Calcium Oxalate Induces Renal Injury through Calcium-Sensing Receptor

CAV1 unveils a novel therapeutic target for nephrolithiasis by modulating CaSR and ER stress

Nephrolithiasis is a complex disease resulted from abnormal crystal deposition in renal tissues. The crystal-cell interaction represents a critical step in kidney stone formation, involving numerous genes and proteins. We previously identified endoplasmic reticulum (ER) stress as a key biological process in the crystal-cell interactions, the precise mechanism of which has remained unclear. In the present study, we found that calcium oxalate monohydrate (COM) crystals induced an overload of intracellular Ca2+ and an upregulation of calcium-sensing receptor (CaSR) expression in the renal tubular epithelial cells HK-2, both of which were reversed by the CaSR inhibitor NPS2390 that also mitigated the COM-induced ER stress. The protein-protein interaction (PPI) network analysis of the genome-wide association studies (GWAS) data and the microarray data from kidney stone patients revealed that caveolin-1 (CAV1), epidermal growth factor receptor (EGFR), and the focal adhesion pathway formed a crucial intersection within the interactional networks. COM exposure induced HK-2 apoptosis, accompanied by a decrease in CAV1 protein levels and damage to EGFR-AKT signaling pathway, which was reversed by CAV1 overexpression. COM did not significantly affect CAV1 mRNA levels. Treatment with the proteasome inhibitor MG-132 prevented the downregulation of CAV1. CAV1 overexpression also inhibited ER stress and the upregulation of CaSR induced by COM. Similar results were observed in in vivo experiments. In conclusion, the present study suggests that CAV1 may be a promising target for nephrolithiasis therapy by modulating CaSR and ER stress.

E53, E96, D162, E247 and D322 in Ca2+-binding domains of annexin A2 are essential for regulating intracellular [Ca2+] and crystal adhesion to renal cells via ERK1/2 and JNK signaling pathways

Annexin A2 (ANXA2) is expressed inside the cytoplasm and on the surface of renal tubular epithelial cells (RTECs) and is documented as a calcium oxalate monohydrate (COM) crystal-binding protein. Nevertheless, its molecular mechanism involved in kidney stone disease (KSD) remains underinvestigated. Herein, we performed various molecular assays to unravel the roles of ANXA2 and core residues (E53, E96, D162, E247 and D322) in its Ca2+-binding domains in the stone formation mechanism, particularly at crystal-cell adhesion step and downstream signaling cascade. ANXA2 was up-regulated in apical membranes, not cytosol, of RTECs after COM crystal exposure. Neutralizing the surface expression of ANXA2 by a specific monoclonal antibody and silencing its expression by small interfering RNA (siRNA) significantly decreased COM crystal-cell adhesion. siRNA also suppressed the COM-induced up-regulation of phospho-ERK1/2 and phospho-JNK, but not that of phospho-p38. Overexpression of ANXA2 wild-type (WT), but not that of E53A, E96A, D162A, E247A and D322A mutants of its Ca2+-binding domains, significantly increased intracellular [Ca2+], COM-cell adhesion, and phospho-ERK1/2 level. Therefore, E53, E96, D162, E247 and D322 in the Ca2+-binding domains of annexin A2 are essential for regulating intracellular [Ca2+] and COM crystal-cell adhesion via ERK1/2 and JNK signaling pathways.

Calcium sensing receptor regulate claudin-14 via PKA-STAT3 pathway in rat model of nephrolithiasis

Background

The calcium-sensitive receptor (CaSR) has been identified as a key factor in the formation of kidney stones. A substantial body of research has illuminated the function of CaSR in stone formation with respect to oxidative stress, epithelial injury, crystal adhesion, and stone-associated proteins. Nevertheless, as a pivotal molecule in renal calcium excretion, its pathway that contributes to stone formation by regulating calcium supersaturation remains underexplored.

