ERK1/2 Regulates NAD+ Metabolism During Acute Kidney Injury Through microRNA‐34a‐Mediated NAMPT Expression
Authors: Collier Justin B. , Schnellmann Rick G. 
Published: June 2021

BackgroundWe previously demonstrated that extracellular signal‐regulated kinase 1/2 (ERK1/2) is activated rapidly following renal ischemia‐reperfusion injury (IRI) and downregulates PGC‐1α, a transcriptional coactivator involved in the regulation of cellular and mitochondrial metabolism. Recently, renal PGC‐1α has been implicated in regulating nicotinamide adenine dinucleotide (NAD+) biosynthesis leading to better outcomes following acute kidney injury (AKI). NAD+ is a vital coenzyme for cellular energy metabolism, redox signaling, and cellular health. NAD+ is often depleted during injury or disease, and restoration or prevention of this depletion averts worsening injury and often promotes recovery. Therefore, we hypothesized early ERK1/2 activation following injury regulates NAD+ metabolism.MethodsThe MEK1/2 inhibitor trametinib (1mg/kg) was administered intraperitoneally to naïve mice, and as a pretreatment 1 hr before 18.5 min of IRI surgery. Kidney function was determined by serum creatinine. Cell signaling and metabolism was measured using RT‐qPCR, NAMPT activity assays, microRNA quantification, and immunoblot analysis.ResultsTrametinib pretreatment blocked renal ERK1/2 phosphorylation 24 hr post‐IRI and attenuated renal dysfunction as measured by serum creatinine. Following IR‐induced AKI, NAD+ decreased 50% compared to sham, and trametinib pretreatment lessened this decrease to 24%. mRNA expression of NAD+ salvage enzymes NAMPT, NMNAT1/2/3, and NRK1 decreased following renal IRI in vehicle and trametinib‐treated groups. The IRI group had a 50% reduction in NAMPT protein and trametinib pretreatment prevented the loss of NAMPT. The enzymatic activity of NAMPT remained unaffected following renal IRI in all experimental groups. Renal NAMPT protein increased 1.4‐fold in naïve mice receiving trametinib despite no change in NAMPT mRNA; however, ERK1/2 inhibition decreased the NAMPT silencing microRNA miR‐34a 55% compared to controls in the naïve mice. Similarly, trametinib pretreatment reduced miR‐34a 34% at 24 hr following IRI.ConclusionThe current studies reveal that ERK1/2 is a key regulator of renal metabolism during injury by decreasing the rate‐limiting NAD+ enzyme NAMPT and resulting in decreased NAD+. We have also linked ERK1/2 inhibition mediated increases in NAMPT protein to miR‐34a in naïve and IRI mice. miR‐34a can bind and silence NAMPT mRNA, therefore, the reduction in miR‐34a due to ERK1/2 inhibition would allow greater NAMPT mRNA to be translated. Our results reveal a physiological and pathological pathway between ERK1/2 activation and NAD+ metabolism through the rate‐limiting salvage enzyme NAMPT.Support or Funding InformationNational Institutes of Health National Institute of General Medical Sciences [Grant R01GM084147] and Department of Veterans Affairs [Grant BX000851] award to R.G.S.Ruth L. Kirschstein National Research Service Award Individual Predoctoral Fellowship through the National Institutes of Health National Institute of Diabetes and Digestive and Kidney Diseases [Grant F31DK105782] awarded to J.B.C.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.