AIM:Renal fibrosis is a major contributor to chronic kidney disease (CKD) progression and eventual organ failure. G protein-coupled bile acid receptor 1 (TGR5) was previously shown to have beneficial effects on kidney diseases. The current study aimed to investigate whether TGR5 activation prevents kidney fibrosis and to clarify the underlying mechanism. METHODS:TGR5 expression was examined in human fibrotic kidneys. Two animal models of renal fibrosis were used: unilateral ureteral obstruction (UUO) and unilateral ischemia-reperfusion injury with contralateral nephrectomy (uIRIx) in wild-type and TGR5 knockout mice. Renal histology, extracellular matrix (ECM) deposition, and renal function were examined. In vitro studies were performed on human proximal tubular HK2 cells by treating them with transforming growth factor-β1 and TGR5 agonists/antagonists. RESULTS:TGR5 was significantly downregulated in fibrotic human kidneys. In both UUO and uIRIx models, TGR5 activation by lithocholic acid alleviated renal fibrosis, reduced ECM deposition, and improved kidney function. Conversely, Tgr5 knockout in mice exacerbated fibrotic injury. Mechanistically, TGR5 activation prevented fibrosis development, probably by enhancing NEDD4L-mediated ubiquitination and degradation of phosphorylated Smad2/3 by inhibiting the upstream PI3K-SGK1 pathway. CONCLUSION:TGR5 activation protects against renal fibrosis by inhibiting the PI3K-SGK1-NEDD4L axis and promoting p-Smad2/3 degradation.

Renal fibrosis is the terminal pathological manifestation of most chronic kidney diseases. The phosphodiesterase type 5 (PDE5) inhibitors have shown therapeutic potentials in a wide array of chronic conditions. LW1646 is a newly identified inhibitor with high specificity and potency against PDE5. The current study aims to investigate the therapeutic effects of LW1646 on renal fibrosis and its underlying mechanisms. mRNA and protein expression level of PDE5 was elevated in renal cortex of mice with unilateral ureter obstruction for seven days (7UUO). LW1646 effectively suppressed pro-fibrotic responses in TGF-β1-stimulated HK-2 cells as well as in mice with 7UUO-induced renal fibrosis. Genetic deletion or knockdown of Pde5a produced similar antifibrotic benefits. Mechanistically, both PDE5 inhibition with LW1646 and Pde5a knockout alleviated ER stress and mitigated mitochondrial dysfunction, as evidenced by restored mitochondrial biogenesis, suppression of excessive fragmentation, preservation of membrane potential, and reduction of oxidative stress. Further investigation revealed that ER stress-driven mitochondrial injury involved augmented mitochondria associated membrane (MAM) formation, characterized by increased expression of the hallmark IP3R1-GRP75-VDAC1 complex. This enhanced interaction facilitated excessive calcium transfer from the ER to mitochondria, culminating in mitochondrial calcium overload. PDE5 inhibition effectively suppressed MAM formation and reduced mitochondrial calcium accumulation, thereby maintaining mitochondrial homeostasis under fibrotic stress. Collectively, these findings identify activation of cGMP-PKG signaling by LW1646 as a promising therapeutic pathway for renal fibrosis through suppression of ER stress and stabilization of mitochondrial homeostasis.

Hypertension is one of the most important risk factors for cardiovascular, cerebrovascular and renal diseases. The molecular mechanism of hypertension is not fully understood largely due to the complexity of pathogenesis involving many factors. The balance of sodium in body fluids plays a key role in blood pressure regulation. High salt intake is an important environmental factor leading to the development of hypertension. In this setting, the kidney plays a major role in the maintenance of blood pressure. The present review aims to summarize the current overview on the involvement of sodium transporters, sodium exchangers and sodium channels in the modulation of blood pressure, including sodium-hydrogen exchanger isoform 3 (NHE3), Na+-K+-2Cl- cotransporter type 2 (NKCC2), sodium-chloride cotransporter (NCC) and epithelial sodium channel (ENaC), which are expressed in different nephron segments and the collecting ducts, respectively. In particular, recent findings on experimental animal models with modified gene of renal ion channels/transporters leading to the identification of several crucial physiological mechanisms involved in hypertension, were also reviewed. These findings could potentially provide novel therapeutic approaches applicable for hypertension.

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.

