Parathyroid hormone-related protein (PTHrP) action in rat articular chondrocytes: comparison of PTH(1-34), PTHrP(1-34), PTHrP(1-141), PTHrP(100-114) and antisense oligonucleotides against PTHrP

Potential effects of teriparatide (PTH (1-34)) on osteoarthritis: a systematic review

Osteoarthritis (OA) is a common and prevalent degenerative joint disease characterized by degradation of the articular cartilage. However, none of disease-modifying OA drugs is approved currently. Teriparatide (PTH (1-34)) might stimulate chondrocyte proliferation and cartilage regeneration via some uncertain mechanisms. Relevant therapies of PTH (1-34) on OA with such effects have recently gained increasing interest, but have not become widespread practice. Thus, we launch this systematic review (SR) to update the latest evidence accordingly. A comprehensive literature search was conducted in PubMed, Web of Science, MEDLINE, the Cochrane Library, and Embase from their inception to February 2022. Studies investigating the effects of the PTH (1-34) on OA were obtained. The quality assessment and descriptive summary were made of all included studies. Overall, 307 records were identified, and 33 studies were included. In vivo studies (n = 22) concluded that PTH (1-34) slowed progression of OA by alleviating cartilage degeneration and aberrant remodeling of subchondral bone (SCB). Moreover, PTH (1-34) exhibited repair of cartilage and SCB, analgesic, and anti-inflammatory effects. In vitro studies (n = 11) concluded that PTH (1-34) was important for chondrocytes via increasing the proliferation and matrix synthesis but preventing apoptosis or hypertrophy. All included studies were assessed with low or unclear risk of bias in methodological quality. The SR demonstrated that PTH (1-34) could alleviate the progression of OA. Moreover, PTH (1-34) had beneficial effects on osteoporotic OA (OPOA) models, which might be a therapeutic option for OA and OPOA treatment.

PTH decreases in vitro human cartilage regeneration without affecting hypertrophic differentiation

Regenerated cartilage formed after Autologous Chondrocyte Implantation may be of suboptimal quality due to postulated hypertrophic changes. Parathyroid hormone-related peptide, containing the parathyroid hormone sequence (PTHrP 1–34), enhances cartilage growth during development and inhibits hypertrophic differentiation of mesenchymal stromal cells (MSCs) and growth plate chondrocytes. This study aims to determine the possible anabolic and/or hypertrophic effect of PTH on human articular chondrocytes. Healthy human articular cartilage-derived chondrocytes (n = 6 donors) were cultured on type II collagen-coated transwells with/without 0.1 or 1.0 μM PTH from day 0, 9, or 21 until the end of culture (day 28). Extracellular matrix production, (pre)hypertrophy and PTH signaling were assessed by RT-qPCR and/or immunohistochemistry for collagen type I, II, X, RUNX2, MMP13, PTHR1 and IHH and by determining glycosaminoglycan production and DNA content. The Bern score assessed cartilage quality by histology. Regardless of the concentration and initiation of supplementation, PTH treatment significantly decreased DNA and glycosaminoglycan content and reduced the Bern score compared with controls. Type I collagen deposition was increased, whereas PTHR1 expression and type II collagen deposition were decreased by PTH supplementation. Expression of the (pre)hypertrophic markers MMP13, RUNX2, IHH and type X collagen were not affected by PTH. In conclusion, PTH supplementation to healthy human articular chondrocytes did not affect hypertrophic differentiation, but negatively influenced cartilage quality, the tissues’ extracellular matrix and cell content. Although PTH may be an effective inhibitor of hypertrophic differentiation in MSC-based cartilage repair, care may be warranted in applying accessory PTH treatment due to its effects on articular chondrocytes.

Fracture healing physiology and the quest for therapies for delayed healing and nonunion

Delayed healing and nonunion of fractures represent enormous burdens to patients and healthcare systems. There are currently no approved pharmacological agents for the treatment of established nonunions, or for the acceleration of fracture healing, and no pharmacological agents are approved for promoting the healing of closed fractures. Yet several pharmacologic agents have the potential to enhance some aspects of fracture healing. In preclinical studies, various agents working across a broad spectrum of molecular pathways can produce larger, denser and stronger fracture calluses. However, untreated control animals in most of these studies also demonstrate robust structural and biomechanical healing, leaving unclear how these interventions might alter the healing of recalcitrant fractures in humans. This review describes the physiology of fracture healing, with a focus on aspects of natural repair that may be pharmacologically augmented to prevent or treat delayed or nonunion fractures (collectively referred to as DNFs). The agents covered in this review include recombinant BMPs, PTH/PTHrP receptor agonists, activators of Wnt/β-catenin signaling, and recombinant FGF-2. Agents from these therapeutic classes have undergone extensive preclinical testing and progressed to clinical fracture healing trials. Each can promote bone formation, which is important for the stability of bridged calluses, and some but not all can also promote cartilage formation, which may be critical for the initial bridging and subsequent stabilization of fractures. Appropriately timed stimulation of chondrogenesis and osteogenesis in the fracture callus may be a more effective approach for preventing or treating DNFs compared with stimulation of osteogenesis alone. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:213-223, 2017.

