L-type calcium channels play a crucial role in the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells

The Characterization and Regulation of Schwann Cells in the Tooth Germ Development and Odontogenic Differentiation

Schwann cells (SCs), a type of glial cell in the peripheral nervous system, can serve as a source of mesenchymal stem cells (MSCs) to repair injured pulp. This study aimed to investigate the role of SCs in tooth germ development and repair of pulp injury. We performed RNA-seq and immunofluorescent staining on tooth germs at different developmental stages. The effect of L-type calcium channel (LTCC) blocker nimodipine on SCs odontogenic differentiation was analyzed by real-time polymerase chain reaction and Alizarin Red S staining. We used the PLP1-CreERT2/ Rosa26-GFP tracing mice model to examine the role of SCs and Cav1.2 in self-repair after pulp injury. SC-specific markers expressed in rat tooth germs at different developmental stages. Nimodipine treatment enhanced mRNA levels of osteogenic markers (DSPP, DMP1, and Runx2) but decreased calcium nodule formation. SCs-derived cells increased following pulp injury and Cav1.2 showed a similar response pattern as SCs. The different SCs phenotypes are coordinated in the whole process to ensure tooth development. Blocking the LTCC with nimodipine promoted SCs odontogenic differentiation. Moreover, SCs participate in the process of injured dental pulp repair as a source of MSCs, and Cav1.2 may regulate this process.

Deletion of the auxiliary α2δ1 voltage sensitive calcium channel subunit in osteocytes and late-stage osteoblasts impairs femur strength and load-induced bone formation in male mice

Osteocytes sense and respond to mechanical force by controlling the activity of other bone cells. However, the mechanisms by which osteocytes sense mechanical input and transmit biological signals remain unclear. Voltage-sensitive calcium channels (VSCCs) regulate calcium (Ca2+) influx in response to external stimuli. Inhibition or deletion of VSCCs impairs osteogenesis and skeletal responses to mechanical loading. VSCC activity is influenced by its auxiliary subunits, which bind the channel's α1 pore-forming subunit to alter intracellular Ca2+ concentrations. The α2δ1 auxiliary subunit associates with the pore-forming subunit via a glycosylphosphatidylinositol anchor and regulates the channel's calcium-gating kinetics. Knockdown of α2δ1 in osteocytes impairs responses to membrane stretch, and global deletion of α2δ1 in mice results in osteopenia and impaired skeletal responses to loading in vivo. Therefore, we hypothesized that the α2δ1 subunit functions as a mechanotransducer, and its deletion in osteocytes would impair skeletal development and load-induced bone formation. Mice (C57BL/6) with LoxP sequences flanking Cacna2d1, the gene encoding α2δ1, were crossed with mice expressing Cre under the control of the Dmp1 promoter (10 kb). Deletion of α2δ1 in osteocytes and late-stage osteoblasts decreased femoral bone quantity (P < .05) by DXA, reduced relative osteoid surface (P < .05), and altered osteoblast and osteocyte regulatory gene expression (P < .01). Cacna2d1f/f, Cre + male mice displayed decreased femoral strength and lower 10-wk cancellous bone in vivo micro-computed tomography measurements at the proximal tibia (P < .01) compared to controls, whereas Cacna2d1f/f, Cre + female mice showed impaired 20-wk cancellous and cortical bone ex vivo micro-computed tomography measurements (P < .05) vs controls. Deletion of α2δ1 in osteocytes and late-stage osteoblasts suppressed load-induced calcium signaling in vivo and decreased anabolic responses to mechanical loading in male mice, demonstrating decreased mechanosensitivity. Collectively, the α2δ1 auxiliary subunit is essential for the regulation of osteoid-formation, femur strength, and load-induced bone formation in male mice.

Inorganic Phosphate as "Bioenergetic Messenger" Triggers M2-Type Macrophage Polarization

The effects of calcium phosphate (CaP) materials on macrophage polarization state vary with their physicochemical properties. The study aims to elucidate the impact of phosphate ion-mediated energy metabolism on M2 macrophage polarization and the corresponding regulatory mechanism. The phosphate ions released from CaP ceramic as bioenergetic factor is identified; its concentration is closely associated with the polarized state. After being taken up by the sodium-dependent phosphate transporter 1, extracellular phosphate ions produce energy via oxidative phosphorylation by facilitating tricarboxylic acid flux, thereby contributing to M2 macrophage polarization. Further mechanistic analysis reveals that the elevation of the bioenergetic basis can drive macrophage M2 polarization via the AMP-activated protein kinase-mammalian target of rapamycin (AMPK-mTOR) axis. Another regulatory effect is that of the adenosine triphosphate (ATP), a signaling molecule. Intracellular ATP is released into the extracellular space and degraded to adenosine, which serves as a signaling molecule through the A2b adenosine receptor to activate the cyclic adenosine monophosphate (cAMP) pathway, thereby promoting M2 macrophage polarization. Overall, these findings may transform the existing knowledge on cell metabolism and energy homeostasis from bystanders to pivotal factors guiding M2 macrophage polarization and have implications for the future design of biomimetic CaP scaffolds.

Platelet-Rich Plasma Lysate Enhances the Osteogenic Differentiation of Adipose-Derived Stem Cells

ABSTRACT

Adipose-derived stem cells (ADSCs) have become an accepted source of cells in bone tissue engineering. This study aimed to investigate whether platelet-rich plasma (PRP) lysate can replace traditional fetal bovine serum as a culture medium with the enhanced proliferation and osteogenic potential of ADSCs. We divided the experiment into 5 groups where the ADSCs were cultured in an osteogenic medium containing 2.5%, 5%, 7.5%, and 10% PRP lysate with 10% fetal bovine serum as the control group. The cell proliferation, alkaline phosphatase (ALP) activity, ALP stain, alizarin red stain, osteocalcin (OCN) protein expression, and osteogenic-specific gene expression were analyzed and compared among these groups. The outcome showed that all PRP lysate-treated groups had good ALP stain and ALP activity performance. Better alizarin red stains were found in the 2.5%, 5%, and 7.5% PRP lysate groups. The 2.5% and 5% PRP lysate groups showed superior results in OCN quantitative polymerase chain reaction, whereas the 5% and 7.5% PRP lysate groups showed higher OCN protein expressions. Early RUNX2 (Runt-related transcription factor 2 () genes were the most expressed in the 5% PRP lysate group, followed by the 2.5% PRP lysate group, and then the 7.5% PRP lysate group. Thus, we concluded that 5% PRP lysate seemed to provide the optimal effect on enhancing the osteogenic potential of ADSCs. Platelet-rich plasma lysate-treated ADSCs were considered to be a good cell source for application in treating nonunion or bone defects in the future.

Regulation of myogenesis and adipogenesis by the electromagnetic perceptive gene

Obesity has been increasing in many regions of the world, including Europe, USA, and Korea. To manage obesity, we should consider it as a disease and apply therapeutic methods for its treatment. Molecular and therapeutic approaches for obesity management involve regulating biomolecules such as DNA, RNA, and protein in adipose-derived stem cells to prevent to be fat cells. Multiple factors are believed to play a role in fat differentiation, with one of the most effective factor is Ca2+. We recently reported that the electromagnetic perceptive gene (EPG) regulated intracellular Ca2+ levels under various electromagnetic fields. This study aimed to investigate whether EPG could serve as a therapeutic method against obesity. We confirmed that EPG serves as a modulator of Ca2+ levels in primary adipose cells, thereby regulating several genes such as CasR, PPARγ, GLU4, GAPDH during the adipogenesis. In addition, this study also identified EPG-mediated regulation of myogenesis that myocyte transcription factors (CasR, MyoG, MyoD, Myomaker) were changed in C2C12 cells and satellite cells. In vivo experiments carried out in this study confirmed that total weight/ fat/fat accumulation were decreased and lean mass was increased by EPG with magnetic field depending on age of mice. The EPG could serve as a potent therapeutic agent against obesity.

