Sonic hedgehog protein promotes proliferation and chondrogenic differentiation of bone marrow-derived mesenchymal stem cells in vitro

Establishment of a mandible defect model in rabbits infected with multiple bacteria and bioinformatics analysis

Objective: A model of chronic infectious mandibular defect (IMD) caused by mixed infection with Staphylococcus aureus and Pseudomonas aeruginosa was established to explore the occurrence and development of IMD and identify key genes by transcriptome sequencing and bioinformatics analysis. Methods: S. aureus and P. aeruginosa were diluted to 3 × 108 CFU/mL, and 6 × 3 × 3 mm defects lateral to the Mandibular Symphysis were induced in 28 New Zealand rabbits. Sodium Morrhuate (0.5%) and 50 μL bacterial solution were injected in turn. The modeling was completed after the bone wax closed; the effects were evaluated through postoperative observations, imaging and histological analyses. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, and protein‒protein interaction (PPI) network analyses were performed to investigate the function of the differentially expressed genes (DEGs). Results: All rabbits showed characteristics of infection. The bacterial cultures were positive, and polymerase chain reaction (PCR) was used to identify S. aureus and P. aeruginosa. Cone beam CT and histological analyses showed inflammatory cell infiltration, pus formation in the medullary cavity, increased osteoclast activity in the defect area, and blurring at the edge of the bone defect. Bioinformatics analysis showed 1,804 DEGs, 743 were upregulated and 1,061 were downregulated. GO and KEGG analyses showed that the DEGs were enriched in immunity and osteogenesis inhibition, and the core genes identified by the PPI network were enriched in the Hedgehog pathway, which plays a role in inflammation and tissue repair; the MEF2 transcription factor family was predicted by IRegulon. Conclusion: By direct injection of bacterial solution into the rabbit mandible defect area, the rabbit chronic IMD model was successfully established. Based on the bioinformatics analysis, we speculate that the Hedgehog pathway and the MEF2 transcription factor family may be potential intervention targets for repairing IMD.

Role of Hedgehog Signaling Pathways in Multipotent Mesenchymal Stem Cells Differentiation

Multipotent mesenchymal stem cells (MSCs) have high self-renewal and multi-lineage differentiation potentials and low immunogenicity, so they have attracted much attention in the field of regenerative medicine and have a promising clinical application. MSCs originate from the mesoderm and can differentiate not only into osteoblasts, cartilage, adipocytes, and muscle cells but also into ectodermal and endodermal cell lineages across embryonic layers. To design cell therapy for replacement of damaged tissues, it is essential to understand the signaling pathways, which have a major impact on MSC differentiation, as this will help to integrate the signaling inputs to initiate a specific lineage. Hedgehog (Hh) signaling plays a vital role in the development of various tissues and organs in the embryo. As a morphogen, Hh not only regulates the survival and proliferation of tissue progenitor and stem populations but also is a critical moderator of MSC differentiation, involving tri-lineage and across embryonic layer differentiation of MSCs. This review summarizes the role of Hh signaling pathway in the differentiation of MSCs to mesodermal, endodermal, and ectodermal cells.

Targeting the hedgehog signaling pathway to improve tendon-to-bone integration

OBJECTIVE

While the role of hedgehog (Hh) signaling in promoting zonal fibrocartilage production during development is well-established, whether this pathway can be leveraged to improve tendon-to-bone repair in adults is unknown. Our objective was to genetically and pharmacologically stimulate the Hh pathway in cells that give rise to zonal fibrocartilaginous attachments to promote tendon-to-bone integration.

DESIGN

Hh signaling was stimulated genetically via constitutive Smo (SmoM2 construct) activation of bone marrow stromal cells or pharmacologically via systemic agonist delivery to mice following anterior cruciate ligament reconstruction (ACLR). To assess tunnel integration, we measured mineralized fibrocartilage (MFC) formation in these mice 28 days post-surgery and performed tunnel pullout testing.

RESULTS

Hh pathway-related genes increased in cells forming the zonal attachments in wild-type mice. Both genetic and pharmacologic stimulation of the Hh pathway increased MFC formation and integration strength 28 days post-surgery. We next conducted studies to define the role of Hh in specific stages of the tunnel integration process. We found Hh agonist treatment increased the proliferation of the progenitor pool in the first week post-surgery. Additionally, genetic stimulation led to continued MFC production in the later stages of the integration process. These results indicate that Hh signaling plays an important biphasic role in cell proliferation and differentiation towards fibrochondrocytes following ACLR.

CONCLUSION

This study reveals a biphasic role for Hh signaling during the tendon-to-bone integration process after ACLR. In addition, the Hh pathway is a promising therapeutic target to improve tendon-to-bone repair outcomes.

Sequential application of small molecule therapy enhances chondrogenesis and angiogenesis in murine segmental defect bone repair

The increasing incidence of physiologic/pathologic conditions that impair the otherwise routine healing of endochondral bone fractures and the occurrence of severe bone injuries necessitate novel approaches to enhance clinically challenging bone fracture repair. To promote the healing of nonunion fractures, we tested an approach that used two small molecules to sequentially enhance cartilage development and conversion to the bone in the callus of a murine femoral segmental defect nonunion model of bone injury. Systemic injections of smoothened agonist 21k (SAG21k) were used to stimulate chondrogenesis through the activation of the sonic hedgehog (SHH) pathway early in bone repair, while injections of the prolyl hydroxylase domain (PHD)2 inhibitor, IOX2, were used to stimulate hypoxia signaling-mediated endochondral bone formation. The expression of SHH pathway genes and Phd2 target genes was increased in chondrocyte cell lines in response to SAG21k and IOX2 treatment, respectively. The segmental defect responded to sequential systemic administration of these small molecules with increased chondrocyte expression of PTCH1, GLI1, and SOX9 in response to SAG and increased expression of hypoxia-induced factor-1α and vascular endothelial growth factor-A in the defect tissues in response to IOX2. At 6 weeks postsurgery, the combined SAG-IOX2 therapy produced increased bone formation in the defect with the bony union over the injury. Clinical significance: This therapeutic approach was successful in promoting cartilage and bone formation within a critical-size segmental defect and established the utility of a sequential small molecule therapy for the enhancement of fracture callus development in clinically challenging bone injuries.

Altered Expression of the Hedgehog Pathway Proteins BMP2, BMP4, SHH, and IHH Involved in Knee Cartilage Damage of Patients With Osteoarthritis and Kashin-Beck Disease

OBJECTIVE

To investigate the expression of Hedgehog (HH) signaling pathway proteins in knee articular cartilage from Kashin-Beck disease (KBD) and osteoarthritis (OA) patients.