Renal ischemia-reperfusion (IR) injury is a major cause of acute kidney injury (AKI), with limited specific therapies. Recombinant human brain natriuretic peptide (rhBNP) shows potential renal protective effects, but its role and mechanism in IR-induced AKI is unclear. The present study showed rhBNP improved renal function recovery and reduced AKI progression in ICU patients. In rat IR models, rhBNP alleviated tubular injury and enhanced kidney function. Selenocysteine lyase (SCLY), an enzyme critical for selenium recycling and selenoprotein synthesis, was identified as the hub gene associated with rhBNP treatment by transcriptome sequencing. rhBNP treatment markedly upregulated the expression of SCLY in rat kidneys with elevated selenium levels. rhBNP also inhibited ferroptosis and apoptosis in the kidney, which was significantly reversed by the knockdown of SCLY. SCLY silencing blocked the protective effect of rhBNP on human HK2 cells subjected to CCCP-R (carbonyl cyanide 3-chlorophenylhydrazone induced ATP depletion-repletion), while SCLY overexpression enhanced it. rhBNP modulated SCLY expression likely through inhibiting the binding of active GTPase RhoA to SCLY protein. In conclusion, rhBNP prevented IR-induced AKI through inhibiting ferroptosis by upregulating SCLY level and promoting selenium recycling, presenting a potentially new target for AKI treatment.

Renal fibrosis is the terminal pathological manifestation of most chronic kidney diseases (CKDs). Inhibitors targeting phosphodiesterase 5 (PDE5) have been used to treat erectile dysfunction and pulmonary arterial hypertension by increasing cGMP levels and activating the cGMP/PKG signaling pathway. Studies have shown that PDE5 inhibitors can attenuate the progression of CKD, although the underlying mechanisms remain unclear. LW1646 is a newly identified inhibitor with higher specificity and potency against PDE5. This study aims to investigate the therapeutic effects of LW1646 on renal fibrosis and its underlying mechanisms. In vitro, pro-fibrotic response in HK2 cells was induced by TGF-β1 and intervened with LW1646. In vivo, renal interstitial fibrosis model was established by unilateral ureteral obstruction for 7 days (7UUO) in Pde5a-/- mice. mRNA expression level of Pde5a was analyzed by qPCR. Western blot was used to assess changes in fibrosis markers, endoplasmic reticulum stress indicators, mitochondrial homeostasis metrics, and components of mitochondrial-associated membranes (MAM). Mitochondrial membrane potential (MMP) and reactive oxygen species were evaluated using flow cytometry, fluorescent imaging was employed to visualize mitochondrial networks, accumulation of mitochondrial calcium (mtCa2+) and formation of MAM. Histological assessments of renal fibrosis were performed using H&E staining and Masson's trichrome staining. Morphology of mitochondria and ER and mitochondria-ER contact in kidney cortex were investigated by transmission electron microscope (TEM). mRNA expression level of Pde5a was elevated in renal cortex in 7UUO-induced kidney fibrosis mice. Expression of fibrosis markers and endoplasmic reticulum stress indicators were markedly upregulated both in vitro and in vivo. Meanwhile, mitochondrial biogenesis was inhibited, which was accompanied by increased oxidative stress, decreased MMP and augmented mitochondrial fission. MAMs formation and mtCa2+ level were enhanced. LW1646 significantly prevented development of fibrosis in mice with 7UUO and exhibited a more pronounced effect than sildenafil. Pde5a knockout was associated with alleviated fibrosis in mice. LW1646 or Pde5a knockout attenuated ER stress and altered mitochondrial homeostasis in fibrotic kidneys and HK2 cells exhibiting pro-fibrotic responses. Our data demonstrated that LW1646 ameliorated renal fibrosis likely through inhibiting ER stress and maintaining mitochondrial homeostasis. Mechanistically, activation of cGPM/PKG pathway by LW1646 or Pde5a knockout conferred mitochondrial protection by inhibiting the formation of MAMs, thereby reducing mtCa2+ overload and alleviating renal fibrosis.

