Epigenetic Regulation of Mesenchymal Stem Cells: A Focus on Osteogenic and Adipogenic Differentiation

Stem cells are characterized by their capability to self-renew and terminally differentiate into multiple cell types. Somatic or adult stem cells have a finite self-renewal capacity and are lineage-restricted. The use of adult stem cells for therapeutic purposes has been a topic of recent interest given the ethical considerations associated with embryonic stem (ES) cells. Mesenchymal stem cells (MSCs) are adult stem cells that can differentiate into osteogenic, adipogenic, chondrogenic, or myogenic lineages. Owing to their ease of isolation and unique characteristics, MSCs have been widely regarded as potential candidates for tissue engineering and repair. While various signaling molecules important to MSC differentiation have been identified, our complete understanding of this process is lacking. Recent investigations focused on the role of epigenetic regulation in lineage-specific differentiation of MSCs have shown that unique patterns of DNA methylation and histone modifications play an important role in the induction of MSC differentiation toward specific lineages. Nevertheless, MSC epigenetic profiles reflect a more restricted differentiation potential as compared to ES cells. Here we review the effect of epigenetic modifications on MSC multipotency and differentiation, with a focus on osteogenic and adipogenic differentiation. We also highlight clinical applications of MSC epigenetics and nuclear reprogramming

Defective Osteogenic Differentiation in the Development of Osteosarcoma

Osteosarcoma (OS) is associated with poor prognosis due to its high incidence of metastasis and chemoresistance. It often arises in areas of rapid bone growth in long bones during the adolescent growth spurt. Although certain genetic conditions and alterations increase the risk of developing OS, the molecular pathogenesis is poorly understood. Recently, defects in differentiation have been linked to cancers, as they are associated with high cell proliferation. Treatments overcoming these defects enable terminal differentiation and subsequent tumor inhibition. OS development may be associated with defects in osteogenic differentiation. While early regulators of osteogenesis are unable to bypass these defects, late osteogenic regulators, including Runx2 and Osterix, are able to overcome some of the defects and inhibit tumor propagation through promoting osteogenic differentiation. Further understanding of the relationship between defects in osteogenic differentiation and tumor development holds tremendous potential in treating OS

Lysophosphatidic Acid Acyltransferase β (LPAATβ) Promotes the Tumor Growth of Human Osteosarcoma

Osteosarcoma is the most common primary malignancy of bone with poorly characterized molecular pathways important in its pathogenesis. Increasing evidence indicates that elevated lipid biosynthesis is a characteristic feature of cancer. We sought to investigate the role of lysophosphatidic acid acyltransferase β (LPAATβ, aka, AGPAT2) in regulating the proliferation and growth of human osteosarcoma cells. LPAATβ can generate phosphatidic acid, which plays a key role in lipid biosynthesis as well as in cell proliferation and survival. Although elevated expression of LPAATβ has been reported in several types of human tumors, the role of LPAATβ in osteosarcoma progression has yet to be elucidated.Endogenous expression of LPAATβ in osteosarcoma cell lines is analyzed by using semi-quantitative PCR and immunohistochemical staining. Adenovirus-mediated overexpression of LPAATβ and silencing LPAATβ expression is employed to determine the effect of LPAATβ on osteosarcoma cell proliferation and migration in vitro and osteosarcoma tumor growth in vivo. We have found that expression of LPAATβ is readily detected in 8 of the 10 analyzed human osteosarcoma lines. Exogenous expression of LPAATβ promotes osteosarcoma cell proliferation and migration, while silencing LPAATβ expression inhibits these cellular characteristics. We further demonstrate that exogenous expression of LPAATβ effectively promotes tumor growth, while knockdown of LPAATβ expression inhibits tumor growth in an orthotopic xenograft model of human osteosarcoma.Our results strongly suggest that LPAATβ expression may be associated with the aggressive phenotypes of human osteosarcoma and that LPAATβ may play an important role in regulating osteosarcoma cell proliferation and tumor growth. Thus, targeting LPAATβ may be exploited as a novel therapeutic strategy for the clinical management of osteosarcoma. This is especially attractive given the availability of selective pharmacological inhibitors

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

Formulation of functionalized PLGA–PEG nanoparticles for in vivo targeted drug delivery

Nanoparticle (NP) size has been shown to significantly effect the biodistribution of targeted and non-targeted NPs in an organ specific manner. Herein we have developed NPs from carboxy-terminated poly (d,l-lactide-co-glycolide)-block-poly(ethylene glycol) (PLGA-b-PEG-COOH) polymer and studied the effects of altering the following formulation parameters on the size of NPs, including: 1) polymer concentration, 2) drug loading, 3) water miscibility of solvent, and 4) the ratio of water to solvent. We found that NP mean volumetric size correlates linearly with polymer concentration for NPs between 70 and 250 nm in diameter (linear coefficient = 0.99 for NPs formulated with solvents studied). NPs with desirable size, drug loading, and polydispersity were conjugated to the A10 RNA aptamer (Apt) that binds to the Prostate Specific Membrane Antigen (PSMA), and NP and NP-Apt biodistribution was evaluated in a LNCaP (PSMA+) xenograft mouse model of PCa. The surface functionalization of NPs with the A10 PSMA aptamer significantly enhanced delivery of NPs to tumors vs. equivalent NPs lacking the A10 PSMA aptamer (a 3.77-fold increase at 24 hrs; NP-Apt 0.83% ± 0.21% vs. NP 0.22% ± 0.07% of injected dose per gram of tissue; mean ± s.d., n = 4, p = 0.002). The ability to control NP size together with targeted delivery may result in favorable biodistribution and development of clinically relevant targeted therapies

The use of charge-coupled polymeric microparticles and micromagnets for modulating the bioavailability of orally delivered macromolecules

Protein drugs have low bioavailability after oral administration, which is due in part to fast transit of the drugs or drug delivery vehicles through the gastrointestinal tract. Increasing the time that the drugs spend in the intestine after dosing would allow for greater absorption and increased bioavailability. We developed a formulation strategy that can be used to prolong intestinal retention of drug delivery vehicles without substantial alterations to current polymeric encapsulation strategies. A model drug, insulin, was encapsulated in negatively-charged poly(lactic-co-glycolic acid) (PLGA) microparticles, and the microparticles were subsequently mixed with positively-charged micromagnets, whose size will prevent them from being absorbed. Stable complexes formed through electrostatic interaction. The complexes were effectively immobilized in vitro in a model of the mouse small intestine by application of an external magnetic field. Mice that were gavaged with radio-labeled complexes and fitted with a magnetic belt retained 32.5% of the 125I-insulin in the small intestine compared with 5.4% for the control group 6 hours after administration (p=0.005). Furthermore, mice similarly gavaged with complexes encapsulating insulin (120 Units/kg) exhibited long-term glucose reduction in the groups with magnetic belts. The corresponding bioavailability of insulin was 5.11% compared with 0.87% for the control group (p=0.007)

The E-F Hand Calcium-Binding Protein S100A4 Regulates the Proliferation, Survival and Differentiation Potential of Human Osteosarcoma Cells

Background/Aims: Osteosarcoma (OS) is the most common primary bone malignancy in children and young adults. Molecular mechanisms underlying the pathogenesis of OS remain to be fully understood. Several members of the E-F hand calcium-binding S100 protein family are differentially expressed in human cancers. We previously showed that S100A6 is highly expressed in OS tumors. In this study, we investigated the role of S100A4 in regulating OS proliferation and osteogenic differentiation. Methods/Results: Endogenous S100 expression was examined by semi-quantitative PCR in human OS lines. Adenoviral vector-mediated overexpression and RNAi knockdown of S100A4 were used to assess S100A4's effects on cell proliferation, migration and invasion and osteogenic differentiation. Apoptosis was assessed by using anti-caspase-3 immunostaining and flow cytometry with annexin V staining. Early osteogenic marker alkaline phosphatase (ALP) and late markers osteocalcin (OCN) and osteopontin (OPN) were assessed to determine the status of osteogenic differentiation. We found that S100A4 was elevated in metastatic MG63.2 cells. S100A4 knockdown inhibited cell proliferation, prolonged cell doubling time, and induced significant apoptosis. Silencing S100A4 expression in OS cells delayed cell wounding closure and diminished the numbers of migrated OS cells in transwell invasion assay. Furthermore, silencing S100A4 expression stimulated ALP activity, as well as late markers OPN and OCN, in both OS cells and mesenchymal stem cells. Conclusion: Our results strongly suggest that S100A4 may promote OS tumor growth by regulating the cell cycle, reducing apoptosis, and inhibiting osteogenic differentiation. Thus, S100A4 may serve as a marker for tumorigenic potential, as well as a therapeutic target

The Calcium-Binding Protein S100A6 Accelerates Human Osteosarcoma Growth by Promoting Cell Proliferation and Inhibiting Osteogenic Differentiation

Background/Aims: Although osteosarcoma (OS) is the most common primary malignancy of bone, its molecular pathogenesis remains to be fully understood. We previously found the calcium-binding protein S100A6 was expressed in ∼80% of the analyzed OS primary and/or metastatic tumor samples. Here, we investigate the role of S100A6 in OS growth and progression. Methods: S100A6 expression was assessed by qPCR and Western blotting. Overexpression or knockdown of S100A6 was carried out to determine S100A6's effect on proliferation, cell cycle, apoptosis, tumor growth, and osteogenic differentiation. Results: S100A6 expression was readily detected in human OS cell lines. Exogenous S100A6 expression promoted cell proliferation in vitro and tumor growth in an orthotopic xenograft model of human OS. S100A6 overexpression reduced the numbers of OS cells in G1 phase and increased viable cells under serum starvation condition. Conversely, silencing S100A6 expression induced the production of cleaved caspase 3, and increased early stage apoptosis. S100A6 knockdown increased osteogenic differentiation activity of mesenchymal stem cells, while S100A6 overexpression inhibited osteogenic differentiation. BMP9-induced bone formation was augmented by S100A6 knockdown. Conclusion: Our findings strongly suggest that S100A6 may promote OS cell proliferation and OS tumor growth at least in part by facilitating cell cycle progression, preventing apoptosis, and inhibiting osteogenic differentiation. Thus, it is conceivable that targeting S100A6 may be exploited as a novel anti-OS therapy