Deletion of the nuclear localization sequence and C-terminus of parathyroid hormone-related protein decreases osteogenesis and chondrogenesis but increases adipogenesis and myogenesis in murine bone marrow stromal cells

The N-terminus of parathyroid hormone-related protein regulates bone marrow stromal cell differentiation. We hypothesized that the nuclear localization sequence and C-terminus are involved. MicroRNA and gene expression analyses were performed on bone marrow stromal cells from mice lacking the nuclear localization sequence and C-terminus (PthrpΔ/Δ ) and age-matched controls. Differentiation assays with microRNA, cytochemical/histologic/morphologic, protein, and gene expression analyses were performed. PthrpΔ/Δ bone marrow stromal cells are anti-osteochondrogenic, pro-adipogenic, and pro-myogenic, expressing more Klf4, Gsk-3β, Lif, Ct-1, and microRNA-434 but less β-catenin, Igf-1, Taz, Osm, and microRNA-22 (p ⩽ 0.024). PthrpΔ/Δ osteoblasts had less mineralization, osteocalcin, Runx2, Osx, Igf-1, and leptin (p ⩽ 0.029). PthrpΔ/Δ produced more adipocytes, Pparγ, and aP2, but less Lpl (p ⩽ 0.042). PthrpΔ/Δ cartilage pellets were smaller with less Sox9 and Pth1r, but greater Col2a1 (p ⩽ 0.024). PthrpΔ/Δ produced more myocytes, Des, and Myog (p ⩽ 0.021). MicroRNA changes supported these findings. In conclusion, the nuclear localization sequence and C-terminus are pro-osteochondrogenic, anti-adipogenic, and anti-myogenic.

An autologous in situ tumor vaccination approach for hepatocellular carcinoma. 1. Flt3 ligand gene transfer increases antitumor effects of a radio-inducible suicide gene therapy in an ectopic tumor model

Hepatocellular carcinoma (HCC) often presents as a diffuse or multifocal tumor making it difficult to control by surgery or radiation. Radio-inducible herpes simplex virus thymidine kinase (HSV-TK) gene therapy has been shown to enhance local tumor control after radiation therapy (RT), while limiting the expression of the transgene in the irradiated tumor tissues. To prevent liver tumor recurrence and control systemic disease while limiting the potential bystander toxicity of HSV-TK therapy, we proposed to stimulate endogenous dendritic cell (DC) proliferation with systemic adenovirus Flt3 ligand (Adeno-Flt3L) gene therapy, followed by primary tumor radiation therapy combined with a radio-inducible HSV-TK gene therapy. We hypothesized that adenovirus-expressing Flt3L gene therapy will stimulate DC proliferation, allowing the upregulated DCs to locally harness tumor antigens released from HSV-TK/RT-treated HCC cells, thereby converting irradiated tumors to an autologous in situ tumor vaccine in mice with primary liver tumors. To test this hypothesis, an expression vector of HSV-TK was constructed under the control of a radio-inducible promoter early-growth response (Egr-TK) and a recombinant adenovirus-expressing human Flt3L was constructed. The Adeno-Flt3L [10(9) plaque forming units (pfu)] was administered intravenously on days 1 and 8 after radiation therapy. The murine hepatoma cell line (BNL1ME) was stably transfected by Egr-TK or Egr-Null (encoding no therapeutic gene). Palpable tumors in BALB/c mice were treated with a localized dose of 25 Gy of radiation followed by ganciclovir (GCV, 100 mg/kg, 14 days). Four treatment cohorts were compared: Egr-Null/GCV + RT + Adeno-LacZ; Egr-Null/GCV + RT + Adeno-Flt3L; Egr-TK/GCV + RT + Adeno-LacZ; and Egr-TK/GCV + RT + Adeno-Flt3L. There was no primary tumor regression in the Egr-Null tumors after radiation therapy alone. In contrast, Egr-TK tumors had nearly complete tumor regression for 3 weeks after radiation therapy (P < 0.01), however, long-term follow-up demonstrated primary tumor recurrence and death secondary to pulmonary metastasis. Flt3L expression was confirmed by serum bioassay (mean = 88 ng/mL) in these animals and Western blotting of tissue culture medium in Adeno-Flt3L-infected BaF/huFlt3L cells. Radiation therapy with Adeno-Flt3L gene therapy effectively retarded primary tumor growth when compared to radiation therapy alone. The trimodality therapy (Egr-TK/GCV + RT + Adeno-Flt3L) was the most efficacious with 40% complete tumor regression (>100 days) and <20% pulmonary metastases, indicating the development of sustained antitumor immune response. These studies provide a rationale for triple modality therapies with radiation-inducible HSV-TK gene therapy and Adeno-Flt3L when used in combination with primary tumor radiation therapy for improved local and systemic control of HCC.

The efficacy and safety of gene transfer into the porcine liver in vivo by HVJ (Sendai virus) liposome

BACKGROUND

Gene transfer systems using viral vectors are efficient; however, most viral vectors also tend to evoke immunologic reactions, thereby clinically causing serial side effects. HVJ-liposome vector is a hybrid vector consisting of liposome and an inactivated Sendai virus (Hemmagglutinating Virus of Japan [HVJ]), which has been reported to be less immunogenic and can also be repeatedly administered. We examined the usefulness of this vector for hepatic gene therapy in a pig model.

METHODS

Genes encoding beta-galactosidase and luciferase were used as reporter genes. The pigs were injected with the reporter gene loaded-HVJ-liposome into the portal vein under total vascular exclusion of the liver. The transfection efficiencies were then assessed by beta-galactosidase staining, a luciferase assay, and RT-PCR for LacZ mRNA. Biochemical and histologic analyses were performed to evaluate tissue toxicity after gene transfer.

RESULTS

The luciferase gene expression in the liver reached its highest level at 7 days after transfection. It continued to be detected up to 28 days after transfection, while all pigs remained healthy throughout the observation period. The transfection efficiency was 15% in the hepatocytes according to beta-galactosidase staining. Extrahepatic transgene expression was slightly observed in the lung and kidney, but not in the spleen or ovary.

