Renal macrophages monitor and remove particles from urine to prevent tubule obstruction

Crosstalk between macrophages and adjacent cells in AKI to CKD transition

Acute kidney injury (AKI), triggered by ischemia, sepsis, toxicity, or obstruction, is marked by a rapid impairment of renal function and could lead to the initiation and advancement of chronic kidney disease (CKD). The concept of AKI to CKD transition has gained much interest. Despite a series of studies highlighting the diverse roles of renal macrophages in the immune response following AKI, the intricate mechanisms of macrophage-driven cell-cell communication in AKI to CKD transition remains incompletely understood. In this review, we introduce the dynamic phenotype change of macrophages under the different stages of kidney injury. Importantly, we present novel perspectives on the extensive interaction of renal macrophages with adjacent cells, including tubular epithelial cells, vascular endothelial cells, fibroblasts, and other immune cells via soluble factors, extracellular vesicles, and direct contact, to facilitate the transition from AKI to CKD. Additionally, we summarize the potential therapeutic strategies based on the adverse macrophage-neighboring cell crosstalk.

Activation of mannose receptor C type 1 in macrophages improves renal fibrosis through mediating fibronectin endocytosis

AIMS

Excess extracellular matrix (ECM) deposition is the characteristic of renal fibrosis, owing to the imbalance between synthesis and degradation. Fibronectin could regulate the deposition of other ECM, thus plays a crucial role in the progression of renal fibrosis. Mannose receptor C type 1 (MRC1), largely expressed on macrophages, owns an extracellular fibronectin type II domain that binds to and internalizes collagen and thus involves in fibrosis modulation. The purpose of the present study was to investigate whether MRC1 participates in the internalization of fibronectin and whether alginate oligosaccharides (AOSC), a degradation product of alginate, has beneficial effects in the resolution of renal fibrosis via MRC1.

MATERIALS AND METHODS

Renal fibrosis models were constructed by unilateral ureteral obstruction (UUO) and unilateral ischemia-reperfusion injury (UIRI) in MRC1-WT and MRC1-KO mice. RAW264.7 cells were treated with TGF-β1 to induce pro-fibrotic responses. Expression of fibrotic markers and fibronectin endocytosis were examined.

KEY FINDINGS

MRC1 gene knockout aggravated renal fibrosis in UUO and UIRI models. Inhibition of MRC1 exacerbated TGF-β1-induced pro-fibrotic responses in RAW264.7 cells. MRC1 regulated integrin β1-mediated fibronectin endocytosis through Arp2/3-Kindlin-2 signaling pathway. AOSC improved renal fibrosis by increasing MRC1 expression and endocytosis of fibronectin.

SIGNIFICANCE

Our findings highlight the importance of MRC1 and fibronectin endocytosis in the development of renal fibrosis, suggesting that activation of MRC1 by AOSC is probably a therapeutic option to delay the progress of kidney fibrosis.

An Ultrasmall Self-Assembled Gallic-Acid-Based Natural Multifunctional Defense Networks for Therapeutic Application in Calcium Oxalate Nephropathies

Kidney stones, which have high prevalence and recurrence rates, often cause severe oxidative damage and inflammation. The ultrasmall hydrodynamic diameter of nanoparticles is crucial for their enrichment in the kidneys to exert biological activity. However, integrating crystallization inhibition and therapeutic functions into a single ultrasmall nanoparticle is challenging. A novel ultrasmall iron (Fe)-gallic acid (Ga) metal-phenolic networks (Fe-Ga MPNs) is developed for treating calcium oxalate (CaOx) nephropathies. These MPNs can specifically adsorb on the high-energy (1 ¯ 01 $\bar{1}01$ ) crystal face to inhibit the growth of CaOx monohydrate (COM), promoting the phase transition from highly toxic COM to low-risk CaOx dihydrate. Fe-Ga MPNs have broad-spectrum free radical scavenging abilities, reducing oxidative damage and inhibiting cell apoptosis. They exhibit sensitivity toward kidney damage, accumulating in injured renal tissue, reducing tubule injury and inflammation, improving tubule function, and inhibiting crystal formation. Fe-Ga MPNs also inhibit pro-inflammatory macrophage polarization and upregulate anti-inflammatory and highly phagocytic macrophage polarization. RNA sequencing analysis shows that Fe-Ga MPNs induce transcriptomic changes mainly involving immune regulation and citrate homeostasis pathways. In conclusion, the multifunctional nanonetwork Fe-Ga MPNs, with crystallization inhibition, antioxidant, and immune regulation properties, show great potential in treating CaOx nephropathies.

