In vivo chemotactic properties and spatial expression of PDGF in developing mesenteric microvascular networks

The recruitment of perivascular cells to developing microvessels is a key c omponent of microvessel assembly. Whereas platelet-derived growth factor (P DGF) signaling is critical for this process during embryonic development, i ts role from the postnatal stages through adulthood remains unclear. We inv estigated the potential role of PDGF signaling during microvessel assembly by measuring in vivo the migration of labeled fibroblasts to PDGF in mesent eric connective tissue and by examining PDGF-B and PDGF receptor-beta (PGDF R-beta) expression in microvascular networks during normal maturation. PDGF -B homodimer (PDGF-BB; 30 ng/ml) application elicited a significant (P < 0. 05) increase (7.8 +/- 4.1 cells) in labeled fibroblasts within 100 mm of th e source micropipette after 2 h. PDGF-A homodimer (30 ng/ ml) application a nd control solution did not elicit directed migration. PDGF-B was expressed in microvessel endothelium and smooth muscle, whereas PDGFR-<beta> was exp ressed in endothelium, smooth muscle, and interstitial fibroblasts. Given t hat PDGF-BB elicits fibroblast migration in the mesentery and that PDGF-B a nd PDGFR-beta are expressed in a pattern that indicates paracrine signaling from microvessels to the interstitium, the results are consistent with a r ole for PDGF-B in perivascular cell recruitment to microvessels.