CONCLUSIONS

These data suggest for the first time that the use of the HVJ-liposome vector is a safe and feasible modality for liver-directed gene transfer in pigs, and it might therefore be suitable for clinical gene therapy trials.

Constitutive hedgehog signaling in chondrosarcoma up-regulates tumor cell proliferation

Chondrosarcoma is a malignant cartilage tumor that may arise from benign precursor lesions, such as enchondromas. Some cases of multiple enchondromas are caused by a mutation that results in constitutive activation of Hedgehog-mediated signaling. We found that chondrosarcomas expressed high levels of the Hedgehog target genes PTCH1 and GLI1. Treatment with parathyroid hormone-related protein down-regulated Indian Hedgehog (IHH) expression in normal growth plates but not in chondrosarcoma or enchondroma organ cultures. Treatment of the chondrosarcoma organ cultures with Hedgehog protein increased cell proliferation rate, whereas addition of chemical inhibitors of Hedgehog signaling decreased the proliferation rate. Chondrosarcoma xenografts from 12 different human tumors were established in NOD-SCID mice. Treatment with triparanol, an inhibitor of Hedgehog signaling, resulted in a 60% decrease in tumor volume, a 30% decrease in cellularity, and a 20% reduction in proliferation rate. These results show that Hedgehog signaling is active in chondrosarcoma and benign cartilage tumors and regulates tumor cell proliferation. Our data raise the intriguing possibility that Hedgehog blockade could serve as an effective treatment for chondrosarcoma, a tumor for which there are currently no universally effective nonsurgical management options.

Chondrocyte calcium-sensing receptor expression is up-regulated in early guinea pig knee osteoarthritis and modulates PTHrP, MMP-13, and TIMP-3 expression

OBJECTIVE

Growth plate chondrocytes up-regulate calcium-sensing receptor (CaR) expression as they mature to hypertrophy. In cells other than chondrocytes, extracellular calcium-sensing via the CaR functions partly to promote expression of parathyroid hormone-related protein (PTHrP), a critical regulator of endochondral development. Moreover, PTHrP is up-regulated in human osteoarthritis (OA) and surgically induced rabbit OA cartilages and may promote both chondrocyte proliferation and osteophyte formation therein. Hence, we examined chondrocyte CaR-mediated calcium-sensing in OA pathogenesis.

METHODS

We studied spontaneous knee OA in male Hartley guinea pigs. We also evaluated cultured bovine knee chondrocytes and immortalized human articular chondrocytes (CH-8 cells), employing the CaR calcimimetic agonist NPS R-467 or altering physiologic extracellular calcium (1.8 mM).

RESULTS

Immunohistochemistry revealed that CaR expression became up-regulated in the superficial zone at 4 months of age in the guinea pig medial tibial plateau cartilage as early OA developed. CaR expression later became up-regulated in the middle zone. PTHrP content, measured by immunoassay, was significantly increased in the medial tibial plateau cartilage as OA developed and progressed. In cultured chondrocytic cells, CaR-mediated extracellular calcium-sensing, stimulated by the calcimimetic NPS R-467, induced PTHrP and matrix metalloproteinase (MMP)-13 expression and suppressed expression of tissue inhibitor of metalloproteinase (TIMP)-3 dose-dependently, effects shared by elevated extracellular calcium (3 mM). Extracellular calcium-sensing appeared essential for PTHrP and interleukin (IL)-1 to induce MMP-13 and for PTHrP 1-34 to suppress TIMP-3 expression.

CONCLUSIONS

Chondrocyte CaR expression becomes up-regulated early in the course of spontaneous guinea pig knee OA. Chondrocyte CaR-mediated extracellular calcium-sensing promotes PTHrP expression, modulates the effects of PTHrP and IL-1, and promotes MMP-13 expression and TIMP-3 depletion. Our results implicate up-regulated extracellular calcium-sensing via the CaR as a novel mediator of OA progression.

Altered expression of inflammatory cytokines in primary osteoarthritis by human T lymphotropic virus type I retrovirus infection: a cross-sectional study

Human T cell leukaemia virus type I (HTLV-I) is known to be involved in late-onset chronic polyarthritis as HTLV-I-associated arthropathy. However, it is unclear whether HTLV-I infection could modify the pathophysiology of osteoarthritis (OA). In this study we compared several inflammatory cytokines, such as C-terminal parathyroid hormone-related peptide (C-PTHrP), soluble interleukin-2 receptor (sIL-2R) and interleukin (IL)-6, and an osteo-destruction marker, deoxypyridinoline, in synovial fluid (SF) samples obtained from 22 HTLV-I carriers and 58 control non-carrier patients with OA. These patients were diagnosed clinically and radiographically with primary OA affecting one or both knee joints, and were similar with regard to age, sex and clinical symptoms. We also performed histopathological examination as well as immunohistochemistry of HTLV-I-derived Tax protein in eight synovial tissues taken from carrier patients. C-PTHrP in SF was significantly higher in HTLV-I carriers (287 ± 280 pM) than in non-carriers (69 ± 34 pM), and the concentration in 13 carriers was above the upper range of OA. In HTLV-I carriers, the concentrations of sIL-2R (741 ± 530 IU/ml), IL-6 (55 ± 86 ng/ml) and deoxypyridinoline (3.1 ± 1.8 nM) were higher than in non-carriers (299 ± 303, 2.5 ± 4.0, 0.96 ± 1.0, respectively), and correlated positively with C-PTHrP. C-PTHrP, sIL-2R and IL-6 concentrations in SF positive for IgM antibody against HTLV-I antigen, a marker of persistent viral replication, were higher than of IgM-negative SF. Histologically, five and two synovia showed mild and moderate synovial proliferation with or without some degree of inflammatory reaction, respectively, and could not be distinguished from OA. Tax-positive synoviocytes were observed sparsely in all samples, and often appeared frequently in actively proliferating regions. Our results suggest that although HTLV-I infection does not necessarily worsen the clinical outcome and local synovitis, the virus can potentially modify the pathophysiology of OA by increasing the inflammatory activity in a subset of carrier patients, especially those with IgM antibody. Longitudinal studies are required to assess the association between HTLV-I infection and OA.