Methods

An in vitro rat calcium oxalate kidney stone model was established through the co-cultivation of calcium oxalate monohydrate (COM) with NRK-52E cells, while an in vivo model was constructed using the ethylene glycol method. Subsequently, the level of the CaSR-claudin-14 pathway was determined. To further elucidate the molecular pathway of CaSR-mediated regulation of claudin-14, drugs were selectively added to the in vitro and ex vivo kidney stone models, and the expression of claudin-14 and the levels of stone formation were detected. Moreover, the direct regulation of claudin-14 by CaSR with STAT3 serving as a transcription factor was examined via the dual luciferase assay. Eventually, a Cldn-14 knockout rat model and a model of kidney stone induction by ethylene glycol were generated using CRISPR-Cas9 technology to further clarify the role of claudin-14 in the CaSR-regulated formation of kidney stones.

Results

In vitro and in vivo observations revealed that calcium oxalate induces high expression of CaSR-claudin-14. Specifically, CaSR regulates claudin-14 expression through phosphorylation modification of STAT3 via protein kinase A (PKA). In vitro, the intervention of PKA and STAT3 reversed the elevated claudin-14 levels and stone formation induced by CaSR. Finally, we generated cldn-14 knockout rats using CRISPR-Cas9 technology and observed that ethylene glycol still induced stone formation in these animals. Nevertheless, the specific activation or inhibition of CaSR demonstrated no notable impact on stone formation.

Conclusion

The results of our study indicate that calcium oxalate crystals induce the activation of the pro-stone pathway of CaSR. That is, activated CaSR regulates claudin-14 levels via the PKA-STAT3 pathway, which further promotes calcium salt stone formation. The role of CaSR in the regulation of stone homeostasis is further enriched.

α-Catenin and Piezo1 Mediate Cell Mechanical Communication via Cell Adhesions

Cell-to-cell distant mechanical communication has been demonstrated using in vitro and in vivo models. However, the molecular mechanisms underlying long-range cell mechanoresponsive interactions remain to be fully elucidated. This study further examined the roles of α-Catenin and Piezo1 in traction force-induced rapid branch assembly of airway smooth muscle (ASM) cells on a Matrigel hydrogel containing type I collagen. Our findings demonstrated that siRNA-mediated downregulation of α-Catenin or Piezo1 expression or chemical inhibition of Piezo1 activity significantly reduced both directional cell movement and branch assembly. Regarding the role of N-cadherin in regulating branch assembly but not directional migration, our results further confirmed that siRNA-mediated downregulation of α-Catenin expression caused a marked reduction in focal adhesion formation, as assessed by focal Paxillin and Integrin α5 localization. These observations imply that mechanosensitive α-Catenin is involved in both cell-cell and cell-matrix adhesions. Additionally, Piezo1 partially localized in focal adhesions, which was inhibited by siRNA-mediated downregulation of α-Catenin expression. This result provides insights into the Piezo1-mediated mechanosensing of traction force on a hydrogel. Collectively, our findings highlight the significance of α-Catenin in the regulation of cell-matrix interactions and provide a possible interpretation of Piezo1-mediated mechanosensing activity at focal adhesions during cell-cell mechanical communication.

Non-Coding RNAs in Kidney Stones

Nephrolithiasis is a major public health concern associated with high morbidity and recurrence. Despite decades of research, the pathogenesis of nephrolithiasis remains incompletely understood, and effective prevention is lacking. An increasing body of evidence suggests that non-coding RNAs, especially microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), play a role in stone formation and stone-related kidney injury. MiRNAs have been studied quite extensively in nephrolithiasis, and a plethora of specific miRNAs have been implicated in the pathogenesis of nephrolithiasis, involving remarkable changes in calcium metabolism, oxalate metabolism, oxidative stress, cell-crystal adhesion, cellular autophagy, apoptosis, and macrophage (Mp) polarization and metabolism. Emerging evidence suggests a potential for miRNAs as novel diagnostic biomarkers of nephrolithiasis. LncRNAs act as competing endogenous RNAs (ceRNAs) to bind miRNAs, thereby modulating mRNA expression to participate in the regulation of physiological mechanisms in kidney stones. Small interfering RNAs (siRNAs) may provide a novel approach to kidney stone prevention and treatment by treating related metabolic conditions that cause kidney stones. Further investigation into these non-coding RNAs will generate novel insights into the mechanisms of renal stone formation and stone-related renal injury and might lead to new strategies for diagnosing and treating this disease.

