Acute renal ischemia rapidly activates the energy sensor AMPK but does not increase phosphorylation of eNOS-Ser¹¹⁷⁷

Abstract

A fundamental aspect of acute renal ischemia is energy depletion, manifest as a falling level of ATP that is associated with a simultaneous rise in AMP. The energy sensor AMP-activated protein kinase (AMPK) is activated by a rising AMP-to-ATP ratio, but its role in acute renal ischemia is unknown. AMPK is activated in the ischemic heart and is reported to phosphorylate both endothelial nitric oxide synthase (eNOS) and acetyl-CoA carboxylase. To study activation of AMPK in acute renal ischemia, the renal pedicle of anesthetized Sprague-Dawley rats was cross-clamped for increasing time intervals. AMPK was strongly activated within 1 min and remained so after 30 min. However, despite the robust activation of AMPK, acute renal ischemia did not increase phosphorylation of the AMPK phosphorylation sites eNOS-Ser(1177) or acetyl-CoA carboxylase-Ser(79). Activation of AMPK in bovine aortic endothelial cells by the ATP-depleting agent antimycin A and the antidiabetic drug phenformin also did not increase phosphorylation of eNOS-Ser(1177), confirming that AMPK activation and phosphorylation of eNOS are dissociated in some situations. Immunoprecipitation studies demonstrated that the dissociation between AMPK activation and phosphorylation of eNOS-Ser(1177) was not due to changes in the physical associations between AMPK, eNOS, or heat shock protein 90. In conclusion, acute renal ischemia rapidly activates the energy sensor AMPK, which is known to maintain ATP reserves during energy stress. The substrates it phosphorylates, however, are different from those in other organs such as the heart.

Mechanistic Analysis of Nonoxygenated Hypothermic Machine Perfusion’s Protection on Warm Ischemic Kidney Uncovers Greater eNOS Phosphorylation and Vasodilation

“…In this work, eNOS phosphorylation occurred specifically during MP and our data suggest that this is an AMPKa-dependent (MP specifically activated AMPKa but not Akt or PKA compared to CS). We also show that AMPKa is dephosphorylated during warm ischemia, contrasting with a reported increased AMPKa phosphorylation after 30 min of renal warm ischemia in rats (40). This inconsistency may be related to a longer warm ischemia in our study or to differences in renal physiology between rodents and pigs (41).…”

Endothelium-dependent vasorelaxation to the AMPK activator AICAR is enhanced in aorta from hypertensive rats and is NO and EDCF dependent

“…A number of cell culture and in vitro biochemical experiments have demonstrated that AMPK can phosphorylate eNOS at activation site Ser 1177 (5, 6, 8, 12, 29, 40) and that AMPK activation has been associated with increased NO release from endothelial cells (5,8,12,40), establishing NO as a potential mediator of endotheliumdependent effects of AMPK. However, AMPK activation does not result in eNOS phosphorylation under some conditions (19,41), suggesting that AMPK activity and eNOS phosphorylation can be dissociated and that the influence of AMPK on NOmediated vasomotor function may also involve other mechanisms in addition to the Ser 1177 phosphorylation-mediated activation of eNOS. Although some studies infer that NO-dependent relaxation stimulated by AMPK-mediated activation of eNOS may be possible, there is limited evidence from previous studies that acute activation of AMPK is capable of generating functional vasodilatory outcomes by this mechanism in an intact blood vessel or in the context of an in vivo vascular system (3,4).…”

AMP-activated protein kinase regulates the vacuolar H+-ATPase via direct phosphorylation of the A subunit (ATP6V1A) in the kidney

“…Coregulation of the proton pump by these two kinases could be critical in scenarios where distal nephron proton secretion is needed to maintain or restore acid-base homeostasis in conjunction with a decrease in kidney perfusion. For example, renal hypoperfusion during shock should activate AMPK acutely (33), which would inhibit V-ATPase-mediated proton secretion. Conversely, increased plasma CO 2 levels would act to increase collecting duct proton secretion (44) via acute activation of sAC and downstream activation of PKA (16,18,57).…”