METHODS

Knee articular cartilage samples were collected from normal (N), OA, and KBD adults (aged 38-60 years) and divided into 3 groups with 6 subjects in each group. The localization of the HH pathway proteins bone morphogenetic protein 2 (BMP2), bone morphogenetic protein 4 (BMP4), Sonic hedgehog (SHH), and Indian hedgehog (IHH) was observed with the microscope after immunohistochemical (IHC) staining. Positive staining cell rates of each proteins were compared.

RESULTS

The strongest stainings of all proteins were observed in the middle zones of all 3 groups. The positive staining rates of BMP4 and IHH were significantly lower in the OA and KBD groups than those in the N group in all 3 zones. The positive staining rates of BMP2 and SHH tend to be lower in the OA and KBD groups than those in the N group in the deep zone, while higher in the OA and KBD groups than those in the N group in superficial and middle zones.

CONCLUSIONS

Altered expression of the HH pathway proteins BMP2, BMP4, SHH, and IHH was found in OA and KBD articular cartilage. There seemed to be a compensatory effect between SHH and IHH in cartilage damage. Further studies on the pathogenesis of OA and KBD may be carried out from these aspects in the future.

Synergistic effects of Indian hedgehog and sonic hedgehog on chondrogenesis during cartilage repair

Sonic hedgehog (Shh) and Indian hedgehog (Ihh) have been shown to control the induction of early cartilaginous differentiation. However, it is unclear whether Ihh and Shh exert synergistic effects on chondrogenesis during articular cartilage repair. Herein, we investigate the effects of chondrogenesis of bone-derived mesenchymal stem cells (BMSCs) following co-transfection with Shh and Ihh via adenoviral vectors in vitro and in vivo. A rotary cell culture system (RCCS) and Cytodex 3 microcarriers were used to create a stereoscopic dynamic environment for cell culture. In the RCCS environment, BMSCs co-transfected with Ihh and Shh displayed stronger chondrogenic differentiation and chondrogenesis than BMSCs transfected with Ihh or Shh alone, and exhibited higher expression levels of Sox 9, ACAN and collagen II, stronger toluidine blue and collagen II immunohistochemical staining. After transplanted into the osteochondral defect at 8 weeks, Ihh/Shh co-transfected BMSCs showed a significantly better cartilage repair than BMSCs transfected with Ihh or Shh alone. Ihh and Shh have synergistic effects on the induction of chondrogenic differentiation and chondrogenesis under a microgravity environment, and help to repair damaged cartilage and reverse subchondral defects during the early stages.

Small molecules for mesenchymal stem cell fate determination

Mesenchymal stem cells (MSCs) are adult stem cells harboring self-renewal and multilineage differentiation potential that are capable of differentiating into osteoblasts, adipocytes, or chondrocytes in vitro, and regulating the bone marrow microenvironment and adipose tissue remodeling in vivo. The process of fate determination is initiated by signaling molecules that drive MSCs into a specific lineage. Impairment of MSC fate determination leads to different bone and adipose tissue-related diseases, including aging, osteoporosis, and insulin resistance. Much progress has been made in recent years in discovering small molecules and their underlying mechanisms control the cell fate of MSCs both in vitro and in vivo. In this review, we summarize recent findings in applying small molecules to the trilineage commitment of MSCs, for instance, genistein, medicarpin, and icariin for the osteogenic cell fate commitment; isorhamnetin, risedronate, and arctigenin for pro-adipogenesis; and atractylenolides and dihydroartemisinin for chondrogenic fate determination. We highlight the underlying mechanisms, including direct regulation, epigenetic modification, and post-translational modification of signaling molecules in the AMPK, MAPK, Notch, PI3K/AKT, Hedgehog signaling pathways etc. and discuss the small molecules that are currently being studied in clinical trials. The target-based manipulation of lineage-specific commitment by small molecules offers substantial insights into bone marrow microenvironment regulation, adipose tissue homeostasis, and therapeutic strategies for MSC-related diseases.

Sonic hedgehog promotes chondrogenesis of rabbit bone marrow stem cells in a rotary cell culture system

BACKGROUND

Sonic hedgehog (Shh) is an important signalling protein involved in the induction of early cartilaginous differentiation. Herein, we demonstrate that Shh markedly induces chondrogenesis of rabbit bone marrow stromal cells (BMSCs) under microgravity conditions, and promotes cartilage regeneration.

RESULTS

In the rotary cell culture system (RCCS), chondrogenic differentiation was revealed by stronger Toluidine Blue and collagen II immunohistochemical staining in the Shh transfection group, and chondroinductive activity of Shh was equivalent to that of TGF-β. Western blotting and qRT-PCR analysis results verified the stronger expression of Sox9, aggrecan (ACAN), and collagen II in rabbit BMSCs treated with Shh or TGF-β in a microgravity environment. Low levels of chondrogenic hypertrophy, osteogenesis, and adipogenesis-related factors were detected in all groups. After transplantation in vivo, histological analysis revealed a significant improvement in cartilage and subchondral repair in the Shh transfection group.

CONCLUSIONS

These results suggested that Shh signalling promoted chondrogenesis in rabbit BMSCs under microgravity conditions equivalent to TGF-β, and improved the early stages of the repair of cartilage and subchondral defects. Furthermore, RCCS provided a dynamic culture microenvironment conducive for cell proliferation, aggregation and differentiation.

Function and regulation of transforming growth factor β1 signalling in antler chondrocyte proliferation and differentiation

OBJECTIVES

Chondrocyte proliferation and differentiation are crucial for endochondral ossification, but their regulatory mechanism remains unclear. The present study aimed to determine the physiological function of TGFβ1 signalling in the proliferation and differentiation of antler chondrocytes and explore its relationship with Notch, Shh signalling and Foxa.

MATERIALS AND METHODS

Immunofluorescence, Western blot, MTS assay, flow cytometry, RNA interference and real-time PCR were used to analyse the function and regulatory mechanisms of TGFβ1 signalling in antler chondrocyte proliferation and differentiation.

RESULTS

TGFβ1, TGFBR1 and TGFBR2 were highly expressed in antler cartilage. TGFβ1 promoted chondrocyte proliferation, increased the proportion of S-phase cells and induced the expression of hypertrophic chondrocyte markers Col X, Runx2 and Alpl. However, this induction was weakened by TGFβ receptor inhibitor SB431542 and Smad3 inhibitor SIS3. Simultaneously, TGFβ1 activated Notch and Shh signalling whose blockage attenuated the above effects of rTGFβ1, whereas addition of rShh rescued the defects in chondrocyte proliferation and differentiation elicited by SB431542 and SIS3. Further analysis revealed that inhibition of Notch signalling impeded TGFβ1 activation of the Shh pathway. Knockdown of Foxa1, Foxa2 and Foxa3 abrogated the effects of TGFβ1 on chondrocyte differentiation. Notch and Shh signalling mediated the regulation of Foxa transcription factors by TGFβ1.

