α-Klotho released from HK-2 cells inhibits osteogenic differentiation of renal interstitial fibroblasts by inactivating the Wnt-β-catenin pathway

Histone deacetylase 6 suppression of renal tubular epithelial cell promotes interstitial mineral deposition via alpha-tubulin acetylation

Randall's plaque (RP) is derived from interstitial mineral deposition and is highly prevalent in renal calcium oxalate (CaOx) stone disease, which is predictive of recurrence. This study shows that histone deacetylase 6 (HDAC6) levels are suppressed in renal tubular epithelial cells in RP samples, in kidney tissues of hyperoxaluria rats, and in hyper-oxalate-treated or mineralized cultured renal tubular epithelial (MDCK) cells in vitro. Mineral deposition in MDCK cells was exacerbated by HDAC6 inhibition but alleviated by HDAC6 overexpression. Surprisingly, the expression of some osteogenic-associated proteins, were not increased along with the increasing of mineral deposition, and result of single-cell RNA sequencing of renal papillae samples revealed that epithelial cells possess lower calcific activity, suggesting that osteogenic-transdifferentiation may not have actually occurred in tubular epithelial cells despite mineral deposition. The initial mineral depositions facilitated by HDAC6 inhibitor were localized in extracellular dome rather than inside the cells, moreover, suppression of HDAC6 significantly increased the calcium content of co-cultured renal interstitial fibroblasts (NRK49F) and enhanced mineral deposition of indirectly co-cultured NRK49F cells, suggesting that HDAC6 may influence trans-MDCK monolayer secretion of mineral. Further experiments revealed that this regulatory role was partially alpha-tubulinLys40 acetylation dependent. Collectively, these results suggest that hyper-oxalate exposure led to HDAC6 suppression in renal tubular epithelial cells, which may contribute to interstitial mineral deposition by promoting alpha-tubulinLys40 acetylation. Therapeutic agents that influence HDAC6 activity may be beneficial in preventing RP and CaOx stone formation.

Understanding formation processes of calcareous nephrolithiasis in renal interstitium and tubule lumen

Kidney stone, one of the oldest known diseases, has plagued humans for centuries, consistently imposing a heavy burden on patients and healthcare systems worldwide due to their high incidence and recurrence rates. Advancements in endoscopy, imaging, genetics, molecular biology and bioinformatics have led to a deeper and more comprehensive understanding of the mechanism behind nephrolithiasis. Kidney stone formation is a complex, multi-step and long-term process involving the transformation of stone-forming salts from free ions into asymptomatic or symptomatic stones influenced by physical, chemical and biological factors. Among the various types of kidney stones observed in clinical practice, calcareous nephrolithiasis is currently the most common and exhibits the most intricate formation mechanism. Extensive research suggests that calcareous nephrolithiasis primarily originates from interstitial subepithelial calcified plaques and/or calcified blockages in the openings of collecting ducts. These calcified plaques and blockages eventually come into contact with urine in the renal pelvis, serving as a nidus for crystal formation and subsequent stone growth. Both pathways of stone formation share similar mechanisms, such as the drive of abnormal urine composition, involvement of oxidative stress and inflammation, and an imbalance of stone inhibitors and promoters. However, they also possess unique characteristics. Hence, this review aims to provide detailed description and present recent discoveries regarding the formation processes of calcareous nephrolithiasis from two distinct birthplaces: renal interstitium and tubule lumen.

Long non-coding RNA NRSN2-AS1 promotes ovarian cancer progression through targeting PTK2/β-catenin pathway

As a common malignant tumor among women, ovarian cancer poses a serious threat to their health. This study demonstrates that long non-coding RNA NRSN2-AS1 is over-expressed in ovarian cancer tissues using patient sample and tissue microarrays. In addition, NRSN2-AS1 is shown to promote ovarian cancer cell proliferation and metastasis both in vitro and in vivo. Mechanistically, NRSN2-AS1 stabilizes protein tyrosine kinase 2 (PTK2) to activate the β-catenin pathway via repressing MG-53-mediated ubiquitinated degradation of PTK2, thereby facilitating ovarian cancer progression. Rescue experiments verify the function of the NRSN2-AS1/PTK2/β-catenin axis and the effects of MG53 on this axis in ovarian cancer cells. In conclusion, this study demonstrates the key role of the NRSN2-AS1/PTK2/β-catenin axis for the first time and explores its potential clinical applications in ovarian cancer.

