Interaction between isolated human myocardial mast cells and cultured fibroblasts

Previously, we reported an increase in interstitial collagen and total mast-cell numbers in heart failure versus normal myocardium. A secondary increase, primarily in chymase-negative mast cells, occurred following LVAD support compared to matched pre-LVAD tissue samples and was associated with a decrease in interstitial collagen and bFGF. To further elucidate the changes in interstitial collagen, we investigated the direct interaction between mast cells, isolated from failing myocardium with or without previous LVAD support, and human fibroblasts in a coculture model. Additionally, the expression of HSP-47, the pro-collagen-specific chaperone protein, was determined in the particular myocardium.

Myocardial tissue was obtained from 10 patients with end-stage dilated cardiomyopathy (DCM) at the time of transplantation. Five patients were transplanted following LVAD support, five patients without previous LVAD support. Mast cells were isolated according to a standard protocol, including collagenase digestion and cell separation. The isolated mast cells were co-cultured with human fibroblasts for 12 h, with or without stimulation of degranulation, and protein synthesis was measured by [(3)H]-proline incorporation. HSP-47 immunostaining was performed in the different myocardial samples and the positive cells were quantified.

Stimulated mast cells isolated from DCM tissue (without previous LVAD support) caused a 92% increase in [(3)H]-proline incorporation and consequently in protein production in fibroblasts compared to mast-cell free culture (P < 0.01), while conversely stimulated mast cells isolated from LVAD supported myocardium decreased the [(3)H]-proline incorporation by 63% (P < 0.01) below baseline. Nonstimulated mast cells did not significantly alter the protein production over baseline. There was also a significant increase in the number of HSP-47-positive cells in DCM myocardium compared to normal (P < 0.01) and there was a shift toward normal after LVAD support (P < 0.01).

We demonstrate that fibroblast protein production in vitro is significantly altered by mast cells and that the direction of change is dependent on whether myocardium was supported by LVAD. We suggest that under long-term LVAD support there is a phenotypic alteration in myocardial mast cells, which leads to a change in concentration and/or composition of mediators, capable of re-remodeling the myocardial matrix.