IRF8-Dependent Type I Conventional Dendritic Cells (cDC1s) Control Post-Ischemic Inflammation and Mildly Protect Against Post-Ischemic Acute Kidney Injury and Disease

IRF8 maintains mononuclear phagocyte and neutrophil function in acute kidney injury

Immune cells are key players in acute tissue injury and inflammation, including acute kidney injury (AKI). Their development, differentiation, activation status, and functions are mediated by a variety of transcription factors, such as interferon regulatory factor 8 (IRF8) and IRF4. We speculated that IRF8 has a pathophysiologic impact on renal immune cells in AKI and found that IRF8 is highly expressed in blood type 1 conventional dendritic cells (cDC1s), monocytes, monocyte-derived dendritic cells (moDCs) and kidney biopsies from patients with AKI. In a mouse model of ischemia‒reperfusion injury (IRI)-induced AKI, Irf8 -/- mice displayed increased tubular cell necrosis and worsened kidney dysfunction associated with the recruitment of a substantial amount of monocytes and neutrophils but defective renal infiltration of cDC1s and moDCs. Mechanistically, global Irf8 deficiency impaired moDC and cDC1 maturation and activation, as well as cDC1 proliferation, antigen uptake, and trafficking to lymphoid organs for T-cell priming in ischemic AKI. Moreover, compared with Irf8 +/+ mice, Irf8 -/- mice exhibited increased neutrophil recruitment and neutrophil extracellular trap (NET) formation following AKI. IRF8 primarily regulates cDC1 and indirectly neutrophil functions, and thereby protects mice from kidney injury and inflammation following IRI. Our results demonstrate that IRF8 plays a predominant immunoregulatory role in cDC1 function and therefore represents a potential therapeutic target in AKI.

Tolerogenic CD11c+dendritic cells regulate CD4+Tregs in replacing delayed ischemic preconditioning to alleviate ischemia-reperfusion acute kidney injury

Ischemia-reperfusion injury (IRI) is one of the primary clinical causes of acute kidney injury (AKI). The key to IRI lies in immune-inflammatory damage, where dendritic cells (DCs) play a central role in eliciting immune responses within the context of inflammation induced by ischemia-reperfusion. Our previous study has confirmed that delayed ischemic preconditioning (DIPC) can reduce the kidney injury by mediating DCs to regulate T-cells. However, the clinical feasibility of DIPC is limited, as pre-clamping of the renal artery is not applicable for the prevention and treatment of ischemia-reperfusion acute kidney injury (I/R-AKI) in clinical patients. Therefore, the infusion of DCs as a substitute for DIPC presents a more viable strategy for preventing renal IRI. In this study, we further evaluated the impact and mechanism of infused tolerogenic CD11c+DCs on the kidneys following IRI by isolating bone marrow-derived dendritic cells and establishing an I/R-AKI model after pre-infusion of DCs. Renal function was significantly improved in the I/R-AKI mouse model after pre-infused with CD11c+DCs. The pro-inflammatory response and oxidative damage were reduced, and the levels of T helper 2 (Th2) cells and related anti-inflammatory cytokines were increased, which was associated with the reduction of autologous DCs maturation mediated by CD11c+DCs and the increase of regulatory T-cells (Tregs). Next, knocking out CD11c+DCs, we found that the reduced immune protection of tolerogenic CD11c+DCs reinfusion was related to the absence of own DCs. Together, pre-infusion of tolerogenic CD11c+DCs can replace the regulatory of DIPC on DCs and T-cells to alleviate I/R-AKI. DC vaccine is expected to be a novel avenue to prevent and treat I/R-AKI.

Recent Advances in Understanding Peripheral and Gut Immune Cell-Mediated Salt-Sensitive Hypertension and Nephropathy

