The efficacy of prior activation of an anti-inflammatory pathway called the cholinergic antiinflammatory pathway (CAP) through vagus nerve stimulation (VNS) has been reported in renal ischemia-reperfusion injury models. However, there have been no reports that have demonstrated the effectiveness of VNS after injury. We investigated the renoprotective effect of VNS in a cisplatin-induced nephropathy model. C57BL/6 mice were injected with cisplatin, and VNS was conducted 24 hours later. Kidney function, histology, and a kidney injury marker (Kim-1) were evaluated 72 hours after cisplatin administration. To further explore the role of the spleen and splenic macrophages, key players in the CAP, splenectomy, and adoptive transfer of macrophages treated with the selective α7 nicotinic acetylcholine receptor agonist GTS-21 were conducted. VNS treatment significantly suppressed cisplatin-induced kidney injury. This effect was abolished by splenectomy, while adoptive transfer of GTS-21-treated macrophages improved renal outcomes. VNS also reduced the expression of cytokines and chemokines, including CCL2, which is a potent chemokine attracting monocytes/macrophages, accompanied by a decline in the number of infiltrating macrophages. Taken together, stimulation of the cAp protected the kidney even after injury in a cisplatin-induced nephropathy model. considering the feasibility and anti-inflammatory effects of VNS, the findings suggest that VNS may be a promising therapeutic tool for acute kidney injury. Despite the advancements in modern medical technology, acute kidney injury (AKI) is still one of the major comorbidities in hospital settings. It is estimated that AKI occurs in approximately 15% of hospitalized patients and 60% of critically ill patients 1 , and morbidity and mortality rates remain high 2,3. In addition, AKI is a risk factor for chronic kidney disease (CKD) and end-stage renal disease (ESRD) 4. Therefore, prevention of AKI development and progression to CKD is essential. Inflammation plays an important role in the pathogenesis of AKI 5. Moreover, chronic inflammation contributes to the progression of CKD. Therefore, suppression of inflammation plays a potential role in treating kidney injury. Recently, a new anti-inflammatory pathway called the cholinergic anti-inflammatory pathway (CAP) has been discovered 6. The CAP consists of both afferent and efferent arms, and both afferent and efferent vagus nerves play important roles. The afferent vagus nerve conducts inflammatory information from the peripheral organs to the central nervous system. In the brainstem, the afferent vagus nerve activates the C1 neurons, which make a major contribution to the central regulation of autonomic function 7 , and further stimulate the efferent vagus nerve 8. Previously, Inoue and Abe et al. reported that vagus nerve stimulation (VNS) protected the kidney from ischemia-reperfusion injury (IRI) through activation of the CAP 9. Although there are many kinds of inflammatory cells such as B cells, T cells, and dendritic cells ...
The relevance of primary cilia shortening in kidney disease and its pathomechanism are largely unknown. Tubular damage in acute kidney injury (AKI) is strongly associated with mitochondrial dysfunction. Thus, we investigated the interaction between primary cilia and mitochondria in cisplatin-induced AKI mouse models. We observed that the expression of intraflagellar transport 88 (IFT88), a ciliary maintenance protein, was decreased in the renal cortex following tubular damage due to cisplatin-induced AKI. This result was consistent with the decreased IFT88 expression in cisplatin-treated RPTEC/TERT1 cells-human primary proximal tubular cells-parallel to the shortening of primary cilia, suggesting a causative link between tubular damage and IFT88-mediated cilia regulation. To address the effect of impaired primary cilia with decreased IFT88 expression on tubular function, RPTEC/TERT1 cells treated with cisplatin and knocked down for IFT88 using siRNA (IFT88-KD) were assessed for phenotypic changes and mitochondrial metabolic function. Both cisplatin and IFT88-KD caused primary cilia shortening, downregulated mitochondrial oxidative phosphorylation capacity, defective fatty acid oxidation (FAO), and decreased ATP production. Furthermore, IFT88 overexpression enhanced mitochondrial respiration, which partially counteracted cisplatin-induced defective FAO. These results are indicative of the contribution of IFT88 to mitochondrial homeostasis. Our findings suggest that tubular mitochondrial dysfunction in cisplatin-induced AKI is mediated, at least in part, by a decrease in IFT88 expression with primary cilia shortening. That is, tubular mitochondrial damage followed by tubular injury in AKI may occur through alteration of IFT88 expression and subsequent ciliary shortening in tubular cells.
