Inhibition of cysteine protease cathepsin L increases the level and activity of lysosomal glucocerebrosidase
Myung Jong Kim, Soojin Kim, Thomas Reinheckel, Dimitri Krainc
Myung Jong Kim, Soojin Kim, Thomas Reinheckel, Dimitri Krainc
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Research Article Cell biology Neuroscience

Inhibition of cysteine protease cathepsin L increases the level and activity of lysosomal glucocerebrosidase

Abstract

The glucocerebrosidase (GCase) encoded by the GBA1 gene hydrolyzes glucosylceramide (GluCer) to ceramide and glucose in lysosomes. Homozygous or compound heterozygous GBA1 mutations cause the lysosomal storage disease Gaucher disease (GD) due to severe loss of GCase activity. Loss-of-function variants in the GBA1 gene are also the most common genetic risk factor for Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). Restoring lysosomal GCase activity represents an important therapeutic approach for GBA1-associated diseases. We hypothesized that increasing the stability of lysosomal GCase protein could correct deficient GCase activity in these conditions. However, it remains unknown how GCase stability is regulated in the lysosome. We found that cathepsin L, a lysosomal cysteine protease, cleaves GCase and regulates its stability. In support of these data, GCase protein was elevated in the brain of cathepsin L–KO mice. Chemical inhibition of cathepsin L increased both GCase levels and activity in fibroblasts from patients with GD. Importantly, inhibition of cathepsin L in dopaminergic neurons from a patient GBA1-PD led to increased GCase levels and activity as well as reduced phosphorylated α-synuclein. These results suggest that targeting cathepsin L–mediated GCase degradation represents a potential therapeutic strategy for GCase deficiency in PD and related disorders that exhibit decreased GCase activity.

Authors

Myung Jong Kim, Soojin Kim, Thomas Reinheckel, Dimitri Krainc

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Figure 7

Chemical inhibition of cathepsin L increases GCase levels and reduces pS129-α-synuclein in dopaminergic neurons derived from a patient with GBA1-PD.

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Chemical inhibition of cathepsin L increases GCase levels and reduces pS...
(A) Control iPSC-dopaminergic neurons derived from a healthy individual at DIV 46 were treated with either DMSO or 5 μM of cathepsin L inhibitor SB 412515 every 2 days for 4 days. Band intensities were normalized to β3-tubulin. The data are presented as the mean ± SEM, n = 3; *P < 0.05, using unpaired 2-tailed t test. (B) Cathepsin L inhibitor (SB 412515) effects on in vitro GCase activity in healthy control iPSC-dopaminergic neurons. Control neurons derived from a healthy individual at DIV 46 were treated with either DMSO or 5 μM SB 412515 every 2 days for 4 days. GCase activity was assayed using 4-MUG substrates. Data are mean ± SEM. Two-tailed unpaired t test. **P < 0.01, n = 3. (C) Cathepsin L inhibitor (SB 412515) effects on GCase and pS129-α-synuclein levels in mutant GBA1 (heterozygous GBA1-c.84dupG frameshift) neurons derived from a patient with PD. Neurons were treated with either DMSO or 5 μM SB 412515 every 2 days for 4 days. Cell lysates were analyzed with immunoblot using indicated antibodies. Band intensities were normalized to β3-tubulin and compared with the DMSO-treated cells. The data are presented as the mean ± SEM, n = 3; *P < 0.05, **P < 0.01, ***P < 0.001, using unpaired 2-tailed t test. (D) Cathepsin L inhibitor (SB 412515) on GCase activity in mutant GBA1 (heterozygous GBA1-c.84dupG frameshift) neurons. Neurons were treated with either DMSO or 5 μM SB 412515 every 2 days for 4 days. In total, 10 µg of lysates were assayed for in vitro GCase assay using 4-MUG substrates. Data are mean ± SEM. Two-tailed unpaired t test. **P < 0.01, n = 3.