Epithelial sodium channel (ENaC), located in the collecting duct principal cells of the kidney, is responsible for the reabsorption of sodium and plays a critical role in the regulation of extracellular fluid volume and consequently blood pressure. The G protein-coupled bile acid receptor (TGR5) is a membrane receptor mediating effects of bile acid and is implicated in kidney diseases. The current study aims to investigate whether TGR5 activation in the kidney regulated ENaC expression and potential mechanism. Lithocholic acid (LCA), a TGR5 agonist, markedly decreased systolic blood pressure induced by DOCA-salt in mice, which was associated with decreased ENaC expression in the kidney. DOCA-salt treatment increased renal expression of histone H3 lysine 4 trimethylation (H3K4me3) and decreased expression of lysine-specific demethylase 5A (KDM5A), a lysine demethylase, which was markedly reversed by LCA. TGR5 knockout caused further increased systolic blood pressure and ENaC expression in mice with DOCA-salt in association with increased H3K4me3 and decreased KDM5A. In immortalized mouse cortical collecting duct (mpkCCD) cells LCA markedly inhibited aldosterone-induced ENaC-mediated current. LCA treatment or TGR5 overexpression markedly inhibited ENaC and H3K4me3 protein expression in association with decreased KDM5A in mpkCCD cells treated with either aldosterone or angiotensin II. Inhibition or knockdown of KDM5A in mpkCCD cells prevented LCA-induced downregulation of ENaC expression by promoting H3K4me3 on the ENaC transcription start site. LCA upregulated KDM5A expression was likely through JNK/c-Jun signal pathway. In conclusion, LCA decreased blood pressure and ENaC protein expression in the kidney of mice with DOCA-salt, likely through activating TGR5 and upregulating KDM5A-induced H3K4me3 demethylation in ENaC promoter region.

Leukocyte immunoglobulin like receptor B4 (LILRB4) was considered to promote tumor progression and immunosuppression in various malignancies. As a murine homolog of LILRB4, gp49B has been employed in numerous mouse models to investigate the immunosuppressive properties of LILRB4. However, gp49B differs significantly from LILRB4 in its amino acid sequence and intracellular domains. In this study, we developed a conditional mouse model that overexpresses LILRB4 specifically in myeloid cells to investigate its effects on solid tumors and hematological malignancies. Our results showed that the physiological structure and overall immune system of LILRB4L/L; Cre mice were normal. LL2 tumors in LILRB4L/L; Cre mice exhibited increased size and weight, with elevated levels of immunosuppressive markers programmed cell death protein 1 (PD-1) and T cell immunoglobulin and mucin-domain containing-3 (TIM-3) on infiltrating CD3+ T cells, alongside a shift in tumor-associated macrophages (TAMs) from M1-type to M2-type. In the C1498 model, LILRB4 overexpression promoted tumor progression and metastasis, evidenced by increased bioluminescence and enhanced infiltration of monocytic myeloid-derived suppressor cells (M-MDSCs). Real-time PCR analysis showed upregulation of immunosuppressive mRNAs, including colony-stimulating factor 1 (CSF1), arginase1 (Arg1), macrophage galactose N-acetyl-galactosamine specific lectin 2 (Mgl2) and interleukin-1β (IL-1β) while downregulating pro-inflammatory markers like nitric oxide synthase 2 (Nos2). These findings indicate that LILRB4 fosters an immunosuppressive microenvironment that supports tumor progression. LILRB4L/L; Cre mice may serve as a promising tool for studying targeted LILRB4 tumor immunotherapy.

Urea is generated by the urea cycle enzymes, which are mainly in the liver but are also ubiquitously expressed at low levels in other tissues of mammals. Urea is then eliminated through fluids, especially urine. Urea also serves as a readily available nitrogen source for the growth of many organisms, including plants and bacteria. Urea transporters are recognized as the primary membrane proteins responsible for urea transport in organisms. However, an increasing body of studies has identified additional membrane proteins in animals, plants, and microbes that exhibit urea transport capabilities or potential. The contribution of these membrane proteins to the maintenance of physiological homeostasis and their interactions with urea transporters remains to be fully elucidated. In this chapter, transport, characteristics, regulation, as well as cellular localization of non-urea-transporter membrane proteins facilitating urea transport, are reviewed to highlight their roles in physiology and pathophysiology. Specifically, the mammalian aquaporins AQP3, AQP6, AQP7, AQP8, AQP9, AQP10, and a sodium-glucose transporter (SGLT1) in the kidney are permeable to urea. In plants, tonoplast intrinsic proteins (TIPs), a member of aquaporin family, and the DUR3 orthologue, potentially play roles in low- and high-affinity urea transport, respectively. Two urea transporters pH-independent (Yut) and pH-dependent transporters (ureI) in bacteria are known to play roles in disease conditions.

