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Priyamvada M Pitale, Vishal M Shinde, Wayne Howse, Oleg Gorbatyuk, Marina S Gorbatyuk; Neuronatin is a novel stress responsive protein of rod photoreceptors. Invest. Ophthalmol. Vis. Sci. 2016;57(12):584. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Neuronatin (NNAT) is a small transmembrane protein with α and β isoforms highly expressed in developing brain neurons and differentiated non-neuronal tissue. It regulates insulin signaling and glucose trafficking, and acts as a Ca2+ modulator. Although the role of NNAT in other tissues has been highlighted, no study regarding NNAT expression in the adult retina has been conducted so far. Therefore, the purpose of the study was to investigate whether NNAT was expressed in healthy and diseased adult retinas.
We used adult mammalian retinas of a wide spectrum. Cryostat retinal sections were obtained from various rod-dominant mammals including wild type (WT) rodents, transgenic rodents expressing mutant S334ter, P23H, or T17M rhodopsins, primates, and humans as well as cone-dominant tree shrews. In addition to immunohistochemical analysis, qRT-PCR and western blotting were used to detect NNAT. Isolation of primary rod photoreceptor cells was performed from the WT rat retinas.
The expression of NNAT in the WT retina was restricted to the outer segments (OS) of photoreceptors without evidence of staining in other retinal cell types across all mammalian species. Moreover, in tree shrew retinas, we found NNAT to be co-localized with rhodopsin protein indicating its expression in rods. The rod-derived expression of NNAT was further confirmed by qRT-PCR in a primary rod photoreceptor cell line. Subsequently, we demonstrated partial mislocalization of NNAT in transgenic retinas suggesting that stress in photoreceptors leads to NNAT accumulation in the outer nuclear layer (ONL) of the retina. In addition, stressed retinas demonstrated an increase in NNAT mRNA and protein levels as compared to WT. We found 2- and 3-fold increases in NNAT mRNA and protein respectively (P<0.0001 and P<0.001) in S334ter rhodopsin retinas.
Our study is the first to provide evidence that NNAT is predominantly expressed in rod photoreceptors in adult mammalian retinas indicating its potential structural role or function involved in cell signaling. Partial mislocalization of NNAT to the ONL and its over-expression associated with retinal degeneration alludes to NNAT being a stress responsive resident protein of rod photoreceptors.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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