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.

Natural biomaterials hold enormous potential for tissue regeneration. The rapid advance of several tissue-engineered biomaterials, such as natural and synthetic polymer-based scaffolds, has led to widespread application of these materials in the clinic and in research. However, biomaterials can have limited repair capacity; obstacles result from immunogenicity, difficulties in mimicking native microenvironments, and maintaining the mechanical and biochemical (i.e., biomechanical) properties of native organs/tissues. The emergence of decellularized extracellular matrix (ECM)-derived biomaterials provides an attractive solution to overcome these hurdles since decellularized ECM provides a nonimmune environment with native three-dimensional structures and bioactive components. More importantly, decellularized ECM can be generated from the tissue of interest, such as the heart, and keep its native macro- and microstructure and tissue-specific composition. These decellularized cardiac matrices/scaffolds can then be reseeded using cardiac cells, and the resulting recellularized construct is considered an ideal choice for regenerating functional organs/tissues. Nonetheless, the decellularization process must be optimized and depends on tissue type, age, and functional goal. Although most decellularization protocols significantly reduce immunogenicity and deliver a matrix that maintains the tissue macrostructure, suboptimal decellularization can change ECM composition and microstructure, which affects the biomechanical properties of the tissue and consequently changes cell-matrix interactions and organ function. Herein, we review methods of decellularization, with particular emphasis on cardiac tissue, and how they can affect the biomechanics of the tissue, which in turn determines success of reseeding and in vivo viability. Moreover, we review recent developments in decellularized ECM-derived cardiac biomaterials and discuss future perspectives.