Autocrine/paracrine role of the angiopoietin-1 and -2/Tie2 system in cell proliferation and chemotaxis of cultured fibroblastic synoviocytes in rheumatoid arthritis

Hypervascularity is a characteristic synovial feature of rheumatoid arthritis (RA). We previously reported that Tie1 and Tie2, endothelium-specific tyrosine kinase receptors essential for angiogenesis, are expressed not only by vascular cells, but also by a subpopulation of synovial lining and stromal cells in the inflamed RA synovium. The present study used immunohistochemistry and in situ hybridization to examine whether angiopoietin-1 and -2 (Ang1 and Ang2), ligands for Tie2, are also expressed in the RA synovium. Ang1 and Ang2 were expressed in all of 15 RA synovial samples, and their distribution pattern was similar to that of Tie2. Intense staining was noted in synovial lining and stromal cells, as well as in small vessels in areas of papillary projection and high cell density. Double immunohistochemistry revealed coexpression of Ang1, Ang2, and Tie2 in synovial components exhibiting proliferating cell nuclear antigen immunoreactivity. In addition, Ang1 and Ang2 were preferentially expressed in vimentin-positive fibroblastic cells. To address the functional role of Ang/Tie signaling in RA pathophysiology, we carried out [(3)H]thymidine incorporation and transwell chemotaxis assays using cultured fibroblastic synoviocytes obtained from 2 RA patients. Incubation with various concentrations of recombinant Ang1 or Ang2 did not alter DNA synthesis, but the ligands enhanced chemotactic migration of RA fibroblastic synoviocytes. Our results suggest that the autocrine/paracrine signaling of the Ang/Tie2 system is important for the up-regulated angiogenesis in the RA synovium, as well as for synoviocyte behavior, by regulating chemotactic cell movement.

Blockade of parathyroid hormone-related protein prevents joint destruction and granuloma formation in streptococcal cell wall-induced arthritis

OBJECTIVE

To determine whether parathyroid hormone-related protein (PTHrP), an interleukin-1beta-inducible, bone-resorbing peptide that is produced in increasing amounts by the synovium in rheumatoid arthritis (RA), may play a role in the pathophysiology of joint destruction in RA.

METHODS

PTHrP expression and the effect of PTHrP 1-34 neutralizing antibody on disease progression were tested in streptococcal cell wall (SCW)-induced arthritis, an animal model of RA.

RESULTS

As has been reported in RA, while serum levels of PTHrP did not change during SCW-induced arthritis, PTHrP expression dramatically increased in the arthritic synovium. Treatment with PTHrP neutralizing antibody (versus control antibody) did not affect joint swelling in SCW-treated animals. However, PTHrP antibody significantly inhibited SCW-induced joint destruction, as measured by its ability to block increases in serum pyridinoline (a marker of cartilage and bone destruction), erosion of articular cartilage, decreases in femoral bone mineral density, and increases in the numbers of osteoclasts in eroded bone. Unexpectedly, granuloma formation at sites of SCW deposition in the liver and spleen was also inhibited by PTHrP antibody, an effect associated with significant decreases in the tissue influx of PTH/PTHrP receptor-positive neutrophils and in SCW-induced neutrophilia. In vitro, neutrophil chemotaxis was stimulated by PTHrP 1-34.

CONCLUSION

These findings suggest that PTHrP, consistent with its previously described osteolytic effects in metastatic bone disease, can also be an important mediator of joint destruction in inflammatory bone disorders, such as RA. Moreover, this study reveals heretofore unknown effects of PTHrP peptides on neutrophil function that could have important implications in the pathogenesis of inflammatory granulomatous disorders.

Role of c-fos in the regulation of type X collagen gene expression by PTH and PTHrP: localization of a PTH/PTHrP-responsive region in the human COL10A1 enhancer

PTH and PTHrP have been shown to inhibit maturation of growth plate chondrocytes and the expression of type X collagen. In order to examine the regulatory mechanisms involved, fetal bovine growth plate chondrocytes were incubated for 24-48 h under serum-free conditions with PTH and PTHrP and various aminoterminal, midregional, and carboxyterminal fragments of these hormones. Analysis of type X collagen mRNA levels by Northern hybridization showed a significant suppression by PTH (1-84), PTH (1-34), and PTHrP (1-40), but not by PTH (28-48) or PTH (53-84). PTH fragment (3-34) did not reduce alpha1(X) mRNA levels, while bis-indolylmaleimide, an inhibitor of the protein-kinase C pathway, did not affect alpha1(X) mRNA suppression by PTH, supporting the notion that the inhibition of type X collagen expression by PTH involves predominantly the adenylate cyclase pathway of the PTH/PTHrP-receptor. Since PTH and PTHrP have been shown to induce c-fos in osteoblasts and chondrocytes, the possibility was tested that c-fos mediated the suppressive effect of PTH/PTHrP on collagen X expression. In fetal bovine hypertrophic chondrocytes PTH (1-34), but not PTH (3-34) nor the midregional or C-terminal PTH fragments induced c-fos expression. In order to identify cis- and trans-acting elements in the COL10A1 gene involved in c-fos-mediated inhibition of collagen X expression by PTH/PTHrP, reporter gene constructs carrying various fragments of the human COL10A1 promoter coupled to the luciferase gene were transfected into hypertrophic chondrocytes. A tissue-specific, strong enhancer region, which we had previously located in the promoter of the human type X collagen gene COL10A1, was further narrowed down to a 530-bp sequence, located between - 1,870- and - 2,407 bp upstream of the transcription start site. The transcriptional activity of this enhancer element in transfected hypertrophic chondrocytes was significantly reduced after incubation with PTH (1-34) or PTHrP (1-40). Transcription of these reporter genes was also inhibited when chondrocytes were cotransfected with a c-fos expression vector. These results indicate the presence of a PTH/PTHrP responsive element in the human COL10A1 enhancer, which may be represented by multiple putative AP-1 sites located in this region.

