Autocrine fibroblast growth factor 18 mediates dexamethasone-induced osteogenic differentiation of murine mesenchymal stem cells

Analysis of the causal relationship between gut microbiota and bone remodeling growth factor from the gene association

BACKGROUND

A growing body of evidence indicates a close association between the gut microbiota (GM) and the bone remodeling (BR) process, raising suspicions that the GM may actively participate in BR by modulating the levels of growth factors. However, the precise causal relationship between them remains unclear. Due to many confounding factors, many microorganisms related to BR growth factors have not been identified. We aimed to elucidate the causal relationship between the GM and BR growth factors.

METHODS

We evaluated the genome-wide association study (GWAS) summary statistics for GM and five common growth factors associated with BR: namely, bone morphogenetic proteins (BMP), transforming growth factors(TGF), insulin growth factors (IGFs), epidermal growth factors (EGFs), and fibroblast growth factors (FGF). The causal relationship between the GM and BR growth factors was studied by double-sample Mendelian randomized analysis. We used five Mendelian randomization (MR) methods, including inverse variance-weighted (IVW), MR-Egger, simple mode, weighted median, and weighted model methods.

RESULTS

Through MR analysis, a total of 56 bacterial genera were co-identified as associated with BMP, TGF, IGF, EGF, and FGF. Among them, eight genera were found to have a causal relationship with multiple growth factors: Marvinbryantia was causally associated with BMP-6 (P = 0.018, OR = 1.355) and TGF-β2 (P = 0.002, OR = 1.475); Lachnoclostridium, BMP-7 (P = 0.021, OR = 0.73) and IGF-1 (P = 0.046, OR = 0.804); Terrisporobacter, TGF-β (P = 0.02, OR = 1.726) and FGF-23 levels (P = 0.016, OR = 1.76); Ruminiclostridium5, TGF-β levels (P = 0.024, OR = 0.525) and FGFR-2 (P = 0.003, OR = 0.681); Erysipelatoclostridium, TGF-β2 (P = 0.001, OR = 0.739) and EGF and its receptor (EGFR) (P = 0.012, OR = 0.795); Eubacterium_brachy_group, FGFR-2 (P = 0.045, OR = 1.153) and EGF (P = 0.013, OR = 0.7); Prevotella9 with EGFR (P = 0.022, OR = 0.818) and FGFR-2 (P = 0.011, OR = 1.233) and Faecalibacterium with FGF-23 (P = 0.02, OR = 2.053) and IGF-1 (P = 0.005, OR = 0.843).

CONCLUSION

We confirmed the causal relationship between the GM and growth factors related to BR, which provides a new perspective for the study of BR, through targeted regulation of specific bacteria to prevent and treat diseases and growth factor-mediated BR disorders.

Cell signaling and transcriptional regulation of osteoblast lineage commitment, differentiation, bone formation, and homeostasis

The initiation of osteogenesis primarily occurs as mesenchymal stem cells undergo differentiation into osteoblasts. This differentiation process plays a crucial role in bone formation and homeostasis and is regulated by two intricate processes: cell signal transduction and transcriptional gene expression. Various essential cell signaling pathways, including Wnt, BMP, TGF-β, Hedgehog, PTH, FGF, Ephrin, Notch, Hippo, and Piezo1/2, play a critical role in facilitating osteoblast differentiation, bone formation, and bone homeostasis. Key transcriptional factors in this differentiation process include Runx2, Cbfβ, Runx1, Osterix, ATF4, SATB2, and TAZ/YAP. Furthermore, a diverse array of epigenetic factors also plays critical roles in osteoblast differentiation, bone formation, and homeostasis at the transcriptional level. This review provides an overview of the latest developments and current comprehension concerning the pathways of cell signaling, regulation of hormones, and transcriptional regulation of genes involved in the commitment and differentiation of osteoblast lineage, as well as in bone formation and maintenance of homeostasis. The paper also reviews epigenetic regulation of osteoblast differentiation via mechanisms, such as histone and DNA modifications. Additionally, we summarize the latest developments in osteoblast biology spurred by recent advancements in various modern technologies and bioinformatics. By synthesizing these insights into a comprehensive understanding of osteoblast differentiation, this review provides further clarification of the mechanisms underlying osteoblast lineage commitment, differentiation, and bone formation, and highlights potential new therapeutic applications for the treatment of bone diseases.

Effect and mechanism of recombinant human fibroblast growth factor 18 on osteoporosis in OVX mice

OBJECTIVES

This study aimed to investigate the effect and the mechanism of recombinant human fibroblast growth factor 18 (rhFGF18) on postmenopausal osteoporosis.

METHODS

The effect of rhFGF18 on the proliferation and apoptosis of osteoblasts and the mechanism underlying such an effect was evaluated using an oxidative stress model of the MC3T3-E1 cell line. Furthermore, ovariectomy was performed on ICR mice to imitate estrogen-deficiency postmenopausal osteoporosis. Bone metabolism and bone morphological parameters in the ovariectomized (OVX) mice were evaluated.

RESULTS

The results obtained from the cell model showed that FGF18 promoted MC3T3-E1 cell proliferation by activating the extracellular signal-regulated kinase (ERK) and p38 instead of c-Jun N-terminal kinase (JNK). FGF18 also prevented cells from damage inflicted by oxidative stress via inhibition of apoptosis. After FGF18 administration, the expression level of anti-apoptotic protein Bcl-2 in the mice was upregulated, whereas those of the pro-apoptotic proteins Bax and caspase-3 were downregulated. Administering FGF18 also improved bone metabolism and bone morphological parameters in OVX mice.

CONCLUSIONS

FGF18 could effectively prevent bone loss in OVX mice by enhancing osteoblastogenesis and protecting osteoblasts from oxidative stress-induced apoptosis.

Growth Factor Delivery Using a Collagen Membrane for Bone Tissue Regeneration

The use of biomaterials and bioactive agents has shown promise in bone defect repair, leading to the development of strategies for bone regeneration. Various artificial membranes, especially collagen membranes (CMs) that are widely used for periodontal therapy and provide an extracellular matrix-simulating environment, play a significant role in promoting bone regeneration. In addition, numerous growth factors (GFs) have been used as clinical applications in regenerative therapy. However, it has been established that the unregulated administration of these factors may not work to their full regenerative potential and could also trigger unfavorable side effects. The utilization of these factors in clinical settings is still restricted due to the lack of effective delivery systems and biomaterial carriers. Hence, considering the efficiency of bone regeneration, both spaces maintained using CMs and GFs can synergistically create successful outcomes in bone tissue engineering. Therefore, recent studies have demonstrated a significant interest in the potential of combining CMs and GFs to effectively promote bone repair. This approach holds great promise and has become a focal point in our research. The purpose of this review is to highlight the role of CMs containing GFs in the regeneration of bone tissue, and to discuss their use in preclinical animal models of regeneration. Additionally, the review addresses potential concerns and suggests future research directions for growth factor therapy in the field of regenerative science.

Effect of spheroid size on gene expression profiles of a mouse mesenchymal stem cell line in spheroid culture

BACKGROUND

Mesenchymal stem cell (MSC)-based therapies offer potential for bone repair. MSC spheroid cultures may harbor enhanced therapeutic potential over MSC monolayers through increased secretion of trophic factors. However, the impact of spheroid size on trophic factor expression is unclear.

OBJECTIVE

We investigated the effect of spheroid size on trophic factor-related gene expression.

METHODS

KUM10, a murine MSC line was used. RNA-seq was used to screen the transcriptional profiles of MSC monolayer and spheroid cultures. Differentially expressed genes identified in RNA-seq were evaluated by q-PCR in cultures of 5 × 104 (S group), 5 × 105 (M group), 5 × 106 (L group) cells/well.

