Abstract

TAR DNA binding protein 43 (TDP-43) is a major disease-associated protein involved in the pathogenesis of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U). Our previous studies found a direct association between TDP-43 and heterogeneous nuclear ribonucleoprotein K (hnRNP K). In this study, utilizing ALS patient fibroblasts harboring a TDP-43(M337V) mutation and NSC-34 motor neuronal cell line expressing TDP-43(Q331K) mutation, we show that hnRNP K expression is impaired in urea soluble extracts from mutant TDP-43 cell models. This was confirmed in vivo using TDP-43(Q331K) and inducible TDP-43(A315T) murine ALS models. We further investigated the potential pathological effects of mutant TDP-43-mediated changes to hnRNP K metabolism by RNA binding immunoprecipitation analysis. hnRNP K protein was bound to antioxidant NFE2L2 transcripts encoding Nrf2 antioxidant transcription factor, with greater enrichment in TDP-43(M337V) patient fibroblasts compared to healthy controls. Subsequent gene expression profiling revealed an increase in downstream antioxidant transcript expression of Nrf2 signaling in the spinal cord of TDP-43(Q331K) mice compared to control counterparts, yet the corresponding protein expression was not up-regulated in transgenic mice. Despite the elevated expression of antioxidant transcripts, we observed impaired levels of glutathione (downstream Nrf2 antioxidant) in TDP-43(M337V) patient fibroblasts and astrocyte cultures from TDP-43(Q331K) mice, indicative of elevated oxidative stress and failure of some upregulated antioxidant genes to be translated into protein. Our findings indicate that further exploration of the interplay between hnRNP K (or other hnRNPs) and Nrf2-mediated antioxidant signaling is warranted and may be an important driver for motor neuron degeneration in ALS.

Authors	Moujalled, Diane; Grubman, Alexandra; Acevedo, Karla; Yang, Shu; Ke, Yazi D.; Moujalled, Donia M.; Duncan, Clare; Caragounis, Aphrodite; Perera, Nirma D.; Turner, Bradley J.; Prudencio, Mercedes; Petrucelli, Leonard; Blair, Ian; Ittner, Lars M.; Crouch, Peter J.; Liddell, Jeffrey R.; White, Anthony R.
Journal	HUMAN MOLECULAR GENETICS
Pages	1732-1746
Volume	26
Date	1/05/2017
Grant ID
Funding Body	Motor Neuron Disease Research Institute of Australia
URL	http://www.ncbi.nlm.nih.gov/pubmed/?term=10.1093/hmg/ddx093