Convergence of Calcium Channel Regulation and Mechanotransduction in Skeletal Regenerative Biomaterial Design.

Cells are known to perceive their microenvironment through extracellular and intracellular mechanical signals. Upon sensing mechanical stimuli, cells can initiate various downstream signaling pathways that are vital to regulating proliferation, growth, and homeostasis. One such physiologic activity modulated by mechanical stimuli is osteogenic differentiation.

β-Catenin Limits Osteogenesis on Regenerative Materials in a Stiffness-Dependent Manner.

Targeted refinement of regenerative materials requires mechanistic understanding of cell-material interactions. The nanoparticulate mineralized collagen glycosaminoglycan (MC-GAG) scaffold is shown to promote skull regeneration in vivo without additive exogenous growth factors or progenitor cells, suggesting potential for clinical translation. This work evaluates modulation of MC-GAG stiffness on canonical Wnt (cWnt) signaling.

The Intersection of Mechanotransduction and Regenerative Osteogenic Materials.

Mechanical signals play a central role in cell fate determination and differentiation in both physiologic and pathologic circumstances. Such signals may be delivered using materials to generate discrete microenvironments for the purposes of tissue regeneration and have garnered increasing attention in recent years. Unlike the addition of progenitor cells or growth factors, delivery of a microenvironment is particularly attractive in that it may reduce the known untoward consequences of the former two strategies, such as excessive proliferation and potential malignant transformation.

Osteoprotegerin reduces osteoclast resorption activity without affecting osteogenesis on nanoparticulate mineralized collagen scaffolds.

The instructive capabilities of extracellular matrix-inspired materials for osteoprogenitor differentiation have sparked interest in understanding modulation of other cell types within the bone regenerative microenvironment. We previously demonstrated that nanoparticulate mineralized collagen glycosaminoglycan (MC-GAG) scaffolds efficiently induced osteoprogenitor differentiation and bone healing. In this work, we combined adenovirus-mediated delivery of osteoprotegerin (AdOPG), an endogenous anti-osteoclastogenic decoy receptor, in primary human mesenchymal stem cells (hMSCs) with MC-GAG to understand the role of osteoclast inactivation in augmentation of bone regeneration.

Nanoparticulate mineralized collagen glycosaminoglycan materials directly and indirectly inhibit osteoclastogenesis and osteoclast activation.

The ability of the extracellular matrix (ECM) to direct cell fate has generated the potential for developing a materials-only strategy for tissue regeneration. Previously, we described a nanoparticulate mineralized collagen glycosaminoglycan (MC-GAG) material that efficiently induced osteogenic differentiation of human mesenchymal stem cells (hMSCs) and calvarial bone healing without exogenous growth factors or progenitor cell expansion. In this work, we evaluated the interactions between MC-GAG and primary human osteoclasts (hOCs).

Nonmineralized and Mineralized Collagen Scaffolds Induce Differential Osteogenic Signaling Pathways in Human Mesenchymal Stem Cells.

The instructive capabilities of extracellular matrix components in progenitor cell differentiation have recently generated significant interest in the development of bioinspired materials for regenerative applications. Previously, a correlation was described between the osteogenic capabilities of nanoparticulate mineralized collagen glycosaminoglycan scaffolds (MC-GAG) and an autogenous activation of small mothers against decapentaplegic ( Smad1/5) in the canonical bone morphogenetic protein receptor (BMPR) pathway with a diminished extracellular signal regulated kinase 1/2 (ERK1/2) activation when compared to nonmineralized collagen glycosaminoglycan scaffolds (Col-GAG). This work utilizes a canonical BMPR inhibitor (dorsomorphin homologue 1, DMH1) and an inhibitor of the mitogen activated protein kinase/ERK kinase (MEK)/(ERK) cascade (PD98059) to characterize the necessity of each pathway for osteogenesis.

Metabolic relationship between diabetes and Alzheimer's Disease affected by Cyclo(His-Pro) plus zinc treatment.

Background: Association of Alzheimer's Disease (AD) with Type 2 Diabetes (T2D) has been well established. Cyclo(His-Pro) plus zinc (Cyclo-Z) treatment ameliorated diabetes in rats and similar improvements have been seen in human patients. Treatment of amyloid precursor protein (APP) transgenic mice with Cyclo-Z exhibited memory improvements and significantly reduced Aβ-40 and Aβ-42 protein levels in the brain tissues of the mice.

Nanoparticulate Mineralized Collagen Scaffolds and BMP-9 Induce a Long-Term Bone Cartilage Construct in Human Mesenchymal Stem Cells.

Engineering the osteochondral junction requires fabrication of a microenvironment that supports both osteogenesis and chondrogenesis. Multiphasic scaffold strategies utilizing a combination of soluble factors and extracellular matrix components are ideally suited for such applications. In this work, the contribution of an osteogenic nanoparticulate mineralized glycosaminoglycan scaffold (MC-GAG) and a dually chondrogenic and osteogenic growth factor, BMP-9, in the differentiation of primary human mesenchymal stem cells (hMSCs) is evaluated.