RESULTS

Comparison of expression levels between KUM10 monolayer and spheroid cultures identified 2140 differentially expressed genes, of which 1047 were upregulated and 1093 were downregulated in KUM10 spheroids. Among these, 12 upregulated genes (Bmp2, Fgf9, Fgf18, Ngf, Pdgfa, Pdgfb, Tgfb1, Vegfa, Vegfc, Wnt4, Wnt5a, Wnt10a) were associated with secretory growth factors. Of these, expression of Fgf9, Fgf18, Vegfa and Vegfc was elevated in the L group, and Pdgfb and Tgfb1 was elevated in the S group.

CONCLUSIONS

Spheroid size may impact trophic factor expression. Our results will be useful for future studies assessing the utility of MSC spheroids for treating bone injury.

Role of FGF-18 in Bone Regeneration

In tissue engineering, three key components are cells, biological/mechanical cues, and scaffolds. Biological cues are normally proteins such as growth factors and their derivatives, bioactive molecules, and the regulators of a gene. Numerous growth factors such as VEGF, FGF, and TGF-β are being studied and applied in different studies. The carriers used to release these growth factors also play an important role in their functioning. From the early part of the 1990s, more research has beenconductedon the role of fibroblast growth factors on the various physiological functions in our body. The fibroblast growth factor family contains 22 members. Fibroblast growth factors such as 2, 9, and 18 are mainly associated with the differentiation of osteoblasts and in bone regeneration. FGF-18 stimulates the PI3K/ERK pathway and smad1/5/8 pathway mediated via BMP-2 by blocking its antagonist, which is essential for bone formation. FGF-18 incorporated hydrogel and scaffolds had showed enhanced bone regeneration. This review highlights these functions and current trends using this growth factor and potential outcomes in the field of bone regeneration.

Augmented effect of fibroblast growth factor 18 in bone morphogenetic protein 2-induced calvarial bone healing by activation of CCL2/CCR2 axis on M2 macrophage polarization

Fibroblast growth factor (FGF) signaling plays essential roles in various biological events. FGF18 is one of the ligands to be associated with osteogenesis, chondrogenesis and bone healing. The mouse critical-sized calvarial defect healing induced by the bone morphogenetic protein 2 (BMP2)-hydrogel is stabilized when FGF18 is added. Here, we aimed to investigate the role of FGF18 in the calvarial bone healing model. We first found that FGF18 + BMP2 hydrogel application to the calvarial bone defect increased the expression of anti-inflammatory markers, including those related to tissue healing M2 macrophage (M2-Mø) prior to mineralized bone formation. The depletion of macrophages with clodronate liposome hindered the FGF18 effect. We then examined how FGF18 induces M2-Mø polarization by using mouse primary bone marrow (BM) cells composed of macrophage precursors and BM stromal cells (BMSCs). In vitro studies demonstrated that FGF18 indirectly induces M2-Mø polarization by affecting BMSCs. Whole transcriptome analysis and neutralizing antibody treatment of BMSC cultured with FGF18 revealed that chemoattractant chemokine (c-c motif) ligand 2 (CCL2) is the major mediator for M2-Mø polarization. Finally, FGF18-augmented activity toward favorable bone healing with BMP2 was diminished in the calvarial defect in Ccr2-deleted mice. Altogether, we suggest a novel role of FGF18 in M2-Mø modulation via stimulation of CCL2 production in calvarial bone healing.

Epstein-Barr virus-induced gene 3 commits human mesenchymal stem cells to differentiate into chondrocytes via endoplasmic reticulum stress sensor

Mesenchymal stem cells (MSC) can differentiate into chondrocytes. Epstein-Barr virus-induced gene 3 (EBI3) is differentially expressed during chondrogenic differentiation and can be produced by MSC. EBI3 is also a subunit of interleukin (IL)-27 and IL-35, and it accumulates in the endoplasmic reticulum (ER) when its partners, such as IL-27 p28 and IL-35 p35, are insufficient. ER stress induced by protein accumulation is responsible for chondrogenic differentiation. However, the role of EBI3 and its relevance to the ER stress in chondrogenic differentiation of MSC have never been addressed. Here, we demonstrate that EBI3 protein is expressed in the early stage of chondrogenic differentiation of MSC. Additionally, knockdown, overexpression, or induction of EBI3 through IL-1β inhibits chondrogenesis. We show that EBI3 localizes and accumulates in the ER of MSC after overexpression or induction by IL-1β and TNF-α, whereas ER stress inhibitor 4-phenylbutyric acid decreases its accumulation in MSC. Moreover, EBI3 modulates ER stress sensor inositol-requiring enzyme 1 α (IRE1α) after induced by IL-1β, and MSC-like cells coexpress EBI3 and IRE1α in rheumatoid arthritis (RA) synovial tissue. Altogether, these data demonstrate that intracellular EBI3 commits to chondrogenic differentiation by regulating ER stress sensor IRE1α.

Dexamethasone-loaded zeolitic imidazolate frameworks nanocomposite hydrogel with antibacterial and anti-inflammatory effects for periodontitis treatment

Periodontitis is a bacterial-induced, chronic inflammatory disease characterized by progressive destruction of tooth-supporting structures. Pathogenic bacteria residing in deep periodontal pockets after traditional manual debridement can still lead to local inflammatory microenvironment, which remains a challenging problem and an urgent need for better therapeutic strategies. Here, we integrated the advantages of metal-organic frameworks (MOFs) and hydrogels to prepare an injectable nanocomposite hydrogel by incorporating dexamethasone-loaded zeolitic imidazolate frameworks-8 (DZIF) nanoparticles into the photocrosslinking matrix of methacrylic polyphosphoester (PPEMA) and methacrylic gelatin (GelMA). The injectable hydrogel could be easily injected into deep periodontal pockets, achieving high local concentrations without leading to antibiotic resistance. The nanocomposite hydrogel had high antibacterial activity and constructs with stable microenvironments maintain cell viability, proliferation, spreading, as well as osteogenesis, and down-regulated inflammatory genes expression in vitro. When evaluated on an experimental periodontitis rat model, micro-computed tomography and histological analyses showed that the nanocomposite hydrogel effectively reduced periodontal inflammation and attenuated inflammation-induced bone loss in a rat model of periodontitis. These findings suggest that the nanocomposite hydrogel might be a promising therapeutic candidate for treating periodontal disease.

Steroid-induced fibroblast growth factors drive an epithelial-mesenchymal inflammatory axis in severe asthma

Asthma and inflammatory airway diseases restrict airflow in the lung, compromising gas exchange and lung function. Inhaled corticosteroids (ICSs) can reduce inflammation, control symptoms, and improve lung function; however, a growing number of patients with severe asthma do not benefit from ICS. Using bronchial airway epithelial brushings from patients with severe asthma or primary human cells, we delineated a corticosteroid-driven fibroblast growth factor (FGF)-dependent inflammatory axis, with FGF-responsive fibroblasts promoting downstream granulocyte colony-stimulating factor (G-CSF) production, hyaluronan secretion, and neutrophilic inflammation. Allergen challenge studies in mice demonstrate that the ICS, fluticasone propionate, inhibited type 2-driven eosinophilia but induced a concomitant increase in FGFs, G-CSF, hyaluronan, and neutrophil infiltration. We developed a model of steroid-induced neutrophilic inflammation mediated, in part, by induction of an FGF-dependent epithelial-mesenchymal axis, which may explain why some individuals do not benefit from ICS. In further proof-of-concept experiments, we found that combination therapy with pan-FGF receptor inhibitors and corticosteroids prevented both eosinophilic and steroid-induced neutrophilic inflammation. Together, these results establish FGFs as therapeutic targets for severe asthma patients who do not benefit from ICS.

