[Show abstract][Hide abstract] ABSTRACT: Parathyroid hormone (PTH) is an osteoanabolic for treating osteoporosis but its potency wanes. Disabling the transcription factor Nmp4 in healthy, ovary-intact mice enhances bone response to PTH and BMP2 and protects from unloading-induced osteopenia. These Nmp4(-/-) mice exhibit expanded bone marrow (BM) populations of osteoprogenitors and supporting CD8(+) T cells. To determine whether the Nmp4(-/-) phenotype persists in an osteoporosis model we compared PTH response in ovariectomized (ovx) wild type (WT) and Nmp4(-/-) mice. To identify potential Nmp4 target genes we performed bioinformatic/pathway profiling on Nmp4 ChIP-seq data. Mice (12wks) were ovx or sham-operated 4wks before the initiation of PTH therapy. Skeletal phenotype analysis included μ CT, histomorphometry, serum profiles, FACS sorting and the growth/mineralization of cultured WT and Nmp4(-/-) BM mesenchymal stem progenitor cells (MSPCs). ChIP-seq data were derived using MC3T3-E1 pre-osteoblasts, murine embryonic stem cells, and two blood cell lines. Ovx Nmp4(-/-) mice exhibited an improved response to PTH coupled with elevated numbers of osteoprogenitors and CD8(+) T cells, but were not protected from ovx-induced bone loss. Cultured Nmp4(-/-) MSPCs displayed enhanced proliferation and accelerated mineralization. ChIP-seq/gene ontology analyses identified target genes likely under Nmp4 control as enriched for negative regulators of biosynthetic processes. Interrogation of mRNA transcripts in non-differentiating and osteogenic differentiating WT and Nmp4(-/-) MSPCs was performed on 90 Nmp4 target genes and differentiation markers. These data suggest that Nmp4 suppresses bone anabolism, in part, by regulating insulin-like growth factor binding protein expression. Changes in Nmp4 status may lead to improvements in osteoprogenitor response to therapeutic cues.
[Show abstract][Hide abstract] ABSTRACT: Neurofibromatosis type 1 (NF1) is an autosomal dominant disease caused by mutations in the NF1 tumor suppressor gene, which affect approximately 1 out of 3000 individuals. Patients with NF1 suffer from a range of malignant and nonmalignant manifestations such as plexiform neurofibromas and skeletal abnormalities. We previously demonstrated that Nf1 haploinsufficiency in mesenchymal stem/progenitor cells (MSPCs) results in impaired osteoblastic differentiation, which may be associated with the skeletal manifestations in NF1 patients. Here we sought to further ascertain the role of Nf1 in modulating the migration and adhesion of MSPCs of the Nf1 haploinsufficient (Nf1+/-) mice. Nf1+/- MSPCs demonstrated increased nuclear-cytoplasmic ratio, increased migration, and increased actin polymerization as compared to wild-type (WT) MSPCs. Additionally, Nf1+/- MSPCs were noted to have significantly enhanced cell adhesion to fibronectin with selective affinity for CH271 with an overexpression of its complimentary receptor, CD49e. Nf1+/- MSPCs also showed hyperactivation of phosphoinositide 3-kinase (PI3-K) and mitogen activated protein kinase (MAPK) signaling pathways when compared to WT MSPCs, which were both significantly reduced in the presence of their pharmacologic inhibitors, LY294002 and PD0325901, respectively. Collectively, our study suggests that both PI3-K and MAPK signaling pathways play a significant role in enhanced migration and adhesion of Nf1 haploinsufficient MSPCs.
