Acellular biomaterial modulates myocardial inflammation and promotes endogenous mechanisms of postinfarct cardiac repair.

Objective: After myocardial infarction, we previously showed that epicardial implantation of porcine small intestinal submucosal extracellular matrix (SIS-ECM) improves postinfarct cardiac function through fibroblast-mediated angiogenic and antifibrotic pathways. Herein, we characterize how SIS-ECM also coordinates a reparative cardiac inflammatory response.

Methods: RNA sequencing and multiplex characterized modulation of fibroblast transcriptional and paracrine activity by SIS-ECM. Inhibitors of fibroblast growth factor 2 and toll-like receptor 9 elucidated mechanism. Mice received coronary ligation (infarction) and either SIS-ECM implantation (treatment) or sham surgery (control). Flow cytometry of SIS-ECM and the murine myocardium quantified monocytes, neutrophils, and proangiogenic subtypes. Microscopy tracked fibroblasts and immune cells, and characterized myocardial angiogenesis.

Results: SIS-ECM increased fibroblast transcription of inflammatory pathways and production of angiogenic vascular endothelial growth factor and inflammatory cytokines via fibroblast growth factor 2 and toll-like receptor 9-dependent pathways. Two-photon microscopy showed that SIS-ECM became engrafted by native fibroblasts and leukocytes, subsequently increasing release of inflammatory cytokines and angiogenic vascular endothelial growth factor. On flow cytometry, SIS-ECM implantation increased day-7 myocardial counts of neutrophils, inflammatory monocytes, and proangiogenic vascular endothelial growth factor recptor 1 subtypes. SIS-ECM has a higher proportion of proangiogenic leukocytes compared with the myocardium. Resonant confocal microscopy showed neovascularization near SIS-ECM.

Conclusions: SIS-ECM promotes engraftment by native fibroblasts and leukocytes, and modulates fibroblast activity via fibroblast growth factor 2 and toll-like receptor 9 to potentiate a proangiogenic inflammatory response. Subsequently, the material increases myocardial counts of reparative proangiogenic leukocytes that can induce neovascularization. This reparative inflammatory response may explain previously reported functional improvements. Fibroblast growth factor 2 and toll-like receptor 9 mechanisms can be leveraged to design next-generation materials for postinfarct cardiac repair.