Inhibition of EZH2 ameliorates hyperoxaluria-induced kidney injury through the JNK/FoxO3a pathway

AIMS

Enhancer of zeste homolog 2 (EZH2), a histone H3 lysine 27 methyltransferase, has been shown to play a role in kidney diseases. However, its role in hyperoxaluria-induced renal tubular epithelial cells (TECs) injury remains unclear.

MATERIALS AND METHODS

A hyperoxaluria rat model was established by providing 0.5% ammonium chloride and drinking water containing 1% ethylene glycol. TECs were exposed to oxalate stress. The 3-DZNeP, a selective EZH2 inhibitor, was administered in vivo and in vitro. Cell viability, ROS production, and apoptosis ratio were evaluated. Crystal deposition was detected by Von Kossa staining and kidney tissue injury was detected by HE staining and TUNEL. EZH2, H3K27me3, cleaved-caspase3, IL-6, and MCP-1 were examined by western blot or immunohistochemistry.

KEY FINDINGS

Inhibition of EZH2 by 3-DZNeP significantly attenuated hyperoxaluria-induced oxidative and inflammatory injury and CaOx crystal deposition in vivo. Similarly, inhibition of EZH2 using 3-DZNeP or shRNA restored cell viability, suppressed LDH release and the production of intracellular ROS in vitro. Furthermore, the MAPK signaling pathway and FoxO3a levels were activated or elevated in TECs exposed to oxalate. EZH2 inhibition using 3-DZNeP blocked these effects. CC90003 (ERK inhibitor) or SB203580 (p38 inhibitor) did not significantly affect the expression of FoxO3a in TECs treated with 3-DZNeP and oxalate; only SP600125 (JNK inhibitor) significantly decreased FoxO3a expression.

SIGNIFICANCE

EZH2 inhibition protects against oxalate-induced TECs injury and reduces CaOx crystal deposition in the kidney may by modulating the JNK/FoxO3a pathway; EZH2 may be a promising therapeutic target in TECs injury.

Calcium-sensing receptor promotes calcium oxalate crystal adhesion and renal injury in Wistar rats by promoting ROS production and subsequent regulation of PS ectropion, OPN, KIM-1, and ERK expression

OBJECTIVES

To explore the mechanism of calcium-sensing receptors (CaSRs) during the development of nephrolithiasis.

MATERIALS AND METHODS

Wistar rats were treated with ethylene glycol to induce calcium oxalate crystallization, and gadolinium chloride (GdCl₃, an agonist of CaSR) and NPS 2390 (an antagonist of CaSR) were added. Oxidative stress (OS) and calcium oxalate crystals in the kidney were observed. CaSR expression and the expression of extracellular signal-regulated protein kinase (ERK), OPN, and KIM-1 were determined by western blotting. In addition, renal tubular epithelial cells were isolated from the kidney to observe phosphatidylserine (PS) ectropion using flow cytometric analysis. Various biochemical parameters were assessed in serum and urine at the end of the experiment.

RESULTS

Calcium oxalate increased OS, crystal adhesion, PS ectropion, and the expression of CaSR and ERK, OPN, and KIM-1 in vivo. In addition, lower levels of urine citrate as well as increased serum creatinine and urea levels were observed after treatment with calcium oxalate (p < .05). Compared with calcium oxalate treatment alone, the above deleterious changes were further significantly confirmed by GdCl₃ but were reversed by NPS-2390. However, urine calcium excretion was decreased after ethylene glycol treatment but was significantly reduced by NPS 2390 and increased by GdCl₃ (p < .05).

CONCLUSIONS

The results suggest that CaSR might play significant roles in the induction of nephrolithiasis in rats by regulating reactive oxygen species (ROS) and PS ectropion and the composition of urine, OPN, KIM-1, and ERK expression.