International Journal of Molecular Sciences 06/2015; 16(6):12345-59. DOI:10.3390/ijms160612345 · 2.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: While nullizygous loss of NF1 leads to myeloid malignancies, haploinsufficient loss of NF1 (Nf1) has been shown to contribute to osteopenia and osteoporosis which occurs in approximately 50 percent of neurofibromatosis type 1 (NF1) patients. Bone marrow mononuclear cells of haploinsufficient NF1 patients and Nf1(+/-) mice exhibit increased osteoclastogenesis and accelerated bone turnover, however the culprit hematopoietic lineages responsible for perpetuating these osteolytic manifestations have yet to be elucidated. Here we demonstrate that conditional inactivation of a single Nf1 allele within the myeloid progenitor cell population (Nf1-LysM) is necessary and sufficient to promote multiple osteoclast gain-in-functions, resulting in enhanced osteoclastogenesis and accelerated osteoclast bone lytic activity in response to pro-resorptive challenge in vivo. Surprisingly, mice conditionally Nf1 heterozygous in mature, terminally differentiated osteoclasts (Nf1-Ctsk) do not exhibit any of these skeletal phenotypes, indicating a critical requirement for Nf1 haploinsufficiency at a more primitive/progenitor stage of myeloid development in perpetuating osteolytic activity. We further identified p21Ras dependent hyper-phosphorylation of Pu.1 within the nucleus of Nf1 haploinsufficent myelomoncytic osteoclast precursors, providing a novel therapeutic target for the potential treatment of NF1 associated osteolytic manifestations. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
Journal of bone and mineral research: the official journal of the American Society for Bone and Mineral Research 04/2015; DOI:10.1002/jbmr.2538 · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Despite the high prevalence and significant morbidity of spinal anomalies in neurofibromatosis type 1 (NF1), the pathogenesis of these defects remains largely unknown. Here, we present two murine models: Nf1flox/-;PeriCre and Nf1flox/-;Col.2.3Cre mice, which recapitulate spinal deformities seen in the human disease. Dynamic histomorphometry and microtomographic studies show recalcitrant bone remodeling and distorted bone microarchitecture within the vertebral spine of Nf1flox/-;PeriCre and Nf1flox/-;Col2.3Cre mice, with analogous histological features present in a human patient with dystrophic scoliosis. Intriguingly, 36-60% of Nf1flox/-;PeriCre and Nf1flox/-;Col2.3Cre mice exhibit segmental vertebral fusion anomalies with boney obliteration of the intervertebral disc (IVD). While analogous findings have not yet been reported in the NF1 patient population, we herein present two case reports of IVD defects and interarticular vertebral fusion in patients with NF1. Collectively, these data provide novel insights regarding the pathophysiology of dystrophic spinal anomalies in NF1, and provide impetus for future radiographic analyses of larger patient cohorts to determine whether IVD and vertebral fusion defects may have been previously overlooked or underreported in the NF1 patient population.
PLoS ONE 03/2015; 10(3):e0119093. DOI:10.1371/journal.pone.0119093 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The study was aimed to investigate the effect of anti-mouse CD122 antibody on the hematopoietic repopulating capacity of cord blood CD34(+) cells in a humanized murine model-non obese diabetic/severe combined immunodeficiency (NOD/SCID) mice. After sublethal irradiation with γ-ray, NOD/SCID mice were intraperitoneally injected with 200 µg mouse isotype control antibody or anti-mouse CD122 antibody. Human cord blood CD34(+)cells or phosphate-buffered saline (PBS) were injected via the tail vein at 6-8 hours later. Cohort of the mice injected with anti-mice CD122 antibody or control antibody alone were sacrificed at different time point (at week 2, 3, and 4 weeks) after the injection, and the percentage of NK cells in the peripheral blood was analyzed by flow cytometry. To evaluate the effect of anti-mouse CD122 antibody on the repopulating capacity of cord blood CD34(+) cells in the recipient mice, phenotype analysis was performed in the bone marrow at 6 and 8 weeks after the transplantation. The results showed that the proportion of NK cells in the peripheral blood were (4.6 ± 0.6)% and (5.7 ± 1.7)% at week 2 and 3 after anti-CD122 antibody injection respectively,which decreased by 60%, compared with the mice injected with isotype control antibody. After 6 and 8 weeks of cord blood CD34(+) cell transplantation,the percentage of human CD45(+) in the bone marrow of the recipient mice treated with anti-mice CD122 antibody was (63.0 ± 12.2)% and (53.2 ± 16.3)%,respectively,which were dramatically higher than that in the mice treated with isotype control antibody (7.7 ± 3.6)% and (6.1 ± 2.4)%. Moreover,at 8 weeks after transplantation,human CD34(+) cells appeared significantly in the recipients treated with anti-CD122 antibody. It is concluded that the anti-mouse CD122 antibody enhances the hematopoietic repopulating capacity of cord blood CD34(+) cells in the NOD/SCID mice through decreasing the proportion of NK cells.
