BMP9-regulated angiogenic signaling plays an important role in the osteogenic differentiation of mesenchymal progenitor cells.

Mesenchymal stromal progenitor cells (MSCs) are multipotent progenitors that can be isolated from numerous tissues. MSCs can undergo osteogenic differentiation under proper stimuli. We have recently demonstrated that bone morphogenetic protein 9 (BMP9) is one of the most osteogenic BMPs. As one of the least studied BMPs, BMP9 has been shown to regulate angiogenesis in endothelial cells. However, it is unclear whether BMP9-regulated angiogenic signaling plays any important role in the BMP9-initiated osteogenic pathway in MSCs. Here, we investigate the functional role of hypoxia-inducible factor 1α (HIF1α)-mediated angiogenic signaling in BMP9-regulated osteogenic differentiation of MSCs. We find that BMP9 induces HIF1α expression in MSCs through Smad1/5/8 signaling. Exogenous expression of HIF1α potentiates BMP9-induced osteogenic differentiation of MSCs both in vitro and in vivo. siRNA-mediated silencing of HIF1α or HIF1α inhibitor CAY10585 profoundly blunts BMP9-induced osteogenic signaling in MSCs. HIF1α expression regulated by cobalt-induced hypoxia also recapitulates the synergistic effect between HIF1α and BMP9 in osteogenic differentiation. Mechanistically, HIF1α is shown to exert its synergistic effect with BMP9 by inducing both angiogenic signaling and osteogenic signaling in MSCs. Thus, our findings should not only expand our understanding of the molecular basis behind BMP9-regulated osteoblastic lineage-specific differentiation, but also provide an opportunity to harness the BMP9-induced synergy between osteogenic and angiogenic signaling pathways in regenerative medicine.

Tetrandrine inhibits Wnt/ß-catenin signaling and suppresses tumor growth of human colorectal cancer.

As one of the most common malignancies, colon cancer is initiated by abnormal activation of the Wnt/ß-catenin pathway. Although the treatment options have increased for some patients, overall progress has been modest. Thus, there is a great need to develop new treatments. We have found that bisbenzylisoquinoline alkaloid tetrandrine (TET) exhibits anticancer activity. TET is used as a calcium channel blocker to treat hypertensive and arrhythmic conditions in Chinese medicine. Here, we investigate the molecular basis underlying TET's anticancer activity. We compare TET with six chemotherapy drugs in eight cancer lines and find that TET exhibits comparable anticancer activities with camptothecin, vincristine, paclitaxel, and doxorubicin, and better than that of 5-fluorouracil (5-FU) and carboplatin. TET IC50 is ≤5 µM in most of the tested cancer lines. TET exhibits synergistic anticancer activity with 5-FU and reduces migration and invasion capabilities of HCT116 cells. Furthermore, TET induces apoptosis and inhibits xenograft tumor growth of colon cancer. TET treatment leads to a decrease in ß-catenin protein level in xenograft tumors, which is confirmed by T-cell factor/lymphocyte enhancer factor and c-Myc reporter assays. It is noteworthy that HCT116 cells with allelic oncogenic ß-catenin deleted are less sensitive to TET-mediated inhibition of proliferation, viability, and xenograft tumor growth. Thus, our findings strongly suggest that the anticancer effect of TET in colon cancer may be at least in part mediated by targeting ß-catenin activity. Therefore, TET may be used alone or in combination as an effective anticancer agent.

TGFbeta/BMP type I receptors ALK1 and ALK2 are essential for BMP9-induced osteogenic signaling in mesenchymal stem cells.

Mesenchymal stem cells (MSCs) are bone marrow stromal cells that can differentiate into multiple lineages. We previously demonstrated that BMP9 is one of the most potent BMPs to induce osteogenic differentiation of MSCs. BMP9 is one of the least studied BMPs. Whereas ALK1, ALK5, and/or endoglin have recently been reported as potential BMP9 type I receptors in endothelial cells, little is known about type I receptor involvement in BMP9-induced osteogenic differentiation in MSCs. Here, we conduct a comprehensive analysis of the functional role of seven type I receptors in BMP9-induced osteogenic signaling in MSCs. We have found that most of the seven type I receptors are expressed in MSCs. However, using dominant-negative mutants for the seven type I receptors, we demonstrate that only ALK1 and ALK2 mutants effectively inhibit BMP9-induced osteogenic differentiation in vitro and ectopic ossification in MSC implantation assays. Protein fragment complementation assays demonstrate that ALK1 and ALK2 directly interact with BMP9. Likewise, RNAi silencing of ALK1 and ALK2 expression inhibits BMP9-induced BMPR-Smad activity and osteogenic differentiation in MSCs both in vitro and in vivo. Therefore, our results strongly suggest that ALK1 and ALK2 may play an important role in mediating BMP9-induced osteogenic differentiation. These findings should further aid us in understanding the molecular mechanism through which BMP9 regulates osteogenic differentiation of MSCs.

