Notes From the 6th Global Arthritis Research Network (GARN) Meeting

Session 4

Saturday, May 12, 2007 (pm)
Molecular Medicine
Chairs: Gyorgy Nagy, Budapest, Hungary and Jean-Pierre Pelletier, Montreal, Canada

Ralph MŸller, Zurich, Switzerland
Hierarchical imaging ofcells and matrix

"You get numbers, but pictures tell a better story…" Ralph MŸller gave an overview of the current imaging strategies in cells and matrix. He began his presentation by providing his ideas of an ideal imaging approach including hierarchical (ie, organ, structure, tissue, cells), volumetric, multicontrast (hard vs soft tissue) and noninvasive aspects. He summarized the fascinating development of imaging procedures during the last century, ranging from the x-ray technology to the high-resolution (HR)CT, micro- and, finally, nano-CT. This technical revolution allows us to visualize structures below 1 µm in a three-dimensional manner. Beyond structural investigations, this noninvasive technique facilitates functional analyses by providing not only qualitative, but also quantitative data. As an example, MŸller showed clinical applications to assess the risk of local fractures in osteoporotic bones, which is reflected on the cellular level by osteocyte density and distribution pattern of blood vessels. For the studies presented, MŸller used the C3H mouse model, which is characterized by high bone mass, whereas B6 control mice show a low bone mass and a distinct radial pattern of blood vessels. As future perspective, a combined imaging of bone and cartilage can be achieved by an overlay of micro-CT and confocal laser scanning microscopy, thus allowing an assessment of gene and cell therapies in osteoarthritis and related joint disorders.

Kazuhiko Yamamoto, Tokyo, Japan
Genetics and functions of genes associated with rheumatoid arthritis

According to Kazuhiko Yamamoto, genes contribute by up to 60% to the development of rheumatoid arthritis (RA), thus offering the opportunity to use linkage studies in monozygotic twins and affected families to investigate the pathogenesis of RA. Since genetic mapping is limited by hypothesis-based analysis of candidate genes, a genome-wide LD mapping with single nucleotide polymorphisms (SNPs) is used in general. During his lecture, Kazuhiko Yamamoto focused on three main polymorphisms: 1) the citrullinating enzyme peptidylarginine deiminase 4 (PADI4), which is involved in the citrullination of protein-intrinsic arginine and, thus, might contribute to the generation of antibodies to citrullinated peptides, 2) the protein tyrosine phosphatase N22 (PTPN22), an essential factor for T-cell receptor signaling, and, 3), Fc receptor-like 3 (FCRL3), a type I transmembrane protein associated with the B-cell receptor downstream signaling. Two main PADI4-haplotypes have been identified, of which type 1 is RA nonsusceptible, whereas type 2 is RA susceptible. This finding has led to the generation of an interesting hypothesis involving PADI4 as initiator of the pathogenetic cascade of RA. Polymorphisms of PTPN22, on the other hand, have been associated with the development of various autoimmune diseases such as diabetes mellitus type 1, systemic lupus erythematosus and rheumatoid arthritis. Whereas polymorphisms of PADI4 have been correlated to the RA pathogenesis in Asian population cohort studies, limited association has been detected in Caucasians. Conversely, the allelic frequency of PTPN22 is highest in Caucasian and lowest in Asian populations. These distributions might help to explain differences of disease prevalence in different ethnic groups. FCRL3, finally, has been found to be overexpressed in CD19+ B cells and secondary lymphoid tissues of RA patients. On a functional level, FCRL3 was shown to reduce the BCR-induced cell death within the germinal center of lymphoid follicules, thus promoting autoreactivity.

