Abstract 1119: Non-Adaptive Fibrosis in Ischemic Cardiomyopathy Results from Fibroblasts of Bone Marrow Origin
Daily, non-lethal coronary occlusion and reperfusion (I/RC) of murine myocardium leads to extensive interstitial fibrosis and ventricular dysfunction mirroring the pathological symptoms of human ischemic cardiomyopathy. Although the deleterious role of non-adaptive fibrosis in chronic heart disease is acknowledged, its mechanisms are still unknown. We hypothesize that uptake and differentiation of fibroblast precursor cells of myeloid origin to myofibroblasts is a critical step.
Methods: C57BL/6 mice were subjected to I/RC with daily administration of either murine serum amyloid P (SAP, 50 μg), or albumin (control, 50 μg). Cardiac function was monitored by echocardiography. Total mRNA was isolated after 3 days, cardiac fibroblasts were isolated by enzymatic digestion after 5 days and analyzed by flow cytometry or cultured in vitro, and paraffin-embedded tissue staining was performed after 7 days of I/RC.
Results: Compared to control, SAP prevented the I/RC-induced development of cardiac fibrosis (4.9±0.4 vs. 2.0±0.2 % collagen area) and cardiac dysfunction (33±2 vs. 43±2 % fractional shortening). However, SAP did not suppress the inflammatory response (macrophage infiltration, tenascin deposition) or attenuate chemokine or cytokine expression. By contrast, SAP inhibition of fibrosis was accompanied by marked reduction of μ-smooth muscle actin positive cells (15.4±6.9 vs. 4.6±1.9 cells/mm2) indicating that SAP specifically suppressed the induction of myofibroblasts. Isolation of cardiac fibroblasts after I/RC revealed a population of highly proliferative, spindle-shaped myofibroblasts that were CD34+ (precursor cell marker) and CD45+ (hematopoietic marker). Studies in chimeric mice with betagalactosidase labeled bone marrow confirmed this CD34+ myofibroblast population to be of bone marrow origin. This population of myofibroblasts was absent in normal myocardium and was reduced >90% in SAP treated I/RC. SAP is a pentraxin related to C-reactive protein that binds to Fcγ receptors. We theorize that SAP inhibits an immune system-related induction of myofibroblasts derived from myeloid cells that mediates fibrosis in I/RC. This population may be the mechanistic link between immune responses and non-adaptive cardiac fibrosis.