ERK1,2 Signalling Pathway along the Nephron and Its Role in Acid-base and Electrolytes Balance

High water intake induces primary cilium elongation in renal tubular cells

BACKGROUND

The primary cilium protrudes from the cell surface and functions as a mechanosensor. Recently, we found that water intake restriction shortens the primary cilia of renal tubular cells, and a blockage of the shortening disturbs the ability of the kidneys to concentrate urine. Here, we investigate whether high water intake (HWI) alters primary cilia length, and if so, what is its underlying mechanism and its role on kidney urine production.

METHODS

Experimental mice were given free access to normal water (normal water intake) or 3% sucrose-containing water for HWI for 2 days. Some mice were administered with U0126 (10 mg/kg body weight), an inhibitor of MEK kinase, from 2 days before HWI, daily. The primary cilium length and urine amount and osmolality were investigated.

RESULTS

HWI-induced diluted urine production and primary cilium elongation in renal tubular cells. HWI increased the expression of α-tubulin acetyltransferase 1 (αTAT1), leading to the acetylation of α-tubulins, a core protein of the primary cilia. HWI also increased phosphorylated ERK1/2 (p-ERK1/2) and exocyst complex component 5 (Exoc5) expression in the kidneys. U0126 blocked HWI-induced increases in αTAT1, p-ERK1/2, and Exoc5 expression. U0126 inhibited HWI-induced α-tubulin acetylation, primary cilium elongation, urine amount increase, and urine osmolality decrease.

CONCLUSION

These results show that increased water intake elongates the primary cilia via ERK1/2 activation and that ERK inhibition prevents primary cilium elongation and diluted urine production. These data suggest that the elongation of primary cilium length is associated with the production of diluted urine.

KDM6A Demethylase Regulates Renal Sodium Excretion and Blood Pressure

BACKGROUND

KDM6A (Lysine-Specific Demethylase 6A) is a specific demethylase for histone 3 lysine (K) 27 trimethylation (H3K27me3). The purpose of this study is to investigate whether KDM6A in renal tubule cells plays a role in the regulation of kidney function and blood pressure.

METHODS

We first crossed Ksp-Cre+/- and KDM6Aflox/flox mice for generating inducible kidney-specific deletion of KDM6A gene.

RESULTS

Notably, conditional knockout of KDM6A gene in renal tubule cells (KDM6A-cKO) increased H3K27me3 levels which leads to a decrease in Na excretion and elevation of blood pressure. Further analysis showed that the expression of NKCC2 (Na-K-2Cl cotransporter 2) and NCC (Na-Cl cotransporters) was upregulated which contributes to impaired Na excretion in KDM6A-cKO mice. The expression of AQP2 (aquaporin 2) was also increased in KDM6A-cKO mice, which may facilitate water reabsorption in KDM6A-cKO mice. The expression of Klotho was downregulated while expression of aging markers including p53, p21, and p16 was upregulated in kidneys of KDM6A-cKO mice, indicating that deletion of KDM6A in the renal tubule cells promotes kidney aging. Interestingly, KDM6A-cKO mice developed salt-sensitive hypertension which can be rescued by treatment with Klotho. KDM6A deficiency induced salt-sensitive hypertension likely through downregulation of the Klotho/ERK (extracellular signal-regulated kinase) signaling and upregulation of the WNK (with-no-lysine kinase) signaling.

CONCLUSIONS

This study provides the first evidence that KDM6A plays an essential role in maintaining normal tubular function and blood pressure. Renal tubule cell specific KDM6A deficiency causes hypertension due to increased H3K27me3 levels and the resultant downregulation of Klotho gene expression which disrupts the Klotho/ERK/NCC/NKCC2 signaling.