BackgroundThe sympathetic nervous system regulates immune cell dynamics. However, the detailed role of sympathetic signaling in inflammatory diseases is still unclear because it varies according to the disease situation and responsible cell types. This study focused on identifying the functions of sympathetic signaling in macrophages in LPS-induced sepsis and renal ischemia-reperfusion injury (IRI).MethodsWe performed RNA sequencing of mouse macrophage cell lines to identify the critical gene that mediates the anti-inflammatory effect of β2-adrenergic receptor (Adrb2) signaling. We also examined the effects of salbutamol (a selective Adrb2 agonist) in LPS-induced systemic inflammation and renal IRI. Macrophage-specific Adrb2 conditional knockout (cKO) mice and the adoptive transfer of salbutamol-treated macrophages were used to assess the involvement of macrophage Adrb2 signaling.ResultsIn vitro, activation of Adrb2 signaling in macrophages induced the expression of T cell Ig and mucin domain 3 (Tim3), which contributes to anti-inflammatory phenotypic alterations. In vivo, salbutamol administration blocked LPS-induced systemic inflammation and protected against renal IRI; this protection was mitigated in macrophage-specific Adrb2 cKO mice. The adoptive transfer of salbutamol-treated macrophages also protected against renal IRI. Single-cell RNA sequencing revealed that this protection was associated with the accumulation of Tim3-expressing macrophages in the renal tissue.ConclusionsThe activation of Adrb2 signaling in macrophages induces anti-inflammatory phenotypic alterations partially via the induction of Tim3 expression, which blocks LPS-induced systemic inflammation and protects against renal IRI.
Necroptosis is a programmed cell death that is characterized by regulated necrosis resulting in plasma membrane rupture and subsequent release of damage-associated molecular patterns (DAMPs). Receptor-interacting protein kinase 3 (RIPK3) is a key mediator of this pathway. Accumulating evidence supports a critical role of RIPK3 and the necroptosis pathway in various human diseases. In this review, we discuss recent investigations that have uncovered pathogenic roles of RIPK3 in both acute kidney injury (AKI) and kidney fibrosis. RIPK3 promotes kidney tubular injury via a mechanism involving mitochondrial dysfunction. Additionally, extracellular mitochondrial DNA, which is one of the necroptotic DAMPs, released from damaged mitochondria correlates with kidney tubular injury and represents a potential novel biomarker. RIPK3 also induces kidney fibrogenesis through AKT-dependent activation of the metabolic enzyme ATP citrate lyase. Thus, the RIPK3-mediated necroptosis pathway may serve as a promising new therapeutic target in AKI and kidney fibrosis.
Systemic iron metabolism is disrupted in chronic kidney disease (CKD). However, little is known about local kidney iron homeostasis and its role in kidney fibrosis. Kidneyspecific effects of iron therapy in CKD also remain elusive. Here, we elucidate the role of macrophage iron status in kidney fibrosis and demonstrate that it is a potential therapeutic target. In CKD, kidney macrophages exhibited depletion of labile iron pool (LIP) and induction of transferrin receptor 1, indicating intracellular iron deficiency. Low LIP in kidney macrophages was associated with their defective antioxidant response and pro-inflammatory polarization. Repletion of LIP in kidney macrophages through knockout of ferritin heavy chain (Fth1) reduced oxidative stress and mitigated fibrosis.Similar to Fth1 knockout, iron dextran therapy, through replenishing macrophage LIP, reduced oxidative stress, decreased the production of pro-inflammatory cytokines, and alleviated kidney fibrosis. Interestingly, iron significantly decreased TGF-β expression and suppressed TGF-β-driven fibrotic response of macrophages. Iron dextran therapy and FtH suppression had an additive protective effect against fibrosis. Adoptive transfer of iron-loaded macrophages alleviated kidney fibrosis, confirming the protective effect of iron-replete macrophages in CKD. Thus, targeting intracellular iron deficiency of kidney macrophages in CKD can serve as a therapeutic opportunity to mitigate disease progression.
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