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

Effects of Improper Mechanical Force on the Production of Sonic Hedgehog, RANKL, and IL-6 in Human Periodontal Ligament Cells In Vitro

Improper mechanical stress may induce side effects during orthodontic treatment. If the roots and alveolar bones are extensively resorbed following excess mechanical stress, unplanned tooth mobility and inflammation can occur. Although multiple factors are believed to contribute to the development of side effects, the cause is still unknown. Sonic hedgehog (Shh), one of the hedgehog signals significantly associated with cell growth and cancer development, promotes osteoclast formation in the jawbone. Shh may be associated with root and bone resorptions during orthodontic treatment. In this study, we investigated the relationships between Shh, RANKL, and IL-6 in human periodontal ligament (hPDL) cells exposed to improper mechanical force. Weights were placed on hPDL cells and human gingival fibroblasts (HGFs) for an optimal orthodontic force group (1.0 g/cm2) and a heavy orthodontic force group (4.0 g/cm2). A group with no orthodontic force was used as a control group. Real-time PCR, SDS-PAGE, and Western blotting were performed to examine the effects of orthodontic forces on the expression of Shh, RANKL, and IL-6 at 2, 4, 6, 8, 12, and 24 h after the addition of pressure. The protein expression of Shh was not clearly induced by orthodontic forces of 1.0 and 4.0 g/cm2 compared with the control in HGFs and hPDL cells. In contrast, RANKL and IL-6 gene and protein expression was significantly induced by 1.0 and 4.0 g/cm2 in hPDL cells for forces lasting 6~24 h. However, neither protein was expressed in HGFs. RANKL and IL-6 expressions in response to orthodontic forces and in the control were clearly inhibited by Shh inhibitor RU-SKI 43. Shh did not directly link to RANKL and IL-6 for root and bone resorptions by orthodontic force but was associated with cell activities to be finally guided by the production of cytokines in hPDL cells.

BMP7-induced osteoblast differentiation requires hedgehog signaling and involves nuclear mechanisms of gene expression control

During the morphological changes occurring in osteoblast differentiation, Sonic hedgehog (Shh) plays a crucial role. While some progress has been made in understanding this process, the epigenetic mechanisms governing the expression of Hh signaling members in response to bone morphogenetic protein 7 (BMP7) signaling in osteoblasts remain poorly understood. To delve deeper into this issue, we treated pre-osteoblasts (pObs) with 100 ng/mL of BMP7 for up to 21 days. Initially, we validated the osteogenic phenotype by confirming elevated expression of well-defined gene biomarkers, including Runx2, Osterix, Alkaline Phosphatase (Alp), and bone sialoprotein (Bsp). Simultaneously, Hh signaling-related members Sonic (Shh), Indian (Ihh), and Desert (Dhh) Hedgehog (Hh) exhibited nuanced modulation over the 21 days in vitro period. Subsequently, we evaluated epigenetic markers, and our data revealed a notable change in the CpG methylation profile, considering the methylation/hydroxymethylation ratio. CpG methylation is a reversible process regulated by DNA methyltransferases and demethylases, including Ten-eleven translocation (Tets), which also exhibited changes during the acquisition of the osteogenic phenotype. Specifically, we measured the methylation pattern of Shh-related genes and demonstrated a positive Pearson correlation for GLI Family Zinc Finger 1 (Gli1) and Patched (Ptch1). This data underscores the significance of the epigenetic machinery in modulating the BMP7-induced osteogenic phenotype by influencing the activity of Shh-related genes. In conclusion, this study highlights the positive impact of epigenetic control on the expression of genes related to hedgehog signaling during the morphogenetic changes induced by BMP7 signaling in osteoblasts.

Sonic hedgehog promotes synovial inflammation and articular damage through p38 mitogen-activated protein kinase signaling in experimental arthritis

