Osteopontin is proteolytically processed by matrix metalloproteinase 9

Abstract

Osteopontin is robustly upregulated following myocardial infarction (MI), which suggests that it has an important role in post-MI remodeling of the left ventricle (LV). Osteopontin deletion results in increased LV dilation and worsened cardiac function. Thus, osteopontin exerts protective effects post-MI, but the mechanisms have yet to be defined. Matrix metalloproteinases (MMPs) regulate LV remodeling post-MI, and osteopontin is a known substrate for MMP-2, -3, -7, and -9, although the cleavage sites have not been mapped. Osteopontin-derived peptides can exert distinct biological functions that may depend on their cleavage sites. We mapped the MMP-9 cleavage sites via LC-MS/MS analysis using label-free and N-terminal labeling methods, and compared them with those of MMP-2, -3, and -7. Each MMP yielded a unique cleavage profile with few overlapping cleavage sites. Using synthetic peptides, we validated 3 sites for MMP-9 cleavage at amino acid positions 151–152, 193–194, and 195–196. Four peptides were synthesized based on the upstream- and downstream-generated fragments and were tested for biological activity in isolated cardiac fibroblasts. Two peptides increased cardiac fibroblast migration rates post-wounding (p < 0.05 compared with the negative control). Our study highlights the importance of osteopontin processing, and confirms that different cleavage sites generate osteopontin peptides with distinct biological functions.

Spatiotemporal expression of osteopontin in the striatum of rats subjected to the mitochondrial toxin 3-nitropropionic acid correlates with microcalcification

“…1a). In addition, smaller molecular-weight OPN proteins (50 kDa or 25 kDa), which have been shown to be cleavage products of matrix metalloproteinase activity505152, were found to be increased in striatal tissue at earlier time points (days 3 and 7). However, the roles and significance of these smaller fragments are unknown.…”

Mechanical regulation of cardiac fibroblast profibrotic phenotypes

“…Reflecting the mechanical environment of this stage of remodeling, OPN mRNA was reduced with stretch of CFBs on 8 kPa PA gels. Interestingly, cardiac MMPs have recently been found to cleave OPN, resulting in OPN fragments with distinct biological functions that are associated with fibrosis ( Lindsey et al. , 2015 ).…”

Matrix Metalloproteinases in Myocardial Infarction and Heart Failure

“…73 In contrast, MMP-9 cleavage of osteopontin generates two biologically active peptides that increased the migration rate of cardiac fibroblasts resulting in enhanced infarct wound healing. 74 For this reason, targeting substrates downstream of MMP-9 may serve as a feasible alternative for predicting and preventing LV dysfunction post-MI.…”