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Calpain-5 Expression in the Retina Localizes to Photoreceptor Synapses.

TitleCalpain-5 Expression in the Retina Localizes to Photoreceptor Synapses.
Publication TypeJournal Article
Year of Publication2016
AuthorsSchaefer, Kellie A., Toral Marcus A., Velez Gabriel, Cox Allison J., Baker Sheila A., Borcherding Nicholas C., Colgan Diana F., Bondada Vimala, Mashburn Charles B., Yu Chen-Guang, Geddes James W., Tsang Stephen H., Bassuk Alexander G., and Mahajan Vinit B.
JournalInvest Ophthalmol Vis Sci
Date Published2016 05 01
KeywordsAnimals, Blotting, Western, Calpain, Cattle, Female, Gene Expression Regulation, Neoplastic, Humans, Immunohistochemistry, Male, Mice, Neoplasms, Experimental, Photoreceptor Cells, Retina, Retinal Neoplasms, Retinoblastoma, RNA, Neoplasm, Synapses, Tumor Cells, Cultured

PURPOSE: We characterize calpain-5 (CAPN5) expression in retinal and neuronal subcellular compartments.

METHODS: CAPN5 gene variants were classified using the exome variant server, and RNA-sequencing was used to compare expression of CAPN5 mRNA in the mouse and human retina and in retinoblastoma cells. Expression of CAPN5 protein was ascertained in humans and mice in silico, in mouse retina by immunohistochemistry, and in neuronal cancer cell lines and fractionated central nervous system tissue extracts by Western analysis with eight antibodies targeting different CAPN5 regions.

RESULTS: Most CAPN5 genetic variation occurs outside its protease core; and searches of cancer and epilepsy/autism genetic databases found no variants similar to hyperactivating retinal disease alleles. The mouse retina expressed one transcript for CAPN5 plus those of nine other calpains, similar to the human retina. In Y79 retinoblastoma cells, the level of CAPN5 transcript was very low. Immunohistochemistry detected CAPN5 expression in the inner and outer nuclear layers and at synapses in the outer plexiform layer. Western analysis of fractionated retinal extracts confirmed CAPN5 synapse localization. Western blots of fractionated brain neuronal extracts revealed distinct subcellular patterns and the potential presence of autoproteolytic CAPN5 domains.

CONCLUSIONS: CAPN5 is moderately expressed in the retina and, despite higher expression in other tissues, hyperactive disease mutants of CAPN5 only manifest as eye disease. At the cellular level, CAPN5 is expressed in several different functional compartments. CAPN5 localization at the photoreceptor synapse and with mitochondria explains the neural circuitry phenotype in human CAPN5 disease alleles.

Alternate JournalInvest. Ophthalmol. Vis. Sci.
PubMed ID27152965
PubMed Central IDPMC4868102
Grant ListF31 EY026789 / EY / NEI NIH HHS / United States
R21 AG050437 / AG / NIA NIH HHS / United States
R01 EY024665 / EY / NEI NIH HHS / United States
K08 EY020530 / EY / NEI NIH HHS / United States
R01 EY024698 / EY / NEI NIH HHS / United States
R01 EY020542 / EY / NEI NIH HHS / United States
R01 EY025225 / EY / NEI NIH HHS / United States
T32 GM007337 / GM / NIGMS NIH HHS / United States