Excessive osteoclast activation by osteoblast paracrine factor RANKL is a major cause of the abnormal long bone phenotype in Apert syndrome model mice

The fibroblast growth factor (FGF)/FGF receptor (FGFR) signaling pathway plays important roles in the development and growth of the skeleton. Apert syndrome caused by gain‐of‐function mutations of FGFR2 results in aberrant phenotypes of the skull, midface, and limbs. Although short limbs are representative features in patients with Apert syndrome, the causative mechanism for this limb defect has not been elucidated. Here we quantitatively confirmed decreases in the bone length, bone mineral density, and bone thickness in the Apert syndrome model of gene knock‐in Fgfr2^S252W/+ (EIIA‐Fgfr2^S252W/+) mice. Interestingly, despite these bone defects, histological analysis showed that the endochondral ossification process in the mutant mice was similar to that in wild‐type mice. Tartrate‐resistant acid phosphatase staining revealed that trabecular bone loss in mutant mice was associated with excessive osteoclast activity despite accelerated osteogenic differentiation. We investigated the osteoblast–osteoclast interaction and found that the increase in osteoclast activity was due to an increase in the Rankl level of osteoblasts in mutant mice and not enhanced osteoclastogenesis driven by the activation of FGFR2 signaling in bone marrow‐derived macrophages. Consistently, Col1a1‐Fgfr2^S252W/+ mice, which had osteoblast‐specific expression of Fgfr2 S252W, showed significant bone loss with a reduction of the bone length and excessive activity of osteoclasts was observed in the mutant mice. Taken together, the present study demonstrates that the imbalance in osteoblast and osteoclast coupling by abnormally increased Rankl expression in Fgfr2^S252W/+ mutant osteoblasts is a major causative mechanism for bone loss and short long bones in Fgfr2^S252W/+ mice.

The phytochemical plumbagin reciprocally modulates osteoblasts and osteoclasts

Bone metabolism is essential for maintaining bone mineral density and bone strength through a balance between bone formation and bone resorption. Bone formation is associated with osteoblast activity whereas bone resorption is linked to osteoclast differentiation. Osteoblast progenitors give rise to the formation of mature osteoblasts whereas monocytes are the precursors for multi-nucleated osteoclasts. Chronic inflammation, auto-inflammation, hormonal changes or adiposity have the potential to disturb the balance between bone formation and bone loss. Several plant-derived components are described to modulate bone metabolism and alleviate osteoporosis by enhancing bone formation and inhibiting bone resorption. The plant-derived naphthoquinone plumbagin is a bioactive compound that can be isolated from the roots of the Plumbago genus. It has been used as traditional medicine for treating infectious diseases, rheumatoid arthritis and dermatological diseases. Reportedly, plumbagin exerts its biological activities primarily through induction of reactive oxygen species and triggers osteoblast-mediated bone formation. It is plausible that plumbagin's reciprocal actions - inhibiting or inducing death in osteoclasts but promoting survival or growth of osteoblasts - are a function of the synergy with bone-metabolizing hormones calcitonin, Parathormone and vitamin D. Herein, we develop a framework for plausible molecular modus operandi of plumbagin in bone metabolism.

MicroRNA-133a Regulates the Viability and Differentiation Fate of Bone Marrow Mesenchymal Stem Cells via MAPK/ERK Signaling Pathway by Targeting FGFR1

Dysfunction of bone marrow mesenchymal stem cells (BMSCs) is recognized critical in bone deteriorations of osteoporosis. However, the specific mechanisms that determine the fate of BMSCs remain elusive. MicroRNA-133a (miR-133a), a highly conserved microRNA, was investigated under both in vitro and in vivo conditions. In the in vitro study, cell proliferation, cell apoptosis, and osteoblast/adipocyte differentiation of BMSCs as a result of overexpression or knockdown of miR-133a was investigated. In the in vivo study, the ovariectomy (OVX) model was applied on mice, with further treatment of the models with BMSC-specific miR-133a antagomir through femur intramedullary injection. Microcomputed tomography scanning and histological analysis of the proximal and middle femur were performed to evaluate the morphological changes. The results revealed that overexpression of miR-133a suppressed cell proliferation, cell viability, and osteoblast differentiation of BMSCs, but increased adipocyte differentiation. We also found that FGFR1, an important upstream regulator of mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) signal pathway, was a major target of miR-133a. We also recorded that BMSC-specific knockdown of miR-133a attenuates bone loss in OVX mice. Our study suggested that miR-133a played an important role in maintaining the viability and balance between osteoblast and adipocyte differentiation of BMSCs through the MAPK/ERK signaling pathway by targeting FGFR1.

miR-133a silencing rescues glucocorticoid-induced bone loss by regulating the MAPK/ERK signaling pathway

BACKGROUND

Dysfunction of mesenchymal stem cells (MSCs) is recognized as critical to the pathogenesis of glucocorticoid-induced osteoporosis (GIO), suggesting the potential of MSC-targeting interventions for this disorder. As the miR-133a has been shown to play an important role in bone metabolism, we hypothesized that miR-133a may also be involved in GIO.

METHODS

In the in vitro study, we examined the effect of miR-133a antagomir on DEX-treated MSCs, including proliferation, apoptosis, osteoblast, and adipocyte differentiation, then, we explored the mechanism of these effects of miR-133a silencing through measuring the phosphorylation of ERK1/2 and its regulator FGFR1 via western blot and qRT-PCR. In the in vivo study, we developed a GIO rat model by injecting methylprednisolone and modulated the miR-133a expression in the femur by intramedullary injection of the miR-133a antagomir, and then micro-CT analyses and histological staining of the femurs were used to investigate the effect of miR-133a silencing on bone loss of the GIO rats.

RESULTS

qRT-PCR analysis indicated that glucocorticoid induced high miR-133a expression in MSCs and animal models. The in vitro study showed that miR-133a antagomir significantly promoted cell proliferation, viability, and osteoblast differentiation and inhibited adipocyte differentiation in DEX-treated MSCs. Furthermore, the expression of p-ERK1/2 and FGFR1 in DEX-treated MSCs was also upregulated by miR-133a antagomir. Then we investigated the effect of miR-133a silencing on the bone architecture of GIO models, micro-CT analysis showed that miR-133a antagomir attenuated the loss of bone mass and improved the trabecular and cortical parameters induced by methylprednisolone. Histological study showed that miR-133a silencing simultaneously increased bone formation and decreased marrow fat accumulation in GIO rats.

CONCLUSIONS

Our findings suggested that miR-133a is strongly associated with GIO and similar disorders induced by glucocorticoids in MSCs. Silencing miR-133a resulted in positive effects on GC-treated MSCs and on bone loss in GIO animal models. Moreover, the FGFR1-MAPK/ERK signaling may be involved in the protective effect of miR-133a silencing.

Combinatorial effect of nano whitlockite/nano bioglass with FGF-18 in an injectable hydrogel for craniofacial bone regeneration

Comparing the bone regeneration potential of nano whitlockite or nano bioglass in combination with FGF-18, loaded in an injectable, shear-thinning chitin/PLGA hydrogel for craniofacial bone regeneration.

Mesenchymal stem cell mediates cardiac repair through autocrine, paracrine and endocrine axes

In the past decade, despite key advances in therapeutic strategies following myocardial infarction, none can directly address the loss of cardiomyocytes following ischemic injury. Cardiac cell-based therapy is at the cornerstone of regenerative medicine that has shown potential for tissue repair. Mesenchymal stem cells (MSC) represent a strong candidate to heal the infarcted myocardium. While differentiation potential has been described as a possible avenue for MSC-based repair, their secreted mediators are responsible for the majority of the ascribed prohealing effects. MSC can either promote their own survival and proliferation through autocrine effect or secrete trophic factors that will act on adjacent cells through a paracrine effect. Prior studies have also documented beneficial effects even when MSCs were remotely delivered, much akin to an endocrine mechanism. This review aims to distinguish the paracrine activity of MSCs from an endocrine-like effect, where remotely transplanted cells can promote healing of the injured myocardium.

