The cytoprotective capacity of processed human cardiac extracellular matrix

Freshly isolated human cardiac extracellular matrix sheets (cECM) have been shown to support stem cell proliferation and tissue-specific lineage commitment. We now developed a protocol for standardized production of durable, bio-functional hcECM microparticles and corresponding hydrogel, and tested its cytoprotective effects on contractile cells subjected to ischemia-like conditions. Human ventricular myocardium was decellularized by a 3-step protocol, including Tris/EDTA, SDS and serum incubation (cECM). Following snap-freezing and lyophilization, microparticles were created and characterized by laser diffraction, dynamic image analysis (DIA), and mass spectrometry. Moreover, cECM hydrogel was produced by pepsin digestion. Baseline cell-support characteristics were determined using murine HL-1 cardiomyocytes, and the cytoprotective effects of ECM products were tested under hypoxia and glucose/serum deprivation. In cECM, glycoproteins (thrombospondin 1, fibronectin, collagens and nidogen-1) and proteoglycans (dermatopontin, lumican and mimecan) were preserved, but residual intracellular and blood-borne proteins were also detected. The median particle feret diameter was 66 μm (15-157 μm) by laser diffraction, and 57 μm (20-182 μm) by DIA with crystal violet staining. HL-1 cells displayed enhanced metabolic activity (39 ± 12 %, P < 0.05) and proliferation (16 ± 3 %, P < 0.05) when grown on cECM microparticles in normoxia. During simulated ischemia, cECM microparticles exerted distinct cytoprotective effects (MTS conversion, 240 ± 32 %; BrdU uptake, 45 ± 14 %; LDH release, -72 ± 7 %; P < 0.01, each). When cECM microparticles were solubilized to form a hydrogel, the cytoprotective effect was initially abolished. However, modifying the preparation process (pepsin digestion at pH 2 and 25 °C, 1 mg/ml final cECM concentration) restored the cytoprotective cECM activity. Extracellular matrix from human myocardium can be processed to yield standardized durable microparticles that exert specific cytoprotective effects on cardiomyocyte-like cells. The use of processed cECM may help to optimize future clinical-grade myocardial tissue engineering approaches.