Biglycan Regulates MG63 Osteosarcoma Cell Growth Through a LPR6/β-Catenin/IGFR-IR Signaling Axis

Biglycan, a small leucine rich proteoglycan (SLRP), is an important participant in bone homeostasis and development as well as in bone pathology. In the present study biglycan was identified as a positive regulator of MG63 osteosarcoma cell growth (p ≤ 0.001). IGF-I was shown to increase biglycan expression (p ≤ 0.01), whereas biglycan-deficiency attenuated significantly both basal and IGF-I induced cell proliferation of MG63 cells (p ≤ 0.001; p ≤ 0.01, respectively). These effects were executed through the IGF-IR receptor whose activation was strongly attenuated (p ≤ 0.01) in biglycan-deficient MG63 cells. Biglycan, previously shown to regulate Wnt/β-catenin pathway, was demonstrated to induce a significant increase in β-catenin protein expression evident at cytoplasmic (p ≤ 0.01), membrane (p ≤ 0.01), and nucleus fractions in MG63 cells (p ≤ 0.05). As demonstrated by immunofluorescence, increase in β-catenin expression is attributed to co-localization of biglycan with the Wnt co-receptor low-density lipoprotein receptor-related protein 6 (LRP6) resulting in attenuated β-catenin degradation. Furthermore, applying anti-β-catenin and anti-pIGF-IR antibodies to MG-63 cells demonstrated a cytoplasmic and to the membrane interaction between these molecules that increased upon exogenous biglycan treatment. In parallel, the downregulation of biglycan significantly inhibited both basal and IGF-I-dependent ERK1/2 activation, (p ≤ 0.001). In summary, we report a novel mechanism where biglycan through a LRP6/β-catenin/IGF-IR signaling axis enhances osteosarcoma cell growth

Insights into the Cellular and Molecular Mechanisms That Govern the Fracture-Healing Process: A Narrative Review

Fracture-healing is a complex multi-stage process that usually progresses flawlessly, resulting in restoration of bone architecture and function. Regrettably, however, a considerable number of fractures fail to heal, resulting in delayed unions or non-unions. This may significantly impact several aspects of a patient’s life. Not surprisingly, in the past few years, a substantial amount of research and number of clinical studies have been designed, aiming at shedding light into the cellular and molecular mechanisms that regulate fracture-healing. Herein, we present the current knowledge on the pathobiology of the fracture-healing process. In addition, the role of skeletal cells and the impact of marrow adipose tissue on bone repair is discussed. Unveiling the pathogenetic mechanisms that govern the fracture-healing process may lead to the development of novel, smarter, and more effective therapeutic strategies for the treatment of fractures, especially of those with large bone defects

Signaling networks and transcription factors regulating mechanotransduction in bone

Mechanical stimulation has a critical role in the development and maintenance of the skeleton. This function requires the perception of extracellular stimuli as well as their conversion into intracellular biochemical responses. This process is called mechanotransduction and is mediated by a plethora of molecular events that regulate bone metabolism. Indeed, mechanoreceptors, such as integrins, G protein-coupled receptors, receptor protein tyrosine kinases, and stretch-activated Ca2+ channels, together with their downstream effectors coordinate the transmission of load-induced signals to the nucleus and the expression of bone-related genes. During the past decade, scientists have gained increasing insight into the molecular networks implicated in bone mechanotransduction. In the present paper, we consider the major signaling cascades and transcription factors that control bone and cartilage mechanobiology and discuss the influence of the mechanical microenvironment on the determination of skeletal morphology

Expression of integrin-linked kinase and its binding partners in chondrosarcoma: Association with prognostic significance

Integrin-linked kinase (ILK) and its binding partners alpha-parvin, beta-parvin, Mig-2 and Migfilin are important components of the cell-matrix adhesions implicated in cell motility, growth, survival and ultimately carcinogenesis. Herein, we investigated immunohistochemically the expression of these molecules in cartilaginous neoplasms and explored their involvement in chondrosarcoma pathobiology and behaviour. Our analyses revealed that ILK, alpha-parvin, beta-parvin and Mig-2 are expressed in the majority of chondrosarcomas but in a small proportion of enchondromas, implying that these proteins might have a role in the development and progression of chondrogenic neoplasms. moreover, our findings highlight the possibilities that ILK might serve as biological marker that could accurately predict a high-grade tumour and that Mig-2 may function as a promising prognostic indicator of high-risk patients. (C) 2008 Elsevier Ltd. All rights reserved

<i>ApoA1</i> Deficiency Reshapes the Phenotypic and Molecular Characteristics of Bone Marrow Adipocytes in Mice

In the present study, we studied the effect of apolipoprotein A-1 (APOA1) on the spatial and molecular characteristics of bone marrow adipocytes, using well-characterized ApoA1 knockout mice. APOA1 is a central regulator of high-density lipoprotein cholesterol (HDL-C) metabolism, and thus HDL; our recent work showed that deficiency of APOA1 increases bone marrow adiposity in mice. We found that ApoA1 deficient mice have greatly elevated adipocytes within their bone marrow compared to wild type counterparts. Morphologically, the increased adipocytes were similar to white adipocytes, and displayed proximal tibial-end localization. Marrow adipocytes from wild type mice were significantly fewer and did not display a bone-end distribution pattern. The mRNA levels of the brown/beige adipocyte-specific markers Ucp1, Dio2, Pat2, and Pgc1a; and the expression of leptin were greatly reduced in the ApoA1 knock-out in comparison to the wild-type mice. In the knock-out mice, adiponectin was remarkably elevated. In keeping with the close ties of hematopoietic stem cells and marrow adipocytes, using flow cytometry we found that the elevated adiposity in the ApoA1 knockout mice is associated with a significant reduction in the compartments of hematopoietic stem cells and common myeloid, but not of the common lymphoid, progenitors. Moreover, the ‘beiging’-related marker osteopontin and the angiogenic factor VEGF were also reduced in the ApoA1 knock-out mice, further supporting the notion that APOA1—and most probably HDL-C—regulate bone marrow microenvironment, favoring beige/brown adipocyte characteristics

Functional alterations in mechanical loading of condylar cartilage induces changes in the bony subcondylar region

Bone remodeling is orchestrated by cells of the osteoblast lineage and involves an intricate network of cell-cell and cell-matrix interactions. This dynamic process engages systemic hormones, locally produced cytokines and growth factors, as well as the mechanical environment of the cells. In growing subjects, the mandibular condyle consists of both articular and growth components and the presence of progenitor cells is verified by their anabolic responses to growth hormones. The pathways of chondrocyte and osteoblast differentiation during endochondral bone formation are interconnected and controlled by key transcription factors. The present study was undertaken to explore the possibility and the extent by which the mechano-transduction events in chondrocytes are ‘sensed’ in the subchondral bony area under altered functional loading. To this end, the involvement of the JNK/ERK-AP-1/Runx2 signaling axe was investigated by immunohistochemistry in temporomandibular joints of young rats subjected to different functional mastication loads. Our results showed that mechanical load triggers differentiation phenomena through the induction of master tissue regulators, namely the expression and/or activation of the JNK-c-Jun signaling pathway components and c-Fos in subchondral osteoblasts, as well as the activation of ERK/MAPK and the cellular expression of the transcription factor Runx2 in subchondral osteoblasts. (C) 2009 Elsevier Ltd. All rights reserved