Accentuated osseointegration in osteogenic nanofibrous coated titanium implants

Anchoring of endosseous implant through osseointegration continues to be an important clinical need. Here, we describe the development of superior endosseous implant demonstrating enhance osseointegration, achieved through surface modification via coating of osteogenic nanofibres. The randomized bio-composite osteogenic nanofibres incorporating polycaprolactone, gelatin, hydroxyapatite, dexamethasone, beta-glycerophosphate and ascorbic acid were electrospun on titanium implants mimicking bone extracellular matrix and subsequently induced osteogenesis by targeting undifferentiated mesenchymal stem cells present in the peri-implant niche to regenerate osseous tissue. In proof-of-concept experiment on rabbit study models (n = 6), micro-computed tomography (Micro-CT), histomorphometric analysis and biomechanical testing in relation to our novel osteogenic nanofibrous coated implants showed improved results when compared to uncoated controls. Further, no pathological changes were detected during gross examination and necropsy on peri-implant osseous tissues regenerated in response to such coated implants. The findings of the present study confirm that osteogenic nanofibrous coating significantly increases the magnitude of osteogenesis in the peri-implant zone and favours the dynamics of osseointegration.

The role of the fibroblast growth factor family in bone-related diseases

Fibroblast growth factor (FGF) family members are important regulators of cell growth, proliferation, differentiation, and regeneration. The abnormal expression of certain FGF family members can cause skeletal diseases, including achondroplasia, craniosynostosis syndrome, osteoarthritis, and Kashin-Beck disease. Accumulating evidence shows that FGFs play a crucial role in the growth and proliferation of bone and in the pathogenesis of certain bone-related diseases. Here, we review the involvement of FGFs in bone-related processes and diseases; FGF1 in the differentiation of human bone marrow mesenchymal stem cells and fracture repair; FGF2, FGF9, and FGF18 in osteoarthritis; FGF6 in bone and muscle injury; FGF8 in osteoarthritis and Kashin-Beck disease; and FGF21 and FGF23 on bone regulation. These findings indicate that FGFs are targets for novel therapeutic interventions for bone-related diseases.

Molecular signaling in bone cells: Regulation of cell differentiation and survival

The achievement of proper bone mass and architecture, and their maintenance throughout life requires the concerted actions of osteoblasts, the bone forming cells, and osteoclasts, the bone resorbing cells. The differentiation and activity of osteoblasts and osteoclasts are regulated by molecules produced by matrix-embedded osteocytes, as well as by cross talk between osteoblasts and osteoclasts through secreted factors. In addition, it is likely that direct contact between osteoblast and osteoclast precursors, and the contact of these cells with osteocytes and cells in the bone marrow, also modulates bone cell differentiation and function. With the advancement of molecular and genetic tools, our comprehension of the intracellular signals activated in bone cells has evolved significantly, from early suggestions that osteoblasts and osteoclasts have common precursors and that osteocytes are inert cells in the bone matrix, to the very sophisticated understanding of a network of receptors, ligands, intracellular kinases/phosphatases, transcription factors, and cell-specific genes that are known today. These advances have allowed the design and FDA-approval of new therapies to preserve and increase bone mass and strength in a wide variety of pathological conditions, improving bone health from early childhood to the elderly. We have summarized here the current knowledge on selected intracellular signal pathways activated in osteoblasts, osteocytes, and osteoclasts.

Fibroblast growth factors in skeletal development

Fibroblast growth factors (FGFs) and their receptors (FGFRs) are expressed throughout all stages of skeletal development. In the limb bud and in cranial mesenchyme, FGF signaling is important for formation of mesenchymal condensations that give rise to bone. Once skeletal elements are initiated and patterned, FGFs regulate both endochondral and intramembranous ossification programs. In this chapter, we review functions of the FGF signaling pathway during these critical stages of skeletogenesis, and explore skeletal malformations in humans that are caused by mutations in FGF signaling molecules.

Type I collagen deposition via osteoinduction ameliorates YAP/TAZ activity in 3D floating culture clumps of mesenchymal stem cell/extracellular matrix complexes

Background

Three-dimensional (3D) floating culture clumps of mesenchymal stem cell (MSC)/extracellular matrix (ECM) complexes (C-MSCs) consist of cells and self-produced ECM. Previous studies have demonstrated that C-MSCs can be transplanted into bony lesions without an artificial scaffold to induce bone regeneration. Moreover, osteoinductive medium (OIM)-treated C-MSCs (OIM-C-MSCs) have shown rapid and increased new bone formation in vivo. To apply OIM-C-MSCs for novel bone regenerative cell therapy, their cellular properties at the molecular level must be elucidated. The transcriptional co-activators yes-associated protein/transcriptional co-activator with PDZ-binding motif (YAP/TAZ) have been recognized as key players in the mechanotransduction cascade, controlling cell lineage commitment in MSCs. It is plausible that 3D C-MSCs/OIM-C-MSCs cultured in floating conditions could provide distinct microenvironments compared to conventional 2D culture systems and thereby induce unique mechanotransduction cascades. Therefore, this study investigated the YAP/TAZ activity in 3D-cultured C-MSCs/OIM-C-MSCs in floating conditions.

Methods

Human bone marrow-derived MSCs were cultured in growth medium supplemented with ascorbic acid. To obtain C-MSCs, confluent cells that had formed on the cellular sheet were scratched using a micropipette tip and were then torn off. The sheet was rolled to make round clumps of cells. Then, YAP/TAZ activity, filamentous actin (F-actin) integrity, collagen type I (COL1) production, and the differentiation potency in 3D floating culture C-MSCs/OIM-C-MSCs were analyzed.

Results

C-MSCs cultured in floating conditions lost their actin cytoskeleton to downregulate YAP/TAZ activity, which directed cells to undergo adipogenesis/chondrogenesis. OIM treatment induced abundant COL1 deposition, which facilitated Intβ1-dependent actin fiber formation and YAP/TAZ activity to elevate the expression levels of osteogenic master transcriptional factor runt-related transcription factor 2 (RUNX2) mRNA in C-MSCs. Importantly, elevation of YAP/TAZ activity via OIM was associated with COL1 deposition and F-actin integrity, suggesting a positive feedback loop in OIM-C-MSCs.

Conclusion

These findings suggest that OIM-C-MSCs, which form a unique microenvironment that maintains high YAP/TAZ activity, can serve as better candidates for bone regenerative cell therapy than C-MSCs.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1085-9) contains supplementary material, which is available to authorized users.