Correlation between serum α-Klotho levels and different stages of periodontitis

BACKGROUND

Periodontitis is an inflammatory disease characterized by inflammation and progressive destruction of periodontal tissues including alveolar bone. α-klotho protein is a multifunctional protein related to age-related diseases, inflammatory diseases, and bone metabolism-related diseases. However, large-sample epidemiological research evidence on the correlation between α-Klotho and the aggravation of periodontitis stages is still lacking.

METHODS

Cross-sectional study data of participants aged between 40 and 79 years in the National Health and Nutrition Examination Survey 2013‒2014 were selected and analyzed. The stages of periodontitis of the participants were determined according to the 2018 World Workshop Classification of Periodontal and Peri-implant Diseases. The serum α-Klotho levels in people with periodontitis in different stages were evaluated. Then the correlation between serum α-Klotho levels and different stages of periodontitis was analyzed by multiple linear regression (stepwise regression method).

RESULTS

A total of 2378 participants were included in the study. The serum α-Klotho levels in people with stage I/II, III and IV periodontitis were 896.16 ± 304.84, 871.08 ± 266.42 and 840.52 ± 286.24 pg/mL, respectively. The levels of α-Klotho in people with stage IV periodontitis were significantly lower than those in people with stage I/II and III periodontitis. Linear regression analysis results showed that compared to stage I/II periodontitis, serum α-Klotho levels were significantly negatively correlated with stage III (B ± SE = -37.28 ± 16.00, 95% CI: -68.66 ~ -25.91, P = 0.020) and stage IV (B ± SE = -69.37 ± 16.11, 95% CI: -100.97 ~ -37.77, P < 0.001) periodontitis.

CONCLUSION

The serum α-Klotho levels were negatively correlated with the severity of periodontitis. With the aggravation of periodontitis stages, the serum α-Klotho levels gradually decreased.

Association between Serum Klotho and Kidney Stones in US Middle-Aged and Older Individuals with Diabetes Mellitus: Results from 2007 to 2016 National Health and Nutrition Survey

INTRODUCTION

Kidney stones (KSs) are associated with hematuria and renal failure and pose a significant clinical and public health concern. Diabetes is associated with a higher risk of KSs. In addition, α-Klotho (Klotho), as a novel antiaging protein, is associated with kidney disease, diabetes, and complications and may participate in the pathological mechanism of KSs. However, studies that used large population-based database research are limited. Therefore, this study aimed to investigate whether or not KS prevalence is associated with serum Klotho levels in diabetic adults in the USA.

METHODS

This nationally representative cross-sectional study used data on diabetic adults in the USA aged 40-79 years from the National Health and Nutrition Examination Survey 2007-2016 cycles. Multivariate logistic regression models were used to calculate the association between Klotho and KS. Restricted cubic splines were used to further test for linearity and explore the shape of the dose-response association. Moreover, we performed stratified and interaction analyses to see if the relationship was stable in different subgroups.

RESULTS

Among the 3,537 diabetic patients included in this study (mean age of 61.4 years, consisting of 51.3% males), 543 participants (15.4%) suffered from KS. In the fully adjusted model, Klotho was negatively associated with KS (OR = 0.72; 95% CI: 0.54-0.96; p = 0.027). A negative relationship was observed between the occurrence of KS and Klotho (nonlinear: p = 0.560). Some differences in the association between Klotho and KS were found in stratified analyses; however, these differences lacked statistical significance.