Tissue-resident macrophages and renal diseases: landscapes and treatment directions

Tissue-resident macrophage (TRM) is a specialized subset of macrophage that resides within specific tissues and organs. TRMs play crucial roles in resisting pathogen invasion, maintaining the homeostasis of the immune microenvironment, and promoting tissue repair and regeneration. The development and function of TRMs exhibit significant heterogeneity across different tissues. Kidney TRMs (KTRMs) originate from both embryonic yolk sac erythro-myeloid progenitors and the fetal liver, demonstrating the capacity for self-renewal independent of bone marrow hematopoiesis. KTRMs are not only essential for the maintenance of renal homeostasis and the monitoring of microvascular environment, but contribute to renal injury due to inflammation, fibrosis and immune dysfunction in kidneys. In this review, we summarize currently available studies on the regulatory role of KTRMs in processes of renal injury and repair. The altering effects and underlying mechanisms of KTRMs in regulating local tissue cells and immune cells in different renal diseases are reviewed, primarily including lupus nephritis, diabetic nephropathy, renal fibrosis, and renal carcinoma. Understanding the plasticity and immune regulatory functions of KTRMs may offer new insights into the pathogenesis and the exploration of therapeutic strategies of kidney diseases.

CREB1/CRTC2 regulated tubular epithelial-derived exosomal miR-93-3p promotes kidney injury induced by calcium oxalate via activating M1 polarization and macrophage extracellular trap formation

BACKGROUND

Calcium oxalate (CaOx) crystals are known to cause renal injury and trigger inflammatory responses. However, the role of exosome-mediated epithelial-macrophage communication in CaOx-induced kidney injury remains unclear.

METHODS

To identify key molecules, miRNA sequencing was conducted on exosomes derived from CaOx-treated (CaOx-exo) and control (Ctrl-exo) epithelial cells, identifying miR-93-3p as significantly upregulated. A combination of dual-luciferase reporter assays, Western blot, RT-qPCR, immunofluorescence staining, flow cytometry, electrophoretic mobility shift assay (EMSA), and chromatin immunoprecipitation-qPCR (CHIP-qPCR) was used to explore the regulation of miR-93-3p by CREB1/CRTC2 and its downstream effects on NFAT5/Akt1/NIK/NF-κB2 signaling in macrophages. The functional roles of NFAT5 in macrophage polarization and macrophage extracellular traps (METs) formation were further evaluated both in vitro and in vivo.

RESULTS

Epithelial exosomes stimulated by CaOx crystals were found to promote kidney injury via macrophage polarization and METs formation. Treatment with NIK SMI1, a NIK inhibitor, or CI-amidine, a METs inhibitor, mitigated crystal deposition and CaOx-induced kidney damage. Overexpression of NFAT5 in a CaOx-induced mouse model reduced renal injury and crystal deposition, downregulated NIK and NF-κB2 levels, and decreased the number of M1-polarized macrophages. Mechanistic studies revealed that miR-93-3p directly targets NFAT5 mRNA, as confirmed by dual-luciferase assays, qRT-PCR, and Western blot. Additionally, we demonstrated that CREB1/CRTC2 acts as a transcriptional activator of miR-93-3p. Inhibition of miR-93-3p partially reversed NIK/NF-κB2 activation and alleviated kidney injury.

CONCLUSIONS

CaOx crystals exacerbate renal interstitial injury by promoting M1 macrophage polarization and METs formation through the CREB1/CRTC2-exosomal miR-93-3p-NIK/NF-κB2 signaling pathway. Targeting this pathway may provide therapeutic avenues for mitigating crystal deposition-induced kidney damage.

