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G. Mohammad, Jr., R. Kowluru; Mitochondrial Dysfunction and Diabetic Retinopathy: Role of Matrix Metalloproteinase-2. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5643.
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Hyperglycemia activates matrix metalloproteinase-2 (MMP-2) in the retina and its capillary cells. We have shown that in the pathogenesis of diabetic retinopathy, MMP-2 acts as pro-apoptotic in the retina and induces mitochondrial dysfunction. However, the mechanism by which MMP2 activation leads mitochondrial dysfunction is not clear. Heat shock protein 60 (HSP60), a nuclear-encoded protein, is considered as a major mitochondrial molecular chaperone, and helps maintain mitochondrial integrity. The present study is designed to elucidate the mechanism by which MMP2 contributes to mitochondrial dysfunction.
Bovine retinal endothelial cells from 4th passage were transfected with MMP2 siRNA, and incubated in 5mm glucose or 20mm glucose for 4 days. The cells without any transfection, incubated in 5mM or 20mM glucose for 4 days, served as controls. At the end of the incubation, mitochondria were prepared by differential centrifugation. The protein expression of MMP-2 was quantified in the mitochondria by western blot, and 8-OHdG levels (a marker of oxidative stress) and membrane potential were quantified by immunofluorescence techniques. Mitochondrial integrity was evaluated by quantifying the protein expressions of HSP60, Bcl-XL, and Bax.
High glucose exposure of retinal endothelial cells elevated the mitochondrial expression of MMP2 and 8-OHdG, and the membrane permeability of mitochondria was increased. The expressions of HSP60 and Bcl-XL were decreased in the mitochondria and that of Bax was increased. Transfection of cells with MMP-2-siRNA prevented glucose-induced activation of MMP-2, and prevented increases in mitochondrial permeability. In the same cell preparations, glucose-induced decreases in the mitochondrial levels of HSP60 and Bcl-XL, and increases in Bax expression and apoptosis were also ameliorated.
These results suggest that modulation of abundance of mitochondrial HSP 60 could be one of the plausible mechanisms via which MMP-2 damages the mitochondria, making them permeable and culminating in the apoptosis of capillary cells. Thus, inhibition of MMP-2 activation has potential to ameliorate the development of diabetic retinopathy by protecting mitochondria from becoming dysfunctional.
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