CONCLUSIONS

TGFβ1 signalling could induce the proliferation and differentiation of antler chondrocytes through Notch-Shh-Foxa pathway.

Chondrogenic differentiation of bone marrow-derived mesenchymal stem cells following transfection with Indian hedgehog and sonic hedgehog using a rotary cell culture system

Background

Indian hedgehog (IHH) and Sonic hedgehog (SHH) are important regulators of chondrogenesis. However, activation of IHH and SHH also promotes chondrocyte hypertrophy and ossification during chondrogenesis. The aims of this study were to investigate the effect of microgravity on IHH- and SHH-induced chondrogenic differentiation and to elucidate the role of microgravity in this process.

Methods

Adenovirus plasmids encoding the rabbit IHH gene and SHH genes were constructed in vitro and transfected into rabbit bone marrow-derived mesenchymal stem cells (BMSCs). A rotary cell culture system (RCCS), in which a dynamic three-dimensional culture system combines the mechanical environment with a three-dimensional culture surface, was used for cell culture and differentiation. During the induction of differentiation, expression levels of cartilage-related and cartilage hypertrophy-related genes and proteins were detected by quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting, respectively. Toluidine blue and collagen II immunohistochemical staining and annexin V-Cy3 staining were used to indicate investigate cartilage matrix synthesis and hypertrophic hypertrophy, respectively, on day 21 after induction of differentiation.

Results

In this study, IHH and SHH were shown to be equipotent inducers of chondrogenesis in rabbit BMSCs, as evidenced by strong staining for proteoglycans and collagen II, and increased expression of mRNAs and proteins associated with chondrogenesis in an RCCS environment. More importantly, chondrogenic hypertrophy and aging were effectively inhibited in the RCCS environment. In addition, levels of cartilage-related markers in the IHH and SHH transfection groups were initially increased and later decreased in the traditional two-dimensional environment, while cartilage hypertrophy-related factors revealed higher mRNA expression levels during induction.

Conclusions

In summary, microgravity significantly promoted chondrogenic differentiation of BMSCs induced by IHH and SHH and attenuated chondrogenic hypertrophy and aging during chondrogenesis. Furthermore, exogenous IHH and SHH had the same effect on chondrogenic differentiation of BMSCs in the RCCS environment. This study provides further evidence of chondrogenic induction of BMSCs in vitro via IHH and SHH gene delivery.

Electronic supplementary material

The online version of this article (10.1186/s11658-019-0144-2) contains supplementary material, which is available to authorized users.

Crosstalk between Hedgehog pathway and energy pathways in human adipose-derived stem cells: A deep sequencing analysis of polysome-associated RNA

Adult stem cells are considered promising candidates for cellular therapies due to their capacity to differentiate and self-renew. Differentiation leads to changes in the metabolism, structure, and gene expression patterns of cells. Hedgehog is one of the pathways that is involved in the enhancement of osteogenesis and chondrogenesis in adult stem cells, but its mechanisms are poorly understood. In this study, we treated adipose tissue-derived stem cells (ADSC) with two well-characterized drugs, purmorphamine (Hedgehog pathway activator) and cyclopamine (Hedgehog pathway inhibitor), and identified mRNAs associated with polysomes in each treatment group to determine the post transcriptional genetic networks governed by the Hedgehog pathway. Activation of the Hedgehog pathway by purmorphamine results in significant upregulation of mRNAs associated with cellular communication and signal transduction. Furthermore, our experiments show that cyclopamine acts late downregulating GLI1 expression in ADSCs but promotes the upregulation of mRNAs associated with energy pathways and metabolism at early times. Through in silico analysis, we identified some miRNAs, such as miR-355, that could regulate these mRNAs association with polysomes and thereby modulate the Hedgehog pathway. Our results suggest that activation of the Hedgehog pathway by purmorphamine also results in a negative regulation of mRNAs in the protein translation machinery.

Lentivirus-mediated silencing of the PTC1 and PTC2 genes promotes recovery from spinal cord injury by activating the Hedgehog signaling pathway in a rat model

This study aimed to investigate the effect of Patched-1 (PTC1) and PTC2 silencing in a rat model, on Hedgehog (Hh) pathway-mediated recovery from spinal cord injury (SCI). An analytical emphasis on the relationship between the sonic hedgehog (Shh) pathway and nerve regeneration was explored. A total of 126 rats were divided into normal, sham, SCI, negative control (NC), PTC1-RNAi, PTC2-RNAi and PTC1/PTC2-RNAi groups. The Basso, Beattie and Bresnahan (BBB) scale was employed to assess hind limb motor function. Quantitative real-time polymerase chain reaction and western blotting were performed to examine the mRNA and protein levels of PTC1, PTC2, Shh, glioma-associated oncogene homolog 1 (Gli-1), Smo and Nestin. Tissue morphology was analyzed using immunohistochemistry, and immunofluorescent staining was conducted to detect neurofilament protein 200 (NF-200) and glial fibrillary acidic protein (GFAP). The PTC1/PTC2-RNAi group displayed higher BBB scores than the SCI and NC groups. Shh, Gli-1, Smo and Nestin expression levels were elevated in the PTC1/PTC2-RNAi group. PTC1 and PTC2 mRNA and protein expression was lower in the PTC1/PTC2-RNAi group than in the normal, sham and SCI groups. Among the seven groups, the PTC1/PTC2-RNAi group had the largest positive area of NF-200 staining, whereas the SCI group exhibited a larger GFAP-positive area than both the normal and the sham groups. The Shh pathway may provide new insights into therapeutic indications and regenerative recovery tools for the treatment of SCI. Activation of the Hh signaling pathway by silencing PTC1 and PTC2 may reduce inflammation and may ultimately promote SCI recovery.