How oxygenation shapes immune responses: emerging roles for physioxia and pathological hypoxia

Most eukaryotes require oxygen for their survival and, with increasing multicellular complexity, oxygen availability and delivery rates vary across the tissues of complex organisms. In humans, healthy tissues have markedly different oxygen gradients, ranging from the hypoxic environment of the bone marrow (where our haematopoietic stem cells reside) to the lungs and their alveoli, which are among the most oxygenated areas of the body. Immune cells are therefore required to adapt to varying oxygen availability as they move from the bone marrow to peripheral organs to mediate their effector functions. These changing oxygen gradients are exaggerated during inflammation, where oxygenation is often depleted owing to alterations in tissue perfusion and increased cellular activity. As such, it is important to consider the effects of oxygenation on shaping the immune response during tissue homeostasis and disease conditions. In this Review, we address the relevance of both physiological oxygenation (physioxia) and disease-associated hypoxia (where cellular oxygen demand outstrips supply) for immune cell functions, discussing the relevance of hypoxia for immune responses in the settings of tissue homeostasis, inflammation, infection, cancer and disease immunotherapy.

EZH2-mediated macrophage-to-myofibroblast transition contributes to calcium oxalate crystal-induced kidney fibrosis

Long-term nephrocalcinosis leads to kidney injury, fibrosis, and even chronic kidney disease (CKD). Macrophage-to-myofibroblast transition (MMT) has been identified as a new mechanism in CKD, however, the effect of MMT in calcium oxalate (CaOx)-induced kidney fibrosis remains unclear. In this study, abundant MMT cells are identified by immunofluorescence (IF) and flow cytometry in kidney tissues of patients with CaOx-related CKD, a male mouse model, and CaOx-treated macrophages. Clodronate liposome (CLO)-mediated macrophage depletion attenuates fibrosis in male nephrocalcinosis mice. Transcriptomic sequencing reveals that histone methyltransferase (HMTs), EZH2, is highly expressed in nephrocalcinosis. Ezh2 inducible knock-out or inhibition by GSK-126 attenuates MMT and renal fibrosis. Mechanistically, ChIP and transcriptomic sequencing show that EZH2 inhibition reduces the enrichment of H3K27me3 on the Dusp23 gene promoter and elevates Dusp23 expression. The Co-IP and molecular docking analysis shows that DUSP23 mediates the dephosphorylation of pSMAD3 (Ser423/425). Thus, our study found that EZH2 promotes kidney fibrosis by meditating MMT via the DUSP23/SMAD3 pathway in nephrocalcinosis.

Characterizing Chemokine Signaling Pathways and Hub Genes in Calcium Oxalate-Induced Kidney Stone Formation: Insights from Rodent Models

The predominant component of kidney stone is calcium oxalate monohydrate (COM), a fact widely acknowledged. Although rodent models are frequently used to induce calcium oxalate (CaOx) crystallization, further exploration of Randall's plaques (RPs) in these models is still needed. We first selected the GSE89028 and GSE75542 datasets from the Gene Expression Omnibus (GEO) database to identify commonly differentially expressed genes (co-DEGs). Based on co-DEGs, we conducted Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses to identify significantly enriched pathways. Additionally, we performed Gene Set Enrichment Analysis (GSEA) to validate the enriched pathways. In order to identify hub genes, we established a network of protein-protein interactions (PPI). Finally, we conducted real-time PCR and Western blot to validate the findings from the bioinformatics analysis. We selected 28 co-DEGs from two datasets. The enrichment analysis using GO, KEGG, and GSEA revealed significant enrichment of chemokine-related signaling pathways. The histogram analysis showed that three chemokine factor-related genes were involved in multiple pathways. We used Cytohubba to confirm the presence of three hub genes. Subsequently, analysis of external datasets and quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot demonstrated significant upregulation of CCL2, CXCL1, and CXCL2 in HK-2 cells following CaOx treatment compared to the control group (p < 0.05). Our study demonstrated that upon stimulation by CaOx, renal tubular epithelial cells release chemokines, including CCL2, CXCL1, and CXCL2. This release of chemokines is accompanied by the activation of signaling pathways such as TNF and IL-17. These findings may provide new directions for future research on Kidney Stone Disease.

