Metabolic acidosis inhibits AMPK function in kidney cells

Abstract

The metabolic sensor AMP‐activated protein kinase (AMPK) is stimulated by cellular metabolic depletion. We have shown that AMPK activation inhibits kidney membrane transport proteins. AMPK‐activated processes protect kidney cells from further metabolic depletion and damage. AMPK is tightly regulated, and its pharmacological activation can protect kidneys from superimposed injury, such as acute kidney injury (AKI). Conversely, AMPK is inhibited in chronic kidney disease (CKD). Therefore, pharmacologic AMPK activators are proposed as therapies to slow CKD progression. However, the mechanisms by which AMPK may promote kidney survival are unclear. CKD results in metabolic acidosis (MA) due to the inability of kidneys to excrete non‐volatile acid. MA, if untreated, has severe health sequelae such as worsening of kidney function. We hypothesized that there is cross‐talk between acid‐base status and AMPK signaling, and that dysregulation of AMPK function by MA disrupts kidney regeneration in the setting of CKD. We used kidney epithelial cell lines in culture and adult male C57BL/6 mice (WT) and AMPKβ1‐KO mice for our experiments. Cells were exposed to media at either pH 7.3–7.4 (control) or 6.9–7.0 (acidic) for 3 d ± an AMPK activator (last 16 h). We found that, as compared to cells grown at pH 7.4, kidney cells grown in acidic media have reduced baseline AMPK activity and blunted pharmacologic AMPK activation. We then evaluated changes in AMPK function in WT mice fed a normal diet vs. WT mice given 1.5% saccharin ± 0.28 M NH4Cl in drinking water for 2 mo. To evaluate the AMPK pathway in kidney tissue, we examined levels of phosphorylation of acetyl CoA carboxylase (pACC) by immunoblot. Mice on the acidogenic diet developed MA without significant weight loss compared to mice on the control diet (blood pH 7.2 vs 7.3 ± 0.01). In mice after UNX, the superimposed MA induced a statistically significant decrease in pACC, compared to mice with UNX on a control diet. We also evaluated differences in BUN in WT vs. AMPKβ1‐KO mice 3 mos. after sham surgery or UNX, a model for reduced kidney mass. Both WT and KO mice post‐UNX had significant worsening of kidney function (higher BUN) compared to sham‐operated mice of the same genotype. However, we did not observe any significant differences in BUN between WT and KO mice following sham or UNX. Our results point to worsening in kidney function post‐UNX and to a direct inhibition of the AMPK pathway in the setting of reduced kidney mass and MA. This AMPK inhibition may be detrimental to kidney regeneration in these settings.Support or Funding InformationKeck School of Medicine of USC; USC/UKRO Kidney Research CenterThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.