MMP3 and myocardial infarction: 1Tregs accumulated in MI heart produced SPARC, which reduced heart rupture by increasing the production of collagen III in fibroblasts. In vitro, coculture of fibroblasts with SPARC-overexpressing Tregs had the same effect (20).2In vitro, Tregs reduced the expression of α-SMA and MMP3 in fibroblasts and attenuated the contraction of fibroblast-populated collagen pads (52).