CONCLUSIONS

Serum Klotho was negatively associated with the incidence of KS; when ln-transformed Klotho concentration increased by 1 unit, the risk of KS was 28% lower.

IKKα aggravates renal fibrogenesis by positively regulating the Wnt/β-catenin pathway

AKI (acute kidney injury) with maladaptive repair plays exacerbated role in renal fibrosis characterized by tubulointerstitial fibrosis. Previously, we reported that IKKα contributed to kidney regeneration and inhibited inflammation. Here, we first identified the role and mechanism of IKKα on TGF-β1-induced fibrosis in human tubular epithelial cells and fibrotic kidneys. IKKα was up-regulated in kidney tubular epithelium in unilateral ureteral obstruction (UUO) and unilateral ischemic reperfusion injury (UIRI) mice. Immunohistochemical staining showed that IKKα was positively correlated with the extent of kidney fibrosis in tissue biopsies from chronic kidney disease (CKD) patients. Compared with wild-type controls, Ksp-IKKα^-/- mice exhibited inactivated Wnt/β-catenin pathway, decreased serum creatinine and interstitial fibrosis in the kidney after IRI. In TGF-β1-stimulated human tubular epithelial cells, IKKα overexpression enhanced β-catenin nuclear translocation. Blocking IKKα by siRNA specifically suppressed β-catenin activation and downstream profibrotic genes such as fibronectin and α-smooth muscle actin (α-SMA). Taken together, our study demonstrated that IKKα aggravated renal fibrogenesis by activating Wnt/β-catenin signalling pathway, providing a new target for the treatment of kidney fibrosis.

OLMALINC/OCT4/BMP2 axis enhances osteogenic-like phenotype of renal interstitial fibroblasts to participate in Randall's plaque formation

BACKGROUND

Randall's plaques (RP) are identified as anchored sites for kidney calcium oxalate stones, but the mechanism remains unclear. Given the importance of osteogenic-like cells in RP formation and OCT4 in reprogramming differentiated cells to osteoblasts, the current study explored the potential role of OCT4 in RP formation.

METHODS

OCT4 and biomineralization were evaluated in RP, and immunofluorescence co-staining was performed to identify these cells with alteration of OCT4 and osteogenic markers. Based on the analysis of tissue, we further investigated the mechanism of OCT4 in regulating osteogenic-like differentiation of primary human renal interstitial fibroblasts (hRIFs) in vitro and vivo.

RESULTS

We identified the upregulated OCT4 in RP, with a positive correlation to osteogenic markers. Interestingly, fibroblast marker Vimentin was partially co-localized with upregulated OCT4 and osteogenic markers in RP. Further investigations revealed that OCT4 significantly enhanced the osteogenic-like phenotype of hRIFs in vitro and in vivo. Mechanically, OCT4 directly bound to BMP2 promoter and facilitated its CpG island demethylation to transcriptionally promote BMP2 expression. Furthermore, combination of RIP and RNA profiling uncovered that lncRNA OLMALINC physically interacted with OCT4 to promote its stabilization via disrupting the ubiquitination. Additionally, OLMALINC was upregulated in fibroblasts in RP visualized by FISH, and a positive correlation was revealed between OLMALINC and OCT4 in RP.

CONCLUSIONS

The upregulation of OCT4 in hRIFs was a pathological feature of RP formation, and OLMALINC/OCT4/BMP2 axis facilitated hRIFs to acquire osteogenic-like phenotype under osteogenic conditions, through which the pathway might participate in RP formation. Our findings opened up a new avenue to better understand RP formation in which osteogenic-like process was partially triggered by lncRNAs and pluripotency maintenance related genes.

