HSC70 expression is reduced in lymphomonocytes of sporadic ALS patients and contributes to TDP-43 accumulation

Abstract

Aim: The demonstration that chaperone-mediated autophagy (CMA) contributes to the degradation of TDP-43, the main constituent of cytoplasmic inclusions typically found in motor neurons of patients with sporadic amyotrophic lateral sclerosis (sALS), has pointed out a possible involvement of CMA in aggregate formation. To explore this possibility, in this study, we verified the presence of a possible systemic CMA alteration in sALS patients and its effect on TDP-43 expression. Materials and methods: Gene and protein expression of the cytosolic chaperone HSC70 and the lysosome receptor LAMP2A, the two pivotal mediators of CMA, was assessed in peripheral blood mononuclear cells (PBMCs) derived from 30 sALS patients and 30 healthy controls. The expression of TDP-43 and co-chaperones BAG1 and BAG3 was also analyzed. Results: We found reduced HSC70 expression in patient cells, with no change in LAMP2A, and increased insoluble TDP-43 protein levels, with an aberrant intracellular localization. We also observed an unbalanced expression of co-chaperones BAG1 and BAG3. HSC70 down-regulation was confirmed in immortalized lymphoblastoid cell lines derived from sporadic and TARDBP mutant ALS patients. Lastly, we demonstrated that HSC70 silencing directly increases TDP-43 protein levels in human neuroblastoma cells. Discussion: Our results do not support the existence of a systemic CMA alteration in sALS patients but indicate a direct involvement of HSC70 alterations in ALS pathogenesis.

Keywords:

• HSC70
• chaperone-mediated autophagy
• TDP-43
• lymphomonocytes

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Acknowledgements

The authors are grateful to all subjects recruited for this study.

Declaration of interest

The authors report no conflict of interest.

Additional information

Funding

Fondazione Telethon, Italy (n. GGP14039 and GGP19218 to A.P.); Fondazione Cariplo, Italy (n. 2014-0686 to A.P. and 2017_0747 to V.C.); Fondazione AriSLA, Italy (n. ALS_HSPB8, ALS_Granulopathy, MLOpathy and Target_RAN to A.P.); Università degli Studi di Milano e piano di sviluppo UNIMI - linea B (to V.C.); Italian Ministry of Health (MinSal) (n. GR-2011-02347198 to V.C.); Fondazione Regionale per la Ricerca Biomedica (FRRB) (TRANS_ALS, Rif. n. 2015-0023 to A.P.); Italian Ministry of University and Research (MIUR), PRIN - Progetti di ricerca di interesse nazionale (n. 2015LFPNMN and 2017F2A2C5 to A.P.); Agenzia Italiana del Farmaco, Bando AIFA 2016 (AIFA-2016-02364678 Co-ALS to A.P.); European Molecular Biology Organization (EMBO), short term fellowship (n. 537 - 2015 to R.C.); EU Joint Programme - Neurodegenerative Disease Research (JPND) project. The project is also supported through the following funding organisations under the aegis of JPND - www.jpnd.eu. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement N° 643417 (Grant ID: 01ED1601A, CureALS to A.P.).