ALS pathology in the spinal cord.…”

“…Given the stereotyped cellular organization of the spinal cord and the known importance of intercellular communication in ALS 3 progression, we reasoned that a spatially resolved view of disease driven gene expression changes would be needed to order these events, reveal the relevant sub-populations of cells involved in each stage in disease progression, and characterize the underlying molecular mechanisms that trigger and maintain the disease phenotype. Spatial Transcriptomics (ST) generates quantitative transcriptome-wide RNA sequencing 5 (RNAseq) data via capture of polyadenylated RNA on arrays of spatially barcoded DNA capture probes (7)(8)(9). We applied ST to spatially profile gene expression in lumbar spinal cord tissue sections (L3-L5) from SOD1-G93A (ALS) and SOD1-WT (control) mice at pre-symptomatic, onset, symptomatic, and end-stage time points (Table S1).…”

Postmortem Cortex Samples Identify Distinct Molecular Subtypes of ALS: Retrotransposon Activation, Oxidative Stress, and Activated Glia

“…The importance of oxidative stress in neurodegenerative disease began with the initial identification of superoxide dismutase 1 (SOD1) as the first ALS-associated mutation (Rosen et al, 1993). Subsequent studies have identified a diverse array of functional pathways altered in SOD1 mutant mouse models, including SOD-1 mediated autophagy (Rudnick et al, 2017), proteotoxic stress (Bruijn et al, 1998), and neuroinflammation (Chiu et al, 2013), reflecting both the pleiotropic roles played by SOD1 protein as well as different manifestations depending on the cellular context in which SOD1 is dysfunctional. Since that initial discovery, several genes with roles in oxidative stress, proteotoxic stress, and autophagy have been linked to ALS (Taylor et al, 2016).…”