Intra-articular injection of miRNA-1 agomir, a novel chemically modified miRNA agonists alleviates osteoarthritis (OA) progression by downregulating Indian hedgehog in rats

Our objective in this study is to determine whether intra-articular injection of miRNA-1 can attenuate the progression of OA in rats by down regulating Ihh. Knee chondrocytes were isolated from male Sprague-Dawley rats aged 2-3 days. Second-generation chondrocytes were transfected with miR-1 mimic and empty vector with lipo3000 for 6 h and then stimulated with 10 ng/mL IL-1β for 24 h. OA-related and cartilage matrix genes were quantified using real-time quantitative polymerase chain reaction (RT-qPCR). Two-month-old male Sprague-Dawley rats were divided into three groups (n = 30?): sham operation group + 50 µL saline, anterior cruciate ligament transection (ACLT) group + 50 µL miR-1 agomir (concentration), and control group ACLT + 50 µL miR-1 agomir. Treatment was started one week after the operation. All animals were euthanized eight weeks after the operation. X-rays and micro-CT were used to detect imaging changes in the knee joints. FMT was used to monitor joint inflammation in vivo. Safranin O staining was used to detect morphological changes in articular cartilage. Immunohistochemistry was used to detect Col2, Col10, metalloproteinase-13 (MMP-13). RT-qPCR was used to detect gene changes includingmiR-1, Col2, Col10, MMP-13, Ihh, Smo, Gli1, Gli2, and Gli3. Overexpression of miR-1 in IL-1β-stimulated chondrocytes reduced the levels of Ihh, MMP-13, and Col10 but increased the levels of Col2 and aggrecan. Intra-articular injection of miR-1 agomir reduced osteophyte formation, inflammation, and prevented cartilage damage. RT-qPCR results indicated that the miR-1 agomir increased articular cartilage anabolism and inhibited cartilage catabonism. miR-1 can attenuate the progression of OA by downregulating Ihh.

ERβ Regulation of Indian Hedgehog Expression in the First Wave of Ovarian Follicles

Increased activation of ovarian primordial follicles in Erβ knockout (ErβKO) rats becomes evident as early as postnatal day 8.5. To identify the ERβ-regulated genes that may control ovarian primordial follicle activation, we analyzed the transcriptome profiles of ErβKO rat ovaries collected on postnatal days 4.5, 6.5, and 8.5. Compared to wildtype ovaries, ErβKO ovaries displayed dramatic downregulation of Indian hedgehog (Ihh) expression. IHH-regulated genes, including Hhip, Gli1, and Ptch1, were also downregulated in ErβKO ovaries. This was associated with a downregulation of steroidogenic enzymes Cyp11a1, Cyp19a1, and Hsd17b1. The expression of Ihh remained very low in ErβKO ovaries despite the high levels of Gdf9 and Bmp15, which are known upregulators of Ihh expression in the granulosa cells of activated ovarian follicles. Strikingly, the downregulation of the Ihh gene in ErβKO ovaries began to disappear on postnatal day 16.5 and recovered on postnatal day 21.5. In rat ovaries, the first wave of primordial follicles is rapidly activated after their formation, whereas the second wave of primordial follicles remains dormant in the ovarian cortex and slowly starts activating after postnatal day 12.5. We localized the expression of Ihh mRNA in postnatal day 8.5 wildtype rat ovaries but not in the age-matched ErβKO ovaries. In postnatal day 21.5 ErβKO rat ovaries, we detected Ihh mRNA mainly in the activated follicles in the ovaries' peripheral regions. Our findings indicate that the expression of Ihh in the granulosa cells of the activated first wave of ovarian follicles depends on ERβ.

Transcriptome profiling of gonad-stimulating factors in thoracic ganglia and a potential role of Indian hedgehog gene in vitellogenesis of banana shrimp Fenneropenaeus merguiensis

Shrimp reproduction is controlled by several factors. Central nervous tissues, especially thoracic ganglia and brain, are known sources of gonad stimulating factors (GSFs) in crustaceans, but the GSFs in shrimp have not yet been clarified. Hence, we aimed to characterize and study putative GSFs from thoracic ganglia of adult female Fenneropenaeus merguiensis. An analysis of thoracic ganglia transcriptome revealed 3224 putative GSFs of a total 77,681 unigenes. Only 376 putative GSFs were differentially expressed during ovarian developmental stages. Eight candidate GSFs were validated for their expression patterns in thoracic ganglia, including the Indian hedgehog gene. F. merguiensis Indian hedgehog (FmIHH) was then investigated for its role in vitellogenesis. The obtained full-length cDNA of FmIHH was similar to other crustacean IHHs rather than Sonic and Desert HHs. The FmIHH was dominantly expressed in thoracic ganglia, and its expression was significantly increased in the vitellogenic stages before being downregulated at the mature stage of ovarian development. Injection of the recombinant FmIHH (His-TF-IHH) protein stimulated vitellogenin expression in ovaries on day 3 and 7, and also increased the gonadosomatic index. In addition, crustacean hyperglycemic hormone expression and total sugar were significantly decreased in eyestalks and hemolymph, respectively, after injection of His-TF-IHH, while lactic acid was increased. Both total sugar and lactic acid were unchanged in ovaries of His-TF-IHH injected shrimp. These results suggested that FmIHH plays a crucial role in vitellogenesis and regulate sugar uptake during ovarian development.

MiR-1 is a critical regulator of chondrocyte proliferation and hypertrophy by inhibiting Indian hedgehog pathway during postnatal endochondral ossification in miR-1 overexpression transgenic mice

Endochondral bone formation from the growth plate plays a critical role in vertebrate limb development and skeletal homeostasis. Although miR-1 is mainly expressed in the hypertrophic region of the growth plate during this process, its role in the endochondral bone formation is unknown. To elucidate the role of miR-1 in cartilage development, chondrocyte-specific transgenic mice with high expression of miR-1 were generated (Col2a1-Cre-ER^T2-GFP^fl/fl-RFP-miR-1). Transgenic mice showed short limbs and delayed formation of secondary ossification centers. In the tibia growth plate of miR-1-overexpressing transgenic mice, the chondrocytes in the proliferative zone were disorganized and their proliferation decreased, and the ColX, MMP-13 and Indian Hedgehog (IHH) in chondrocytes showed a downward trend, resulting in decreased terminal differentiation in the hypertrophic zone. In addition, the apoptosis index caspase-3 also showed a downward trend in the tibia growth plate. It was concluded that miR-1 overexpression affects chondrocyte proliferation, hypertrophic differentiation, and apoptosis, thereby delaying the formation of secondary ossification centers and leading to short limbs. It was also verified that miR-1 affects endochondral ossification through the IHH pathway. The above results suggest that miR-1 overexpression can affect endochondral osteogenesis by inhibiting chondrocyte proliferation, hypertrophic differentiation, and apoptosis, thus causing limb hypoplasia in mice. This work gives potential for new therapeutic directions and insights for the treatment of dwarf-related diseases.

Inactivation of Ihh in Sp7-Expressing Cells Inhibits Osteoblast Proliferation, Differentiation, and Bone Formation, Resulting in a Dwarfism Phenotype with Severe Skeletal Dysplasia in Mice

Indian hedgehog (Ihh) is an indispensable paracrine factor for proper tissue patterning, skeletogenesis, and cellular proliferation. Recent genetic studies have revealed critical roles of chondrocyte-derived Ihh in regulating chondrocyte proliferation, hypertrophy and cartilage ossification. However, the functions of Sp7-expressing cell-derived Ihh in osteoblast differentiation and bone formation remain unclear. Sp7 is an essential transcription factor for osteoblast differentiation. In the current study, we generated Sp7-iCre; Ihh^fl/fl mice, in which the Ihh gene was specifically deleted in Sp7-expressing cells to investigate the roles of Ihh. Ihh ablation in Sp7-expressing cells resulted in a dwarfism phenotype with severe skeletal dysplasia and lethality at birth, but with normal joint segmentation. Sp7-iCre; Ihh^fl/fl mice had fewer osteoblasts, almost no cortical and trabecular bones, smaller skulls, and wider cranial sutures. Additionally, the levels of osteogenesis- and angiogenesis-related genes, and of major bone matrix protein genes were significantly reduced. These results demonstrated that Ihh regulates bone formation in Sp7-expressing cells. Ihh deficiency in primary osteoblasts cultured in vitro inhibited their proliferation, differentiation, and mineralization ability, and reduced the expression of osteogenesis-related genes. Moreover, the deletion of Ihh also attenuated the Bmp2/Smad/Runx2 pathway in E18.5 tibial and primary osteoblasts. The activity of primary osteoblasts in mutant mice was rescued after treatment with rhBMP2. In summary, our data revealed that Ihh in Sp7-expressing cells plays an indispensable role in osteoblast differentiation, mineralization, and embryonic osteogenesis, further implicated that its pro-osteogenic role may be mediated through the canonical Bmp2/Smad/Runx2 pathway.

