Glutamine metabolism modulates chondrocyte inflammatory response.

Osteoarthritis is the most common joint disease in the world with significant societal consequences but lacks effective disease-modifying interventions. The pathophysiology consists of a prominent inflammatory component that can be targeted to prevent cartilage degradation and structural defects. Intracellular metabolism has emerged as a culprit of the inflammatory response in chondrocytes, with both processes co-regulating each other.

Anti-Interleukin-6 Therapy Decreases Hip Synovitis and Bone Resorption and Increases Bone Formation Following Ischemic Osteonecrosis of the Femoral Head.

Legg-Calvé-Perthes disease (LCPD) is a juvenile form of ischemic femoral head osteonecrosis, which produces chronic hip synovitis, permanent femoral head deformity, and premature osteoarthritis. Currently, there is no medical therapy for LCPD. Interleukin-6 (IL-6) is significantly elevated in the synovial fluid of patients with LCPD.

Inflammatory osteolysis is regulated by site-specific ISGylation of the scaffold protein NEMO.

Inflammatory osteolysis is governed by exacerbated osteoclastogenesis. Ample evidence points to central role of NF-κB in such pathologic responses, yet the precise mechanisms underpinning specificity of these responses remain unclear. We propose that motifs of the scaffold protein IKKγ/NEMO partly facilitate such functions.

Cbl-PI3K interaction regulates Cathepsin K secretion in osteoclasts.

Effective bone resorption by osteoclasts is critical for balanced bone remodeling. We have previously reported that mice harboring a substitution mutation of tyrosine 737 to phenylalanine in the adapter protein Cbl (Cbl, YF) have increased bone volume partly due to decreased osteoclast-mediated bone resorption. The Cbl mutation abrogates interaction between Cbl and the p85 subunit of PI3K.

Protease-Activated Receptor 1 Deletion Causes Enhanced Osteoclastogenesis in Response to Inflammatory Signals through a Notch2-Dependent Mechanism.

We found that protease-activated receptor 1 (PAR1) was transiently induced in cultured osteoclast precursor cells. Therefore, we examined the bone phenotype and response to resorptive stimuli of PAR1-deficient (knockout [KO]) mice. Bones and bone marrow-derived cells from PAR1 KO and wild-type (WT) mice were assessed using microcomputed tomography, histomorphometry, in vitro cultures, and RT-PCR.

PI3K activation increases SDF-1 production and number of osteoclast precursors, and enhances SDF-1-mediated osteoclast precursor migration.

Our previous studies showed that in a mouse model in which PI3K-AKT activation was increased (YF mice), osteoclast numbers and levels of SDF-1, a chemokine, were augmented. The purpose of this study was to delineate the role of PI3K activation in regulating SDF-1 production and examine whether SDF-1 can stimulate differentiation and/or migration of osteoclast precursors. Using flow cytometric analysis, we demonstrated that compared to wild type mice, bone marrow of YF mice had increased numbers of CXCL12 abundant reticular (CAR) cells, that are a major cell type responsible for producing SDF-1.

Interleukin-6 deletion stimulates revascularization and new bone formation following ischemic osteonecrosis in a murine model.

Legg-Calvé-Perthes disease (LCPD) is a childhood form of ischemic osteonecrosis of the femoral head which can produce a permanent femoral head deformity and early osteoarthritis. The femoral head deformity results from increased bone resorption and decreased bone formation during repair and remodeling of the necrotic femoral head. A recent study showed that a pro-inflammatory cytokine, interleukin-6 (IL-6), is significantly elevated in the synovial fluid of patients with LCPD.

A genome-wide transcriptomic analysis of articular cartilage during normal maturation in pigs.

Objective: The articular cartilage undergoes dramatic changes in structure and composition during post-natal maturation, but the associated transcriptional changes are not well characterized. Compared to a mature stage, the immature articular cartilage shows developmental features such as increased thickness, presence of blood vessels, and the presence of a deep layer of growth cartilage which undergoes endochondral ossification. These features decrease during normal development.

Targeted Disruption of NF1 in Osteocytes Increases FGF23 and Osteoid With Osteomalacia-like Bone Phenotype.

Neurofibromatosis type 1 (NF1, OMIM 162200), caused by NF1 gene mutations, exhibits multi-system abnormalities, including skeletal deformities in humans. Osteocytes play critical roles in controlling bone modeling and remodeling. However, the role of neurofibromin, the protein product of the NF1 gene, in osteocytes is largely unknown.

Necrotic Bone Stimulates Proinflammatory Responses in Macrophages through the Activation of Toll-Like Receptor 4.

