Inhibition of JNK and ERK pathways by SP600125- and U0126-enhanced osteogenic differentiation of bone marrow stromal cells

Bone repair and key signalling pathways for cell-based bone regenerative therapy: A review

Advances in cell-based regenerative therapy create new opportunities for the treatment of bone-related disorders and injuries, by improving the reparative phase of bone healing. Apart from the classical approach of bone grafting, the application of cell-based therapies, particularly stem cells (SCs), has gained a lot of attention in recent years. SCs play an important role in regenerative therapy due to their excellent ability to differentiate into bone-forming cells. Regeneration of new bone is regulated by a wide variety of signalling molecules and intracellular networks, which are responsible for coordinating cellular processes. The activated signalling cascade is significantly involved in cell survival, proliferation, apoptosis, and interaction with the microenvironment and other types of cells within the healing site. Despite the increasing evidence from studies conducted on signalling pathways associated with bone formation, the exact mechanism involved in controlling the differentiation stage of transplanted cells is not well understood. Identifying the key activated pathways involved in bone regeneration may allow for precise manipulation of the relevant signalling molecules within the progenitor cell population to accelerate the healing process. The in-depth knowledge of molecular mechanisms would be advantageous in improving the efficiency of personalised medicine and targeted therapy in regenerative medicine. In this review, we briefly introduce the theory of bone repair mechanism and bone tissue engineering followed by an overview of relevant signalling pathways that have been identified to play an important role in cell-based bone regenerative therapy.

MAPK Pathway under Chronic Copper Excess in Green Macroalgae (Chlorophyta): Influence on Metal Exclusion/Extrusion Mechanisms and Photosynthesis

There is currently no information regarding the role that whole mitogen activated protein kinase (MAPK) pathways play in counteracting environmental stress in photosynthetic organisms. To address this gap, we exposed Ulva compressa to chronic levels of copper (10 µM) specific inhibitors of Extracellular Signal Regulated Kinases (ERK), c-Jun N-terminal Kinases (JNK), and Cytokinin Specific Binding Protein (p38) MAPKs alone or in combination. Intracellular copper accumulation and photosynthetic activity (in vivo chlorophyll a fluorescence) were measured after 6 h, 24 h, 48 h, and 6 days of exposure. By day 6, when one (except JNK) or more of the MAPK pathways were inhibited under copper stress, there was a decrease in copper accumulation compared with algae exposed to copper alone. When at least two MAPKs were blocked, there was a decrease in photosynthetic activity expressed in lower productivity (ETRmax), efficiency (αETR), and saturation of irradiance (EkETR), accompanied by higher non-photochemical quenching (NPQmax), compared to both the control and copper-only treatments. In terms of accumulation, once the MAPK pathways were partially or completely blocked under copper, there was crosstalk between these and other signaling mechanisms to enhance metal extrusion/exclusion from cells. Crosstalk occurred among MAPK pathways to maintain photosynthesis homeostasis, demonstrating the importance of the signaling pathways for physiological performance. This study is complemented by a parallel/complementary article Rodríguez-Rojas et al. on the role of MAPKs in copper-detoxification.

Induction of Fibrogenic Phenotype in Human Mesenchymal Stem Cells by Connective Tissue Growth Factor in a Hydrogel Model of Soft Connective Tissue

Scar formation is the typical endpoint of wound healing in adult mammalian tissues. An overactive or prolonged fibrogenic response following injury leads to excessive deposition of fibrotic proteins that promote tissue contraction and scar formation. Although well-defined in the dermal tissue, the progression of fibrosis is less explored in other connective tissues, such as the vocal fold. To establish a physiologically relevant 3D model of loose connective tissue fibrosis, we have developed a synthetic extracellular matrix using hyaluronic acid (HA) and peptidic building blocks carrying complementary functional groups. The resultant network was cell adhesive and protease degradable, exhibiting viscoelastic properties similar to the human vocal fold. Human mesenchymal stem cells (hMSCs) were encapsulated in the HA matrix as single cells or multicellular aggregates and cultured in pro-fibrotic media containing connective tissue growth factor (CTGF) for up to 21 days. hMSCs treated with CTGF-supplemented media exhibited an increased expression of fibrogenic markers and ECM proteins associated with scarring. Incorporation of α-smooth muscle actin into F-actin stress fibers was also observed. Furthermore, CTGF treatment increased the migratory capacity of hMSCs as compared to the CTGF-free control groups, indicative of the development of a myofibroblast phenotype. Addition of an inhibitor of the mitogen-activated protein kinase (MAPK) pathway attenuated cellular expression of fibrotic markers and related ECM proteins. Overall, this study demonstrates that CTGF promotes the development of a fibrogenic phenotype in hMSCs encapsulated within an HA matrix and that the MAPK pathway is a potential target for future therapeutic endeavors towards limiting scar formation in loose connective tissues.

