A Feedback Loop between TGF-β1 and ATG5 Mediated by miR-122-5p Regulates Fibrosis and EMT in Human Trabecular Meshwork Cells

Abstract

Autophagy is a cell’s evolutionary conserved process for degrading and recycling cellular proteins and removing damaged organelles. There has been an increasing interest in identifying the basic cellular mechanism of autophagy and its implications in health and illness during the last decade. Many proteinopathies such as Alzheimer’s and Huntington’s disease are reported to be associated with impaired autophagy. The functional significance of autophagy in exfoliation syndrome/exfoliation glaucoma (XFS/XFG), remains unknown though it is presumed to be impaired autophagy to be responsible for the aggregopathy characteristic of this disease. In the current study we have shown that autophagy or ATG5 is enhanced in response to TGF-β1 in human trabecular meshwork (HTM) cells and TGF-β1 induced autophagy is necessary for increased expression of profibrotic proteins and epithelial to mesenchymal (EMT) through Smad3 that lead to aggregopathy. Inhibition of ATG5 by siRNA mediated knockdown reduced profibrotic and EMT markers and increased protein aggregates in the presence of TGF-β1 stimulation. The miR-122-5p, which was increased upon TGF exposure, was also reduced upon ATG5 inhibition. We thus conclude that TGF-β1 induces autophagy in primary HTM cells and a positive feedback loop exists between TGF-β1 and ATG5 that regulated TGF downstream effects mainly mediated by Smad3 signaling with miR-122-5p also playing a role.

The TGFβ Induced MicroRNAome of the Trabecular Meshwork

“…miR-122-5p was one of the highest upregulated miRNAs in response to TGFβ1 in the TM in our study. This response was also previously reported in the TM, and miR-122 was associated with the regulation of the TGFβ/Smad pathway [ 71 ]. Within the TGFβ signalling pathway, miR-122-5p has predicted target interactions with TGFβR1, TGFβR2, LTBP1, and SMAD2.…”

The TGFβ Induced MicroRNAome of the Trabecular Meshwork

“…Increased levels of TGFβ in the anterior segment of the eye induce fibrotic changes in the TM in glaucoma (POAG and XFG) including altered turnover of extracellular matrix (ECM) components, formation of cross-linked actin networks (CLANS), upregulation of alpha-smooth muscle actin (αSMA), aberrant formation of actin stress fibres and epithelial to mesenchymal transition (EMT) (Keller et miR-122-5p was one of the highest upregulated miRNAs in response to TGFβ1 in the TM in our study. This response was also previously reported in the TM and miR-122 was associated with the regulation of the TGFβ/Smad pathway [75]. Within the TGFβ signalling pathway, miR-122-5p has predicted target interactions with TGFβR1, TGFβR2, LTBP1 and SMAD2.…”