In Legg-Calvé-Perthes disease, loss of blood supply results in ischemic osteonecrosis of the femoral head (ONFH). Generally, macrophages play important roles in inflammatory responses to tissue necrosis, but their role in ONFH is not known. The purpose of this study was to determine the macrophage-inflammatory responses after ONFH and the receptor mechanisms involved in sensing the necrotic bone, using a piglet model of Legg-Calvé-Perthes disease.

Targeted disruption of BMP signaling through type IA receptor (BMPR1A) in osteocyte suppresses SOST and RANKL, leading to dramatic increase in bone mass, bone mineral density and mechanical strength.

Recent studies suggest a critical role of osteocytes in controlling skeletal development and bone remodeling although the molecular mechanism is largely unknown. This study investigated BMP signaling in osteocytes by disrupting Bmpr1a under the Dmp1-promoter. The conditional knockout (cKO) mice displayed a striking osteosclerotic phenotype with increased trabecular bone volume, thickness, number, and mineral density as assessed by X-ray and micro-CT.

HIF-1-Dependent IL-6 Activation in Articular Chondrocytes Initiating Synovitis in Femoral Head Ischemic Osteonecrosis.

Background: Ischemic osteonecrosis of the femoral head in children is associated with chronic hip synovitis and increased levels of the pro-inflammatory cytokine interleukin-6 (IL-6) in the synovial fluid due to unknown mechanisms. The purpose of this study was to investigate hypoxia-inducible factor-1 (HIF-1) activation as a molecular mechanism linking the induction of ischemic osteonecrosis to IL-6 production and the initiation of hip synovitis.

Methods: Ischemic osteonecrosis was surgically induced in the right femoral head of 6 piglets.

Comprehensive Genome-Wide Transcriptomic Analysis of Immature Articular Cartilage following Ischemic Osteonecrosis of the Femoral Head in Piglets.

Objective: Ischemic osteonecrosis of the femoral head (ONFH) in piglets results in an ischemic injury to the immature articular cartilage. The molecular changes in the articular cartilage in response to ONFH have not been investigated using a transcriptomic approach. The purpose of this study was to perform a genome-wide transcriptomic analysis to identify genes that are upregulated in the immature articular cartilage following ONFH.

Role of Cbl-PI3K Interaction during Skeletal Remodeling in a Murine Model of Bone Repair.

Mice in which Cbl is unable to bind PI3K (YF mice) display increased bone volume due to enhanced bone formation and repressed bone resorption during normal bone homeostasis. We investigated the effects of disrupted Cbl-PI3K interaction on fracture healing to determine whether this interaction has an effect on bone repair. Mid-diaphyseal femoral fractures induced in wild type (WT) and YF mice were temporally evaluated via micro-computed tomography scans, biomechanical testing, histological and histomorphometric analyses.

Development of a mouse model of ischemic osteonecrosis.

Background: Availability of a reliable mouse model of ischemic osteonecrosis could accelerate the development of novel therapeutic strategies to stimulate bone healing after ischemic osteonecrosis; however, no mouse model of ischemic osteonecrosis is currently available.

Questions/purposes: To develop a surgical mouse model of ischemic osteonecrosis, we asked, (1) if the blood vessels that contribute to the blood supply of the distal femoral epiphysis are cauterized, can we generate an osteonecrosis mouse model; (2) what are the histologic changes observed in this mouse model, and (3) what are the morphologic changes in the model.

Methods: We performed microangiography to identify blood vessels supplying the distal femoral epiphysis in mice, and four vessels were cauterized using microsurgical techniques to induce ischemic osteonecrosis.

Legg-Calvé-Perthes disease produces chronic hip synovitis and elevation of interleukin-6 in the synovial fluid.

Legg-Calvé-Perthes disease (LCPD) is a childhood hip disorder of ischemic osteonecrosis of the femoral head. Hip joint synovitis is a common feature of LCPD, but the nature and pathophysiology of the synovitis remain unknown. The purpose of this study was to determine the chronicity of the synovitis and the inflammatory cytokines present in the synovial fluid at an active stage of LCPD.

Loss of Cbl-PI3K interaction in mice prevents significant bone loss following ovariectomy.

Cbl and Cbl-b are E3 ubiquitin ligases and adaptor proteins, which perform regulatory roles in bone remodeling. Cbl-/- mice have delayed bone development due to decreased osteoclast migration. Cbl-b-/- mice are osteopenic due to increased bone resorbing activity of osteoclasts.

Altered hematopoietic stem cell and osteoclast precursor frequency in cathepsin K null mice.

