Trabecular meshwork cellular mis-trafficking of near-native and premature stop variants in glaucoma-relevant myocilin

Mutations in the myocilin olfactomedin (OLF) domain can cause vision loss in glaucoma by inducing protein misfolding in trabecular meshwork cells. However, not all mutations are causal for the disease. Here, we compare the cellular behaviors of two variants with uncertain contribution to glaucoma - namely, the missense variant A427T and premature stop variant Q368X - to those of wild type (WT) and disease variant Y437H. When expressed in an inducible immortalized trabecular meshwork cell line, inhibition of the proteasome rerouted WT myocilin from endoplasmic reticulum-associated degradation to autophagy. By contrast, neither Y437H, A427T nor Q368X could be rerouted for degradation. Conversely, inhibition of autophagy caused accumulation of WT myocilin and did not promote clearance of any tested mutant myocilins. Although the Q368X OLF mutant is misfolded, the crystal structure of the A427T OLF mutant showed modest perturbations that were largely confined to the mutation site. Our study demonstrates that a full range of misfolded states of mutant myocilin can present challenges for protein quality control clearance pathways and expands the range of defects known to impair mutant myocilin clearance.