Zhongguo shi yan xue ye xue za zhi / Zhongguo bing li sheng li xue hui = Journal of experimental hematology / Chinese Association of Pathophysiology 11/2014; 22(6):1673-7.
[Show abstract][Hide abstract] ABSTRACT: Neurofibromatosis type 2 (NF2) is an autosomal dominant genetic disorder resulting from germline mutations in the NF2 gene. Bilateral vestibular schwannomas, tumors on cranial nerve VIII, are pathognomonic for NF2 disease. Furthermore, schwannomas
also commonly develop in other cranial nerves, dorsal root ganglia and peripheral nerves. These tumors are a major cause of
morbidity and mortality, and medical therapies to treat them are limited. Animal models that accurately recapitulate the full
anatomical spectrum of human NF2-related schwannomas, including the characteristic functional deficits in hearing and balance
associated with cranial nerve VIII tumors, would allow systematic evaluation of experimental therapeutics prior to clinical
use. Here, we present a genetically engineered NF2 mouse model generated through excision of the Nf2 gene driven by Cre expression under control of a tissue-restricted 3.9kbPeriostin promoter element. By 10 months of age, 100% of Postn-Cre; Nf2flox/flox mice develop spinal, peripheral and cranial nerve tumors histologically identical to human schwannomas. In addition, the
development of cranial nerve VIII tumors correlates with functional impairments in hearing and balance, as measured by auditory
brainstem response and vestibular testing. Overall, the Postn-Cre; Nf2flox/flox tumor model provides a novel tool for future mechanistic and therapeutic studies of NF2-associated schwannomas.
Human Molecular Genetics 08/2014; 24(1). DOI:10.1093/hmg/ddu414 · 6.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Additional sex comb-like 1 ( ASXL1) is an enhancer of Trithorax and Polycomb family, which are necessary for the maintenance of stable repression of homeotic and other loci. Recently, alterations of ASXL1 gene were identified in the hematopoietic cells from patients with a variety of myeloid malignancies, including chronic myelomonocytic leukemia (CMML, 43% of cases), myelodysplastic syndrome (MDS, 20%), myeloproliferative neoplasms (MPN, 10%) and acute myeloid leukemia (AML, 20%). The majority of ASXL1 mutations are frameshift and nonsense mutations. These clinical data suggest an important role of ASXL1 in the pathogenesis and/or transformation of myeloid malignancies. However, the role of ASXL1 in the pathogenesis of myeloid malignancies and in normal hematopoiesis in vivo, as well as the underlying mechanisms remains unknown. This article reviews the structure and function of ASXL1, the clinical characteristic and prognostic significance of ASXL1 mutation, the association of ASXL1 with other gene mutation, as well as ASXL1 knock-down or silence in vitro and in vivo models.
Zhongguo shi yan xue ye xue za zhi / Zhongguo bing li sheng li xue hui = Journal of experimental hematology / Chinese Association of Pathophysiology 07/2014; 22(4):1183-7.
[Show abstract][Hide abstract] ABSTRACT: Dysregulated TGF-β signaling is associated with a spectrum of osseous defects as seen in Loeys-Dietz syndrome, Marfan syndrome, and Camurati-Engelmann disease. Intriguingly, neurofibromatosis type 1 (NF1) patients exhibit many of these characteristic skeletal features including kyphoscoliosis, osteoporosis, tibial dysplasia, and pseudarthrosis; however, the molecular mechanisms mediating these phenotypes remain unclear. Here, we provide genetic and pharmacologic evidence that hyperactive TGF-β1 signaling pivotally underpins osseous defects in Nf1(flox/-) ;Col2.3Cre mice, a model which closely recapitulates the skeletal abnormalities found in the human disease. Compared to controls, we show that serum TGF-β1 levels are 5-6 fold increased both in Nf1(flox/-) ;Col2.3Cre mice and in a cohort of NF1 patients. Nf1 deficient osteoblasts, the principal source of TGF-β1 in bone, overexpress TGF-β1 in a gene dosage dependent fashion. Moreover, Nf1 deficient osteoblasts and osteoclasts are hyperresponsive to TGF-β1 stimulation, potentiating osteoclast bone resorptive activity while inhibiting osteoblast differentiation. These cellular phenotypes are further accompanied by p21-Ras dependent hyperactivation of the canonical TGF-β1-Smad pathway. Re-expression of the human, full-length neurofibromin GTPase-activating protein (GAP) related domain (NF1 GRD) in primary Nf1 deficient osteoblast progenitors, attenuated TGF-β1 expression levels and reduced Smad phosphorylation in response to TGF-β1 stimulation. As an in vivo proof of principle, we demonstrate that administration of the TβRI kinase inhibitor, SD-208, can rescue bone mass deficits and prevent tibial fracture non-union in Nf1(flox/-) ;Col2.3Cre mice. In sum, these data demonstrate a pivotal role for hyperactive TGF-β1 signaling in the pathogenesis of NF1 associated osteoporosis and pseudarthrosis, thus implicating the TGF-β signaling pathway as a potential therapeutic target in the treatment of NF1 osseous defects which are refractory to current therapies.
