Angiogenesis of brain after ischemia/reperfusion injury of brain in aged rats and changes in expressions of basic fibroblast growth factor and transformation growth factor-β1

Abstract

To elucidate the mechanism of angiogenesis after cerebral ischemia/reperfusion (I/R) in the aged rats by observing the changes in expressions of basic fibroblast growth factor (bFGF) and transformation growth factor-β1 (TGF-β1). Young Sprague-Dawley (SD) rats were classified into groups by random digits table, and aged SD rats were stratified by different body weight. Rats were randomly divided into groups of sham operation, ischemia (I) 3 hours, I/R 1, 3, 6, 12 days, with 6 rats in each group. Focal cerebral I/R model was reproduced by intraluminal filament technique. Microvessel density (MVD) of brain tissue, sum area of lumens were observed, and the expressions of bFGF protein, TGF-β1 protein and TGF-β1 mRNA were assessed with immunohistochemistry and hybridization in situ. MVD in young model group began to increase at I 3 hours, peaking at I/R 6 days, maintained up to I/R 12 days. MVD in aged model group began to descend at I 3 hours and continued to I/R 12 days. Sum area of lumens in young model group increased markedly at I/R 1 day, gradually lowered at I/R 1-6 days, and increased obviously again at I/R 12 days. Sum area of lumens in aged model group reached peak at I/R 1 day, gradually decreased subsequently. MVD in aged sham operation group were higher than that in young sham operation group (6.88±1.60 vs. 5.50±1.53, P<0.01). MVD and sum area of lumens in aged model group at I/R 1, 3, 6, 12 days were lower than young model group. Expressions of bFGF protein, TGF-β1 protein in young and aged model group were both gradually up-regulated, all of them reaching peak at I/R 3 days, and lowered gradually at I/R 3-12 days subsequently. Expressions of bFGF protein (grey level) in both aged sham operation group and those of model group at I 3 hours, I/R 1, 3, 12 days were lower than those of young sham operation and those of the model group at the same time points (176.80±5.10 vs. 172.82±1.53, 171.81±2.43 vs. 167.85±2.41, 167.99±5.51 vs. 164.90±2.15, 152.98±4.11 vs. 150.75±1.11, 165.67±3.55 vs. 161.73±1.29, P<0.05 or P<0.01). Expressions of TGF-β1 protein (grey level) in both aged sham operation and those of model group at I 3 hours, I/R 1, 3, 6, 12 days were all lower than those of young sham operation and those of model group at the same time points (182.69±3.12 vs. 176.13±4.08, 176.89±2.30 vs. 170.56±7.47, 171.74±2.70 vs. 165.43±2.91, 157.17±5.20 vs. 150.43±4.28, 161.72±4.81 vs. 155.37±2.92, 167.69±2.18 vs. 160.28±3.59, all P<0.01). TGF-β1 mRNA expressions in both young model group and aged model group reached peak at I/R 1 day, gradually lowered subsequently. Expressions of TGF-β1 mRNA (gray level) in both aged sham operation and those of model group at I 3 hours, I/R 3, 6, 12 days were lower than those of young sham operation and also model group at the same time points (176.51±9.52 vs. 169.09±5.08, 176.75±5.74 vs. 165.36±4.78, 177.33±5.68 vs. 165.25±8.14, 178.46±4.91 vs. 170.51±4.29, 203.95±4.51 vs. 181.98±5.59, all P<0.01). Angiogenesis is obviously weak after cerebral I/R in the aged, and the mechanism of which might be related to the down-regulation of expressions of bFGF protein, TGF-β1 protein and TGF-β1 mRNA. Aging factor may be one of the main reasons which induce the down regulation of expressions mentioned above.