Introduction: Macrophage colony stimulating factor (M-CSF) is a key factor for monocyte and macrophage survival and proliferation. M-CSF has been implicated in cardiac healing and repair after myocardial infarction.
Methods and results: We show by immunohistochemistry and Western blotting analysis that M-CSF protein is present in human heart tissue. Cultured human adult cardiac myocytes (HACM) and human adult cardiac fibroblasts (HACF) isolated from human myocardial tissue constitutively express M-CSF. When HACM and HACF were treated with tumor necrosis factor-alpha (TNF-alpha) M-CSF protein production and M-CSF mRNA expression, determined by ELISA or by using RT-PCR, respectively, was significantly increased. To determine a possible role of nuclear factor kappaB (NF-kappaB) and activating protein 1 (AP-1) in M-CSF regulation, blockers to both pathways and an adenovirus overexpressing a dominant negative (dn) form of IkappaB kinase 2 (IKK2) were used. Only the NF-kappaB blocker dimethylfumarate and the dn IKK2, but not januskinase inhibitor-1 (JNK-I), were able to block the TNF-alpha-induced increase in M-CSF production in these cells, suggesting that the induction of M-CSF through TNF-alpha is mainly dependent on the activation of the NF-kappaB pathway. The monocyte activation marker CD11b was significantly increased after incubating U937 cells with conditioned medium from HACM or HACF as determined by FACS analysis.
Conclusions: Our in vitro data taken together with our immunohistochemistry data suggest that human cardiac cells constitutively express M-CSF. This expression of M-CSF in the human heart and its upregulation by TNF-alpha might contribute to monocyte and macrophage survival and differentiation.