mTOR Inhibitors Modulate the Biological Nature of TGF-β2-Treated or -Untreated Human Trabecular Meshwork Cells in Different Manners

Background/Objectives: Mammalian target of rapamycin (mTOR) inhibition may have been suggested to have a beneficial effect on the glaucomatous human trabecular meshwork (HTM). To study the effects of the mTOR inhibitors rapamycin (Rapa) and Torin1 on the glaucomatous HTM, transforming growth factor-beta 2 (TGF-beta 2)-treated two-dimensionally (2D) and three-dimensionally (3D) cultured HTM cells were used. Methods: We evaluated (1) the levels of autophagy via Western blot analysis using a specific antibody against microtubule-associated protein 1 light chain 3 (LC3), (2) barrier capacity based on transepithelial electrical resistance (TEER) and fluorescein isothiocyanate (FITC) permeability (2D), (3) cellular metabolic functions (2D), (4) the size and stiffness of spheroids, and (5) the mRNA expression of ECM proteins. Results: TGF-beta 2-induced inhibition of autophagy was significantly inhibited by Rapa and Torin1. Rapa and Torin1 substantially decreased barrier capacity in both TGF-beta 2-untreated and TGF-beta 2-treated HTM cells. Cellular metabolic analysis indicated that Rapa, but not Torin1, substantially enhanced both mitochondrial and glycolytic functions of TGF-beta 2-untreated HTM cells. In the physical properties of spheroids, TGF-beta 2 resulted in the formation of down-sized and stiffened spheroids. mTOR inhibitors decreased the size but not the stiffness of TGF-beta 2-untreated spheroids and significantly reduced the TGF-beta 2-related increase in the stiffness but not the size of spheroids. The diverse effects of mTOR inhibitors on TGF-beta 2-untreated and TGF-beta 2-treated spheroids were also observed in the mRNA expression of extracellular matrix proteins. Conclusions: The results taken together suggest that mTOR inhibitors significantly influence the biological aspects of both a single layer and multiple layers of the TGF-beta 2-treated HTM and untreated HTM.