Journal of bone and mineral research: the official journal of the American Society for Bone and Mineral Research 12/2013; 28(12). DOI:10.1002/jbmr.1992 · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: ASXL1 is mutated/deleted with high frequencies in multiple forms of myeloid malignancies and its alterations are associated with poor prognosis. De novo ASXL1 mutations cause Bohring-Opitz syndrome characterized by multiple congenital malformations. We show that Asxl1-deletion in mice led to developmental abnormalities including dwarfism, anophthalmia and 80% embryonic lethality. Surviving Asxl1(-/-) mice lived for up to 42 days and developed features of MDS, including dysplastic neutrophils and multiple lineage cytopenia. Asxl1(-/-) mice had a reduced HSC-pool and Asxl1(-/-) HSCs exhibited decreased hematopoietic repopulating capacity with skewed cell differentiation favoring granulocytic lineage. Importantly, Asxl1(+/-) mice also developed mild MDS-like disease, which could progress to MDS/MPN, demonstrating a haploinsufficient effect of Asxl1 in the pathogenesis of myeloid malignancies. Asxl1-loss led to an increased apoptosis and mitosis in LK cells, consistent with human MDS. Furthermore, Asxl1(-/-) LK cells exhibited decreased global levels of H3K27me3 and H3K4me3, and altered expression of genes regulating apoptosis (Bcl2, Bcl2l12 and Bcl2l13). Collectively, we report a novel ASXL1 murine model which recapitulates human myeloid malignancies, implying that Asxl1 functions as a tumor suppressor to maintain hematopoietic cell homeostasis. Future work is necessary to clarify the contribution of microenvironment to the hematopoietic phenotypes observed in the constitutional Asxl1(-/-) mice.
[Show abstract][Hide abstract] ABSTRACT: Neurofibromatosis type 1 (NF1) is a common genetic disorder affecting 1 in 3500 individuals. Patients with NF1 are predisposed to debilitating skeletal manifestations, including osteopenia/osteoporosis and long bone pseudarthrosis (non-union fracture). Hyperactivation of the Ras/mitogen-activated protein kinase (MAPK) pathway in NF1 is known to underlie aberrant proliferation and differentiation in cell lineages, including osteoclast progenitors and mesenchymal stem cells (MSCs) also known as osteoblast progenitors (pro-OBLs). Our current study demonstrates the hyper Ras/MAPK as a critical pathway underlying the pathogenesis of NF1 associated fracture repair deficits. Nf1-deficient pro-OBLs exhibit Ras/MAPK hyperactivation. Introduction of the NF1 GTPase activating related domain (NF1 GAP-related domain) in vitro is sufficient to rescue hyper Ras activity and enhance osteoblast (OBL) differentiation in Nf1(-/-) pro-OBLs and NF1 human (h) MSCs cultured from NF1 patients with skeletal abnormalities including pseudarthrosis or scoliosis. Pharmacologic inhibition of mitogen-activated protein kinase kinase (MEK) signaling with PD98059 partially rescues aberrant Erk activation while enhancing OBL differentiation and expression of OBL markers, osterix and osteocalcin, in Nf1-deficient murine pro-OBLs. Similarly, MEK inhibition enhances OBL differentiation of hMSCs. In addition, PD98059 rescues aberrant osteoclast maturation in Nf1 haploinsufficient bone marrow mononuclear cells. Importantly, MEK inhibitor significantly improves fracture healing in an NF1 murine model, Col2.3Cre;Nf1(flox/-). Collectively, these data indicate the Ras/MAPK cascade as a critical pathway in the pathogenesis of bone loss and pseudarthrosis related to NF1 mutations. These studies provide evidence for targeting the MAPK pathway to improve bone mass and treat pseudarthrosis in NF1.