Epiregulin enhances odontoblastic differentiation of dental pulp stem cells via activating MAPK signalling pathway

Objectives

The odontoblastic differentiation of dental pulp stem cells (DPSCs) contributes to tertiary dentin formation. Our previous study indicated that epiregulin (EREG) enhanced odontogenesis potential of dental pulp. Here, we explored the effects of EREG during DPSC odontoblastic differentiation.

Methods

The changes in EREG were detected during tertiary dentin formation. DPSCs were treated with recombinant human EREG (rhEREG), EREG receptor inhibitor gefitinib and short hairpin RNAs. The odontoblastic differentiation was assessed with ALP staining, ALP activity assay, alizarin red S staining and real‐time RT‐PCR of DSPP, OCN, RUNX2 and OSX. Western blot was conducted to examine the levels of p38 mitogen‐activated protein kinase (p38 MAPK), c‐Jun N‐terminal kinase (JNK) and extracellular signal‐regulated kinase 1/2 (Erk1/2). The expression of EREG and odontoblastic differentiation‐related markers was investigated in human dental pulp from teeth with deep caries and healthy teeth.

Results

Epiregulin was upregulated during tertiary dentin formation. rhEREG enhanced the odontoblastic differentiation of DPSCs following upregulated p38 MAPK and Erk1/2 phosphorylation, but not JNK, whereas depletion of EREG suppressed DPSC differentiation. Gefitinib decreased odontoblastic differentiation with decreased phosphorylation of p38 MAPK and Erk1/2. And suppression of p38 MAPK and Erk1/2 pathways attenuated DPSC differentiation. In human dental pulp tissue, EREG upregulation in deep caries correlates with odontoblastic differentiation enhancement.

Conclusion

Epiregulin is released during tertiary dentin formation. And EREG enhanced DPSC odontoblastic differentiation via MAPK pathways.

BMP2/7 heterodimer enhances osteogenic differentiation of rat BMSCs via ERK signaling compared with respective homodimers

Bone morphogenetic protein (BMP)2/7 heterodimer shows greater efficacy in enhancing bone regeneration. However, the precise mechanism and the role of mitogen-activated protein kinase (MAPK) signaling network in BMP2/7-driven osteogenesis remain ambiguous. In this study, we evaluated the effects of BMP2/7 heterodimers on osteoblastic differentiation in rat bone marrow mesenchymal stem cells (BMSCs), with the aim to elaborate how MAPKs might be involved in this cellular process by treatment of rat BMSCs with BMP2/-7 with a special signal-pathway inhibitor. We found that BMP2/7 heterodimer induced a much stronger osteogenic response in rat BMSCs compared with either homodimer. Most interestingly, extracellular signal-regulated kinase (ERK) demonstrated a highly sustained phosphorylation and activation in the BMP2/7 heterodimer treatment groups, and inhibition of ERK cascades using U0126 special inhibitor that significantly reduced the activity of ALP and calcium mineralization to a substantial degree in rat BMSCs treated with BMP2/7 heterodimers. Collectively, we demonstrate that BMP2/7 heterodimer shows a potent ability to stimulate osteogenesis in rat BMSCs. The activated ERK signaling pathway involved in this process may contribute partially to an increased osteogenic potency of heterodimeric BMP2/7 growth factors.

