Center for Cancer, Genetic Diseases and Gene Regulation, Department of Biological Sciences, Fordham University, Bronx, NY 10458, USA.
Int J Mol Sci. 2022 Aug 22;23(16):9466. doi: 10.3390/ijms23169466.
In all mammalian species tested to date, rod photoreceptor outer segment renewal is a circadian process synchronized by light with a burst of outer segment fragment (POS) shedding and POS phagocytosis by the adjacent retinal pigment epithelium (RPE) every morning at light onset. Recent reports show that RPE phagocytosis also increases shortly after dark onset in C57BL/6 (C57) mice. Genetic differences between C57 mice and 129T2/SvEmsJ (129) mice may affect regulation of outer segment renewal. Here, we used quantitative methods to directly compare outer segment renewal in C57 and 129 mouse retina. Quantification of rhodopsin-positive phagosomes in the RPE showed that in 129 mice, rod POS phagocytosis after light onset was significantly increased compared to C57 mice, but that 129 mice did not show a second peak after dark onset. Cone POS phagosome content of RPE cells did not differ by mouse strain with higher phagosome numbers after light than after dark. We further quantified externalization of the "eat me" signal phosphatidylserine by outer segment tips, which precedes POS phagocytosis. Live imaging of retina ex vivo showed that rod outer segments extended PS exposure in both strains but that frequency of outer segments with exposed PS after light onset was lower in C57 than in 129 retina. Taken together, 129 mice lacked a burst of rod outer segment renewal after dark onset. The increases in rod outer segment renewal after light and after dark onset in C57 mice were attenuated compared to the peak after light onset in 129 mice, suggesting an impairment in rhythmicity in C57 mice.
在迄今为止测试的所有哺乳动物物种中，杆状光感受器外节的更新是一个昼夜节律过程，通过光与外节碎片（POS）的爆发性脱落以及相邻视网膜色素上皮（RPE）的 POS 吞噬作用同步，每天早晨在光照开始时发生。最近的报告显示，在 C57BL/6（C57）小鼠中，暗期开始后不久，RPE 吞噬作用也会增加。C57 小鼠和 129T2/SvEmsJ（129）小鼠之间的遗传差异可能会影响外节更新的调节。在这里，我们使用定量方法直接比较 C57 和 129 小鼠视网膜的外节更新。RPE 中视紫红质阳性吞噬体的定量显示，与 C57 小鼠相比，129 小鼠在光照后杆状 POS 吞噬作用显著增加，但 129 小鼠在暗期开始后没有出现第二个峰值。RPE 细胞中的锥体 POS 吞噬体含量不因小鼠品系而异，光照后吞噬体数量高于暗期。我们进一步定量了外节尖端“吃我”信号磷脂酰丝氨酸的外化，这先于 POS 吞噬作用。体外视网膜的实时成像显示，杆状外节延伸了 PS 暴露，但在 C57 视网膜中，光照后外节 PS 暴露的频率低于 129 视网膜。总之，129 小鼠在暗期开始后没有杆状外节更新的爆发。与 129 小鼠光照后峰值相比，C57 小鼠光照后和暗期开始后的杆状外节更新增加幅度降低，表明 C57 小鼠的节律性受损。
