Inhibition of cathepsin X activity as a novel strategy for the treatment of Parkinson's disease




01. July 2018 - 30. June 2021


0,34 FTE


Anja Pišlar


3.03 Medical sciences/ Neurobiology

Research Organisation:







Parkinson’s disease (PD) is the second most common neurodegenerative disease characterized by a progressive degeneration of the dopaminergic projection between the substantia nigra compacta (SNc) and the striatum with associated movement impairments. It represents a very important health issue, as there is no cure for this devastating disease. Although the ethiology of PD and the underlying mechanisms for disease development remain incompletely understood, increasing evidence suggests that inflammatory processes play a key role in the pathogenesis of PD. Lysosomal cysteine peptidases have been found to participate in the neuroinflammatory processes associated with neurodegeneration in the central nervous system. In particular, the excessive expression and activity of cysteine cathepsin X in brain cells was linked with these neurodegenerative processes. High levels of cathepsin X have been observed in aged brain and in degenerating brain regions in different transgenic models of neurodegeneration. Its upregulation in microglial cells surrounding amyloid plaques was observed, where cathepsin X co-localized with its target gamma-enolase.  Later the contribution of cathepsin X to amyloid-β-related neurodegeneration through proteolytic cleavage of the C-terminal dipeptide of γ-enolase has been proposed. In rat model of PD, cathepsin X expression was found to be strongly upregulated in damaged dopaminergic neurons of the substantia nigra compacta. Additionally, a significant role of cathepsin X in neurotoxin-mediated apoptosis of dopaminergic neurons has been demonstrated. Cathepsin X has also been associated with inflammation processes leading to neurodegeneration. It has been shown to be disproportionately expressed and secreted by microglia and astrocytes in response to inflammatory stimulus leading to neuronal damage and the inhibition of cathepsin X was shown to reduce the strength of the microglia activation-mediated neurodegeneration. Therefore, due to the harmful action of cathepsin X in inflammation-induced neurodegeneration, cathepsin X inhibitors represent a possible tool for therapeutic interventions to impair excessive proteolytic activity of the enzyme.
The number of existing inhibitors of cathepsin X is very low. So far, only epoxysuccinyl irreversible inhibitor AMS36 is frequently used in in vitro studies as cathepsin X specific inhibitor and exerts neuroprotective action towards neurodegenerative processes common for PD. However, this inhibitor forms an irreversible covalent bond with the catalytic cysteine in the active site of cathepsin X and potentially other cathepsins, the feature which may significantly decrease the specificity and cause off-target effects. Therefore, there is a great need to apply more specific cathepsin X inhibitors and a new generation of triazole-based reversible cathepsin X inhibitors with much better selectivity are expected to significantly improve the protease-targeted therapy of neurodegenerative diseases such as PD. Therefore, our hypothesis is that novel selective and reversible cathepsin X inhibitors can better impair neurodegenerative processes in PD.
Through the proposed project the new cathepsin X inhibitors will be evaluated in in vitro and in vivo models of neurodegeneration. We will first select the candidates that are non-toxic for brain cells using neuronal and glial cell cultures. Selected inhibitors will be tested in in vitro cell models of neurodegeneration, which mimic the neuropathological and biochemical conditions in PD. The inhibitors, revealing the best pharmacological properties on cell culture models will be evaluated in vivo on animal models of PD. We expect that novel reversible and selective cathepsin X inhibitors will reduce neurodegenerative processes associated with neuroinflammation and that our results will enable their further testing in clinical studies for treating PD.



Bibliographical references, arising directly from the implementation of the project:


Financed by:

Research projects (co)funded by the Slovenian Research Agency.