Recruited bone marrow cells expressing the EP3 prostaglandin E receptor subtype enhance angiogenesis during chronic inflammation

Chronic inflammation, which is characterized by the proliferation of granulation tissues, is known to be regulated by angiogenesis. Recent results suggest that bone marrow-derived (BM-derived) hematopoietic cells regulate angiogenesis in vivo. We previously reported that the angiogenesis occurring during chronic inflammation is enhanced in response to the endogenous prostaglandins (PGs) derived from an inducible cyclooxygenase-2 (COX-2). In the present study, we examined the role of BM-derived cells expressing an E-type PG receptor subtype, EP3, in sponge-induced angiogenesis. The replacement of wild-type (WT) BM with BM cells (BMCs) from green fluorescent protein (GFP) transgenic mice revealed that the formation of granulation tissue around the sponge implants developed via the recruitment of BMCs. This recruitment was enhanced by topical injections of vascular endothelial growth factor (VEGF)-A, and a VEGF-dependent increase in the recruitment of BMCs was inhibited by a COX-2 inhibitor, celecoxib. FACS analysis of the granulation tissues after treatment with collagenase revealed that the Mac-1-positive macrophage fraction was enhanced by topical injections of VEGF-A, and that this increased recruitment of Mac-1-positive BMCs was inhibited by celecoxib. Selective knockdown of EP3 performed by BM transplantation with BMCs isolated from EP3 knockout (EP3) mice reduced sponge-induced angiogenesis, as estimated by mean vascular number and CD31 expression in the granulation tissues. This reduction in angiogenesis in EP3−/− BM chimeric mice was accompanied by reductions in the recruitment of BMCs, especially of Mac-1-positive cells and Gr-1-positive cells. These results indicate that the recruited bone marrow cells that express the EP3 receptor have a significant role in enhancing angiogenesis during chronic proliferative inflammation.