#3665 DCR2 PROMOTES TUBULAR MALADAPTIVE REPAIR BY INHIBITING KETONE BODY–INDUCED FOXO3 SIGNALING AFTER ACUTE KIDNEY INJURY
Authors: Chen Jia , Chen Kehong , Wang Liming , Luo Jia , He Yani 
Published: June 2023

Abstract

Background and Aims
The proximal tubule has a capacity for repair after acute kidney injury (AKI), but this capacity is limited, especially in severe AKI. Tubular maladaptive repair after AKI leads to chronic kidney disease (CKD), even to end-stage renal disease (ESRD). However, the mechanism of maladaptive repair is not fully clarified, and there is a lack of effective treatment for AKI in clinic. Our previous study found that decoy receptor 2 (DcR2), a trans-membrane receptor of tumor necrosis factor-related apoptosis inducing ligand (TRAIL), was specifically expressed renal tubules and did not have the ability of proliferation in AKI, suggesting DcR2 may be associated with maladaptive repair of tubular cells. This study aims to investigate the role and mechanism of DcR2-positive tubular cells in the repair of AKI.

Method
The DcR2-GFP lineage trace mice,KSP-creDcR2f/f mice (Distal tubular DcR2 Conditional Knockout CKO) mice and GGT1-creDcR2f/f (proximal tubular DcR2 Conditional Knockout CKO) mice were constructed, and three AKI mouse models (moderate and severe ischemia-reperfusion injury and cisplatin-induced AKI) were conducted. Light microscopic examination of paraffin-embedded sections stained with haematoxylin and eosin, periodic acid–Schiff stain and Masson stain. Confocal analysis the co-expression of DcR2-GFP and proximal tubular markers(AQP1, Villin), distal markers (AQP2), failed repair markers (Vcam1, Dcdc2), proliferative markers (Ki-67, Edu, PCNA), Kim1, differentiated markers (pax2, sox9, six2), senescent markers (P16, P21, SA-β-gal), senescent phenotype (IL-6, TGF-β1) and fibrotic markers (a-SMA, collagen I, Fibronectin). And wild type (WT) mice and DcR2 CKO mice were used to compare the degree of kidney injury, renal function and tubular repair after AKI. Furthermore, quantitative proteomics and bioinformatics analyzed the downstream molecules of DcR2 in renal tissues from WT-AKI and CKO-AKI, and validated studied were done.

Results
In this study, we found decoy receptor DcR2 was highly expressed in renal tubules and associated with kidney damage in AKI patients and mouse models. DcR2-GFP transgenic mice verified that DcR2 was specifically expressed in proximal tubular epithelial cells (PTECs) after AKI. The levels of Scr, BUN and urinary DcR2 and renal acute and chronic injury scores were significantly lower inGGT1-creDcR2f/f -AKI than that of WT-AKI. Meanwhile, the proliferative markers, senescent markers and area of renal fibrosis and fibrotic markers expression was decreased inGGT1-creDcR2f/f mice compared with WT. However, the above effects were not obviously improved in KSP-creDcR2f/f mice after AKI. These results suggested that proximal tubular DcR2 knockout alleviated kidney injury and promote tubular repair after AKI. Consistent with findings in vivo, DcR2 promoted cell senescence and inhibited cell proliferation in hypoxia-reoxygenation and cisplatin-treated primary PTECs. Further quantitative proteomics and validated studies showed Hmgcs2, a key enzyme for ketone synthesis, was increased in GGT1-creDcR2f/f mice compared with WT. And the levels of urinary and renal β-hydroxybutyrate (β-OHB) were higher inGGT1-creDcR2f/f mice, suggesting DcR2 affects the synthesis of β-hydroxybutyrate through regulating the expression of Hmgcs2. Inhibition or deletion of Hmgcs2 aggravated kidney damage and repressed renal repair, but administration with β-OHB rescued these phenomena. Subsequently, PTEC-specific DcR2/Hmgcs2 double deletion decreased β-OHB levels, which inhibited FOXO3 signaling by regulating histone acetylation, thereby boosting tubular maladaptive repair after AKI.

Conclusion
DcR2 promotes maladaptive repair of tubular cells by regulating Hmgcs2-induced β-OHB production, and β-OHB affects FOXO3 signaling by regulating histone acetylation. The findings suggests that DcR2/Hmgcs2/ketogenesis/FOXO3 signaling mediates tubular maladaptive repair, and DcR2 could serve as a promising target for improving renal repair and AKI prognosis.