GSK-3 inhibitors enhance TRAIL-mediated apoptosis in human gastric adenocarcinoma cells

Resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis has been reported in some cancer cells, including AGS human gastric adenocarcinoma cells. Reducing this resistance might shed light on the treatment of human gastric adenocarcinoma. In this study, we examined whether glycogen synthase kinase-3 (GSK-3) inhibitors can restore TRAIL responsiveness in gastric adenocarcinoma cells. The effect of two GSK-3 inhibitors, SB-415286, and LiCl, on apoptosis signaling of TRAIL in human gastric adenocarcinoma cell lines and primary gastric epithelial cells was analyzed. Both inhibitors can sensitize gastric adenocarcinoma cells, but not primary gastric epithelial cells, to TRAIL-induced apoptosis by increasing caspase-8 activity and its downstream signal transmission. Adding p53 siRNA can downregulate GSK-3 inhibitor-related sensitization to TRAIL-induced apoptosis and caspase-3 activity. GSK-3 inhibitors strongly activate the phosphorylation of JNK. Inhibition of JNK leads to earlier and more intense apoptosis, showing that the activation of JNK may provide anti-apoptotic equilibrium of pro-apoptotic cells. Our observations indicate that GSK-3 inhibitors can sentize AGS gastric adenocarcinoma cells to TRAIL-induced apoptosis. Therefore, in certain types of gastric adenocarcinoma, GSK-3 inhibitor might enhance the antitumor activity of TRAIL and mightbe a promising candidate for the treatment of certain types of gastric adenocarcinoma.

Influence of collagen-based integrin α1 and α2 mediated signaling on human mesenchymal stem cell osteogenesis in three dimensional contexts

Collagen I interactions with integrins α1 and α2 are known to support human mesenchymal stem cell (hMSC) osteogenesis. Nonetheless, elucidating the relative impact of specific integrin interactions has proven challenging, in part due to the complexity of native collagen. In the present work, we employed two collagen-mimetic proteins-Scl2-2 and Scl2-3- to compare the osteogenic effects of integrin α1 versus α2 signaling. Scl2-2 and Scl2-3 were both derived from Scl2-1, a triple helical protein lacking known cell adhesion, cytokine binding, and matrix metalloproteinase sites. However, Scl2-2 and Scl2-3 were each engineered to display distinct collagen-based cell adhesion motifs: GFPGER (binding integrins α1 and α2 ) or GFPGEN (binding only integrin α1 ), respectively. hMSCs were cultured within poly(ethylene glycol) (PEG) hydrogels containing either Scl2-2 or Scl2-3 for 2 weeks. PEG-Scl2-2 gels were associated with increased hMSC osterix expression, osteopontin production, and calcium deposition relative to PEG-Scl2-3 gels. These data indicate that integrin α2 signaling may have an increased osteogenic effect relative to integrin α1 . Since p38 is activated by integrin α2 but not by integrin α1 , hMSCs were further cultured in PEG-Scl2-2 hydrogels in the presence of a p38 inhibitor. Results suggest that p38 activity may play a key role in collagen-supported hMSC osteogenesis. This knowledge can be used toward the rational design of scaffolds which intrinsically promote hMSC osteogenesis. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2594-2604, 2018.

ERK signaling is required for VEGF-A/VEGFR2-induced differentiation of porcine adipose-derived mesenchymal stem cells into endothelial cells

Background

Cell-based therapy that can rejuvenate the endothelium with stimulated adipose-derived mesenchymal stem cells (AMSCs) is a promising therapeutic strategy for the re-endothelialization of denuded arteries at the stenting site. Previously, we have shown that silencing of MMP-2 and MMP-14 inhibits vascular endothelial growth factor receptor type 2 (VEGFR2) cleavage, and induces differentiation of AMSCs toward the endothelial cell (EC) lineage. In this study, we examined the underlying signaling pathways that regulate differentiation of AMSCs to ECs in vitro through VEGFR2.

Methods

AMSCs were isolated from porcine abdominal adipose tissue. The isolated AMSCs were characterized by positive expression of CD29, CD44, and CD90 and negative expression of CD11b and CD45. The isolated MSCs were transfected with siRNA to silence MMP-2, MMP-14, and angiotensin receptor 2 (ATR2). Cells were suspended either in endothelial basal media (EBM) or endothelial growth media (EGM) with various treatments. Flow cytometry was performed to examine the expression of EC markers, and western blot analysis was performed to examine the expression and activity of various kinases. Scratch assay was performed to examine the cell migration. Data were analyzed by ANOVA using PRISM GraphPad.