Advanced Progress of the Relationship Between Antihypertensive Drugs and Bone Metabolism

Hypertension and osteoporosis are common comorbidities among elderly individuals. Drug therapy has been widely used in clinical practice as the preferred antihypertensive treatment. Therefore, antihypertensive drugs have become some of the most commonly prescribed drugs in healthcare settings. However, antihypertensive drugs have different effects on bone metabolism. The results of animal and clinical studies on the effects of antihypertensive drugs on osteoporosis or fracture risk are controversial and have aroused widespread concern among clinicians. Recent studies found that angiotensin receptor blockers, selective β-adrenergic receptor blockers, and thiazide diuretics might improve bone trabecular number and bone mineral density by stimulating osteoblast differentiation, reducing osteoclast generation, and other mechanism. Furthermore, nonselective β-adrenergic receptor blockers and dihydropyridine calcium channel blockers were found to have no significant relationship with bone mineral density or bone strength, and α-adrenergic receptor blockers and loop diuretics might increase fracture risk by decreasing bone mineral density. This article aimed to review previous animal experiments, clinical studies, and meta-analyses focusing on the effects of different antihypertensive drugs on bone metabolism, and to provide a new approach for the prevention and treatment of osteoporosis.

Transglutaminase 2 Prevents Premature Senescence and Promotes Osteoblastic Differentiation of Mesenchymal Stem Cells through NRF2 Activation

Transglutaminase 2 (TG2) is a multifunctional enzyme that exhibits transamidase, GTPase, kinase, and protein disulfide isomerase (PDI) activities. Of these, transamidase-mediated modification of proteins regulates apoptosis, differentiation, inflammation, and fibrosis. TG2 is highly expressed in mesenchymal stem cells (MSCs) compared with differentiated cells, suggesting a role of TG2 specific for MSC characteristics. In this study, we report a new function of TG2 in the regulation of MSC redox homeostasis. During in vitro MSC expansion, TG2 is required for cell proliferation and self-renewal by preventing premature senescence but has no effect on the expression of surface antigens and oxidative stress-induced cell death. Moreover, induction of differentiation upregulates TG2 that promotes osteoblastic differentiation. Molecular analyses revealed that TG2 mediates tert-butylhydroquinone, but not sulforaphane, -induced nuclear factor erythroid 2-related factor 2 (NRF2) activation in a transamidase activity-independent manner. Differences in the mechanism of action between two NRF2 activators suggest that PDI activity of TG2 may be implicated in the stabilization of NRF2. The role of TG2 in the regulation of antioxidant response was further supported by transcriptomic analysis of MSC. These results indicate that TG2 is a critical enzyme in eliciting antioxidant response in MSC through NRF2 activation, providing a target for optimizing MSC manufacturing processes to prevent premature senescence.

Examining Mechanisms for Voltage-Sensitive Calcium Channel-Mediated Secretion Events in Bone Cells

In addition to their well-described functions in cell excitability, voltage-sensitive calcium channels (VSCCs) serve a critical role in calcium (Ca2+)-mediated secretion of pleiotropic paracrine and endocrine factors, including those produced in bone. Influx of Ca2+ through VSCCs activates intracellular signaling pathways to modulate a variety of cellular processes that include cell proliferation, differentiation, and bone adaptation in response to mechanical stimuli. Less well understood is the role of VSCCs in the control of bone and calcium homeostasis mediated through secreted factors. In this review, we discuss the various functions of VSCCs in skeletal cells as regulators of Ca2+ dynamics and detail how these channels might control the release of bioactive factors from bone cells. Because VSCCs are druggable, a better understanding of the multiple functions of these channels in the skeleton offers the opportunity for developing new therapies to enhance and maintain bone and to improve systemic health.

Electrical Stimulation in Cartilage Tissue Engineering

Electrical stimulation (ES) has been frequently used in different biomedical applications both in vitro and in vivo. Numerous studies have demonstrated positive effects of ES on cellular functions, including metabolism, proliferation, and differentiation. The application of ES to cartilage tissue for increasing extracellular matrix formation is of interest, as cartilage is not able to restore its lesions owing to its avascular nature and lack of cells. Various ES approaches have been used to stimulate chondrogenic differentiation in chondrocytes and stem cells; however, there is a huge gap in systematizing ES protocols used for chondrogenic differentiation of cells. This review focuses on the application of ES for chondrocyte and mesenchymal stem cell chondrogenesis for cartilage tissue regeneration. The effects of different types of ES on cellular functions and chondrogenic differentiation are reviewed, systematically providing ES protocols and their advantageous effects. Moreover, cartilage 3D modeling using cells in scaffolds/hydrogels under ES are observed, and recommendations on reporting about the use of ES in different studies are provided to ensure adequate consolidation of knowledge in the area of ES. This review brings novel insights into the further application of ES in in vitro studies, which are promising for further cartilage repair techniques.

Soluble guanylate cyclase agonist, isoliquiritigenin attenuates renal damage and aortic calcification in a rat model of chronic kidney failure

AIMS

Chronic kidney disease (CKD) is a growing fatal health problem worldwide associated with vascular calcification. Therapeutic approaches are limited with higher costs and poor outcomes. Adenine supplementation is one of the most relevant CKD models to human. Insufficient Nitric Oxide (NO)/ cyclic Guanosine Monophosphate (cGMP) signaling plays a key role in rapid development of renal fibrosis. Natural products display proven protection against CKD. Current study therefore explored isoliquiritigenin, a bioflavonoid extracted from licorice roots, potential as a natural activator for soluble Guanylate Cyclase (sGC) in a CKD rat model.

MATERIALS AND METHODS

60 male Wistar rats were grouped into Control group (n = 10) and the remaining rats received adenine (200 mg/kg, p.o) for 2 wk to induce CKD. They were equally sub-grouped into: Adenine untreated group and 4 groups orally treated by isoliquiritigenin low or high dose (20 or 40 mg/kg) with/without a selective sGC inhibitor, ODQ (1-H(1,2,4)oxadiazolo(4,3-a)-quinoxalin-1-one, 2 mg/kg, i.p) for 8 wk.

KEY FINDINGS

Long-term treatment with isoliquiritigenin dose-dependently and effectively amended adenine-induced chronic renal and endothelial dysfunction. It not only alleviated renal fibrosis and apoptosis markers but also aortic calcification. Additionally, this chalcone neutralized renal inflammatory response and oxidative stress. Isoliquiritigenin beneficial effects were associated with up-regulation of serum NO, renal and aortic sGC, cGMP and its dependent protein kinase (PKG). However, co-treatment with ODQ antagonized isoliquiritigenin therapeutic impact.

SIGNIFICANCE

Isoliquiritigenin seems to exert protective effects against CKD and vascular calcification by activating sGC, increasing cGMP and its downstream PKG.

Ultra-low binder content 3D printed calcium phosphate graphene scaffolds as resorbable, osteoinductive matrices that support bone formation in vivo

Bone regenerative engineering could replace autografts; however, no synthetic material fulfills all design criteria. Nanocarbons incorporated into three-dimensional printed (3DP) matrices can improve properties, but incorporation is constrained to low wt%. Further, unmodified nanocarbons have limited osteogenic potential. Functionalization to calcium phosphate graphene (CaPG) imparts osteoinductivity and osteoconductivity, but loading into matrices remained limited. This work presents ultra-high content (90%), 3DP-CaPG matrices. 3DP-CaPG matrices are highly porous (95%), moderately stiff (3 MPa), and mechanically robust. In vitro, they are cytocompatible and induce osteogenic differentiation of human mesenchymal stem cells (hMSCs), indicated by alkaline phosphatase, mineralization, and COL1α1 expression. In vivo, bone regeneration was studied using a transgenic fluorescent-reporter mouse non-union calvarial defect model. 3DP-CaPG stimulates cellular ingrowth, retains donor cells, and induces osteogenic differentiation. Histology shows TRAP staining around struts, suggesting potential osteoclast activity. Apparent resorption of 3DP-CaPG was observed and presented no toxicity. 3DP-CaPG represents an advancement towards a synthetic bone regeneration matrix.