Flow induces common and specific transcriptional changes in renal tubular epithelial cells involving the PI3K pathway

Flow-induced shear stress affects renal epithelial cells in the nephron tubule with potential implications for differential functionalities of the individual segments. Disruptions of cellular mechanosensation or flow conditions are associated with the development and progression of various renal diseases. This study investigates the effects of flow on the transcriptome of various renal tubular epithelial cell types. We analyzed the transcriptome of induced renal epithelial cells (iREC) cultured under physiological flow (0.57 ± 0.05 dyn/cm2 ) or in static conditions for 72 h. RNA sequencing showed 861 differentially expressed genes (DEGs), with 503 up- and 358 downregulated under flow. DEGs were linked to extracellular matrix (ECM) components (e.g. Col1a1, Col4a3, Col4a4, Fn1, Smoc2), junctions (Gja1, Tubb5), channel activities (Abcc4, Aqp1), and transcription factors (Foxq1, Lgr6). Next, we performed a meta-analysis comparing our data with three published datasets that subjected epithelial cell lines from distinct segments to flow, including proximal tubule and collecting duct cells. We found that TGF-ß, p53, MAPK, and PI3K are common flow-regulated pathways. Tfrc expression and thus the capability of iron uptake is commonly upregulated under flow. Many DEGs were related to kidney diseases, such as fibrosis (e.g. Tgfb1-3 and Serpine1). To obtain further mechanistic insights we investigated the role of the PI3K pathway in flow sensing. Applying flow and inhibition of PI3K showed significantly altered expression of transcripts related to ECM remodeling, angiogenesis, and ion transport. This suggests that the PI3K pathway is a critical mediator in flow-dependent cellular processes and gene expression, potentially influencing renal development and tissue remodeling. Finally, we derived a cross-cell-line summary of common as well as segment-specific transcriptomic effects, thus providing insights into the molecular mechanisms underlying flow sensing in the nephron tubule.

MAPK-ERK Pathway

The name extracellular signal-regulated kinase (ERK) was first used for a cell cycle regulating Ser/Thr protein kinase cloned in mammalian cells [...].

Impact of Thyroid Cancer Treatment on Renal Function: A Relevant Issue to Be Addressed

Thyroid cancers require complex and heterogeneous therapies with different impacts on renal function. In our systematic literature review, we analyzed several aspects: renal function assessment, the impact of radiotherapy and thyroid surgery on kidney functioning, and mechanisms of nephrotoxicity of different chemotherapy, targeted and immunologic drugs. Our study revealed that the renal impact of thyroid cancer therapy can be a limiting factor in all radiotherapy, surgery, and pharmacological approaches. It is advisable to conduct a careful nephrological follow-up imposing the application of body surface based estimated Glomerular Filtration Rate (eGFR) formulas for the purpose of an early diagnosis and treatment of renal failure, guaranteeing the therapy continuation to thyroid cancer patients.

Stem Cells in Kidney Ischemia: From Inflammation and Fibrosis to Renal Tissue Regeneration

Ischemic nephropathy consists of progressive renal function loss due to renal hypoxia, inflammation, microvascular rarefaction, and fibrosis. We provide a literature review focused on kidney hypoperfusion-dependent inflammation and its influence on renal tissue's ability to self-regenerate. Moreover, an overview of the advances in regenerative therapy with mesenchymal stem cell (MSC) infusion is provided. Based on our search, we can point out the following conclusions: 1. endovascular reperfusion is the gold-standard therapy for RAS, but its success mostly depends on treatment timeliness and a preserved downstream vascular bed; 2. anti-RAAS drugs, SGLT2 inhibitors, and/or anti-endothelin agents are especially recommended for patients with renal ischemia who are not eligible for endovascular reperfusion for slowing renal damage progression; 3. TGF-β, MCP-1, VEGF, and NGAL assays, along with BOLD MRI, should be extended in clinical practice and applied to a pre- and post-revascularization protocols; 4. MSC infusion appears effective in renal regeneration and could represent a revolutionary treatment for patients with fibrotic evolution of renal ischemia.

Mechanisms of Cardiorenal Protection With SGLT2 Inhibitors in Patients With T2DM Based on Network Pharmacology

Purpose

Sodium-glucose cotransporter 2 (SGLT2) inhibitors have cardiorenal protective effects regardless of whether they are combined with type 2 diabetes mellitus, but their specific pharmacological mechanisms remain undetermined.

Materials and Methods

We used databases to obtain information on the disease targets of “Chronic Kidney Disease,” “Heart Failure,” and “Type 2 Diabetes Mellitus” as well as the targets of SGLT2 inhibitors. After screening the common targets, we used Cytoscape 3.8.2 software to construct SGLT2 inhibitors' regulatory network and protein-protein interaction network. The clusterProfiler R package was used to perform gene ontology functional analysis and Kyoto encyclopedia of genes and genomes pathway enrichment analyses on the target genes. Molecular docking was utilized to verify the relationship between SGLT2 inhibitors and core targets.