A role for parathyroid hormone-related protein in the pathogenesis of inflammatory/autoimmune diseases

Our increased understanding of the critical role of cytokines in chronic inflammatory/autoimmune diseases has led to the recent development of effective anti-cytokine treatments. In particular, agents blocking the function of TNF-alpha, a cytokine first identified as an endotoxin-inducible mediator of tumor cell necrosis, are now licensed for the treatment of rheumatoid arthritis (RA) and inflammatory bowel disease. However, TNF-alpha is but one member of a cytokine network that is responsible for mediating these inflammatory disorders. Therefore, as our understanding of the pathophysiologic role of other members of this inflammatory network increases, other cytokines may similarly be identified as effective targets for treatment. In this article, we will review evidence which suggests that parathyroid hormone-related protein (PTHrP), a peptide which, like TNF-alpha, was first identified because of its effects in the setting of malignancy, may in fact serve an important non-neoplastic, physiologic function by mediating the inflammatory/autoimmune host response. Data identifying PTHrP as a member of the cytokine network induced in multi-organ inflammation and rheumatoid arthritis will be summarized, initial evidence comparing the therapeutic efficacy of PTHrP- vs. TNF-alpha-blockade in the treatment of endotoxemia will be reviewed, and potential future areas of research, including assessment of the effects of PTHrP blockade in the treatment of RA, will be discussed.

The chondrogenic transcription factor Sox9 is a target of signaling by the parathyroid hormone-related peptide in the growth plate of endochondral bones

In the growth plate of endochondral bones, parathyroid hormone (PTH)-related peptide (PTHrP) regulates the rate of chondrocyte maturation from prehypertrophic chondrocytes to hypertrophic chondrocytes. Using an antibody specific for Sox9 phosphorylated at serine 181 (S(181)), one of the two consensus protein kinase A phosphorylation sites of Sox9, we showed that the addition of PTHrP strongly increased the phosphorylation of SOX9 in COS7 cells transfected with both SOX9- and PTH/PTHrP receptor-expressing vectors. PTHrP also increased the SOX9-dependent activity of chondrocyte-specific enhancers in the gene for type II collagen (Col2a1) in transient transfection experiments. This increased enhancer activity did not occur with a Sox9 mutant harboring serine-to-alanine substitutions in its two consensus protein kinase A phosphorylation sites. Consistent with these results, PTHrP also increased Col2a1 mRNA levels in rat chondrosarcoma cells as well as 10T1/2 mesenchymal cells transfected with a PTH/PTHrP receptor expressing plasmid. No phosphorylation of Sox9 at S(181) was detected in prehypertrophic chondrocytes of the growth plate or any chondrocytes of PTH/PTHrP receptor null mutants. In contrast in wild-type mouse embryos, previous immunohistochemistry experiments indicated that Sox9 phosphorylated at S(181) was detected almost exclusively in chondrocytes of the prehypertrophic zone. Sox9, regardless of the phosphorylation state, was present in all chondrocytes of both genotypes except hypertrophic chondrocytes. Our results indicated that Sox9 is a target of PTHrP signaling in prehypertrophic chondrocytes in the growth plate. We hypothesize that Sox9 mediates at least some effects of PTHrP in the growth plate and that the PTHrP-dependent increased transcriptional activity of Sox9 helps maintain the chondrocyte phenotype of cells in the prehypertrophic zone and inhibits their maturation to hypertrophic chondrocytes.

The chondrogenic transcription factor Sox9 is a target of signaling by the parathyroid hormone-related peptide in the growth plate of endochondral bones

In the growth plate of endochondral bones, parathyroid hormone (PTH)-related peptide (PTHrP) regulates the rate of chondrocyte maturation from prehypertrophic chondrocytes to hypertrophic chondrocytes. Using an antibody specific for Sox9 phosphorylated at serine 181 (S(181)), one of the two consensus protein kinase A phosphorylation sites of Sox9, we showed that the addition of PTHrP strongly increased the phosphorylation of SOX9 in COS7 cells transfected with both SOX9- and PTH/PTHrP receptor-expressing vectors. PTHrP also increased the SOX9-dependent activity of chondrocyte-specific enhancers in the gene for type II collagen (Col2a1) in transient transfection experiments. This increased enhancer activity did not occur with a Sox9 mutant harboring serine-to-alanine substitutions in its two consensus protein kinase A phosphorylation sites. Consistent with these results, PTHrP also increased Col2a1 mRNA levels in rat chondrosarcoma cells as well as 10T1/2 mesenchymal cells transfected with a PTH/PTHrP receptor expressing plasmid. No phosphorylation of Sox9 at S(181) was detected in prehypertrophic chondrocytes of the growth plate or any chondrocytes of PTH/PTHrP receptor null mutants. In contrast in wild-type mouse embryos, previous immunohistochemistry experiments indicated that Sox9 phosphorylated at S(181) was detected almost exclusively in chondrocytes of the prehypertrophic zone. Sox9, regardless of the phosphorylation state, was present in all chondrocytes of both genotypes except hypertrophic chondrocytes. Our results indicated that Sox9 is a target of PTHrP signaling in prehypertrophic chondrocytes in the growth plate. We hypothesize that Sox9 mediates at least some effects of PTHrP in the growth plate and that the PTHrP-dependent increased transcriptional activity of Sox9 helps maintain the chondrocyte phenotype of cells in the prehypertrophic zone and inhibits their maturation to hypertrophic chondrocytes.

