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G.-F. Yam, L. Jia, D.-C. Lam, C.-P. Pang; Chemical Chaperones Correct the Mutant Phenotype of Myocilin - A New Concept of Glaucoma Treatment. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3814.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the potential use of chemical chaperones in correcting mutant phenotype of a glaucoma-causing myocilin variant.
In a 5-generation family affected with juvenile onset open-angle glaucoma (JOAG) and ocular hypertension, we screened myocilin (MYOC), optineurin (OPTN) and WDR36 for mutations in 44 family members. Normal controls included 200 unrelated Chinese subjects. The human trabecular meshwork (HTM) cells were transfected to express wildtype or mutant MYOC proteins. Secreted and cellular MYOC proteins were assayed by immunoprecipitation, Western blotting and immunofluorescence, respectively. The effects of low temperature and chemical chaperone (4-phenylbutyric acid and trimethylamine N-oxide) on mutant MYOC solubility and secretion, ER stress and apoptosis were examined.
One missense MYOC mutation, 1150G>A (OMIM 601652), was identified to be causative for glaucoma in this family. The encoded Asp384Asn MYOC protein was not secreted and remained sequestered intracellularly in HTM cells. The mutant was Triton X-100 insoluble as compared to the wildtype and was not degraded by ubiquitin-proteasome pathway. Mutant-expressing cells showed up-regulated BiP expression, indicating of ER stress, and underwent apoptosis as shown by a higher rate of nuclear fragmentation. Treatment of cells with low temperature (30ºC) or chemical chaperones (1 mM 4-phenylbutyric acid or 50 mM trimethylamine N-oxide) substantially improved Asp384Asn MYOC protein solubility and secretion. No transcriptional up-regulation of MYOC was observed. Reduced apoptosis of mutant cells was found after treatments.
The protein phenotype of the novel Asp384Asn mutant MYOC was effectively corrected by chemical chaperones. This suggests that use of chemical chaperones may provide a potential future therapeutic approach for primary open-angle glaucoma.
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