Nanoparticulate mineralized collagen scaffolds induce in vivo bone regeneration independent of progenitor cell loading or exogenous growth factor stimulation.

Current strategies for skeletal regeneration often require co-delivery of scaffold technologies, growth factors, and cellular material. However, isolation and expansion of stem cells can be time consuming, costly, and requires an additional procedure for harvest. Further, the introduction of supraphysiologic doses of growth factors may result in untoward clinical side effects, warranting pursuit of alternative methods for stimulating osteogenesis.

Induction of CXC chemokines in human mesenchymal stem cells by stimulation with secreted frizzled-related proteins through non-canonical Wnt signaling.

Aim: To investigate the effect of secreted frizzled-related proteins (sFRPs) on CXC chemokine expression in human mesenchymal stem cells (hMSCs).

Methods: CXC chemokines such as CXCL5 and CXCL8 are induced in hMSCs during differentiation with osteogenic differentiation medium (OGM) and may be involved in angiogenic stimulation during bone repair. hMSCs were treated with conditioned medium (CM) from L-cells expressing non-canonical Wnt5a protein, or with control CM from wild type L-cells, or directly with sFRPs for up to 10 d in culture.

Optimizing Collagen Scaffolds for Bone Engineering: Effects of Cross-linking and Mineral Content on Structural Contraction and Osteogenesis.

Introduction: Osseous defects of the craniofacial skeleton occur frequently in congenital, posttraumatic, and postoncologic deformities. The field of scaffold-based bone engineering emerged to address the limitations of using autologous bone for reconstruction of such circumstances. In this work, the authors evaluate 2 modifications of three-dimensional collagen-glycosaminoglycan scaffolds in an effort to optimize structural integrity and osteogenic induction.

Osteogenesis on nanoparticulate mineralized collagen scaffolds via autogenous activation of the canonical BMP receptor signaling pathway.

Skeletal regenerative medicine frequently incorporates deliverable growth factors to stimulate osteogenesis. However, the cost and side effects secondary to supraphysiologic dosages of growth factors warrant investigation of alternative methods of stimulating osteogenesis for clinical utilization. In this work, we describe growth factor independent osteogenic induction of human mesenchymal stem cells (hMSCs) on a novel nanoparticulate mineralized collagen glycosaminoglycan scaffold (MC-GAG).

Th17 cells in inflammation and autoimmunity.

T helper 17 (Th17), a distinct subset of CD4(+) T cells with IL-17 as their major cytokine, orchestrate the pathogenesis of inflammatory and autoimmune diseases. Dysregulated Th17 cells contribute to inflammatory and autoimmune diseases. Candidate biologics are in development for targeting IL-17, IL-17 receptors or IL-17 pathways.

"Ins" and "Outs" of mesenchymal stem cell osteogenesis in regenerative medicine.

Repair and regeneration of bone requires mesenchymal stem cells that by self-renewal, are able to generate a critical mass of cells with the ability to differentiate into osteoblasts that can produce bone protein matrix (osteoid) and enable its mineralization. The number of human mesenchymal stem cells (hMSCs) diminishes with age and ex vivo replication of hMSCs has limited potential. While propagating hMSCs under hypoxic conditions may maintain their ability to self-renew, the strategy of using human telomerase reverse transcriptase (hTERT) to allow for hMSCs to prolong their replicative lifespan is an attractive means of ensuring a critical mass of cells with the potential to differentiate into various mesodermal structural tissues including bone.

Constitutive expression of human telomerase enhances the proliferation potential of human mesenchymal stem cells.

Human mesenchymal stem cells (hMSCs) are highly desirable cells for bone engineering due to the inherent multipotent nature of the cells. Unfortunately, there is a high degree of variability, as primary hMSC cultures quickly undergo replicative senescence with loss of proliferative potential as they are continually propagated in cell culture. We sought to reduce the variability of these cells by insertion and expression of human telomerase reverse transcriptase (TERT) to immortalize the cell line.

In vitro mineralization of human mesenchymal stem cells on three-dimensional type I collagen versus PLGA scaffolds: a comparative analysis.

Background: Development of a tissue engineered bone graft requires efficient bioactivity screening of biomaterials in clinically relevant three-dimensional systems. The authors analyzed the relative osteogenic potential of two three-dimensional biomaterials--type I collagen and poly(L-lactide-co-glycolide) (PLGA)--to support in vitro mineralization of human mesenchymal stem cells.

Methods: Human mesenchymal stem cells were seeded onto three-dimensional PLGA or type I collagen scaffolds; incubated in osteogenic media; and harvested at 1, 4, and 7 days.

CXC receptor knockout mice: characterization of skeletal features and membranous bone healing in the adult mouse.