Water reabsorption in the renal collecting duct, mediated by aquaporin-2 (AQP2), is essential for body fluid balance. Piezo1, a mechanosensitive cation channel, is highly expressed in the collecting ducts to sense mechanical and osmotic stress. The signal recognition particle 54 kDa subunit (Srp54), a key regulator of protein translocation, modulates protein transcription and translation. The present study aims to investigate whether Piezo1 activation affects intracellular trafficking and expression of AQP2 in the principal cells and the potential involvement of Srp54. In vitro, mpkCCD cells overexpressed AQP2 and primary rat inner medullary collecting duct (IMCD) cells were treated with Piezo1 agonist Yoda1, mechanical stretch or hypoosmotic stress, respectively. AQP2 distribution and cell volume were assessed by super-resolution fluorescence imaging, Western blot, and qRT-PCR. Transcriptomic analysis and bioinformatic tools (catRAPID, JASPAR) were used to examine gene expression and molecular interactions. In vivo, C57BL/6 mice were subjected to dehydration and expression levels of protein and mRNA in the kidney inner medulla were analyzed. Statistical significance was assessed using one-way ANOVA (P < 0.05). Piezo1 activation with Yoda1 increased protein expression and plasma membrane distribution of AQP2 in renal collecting duct principal cells and mpkCCD cells, which was associated with enhanced trafficking of AQP2 in endoplasmic reticulum. Hypoosmotic stress or mechanical stretch upregulated AQP2 protein expression, which was markedly inhibited by GsMT×4, a Piezo1 antagonist. EGTA, a calcium chelator, significantly inhibited hypoosmotic stress-induced upregulation of AQP2 protein in mpkCCD cells. In Piezo1+/− mice, AQP2 expression was moderately decreased in the renal inner medulla, compared to wildtype mice. These data indicate a role of Piezo1 in modulating expression of AQP2 protein. In mpkCCD cells, Yoda1, hypoosmotic stress, or mechanical stretch activated CREB and YAP signaling pathways. Transcriptomic analysis showed increased Srp54 mRNA levels and enhanced AQP2 processing in mpkCCD cells treated with Yoda1. Bioinformatic predictions revealed strong Srp54 binding to AQP2 mRNA and YAP-TEAD binding to the Srp54 promoter. Srp54 knockdown in mpkCCD cells treated with Yoda1 was shown to promote maturation of AQP2 mRNA. In mice, dehydration caused increased protein expression of AQP2 and Piezo1 in association with decreased Srp54 and less AQP2 precursor mRNA in inner medulla of the kidney. Under mechanical or osmotic stimulation, Piezo1 promotes protein expression and plasma membrane distribution of AQP2 through increasing ER trafficking in collecting duct principal cells, in which Srp54 is essential for AQP2 mRNA maturation and transcription. These findings offer novel insights into renal function and potential therapeutic targets for water balance disorders.

Acute kidney injury (AKI) is a clinical syndrome that is defined as a sudden decline in renal function and characterized by inflammation and tubular injury. Alginate oligosaccharide (AOSC), a natural product obtained from alginate by acidolysis and hydrolysis, shows activities of antioxidant, immunomodulation, and anti-inflammation. In this study, we investigated the potential of AOSC in the treatment of AKI. Renal ischemia-reperfusion (I/R) was induced in male rats by clipping both the renal artery and vein for 45 min followed by reperfusion for 24 h. The rats were treated with AOSC (100 mg/kg, i.g.) before surgery. At the end of the experiments, both kidneys were collected for protein, mRNA measurement, or histological analysis. We showed that AOSC pretreatment significantly improved glomerular and tubular function in the kidney of I/R rats. AOSC markedly inhibited I/R-induced activation of TLR4/MyD88/NF-κB/IL-1β inflammatory signaling and prevented apoptosis in the kidney. In HK2 cells subjected to hypoxia/reoxygenation (H/R) stimulation, AOSC (250–1000 μg/ml) dose-dependently prevented pro-inflammatory responses and cell apoptosis. Transcriptomic analysis revealed that I/R increased the expression levels of mannose receptor type C1 (MRC1) in the kidney, which was markedly inhibited by AOSC. Molecular docking showed that AOSC interacted with E725, N727, E733, T743, S745, and N747 of MRC1 through hydrogen bonds. MRC1 gene knockout significantly improved renal function and attenuated I/R-induced kidney inflammation and apoptosis in mice. In line with this, AOSC failed to prevent I/R-induced kidney injury in MRC1 gene knockout mice. UPLC analysis showed that the protection of AOSC in HK2 cells subjected to H/R was likely attributed to MRC1-mediated intracellular endocytosis. In conclusion, AOSC prevents I/R-induced AKI, which is at least partially mediated by MRC1.

Arginine vasopressin (AVP) plays a crucial role in various physiological processes including water reabsorption, cardiovascular homeostasis, hormone secretion, and social behavior. AVP acts through three distinct receptor subtypes, i.e., V1a, V1b, and V2. Among them, the vasopressin V2 receptor (V2R) was initially discovered in the principal cells of renal collecting ducts, where it is primarily involved in regulating water reabsorption. However, in recent years, with the advancement of imaging and bioinformatics techniques, there has been a deeper understanding of the microstructure, protein binding capacity, and specific tissue distribution of V2R. Additionally, the pathogenic roles and target effects of V2R in various diseases have been uncovered through ectopic overexpression, activation, or antagonism. This paper aims to provide a brief overview of current research status on the physiological functions, pathophysiological mechanisms, and drug development related to V2R in recent years.

