Epithelial sodium channel enhanced osteogenesis via cGMP/PKGII/ENaC signaling in rat osteoblast

Phenytoin regulates osteogenic differentiation of human bone marrow stem cells by PI3K/Akt pathway

Background

We mainly studied the mechanism by which phenytoin promotes osteogenic differentiation of human jawbone marrow stem cells.

Methods

Bone marrow stem cells were extracted from jaw bone tissue debris obtained from 5 subjects undergoing implant restoration. Osteogenic and adipogenic experiments proved cells stemness, and the expression of ALP, RUNX2, and OSX were detected by qPCR and Western blot. High-throughput sequencing was used to extract differentially expressed genes, the network database predicted phenytoin drug targets, GO and KEGG enrichment combined with PPI network diagram to analyze the osteogenesis mechanism.

Results

Calcium nodules and lipid droplet formation were observed in osteogenic and adipogenic experiments. The concentration of phenytoin within 100 mg/L does not produce cytotoxicity. The results of PCR and WB indicated that 50 mg/L phenytoin significantly promoted the expression of ALP and RUNX2, and 25 mg/L phenytoin significantly promoted the expression of OSX. The results of network pharmacology suggest that phenytoin promotes bone formation by up-regulating FGFR2, S1PR1, TGFB3, VCAN core proteins and activating PI3K/Akt pathway.

Conclusions

Phenytoin activated the PI3K/Akt pathway to regulate the osteogenic differentiation of human jawbone marrow stem cells. https://data.mendeley.com/datasets/t3xstktt93/1.

The Impact of Plasma Membrane Ion Channels on Bone Remodeling in Response to Mechanical Stress, Oxidative Imbalance, and Acidosis

The extracellular milieu is a rich source of different stimuli and stressors. Some of them depend on the chemical–physical features of the matrix, while others may come from the ‘outer’ environment, as in the case of mechanical loading applied on the bones. In addition to these forces, a plethora of chemical signals drives cell physiology and fate, possibly leading to dysfunctions when the homeostasis is disrupted. This variety of stimuli triggers different responses among the tissues: bones represent a particular milieu in which a fragile balance between mechanical and metabolic demands should be tuned and maintained by the concerted activity of cell biomolecules located at the interface between external and internal environments. Plasma membrane ion channels can be viewed as multifunctional protein machines that act as rapid and selective dual-nature hubs, sensors, and transducers. Here we focus on some multisensory ion channels (belonging to Piezo, TRP, ASIC/EnaC, P2XR, Connexin, and Pannexin families) actually or potentially playing a significant role in bone adaptation to three main stressors, mechanical forces, oxidative stress, and acidosis, through their effects on bone cells including mesenchymal stem cells, osteoblasts, osteoclasts, and osteocytes. Ion channel-mediated bone remodeling occurs in physiological processes, aging, and human diseases such as osteoporosis, cancer, and traumatic events.

Prkg2 regulates alveolar type 2-mediated re-alveolarization

BACKGROUND

The cGMP-dependent type 2 protein kinase, encoded by the prkg2 gene, is highly expressed in alveolar type 2 epithelial (AT2) cells. It is unclear whether prkg2 regulates AT2 cell homeostasis and re-alveolarization of injured lungs. This study aimed to investigate the role of prkg2 in the regulation of the fate of AT2 in vitro.

METHODS

Primary AT2 cells of wild-type (wt) and prkg2^-/- mice were co-cultured with fibroblasts as three-dimensional organoids. The colony formation was analyzed between days 4 and 12 post-seeding. EdU assay was used to detect cells with active DNA synthesis. AT1 and AT2 cells in organoids were visualized with anti-podoplanin and anti-surfactant protein C antibodies, respectively.

RESULTS

Prkg2^-/- AT2 cells developed a greater number of organoids than wt controls. However, compared to wt organoids, a lower number of AT2 but a greater number of AT1 cells were visualized. In addition, a lower number of proliferated cells (EdU⁺) were observed in prkg2^-/- organoids compared to wt controls. The numbers of organoids and EdU⁺ cells were significantly reduced in protein kinase A (PKA) inhibitor H89-treated wt and prkg2^-/- cultures. Organoids and EdU⁺ cells were increased by lipopolysaccharides (LPS) in both wt and prkg2^-/- groups. The increase in the proportion of AT1 and AT2 cells in organoids was only seen in wt controls.

CONCLUSIONS

Prkg2 may regulate the lineage of AT2 cells, which is affected by endotoxins and the interactive PKA signaling pathway.

Luteolin attenuates lipopolysaccharide-induced acute lung injury/acute respiratory distress syndrome by activating alveolar epithelial sodium channels via cGMP/PI3K pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Luteolin (Lut) was recently identified as the major active ingredient of Mosla scabra, which was a typical representative traditional Chinese medicine and had been used to treat pulmonary diseases for thousands of years.

