Increased lymphangiogenesis in joints of mice with inflammatory arthritis

Inflammation induces lymphangiogenesis through up-regulation of VEGFR-3 mediated by NF-kappaB and Prox1

The concept of inflammation-induced lymphangiogenesis (ie, formation of new lymphatic vessels) has long been recognized, but the molecular mechanisms remained largely unknown. The 2 primary mediators of lymphangiogenesis are vascular endothelial growth factor receptor-3 (VEGFR-3) and Prox1. The key factors that regulate inflammation-induced transcription are members of the nuclear factor-kappaB (NF-kappaB) family; however, the role of NF-kappaB in regulation of lymphatic-specific genes has not been defined. Here, we identified VEGFR-3 and Prox1 as downstream targets of the NF-kappaB pathway. In vivo time-course analysis of inflammation-induced lymphangiogenesis showed activation of NF-kappaB followed by sequential up-regulation of Prox1 and VEGFR-3 that preceded lymphangiogenesis by 4 and 2 days, respectively. Activation of NF-kappaB by inflammatory stimuli also elevated Prox1 and VEGFR-3 expression in cultured lymphatic endothelial cells, resulting in increased proliferation and migration. We also show that Prox1 synergizes with the p50 of NF-kappaB to control VEGFR-3 expression. Collectively, our findings suggest that induction of the NF-kappaB pathway by inflammatory stimuli activates Prox1, and both NF-kappaB and Prox1 activate the VEGFR-3 promoter leading to increased receptor expression in lymphatic endothelial cells. This, in turn, enhances the responsiveness of preexisting lymphatic endothelium to VEGFR-3 binding factors, VEGF-C and VEGF-D, ultimately resulting in robust lymphangiogenesis.

Inhibition of lymphangiogenesis and lymphatic drainage via vascular endothelial growth factor receptor 3 blockade increases the severity of inflammation in a mouse model of chronic inflammatory arthritis

OBJECTIVE

This study was undertaken to investigate the effect of lymphatic inhibition on joint and draining lymph node (LN) pathology during the course of arthritis progression in mice.

METHODS

Tumor necrosis factor (TNF)-transgenic mice were used as a model of chronic inflammatory arthritis. Mice were subjected to contrast-enhanced magnetic resonance imaging to obtain ankle and knee joint synovial volumes and draining popliteal LN volumes before and after 8 weeks of treatment with vascular endothelial growth factor receptor 3 (VEGFR-3) neutralizing antibody, VEGFR-2 neutralizing antibody, or isotype IgG. Animals were subjected to near-infrared lymphatic imaging to determine the effect of VEGFR-3 neutralization on lymph transport from paws to draining popliteal LNs. Histologic, immunohistochemical, and reverse transcriptase-polymerase chain reaction analyses were used to examine lymphatic vessel formation and the morphology of joints and popliteal LNs.

RESULTS

Compared with IgG treatment, VEGFR-3 neutralizing antibody treatment significantly decreased the size of popliteal LNs, the number of lymphatic vessels in joints and popliteal LNs, lymphatic drainage from paws to popliteal LNs, and the number of VEGF-C-expressing CD11b+ myeloid cells in popliteal LNs. However, it increased the synovial volume and area of inflammation in ankle and knee joints. VEGFR-2 neutralizing antibody, in contrast, inhibited both lymphangiogenesis and joint inflammation.

CONCLUSION

These findings indicate that lymphangiogenesis and lymphatic drainage are reciprocally related to the severity of joint lesions during the development of chronic arthritis. Lymphatic drainage plays a beneficial role in controlling the progression of chronic inflammation.

Psoriatic arthritis and chronic lymphoedema: treatment efficacy by adalimumab

Lymphoedema is a rare complication of psoriatic arthritis (PsA) and inflammatory joint disease, with no response noted to disease-modifying drugs. However, reports are emerging of a beneficial effect on lymphoedema in patients treated with tumor necrosis factor-alpha antagonists for PsA (Etanercept), rheumatoid arthritis (Etanercept) and ankylosing spondylitis (Infliximab). We describe a psoriatic arthritis patient whose lymphoedema greatly improved following commencement of adalimumab.

Translational perspectives on psoriatic arthritis

The term psoriatic disease encompasses the array of disorders (arthritis, inflammatory bowel disease, uveitis, obesity, metabolic syndrome, type II diabetes, and cardiovascular disease) that are associated with psoriasis. Psoriatic arthritis (PsA) is present in about 25% of patients with psoriasis; in most cases, the psoriasis precedes joint disease by about 10 years. Previous studies revealed that osteoclast precursors (OCP) are elevated in PsA and that the frequency of these circulating cells correlates with bone destruction. More recently OCP were found to be increased also in early rheumatoid arthritis and in 25% of psoriasis patients without arthritis. Bone marrow edema, observed on magnetic resonance imaging, in PsA represents infiltration of underlying marrow with inflammatory cells based on studies in transgenic tumor necrosis factor (TNF) arthritis murine models. Studies in the TNF transgenic mouse model also revealed that changes in lymph node volume precede joint flare. These translational studies point to potential biomarkers of arthritis in psoriasis patients and generate alternative hypotheses to explain the events that lead to arthritic flare.

