Funk JA, Schnellmann RG. Persistent disruption of mitochondrial homeostasis after acute kidney injury. Am J Physiol Renal Physiol 302: F853-F864, 2012. First published December 7, 2011 doi:10.1152/ajprenal.00035.2011.-While mitochondrial dysfunction is a pathological process that occurs after acute kidney injury (AKI), the state of mitochondrial homeostasis during the injury and recovery phases of AKI remains unclear. We examined markers of mitochondrial homeostasis in two nonlethal rodent AKI models. Myoglobinuric AKI was induced by glycerol injection into rats, and mice were subjected to ischemic AKI. Animals in both models had elevated serum creatinine, indicative of renal dysfunction, 24 h after injury which partially recovered over 144 h postinjury. Markers of proximal tubule function/injury, including neutrophil gelatinase-associated lipocalin and urine glucose, did not recover during this same period. The persistent pathological state was confirmed by sustained caspase 3 cleavage and evidence of tubule dilation and brush-border damage. Respiratory proteins NDUFB8, ATP synthase ␤, cytochrome c oxidase subunit I (COX I), and COX IV were decreased in both injury models and did not recover by 144 h. Immunohistochemical analysis confirmed that COX IV protein was progressively lost in proximal tubules of the kidney cortex after ischemia-reperfusion (I/R). Expression of mitochondrial fission protein Drp1 was elevated after injury in both models, whereas the fusion protein Mfn2 was elevated after glycerol injury but decreased after I/R AKI. LC3-I/II expression revealed that autophagy increased in both injury models at the later time points. Markers of mitochondrial biogenesis, such as PGC-1␣ and PRC, were elevated in both models. These findings reveal that there is persistent disruption of mitochondrial homeostasis and sustained tubular damage after AKI, even in the presence of mitochondrial recovery signals and improved glomerular filtration.

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Mitochondrial biogenesis occurs under basal conditions and is an adaptive response initiated by cells to maintain energetic demands and metabolic homeostasis after injuries targeting mitochondrial function. Identifying pharmacological agents that stimulate mitochondrial biogenesis is a critical step in the development of new therapeutics for the treatment of these injuries and to test the hypothesis that these agents will expedite recovery of cell and organ function after acute organ injuries. In this study, we examined the effects of

Mitochondrial biogenesis may be an adaptive response necessary for meeting the increased metabolic and energy demands during organ recovery after acute injury, and renal mitochondrial dysfunction has been implicated in the pathogenesis of AKI. We proposed that stimulation of mitochondrial biogenesis 24 hours after ischemia/ reperfusion (I/R)-induced AKI, when renal dysfunction is maximal, would accelerate recovery of mitochondrial and renal function in mice. We recently showed that formoterol, a potent, highly specific, and long-acting b 2 -adrenergic agonist, induces renal mitochondrial biogenesis in naive mice. Animals were subjected to sham or I/Rinduced AKI, followed by once-daily intraperitoneal injection with vehicle or formoterol beginning 24 hours after surgery and continuing through 144 hours after surgery. Treatment with formoterol restored renal function, rescued renal tubules from injury, and diminished necrosis after I/R-induced AKI. Concomitantly, formoterol stimulated mitochondrial biogenesis and restored the expression and function of mitochondrial proteins. Taken together, these results provide proof of principle that a novel drug therapy to treat AKI, and potentially other acute organ failures, works by restoring mitochondrial function and accelerating the recovery of renal function after injury has occurred.