TGF-β promotes pericyte-myofibroblast transition in subretinal fibrosis through the Smad2/3 and Akt/mTOR pathways

Subretinal fibrosis remains a major obstacle to the management of neovascular age-related macular degeneration. Choroidal pericytes were found to be a significant source of subretinal fibrosis, but the underlying mechanisms of pericyte-myofibroblast transition (PMT) remain largely unknown. The goal of this study was to explore the role and potential mechanisms by which PMT contributes to subretinal fibrosis. Choroidal neovascularization (CNV) was induced by laser photocoagulation in transgenic mice with the collagen1 alpha 1-green fluorescent protein (Col1 alpha 1-GFP) reporter, and recombinant adeno-associated virus 2 (rAAV2)-mediated TGF-beta 2 (rAAV2-TGF-beta 2) was administered intravitreally to further induce PMT. Primary mouse choroidal GFP-positive pericytes were treated with TGF-beta 2 in combination with siRNAs targeting Smad2/3, the Akt inhibitor MK2206 or the mTOR inhibitor rapamycin to examine cell proliferation, migration, and differentiation into myofibroblasts. The involvement of the Akt/mTOR pathway in PMT in subretinal fibrosis was further investigated in vivo. Intraocular TGF-beta 2 overexpression induced GFP-positive pericyte infiltration and PMT in subretinal fibrosis, which was mimicked in vitro. Knockdown of Smad2/3 or inhibition of Akt/mTOR decreased cell proliferation, PMT and migration in primary mouse pericytes. Combined inhibition of Smad2/3 and mTOR showed synergistic effects on attenuating alpha-smooth muscle actin (alpha-SMA) expression and cell proliferation. In mice with laser-induced CNV, the administration of the Akt/mTOR inhibitors suppressed pericyte proliferation and alleviated the severity of subretinal fibrosis. Our results showed that PMT plays a pivotal role in subretinal fibrosis, which was induced by TGF-beta 2 through the Smad2/3 and Akt/mTOR pathways. Thus, inhibiting PMT may be a novel strategy for the treatment of subretinal fibrosis. Eye disease: Revealing the mechanisms behind subretinal fibrosis The identification of a new cell type that plays a crucial role in causing fibrosis under the retina could improve treatment of eye disease. Effective treatments exist for diseases that cause impairment and loss of vision in elderly people, but success can be limited by the development of subretinal fibrosis. Jingfa Zhang at Shanghai Jiao Tong University, China, and co-workers used mice with laser-induced retinal damage to explore how subretinal fibrosis may result from transition of pericytes, multi-functional cells in the capillaries, into myofibroblasts, cells associated with fibrosis. The overexpression of a growth factor called TGF-beta 2 induced pericytes to infiltrate the subretinal area and pericyte-myofibroblast transition via two signalling pathways. Inhibiting these pathways may help to treat subretinal fibrosis, and one option is the use of inhibitors of AKT/mTOR which may slow the ageing process.

Automated summary

The transition of choroidal pericytes into myofibroblasts plays a crucial role in subretinal fibrosis. Inhibiting the Smad2/3 and Akt/mTOR pathways can reduce cell proliferation, transition, and migration, thereby alleviating the severity of fibrosis.