Adult microvascular networks and neuron-glia antigen 2 (NG2): Differential arterial/venous expression and dynamics during microvascular remodeling

The overall objectives of this work are to evaluate the cellular and spatial distribution of Neuron-Glia Antigen 2 (NG2) expression in adult rat microvascular networks and to assess the contribution of NG2 expression to microvascular remodeling. Mesenteric tissue was harvested from 250 g, female, Sprague-Dawley rats and stained for either NG2 and smooth muscle (SM) alpha-actin or NG2 and CD31. NG2 expression was evaluated along microvessels in quiescent and remodeling networks stimulated by 20 minute exteriorization of the rat mesentery. In order to assess the functional role of NG2, NG2 antibody was delivered in vivo via an osmotic mini-pump over the time course of microvascular remodeling in the mesentery and during bFGF-induced angiogenesis in a chorioallantoic membrane (CAM) assay. In quiescent mesenteric microvascular networks, positive NG2 staining co-localized to perivascular cells along arterioles and capillaries, but not along venules greater than 20 mum. At 1 day post stimulation, NG2 expression was observed along 27 +/- 30% of network draining venules (14 mum-55 mum) and after 3 days, 59 +/- 28% of draining venules (13 mum-59 mum) stained positive for the proteoglycan. By 5 days post stimulation, the percentage of network draining venules (18 mum-59 mum) staining positive for NG2 returned to 18 +/- 20% indicating a subsequent down regulation of the proteoglycan's gene expression or equivalent effect of co-factor molecules, such as inhibitors, proteases, or masking agents. While in vivo delivery of rabbit polyclonal NG2 antibody attenuated bFGF-induced microvascular growth in a CAM assay, delivery of the antibody during microvascular remodeling in rat mesenteric tissue did not have an effect on vascular area, vascular density, or the number of capillary sprouts. These novel findings suggest that NG2 is a marker of arterial/venous (A/V) differentiation in adult quiescent microvascular networks and is transiently upregulated along venules during angiogenesis. Though the antibody blocking studies confirm a functional role for NG2, the results also suggest that NG2's regulatory effect is insufficient or redundant during at least microvascular growth associated with 20 minute exteriorization of rat mesentery. Supported by NIH HL65958.