AIM OF THE STUDY

This study was to explore the effects and relative mechanisms of Lut in LPS-induced acute lung injury/acute respiratory distress syndrome (ALI/ARDS). The main characteristic of ALI/ARDS is pulmonary edema, and epithelial sodium channel (ENaC) is a key factor in effective removal of excessive alveolar edematous fluid, which is essential for repairing gas exchange and minimizing damage to the peripheral tissues. However, whether the therapeutic effects of Lut on respiratory diseases are relative with ENaC is still unknown.

MATERIALS AND METHODS

Alveolar fluid clearance was calculated in BALB/c mice and ENaC function was measured in H441 cells. Moreover, ENaC membrane protein and mRNA were detected by Western blot and real-time PCR, respectively. We also studied the involvement of cGMP/PI3K pathway during the regulation of Lut on ENaC during LPS-induced ALI/ARDS by ELISA method and applying cGMP/PI3K inhibitors/siRNA.

RESULTS

The beneficial effects of Lut in ALI/ARDS were evidenced by the alleviation of pulmonary edema, and enhancement of both amiloride-sensitive alveolar fluid clearance and short-circuit currents. Lut could alleviate the LPS decreased expression levels of ENaC mRNA and membrane protein in H441 cells and mouse lung. In addition, cGMP concentration was increased after the administration of Lut in ALI/ARDS mice, while the inhibition of cGMP/PI3K pathway could abrogate the enhanced AFC and ENaC protein expression of Lut.

CONCLUSION

These results implied that Lut could attenuate pulmonary edema via enhancing the abundance of membrane ENaC at least partially through the cGMP/PI3K pathway, which could provide a promising therapeutic strategy for treating ALI/ARDS.

Ferulic acid ameliorates lipopolysaccharide-induced tracheal injury via cGMP/PKGII signaling pathway

BACKGROUND

Tracheal injury is a common clinical condition that still lacks an effective therapy at present. Stimulation of epithelial sodium channel (ENaC) increases Na⁺ transport, which is a driving force to keep tracheal mucosa free edema fluid during tracheal injury. Ferulic acid (FA) has been proved to be effective in many respiratory diseases through exerting anti-oxidant, anti-inflammatory, and anti-thrombotic effects. However, these studies rarely involve the level of ion transport, especially ENaC.

METHODS

C57BL/J male mice were treated intraperitoneally with normal saline or FA (100 mg/kg) 12 h before, and 12 h after intratracheal administration of lipopolysaccharide (LPS, 5 mg/kg), respectively. The effects of FA on tracheal injury were not only assessed through HE staining, immunofluorescence assay, and protein/mRNA expressions of ENaC located on tracheas, but also evaluated by the function of ENaC in mouse tracheal epithelial cells (MTECs). Besides, to explore the detailed mechanism about FA involved in LPS-induced tracheal injury, the content of cyclic guanosine monophosphate (cGMP) was measured, and Rp-cGMP (cGMP inhibitor) or cGMP-dependent protein kinase II (PKGII)-siRNA (siPKGII) were applied in primary MTECs, respectively.

RESULTS

Histological examination results demonstrated that tracheal injury was obviously attenuated by pretreatment of FA. Meanwhile, FA could reverse LPS-induced reduction of both protein/mRNA expressions and ENaC activity. ELISA assay verified cGMP content was increased by FA, and administration of Rp-cGMP or transfection of siPKGII could reverse the FA up-regulated ENaC protein expression in MTECs.

CONCLUSIONS

Ferulic acid can attenuate LPS-induced tracheal injury through up-regulation of ENaC at least partially via the cGMP/PKGII pathway, which may provide a promising new direction for preventive and therapeutic strategy in tracheal injury.

The mechanosensory and mechanotransductive processes mediated by ion channels and the impact on bone metabolism: A systematic review

Mechanical environments were associated with alterations in bone metabolism. Ion channels present on bone cells are indispensable for bone metabolism and can be directly or indirectly activated by mechanical stimulation. This review aimed to discuss the literature reporting the mechanical regulatory effects of ion channels on bone cells and bone tissue. An electronic search was conducted in PubMed, Embase and Web of Science. Studies about mechanically induced alteration of bone cells and bone tissue by ion channels were included. Ion channels including TRP family channels, Ca²⁺ release-activated Ca²⁺ channels (CRACs), Piezo1/2 channels, purinergic receptors, NMDA receptors, voltage-sensitive calcium channels (VSCCs), TREK2 potassium channels, calcium- and voltage-dependent big conductance potassium (BK_Ca) channels, small conductance, calcium-activated potassium (SK_Ca) channels and epithelial sodium channels (ENaCs) present on bone cells and bone tissue participate in the mechanical regulation of bone development in addition to contributing to direct or indirect mechanotransduction such as altered membrane potential and ionic flux. Physiological (beneficial) mechanical stimulation could induce the anabolism of bone cells and bone tissue through ion channels, but abnormal (harmful) mechanical stimulation could also induce the catabolism of bone cells and bone tissue through ion channels. Functional expression of ion channels is vital for the mechanotransduction of bone cells. Mechanical activation (opening) of ion channels triggers ion influx and induces the activation of intracellular modulators that can influence bone metabolism. Therefore, mechanosensitive ion channels provide new insights into therapeutic targets for the treatment of bone-related diseases such as osteopenia and aseptic implant loosening.

