The absence of fluid shear stress reduces AMPK activity in the renal I/R process

Objective To investigate the mechanism of renal injury induced by changes in flow shear stress (FSS) during renal ischemia/reperfusion (I/R). Methods 1. In vitro, HUVECs were divided into 4 groups: (1) HUVECs were loaded with 12 dyn/cm2 force for 30, 45, and 90 min by using plate fluid chamber system. (2) Cells were loaded with FSS for 2 h, and then cultured for 1, 3, 8 and 12 h respectively; (3) HUVECs were pretreated with 0, 1, 2, 4 and 8 mmol metformin and cultured for 24 h. (4) HUVECs in control group were cultured normally. The expression of p-AMPK/AMPK protein was detected by Western blotting in each group. 2. In vivo, 16 SD rats with successful establishment of IR model were randomly divided into 4 groups (n=4 in each group): (1) static cold storage (CS) group: isolated kidneys were stored for 4 h; (2) hypothermia machine perfusion (HMP) group: isolated kidneys were continuously perfused with 0 ℃ lactated Ringer's solution for 4 h; (3)metformin treatment group (Met-CS): metformin was intraperitoneally injected 3 days before surgery, and the isolated kidneys were obtained after cold preservation for 4 h; (4)rat kidneys of control group were just subjected to thermal ischemia for 30 min. The injury of renal tissue in each group was observed by TUNEL and HE staining. The expression and distribution of p-AMPK protein in renal tissues were detected by immunohistochemistry. The correlation between FSS loss and AMPK expression in kidney tissue was analyzed. Results The expression of p-AMPK in HUVECs could be up-regulated by FSS, and the expression of p-AMPK protein increased with the prolongation of time. After stopping FSS, the expression of p-AMPK protein in HUVECs gradually decreased with time (P<0.05). Metformin could activate AMPK activity in a concentration-dependent manner (P<0.05). The content of p-AMPK in renal tissue of HMP group was significantly higher than that of CS group (P<0.05). The expression of p-AMPK in renal tissue of HMP group mainly distributed in the renal tubules, and few in glomerular endothelial cells and blood vessels. The apoptosis rate of renal tissue in HMP group was significantly lower than that in CS group (P<0.05). In the HMP group, the damage of the renal tissue was mild, there was no swelling, and the renal tubules were slightly expanded. In the CS group, the renal tissue was severely damaged and the renal tubules were markedly swollen. Conclusion During the course of renal IR in rats, changes in FSS may affect renal tissue damage through the AMPK pathway. Key words: Rats; Ischemia-reperfusion; Fluid shear stress; Hypothermia machine perfusion; AMPK; Metformin