#921 Interferon regulatory factor 4 (IRF4)-specific deletion on dendritic cells protects against kidney inflammation and injury in IRI-induced AKI/AKD
Authors: Long Hao , Anders Hans Joachim , Lichtnekert Julia 
Published: May 2024

Abstract

Background and Aims
Ischemia-reperfusion injury (IRI) is a frequent clinical cause of acute kidney injury and disease (AKI/AKD) which can lead to acute tubular necrosis and irreversible kidney function loss. Mononuclear phagocytes, including dendritic cells (DCs), Monocytes, and macrophages, play important roles in various phases of injury and repair processes. Previous research has indicated that conventional dendritic cells (cDCs) are subdivided into cDC1s and cDC2s, and these two subsets could have opposing functions. We also demonstrated that cDC1s have a protective role as deficiency of cDC1s results in aggravated inflammation and injury in the IRI-induced AKI/AKD model in our previous study. Based on these researches, we aim to investigate the function of cDC2s in the IRI-induced AKI/AKD model.

Method
We used interferon regulatory factor 4 (IRF4)-deficient mice (IRF4fl/flClec9acre) to specifically delete IRF4 on DC lineage cells as our experimental group, and used wide-type mice as our control group. After unilateral IRI (UIRI) surgery, we measured the GFR and plasma creatinine of the mice on day 1 (D1) and day 5 (D5), then collected the injured kidney issue after sacrificing mice. We compared the differences between IRF4fl/flClec9acre mice and wild-type mice in terms of DC subpopulation changes, neutrophil accumulation, T cell differentiation, intensity of inflammatory responses, and tissue repair capabilities in damaged kidney tissue, by using techniques such as immunohistochemistry, immunofluorescence, flow cytometry, qRT-PCR, etc.

Results
([KOMean-WTMean] ± SEM): IRF4fl/flClec9acre mice showed a lower percentage of cDC2s without affecting cDC1s in the kidney compared with wide-type mice (D1: −0.04467 ± 0.01356, P = 0.0301; D5: −1.108 ± 0.2248, P = 0.0004). During post-ischemic AKI/AKD, IRF4 deficiency in cDCs had several beneficial effects compared to wild-type mice, including reducing renal tubular cell injury (PAS score D1: −0.9375 ± 0.1523, P &lt; 0.0001; PAS score D5: −1.119 ± 0.1445, P &lt; 0.0001), decreasing loss of kidney function (GFR D1: 8.983 ± 4.091, P = 0.1041; GFR D5: 14.9 ± 5.01, P = 0.0172), and promoting kidney function recovery. This was associated with increased expression of anti-inflammatory cytokines (IL-4 D1: 4.486 ± 1.363, P = 0.0079; IL-4 D5: 3.403 ± 1.447, P = 0.0366; IL-10 D1: 2.103 ± 0.7342, P = 0.0299; IL-10 D5: 2.654 ± 0.8859, P = 0.0166), decreased expression of pro-inflammatory cytokines(TNF-α D1: −1.418 ± 0.5467, P = 0.0433; TNF-α D5: −2.434 ± 1.919, P = 0.0074; IL-23a D1: −1.320 ± 0.3432, P = 0.0061; IL-23a D5: −16.12 ± 3.587, P = 0.0004) and acute tubular cell death, reduced neutrophil chemoattractant expression (CXCL-2) (Fig. 6) and recruitment of neutrophils (−6.107 ± 1.664, P = 0.0214), and differentiation of Th2 (−0.1867 ± 0.03333, P = 0.005) and Th17 cells (−0.1767 ± 0.01333, P = 0.0002).

Conclusion
In conclusion, our data demonstrate a critical role of IRF4 in the kidney cDC2 subset and highlight that deficiency of cDC2s can protect against kidney inflammation, reduce kidney injury, and promote kidney recovery in the IRI-induced AKI/AKD model. This suggests that cDC2s have an immunoregulatory role in AKI/AKD and could serve as a potential therapeutic target for kidney inflammation.