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Mutant ubiquitin UBB+1 is observed in a variety of aging-related neurodegenerative diseases and acts as a potent inhibitor of the ubiquitin proteasome system (UPS). In the present study, we investigated the relationship between impaired UPS (using ectopic expression of UBB+1) and mitochondrial dynamics in astrocytes, which are the most abundant glial cells in the central nervous system. Immunocytochemistry and fluorescence recovery after photobleaching revealed that ectopic expression of UBB+1 induced mitochondrial elongation. We further demonstrated that overexpression of UBB+1 destabilized mitochondrial fission-specific proteins including Drp1, Fis1, and OPA3, but not the mitochondrial fusion-specific proteins Mfn1, Mfn2, and OPA1. The reduction in mitochondrial fission-specific proteins by UBB+1 was prevented by inhibiting the 26 S proteasome using chemical inhibitors, including MG132, lactacystin and epoxomicin. We then assessed the involvement of proteases that target mitochondrial proteins by using various protease inhibitors. Finally, we confirmed that either overexpression of UBB+1 or inhibiting the proteasome can protect astrocytic cells from H2O2-induced cell death compared with control cells. Our results suggest that UBB+1 destabilizes mitochondrial fission-specific proteins, leading to mitochondrial fusion and the subsequent resistance to oxidative stress. We therefore propose a protective role of UBB+1 overexpression or the proteasome inhibition in astrocytes in degenerative brains. [ABSTRACT FROM AUTHOR]

Transforming growth factor-β signaling is known to be a key signaling pathway in the induction of epithelial–mesenchymal transition. However, the mechanism of TGF-β signaling in the modulation of EMT remains unclear. In this study, we found that TGF-β treatment resulted in elongation of mitochondria accompanied by induction of N-cadherin, vimentin, and F-actin in retinal pigment epithelial cells. Moreover, OPA3, which plays a crucial role in mitochondrial dynamics, was downregulated following TGF-β treatment. Suppression of TGF-β signaling using Smad2 siRNA prevented loss of OPA3 induced by TGF-β. Knockdown of OPA3 by siRNA and inducible shRNA significantly increased stress fiber levels, cell length, cell migration and mitochondrial elongation. In contrast, forced expression of OPA3 in ARPE-19 cells inhibited F-actin rearrangement and induced mitochondrial fragmentation. We also showed that Drp1 depletion increased cell length and induced rearrangement of F-actin. Depletion of Mfn1 blocked the increase in cell length during TGF-β-mediated EMT. These results collectively substantiate the involvement of mitochondrial dynamics in TGF-β-induced EMT. [ABSTRACT FROM AUTHOR]