ABSTRACT
AIM:To investigate the mechanism of angiotensinⅡ(AngⅡ)/angiotensinⅡ type 1 receptor (AT1R)pathway activating protein phosphatase 2A(PP2A)which leads to down-regulation endothelial nitric oxide syn-thase(eNOS)phosphorylation level in mesenteric arteries of rats.METHODS: METHODS: The mesenteric arteries of adult male SD rats(weighing 160~180 g;n=90)were isolated under aseptic conditions.Firstly,to determine the effect of angiotensinⅡdown-regulated eNOS(Ser1177)phosphorylation level,the mesenteric arteries were randomly divided into normal control(control)group and AngⅡgroup.The mesenteric arteries in AngⅡgroup were incubated with AngⅡat 1×10 -7mol/L,1×10 -6mol/L and 1×10 -5mol/L for 6 h,12 h and 24 h,respectively.Secondly,to investigate the mo-lecular mechanism by which angiotensinⅡ activated PP2A leading to down-regulation eNOS(Ser1177)phosphorylation level,the mesenteric arteries were randomly divided into control group, AngⅡ group and candesartan(CAN; a specific AT1R blocker)+AngⅡgroup.The mesenteric arteries were pretreated with 1×10 -5mol /L CAN for 1 h,then incubated with 1×10 -7mol/L AngⅡfor 12 h in CAN+AngⅡgroup.The protein levels of eNOS,p-eNOS(Ser1177),PP2Ac,p-PP2Ac(Tyr307)and protein phosphatase 2A inhibitor 2(IPP2A2 )in the arteries were determined by Western blot.The ac-tivity of PP2A in the arteries was detected by PP2A activity kit.RESULTS:Compared with the control group,the protein level of p-eNOS(Ser1177)in the mesenteric arteries was decreased after incubated with AngⅡfor 6 h,12 h and 24 h(P<0.05).The decreasing tendency of p-eNOS(Ser1177)showed concentration-dependently,especially in 12 h and 24 h groups.The expression of eNOS protein showed no significant difference in each group.Compared with the control group, the mesenteric arteries of the rats were incubated with AngⅡ at 1×10-7mol/L for 12 h in vitro, the protein levels of p-eNOS(Ser1177)were down-regulated(P<0.05); pretreatment with CAN significantly increased the protein level of p-eNOS(Ser1177)(P<0.05);the protein levels of eNOS showed no significant difference in each group.Compared with the control group,the protein levels of p-PP2Ac(Tyr307)and IPP2A2 were decreased after the mesenteric arteries were trea-ted with AngⅡat 1×10 -7mol/L for 12 h(P<0.05).Candesartan pretreatment restored the protein levels of p-PP2Ac (Tyr307)and IPP2A2 (P<0.05),however the expression of PP2Ac protein showed no significant difference in each group. Compared with the control group,the activity of PP2A was increased in the mesenteric arteries incubated with AngⅡat 1× 10-7mol/L for 12 h(P<0.05).Candesarten pretreatment inhibited the activity of PP 2A significantly(P<0.05).CON-CLUSION:AngⅡincreases PP2A activity via AT1R pathway,thus leading to down-regulation eNOS(Ser1177)phospho-rylation level in mesenteric arteries.The molecular mechanism of PP2A activation may be associated with decreasing the protein levels of p-PP2Ac(Tyr307)and IPP2A2.