Results

After 10 days of stimulation for EC differentiation, the morphology of AMSCs changed to a morphology similar to that of ECs. Silencing MMP-2 and MMP-14 resulted in significant decrease in the number of migrated cells compared with the EGM-only group. ATR2 siRNA transfection did not affect the migration and differentiation of AMSCs to ECs. Stimulation of AMSCs for EC differentiation with or without MMP-2 or MMP-14 siRNA resulted in significant increase in p-ERK, and significant decrease in p-JNK. There was no significant change in p-p38 in all three groups compared with the EBM group. ERK inhibition resulted in significant decrease in the expression of EC markers in the EGM, EGM + MMP-2 siRNA, and EGM + MMP-14 siRNA groups. The VEGFR2 kinase inhibitor induced a dose-dependent inhibition of ERK.

Conclusion

The ERK signaling pathway is critical for VEGF-A/VEGFR2-induced differentiation of AMSCs into ECs. These findings provide new insights into the role of the ERK signaling pathway in AMSC differentiation to ECs for potential clinical use in cardiovascular diseases.

Impact of the source and serial passaging of goat mesenchymal stem cells on osteogenic differentiation potential: implications for bone tissue engineering

BACKGROUND

Adult mesenchymal stem cells (MSCs) can be conveniently sampled from bone marrow, peripheral blood, muscle, adipose and connective tissue, harvested from various species, including, rodents, dogs, cats, horses, sheep, goats and human beings. The MSCs isolated from adult tissues vary in their morphological and functional properties. These variations are further complicated when cells are expanded by passaging in culture. These differences and changes in MSCs must be considered prior to their application in the clinic or in a basic research study. Goats are commonly used as animal models for bone tissue engineering to test the potential of stem cells for bone regeneration. As a result, goat MSCs isolated from bone marrow or adipose tissue should be evaluated using in vitro assays, prior to their application in a tissue engineering project.

RESULTS

In this study, we compared the stem cell properties of MSCs isolated from goat bone marrow and adipose tissue. We used quantitative and qualitative assays with a focus on osteogenesis, including, colony forming unit, rate of cell proliferation, tri-lineage differentiation and expression profiling of key signal transduction proteins to compare MSCs from low and high passages. Primary cultures generated from each source displayed the stem cell characteristics, with variations in their osteogenic potentials. Most importantly, low passaged bone marrow MSCs displayed a significantly higher and superior osteogenic potential, and hence, will be the preferred choice for bone tissue engineering in future in vivo experiments. In the bone marrow MSCs, this process is potentially mediated by the p38 MAPK pathway. On the other hand, osteogenic differentiation in the adipose tissue MSCs may involve the p44/42 MAPK pathway.

CONCLUSIONS

Based on these data, we can conclude that bone marrow and fat-derived MSCs undergo osteogenesis via two distinct signaling pathways. Even though the bone marrow MSCs are the preferred source for bone tissue engineering, the adipose tissue MSCs are an attractive alternative source and undergo osteo-differentiation differently from the bone marrow MSCs and hence, might require a cell-based enhancer/inducer to improve their osteogenic regenerative capacity.

Activation of the Extracellular Signal-Regulated Kinase Signaling Is Critical for Human Umbilical Cord Mesenchymal Stem Cell Osteogenic Differentiation

Human umbilical cord mesenchymal stem cells (hUCMSCs) are recognized as candidate progenitor cells for bone regeneration. However, the mechanism of hUCMSC osteogenesis remains unclear. In this study, we revealed that mitogen-activated protein kinases (MAPKs) signaling is involved in hUCMSC osteogenic differentiation in vitro. Particularly, the activation of c-Jun N-terminal kinases (JNK) and p38 signaling pathways maintained a consistent level in hUCMSCs through the entire 21-day osteogenic differentiation period. At the same time, the activation of extracellular signal-regulated kinases (ERK) signaling significantly increased from day 5, peaked at day 9, and declined thereafter. Moreover, gene profiling of osteogenic markers, alkaline phosphatase (ALP) activity measurement, and alizarin red staining demonstrated that the application of U0126, a specific inhibitor for ERK activation, completely prohibited hUCMSC osteogenic differentiation. However, when U0126 was removed from the culture at day 9, ERK activation and osteogenic differentiation of hUCMSCs were partially recovered. Together, these findings demonstrate that the activation of ERK signaling is essential for hUCMSC osteogenic differentiation, which points out the significance of ERK signaling pathway to regulate the osteogenic differentiation of hUCMSCs as an alternative cell source for bone tissue engineering.

