Negative Feedback for Endothelial Apoptosis: A Potential Physiological Role for Fibroblast Growth Factor

Abstract

Although most physiologically important processes are regulated through negative feedback loops and numerous factors regulating endothelial apoptosis are identified, little is known about negative feedback mechanisms for endothelial apoptosis. Here we describe the release of soluble anti-apoptotic activity by endothelial cells undergoing apoptosis, and identify fibroblast growth factor-2 (FGF-2) as contributing to this. In brief, apoptosis of human umbilical vein endothelial cells was induced by serum deprivation and confirmed by transmission electron microscopy, DNA gel electrophoresis and a sub-diploid population seen by fluorescence-activated cell scanning analysis. Apoptosis was most rapid early during culture, and this was demonstrated to be due to the accumulation of soluble anti-apoptotic activity in experiments replacing culture medium with fresh medium, or alternatively returning conditioned medium to cells. FGF-2 antigen was detected in both conditioned medium and cell lysates, while neutralizing antibodies reduced the protective effect of medium conditioned by apoptotic endothelium. Experiments with the highly specific FGF-2 receptor tyrosine kinase inhibitor SU5402 indicated that FGF-2 accounted for the protective activity. We propose FGF-2 negative feedback as potentially important in microvascular remodelling. This is consistent with the absence of a secretory signal sequence in FGF-2, as well as canalicular fragmentation, which is unique to endothelial apoptosis and appears to result in minor cytoplasmic leakage.

A prosurvival and proangiogenic stem cell delivery system to promote ischemic limb regeneration

“…Besides promoting MSC survival and proliferation, the released bFGF stimulated host cell proliferation in the ischemic limb as the density of Ki67+ cells in the Gel/bFGF group was significantly higher than that in the Gel and non-injection groups (Figure 7). These results are consistent with those reported previously that bFGF can inhibit apoptosis of osteoblasts[74] and endothelial cells [75] under ischemic conditions. In these reports, the improved cell survival is a result of bFGF activating osteoblast PI3k/Akt pathway[74] and endothelial cell hypoxia-induced factor-1 (HIF-1) pathway [75], respectively.…”

“…These results are consistent with those reported previously that bFGF can inhibit apoptosis of osteoblasts[74] and endothelial cells [75] under ischemic conditions. In these reports, the improved cell survival is a result of bFGF activating osteoblast PI3k/Akt pathway[74] and endothelial cell hypoxia-induced factor-1 (HIF-1) pathway [75], respectively. In this work, we demonstrated that the prosurvival effect on MSCs is due to bFGF activating KLF4 pathway, an important protective factor in disease states and mediator to nitric oxide in ischemic tissues (Figure 3).…”

Arecoline increases basic fibroblast growth factor but reduces expression of IL‐1, IL‐6, G‐CSF and GM‐CSF in human umbilical vein endothelium

“…Although we have interpreted endothelial bFGF release as potentially important for OSF fibrosis, it can equally well be argued that such release would help restore tissue vascularity via endothelial mitogenesis following endothelial necrosis. Related to this, while there was no evidence for arecoline‐induced endothelial apoptosis in any of the current experiments described, or in our previous work , it is interesting that bFGF inhibits HUVEC apoptosis ; endothelial apoptosis is induced upon bFGF withdrawal ; and apoptotic endothelium exerts negative feedback for further apoptosis via release of bFGF . On this basis, evolution may have selected for a comparable bFGF‐mediated mechanism to both restore vascularity following toxic injury and to limit excessive endothelial apoptosis during tissue remodeling.…”

Arecoline is cytotoxic for human endothelial cells

“…Cell survival was established by direct cell counts of remaining adherent cells, accepted as providing an unambiguous measure for endothelial survival . Results of cell counting experiments were essentially paralleled by those of the LDH and MTT assays, indicating the absence of a clear effect of arecoline at levels insufficient to cause cell death, on either plasma membrane integrity or NADH production by mitochondria.…”