Parathyroid hormone and transforming growth factor-beta1 coregulate chondrocyte differentiation in vitro

Parathyroid hormone (1-34) (PTH(1-34) and transforming growth factor-beta1 (TGF-beta1) regulate chondrocyte proliferation, differentiation, and matrix synthesis. Both proteins mediate their effects in a dose- and time-dependent manner, and the effects are cell maturation specific. Moreover, similar signaling pathways are used, suggesting that there may be cross talk leading to coregulated cell response. To test this hypothesis, confluent cultures of rat costochondral resting zone and growth zone chondrocytes were treated with 0.22, 0.44, or 0.88 ng/mL of rhTGF-beta1 for 24 h, followed by treatment with 10(-11) to 10(-8) M PTH(1-34) for 10 min or 24 h. [3H]-Thymidine incorporation, specific activity of alkaline phosphatase (AP), and [35S]-sulfate incorporation were measured. PTH(1-34) had no effect on [3H]-thymidine incorporation by growth zone cells pretreated with 0.22 or 0.44 ng/mL of TGF-beta1, but in cultures treated with 0.88 ng/mL, PTH(1-34) caused a dose-dependent decrease that was maximal at the lowest concentration tested. By contrast, PTH(1-34) stimulated [3H]-thymidine incorporation by resting zone cells, and this effect was additive with the stimulation caused by 0.22 ng/mL of TGF-beta1. PTH(1-34) caused a synergistic increase in AP in growth zone cells treated with 0.44 or 0.88 ng/mL of TGF-beta1, but not in cells treated with 0.22 ng/mL of TGF-beta1. It had no effect on AP in resting zone cells pretreated with any concentration of TGF-beta1. PTH(1-34) increased [35S]-sulfate incorporation in growth zone and resting zone cell cultures treated with 0.22 ng/mL of TGF-beta1 to levels seen in cultures treated with 0.88 ng/mL of TGF-beta1 alone. These results support the hypothesis that PTH(1-34) and TGF-beta1 coregulate growth plate chondrocytes and that the effects are cell maturation dependent.

The tetrabasic KKKK(147-150) motif determines intracrine regulatory effects of PthrP 1-173 on chondrocyte PPi metabolism and matrix synthesis

Expression of PTHrP is a major regulator of growth cartilage development and also becomes robust in osteoarthritic cartilage. We further defined how PTHrP 1-173, which we observed to be the preferentially expressed PTHrP isoform in normal and osteoarthritic cartilage, functions in chondrocytes. We transfected both immortalized human juvenile costal chondrocytes (TC28 cells) and rabbit articular chondrocytes with wild-type PTHrP 1-173 and mutants of putative PTHrP 1-173 endoproteolytic processing sites. Wild-type PTHrP 1-173 inhibited collagen synthesis and decreased extracellular PPi (which critically regulates hydroxyapatite deposition) by 50-80% in both chondrocytic cell types. In contrast, PTHrP 1-173 mutated at the PTHrP 147-150 motif KKKK (but not the other site-directed mutants) and increased both extracellular PPi and collagen synthesis by >50%. Synthetic PTHrP 140-173 mutated at amino acids 147-150 and also increased extracellular PPi, and wild-type 140-173 decreased extracellular PPi in permeabilized cells. The 147-nuclear localization of PTHrP. We conclude that the tetrabasic 147-150 motif functions to determine how PTHrP 1-173 regulates collagen synthesis and levels of extracellular PPi by an intracrine mechanism in chondrocytes, and it may prove useful as a therapeutic target for regulation of mineralization.

Parathyroid hormone-related peptide is involved in protection against invasion of tooth germs by bone via promoting the differentiation of osteoclasts during tooth development

In order to elucidate the role of parathyroid hormone-related peptide (PTHrP) in tooth development, we treated tooth germ explants of mouse molars with antisense phosphorothioate-oligodeoxynucleotide (ODN) against PTHrP. Antisense ODN-treatment of the explants resulted in the invasion of the tooth germs by bone. The number of tartrate-resistant acid phosphatase (TRAP)-positive cells around the tooth germs in antisense ODN-treated explants was much lower than that of the control explants. Electron microscopic examination suggested that the antisense ODN-treatment inhibited differentiation of osteoclasts. Treatment of the explants with bisphosphonate or vitamin K2, inhibitors of the differentiation of osteoclasts, induced the invasion by bone into the tooth germs as observed in the antisense ODN-treated explants. The results obtained suggest that PTHrP is involved in the mechanism protecting tooth germs from bone invasion by promoting the differentiation of osteoclasts around them.