Generation of an Ihh-mKate2-Dre knock-in mouse line

Indian hedgehog (Ihh), a member of the Hh family, plays important roles in vertebrate development and homeostasis. To improve our understanding of the function of Ihh-expressing cells and their progeny as well, we generate an Ihh-mKate2^tomm20 -Dre knock-in mouse line that can label Ihh-positive cells with a fluorescence protein mKate2 and trace Ihh-positive cells and their progeny via Dre-mediated recombination. Consistent with previous reports, we verified Ihh expression in hypertrophic chondrocytes of growth plate and granulosa cells of ovarian follicles by mKate2 immunostaining, and meanwhile confirmed Dre activity in these cells via a Dre reporter mouse line Rosa26-confetti2. We also found, for the first time, that Ihh can mark some cell types, including retinal ganglion cells, Purkinje cells, and gallbladder epithelial cells. Taken together, the Ihh-mKate2^tomm20 -Dre mouse is a genetic tool for examining the precise expression profile of Ihh and tracing Ihh-expressing cells and their progeny.

Altered microRNAs in C3H10T1/2 cells induced by p.E95K mutant IHH signaling

Background

Indian Hedgehog (IHH), an important cell signaling protein, plays a key regulatory role in development of cartilage and chondrogenesis. Earlier studies have shown that heterozygous missense mutations in IHH gene may cause brachydactyly type A1 (BDA1), an autosomal dominant inheritance disease characterized by apparent shortness or absence of the middle phalanges of all digits. MicroRNAs (miRNAs) have been found to be significant post-transcriptional regulators of gene expression and significantly influence the process of bone-development. Therefore, it is possible that miRNAs are involved in the mechanism underlying the development of BDA1. However, the relationship between miRNAs and the pathogenesis of BDA1 remains unclear.

Methods

In this study, we used microarray-based miRNA profiling to investigate the role of miRNAs in BDA1 by characterization of differentially expressed miRNAs in C3H10T1/2 cell line induced by wild type (WT) and p.E95K mutant (MT) IHH signaling.

Results

Our results identified 6 differentially expressed miRNAs between WT and control (CT) group and 5 differentially expressed miRNAs between MT and CT groups. In particular, miR-135a-1-3p was found to be a significantly differentially expressed miRNA between WT and CT group. Results of dual-luciferase reporter gene experiment successfully discovered Hoxd10 was one of the target gene of miR-135a-1-3p. Additionally, our pathway analysis revealed that the targets of these miRNAs of interest were highly involved with Runx1/2, Notch and collagen-related pathways.

Conclusions

Taken together, our findings provided important clue for future study of the process of miRNA-regulation in IHH signaling and novel insights into the regulatory role of miRNA in pathogenesis of BDA1.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41065-021-00207-8.

SAG therapy restores bone growth and reduces enchondroma incidence in a model of skeletal chondrodysplasias caused by Ihh deficiency

Inactivation mutations in the Indian hedgehog (Ihh) gene in humans cause numerous skeletal chondrodysplasias, including acrocapitofemoral dysplasia, brachydactyly type A1, and human short stature. The lack of an appropriate human-relevant model to accurately represent these chondrodysplasias has hampered the identification of clinically effective treatments. Here, we established a mouse model of human skeletal dysplasia induced by Ihh gene mutations via ablation of Ihh in Aggrecan-positive (Acan+) cells using Aggrecan (Acan)-creERT transgenic mice. Smoothen agonist (SAG) promoted Hh activity and rescued chondrocyte proliferation and differentiation by stimulating smoothened trafficking to the cilium in Ihh-silenced cells. SAG treatment corrected mouse stature and significantly decreased mortality without evidence of toxicity. Moreover, Ihh ablation in Acan+ cells produced enchondroma-like tissues near the growth plates that were significantly reduced by SAG treatment. These results demonstrated that SAG effectively treats skeletal dysplasia caused by Ihh gene mutations in a mouse model, suggesting that SAG may represent a potential drug for the treatment of these diseases and/or enchondromas.

The Effects of Fluvastatin on Indian Hedgehog Pathway in Endochondral Ossification

Statins have demonstrated to be effective for treating chondrodysplasia and its effects were believed to be associated with the fibroblast growth factor receptor 3 (FGFR3). Statins promoted the degradation of FGFR3 in studies using disease-specific induced pluripotent stem cells and model mice, however, recent studies using normal chondrocytes reported that statins did not degrade FGFR3. In order to further investigate the effects of statins in endochondral ossification, this study examined the influence of statins on Indian hedgehog (Ihh), another important component of endochondral ossification, and its related pathways. The chondrocyte cell line ATDC5 was used to investigate changes in cell proliferation, mRNA, and protein expression levels. In addition, an organ culture of a mouse metatarsal bone was performed followed by hematoxylin-eosin staining and fluorescent immunostaining. Results indicated that expression level of Ihh increased with the addition of statins, which activated the Ihh pathway and altered the localization of Ihh. Changes in cholesterol modification may have affected Ihh diffusibility; however, further experiments are necessary. A reactive increase in parathyroid hormone-related protein (PTHrP) was observed in addition to changes in the Wnt pathway through secreted-related protein 2/3 and low-density lipoprotein 5/6. This led to the promotion of cell proliferation, increase of the hypertrophic chondrocyte layer, inhibition of apoptosis, and decrease in mineralization. This study demonstrated that statins had an influence on Ihh, and that the hyperfunction of Ihh may prevent premature cell death caused by FGFR3-related chondrodysplasia through an indirect increase in the expression of PTHrP.

The articular cartilage preservative effects of genistein in an experimental model of knees osteoarthritis

The study aimed to investigate the preservative effects of genistein on articular cartilage in an experimental model of knee osteoarthritis in rats. Thirty male Wistar rats were assigned to 3 equal groups: sham group, osteoarthritis control group (OAG), and genistein-treated osteoarthritis group (GTG). Intra-articular injections of monosodium iodoacetate were used for osteoarthritis induction. After 2 weeks of rest for the induction of the inflammatory process, genistein (30 mg/kg/day) vs. saline gavage was administered for 8 weeks. The expression of matrix metalloproteinase (MMP)-8 and MMP-13, Sox5/Sox6, Indian hedgehog (IHH), and Col2 were evaluated in medial femoral condyle sections by immunohistochemical staining. The number of chondrocytes and cartilage thicknesses were also measured and compared among the groups. No significant change in cartilage thickness was observed in GTG compared with OAG (p = 0.188). Chondrocyte count was significantly higher in the articular cartilage of GTG compared with OAG (p = 0.006). Induction of osteoarthritis significantly increased the expression of MMP-8, MMP-13, and IHH, but decreased Col2, Sox5, and Sox6 expression (p < 0.001); these were partially prevented in the GTG. Our findings support the effectiveness of genistein treatment in the prevention of articular cartilage damage in the experimental model of knee osteoarthritis. The proposed mechanism of action is through the suppression of the MMP, IHH, and Col2 pathways, besides the induction of Sox5 and Sox6 expression. Novelty: Genistein prevents articular cartilage damage in the experimental model of knee osteoarthritis. The osteoprotective effect is manifested by the modulation of expression of MMP, Sox, IHH, and Col2 proteins.

Acrocapitofemoral dysplasia: Novel mutation in IHH in two adult patients from the third family in the literature and progression of the disease

Acrocapitofemoral dysplasia (ACFD) is a rare autosomal recessive skeletal dysplasia characterized by short stature with short limb dwarfism, brachydactyly, and a narrow thorax. Major radiographic features are egg-shaped capital femoral epiphyses with a short femoral neck and cone-shaped epiphyses, mainly in the hands and hips. To date, only four child patients from two families have been reported. We describe two adult patients with ACFD with a novel homozygous c.478C>T (p.Arg160Cys) mutation in IHH in the third family of the literature. The reported cases showed a middle phalanges which fused with distal phalanges in the fifth toes, the typical configuration of metacarpals, radial angulation and extremely short femoral neck. These findings could help the diagnosis of ACFD in adult patients. We hope that this new family will be a helpful guide for predicting and managing the prognosis of diagnosed children.