Inhibiting PKCβ2 protects HK-2 cells against meglumine diatrizoate and AGEs-induced apoptosis and autophagy

Background

Contrast induced diabetic nephropathy (CIN) is an important cause of hospital-acquired acute renal failure. Our aim was to observe the effect of protein kinase C β2 (PKCβ2) knockdown on human proximal tubular epithelial cells (HK-2 cells) against meglumine diatrizoate and advanced glycation end products (AGEs)-induced apoptosis and autophagy.

Methods

Cell viability was detected using cell counting kit-8 (CCK-8) assay in HK-2 cells after disposal with meglumine diatrizoate and AGEs with or without PKCβ2 siRNA/inhibitor LY333531. Flow cytometry and western blot were used to test cell apoptosis and the related protein levels in meglumine diatrizoate and AGEs co-treated HK-2 cells with or without PKCβ2 siRNA/inhibitor LY333531. Autophagy related proteins were detected using western blot. Immunofluorescence staining was used to examine the autophagy-specific protein light chain 3 (LC3), and autophagosome and autolysosome formation was observed under a transmission electron microscopy.

Results

CCK-8 assay results showed that meglumine diatrizoate inhibited AGEs-induced HK-2 cell viability. Furthermore, meglumine diatrizoate promoted cell apoptosis and the expression level of caspase3 in AGEs-induced HK-2. Western blot results showed that meglumine diatrizoate elevated the expression levels of PKCβ2 and p-PKCβ2 in AGEs-induced HK-2 cells, and up-regulated the expression level of Beclin-1 and the ratio of LC3 II/LC3 I, and down-regulated the expression level of p62 in AGEs-induced HK-2 cells. We found that PKCβ2 knockdown alleviated meglumine diatrizoate and AGEs-induced HK-2 cell apoptosis and autophagy. Intriguingly, PKCβ2 inhibitor LY333531 reversed 3-methyladenine (3-MA)-induced autophagy inhibition in meglumine diatrizoate and AGEs-induced HK-2 cells.

Conclusions

Our findings reveal that inhibiting PKCβ2 protects HK-2 cells against meglumine diatrizoate and AGEs-induced apoptosis and autophagy, which provide a novel therapeutic insight for CIN in diabetic patients.

Circulating human microRNA biomarkers of oxalic acid-induced acute kidney injury

Oxalic acid-induced nephrotoxicity and acute kidney injury result from formation of calcium oxalate crystals. Oxalic acid-induced acute kidney injury is a significant problem in many parts of the world. Circulating biomarkers that can accurately and reproducibly detect acute kidney injury are highly desirable. We used a high sensitivity discovery platform to identify signature microRNAs to distinguish healthy individuals never exposed to oxalic acid (n = 4) from those who were exposed to oxalic acid but had no injury (NOAKI; n = 4), moderate injury (AKIN2; n = 4) or severe injury (AKIN3; n = 4). Longitudinal analyses identified 4-8 h post-ingestion as the best time to detect AKIN2/3. We validated a signature of 53 microRNAs identified in the discovery, in a second cohort of individuals exposed to oxalic acid (NOAKI = 11, AKIN2 = 8 and AKIN3 = 18) and healthy controls (n = 19). Thirteen microRNAs were significantly downregulated in acute kidney injury patients compared to NOAKI within 8-h post-ingestion. Five microRNAs (miR-20a, miR-92a, miR-93, miR-195, miR-451) had a highly significant correlation with normalized urinary albumin, serum creatinine at 24 h and creatinine clearance. Logistic regression of these microRNAs had AUC-ROC of 0.85 predicting AKIN2/3 and discriminated patients from healthy controls (AUC-ROC = 0.93). mRNA targets of these microRNAs identified oxidative stress pathways of nephrotoxicity in proximal tubule and glomeruli nephrotoxicity. In conclusion, the downregulation of multiple circulating microRNAs in patients correlated with the severity of oxalic acid-induced acute kidney injury. A set of microRNAs (miR-20a, miR-92a, miR-93, miR-195, miR-451) could be promising biomarkers for early detection of oxalic acid-induced acute kidney injury.

