Ribosomal protein synthesis is decreased in tauopathy as revealed by noncanonical amino acid labelling

Abstract

AbstractBackgroundTau is a scaffolding protein which serves multiple cellular functions that are perturbed in neurodegenerative diseases, including Alzheimer’s disease (AD) and frontotemporal dementia (FTD). Recently we demonstrated that amyloid‐b, the second hallmark of AD, induces de novo protein synthesis of tau, with this activation being found to be tau‐dependent. This raised the question of whether FTD‐tau by itself affects protein synthesis.MethodIn order to examine protein synthesis, we optimised non‐canonical amino acid (NCAA) labelling to label newly synthesised proteins in vivo in the K369I tau transgenic K3 mouse model of FTD. Combining this technique with either fluorescent non‐canonical amino acid tagging (FUNCAT) or bio‐orthogonal non‐canonical amino acid tagging (BONCAT), we were able to visualise and purify newly synthesised proteins from mouse brain tissue. We also used polysome profiling in primary neurons to further explore the effect of tau on ribosome biogenesis.ResultOur analysis reveals massively decreased protein synthesis in neurons containing pathologically phosphorylated tau, a finding we confirmed in P301L mutant tau transgenic rTg4510 mice. Using quantitative SWATH‐MS proteomics, we identify alterations in the synthesis of 247 proteins in de novo proteome of K3 mice, including the decreased synthesis of the ribosomal subunit proteins RPL23, RPLP0, RPL19 and RPS16, a finding that was validated in both K3 and rTg4510 mice. We also demonstrate that there is a decrease in overall abundance of one of these proteins, RPL23, and that this decrease correlated with the levels of both total and AT8 phosphorylated tau. Lastly, we recapultate these findings in human tissue, with FTD‐brains showing significantly lower levels of RPL23 than healthy controls.ConclusionTogether, our findings present a potential pathomechanism by which pathological tau interferes with cellular functions through the dysregulation of ribosomal protein synthesis.