Human Molecular Genetics 07/2013; 22(23). DOI:10.1093/hmg/ddt333 · 6.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The ten-eleven translocation 1 (TET1) gene is the founding member of the TET family of enzymes (TET1/2/3) that convert 5-methylcytosine to 5-hydroxymethylcytosine. Although TET1 was first identified as a fusion partner of the mixed lineage leukemia (MLL) gene in acute myeloid leukemia carrying t(10,11), its definitive role in leukemia is unclear. In contrast to the frequent down-regulation (or loss-of-function mutations) and critical tumor-suppressor roles of the three TET genes observed in various types of cancers, here we show that TET1 is a direct target of MLL-fusion proteins and is significantly up-regulated in MLL-rearranged leukemia, leading to a global increase of 5-hydroxymethylcytosine level. Furthermore, our both in vitro and in vivo functional studies demonstrate that Tet1 plays an indispensable oncogenic role in the development of MLL-rearranged leukemia, through coordination with MLL-fusion proteins in regulating their critical cotargets, including homeobox A9 (Hoxa9)/myeloid ecotropic viral integration 1 (Meis1)/pre-B-cell leukemia homeobox 3 (Pbx3) genes. Collectively, our data delineate an MLL-fusion/Tet1/Hoxa9/Meis1/Pbx3 signaling axis in MLL-rearranged leukemia and highlight TET1 as a potential therapeutic target in treating this presently therapy-resistant disease.
Proceedings of the National Academy of Sciences 07/2013; 110(29). DOI:10.1073/pnas.1310656110 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mitosis is controlled by a network of kinases and phosphatases. We screened a library of small interfering RNAs against a genome-wide set of phosphatases to comprehensively evaluate the role of human phosphatases in mitosis. We found four candidate spindle checkpoint phosphatases, including the tumor suppressor CDKN3. We show that CDKN3 is essential for normal mitosis and G1/S transition. We demonstrate that subcellular localization of CDKN3 changes throughout the cell cycle. We show that CDKN3 dephosphorylates threonine-161 of CDC2 during mitotic exit and we visualize CDC2(pThr-161) at kinetochores and centrosomes in early mitosis. We performed a phosphokinome-wide mass spectrometry screen to find effectors of the CDKN3-CDC2 signaling axis. We found that one of the identified downstream phosphotargets, CKβ phosphorylated at serine 209, localizes to mitotic centrosomes and controls the spindle checkpoint. Finally, we show that CDKN3 protein is down-regulated in brain tumors. Our findings indicate that CDKN3 controls mitosis through the CDC2 signaling axis. These results have implications for targeted anticancer therapeutics.
The Journal of Cell Biology 06/2013; 201(7). DOI:10.1083/jcb.201205125 · 9.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: BACKGROUND:: Neurofibromatosis 1 (NF1) is an autosomal dominant disorder with various skeletal abnormalities occurring as part of a complex phenotype. Tibial dysplasia, which typically presents as anterolateral bowing of the leg with subsequent fracture and nonunion (pseudarthrosis), is a serious but infrequent osseous manifestation of NF1. Over the past several years, results from clinical and experimental studies have advanced our knowledge of the role of NF1 in bone. On the basis of current knowledge, we propose a number of concepts to consider as a theoretical approach to the optimal management of tibial pseudarthrosis. METHODS:: A literature review for both clinical treatment and preclinical models for tibial dysplasia in NF1 was performed. Concepts were discussed and developed by experts who participated in the Children's Tumor Foundation sponsored International Bone Abnormalities Consortium meeting in 2011. RESULTS:: Concepts for a theoretical approach to treating tibial pseudarthrosis include: bone fixation appropriate to achieve stability in any given case; debridement of the "fibrous pseudarthrosis tissue" between the bone segments associated with the pseudarthrosis; creating a healthy vascular bed for bone repair; promoting osteogenesis; controlling overactive bone resorption (catabolism); prevention of recurrence of the "fibrous pseudarthrosis tissue"; and achievement of long-term bone health to prevent recurrence. CONCLUSIONS:: Clinical trials are needed to assess effectiveness of the wide variation of surgical and pharmacologic approaches currently in practice for the treatment of tibial pseudarthrosis in NF1. LEVEL OF EVIDENCE:: Level V, expert opinion.