Differentiated adipose-derived stem cell cocultures for bone regeneration in RADA16-I in vitro

Craniofacial defects can cause morbidness. Adipose-derived stem cells (ADSCs) have shown great promise for osteogeneration and vascularization; therefore cocultures of differentiated ADSCs are explored to increase bone and vessel formation. In this study, ADSCs were induced into osteogenic ADSCs (os-ADSCs) and endothelial ADSCs (endo-ADSCs) cells, which were then cocultured in variable proportions (os-ADSCs/endo-ADSCs = 2:1, 1:1, 1:2). The os-ADSCs in a ratio of 1:1 expressed more ALP, RUNX2 and COL-I, whereas VEGF, vWF and CD31 were upregulated in the endo-ADSCs of this group. Next generation RNA sequencing (RNA-seq) was performed to evaluate the molecular mechanisms of cocultured ADSCs. The os-ADSCs and endo-ADSCs interacted with each other during osteogenic and angiogenic differentiation, especially at the ratio of 1:1, and were regulated by vascular-related genes, cell-mediated genes, bone-related genes and the transforming growth factor β signaling pathway (TGF-β), mitogen-activated protein kinase signaling pathway (MAPK) and wnt signaling pathway (Wnt). Angptl4, apoe, mmp3, bmp6, mmp13 and fgf18 were detected to be up-regulated, and cxcl12 and wnt5a were down-regulated. The results showed that the gene expression levels were consistent with that in RNA-seq. The cells were then seeded into self-assembling peptide RADA16-I scaffolds as cocultures (1:1) and monocultures (ADSCs, os-ADSCs, endo-ADSCs). The results showed that the cells of all groups grew and proliferated well on the scaffolds, and the cocultured group exhibited better osteogeneration and vascularization. In conclusion, cocultured os-ADSCs and endo-ADSCs at the ratio of 1:1 showed strong osteogenic and angiogenic differentiation. There is a great potential for osteogenesis and vascularization by 3D culturing cells in a 1:1 ratio in self-assembling peptide RADA16-I scaffolds, which requires evaluation for bone regeneration in vivo.

Insulin-Like Growth Factor Axis Expression in Dental Pulp Cells Derived From Carious Teeth

The insulin-like growth factor (IGF) axis plays an important role in dental tissue regeneration and most components of this axis are expressed in human dental pulp cells (DPCs). In our previous study, we analyzed IGF axis gene expression in DPCs and demonstrated a novel role of IGF binding protein (IGFBP)-2 and -3 in coordinating mineralized matrix formation in differentiating DPCs. A more recent study from our laboratory partially characterized dental pulp stem cells from teeth with superficial caries (cDPCs) and showed that their potential to differentiate odontoblasts and/or into osteoblasts is enhanced by exposure to the mild inflammatory conditions characteristic of superficial caries. In the present study, we examine whether changes apparent in IGF axis expression during osteogenic differentiation of healthy DPCs are also apparent in DPCs derived from carious affected teeth.

Released fibroblast growth factor18 from a collagen membrane induces osteoblastic activity involved with downregulation of miR-133a and miR-135a

We have developed a unique delivery system of growth factors using collagen membranes (CMs) to induce bone regeneration. We hypothesized that fibroblast growth factor18 (FGF-18), a pleiotropic protein that stimulates proliferation in several tissues, can be a good candidate to use our delivery system for bone regeneration. Cell viability, cell proliferation, alkaline phosphatase activity, mineralization, and marker gene expression of osteoblastic differentiation were evaluated after mouse preosteoblasts were cultured with a CM containing FGF-18, a CM containing platelet-derived growth factor, or a CM alone. Furthermore, expression of microRNA, especially miR-133a and miR-135a involving inhibition of osteogenic factors, was measured in preosteoblasts with CM/FGF-18 or CM alone. A sustained release of FGF-18 from the CM was observed over 21 days. CM/FGF-18 significantly promoted cell proliferation, alkaline phosphatase activity, and mineralization compared to CM alone. Gene expression of type I collagen, runt-related transcription factor 2, osteocalcin, Smad5, and osteopontin was significantly upregulated in CM/FGF-18 compared to CM alone, and similar to CM/platelet-derived growth factor. Additionally, CM/FGF-18 downregulated expression of miR-133a and miR-135a. These results suggested that released FGF-18 from a CM promotes osteoblastic activity involved with downregulation of miR-133a and miR-135a.

Lack of Fgf18 causes abnormal clustering of motor nerve terminals at the neuromuscular junction with reduced acetylcholine receptor clusters

FGF receptor 2 is involved in the formation of the neuromuscular junction (NMJ), but its in vivo ligand remains to be determined. Laser capture microdissection of the mouse spinal motor neurons (SMNs) revealed that Fgf18 mRNA is highly expressed in SMNs in adults. Expression of Fgf18 mRNA was the highest in the spinal cord at embryonic day (E) 15.5, which gradually decreased to postnatal day 7. FGF18 protein was localized at the NMJs of the tibialis anterior muscle at E18.5 and in adults. Fgf18−/− mice at E18.5 showed decreased expressions of the NMJ-specific Chrne and Colq genes in the diaphragm. In Fgf18−/− diaphragms, the synaptophysin-positive areas at the nerve terminals and the acetylcholine receptor (AChR)-positive areas at the motor endplates were both approximately one-third of those in wild-type embryos. Fgf18−/− diaphragms ultrastructurally showed abnormal aggregation of multiple nerve terminals making a gigantic presynapse with sparse synaptic vesicles, and simplified motor endplates. In Fgf18−/− diaphragms, miniature endplate potentials were low in amplitude with markedly reduced frequency. In C2C12 myotubes, FGF18 enhanced AChR clustering, which was blocked by inhibiting FGFRs or MEK1. We propose that FGF18 plays a pivotal role in AChR clustering and NMJ formation in mouse embryogenesis.

Driving mesenchymal stem cell differentiation from self-assembled monolayers

The utilization of self-assembled monolayer (SAM) systems to direct Mesenchymal Stem Cell (MSC) differentiation has been covered in the literature for years, but finding a general consensus pertaining to its exact role over the differentiation of stem cells had been rather challenging. Although there are numerous reports on surface functional moieties activating and inducing differentiation, the results are often different between reports due to the varying surface conditions, such as topography or surface tension. Herein, in view of the complexity of the subject matter, we have sought to catalogue the recent developments around some of the more common functional groups on predominantly hard surfaces and how these chemical groups may influence the overall outcome of the mesenchymal stem cells (MSC) differentiation so as to better establish a clearer underlying relationship between stem cells and their base substratum interactions.

Graphical illustration showing the functional groups that drive MSC differentiation without soluble bioactive cues within the first 14 days.

Bone Tissue Engineering Strategies in Co-Delivery of Bone Morphogenetic Protein-2 and Biochemical Signaling Factors

Administration of bone morphogenetic protein-2 (BMP-2), which is commercially approved by the food and drug administration to damaged bone sites has been investigated for the purpose of bone tissue regeneration. BMP-2 can promote osteoblastic differentiation of mesenchymal stem cells as well as regeneration of bone formation in early phase. This review highlights various factors such as vitamin D, dexamethasone, platelet-derived growth factor, placental growth factor, BMP-7, and NEL-like protein-1 that enhance and stimulate angiogenesis, cell differentiation, and bone regeneration. These biochemical signals and growth factors (GFs) accelerate bone repair and remodeling either synergistically or individually. Delivery systems and scaffolds are used for sustained release of these cargo molecules and support at damaged bone sites. Compared with direct administration of BMP-2, current studies have demonstrated that a combination of multiple GFs and/or therapeutic chemical factors with delivery platforms synergistically facilitates bone regeneration. Therefore, in the future, multiple combinations of various GFs, chemicals, and materials could provide patients and surgeons with non-invasive treatment options without secondary surgery and pain. To the end, this review summarizes the biological functions and synergistic effects of dual administration modalities involving BMP-2 as well as recent developments in bone tissue engineering applications.