BMP-2 Enhances Osteogenic Differentiation of Human Adipose-Derived and Dental Pulp Stem Cells in 2D and 3D In Vitro Models

Bone tissue provides support and protection to different organs and tissues. Aging and different diseases can cause a decrease in the rate of bone regeneration or incomplete healing; thus, tissue-engineered substitutes can be an acceptable alternative to traditional therapies. In the present work, we have developed an in vitro osteogenic differentiation model based on mesenchymal stem cells (MSCs), to first analyse the influence of the culture media and the origin of the cells on the efficiency of this process and secondly to extrapolate it to a 3D environment to evaluate its possible application in bone regeneration therapies. Two osteogenic culture media were used (one commercial from Stemcell Technologies and a second supplemented with dexamethasone, ascorbic acid, glycerol-2-phosphate, and BMP-2), with human cells of a mesenchymal phenotype from two different origins: adipose tissue (hADSCs) and dental pulp (hDPSCs). The expression of osteogenic markers in 2D cultures was evaluated in several culture periods by means of the immunofluorescence technique and real-time gene expression analysis, taking as reference MG-63 cells of osteogenic origin. The same strategy was extrapolated to a 3D environment of polylactic acid (PLA), with a 3% alginate hydrogel. The expression of osteogenic markers was detected in both hADSCs and hDPSCs, cultured in either 2D or 3D environments. However, the osteogenic differentiation of MSCs was obtained based on the culture medium and the cell origin used, since higher osteogenic marker levels were found when hADSCs were cultured with medium supplemented with BMP-2. Furthermore, the 3D culture used was suitable for cell survival and osteogenic induction.

Improved activity of MC3T3-E1 cells by the exciting piezoelectric BaTiO3/TC4 using low-intensity pulsed ultrasound

Developing bioactive materials for bone implants to enhance bone healing and bone growth has for years been the focus of clinical research. Barium titanate (BT) is an electroactive material that can generate electrical signals in response to applied mechanical forces. In this study, a BT piezoelectric ceramic coating was synthesized on the surface of a TC4 titanium alloy, forming a BT/TC4 material, and low-intensity pulsed ultrasound (LIPUS) was then applied as a mechanical stimulus. The combined effects on the biological responses of MC3T3-E1 cells were investigated. Results of scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction showed that an uniform nanospheres -shaped BT coating was formed on TC4 substrate. Piezoelectric behaviors were observed using piezoelectric force microscopy with the piezoelectric coefficient d33 of 0.42 pC/N. Electrochemical measures indicated that LIPUS-stimulated BT/TC4 materials could produce a microcurrent of approximately 10 μA/cm2. In vitro, the greatest osteogenesis (cell adhesion, proliferation, and osteogenic differentiation) was found in MC3T3-E1 cells when BT/TC4 was stimulated using LIPUS. Furthermore, the intracellular calcium ion concentration increased in these cells, possibly because opening of the L-type calcium ion channels was promoted and expression of the CaV1.2 protein was increased. Therefore, the piezoelectric BT/TC4 material with LIPUS loading synergistically promoted osteogenesis, rending it a potential treatment for early stage formation of reliable bone-implant contact.

Calcium channels and their role in regenerative medicine

Stem cells hold indefinite self-renewable capability that can be differentiated into all desired cell types. Based on their plasticity potential, they are divided into totipotent (morula stage cells), pluripotent (embryonic stem cells), multipotent (hematopoietic stem cells, multipotent adult progenitor stem cells, and mesenchymal stem cells [MSCs]), and unipotent (progenitor cells that differentiate into a single lineage) cells. Though bone marrow is the primary source of multipotent stem cells in adults, other tissues such as adipose tissues, placenta, amniotic fluid, umbilical cord blood, periodontal ligament, and dental pulp also harbor stem cells that can be used for regenerative therapy. In addition, induced pluripotent stem cells also exhibit fundamental properties of self-renewal and differentiation into specialized cells, and thus could be another source for regenerative medicine. Several diseases including neurodegenerative diseases, cardiovascular diseases, autoimmune diseases, virus infection (also coronavirus disease 2019) have limited success with conventional medicine, and stem cell transplantation is assumed to be the best therapy to treat these disorders. Importantly, MSCs, are by far the best for regenerative medicine due to their limited immune modulation and adequate tissue repair. Moreover, MSCs have the potential to migrate towards the damaged area, which is regulated by various factors and signaling processes. Recent studies have shown that extracellular calcium (Ca²⁺) promotes the proliferation of MSCs, and thus can assist in transplantation therapy. Ca²⁺ signaling is a highly adaptable intracellular signal that contains several components such as cell-surface receptors, Ca²⁺ channels/pumps/exchangers, Ca²⁺ buffers, and Ca²⁺ sensors, which together are essential for the appropriate functioning of stem cells and thus modulate their proliferative and regenerative capacity, which will be discussed in this review.

Skeletal Functions of Voltage Sensitive Calcium Channels

Voltage-sensitive calcium channels (VSCCs) are ubiquitous multimeric protein complexes that are necessary for the regulation of numerous physiological processes. VSCCs regulate calcium influx and various intracellular processes including muscle contraction, neurotransmission, hormone secretion, and gene transcription, with function specificity defined by the channel's subunits and tissue location. The functions of VSCCs in bone are often overlooked since bone is not considered an electrically excitable tissue. However, skeletal homeostasis and adaptation relies heavily on VSCCs. Inhibition or deletion of VSCCs decreases osteogenesis, impairs skeletal structure, and impedes anabolic responses to mechanical loading. RECENT FINDINGS: While the functions of VSCCs in osteoclasts are less clear, VSCCs have distinct but complementary functions in osteoblasts and osteocytes. PURPOSE OF REVIEW: This review details the structure, function, and nomenclature of VSCCs, followed by a comprehensive description of the known functions of VSCCs in bone cells and their regulation of bone development, bone formation, and mechanotransduction.

Synergic effects of extremely low-frequency electromagnetic field and betaine on in vitro osteogenic differentiation of human adipose tissue-derived mesenchymal stem cells

Human adipose tissue-derived mesenchymal stem cells (hADSCs) due to easy extraction, relative abundance, in vitro expansion and differentiation potential, frozen storage capability, and ability to secrete cytokines, compared to other stem cells, are appropriate candidate in regenerative medicine. Extremely low-frequency electromagnetic fields (ELF-EMF) and betaine are two safe factors in bone lesions repair. This study was designed to assess the osteogenic differentiation potential of these factors on hADSCs. The samples were collected from women undergoing liposuction after obtaining written consent. The hADSCs were extracted and treated with osteogenesis differentiation medium (OD) as the positive control, with OD and betaine (BET group), with OD and EMF (EMF group), and with OD and betaine and EMF (BET+EMF group) for 21 d; the negative control consisted of cells without treatment. Betaine 10 mM and EMF with 50-Hz frequency, 1-mT intensity (8 h daily), and in the form of sinus wave were used. Osteogenic differentiation was evaluated by Alizarin Red staining, alkaline phosphatase activity, calcium deposition, and real-time PCR. A significant increase in calcium deposition in the BET+EMF group was observed compared to the other groups. The activity of alkaline phosphatase in the positive control and BET groups was increased significantly compared to EMF and BET + EMF groups and a significant increase of this enzyme activity in the BET + EMF compared to EMF group was observed. The expression of RUNX2 and OCN genes in the EMF-treated groups were significantly reduced compared to the non-EMF-treated groups, and BET+EMF showed a significant increase of RUNX2 gene expression as compared the EMF group. The ELF-EMF leads to a decrease in the osteogenic differentiation and the expression RUNX2 and OCN genes in hADSCs. But osteogenic differentiation and RUNX2 gene expression were increased post-induction by betaine. The synergic effect of betaine and EMF on the osteogenic differentiation and related genes expression of hADSCs was higher than EMF.