Activated fibroblast-like synoviocytes (FLS) play a pivotal role in synovial inflammation and joint destruction of rheumatoid arthritis (RA). The mechanisms by which sonic hedgehog (SHH) signaling promotes RA FLS-mediated chronic inflammation and tissue damage are not fully understood. The present study aims to determine the role of SHH signaling in the pathogenesis of RA and to explore the potential mechanism(s). We found that the components of SHH signaling were highly expressed in FLS and synovial tissue from patients with RA and in the joint tissue of collagen-induced arthritis (CIA) mice. Overexpression of SHH aggravated the synovial inflammation and joint destruction of CIA and exacerbated cartilage degradation in the cartilage and RA FLS-engrafted severe combined immunodeficiency (SCID) model. Conversely, inhibition of SHH signaling significantly alleviated arthritis severity and reduced cartilage destruction caused by the invasion of RA FLS in vivo. Moreover, we found that p38 mitogen-activated protein kinase (MAPK) cascade was regulated by SHH signaling in RA FLS and the level of phospho-p38 in the joint tissue of CIA was decreased after blockade of SHH signaling. Inhibition of p38 MAPK abolished the effect of SHH overexpression on synovial inflammation and articular destruction of CIA and suppressed the aggressive properties of RA FLS, which were promoted by SHH agonist. In conclusion, our study suggests that SHH signaling aggravates synovial inflammation and joint destruction of experimental arthritis and promotes the abnormal behavior of RA FLS in a p38-dependent manner. SHH-p38 MAPK signaling could be a potential target for the treatment of RA.

Hedgehog signalling in bone and osteoarthritis: the role of Smoothened and cholesterol

Hedgehog signalling is essential for development, crucial for normal anatomical arrangement and activated during tissue damage repair. Dysregulation of hedgehog signalling is associated with cancer, developmental disorders and other diseases including osteoarthritis (OA). The hedgehog gene was first discovered in Drosophila melanogaster, and the pathway is evolutionarily conserved in most animals. Although there are several hedgehog ligands with different protein expression patterns, they share a common plasma membrane receptor, Patched1 and hedgehog signalling pathway activation is transduced through the G-protein-coupled receptor-like protein Smoothened (SMO) and downstream effectors. Functional assays revealed that activation of SMO is dependent on sterol binding, and cholesterol was observed bound to SMO in crystallography experiments. In vertebrates, hedgehog signalling coordinates endochondral ossification and balances osteoblast and osteoclast activation to maintain homeostasis. A recently discovered mutation of SMO in humans (SMO^R173C ) is predicted to alter cholesterol binding and is associated with a higher risk of hip OA. Functional studies in mice and human tissue analysis provide evidence that hedgehog signalling is pathologically activated in chondrocytes of osteoarthritic cartilage.

The Pleiotropic Intricacies of Hedgehog Signaling: From Craniofacial Patterning to Carcinogenesis

Hedgehog signaling was discovered more than 40 years ago in experiments demonstrating that it is a fundamental mediator of limb development. Since that time, it has been shown to be important in development, homeostasis, and disease. The hedgehog pathway proceeds through a pathway highly conserved throughout animals beginning with the extracellular diffusion of hedgehog ligands, proceeding through an intracellular signaling cascade, and ending with the activation of specific target genes. A vast amount of research has been done elucidating hedgehog signaling mechanisms and regulation. This research has found a complex system of genetics and signaling that helps determine how organisms develop and function. This review provides an overview of what is known about hedgehog genetics and signaling, followed by an in-depth discussion of the role of hedgehog signaling in craniofacial development and carcinogenesis.

Identification of Novel Genetic Variants Related to Trabecular Bone Score in Community-Dwelling Older Adults

BACKGROUND

As the genetic variants of trabecular bone microarchitecture are not well-understood, we performed a genome-wide association study to identify genetic determinants of bone microarchitecture analyzed by trabecular bone score (TBS).

METHODS

TBS-associated genes were discovered in the Ansung cohort (discovery cohort), a community-based rural cohort in Korea, and then validated in the Gene-Environment Interaction and Phenotype (GENIE) cohort (validation cohort), consisting of subjects who underwent health check-up programs. In the discovery cohort, 2,451 participants were investigated for 1.42 million genotyped and imputed markers.

RESULTS

In the validation cohort, identified as significant variants were evaluated in 2,733 participants. An intronic variant in iroquois homeobox 3 (IRX3), rs1815994, was significantly associated with TBS in men (P=3.74E-05 in the discovery cohort, P=0.027 in the validation cohort). Another intronic variant in mitogen-activated protein kinase kinase 5 (MAP2K5), rs11630730, was significantly associated with TBS in women (P=3.05E-09 in the discovery cohort, P=0.041 in the validation cohort). Men with the rs1815994 variant and women with the rs11630730 variant had lower TBS and lumbar spine bone mineral density. The detrimental effects of the rs1815994 variant in men and rs11630730 variant in women were also identified in association analysis (β=-0.0281, β=-0.0465, respectively).

CONCLUSION

In this study, the rs1815994 near IRX3 in men and rs11630730 near MAP2K5 in women were associated with deterioration of the bone microarchitecture. It is the first study to determine the association of genetic variants with TBS. Further studies are needed to confirm our findings and identify additional variants contributing to the trabecular bone microarchitecture.

SHH Signaling Pathway Drives Pediatric Bone Sarcoma Progression

Primary bone tumors can be divided into two classes, benign and malignant. Among the latter group, osteosarcoma and Ewing sarcoma are the most prevalent malignant primary bone tumors in children and adolescents. Despite intensive efforts to improve treatments, almost 40% of patients succumb to the disease. Specifically, the clinical outcome for metastatic osteosarcoma or Ewing sarcoma remains poor; less than 30% of patients who present metastases will survive 5 years after initial diagnosis. One common and specific point of these bone tumors is their ability to deregulate bone homeostasis and remodeling and divert them to their benefit. Over the past years, considerable interest in the Sonic Hedgehog (SHH) pathway has taken place within the cancer research community. The activation of this SHH cascade can be done through different ways and, schematically, two pathways can be described, the canonical and the non-canonical. This review discusses the current knowledge about the involvement of the SHH signaling pathway in skeletal development, pediatric bone sarcoma progression and the related therapeutic options that may be possible for these tumors.

Could use of Selective Serotonin Reuptake Inhibitors During Lactation Cause Persistent Effects on Maternal Bone?

The lactating mammary gland elegantly coordinates maternal homeostasis to provide calcium for milk. During lactation, the monoamine serotonin regulates the synthesis and release of various mammary gland-derived factors, such as parathyroid hormone-related protein (PTHrP), to stimulate bone resorption. Recent evidence suggests that bone mineral lost during prolonged lactation is not fully recovered following weaning, possibly putting women at increased risk of fracture or osteoporosis. Selective Serotonin Reuptake Inhibitor (SSRI) antidepressants have also been associated with reduced bone mineral density and increased fracture risk. Therefore, SSRI exposure while breastfeeding may exacerbate lactational bone loss, compromising long-term bone health. Through an examination of serotonin and calcium homeostasis during lactation, lactational bone turnover and post-weaning recovery of bone mineral, and the effect of peripartum depression and SSRI on the mammary gland and bone, this review will discuss the hypothesis that peripartum SSRI exposure causes persistent reductions in bone mineral density through mammary-derived PTHrP signaling with bone.

The Hedgehog signalling pathway in bone formation

The Hedgehog (Hh) signalling pathway plays many important roles in development, homeostasis and tumorigenesis. The critical function of Hh signalling in bone formation has been identified in the past two decades. Here, we review the evolutionarily conserved Hh signalling mechanisms with an emphasis on the functions of the Hh signalling pathway in bone development, homeostasis and diseases. In the early stages of embryonic limb development, Sonic Hedgehog (Shh) acts as a major morphogen in patterning the limb buds. Indian Hedgehog (Ihh) has an essential function in endochondral ossification and induces osteoblast differentiation in the perichondrium. Hh signalling is also involved intramembrane ossification. Interactions between Hh and Wnt signalling regulate cartilage development, endochondral bone formation and synovial joint formation. Hh also plays an important role in bone homeostasis, and reducing Hh signalling protects against age-related bone loss. Disruption of Hh signalling regulation leads to multiple bone diseases, such as progressive osseous heteroplasia. Therefore, understanding the signalling mechanisms and functions of Hh signalling in bone development, homeostasis and diseases will provide important insights into bone disease prevention, diagnoses and therapeutics.

Roles for Hedgehog signaling in adult organ homeostasis and repair

The hedgehog (HH) pathway is well known for its mitogenic and morphogenic functions during development, and HH signaling continues in discrete populations of cells within many adult mammalian tissues. Growing evidence indicates that HH regulates diverse quiescent stem cell populations, but the exact roles that HH signaling plays in adult organ homeostasis and regeneration remain poorly understood. Here, we review recently identified functions of HH in modulating the behavior of tissue-specific adult stem and progenitor cells during homeostasis, regeneration and disease. We conclude that HH signaling is a key factor in the regulation of adult tissue homeostasis and repair, acting via multiple different routes to regulate distinct cellular outcomes, including maintenance of plasticity, in a context-dependent manner.

