Neuronal overexpression of potassium channel subunit Kcnn1 prolongs survival of SOD1-linked ALS and A53T alpha-synuclein mouse models

Abstract

Eye muscles and the motor neurons in the innervating cranial nerve nuclei are relatively spared in human ALS, and likewise, these cranial motor neurons are spared of SOD1YFP aggregation in a transgenic mouse model of SOD1-linked ALS, G85R SOD1YFP. RNA profiling of mouse oculomotor (CN3) neurons (resistant) vs hypoglossal (CN12) and spinal cord motor neurons (susceptible) from nontransgenic mice identified differentially expressed channel and receptor genes. A number were evaluated for effects on survival of the ALS strain by transgenesis or knockout to emulate the relative RNA level in oculomotor neurons. Transgenesis of Thy1.2-driven cDNA for mouse Kcnn1, a potassium channel subunit, extended the median days of survival time to paralysis of mutant G85R SOD1YFP mice by up to 100%, associated with absence of fluorescent aggregates; extended the median time to paralysis of G93A SOD1 mice by up to 55%; and extended the median time to endstage motor disease of a Thy1.2-driven alpha-synuclein transgenic strain by up to greater than 100%. The overexpressed Kcnn1 subunit was diffusely cytoplasmic in motor neurons and found to induce a multifaceted stress response as judged by RNAseq and immunostaining, including ER stress response, mitochondrial stress response, and an integrated stress response. Like other potassium channel subunits, Kcnn1 subunit is likely targeted to the ER, but as reported earlier in rodent Kcnn1-transfected cultured cells, in the absence of Kcnn2 with which to co-assemble, Kcnn1 is channel-inactive and is diffusely cytoplasmic. Thus, a nonassembled and potentially misfolded state of overexpressed Kcnn1 targeted to the ER of neurons may explain the stress responses, which in the mutant SOD1 and A53T alpha-synuclein mice, protect against the pathogenic proteins. Major neurodegenerative diseases, including Alzheimers Disease and Parkinsons Disease, are associated with the accumulation of characteristic proteins, Abeta/Tau and alpha-synuclein in AD and PD, respectively, that misfold, aggregate, and in many cases form amyloid fibrils (e.g. Long and Holtzman, 2019; Sierksma et al, 2020; Tanner et al, 2024). Such pathogenic behavior is associated with malfunction/death of specific neuronal populations, producing consequent clinical symptoms. It seems counterintuitive to observe proteinopathy as a major facet of these diseases considering that there is generally a quality control machinery in all cells, consisting of effectors - molecular chaperones, ubiquitin/proteasomal components, and autophagy/lysosome components - governed by a "sensor" circuitry - e.g. UPR, ISR, HSF - that can detect such misbehavior and induce protective responses. While neurons may be particularly susceptible because they are postmitotic and unable to distribute damaging protein species to daughter cells as a protective means, it has remained unclear whether the endogenous sensor/effector pathways can be induced sufficiently in vivo so as to mediate protection. Here, we report that neuronal overexpression of a potassium channel subunit, mouse Kcnn1, in two different transgenic mouse neurodegenerative models, protects against aggregation and cell loss by apparent induction of multiple stress response pathways, substantially extending survival of the mice.