Complement C3a signaling mediates production of angiogenic factors in mesenchymal stem cells

Abstract

A major portion of the beneficial effect of mesenchymal stem cells (MSC) is due to the production of trophic and angiogenic factors by these cells, and one of the efforts to improve the therapeutic efficacy of these cells lies in enhancing this capacity. Since there is complement activation in all areas of tissue injury, and both C3a and C5a activate MSC, it was asked whether stimulation with C3a or C5a would upregulate the production of trophic factors by MSC. C3a caused significant up-regulation of various angiogenic factors, including VEGF, CXCL8/IL-8 and IL-6. In contrast there was no detectable production of the pro-inflammatory cytokines TNF-α and IL-1β in spite of nuclear translocation of NFκB. Although C5a also caused moderate up-regulation of angiogenic factors, the effect was borderline significant. Furthermore the production of angiogenic factors induced by C3a was of physiological relevance: Supernatants of MSCs cultured under serum-free conditions induced minimal tube formation of HUVECs as an in vitro measure of angiogenesis; tube formation was considerably enhanced, when supernatants from C3a-stimulated MSC were used, while C3a itself had no direct angiogenic effect on HUVECs. The signaling cascade responsible for the production of angiogenic factors by C3a or C5a could be defined as activation of the rho cascade which was necessary for nuclear translocation of NFκB p65 and of phospho-ERK1/2. Although rho was only transiently activated, inhibition of the rho or “downstream of it” of the NFκB pathway, prevented C3a-and C5a-induced up-regulation of angiogenic factors.