Overexpressing sonic hedgehog peptide restores periosteal bone formation in a murine bone allograft transplantation model

Although activation of hedgehog (Hh) signaling has been shown to induce osteogenic differentiation in vitro and bone formation in vivo, the underlying mechanisms and the potential use of Hh-activated mesenchymal progenitors in bone defect repair remain elusive. In this study, we demonstrated that implantation of periosteal-derived mesenchymal progenitor cells (PDMPCs) that overexpressed an N-terminal sonic hedgehog peptide (ShhN) via an adenoviral vector (Ad-ShhN) restored periosteal bone collar formation in a 4-mm segmental bone allograft model in immunodeficient mice. Ad-ShhN enhanced donor cell survival and microvessel formation in collagen scaffold at 2 weeks after surgery and induced donor cell-dependent bone formation at 6 weeks after surgery. Fluorescence-activated cell sorting analysis further showed that Ad-ShhN-PDMPC-seeded scaffold contained a twofold more CD45(-)Sca-1(+)CD34(+)VEGFR2(+) endothelial progenitors than Ad-LacZ-PDMPC-seeded scaffold at day 7 after surgery. Ad-ShhN-transduced PDMPCs induced a 1.8-fold more CD31(+) microvessel formation than Ad-LacZ-transduced PDMPCs in a coculture of endothelial progenitors and PDMPCs. Taken together, our data show that overexpression of ShhN in mesenchymal progenitors improves bone defect reconstruction by enhancing donor progenitor cell survival, differentiation, and scaffold revascularization at the site of compromised periosteum. Hh agonist-based therapy, therefore, merits further investigation in tissue engineering-based applications aimed at enhancing bone defect repair and reconstruction.

Osterix is required for Sonic hedgehog-induced osteoblastic MC3T3-E1 cell differentiation

It has been shown that hedgehog (Hh) signaling plays an important role during bone development. However, the mechanism(s) by which Hh stimulates osteoblast differentiation are not fully elucidated. This study was performed to examine if Sonic hedgehog (Shh) affects osteoblast differentiation in osteoblastic MC3T3-E1 cells and determine the exact role of osterix (Osx) involved in Hh-induced osteoblast differentiation. Our real-time RT-PCR result shows that Shh significantly induced osteoblast differentiation by up-regulation of osteocalcin, alkaline phosphatase, bone sialoprotein, Type I collagen, runt-related transcription factor 2 (Runx2), and Osx RNA expression in MC3T3-E1 cells. ALP protein activity, Osx protein expression, as well as Osx promoter activity was also enhanced by Shh treatment in cell culture. Interestingly, Shh-induced Osx up-regulation was only slightly affected by knocking down Runx2 using siRNA in cells within 3 days of culture, however, knocking down Osx expression in cells totally blocked Shh-induced osteoblast differentiation. These findings demonstrate for the first time that Shh stimulates early osteoblast differentiation mainly through up-regulation of the expression of Osx in osteoblastic MC3T3-E1 cells in both Runx2-dependent and Runx2-independent manner.

Morphoproteomics provides support for TGF-β pathway signaling in the osteoclastogenesis and immune dysregulation of osteolytic Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) has a challenging and still unclear pathogenesis. A body of literature points to impaired maturation of the lesional dendritic cells, and to immune dysregulation in the form of increased FoxP3 cells. Various cytokine abnormalities such as expression of transforming growth factor (TGF)-β have been reported, as well as abnormalities in lipid content in LCH cells. Morphoproteomic techniques were applied to identify the signal transduction pathways that could influence histogenesis and immune regulation in osteolytic LCH. Five pediatric cases of osteolytic LCH were examined, using antibodies against CD1a, S100, CD68, CD8, FoxP3, phosphorylated (p)-STAT3 (Tyr705), protein kinase C (PKC)-α, phospholipase (PL)D1, fatty acid synthase (FASN), and zinc finger protein, Gli2. Positive and negative controls were performed. A FoxP3(+)/CD8(+) cell ratio was calculated by counting the FoxP3+ and CD8+ cells in 10 high power fields for each case. There is induction of sonic hedgehog (SHH) mediators consistent with TGF-β signaling pathway through Smad3-dependent activation of Gli2, findings supported by the plasmalemmal and cytoplasmic expression of PKC-α and PLD1, and nuclear expression of Gli2, in lesional cells. The FoxP3+/CD8+ cell ratio is increased, ranging from 1.7-7.94. There is moderate cytoplasmic expression of FASN in most of the Langerhans cells, a finding that supports previously published phospholipid abnormalities in LCH and is consistent with PKC-α/PLD1/TGF-β signaling. With our study, we strongly suggest that the TGF-β cell signaling pathway is a major player in the pathogenesis of LCH, leading to non-canonical induction of nuclear Gli2 expression, thereby contributing to osteoclastogenesis in LCH histiocytes. It could also cause a state of immune frustration in LCH, by inducing the transformation of CD4(+)CD25(-) cells into CD4(+)/FoxP3(+) cells. This coincides with the clinical evidence of a response to thalidomide in patients with osteolytic LCH, given its reported ability to reduce TGF-beta 1 and FoxP3 cells. Such TGF-β signaling in osteoclastogenesis and immune dysregulation, and the presence of FASN in the majority of cells, have additional therapeutic implications for osteolytic LCH.