Toshihiro Nakajima, Kawasaki, Japan
Crosstalk between ER stress and p53 pathway in rheumatoid synoviocytes

Toshihiro Nakajima presented his data on Synoviolin, a novel pathogenic factor in rheumatoid arthritis (RA), which was initially identified from a human cDNA library of rheumatoid synovial cells (RSC) by immunoscreening with anti-RSC antibodies. In vivo experiments with transgenic mice, flies and zebrafish confirmed its role as cell growth mediator, valuable biomarker and potential therapeutic target in RA. Experimental studies indicate that this endoplasmic reticulum (ER-)resident E3 ubiquitin ligase, which proved to be upregulated in proliferating RSCs, has important functions in the ER-associated degradation (ERAD) system. In summary, the data suggest that RSCs are extraordinarily refractory to ER stress-induced apoptosis. This special property of RSCs, termed "hyper-ERAD," is mediated by Synoviolin and thus may cause synovial hyperplasia. To investigate the underlying molecular mechanisms, further experiments were performed. As a result, the tumor suppressor gene p53 was identified as a substrate of Synoviolin. Synoviolin sequestrated and metabolized p53 in the cytoplasm and negatively regulated its cellular level and biological functions, including transcription, cell cycle regulation and apoptosis.

Chairs: Philip L. Cohen, Philadelphia, PA, USA and Rene Toes, Leiden, NL

Martin E. Schwab, Zurich, Switzerland
Structural and functional repair after spinal cord injury
"Antibodies probably make the only connection to your topic..."

Martin Schwab presented intriguing data on the functional recovery following spinal lesions. As background, he explained the potential mechanisms of limited neuronal response to axotomy, including the spontaneous increase of immediate early genes, of GAP-43 and cytoskeletal proteins, as well as axonal sprouting. In addition, inflammatory and cytokine response might play an important role. The common dogma of missing sprouting within the central nervous system (CNS) was challenged by the experiments presented by Schwab. His group could show that following spinal cord injury a new electric circuit formation could be achieved. These findings may represent the basis for future human rehabilitation after spinal lesions. Years ago, Schwab was already able to prove that neurite growth in the adult CNS is restricted to 0.2-1mm by growth inhibitors (so-called NOGO areas). Thereby, the expression of the myelin protein NOGO-A is restricted to the CNS and cannot be found in the peripheral nervous system. By applying monoclonal antibodies against NOGO-A by an intrathecal pump into the spinal cord of injured rats, axon regeneration can be enhanced. Further experiments proved that these sprouting fibers form functional connections with both motor and sensory properties. The importance of the NOGO-antibodies in triggering these processes was underlined by its distinct distribution within spinal cord and brain tissue. As a second in vivo model, Macaque monkeys were tested accordingly and showed similar data. The functional recovery of NOGO-antibodies treated animals was vividly illustrated by several movie clips. As future outlook, Schwab closed his fascinating talk by a few words on ongoing phase 1 clinical trials in patients with spinal cord injury. Taken together, the neutralization of NOGO-A resulted in enhanced compensatory nerve fiber growth, as well as functional recovery and axonal regeneration.

Roger Nitsch, Zurich, Switzerland
Novel therapeutic targets for Alzheimer's disease
"The excitement for an immunotherapy despite the initial disappointment is high..."

Roger Nitsch began his talk with a short explanation on neuropathology and pathogenesis of Alzheimer's disease. Since -amyloid related toxicity causes axonal degeneration and formation of neurofibrillar tangles, the formation of these fibrils might represent a potential therapeutic target. By using an in vivo transgenic mouse model overexpressing arcA , he could show that a -immunotherapy removed a -amyloid, protected neurons against a -toxicity, rescued a -mediated behavioral deficits, and improved brain blood flow in amyloid affected vessels. Moreover, in 2003 a first clinical trial was started using an active vaccination. However, due to the development of a subacute meningoencephalitis in 6% of the patients, the trial had to be stopped after 2 months. Nonetheless, the follow-up of enrolled patients led to findings of high scientific interest. In particular, the immunotherapy against -amyloid slowed the cognitive decline in Alzheimer's disease and prevented hippocampal atrophy. Finally, preclinical as well as phase II studies comprise promising ongoing developments.

Session 4 summarised by Lars C. Huber and Britta Maurer

6th Global Arthritis Research Network Meeting

• Introduction
• Notes From Session 1
• Notes From Session 2
• Notes From Session 3
• Notes From Session 4