Transient receptor potential vanilloid 2 mediates the inhibitory effect of far-infrared irradiation on adipogenic differentiation of tonsil-derived mesenchymal stem cells

AIMS

Far-infrared (FIR) irradiation inhibits adipogenic differentiation of tonsil-derived mesenchymal stem cells (TMSCs) by activating Ca²⁺-dependent protein phosphatase 2B (PP2B), but it stimulates osteogenic differentiation in a PP2B-independent pathway. We investigated the potential involvement of transient receptor potential vanilloid (TRPV) channels, a well-known Ca²⁺-permeable channel, in the effects of FIR irradiation on adipogenic or osteogenic differentiation of TMSCs.

METHODS

TMSCs, in the absence or presence of activators or inhibitors, were exposed to FIR irradiation followed by adipogenic or osteogenic differentiation, which was assessed using Oil red O or Alizarin red S staining, respectively. RT-PCR, qRT-PCR, and Western blotting were used to determine gene and protein expression of calcium channels and adipocyte-specific markers.

RESULTS

Treatment with the calcium ionophore ionomycin simulated the inhibitory effect of FIR irradiation on adipogenic differentiation but had no effect on osteogenic differentiation, indicating the involvement of intracellular Ca²⁺ in adipogenic differentiation. Inhibition of pan-TRP channels using ruthenium red reversed the FIR irradiation-induced inhibition of adipogenic differentiation. Among the TRP channels tested, inhibition of the TRPV2 channel by tranilast or siRNA against TRPV2 attenuated the inhibitory effect of FIR irradiation on adipogenic differentiation, accompanied by a decrease in intracellular Ca²⁺ levels. By contrast, activation of the TRPV2 channel by probenecid simulated FIR irradiation-induced inhibition of adipogenic differentiation. Expectedly, the stimulatory effect of FIR irradiation on osteogenic differentiation was independent of the TRPV2 channel.

CONCLUSION

Our data demonstrate that the TRPV2 channel is a sensor/receptor for the inhibited adipogenic differentiation of TMSCs associated with FIR irradiation.

TRPM8 Channel Promotes the Osteogenic Differentiation in Human Bone Marrow Mesenchymal Stem Cells

Various families of ion channels have been characterized in mesenchymal stem cells (MSCs), including some members of transient receptor potential (TRP) channels family. TRP channels are involved in critical cellular processes as differentiation and cell proliferation. Here, we analyzed the expression of TRPM8 channel in human bone marrow MSCs (hBM-MSCs), and its relation with osteogenic differentiation. Patch-clamp recordings showed that hBM-MSCs expressed outwardly rectifying currents which were increased by exposure to 500 μM menthol and were partially inhibited by 10 μM of BCTC, a TRPM8 channels antagonist. Additionally, we have found the expression of TRPM8 by RT-PCR and western blot. We also explored the TRPM8 localization in hBM-MSCs by immunofluorescence using confocal microscopy. Remarkably, hBM-MSCs treatment with 100 μM of menthol or 10 μM of icilin, TRPM8 agonists, increases osteogenic differentiation. Conversely, 20 μM of BCTC, induced a decrease of osteogenic differentiation. These results suggest that TRPM8 channels are functionally active in hBM-MSCs and have a role in cell differentiation.

Bioglass/carbonate apatite/collagen composite scaffold dissolution products promote human osteoblast differentiation

OssiMend® Bioactive (Collagen Matrix Inc., NJ) is a three-component porous composite bone graft device of 45S5 Bioglass/carbonate apatite/collagen. Our in vitro studies showed that conditioned media of the dissolution products of OssiMend Bioactive stimulated primary human osteoblasts to form mineralized bone-like nodules in vitro in one week, in basal culture media (no osteogenic supplements). Osteoblast differentiation was followed by gene expression analysis and a mineralization assay. In contrast, the dissolution products from commercial OssiMend (Bioglass-free carbonate apatite/collagen scaffolds), or from 45S5 Bioglass particulate alone, did not induce the mineralization of the extracellular matrix, but did induce osteoblast differentiation to mature osteoblasts, evidenced by the strong upregulation of BGLAP and IBSP mRNA levels. The calcium ions and soluble silicon species released from 45S5 Bioglass particles and additional phosphorus release from OssiMend mediated the osteostimulatory effects. Medium conditioned with OssiMend Bioactive dissolution had a much higher concentration of phosphorus and silicon than media conditioned with OssiMend and 45S5 Bioglass alone. While OssiMend and OssiMend Bioactive led to calcium precipitation in cell culture media, OssiMend Bioactive produced a higher concentration of soluble silicon than 45S5 Bioglass and higher dissolution of phosphorus than OssiMend. These in vitro results suggest that adding 45S5 Bioglass to OssiMend produces a synergistic osteostimulation effect on primary human osteoblasts. In summary, dissolution products of a Bioglass/carbonate apatite/collagen composite scaffold (OssiMend® Bioactive) stimulate human osteoblast differentiation and mineralization of extracellular matrix in vitro without any osteogenic supplements. The mineralization was faster than for dissolution products of ordinary Bioglass.

Human adipose-derived stem cell spheroids incorporating platelet-derived growth factor (PDGF) and bio-minerals for vascularized bone tissue engineering

Stem cells with mineralized materials have been used for bone regeneration; however, engineering the complex vascularized structure of the natural bone remains a challenge. Here, we developed platelet-derived growth factor (PDGF) and bio-mineral coated fibers which were then assembled with human adipose-derived stem cells (hADSCs) to form spheroids as building blocks for vascularized bone regeneration. The PDGF incorporated within the spheroid increased the proliferation of hADSCs, which was characterized by Ki-67 staining and DNA contents. Furthermore, the PDGF enhanced not only osteogenic differentiation, but also endothelial differentiation of hADSCs; the cells within the spheroids showed significantly greater gene expression by 2.46 ± 0.14 fold for osteocalcin (OCN) and by 12.85 ± 3.36 fold for von Willebrand factor (vWF) than those without PDGF. Finally, at two months following transplantation of PDGF-incorporated spheroids onto in vivo mouse calvarial defect, the regenerated bone area (42.48 ± 10.84%) was significantly enhanced and the greatest number of capillaries and arterioles with indication of transplanted hADSCs were observed. Moreover, millimeter-scale in vitro tissue prepared by fused assembly of the spheroids exhibited greater mRNA expression-associated to endothelial lineage. Taken together, these findings indicate that stem cell spheroids incorporating PDGF and bio-minerals could be used as a module for successful vascularized bone regeneration.

Screening and functional identification of lncRNAs in antler mesenchymal and cartilage tissues using high-throughput sequencing

Long non-coding RNA (lncRNA) is a transcription product of the mammalian genome that regulates the development and growth in the body. The present study aimed to analyze the expression dynamics of lncRNA in sika antler mesenchymal and cartilage tissues by high-throughput sequencing. Bioinformatics was applied to predict differentially expressed lncRNAs and target genes and screen lncRNAs and mRNAs related to osteogenic differentiation, cell proliferation, and migration. Finally, the expression of the lncRNAs and target genes were analyzed by qRT-PCR. The results showed that compared to the cartilage tissue, the transcription levels of lncRNA and mRNA, 1212 lncRNAs and 518 mRNAs, in mesenchymal tissue were altered significantly. Thus, a complex interaction network was constructed, and the lncRNA-mRNA interaction network correlation related to osteogenic differentiation, cell proliferation, and migration was analyzed. Among these, the 26 lncRNAs and potential target genes were verified by qRT-PCR, and the results of qRT-PCR were consistent with high-throughput sequencing results. These data indicated that lncRNA promotes the differentiation of deer antler mesenchymal tissue into cartilage tissue by regulating the related osteogenic factors, cell proliferation, and migration-related genes and accelerating the process of deer antler regeneration and development.