Alterations in peripheral blood memory B cells in patients with active rheumatoid arthritis are dependent on the action of tumour necrosis factor

INTRODUCTION

Disturbances in peripheral blood memory B cell subpopulations have been observed in various autoimmune diseases, but have not been fully delineated in rheumatoid arthritis (RA). Additionally, the possible role of tumour necrosis factor (TNF) in regulating changes in specific peripheral blood memory B cell subsets in RA is still unclear.

METHODS

The frequency and distribution of B cell subsets in the peripheral blood and synovial membrane of active RA patients with long-standing disease have been analysed. Additionally, the possible role of TNF in causing disturbances in memory B cell subsets in RA patients was assessed in a clinical trial with the specific TNF-neutralising antibody, infliximab.

RESULTS

RA patients, independent of disease duration, have a significantly lower frequency of peripheral blood pre-switch IgD+CD27+ memory B cells than healthy individuals, whereas post-switch IgD-CD27+ accumulate with increased disease duration. Notably, both pre-switch IgD+CD27+ and post-switch IgD-CD27+ memory B cells accumulate in the synovial membrane of RA patients. Finally, anti-TNF therapy increased the frequency of pre-switch IgD+CD27 memory B cells in the peripheral blood.

CONCLUSIONS

The data suggest that decreases in peripheral blood IgD+CD27+ pre-switch memory B cells in RA reflect their accumulation in the synovial tissue. Moreover, the significant increase in the peripheral blood pre-switch memory B cells in patients who underwent specific TNF-blockade with infliximab indicates that trafficking of memory B cells into inflamed tissue in RA patients is regulated by TNF and can be corrected by neutralising TNF.

Osteoclast injection: a promising approach of cell therapy to obtain higher bone union ratio

Bone nonunion can occur for a number of reasons. Previous studies have tended to focus on the issue as a dysfunction of osteoblasts, as well as a lack of angiogenesis. The functions of osteoclasts are often ignored, even though, in fact, osteoclasts are involved in the whole bone fracture healing and reconstruction process. Inhibition of osteoclastogenesis or dysfunction of osteoclasts can seriously affect the course of fracture healing, increasing the risk of bone nonunion. Therefore, we hypothesized that, by injection of osteoclast at certain bone healing stages, the bone nonunion ratio could be reduced, especially for the sclerosis nonunion that occurs mainly because of the disabling of osteoclastogenesis which leading to the final medullary cavity closure.

Lymphatic endothelial cells, lymphedematous lymphangiogenesis, and molecular control of edema formation

Lymphedema, defined as the abnormal accumulation of protein-rich fluid in soft tissues, results from the dysfunction of lymphatic system, an imbalance between lymph formation and its absorption into the initial lymphatics. Primary lymphedema occurs rarely on idiopathic or developmental abnormalities, especially hypoplasia or aplasia of lymphatics. Secondary lymphedema commonly develops when lymph transport is impaired due to lymphatic damage or resection of lymph nodes in surgery, infection, and radiation. Lymphatic endothelial cells (LECs) actively participate in the phenotypic consequences of a deranged lymphangiogenesis relating to tissue fluid accumulation in the pathogenesis of lymphedema. Recent insights into molecular genetic bases have shown an updated genotype-phenotype correlation between lymphangiogenesis, lymphatic function, and lymphedema. FOXC2, EphrinB2, VEGFR-3, VEGF-C, angiopoietin-2, Prox-1 and podoplanin have proved to be important factors of the genetic cascade linking to hereditary lymphedema, and embryonic and postnatal lymphatic development. FOXC2 may have a key role in regulating interactions between LECs and smooth muscle cells, and in the morphogenesis of lymphatic valves. Reduced VEGFR-3 tyrosine kinase activity and subsequent failure in transducing sufficient physiological VEGF-C/-D signals may affect LEC function and structure in the intercellular junctions and peri-lymphatic components. Identification of genetic markers in humans and animal models would facilitate the management of environmental factors influencing the expression and severity of lymphedema, and provide a basis for developing novel targeted therapies for the disease.

The lymphatic system in health and disease

The lymphatic vascular system has an important role in the regulation of tissue pressure, immune surveillance and the absorption of dietary fat in the intestine. There is growing evidence that the lymphatic system also contributes to a number of diseases, such as lymphedema, cancer metastasis and different inflammatory disorders. The discovery of various molecular markers allowing the distinction of blood and lymphatic vessels, together with the availability of a increasing number of in vitro and in vivo models to study various aspects of lymphatic biology, has enabled tremendous progress in research into the development and function of the lymphatic system. This review discusses recent advances in our understanding of the embryonic development of the lymphatic vasculature, the molecular mechanisms mediating lymphangiogenesis in the adult, the role of lymphangiogenesis in chronic inflammation and lymphatic cancer metastasis, and the emerging importance of the lymphatic vasculature as a therapeutic target.

