Ashima Bhattacharjee

Molecular Basis for Involvement of CYP1B1 in MYOC Upregulation and Its Potential Implication in Glaucoma Pathogenesis

CYP1B1 has been implicated in primary congenital glaucoma with autosomal recessive mode of inheritance. Mutations in CYP1B1 have also been reported in primary open angle glaucoma (POAG) cases and suggested to act as a modifier of the disease along with Myocilin (MYOC). Earlier reports suggest that over-expression of myocilin leads to POAG pathogenesis. Taken together, we propose a functional interaction between CYP1B1 and myocilin where 17β estradiol acts as a mediator. Therefore, we hypothesize that 17β estradiol can induce MYOC expression through the putative estrogen responsive elements (EREs) located in its promoter and CYP1B1 could manipulate MYOC expression by metabolizing 17β estradiol to 4-hydroxy estradiol, thus preventing it from binding to MYOC promoter. Hence any mutation in CYP1B1 that reduces its 17β estradiol metabolizing activity might lead to MYOC upregulation, which in turn might play a role in glaucoma pathogenesis. It was observed that 17β estradiol is present in Human Trabecular Meshwork cells (HTM) and Retinal Pigment Epithelial cells (RPE) by immunoflouresence and ELISA. Also, the expression of enzymes related to estrogen biosynthesis pathway was observed in both cell lines by RT-PCR. Subsequent evaluation of the EREs in the MYOC promoter by luciferase assay, with dose and time dependent treatment of 17β estradiol, showed that the EREs are indeed active. This observation was further validated by direct binding of estrogen receptors (ER) on EREs in MYOC promoter and subsequent upregulation in MYOC level in HTM cells on 17β estradiol treatment. Interestingly, CYP1B1 mutants with less than 10% enzymatic activity were found to increase the level of endogenous myocilin in HTM cells. Thus the experimental observations are consistent with our proposed hypothesis that mutant CYP1B1, lacking the 17β estradiol metabolizing activity, can cause MYOC upregulation, which might have a potential implication in glaucoma pathogenesis.

Complex genetics of glaucoma: defects in CYP1B1 , and not MYOC , cause pathogenesis in an early-onset POAG patient with double variants at both loci

Glaucoma is the second largest cause of blindness worldwide, affecting almost 60 million people (Quigley and Broman 2006). Defects in MYOC and CYP1B1 have been implicated in primary open angle glaucoma (POAG) and primary congenital glaucoma (PCG), respectively. Variants in both the genes have been detected in both the diseases indicating a higher complexity in the pathogenesis of the disease. In this context, we present here the case of a POAG patient who is found to be a compound heterozygote for CYP1B1 mutations and a homozygote for MYOC variant. None of the three nonsynonymous changes were found in 170-unrelated controls with matched age and ethnicity. Analysis of the family members reveal that proband’s younger sister, not affected, was homozygous for the MYOC variant but lacked one variant in CYP1B1. This is in contrast to other reports that showed implication of CYP1B1 in POAG. This case is unique, since both parents of the proband do not show any symptom of POAG, despite of having one defective allele for both MYOC and CYP1B1.