Mitochondrial bioenergetic dysfunction and cryptic splicing of stathmin-2 are neuropathological markers of disease duration in sporadic amyotrophic lateral sclerosis

A striking feature of sporadic amyotrophic lateral sclerosis (ALS) is the marked heterogeneity in disease duration; despite the stark median survival of three years from symptom onset, 10-20% of people with ALS survive longer than 10 years. An improved understanding of the mechanisms underpinning this is vital to revealing the biological basis of disease resilience. Accumulating experimental and pathological evidence implicates mitochondrial bioenergetic dysfunction and TDP-43 nuclear loss-of-function in the aetiopathogenesis of ALS. However, the relevance of these two molecular dysfunctions to disease duration and resilience in ALS is unknown. We curated a cohort of sporadic ALS cases comprising clinically linked autopsy samples to identify molecular neuropathological correlates of disease duration. We developed a novel dual BaseScope RNA in situ hybridisation probe that labels mitochondrial complex 1 transcript (MT-ND2) and truncated stathmin-2 (STMN2) transcripts to measure mitochondrial bioenergetic function and TDP-43 loss-of-function, respectively, in ventral horn neurons. We first show that there is dysfunctional mitochondrial bioenergetics in sporadic ALS. We observed reduced expression of MT-ND2 and increased expression of truncated STMN2 in ALS cases (N=20) compared to sex- and age-matched controls (N=10). We show that these findings correlate with ALS disease duration. Further mechanistic studies are needed to explore whether manipulation of STMN2 expression, by either suppressing cryptic splicing or overexpression, could modify disease duration. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement A.R.M. was a Lady Edith Wolfson Clinical Fellow, jointly funded by the Medical Research Council (MRC) and the Motor Neurone Disease Association (MR/R001162/1). He also acknowledges support from the Rowling Scholars scheme, administered by the Anne Rowling Regenerative Neurology Clinic (ARRNC), University of Edinburgh. S.C. is supported by the Euan MacDonald Centre for Motor Neuron Disease Research, ARRNC, My Name'5 Doddie Foundation, and the UK Dementia Research Institute (which also supports M.-D.R.), which receives its funding from UK DRI Ltd, funded by the MRC, Alzheimer's Society and Alzheimer's Research UK. C.S. was supported by a Medical Research Council grant (MR/L016400/1). B.T.S. is a UK DRI Emerging Leader and Rowling-DRI Fellow. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Ethical approval was granted by the Scotland A Research Ethics Committee for the Scottish Clinical Audit Research Evaluation for Motor Neuron Disease platform (CARE-MND; 15/SS/0216), now a sub-registry of Rowling CARE (16/SS/0156; IRAS ID 200777), for this and related studies. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors.