Citations

AbstractNuclear actin plays a critical role in mediating mesenchymal stem cell (MSC) fate commitment. In marrow-derived MSCs, the principal diaphanous-related formin Diaph3 (mDia2) is present in the nucleus and regulates intranuclear actin polymerization, whereas Diaph1 (mDia1) is localized to the cytoplasm and controls cytoplasmic actin polymerization. We here show that mDia2 can be used as a tool to query actin-lamin nucleoskeletal structure. Silencing mDia2 affected the nucleoskeletal lamin scaffold, altering nuclear morphology without affecting cytoplasmic actin cytoskeleton, and promoted MSC differentiation. Attempting to target intranuclear actin polymerization by silencing mDia2 led to a profound loss in lamin B1 nuclear envelope structure and integrity, increased nuclear height, and reduced nuclear stiffness without compensatory changes in other actin nucleation factors. Loss of mDia2 with the associated loss in lamin B1 promoted Runx2 transcription and robust osteogenic differentiation and suppressed adipogenic differentiation. Hence, mDia2 is a potent tool to query intranuclear actin-lamin nucleoskeletal structure, and its presence serves to retain multipotent stromal cells in an undifferentiated state.

Aims Dupuytren’s contracture is a benign, myoproliferative condition affecting the palmar fascia that results in progressive contractures of the fingers. Despite increased knowledge of the cellular and connective tissue changes involved, neither a cure nor an optimum form of treatment exists. The aim of this systematic review was to summarize the best available evidence on the management of this condition. Materials and Methods A comprehensive database search for randomized controlled trials (RCTs) was performed until August 2017. We studied RCTs comparing open fasciectomy with percutaneous needle aponeurotomy (PNA), collagenase clostridium histolyticum (CCH) with placebo, and CCH with PNA, in addition to adjuvant treatments aiming to improve the outcome of open fasciectomy. A total of 20 studies, involving 1584 patients, were included. Results PNA tended to provide higher patient satisfaction with fewer adverse events, but had a higher rate of recurrence compared with limited fasciectomy. Although efficacious, treatment with CCH had notable recurrence rates and a high rate of transient adverse events. Recent comparative studies have shown no difference in clinical outcome between patients treated with PNA and those treated with CCH. Conclusion Currently there remains limited evidence to guide the management of patients with Dupuytren’s contracture. Cite this article: Bone Joint J 2018;100-B:1138–45.

Abstract The endosteal niche is a component of the bone marrow microenvironment that can serve to protect hematological malignancies such as acute myeloid leukemia (AML) from standard chemotherapies such as cytarabine (Ara-C). Surviving AML cells harbored by this niche can eventually lead to relapse. The endosteal niche is rich in osteoblast lineage cells. U937 or KG1a AML cell lines were cultured with or without osteoblast lineage cells (MC3T3 or W-20-17 cell lines), challenged with doses of 0µM, 0.1µM, 0.5µM, 1µM, 5µM, or 10µM of Ara-C, and assayed for apoptosis via annexin-V staining and flow cytometry. Osteoblast lineage cells (MC3T3 or W-20-17 cell lines) were able to protect AML cells (U937 or KG1a cell lines) from Ara-C-induced apoptosis. Histone deacetylase inhibitors (HDACi) globally alter gene expression within cells. When we pre-treated osteoblast lineage cells (MC3T3) with the HDACi vorinostat (suberoylanilide hydroxamic acid, SAHA), it reduced the ability of the osteoblast lineage cells (MC3T3) to protect AML cells (U937) from Ara-C-induced apoptosis, which we have previously confirmed in the KG1a AML cell line as well. This indicates that osteoblast lineage cell-mediated protection of AML from Ara-C occurs via an HDACi sensitive mechanism. To begin to further explore the mechanism of action, we co-cultured AML cells (KG1a or U937) with and without osteoblast lineage cells (MC3T3) in the presence or absence of a transwell. We found that the presence of the transwell reduced the osteoblast lineage cell-mediated protection, indicating that osteoblast lineage cell-mediated protection of AML from Ara-C is cell contact dependent. Thus, osteoblast lineage cells can protect AML cells from Ara-C induced apoptosis, this protection can be reduced by pre-treatment of the osteoblast lineage cells with the HDACi vorinostat, and osteoblast lineage cell-mediated protection from Ara-C is cell contact dependent. These studies begin to characterize the mechanisms of osteoblast lineage cell-mediated protection of AML from Ara-C. Manipulating the protective properties of osteoblast lineage cells of the endosteal niche may help make AML cells more susceptible to chemotherapeutics. Therefore, developing combination therapies that target the protective mechanisms of osteoblast-lineage cells may help to further deplete the bone marrow microenvironment of AML cells and prevent relapse of disease. Citation Format: Rosalie M. Sterner, Kimberly N. Kremer, Meagan R. Rollins, Amel Dudakovic, Jennifer J. Westendorf, Andre J. van Wijnen, Karen E. Hedin. Osteoblast-lineage cells protect AML cells from cytarabine-induced apoptosis via a mechanism sensitive to HDACi and reduced cell-cell contact [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2137.