Kidney immunology from pathophysiology to clinical translation

Kidney diseases are widespread and represent a considerable medical, social and economic burden. However, there has been marked progress in understanding the immunological aspects of kidney disease. This includes the identification of distinct intrarenal immunological niches and characterization of kidney disease endotypes according to the underlying molecular immunopathology, as well as a better understanding of the pathological roles for T cells, mononuclear phagocytes and B cells and the renal elements they target. These insights have improved the diagnosis of kidney disease. Here, we discuss new developments in our understanding of kidney immunology, focusing on immune mechanisms of disease and their translational implications for the diagnosis and treatment of kidney disease. We also describe the immune-mediated crosstalk between the kidney and other organs that influences kidney disease and extrarenal inflammation.

Revealing the molecular landscape of calcium oxalate renal calculi utilizing a tree shrew model: a transcriptomic analysis of the kidney

Our comprehensive genomic investigation employing tree shrew calcium oxalate stone models unveils intricate links between kidney stone formation and diverse physiological systems. We identify a constellation of genes whose expression patterns point to multifaceted interactions among cardiovascular health, renal fibrosis, and bone homeostasis in the pathogenesis of renal calculi. Key players include CHIT1, TNFRSF18, CLEC4E, RGS1, DCSTAMP, and SLC37A2, which emerge as pivotal actors in arteriosclerosis, renal fibrosis, and osteoclastogenesis respectively, showcasing the complexity of stone disease. The downregulation of ADRA1D, LVRN, and ABCG8 underscores roles in urodynamics, epithelial-mesenchymal transition, and vitamin D metabolism, linking these to nephrolithiasis. Comparative genomics across tree shrew, human (Randall's plaque), rat, and mouse identifies shared KEGG pathways including Calcium signaling, Actin cytoskeleton regulation, Neuroactive ligand-receptor interactions, Complement and coagulation cascades, TRP channel regulation by inflammatory mediators, p53 signaling, and Fc gamma R-mediated phagocytosis. These pathways underscore the interconnectedness of immune, inflammatory, and metabolic processes in stone development. Our findings suggest novel targets for future therapeutics and prevention strategies against nephrolithiasis, highlighting the need for a holistic view of the disease encompassing multiple pathogenic factors.

Osteogenic-Like Microenvironment of Renal Interstitium Induced by Osteomodulin Contributes to Randall's Plaque Formation

Calcium oxalate (CaOx) kidney stones are common and recurrent, lacking pharmacological prevention. Randall's plaques (RPs), calcium deposits in renal papillae, serve as niduses for some CaOx stones. This study explores the role of osteogenic-like cells in RP formation resembling ossification. CaP crystals deposit around renal tubules, interstitium, and blood vessels in RP tissues. Human renal interstitial fibroblasts (hRIFs) exhibit the highest osteogenic-like differentiation potential compared to chloride voltage-gated channel Ka positive tubular epithelial cells, aquaporin 2 positive collecting duct cells, and vascular endothelial cells, echoing the upregulated osteogenic markers primarily in hRIFs within RP tissues. Utilizing RNA-seq, osteomodulin (OMD) is found to be upregulated in hRIFs within RP tissues and hRIFs following osteogenic induction. Furthermore, OMD colocalizes with CaP crystals and calcium vesicles within RP tissues. OMD can enhance osteogenic-like differentiation of hRIFs in vitro and in vivo. Additionally, crystal deposits are attenuated in mice with Omd deletion in renal interstitial fibroblasts following CaOx nephrocalcinosis induction. Mechanically, a positive feedback loop of OMD/BMP2/BMPR1A/RUNX2/OMD drives hRIFs to adopt osteogenic-like fates, by which OMD induces osteogenic-like microenvironment of renal interstitium to participate in RP formation. We identify OMD upregulation as a pathological feature of RP, paving the way for preventing CaOx stones.

