Urinary ATP Synthase Subunit β Is a Novel Biomarker of Renal Mitochondrial Dysfunction in Acute Kidney Injury

Abstract

Although the importance of mitochondrial dysfunction in acute kidney injury (AKI) has been documented, noninvasive early biomarkers of mitochondrial damage are needed. We examined urinary ATP synthase subunit β (ATPSβ) as a biomarker of renal mitochondrial dysfunction during AKI. Mice underwent sham surgery or varying degrees (5, 10, or 15 min ischemia) of ischemia/reperfusion (I/R)-induced AKI. Serum creatinine, BUN, and neutrophil gelatinase-associated lipocalin were elevated only in the 15 min I/R group at 24 h. Immunoblot analysis of urinary ATPSβ revealed two bands (full length ∼52 kDa and cleaved ∼25 kDa), both confirmed as ATPSβ by LC-MS/MS, that increased at 24 h in 10- and 15-min I/R groups. These changes were associated with mitochondrial dysfunction evidenced by reduced renal cortical expression of mitochondrial proteins, ATPSβ and COX1, proximal tubular oxygen consumption, and ATP. Furthermore, in the 15-min I/R group, urinary ATPSβ was elevated until 72 h before returning to baseline 144 h after reperfusion with recovery of renal function. Evaluation of urinary ATPSβ in a nonalcoholic steatohepatitis model of liver injury only revealed cleaved ATPSβ, suggesting specificity of full-length ATPSβ for renal injury. Immunoblot analyses of patient urine samples collected 36 h after cardiac surgery revealed increased urinary ATPSβ levels in patients with postcardiac surgery-induced AKI. LC-MS/MS urinalysis in human subjects with AKI confirmed increased ATPSβ. These translational studies provide evidence that ATPSβ may be a novel and sensitive urinary biomarker of renal mitochondrial dysfunction and could serve as valuable tool for the testing of potential therapies for AKI and chemical-induced nephrotoxicity.

Urinary mitochondrial DNA is a biomarker of mitochondrial disruption and renal dysfunction in acute kidney injury

“…Cytochrome c is a poor renal biomarker as it is only transiently elevated following injury and thus likely serves as a better predictor of degree of renal damage rather than recovery and disease progression. Our group recently reported that urinary levels of the ATP synthase subunit β serve as a biomarker of CPB-induced AKI and I/R-induced AKI in mice; however, the predictive value in this study was not assessed 28 .…”

“…To explore the biological correlates of UmtDNA in the kidney, we used a mouse model of renal I/R injury. Mice were subjected to sham surgery (n=12) or bilateral renal pedicle ligation for 5 (n=4), 10 (n=9) or 15 min (n=11) corresponding to mild, moderate and severe renal histological damage 28 . Mice that produced no or insufficient urine for detection of UmtDNA (n=6) were excluded from further analyses.…”

“…Nevertheless, many previous animal studies have clearly demonstrated mitochondrial damage and dysfunction as key pathophysiological components of the initiation and recovery from I/R-induced AKI. 28 , 41 , 42 .…”

The utility of a differentiated preclinical liver model, HepaRG cells, in investigating delayed toxicity via inhibition of mitochondrial-replication induced by fialuridine

“…Subsequent to this a decrease in ALR was observed, in line with the decrease in cellular ATP-content observed. Using the framework postulated by Kamalian et al for the mechanistic interpretation of Seahorse data, a decrease in ALR and SRC occurring in tandem with a decrease in BR indicates that FIAU inhibits activity of the electron transport chain ( Whitaker et al, 2015 ; Ball et al, 2016 ; Kamalian et al, 2018 ). Further analysis offers additional mechanistic insight.…”

Proteomic Analysis of Kidney Preservation Solutions Prior to Renal Transplantation

“…In our study we found significant correlation between the CIT and the levels of mitochondrial hydroxyl acyl coenzyme A dehydrogenase and ATP synthase subunit beta which suggests an increase in mitochondrial disruption with CIT. Whitaker et al have recently shown increased urinary ATP synthase subunit beta in mice with renal injury and concluded that urinary ATP synthase subunit beta may be a novel and sensitive biomarker of renal mitochondrial dysfunction [37]. …”