Injectable Shear-Thinning CaSO4/FGF-18-Incorporated Chitin-PLGA Hydrogel Enhances Bone Regeneration in Mice Cranial Bone Defect Model

For craniofacial bone regeneration, shear-thinning injectable hydrogels are favored over conventional scaffolds because of their improved defect margin adaptability, easier handling, and ability to be injected manually into deeper tissues. The most accepted method, after autografting, is the use of recombinant human bone morphogenetic protein-2 (BMP-2); however, complications such as interindividual variations, edema, and poor cost-efficiency in supraphysiological doses have been reported. The endogenous synthesis of BMP-2 is desirable, and a molecule which induces this is fibroblast growth factor-18 (FGF-18) because it can upregulate the BMP-2 expression  by supressing noggin. We developed a chitin-poly(lactide-co-glycolide) (PLGA) composite hydrogel by regeneration chemistry and then incorporated CaSO₄ and FGF-18 for this purpose. Rheologically, a 7-fold increase in the elastic modulus was observed in the CaSO₄-incorporated chitin-PLGA hydrogels as compared to the chitin-PLGA hydrogel. Shear-thinning Herschel-Bulkley fluid nature was observed for both hydrogels. Chitin-PLGA/CaSO₄ gel showed sustained release of FGF-18. In vitro osteogenic differentiation showed an enhanced alkaline phosphatase (ALP) expression in the FGF-18-containing chitin-PLGA/CaSO₄ gel when compared to cells alone. Further, it was confirmed by studying the expression of osteogenic genes [RUNX2, ALP, BMP-2, osteocalcin (OCN), and osteopontin (OPN)], immunofluorescence staining of BMP-2, OCN, and OPN, and alizarin red S staining. Incorporation of FGF-18 in the hydrogel increased the endothelial cell migration. Further, the regeneration potential of the prepared hydrogels was tested in vivo, and longitudinal live animal μ-CT was performed. FGF-18-loaded chitin-PLGA/CaSO₄ showed early and almost complete bone healing in comparison with chitin-PLGA/CaSO₄, chitin-PLGA/FGF-18, chitin-PLGA, and sham control systems, as confirmed by hematoxylin and eosin and osteoid tetrachrome stainings. This shows that the CaSO₄ and FGF-18-incorporated hydrogel is a potential candidate for craniofacial bone defect regeneration.

Role of fibroblast growth factors in bone regeneration

Bone is a metabolically active organ that undergoes continuous remodeling throughout life. However, many complex skeletal defects such as large traumatic bone defects or extensive bone loss after tumor resection may cause failure of bone healing. Effective therapies for these conditions typically employ combinations of cells, scaffolds, and bioactive factors. In this review, we pay attention to one of the three factors required for regeneration of bone, bioactive factors, especially the fibroblast growth factor (FGF) family. This family is composed of 22 members and associated with various biological functions including skeletal formation. Based on the phenotypes of genetically modified mice and spatio-temporal expression levels during bone fracture healing, FGF2, FGF9, and FGF18 are regarded as possible candidates useful for bone regeneration. The role of these candidate FGFs in bone regeneration is also discussed in this review.

Physiological Bone Remodeling: Systemic Regulation and Growth Factor Involvement

Bone remodeling is essential for adult bone homeostasis. It comprises two phases: bone formation and resorption. The balance between the two phases is crucial for sustaining bone mass and systemic mineral homeostasis. This review highlights recent work on physiological bone remodeling and discusses our knowledge of how systemic and growth factors regulate this process.

RSPO3-LGR4 Regulates Osteogenic Differentiation Of Human Adipose-Derived Stem Cells Via ERK/FGF Signalling

The four R-spondins (RSPOs) and their three related receptors, LGR4, 5 and 6, have emerged as a major ligand-receptor system with critical roles in development and stem cell survival. However, the exact roles of the RSPO-LGR system in osteogenesis remain largely unknown. In the present study, we showed that RSPO3-shRNA increased the osteogenic potential of human adipose-derived stem cells (hASCs) significantly. Mechanistically, we demonstrated that RSPO3 is a negative regulator of ERK/FGF signalling. We confirmed that inhibition of the ERK1/2 signalling pathway blocked osteogenic differentiation in hASCs, and the increased osteogenic capacity observed after RSPO3 knockdown in hASCs was reversed by inhibition of ERK signalling. Further, silencing of LGR4 inhibited the activity of ERK signalling and osteogenic differentiation of hASCs. Most importantly, we found that loss of LGR4 abrogated RSPO3-regulated osteogenesis and RSPO3-induced ERK1/2 signalling inhibition. Collectively, our data show that ERK signalling works downstream of LGR4 and RSPO3 regulates osteoblastic differentiation of hASCs possibly via the LGR4-ERK signalling.

Bioinformatics analysis on the differentiation of bone mesenchymal stem cells into osteoblasts and adipocytes

The present study aimed to screen several differentially expressed genes (DEGs) and differentially expressed microRNAs (miRNAs) for two types of mesenchymal stem cell (MSC) differentiation. Bone morphogenetic protein 6 (BMP-6) and dexamethasone were used to induce MSCs towards osteoblastic differentiation or adipocytic differentiation. The t-test in the Bioconductor bioinformatics software tool was used to screen DEGs and differentially expressed miRNAs in the two samples. Subsequent gene ontology (GO) and pathway analyses on the DEGs were performed using the GO and Kyoto Encyclopedia of Genes and Genomes databases, respectively; potential target genes for the screened miRNAs were predicted using the TargetScan database. In addition, an interaction network between the DEGs and miRNAs was constructed. Numerous DEGs and miRNAs were screened during osteoblastic and adipocytic differentiation of MSCs. Important pathways, such as glutathione metabolism, pathogenic Escherichia coli infection and Parkinson's disease, and GO terms, including cytoskeletal protein binding and phospholipase inhibitor activity, were enriched in the screened DEGs from MSCs undergoing osteogenic differentiation and adipocytic differentiation. miRNAs, including miRNA (miR)-382 and miR-203, and DEGs, including neuronal growth regulator 1 (NEGR1), phosphatidic acid phosphatase 2B (PPAP2B), platelet-derived growth factor receptor alpha (PDGFRA), interleukin 6 signal transducer (IL6ST) and sortilin 1 (SORT1), were demonstrated to be involved in osteoblastic differentiation. In addition, the downregulated miRNAs (including miR-495, miR-376a and miR-543), the upregulated miR-106a, the upregulated DEGs, including enabled homolog (ENAH), polypeptide N-acetylgalactosaminyltransferase 1 and acyl-CoA synthetase long-chain family member 1, and the downregulated repulsive guidance molecule family member B and semaphorin SEMA7A were demonstrated to be involved in adipocytic differentiation. The results of the present study suggested that miRNAs (miR-203 and miR-382) and DEGs (NEGR1, PPAP2B, PDGFRA, IL6ST and SORT1) may serve pivotal functions in the osteoblastic differentiation of MSCs, whereas miR-495, which is also involved in osteoblast differentiation and had four targets, including NEGR1, miR-376a, miR-543 and ENAH may have crucial roles in adipocytic differentiation of MSCs.

External factors influencing mesenchymal stem cell fate in vitro

Mesenchymal stem cells (MSCs) have extensive potentials, which make them attractive candidates for the developmental biology, drug discovery and regenerative medicine. However, the use of MSCs is limited by their scarceness in tissues and in culture conditions. They also exhibit various degrees of potency which subsequently influencing their applications. Nowadays, questions remain about how self-renewal and differentiation of MSCs can be controlled in vitro and in vivo, how they will behave and migrate to the right place and how they modulate the immune system. Therefore, identification of factors and culture conditions to affect the fate and function of MSCs may be effective to enhance their applications in clinical situations. Studies have indicated that the fate of MSCs in culture is influenced by various external factors, including the specific cell source, donor age, plating density, passage number and plastic surface quality. Some other factors such as cell culture media and their supplementary factors, O₂ concentration, mechano-/electro-stimuli and three-dimensional scaffolds are also shown to be influential. This review addresses the current state of MSC research for describing and discussing the findings about external factors that influence the fate and function of MSCs. Additionally, the new discoveries and suggestions regarding their molecular mechanisms will be explained.