Abstract The bone marrow microenvironment harbors and protects leukemic cells from apoptosis-inducing agents via mechanisms that are incompletely understood. We previously showed SDF-1 (CXCL-12), a chemokine readily abundant within the bone marrow microenvironment, induces apoptosis in acute myeloid leukemia (AML) cells that express high levels of the SDF-1 receptor CXCR4. However, differentiating osteoblasts found within this niche protect cocultured AML cells from apoptosis. Additionally, this protection was abrogated upon treatment of the differentiating osteoblasts with histone deacetylase inhibitors (HDACi). In this study, we begin to characterize and target the molecular mechanisms that mediate this osteoblast protection. Quantitative RT-PCR revealed that HDACi treatment of differentiating osteoblasts (mouse MC3T3 osteoblast cell line) reduced expression of multiple genes required for osteoblast differentiation, including genes important for producing mineralized bone matrix. Interestingly, pretreating differentiating osteoblasts with cyclosporine A, a drug known to inhibit osteoblast differentiation, similarly impaired osteoblast-mediated protection of cocultured AML cells (KG1a and U937 human AML cell lines). Both HDACi and cyclosporine A reduced osteoblast expression of the key mineralization enzyme tissue-nonspecific alkaline phosphatase (TNAP; encoded by Alpl). Moreover, specifically reducing TNAP expression or activity in differentiating osteoblasts significantly impaired the ability of the osteoblasts to protect cocultured AML cells. Together, our results indicate that inhibiting osteoblast matrix mineralization by specifically targeting TNAP is sufficient to significantly impair osteoblast-mediated protection of AML cells. Therefore, designing combination therapies that additionally target the osteoblast-produced mineralized bone matrix may improve treatment of AML by reducing the protection of leukemic cells within the bone marrow microenvironment.

AbstractTendon graft healing in bone tunnels for the fixation of intra‐articular ligament reconstructions may limit clinical outcome by delaying healing. This study assesses the effects of hydrogel‐mediated delivery of bone anabolic growth factors in a validated model of tendon‐to‐bone tunnel healing. Forty‐five Wistar rats were randomly allocated into three groups (BMP2‐treated, GSK126‐treated, and placebo). All animals underwent a tendon‐to‐bone tunnel reconstruction. Healing was evaluated at 4 weeks by biomechanical assessment, micro‐computed tomography (bone mineral density, bone volume, cross sectional area of bone tunnels), and traditional histology. Adverse events associated with the hydrogel‐mediated delivery of drugs were not observed. Results of our biomechanical assessment demonstrated favorable trends in animals treated with bone anabolic factors for energy absorption (P = 0.116) and elongation (P = 0.054), while results for force to failure (P = 0.691) and stiffness (P = 0.404) did not show discernible differences. Cross sectional areas for BMP2‐treated animals were reduced, but neither BMP2 nor GSK126 administration altered bone mineral density (P = 0.492) or bone volume in the bone tunnel. These results suggest a novel and positive effect of bone anabolic factors on tendon‐to‐bone tunnel healing. Histological evaluation confirmed absence of collagen fibers crossing the soft tissue‐bone interface indicating immature graft integration as expected at this time point. Our study indicates that hydrogel‐mediated delivery of BMP2 and GSK126 appears to be safe and has the potential to enhance tendon‐to‐bone tunnel healing in ligament reconstructions.

AbstractThe Melatonin Osteoporosis Prevention Study (MOPS) demonstrated that nightly melatonin resulted in a time‐dependent decrease in equilibrium ratios of serum osteoclasts and osteoblasts in perimenopausal women. This study examines mechanisms related to the ratios of osteoblasts and osteoclasts using coculture models (transwell or layered) of human mesenchymal stem cell (MSC) and human peripheral blood monocytes (PBMCs). Human MSC/PBMC cocultures exposed to melatonin in osteogenic (OS+) medium for 21 days induced osteoblast differentiation and mineralization; however, only in layered cocultures did melatonin inhibit osteoclastogenesis. Melatonin effects were mediated through MT2 melatonin receptors, MEK1/2, and MEK5. In layered but not transwell cocultures, melatonin increased OPG:RANKL ratios by inhibiting RANKL, suggesting that contact with osteoclasts during osteoblastogenesis inhibits RANKL secretion. Melatonin modulated expression of ERK1/2, ERK5, β1 integrin, GLUT4, and IRβ that was dependent upon the type of coculture; however, in both cultures, melatonin increased RUNX2 and decreased PPARγ expression, indicating a role for metabolic processes that control osteogenic vs adipogenic cell fates of MSCs. Furthermore, melatonin also has osteoblast‐inducing effects on human adipose‐derived MSCs. In vivo, one‐year nightly melatonin (15 mg/L) given to neu female mice in their drinking water increased pErk1/2, pErk5, Runx2, and Opg and Rankl levels in bone consistent with melatonin's already reported bone‐enhancing effects. Finally, analysis of daily logs from the MOPS demonstrated a significant improvement in mood and perhaps sleep quality in women receiving melatonin vs placebo. The osteoblast‐inducing, bone‐enhancing effects of melatonin and improvement in quality of life suggest that melatonin is a safe and effective bone loss therapy.