Memory alloreactive B cells and alloantibodies prevent anti-CD154-mediated allograft acceptance.

The impact of memory B cells and alloantibodies on the ability to induce transplantation tolerance has not been elucidated. We have developed a murine heart transplant model that isolates the contributions of functional memory B cells from memory T cells in allograft rejection. Memory 3-83 B cells with dual specificity for H-2K(k) and H-2K(b) were generated in 3-83 Igi BCR knockin (BALB/c background) mice by the transplantation of C3H (H-2K(k)) hearts in the absence of immunosuppression. To test the effect of functional memory 3-83 B cells, C3H-primed 3-83 Igi recipients were challenged with C57BL/6 hearts (H-2K(b)) at 60-90 days post-C3H heart transplant and treated with anti-CD154 mAbs. Despite immunosuppression, the C57BL/6 hearts were acutely rejected within 10-13 days and graft rejection was associated with increased frequencies of C57BL/6-specific IFN-gamma-producing T cells. Histology revealed significant numbers of infiltrating T cells, consistent with acute T cell-mediated rejection. The resistance to tolerance induction was dependent on the synergistic effects of memory 3-83 B cells and alloantibodies, whereas memory T cells are not necessary. We conclude that the combined effects of functional memory B cells and alloantibodies prevent anti-CD154-mediated graft acceptance by facilitating the CD40-CD154-independent activation of alloreactive T cells. This study provides insight into the potential ability of memory B cells and alloantibodies to prevent anti-CD154-mediated graft acceptance.

The role of the intravascular microenvironment in spontaneous metastasis development.

Metastasis is primarily responsible for the morbidity and mortality of cancer. Improved therapeutic outcomes and prognosis depend on improved understanding of mechanisms regulating the establishment of early metastasis. In this study, use of green fluorescent protein (GFP)-expressing PC-3 orthotopic model of human prostate cancer and two complementary fluorescence in vivo imaging systems (Olympus OV100 and VisEn FMT) allowed for the first time real-time characterization of cancer cell-endothelium interactions during spontaneous metastatic colonization of the liver and lung in live mice. We observed that prior to the detection of extra-vascular metastases, GFP-expressing PC-3 cancer cells resided initially inside the blood vessels of the liver and the lung, where they proliferated and expressed Ki-67 and exhibited matrix metalloprotenases (MMP) activity. Thus, the intravascular cancer cells produced their own microenvironment, where they could continue to proliferate. Extravasation occurred earlier in the lung than in the liver. Our results demonstrate that the intravascular microenvironment is a critical staging area for the development of metastasis that later can invade the parenchyma. Intravascular tumor cells may represent a therapeutic target to inhibit the development of extravascular metastases. Therefore, this imageable model of intravascular metastasis may be used for evaluation of novel anti-metastatic agents.

Activation of RXR and RAR signaling promotes myogenic differentiation of myoblastic C2C12 cells.

