Objective: To investigate possible mechanism of angiogenesis in brain tissue of neonatal rat hypoxic-ischemic encephalopathy (HIE).
Methods: Forty seven-day old neonatal rats were randomly assigned to hypoxic-ischemic (Model group) or sham treatment (Sham group), each group had 20 rats. Five rats from each group were sacrificed on days 1, 3, 7 and 14 after hypoxia-ischemia. Paraffin sections of the brain were stained with anti-endothelial cell, anti-proliferating cell nuclear antigen (PCNA) or anti-vascular endothelial growth factor (VEGF) by using single or double immunohistochemistry. The brain capillary density index (BCDI), brain proliferating capillary density index (BPCDI) and the expression of VEGF were analyzed under the microscope. The expression of VEGF and hypoxia-inducible factor-1alpha (HIF-1alpha) mRNA in hypoxic-ischemic side of the brain was measured by RT-PCR.
Results: BCDI around infarct brain tissue in the model group began to rise on day 3 and remained higher than that of the sham group from day 3 to day 14 [day 3: (9.80 +/- 1.05)/HPF vs. (4.90 +/- 0.66)/HPF, P < 0.01;day 14: (13.29 +/- 3.90)/HPF vs. (6.08 +/- 1.50)/HPF, P < 0.01]. Occasional proliferating capillary was found in brain tissue of normal neonatal rats. The density of proliferating brain capillary on day 3 and day 7 of Model group [(0.54 +/- 0.15)/HPF vs. (0.90 +/- 0.25)/HPF] were significantly higher than those of Sham group [(0.12 +/- 0.05)/HPF vs. (0.13 +/- 0.07)/HPF, P < 0.01]. VEGF was mainly expressed in the cytoplasm of neurons, capillary endothelial cells and pial cells. Viable neurons and endothelial cells in the infarct areas also expressed VEGF. The expression of VEGF mRNA in hypoxic-ischemic brain tissue was significantly higher than that of normal control (P < 0.01) and temporally preceded angiogenesis. The expression of VEGF mRNA at 12 hours of HIE model was significantly higher than that of normal control (1.56 +/- 0.27 vs. 0.95 +/- 0.21, P < 0.05). It reached its peak on day 1 and day 3 (1.85 +/- 0.31 vs. 1.86 +/- 0.39), significantly higher than that of normal control (P < 0.01), and decreased by day 7 and day 14, without significant difference compared with normal control (P > 0.05). The expression of HIF-1alpha mRNA was also up-regulated after hypoxic-ischemic treatment. The expression of HIF-1alpha mRNA (1.07 +/- 0.21) was significantly higher than that of normal control (0.64 +/- 0.28, P = 0.048) at 3-hour of HIE model, reached its peak on day 1 (1.73 +/- 0.42, P < 0.01), remained at high expression level on day 3 (1.44 +/- 0.36, P < 0.05) and began to decline by day 7 and day 14 when it was not significantly different from normal control.
Conclusions: Angiogenesis exists in the brain tissue of neonatal rat HIE model. Up-regulation of VEGF expression mediated by HIF-1 may play an important role in the process of angiogenesis.