Wilmer's Glia Research Laboratory uses rat spontaneous mutants and genetically engineered mice as genetic tools to explore the functions of glia and glia-like (retinal pigmented epithelium) cells during normal retinal development and to probe how abnormalities in these cells lead to some retinal diseases. Genetic defects in laboratory animals provide highly reproducible genetic tools for examining the events governing proper development and can give insight into human diseases. In recent years this has become an especially powerful approach since it has become much easier to identify the gene and type of mutation responsible for the disorder.
We have described a naturally occurring mutation (Nuc1) in the Sprague-Dawley rat with a novel eye phenotype. Nuc1 is inherited as a single Mendelian locus with viable, but severely affected homozygotes and an intermediate phenotype in heterozygotes. We reported that the mutation causing Nuc1 is a 27 base pair insertion in exon 6 of the bA3/A1-crystallin gene on rat chromosome 10. The 27 base pair insertion is composed of near-perfect tandem repeats of a 7 base pair sequence, TGACTAT. We showed for the first time, that bA3/A1-crystallin, a major structural protein of the ocular lens, is expressed in the astrocytes and Retinal Pigmented Epithelium (RPE) cells of the retina. Our studies by utilizing the Nuc1 rat, in which the bA3/A1-crystallin gene is mutated, show that bA3/A1-crystallin expressed in astrocytes is required during remodeling of the retina. While in RPE cells, we show that this protein may be a novel lysosomal component required in both the processes of autophagy and phagocytosis.
We have used the Cre-loxP system to delete bA3/A1-crystallin selectively from RPE cells. The conditional knockout mice in which bA3/A1-crystallin has been deleted specifically from RPE will help us to elucidate the possible mechanisms of clearance in both phagocytosis and autophagy in RPE both under in-vitro and in-vivo conditions.
We are also using the Cre-loxP system to delete bA3/A1-crystallin selectively from astrocytes. Using genetically engineered mouse models, we will be able to examine the effects of bA3/A1-crystallin function on astrocyte development, as well as on neuronal and vascular remodeling in the retina. The conditional knockout mice in which bA3/A1-crystallin has been deleted specifically from astrocytes will help us to elucidate the possible cellular and molecular mechanisms of astrocyte template formation, in the context of astrocyte-mediated retinal remodeling.
1. Valapala M et al. Lysosomal-mediated waste clearance in retinal pigmented epithelial cells is regulated by CRYBA1/A3/A1-crystallin via V-ATPase-MTORC1 signaling. Autophagy, 2014; 10:3, 480-496. http://www.ncbi.nlm.nih.gov/pubmed/24468901
2. Valapala M et al. Impaired endolysosomal function disrupts Notch signaling in optic nerve astrocytes. Nature Communications, 2013; 4: 1629. http://www.ncbi.nlm.nih.gov/pubmed/23535650
3. Ma B et al. bA3/A1-crystallin controls anoikis-mediated cell death in astrocytes by modulating PI3K/AKT/mTOR and ERK survival pathways via the PKD/Bit1 signaling axis. Cell Death and Disease, 2011 Oct 13; 2:e217. http://www.ncbi.nlm.nih.gov/pubmed/21993393
4. Zhang C et al. A developmental defect in astrocytes inhibits programmed regression of the hyaloid vasculature in the mammalian eye. European Journal of Cell Biology, 2011; 90 (5): 440-448. http://www.ncbi.nlm.nih.gov/pubmed/21354650
5. Zigler, Jr. JS et al. Mutation in the βA3/A1-crystallin gene impairs phagosome degradation in the retinal pigment epithelium of the rat. Journal of Cell Science, 2011; 124: 523-531. http://www.ncbi.nlm.nih.gov/pubmed/21266465
1. Kaarniranta K et al. Autophagy and heterophagy dysregulation leads to retinal pigment epithelium dysfunction and development of age-related macular degeneration. Autophagy. 2013; 9(7). In Press. http://www.ncbi.nlm.nih.gov/pubmed/23590900
2. Whitcup SM et al. The role of the immune response in age-related macular degeneration. International Journal of Inflammation, 2013; In Press. http://www.ncbi.nlm.nih.gov/pubmed/23762772