Characterization of FGFR signaling pathway as therapeutic targets for sarcoma patients

The fibroblast growth factor receptor (FGFR) family plays important roles in regulating cell growth, proliferation, survival, differentiation and angiogenesis. Deregulation of the FGF/FGFR signaling pathway has been associated with multiple development syndromes and cancers, and thus therapeutic strategies targeting FGFs and FGFR in human cancer are currently being explored. However, few studies on the FGF/FGFR pathway have been conducted in sarcoma, which has a poor outcome with traditional treatments such as surgery, chemotherapy, and radiotherapy. Hence, in the present review, we provide an overview of the role of the FGF/FGFR pathway signal in sarcoma and FGFR inhibitors, which might be new targets for the treatment of sarcomas according to recent research.

PGE2 maintains self-renewal of human adult stem cells via EP2-mediated autocrine signaling and its production is regulated by cell-to-cell contact

Mesenchymal stem cells (MSCs) possess unique immunomodulatory abilities. Many studies have elucidated the clinical efficacy and underlying mechanisms of MSCs in immune disorders. Although immunoregulatory factors, such as Prostaglandin E₂ (PGE₂), and their mechanisms of action on immune cells have been revealed, their effects on MSCs and regulation of their production by the culture environment are less clear. Therefore, we investigated the autocrine effect of PGE₂ on human adult stem cells from cord blood or adipose tissue, and the regulation of its production by cell-to-cell contact, followed by the determination of its immunomodulatory properties. MSCs were treated with specific inhibitors to suppress PGE₂ secretion, and proliferation was assessed. PGE₂ exerted an autocrine regulatory function in MSCs by triggering E-Prostanoid (EP) 2 receptor. Inhibiting PGE₂ production led to growth arrest, whereas addition of MSC-derived PGE₂ restored proliferation. The level of PGE₂ production from an equivalent number of MSCs was down-regulated via gap junctional intercellular communication. This cell contact-mediated decrease in PGE₂ secretion down-regulated the suppressive effect of MSCs on immune cells. In conclusion, PGE₂ produced by MSCs contributes to maintenance of self-renewal capacity through EP2 in an autocrine manner, and PGE₂ secretion is down-regulated by cell-to-cell contact, attenuating its immunomodulatory potency.

Fibroblast growth factor signaling in skeletal development and disease

Fibroblast growth factor (FGF) signaling pathways are essential regulators of vertebrate skeletal development. FGF signaling regulates development of the limb bud and formation of the mesenchymal condensation and has key roles in regulating chondrogenesis, osteogenesis, and bone and mineral homeostasis. This review updates our review on FGFs in skeletal development published in Genes & Development in 2002, examines progress made on understanding the functions of the FGF signaling pathway during critical stages of skeletogenesis, and explores the mechanisms by which mutations in FGF signaling molecules cause skeletal malformations in humans. Links between FGF signaling pathways and other interacting pathways that are critical for skeletal development and could be exploited to treat genetic diseases and repair bone are also explored.

Biology of Bone Tissue: Structure, Function, and Factors That Influence Bone Cells

Bone tissue is continuously remodeled through the concerted actions of bone cells, which include bone resorption by osteoclasts and bone formation by osteoblasts, whereas osteocytes act as mechanosensors and orchestrators of the bone remodeling process. This process is under the control of local (e.g., growth factors and cytokines) and systemic (e.g., calcitonin and estrogens) factors that all together contribute for bone homeostasis. An imbalance between bone resorption and formation can result in bone diseases including osteoporosis. Recently, it has been recognized that, during bone remodeling, there are an intricate communication among bone cells. For instance, the coupling from bone resorption to bone formation is achieved by interaction between osteoclasts and osteoblasts. Moreover, osteocytes produce factors that influence osteoblast and osteoclast activities, whereas osteocyte apoptosis is followed by osteoclastic bone resorption. The increasing knowledge about the structure and functions of bone cells contributed to a better understanding of bone biology. It has been suggested that there is a complex communication between bone cells and other organs, indicating the dynamic nature of bone tissue. In this review, we discuss the current data about the structure and functions of bone cells and the factors that influence bone remodeling.

p38 mitogen-activated protein kinase inhibits USP22 transcription in HeLa cells

Elevated expression of ubiquitin-specific processing enzyme 22 (USP22) was identified in multiple types of human cancers, and was correlated with tumorigenesis and progression. Despite an increase in the numbers of studies in the physiological function of USP22, little is known regarding the regulation of its expression. The 5' flanking sequence of the USP22 gene was recently characterized. In the present study, USP22 transcription was regulated by p38 mitogen-activated protein kinase (MAPK). Treatment of human cervical carcinoma (HeLa) cells with SB203580, an inhibitor of p38 MAPK, enhanced basal USP22 promoter activity and mRNA abundance. Transfection of MAPK kinase 6 (MKK6), an upstream activator of p38 MAPK, resulted in a 40% decrease in USP22 mRNA, while the dominant negative MKK6 increased the transcription level of the USP22, similar to SB203580. Dual luciferase report assays showed that mutations of the Sp1 binding site ahead of the transcription start site abolished the promoting effect of the USP22 promoter by SB203580. Cisplatin, the activator of p38 MAPK, also suppressed USP22 expression. This suppression was blocked by SB203580. In conclusion, p38 MAPK acts as an upstream negative regulator of USP22 transcription in HeLa cells.

Osteoblast and osteocyte: games without frontiers

The portrait of osteoblasts and osteocytes has been subjected to a revision, since a large body of evidence is attributing these cells amazing roles both inside and outside the bone. The osteoblast, long confined to its bone building function, is actually a very eclectic cell, actively regulating osteoclast formation and function as well as hematopoietic stem cells homeostasis. It is also an endocrine cell, affecting energy metabolism, male fertility and cognition through the release of osteocalcin, a perfect definition-fitting hormone in its uncarboxylated state. As for the osteocytes, many evidence shows that they do not merely represent the final destination of the osteoblasts, but they are instead very active cells that, besides a mechanosensorial function, actively contribute to the bone remodelling by regulating bone formation and resorption. The regulation is exerted by the production of sclerostin (SOST), which in turn inhibits osteoblast differentiation by blocking Wnt/beta-catenin pathway. At the same time, osteocytes influence bone resorption both indirectly, by producing RANKL, which stimulates osteoclastogenesis, and directly by means of a local osteolysis, which is observed especially under pathological conditions. The great versatility of both these cells reflects the complexity of the bone tissue, which has not only a structural role, but influences and is influenced by different organs, taking part in homeostatic and adaptive responses affecting the whole organism.

Divergence of intracellular signaling pathways and early response genes of two closely related fibroblast growth factors, FGF8 and FGF18, in bovine ovarian granulosa cells

Fibroblast growth factors (FGFs) modulate ovarian function, including FGF8 and FGF18. These FGFs activate the same receptors, although FGF18 is unusual in that it increases apoptosis in ovarian granulosa cells whereas the 'typical' response to FGF is increased proliferation. The objective of the present study was to determine which early response genes and pathways are activated by FGF8 and FGF18 in bovine granulosa cells. FGF8 increased abundance of mRNA encoding the FGF-responsive genes SPRY1, SPRY2, SPRY4, NR4A1 and NR4A3 whereas FGF18 did not. FGF8 increased but FGF18 decreased levels of mRNA encoding the growth arrest associated protein, GADD45B. FGF8 increased ERK1/2 phosphorylation but FGF18 did not. Microarray analysis identified EGR1, FOS, FOSL1, BAMBI, XIRP1 and PLK2 as other FGF8 immediate-early response genes, and FGF18 stimulated EGR1, FOSL1, BAMBI and PLK2, but not FOS or XIRP1. This study demonstrates that FGF8 and FGF18 signal through divergent pathways in ovarian granulosa cells, despite reportedly similar receptor activation patterns.

