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

Abstract

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.

Homozygous p.G61E mutation in a consanguineous Pakistani family with co-existence of juvenile-onset open angle glaucoma and primary congenital glaucoma

“…Adult-onset POAG occurs after the age of 40 years and exhibits a complex inheritance pattern due to the involvement of multiple genetic and environmental factors (Vincent et al, 2002). Thirty-three chromosomal loci of POAG have been mapped and only four genes MYOC, OPTN, WDR36 and NTF4 have been identified so far (Mookherjee et al, 2012).…”

Functional Coupling of ATP-binding Cassette Transporter Abcb6 to Cytochrome P450 Expression and Activity in Liver

“…In light of our data, it will be of great interest to investigate whether some of these disease pathologies could be explained by loss of expression and activity of CYP450s. For example, retinal defects leading to ocular disease in humans has a strong association with loss of CYP1B1 expression (52,53). A similar association in retinal defects is also seen with loss of ABCB6 expression in humans (22).…”

Delineation of a de novo 7q21.3q31.1 Deletion by CGH-SNP Arrays in a Girl with Multiple Congenital Anomalies Including Severe Glaucoma

“…Glaucoma, a clinically and genetically heterogeneous condition, is characterised by loss of retinal ganglion cells and atrophy of the optic nerve [Izzotti et al, 2011;Mookherjee et al, 2012]. The major clinical criterion of increased intraocular pressure usually results from resistance of the trabecular meshwork to the aqueous humour .…”

“…Alterations in trabecular meshwork have frequently been found in patients with congenital glaucoma. Congenital glaucoma, cloudy cornea, primary open-angle glaucoma, and juvenile open-angle glaucoma are some of the subtypes of glaucoma and have been related to diverse loci such as GLC1A or MYOC (1q24.3), CYP1B1 (2p22.2), and CAV1 / CAV2 (7q31.2) [Stoilov et al, 1997;Alward et al, 1998;Thorleifsson et al, 2010;Kennedy et al, 2012;Mookherjee et al, 2012].…”