Mitochondrial Dysfunction and Diabetic Retinopathy: Role of Matrix Metalloproteinase-2

Abstract

Purpose: : 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.

Methods: : Bovine retinal endothelial cells from 4^th 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.

Results: : 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.

Conclusions: : 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.

Keywords: diabetic retinopathy • mitochondria • apoptosis/cell death