Pharmacological Disruption of Phosphorylated Eukaryotic Initiation Factor-2α/Activating Transcription Factor 4/Indian Hedgehog Protects Intervertebral Disc Degeneration via Reducing the Reactive Oxygen Species and Apoptosis of Nucleus Pulposus Cells

Excessive reactive oxygen species (ROS) and apoptosis in nucleus pulposus (NP) cells accelerate the process of intervertebral disc degeneration (IDD). Here, we integrated pathological samples and in vitro and in vivo framework to investigate the impact of phosphorylation of eukaryotic initiation factor-2α (eIF2α)/activating transcription factor 4 (ATF4)/Indian hedgehog (Ihh) signaling in the IDD. From the specimen analysis of the IDD patients, we found phosphorylated eIF2α (p-eIF2α), ATF4 and Ihh protein levels were positively related while the NP tissue went degenerative. In vitro, tumor necrosis factor (TNF)-α caused the NP cell degeneration and induced a cascade of upregulation of p-eIF2α, ATF4, and Ihh. Interestingly, ATF4 could enhance Ihh expression through binding its promoter region, and silencing of ATF4 decreased Ihh and protected the NP cells from degeneration. Moreover, ISRIB inhibited the p-eIF2α, which resulted in a suppression of ATF4/Ihh, and alleviated the TNF-α-induced ROS production and apoptosis of NP cells. On the contrary, further activating p-eIF2α aggravated the NP cell degeneration, with amplification of ATF4/Ihh and a higher level of ROS and apoptosis. Additionally, applying cyclopamine (CPE) to suppress Ihh was efficient to prevent NP cell apoptosis but did not decrease the ROS level. In an instability-induced IDD model in mice, ISRIB suppressed p-eIF2α/ATF4/Ihh and prevented IDD via protecting the anti-oxidative enzymes and decreased the NP cell apoptosis. CPE prevented NP cell apoptosis but did not affect anti-oxidative enzyme expression. Taken together, p-eIF2α/ATF4/Ihh signaling involves the ROS level and apoptosis in NP cells, the pharmacological disruption of which may provide promising methods in preventing IDD.

TL1A/TNFR2 Axis Enhances Immunoregulatory Effects of Bone Marrow Derived Mesenchymal Stem Cell by Indian Hedgehog Signaling Pathway

Background and Objectives

The immunomodulatory potential of mesenchymal stem cells (MSCs) can be regulated by a variety of molecules, especially cytokines. The inflammatory cytokine, TNF-like ligand 1A (TL1A), has been reported as an inflammation stimulator in-multiple autoimmune diseases. Here, we studied the effects of TL1A/TNF-receptor 2 (TNFR2) pathway on the therapeutic potency of bone marrow-derived MSCs (BMSCs).

Methods and Results

BMSCs, fibroblast-like synoviocytes (FLSs), and H9 and jurkat human T lymphocytes were used in this study. BMSCs paracrine activities, differentiation, proliferation, and migration were investigated after stimulation with TL1A, and intervened with anti-TNFR2. Additionally, the effects of TL1A on BMSCs therapeutic potency were evaluated by treating RA-FLSs, and H9 and jurkat T cells with TL1A-stimulated BMSCs conditioned medium (CM). Indian hedgehog (IHH) involvement was determined by gene silencing and treatment by recombinant IHH (rIHH). TL1A induced BMSCs stemness-related genes, COX-2, IL-6, IDO, TGF-β and HGF through TNFR2. Also, TL1A corrected biased differentiation and increased proliferation, and migration through TNFR2. Meanwhile, CM of TL1A-stimulated BMSCs decreased the inflammatory markers of RA-FLSs and T cells. Moreover, TL1A-stimulated BMSCs experienced IHH up-regulation coupled with NF-κB and STAT3 signaling up-regulation, while p53 and oxidative stress were down-regulated. Furthermore, treatment of BMSCs by rIHH increased their anti-inflammatory effects. More importantly, knockdown of IHH decreased the ability of TL1A-stimulated BMSCs to alleviating the inflammation in RA-FLSs and T cells.

Conclusions

This study reports the effects of TL1A/TNFR2 pathway on the biological behaviors and therapeutic potency of BMSCs through IHH. These findings could introduce novel procedures to increase the stemness of MSCs in cellular therapy.

Cyclic stretch promotes the ossification of ligamentum flavum by modulating the Indian hedgehog signaling pathway

The Indian hedgehog (IHH) signaling pathway is an important pathway for bone growth and development. The aim of the present study was to examine the role of the IHH signaling pathway in the development of the ossification of ligamentum flavum (OLF) at the cellular and tissue levels. The expression levels and localization of the osteogenic genes Runt-related transcription factor 2 (RUNX2), Osterix, alkaline phosphatase (ALP), osteocalcin (OCN) and IHH were evaluated in OLF tissues by reverse transcription-quantitative PCR (RT-qPCR) and immunohistochemistry. Non-ossified ligamentum flavum (LF) sections were used as control samples. The tissue explant method was used to obtain cultured LF cells. In addition, OLF cells were subjected to cyclic stretch application for 0, 6, 12 or 24 h. The expression levels of osteogenic genes, and the IHH signaling pathway genes IHH, Smoothened (SMO), GLI family zinc finger 1 (GLI1), GLI2 and GLI3 were evaluated with RT-qPCR and western blotting. Osteogenic differentiation was further evaluated by assessing ALP activity and staining. Moreover, the effect of cyclopamine (Cpn), an IHH signaling inhibitor, on osteogenic differentiation was examined. The RT-qPCR and immunohistochemical results indicated that the mRNA and protein expression levels of RUNX2, Osterix, ALP, OCN and IHH were significantly higher in the OLF group compared with the LF group. Furthermore, application of cyclic stretch to OLF cells resulted in greater ALP activity, and significant increases in mRNA and protein expression levels of RUNX2, Osterix, ALP and OCN in a time-d00ependent manner. Cyclic stretch application also led to significant increases in IHH signaling pathway genes, including IHH, SMO, GLI1 and GLI2, while no significant effect was found on GLI3 expression level. In addition, it was found that Cpn significantly reversed the effect of cyclic stretch on the ALP activity, and the expression levels of RUNX2, Osterix, ALP, OCN, GLI1 and GLI2. Collectively, the present results suggested that the IHH signaling pathway may mediate the effect of cyclic stretch on the OLF cells.

Taladegib controls early chondrocyte hypertrophy via inhibiting smoothened/Gli1 pathway

Chondrocyte hypertrophy is a common phenomenon in osteoarthritis (OA). Indian hedgehog (Ihh) is secreted by pre-hypertrophic chondrocytes, which regulates the hypertrophy and mineralization of chondrocytes during cartilage osteogenesis. Smoothened (Smo) is a connecting protein among the Ihh signaling pathway that triggers glioma-associated oncogene homologue 1 (Gli1) to active the hypertrophic process. In this study, we aimed to examine a new inhibitor of Smo in the prevention of chondrocyte hypertrophy during OA. We collected human joint cartilage from the OA patients undergoing knee arthroplasty. Chondrocytes in different OA degrees were isolated and divided them into mild and severe groups. Alginate beads (ABs) was used to establish a chondrocyte hypertrophy model. The expression of type X collagen, MMP-13, Runx-2, type II collagen, SOX-9, and aggrecan were determined using immunofluorescence, Western blot, real-time polymerase chain reaction (qRT-PCR). Cell counting kit-8 (CCK-8) assay was performed to assess the viability of chondrocytes. ABs treatment accelerated the process of chondrocyte hypertrophy and upregulated the expression of type X collagen, Matrix metalloproteinase-13 (MMP-13), Runx-2 but decreased type II collagen, SOX-9, and aggrecan both in protein and mRNA levels, which abolished by the present of Taladegib with the activation of Smo and Gli1. However, in the severe OA chondrocytes, Taladegib lost the ability to reverse hypertrophic chondrocytes to a healthy state and made no sense to the expression of type X collagen and Gli1. Our results reveal Taladegib as a novel drug in controlling chondrocyte hypertrophy depending on Smo blocking, which plays a vital role in the homeostasis of cartilage and the development of OA. Besides, we found that Taladegib only works in the previous stage of chondrocytes hypertrophy but not in the later of the process.

Skeletal Toxicity of Coplanar Polychlorinated Biphenyl Congener 126 in the Rat Is Aryl Hydrocarbon Receptor Dependent

Epidemiological evidence links polychlorinated biphenyls (PCBs) to skeletal toxicity, however mechanisms whereby PCBs affect bone are poorly studied. In this study, coplanar PCB 126 (5 μmol/kg) or corn oil vehicle was administered to N = 5 and 6 male and female, wild type (WT) or AhR -/- rats via intraperitoneal injection. Animals were sacrificed after 4 weeks. Bone length was measured; bone morphology was assessed by microcomputed tomography and dynamic histomorphometry. Reduced bone length was the only genotype-specific effect and only observed in males (p < .05). WT rats exposed to PCB 126 had reduced serum calcium, and smaller bones with reduced tibial length, cortical area, and medullary area relative to vehicle controls (p < .05). Reduced bone formation rate observed in dynamic histomorphometry was consistent with inhibition of endosteal and periosteal bone growth. The effects of PCB 126 were abolished in AhR -/- rats. Gene expression in bone marrow and shaft were assessed by RNA sequencing. Approximately 75% of the PCB-regulated genes appeared AhR dependent with 89 genes significantly (p < .05) regulated by both PCB 126 and knockout of the AhR gene. Novel targets significantly induced by PCB 126 included Indian hedgehog (Ihh) and connective tissue growth factor (Ctgf/Ccn2), which regulate chondrocyte proliferation and differentiation in the bone growth plate and cell-matrix interactions. These data suggest the toxic effects of PCB 126 on bone are mediated by AhR, which has direct effects on the growth plate and indirect actions related to endocrine disruption. These studies clarify important mechanisms underlying skeletal toxicity of dioxin-like PCBs and highlight potential therapeutic targets.

