Aberrant association of misfolded SOD1 with Na+/K+ATPase-α3 impairs its activity and contributes to motor neuron vulnerability in ALS

Abstract

Amyotrophic lateral sclerosis (ALS) is an adult onset progressive motor neuron disease with no cure. Transgenic mice overexpressing familial ALS associated human mutant SOD1 are a commonly used model for examining disease mechanisms. Presently, it is well accepted that alterations in motor neuron excitability and spinal circuits are pathological hallmarks of ALS, but the underlying molecular mechanisms remain unresolved. Here, we sought to understand whether the expression of mutant SOD1 protein could contribute to altering processes governing motor neuron excitability. We used the conformation specific antibody B8H10 which recognizes a misfolded state of SOD1 (misfSOD1) to longitudinally identify its interactome during early disease stage in SOD1G93A mice. This strategy identified a direct isozyme-specific association of misfSOD1 with Na(+)/K(+)ATPase-α3 leading to the premature impairment of its ATPase activity. Pharmacological inhibition of Na(+)/K(+)ATPase-α3 altered glutamate receptor 2 expression, modified cholinergic inputs and accelerated disease pathology. After mapping the site of direct association of misfSOD1 with Na(+)/K(+)ATPase-α3 onto a 10 amino acid stretch that is unique to Na(+)/K(+)ATPase-α3 but not found in the closely related Na(+)/K(+)ATPase-α1 isozyme, we generated a misfSOD1 binding deficient, but fully functional Na(+)/K(+)ATPase-α3 pump. Adeno associated virus (AAV)-mediated expression of this chimeric Na(+)/K(+)ATPase-α3 restored Na(+)/K(+)ATPase-α3 activity in the spinal cord, delayed pathological alterations and prolonged survival of SOD1G93A mice. Additionally, altered Na(+)/K(+)ATPase-α3 expression was observed in the spinal cord of individuals with sporadic and familial ALS. A fraction of sporadic ALS cases also presented B8H10 positive misfSOD1 immunoreactivity, suggesting that similar mechanism might contribute to the pathology.

TNF receptor associated factor 6 interacts with ALS-linked misfolded superoxide dismutase 1 and promotes aggregation

“…Gene ontology analyses revealed a convergence on cellular responses related to unfolded proteins and protein ubiquitination. It is noteworthy that a number of interactors identified here are chaperone family members, which is in agreement with studies performed by others in different SOD1 models (69)(70)(71)(72). In addition, we confirmed the previously reported interaction between human misfolded SOD1 and VDAC1 in rat spinal cord mitochondria (20).…”

ALS‐Associated Endoplasmic Reticulum Proteins in Denervated Skeletal Muscle: Implications for Motor Neuron Disease Pathology

“…Still, the G93ASOD1 transgene is not only expressed in alpha MNs, where it leads to aggregation of misfolded SOD1 (10, 52, 70) but also expressed in muscle fibres. Recently, evidence has accumulated that aggregation of misfolded SOD1 protein is also present in alpha‐MNs of human familial and sporadic ALS cases and may play a role in the disease process .…”

The Structure and Function of the Na,K-ATPase Isoforms in Health and Disease

“…Amyloid-beta as well as alpha-synuclein assemblies were found to interact with alpha3, and mapping of the interaction domain located a specific extracellular loop in the pump as the target in both cases (Ohnishi et al, 2015; Shrivastava et al, 2015). Furthermore, misfolded SOD1 protein, which is associated with amyotrophic lateral sclerosis, can bind an intracellular domain of alpha3 and inhibit the pump function (Ruegsegger et al, 2016). …”