Differentiation of embryonic and adult myogenic progenitors undergoes a complex series of cell rearrangements and specification events which are controlled by distinct gene regulatory networks. Delineation of the molecular mechanisms that regulate skeletal muscle specification and formation should be important for understanding congenital myopathies and muscular degenerative diseases. Retinoic acid (RA) signaling plays an important role in development. However, the role of RA signaling in adult myogenic progenitors is poorly understood. Here, we investigate the role of RA signaling in regulating myogenic differentiation of myoblastic progenitor cells. Using the mouse myoblast progenitor C2C12 line as a model, we have found that the endogenous expression of most RAR and RXR isotypes is readily detected. While the nuclear receptor co-repressors are highly expressed, two of the three nuclear receptor co-activators and the enzymes involved in RA synthesis are expressed at low level or undetectable, suggesting that the RA signaling pathway may be repressed in myogenic progenitors. Using the alpha-myosin heavy chain promoter-driven reporter (MyHC-GLuc), we have demonstrated that either ATRA or 9CRA is able to effectively induce myogenic differentiation, which can be synergistically enhanced when both ATRA and 9CRA are used. Upon ATRA and 9CRA treatment of C2C12 cells the expression of late myogenic markers significantly increases. We have further shown that adenovirus-mediated exogenous expression of RARalpha and/or RXRalpha is able to effectively induce myogenic differentiation in a ligand-independent fashion. Morphologically, ATRA- and 9CRA-treated C2C12 cells exhibit elongated cell body and become multi-nucleated myoblasts, and even form myoblast fusion. Ultrastructural analysis under transmission electron microscope reveals that RA-treated myogenic progenitor cells exhibit an abundant presence of muscle fibers. Therefore, our results strongly suggest that RA signaling may play an important role in regulating myogenic differentiation.

BMP-9-induced osteogenic differentiation of mesenchymal progenitors requires functional canonical Wnt/beta-catenin signalling.

Bone morphogenetic protein 9 (BMP-9) is a member of the transforming growth factor (TGF)-beta/BMP superfamily, and we have demonstrated that it is one of the most potent BMPs to induce osteoblast differentiation of mesenchymal stem cells (MSCs). Here, we sought to investigate if canonical Wnt/beta-catenin signalling plays an important role in BMP-9-induced osteogenic differentiation of MSCs. Wnt3A and BMP-9 enhanced each other's ability to induce alkaline phosphatase (ALP) in MSCs and mouse embryonic fibroblasts (MEFs). Wnt antagonist FrzB was shown to inhibit BMP-9-induced ALP activity more effectively than Dkk1, whereas a secreted form of LPR-5 or low-density lipoprotein receptor-related protein (LRP)-6 exerted no inhibitory effect on BMP-9-induced ALP activity. beta-Catenin knockdown in MSCs and MEFs diminished BMP-9-induced ALP activity, and led to a decrease in BMP-9-induced osteocalcin reporter activity and BMP-9-induced expression of late osteogenic markers. Furthermore, beta-catenin knockdown or FrzB overexpression inhibited BMP-9-induced mineralization in vitro and ectopic bone formation in vivo, resulting in immature osteogenesis and the formation of chondrogenic matrix. Chromatin immunoprecipitation (ChIP) analysis indicated that BMP-9 induced recruitment of both Runx2 and beta-catenin to the osteocalcin promoter. Thus, we have demonstrated that canonical Wnt signalling, possibly through interactions between beta-catenin and Runx2, plays an important role in BMP-9-induced osteogenic differentiation of MSCs.

Recovery of islet beta-cell function in streptozotocin- induced diabetic mice: an indirect role for the spleen.

Limitations in islet beta-cell transplantation as a therapeutic option for type 1 diabetes have prompted renewed interest in islet regeneration as a source of new islets. In this study we tested whether severely diabetic adult C57BL/6 mice can regenerate beta-cells. Diabetes was induced in C57BL/6 mice with high-dose streptozotocin (160-170 mg/kg). In the absence of islet transplantation, all diabetic mice remained diabetic (blood glucose >400 mg/dl), and no spontaneous reversal of diabetes was observed. When syngeneic islets (200/mouse) were transplanted into these diabetic mice under a single kidney capsule, stable restoration of euglycemia for >/=120 days was achieved. Removal of the kidney bearing the transplanted islets at 120 days posttransplantation revealed significant restoration of endogenous beta-cell function. This restoration of islet function was associated with increased beta-cell mass, as well as beta-cell hypertrophy and proliferation. The restoration of islet cell function was facilitated by the presence of a spleen; however, the facilitation was not due to the direct differentiation of spleen-derived cells into beta-cells. This study supports the possibility of restoring beta-cell function in diabetic individuals and points to a role for the spleen in facilitating this process.

Mechanistic study of malononitrileamide FK778 in cardiac transplantation and CMV infection in rats.

