Center for Cancer, Genetic Diseases and Gene Regulation, Department of Biological Sciences, Fordham University, Bronx, New York, United States.
Invest Ophthalmol Vis Sci. 2021 Feb 1;62(2):7. doi: 10.1167/iovs.62.2.7.
Galectin-3 (gal-3) is a soluble glycoprotein that has been associated with diverse forms of phagocytosis, including some mediated by the engulfment receptor MerTK. Retinal pigment epithelium (RPE) in vivo uses MerTK (or the related Tyro3) for phagocytosis of shed outer segment fragments during diurnal outer segment renewal. Here, we test if gal-3 plays a role in outer segment renewal in mice and if exogenous gal-3 can promote MerTK-dependent engulfment of isolated outer segment fragments by primary RPE cells in culture.
We explored age- and strain-matched wild-type (wt), lgals3-/- and mertk-/- mice. Immunofluorescence and immunoblotting characterized gal-3 and RPE/retina protein expression, respectively. Outer segment renewal was investigated by live imaging of phosphatidylserine (PS) exposure on photoreceptor outer segment distal tips and by microscopy of rhodopsin-labeled RPE phagosomes in tissue sections. Retinal function was assessed by recording electroretinograms (ERGs). Phagocytosis assays feeding purified outer segment fragments (POS) were conducted with added recombinant proteins testing unpassaged primary mouse RPE.
Gal-3 localizes to neural retina and RPE in wt mice. The lgals3-/- photoreceptor outer segments display normal diurnal PS exposure at distal tips. The number of rhodopsin-positive phagosomes in wt and lgals3-/- RPE does not differ at peak or trough of diurnal phagocytosis activity. lgals3-/- mice show light responses like wt, and their eyes contain wt levels of retinal and RPE proteins. Unlike purified protein S, recombinant gal-3 fails to promote POS engulfment by mouse primary RPE in culture.
Gal-3 has no essential role in MerTK-dependent outer segment renewal in mice.
半乳糖凝集素-3（gal-3）是一种可溶性糖蛋白，与多种形式的吞噬作用有关，包括一些由吞噬受体 MerTK 介导的吞噬作用。体内的视网膜色素上皮（RPE）在白天的外节更新过程中使用 MerTK（或相关的 Tyro3）吞噬脱落的外节片段。在这里，我们测试 gal-3 是否在外节更新中发挥作用，以及外源性 gal-3 是否可以促进原代 RPE 细胞在培养中对分离的外节片段进行 MerTK 依赖性吞噬。
我们研究了年龄和品系匹配的野生型（wt）、lgals3-/-和 mertk-/-小鼠。免疫荧光和免疫印迹分别用于鉴定 gal-3 和 RPE/视网膜蛋白的表达。通过对感光器外节远端尖端上的磷脂酰丝氨酸（PS）暴露进行活体成像，以及通过组织切片中视紫红质标记的 RPE 吞噬体的显微镜观察，研究外节更新。通过记录视网膜电图（ERGs）评估视网膜功能。进行吞噬试验，用添加重组蛋白的纯化外节片段（POS）喂养，检测未传代的原代小鼠 RPE。
Gal-3 在 wt 小鼠的神经视网膜和 RPE 中定位。lgals3-/- 感光器外节在远端尖端显示正常的昼夜 PS 暴露。在 wt 和 lgals3-/- RPE 的峰值或低谷时，视紫红质阳性吞噬体的数量没有差异。lgals3-/- 小鼠的光反应与 wt 相似，并且它们的眼睛含有 wt 水平的视网膜和 RPE 蛋白。与纯化蛋白 S 不同，重组 gal-3 不能促进原代培养的小鼠 RPE 对 POS 的吞噬作用。
Gal-3 在 MerTK 依赖性外节更新中对小鼠没有必需作用。
