Endoplasmic reticulum stress associated retinal photoreceptor cell death in the transgenic mutant rhodopsin S334ter-3 rats

Retinitis pigmentosa (RP) is associated with the expression of a mutant photoreceptor-specific protein. We hypothesized that missorted mutant rhodopsin induces an evolutionarily conserved compensatory mechanism known as the unfolded protein response (UPR). Although, the endoplasmic reticulum (ER) stress is a protective cellular response against stresses, chronic ER stress activates a UPR-dependent death pathway that results in retinal degeneration. The purpose of this study was to determine whether ER stress is one of the causes for photoreceptor cell death. Here, we used retinal 661W cells and transgenic mutant rhodopsin S334ter-3 and S334ter-4 rats. The ER stressors such as homocysteine and calcimycin activated the UPR-specific proteins, ATF4, Bip, CHOP, and procaspase-12; caused overproduction of ROS; and induced cell death in cultured retinal 661W cells. Similarly, retinas of transgenic S334ter-3 but not S334ter-4 rats revealed the activation of UPR-specific proteins Bip, ATF4, CHOP, calnexin, and procaspase-12. Retinal slices of S334ter-3 rats at postnatal day 5 exhibited overproduction of ROS and dead cells in the photoreceptor cell layer. Thus, the activated apoptotic UPR in retinal photoreceptor cells of transgenic mutant rhodopsin S334ter-3 rats suggested that UPR might play a role in retinal photoreceptor cell death in S334ter-3 rats.