Cellular processing of myocilin

Area of Science:

• Ophthalmology
• Molecular Biology
• Cell Biology

Background:

• Myocilin (MYOC) gene mutations are linked to juvenile and adult-onset open-angle glaucoma.
• Specific mutations like Pro370Leu (P370L) and Gln368stop (Q368X) have been identified in glaucoma patients.
• Investigating myocilin processing in human trabecular meshwork (TM) cells and RGC5 cell lines is crucial.

Purpose of the Study:

• To investigate the processing and degradation pathways of myocilin in human TM cells.
• To understand how MYOC mutations affect protein turnover and cellular pathways.
• To identify potential therapeutic targets for myocilin-related glaucoma.

Main Methods:

• Utilized turnover and photoactivation experiments in human TM cells.
• Employed inducible, stable RGC5 cell lines overexpressing wild-type and mutant myocilin-GFP fusion proteins.
• Analyzed protein ubiquitination, lysosomal and proteasomal inhibition, and autophagy markers (LC3).

Main Results:

• Endogenous myocilin in TM cells is a short-lived protein degraded via ubiquitin-proteasome and lysosomal pathways.
• Lysosomal and proteasomal inhibitors increased endogenous myocilin levels, indicating their role in degradation.
• Mutant and overexpressed myocilin prolonged turnover, compromised proteasome function, induced autophagy, and altered PSMB5 and LC3 levels.

Conclusions:

• Myocilin turnover in homeostasis relies on ubiquitin-proteasome and lysosomal pathways.
• Upregulation or mutation of myocilin disrupts these pathways, leading to compromised proteasome function and induced autophagy.
• Understanding these degradation mechanisms is vital for developing novel therapeutic strategies for myocilin-related glaucoma.