Ionomycin ameliorates hypophosphatasia via rescuing alkaline phosphatase deficiency-mediated L-type Ca2+ channel internalization in mesenchymal stem cells

The loss-of-function mutations in the ALPL result in hypophosphatasia (HPP), an inborn metabolic disorder that causes skeletal mineralization defects. In adults, the main clinical features are early loss of primary or secondary teeth, osteoporosis, bone pain, chondrocalcinosis, and fractures. However, guidelines for the treatment of adults with HPP are not available. Here, we show that ALPL deficiency caused a reduction in intracellular Ca2+ influx, resulting in an osteoporotic phenotype due to downregulated osteogenic differentiation and upregulated adipogenic differentiation in both human and mouse bone marrow mesenchymal stem cells (BMSCs). Increasing the intracellular level of calcium in BMSCs by ionomycin treatment rescued the osteoporotic phenotype in alpl+/- mice and BMSC-specific (Prrx1-alpl-/-) conditional alpl knockout mice. Mechanistically, ALPL was found to be required for the maintenance of intracellular Ca2+ influx, which it achieves by regulating L-type Ca2+ channel trafficking via binding to the α2δ subunits to regulate the internalization of the L-type Ca2+ channel. Decreased Ca2+ flux inactivates the Akt/GSK3β/β-catenin signaling pathway, which regulates lineage differentiation of BMSCs. This study identifies a previously unknown role of the ectoenzyme ALPL in the maintenance of calcium channel trafficking to regulate stem cell lineage differentiation and bone homeostasis. Accelerating Ca2+ flux through L-type Ca2+ channels by ionomycin treatment may be a promising therapeutic approach for adult patients with HPP.

KMUP-1 regulates the vascular calcification in chronic renal failure by mediating NO/cGMP/PKG signaling pathway

OBJECTIVE

To explore the potential mechanism of KMUP-1 in the vascular calcification of chronic renal failure (CRF) through mediating NO/cGMP/PKG pathway, and provide novel insights into the CRF treatment.

METHODS

CRF rats were treated by KMUP-1 with/without L-NNA (a NOS inhibitor) and then performed by ELISA, alizarin red staining, Von Kossa staining, Masson's trichrome, Sirius red staining and CD3 immunohistochemical staining. Simultaneously, vascular smooth muscle cells (VSMCs) were collected from rats to confirm the effect of KMUP-1 on vascular calcification in vitro via NO/cGMP/PKG pathway. Besides, protein and mRNA expressions were determined via Western blotting and qRT-PCR, respectively.

RESULTS

CRF rats were elevated in 24-h urine protein, blood urea nitrogen (BUN), serum creatinine, Cys-C levels and inflammatory cytokines. Besides, CRF rats also showed increased calcium content and ALP level with up-regulated mRNA of osteogenic differentiation-related markers. Furthermore, the up-regulated expressions of eNOS and PKG, as well as down-regulated levels of NOx and cGMP were also found in CRF rats. However, renal failure and vascular calcification of CRF were improved significantly by KMUP-1 treatment via activation of NO/cGMP/PKG pathway. Moreover, KMUP-1 treatment attenuated calcified VSMCs, accompanied by the decreases in the calcified nodules, level of calcium and activity of ALP. In addition, either L-NNA treatment for CRF rats or the calcified VSMCs could antagonize the improving effect of KMUP-1.

CONCLUSION

KMUP-1 can improve the renal function and vascular calcification in CRF rats at least in part by activating NO/cGMP/PKG pathway.

Calcium Channels as Novel Therapeutic Targets for Ovarian Cancer Stem Cells

Drug resistance in epithelial ovarian cancer (EOC) is reportedly attributed to the existence of cancer stem cells (CSC), because in most cancers, CSCs still remain after chemotherapy. To overcome this limitation, novel therapeutic strategies are required to prevent cancer recurrence and chemotherapy-resistant cancers by targeting cancer stem cells (CSCs). We screened an FDA-approved compound library and found four voltage-gated calcium channel blockers (manidipine, lacidipine, benidipine, and lomerizine) that target ovarian CSCs. Four calcium channel blockers (CCBs) decreased sphere formation, viability, and proliferation, and induced apoptosis in ovarian CSCs. CCBs destroyed stemness and inhibited the AKT and ERK signaling pathway in ovarian CSCs. Among calcium channel subunit genes, three L- and T-type calcium channel genes were overexpressed in ovarian CSCs, and downregulation of calcium channel genes reduced the stem-cell-like properties of ovarian CSCs. Expressions of these three genes are negatively correlated with the survival rate of patient groups. In combination therapy with cisplatin, synergistic effect was shown in inhibiting the viability and proliferation of ovarian CSCs. Moreover, combinatorial usage of manidipine and paclitaxel showed enhanced effect in ovarian CSCs xenograft mouse models. Our results suggested that four CCBs may be potential therapeutic drugs for preventing ovarian cancer recurrence.

Calcite incorporated in silica/collagen xerogels mediates calcium release and enhances osteoblast proliferation and differentiation

Multiphasic silica/collagen xerogels are biomaterials designed for bone regeneration. Biphasic silica/collagen xerogels (B30) and triphasic xerogels (B30H20 or B30CK20) additionally containing hydroxyapatite or calcite were demonstrated to exhibit several structural levels. On the first level, low fibrillar collagen serves as template for silica nanoparticle agglomerates. On second level, this silica-enriched matrix phase is fiber-reinforced by collagen fibrils. In case of hydroxyapatite incorporation in B30H20, resulting xerogels exhibit a hydroxyapatite-enriched phase consisting of hydroxyapatite particle agglomerates next to silica and low fibrillar collagen. Calcite in B30CK20 is incorporated as single non-agglomerated crystal into the silica/collagen matrix phase with embedded collagen fibrils. Both the structure of multiphasic xerogels and the manner of hydroxyapatite or calcite incorporation have an influence on the release of calcium from the xerogels. B30CK20 released a significantly higher amount of calcium into a calcium-free solution over a three-week period than B30H20. In calcium containing incubation media, all xerogels caused a decrease in calcium concentration as a result of their bioactivity, which was superimposed by the calcium release for B30CK20 and B30H20. Proliferation of human bone marrow stromal cells in direct contact to the materials was enhanced on B30CK20 compared to cells on both plain B30 and B30H20.

Multimaterial Dual Gradient Three-Dimensional Printing for Osteogenic Differentiation and Spatial Segregation

In this study of three-dimensional (3D) printed composite β-tricalcium phosphate (β-TCP)-/hydroxyapatite/poly(ɛ-caprolactone)-based constructs, the effects of vertical compositional ceramic gradients and architectural porosity gradients on the osteogenic differentiation of rabbit bone marrow-derived mesenchymal stem cells (MSCs) were investigated. Specifically, three different concentrations of β-TCP (0, 10, and 20 wt%) and three different porosities (33% ± 4%, 50% ± 4%, and 65% ± 3%) were examined to elucidate the contributions of chemical and physical gradients on the biochemical behavior of MSCs and the mineralized matrix production within a 3D culture system. By delaminating the constructs at the gradient transition point, the spatial separation of cellular phenotypes could be specifically evaluated for each construct section. Results indicated that increased concentrations of β-TCP resulted in upregulation of osteogenic markers, including alkaline phosphatase activity and mineralized matrix development. Furthermore, MSCs located within regions of higher porosity displayed a more mature osteogenic phenotype compared to MSCs in lower porosity regions. These results demonstrate that 3D printing can be leveraged to create multiphasic gradient constructs to precisely direct the development and function of MSCs, leading to a phenotypic gradient. Impact Statement In this study, three-dimensional (3D) printed ceramic/polymeric constructs containing discrete vertical gradients of both composition and porosity were fabricated to precisely control the osteogenic differentiation of mesenchymal stem cells. By making simple alterations in construct architecture and composition, constructs containing heterogenous populations of cells were generated, where gradients in scaffold design led to corresponding gradients in cellular phenotype. The study demonstrates that 3D printed multiphasic composite constructs can be leveraged to create complex heterogeneous tissues and interfaces.