Effects of salvianolic acid A and salvianolic acid B in renal interstitial fibrosis via PDGF-C/PDGFR-α signaling pathway

BACKGROUND

Renal interstitial fibrosis (RIF) is the main pathological feature of end-stage renal disease (ESRD) caused by various chronic kidney diseases (CKD), and is closely related to renal dysfunction and patient prognosis. Salvianolic acid A (Sal A) and salvianolic acid B (Sal B), isolated from traditional Chinese medicine Salviae miltiorrhizae, have been confirmed to have anti-fibrotic effects on liver, cardiac and kidney. However, the precise molecular mechanism underlying the nephroprotective effects of Sal A and Sal B, and whether there is a difference between the two in RIF are still unclear.

PURPOSE

This study investigated the pharmacological effects of Sal A and Sal B in RIF and explore the underlying mechanisms by in vivo and in vitro experiments.

METHODS

The nephroprotective effects of Sal A, Sal B and Sal A+B were evaluated by assessing the parameters related to kidney function such as renal histology, renal function, urinary protein NAG, urinary β2 microglobulin. In addition, RIF-related markers such as CTCF and Par3 were also detected. Thereafter, the related protein or gene levels of PDGF-C/PDGFR-α signaling pathways, apoptosis and endoplasmic reticulum stress (ERS) were determined by western blot, real-time PCR, flow cytometry or immunofluorescence staining.

RESULTS

In vivo, the results showed that Sal A, Sal B and Sal A+B partially improved kidney dysfunction, increased the expression of Par-3 and reduced the expression of CTGF, PDGF-C and PDGFR-α. In vitro, the results also showed that Sal A, Sal B and Sal A+B reversed apoptosis and ERS in HSA-induced HK-2 cells via regulating PDGF-C/PDGFR-α signaling pathway.

CONCLUSION

This article revealed a novel mechanism linking PDGF-C/PDGFR-α signaling pathway to RIF and suggested that Sal A, Sal B and Sal A+B were considered as potential therapeutic agents for the amelioration of RIF.

Shenkang injection improves chronic kidney disease by inhibiting multiple renin-angiotensin system genes by blocking the Wnt/β-catenin signalling pathway

Chronic kidney disease (CKD) is a major worldwide public health problem. The increase in the number of patients with CKD and end-stage kidney disease requesting renal dialysis or transplantation will progress to epidemic proportions in the next several decades. Although blocking the renin-angiotensin system (RAS) has been used as a first-line standard therapy in patients with hypertension and CKD, patients still progress towards end-stage kidney disease, which might be closely associated with compensatory renin expression subsequent to RAS blockade through a homeostatic mechanism. The Wnt/β-catenin signalling pathway is the master upstream regulator that controls multiple intrarenal RAS genes. As Wnt/β-catenin regulates multiple RAS genes, we inferred that this pathway might also be implicated in blood pressure control. Therefore, discovering new medications to synchronously target multiple RAS genes is necessary and essential for the effective treatment of patients with CKD. We hypothesized that Shenkang injection (SKI), which is widely used to treat CKD patients, might ameliorate CKD by inhibiting the activation of multiple RAS genes via the Wnt/β-catenin signalling pathway. To test this hypothesis, we used adenine-induced CKD rats and angiotensin II (AngII)-induced HK-2 and NRK-49F cells. Treatment with SKI inhibited renal function decline, hypertension and renal fibrosis. Mechanistically, SKI abrogated the increased protein expression of multiple RAS elements, including angiotensin-converting enzyme and angiotensin II type 1 receptor, as well as Wnt1, β-catenin and downstream target genes, including Snail1, Twist, matrix metalloproteinase-7, plasminogen activator inhibitor-1 and fibroblast-specific protein 1, in adenine-induced rats, which was verified in AngII-induced HK-2 and NRK-49F cells. Similarly, our results further indicated that treatment with rhein isolated from SKI attenuated renal function decline and epithelial-to-mesenchymal transition and repressed RAS activation and the hyperactive Wnt/β-catenin signalling pathway in both adenine-induced rats and AngII-induced HK-2 and NRK-49F cells. This study first revealed that SKI repressed epithelial-to-mesenchymal transition by synchronously targeting multiple RAS elements by blocking the hyperactive Wnt/β-catenin signalling pathway.