BACKGROUND: FK778 is a malononitrilamide, a class of immune suppressive compounds with antiviral features and experimental activity in chronic rejection, a potentially interesting combination for organ transplantation. The goal of this project was to study the tolerability, immune suppressive efficacy, and anti-cytomegalovirus (CMV) activity of FK778 and to assess the in vivo relevance of its previously described inhibition of de novo pyrimidine synthesis. METHODS: Heart transplants were performed in rats (Brown Norway [BN] to Lewis) and treated with varying doses of FK778 or leflunomide for 28 days. At 28 days, at the time of rejection or at the death of the animal, the allograft and other vital organs were obtained for study by light microscopy and immunohistochemistry. In separate experiments, Lewis rats were given sublethal irradiation, inoculated with rat CMV (Maastricht strain), and treated with varying doses of FK778 and leflunomide. In both the transplant and CMV studies, IP uridine was given at 250 mg/kg to cohorts or animals receiving FK778 and leflunomide. RESULTS: FK778 controls acute rejection and inhibits CMV replication at 20 mg/kg but is toxic at 25 mg/kg. Toxicity is manifested as anemia, changes in hepatic and intestinal histology, and mortality. The toxicity but not the immune suppressive or antiviral efficacy, is reduced significantly by exogenous uridine administration. CONCLUSION: FK778 has both immune suppressive and antiviral activities, neither of which is entirely dependent on inhibition of pyrimidine synthesis. These, and other published observations, suggest that the antiviral activity and a considerable part of the efficacy of the malononitrilamide family of drugs is attributable to activities other than drug induced pyrimidine deficiency.

Inverse correlation between heparan sulfate composition and heparanase-1 gene expression in thyroid papillary carcinomas: a potential role in tumor metastasis.

PURPOSE: Heparanase-1 (HPR1) is an endoglycosidase that degrades the side chains of heparan sulfate proteoglycan (HSPG), a key component in cell surfaces, the extracellular matrix (ECM), and the basement membrane (BM). The purpose of this study was to evaluate HPR1 expression in thyroid neoplasms and its effect in degrading the HSPG substrates in the ECM and BM and to determine its role in thyroid tumor metastasis. EXPERIMENTAL DESIGN: HPR1 mRNA expression was analyzed by using in situ hybridization with a digoxigenin-labeled antisense RNA probe on paraffin-embedded tumor sections and reverse transcription-PCR (RT-PCR) in fresh tumor tissues. HPR1 protein expression was analyzed by using immunohistochemical staining with an anti-HPR1 rabbit antiserum and immunofluorescence (IF) with an anti-HPR1 monoclonal antibody. The effect of HPR1 expression in thyroid neoplasms was analyzed by examining the presence and integrity of the HSPG substrates in the ECM and BM using IF staining with a specific monoclonal antibody against heparan sulfate. The relationship of HPR1 expression in papillary thyroid carcinomas (PTCs) with various clinicopathological parameters was analyzed statistically. The role of HPR1 in thyroid tumor metastasis was further examined by comparing HPR1 levels in 10 thyroid tumor cell lines to their invasive and metastatic potential. RESULTS: In situ hybridization analysis of 81 tumor samples (62 papillary carcinomas and 19 follicular adenomas) revealed that HPR1 was expressed at a much higher frequency in PTCs than in follicular adenomas (P<0.05). RT-PCR analyses of fresh tumor tissues revealed that HPR1 mRNA could be detected in primary and metastatic thyroid papillary carcinomas. HPR1 expression was confirmed at the protein level by immunohistochemical staining and IF stainings. IF analysis of HSPG revealed that HS was deposited abundantly in the BM of normal thyroid follicles and benign follicular adenomas but was absent in most thyroid papillary carcinomas. A lack of heparan sulfate in PTCs inversely correlated with HPR1 expression. Clinicopathological data analyses revealed that PTCs with local and distant metastases scored HPR1 positive at a significantly higher frequency than nonmetastatic thyroid cancers (P=0.02). To further explore the role of HPR1 in tumor metastases, we characterized HPR1 expression in 10 thyroid tumor cell lines using RT-PCR and Western blot and measured HPR1 enzymatic activity using a novel ELISA. HPR1 was differentially expressed in different types of cell lines; overexpression of HPR1 in two tumor cell lines led to a dramatic increase of their invasive potential in vitro in an artificial BM. CONCLUSIONS: Our study suggests that HPR1 expressed in papillary carcinomas is functional and that HPR1 expression is associated with thyroid tumor malignancy and may significantly contribute to thyroid tumor metastases.

