Objectives Wound healing is a complex and dynamic process of restoring cellular structures and tissue layers. The human adult wound healing process can be divided into 3 distinct phases: the inflammatory phase, the proliferative phase, and the remodelling phase. Serum Amyloid A (SAA) is an acute-phase protein produced in liver and circulating blood levels can increase up to 1000-fold in the presence of chronic inflammation such as in the case of diabetes mellitus where poor wound healing impacts on quality of life.
Methods Human carotid artery cells (HCtAECs) were cultured to full confluence at 37 °C. Subsequently, cell migration and proliferation was monitored for up to 6 h in the presence or absence of SAA (final concentration 10 mg/mL) or PBS (as control). In some studies cells were pre-treated with the pharmacological inhibitor of vascular endothelial growth factor (VEGF) receptor (BIBF1120). Endothelial tube formation was also assessed after seeding HCtAECs in a 96-well plate coated with Matrigel with tube formation determined with or without added SAA and monitored for up to 6h post stimulation. The pro-inflammatory/thrombotic activity of SAA on the vascular endothelial cells was verified by determining gene regulation in the presence or absence of SAA (final concentration 0, 1 or 10 mg/mL).
Results As anticipated, exposure of endothelial cells to SAA increased the expression of pro-inflammatory tumour necrosis factor (TNF) and pro-coagulative tissue factor (TF) and this was accompanied by increased expression of the transcription factor nFkB. The increase in TNF was paralleled by increased expression of VEGF in endothelial cells exposed to SAA as demonstrated by Western blotting studies. In the presence of SAA, regrowth of HCtAECs into the damaged area increased significantly (∼1.22-fold relative to the control) and cell migration also increased significantly (1.6 ± 0.1-fold relative to the control). Notably, treatment of HCtAECs with SAA enhanced tube formation with both larger and greater number of tubes being formed than the control. The enhanced cell migration, proliferation and tube-forming activity of SAA was inhibited markedly by added BIBF1120.
Conclusions Elevated levels of SAA may play a novel role in promoting tissue recovery through a process that involves increased expression of TNF and VEGF, which together stimulate factors associated with angiogenesis. Pharmacological blockade of the VEGF receptor inhibited this pro-angiogenic activity of SAA on vascular endothelial cells. These data indicate that elevated circulating levels of SAA may play a beneficial role in tissue healing by stimulating the formation of neo-blood vessels.
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