Laser irradiation promotes the proliferation of mouse pre-osteoblast cell line MC3T3-E1 through hedgehog signaling pathway

Low-level laser could promote osteoblast proliferation, and it has been applied in clinical practice to promote wound healing and tissue regeneration. However, the mechanism related to laser irradiation remains unclear. This study aimed to investigate the effects of low-level laser irradiation on the cell proliferation and the expressions of hedgehog signaling molecules Indian hedgehog (Ihh), Ptch, and Gli in vitro. In our present study, the MTT method was used to evaluate the effect on cell proliferation of laser irradiation on MC3T3-E1 cells. And cell cycle was examined by flow cytometry. Gene and protein expressions of hedgehog signaling molecules, including Ihh, Ptch, Smoothened (Smo), and Gli, were examined by qRT-PCR and western blot analysis. The results showed that laser irradiation at dosage of 3.75 J/cm² enhances the proliferation of MC3T3-E1 cells compared with control groups (p = 0.00). Moreover, laser irradiation (3.75 J/cm²) increased the cell amount at S phase (p = 0.00). In addition, the expressions of Ihh, Ptch, Smo, and Gli were significantly increased compared to the control during laser irradiation (3.75 J/cm²)-induced MC3T3-E1 osteoblast proliferation. After adding the hedgehog signaling inhibitor CY (cyclopamine), cell proliferation and Ihh, Ptch, Smo, and Gli expressions were inhibited (p = 0.00), and the cell amount at S phase was reduced compared with combination groups (p = 0.00). These results indicated that laser irradiation promotes proliferation of MC3T3-E1 cells through hedgehog signaling pathway. Our findings provide insights into the mechanistic link between laser irradiation-induced osteogenesis and hedgehog signaling pathway.

From inflammation to gastric cancer - the importance of Hedgehog/GLI signaling in Helicobacter pylori-induced chronic inflammatory and neoplastic diseases

Infections with the human pathogen Helicobacter pylori (H. pylori) are closely associated with the development of inflammatory disorders and neoplastic transformation of the gastric epithelium. Drastic changes in the micromilieu involve a complex network of H. pylori-regulated signal transduction pathways leading to the release of proinflammatory cytokines, gut hormones and a wide range of signaling molecules. Besides controlling embryonic development, the Hedgehog/GLI signaling pathway also plays important roles in epithelial proliferation, differentiation, and regeneration of the gastric physiology, but also in the induction and progression of inflammation and neoplastic transformation in H. pylori infections. Here, we summarize recent findings of H. pylori-associated Hedgehog/GLI signaling in gastric homeostasis, malignant development and the modulation of the gastric tumor microenvironment.

Orthopedic tissue regeneration: cells, scaffolds, and small molecules

Orthopedic tissue regeneration would benefit the aging population or patients with degenerative bone and cartilage diseases, especially osteoporosis and osteoarthritis. Despite progress in surgical and pharmacological interventions, new regenerative approaches are needed to meet the challenge of creating bone and articular cartilage tissues that are not only structurally sound but also functional, primarily to maintain mechanical integrity in their high load-bearing environments. In this review, we discuss new advances made in exploiting the three classes of materials in bone and cartilage regenerative medicine--cells, biomaterial-based scaffolds, and small molecules--and their successes and challenges reported in the clinic. In particular, the focus will be on the development of tissue-engineered bone and cartilage ex vivo by combining stem cells with biomaterials, providing appropriate structural, compositional, and mechanical cues to restore damaged tissue function. In addition, using small molecules to locally promote regeneration will be discussed, with potential approaches that combine bone and cartilage targeted therapeutics for the orthopedic-related disease, especially osteoporosis and osteoarthritis.

Sonic Hedgehog Promotes Cementoblastic Differentiation via Activating the BMP Pathways

Although sonic hedgehog (SHH), an essential molecule in embryogenesis and organogenesis, stimulates proliferation of human periodontal ligament (PDL) stem cells, the effects of recombinant human SHH (rh-SHH) on osteoblastic differentiation are unclear. To reveal the role of SHH in periodontal regeneration, expression of SHH in mouse periodontal tissues and its effects on the osteoblastic/cementoblastic differentiation in human cementoblasts were investigated. SHH is immunolocalized to differentiating cementoblasts, PDL cells, and osteoblasts of the developing mouse periodontium. Addition of rh-SHH increased cell growth, ALP activity, and mineralization nodule formation, and upregulated mRNA expression of osteoblastic and cementoblastic markers. The osteoblastic/cementoblastic differentiation of rh-SHH was abolished by the SHH inhibitor cyclopamine (Cy) and the BMP antagonist noggin. rh-SHH increased the expression of BMP-2 and -4 mRNA, as well as levels of phosphorylated Akt, ERK, p38, and JNK, and of MAPK and NF-κB activation, which were reversed by noggin, Cy, and BMP-2 siRNA. Collectively, this study is the first to demonstrate that SHH can promote cell growth and cell osteoblastic/cementoblastic differentiation via BMP pathway. Thus, SHH plays important roles in the development of periodontal tissue, and might represent a new therapeutic target for periodontitis and periodontal regeneration.

Collagen Type II enhances chondrogenic differentiation in agarose-based modular microtissues

BACKGROUND AIMS

Cell-based therapies have made an impact on the treatment of osteoarthritis; however, the repair and regeneration of thick cartilage defects is an important and growing clinical problem. Next-generation therapies that combine cells with biomaterials may provide improved outcomes. We have developed modular microenvironments that mimic the composition of articular cartilage as a delivery system for consistently differentiated cells.

METHODS

Human bone marrow-derived mesenchymal stem cells (MSC) were embedded in modular microbeads consisting of agarose (AG) supplemented with 0%, 10% and 20% collagen Type II (COL-II) using a water-in-oil emulsion technique. AG and AG/COL-II microbeads were characterized in terms of their structural integrity, size distribution and protein content. The viability of embedded MSC and their ability to differentiate into osteogenic, adipogenic and chondrogenic lineages over 3 weeks in culture were also assessed.

RESULTS

Microbeads made with <20% COL-II were robust, generally spheroidal in shape and 80 ± 10 µm in diameter. MSC viability in microbeads was consistently high over a week in culture, whereas viability in corresponding bulk hydrogels decreased with increasing COL-II content. Osteogenic differentiation of MSC was modestly supported in both AG and AG/COL-II microbeads, whereas adipogenic differentiation was strongly inhibited in COL-II containing microbeads. Chondrogenic differentiation of MSC was clearly promoted in microbeads containing COL-II, compared with pure AG matrices.

CONCLUSIONS

Inclusion of collagen Type II in agarose matrices in microbead format can potentiate chondrogenic differentiation of human MSC. Such compositionally tailored microtissues may find utility for cell delivery in next-generation cartilage repair therapies.

Multifaceted signaling regulators of chondrogenesis: Implications in cartilage regeneration and tissue engineering

Defects of articular cartilage present a unique clinical challenge due to its poor self-healing capacity and avascular nature. Current surgical treatment options do not ensure consistent regeneration of hyaline cartilage in favor of fibrous tissue. Here, we review the current understanding of the most important biological regulators of chondrogenesis and their interactions, to provide insight into potential applications for cartilage tissue engineering. These include various signaling pathways, including: fibroblast growth factors (FGFs), transforming growth factor β (TGF-β)/bone morphogenic proteins (BMPs), Wnt/β-catenin, Hedgehog, Notch, hypoxia, and angiogenic signaling pathways. Transcriptional and epigenetic regulation of chondrogenesis will also be discussed. Advances in our understanding of these signaling pathways have led to promising advances in cartilage regeneration and tissue engineering.