The Effects of the Endocannabinoids Anandamide and 2-Arachidonoylglycerol on Human Osteoblast Proliferation and Differentiation

The endocannabinoid system is expressed in bone, although its role in the regulation of bone growth is controversial. Many studies have examined the effect of endocannabinoids directly on osteoclast function, but few have examined their role in human osteoblast function, which was the aim of the present study. Human osteoblasts were treated from seeding with increasing concentrations of anandamide or 2-arachidonoylglycerol for between 1 and 21 days. Cell proliferation (DNA content) and differentiation (alkaline phosphatase (ALP), collagen and osteocalcin secretion and calcium deposition) were measured. Anandamide and 2-arachidonoylglycerol significantly decreased osteoblast proliferation after 4 days, associated with a concentration-dependent increase in ALP. Inhibition of endocannabinoid degradation enzymes to increase endocannabinoid tone resulted in similar increases in ALP production. 2-arachidonoylglycerol also decreased osteocalcin secretion. After prolonged (21 day) treatment with 2-arachidonoylglycerol, there was a decrease in collagen content, but no change in calcium deposition. Anandamide did not affect collagen or osteocalcin, but reduced calcium deposition. Anandamide increased levels of phosphorylated CREB, ERK 1/2 and JNK, while 2-arachidonoylglycerol increased phosphorylated CREB and Akt. RT-PCR demonstrated the expression of CB2 and TRPV1, but not CB1 in HOBs. Anandamide-induced changes in HOB differentiation were CB1 and CB2-independent and partially reduced by TRPV1 antagonism, and reduced by inhibition of ERK 1/2 and JNK. Our results have demonstrated a clear involvement of anandamide and 2-arachidonoylglycerol in modulating the activity of human osteoblasts, with anandamide increasing early cell differentiation and 2-AG increasing early, but decreasing late osteoblast-specific markers of differentiation.

Flavonoid 4'-O-Methylkuwanon E from Morus alba Induces the Differentiation of THP-1 Human Leukemia Cells

Aims. In this work we studied cytodifferentiation effects of newly characterized prenyl flavonoid 4′-O-methylkuwanon E (4ME) isolated from white mulberry (Morus alba L.). Main Methods. Cell growth and viability were measured by dye exclusion assay; cell cycle and surface antigen CD11b were monitored by flow cytometry. For the cytodifferentiation of cells the NBT reduction assay was employed. Regulatory proteins were assessed by western blotting. Key Findings. 4ME induced dose-dependent growth inhibition of THP-1 cells, which was not accompanied by toxic effect. Inhibition of cells proliferation caused by 4ME was associated with the accumulation in G1 phase and with downregulation of hyperphosphorylated pRb. Treatment with 4ME led to significant induction of NBT-reducing activity of PMA stimulated THP-1 cells and upregulation expression of differentiation-associated surface antigen CD11b. Our results suggest that monocytic differentiation induced by 4ME is connected with up-regulation of p38 kinase activity. Significance. Our study provides the first evidence that 4ME induces the differentiation of THP-1 human monocytic leukemia cells and thus is a potential cytodifferentiating anticancer agent.

Skeletal (stromal) stem cells: an update on intracellular signaling pathways controlling osteoblast differentiation

Skeletal (marrow stromal) stem cells (BMSCs) are a group of multipotent cells that reside in the bone marrow stroma and can differentiate into osteoblasts, chondrocytes and adipocytes. Studying signaling pathways that regulate BMSC differentiation into osteoblastic cells is a strategy for identifying druggable targets for enhancing bone formation. This review will discuss the functions and the molecular mechanisms of action on osteoblast differentiation and bone formation; of a number of recently identified regulatory molecules: the non-canonical Notch signaling molecule Delta-like 1/preadipocyte factor 1 (Dlk1/Pref-1), the Wnt co-receptor Lrp5 and intracellular kinases. This article is part of a Special Issue entitled: Stem Cells and Bone.