[Show abstract][Hide abstract] ABSTRACT: Human bone marrow is the major source of mesenchymal stem cells (MSC). It was reported that the standard density gradient centrifugation method was not efficient in isolating MSC and it may be caused by the existing of bone marrow particles. In previous studys, a lot of MSC were obtained by culturing bone marrow particles alone combined with standard method. However, it is time- and labor-consuming to obtain bone marrow particles by filtering and to isolate MNC by density gradient centrifugation. This study was purposed to explore the more simple and efficient method to isolate MSC from bone marrow. Seven normal bone marrow aspirates were collected and centrifugated. The bone marrow particles floated on surface layers were cultured by modified primary explant culture, whereas the bone marrow aspirates deposited were cultured by direct plating method, then the immun phenotype and differentiation capability of isolated cells were analyzed. The results showed that in 3 of 7 aspirates, bone marrow particles were floated on surface layers, whereas the other bone marrow cells and some particles were deposited after centrifugation. The MSC were reliably isolated from the floating layers or deposited aspirates by modified primary explant culture and direct plating method separately. After 3 passages the isolated MSC did not express CD45 and CD34, but expressed CD105, CD73, CD44, CD90, CD49e and they could differentiate into chondrocytes and adipocytes. It is concluded that normal human bone marrow MSC can be isolated simply and efficiently by direct plating method in combination with modified primary explant culture.
Zhongguo shi yan xue ye xue za zhi / Zhongguo bing li sheng li xue hui = Journal of experimental hematology / Chinese Association of Pathophysiology 03/2013; 21(2):451-4.
[Show abstract][Hide abstract] ABSTRACT: Neurofibromatosis type 1 (NF1) predisposes individuals to the development of juvenile myelomonocytic leukemia (JMML), a fatal myeloproliferative disease (MPD). In genetically engineered murine models, nullizygosity of Nf1, a tumor suppressor gene that encodes a Ras-GTPase-activating protein, results in hyperactivity of Raf/Mek/Erk in hematopoietic stem and progenitor cells (HSPCs). Activated Erk1/2 phosphorylate kinases and transcription factors with myriad mitogenic roles in diverse cell types. However, genetic studies examining Erk1/2's differential and/or combined control of normal and Nf1-deficient myelopoiesis are lacking. Moreover, prior studies relying on chemical Mek/Erk inhibitors have reached conflicting conclusions in normal and Nf1-deficient mice. Here, we show that while single Erk1 or Erk2 disruption did not grossly compromise myelopoiesis, dual Erk1/2 disruption rapidly ablated granulocyte and monocyte production in vivo, diminished progenitor cell number, and prevented HSPC proliferation in vitro. Genetic disruption of Erk1/2 in the context of Nf1 nullizygosity (Mx1Cre+Nf1flox/floxErk1-/-Erk2flox/flox) fully protects against the development of MPD. Collectively, we identified a fundamental requirement for Erk1/2 signaling in normal and Nf1-deficient hematopoiesis, elucidating a critical hematopoietic function for Erk1/2 while genetically validating highly selective Mek/Erk inhibitors in a leukemia that is otherwise resistant to traditional therapy.
The Journal of clinical investigation 12/2012; 123(1). DOI:10.1172/JCI66167 · 13.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Chronic degenerative diseases are increasing with the aging U.S. population. One consequence of this phenomenon is the need for long-term osteoporosis therapies. Parathyroid hormone (PTH), the only FDA-approved treatment that adds bone to the aged skeleton, loses its potency within two years of initial treatment but the mechanism regulating its limited "anabolic window" is unknown. We have discovered that disabling the nucleocytoplasmic shuttling transcription factor nuclear matrix protein 4/cas interacting zinc finger protein (Nmp4/CIZ) in mice extends the PTH bone-forming capacity. Nmp4 was discovered during our search for nuclear matrix transcription factors that couple this hormone's impact on osteoblast cytoskeletal and nuclear organization with its anabolic capacity. CIZ was independently discovered as a protein that associates with the focal adhesion-associated mechanosensor p130Cas. The Nmp4/CIZ-knockout (KO) skeletal phenotype exhibits a modestly enhanced bone mineral density but manifests an exaggerated response to both PTH and to BMP2 and is resistant to disuse-induced bone loss. The cellular basis of the global Nmp4/CIZ-KO skeletal phenotype remains to be elucidated but may involve an expansion of the bone marrow osteoprogenitor population along with modestly enhanced osteoblast and osteoclast activities supporting anabolic bone turnover. As a shuttling Cys2His2 zinc finger protein, Nmp4/CIZ acts as a repressive transcription factor perhaps associated with epigenetic remodeling complexes, but the functional significance of its interaction with p130Cas is not known. Despite numerous remaining questions, Nmp4/CIZ provides insights into how the anabolic window is regulated, and itself may provide an adjuvant therapy target for the treatment of osteoporosis by extending PTH anabolic efficacy.
