MMP2 and diabetic retinopathy: Activation of MMP-2 and/or MMP-9 has been found to play an important role in the pathogenesis of diabetic retinopathy [60, 61], nephropathy [62], neuropathy [63], vascular complications [64], skin complications [65], etc. In this study, MMP-9 expression and enzymatic activity were found to be increased upon PM2.5 exposure in mouse alveolar macrophages and this effect was enhanced in cells with high glucose pretreatment.