The roles of calcium-sensing receptor (CaSR) in heavy metals-induced nephrotoxicity

The kidney is a vital organ responsible for regulating water, electrolyte and acid-base balance as well as eliminating toxic substances from the blood in the body. Exposure of humans to heavy metals in their natural and occupational environments, foods, water, and drugs has serious implications on the kidney's health. The accumulation of heavy metals in the kidney has been linked to acute or chronic renal injury, kidney stones or even renal cancer, at the expense of expensive treatment options. Therefore, unearthing novel biomarkers and potential therapeutic agents or targets against kidney injury for efficient treatment are imperative. The calcium-sensing receptor (CaSR), a G-protein-coupled receptor (GPCR) is typically expressed in the parathyroid glands and renal tubules. It modulates parathyroid hormone secretion according to the serum calcium (Ca²⁺) concentration. In the kidney, it modulates electrolyte and water excretion by regulating the function of diverse tubular segments. Notably, CaSR lowers passive and active Ca²⁺ reabsorption in distal tubules, which facilitates phosphate reabsorption in proximal tubules and stimulates proton and water excretion in collecting ducts. Moreover, at the cellular level, modulation of the CaSR regulates cytosolic Ca²⁺ levels, reactive oxygen species (ROS) generation and the mitogen-activated protein kinase (MAPK) signaling cascades as well as autophagy and the suppression of apoptosis, an effect predominantly triggered by heavy metals. In this regard, we present a review on the CaSR at the cellular level and its potential as a therapeutic target for the development of new and efficient drugs against heavy metals-induced nephrotoxicity.

Calcium-sensing receptor mediates interleukin-1β-induced collagen expression in mouse collecting duct cells

The mechanisms that underlie the profibrotic effect of interleukin (IL)-1β are complicated and not fully understood. Recent evidence has suggested the involvement of the calcium-sensing receptor (CaSR) in tubular injury. Therefore, the current study aimed to investigate whether CaSR mediates IL-1β-induced collagen expression in cultured mouse inner medullary collecting duct cells (mIMCD3) and to determine the possible downstream signaling effector. The results showed that IL-1β significantly upregulated the expression of type I and III collagens in a concentration- and time-dependent manner. Moreover, CaSR was expressed in mIMCD3 cells, and its expression was increased by increasing the concentrations and times of IL-1β treatment. Selective inhibitors (Calhex231 or NPS2143) or the siRNA of CaSR attenuated the enhanced expression of type I and III collagens. Furthermore, IL-1β increased nuclear β-catenin protein levels and decreased cytoplasmic β-catenin expression in cells. In contrast, blockage of CaSR by the pharmacological antagonists or siRNA could partially attenuate such changes in the IL-1β-induced nuclear translocation of β-catenin. DKK1, an inhibitor of β-catenin nuclear translocation, further inhibited the expression of type I and III collagens in cells treated with IL-1β plus CaSR antagonist. In summary, these data demonstrated that IL-1β-induced collagen I and III expressions in collecting duct cells might be partially mediated by CaSR and the downstream nuclear translocation of β-catenin.

Metabolomic analysis reveals a protective effect of Fu-Fang-Jin-Qian-Chao herbal granules on oxalate-induced kidney injury

Nephrolithiasis is one of the world’s major public health burdens with a high incidence and a risk of persistent renal dysfunction. Fu-Fang-Jin-Qian-Chao granules (FFJQC), a traditional Chinese herb formula, is commonly used in treatment of nephrolithiasis. However, the therapeutic mechanism of FFJQC on kidney stone has still been a mystery. The objective of the present study is to explore the therapeutic mechanism of FFJQC on kidney injury and identify unique metabolomics patterns using a mouse model of kidney stone induced by a calcium oxalate (CaOx) deposition. Von Kossa staining and immuno-histopathological staining of osteopontin (OPN), cluster of differentiation 44 (CD44) and calbindin-D28k were conducted on renal sections. Biochemical analysis was performed on serum, urine, and kidney tissues. A metabolomics approach based on ultra-HPLC coupled with quadrupole-TOF-MS (UHPLC-Q-TOF/MS) was used for serum metabolic profiling. The immunohistopathological and biochemical analysis showed the therapeutic benefits of FFJQC. The expression levels of OPN and CD44 were decreased while calbindin-D28k increased after the CaOx injured mice were treated with FFJQC. In addition, total of 81 serum metabolites were identified to be associated with protective effects of FFJQC on CaOx crystal injured mice. Most of these metabolites were involved in purine, amino acid, membrane lipid and energy metabolism. Potential metabolite biomarkers were found for CaOx crystal-induced renal damage. Potential metabolite biomarkers of CaOx crystal-induced renal damage were found. FFJQC shows therapeutic benefits on CaOx crystal injured mice via regulation of multiple metabolic pathways including amino acids, purine, pyrimidine, glycerolipid, arachidonic acid (AA), sphingolipid, glycerophospholipid, and fatty acid.