Mineralized nanofibrous scaffold promotes phenamil-induced osteoblastic differentiation while mitigating adipogenic differentiation

Large bone defects represent a significant unmet medical challenge. Cost effectiveness and better stability make small molecule organic compounds a more promising alternative compared with biomacromolecules, for example, growth factors/hormones, in regenerative medicine. However, one common challenge for the application of these small compounds is their side-effect issue. Phenamil is emerging as an intriguing small molecule to promote bone repair by strongly activating bone morphogenetic protein signaling pathway. In addition to osteogenesis, phenamil also induces significant adipogenesis based on some in vitro studies, which is a concern that impedes it from potential clinical applications. Besides the soluble chemical signals, cellular differentiation is heavily dependent on the microenvironments provided by the 3D scaffolds. Therefore, we developed a 3D nanofibrous biomimetic scaffold-based strategy to harness the phenamil-induced stem cell lineage differentiation. Based on the gene expression, alkaline phosphatase activity, and mineralization data, we indicated that bone-matrix mimicking mineralized-gelatin nanofibrous scaffold effectively improved phenamil-induced osteoblastic differentiation, while mitigating the adipogenic differentiation in vitro. In addition to normal culture conditions, we also indicated that mineralized matrix can significantly improve phenamil-induced osteoblastic differentiation in simulated inflammatory condition. In viewing of the crucial role of mineralized matrix, we developed an innovative and facile mineral deposition-based strategy to sustain release of phenamil from 3D scaffolds for efficient local bone regeneration. Overall, our study demonstrated that biomaterials played a crucial role in modulating small molecule drug phenamil-induced osteoblastic differentiation by providing a bone-matrix mimicking mineralized gelatin nanofibrous scaffolds.

Cav 1.2 regulates osteogenesis of bone marrow-derived mesenchymal stem cells via canonical Wnt pathway in age-related osteoporosis

Aims

Age‐related bone mass loss is one of the most prevalent diseases that afflict the elderly population. The decline in the osteogenic differentiation capacity of bone marrow‐derived mesenchymal stem cells (BMMSCs) is regarded as one of the central mediators. Voltage‐gated Ca²⁺ channels (VGCCs) play an important role in the regulation of various cell biological functions, and disruption of VGCCs is associated with several age‐related cellular characteristics and systemic symptoms. However, whether and how VGCCs cause the decreased osteogenic differentiation abilities of BMMSCs have not been fully elucidated.

Methods

Voltage‐gated Ca²⁺ channels related genes were screened, and the candidate gene was determined in several aging models. Functional role of determined channel on osteogenic differentiation of BMMSCs was investigated through gain and loss of function experiments. Molecular mechanism was explored, and intervention experiments in vivo and in vitro were performed.

Results

We found that Ca_v1.2 was downregulated in these aging models, and downregulation of Ca_v1.2 in Zmpste24−/− BMMSCs contributed to compromised osteogenic capacity. Mechanistically, Ca_v1.2 regulated the osteogenesis of BMMSCs through canonical Wnt/β‐catenin pathway. Moreover, upregulating the activity of Ca_v1.2 mitigated osteoporosis symptom in Zmpste24−/− mice.

Conclusion

Impaired osteogenic differentiation of Zmpste24−/− BMMSCs can be partly attributed to the decreased Ca_v1.2 expression, which leads to the inhibition of canonical Wnt pathway. Bay K8644 treatment could be an applicable approach for treating age‐related bone loss by ameliorating compromised osteogenic differentiation capacity through targeting Ca_v1.2 channel.

L-type voltage-gated calcium channels in stem cells and tissue engineering

L-type voltage-gated calcium ion channels (L-VGCCs) have been demonstrated to be the mediator of several significant intracellular activities in excitable cells, such as neurons, chromaffin cells and myocytes. Recently, an increasing number of studies have investigated the function of L-VGCCs in non-excitable cells, particularly stem cells. However, there appear to be no systematic reviews of the relationship between L-VGCCs and stem cells, and filling this gap is prescient considering the contribution of L-VGCCs to the proliferation and differentiation of several types of stem cells. This review will discuss the possible involvement of L-VGCCs in stem cells, mainly focusing on osteogenesis mediated by mesenchymal stem cells (MSCs) from different tissues and neurogenesis mediated by neural stem/progenitor cells (NSCs). Additionally, advanced applications that use these channels as the target for tissue engineering, which may offer the hope of tissue regeneration in the future, will also be explored.

Tissue engineered bone mimetics to study bone disorders ex vivo: Role of bioinspired materials

Recent advances in materials development and tissue engineering has resulted in a substantial number of bioinspired materials that recapitulate cardinal features of bone extracellular matrix (ECM) such as dynamic inorganic and organic environment(s), hierarchical organization, and topographical features. Bone mimicking materials, as defined by its self-explanatory term, are developed based on the current understandings of the natural bone ECM during development, remodeling, and fracture repair. Compared to conventional plastic cultures, biomaterials that resemble some aspects of the native environment could elicit a more natural molecular and cellular response relevant to the bone tissue. Although current bioinspired materials are mainly developed to assist tissue repair or engineer bone tissues, such materials could nevertheless be applied to model various skeletal diseases in vitro. This review summarizes the use of bioinspired materials for bone tissue engineering, and their potential to model diseases of bone development and remodeling ex vivo. We largely focus on biomaterials, designed to re-create different aspects of the chemical and physical cues of native bone ECM. Employing these bone-inspired materials and tissue engineered bone surrogates to study bone diseases has tremendous potential and will provide a closer portrayal of disease progression and maintenance, both at the cellular and tissue level. We also briefly touch upon the application of patient-derived stem cells and introduce emerging technologies such as organ-on-chip in disease modeling. Faithful recapitulation of disease pathologies will not only offer novel insights into diseases, but also lead to enabling technologies for drug discovery and new approaches for cell-based therapies.

Antimicrobial Imidazolium Ionic Liquids for the Development of Minimal Invasive Calcium Phosphate-Based Bionanocomposites

Biofilm formation is one of the main obstacles that occur during in vivo implantation, which compromises the implant functionality and patients' health. This is the inspiration for the development of novel implant materials that contain broad-spectrum antimicrobial activity, including antibacterial and antifungal, and enable the local release of antimicrobial agents. Here, multifunctional calcium phosphate-ionic liquid (IL) materials, possessing antimicrobial and repair/regeneration features plus injectability, are proposed as implants in minimally invasive surgery. This approach was based on the loading of 1-alkyl-3-alkylimidazolium chloride ionic liquids (ILs) (C _nMImCl ( n = 4, 10, 16) and (C₁₀)₂MImCl) during the in situ sol-gel synthesis of calcium phosphates (CaP) and study of their effects on CaP crystallization and biological properties. Physical, morphological, and biological investigations were performed to evaluate the bionanocomposites' properties. The IL N-alkyl chain length influenced the crystallization of CaP and, consequently, the biological properties, which afforded bionanocomposites (when loaded with C₁₆MImCl or (C₁₀)₂MImCl) that, (i) inhibit both in vitro bacterial and fungal growth; (ii) reduce the in vitro inflammatory response; (iii) induce osteogenic differentiation in the basal medium of human mesenchymal stem cells; and (iv) are injectable. This will enable the design of multifunctional injectable implants with antimicrobial, anti-inflammatory, and regenerative properties to be used in minimally invasive surgery of bone and maxillofacial defects.