Cathepsin K (CatK) is a lysosomal cysteine protease necessary for bone resorption by osteoclasts (OCs), which originate from myeloid hematopoietic precursors. CatK-deficient (CatK(-/-) ) mice show osteopetrosis due to defective resorption by OCs, which are increased in number in these mice. We investigated whether genetic ablation of CatK altered the number of hematopoietic stem cells (HSCs) and OC precursor cells (OCPs) using two mouse models: CatK(-/-) mice and a knock-in mouse model in which the CatK gene (ctsk) is replaced by cre recombinase.

Loss of Cbl-PI3K interaction enhances osteoclast survival due to p21-Ras mediated PI3K activation independent of Cbl-b.

Cbl family proteins, Cbl and Cbl-b, are E3 ubiquitin ligases and adaptor proteins, which play important roles in bone-resorbing osteoclasts. Loss of Cbl in mice decreases osteoclast migration, resulting in delayed bone development where as absence of Cbl-b decreases bone volume due to hyper-resorptive osteoclasts. A major structural difference between Cbl and Cbl-b is tyrosine 737 (in YEAM motif) only on Cbl, which upon phosphorylation interacts with the p85 subunit of phosphatidylinositol-3 Kinase (PI3K).

TULA-2, a novel histidine phosphatase, regulates bone remodeling by modulating osteoclast function.

Bone is a dynamic tissue that depends on the intricate relationship between protein tyrosine kinases (PTK) and protein tyrosine phosphatases (PTP) for maintaining homeostasis. PTKs and PTPs act like molecular on and off switches and help modulate differentiation and the attachment of osteoclasts to bone matrix regulating bone resorption. The protein T cell ubiquitin ligand-2 (TULA-2), which is abundantly expressed in osteoclasts, is a novel histidine phosphatase.

Abrogation of Cbl-PI3K interaction increases bone formation and osteoblast proliferation.

Cbl is an adaptor protein and E3 ligase that plays both positive and negative roles in several signaling pathways that affect various cellular functions. Tyrosine 737 is unique to Cbl and phosphorylated by Src family kinases. Phosphorylated CblY737 creates a binding site for the p85 regulatory subunit of phosphatidylinositol 3 kinase (PI3K) that also plays an important role in the regulation of bone homeostasis.

The loss of Cbl-phosphatidylinositol 3-kinase interaction perturbs RANKL-mediated signaling, inhibiting bone resorption and promoting osteoclast survival.

Cbl is an adaptor protein and an E3 ligase that plays both positive and negative roles in several signaling pathways that affect various cellular functions. Tyrosine 737 is unique to Cbl and is phosphorylated by Syk and Src family kinases. Phosphorylated Cbl Tyr(737) creates a binding site for the p85 regulatory subunit of PI3K, which also plays an important role in the regulation of bone resorption by osteoclasts.

Cbl-phosphatidylinositol 3 kinase interaction differentially regulates macrophage colony-stimulating factor-mediated osteoclast survival and cytoskeletal reorganization.

The Cbl protein is a key player in macrophage colony-stimulating factor (M-CSF)-induced signaling. To examine the role of Cbl in M-CSF-mediated cellular events, we used Cbl(YF/YF) knockin mice in which the regulatory tyrosine 737, which when phosphorylated binds to the p85 subunit of phosphatidylinositol 3 kinase (PI3K), is substituted to phenylalanine. In ex vivo cultures, M-CSF and receptor activator of nuclear factor-kappaB ligand-mediated differentiation of bone marrow precursors from Cbl(YF/YF) mice generated increased number of osteoclasts; however, osteoclast numbers in Cbl(YF/YF) cultures were unchanged with increasing doses of M-CSF.

Loss of Cbl-b increases osteoclast bone-resorbing activity and induces osteopenia.

Cbl proteins are multifunctional adaptor molecules that modulate cellular activity by targeting the ubiquitylating system, endocytic complexes, and other effectors to a wide variety of regulatory proteins, especially activated receptor and nonreceptor tyrosine kinases. Cbl and Cbl-b perform unique functions in various cells, in addition to redundant functions that are required for embryonic development. We previously showed that eliminating Cbl impaired osteoclast motility, which modestly delayed embryonic bone development.

Curcumin overcomes the inhibitory effect of nitric oxide on Leishmania.

Upon Leishmania infection, macrophages are activated to produce nitrogen and oxygen radicals simultaneously. It is well established that the infected host cells rely on nitric oxide (NO) as the major weapon against the intracellular parasite. In India where leishmaniasis is endemic, the spice turmeric is used prolifically in food and for insect bites.