Hypertension is the primary modifiable risk factor for cardiovascular, renal, and cerebrovascular diseases and is considered the main contributing factor to morbidity and mortality worldwide. Approximately 50% of hypertensive and 25% of normotensive people exhibit salt sensitivity of blood pressure, which is an independent risk factor for cardiovascular disease. Human and animal studies demonstrate that the immune system plays an important role in the etiology and pathogenesis of salt sensitivity of blood pressure, kidney damage, and vascular diseases. Antigen-presenting and adaptive immune cells are implicated in salt-sensitive hypertension and salt-induced renal and vascular injury. Elevated sodium activates antigen-presenting cells to release proinflammatory cytokines including IL (interleukin) 6, tumor necrosis factor-α, IL-1β, and accumulate isolevuglandin-protein adducts. In turn, these activate T cells release prohypertensive cytokines including IL-17A. Moreover, high-salt intake is associated with gut dysbiosis, leading to inflammation, oxidative stress, and blood pressure elevation but the mechanistic contribution to salt-sensitivity of blood pressure is not clearly understood. Here, we discuss recent advances in research investigating the cause, potential biomarkers, and therapeutic targets for salt-sensitive hypertension as they pertain to the gut microbiome, immunity, and inflammation.

Advances in understanding of dendritic cell in the pathogenesis of acute kidney injury

Acute kidney injury (AKI) is characterized by a rapid decline in renal function and is associated with a high morbidity and mortality rate. At present, the underlying mechanisms of AKI remain incompletely understood. Immune disorder is a prominent feature of AKI, and dendritic cells (DCs) play a pivotal role in orchestrating both innate and adaptive immune responses, including the induction of protective proinflammatory and tolerogenic immune reactions. Emerging evidence suggests that DCs play a critical role in the initiation and development of AKI. This paper aimed to conduct a comprehensive review and analysis of the role of DCs in the progression of AKI and elucidate the underlying molecular mechanism. The ultimate objective was to offer valuable insights and guidance for the treatment of AKI.

Macrophages and fibrosis: how resident and infiltrating mononuclear phagocytes account for organ injury, regeneration or atrophy

Mononuclear phagocytes (MP), i.e., monocytes, macrophages, and dendritic cells (DCs), are essential for immune homeostasis via their capacities to clear pathogens, pathogen components, and non-infectious particles. However, tissue injury-related changes in local microenvironments activate resident and infiltrating MP towards pro-inflammatory phenotypes that contribute to inflammation by secreting additional inflammatory mediators. Efficient control of injurious factors leads to a switch of MP phenotype, which changes the microenvironment towards the resolution of inflammation. In the same way, MP endorses adaptive structural responses leading to either compensatory hypertrophy of surviving cells, tissue regeneration from local tissue progenitor cells, or tissue fibrosis and atrophy. Under certain circumstances, MP contribute to the reversal of tissue fibrosis by clearance of the extracellular matrix. Here we give an update on the tissue microenvironment-related factors that, upon tissue injury, instruct resident and infiltrating MP how to support host defense and recover tissue function and integrity. We propose that MP are not intrinsically active drivers of organ injury and dysfunction but dynamic amplifiers (and biomarkers) of specific tissue microenvironments that vary across spatial and temporal contexts. Therefore, MP receptors are frequently redundant and suboptimal targets for specific therapeutic interventions compared to molecular targets upstream in adaptive humoral or cellular stress response pathways that influence tissue milieus at a contextual level.

Asymptomatic Hyperuricemia Promotes Recovery from Ischemic Organ Injury by Modulating the Phenotype of Macrophages

Acute organ injury, such as acute kidney injury (AKI) and disease (AKD), are major causes of morbidity and mortality worldwide. Hyperuricemia (HU) is common in patients with impaired kidney function but the impact of asymptomatic HU on the different phases of AKI/AKD is incompletely understood. We hypothesized that asymptomatic HU would attenuate AKD because soluble, in contrast to crystalline, uric acid (sUA) can attenuate sterile inflammation. In vitro, 10 mg/dL sUA decreased reactive oxygen species and interleukin-6 production in macrophages, while enhancing fatty acid oxidation as compared with a physiological concentration of 5 mg/dL sUA or medium. In transgenic mice, asymptomatic HU of 7–10 mg/dL did not affect post-ischemic AKI/AKD but accelerated the recovery of kidney excretory function on day 14. Improved functional outcome was associated with better tubular integrity, less peritubular inflammation, and interstitial fibrosis. Mechanistic studies suggested that HU shifted macrophage polarization towards an anti-inflammatory M2-like phenotype characterized by expression of anti-oxidative and metabolic genes as compared with post-ischemic AKI-chronic kidney disease transition in mice without HU. Our data imply that asymptomatic HU acts as anti-oxidant on macrophages and tubular epithelial cells, which endorses the recovery of kidney function and structure upon AKI.