Sigma 1 Receptor (Sig1R) regulates retinal ER & Oxidative (OX) Stress

Abstract

Purpose : Sig1R is a unique transmembrane protein whose biological role is uncertain. We reported recently that activation of Sig1R affords profound rescue of cone photoreceptor (PRC) function in Pde6b^rd10 (rd10) mice (Wang et al, PNAS, 2016). rd10 mice show peak rod loss at P25 and cone loss at P35. Interestingly, although Sig1R^-/- mice have mild, late-onset ganglion cell loss and no PRC loss (Ha et al, 2011), rd10 mice lacking Sig1R (rd10/Sig1R^-/-) have markedly accelerated cone dysfunction at P25 with only ~3 rows of PRC nuclei v. 6-7 in rd10 mice (Smith et al, ARVO, 2016). We hypothesized that elevated ER and OX stress contribute significantly to the accelerated retinal dysfunction in rd10/Sig1R^-/- mice.

Methods : Neural retinas isolated from P21 rd10/Sig1R^-/-, rd10, WT mice were used for qRT-PCR (n=4/group) and western blotting (n=11-16/group) to assess ER stress (Ire1α, Xbp1, Atf4, Chop, Bip, Perk, Atf6) and OX stress (Nrf2, Keap1, Sod1, Cat, Nqo1, Hmox1) genes/proteins. Since microRNAs can regulate multiple components of ER and OX stress pathways in response to changes in cellular environment, we quantified retinal miRNA levels using miScript miRNA PCR array (n=3/group). Data were analyzed by ANOVA.

Results : ER stress: at P21 there were few differences between rd10 and WT mice (except for CHOP). However, a significant increase in ER stress was detected in rd10/Sig1R^-/- mice, notably in gene/protein levels of CHOP (6 fold), BIP (6 fold) & XBP1 (12 fold), and 1-2 fold increases in PERK & ATF4. OX stress: there were ~1 fold increases in NRF2, NQO1, HMOX1 in rd10 v. WT mice, but more significant increases in these proteins & the encoding genes in rd10/Sig1R^-/- retinas including NRF2 (3.5±0.5 fold), NQO1 (4.4±0.3 fold), HMOX1 (8.47±1.3 fold). Consistent with these findings, were significant increases in 12 miRNAs in rd10/Sig1R^-/- v. rd10, most notably miR-199a-5p (3.5 fold), miR-214-3p (5.1 fold), and miR-155-5P (2.6 fold).

Conclusions : Absence of Sig1R in the rd10 model of retinal degeneration is accompanied by increased ER and OX stress, which may account for accelerated PRC loss and cone dysfunction. Sig1R represents a novel, promising therapeutic target for retinopathy and, while its biological role is not certain, our data provide strong evidence for Sig1R in modulating retinal homeostasis.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.