Lung fibroblasts share mesenchymal stem cell features which are altered in chronic obstructive pulmonary disease via the overactivation of the Hedgehog signaling pathway

Background

Alteration of functional regenerative properties of parenchymal lung fibroblasts is widely proposed as a pathogenic mechanism for chronic obstructive pulmonary disease (COPD). However, what these functions are and how they are impaired in COPD remain poorly understood. Apart from the role of fibroblasts in producing extracellular matrix, recent studies in organs different from the lung suggest that such cells might contribute to repair processes by acting like mesenchymal stem cells. In addition, several reports sustain that the Hedgehog pathway is altered in COPD patients thus aggravating the disease. Nevertheless, whether this pathway is dysregulated in COPD fibroblasts remains unknown.

Objectives and Methods

We investigated the stem cell features and the expression of Hedgehog components in human lung fibroblasts isolated from histologically-normal parenchymal tissue from 25 patients—8 non-smokers/non-COPD, 8 smokers-non COPD and 9 smokers with COPD—who were undergoing surgery for lung tumor resection.

Results

We found that lung fibroblasts resemble mesenchymal stem cells in terms of cell surface marker expression, differentiation ability and immunosuppressive potential and that these properties were altered in lung fibroblasts from smokers and even more in COPD patients. Furthermore, we showed that some of these phenotypic changes can be explained by an over activation of the Hedgehog signaling in smoker and COPD fibroblasts.

Conclusions

Our study reveals that lung fibroblasts possess mesenchymal stem cell-features which are impaired in COPD via the contribution of an abnormal Hedgehog signaling. These processes should constitute a novel pathomechanism accounting for disease occurrence and progression.

Tissue-engineered cartilage: the crossroads of biomaterials, cells and stimulating factors

Damage to cartilage represents one of the most challenging tasks of musculoskeletal therapeutics due to its limited propensity for healing and regenerative capabilities. Lack of current treatments to restore cartilage tissue function has prompted research in this rapidly emerging field of tissue regeneration of functional cartilage tissue substitutes. The development of cartilaginous tissue largely depends on the combination of appropriate biomaterials, cell source, and stimulating factors. Over the years, various biomaterials have been utilized for cartilage repair, but outcomes are far from achieving native cartilage architecture and function. This highlights the need for exploration of suitable biomaterials and stimulating factors for cartilage regeneration. With these perspectives, we aim to present an overview of cartilage tissue engineering with recent progress, development, and major steps taken toward the generation of functional cartilage tissue. In this review, we have discussed the advances and problems in tissue engineering of cartilage with strong emphasis on the utilization of natural polymeric biomaterials, various cell sources, and stimulating factors such as biophysical stimuli, mechanical stimuli, dynamic culture, and growth factors used so far in cartilage regeneration. Finally, we have focused on clinical trials, recent innovations, and future prospects related to cartilage engineering.

Gastritis promotes an activated bone marrow-derived mesenchymal stem cell with a phenotype reminiscent of a cancer-promoting cell

BACKGROUND

Bone marrow-derived mesenchymal stem cells (BM-MSCs) promote gastric cancer in response to gastritis. In culture, BM-MSCs are prone to mutation with continued passage but it is unknown whether a similar process occurs in vivo in response to gastritis.

AIM

The purpose of this study was to identify the role of chronic gastritis in the transformation of BM-MSCs leading to an activated cancer-promoting phenotype.

METHODS

Age matched C57BL/6 (BL/6) and gastrin deficient (GKO) mice were used for isolation of stomach, serum and mesenchymal stem cells (MSCs) at 3 and 6 months of age. MSC activation was assessed by growth curve analysis, fluorescence-activated cell sorting and xenograft assays. To allow for the isolation of bone marrow-derived stromal cells and assay in response to chronic gastritis, IRG/Vav-1(Cre) mice that expressed both enhanced green fluorescent protein-expressing hematopoietic cells and red fluorescent protein-expressing stromal cells were generated. In a parabiosis experiment, IRG/Vav-1(Cre) mice were paired to either an uninfected Vav-1(Cre) littermate or a BL/6 mouse inoculated with Helicobacter pylori.

RESULTS

GKO mice displayed severe atrophic gastritis accompanied by elevated gastric tissue and circulating transforming growth factor beta (TGFβ) by 3 months of age. Compared to BM-MSCs isolated from uninflamed BL/6 mice, BM-MSCs isolated from GKO mice displayed an increased proliferative rate and elevated phosphorylated-Smad3 suggesting active TGFβ signaling. In xenograft assays, mice injected with BM-MSCs from 6-month-old GKO animals displayed tumor growth. RFP+ stromal cells were rapidly recruited to the gastric mucosa of H. pylori parabionts and exhibited changes in gene expression.

CONCLUSIONS

Gastritis promotes the in vivo activation of BM-MSCs to a phenotype reminiscent of a cancer-promoting cell.

Hedgehog signalling is dispensable in the proliferation of stem cells from human exfoliated deciduous teeth

The hedgehog (Hh) signalling pathway is one of the key regulators in development with a dual role in cell fate specification, proliferation, and survival on different target cells. We have investigated the effect of recombinant sonic hedgehog (r-SHH) on extracted multipotent stem cells from human exfoliated deciduous teeth (SHED), which represent a potential stem cell population for therapeutic applications. Cell proliferation and cycle assays shown that r-SHH did not have a distinctive effect on cell cycle progression, nor did it increase cell number over a wide range of concentrations. Quantitative polymerase chain reaction (Q-PCR) also suggests that r-SHH treatment has no demonstrable influence on expression of proliferative genes (CCNE1 and KI67); in contrast, the anti-proliferative gene (CDKN1A) is overexpressed in response to SHH. Our findings have suggested the possibility that SHEDs demonstrate a different potential from human bone marrow mesenchymal stem cells (h-BMSCs) and dorsal neural progenitor in response to growth factors such as SHH.