The role of bone marrow edema and lymphangiogenesis in inflammatory-erosive arthritis

A common feature of autoimmune diseases is the perpetual production of macrophage, dendritic and/or osteoclast effector cells, which mediate parenchymal tissue destruction in end organs. In support of this, we have demonstrated previously that patients and mice with inflammatory-erosive arthritis have a marked increase in circulating CD11b+ precursor cells, which are primed for osteoclastogenesis, and that this increase in osteoclast precursors (OCPs) is due to systemically increased TNF production. From these data, we proposed a unifying hypothesis to explain these osteoimmunologic findings during the pathogenesis of inflammatory-erosive arthritis, which has three postulates: (1) myelopoiesis chronically induced by TNF has profound effects on the bone marrow and joint tissues that should be evident from a longitudinal MRI; (2) TNF alters the chemokine/chemokine receptor axis in the bone marrow to stimulate OCP release into the blood, and (3) OCP-mediated lymphangiogenesis occurs in the end organ as a compensatory mechanism to drain the inflammation and remove by-products of joint catabolism. Here, we describe our recent experimental findings that support these hypotheses and speculate on how this information can be used as diagnostic biomarkers and tools to discover novel therapies to treat patients with inflammatory-erosive arthritis.

Advancing treatment for metastatic bone cancer: consensus recommendations from the Second Cambridge Conference

PURPOSE

Summarize current knowledge, critical gaps in knowledge, and recommendations to advance the field of metastatic bone cancer.

EXPERIMENTAL DESIGN

A multidisciplinary consensus conference was convened to review recent progress in basic and clinical research, assess critical gaps in current knowledge, and prioritize recommendations to advance research in the next 5 years. The program addressed three principal topics: biology of metastasis, preserving normal bone health, and optimizing bone-targeted therapies.

RESULTS

A variety of specific recommendations were identified as important to advance research and clinical care over the next 5 years.

CONCLUSIONS

Priorities for research in bone biology include characterizing components of the stem cell niche in bone, developing oncogenic immunocompetent animal models of bone metastasis, and investigating the unique contribution of the bone microenvironment to tumor growth and dormancy. Priorities for research in preserving normal bone health include developing methods to measure and characterize disseminating tumor cells, assessing outcomes from the major prevention trials currently in progress, and improving methodologies to assess risks and benefits of treatment. Priorities for optimizing bone-targeted therapies include advancing studies of serum proteomics and genomics to reliably identify patients who will develop bone metastases, enhancing imaging for early detection of bone metastases and early response evaluation, and developing new tests to evaluate response to bone-directed treatments.

Functions of RANKL/RANK/OPG in bone modeling and remodeling

The discovery of the RANKL/RANK/OPG system in the mid 1990s for the regulation of bone resorption has led to major advances in our understanding of how bone modeling and remodeling are regulated. It had been known for many years before this discovery that osteoblastic stromal cells regulated osteoclast formation, but it had not been anticipated that they would do this through expression of members of the TNF superfamily: receptor activator of NF-kappaB ligand (RANKL) and osteoprotegerin (OPG), or that these cytokines and signaling through receptor activator of NF-kappaB (RANK) would have extensive functions beyond regulation of bone remodeling. RANKL/RANK signaling regulates osteoclast formation, activation and survival in normal bone modeling and remodeling and in a variety of pathologic conditions characterized by increased bone turnover. OPG protects bone from excessive resorption by binding to RANKL and preventing it from binding to RANK. Thus, the relative concentration of RANKL and OPG in bone is a major determinant of bone mass and strength. Here, we review our current understanding of the role of the RANKL/RANK/OPG system in bone modeling and remodeling.

VEGF-C, a lymphatic growth factor, is a RANKL target gene in osteoclasts that enhances osteoclastic bone resorption through an autocrine mechanism

Osteoclasts are bone-resorbing cells, but they also secrete and respond to cytokines. Here, we test the hypothesis that osteoclasts secrete the lymphatic growth factor, VEGF-C, to increase their resorptive activity. Osteoclasts and osteoclast precursors were generated by culturing splenocytes with macrophage colony-stimulating factor and RANKL from wild-type, NF-kappaBp50(-/-)/p52(-/-), and Src(-/-) mice. Expression of VEGFs was measured by real time reverse transcription-PCR, Western blotting, and immunostaining. The effect of VEGF-C signaling on osteoclast function was determined by osteoclastogenesis and pit assays. RANKL increased the expression of VEGF-C but not of other VEGFs in osteoclasts and their precursors. RANKL-induced VEGF-C expression was reduced in NF-kappaBp50(-/-)/p52(-/-) precursors or wild-type cells treated with an NF-kappaB inhibitor. VEGF-C directly stimulated RANKL-mediated bone resorption, which was reduced by the VEGF-C-specific receptor blocker, VEGFR3:Fc. Osteoclasts express VEGFR3, and VEGF-C stimulated Src phosphorylation in osteoclasts. VEGF-C-mediated bone resorption was abolished in Src(-/-) osteoclasts or cells treated with an Src inhibitor. We conclude that RANKL stimulates osteoclasts and their precursors to release VEGF-C through an NF-kappaB-dependent mechanism, indicating that VEGF-C is a new RANKL target gene in osteoclasts and functions as an autocrine factor regulating osteoclast activity.