TGF-ß Regulates Cathepsin Activation during Normal and Pathogenic Development.

Area of Science:

• Biochemistry
• Developmental Biology
• Molecular Biology

Background:

• Cysteine cathepsins are crucial proteases involved in lysosomal protein degradation.
• Their roles extend beyond lysosomal turnover, impacting development and disease processes.
• Lysosomal storage diseases, such as mucolipidosis II (MLII), disrupt normal cellular functions.

Purpose of the Study:

• To investigate the activity and regulation of cysteine cathepsins in zebrafish embryos with MLII.
• To elucidate the molecular mechanisms linking lysosomal dysfunction to altered cathepsin activity.
• To explore therapeutic strategies targeting cathepsin dysregulation in MLII.

Main Methods:

• Utilized a fluorescent activity-based probe (ABP), BMV109, to visualize and quantify cysteine cathepsin activity in vivo.
• Employed a zebrafish model of mucolipidosis II to study disease-specific alterations.
• Investigated the role of TGF-ß signaling and chondroitin 4-sulfate (C4-S) in cathepsin processing.

Main Results:

• Loss of carbohydrate-dependent lysosomal sorting in MLII alters the activity of multiple cathepsin proteases.
• Elevated C4-S levels in MLII correlate with increased TGF-ß signaling and chst11 expression.
• Inhibition of chst11 reduces C4-S, impairs cathepsin C (Ctsk) activation, and ameliorates MLII phenotypes.

Conclusions:

• A regulatory loop exists between TGF-ß signaling and cathepsin C activation, which is disrupted in lysosomal diseases like MLII.
• Chondroitin 4-sulfate plays a key role in modulating cathepsin C activation in the context of lysosomal dysfunction.
• Activity-based probes are powerful tools for dissecting pathogenic mechanisms during development in living organisms.