Macrophage polarization regulation shed lights on immunotherapy for CaOx kidney stone disease

Kidney stone disease (KSD) is a major public health concern associated with high morbidity and recurrence, places a significant burden on the health care system worldwide. Calcium oxalate (CaOx) alone or a mixture of CaOx and calcium phosphate stones accounting for more than 80 % of cases. However, beyond surgical removal, the prevention and reduction of recurrence of CaOx kidney stones have always been a challenge. Given that macrophages are traditional innate immune cells that play critical roles in the clearance of pathogens and the maintenance of tissue homeostasis, which have gained more and more interests in nephrolithiasis. Several studies recently clearly demonstrated that M2-macrophage could reduce the renal calcium oxalate (CaOx) crystal acumination, and provide premise insights and therapeutic options for KSD by modulating the macrophage phenotypes. However, the mechanism of macrophage-polarization regulation and that effects on kidney stone prevention and treatments are far from clear. Here, we comprehensively reviewed the literatures related to cytokines, epigenetic modifications and metabolic reprograming of macrophage in CaOx kidney stone disease, aimed to provide better understandings on macrophage polarization regulation as well as its potential clinical applications in CaOx kidney stone disease treatments and prevention.

The identification of key molecules and pathways in the crosstalk of calcium oxalate-treated TCMK-1 cells and macrophage via exosomes

The interplay between crystals and epithelial cells forms the cornerstone of kidney stone development, communication between epithelial cells and macrophages emerging as a pivotal role in this process. We conducted next-generation sequencing on the secreted exosomes of TCMK-1 cells treated with calcium oxalate monohydrate (OX_EXO) or controls (NC_EXO), and on the macrophage cell line RAW264.7 stimulated with OX_EXO or NC_EXO, followed by validation of differentially expressed target proteins and miRNAs through Western blot and PCR. UPSET plots were employed to identify genes co-targeted by exosomal miRNAs. Various bioinformatic analyses were employed to predict potential mechanisms of the dysregulated genes. We integrated sequencing data from the GEO database, and validated findings using clinical patient urine and kidney tissues. We identified 665 differentially expressed exosomal miRNAs between OX_EXO and NC_EXO. Among the top 10 down-regulated miRNAs, the most targeted genes were AAK1 and NUFIP2, whereas PLCB1 was significantly targeted among the top 10 up-regulated miRNAs. In clinical specimens, we confirmed the differential expressions of five homologous miRNAs, as well as CNOT3, CNCNA1C, APEX1, and TMEM199. In conclusion, treatment of TCMK-1 cells with calcium oxalate significantly alerted the expression profile of exosomal miRNAs, subsequently influencing gene expression in macrophages, thereby modulating the processes of kidney stone formation.

Polymer-drug and polymer-protein conjugated nanocarriers: Design, drug delivery, imaging, therapy, and clinical applications

Polymer-drug conjugates and polymer-protein conjugates have been pivotal in the realm of drug delivery systems for over half a century. These polymeric drugs are characterized by the conjugation of therapeutic molecules or functional moieties to polymers, enabling a range of benefits including extended circulation times, targeted delivery, controlled release, and decreased immunogenicity. This review delves into recent advancements and challenges in the clinical translations and preclinical studies of polymer-drug conjugates and polymer-protein conjugates. The design principles and functionalization strategies crucial for the development of these polymeric drugs were explored followed by the review of structural properties and characteristics of various polymer carriers. This review also identifies significant obstacles in the clinical translation of polymer-drug conjugates and provides insights into the directions for their future development. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Kidney macrophages tap the stream

Tissue-resident macrophages are essential for maintaining organismal homeostasis, but the precise mechanisms that macrophages use to perform this function are not fully understood. In this issue of Immunity, He et al. demonstrate that renal macrophages surveil and sample urine particles, ensuring optimal collecting duct flow and preventing kidney stone development.