Proliferative regulation of alveolar epithelial type 2 progenitor cells by human Scnn1d gene

Lung epithelial sodium channel (ENaC) encoded by Scnn1 genes is essential for maintaining transepithelial salt and fluid homeostasis in the airway and the lung. Compared to α, β, and γ subunits, the role of respiratory δ-ENaC has not been studied in vivo due to the lack of animal models.

Methods: We characterized full-length human δ₈₀₂-ENaC expressed in both Xenopus oocytes and humanized transgenic mice. AT2 proliferation and differentiation in 3D organoids were analysed with FACS and a confocal microscope. Both two-electrode voltage clamp and Ussing chamber systems were applied to digitize δ₈₀₂-ENaC channel activity. Immunoblotting was utilized to analyse δ₈₀₂-ENaC protein. Transcripts of individual ENaC subunits in human lung tissues were quantitated with qPCR.

Results: The results indicate that δ₈₀₂-ENaC functions as an amiloride-inhibitable Na⁺ channel. Inhibitory peptide α-13 distinguishes δ₈₀₂- from α-type ENaC channels. Modified proteolysis of γ-ENaC by plasmin and aprotinin did not alter the inhibition of amiloride and α-13 peptide. Expression of δ₈₀₂-ENaC at the apical membrane of respiratory epithelium was detected with biophysical features similar to those of heterologously expressed channels in oocytes. δ₈₀₂-ENaC regulated alveologenesis through facilitating the proliferation of alveolar type 2 epithelial cells.

Conclusion: The humanized mouse line conditionally expressing human δ₈₀₂-ENaC is a novel model for studying the expression and function of this protein in vivo .

Transepithelial Fluid and Salt Re-Absorption Regulated by cGK2 Signals

Transepithelial fluid and salt re-absorption in epithelial tissues play an important role in fluid and salt homeostasis. In absorptive epithelium, fluid and salt flux is controlled by machinery mainly composed of epithelial sodium channels (ENaC), cystic fibrosis transmembrane conductance regulator (CFTR), Na⁺/H⁺ exchanger (NHE), aquaporin, and sodium potassium adenosine triphosphatase (Na⁺/K⁺-ATPase). Dysregulation of fluid and salt transport across epithelium contributes to the pathogenesis of many diseases, such as pulmonary edema and cystic fibrosis. Intracellular and extracellular signals, i.e., hormones and protein kinases, regulate fluid and salt turnover and resolution. Increasing evidence demonstrates that transepithelial fluid transport is regulated by cyclic guanosine monophosphate-dependent protein kinase (cGK) signals. cGK2 was originally identified and cloned from intestinal specimens, the presence of which has also been confirmed in the kidney and the lung. cGK2 regulates fluid and salt through ENaC, CFTR and NHE. Deficient cGK2 regulation of transepithelial ion transport was seen in acute lung injury, and cGK2 could be a novel druggable target to restore edematous disorder in epithelial tissues.

[Effects of aldosterone on osteoblast proliferation, differentiation and osteogenic gene expressions in vitro]

OBJECTIVE

To study the effect of aldosterone on cell proliferation, alkaline phosphatase (AKP) activity and osteogenic gene expression in rat osteoblasts and explore the mechanisms.

METHODS

Osteoblasts isolated from the skull of neonatal SD rats by enzyme digestion were cultured and treated with different concentrations of aldosterone. The cell proliferation and AKP activity were evaluated using CCK-8 assay kit and AKP assay kit, respectively. The effects of aldosterone on mRNA and protein expressions of the osteogenic genes and epithelial sodium channel (ENaC) gene were investigated using semi-quantitative PCR and Western blotting.

RESULTS

Compared with the control cells, the cells treated with 0.01-1.0 µmol/L aldosterone showed obviously enhanced proliferation while lower (1×10^-3 µmol/L) or higher (10 µmol/L) concentrations of aldosterone did not significantly affect the cell proliferation. Aldosterone within the concentration range of 1×10^-3 to 10 µmol/L did not cause significant changes in AKP activity in the osteoblasts. Treatment with 0.01 to 1.0 µmol/L aldosterone significantly upregulated the expressions of the osteogenic genes and α-ENaC gene at both the mRNA and protein levels.

