SUN-004 Osteocrin, a bone-originated humoral factor, exerts a renoprotective role in ischemia-reperfusion injury in mice

Abstract

Natriuretic peptides (NPs; atrial, brain and C-type NPs: ANP, BNP and CNP) constitute the hormonal basis of the heart-kidney network, in which the remote organs influence each other under physiological and pathophysiological conditions. We recently reported that osteocrin (Ostn), originally identified as a secretory peptide in the bone and muscle, exerted bone elongation and cardioprotective effects through antagonizing NP clearance receptor NPR3. Of note, SNPs of the Ostn and NPPA/NPPB gene loci are reportedly related to a renal function decline risk by genome-wide association studies. However, the role of Ostn in the kidney has not been clarified yet. To investigate the role of Ostn, we generated systemic Ostn knockout (KO) mice, and mated with liver-specific SAP promoter-driven Ostn-transgenic mice (KO-Tg). Wild-type (WT), KO and KO-Tg mice were subjected to ischemia-reperfusion injury (IRI) by unilateral renal artery clamping. Samples were collected at 3 weeks after IRI. Ostn expression in the kidney was evaluated by X-gal immunostaining using Ostn-LacZ knockin mice. To explore the detailed alteration of Wnt-βcatenin pathway which is important for kidney fibrosis, we performed PCR-array analysis in the kidney between KO and KO-Tg mice. In atrophic and fibrotic kidneys after IRI of WT, Ostn mRNA was increased in parallel with NPR3 and CNP upregulation, but not in the contralateral or pre-IRI kidneys. Furthermore, CNP expression was markedly suppressed in the contralateral kidney after IRI. These changes were either enhanced or suppressed in KO or KO-Tg, respectively, suggesting that Ostn affects the regulation of CNP and NPR3 expression in the kidney. In KO kidneys, mRNA expression of neutrophil gelatinase-associated lipocalin (NGAL) and IL-1b was further enhanced. In KO-Tg, fibrosis and atrophy were significantly ameliorated compared to WT and KO, together with the decreased expression of pro-fibrotic (aSMA, TGF-b), pro-inflammatory (IL-1b, TNFa) and tubular injury maker (NGAL, KIM-1) genes. And also, PCR-array analysis revealed that the upregulation of Wnt-βcatenin pathway was suppressed in KO-Tg compared with KO. Similar results were obtained from MMP-7 and Myc which are induced in the downstream target of this pathway. Furthermore, X-gal immunostaining revealed that endogenous Ostn expression was induced by IRI in damaged-tubular epithelial cells of corticomedullary junction in the kidney. This was co-localized with the expression of MMP-7 and Wnt2, also induced by IRI. Exacerbation of IRI-induced kidney injury in Ostn-deficient mice was attenuated by ectopic overexpression of Ostn. Our data suggest a renoprotective role of Ostn, and could provide a potential therapeutic strategy against acute kidney injury.