The key regulatory roles of the PI3K/Akt signaling pathway in the functionalities of mesenchymal stem cells and applications in tissue regeneration

Mesenchymal stem cells (MSCs) are multipotent cells that can differentiate into various cell types and have been widely used in tissue engineering application. In tissue engineering, a scaffold, MSCs and growth factors are used as essential components and their interactions have been regarded to be important for regeneration of tissues. A critical problem for MSCs in tissue engineering is their low survival ability and functionality. Most MSCs are going to be apoptotic after transplantation. Therefore, increasing MSC survival ability and functionalities is the key for potential applications of MSCs. Several approaches have been studied to increase MSC tissue forming capacity including application of growth factors, overexpression of stem cell regulatory genes, and improvement of biomaterials for scaffolds. The effects of these approaches on MSCs have been associated with activation of the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway. The pathway plays central regulatory roles in MSC survival, proliferation, migration, angiogenesis, cytokine production, and differentiation. In this review, we summarize and discuss the literatures related to the roles of the PI3K/Akt pathway in the functionalities of MSCs and the involvement of the pathway in biomaterials-increased MSC functionalities. Biomaterials have been modified in their properties and surface structure and loaded with growth factors to increase MSC functionalities. Several studies demonstrated that the biomaterials-increased MSC functionalities are mediated by the activation of the PI3K/Akt pathway.

Tailoring adipose stem cell trophic factor production with differentiation medium components to regenerate chondral defects

Recent endeavors to use stem cells as trophic factor production sources have the potential to translate into viable therapies for damaged or diseased musculoskeletal tissues. Adipose stem cells (ASCs) can be differentiated into chondrocytes using the chondrogenic medium (CM), but it is unknown if this approach can optimize ASC growth factor secretion for cartilage regeneration by increasing the chondrogenic factor production, while decreasing angiogenic and hypertrophic factor production. The objective of this study was to determine the effects the CM and its components have on growth factor production from ASCs to promote cartilage regeneration. ASCs isolated from male Sprague-Dawley rats and cultured in monolayer or alginate microbeads were treated with either the growth medium (GM) or the CM for 5 days. In subsequent studies, ASC monolayers were treated with either the GM supplemented with different combinations of 50 μg/mL ascorbic acid-2-phosphate (AA2P), 100 nM dexamethasone (Dex), 10 ng/mL transforming growth factor (TGF)-β1, and 100 ng/mL bone morphogenetic protein (BMP)-6 or with the CM excluding different combinations of AA2P, Dex, TGF-β1, and BMP-6. mRNA levels and growth factor production were quantified at 8 and 24 h after the last media change, respectively. The CM increased chondrogenic factor secretion (TGF-β2, TGF-β3, and insulin-like growth factor [IGF]-I) and decreased angiogenic factor production (the vascular endothelial growth factor [VEGF]-A, the fibroblast growth factor [FGF]-2). Microencapsulation in the GM increased production of the chondrogenic (IGF-I, TGF-β2) and angiogenic (VEGF-A) factors. AA2P increased secretion of chondrogenic factors (IGF-I, TGF-β2), and decreased angiogenic factor (VEGF-A) secretion, in addition to decreasing mRNA levels for factors associated with chondrocyte hypertrophy (FGF-18). Dex increased mRNA levels for hypertrophic factors (BMP-2, FGF-18) and decreased angiogenic factor secretion (VEGF-A). TGF-β1 increased angiogenic factor production (FGF-2, VEGF-A) and decreased chondrogenic factor mRNA levels (IGF-I, PTHrP). BMP-6 increased hypertrophic mRNA levels (FGF-18) and chondrogenic factor production (TGF-β2). When ASC microbeads preconditioned with the CM were implanted in a focal cartilage defect and immobilized within an RGD-conjugated hydrogel, tissue infiltration from the edges of the defect and perichondrium was observed. These results show that differentiation media components have distinct effects on ASC's production of angiogenic, chondrogenic, and hypertrophic factors and that AA2P may be the most beneficial CM component for preconditioning ASCs to stimulate cartilage regeneration.

Controlled release of dexamethasone from peptide nanofiber gels to modulate inflammatory response

New biomaterials that have the ability to locally suppress an immune response could have broad therapeutic use in the treatment of diseases characterized by acute or chronic inflammation or as a strategy to facilitate improved efficacy in cell or tissue transplantation. We report here on the preparation of a modular peptide amphiphile (PA) capable of releasing an anti-inflammatory drug, dexamethasone (Dex), by conjugation via a labile hydrazone linkage. This molecule self-assembled in water into long supramolecular nanofibers when mixed with a similar PA lacking the drug conjugate, and the addition of calcium salt to screen electrostatic repulsion between nanofibers promoted gel formation. These nanofiber gels demonstrated sustained release of soluble Dex for over one month in physiologic media. The Dex released from these gels maintained its anti-inflammatory activity when evaluated in vitro using a human inflammatory reporter cell line and furthermore preserved cardiomyocyte viability upon induced oxidative stress. The ability of this gel to mitigate the inflammatory response in cell transplantation strategies was evaluated using cell-surrogate polystyrene microparticles suspended in the nanofiber gel that were then subcutaneously injected into mice. Live animal luminescence imaging using the chemiluminescent reporter molecule luminol showed a significant reduction in inflammation at the site where particles were injected with Dex-PA compared to the site of injection for particles within a control PA in the same animal. Histological evidence suggested a marked reduction in the number of infiltrating inflammatory cells when particles were delivered within Dex-PA nanofiber gels, and very little inflammation was observed at either 3 days or 21 days post-implantation. The use of Dex-PA could facilitate localized anti-inflammatory activity as a component of biomaterials designed for various applications in regenerative medicine and could specifically be a useful module for PA-based therapies. More broadly, these studies define a versatile strategy for facile synthesis of self-assembling peptide-based materials with the ability to control drug release.

Investigating the role of FGF18 in the cultivation and osteogenic differentiation of mesenchymal stem cells

Fibroblast growth factor18 (FGF18) belongs to the FGF family and is a pleiotropic protein that stimulates proliferation in several tissues. Bone marrow mesenchymal stem cells (BMSCs) participate in the normal replacement of damaged cells and in disease healing processes within bone and the haematopoietic system. In this study, we constructed FGF18 and investigated its effects on rat BMSCs (rBMSCs). The proliferative effects of FGF18 on rBMSCs were examined using an MTS assay. To validate the osteogenic differentiation effects of FGF18, ALP and mineralization activity were examined as well as osteogenic differentiation-related gene levels. FGF18 significantly enhanced rBMSCs proliferation (p<0.001) and induced the osteogenic differentiation by elevating ALP and mineralization activity of rBMSCs (p<0.001). Furthermore, these osteogenic differentiation effects of FGF18 were confirmed via increasing the mRNA levels of collagen type I (Col I), bone morphogenetic protein 4 (BMP4), and Runt-related transcription factor 2 (Runx2) at 3 and 7 days. These results suggest that FGF18 could be used to improve bone repair and regeneration.

FGF/FGFR signaling in bone formation: progress and perspectives

Fibroblast growth factors (FGFs) are important molecules that control bone formation. FGF act by activating FGF receptors (FGFRs) and downstream signaling pathways that control cells of the osteoblast lineage. Recent advances have been made in the identification of FGF/FGFR signaling pathways that control osteogenesis. Indeed, studies of mouse and human models provided novel insights into the signaling pathways that control bone formation. Genomic studies also highlighted the implication of molecular targets of FGF/FGFR signaling regulating osteoblastogenesis. Recent studies further revealed the important role of crosstalks between FGF/FGFR signaling and other signaling pathways in the regulation of osteogenesis. Finally, the importance of the mechanisms modulating FGFR degradation in the control of osteoblast differentiation has been recently revealed. This short review summarizes the recently described mechanisms underlying FGF/FGFR signaling that are involved in the control of osteoblastogenesis. This knowledge may have potential therapeutic implications in skeletal disorders characterized by abnormal bone formation.