Renalase Prevents AKI Independent of Amine Oxidase Activity
Ling Wang*†, Heino Velazquez*, Gilbert Moeckel‡, John Chang*, Ahrom Ham§, H. Thomas
Lee§, Robert Safirstein* and Gary V. Desir*
Author Affiliations
1. *Department of Medicine, Veterans Affairs Connecticut Healthcare System, Yale
University, New Haven, Connecticut;
2. †Renal Division, Renji Hospital, Shanghai Jiaotong University School of Medicine,
Shanghai, China;
3. ‡Department of Pathology, Yale University, New Haven, Connecticut; and
4. §Department of Anesthesiology, College of Physicians and Surgeons of Columbia
University, New York, New York
JASN June 2014 ; vol 25 no. 6 :1226-1235
Correspondence:
Dr. Gary Desir, Section of Nephrology, Department of Medicine, Yale School of Medicine,
P.O. Box 208029, New Haven, CT 06520-8029. Email: gary.desir@yale.edu
ABSTRACT
AKI is characterized by increased catecholamine levels and hypertension. Renalase, a
secretory flavoprotein that oxidizes catecholamines, attenuates ischemic injury and the
associated increase in catecholamine levels in mice. However, whether the amine oxidase
activity of renalase is involved in preventing ischemic injury is debated. In this study,
recombinant renalase protected human proximal tubular (HK- 2) cells against cisplatin- and
hydrogen peroxide–induced necrosis. Similarly, genetic depletion of renalase in mice
(renalase knockout) exacerbated kidney injury in animals subjected to cisplatin-induced AKI.
Interestingly, compared with the intact renalase protein, a 20–amino acid peptide (RP-220),
which is conserved in all known renalase isoforms, but lacks detectable oxidase activity, was
equally effective at protecting HK-2 cells against toxic injury and preventing ischemic injury in
wild-type mice. Furthermore, in vitro treatment with RP-220 or recombinant renalase rapidly
activated Akt, extracellular signal-regulated kinase, and p38 mitogen-activated protein
kinases and downregulated c-Jun N-terminal kinase. In summary, renalase promotes cell
survival and protects against renal injury in mice through the activation of intracellular
signaling cascades, independent of its ability to metabolize catecholamines, and we have
identified the region of renalase required for these effects. Renalase and related peptides
show potential as therapeutic agents for the prevention and treatment of AKI.
COMMENTS
Renalase is a novel secretory flavoprotein with amine oxidase activity. In vitro, renalase
metabolizes epinephrine, norepinephrine, and dopamine and also possesses significant
intrinsic nicotinamide adenine dinucleotide (NADH) oxidase activity. Other investigators have
questioned the amine oxidase activity of renalase. We had proposed that, in contrast to the
classic amine oxidases, renalase reacts with oxygen to generate superoxide anions and
hydrogen peroxide, with subsequent oxidation of catecholamines to their respective
aminochromes.
Recent results indicate that renalase functions as an oxidase/anomerase, using molecular
oxygen to convert α-NAD(P)H to β-NAD+ , with hydrogen peroxide as reaction byproduct.
Because it was also shown to bind epinephrine, the authors pointed out that the hydrogen
peroxide (H2O2) generated from the anomerase reaction will drive the oxidation of
epinephrine to adrenochrome, albeit at a slower rate.
Single-nucleotide polymorphisms present in the gene are associated with hypertension,
cardiac disease, and diabetes. The administration of renalase in wildtype (WT) mice lowers
plasma catecholamines and systemic BP. In contrast, the deficiency of renalase in renalase
knockout (KO) mice raises catecholamine levels and BP.
Renalase also modulates the severity of renal ischemia and reperfusion injury. In WT mice,
the administration of recombinant human renalase before induction of renal ischemia
significantly blunts the severity of renal injury, with less renal tubular necrosis, inflammation,
and apoptosis. In contrast, the lack of renalase in renalase KO mice exacerbates the renal
damage after similar ischemic injury.
AKI is characterized by an elevation in plasma catecholamine levels. It has been postulated
that, in addition to causing hypertension, excess catecholamines in AKI may produce an
inflammatory response, aggravating tissue damage and contributing to multiorgan
dysfunction. Interestingly, renalase levels in the blood and kidneys of WT mice are reduced
following acute renal ischemia. Because the renalase in blood is secreted from the kidneys
and is thought to metabolize circulating catecholamines, the excess catecholamines in AKI
may be a direct consequence of the concurrent renalase deficiency. Notably, the
administration of renalase to WT mice before induction of ischemia, which greatly attenuates
ischemic renal injury, dampens the rise in blood catecholamine levels.
The novel findings are that renalase and short renalase peptides devoid of amine oxidase
activity signal via the AKT and MAPK pathways and that the peptides fully mimic the
cytoprotective actions of recombinant renalase.
The authors have identified the critical region of renalase molecule that mediates its
cytoprotective effects. Finally, renalase protects against toxic and ischemic injury not by its
amine oxidase property but rather by its interaction with an as-yet-unidentified receptor that
activates intracellular signaling in a manner that promotes cell survival.
Pr. Jacques CHANARD
Professor of Nephrology