| Background and objective The continuous hyperglycemia is first responsible for injury of vascular endothelium. The diabetes-related micro-vascular dysfunctional is closely connected with the development of diabetic nephropathy(DN). Angiogenesis, the development of new blood vessels from preexisting ones, has been demonstrated by morphology in diabetic glomeruli of early rats or human with increased albuminuria. The angiopoietin-l(Ang-l) and -2(Ang-2), two members of angiopoietin family, were discovered recently as ligands for the Tie-2. Both are concerned with physiologic and pathologic angiogenesis in cooperation with vascular endothelial growth factor(VEGF). VEGF is required to initiate the formation of immature , unstable and leak vessels by vasculogenesis or angiogenic sporting during development as well as in the adult. Ang-1 is subsequently required for further remodeling and maturation of this initially immature vasculature, and seems to continue to be important in maintaining the quiescence and stability of the mature vasculature. Ang-2 is a competitive antagonist of the actions of Ang-1 on the Tie-2 receptor, and might provide akey role in destabilizing the vasculature in a manner that is necessary for some post-natal vascular remodeling events. Ang-2 may lead to endothelial apoptosis and vessel regression in the absence of VEGF, and promote occurrence of new vessel growth in the presence of VEGF. Recently published data support the hypothesis that a hyperglycemia-induced rise in renal VEGF levels may play a central role in some of the renal changes leading to the development of DN. However, the detailed change of Ang/Tie-2 axis in diabetic renal is rarely reported, the relationship between Ang/Tie-2 axis and the diabetes-related renal microvascular changes is still unknown. We supposed that the change of Ang/Tie-2 axis is associated with diabetic renal microvasculopathy, and the angiogenesis also occurs in renal peritubuli during development of DN..Methods Adult Sprague-Dawley male rats were divided into diabetic group, which were injected with a single intraperitoneal injection of streptozotocin, and control group. Urinary protein, blood sugar, serum urea ,and serum creatinine were monitored respectively at 2, 4, 8, 12, 16, 20, and 24 weeks. Paraffin sections of renal tissue of rats at the same time points were stained by routine methods and immunohistochemistry. The changes of Ang-1, Ang-2, Tie-2, and thrombomodulin-1 (TM-1) were quantificationally analyzed. The expression of Ang-1, Ang-2, and Tie-2 mRNA in renal at the same time points were detected by RT-PCR, and quantified by computer image analysis.Results (DAng-1 mRNA in diabetic renal was significantly upregulated at 4 and 8 weeks, compared with diabetic group at other time points or control group at the same time points, and then downregulatedgradually after 12 weeks. The level of Ang-1 mRNA was evidently decreased at 24 week. Ang-1 was outstandingly expressed in glomeruli. From 4-week to 24-week, the number of Ang-1 staining in diabetic glomeruli was significantly increased as compared with control group, being maximal at 4 and 8 weeks, and subsequently decreased after 12 week. (2) Form 4-week to 16-week, Tie-2 mRNA in diabetic renal was obviously upgrgulated as ompared with controls, with the peak levels at 8 and 12 weeks. Subqequently, this gene became downregulated gradually after 16 week. The expression of Tie-2 was mainly found in glomeruli.Throughout experimental period, the number of Tie-2 staining in diabetic glomeruli was apparently increased as compared with control group, with peak levels at 4 and 8 weeks, and then reduced gradually after 16 week. (3) Ang-2 mRNA in diabetic renal was only detected at 16 and 20 weeks. Ang-2-expressing peritubular microvessel in diabetic renal cortex was found by immuno-histochemistry from 12 -week to 24-week with peak levels at 16 week, but not detected before 8 weeks. (4) TM-1 staining level in diabetic glomeruli was also increased significantly compared with control group at the same time points from 2-week to 20-week. Compared to diabetic group at other time points, the expression of TM-1 was apparently decreased at 24 week. (5) In diabetic group, a strong correlation between Ang-1 and Tie-2 levels was found, and their levels were directly related to TM-1. Ang-1, Tie-2, and TM-1 levels were correlated with renal/body weight, glomerular volume, glomerular area, and urine protein excretion, respectively. (6) In control renal, Ang-1 and Tie-2 mRNA, together with their immunostaining, were also detected, but there were not significant changes at different time pointsduring experiment. No detecable Ang-2 mRNA and immunostaining were found in control renal.Conclusions (1) The change of Ang/Tie-2 axis, which may be the compensative mechanism under diseases conditions, exists in diabetic renal. It is a fact that Ang-1 and Tie-2 are early upregulation, and late down-regulation along with Ang-2 upregulatioh. (2) In diabetic kidney, the change of Ang/Tie-2 axis is partly connected with the renal angiogenesis which is mainly responsible for Ang-1 downregulation and Ang-2 upregulation. (3) It is very important that the formation of new peritubular microvessels may be prevent the development of DN if the angiogenesis become mature, stable and functional vessel by the correct intervention.
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