Abstract Strategies for musculoskeletal tissue regeneration apply adult mesenchymal stem/stromal cells (MSCs) that can be sourced from bone marrow- and lipo-aspirates. Adipose tissue-derived MSCs are more easily harvested in the large quantities required for skeletal tissue-engineering approaches, but are generally considered to be less osteogenic than bone marrow MSCs. Therefore, we tested a new molecular strategy to improve their osteogenic lineage-differentiation potential using the fungal metabolite cytochalasin D (CytoD). We show that CytoD, which may function by redistributing the intracellular location of β-actin (ACTB), is a potent osteogenic stimulant as reflected by significant increases in alkaline phosphatase activity, extracellular matrix mineralization, and osteoblast-related gene expression (e.g., RUNX2, ALPL, SPARC, and TGFB3). RNA sequencing analyses of MSCs revealed that acute CytoD treatment (24 hours) stimulates a broad program of osteogenic biomarkers and epigenetic regulators. CytoD decreases mRNA and protein levels of the Polycomb chromatin regulator Enhancer of Zeste Homolog 2 (EZH2), which controls heterochromatin formation by mediating trimethylation of histone 3 lysine 27 (H3K27me3). Reduced EZH2 expression decreases cellular H3K27me3 marks indicating a global reduction in heterochromatin. We conclude that CytoD is an effective osteogenic stimulant that mechanistically functions by blocking both cytoplasmic actin polymerization and gene-suppressive epigenetic mechanisms required for the acquisition of the osteogenic phenotype in adipose tissue-derived MSCs. This finding supports the use of CytoD in advancing the osteogenic potential of MSCs in skeletal regenerative strategies.

Abstract The hematological malignancy acute myeloid leukemia (AML) interacts closely with osteoblasts within the protective bone marrow microenvironment. The bone marrow microenvironment protects tumor cells from chemotherapies, which can prevent sufficient eradication of tumor cells. To study the role of osteoblasts in the bone marrow microenvironment, our lab utilized a co-culture model of osteoblasts (MC3T3 osteoblast cell line) and acute myelogenous leukemia cells (KG1a AML cell line or AML patient samples from bone marrow aspirates). Osteoblasts were cultured with AML cells, or AML cells were cultured alone; AML cells were challenged with the standard chemotherapeutic agent cytarabine (Ara-C) at doses of 0µM, 0.1µM, 0.5µM, 1µM, 5µM, or 10µM in the presence or absence of osteoblasts; and AML cells were assayed by flow cytometry to assess cell death via annexin-V staining. Our lab has previously found that differentiating osteoblasts protect AML cells from an apoptosis inducing agent naturally present in the bone marrow. We now show that osteoblasts are also capable of protecting AML cells from the standard chemotherapeutic cytarabine. In addition, we have found that treatment of osteoblasts with the histone deacetylase inhibitor (HDACi) suberoylanilide hydroxamic acid (SAHA) prevents these treated osteoblasts from protecting AML cells from cytarabine treatment, which is consistent with our lab’s previous findings that HDACi treatment inhibits protection of AML cells from an apoptosis inducing agent naturally present in the bone marrow. We have preliminary data that indicates that TAZS89A over-expression, a constitutively active form of TAZ, which is a transcriptional modulator that regulates osteoblast differentiation, may be sufficient to inhibit osteoblast mediated protection of AML cells from cytarabine. This finding would be consistent with the HDACi manipulated Nherf1-protein phosphatase 1α-TAZ signaling pathway that we have previously found to be sufficient to inhibit protection of AML cells from an apoptosis inducing agent naturally present in the bone marrow. Overall, these studies have delivered insights into the role of osteoblasts in protecting AML cells from chemotherapy in the bone marrow microenvironment and begun the characterization of mechanisms and targets responsible for the protective effects of osteoblasts. Manipulating differentiating osteoblasts within the bone marrow microenvironment therapeutically could aid in more complete destruction of the tumor cell burden and improve patient survival. Citation Format: Rosalie M. Sterner, Kimberly N. Kremer, Amel Dudakovic, Jennifer J. Westendorf, Andre J. van Wijnen, Karen E. Hedin. Osteoblasts protect AML cells from cytarabine-induced death [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5930. doi:10.1158/1538-7445.AM2017-5930