Attenuation of Ischemic Myocardial Injury and Dysfunction by Cardiac Fibroblast-Derived Factor(s)

Abstract

: Fibroblasts, the majority of non -cardiomyocytes in the heart, are known to release several kinds of substances such as cytokines and hormones that affect cell and tissue functions. We hypothesized that undefined substance(s) derived from cardiac fibroblasts may have the potential to protect against ischemic myocardium. To assess our hypothesis, using rats, we investigated : 1) the effect of cardiac fibroblast -conditioned medium (CM) on the viability of hypoxic cardiomyocytes in vitro, 2) the effect of CM on left ventricular (LV) function in global ischemia -reperfusion in an ex vivo model, 3) the mechanism underlying cardioprotection by CM. Seventy -two hours after starting a hypoxic culture, the viability of cardiomyocytes was higher (P<0.05) in the CM treated group (41.4%) compared to the control (20.5%). In Langendorff's preparation, 30 min after ischemia -reperfusion, LV end -diastolic pressure was lower, and LV developed pressure and -LVdP/dt were higher (P<0.01 or P<0.05) in the CM group than in the control, although coronary flow did not differ between the two groups. Pretreatment with a protein kinase C inhibitor or a mitochondrial ATPsensitive K + channel blocker attenuated these changes of LV function in the CM group. Such cardioprotection was achieved by a fraction of the CM having a molecular weight (MW) > 50,000, but not by that of the CM with a lower MW. In addition, a specific antibody against hepatocyte growth factor (HGF, MW is 84,000) did not reduce the cardioprotection afforded by CM. There may be an unknown cardioprotective substance other than HGF in rats, which mimics ischemic preconditioning and has MW>50,000.

Origin, development, and differentiation of cardiac fibroblasts

“…TGFβ1, in particular, is thought to be sufficient for CF differentiation into myoCFs [1, 66, 67, 69, 70]. This pro-inflammatory, pro-fibrotic environment is initially adaptive as factors secreted from CFs and myoCFs protect the injured myocardium, and while they may lead to temporary cellular hypertrophy, they promote cardiomyocyte survival [2]. TGFβ1, for example, has been shown to decrease cardiomyocyte death when delivered exogenously during the reperfusion stage of an ischemia-reperfusion rat model [67].…”

“…TGFβ1, for example, has been shown to decrease cardiomyocyte death when delivered exogenously during the reperfusion stage of an ischemia-reperfusion rat model [67]. Similarly, in vitro and ex vivo Langendoff studies have suggested a role for non-cardiomyocytes, especially CFs, in mitigating cardiomyocyte injury following hypoxia and ischemia-reperfusion exposure via secretion of unknown cardioprotective substance/s [2]. In addition to pro-inflammatory cytokines, myoCFs also secrete Angiotensin II, Endothelin-1, Natriuretic peptides, and VEGF to facilitate the wound healing process [64].…”

“…Similarly, paracrine signals released from CFs can have paradoxical effects upon the cardiomyocyte lineage. CFs secrete factors that have been shown in in vitro and ex vivo models to have cardioprotective effects under ischemic conditions [2, 3]; however, some of these same paracrine factors will ultimately lead to heart failure via cardiomyocyte hypertrophy and eventual apoptosis [3]. Contributions of CFs to the electrical milieu of the heart, while less extensively investigated, seem to follow the same dichotomy.…”

TGF-β1, Released by Myofibroblasts, Differentially Regulates Transcription and Function of Sodium and Potassium Channels in Adult Rat Ventricular Myocytes

“…[2] Cardiac fibroblast conditioned medium (FCM) from neonatal rats has been shown to protect cardiac myocytes against hypoxia induced injury in isolated cells and the growth factors in such medium also had a protective effect against ischemia-reperfusion injury. [3] Protein analysis of the neonatal rat FCM has shown that these cells release proinflammatory cytokines, such as transforming growth factor β-1 (TGF-β1), fibroblast growth factor (FGF), interferon-γ (IFN-γ), cytokine-induced neutrophil chemoattractant (CINC-1), macrophage migration inhibitory factor (MIF), vascular endothelial growth factor (VEGF) and tumor necrosis factor, [2] many of which are significantly upregulated after myocardial injury. [4], [5] Neonatal rat fibroblast also release significant amounts of IGF-1, endothelin A and leukemia inhibitory factor proteins, which are some of the proteins responsible for hypertrophy in cardiac myocytes and increased collagen synthesis in fibroblasts due to FCM.…”

Ischemia and reperfusion related myocardial inflammation: A network of cells and mediators targeting the cardiomyocyte

“…Cardiac fibroblast‐conditioned medium was reported to induce cardioprotective effects in hypoxic cardiomyocytes in vitro and in an ex vivo model of global I/R injury. However, the secretory product of cardiac fibroblasts, which induced these effects, remains to be elucidated .…”