Steroids and photoreceptor survival in two models of retinal degeneration.

MARQUIONI RAMELLA, MD; TATE PS; MARAZITA, MC; SUBURO, AM

Vancouver

Congreso; Association for Research in Vision and Ophthalmology (ARVO) Annual Meeting; 2019

ARVO

Visual loss in degenerating retinal diseases usually implies photoreceptor loss. Current evidence shows that glucocorticoids and progestogens enhance photoreceptor survival. By contrast, we have previously demonstrated that mifepristone (M), a glucocorticoid and progesterone receptor blocker, rapidly induces photoreceptor death in male mice. With the aim of understanding steroid-dependent mechanisms involved in photoreceptor survival, we have compared the effect of dexamethasone (D) and progesterone (P) in light- and M-induced retinal degeneration models. Glucocorticoid effects on the M-induced degeneration have been previously reported. Male balb/c mice (5-7 weeks) were reared under cyclic illumination (12 hs light-12 hs dark, ≤ 60 lux). For M-induced damage, mice received a single 10 mg/kg M injection, whereas for light damage, mice were exposed to 1500 lux during 48 h. Steroid treated animals received 4 mg/kg/day D or 1-4 mg/kg/day P during the exposure period. Control mice were given 0.9% NaCl. Animals were euthanized at the 48 h end-point and retinal extracts were prepared for Western blot (WB) or histochemical determination of cell death and survival markers. Some animals were euthanized in day 7 days and their eyes sectioned to measure the thickness of the outer nuclear layer (ONL).Activated caspase 3 (CASP3) immunohistochemistry and TUNEL showed that signs of cell death were restricted to the ONL. Day 7 histological sections showed only 43% and 35% photoreceptor nuclei survived M or 1500 lux, respectively. However, 4 mg/kg D or P preserved >90% photoreceptor nuclei in both models. WBs showed similar changes of cell death and survival markers in both models. CASP3 disappeared when mice were treated with D or P, whereas phosphorylated histone H2AX (p-H2AX) was greatly reduced. BCL-XL, BAX and BID responded similarly to each steroid in both degenerating models. By contrast, BCL2 disappeared in treated M-mice but increased above control levels in treated light-exposed mice. Most important, the steroid survival responses could be correlated with D- and P- effects on BCL-XL, BAX and BID levels in undamaged animals. In addition, the latter mice showed significant rhodopsin increases after D and P treatment. Results show that M and excessive light killed a similar proportion of photoreceptors. Similarly, both P and D were efficient photoreceptor protectors in both models. In addition, the effect of these steroids on cell death regulators, together with the photoreceptor attrition triggered by the inhibition of glucocorticoid and progesterone receptors strongly suggest that these hormones are essential for the survival of photoreceptors even under standard illumination conditions.