Determining the molecular mechanisms of vascular sympathetic innervation.

摘要

The sympathetic nervous system is integral to blood pressure regulation through changes in peripheral vascular resistance. Disruption of vascular sympathetic nerve plexuses has been implicated in the etiology of several diseases, including hypertension, diabetes and cardiac transplantation. Sympathetic nerves innervate major feed arteries and extend through the pre-capillary arteriolar network, but not into capillaries, venules or collecting veins. In addition, tissue specific differences in vascular sympathetic innervation exist. During development, sympathetic ganglia coalesce from migrating neural crest cells, which proliferate, differentiate and extend axons, often along arterial networks, towards peripheral targets. These growing axons follow complex gradients of both local and long-range molecular guidance cues that govern whether or not they turn towards and innervate a particular tissue. Much is known about how axon guidance molecules promote innervation of a variety of targets, but until now vessels have been largely ignored. The selective innervation of pre-capillary vessels suggests that cues that could promote chemoattraction between arteries and neurons or chemorepulsion between veins and neurons exist and may be expressed by vascular cells. To investigate this hypothesis we have quantified regional and developmental densities of vascular sympathetic innervation to better understand the spatiotemporal profile. We developed an in vitro three-dimensional co-culture model, which was used to evaluate differences in axon outgrowth towards particular vessels. Arteries innervated in vivo promoted increased average axon length compared arteries non-innervated in vivo, which block increased axon outgrowth. Thus, it is likely that there are both vascular-derived attractive and repulsive cues that govern the overall pattern of sympathetic axon outgrowth. We have also utilized the in vitro co-culture model to evaluate the effects of a variety of candidate molecules in regulating directed neurite outgrowth. We evaluated the influence of previously identified molecules, such as Semaphorin3A and VEGF-A, which block and promote axon outgrowth respectively. In addition, a suppression subtractive hybridization has been used to investigate the differential gene expression profiles of innervated and non-innervated blood vessels, which has generated a list of additional candidates that may play a role in directing axon outgrowth and possibly sympathetic vascular innervation. Several of these novel candidates, including alpha8 integrin and fibronectin, have been studied in vitro.