Hedgehog signaling in tumor cells facilitates osteoblast-enhanced osteolytic metastases

The remodeling process in bone yields numerous cytokines and chemokines that mediate crosstalk between osteoblasts and osteoclasts and also serve to attract and support metastatic tumor cells. The metastatic tumor cells disturb the equilibrium in bone that manifests as skeletal complications. The Hedgehog (Hh) pathway plays an important role in skeletogenesis. We hypothesized that the Hh pathway mediates an interaction between tumor cells and osteoblasts and influences osteoblast differentiation in response to tumor cells. We have determined that breast tumor cells have an activated Hh pathway characterized by upregulation of the ligand, IHH and transcription factor GLI1. Breast cancer cells interact with osteoblasts and cause an enhanced differentiation of pre-osteoblasts to osteoblasts that express increased levels of the osteoclastogenesis factors, RANKL and PTHrP. There is sustained expression of osteoclast-promoting factors, RANKL and PTHrP, even after the osteoblast differentiation ceases and apoptosis sets in. Moreover, tumor cells that are deficient in Hh signaling are compromised in their ability to induce osteoblast differentiation and consequently are inefficient in causing osteolysis. The stimulation of osteoblast differentiation sets the stage for osteoclast differentiation and overall promotes osteolysis. Thus, in the process of developing newer therapeutic strategies against breast cancer metastasis to bone it would worthwhile to keep in mind the role of the Hh pathway in osteoblast differentiation in an otherwise predominant osteolytic phenomenon.

Sonic Hedgehog-mediated synergistic effects guiding angiogenesis and osteogenesis

Sonic hedgehog (Shh) is a morphogen controlling the skeletal and vascular development in the embryo but is also reactivated during adult repair processes. Thus, this molecule holds great therapeutic potential for biotechnological and biomedical approaches aiming to enhance tissue regeneration or to replace damaged tissues. According to present knowledge, Shh signaling controls the expression of several families of growth factors involved in neovascularization and vessel maturation and acts upstream of the most prominent angiogenic growth factor, vascular endothelial growth factor. In this context, a very interesting feature of Shh is that it controls both angiogenic activity and vessel stabilization by mural cells. In parallel, Shh seems to have a direct effect on endothelial cell tube formation and seems to trigger the differentiation process of mesenchymal stem cells toward the osteogenic lineage. In this chapter, we will therefore shortly summarize the multifaceted potential of Shh for bone repair and vascularization according to the current literature. In addition, we will show how coculture models based on outgrowth endothelial cells and primary osteoblasts can be used to reveal some of the relevant mechanisms by which Shh drives and connects bone regeneration and vascularization.

Sonic hedgehog expands diaphyseal trabecular bone altering bone marrow niche and lymphocyte compartment

Bone marrow contains distinct microenvironments that regulate hematopoietic stem cells (HSCs). The endosteal HSC niche includes osteoblasts, mineral, and extracellular matrix proteins that interact through various molecular signals to control HSCs. Sonic hedgehog (Shh) is a morphogen involved in the regulation of skeletal development and hematopoiesis, but the effects of Shh on bone in relation to the HSC niche are not well understood. We demonstrate that systemic overexpression of Shh in mice increases osteoblast number with the resultant formation of new trabeculae in the femoral diaphysis. Suggestive of a functional change in the hematopoietic niche, numbers of Lin(-) Sca-1(+) c-Kit(+) cells with hematopoietic progenitor function expand, although cells with in vivo repopulating capacity in the wild-type environment do not increase. Instead, Shh mediates a decrease in number of bone marrow lymphocytes accompanied by a decreased expression of stromal-derived growth factor 1 (SDF-1) and a decrease in Flk2-expressing Lin(-) Sca-1(+) c-Kit(+) cells, indicating a modulation of early lymphopoiesis. This is caused by a microenvironment-induced mechanism as Shh treatment of bone marrow recipients, but not donors, results in a dramatic depletion of lymphocytes. Together, these data suggest that Shh mediates alterations in the bone marrow hematopoietic niche affecting the early lymphoid differentiation.