Functional validation of a humanCAPN5exome variant by lentiviral transduction into mouse retina

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Abstract

Exome sequencing indicated that the gene encoding the calpain-5 protease,CAPN5, is the likely cause of retinal degeneration and autoimmune uveitis in human patients with autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV, OMIM #193235). To explore the mechanism of ADNIV, a humanCAPN5disease allele was expressed in mouse retinas with a lentiviral vector created to express either the wild-type human (h)CAPN5or the ADNIV mutanthCAPN5-R243Lallele under a rhodopsin promoter with tandem green fluorescent protein (GFP) expression. Vectors were injected into the subretinal space of perinatal mice. Mouse phenotypes were analyzed using electroretinography, histology and inflammatory gene expression profiling. Mouse calpain-5 showed high homology to its human ortholog with >98% sequence identity that includes the ADNIV mutant residue. Calpain-5 protein was expressed in the inner and outer segments of the photoreceptors and in the outer plexiform layer. Expression of thehCAPN5-R243Lallele caused loss of the electroretinogramb-wave, photoreceptor degeneration and induction of immune cell infiltration and inflammatory genes in the retina, recapitulating major features of the ADNIV phenotype. Intraocular neovascularization and fibrosis were not observed during the study period. Our study shows that expression of thehCAPN5-R243Ldisease allele elicits an ADNIV-like disease in mice. It further suggests that ADNIV is due toCAPN5gain-of-function rather than haploinsufficiency, and retinal expression may be sufficient to generate an autoimmune response. Genetic models of ADNIV in the mouse can be used to explore protease mechanisms in retinal degeneration and inflammation as well as preclinical therapeutic testing.

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