Cathepsin D Variants Associated With Neurodegenerative Diseases Show Dysregulated Functionality and Modified α-Synuclein Degradation Properties
Authors: Lina Walther
Jan Philipp Dobert
Josina Bunk
Friederike Zunke
Stefan Rose-John
Susy Prieto Huarcaya
Philipp Arnold
Alice Drobny
Journal: Frontiers in Cell and Developmental Biology (2021)
Discipline: MOLECULAR BIOLOGY & GENETICS
Keywords: Parkinson’s disease; alpha-synuclein; cathepsin D; lysosomal degradation; lysosomes
Affiliations: Institute of Biochemistry, Christian-Albrechts-Universität zu Kiel, Kiel, Germany., Department of Molecular Neurology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany., Institute of Anatomy, Christian-Albrechts-Universität zu Kiel, Kiel, Germany., Institute of Anatomy, Functional and Clinical Anatomy, Friedrich-Alexander-University Erlangen-Nürnberg, Erlangen, Germany.

Abstract:  Cathepsin D (CTSD) is a lysosomal protease important for the degradation of various substrates, including disease-associated proteins like α-synuclein (a-syn), amyloid precursor protein (APP) and tau, all of which tend to aggregate if not efficiently degraded. Hence, it is not surprising that genetic variants within the CTSD gene have been linked to neurodegenerative diseases, like Parkinson's and Alzheimer's disease (PD, AD), as well as the lysosomal storage disorder neuronal ceroid lipofuscinosis type-10 (NCL10). Although recent studies have shown the molecular dependence of substrate degradation via CTSD within autophagic pathways, only little is known about the precise role of lysosomal CTSD function in disease development. We here performed biochemical, cellular and structural analyses of eleven disease-causing CTSD point mutations found in genomic sequencing data of patients to understand their role in neurodegeneration. These CTSD variants were analyzed for cellular localization, maturation and enzymatic activity in overexpression analyses. Moreover, for PD-associated mutants, intracellular degradation of a-syn was monitored. In summary, our results suggest that NCL10-associated CTSD variants are significantly impaired in lysosomal maturation and enzymatic activity, whereas the AD- and PD-associated variants seemed rather unaffected, indicating normal maturation, and lysosomal presence. Interestingly, a PD-associated CTSD variant (A239V) exhibited increased enzymatic activity accompanied by enhanced a-syn degradation. By structural analyses of this mutant utilizing molecular dynamics simulation (MDS), we identified a structural change within a loop adjacent to the catalytic center leading to a higher flexibility and potentially accelerated substrate exchange rates. Our data sheds light onto the role of CTSD in disease development and helps to understand the structural regulation of enzymatic function, which could be utilized for targeted CTSD activation. Because of the degradative function of CTSD, this enzyme is especially interesting for therapeutic strategies tackling protein aggregates in neurodegenerative disorders. 

Retracted: No

PubPeer comments:
 Dear authors, Could you please check Figure 1: GAPDH and CBB do not match in terms of lanes ![file] , 
 https: www.frontiersin.org articles 10.3389 fcell.2021.671532 full **A Corrigendum on** *Cathepsin D Variants Associated With Neurodegenerative Diseases Show Dysregulated Functionality and Modified u03b1-Synuclein Degradation Properties* In the original article, there was a mistake in Figure 1C as published. In the Coomassie brilliant blue (CBB) protein staining, which was used as additional loading control (besides GAPDH), 11 instead of 10 sample lanes (+ protein ladder) were shown in the original Figure 1C. This mistake resulted from an additional sample (transfection control), that was loaded on the far right. This lane was not shown in both immunoblots (CTSD and GAPDH), but accidentally was still shown in the CBB control. The corrected Figure 1C appears below. The authors apologize for this error and state that this does not change the scientific conclusions of the article in any way. The original article has been updated. ,