Induction of mesenchymal stem cell chondrogenesis through sequential administration of growth factors within specific temporal windows

Human mesenchymal stem cells (hMSCs) are capable of differentiating into chondrocyte-like cells but fail to produce the quality or quantity of cartilage matrix compared to articular chondrocytes using current differentiation protocols. In this study, we aim to improve the chondrogenic differentiation of hMSCs through the sequential administration of multiple growth factors (GFs). We began by looking at differentiating hMSCs' cell surface GF receptor expression every 3 days throughout differentiation using flow cytometry and found that not only was receptor expression dynamic throughout differentiation, but ligand sensitivity was positively correlated with receptor expression, suggesting that differentiating hMSCs may have varying GF requirements depending on their stage of differentiation. We then constructed GF sequences by administering several prochondrogenic GFs singly every 3 days throughout differentiation and assaying the expression of a variety of cartilage-related genes using qPCR. The resulting chondrocytic phenotype of sequentially induced hMSCs was then compared to that of hMSCs induced under standard culture conditions using qPCR, dimethylmethylene blue assay, and histology. We found that while the initial GF sequence was unable to improve hMSC chondrogenesis, withdrawal of GF treatment at Day 9 of differentiation in pellet culture vastly improved the success of differentiation beyond that induced by TGFβ1 alone. Additional modifications allowed us to further improve chondrogenesis to levels comparable to that obtained by co-administration of TGFβ1 and BMP7 throughout differentiation. Taken together, we demonstrated the ability to improve the chondrocytic phenotype of differentiated hMSCs through the sequential administration of multiple GFs.

Sonic hedgehog mediates the proliferation and recruitment of transformed mesenchymal stem cells to the stomach

Studies using Helicobacter-infected mice show that bone marrow-derived mesenchymal stem cells (MSCs) can repopulate the gastric epithelium and promote gastric cancer progression. Within the tumor microenvironment of the stomach, pro-inflammatory cytokine interferon-gamma (IFNγ) and Sonic hedgehog (Shh) are elevated. IFNγ is implicated in tumor proliferation via activation of the Shh signaling pathway in various tissues but whether a similar mechanism exists in the stomach is unknown. We tested the hypothesis that IFNγ drives MSC proliferation and recruitment, a response mediated by Shh signaling. The current study uses transplantation of an in vitro transformed mesenchymal stem cell line (stMSC^vect), that over-expresses hedgehog signaling, in comparison to non-transformed wild-type MSCs (wtMSCs), wtMSCs transfected to over-express Shh (wtMSC^Shh), and stMSCs transduced with lentiviral constructs containing shRNA targeting the Shh gene (stMSC^ShhKO). The effect of IFNγ on MSC proliferation was assessed by cell cycle analysis in vitro using cells treated with recombinant IFNγ (rmIFNγ) alone, or in combination with anti-Shh 5E1 antibody, and in vivo using mice transplanted with MSCs treated with PBS or rmIFNγ. In vitro, IFNγ significantly increased MSC proliferation, a response mediated by Shh that was blocked by 5E1 antibody. The MSC population collected from bone marrow of PBS- or IFNγ-treated mice showed that IFNγ significantly increased the percentage of all MSC cell lines in S phase, with the exception of the stMSCs^ShhKO cells. While the MSC cell lines with intact Shh expression were recruited to the gastric mucosa in response to IFNγ, stMSCs^ShhKO were not. Hedgehog signaling is required for MSC proliferation and recruitment to the stomach in response to IFNγ.

Dexamethasone induces osteogenesis via regulation of hedgehog signalling molecules in rat mesenchymal stem cells

PURPOSE

Hedgehog signalling plays an important role during the development of tissues and organs, including bone and limb. Dexamethasone (DEX), a synthetic and widely used glucocorticoid, affects osteogenesis of bone marrow mesenchymal stem cells (MSCs), while the signalling pathway by which DEX affects osteoblast differentiation remains obscure. This study aimed to investigate expressions of hedgehog signalling molecules Shh, Ihh and Gli1 during DEX-induced osteogenesis of rat MSCs in vitro.

METHODS

DEX promoted osteoblast differentiation of MSCs at 10(-8) mol/L from seven days to 21 days, demonstrated by enhancing alkaline phosphatase (ALP) activity and osteoblast-associated marker type I collagen expression during osteoblastic differentiation. Gene and protein expressions of hedgehog signalling molecules, Shh, Ihh and Gli1 were tested by RT-PCR and western blot analysis during osteoblast differentiation.

RESULTS

Shh expression was increased compared to the control while Ihh and Gli1 expressions were decreased on both mRNA and protein level during DEX-induced osteoblast differentiation of MSCs from seven days to 21 days. Altogether, these data demonstrate that DEX can enhance Shh expression via a Gli1-independent mechanism during osteoblast differentiation of MSCs.

CONCLUSIONS

These results indicate that different patterns of hedgehog signalling are involved in DEX-induced osteogenesis and these findings provide insights into the mechanistic link between glucocorticoid-induced osteogenesis and hedgehog signalling pathway.

The effects of inhibiting hedgehog signaling pathways by using specific antagonist cyclopamine on the chondrogenic differentiation of mesenchymal stem cells

This study aimed to investigate the effects of cyclopamine, a specific inhibitor of Hedgehog signaling pathways, on the chondrogenic differentiation of mesenchymal stem cells (MSCs). During culture, the experimental groups were treated with cyclopamine and their cell proliferation status was assessed using the MTT test. The extra-bone cellular matrix (ECM) and Collagen II (Col II) was detected by toluidine blue staining and immunohistochemistry of cells. The concentrations of Col II and aggrecan in the culture solution and cytosol were detected using ELISA on the 7th, 14th, and 21st days of cyclopamine induction. Gene and protein expression of Col II and aggrecan were analyzed on the 14th day of cyclopamine induction using real-time PCR and western blot analyses. No significant differences in proliferation of mesenchymal stem cells were found between the control group and the group treated with cyclopamine. Compared to the blank control group, the ECM level was low and the protein and mRNA concentrations of Collagen II (Col II) and aggrecan in the culture solution and cytosol, respectively, were significantly reduced in the experimental group. The Smo acted as a key point in the regulations of Hedgehog signaling pathway on the chondrogenic differentiation of rabbit MSCs.

Sonic hedgehog enhances the proliferation and osteogenic differentiation of bone marrow-derived mesenchymal stem cells

MSCs (mesenchymal stem cells) may be promising seed cells for tissue regeneration because of their self-renewal and multi-differentiation potential. Shh (sonic hedgehog) is involved in the skeletal formation during embryo development and skeletal regeneration. However, how Shh regulates the biological characteristics of BM-MSCs (bone marrow-derived MSCs) is poorly understood. We have investigated the effect of rShh-N (recombinant N-terminal Shh) on the proliferation and osteogenic differentiation of rBM-MSCs (rat BM-MSCs) in vitro. rBM-MSCs were treated with rShh-N at concentrations up to 200 ng/ml. Proliferation and colony-forming ability of rBM-MSCs were increased in a dose-dependent manner. rShh-N increased the ratio of cells in S and G2/M phase, as well as the number of Ki-67+ cells. In addition, ALP (alkaline phosphatase) activity and matrix mineralization were enhanced by 200 ng/ml rShh-N. Real-time PCR showed that rShh-N (200 ng/ml) up-regulated the expression of genes encoding Cbfa-1 (core-binding factor α1), osteocalcin, ALP and collagen type I in rBM-MSCs. This information reveals some potential of rShh-N in the therapeutics of bone-related diseases.

