αB-Crystallin Regulates Subretinal Fibrosis by Modulation of Epithelial-Mesenchymal Transition

Abstract

Subretinal fibrosis is an end stage of neovascular age-related macular degeneration, characterized by fibrous membrane formation after choroidal neovascularization. An initial step of the pathogenesis is an epithelial-mesenchymal transition (EMT) of retinal pigment epithelium cells. aB-crystallin plays multiple roles in age-related macular degeneration, including cytoprotection and angiogenesis. However, the role of aB-crystallin in subretinal EMT and fibrosis is unknown. Herein, we showed attenuation of subretinal fibrosis after regression of laser-induced choroidal neovascularization and a decrease in mesenchymal retinal pigment epithelium cells in aB-crystallin knockout mice compared with wild-type mice. aB-crystallin was prominently expressed in subretinal fibrotic lesions in mice. In vitro, overexpression of aB-crystallin induced EMT, whereas suppression of aB-crystallin induced a mesenchymal-epithelial transition. Transforming growth factor-b2einduced EMT was further enhanced by overexpression of aB-crystallin but was inhibited by suppression of aB-crystallin. Silencing of aB-crystallin inhibited multiple fibrotic processes, including cell proliferation, migration, and fibronectin production. Bone morphogenetic protein 4 upregulated aB-crystallin, and its EMT induction was inhibited by knockdown of aB-crystallin. Furthermore, inhibition of aB-crystallin enhanced monotetraubiquitination of SMAD4, which can impair its nuclear localization. Overexpression of aB-crystallin enhanced nuclear translocation and accumulation of SMAD4 and SMAD5. Thus, aB-crystallin is an important regulator of EMT, acting as a molecular chaperone for SMAD4 and as its potential therapeutic target for preventing subretinal fibrosis development in neovascular age-related macular degeneration. (Am J Pathol 2016, 186: 859e873; http:// dx

SWATH-MS Proteomic Analysis of Oxygen-Induced Retinopathy Reveals Novel Potential Therapeutic Targets

“…Furthermore, the dysregulation of the cross talk between vasculature and retinal neuroglia and neuronal cells has been shown to contribute to the pathogenesis of DR. [23][24][25] During the hypoxic phase, the most upregulated proteins were crystallins, which are small heat shock proteins that act as molecular chaperones by binding misfolded proteins to prevent their denaturation and aggregation. 26,27 They protect cells from hypoxia and maintain mitochondrial integrity. 26,28 In addition to their neuroprotective role, crystallins also have other roles in vascular biology.…”

“…28,[32][33][34] Their expression is dramatically upregulated in numerous retinal diseases, such as mechanical injury, ischemic insults, age-related macular degeneration (AMD), uveoretinitis, and DR. 28 Concerning the potential therapeutic value of crystallins in retinal diseases, their exact functions are emerging. 27,35 Namely, the recently discovered roles for aBcrystallin in mediating TGF-b induced epithelial-mesenchymal transformation (EMT) and subretinal fibrosis in AMD, 27 while aA-crystallin providing neuroprotection for retina in DR, 35 point out the opposite therapeutic values for these crystallinfamily members. 27,36 A large number of proteins was also downregulated in response to hypoxia in retina.…”

“…27,35 Namely, the recently discovered roles for aBcrystallin in mediating TGF-b induced epithelial-mesenchymal transformation (EMT) and subretinal fibrosis in AMD, 27 while aA-crystallin providing neuroprotection for retina in DR, 35 point out the opposite therapeutic values for these crystallinfamily members. 27,36 A large number of proteins was also downregulated in response to hypoxia in retina. Among these proteins were Cnga1, Gucy2e, Rom1, and Grk1, proteins associated with phototransduction.…”

“…69 This inflammation-TGF-b circuit in vasculature also promotes fibrosis in the surrounding tissue, and it is largely irreversible. 68,69 The recently identified association between TGF-b signaling and ab-crystallin in the EMT and subretinal scarring, 27 the massive induction of crystallins by hypoxia and the subsequent activation of TGF-b/Mkl2-signaling pathways in OIR provide clues about the potential interplay that leads to retinal fibrosis in the human neovascular diseases of retina.…”

Potential Role of Myeloid-Derived Suppressor Cells (MDSCs) in Age-Related Macular Degeneration (AMD)

“…Choroidal neovascularization does not only cause rapid vision loss due to bleeding and swelling at the retina, but it also results in subretinal fibrosis that can develop despite the anti-VEGF therapy that prevents the neovessel formation (137). Conversely, epithelial-mesenchymal transition (EMT) can also cause resistance to anti-VEGF drugs, as suggested by studies on pancreatic cancer cells (138).…”