Activation of Akt/protein kinase B mediates the protective effects of mechanical stretching against myocardial ischemia-reperfusion injury

Akt/protein kinase B is a well-known cell survival factor and activated by many stimuli including mechanical stretching. Therefore, we evaluated the cardioprotective effect of a brief mechanical stretching of rat hearts and determined whether activation of Akt through phosphatidylinositol 3-kinase (PI3K) is involved in stretch-induced cardioprotection (SIC). Stretch preconditioning reduced infarct size and improved post-ischemic cardiac function compared to the control group. Phosphorylation of Akt and its downstream substrate, GSK-3beta, was increased by mechanical stretching and completely blocked by wortmannin, a PI3K inhibitor. Treatment with lithium or SB216763 (GSK-3beta inhibitors) before ischemia induction mimicked the protective effects of SIC on rat heart. Gadolinium (Gd3+), a blocker of stretch-activated ion channels (SACs), inhibited the stretch-induced phosphorylation of Akt and GSK-3beta. Furthermore, SIC was abrogated by wortmannin and Gd3+. In vivo stretching induced by an aorto-caval shunt increased Akt phosphorylation and reduced myocardial infarction; these effects were diminished by wortmannin and Gd3+ pretreatment. Our results showed that mechanical stretching can provide cardioprotection against ischemia-reperfusion injury. Additionally, the activation of Akt, which might be regulated by SACs and the PI3K pathway, plays an important role in SIC.

Effect of different cyclic stretching strengths on expressions of phospholipase A2 and cyclooxygenase in human tenocytes in vitro / 中华创伤杂志

ObjectiveTo investigate the effect of different cyclic strengths on expressions of phospholipase A2 (PLA2) and cyclooxygenase (COX) in human tenocytes.MethodsHuman tenocytes were uniaxially stretched with different stretching intensity (4％, 8％ and 12％) under 0.5 Hz for four hours.Non-stretched tenocytes were applied to the control group.The expressions of cytosolic PLA2(cPLA2), COX1 and COX2 were measured by Western blot and RT-PCR.The secretion of secretory PLA2 (sPLA2) was measured by ELISA.Results The mRNA expressions of cPLA2, COX1 and COX2 in control group, 4％, 8％ and 12％ stretch groups showed an increase trend.But protein expressions of cPLA2 and COX1 in 4％ stretch group were increased insignificantly compared with the control group (P ＞ 0.05).Protein expressions of cPLA2 and COX1 in 8％ and 12％ stretch groups were increased more significantly compared with the control group (P ＜ 0.01).The COX2 expression in 4％,8％ and 12％ stretch groups showed statistical difference compared with that in the control group (P ＜0.01) and the difference increased with stretch intensity.There was no different expression of sPLA2 between 4％ stretch group and control group (P = 0.260).However, expression of sPLA2 was increased markedly in 8％ and 12％ stretch groups (P ＜ 0.01).ConclusionsThe expressions of human tendnocytes PLA2, COX1 and COX2 in vitro are positively correlated with stretch intensity.PLA2/COX system may be a new molecule target in clinical treatment of tendinopathy.

Relationship of cyclic stretching of human patellar tendon fibroblasts with abnormal increase of prostaglandins E2 and leukotriene B4 / 中华创伤杂志

Objective To investigate the relationship between tendinopathy and higher production of prostaglandins E2 (PGE2) and leukotriene B4 (LTB4) induced by cyclic stretching of human patellar tendon fibroblasts. Methods We used a novel in vitro model system to mimic in vivo conditions, where human patellar tendon fibroblasts (HPTFs) were uniaxially stretched with different magnitudes of stretching (4%, 8% and 12%). Non-stretched fibroblasts were used as control. The productions of PGE2 and LTB4 as well as the expression of cycloxygenase (COX) and 5-lipoxygenase (5-LO) were then measured every four hours of cyclic stretching. In addition, we treated the cells with inhibitors of COX or 5-LO. Results It was found that cyclic stretching of fibroblasts at 8% and 12% of stretching increased PGE2 and LTB4 levels. Blocking the COX enzyme with indomethacin (25 mol/L) decreased PGE2 levels but increased LTB4 production and vice versa. Whereas decreasing LTB4 production with MK-886 (10 ?mol/L) could increase PGE2 levels compared to cells stretched without inhibitors. Conclusions Cyclic stretching of HPTFs produces high levels of PGE2 and LTB4, where a balance exists: blocking PGE2 production increases the production of LTB4, and vice versa. Therefore, this study raises the possibility that the routine use of COX inhibitors in clinical treatment of tendinopathy may exacerbate the condition by causing neutrophil-mediated inflammatory and degenerative changes in the tendon due to increased levels of LTB4, which is a potent chemoattractant for neutrophils.