Clinical and Molecular Perspectives of Reparative Dentin Formation: Lessons Learned from Pulp-Capping Materials and the Emerging Roles of Calcium

The long-term use of calcium hydroxide and the recent increase in the use of hydraulic calcium-silicate cements as direct pulp-capping materials provide important clues in terms of how reparative dentin may be induced to form a "biological seal" to protect the underlying pulp tissues. In this review article, we discuss clinical and molecular perspectives of reparative dentin formation based on evidence learned from the use of these pulp-capping materials. We also discuss the emerging role of calcium as an odontoinductive component in these pulp-capping materials.

Fabrication of in vitro 3D mineralized tissue by fusion of composite spheroids incorporating biomineral-coated nanofibers and human adipose-derived stem cells

Development of a bone-like 3D microenvironment with stem cells has always been intriguing in bone tissue engineering. In this study, we fabricated composite spheroids by combining functionalized fibers and human adipose-derived stem cells (hADSCs), which were fused to form a 3D mineralized tissue construct. We prepared fragmented poly (ι-lactic acid) (PLLA) fibers approximately 100 μm long by partial aminolysis of electrospun fibrous mesh. PLLA fibers were then biomineralized with various concentrations of NaHCO₃ (0.005, 0.01, and 0.04 M) to form mineralized fragmented fibers (mFF1, mFF2, and mFF3, respectively). SEM analysis showed that the minerals in mFF2 and mFF3 completely covered the fiber surface, and surface chemistry analysis confirmed the presence of hydroxyapatite peaks. Additionally, mFFs formed composite spheroids with hADSCs, demonstrating that the cells were strongly attached to mFFs and homogeneously distributed throughout the spheroid. In vitro culture of spheroids in the media without osteogenic supplements showed significantly enhanced expression of osteogenic genes including Runx2 (20.83 ± 2.83 and 22.36 ± 2.18 fold increase), OPN (14.24 ± 1.71 and 15.076 ± 1.38 fold increase), and OCN (4.36 ± 0.41 and 5.63 ± 0.51 fold increase) in mFF2 and mFF3, respectively, compared to the no mineral fiber group. In addition, mineral contents were significantly increased at day 7. Blocking the biomineral-mediated signaling by PSB 603 significantly down regulated the expression of these genes in mFF3 at day 7. Finally, we fused composite spheroids to form a mineralized 3D tissue construct, which maintained the viability of cells and showed pervasively distributed minerals within the structure. Our composite spheroids could be used as an alternative platform for the development of in vitro bone models, in vivo cell carriers, and as building blocks for bioprinting 3D bone tissue.

STATEMENT OF SIGNIFICANCE

This manuscript described our recent work for the preparation of biomimeral-coated fibers that can be assembled with mesenchymal stem cells and provide bone-like environment for directed control over osteogenic differentiation. Biomineral coating onto synthetic, biodegradable single fibers was successfully carried out using multiple steps, combination of template protein coating inspired from mussel adhesion and charge-charge interactions between template proteins and mineral ions. The biomineral-coated single micro-scale fibers (1-2.5 μm in diameter) were then assembled with human adipose tissue derived stem cells (hADSCs). The assembled structure exhibited spheroidal architecture with few hundred micrometers. hADSCs within the spheroids were differentiated into osteogenic lineage in vitro and mineralized in the growth media. These spheroids were fused to form in vitro 3D mineralized tissue with larger size.

Pretreating mesenchymal stem cells with electrical stimulation causes sustained long-lasting pro-osteogenic effects

Background

Electrical stimulation (ES) has a long history of successful use in the clinical treatment of refractory, non-healing bone fractures and has recently been proposed as an adjunct to bone tissue-engineering treatments to optimize their therapeutic potential. This idea emerged from ES’s demonstrated positive effects on stem cell migration, proliferation, differentiation and adherence to scaffolds, all cell behaviors recognized to be advantageous in Bone Tissue Engineering (BTE). In previous in vitro experiments we demonstrated that direct current ES, administered daily, accelerates Mesenchymal Stem Cell (MSC) osteogenic differentiation. In the present study, we sought to define the optimal ES regimen for maximizing this pro-osteogenic effect.

Methods

Rat bone marrow-derived MSC were exposed to 100 mV/mm, 1 hr/day for three, seven, and 14 days, then osteogenic differentiation was assessed at Day 14 of culture by measuring collagen production, calcium deposition, alkaline phosphatase activity and osteogenic marker gene expression.

Results

We found that exposing MSC to ES for three days had minimal effect, while seven and 14 days resulted in increased osteogenic differentiation, as indicated by significant increases in collagen and calcium deposits, and expression of osteogenic marker genes Col1a1, Osteopontin, Osterix and Calmodulin. We also found that cells treated with ES for seven days, maintained this pro-osteogenic activity long (for at least seven days) after discontinuing ES exposure.

Discussion

This study showed that while three days of ES is insufficient to solicit pro-osteogenic effects, seven and 14 days significantly increases osteogenic differentiation. Importantly, we found that cells treated with ES for only seven days, maintained this pro-osteogenic activity long after discontinuing ES exposure. This sustained positive osteogenic effect is likely due to the enhanced expression of RunX2 and Calmodulin we observed. This prolonged positive osteogenic effect, long after discontinuing ES treatment, if incorporated into BTE treatment protocols, could potentially improve outcomes and in doing so help BTE achieve its full therapeutic potential.

Mineralized Biomaterials Mediated Repair of Bone Defects Through Endogenous Cells

Synthetic biomaterials that create a dynamic calcium (Ca²⁺)-, phosphate (PO₄^3-) ion-, and calcium phosphate (CaP)-rich microenvironment, similar to that found in native bone tissue, have been shown to promote osteogenic commitment of stem cells in vitro and in vivo. The intrinsic osteoconductivity and osteoinductivity of such biomaterials make them promising bone grafts for the treatment of bone defects. We thus aimed to evaluate the potential of mineralized biomaterials to induce bone repair of a critical-sized cranial defect in the absence of exogenous cells and growth factors. Our results demonstrate that the mineralized biomaterial alone can support complete bone formation within critical-sized bone defects through recruitment of endogenous cells and neo-bone tissue formation in mice. The newly formed bone tissue recapitulated many key characteristics of native bone such as formation of bone minerals reaching similar bone mineral density, presence of bone-forming osteoblasts and tartrate-resistant acid phosphatase-expressing osteoclasts, as well as vascular networks. Biomaterials that recruit endogenous cells and provide a tissue-specific microenvironment to modulate cellular behavior and support generation of functional tissues are a key step forward in moving bench-side tissue engineering approaches to the bedside. Such tissue engineering strategies could eventually pave the path toward readily available therapies that significantly reduce patient cost of care and improve overall clinical outcomes.

Applications of Metals for Bone Regeneration

The regeneration of bone tissue is the main purpose of most therapies in dental medicine. For bone regeneration, calcium phosphate (CaP)-based substitute materials based on natural (allo- and xenografts) and synthetic origins (alloplastic materials) are applied for guiding the regeneration processes. The optimal bone substitute has to act as a substrate for bone ingrowth into a defect, as well as resorb in the time frame needed for complete regeneration up to the condition of restitution ad integrum. In this context, the modes of action of CaP-based substitute materials have been frequently investigated, where it has been shown that such materials strongly influence regenerative processes such as osteoblast growth or differentiation and also osteoclastic resorption due to different physicochemical properties of the materials. However, the material characteristics needed for the required ratio between new bone tissue formation and material degradation has not been found, until now. The addition of different substances such as collagen or growth factors and also of different cell types has already been tested but did not allow for sufficient or prompt application. Moreover, metals or metal ions are used differently as a basis or as supplement for different materials in the field of bone regeneration. Moreover, it has already been shown that different metal ions are integral components of bone tissue, playing functional roles in the physiological cellular environment as well as in the course of bone healing. The present review focuses on frequently used metals as integral parts of materials designed for bone regeneration, with the aim to provide an overview of currently existing knowledge about the effects of metals in the field of bone regeneration.

