Acute Elevation of Renal Perfusion Pressure Activates Mechanistic Target of Rapamycin Complex 1 in Rats

We have recently reported that the chronic elevation of renal perfusion pressure (RPP) drives the infiltration of renal inflammatory cells in two models of hypertension, the Dahl salt‐sensitive (SS) rats fed a high‐salt diet and Sprague‐Dawley (SD) rats infused with Angiotensin II. In other studies, we have found that chronic inhibition of mechanistic target of rapamycin complex 1 (mTORC1) reduces salt‐induced hypertension in SS rats and inhibits renal immune cell infiltration. mTOR, a kinase, is comprised of two complexes (mTORC1 and mTORC2) which serve to sense and integrate both intracellular and extracellular signals and signal changes of many cellular activities ranging from cell proliferation/growth to immune responses. However, the direct effect of acute RPP on mTOR signaling is largely unknown. In the present study, the effects of acute step changes of RPP upon mTORC1 and mTORC2 signaling were evaluated. Male SD rats (10‐12 weeks of age) were anesthetized with ketamine and thiobutabarbital and aortic and venous catheters inserted for measurement of RPP and infusion of saline containing 2.0% bovine serum albumin. Both ureters were catheterized for urine collection and an ultrasonic flow probe (Transonic) placed around the renal artery to measure renal blood flow (RBF). After 1 hour of equilibrium, control blood pressure (BP), RBF and urine volume was measured for 20 min and BP then raised by ~40 mmHg by aortic occlusion below the left renal artery with ligation of the celiac and mesenteric arteries. After 30 minutes, kidneys were removed for molecular analysis. Sham rats were prepared and studied in the same way, but BP was not changed. RPP was increased from 107 ± 4 to 150 ± 5 mmHg (p<0.05, n=5). RBF remained unchanged averaging 6.9 ± 0.5 vs 7.0 ± 0.8 ml/min/gkw, (p=0.68, n=5) with elevation of RPP. Urine volume was increased from 3.7 ± 0.8 to 21.3 ± 4.9 μl/min/gkw (p< 0.05, n=5). Elevation of RPP increased the functional marker of mTORC1 activity (pS6 S235/236 /S6) in renal cortex (2.8 ± 0.4 vs 4.8 ± 0.5 A.U.; p<0.05, n=5) and outer medulla (2.0 ± 0.3 vs 5.0 ± 0.6 A.U.; p<0.05, n=5) compared to sham rats. In contrast, pAKT S473 /AKT (marker of mTORC2 activity) was not statistically changed in either region. Increased RPP resulted in increases of mRNA expression of Cd68 (marker of monocytes) (5.7 ± 0.4 vs 9.9 ± 1.0 /10 6 18s.; p<0.05, n=5), Lcn2 (marker of innate immune response) (8.8 ± 2.4 vs 25.6 ± 4.5 /10 6 18s.; p<0.05, n=5), Cox2 (prostanoid) (3.1 ± 0.8 vs 11.7 ± 1.0 /10 6 18s.; p<0.05, n=5) and Hmox1 (heme oxygenase) (5.0 ± 5.3 vs 102.9 ± 123.7 /10 6 18s.; p<0.05, n=5) in outer medulla compared to sham rats, and relatively smaller increase in cortex (Cd68 (2.6 ± 0.5 vs 4.0 ± 0.4 /10 6 18s.; p<0.05, n=7), Lcn2 (3.2 ± 0.7 vs 5.0 ± 0.5 /10 6 18s.; p=0.06, n=7), Cox2 (4.0 ± 0.6 vs 7.0 ± 1.0 /10 6 18s.; p=0.08, n=5) and Hmox1 (14.4 ± 6.9 vs 163.1 ± 101.5 /10 6 18s.; p=0.16, n=7)). Acute increases of RPP within the autoregulatory range of the kidney resulted in activation of mTORC1 and inflammation‐related genes within 30 minutes of the stimulus. How mTORC1 senses changes of RPP remains to be determined but it is clear these responses are rapid and most prominent in the renal outer medulla.