Allograft tolerance induced by intact active bone co-transplantation and anti-CD40L monoclonal antibody therapy.

BACKGROUND: One of the most promising approaches to achieving allograft tolerance involves the transient inhibition of co-stimulatory signals in T cells. There is, however, increasing evidence that this approach alone cannot universally elicit allograft tolerance and that adjunct therapies capable of synergizing with co-stimulation blockade may be necessary. METHODS: We developed a novel tolerance strategy involving co-transplantation of intact allogeneic bone fragments containing active bone marrow (intact active bone [IAB]) with heart allograft and transient anti-CD40L monoclonal antibody therapy. RESULTS: Mice treated with IAB and anti-CD40L were tolerant to major histocompatibility complex and minor antigen-mismatched cardiac and skin allografts. Heart allografts had normal histology up to 270 days posttransplantation, and the production of graft-reactive antibodies was inhibited. Microchimerism, but no macrochimerism, of donor cells was detected in the peripheral blood or lymphoid organs of tolerant mice receiving IAB and anti-CD40L. Lymphocytes from tolerant mice retained normal proliferative responsiveness to donor cells in vitro but demonstrated a donor-specific loss in the priming of interferon-gamma responses. The ability to produce interleukin-2 or -4 when stimulated with donor cells was normal. CONCLUSIONS: Contrary to previous reports of the ability of bone marrow cells to induce central deletional tolerance, our data suggest that the regimen involving co-transplantation of IAB on the day of heart allograft transplantation and transient anti-CD40L therapy induces a robust donor-specific peripheral tolerance.

Mouse-heart grafts expressing an incompatible carbohydrate antigen. II. Transition from accommodation to tolerance.

BACKGROUND: Immune response to incompatible ABO antigens on allografts may result in rejection, accommodation, or immune tolerance. Our objective has been to develop a model for studying these three types of immune response to incompatible carbohydrate antigen in alpha1,3-galactosyltransferase knockout (KO) mice. KO mice lack the alpha-gal epitope and can produce the anti-Gal antibody against it after immunization with pig kidney membranes (PKM) that express this epitope. METHODS: KO mice were transplanted with syngeneic wild-type (WT) heart expressing alpha-gal epitopes. Subsequently, the mice were lethally irradiated and received lymphocytes including memory anti-Gal B cells from PKM immunized KO mice. Immune response to incompatible alpha-gal epitopes on the graft was determined by transplanted-heart function and by production of anti-Gal after PKM immunizations. RESULTS: Anti-Gal B cells exposed for 1 to 2 weeks to alpha-gal epitopes of WT hearts differentiate into cells producing noncytolytic accommodating antibodies. Exposure for longer periods (2-4 weeks) induces a transition from accommodation into tolerance, indicated by the inability of mice to produce anti-Gal antibodies despite repeated PKM immunizations. WT hearts in accommodating and in tolerized mice continue to function for months. CONCLUSIONS: In the absence of T-cell help, anticarbohydrate B cells exposed to incompatible carbohydrate antigens of transplanted organs differentiate first into cells capable of producing accommodating antibodies, but, after prolonged exposure, these B cells gradually become tolerized. These findings suggest that prolonged T-cell suppression in recipients of ABO-incompatible allografts may result in a similar induction of tolerance to incompatible blood-group antigens.

A mouse model for studying intrahepatic islet transplantation.

Intrahepatic human islet transplantation has raised hopes for a cure for diabetes mellitus, especially in patients with type 1 diabetes; however, the need for a substantial amount of islets and, in many instances, repeated transplantations demonstrates underlying problems with this procedure, such as failure of angiogenesis and immunologic rejection. Studies using rodent models may be helpful in improving the success of islet transplantation. However, most of the studies using rodents for islet transplantation have been under the kidney capsule rather than the liver. Using islets from transgenic mice expressing green fluorescent protein under the control of mouse insulin I promoter, the authors have developed a method with which to visualize histologic and pathologic changes in intraportally transplanted islets and surrounding hepatic tissue using reflected light confocal imaging. Initial events 24 hr after islet transplantation in the liver include beta-cell loss and hepatic ischemic injuries.