Activation of specific MEK-ERK cascade is necessary for TGFbeta signaling and crosstalk with PKA and PKC pathways in cultured rat articular chondrocytes

OBJECTIVE

TGFbeta is a potent stimulator of cell growth in cultured rat articular chondrocytes (CRAC). The stimulatory effect is mediated through the immediate induction of c-fos gene by activating ERK of MAPK. The present study was undertaken to investigate the upstream regulators involved in TGFbeta-induced ERK activation in CRAC and to compare the results with the events in HepG2 cells.

RESULTS

In vitro kinase and trans-reporting assays showed that TGFbeta preferentially activated ERK and JNK pathways in CRAC and HepG2, respectively. ERK activation in CRAC was selectively inhibited by PD98059, a MEK inhibitor. Overexpression of wild or active forms of MEKK1, the upstream activator of ERK and JNK, decreased the TGFbeta-induced 3TP-luciferase activity in CRAC. In contrast, in HepG2 dominant negative form of MEKK1 or SEK1 ligand-dependent reporter activity was diminished. Transfection of TAK1, another MAPKKK, also positively and negatively regulated 3TP transcriptional activity of HepG2 and CRAC, respectively. Activation of PKA by 8-bromo-cyclic AMP or forskolin, and inhibition of PKC by calphostin C, resulted in a significant decrease in 3TP activity as well as in vitro ERK kinase activity in CRAC.

CONCLUSIONS

The results indicate that TGFbeta transduces a predominant signal pathway through MEK-ERK-Elk1, independent of MEKK1 or TAK1 pathway in CRAC. However, in HepG2, activation of MEKK1 and TAK1 is essential for TGFbeta-induced signal transmission. The results also demonstrated that in CRAC, MEK-ERK pathway activated by TGFbeta is negatively regulated by PKA cascade but transactivated by PKC.

Endogenous parathyroid hormone-related peptide enhances proliferation and inhibits differentiation in the osteoblast-like cell line ROS 17/2.8

To investigate potential effects of endogenous parathyroid hormone-related peptide (PTHrP) on osteoblast function, ROS 17/2.8 cells were transfected with full-length PTHrP cDNA in a sense or antisense orientation to alter PTHrP production. Compared with vector-transfected control cells, PTHrP-overproducing (sense-transfected) cells showed increased DNA synthesis ([(3)H]-thymidine incorporation) and increased growth (cell number). The extent of apoptosis was compared for the different clones using the terminal deoxynucleotide-mediated dUTP nick-end-labeling assay (TUNEL) and Hoechst staining. No differences in percentages of apoptotic cells were found under basal culture conditions or after 3 days of serum deprivation, which, itself, markedly increased numbers of apoptotic cells. The effect of PTHrP on osteoblast differentiation was assessed by examining two protein markers of differentiation, alkaline phosphatase, and bone morphogenetic protein (BMP)-2. Alkaline phosphatase activity was decreased in sense-transfected cells and increased in antisense-transfected cells, compared with cells transfected with empty vector. PTHrP-overproducing cells also showed decreased numbers of BMP-2-positive cells, whereas antisense-transfected cells showed no difference compared with vector control. The results indicate that: (a) endogenously produced PTHrP can increase growth of these osteoblastic cells by stimulating proliferation while not affecting apoptosis; and (b) the increased cell proliferation produced by PTHrP was accompanied by a reduction in activity or amount of two proteins normally expressed by differentiated osteoblasts.

Regression of hepatocellular carcinoma in vitro and in vivo by radiosensitizing suicide gene therapy under the inducible and spatial control of radiation

To improve the efficacy and selectivity of gene therapy for hepatocellular carcinoma (HCC), we designed a strategy for suicide gene therapy in conjunction with radiation therapy using an HVJ-liposome vector system. The radio-inducible suicide gene was constructed by insertion of the early growth response gene 1 (Egr-1) promoter upstream of the HSV-tk gene (EGF-tk). First, to test the tumor specificity of Egr-1, RT-PCR and immunohistochemistry were performed. The Egr-1 gene was highly expressed in HCC compared with normal liver, where expression was barely detectable. Next, radiation-inducible activity of the Egr-1 promoter was examined in primary cultured normal hepatocytes and human hepatoma cell lines Huh7, HepG2, and PLC/PRF/5 by luciferase assay as a reporter gene system. Egr-1 promoter activity was markedly increased in hepatoma cell lines in a radiation dose-dependent manner, with maximum activation (15- to 28-fold) 12 hr after irradiation. In contrast, only a twofold increase in activation was noted in normal hepatocytes. An in vitro gene therapy experiment showed that EGR-tk-transduced hepatoma cells became highly sensitive to ganciclovir (GCV) after irradiation, but not without irradiation. GCV with or without irradiation did not show any cytotoxic effects against control gene-transfected cells. In addition, a "radiosensitization effect" was also demonstrated by combination therapy with the HSV-tk/GCV system and irradiation. To examine the efficacy of this EGR-tk/GCV gene therapy in vivo, xenografted liver tumors in nude mice were targeted using the HVJ-liposome vector system. EGR-tk-transfected tumors regressed significantly after a combination therapy of irradiation and GCV in all mice (n = 8), and almost disappeared in 3 weeks without any side effects. In comparison, tumors continued to grow in all mice (n = 8 in each group) treated by transfer of EGR-tk followed by either irradiation without GCV or GCV without irradiation. Our data indicate that HSV-tk gene therapy under the control of a radioinducible promoter is effective, and might be selective for hepatoma cells because of its inducible and radiosensitive capacity after radiation exposure as well as its tumor-specific activation.

