The retina is one of the most metabolically active tissues, yet the processes that control retinal metabolism remains poorly understood. The mTOR complex (mTORC) that drives protein and lipid biogenesis and autophagy has been studied extensively in regards to retinal development and responses to optic nerve injury but the processes that regulate homeostasis in the adult retina have not been determined. We previously demonstrated that normal adult retina has high rates of protein synthesis compared to skeletal muscle, associated with high levels of mechanistic target of rapamycin (mTOR), a kinase that forms multi-subunit complexes that sense and integrate diverse environmental cues to control cell and tissue physiology. This study was undertaken to: 1) quantify expression of mTOR complex 1 (mTORC1)- and mTORC2-specific partner proteins in normal adult rat retina, brain and liver; and 2) to localize these components in normal human, rat, and mouse retinas. Immunoblotting and immunoprecipitation studies revealed greater expression of raptor (exclusive to mTORC1) and rictor (exclusive for mTORC2) in normal rat retina relative to liver or brain, as well as the activating mTORC components, pSIN1 and pPRAS40. By contrast, liver exhibits greater amounts of the mTORC inhibitor, DEPTOR. Immunolocalization studies for all three species showed that mTOR, raptor, and rictor, as well as most other known components of mTORC1 and mTORC2, were primarily localized in the inner retina with mTORC1 primarily in retinal ganglion cells (RGCs) and mTORC2 primarily in glial cells. In addition, phosphorylated ribosomal protein S6, a direct target of the mTORC1 substrate ribosomal protein S6 kinase beta-1 (S6K1), was readily detectable in RGCs, indicating active mTORC1 signaling, and was preserved in human donor eyes. Collectively, this study demonstrates that the inner retina expresses high levels of mTORC1 and mTORC2 and possesses active mTORC1 signaling that may provide cell- and tissue-specific regulation of homeostatic activity. These findings help to define the physiology of the inner retina, which is key for understanding the pathophysiology of optic neuropathies, glaucoma and diabetic retinopathy.

视网膜是代谢最活跃的组织之一，但控制视网膜代谢的过程仍然知之甚少。驱动蛋白质和脂质生物发生和自噬的 mTOR 复合物 (mTORC) 已在视网膜发育和对视神经损伤的反应方面进行了广泛研究，但尚未确定调节成人视网膜内稳态的过程。我们之前已经证明，与骨骼肌相比，正常成人视网膜的蛋白质合成率较高，这与雷帕霉素 (mTOR) 的高水平机械靶点有关，mTOR 是一种形成多亚基复合物的激酶，可感知和整合各种环境线索以控制细胞和组织生理学。这项研究是为了：1) 量化正常成年大鼠视网膜、大脑和肝脏中 mTOR 复合物 1 (mTORC1) 和 mTORC2 特异性伴侣蛋白的表达；2) 在正常人、大鼠和小鼠视网膜中定位这些成分。免疫印迹和免疫沉淀研究显示，相对于肝脏或大脑，正常大鼠视网膜中 raptor（mTORC1 独有）和 rictor（mTORC2 独有）以及激活的 mTORC 成分 pSIN1 和 pPRAS40 的表达更高。相比之下，肝脏表现出更多的 mTORC 抑制剂 DEPTOR。所有三个物种的免疫定位研究表明，mTOR、raptor 和 rictor，以及 mTORC1 和 mTORC2 的大多数其他已知成分，主要位于视网膜内层，mTORC1 主要位于视网膜神经节细胞 (RGC) 中，mTORC2 主要位于神经胶质细胞中. 此外，磷酸化核糖体蛋白 S6 是 mTORC1 底物核糖体蛋白 S6 激酶 beta-1 (S6K1) 的直接靶标，在 RGC 中很容易检测到，表明 mTORC1 信号传导活跃，并保存在人类供体眼中。总的来说，这项研究表明内部视网膜表达高水平的 mTORC1 和 mTORC2 并具有活跃的 mTORC1 信号传导，可以提供细胞和组织特异性调节稳态活动。这些发现有助于确定内部视网膜的生理学，这是了解视神经病变、青光眼和糖尿病性视网膜病变的病理生理学的关键。这项研究表明，内部视网膜表达高水平的 mTORC1 和 mTORC2 并具有活跃的 mTORC1 信号传导，可以提供细胞和组织特异性调节稳态活动。这些发现有助于确定内部视网膜的生理学，这是了解视神经病变、青光眼和糖尿病性视网膜病变的病理生理学的关键。这项研究表明，内部视网膜表达高水平的 mTORC1 和 mTORC2 并具有活跃的 mTORC1 信号传导，可以提供细胞和组织特异性调节稳态活动。这些发现有助于确定内部视网膜的生理学，这是了解视神经病变、青光眼和糖尿病性视网膜病变的病理生理学的关键。