Antibody-mediated accommodation of heart grafts expressing an incompatible carbohydrate antigen.

BACKGROUND: Accommodation in patients transplanted with ABO incompatible allografts describes a state in which antibodies are produced against the incompatible blood group carbohydrate antigen; however, the graft is not rejected. The present study describes an experimental model for antibody-mediated accommodation of organs expressing incompatible carbohydrate antigens. METHODS: The model includes alpha1,3galactosyltransferase knockout mice that lack the alpha-gal epitope (Galalpha1-3Galbeta1-4GlcNAc-R), transplanted heterotopically with wild-type (WT) hearts expressing this epitope. The mice are irradiated and receive memory anti-Gal B cells by adoptive transfer. Immunization of these mice with pig-kidney membranes induces the production of large amounts of anti-Gal, which binds specifically to alpha-gal epitopes. RESULTS: Under the described accommodation protocol, transplanted mice produce anti-Gal that binds to alpha-gal epitopes on endothelial cells of the grafted WT heart; however, the WT hearts continued to function for months. Second WT hearts transplanted into accommodating, anti-Gal producing mice, were not rejected. Anti-Gal in accommodating mice was not cytolytic, whereas anti-Gal in rejecting mice readily induced complement-mediated lysis of cells expressing alpha-gal epitopes. In addition, accommodating mice displayed a preferential increase in the anti-Gal immunoglobulin (Ig)G2b subclass. CONCLUSIONS: The immune system may be manipulated to accommodate grafts expressing incompatible carbohydrate antigens by preferential production of noncytolytic anticarbohydrate antibodies.

Role of CD4+ and CD8+ T cells in the rejection of concordant pancreas xenografts.

BACKGROUND: We studied the ability of CD4 and CD8 T cells to induce rejection of pancreas xenografts in a concordant combination using rat pancreas xenografts as donors and chemically induced diabetic mice as recipients. METHODS: Lewis rat (2 to 3 weeks old) pancreas xenografts were transplanted into streptozotocin (STZ)-induced diabetic mice. Lymphocyte proliferation and cytokine production were analyzed in vitro. All pancreas xenografts were assessed by functional (blood glucose) and histopathologic examinations. RESULTS: Lewis rat pancreas grafts were rejected within 10 to 13 days, with mononuclear cell infiltrate and tissue necrosis in STZ-induced diabetic mice. A predominant T cell receptor alphabeta -CD4 cell (on day 4) and T cell receptor alphabeta -CD8 cell (on day 8) infiltrate and IgM deposition were found in the pancreas xenografts after transplantation. Anti-CD4 (GK1.5), but not anti-CD8 (YTS169.4), monoclonal antibodies resulted in a prolonged survival of Lewis rat pancreas xenografts. Lewis pancreas xenografts were permanently accepted by CD4 knockout mice but not by CD8 knockout mice. The pancreas xenografts were acutely rejected with a mean survival time of 15.3 days in B cell-deficient mice (microMT/microMT). Transfer of CD4 but not CD8 spleen cells from naïve C57BL/6 mice into Rag2 mice led to acute rejection of transplanted pancreas xenografts. However, activated CD8 spleen cells elicited rejection of Lewis rat pancreas xenografts in SZT-induced diabetic mice. CONCLUSION: The current results show that CD4 T cells are necessary and sufficient for mediating the rejection of Lewis rat pancreas xenografts in STZ-induced diabetic mice. However, CD8 cells, when activated, can also induce acute rejection of concordant pancreas xenografts.

Skin graft survival in genetically identical cloned pigs.

Nuclear transfer technology allows for the reprogramming of somatic cells, and the production of embryonic stem cells and animals that are genetically identical in terms of nuclear DNA to the parental somatic cell. It is assumed that these products of nuclear transfer technology will be immunologically compatible to each other in spite of the fact that there are data that show differences in the expression patterns and phenotypes between animals produced by nuclear transfer. We have produced a series of cloned pigs from embryonic fibroblasts. Microsatellite analysis was used to confirm that the clones were genetically identical. Skin transplants were performed to assess immunological reactivity. Skin transplants between genetically identical cloned pigs were accepted, whereas third party grafts were rejected. Histological analysis of the grafts showed edema and mononuclear cell infiltrates in the recipient's skin in rejected grafts and not in grafts that were accepted. Our data supports the notion that genetically identical cloned pigs are immunologically compatible.

