Klotho prevents transforming growth factor-β2-induced senescent-like morphological changes in the retinal pigment epithelium

Abstract

Degenerative changes of the retinal pigment epithelium (RPE) triggered by transforming growth factor-β2 (TGF-β2) and oxidative stress play a critical role in the progression of age-related macular degeneration (AMD). The expression of α-klotho, an antiaging protein, declines with age, increasing the risk factors for age-related diseases. Here, we investigated the protective effects of soluble α-klotho on TGF-β2-induced RPE degeneration. The morphological changes induced by TGF-β2, including epithelial-mesenchymal transition (EMT), were attenuated in the mouse RPE by the intravitreal injection (IVT) of α-klotho. In ARPE19 cells, EMT and morphological alterations by TGF-β2 were attenuated by co-incubation with α-klotho. TGF-β2 decreased miR-200a accompanied by zinc finger e-box binding homeobox1 (ZEB1) upregulation and EMT, all of which were prevented by α-klotho co-treatment. Inhibitor of miR-200a mimicked TGF-β2-induced morphological changes, which were recovered by ZEP1 silencing, but not by α-klotho, implying the upstream regulation of α-klotho on miR-200a-ZEP1-EMT axis. α-Klotho inhibited receptor binding of TGF-β2, Smad2/3 phosphorylation, extracellular signal-regulated protein kinase 1/2 (ERK1/2)-a mechanistic target of rapamycin (mTOR) activation and oxidative stress via NADPH oxidase 4 (NOX4) upregulation. Furthermore, α-klotho recovered the TGF-β2-induced mitochondrial activation and superoxide generation. Interestingly, TGF-β2 upregulated α-klotho expression in the RPE cells, and genetic suppression of endogenous α-klotho aggravated TGF-β2-induced oxidative stress and EMT. Lastly, α-klotho abrogated senescence-associated signaling molecules and phenotypes induced by long-term incubation with TGF-β2. Hence, our findings indicate that the antiaging α-klotho plays a protective role against EMT and degeneration of the RPE, demonstrating the therapeutic potential for age-related retinal diseases, including the dry type of AMD.

Absence of the Klotho Function Causes Cornea Degeneration with Specific Features Resembling Fuchs Endothelial Corneal Dystrophy and Bullous Keratopathy

“…Although the pathogenesis due to the Klotho null mutation has been extensively investigated in many organs, the effects on the ocular system remain largely unknown. Only a few reports on the retina [ 27 , 28 , 29 ], optic nerve [ 30 ], and lens [ 18 ], in relation to the Klotho null mutation, have been published, with the underlying pathogenesis mechanisms only specified in a limited manner. Adding to the previously published information, we show that the Klotho null mutation leads to lacrimal gland degeneration with characteristics of histopathological changes, altered neurosecretion, and reduced tear volume [ 31 ].…”

The Research Progress in Transforming Growth Factor-β2

“…Human retinal pigment epithelial cell and human lens epithelial cells (10 ng/mL or 12.5 ng/mL TGF-β2) [81,82] Promote autophagy and EMT (Autophagy plays an important role in fibrotic cataracts)…”

“…Nintedanib, a tyrosine kinase inhibitor that has anti-inflammation and anti-fibrosis effects, prevents TGF-β2-driven EMT in retinal pigment epithelium cells and may serve as a potential drug for the treatment of proliferative vitreoretinopathies [80]. Similarly, alpha-Klotho, an anti-ageing protein that diminishes with age, reversed EMT and senescence-like morphological alterations triggered by TGF-β2 in retinal pigment epithelium cells [81]. In addition, TGF-β2 has also been shown to be involved in agerelated cataracts by promoting EMT and cell proliferation and inhibiting apoptosis in lens epithelial cells (LECs) [82].…”