The host defence responses play vital roles in viral infection and are regulated by complex interactive networks. The host immune system recognizes viral pathogens through the interaction of pattern-recognition receptors (PRRs) with pathogen-associated molecular patterns (PAMPs). As a PRR mainly in the cytoplasm, cyclic GMP-AMP synthase (cGAS) senses and binds virus DNA and subsequently activates stimulator of interferon genes (STING) to trigger a series of intracellular signalling cascades to defend against invading pathogenic microorganisms. Integrated omic and functional analyses identify the cGAS-STING pathway regulating various host cellular responses and controlling viral infections. Aside from its most common function in regulating inflammation and type I interferon, a growing body of evidence suggests that the cGAS-STING signalling axis is closely associated with a series of cellular responses, such as oxidative stress, autophagy, and endoplasmic reticulum stress, which have major impacts on physiological homeostasis. Interestingly, these host cellular responses play dual roles in the regulation of the cGAS-STING signalling axis and the clearance of viruses. Here, we outline recent insights into cGAS-STING in regulating type I interferon, inflammation, oxidative stress, autophagy and endoplasmic reticulum stress and discuss their interactions with viral infections. A detailed understanding of the cGAS-STING-mediated potential antiviral effects contributes to revealing the pathogenesis of certain viruses and sheds light on effective solutions for antiviral therapy.

Piezo1 is an essential mechanosensitive transduction ion channel in mammals. Its unique structure makes it capable of converting mechanical cues into electrical and biological signals, modulating biological and (patho)physiological processes in a wide variety of cells. There is increasing evidence demonstrating that the piezo1 channel plays a vital role in renal physiology and disease conditions. This review summarizes the current evidence on the structure and properties of Piezo1, gating modulation, and pharmacological characteristics, with special focus on the distribution and (patho)physiological significance of Piezo1 in the kidney, which may provide insights into potential treatment targets for renal diseases involving this ion channel.

目的探讨激活胆汁酸受体TGR5在单肾缺血再灌注损伤合并对侧肾摘除（uIRIx）模型诱导的肾脏纤维化中的作用。方法体内实验：将C57BL/6J小鼠随机分成假手术（Sham）组、uIRIx组及uIRIx+石胆酸（LCA）组，每组6只，使用uIRIx模型诱导肾脏纤维化，通过血和尿生化指标评估肾脏功能，利用HE染色评估肾脏损伤程度，使用Masson染色及免疫组化对肾脏纤维化程度进行评估，并用Western Blotting检测肾脏皮质纤维化相关指标蛋白表达；分别在TGR5+/+小鼠及TGR5-/-小鼠中设置Sham组及uIRIx组，每组6只，利用Western Blotting检测各组肾脏纤维化程度。体外实验：在人源肾上皮细胞系HK2细胞中给予TGF-β1诱导促纤维化反应，给予LCA进行药物干预，利用鬼笔环肽染色标记细胞骨架，使用Western Blotting检测HK2细胞内纤维化相关指标蛋白表达。结果体内实验：与Sham组相比，uIRIx组小鼠血浆肌酐水平（P=0.007）及尿白蛋白/肌酐比（P=0.041）明显增加，肾脏皮质蛋白TGR5表达（P=0.002）下降，Fibronectin表达（P=0.020）及COL1A1表达（P<0.001）上升，同时伴有肾脏结构受损及胶原沉积加重，LCA干预有效改善肾脏功能，缓解肾脏损伤及纤维化程度；TGR5+/+小鼠与TGR5-/-小鼠相比，uIRIx诱导引起的Fibronectin表达（P<0.001）及COL1A1表达（P=0.001）增加。体外实验：TGF-β1诱导HK2细胞形态改变，细胞骨架解聚重组，促纤维化指标蛋白上调；LCA可有效抑制TGF-β1诱导的细胞形态改变及骨架解聚重组，呈浓度依赖性下调纤维化相关指标蛋白表达。结论LCA缓解uIRIx模型诱导的肾脏纤维化，TGR5基因敲除加重uIRIx诱导的肾脏纤维化；在HK2细胞中，LCA缓解TGF-β1诱导的细胞促纤维化反应。研究结果提示激活TGR5缓解缺血再灌注后肾脏纤维化损伤进程。