Protection from lipopolysaccharide-induced pulmonary microvascular endothelial cell injury by activation of hedgehog signaling pathway

Pulmonary microvascular endothelial cells (PMVECs) are critically involved in the pathogenesis of acute lung injury. Hedgehog signaling pathway plays a fundamental role in embryonic development as well as adult morphogenesis and carcinogenesis. As the priming protein of hedgehog signaling pathway, sonic hedgehog (Shh) may recently be advantage for decreasing endothelial injury and promoting the repair of endothelial barrier function. To investigate the expression and role of hedgehog signal pathway in PMVECs injured by lipopolysaccharide (LPS), cells were divided into six groups: control group, LPS group, rhShh group, LPS+rhShh group, rhShh+cyclopamine group, and LPS+rhShh+cyclopamine group. Real time RT-PCR and Western blotting were used to detect the mRNA and protein expression of hedgehog signal molecules including Shh, Patched-1 (Ptc-1) and Gli1 in nucleus. The activity of PMVECs was examined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. In this study, we found that Shh, Ptch1, and Gli1 were expressed in rat PMVECs and their expression decreased when cells were treated by LPS. In the other hand, LPS inhibited the activity of rat PMVECs and caused the cells injury. Activation of Hedgehog signaling pathway by Shh could elevate the activity of PMVECs with pretreatment by LPS. Therefore, hedgehog signaling pathway should play a protective role on injury PMVECs by LPS.

Inactivation of Patched1 in the mouse limb has novel inhibitory effects on the chondrogenic program

The bones of the vertebrate limb form by the process of endochondral ossification, whereby limb mesenchyme condenses to form an intermediate cartilage scaffold that is then replaced by bone. Although Indian hedgehog (IHH) is known to control hypertophic differentiation of chondrocytes during this process, the role of hedgehog signaling in the earlier stages of chondrogenesis is less clear. We have conditionally inactivated the hedgehog receptor Ptc1 in undifferentiated limb mesenchyme of the mouse limb using Prx1-Cre, thus inducing constitutively active ligand-independent hedgehog signaling. In addition to major patterning defects, we observed a marked disruption to the cartilage elements in the limbs of Prx1-Cre:Ptc1(c/c) embryos. Using an in vitro micromass culture system we show that this defect lies downstream of mesenchymal cell condensation and likely upstream of chondrocyte differentiation. Despite early increases in levels of chondrogenic genes, soon after mesenchymal condensation the stromal layer of Prx1-Cre:Ptc1(c/c)-derived micromass cultures is characterized by a loss of cell integrity, which is associated with increased cell death and a striking decrease in Alcian blue staining cartilage nodules. Furthermore, inhibition of the hedgehog pathway activation using cyclopamine was sufficient to essentially overcome this chondrogenic defect in both micromass and ex vivo explant assays of Prx1-Cre:Ptc1(c/c) limbs. These data demonstrate for the first time the inhibitory effect of cell autonomously activated hedgehog signaling on chondrogenesis, and stress the importance of PTC1 in maintaining strict control of signaling levels during this phase of skeletal development.

[Molecular tools to remodel osteoarthritic articular cartilage : growth, transcription, and signaling factors]

Osteoarthritis (OA) is a chronic disorder of the diarthrodial joints, mostly characterized by gradual deterioration of the articular cartilage. This disease still has no effective treatment. An emerging strategy for treating OA is based on molecular concepts using growth factors, transcription factors, and signaling molecules in light of their effects on the restoration of cartilage integrity. Recent studies have demonstrated that overexpression of such candidate molecules using direct gene transfer or ex vivo protocols is capable of stimulating cell proliferation and matrix synthesis in normal human and OA cartilage explants in vitro as well as in animal models in vivo. As a result, the structure of the articular cartilage can be improved. More insights into the pathophysiology of human OA and further studies in animal models are needed, however, to facilitate clinical translation of these molecular approaches. In conclusion, recent experimental findings permit cautious optimism, holding promise for treating human OA in the future.

Cartilage tissue engineering: towards a biomaterial-assisted mesenchymal stem cell therapy

Injuries to articular cartilage are one of the most challenging issues of musculoskeletal medicine due to the poor intrinsic ability of this tissue for repair. Despite progress in orthopaedic surgery, the lack of efficient modalities of treatment for large chondral defects has prompted research on tissue engineering combining chondrogenic cells, scaffold materials and environmental factors. The aim of this review is to focus on the recent advances made in exploiting the potentials of cell therapy for cartilage engineering. These include: 1) defining the best cell candidates between chondrocytes or multipotent progenitor cells, such as multipotent mesenchymal stromal cells (MSC), in terms of readily available sources for isolation, expansion and repair potential; 2) engineering biocompatible and biodegradable natural or artificial matrix scaffolds as cell carriers, chondrogenic factors releasing factories and supports for defect filling, 3) identifying more specific growth factors and the appropriate scheme of application that will promote both chondrogenic differentiation and then maintain the differentiated phenotype overtime and 4) evaluating the optimal combinations that will answer to the functional demand placed upon cartilage tissue replacement in animal models and in clinics. Finally, some of the major obstacles generally encountered in cartilage engineering are discussed as well as future trends to overcome these limiting issues for clinical applications.

Transient overexpression of sonic hedgehog alters the architecture and mechanical properties of trabecular bone

Bone formation and remodeling involve coordinated interactions between osteoblasts and osteoclasts through signaling networks involving a variety of molecular pathways. We hypothesized that overexpression of Sonic hedgehog (Shh), a morphogen with a crucial role in skeletal development, would stimulate osteoblastogenesis and bone formation in adult animals in vivo. Systemic administration of adenovirus expressing the N-terminal form of Shh into adult mice resulted in a primary increase in osteoblasts and their precursors. Surprisingly, however, this was associated with altered trabecular morphology, decreased bone volume, and decreased compressive strength in the vertebrae. Whereas no change was detected in the number of osteoclast precursors, bone marrow stromal cells from Shh-treated mice showed enhanced osteoclastogenic potential in vitro. These effects were mediated by the PTH/PTH-related protein (PTHrP) pathway as evidenced by increased sensitivity to PTH stimulation and upregulation of the PTH/PTHrP receptor (PPR). Together, these data show that Shh has stimulatory effects on osteoprogenitors and osteoblasts in adult animals in vivo, which results in bone remodeling and reduced bone strength because of a secondary increase in osteoclastogenesis.