[Show abstract][Hide abstract] ABSTRACT: Skeletal abnormalities including osteoporosis and osteopenia occur frequently in both pediatric and adult neurofibromatosis type 1 (NF1) patients. NF1 (Nf1) haploinsufficient osteoclasts and osteoclast progenitors derived from both NF1 patients and Nf1(+/-) mice exhibit increased differentiation, migration, and bone resorptive capacity in vitro, mediated by hyperactivation of p21(Ras) in response to limiting concentrations of macrophage-colony stimulating factor (M-CSF). Here, we show that M-CSF binding to its receptor, c-Fms, results in increased c-Fms activation in Nf1(+/) (-) osteoclast progenitors, mediating multiple gain-in-functions through the downstream effectors Erk1/2 and p90RSK. PLX3397, a potent and selective c-Fms inhibitor, attenuated M-CSF mediated Nf1(+/-) osteoclast migration by 50%, adhesion by 70%, and pit formation by 60%. In vivo, we administered PLX3397 to Nf1(+/-) osteoporotic mice induced by ovariectomy (OVX) and evaluated changes in bone mass and skeletal architecture. We found that PLX3397 prevented bone loss in Nf1(+/-)-OVX mice by reducing osteoclast differentiation and bone resorptive activity in vivo. Collectively, these results implicate the M-CSF/c-Fms signaling axis as a critical pathway underlying the aberrant functioning of Nf1 haploinsufficient osteoclasts and may provide a potential therapeutic target for treating NF1 associated osteoporosis and osteopenia.
PLoS ONE 11/2012; 7(11):e46900. DOI:10.1371/journal.pone.0046900 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Plexiform neurofibromas are slow-growing chemoradiotherapy-resistant tumours arising in patients with neurofibromatosis type 1 (NF1). Currently, there are no viable therapeutic options for patients with plexiform neurofibromas that cannot be surgically removed because of their proximity to vital body structures. We undertook an open-label phase 2 trial to test whether treatment with imatinib mesylate can decrease the volume burden of clinically significant plexiform neurofibromas in patients with NF1.
The Lancet Oncology 10/2012; 13(12). DOI:10.1016/S1470-2045(12)70414-X · 24.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mast cells coordinate allergy and allergic asthma and are crucial cellular targets in therapeutic approaches to inflammatory disease. Allergens cross-link IgE bound at high-affinity receptors on the mast cell's surface, causing release of pre-formed cytoplasmic granules containing inflammatory molecules, including histamine, a principal effector of fatal septic shock. Both p21 activated kinase 1 (Pak1) and protein phosphatase 2A (PP2A) modulate mast cell degranulation, but the molecular mechanisms underpinning these observations and their potential interactions in common or disparate pathways are unknown. Here, we use genetic and other approaches to show that Pak1's kinase-dependent interaction with PP2A potentiates PP2A's subunit assembly and activation. PP2A then dephosphorylates threonine 567 of Ezrin/Radixin/Moesin (ERM), molecules that have been shown to couple F-actin to the plasma membrane in other cell systems. In our study, the activity of this Pak1-PP2A-ERM axis correlates with impaired systemic histamine release in Pak1(-/-) mice and defective F-actin rearrangement and impaired degranulation in Ezrin disrupted (Mx1Cre(+)Ezrin(flox/flox)) primary mast cells. This heretofore unknown mechanism of mast cell degranulation provides novel therapeutic targets in allergy and asthma and may inform studies of kinase regulation of cytoskeletal dynamics in other cell lineages.