An in-depth analysis of phosphorylated tau in amyotrophic lateral sclerosis post-mortem motor cortex and cerebrospinal fluid

Although the molecular mechanisms underlying amyotrophic lateral sclerosis (ALS) are not yet fully understood, recent studies have described alterations in tau protein in both sporadic and familial ALS. However, it is unclear whether alterations in tau contribute to ALS pathogenesis. Here, we leveraged the ALS Knowledge Portal and Project MinE data sets and identified specific genetic variants clustering within the microtubule-binding domain of MAPT , which were unique to ALS cases. Furthermore, our analysis in a large post-mortem cohort of ALS and control motor cortex demonstrates that although there was no significant difference in the presence of phosphorylated tau (pTau) neuropil threads and neurofibrillary tangles between the two groups, pTau-S396 and pTau-S404 mis-localized to the nucleus and synapses in ALS. This was specific to the C-terminus phosphorylation sites as there was a significant decrease in pTau-T181 in ALS synaptoneurosomes compared to controls. Lastly, while there was no change in total tau or pTau-T181 in ALS CSF, there was a decrease in pTau-T181:tau ratio in ALS CSF, as previously reported. Importantly, CSF tau levels were increased in ALS patients diagnosed with bulbar onset ALS, while pTau-T181:tau ratio was decreased in ALS patients diagnosed with both bulbar and limb onset. Additionally, there was an inverse correlation between tau levels in the CSF and the revised ALS functional rating scale (ALSFRS-R) as well as a correlation between pTau-T181:tau ratio and ALSFRS-R. While there were no longitudinal alterations in tau, pTau-T181 and pTau-T181:tau ratio, there was an increase in the rate of ALSFRS-R decline per month associated with increases in tau levels. This decline was also inversely correlated with increases in pTau-T181 in relation to tau levels. Taken together, our findings demonstrate that, like Alzheimer’s disease, hyperphosphorylated tau is mis-localized in ALS and that decreases in CSF pTau-T181 may serve as a biomarker in ALS. ### Competing Interest Statement TSJ is on the scientific advisory board of Cognition Therapeutics and receives collaborative grant funding from 3 industrial partners. None of these had any influence over the current paper. ### Funding Statement T.P. was supported by an award from the Judith and Jean Pape Adams Charitable Foundation and Byrne Family Endowed Fellowship in ALS Research. SD was supported by the Alzheimer's association (2018-AARF-591935) and the Jack Satter Foundation. S.M.K.F. was supported by the ALS Canada Tim E. Noel Postdoctoral Fellowship. ### 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: The study was approved by the Partners Healthcare Institutional Review Board (IRB). Written informed consent was obtained from all participants prior to study enrollment. Post-mortem consent was obtained from the appropriate representative (next of kin or health care proxy) prior to autopsy. All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. 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 The data that support the findings in this study can be requested from the corresponding author and made available pending review of reasonable requests for academic use