Indian Hedgehog regulates senescence in bone marrow-derived mesenchymal stem cell through modulation of ROS/mTOR/4EBP1, p70S6K1/2 pathway

Premature senescence of bone marrow-derived mesenchymal stem cells (BMSC) remains a major concern for their application clinically. Hedgehog signaling has been reported to regulate aging-associated markers and MSC skewed differentiation. Indian Hedgehog (IHH) is a ligand of Hedgehog intracellular pathway considered as an inducer in chondrogenesis of human BMSC. However, the role of IHH in the aging of BMSC is still unclear. This study explored the role IHH in the senescence of BMSC obtained from human samples and senescent mice. Isolated BMSC were transfected with IHH siRNA or incubated with exogenous IHH protein and the mechanisms of aging and differentiation investigated. Moreover, the interactions between IHH, and mammalian target of rapamycin (mTOR) and reactive oxygen species (ROS) were evaluated using the corresponding inhibitors and antioxidants. BMSC transfected with IHH siRNA showed characteristics of senescence-associated features including increased senescence-associated β-galactosidase activity (SA-β-gal), induction of cell cycle inhibitors (p53/p16), development of senescence-associated secretory phenotype (SASP), activation of ROS and mTOR pathways as well as the promotion of skewed differentiation. Interestingly, BMSC treatment with IHH protein reversed the senescence markers and corrected biased differentiation. Moreover, IHH shortage-induced senescence signs were compromised after mTOR and ROS inhibition. Our findings presented anti-aging activity for IHH in BMSC through down-regulation of ROS/mTOR pathways. This discovery might contribute to increasing the therapeutic, immunomodulatory and regenerative potency of BMSC and introduce a novel remedy in the management of aging-related diseases.

Indian hedgehog in craniofacial neural crest cells links to skeletal malocclusion by regulating associated cartilage formation and gene expression

The frontal craniofacial skeleton derived from neural crest cells is vital for facial structure and masticatory functions. The exact role of Indian hedgehog (Ihh) in facial and masticatory development has not been fully explored. In this study, we generated craniofacial neural crest cells-specific Ihh deletion mice (Wnt1-Cre;Ihh^fl/fl ;Tomato^fl/+ ) and found the gradual dwarfism without perinatal lethality. Morphological and histological analyses revealed unambiguous craniofacial phenotypes in mutants, where we observed skeletal malocclusion accompanied by markedly hypoplastic nasomaxillary complex and reversed incisor occlusion. Both the replacement of nasal concha cartilage by turbinate bones and the endochondral ossification of nasal septum ethmoid bone were substantially delayed. We also observed hypoplastic mandibles in mutants where the mandibular ramus was unexpectedly the most affected. Both the condylar process and mandibular angle cartilages were distorted. However, dental examination showed no significant changes in teeth and dentition. Finally, a comprehensive RNA sequence analysis utilizing condylar cartilage identified Ihh-associated gene network including several cell cycle genes and 16 genes related to the extracellular matrix, sulfate transporters, transcription factors, receptors, a ciliogenesis factor, and an adhesion molecule. Our data provide direct in vivo evidence that Ihh plays crucial roles in midface and masticatory system formation, likely by activating key genes.

Chondral Differentiation of Induced Pluripotent Stem Cells Without Progression Into the Endochondral Pathway

A major problem with chondrocytes derived in vitro from stem cells is undesired hypertrophic degeneration, to which articular chondrocytes (ACs) are resistant. As progenitors of all adult tissues, induced pluripotent stem cells (iPSCs) are in theory able to form stable articular cartilage. In vitro differentiation of iPSCs into chondrocytes with an AC-phenotype and resistance to hypertrophy has not been demonstrated so far. Here, we present a novel protocol that succeeded in deriving chondrocytes from human iPSCs without using pro-hypertrophic bone-morphogenetic-proteins. IPSC-chondrocytes had a high cartilage formation capacity and deposited two-fold more proteoglycans per cell than adult ACs. Importantly, cartilage engineered from iPSC-chondrocytes had similar marginal expression of hypertrophic markers (COL10A1, PTH1R, IBSP, ALPL mRNAs) like cartilage from ACs. Collagen X was barely detectable in iPSC-cartilage and 30-fold lower than in hypertrophic cartilage derived from mesenchymal stromal cells (MSCs). Moreover, alkaline phosphatase (ALP) activity remained at basal AC-like levels throughout iPSC chondrogenesis, in contrast to a well-known significant upregulation in hypertrophic MSCs. In line, iPSC-cartilage subjected to mineralizing conditions in vitro showed barely any mineralization, while MSC-derived hypertrophic cartilage mineralized strongly. Low expression of Indian hedgehog (IHH) like in ACs but rising BMP7 expression like in MSCs suggested that phenotype stability was linked to the hedgehog rather than the bone morphogenetic protein (BMP) pathway. Taken together, unlimited amounts of AC-like chondrocytes with a high proteoglycan production reminiscent of juvenile chondrocytes and resistance to hypertrophy and mineralization can now be produced from human iPSCs in vitro. This opens new strategies for cartilage regeneration, disease modeling and pharmacological studies.

Inhibition of Ihh Reverses Temporomandibular Joint Osteoarthritis via a PTH1R Signaling Dependent Mechanism

The temporomandibular joint (TMJ), which is biomechanically related to dental occlusion, is often insulted by osteoarthritis (OA). This study was conducted to clarify the relationship between Indian hedgehog (Ihh) and parathyroid hormone receptor 1 (PTH1R) signaling in modulating the enhanced chondrocyte terminal differentiation in dental stimulated TMJ osteoarthritic cartilage. A gain- and loss-of-function strategy was used in an in vitro model in which fluid flow shear stress (FFSS) was applied, and in an in vivo model in which the unilateral anterior cross-bite (UAC) stimulation was adopted. Ihh and PTH1R signaling was modulated through treating the isolated chondrocytes with inhibitor/activator and via deleting Smoothened (Smo) and/or Pth1r genes in mice with the promoter gene of type 2 collagen (Col2-CreER) in the tamoxifen-inducible pattern. We found that both FFSS and UAC stimulation promoted the deep zone chondrocytes to undergo terminal differentiation, while cells in the superficial zone were robust. We demonstrated that the terminal differentiation process in deep zone chondrocytes promoted by FFSS and UAC was mediated by the enhanced Ihh signaling and declined PTH1R expression. The FFSS-promoted terminal differentiation was suppressed by administration of the Ihh inhibitor or PTH1R activator. The UAC-promoted chondrocytes terminal differentiation and OA-like lesions were rescued in Smo knockout, but were enhanced in Pth1r knockout mice. Importantly, the relieving effect of Smo knockout mice was attenuated when Pth1r knockout was also applied. Our data suggest a chondrocyte protective effect of suppressing Ihh signaling in TMJ OA cartilage which is dependent on PTH1R signaling.

Ipriflavone attenuates the degeneration of cartilage by blocking the Indian hedgehog pathway

BACKGROUND

To determine if ipriflavone, a novel and safe inhibitor of Indian hedgehog (Ihh) signaling, can attenuate cartilage degeneration by blocking the Ihh pathway.

METHODS

Human chondrocytes were used to evaluate Ihh signaling, cell proliferation, apoptosis, gene, and protein expression of chondrocytes by cell proliferation and apoptosis assays, real-time qPCR, and Western blotting at 48 h after ipriflavone treatment. Human cartilage explants were further used to validate the cell culture results. The effects of ipriflavone on cartilage degeneration in vivo were assessed using the rat ACLT OA model. Two-month-old male SD rats were randomized into 3 groups (n = 75): (1) sham, (2) ACLT alone, and (3) ACLT+ ipriflavone. Ipriflavone was administered intragastrically at 24 h after ACLT for 6 weeks. The extent of OA progression was evaluated by the OARSI score and immunohistochemistry at 12 weeks after surgery. The Ihh signaling pathway and OA-related genes were quantified by real-time PCR.

RESULTS

Cell proliferation in the cells treated with ipriflavone was increased to 36.40% ± 1.32% (5 μM) and 28.54% ± 0.74% (10 μM) from 11.99% ± 0.35% (DMSO) (P < 0.001), and apoptosis was decreased to 12.64% ± 3.7% (5 μM) and 15.18% ± 3.13% (10 μM) from 25.76% ± 5.1% (DMSO) (P < 0.05). Ipriflavone blocked Runx-2 mainly through the Smo-Gli2 pathway. A similar result was found in the cartilage explant culture. Ihh signaling in vivo was inhibited in animals treated with ipriflavone. Safranin-O staining revealed a less cartilage damage with lower OARSI scores (P < 0.05) in the ipriflavone-treated animals compared with untreated animals. The gene expression of Smo and Gli2 was inhibited significantly by ipriflavone (P < 0.05). The OA-related gene and protein type X, MMP-13, and type II collagen-C fragment were reduced, while type II collagen and Agg were increased in the ipriflavone-treated animals (P < 0.05).