CONCLUSION

Aldosterone within the concentration range of 0.01-1.0 µmol/L stimulates the proliferation and osteogenic gene expressions and enhances α-ENaC gene expression in rat osteoblasts in vitro, suggesting the possibility that ENaC participates in aldosterone-mediated regulation of osteoblast functions.

Role of Epithelium Sodium Channel in Bone Formation

Objective:

To review the recent developments in the mechanisms of epithelium sodium channels (ENaCs) induced bone formation and regulation.

Data Sources:

Studies written in English or Chinese were searched using Medline, PubMed and the index of Chinese-language literature with time restriction from 2005 to 2014. Keywords included ENaC, bone, bone formation, osteonecrosis, estrogen, and osteoporosis. Data from published articles about the structure of ENaC, mechanism of ENaC in bone formation in recent domestic and foreign literature were selected.

Study Selection:

Abstract and full text of all studies were required to obtain. Studies those were not accessible and those did not focus on the keywords were excluded.

Results:

ENaCs are tripolymer ion channels which are assembled from homologous α, β, and γ subunits. Crystal structure of ENaCs suggests that ENaC has a central ion-channel located in the central symmetry axis of the three subunits. ENaCs are protease sensitive channels whose iron-channel activity is regulated by the proteolytic reaction. Channel opening probability of ENaCs is regulated by proteinases, mechanical force, and shear stress. Several molecules are involved in regulation of ENaCs in bone formation, including nitride oxide synthases, voltage-sensitive calcium channels, and cyclooxygenase-2.

Conclusion:

The pathway of ENaC involved in shear stress has an effect on stimulating osteoblasts even bone formation by estrogen interference.

Epithelial Sodium Channels in Pulmonary Epithelial Progenitor and Stem Cells

Regeneration of the epithelium of mammalian lungs is essential for restoring normal function following injury, and various cells and mechanisms contribute to this regeneration and repair. Club cells, bronchioalveolar stem cells (BASCs), and alveolar type II epithelial cells (ATII) are dominant stem/progenitor cells for maintaining epithelial turnover and repair. Epithelial Na(+) channels (ENaC), a critical pathway for transapical salt and fluid transport, are expressed in lung epithelial progenitors, including club and ATII cells. Since ENaC activity and expression are development- and differentiation-dependent, apically located ENaC activity has therefore been used as a functional biomarker of lung injury repair. ENaC activity may be involved in the migration and differentiation of local and circulating stem/progenitor cells with diverse functions, eventually benefiting stem cells spreading to re-epithelialize injured lungs. This review summarizes the potential roles of ENaC expressed in native progenitor and stem cells in the development and regeneration of the respiratory epithelium.

KMUP-1 Promotes Osteoblast Differentiation Through cAMP and cGMP Pathways and Signaling of BMP-2/Smad1/5/8 and Wnt/β-Catenin

Phosphodiesterase (PDE) inhibitors have been suggested as a possible candidate for the treatment of osteopenia, including osteoporosis. KMUP-1 is a novel xanthine derivative with inhibitory activities on the PDE 3, 4, and 5 iso-enzymes to suppress the degradation of cAMP and cGMP. This study aimed to investigate the effect of KMUP-1 on osteoblast differentiation and the underlying cellular and molecular mechanisms. Primary osteoblasts and osteoblastic MC3T3-E1 cells were examined. KMUP-1 enhanced alkaline phosphatase (ALP) activity and mineralization compared to untreated controls in primary osteoblasts and MC3T3-E1 cells. KMUP-1 also increased the mRNA expression of the osteoblastic differentiation markers, including collagen type 1a, ALP, osteocalcin, osteoprotegerin, BMP-2, and Runx2, a key transcription regulator for osteoblastic differentiation. The osteogenic effect of KMUP-1 was abolished by BMP signaling inhibitor, noggin. Furthermore, we found that KMUP-1 upregulated Smad1/5/8 phosphorylations with subsequent BRE-Luc activation confirmed by transient transfection assay. In addition, KMUP-1 inactivated glycogen synthase kinase-3β (GSK-3β), with associated nuclear translocation of β-catenin. Co-treatment with H89 and KT5823, cAMP and cGMP pathway inhibitors, respectively, reversed the KMUP-1-induced activations of Smad1/5/8, β-catenin, and Runx2. The findings demonstrate for the first time that KMUP-1 can promote osteoblast maturation and differentiation in vitro via BMP-2/Smad1/5/8 and Wnt/β-catenin pathways. These effects are mediated, in part, by the cAMP and cGMP signaling. Thus, KMUP-1 may be a novel osteoblast activator and a potential new therapy for osteoporosis.