IGFBP5 domains exert distinct inhibitory effects on the tumorigenicity and metastasis of human osteosarcoma.

Osteosarcoma (OS) is the most common primary malignancy of bone. We investigated the roles of insulin-like growth factor binding protein 5 (IGFBP5) domains in modulating OS tumorigenicity and metastasis. The N-terminal (to a lesser extent the C-terminal) domain inhibited cell proliferation and induced apoptosis while the C-terminal domain inhibited cell migration and invasion. The Linker domain had no independent effects. In vivo, the N-terminal domain decreased tumor growth without affecting pulmonary metastases while the C-terminal domain inhibited tumor growth and metastases. In summary, the N- and C-terminal domains modulated OS tumorigenic phenotypes while the C-terminal domain inhibited OS metastatic phenotypes.

Conditionally immortalized mouse embryonic fibroblasts retain proliferative activity without compromising multipotent differentiation potential.

Mesenchymal stem cells (MSCs) are multipotent cells which reside in many tissues and can give rise to multiple lineages including bone, cartilage and adipose. Although MSCs have attracted significant attention for basic and translational research, primary MSCs have limited life span in culture which hampers MSCs' broader applications. Here, we investigate if mouse mesenchymal progenitors can be conditionally immortalized with SV40 large T antigen and maintain long-term cell proliferation without compromising their multipotency. Using the system which expresses SV40 large T antigen flanked with Cre/loxP sites, we demonstrate that mouse embryonic fibroblasts (MEFs) can be efficiently immortalized by SV40 large T antigen. The conditionally immortalized MEFs (iMEFs) exhibit an enhanced proliferative activity and maintain long-term cell proliferation, which can be reversed by Cre recombinase. The iMEFs express most MSC markers and retain multipotency as they can differentiate into osteogenic, chondrogenic and adipogenic lineages under appropriate differentiation conditions in vitro and in vivo. The removal of SV40 large T reduces the differentiation potential of iMEFs possibly due to the decreased progenitor expansion. Furthermore, the iMEFs are apparently not tumorigenic when they are subcutaneously injected into athymic nude mice. Thus, the conditionally immortalized iMEFs not only maintain long-term cell proliferation but also retain the ability to differentiate into multiple lineages. Our results suggest that the reversible immortalization strategy using SV40 large T antigen may be an efficient and safe approach to establishing long-term cell culture of primary mesenchymal progenitors for basic and translational research, as well as for potential clinical applications.

Growth hormone synergizes with BMP9 in osteogenic differentiation by activating the JAK/STAT/IGF1 pathway in murine multilineage cells.

Growth hormone (GH) is usually released by somatotrophs in the anterior pituitary in response to the GH-releasing hormone and plays an important role in skeleton development and postnatal growth. However, it is unclear if extrapituitary GH exerts any effect on murine multilineage cells (MMCs). MMCs are multipotent progenitors that give rise to several lineages, including bone, cartilage, and fat. We have identified bone morphogenic protein 9 (BMP9) as one of the most osteogenic BMPs in MMCs by regulating a distinct set of downstream mediators. In this study, we find that GH is one of the most significantly upregulated genes by BMP9 in mouse MMCs through expression-profiling analysis. We confirm that GH is a direct early target of and upregulated by BMP9 signaling. Exogenous GH synergizes with BMP9 on inducing early and late osteogenic markers in MMCs. Furthermore, BMP9 and GH costimulation leads to a significant expansion of growth plate in cultured limb explants. Although GH alone does not induce de novo bone formation in an ectopic bone formation model, BMP9 and GH costimulated MMCs form more mature bone, which can be inhibited by silencing GH expression. The synergistic osteogenic activity between BMP9 and GH can be significantly blunted by JAK/STAT inhibitors, leading to a decrease in GH-regulated insulin-like growth factor 1 (IGF1) expression in MMCs. Our results strongly suggest that BMP9 may effectively regulate extrapituitary GH expression in MMCs. Thus, it is conceivable that the BMP9-GH-IGF axis may be exploited as an innovative strategy to enhance osteogenesis in regenerative medicine.