CONCLUSIONS

Catabolic genes were disrupted by blocking the Ihh pathway. This finding suggests that disruption of Ihh signaling with ipriflavone provides chondral protection in rat posttraumatic OA.

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.

p.E95K mutation in Indian hedgehog causing brachydactyly type A1 impairs IHH/Gli1 downstream transcriptional regulation

Background

Brachydactyly type A1 (BDA1, OMIM 112500) is a rare inherited malformation characterized primarily by shortness or absence of middle bones of fingers and toes. It is the first recorded disorder of the autosomal dominant Mendelian trait. Indian hedgehog (IHH) gene is closely associated with BDA1, which was firstly mapped and identified in Chinese families in 2000. Previous studies have demonstrated that BDA1-related mutant IHH proteins affected interactions with its receptors and impaired IHH signaling. However, how the altered signaling pathway affects downstream transcriptional regulation remains unclear.

Results

Based on the mouse C3H10T1/2 cell model for IHH signaling activation, two recombinant human IHH-N proteins, including a wild type protein (WT, amino acid residues 28–202) and a mutant protein (MT, p.E95k), were analyzed. We identified 347, 47 and 4 Gli1 binding sites in the corresponding WT, MT and control group by chromatin immunoprecipitation and the overlapping of these three sets was poor. The putative cis regulated genes in WT group were enriched in sensory perception and G-protein coupled receptor-signaling pathway. On the other hand, putative cis regulated genes were enriched in Runx2-related pathways in MT group. Differentially expressed genes in WT and MT groups indicated that the alteration of mutant IHH signaling involved cell-cell signaling and cellular migration. Cellular assay of migration and proliferation validated that the mutant IHH signaling impaired these two cellular functions.

Conclusions

In this study, we performed integrated genome-wide analyses to characterize differences of IHH/Gli1 downstream regulation between wild type IHH signaling and the E95K mutant signaling. Based on the cell model, our results demonstrated that the E95K mutant signaling altered Gli1-DNA binding pattern, impaired downstream gene expressions, and leaded to weakened cellular proliferation and migration. This study may help to deepen the understanding of pathogenesis of BDA1 and the role of IHH signaling in chondrogenesis.

Electronic supplementary material

The online version of this article (10.1186/s12863-018-0697-5) contains supplementary material, which is available to authorized users.

Whole-exome sequencing identifies a novel IHH insertion in an Ontario family with brachydactyly type A1

Isolated brachydactyly is an umbrella term describing disproportionally shortened fingers and toes, often following an autosomal dominant mode of inheritance. Various forms of brachydactyly have been characterized and several causative genes have been found, but many types remain genetically undefined. We describe an Ontario family with mild brachydactyly in which whole-exome sequencing identified a novel variant for brachydactyly type A1 (exon 1, c.285_287dupGAA, p.Glu95_Asn96insLys) in the Indian hedgehog (IHH) gene. This rare variant co-segregated with affected status in the pedigree and was associated with (1) shortened middle phalange length by 21.1% (p < 0.001); (2) shortened palm length by 13.8% (p < 0.01); (3) reduced digit-palm ratio by 6.8% (p < 0.03); and (4) reduced stature by 9.5% (p < 0.001). We report the first IHH in-frame insertion causing brachydactyly type A1.

The Effects of Indian Hedgehog Deletion on Mesenchyme Cells: Inducing Intermediate Cartilage Scaffold Ossification to Cause Growth Plate and Phalange Joint Absence, Short Limb, and Dwarfish Phenotypes

The endochondral ossification plays a critical role in vertebrate limb development and skeletal homeostasis, where limb mesenchyme cells form an intermediate cartilage scaffold that develops into growth plates and then replaced by bone. Although Indian hedgehog (Ihh) is known to control the hypertrophic differentiation process of chondrocytes, its role from the mesenchyme cells to the early stages of chondrogenesis is unclear. To define the function of Ihh in the mesenchymal cell's early stages of chondrogenesis, we specifically delete Ihh in Prx1-expressed mesenchyme cells at E9.5 using Prx1-Cre;Ihh^fl/fl;Rosa26^-ZsGreen1 mice. We found that deleting Ihh in the mesenchyme cells results in an early and quick ossification of the intermediate cartilage scaffold, causing the growth plate and phalange joint absence, short limbs, and dwarfishness. The green fluorescent protein (GFP)-positive cells derived from deleted Ihh mesenchyme cells overlap with von Kossa- and osteocalcin-positive staining area. These deleted Ihh/GFP-positive cells isolated from Prx1-Cre;Ihh^fl/fl;Rosa26^-ZsGreen1 newborn mice had osteogenic differentiation by showing a positive Alizarin red and von Kossa staining, as well as an enhanced Col1a1, osteocalcin, and Runx2 expression. Our findings demonstrate that deleting Ihh in mesenchyme cells during early limb development promotes intermediate cartilage scaffold ossification, which prevents growth plate formation that causes phalange joint absence, short limb, and dwarfish phenotype.

Part I: Development and Physiology of the Temporomandibular Joint

PURPOSE OF REVIEW

Investigate the developmental physiology of the temporomandibular joint (TMJ), a unique articulation between the cranium and the mandible.

RECENT FINDINGS

Principal regulatory factors for TMJ and disc development are Indian hedgehog (IHH) and bone morphogenetic protein (BMP-2). The mechanism is closely associated with ear morphogenesis. Secondary condylar cartilage emerges as a subperiosteal blastema on the medial surface of the posterior mandible. The condylar articular surface is immunoreactive for tenascin-C, so it is a modified fibrous periosteum with an underlying proliferative zone (cambrium layer) that differentiates into fibrocartilage. The latter cushions high loads and subsequently produces endochondral bone. The TMJ is a heavily loaded joint with three cushioning layers of fibrocartilage in the disc, as well as in subarticular zones in the fossa and mandibular condyle. The periosteal articular surface produces fibrocartilage to resist heavy loads, and has unique healing and adaptive properties for maintaining life support functions under adverse environmental conditions.

Transfection of the IHH gene into rabbit BMSCs in a simulated microgravity environment promotes chondrogenic differentiation and inhibits cartilage aging

The effect of overexpressing the Indian hedgehog (IHH) gene on the chondrogenic differentiation of rabbit bone marrow-derived mesenchymal stem cells (BMSCs) was investigated in a simulated microgravity environment. An adenovirus plasmid encoding the rabbit IHH gene was constructed in vitro and transfected into rabbit BMSCs. Two large groups were used: conventional cell culture and induction model group and simulated microgravity environment group. Each large group was further divided into blank control group, GFP transfection group, and IHH transfection group. During differentiation induction, the expression levels of cartilage-related and cartilage hypertrophy-related genes and proteins in each group were determined. In the conventional model, the IHH transfection group expressed high levels of cartilage-related factors (Coll2 and ANCN) at the early stage of differentiation induction and expressed high levels of cartilage hypertrophy-related factors (Coll10, annexin 5, and ALP) at the late stage. Under the simulated microgravity environment, the IHH transfection group expressed high levels of cartilage-related factors and low levels of cartilage hypertrophy-related factors at all stages of differentiation induction. Under the simulated microgravity environment, transfection of the IHH gene into BMSCs effectively promoted the generation of cartilage and inhibited cartilage aging and osteogenesis. Therefore, this technique is suitable for cartilage tissue engineering.

The inhibitory roles of Ihh downregulation on chondrocyte growth and differentiation

The proliferative rate of chondrocytes affects bone elongation. Chondrocyte hypertrophy is required for endochondral bone formation as chondrocytes secrete factors required for osteoblast differentiation and maturation. Previous studies have demonstrated that the Indian hedgehog (Ihh) signaling pathway is a key regulator of skeletal development and homeostasis. The aim of the present study was to investigate the function of Ihh in chondrocyte proliferation and differentiation, as well as the underlying mechanisms. Ihh was knocked down in mouse chondrocyte cells using short hairpin RNA. Chondrocyte apoptosis and cell cycle arrest were assessed using flow cytometry and the results indicated that knockdown of Ihh significantly inhibited cell growth (P<0.05) and increased apoptosis (P<0.001) compared with negative control cells. Downregulation of Ihh also resulted in cell cycle arrest at G1 to S phase in chondrocytes. It was also observed that knockdown of Ihh decreased alkaline phosphatase activity and mineral deposition of chondrocytes. The inhibitory roles of Ihh downregulation on chondrocyte growth and differentiation may be associated with the transforming growth factor-β/mothers against decapentaplegic and osteoprotegerin/receptor activator of nuclear factor κB ligand signaling pathway. The results of the present study suggest that chondrocyte-derived Ihh is essential for maintaining bone growth plates and that manipulation of Ihh expression or its signaling components may be a novel therapeutic technique for the treatment of skeletal diseases, including achondroplasia.

