Differences in angiogenic potential of classically vs alternatively activated macro phages

Macrophages (M Phi) are important for angiogenesis during inflammation, wound repair, and tumor growth. However, well-characterized M Phi subsets such as IFN-gamma-induced, classically activated (ca) M Phi or IL-4/glucocorticoid-induced, alternatively activated (aa) M Phi, have not been thoroughly examined for a positive or negative association with angiogenesis. While caM Phi populate early inflammatory reactions and high-turnover granulomas, aaM Phi occur in healing wounds and chronic inflammation. In contrast to caM Phi-dominated lesions, aaM Phi-rich lesions are highly vascularized. In order to determine their angiogeneic potential in vitro, these M Phi subsets as well as unstimulated control macrophages (coM Phi) were analyzed by RT-PCR for mRNA expression of 10 angiogenic factors after 3 and 6 days of culture. Early during activation, caM Phi, and coM Phi expressed equal levels of 8 of 10 angiogenic factors (PDGF-A, MK, TNF-alpha, TGF-beta(1), PDGF-B, HGF, TGF-alpha, IGF-1), while aaM Phi showed expression of only 4 of these factors (TGF-beta(1), PDGF-B, HGF, GF-1). After maturation, TGF-alpha and IGF-1 showed a shift in mRNA expression from caM Phi to aaM Phi resulting in a considerably enhanced expression of these factors in day-6 aaM Phi as compared to day-6 caM Phi and coM Phi while PDGF-A, MK, and TNF-alpha remained suppressed in day 6 aaM Phi. In all M Phi subsets including controls, mRNA expression of aFGF and bFGF was minimal or absent while TGFG-beta(1), HGF, and ODGF-B were constitutively expressed. In order to functionally integrate angiogenic factor mRNA expression profiles, mitogenic activity of M Phi, subsets towards microvascular endothelium was assessed by cocultivation. Coculture experiments revealed that endothelial proliferation induced by aaM Phi was 3.0-3.5x higher than induced by caM Phi. In conclusion. mature aaM Phi are well equipped to play an important role in protracted M Phi-associated angiogenic processes. Presumably due to expression of predominantly angioinhibitory cytokines such as TNF-alpha by caM Phi but much less by aaM Phi, caM Phi exhibit only a low angiogenic potential in vitro and in vivo despite considerable expression of angiogenic factor mRNA.