The epithelial sodium channel is involved in dexamethasone-induced osteoblast differentiation and mineralization

Upregulation of α-ENaC induces pancreatic β-cell dysfunction, ER stress, and SIRT2 degradation

Islet beta cells (β-cells) produce insulin in response to high blood glucose levels, which is essential for preserving glucose homeostasis. Voltage-gated ion channels in β-cells, including Na +, K +, and Ca 2+ channels, aid in the release of insulin. The epithelial sodium channel alpha subunit (α-ENaC), a voltage-independent sodium ion channel, is also expressed in human pancreatic endocrine cells. However, there is no reported study on the function of ENaC in the β-cells. In the current study, we found that α-ENaC was expressed in human pancreatic glandule and pancreatic islet β-cells. In the pancreas of db/db mice and high-fat diet-induced mice, and in mouse islet β-cells (MIN6 cells) treated with palmitate, α-ENaC expression was increased. When α-ENaC was overexpressed in MIN6 cells, insulin content and glucose-induced insulin secretion were significantly reduced. On the other hand, palmitate injured islet β-cells and suppressed insulin synthesis and secretion, but increased α-ENaC expression in MIN6 cells. However, α-ENaC knockout ( Scnn1a -/-) in MIN6 cells attenuated β-cell disorder induced by palmitate. Furthermore, α-ENaC regulated the ubiquitylation and degradation of sirtuin 2 in β-cells. α-ENaC also modulated β-cell function in correlation with the inositol-requiring enzyme 1 alpha/X-box binding protein 1 (IRE1α/XBP1) and protein kinase RNA-like endoplasmic reticulum kinase/C/EBP homologous protein (PERK/CHOP) endoplasmic reticulum stress pathways. These results suggest that α-ENaC may play a novel role in insulin synthesis and secretion in the β-cells, and the upregulation of α-ENaC promotes islet β-cell dysfunction. In conclusion, α-ENaC may be a key regulator involved in islet β-cell damage and a potential therapeutic target for type 2 diabetes mellitus.

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.

Mechanical Strain-Mediated Tenogenic Differentiation of Mesenchymal Stromal Cells Is Regulated through Epithelial Sodium Channels

It has been suggested that mechanical strain may elicit cell differentiation in adult somatic cells through activation of epithelial sodium channels (ENaC). However, such phenomenon has not been previously demonstrated in mesenchymal stromal cells (MSCs). The present study was thus conducted to investigate the role of ENaC in human bone marrow-derived MSCs (hMSCs) tenogenic differentiation during uniaxial tensile loading. Passaged-2 hMSCs were seeded onto silicone chambers coated with collagen I and subjected to stretching at 1 Hz frequency and 8% strain for 6, 24, 48, and 72 hours. Analyses at these time points included cell morphology and alignment observation, immunocytochemistry and immunofluorescence staining (collagen I, collagen III, fibronectin, and N-cadherin), and gene expression (ENaC subunits, and tenogenic markers). Unstrained cells at similar time points served as the control group. To demonstrate the involvement of ENaC in the differentiation process, an ENaC blocker (benzamil) was used and the results were compared to the noninhibited hMSCs. ENaC subunits' (α, β, γ, and δ) expression was observed in hMSCs, although only α subunit was significantly increased during stretching. An increase in tenogenic genes' (collagen1, collagen3, decorin, tenascin-c, scleraxis, and tenomodulin) and proteins' (collagen I, collagen III, fibronectin, and N-cadherin) expression suggests that hMSCs underwent tenogenic differentiation when subjected to uniaxial loading. Inhibition of ENaC function resulted in decreased expression of these markers, thereby suggesting that ENaC plays a vital role in tenogenic differentiation of hMSCs during mechanical loading.

Downregulated microRNA-488 enhances odontoblast differentiation of human dental pulp stem cells via activation of the p38 MAPK signaling pathway

Human dental pulp stem cells (hDPSCs) are primarily derived from the pulp tissues of permanent third molar teeth. They were widely used in human bone tissue engineering. It was previously indicated that microRNA (miR) expressions are closely associated with hDPSCs development. However, the specific effect of miR-488 on hDPSCs still remains unclear. In this study, we aimed to investigate effects of miR-488 on the differentiation of hDPSCs into odontoblast cells through the p38 mitogen-activated protein kinases (MAPK) signaling pathway by binding to MAPK1. The hDPSCs were isolated and cultured in vitro. Dual-luciferase reporter gene assay was performed to test the relationship between MAPK1 (p38) and miR-488. Reverse transcription quantitative polymerase chain reaction and western blot analysis were used to detect the mRNA and protein expressions of p38 MAPK signaling pathway-related genes (MAPK1, Ras, and Mitogen-activated protein kinase kinase 3/6 [MKK3/6]), along with expressions of dentin Sialophosphoprotein (DSPP), alkaline phosphatase (ALP), and osteonectin (OCN). ALP staining and alizarin red staining were conducted to detect ALP activity and degree of mineralization. Initially, we found that MAPK1 was the target gene of miR-488. Besides, downregulation of miR-488 was observed to stimulate the p38 MAPK signaling pathway and to increase the messenger RNA and protein expressions of DSPP, ALP, and OCN. Furthermore, ALP activity and formation of a mineralized nodule in hDPSCs were enhanced upon downregulation of miR-488. The aforementioned findings provided evidence supporting that downregulation of miR-488 promotes odontoblastic differentiation of hDPSCs through the p38 MAPK signaling pathway by targeting MAPK1, paving the basis for further study about hDPSCs.

[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.