The potential role of CXC chemokines bearing the glu-leu-arg (ELR) motif in bone repair was studied using a cranial defect (CD) model in mice lacking the CXC receptor (mCXCR(-/-) knockout mice), which is homologous to knockout of the human CXC receptor 2 (CXCR2) gene. During the inflammatory stage of bone repair, ELR CXC chemokines are released by inflammatory cells and serve as chemotactic and angiogenic factors. mCXCR(-/-) mice were smaller in weight and length from base of tail to nose tip, compared to WT littermates.

A synopsis of phosphate disorders in the nursing home.

Elderly patients are at an increased risk of developing both hypophosphatemia and hyperphosphatemia. Renal insufficiency predisposes elderly patients to elevated serum concentrations of phosphate. On the other hand, poor dietary intake and loss of phosphorus in the urine can lead to deficiency states.

Extracellular-signal-related kinase 1/2 is responsible for inhibition of osteogenesis in three-dimensional cultured MC3T3-E1 cells.

We have previously demonstrated that osteogenic differentiation is inhibited and angiogenic expression is enhanced in murine preosteoblasts (MC3T3-E1) cultured on three-dimensional (3D) poly-L-lactide-co-glycolide (PLGA) scaffolds when compared to two-dimensional (2D) PLGA films. In the present work we investigated the role of the extracellular signal-related kinase 1/2 (ERK1/2) pathway in modulating osteogenic and angiogenic differentiation in 2D and 3D systems made of two distinct biomaterials-type I collagen and PLGA. The addition of a third dimension, regardless of biomaterials, substantially increased ERK1/2 activation as demonstrated by an increase in phosphorylated ERK1/2.

Human and mouse osteoprogenitor cells exhibit distinct patterns of osteogenesis in three-dimensional tissue engineering scaffolds.

Background: Understanding interspecies variation between animal models and humans is essential to develop tissue-engineered bone. The authors studied osteogenic and angiogenic marker expression in human and murine osteoblasts and mesenchymal stem cells.

Methods: Three human cells (human mesenchymal stem cells, multilineage progenitor cells, and normal human osteoblasts) and three murine cells (MC3T3-E1, C3H10T1/2, and M2-10B4) were used.

TNAP, TrAP, ecto-purinergic signaling, and bone remodeling.

Bone remodeling is a process of continuous resorption and formation/mineralization carried out by osteoclasts and osteoblasts, which, along with osteocytes, comprise the bone multicellular unit (BMU). A key component of the BMU is the bone remodeling compartment (BRC), isolated from the marrow by a canopy of osteoblast-like lining cells. Although much progress has been made regarding the cytokine-dependent and hormonal regulation of bone remodeling, less attention has been placed on the role of extracellular pH (pH(e)).

Pretreatment of poly(l-lactide-co-glycolide) scaffolds with sodium hydroxide enhances osteoblastic differentiation and slows proliferation of mouse preosteoblast cells.

Background: Surface topography is important in the creation of a scaffold for tissue engineering. Chemical etching of poly(l-lactide-co-glycolide) with sodium hydroxide has been shown to enhance adhesion and function of numerous cell types. The authors investigated the effects of sodium hydroxide pretreatment of three-dimensional poly(l-lactide-co-glycolide) scaffolds on the adhesion, differentiation, and proliferation of MC3T3-E1 murine preosteoblasts.

Genetic markers of osteogenesis and angiogenesis are altered in processed lipoaspirate cells when cultured on three-dimensional scaffolds.

Background: Liposuction-derived stem cells (processed lipoaspirate) have recently been shown to be capable of differentiating into bone. Most studies on osteoblastic growth and differentiation have been conducted in a conventional two-dimensional culture system; however, in native bone, osteoblasts are situated in a three-dimensional configuration. There have been limited studies of processed lipoaspirate behavior in three-dimensional systems.

Acidic pH stimulates the production of the angiogenic CXC chemokine, CXCL8 (interleukin-8), in human adult mesenchymal stem cells via the extracellular signal-regulated kinase, p38 mitogen-activated protein kinase, and NF-kappaB pathways.

Blood vessel injury results in limited oxygen tension and diffusion leading to hypoxia, increased anaerobic metabolism, and elevated production of acidic metabolites that cannot be easily removed due to the reduced blood flow. Therefore, an acidic extracellular pH occurs in the local microenvironment of disrupted bone. The potential role of acidic pH and glu-leu-arg (ELR(+)) CXC chemokines in early events in bone repair was studied in human mesenchymal stem cells (hMSCs) treated with medium of decreasing pH (7.

Characterization of growth and osteogenic differentiation of rabbit bone marrow stromal cells.

Background: The rabbit is recognized as an excellent model to study the repair of bony defects with tissue engineered constructs. However, the use of rabbit bone marrow stromal cells (RBMSCs) has been limited despite the proven benefits of autologous BMSCs in the formation of bone. The purpose of this study was to characterize the growth and differentiation pattern of RBMSCs and their response to growth factors.