June 2017
Volume 58, Issue 8
Open Access
ARVO Annual Meeting Abstract  |   June 2017
Investigating the role of pexophagy in the development of the ocular lens and cataractogenesis
Author Affiliations & Notes
  • Muhammad Ali
    The Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States
  • Shahid Yar Khan
    The Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States
  • Firoz Kabir
    The Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States
  • Sheikh Riazuddin
    National Centre of Excellence in Molecular Biology, University of the Punjab, Lahore, Pakistan
    National Centre for Genetic Diseases, Shaheed Zulfiqar Ali Bhutto Medical University, Islamabad, Pakistan
  • J. Fielding Hejtmancik
    Ophthalmic Genetics and Visual Function Branch, National Eye Institute, National Institutes of Health, Bethesda, Maryland, United States
  • S Amer Riazuddin
    The Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States
    McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States
  • Footnotes
    Commercial Relationships   Muhammad Ali, None; Shahid Khan, None; Firoz Kabir, None; Sheikh Riazuddin, None; J. Fielding Hejtmancik, None; S Amer Riazuddin, None
  • Footnotes
    Support  R01EY022714
Investigative Ophthalmology & Visual Science June 2017, Vol.58, 2042. doi:
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      Muhammad Ali, Shahid Yar Khan, Firoz Kabir, Sheikh Riazuddin, J. Fielding Hejtmancik, S Amer Riazuddin; Investigating the role of pexophagy in the development of the ocular lens and cataractogenesis. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2042.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : To determine the genetic basis of congenital cataracts in an inbred familal case and investigate the role of pexophagy in the development of the ocular lens and cataractogenesis.

Methods : We recruited a large family with multiple members having congenital cataracts. All participating members underwent clinical and ophthalmic examinations. Genomic DNAs of three individuals with cataracts were selected for whole-exome sequencing. The exome data analysis was performed using Lasergene Genomics Suite. A tandem fluorochrome pexophagy assay was performed to quantitate the mRFP/EGPF-SKL ratio using a flow cytometer in a human lens epithelial cell line (HLE). The localization patterns of PXMP2 (a peroxisome marker), wild-type and mutant PEX5, and substrate harboring peroxisome target sequence (PTS1) were examined.

Results : The ophthalmological examinations of affected members indicated congenital cataracts. We identified 2,201 homozygous variants shared among the three affected individuals. Of these, only a variant in PEX5 (c.653T>C; p.F218S) showed segregation with the disease phenotype in the family, and was absent in ethnically matched control chromosomes. Furthermore, F218 is completely conserved in orthologs of PEX5, and in silico analysis predicted that the mutant allele would be disruptive to the native protein structure. PEX5 is a receptor protein that is indispensable for pexophagy, the selective degradation of peroxisomes. Importantly, it is expressed in the developing murine lens transcriptome and proteome. To understand the physiological significance of PEX5 in the development of the ocular lens and the role of the causative mutation in cataractogenesis, we performed a flow cytometry-based tandem fluorochrome pexophagy assay in an HLE cell line. This analysis revealed H2O2-induced pexophagy in the wild-type HLE cells. Immunofluorescence tracking showed a peroxisomal localization pattern for both the wild-type and mutant PEX5 proteins. However, the mutant protein did not transport the substrate harboring PTS1 to the peroxisome. These results suggest that the mutation compromises the ability of PEX5 to transport cargo bearing the PTS1 signal.

Conclusions : Here, we report a novel missense mutation in PEX5 responsible for cataractogenesis. To the best of our knowledge, this is the first report implicating pexophagy in cataractogenesis.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

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