Calcium-sensing receptor: evidence and hypothesis for its role in nephrolithiasis

Calcium-sensing receptor (CaSR) is a plasma-membrane G protein-coupled receptor activated by extracellular calcium and expressed in kidney tubular cells. It inhibits calcium reabsorption in the ascending limb and distal convoluted tubule when stimulated by the increase of serum calcium levels; therefore, these tubular segments are enabled by CaSR to play a substantial role in the regulation of serum calcium levels. In addition, CaSR increases water and proton excretion in the collecting duct and promotes phosphate reabsorption and citrate excretion in the proximal tubule. These CaSR activities form a network in which they are integrated to protect the kidney against the negative effects of high calcium concentrations and calcium precipitates in urine. Therefore, the CaSR gene has been considered as a candidate to explain calcium nephrolithiasis. Epidemiological studies observed that calcium nephrolithiasis was associated with polymorphisms of the CaSR gene regulatory region, rs6776158, located within the promoter-1, rs1501899 located in the intron 1, and rs7652589 in the 5'-untranslated region. These polymorphisms were found to reduce the transcriptional activity of promoter-1. Activating rs1042636 polymorphism located in exon 7 was associated with calcium nephrolithiasis and hypercalciuria. Genetic polymorphisms decreasing CaSR expression could predispose individuals to stones because they may impair CaSR protective effects against precipitation of calcium phosphate and oxalate. Activating polymorphisms rs1042636 could predispose to calcium stones by increasing calcium excretion. These findings suggest that CaSR may play a complex role in lithogenesis through different pathways having different relevance under different clinical conditions.

Calcium Oxalate Differentiates Human Monocytes Into Inflammatory M1 Macrophages

Purpose

A number of hyperoxaluric states have been associated with calcium oxalate (CaOx) deposits in the kidneys. In animal models of stone disease, these crystals interact with circulating monocytes that have migrated into the kidney as part of innate immunity. Similarly, macrophages surround CaOx crystals in kidneys of patients excreting high levels of oxalate. We investigate the effect of this exposure and subsequent human immunological response in vitro.

Materials and methods

Primary human monocytes were collected from healthy donors and exposed to CaOx, potassium oxalate, and zinc oxalate (ZnOx). Cytokine production was measured with a multiplex ELISA. Quantitative reverse transcription-polymerase chain reaction was done to validate the mRNA profile expression. M1 macrophage phenotype was confirmed with immunofluorescence microscopy.

Results

Both primary monocytes and THP-1 cells, a human monocytic cell line, respond strongly to CaOx crystals in a dose-dependent manner producing TNF-α, IL-1β, IL-8, and IL-10 transcripts. Exposure to CaOx followed by 1 h with LPS had an additive effect for cytokine production compared to LPS alone, however, LPS followed by CaOx led to significant decrease in cytokine production. Supernatants taken from monocytes were previously exposed to CaOx crystals enhance M2 macrophage crystal phagocytosis. CaOx, but not potassium or ZnOx, promotes monocyte differentiation into inflammatory M1-like macrophages.

Conclusion

In our in vitro experiment, human monocytes were activated by CaOx and produced inflammatory cytokines. Monocytes recognized CaOx crystals through a specific mechanism that can enhance or decrease the innate immune response to LPS. CaOx promoted M1 macrophage development. These results suggest that monocytes have an important role promoting CaOx-induced inflammation.