Effect of nerve growth factor on angiogenesis in a rat model of sciatic nerve regeneration

BACKGROUND:It remains to be determined whether nerve growth factor(NGF) can promote angiogenesis in regenerating peripheral nerves during repairing peripheral nerve injury. OBJECTIVE:To evaluate the effects of NGF on angiogenesis,and to analyze the influencing mechanisms of NGF,according to the expression patterns of CD34,von Willebrand factor(vWF), vascular endothelial cell growth factor(VEGF),and the NGF receptor TrkA in proliferating vascular endothelial cells from a rat model of sciatic nerve injury. DESIGN,TIME AND SETTING:Randomized,controlled study performed at the Research Institute of Field Surgery,Daping Hospital affiliated to the Third Military Medical University of Chinese PLA,between October 2003 and July 2005. MATERIALS:Forty-five healthy,adult,Wistar rats underwent sciatic nerve injury.The rats were randomly divided into four groups:NGF+chitosan(n=15),NGF+chitosan+anti-VEGF(n=10), chitosan(n=10),and physiological saline(n=10). METHODS:A 1-cm defected sciatic nerve was bridged with a silica gel conduit.NGF+chitosan group:100μL chitosan and 5μL NGF(20 mg/L) were injected into the silica gel conduit;NGF + chitosan+anti-VEGF group:an additional 5μL anti-VEGF monoclonal antibody(1 g/L) was injected into the silica gel conduit;chitosan group:100μL chitosan and 5μL physiological saline were injected into the silica gel conduit;physiological saline group:only 5μL physiological saline was injected into the silica gel conduit. MAIN OUTCOME MEASURES:CD34 and vWf were used to label blood capillaries and large-diameter blood vessels in the regenerating peripheral nerves,respectively.At day 14 following surgery,immunohistochemistry was used to detect and semi-quantitatively analyze expressions of CD34,vWf,VEGF,and TrkA in proliferating vascular endothelial cells in the regenerating sciatic nerve.A confocal laser microscope was used to determine co-expression. RESULTS:Expressions of TrkA,CD34,vWf,and VEGF in the NGF+chitosan group were significantly greater than the physiological saline and chitosan groups(P<0.05-0.01). Expressions of CD34 and VEGF in the NGF+chitosan+anti-VEGF group were completely inhibited,while expressions of vWf and TrkA gradually decreased,compared with the NGF + chitosan group(P<0.01).Confocal microscopy revealed strong co-expression of VEGF and CD34 in the regenerating sciatic nerve,and CD34 expression positively correlated with VEGF expression.In addition,VEGF expression was greater than CD34 expression,and coexpression of VEGF and vWf was also strong. CONCLUSION:VEGF was expressed in blood capillaries and large-diameter blood vessels,while exogenous NGF promoted VEGF expression in regenerating sciatic nerves,thereby increasing angiogenesis.