Comparison of recombinant human PTH(1-34) (LY333334) with a C-terminally substituted analog of human PTH-related protein(1-34) (RS-66271): In vitro activity and in vivo pharmacological effects in rats

Parathyroid hormone (PTH) and PTH-related protein (PTHrP) are believed to exert their biological actions through binding and activation of a common cell surface receptor. Recently, an analog of PTHrP (RS-66271), was described that demonstrated reduced binding affinity for the PTH/PTHrP receptor compared with bovine PTH(1-34) but retained equal biological activity. The present study investigated the receptor binding affinities of synthetic RS-66271 and recombinant human PTH(1-34) (LY333334) and compared their in vitro and in vivo pharmacological effects. RS-66271 had one hundredth the activity of PTH(1-34) in competing for the binding of [125I] [Nle8,18, Tyr34]human PTH(1-34) to the human PTH/PTHrP receptor stably expressed in a human kidney cell line. Despite this reduced binding affinity, RS-66271 had equivalent activity in increasing both cAMP production in osteoblast-like cells and bone resorption in neonatal mouse calvariae. However, RS-66271 was 7. 6-fold less active in stimulating inositol phosphate production. For in vivo studies, young, male Fisher rats received a daily subcutaneous dose of either 10 or 40 microg/kg of peptide for 1, 2, or 4 weeks. Volumetric bone mineral density and total bone mineral content of the proximal tibia were determined by peripheral quantitative computerized tomography. Trabecular and cortical bone of the distal femur were analyzed for calcium and dry weight. Lumbar vertebrae (L4-L6) were analyzed by histomorphometry. Trabecular and cortical bone mass showed a dose- and time-dependent increase in the treated animals compared with the controls. These increases were evident as early as 1 week after initiation of dosing. There were no consistent significant differences in the comparative effects of PTH(1-34) and RS-66271 on the measured bone parameters. In conclusion, despite the reduced binding affinity of RS-66271 for the PTH/PTHrP receptor compared with human PTH(1-34), both peptides displayed similar in vitro and in vivo pharmacological effects.

Vis-à-vis cells and the priming of bone formation

Bone formation throughout skeletal growth and remodeling always entails deposition of new bone onto a pre-existing mineralized surface. In contrast, the initial deposition of bone in development requires the formation, ex novo, of the first mineralized structure in a nonmineralized tissue. We investigated the cellular events associated with this initial bone formation, with specific reference to the respective role of cartilage and bone cells in bones which form via a cartilage model. The cellular architecture of initial osteogenic sites was investigated by light, confocal, and electron microscopy (EM) in the membranous ossification of fetal calvarial bones (not forming via a cartilage model) and in the membranous ossification of the bony collars of endochondral bones. Bone sialoprotein (BSP), which is expressed during early phases of bone deposition and has been proposed to be involved in the control of both mineral formation and bone cell-matrix interactions, was used as a marker of initial bone formation. We found that at all sites, BSP-producing cells (as identified by intracellular immunoreactivity) are arranged in a characteristic vis-à-vis (face to face) pattern prior to the appearance of the first mineralizing BSP-immunoreactive extracellular matrix. In perichondral osteogenesis, the vis-à-vis pattern comprises osteoblasts differentiating from the perichondrium/periosteum and early hypertrophic chondrocytes located at the lateral aspects of the rudiment. By EM, the first mineral and the first BSP-immunoreactive sites coincide temporally and spatially in the extracellular matrix at the boundary between cartilage and periosteum. We further showed that in an in vitro avian model of chondrocyte differentiation in vitro to osteoblast-like cells, early hypertrophic chondrocytes replated as adherent cells turned on the expression of high levels of BSP in conjunction with the switch to collagen type I synthesis and matrix mineralization. We propose a model for the priming of bone deposition, i.e., the formation of the first bone structure, in which the architectural layout of cells competent to deposit a mineralizing matrix (the vis-à-vis pattern) determines the polarized deposition of bone. For bones forming via a cartilage model, the priming of bone deposition involves and requires cells that differentiate from early hypertrophic chondrocytes.

Parathyroid hormone-related proteins is abundant in osteoarthritic cartilage, and the parathyroid hormone-related protein 1-173 isoform is selectively induced by transforming growth factor beta in articular chondrocytes and suppresses generation of extracellular inorganic pyrophosphate

OBJECTIVE

Parathyroid hormone-related protein (PTHrP) is a major, locally expressed regulator of growth cartilage chondrocyte proliferation, differentiation, synthetic function, and mineralization. Because mechanisms that limit cartilage chondrocytes from maturing and mineralizing are diminished in osteoarthritis (OA), we studied PTHrP expression by articular chondrocytes.

METHODS

PTHrP was studied in normal knee cartilage samples and cultured articular chondrocytes, and in cartilage specimens from knees with advanced OA, obtained at the time of joint replacement.

RESULTS

PTHrP was more abundant in OA than in normal human knee articular cartilage. Both demonstrated PTH/PTHrP receptor expression. PTHrP 1-173, one of three alternatively spliced PTHrP isoforms, was exclusively expressed and induced by transforming growth factor beta in cultured chondrocytes. Chondrocytes mainly used the GC-rich P2 alternative promoter to express PTHrP messenger RNA. Inhibition by PTHrP 1-173, but not by PTHrP 1-146 or PTHrP 1-87, of inorganic pyrophosphate (PPi) elaboration suggested selective functional properties of the 1-173 isoform. Exposure to a neutralizing antibody to PTHrP increased PPi elaboration by articular chondrocytes.

CONCLUSION

Increased expression of PTHrP, including the 1-173 isoform, has the potential to contribute to the pathologic differentiated functions of chondrocytes, including mineralization, in OA.