Kantorow, Marc

The mitochondrion is the powerhouse of the cell. Therefore, it is critical to the homeostasis of the cell that populations of mitochondria that are damaged or in excess are degraded. The process of targeted elimination of damaged or excess mitochondria by autophagy is called mitophagy. In this report, analysis of the mitophagy regulators PINK1/PARKIN and BNIP3L and their roles are assessed in the lens. PARKIN, an E3 ubiquitin ligase, has been shown to play a role in directing damaged mitochondria for degradation. While BNIP3L, an outer mitochondrial membrane protein, increases in expression in response to excess mitochondria and organelle degradation during cellular differentiation. We have shown that PARKIN is both induced and translocates from the cytoplasm to the mitochondria in human epithelial lens cells upon oxidative stress exposure. In addition, our findings also show that overexpression of BNIP3L causes premature clearance of mitochondria and other organelles, while loss of BNIP3L results in lack of clearance. Prior to this work, PARKIN mediated mitophagy had not been shown to act as a protective cellular response to oxidative stress in the lens. This project also resulted in the novel finding that BNIP3L-mediated mitophagy mechanisms are required for targeted organelle degradation in the lens.

Purpose. To identify genes important for maintaining the specialized functions of lens epithelial and fiber cells. Methods. The expression profiles of 22,215 genes between human lens epithelial and fiber cells were analyzed using oligonucleotide microarray hybridization and RT-PCR. Selected genes were functionally clustered using the EASE bioinformatics software package. Results. Analysis of microarray hybridizations revealed 1430 transcripts that were significantly increased and 901 transcripts that were significantly decreased. Microarray data was confirmed using RT-PCR on 11 randomly selected genes. Functional clustering of the identified gene expression patterns revealed altered gene expression in cellular pathways including oxidative stress, cell proliferation, and apoptosis. The methionine sulfoxide reductase class of enzymes were further analyzed and demonstrated to be expressed throughout the human body, indicating a significant protective role. Conclusions. These data reveal novel and previously identified gene expression differences that provide insight into those mechanisms that may be important for lens cell differentiation.