Results

Seven different SGLT2 inhibitors were found to have cardiorenal protective effects on 146 targets. The main mechanisms of action may be associated with lipid and atherosclerosis, MAPK signaling pathway, Rap1 signaling pathway, endocrine resistance, fluid shear stress, atherosclerosis, TNF signaling pathway, relaxin signaling pathway, neurotrophin signaling pathway, and AGEs-RAGE signaling pathway in diabetic complications were related. Docking of SGLT2 inhibitors with key targets such as GAPDH, MAPK3, MMP9, MAPK1, and NRAS revealed that these compounds bind to proteins spontaneously.

Conclusion

Based on pharmacological networks, this study elucidates the potential mechanisms of action of SGLT2 inhibitors from a systemic and holistic perspective. These key targets and pathways will provide new ideas for future studies on the pharmacological mechanisms of cardiorenal protection by SGLT2 inhibitors.

A B-Raf V600E gene signature for melanoma predicts prognosis and reveals sensitivity to targeted therapies

BACKGROUND

B-Raf V600E mutations account for about half of all skin cutaneous melanoma cases, and patients with this mutation are sensitive to BRAF inhibitors. However, aberrations in other genes in the MAPK/ERK pathway may cascade a similar effect as B-Raf V600E mutations, rendering those patients sensitive to BRAF inhibitors. We rationalized that defining a signature based on B-Raf pathway activity may be more informative for prognosis and drug sensitivity prediction than a binary indicator such as mutation status.

METHODS

In this study, we defined a B-Raf signature score using RNA-seq data from TCGA. A higher score is shown to not only predict B-Raf mutation status, but also predict other aberrations that could similarly activate the MAPK/ERK pathway, such as B-Raf amplification, RAS mutation, and EGFR amplification.

RESULTS

We showed that patients dichotomized by the median B-Raf score is more significantly stratified than by other metrics of measuring B-Raf aberration, such as mutation status, gene expression, and protein expression. We also demonstrated that high B-Raf score predicts higher sensitivity to B-Raf inhibitors SB590885 and PLX4720, as expected, but also correlated with sensitivity to drugs targeting other relevant oncogenic pathways.

CONCLUSION

The BRAF signature may better help guide targeted therapy for melanoma, and such a framework can be applied to other cancers and mutations to provide more information than mutation status alone.

Comparative analysis of gene expression profiles in differentiated subcutaneous adipocytes between Jiaxing Black and Large White pigs

Background

Chinese domestic pig breeds are reputed for pork quality, but their low ratio of lean-to-fat carcass weight decreases production efficiency. A better understanding of the genetic regulation network of subcutaneous fat tissue is necessary for the rational selection of Chinese domestic pig breeds. In the present study, subcutaneous adipocytes were isolated from Jiaxing Black pigs a Chinese indigenous pig breed with redundant subcutaneous fat deposition and Large White pigs a lean-type pig breed with relatively low subcutaneous fat deposition. The expression profiles of mRNAs and lncRNAs were compared by RNA-seq analysis to identify biomarkers correlated with the differences of subcutaneous fat deposition between the two breeds.

Results

A total of 1058 differentially expressed genes and 221 differentially expressed lncRNAs were identified in subcutaneous adipocytes between Jiaxing Black and Large White pigs, which included 275 up-regulated mRNAs, 783 down-regulated mRNAs, 118 up-regulated lncRNAs and 103 down-regulated lncRNAs. Gene Ontology and KEGG pathway enrichment analyses revealed that the differentially expressed genes and differentially expressed lncRNAs were mainly involved in the immune response, cell fate determination, PI3K-Akt signaling pathway and MAPK signaling pathway, which are known to be related to adipogenesis and lipid metabolism. The expression levels of differentially expressed genes and differentially expressed lncRNAs according to the RNA-seq data were verified by quantitative PCR, which showed 81.8% consistency. The differences in MAPK pathway activity between Jiaxing Black and Large White pigs was confirmed by western blot analysis, which revealed elevated p38 phosphorylation in Jiaxing Black pigs.

