Heme oxygenase-1 induction enhances cell survival and restores contractility to unvascularized three-dimensional adult cardiomyocyte grafts implanted in vivo.

Autologous adult cardiomyocytes are not utilized for heart repair strategies because of their rapid apoptosis after implantation. We examined whether induction of heme oxygenase-1 (HO-1), a mediator of preconditioning, could enhance early postimplant myocyte survival. Three-dimensional 5×5 mm patches of full-thickness adult murine atrial wall, including cardiomyocytes, capillary networks, and extracellular matrix, were cultured with or without HO-1 inducer cobalt protoporphyrin (CoPP), or the HO-1 inhibitor, tin protoporphyrin (SnPP), or both. Patches were then implanted subcutaneously. Freshly procured atrial wall patches implanted without preculturing served as additional controls. By 14 days postimplant, graft cardiomyocyte content was significantly greater in CoPP-treated patches than in either control group (p<0.02). Adult cardiomyocytes did not contract in culture or immediately after implantation. However, by 14 days postimplant, spontaneous contraction had recovered in 47% of CoPP-treated patches, but in only 6% of precultured patches without CoPP, 0% of SnPP-treated patches, and 0% of uncultured patches (p<0.03). CoPP-treated adult cardiomyocyte patches were also observed to remodel spontaneously into endothelial-lined chambers that pumped nonclotting blood. These findings demonstrate that adult cardiomyocytes have more plasticity and capacity for functional recovery than previously recognized and could have application as an autologous cardiomyocyte source for tissue engineering.

Hyaluronan accumulation is elevated in cultures of low density lipoprotein receptor-deficient cells and is altered by manipulation of cell cholesterol content.

The extracellular matrix molecule hyaluronan (HA) accumulates in human atherosclerotic lesions. Yet the reasons for this accumulation have not been adequately addressed. Because abnormalities in lipid metabolism promote atherosclerosis, we have asked whether disrupted cholesterol homeostasis alters HA accumulation in low density lipoprotein receptor-deficient cell cultures. Cultured aortic smooth muscle cells (ASMC) from Watanabe heritable hyperlipidemic (WHHL) rabbits and skin fibroblasts from homozygous patients with familial hypercholesterolemia accumulated 2-4-fold more HA than corresponding cells from age- and sex-matched normolipidemic rabbits and individuals. This occurred in both cell-associated and secreted HA fractions and was independent of cell density or medium serum concentration. WHHL ASMC cultures synthesized twice the proportion of high molecular mass HA (>2x10(6) Da) as normal rabbit ASMC but showed a lower capacity to degrade exogenous [3H]HA. Most importantly, cholesterol depletion or blocking cholesterol synthesis markedly reduced HA accumulation in WHHL ASMC cultures, whereas cholesterol replenishment or stimulation of cholesterol synthesis restored elevated HA levels. We conclude the following: 1) maintaining normal HA levels in cell cultures requires normal cell cholesterol homeostasis; 2) HA degradation may contribute to but is not the predominant mechanism to increase high molecular mass HA accumulation in low density lipoprotein receptor-deficient WHHL ASMC cultures; and 3) elevated accumulation of HA depends on cellular or membrane cholesterol content and, potentially, intact cholesterol-rich microdomains.