Regulation of PXDN in eye development and PXDN gene variant screening within a South African cohort of patients presenting with anterior segment dysgenesis
Peroxidasin (PXDN) is an extracellular matrix-associated haem-peroxidase predominantly expressed in the vasculature and eye. PXDN crosslinks collagen IV through sulfilimine bond formation in the basement membrane. Aberrant PXDN expression is associated with fibrosis, heart failure and cancer, and various pathologies of the eye, where PXDN likely provides structural support via basement membrane synthesis in the cornea and lens during eye development, as well as protect the lens, trabecular meshwork and cornea against oxidative damage. Furthermore, PXDN pathogenic variants have been associated with anterior segment dysgenesis (ASD), congenital cataracts and corneal opacity. To further understand the role of PXDN in the eye, first we aimed to identify PXDN as a novel target of key transcriptional regulators of eye development, namely PAX6, FOXC1 and PITX2, and second, to screen a cohort of South African patients with ASD to look for pathogenic variants in PXDN and other ASD genes. Protein expression of PAX6, FOXC1, PITX2 and PXDN, in response to Fibroblast Growth Factor-2 (FGF-2) were quantified by western blotting and localisation visualised using immunofluorescence confocal microscopy. Chromatin immunoprecipitation-PCR and luciferase assays were employed to detect transcription factor-PXDN promoter interactions. Expression data established that PXDN, PAX6, FOXC1 and PITX2 were induced by FGF2 at varying time points. Putative binding sites for all three transcription factors were identified in the PXDN promoter and ChIP-PCR confirmed that PAX6, FOXC1 and PITX2 interact with various regions of the promoter. Luciferase reporter assays are currently underway. Next Generation Sequencing of genomic DNA from South African patients exhibiting ASD disorders. identified disease causing variants in PAX6 and GJA8. Variants of uncertain significance were identified in PXDN, BCOR, EPHA2 and LTBP2 genes and are being investigated further. In conclusion, we identified PXDN as a novel target of PAX6, FOXC1 and PITX2 that further supports for the integral role of PXDN in eye development.
A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Science, School of Molecular and Cell Biology, University of the Witwatersrand, Johannesburg, 2023
Peroxidasin (PXDN), Pathogenic variants