Conclusions

This study offers a detailed characterization of mRNAs and lncRNAs in fat- and lean-type pig breeds. The activity of the MAPK signaling pathway was found to be associated with subcutaneous adipogenesis. These results provide new targets for further investigation of the molecular mechanisms regulating subcutaneous fat deposition in pigs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-020-07361-9.

Pancreatic stellate cells exhibit adaptation to oxidative stress evoked by hypoxia

BACKGROUND INFORMATION

Pancreatic stellate cells play a key role in the fibrosis that develops in diseases such as pancreatic cancer. In the growing tumour, a hypoxia condition develops under which cancer cells are able to proliferate. The growth of fibrotic tissue contributes to hypoxia. In this study, the effect of hypoxia (1% O₂ ) on pancreatic stellate cells physiology was investigated. Changes in intracellular free-Ca²⁺ concentration, mitochondrial free-Ca²⁺ concentration and mitochondrial membrane potential were studied by fluorescence techniques. The status of enzymes responsible for the cellular oxidative state was analyzed by quantitative reverse transcription-polymerase chain reaction, high-performance liquid chromatography, spectrophotometric and fluorimetric methods and by Western blotting analysis. Cell viability and proliferation were studied by crystal violet test, 5-bromo-2-deoxyuridine cell proliferation test and Western blotting analysis. Finally, cell migration was studied employing the wound healing assay.

RESULTS

Hypoxia induced an increase in intracellular and mitochondrial free-Ca²⁺ concentration, whereas mitochondrial membrane potential was decreased. An increase in mitochondrial reactive oxygen species production was observed. Additionally, an increase in the oxidation of proteins and lipids was detected. Moreover, cellular total antioxidant capacity was decreased. Increases in the expression of superoxide dismutase 1 and 2 were observed and superoxide dismutase activity was augmented. Hypoxia evoked a decrease in the oxidized/reduced glutathione ratio. An increase in the phosphorylation of nuclear factor erythroid 2-related factor and in expression of the antioxidant enzymes catalytic subunit of glutamate-cysteine ligase, catalase, NAD(P)H-quinone oxidoreductase 1 and heme oxygenase-1 were detected. The expression of cyclin A was decreased, whereas expression of cyclin D and the content of 5-bromo-2-deoxyuridine were increased. This was accompanied by an increase in cell viability. The phosphorylation state of c-Jun NH₂ -terminal kinase was increased, whereas that of p44/42 and p38 was decreased. Finally, cells subjected to hypoxia maintained migration ability.

CONCLUSIONS AND SIGNIFICANCE

Hypoxia creates pro-oxidant conditions in pancreatic stellate cells to which cells adapt and leads to increased viability and proliferation.

The melatonin receptor antagonist luzindole induces the activation of cellular stress responses and decreases viability of rat pancreatic stellate cells

In this study, we have examined the effects of luzindole, a melatonin receptor-antagonist, on cultured pancreatic stellate cells. Intracellular free-Ca²⁺ concentration, production of reactive oxygen species (ROS), activation of mitogen-activated protein kinases (MAPK), endoplasmic reticulum stress and cell viability were analyzed. Stimulation of cells with the luzindole (1, 5, 10 and 50 μm) evoked a slow and progressive increase in intracellular free Ca²⁺ ([Ca²⁺ ]_i ) towards a plateau. The effect of the compound on Ca²⁺ mobilization depended on the concentration used. Incubation of cells with the sarcoendoplasmic reticulum Ca²⁺ -ATPase inhibitor thapsigargin (1 μm), in the absence of Ca²⁺ in the extracellular medium, induced a transient increase in [Ca²⁺ ]_i . In the presence of thapsigargin, the addition of luzindole to the cells failed to induce further mobilization of Ca²⁺ . Luzindole induced a concentration-dependent increase in ROS generation, both in the cytosol and in the mitochondria. This effect was smaller in the absence of extracellular Ca²⁺ . In the presence of luzindole the phosphorylation of p44/42 and p38 MAPKs was increased, whereas no changes in the phosphorylation of JNK could be noted. Moreover, the detection of the endoplasmic reticulum stress-sensor BiP was increased in the presence of luzindole. Finally, viability was decreased in cells treated with luzindole. Because cellular membrane receptors for melatonin have not been detected in pancreatic stellate cells, we conclude that luzindole could exert direct effects that are not mediated through its action on melatonin membrane receptors.