TRPV4-mediates oscillatory fluid shear mechanotransduction in mesenchymal stem cells in part via the primary cilium

Skeletal homeostasis requires the continued replenishment of the bone forming osteoblast from a mesenchymal stem cell (MSC) population, a process that has been shown to be mechanically regulated. However, the mechanisms by which a biophysical stimulus can induce a change in biochemical signaling, mechanotransduction, is poorly understood. As a precursor to loading-induced bone formation, deciphering the molecular mechanisms of MSC osteogenesis is a critical step in developing novel anabolic therapies. Therefore, in this study we characterize the expression of the mechanosensitive calcium channel Transient Receptor Potential subfamily V member 4 (TRPV4) in MSCs and demonstrate that TRPV4 localizes to areas of high strain, specifically the primary cilium. We demonstrate that TRPV4 is required for MSC mechanotransduction, mediating oscillatory fluid shear induced calcium signaling and early osteogenic gene expression. Furthermore, we demonstrate that TRPV4 can be activated pharmacologically eliciting a response that mirrors that seen with mechanical stimulation. Lastly, we show that TRPV4 localization to the primary cilium is functionally significant, with MSCs with defective primary cilia exhibiting an inhibited osteogenic response to TRPV4 activation. Collectively, this data demonstrates a novel mechanism of stem cell mechanotransduction, which can be targeted therapeutically, and further highlights the critical role of the primary cilium in MSC biology.

Electric Field-Induced Osteogenic Differentiation on TiO2 Nanotubular Layer

On biocompatible implant surfaces, cellular behavior and fate of stem cells are determined not only by microenvironmental signals but also by electrochemical signals. The potential of electric fields (EFs) to stimulate bone growth and bone healing has been widely demonstrated, but the molecular mechanism linking EFs to osteogenic differentiation has remained elusive. Here we show that constant EFs triggered osteogenic induction of mesenchymal stem cells (MSCs) on a defined nanotubular TiO2 substrate. EFs stimulate the formation of plasma membrane protrusions and the transport of connexin 43 to these protrusions. Connexin 43 is required for the EF-induced lasting intracellular calcium increase, which rapidly propagates to neighboring cells by gap junctions. This enables simultaneous osteogenic induction following downstream calcineurin/CAMKII/NFAT signaling. We propose that connexin 43-mediated, EF-induced osteogenic differentiation of MSCs on a defined nanotubular titanium oxide surface may give new insight on therapeutic interventions for bone regeneration and tissue engineering approaches.

Enhancement of mesenchymal stem cell chondrogenesis with short-term low intensity pulsed electromagnetic fields

Pulse electromagnetic fields (PEMFs) have been shown to recruit calcium-signaling cascades common to chondrogenesis. Here we document the effects of specified PEMF parameters over mesenchymal stem cells (MSC) chondrogenic differentiation. MSCs undergoing chondrogenesis are preferentially responsive to an electromagnetic efficacy window defined by field amplitude, duration and frequency of exposure. Contrary to conventional practice of administering prolonged and repetitive exposures to PEMFs, optimal chondrogenic outcome is achieved in response to brief (10 minutes), low intensity (2 mT) exposure to 6 ms bursts of magnetic pulses, at 15 Hz, administered only once at the onset of chondrogenic induction. By contrast, repeated exposures diminished chondrogenic outcome and could be attributed to calcium entry after the initial induction. Transient receptor potential (TRP) channels appear to mediate these aspects of PEMF stimulation, serving as a conduit for extracellular calcium. Preventing calcium entry during the repeated PEMF exposure with the co-administration of EGTA or TRP channel antagonists precluded the inhibition of differentiation. This study highlights the intricacies of calcium homeostasis during early chondrogenesis and the constraints that are placed on PEMF-based therapeutic strategies aimed at promoting MSC chondrogenesis. The demonstrated efficacy of our optimized PEMF regimens has clear clinical implications for future regenerative strategies for cartilage.

Ion channel signaling influences cellular proliferation and phagocyte activity during axolotl tail regeneration

Little is known about the potential for ion channels to regulate cellular behaviors during tissue regeneration. Here, we utilized an amphibian tail regeneration assay coupled with a chemical genetic screen to identify ion channel antagonists that altered critical cellular processes during regeneration. Inhibition of multiple ion channels either partially (anoctamin1/Tmem16a, anoctamin2/Tmem16b, KV2.1, KV2.2, L-type CaV channels and H/K ATPases) or completely (GlyR, GABAAR, KV1.5 and SERCA pumps) inhibited tail regeneration. Partial inhibition of tail regeneration by blocking the calcium activated chloride channels, anoctamin1&2, was associated with a reduction of cellular proliferation in tail muscle and mesenchymal regions. Inhibition of anoctamin 1/2 also altered the post-amputation transcriptional response of p44/42 MAPK signaling pathway genes, including decreased expression of erk1/erk2. We also found that complete inhibition via voltage gated K+ channel blockade was associated with diminished phagocyte recruitment to the amputation site. The identification of H+ pumps as required for axolotl tail regeneration supports findings in Xenopus and Planaria models, and more generally, the conservation of ion channels as regulators of tissue regeneration. This study provides a preliminary framework for an in-depth investigation of the mechanistic role of ion channels and their potential involvement in regulating cellular proliferation and other processes essential to wound healing, appendage regeneration, and tissue repair.

Betaine promotes cell differentiation of human osteoblasts in primary culture

BACKGROUND

Betaine (BET), a component of many foods, is an essential osmolyte and a source of methyl groups; it also shows an antioxidant activity. Moreover, BET stimulates muscle differentiation via insulin like growth factor I (IGF-I). The processes of myogenesis and osteogenesis involve common mechanisms with skeletal muscle cells and osteoblasts sharing the same precursor. Therefore, we have hypothesized that BET might be effective on osteoblast cell differentiation.

METHODS

The effect of BET was tested in human osteoblasts (hObs) derived from trabecular bone samples obtained from waste material of orthopedic surgery. Cells were treated with 10 mM BET at 5, 15, 60 min and 3, 6 and 24 h. The possible effects of BET on hObs differentiation were evaluated by real time PCR, western blot and immunofluorescence analysis. Calcium imaging was used to monitor intracellular calcium changes.

RESULTS

Real time PCR results showed that BET stimulated significantly the expression of RUNX2, osterix, bone sialoprotein and osteopontin. Western blot and immunofluorescence confirmed BET stimulation of osteopontin protein synthesis. BET stimulated ERK signaling, key pathway involved in osteoblastogenesis and calcium signaling. BET induced a rise of intracellular calcium by means of the calcium ions influx from the extracellular milieu through the L-type calcium channels and CaMKII signaling activation. A significant rise in IGF-I mRNA at 3 and 6 h and a significant increase of IGF-I protein at 6 and 24 h after BET stimulus was detected. Furthermore, BET was able to increase significantly both SOD2 gene expression and protein content.

CONCLUSIONS

Our study showed that three signaling pathways, i.e. cytosolic calcium influx, ERK activation and IGF-I production, are enhanced by BET in human osteoblasts. These pathways could have synergistic effects on osteogenic gene expression and protein synthesis, thus potentially leading to enhanced bone formation. Taken together, these results suggest that BET could be a promising nutraceutical therapeutic agent in the strategy to counteract the concomitant and interacting impact of sarcopenia and osteoporosis, i.e. the major determinants of senile frailty and related mortality.