He Feng, Agosto Melina A, Anastassov Ivan A, Tse Dennis Y, Wu Samuel M, Wensel Theodore G
Verna and Marrs McLean Department of Biochemistry and Molecular Biology , Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
Department of Ophthalmology, Baylor College of Medicine, One Baylor Plaza, Houston, TX, 77030, USA.
Sci Rep. 2016 Jun 1;6:26978. doi: 10.1038/srep26978.
Phosphoinositides play important roles in numerous intracellular membrane pathways. Little is known about the regulation or function of these lipids in rod photoreceptor cells, which have highly active membrane dynamics. Using new assays with femtomole sensitivity, we determined that whereas levels of phosphatidylinositol-3,4-bisphosphate and phosphatidylinositol-3,4,5-trisphosphate were below detection limits, phosphatidylinositol-3-phosphate (PI(3)P) levels in rod inner/outer segments increased more than 30-fold after light exposure. This increase was blocked in a rod-specific knockout of the PI-3 kinase Vps34, resulting in failure of endosomal and autophagy-related membranes to fuse with lysosomes, and accumulation of abnormal membrane structures. At early ages, rods displayed normal morphology, rhodopsin trafficking, and light responses, but underwent progressive neurodegeneration with eventual loss of both rods and cones by twelve weeks. The degeneration is considerably faster than in rod knockouts of autophagy genes, indicating defects in endosome recycling or other PI(3)P-dependent membrane trafficking pathways are also essential for rod survival.
磷酸肌醇在众多细胞内膜途径中发挥重要作用。对于这些脂质在具有高度活跃膜动力学的视杆光感受器细胞中的调节或功能，我们了解甚少。通过使用具有飞摩尔灵敏度的新检测方法，我们确定，虽然磷脂酰肌醇 - 3,4 - 二磷酸和磷脂酰肌醇 - 3,4,5 - 三磷酸的水平低于检测限，但光照后视杆内/外段中的磷脂酰肌醇 - 3 - 磷酸（PI(3)P）水平增加了30多倍。这种增加在PI - 3激酶Vps34的视杆特异性敲除中被阻断，导致内体和自噬相关膜无法与溶酶体融合，并积累异常膜结构。在早期，视杆显示出正常的形态、视紫红质运输和光反应，但在十二周时经历渐进性神经退行性变，最终视杆和视锥细胞均丧失。这种退行性变比自噬基因视杆敲除中的情况快得多，表明内体再循环或其他PI(3)P依赖性膜运输途径中的缺陷对视杆存活也至关重要。