Shh promotes direct interactions between epidermal cells and osteoblast progenitors to shape regenerated zebrafish bone

Zebrafish innately regenerate amputated fins by mechanisms that expand and precisely position injury-induced progenitor cells to re-form tissue of the original size and pattern. For example, cell signaling networks direct osteoblast progenitors (pObs) to rebuild thin cylindrical bony rays with a stereotypical branched morphology. Hedgehog/Smoothened (Hh/Smo) signaling has been variably proposed to stimulate overall fin regenerative outgrowth or promote ray branching. Using a photoconvertible patched2 reporter, we resolve active Hh/Smo output to a narrow distal regenerate zone comprising pObs and adjacent motile basal epidermal cells. This Hh/Smo activity is driven by epidermal Sonic hedgehog a (Shha) rather than Ob-derived Indian hedgehog a (Ihha), which nevertheless functions atypically to support bone maturation. Using BMS-833923, a uniquely effective Smo inhibitor, and high-resolution imaging, we show that Shha/Smo is functionally dedicated to ray branching during fin regeneration. Hh/Smo activation enables transiently divided clusters of Shha-expressing epidermis to escort pObs into similarly split groups. This co-movement likely depends on epidermal cellular protrusions that directly contact pObs only where an otherwise occluding basement membrane remains incompletely assembled. Progressively separated pObs pools then continue regenerating independently to collectively re-form a now branched skeletal structure.

[Influence on Indian hedgehog-parathyroid hormone-like related protein pathway induced by altered masticatory loading in the condylar cartilage of growing rabbits]

OBJECTIVE

To determine the influence of altered masticatory loading on Indian hedgehog (Ihh)-parathyroid hormone-like related protein (PThrP) pathway in the condylar cartilage of growing rabbits.

METHODS

A total of 48 10-day-old rabbits were randomly divided into two groups and fed different kinds of food, such as solid diet and soft diet. The animals were sacrificed after 2, 4, 6, and 8 weeks. Difference of Ihh and PThrP expression levels induced by altered masticatory loading was tested by hematoxylin-eosin (HE), immunohistochemistry, Western blot, and real-time polymerase chain reaction (PCR).

RESULTS

The thickness of condylar cartilage and expression levels of Ihh and PThrP proteins and mRNA of the solid diet groups exceeded those of the soft diet groups. The decreasing tendencies of the expression levels of Ihh and PThrP proteins and mRNA were observed at 2, 4, 6, 8 weeks.

CONCLUSIONS

Low masticatory loading may delay or inhibit the development of condylar cartilage and its growing factors Ihh and PThrP. Therefore, masticatory loading plays an important role in the development of condylar cartilage.

Involvement of Indian hedgehog signaling in mesenchymal stem cell-augmented rotator cuff tendon repair in an athymic rat model

BACKGROUND

Bone marrow aspirate has been used in recent years to augment tendon-to-bone healing, including in rotator cuff repair. However, the healing mechanism in cell-based therapy has not been elucidated in detail.

METHODS

Sixteen athymic nude rats were randomly allocated to 2 groups: experimental (human mesenchymal stem cells in fibrin glue carrier) and control (fibrin glue only). Animals were sacrificed at 2 and 4 weeks. Immunohistochemical staining was performed to evaluate Indian hedgehog (Ihh) signaling and SOX9 signaling in the healing enthesis. Macrophages were identified using CD68 and CD163 staining, and proliferating cells were identified using proliferating cell nuclear antigen staining.

RESULTS

More organized and stronger staining for collagen II and a higher abundance of SOX9⁺ cells were observed at the enthesis in the experimental group at 2 weeks. There was significantly higher Gli1 and Patched1 expression in the experimental group at the enthesis at 2 weeks and higher numbers of Ihh⁺ cells in the enthesis of the experimental group vs control at both 2 weeks and 4 weeks postoperatively. There were more CD68⁺ cells localized to the tendon midsubstance at 2 weeks compared with 4 weeks, and there was a higher level of CD163 staining in the tendon midsubstance in the experimental group than in the control group at 4 weeks.

CONCLUSION

Stem cell application had a positive effect on fibrocartilage formation at the healing rotator cuff repair site. Both SOX9 and Ihh signaling appear to play an important role in the healing process.

Lizard tail skeletal regeneration combines aspects of fracture healing and blastema-based regeneration

Lizards are amniotes with the remarkable ability to regenerate amputated tails. The early regenerated lizard tail forms a blastema, and the regenerated skeleton consists of a cartilage tube (CT) surrounding the regenerated spinal cord. The proximal, but not distal, CT undergoes hypertrophy and ossifies. We hypothesized that differences in cell sources and signaling account for divergent cartilage development between proximal and distal CT regions. Exogenous spinal cord implants induced ectopic CT formation in lizard (Anolis carolinensis) blastemas. Regenerated spinal cords expressed Shh, and cyclopamine inhibited CT induction. Blastemas containing vertebrae with intact spinal cords formed CTs with proximal hypertrophic regions and distal non-hypertrophic regions, whereas removal of spinal cords resulted in formation of proximal CT areas only. In fate-mapping studies, FITC-labeled vertebra periosteal cells were detected in proximal, but not distal, CT areas. Conversely, FITC-labeled blastema cells were restricted to distal CT regions. Proximal cartilage formation was inhibited by removal of periosteum and could be recapitulated in vitro by periosteal cells treated with Ihh and BMP-2. These findings suggest that proximal CTs are directly derived from vertebra periosteal cells in response to BMP and Ihh signaling, whereas distal CTs form from blastema cells in response to Shh signals from regenerated spinal cords.

Altered interaction and distribution of glycosaminoglycans and growth factors in mucopolysaccharidosis type I bone disease

The mucopolysaccharidoses (MPSs) comprise a group of lysosomal storage disorders characterized by deficient degradation and subsequent accumulation of glycosaminoglycans (GAGs). Progressive bone and joint disease are a major cause of morbidity, and current therapeutic strategies have limited effect on these symptoms. By elucidating pathophysiological mechanisms underlying bone disease, new therapeutic targets may be identified. Longitudinal growth is regulated by interaction between GAGs and growth factors. Because GAGs accumulate in the MPSs, we hypothesized that altered interaction between growth factors and GAGs contribute to the pathogenesis of MPS bone disease. In this study, binding between GAGs from MPS I chondrocytes and fibroblast growth factor 2 (FGF2) was not significantly different from binding of FGF2 to GAGs from control chondrocytes. FGF2 signaling, however, was increased in MPS I chondrocytes after incubation with FGF2, as compared to control chondrocytes. Using bone cultures, we demonstrated decreased growth of WT mouse bones after incubation with FGF2, but no effect on MPS I bone growth. However, MPS I bones showed decreased growth in the presence of GAGs from MPS I chondrocytes. Finally, we demonstrate altered GAG distribution in MPS I chondrocytes, and altered GAG, FGF2 and Indian hedgehog distribution in growth plates from MPS I mice. In summary, our results suggest that altered interaction and distribution of growth factors and accumulated GAGs may contribute to the pathogenesis of MPS bone disease. In the future, targeting growth factor regulation or the interaction between in growth factors and GAGs might be a promising therapeutic strategy for MPS bone disease.

Indian hedgehog signaling and the role of graft tension in tendon-to-bone healing: Evaluation in a rat ACL reconstruction model

The structure and composition of the native enthesis is not recapitulated following tendon-to-bone repair. Indian Hedgehog (IHH) signaling has recently been shown to be important in enthesis development in a mouse model but no studies have evaluated IHH signaling in a healing model. Fourteen adult male rats underwent ACL reconstruction using a flexor tendon graft. Rats were assigned to two groups based on whether or not they received 0N or 10N of pre-tension of the graft. Specimens were evaluated at 3 and 6 weeks post-operatively using immunohistochemistry for three different protein markers of IHH signaling. Quantitative analysis of staining area and intensity using custom software demonstrated that IHH signaling was active in interface tissue formed at the healing tendon-bone interface. We also found increased staining area and intensity of IHH signaling proteins at 3 weeks in animals that received a pre-tensioned tendon graft. No significant differences were seen between the 3-week and 6-week time points. Our data suggests that the IHH signaling pathway is active during the tendon-bone healing process and appears to be mechanosensitive, as pre-tensioning of the graft at the time of surgery resulted in increased IHH signaling at three weeks.

