Paracrine effects of hypoxic fibroblast-derived factors on the MPT-ROS threshold and viability of adult rat cardiac myocytes

Abstract

Cardiac fibroblasts contribute to multiple aspects of myocardial function and pathophysiology. The pathogenetic relevance of cytokine production by these cells under hypoxia, however, remains unexplored. With the use of an in vitro cell culture model, this study evaluated cytokine production by hypoxic cardiac fibroblasts and examined two distinct effects of hypoxic fibroblast-conditioned medium (HFCM) on cardiac myocytes and fibroblasts. Hypoxia caused a marked increase in the production of tumor necrosis factor (TNF)-alpha by cardiac fibroblasts. HFCM significantly enhanced the susceptibility of cardiac myocytes to reactive oxygen species (ROS)-induced mitochondrial permeability transition (MPT), determined by high-precision confocal line-scan imaging following controlled, photoexcitation-induced ROS production within individual mitochondria. Furthermore, exposure of cardiac myocytes to HFCM for 5 h led to loss of viability, as evidenced by change in morphology and annexin staining. HFCM also decreased DNA synthesis in cardiac fibroblasts. Normoxic fibroblast-conditioned medium spiked with TNF-alpha at 200 pg/ml, a concentration comparable to that in HFCM, promoted loss of myocyte viability and decreased DNA synthesis in cardiac fibroblasts. These effects of HFCM are similar to the reported effects of hypoxia per se on these cell types, showing that hypoxic fibroblast-derived factors may amplify the distinct effects of hypoxia on cardiac cells. Importantly, because both hypoxia and oxidant stress prevail in a setting of ischemia and reperfusion, the effects of soluble factors from hypoxic fibroblasts on the MPT-ROS threshold and viability of myocytes may represent a novel paracrine mechanism that could exacerbate ischemia-reperfusion injury to cardiomyocytes.

Mst1 inhibition rescues β1-adrenergic cardiomyopathy by reducing myocyte necrosis and non-myocyte apoptosis rather than myocyte apoptosis

“…Given that 75 % of the cells in the heart are non-myocytes [17], we discriminated the effects of the cardiomyopathy and its rescue with DN-Mst1 on myocyte vs. non-myocyte apoptosis. The finding that apoptosis predominantly occurred in non-myocytes and DN-Mst1 predominantly rescued non-myocyte apoptosis, supports the hypothesis that DN-Mst1 protects against necrosis, since non-myocytes, e.g., fibroblasts, macrophages, neutrophils, endothelial cells [33, 34, 36, 40], are all known to be involved in inflammation [9, 18, 39], which is more closely coupled to necrosis, rather than apoptosis [7, 10, 20, 22, 29, 38]. In further support of the role of necrosis, we also found that myocardial fibrosis, which is generally thought to be an outcome of necrosis rather than apoptosis [3, 10], was also rescued in the bigenic mice.…”

NF-κB inhibition compromises cardiac fibroblast viability under hypoxia

“…The findings presented here support the postulation that Bcl-2 may be involved in the “house-keeping” control of the apoptotic threshold in cardiac fibroblasts whereas cIAP-2 may be a dynamic regulator of apoptosis, induced under hypoxic stress. The pro-survival role of cIAP-2 under hypoxia may be particularly important in light of our recent report that hypoxia causes a dramatic increase in TNF-α production in cardiac fibroblasts that does not compromise fibroblast viability but exerts paracrine effects to promote cardiomyocyte apoptosis [39]. TNF-α is a potent inducer of apoptosis by the extrinsic pathway, which is inhibited by cIAP-2 but not by Bcl-2 [40].…”

Fibroblasts in post-infarction inflammation and cardiac repair

“…In vitro, cardiac fibroblasts respond to hypoxia by acquiring a pro-inflammatory and fibrogenic phenotype characterized by enhanced cytokine expression [40], myofibroblast transdifferentiation [41] and increased collagen synthesis [42]. In contrast, hypoxia-mediated actions on fibroblast proliferation and on matrix metabolism appear inconsistent and gender-dependent [43], [44], [45], [46].…”