Biglycan Regulates MG63 Osteosarcoma Cell Growth Through a LPR6/ß-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/ß-catenin pathway, was demonstrated to induce a significant increase in ß-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 ß-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 ß-catenin degradation. Furthermore, applying anti-ß-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/ß-catenin/IGF-IR signaling axis enhances osteosarcoma cell growth.

The biology of small leucine-rich proteoglycans in bone pathophysiology.

The class of small leucine-rich proteoglycans (SLRPs) is a family of homologous proteoglycans harboring relatively small (36-42 kDa) protein cores compared with the larger cartilage and mesenchymal proteoglycans. SLRPs have been localized to most skeletal regions, with specific roles designated during all phases of bone formation, including periods relating to cell proliferation, organic matrix deposition, remodeling, and mineral deposition. This is mediated by key signaling pathways regulating the osteogenic program, including the activities of TGF-ß, bone morphogenetic protein, Wnt, and NF-κB, which influence both the number of available osteogenic precursors and their subsequent development, differentiation, and function. On the other hand, SLRP depletion is correlated with degenerative diseases such as osteoporosis and ectopic bone formation. This minireview will focus on the SLRP roles in bone physiology and pathology.

Limb salvage after gas gangrene: a case report and review of the literature.

Gas gangrene is a necrotic infection of soft tissue associated with high mortality, often necessitating amputation in order to control the infection. Herein we present a case of gas gangrene of the arm in an intravenous drug user with a history of intramuscular injections with normal saline in the shoulder used to provoke pain for recovery after drug induced coma. The patient was early treated with surgery and antibiotics rendering possible the preservation of the limb and some of its function. Additionally, a review of the literature regarding case reports of limb salvage after gas gangrene is presented.

Lumican regulates osteosarcoma cell adhesion by modulating TGFß2 activity.

Human osteosarcoma cell lines were recently shown to express and secrete the small leucine rich proteoglycan (SLRP) lumican, with the ability to regulate the growth and motility of these cells. In this study, lumican-deficient Saos 2 cells were demonstrated to have increased adhesive capability onto fibronectin (FN) (p≤0.01). Upon neutralization of endogenous transforming growth factor ß2 (TGF-ß2) activity, no difference in the ability of lumican siRNA-transfected and scramble siRNA-transfected Saos 2 cells to adhere onto FN was detected (p=NS). Exogenous TGF-ß2 was shown to stimulate Saos 2 cell adhesion to FN (p≤0.01). These results therefore, suggest that the inverse correlation existing between lumican expression and Saos 2 cell adhesion is dependent on active TGF-ß2 signaling. Furthermore, the significant increase in Smad 2 activation present in lumican-deficient cells (p≤0.01) was annulled in the presence of the anti-TGF-ß2 peptide, demonstrating that lumican is an upstream regulator of the TGF-ß2/Smad 2 signaling cascade. Crucial to FN-dependent adhesion, ß1 integrin expression and pFAK activation were likewise identified as downstream TGF-ß2 effectors regulated by lumican expression. In conclusion, this study demonstrates a novel out-in signaling circuit in human osteosarcoma cells: secreted to extracellular matrix lumican is an endogenous inhibitor of TGF-ß2 activity, resulting in downstream effector modulation including pSmad 2, integrin ß1 and pFAK to regulate osteosarcoma adhesion.