Ihh and PTH1R signaling in limb mesenchyme is required for proper segmentation and subsequent formation and growth of digit bones

Digit formation is a process, which requires the proper segmentation, formation and growth of phalangeal bones and is precisely regulated by several important factors. One such factor is Ihh, a gene linked to BDA1 and distal symphalangism in humans. In existing mouse models, mutations in Ihh have been shown to cause multiple synostosis in the digits but lead to perinatal lethality. To better study the exact biological and pathological events which occur in these fused digits, we used a more viable Prx1-Cre;Ihh(fl/fl) model in which Cre recombinase is expressed during mesenchymal condensation in the earliest limb buds at E9.5 dpc and found that mutant digits continuously fuse postnatally until phalanges are finally replaced by an unsegmented "one-stick bone". Mutant mice displayed osteocalcin-positive mature osteoblasts, but had reduced proliferation and abnormal osteogenesis. Because of the close interaction between Ihh and PTHrP during endochondral ossification, we also examined the digits of Prx1-Cre;PTH1R(fl/fl) mice, where the receptor for PTHrP was conditionally deleted. Surprisingly, we found PTH1R deletion caused symphalangism, demonstrating another novel function of PTH1R signaling in digit formation. We characterized the symphalangism process whereby initial cartilaginous fusion prevented epiphyseal growth plate formation, resulting in resorption and replacement of the remaining cartilage by bony tissue. Chondrocyte differentiation displayed abnormal directionality in both mutants. Lastly, Prx1-Cre;Ihh(fl/fl);Jansen Tg mice, in which a constitutively active PTH1R allele was introduced into Ihh mutants, were established to address the possible involvement of PTH1R signaling in Ihh mutant digits. These rescue mice failed to show significantly improved phenotype, suggesting that PTH1R signaling in chondrocytes is not sufficient to restore digit formation. Our results demonstrate that Ihh and PTH1R signaling in limb mesenchyme are both essential to regulate proper development of digit structures, although they appear to use different mechanisms.

Augmented Indian hedgehog signaling in cranial neural crest cells leads to craniofacial abnormalities and dysplastic temporomandibular joint in mice

Extensive studies have pinpointed the crucial role of Indian hedgehog (Ihh) signaling in the development of the appendicular skeleton and the essential function of Ihh in the formation of the temporomandibular joint (TMJ). In this study, we have investigated the effect of augmented Ihh signaling in TMJ development. We took a transgenic gain-of-function approach by overexpressing Ihh in the cranial neural crest (CNC) cells using a conditional Ihh transgenic allele and the Wnt1-Cre allele. We found that Wnt1-Cre-mediated tissue-specific overexpression of Ihh in the CNC lineage caused severe craniofacial abnormalities, including cleft lip/palate, encephalocele, anophthalmos, micrognathia, and defective TMJ development. In the mutant TMJ, the glenoid fossa was completely absent, whereas the condyle and the articular disc appeared relatively normal with slightly delayed chondrocyte differentiation. Our findings thus demonstrate that augmented Ihh signaling is detrimental to craniofacial development, and that finely tuned Ihh signaling is critical for TMJ formation. Our results also provide additional evidence that the development of the condyle and articular disc is independent of the glenoid fossa.

Pituitary Adenylate Cyclase Activating Polypeptide (PACAP) Pathway Is Induced by Mechanical Load and Reduces the Activity of Hedgehog Signaling in Chondrogenic Micromass Cell Cultures

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neurohormone exerting protective function during various stress conditions either in mature or developing tissues. Previously we proved the presence of PACAP signaling elements in chicken limb bud-derived chondrogenic cells in micromass cell cultures. Since no data can be found if PACAP signaling is playing any role during mechanical stress in any tissues, we aimed to investigate its contribution in mechanotransduction during chondrogenesis. Expressions of the mRNAs of PACAP and its major receptor, PAC1 increased, while that of other receptors, VPAC1, VPAC2 decreased upon mechanical stimulus. Mechanical load enhanced the expression of collagen type X, a marker of hypertrophic differentiation of chondrocytes and PACAP addition attenuated this elevation. Moreover, exogenous PACAP also prevented the mechanical load evoked activation of hedgehog signaling: protein levels of Sonic and Indian Hedgehogs and Gli1 transcription factor were lowered while expressions of Gli2 and Gli3 were elevated by PACAP application during mechanical load. Our results suggest that mechanical load activates PACAP signaling and exogenous PACAP acts against the hypertrophy inducing effect of mechanical load.

Vegfa regulates perichondrial vascularity and osteoblast differentiation in bone development

Vascular endothelial growth factor A (Vegfa) has important roles in endochondral bone formation. Osteoblast precursors, endothelial cells and osteoclasts migrate from perichondrium into primary ossification centers of cartilage templates of future bones in response to Vegfa secreted by (pre)hypertrophic chondrocytes. Perichondrial osteolineage cells also produce Vegfa, but its function is not well understood. By deleting Vegfa in osteolineage cells in vivo, we demonstrate that progenitor-derived Vegfa is required for blood vessel recruitment in perichondrium and the differentiation of osteoblast precursors in mice. Conditional deletion of Vegfa receptors indicates that Vegfa-dependent effects on osteoblast differentiation are mediated by Vegf receptor 2 (Vegfr2). In addition, Vegfa/Vegfr2 signaling stimulates the expression and activity of Indian hedgehog, increases the expression of β-catenin and inhibits Notch2. Our findings identify Vegfa as a regulator of perichondrial vascularity and osteoblast differentiation at early stages of bone development.

Direct bone morphogenetic protein 2 and Indian hedgehog gene transfer for articular cartilage repair using bone marrow coagulates

OBJECTIVE

Bone morphogenetic protein 2 (BMP-2, encoded by BMP2) and Indian hedgehog protein (IHH, encoded by IHH) are well known regulators of chondrogenesis and chondrogenic hypertrophy. Despite being a potent chondrogenic factor BMP-2 was observed to induce chondrocyte hypertrophy in osteoarthritis (OA), growth plate cartilage and adult mesenchymal stem cells (MSCs). IHH might induce chondrogenic differentiation through different intracellular signalling pathways without inducing subsequent chondrocyte hypertrophy. The primary objective of this study is to test the efficacy of direct BMP2 and IHH gene delivery via bone marrow coagulates to influence histological repair cartilage quality in vivo.

METHOD

Vector-laden autologous bone marrow coagulates with 10(11) adenoviral vector particles encoding BMP2, IHH or the Green fluorescent protein (GFP) were delivered to 3.2 mm osteochondral defects in the trochlea of rabbit knees. After 13 weeks the histological repair cartilage quality was assessed using the ICRS II scoring system and the type II collagen positive area.

RESULTS

IHH treatment resulted in superior histological repair cartilage quality than GFP controls in all of the assessed parameters (with P < 0.05 in five of 14 assessed parameters). Results of BMP2 treatment varied substantially, including severe intralesional bone formation in two of six joints after 13 weeks.

CONCLUSION

IHH gene transfer is effective to improve repair cartilage quality in vivo, whereas BMP2 treatment, carried the risk intralesional bone formation. Therefore IHH protein can be considered as an attractive alternative candidate growth factor for further preclinical research and development towards improved treatments for articular cartilage defects.

Enthesis fibrocartilage cells originate from a population of Hedgehog-responsive cells modulated by the loading environment

Tendon attaches to bone across a specialized tissue called the enthesis. This tissue modulates the transfer of muscle forces between two materials, i.e. tendon and bone, with vastly different mechanical properties. The enthesis for many tendons consists of a mineralized graded fibrocartilage that develops postnatally, concurrent with epiphyseal mineralization. Although it is well described that the mineralization and development of functional maturity requires muscle loading, the biological factors that modulate enthesis development are poorly understood. By genetically demarcating cells expressing Gli1 in response to Hedgehog (Hh) signaling, we discovered a unique population of Hh-responsive cells in the developing murine enthesis that were distinct from tendon fibroblasts and epiphyseal chondrocytes. Lineage-tracing experiments revealed that the Gli1 lineage cells that originate in utero eventually populate the entire mature enthesis. Muscle paralysis increased the number of Hh-responsive cells in the enthesis, demonstrating that responsiveness to Hh is modulated in part by muscle loading. Ablation of the Hh-responsive cells during the first week of postnatal development resulted in a loss of mineralized fibrocartilage, with very little tissue remodeling 5 weeks after cell ablation. Conditional deletion of smoothened, a molecule necessary for responsiveness to Ihh, from the developing tendon and enthesis altered the differentiation of enthesis progenitor cells, resulting in significantly reduced fibrocartilage mineralization and decreased biomechanical function. Taken together, these results demonstrate that Hh signaling within developing enthesis fibrocartilage cells is required for enthesis formation.