Combined MEK inhibition and BMP2 treatment promotes osteoblast differentiation and bone healing in Nf1Osx -/- mice

Neurofibromatosis type I (NF1) is an autosomal dominant disease with an incidence of 1/3000, caused by mutations in the NF1 gene, which encodes the RAS/GTPase-activating protein neurofibromin. Non-bone union after fracture (pseudarthrosis) in children with NF1 remains a challenging orthopedic condition to treat. Recent progress in understanding the biology of neurofibromin suggested that NF1 pseudarthrosis stems primarily from defects in the bone mesenchymal lineage and hypersensitivity of hematopoietic cells to TGFβ. However, clinically relevant pharmacological approaches to augment bone union in these patients remain limited. In this study, we report the generation of a novel conditional mutant mouse line used to model NF1 pseudoarthrosis, in which Nf1 can be ablated in an inducible fashion in osteoprogenitors of postnatal mice, thus circumventing the dwarfism associated with previous mouse models where Nf1 is ablated in embryonic mesenchymal cell lineages. An ex vivo-based cell culture approach based on the use of Nf1(flox/flox) bone marrow stromal cells showed that loss of Nf1 impairs osteoprogenitor cell differentiation in a cell-autonomous manner, independent of developmental growth plate-derived or paracrine/hormonal influences. In addition, in vitro gene expression and differentiation assays indicated that chronic ERK activation in Nf1-deficient osteoprogenitors blunts the pro-osteogenic property of BMP2, based on the observation that only combination treatment with BMP2 and MEK inhibition promoted the differentiation of Nf1-deficient osteoprogenitors. The in vivo preclinical relevance of these findings was confirmed by the improved bone healing and callus strength observed in Nf1osx (-/-) mice receiving Trametinib (a MEK inhibitor) and BMP2 released locally at the fracture site via a novel nanoparticle and polyglycidol-based delivery method. Collectively, these results provide novel evidence for a cell-autonomous role of neurofibromin in osteoprogenitor cells and insights about a novel targeted approach for the treatment of NF1 pseudoarthrosis.

Inhibition of apoptosis signal-regulating kinase 1 enhances endochondral bone formation by increasing chondrocyte survival

Endochondral ossification is the result of chondrocyte differentiation, hypertrophy, death and replacement by bone. The careful timing and progression of this process is important for normal skeletal bone growth and development, as well as fracture repair. Apoptosis Signal-Regulating Kinase 1 (ASK1) is a mitogen-activated protein kinase (MAPK), which is activated by reactive oxygen species and other cellular stress events. Activation of ASK1 initiates a signaling cascade known to regulate diverse cellular events including cytokine and growth factor signaling, cell cycle regulation, cellular differentiation, hypertrophy, survival and apoptosis. ASK1 is highly expressed in hypertrophic chondrocytes, but the role of ASK1 in skeletal tissues has not been investigated. Herein, we report that ASK1 knockout (KO) mice display alterations in normal growth plate morphology, which include a shorter proliferative zone and a lengthened hypertrophic zone. These changes in growth plate dynamics result in accelerated long bone mineralization and an increased formation of trabecular bone, which can be attributed to an increased resistance of terminally differentiated chondrocytes to undergo cell death. Interestingly, under normal cell culture conditions, mouse embryonic fibroblasts (MEFs) derived from ASK1 KO mice show no differences in either MAPK signaling or osteogenic or chondrogenic differentiation when compared with wild-type (WT) MEFs. However, when cultured with stress activators, H₂O₂ or staurosporine, the KO cells show enhanced survival, an associated decrease in the activation of proteins involved in death signaling pathways and a reduction in markers of terminal differentiation. Furthermore, in both WT mice treated with the ASK1 inhibitor, NQDI-1, and ASK1 KO mice endochondral bone formation was increased in an ectopic ossification model. These findings highlight a previously unrealized role for ASK1 in regulating endochondral bone formation. Inhibition of ASK1 has clinical potential to treat fractures or to slow osteoarthritic progression by enhancing chondrocyte survival and slowing hypertrophy.