Fibrochondrogenesis of hESCs: growth factor combinations and cocultures

The successful differentiation of human embryonic stem cells (hESCs) to fibrochondrocyte-like cells and characterization of these differentiated cells is a critical step toward tissue engineering of musculoskeletal fibrocartilages (e.g., knee meniscus, temporomandibular joint disc, and intervertebral disc). In this study, growth factors and primary cell cocultures were applied to hESC embryoid bodies (EBs) for 3 weeks and evaluated for their effect on the synthesis of critical fibrocartilage matrix components: glycosaminoglycans (GAG) and collagens (types I, II, and VI). Changes in surface markers (CD105, CD44, SSEA, PDGFR alpha) after the differentiation treatments were also analyzed. The study was conducted in three phases: (1) examination of growth factors (TGF-beta 3, BMP-2, BMP-4, BMP-6, PDGF-BB, sonic hedgehog protein); (2) comparison of two cocultures (primary chondrocytes or fibrochondrocytes); and (3) the combination of the most effective growth factor and coculture regimen. TGF-beta 3 with BMP-4 yielded EBs positive for collagens I, II, and VI, with up to 6.7- and 4.8-fold increases in GAG and collagen, respectively. Analysis of cell surface markers showed a significant increase in CD44 with the TGF-beta 3 + BMP-4 treatment compared to the controls. Coculture with fibrochondrocytes resulted in up to a 9.8-fold increase in collagen II production. The combination of the growth factors BMP-4 + TGF-beta 3 with the fibrochondrocyte coculture led to an increase in cell proliferation and GAG production compared to either treatment alone. This study determined two powerful treatments for inducing fibrocartilaginous differentiation of hESCs and provides a foundation for using flow cytometry to purify these differentiated cells.

Mesodermal deletion of transforming growth factor-beta receptor II disrupts lung epithelial morphogenesis: cross-talk between TGF-beta and Sonic hedgehog pathways

In vertebrates, Sonic hedgehog (Shh) and transforming growth factor-beta (TGF-beta) signaling pathways occur in an overlapping manner in many morphogenetic processes. In vitro data indicate that the two pathways may interact. Whether such interactions occur during embryonic development remains unknown. Using embryonic lung morphogenesis as a model, we generated transgenic mice in which exon 2 of the TbetaRII gene, which encodes the type II TGF-beta receptor, was deleted via a mesodermal-specific Cre. Mesodermal-specific deletion of TbetaRII (TbetaRII(Delta/Delta)) resulted in embryonic lethality. The lungs showed abnormalities in both number and shape of cartilage in trachea and bronchi. In the lung parenchyma, where epithelial-mesenchymal interactions are critical for normal development, deletion of mesenchymal TbetaRII caused abnormalities in epithelial morphogenesis. Failure in normal epithelial branching morphogenesis in the TbetaRII(Delta/Delta) lungs caused cystic airway malformations. Interruption of the TbetaRII locus in the lung mesenchyme increased mRNA for Patched and Gli-1, two downstream targets of Shh signaling, without alterations in Shh ligand levels produced in the epithelium. Therefore, we conclude that TbetaRII-mediated signaling in the lung mesenchyme modulates transduction of Shh signaling that originates from the epithelium. To our knowledge, this is the first in vivo evidence for a reciprocal and novel mode of cross-communication between Shh and TGF-beta pathways during embryonic development.

Hedgehog-mediated paracrine interaction between hepatic stellate cells and marrow-derived mesenchymal stem cells

During liver injury, bone marrow-derived mesenchymal stem cells (MSCs) can migrate and differentiate into hepatocytes. Hepatic stellate cell (SC) activation is a pivotal event in the development of liver fibrosis. Therefore, we hypothesized that SCs may play an important role in regulating MSC proliferation and differentiation through the paracrine signaling pathway. We demonstrate that MSCs and SCs both express hedgehog (Hh) pathway components, including its ligands, receptors, and target genes. Transwell co-cultures of SCs and MSCs showed that the SCs produced sonic hedgehog (Shh), which enhanced the proliferation and differentiation of MSCs. These findings demonstrate that SCs indirectly modulate the activity of MSCs in vitro via the Hh pathway, and provide a plausible explanation for the mechanisms of transplanted MSCs in the treatment of liver fibrosis.

SOX9cre1, a cis-acting regulatory element located 1.1 Mb upstream of SOX9, mediates its enhancement through the SHH pathway

SOX9 is a temporal and tissue-specific transcription factor involved in male sexual development and bone formation. Haploinsufficiency of SOX9 is known to cause campomelic dysplasia (CD). CD cases without SOX9 coding region mutations have been described in association with translocations that have breakpoints mapping as far as 932 kb upstream from the gene. These rearrangements suggest that position effects acting from a great distance regulate SOX9 gene expression. Studies of one such case (900 kb upstream to SOX9) have led to the delineation of a potential 2.1 kb cis-acting regulatory element 1.1 Mb upstream of SOX9, termed SOX9cre1. We investigated the role of this putative regulator in SOX9 expression. SOX9cre1 increases the activity of a minimal SOX9 promoter in reporter constructs in a dose-dependent and tissue-specific manner, consistent with an enhancer role. In silico studies identify a putative binding site within SOX9cre1 for GLI1, a downstream mediator of sonic hedgehog (SHH). Furthermore, the stimulation of primary human chondrocyte cells in culture with SHH increases endogenous SOX9 expression 3-fold. Electrophoresis mobility shift assay (EMSA) studies that demonstrate physical interactions between the GLI1 transcription factor and a putative binding site within SOX9cre1, as well as experiments in which reporter constructs are co-transfected with GLI1, suggest a direct interaction between GLI1 and SOX9cre1. GLI1-SOX9cre1 interactions are verified in chromatin immunoprecipitation experiments. These data support a direct molecular link between the Hh signaling pathway and SOX9 regulation, wherein SHH stimulates SOX9 through its mediator GLI1, and are consistent with a mechanism of SOX9 regulation through distal chromatin interactions.

Differentiation of an ameloblast-lineage cell line (ALC) is induced by Sonic hedgehog signaling

Sonic hedgehog (Shh), one of the essential molecules for embryogenesis and organogenesis, is strongly expressed in the enamel knot, which represents the signaling center for odontogenesis due to the presence of essential secretory molecules. Here, we investigated the effects of Shh on ameloblast differentiation using a mouse ameloblast-lineage cell line (ALC). In the presence of Shh, the expression of amelogenin and ameloblastin was up-regulated, and their promoter activities were also elevated. Subcutaneous implantation of Shh-treated ALC into the dorsa of C57/Bl6J mouse caused increased expression of amelogenin and ameloblastin. Forced expression of Gli1, a major transcription factor in Shh signaling, up-regulated both amelogenin and ameloblastin, while Gli1-specific RNAi blocked their expression. These results suggest that Shh directly promotes ALC differentiation, and that Gli1 may be responsible for the signal mediation of Shh.