Age-related differential gene and protein expression in postnatal cartilage canal and osteochondral junction chondrocytes

Wnt/β-catenin, Indian hedgehog (Ihh)/Parathyroid-related peptide (PTHrP) and retinoid signaling pathways regulate cartilage differentiation, growth, and function during development and play a key role in endochondral ossification. The objective of this study was to elucidate the gene and protein expression of signaling molecules of these regulatory pathways in chondrocytes surrounding cartilage canals and the osteochondral junction during neonatal and pre-adolescent development. This study revealed cell-specific and age-related differences in gene and protein expression of signaling molecules of these regulatory pathways. A trend for higher gene expression of PTHrP along the cartilage canals and Ihh along the osteochondral junction suggests the presence of paracrine feedback in articular-epiphyseal cartilage. Differential expression of canonical (β-catenin, Wnt-4, Lrp4, Lrp6) and noncanonical Wnt signaling (Wnt-5b, Wnt-11) and their inhibitors (Dkk1, Axin1, sFRP3, sFRP5, Wif-1) surrounding the cartilage canals and osteochondral junction provides evidence of the complex interactions occurring during endochondral ossification.

Expression of Indian hedgehog is negatively correlated with APC gene mutation in colorectal tumors

The regulatory mechanism of Indian hedgehog (IHH) in colorectal carcinogenesis has not been elucidated. In the current study, the expression of IHH were investigated in 7 digestive tract cancer cell lines, and in 10 normal colorectal mucosas (NCs), 30 hyperplastic polyps (HPs), 35 colorectal adenomas (ADs), and 40 colorectal adenocarcinomas (CAs) by semi-quantitative RT-PCR and immunohistochemical staining. Moreover, the mutational status of adenomatous polyposis coli (APC) and β-catenin in these tumors were analyzed by direct sequencing. IHH mRNA was lost in the 4 colon cancer cell lines harboring APC mutation. IHH mRNA was significantly decreased in CAs (0.17 ± 0.22), compared with that in ADs (0.38 ± 0.35) and HPs (0.56 ± 0.38, P < 0.05). IHH protein was expressed at a very low level or absent in both ADs (7.51 ± 11.92) and CAs (5.15 ± 9.21) in comparison to that in HPs (19.47 ± 17.91) and NCs (42.40 ± 13.67, P < 0.05). Moreover, APC mutations were negatively correlated with IHH mRNA expression (Spearman's R = -0.636, P < 0.01) and IHH protein expression (Spearman's R = -0.426, P < 0.01). In conclusion, down-regulation of IHH expression might be an early event during the carcinogenesis of colorectal cancer. The activation of Wnt signaling by APC mutation might contribute to the down-regulation or loss of IHH expression in colorectal tumors.

Reprint of: Heparan sulfate as a regulator of endochondral ossification and osteochondroma development

Most elements of the vertebrate skeleton are formed by endochondral ossification. This process is initiated with mesenchymal cells that condense and differentiate into chondrocytes. These undergo several steps of differentiation from proliferating into hypertrophic chondrocytes, which are subsequently replaced by bone. Chondrocyte proliferation and differentiation are tightly controlled by a complex network of signaling molecules. During recent years, it has become increasingly clear that heparan sulfate (HS) carrying proteoglycans play a critical role in controlling the distribution and activity of these secreted factors. In this review we summarize the current understanding of the role of HS in regulating bone formation. In human, mutations in the HS synthetizing enzymes Ext1 and Ext2 induce the Multiple Osteochondroma syndrome, a skeletal disorder characterized by short stature and the formation of benign cartilage-capped tumors. We review the current insight into the origin of the disease and discuss its possible molecular basis. In addition, we summarize the existing insight into the role of HS as a regulator of signal propagation and signaling strength in the developing skeleton.

TMJ degeneration in SAMP8 mice is accompanied by deranged Ihh signaling

The temporomandibular joint (TMJ) functions as a load-bearing diarthrodial joint during mastication, and its continuous use and stress can lead to degeneration over age. Using senescence-accelerated (SAMP8) mice that develop early osteoarthritis-like changes in synovial joints at high frequency, we analyzed possible molecular mechanisms of TMJ degeneration and tested whether and how malocclusion may accelerate it. Condylar articular cartilage in young SAMP8 mice displayed early-onset osteoarthritic changes that included reductions in superficial/chondroprogenitor cell number, proteoglycan/collagen content, and Indian hedgehog (Ihh)-expressing chondrocytes. Following malocclusion induced by tooth milling, the SAMP8 condyles became morphologically defective, displayed even lower proteoglycan levels, and underwent abnormal chondrocyte maturation compared with malocclusion-treated condyles in wild-type mice. Malocclusion also induced faster progression of pathologic changes with increasing age in SAMP8 condyles as indicated by decreased PCNA-positive proliferating chondroprogenitors and increased TUNEL-positive apoptotic cells. These changes were accompanied by steeper reductions in Ihh signaling and by expression of matrix metalloproteinase 13 at the chondro-osseous junction in SAMP8 articular cartilage. In sum, we show for the first time that precocious TMJ degeneration in SAMP8 mice is accompanied by--and possibly attributable to--altered Ihh signaling and that occlusal dysfunction accelerates progression toward degenerative TMJ disease in this model.

Heparan sulfate as a regulator of endochondral ossification and osteochondroma development

Most elements of the vertebrate skeleton are formed by endochondral ossification. This process is initiated with mesenchymal cells that condense and differentiate into chondrocytes. These undergo several steps of differentiation from proliferating into hypertrophic chondrocytes, which are subsequently replaced by bone. Chondrocyte proliferation and differentiation are tightly controlled by a complex network of signaling molecules. During recent years, it has become increasingly clear that heparan sulfate (HS) carrying proteoglycans play a critical role in controlling the distribution and activity of these secreted factors. In this review we summarize the current understanding of the role of HS in regulating bone formation. In human, mutations in the HS synthetizing enzymes Ext1 and Ext2 induce the Multiple Osteochondroma syndrome, a skeletal disorder characterized by short stature and the formation of benign cartilage-capped tumors. We review the current insight into the origin of the disease and discuss its possible molecular basis. In addition, we summarize the existing insight into the role of HS as a regulator of signal propagation and signaling strength in the developing skeleton.

Epiphyseal abnormalities, trabecular bone loss and articular chondrocyte hypertrophy develop in the long bones of postnatal Ext1-deficient mice

Long bones are integral components of the limb skeleton. Recent studies have indicated that embryonic long bone development is altered by mutations in Ext genes and consequent heparan sulfate (HS) deficiency, possibly due to changes in activity and distribution of HS-binding/growth plate-associated signaling proteins. Here we asked whether Ext function is continuously required after birth to sustain growth plate function and long bone growth and organization. Compound transgenic Ext1(f/f);Col2CreERT mice were injected with tamoxifen at postnatal day 5 (P5) to ablate Ext1 in cartilage and monitored over time. The Ext1-deficient mice exhibited growth retardation already by 2weeks post-injection, as did their long bones. Mutant growth plates displayed a severe disorganization of chondrocyte columnar organization, a shortened hypertrophic zone with low expression of collagen X and MMP-13, and reduced primary spongiosa accompanied, however, by increased numbers of TRAP-positive osteoclasts at the chondro-osseous border. The mutant epiphyses were abnormal as well. Formation of a secondary ossification center was significantly delayed but interestingly, hypertrophic-like chondrocytes emerged within articular cartilage, similar to those often seen in osteoarthritic joints. Indeed, the cells displayed a large size and round shape, expressed collagen X and MMP-13 and were surrounded by an abundant Perlecan-rich pericellular matrix not seen in control articular chondrocytes. In addition, ectopic cartilaginous outgrowths developed on the lateral side of mutant growth plates over time that resembled exostotic characteristic of children with Hereditary Multiple Exostoses, a syndrome caused by Ext mutations and HS deficiency. In sum, the data do show that Ext1 is continuously required for postnatal growth and organization of long bones as well as their adjacent joints. Ext1 deficiency elicits defects that can occur in human skeletal conditions including trabecular bone loss, osteoarthritis and HME.

The Ihh signal is essential for regulating proliferation and hypertrophy of cultured chicken chondrocytes

The Indian hedgehog (Ihh) signal plays a vital role in regulating proliferation and hypertrophy of chondrocytes. To investigate its function in postnatal chicken (Gallus gallus) chondrocytes, cyclopamine was used to inhibit Ihh signaling. The MTT and ALP assays revealed the downgrade-proliferation and upgrade-differentiation of chondrocytes. To further elucidate the mechanism, the mRNA expression levels of Ihh, parathyroid hormone related protein (PTHrP), Gli-2, Bcl-2, Bone Morphogenetic Protein 6 (BMP-6), type X collagen (Col X) and type II collagen (Col II) were detected by quantitative real-time RT-PCR analysis, and the protein expressions of Ihh, Col X, and Col II were determined using Western blot analysis. After the Ihh signal was blocked, chondrocytes demonstrated high expression levels of PTHrP and Col X and low levels of Gli-2, BMP-6, Bcl-2 and Col II although Ihh expression was increased. Based on these results, the Ihh signal is essential for balancing chicken chondrocyte proliferation and hypertrophy, and the regulatory function of PTHrP acts in an Ihh-dependent manner. Furthermore, BMP-6 and Bcl-2 played roles in maintaining the development of chondrocytes and may be downstream regulatory factors of Ihh signaling.