Extraoral Taste Receptor Discovery: New Light on Ayurvedic Pharmacology

More and more research studies are revealing unexpectedly important roles of taste for health and pathogenesis of various diseases. Only recently it has been shown that taste receptors have many extraoral locations (e.g., stomach, intestines, liver, pancreas, respiratory system, heart, brain, kidney, urinary bladder, pancreas, adipose tissue, testis, and ovary), being part of a large diffuse chemosensory system. The functional implications of these taste receptors widely dispersed in various organs or tissues shed a new light on several concepts used in ayurvedic pharmacology (dravyaguna vijnana), such as taste (rasa), postdigestive effect (vipaka), qualities (guna), and energetic nature (virya). This review summarizes the significance of extraoral taste receptors and transient receptor potential (TRP) channels for ayurvedic pharmacology, as well as the biological activities of various types of phytochemical tastants from an ayurvedic perspective. The relative importance of taste (rasa), postdigestive effect (vipaka), and energetic nature (virya) as ethnopharmacological descriptors within Ayurveda boundaries will also be discussed.

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.

Effects of short-term glucocorticoid administration on bone mineral density, biomechanics and microstructure in rats’ femur

The effects of short-term use of oral glucocorticoid (GC) on the skeleton are not well defined. To address this gap, the influences of 7 days, 21 days of GC administration on femurs of intact rats were investigated. Forty 4-month-old female Sprague–Dawley rats were randomly divided into control group (Cont) and prednisone-treated group (Pre) and administered either distilled water or prednisone acetate at doses of 3.5 mg/kg/day for 0, 7 and 21 days, respectively. All the femurs were harvested for dual-energy X-ray absorptiometry scan, biomechanical testing and micro computed tomography scan. The whole body weight, femur bone mineral density (BMD), all three-point bending test parameters, microstructural parameters increased or improved significantly in Cont at day 21 when compared to day 0. The whole body weight, distal femur BMD, Young’s modulus, bending stiffness, density of tissue volume and trabecular thickness (Tb.Th) decreased, while structure model index and trabecular separation (Tb.Sp) increased significantly in Pre at day 21 when compared to age-matched control but had no significant differences between day 7 and day 21. Our data demonstrate that 7-day use of prednisone does not influence on rats’ femur, and 21-day use of prednisone slows in rate of whole body weight gain, decreases femur metaphysis BMD and bone stiffness which mainly due to the deteriorated bone microstructure.

Enhanced osteogenic differentiation of stem cells via microfluidics synthesized nanoparticles

Advancement of bone tissue engineering as an alternative for bone regeneration has attracted significant interest due to its potential in reducing the costs and surgical trauma affiliated with the effective treatment of bone defects. We have improved the conventional approach of producing polymeric nanoparticles, as one of the most promising choices for drug delivery systems, using a microfluidics platform, thus further improving our control over osteogenic differentiation of mesenchymal stem cells. Molecular dynamics simulations were carried out for theoretical understanding of our experiments in order to get a more detailed molecular-scale insight into the drug-carrier interactions. In this work, with the sustained intracellular delivery of dexamethasone from microfluidics-synthesized nanoparticles, we explored the effects of particle design on controlling stem cell fates. We believe that the insights learned from this work will lead to the discovery of new strategies to tune differentiation for in situ differentiation or stem cell therapeutics.

FROM THE CLINICAL EDITOR

The use of mesenchymal stem cells has been described by many researchers as a novel therapy for bone regeneration. One major hurdle in this approach is the control of osteogenic differentiation. In this article, the authors described elegantly their microfluidic system in which dexamethasone loaded nanoparticles were produced. This system would allow precise fabrication of nanoparticles and consequently higher efficiency in cellular differentiation.

Implications of combined ovariectomy and glucocorticoid (dexamethasone) treatment on mineral, microarchitectural, biomechanical and matrix properties of rat bone

Osteoporosis is one of the deleterious side effects of long-term glucocorticoid therapy. Since the condition is particularly aggressive in postmenopausal women who are on steroid therapy, in this study we have attempted to analyse the combined effect of glucocorticoid (dexamethasone) treatment and cessation of oestrogen on rat bone. The dual aim was to generate osteoporotic bone status in a short time scale and to characterise the combination of glucocorticoid-postmenopausal osteoporotic conditions. Sprague Dawley rats (N = 42) were grouped randomly into three groups: untreated control, sham-operated and ovariectomized-steroid (OVX-Steroid) rats. Control animals were euthanized with no treatment [Month 0 (M0)], while sham and OVX-Steroid rats were monitored up to 1 month (M1) and 3 months (M3) post laparotomy/post OVX-Steroid treatment. Histology, dual-energy X-ray absorptiometry (DXA), micro-computed tomography (micro-CT), and biomechanical and mRNA expression analysis of collagenous, non-collagenous matrix proteins and osteoclast markers were examined. The study indicated enhanced osteoclastogenesis and significantly lower bone mineral density (BMD) in the OVX-Steroid rats with Z-scores below -2.5, reduced torsional strength, reduced bone volume (BV/TV%), significantly enhanced trabecular separation (Tb.S), and less trabecular number (Tb.N) compared with sham rats. Osteoclast markers, cathepsin K and MMP 9 were upregulated along with Col1α1 and biglycan with no significant expression variation in fibronectin, MMP 14, LRP-5, Car II and TNC. These results show higher bone turnover with enhanced bone resorption accompanied with reduced torsional strength in OVX-Steroid rats; and these changes were attained within a short timeframe. This could be a useful model which mimics human postmenopausal osteoporosis that is associated with steroid therapy and could prove of value both in disease diagnosis and for testing generating and testing biological agents which could be used in treatment.