Abstract
Increasing evidence suggests that necroptosis, a form of programmed cell death (PCD), contributes to neurodegeneration in several disorders, including ALS. Supporting this view, investigations in both in vitro and in vivo models of ALS have implicated key molecular determinants of necroptosis in the death of spinal motor neurons (MNs). Consistent with a pathogenic role of necroptosis in ALS, we showed increased mRNA levels for the three main necroptosis effectors Ripk1, Ripk3, and Mlkl in the spinal cord of mutant superoxide dismutase-1 (SOD1G93A) transgenic mice (Tg), an established model of ALS. In addition, protein levels of receptor-interacting protein kinase 1 (RIPK1; but not of RIPK3, MLKL or activated MLKL) were elevated in spinal cord extracts from these Tg SOD1G93A mice. In postmortem motor cortex samples from sporadic and familial ALS patients, no change in protein levels of RIPK1 were detected. Silencing of Ripk3 in cultured MNs protected them from toxicity associated with SOD1G93A astrocytes. However, constitutive deletion of Ripk3 in Tg SOD1G93A mice failed to provide behavioral or neuropathological improvement, demonstrating no similar benefit of Ripk3 silencing in vivo. Lastly, we detected no genotype-specific myelin decompaction, proposed to be a proxy of necroptosis in ALS, in either Tg SOD1G93A or Optineurin knock-out mice, another ALS mouse model. These findings argue against a role for RIPK3 in Tg SOD1G93A-induced neurodegeneration and call for further preclinical investigations to determine if necroptosis plays a critical role in the pathogenesis of ALS.
Footnotes
The authors declare no competing financial interests.
This work was supported by National Institute of Neurological Disorders and Stroke Grants NS099862, NS072428, and NS107442 (to S.P.), NS101966 (to E.J.P.-T.), NS101575 (to F.L.), and NS073776 (to L.L. and N.A.S.); the United States Department of Defense Award W81XWH-13-1-0416 (to S.P.); the Project-ALS/Columbia University Preclinical Core (F.L., N.A.S, and S.P.); Innovation Awards from the Thompson Family Foundation Initiative (S.P. and F.L.); the National Science Foundation Grant DGE 1644869 (to K.A.P.); the National Institutes of Health and National Center for Advancing Translational Sciences Grant TL1 TR000082-07 (to K.A.P.); the Medical Scientist Training Program GM007367 (to E.J.P.-T.); and the ALS Therapy Alliance (L.L. and N.A.S.).
↵^ G.D., K.A.P., and L.L. have equally contributed to this work.
This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
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