Rheumatoid arthritis (RA) is a chronic infl ammatory disease of synovial joints that is associated with cartilage and bone destruction. Death Receptor 3 (DR3), a tumor necrosis factor (TNF) receptor superfamily member, has recently been associated with the pathogenesis of RA. We demonstrate that absence of DR3 confers resistance to the development of adverse bone pathology in experimental antigen-induced arthritis (AIA). DR3 ko mice exhibited a reduction in all histopathological hallmarks of AIA but, in particular, failed to develop subchondral bone erosions and were completely protected from this characteristic of AIA. In contrast, TNF-like protein 1A (TL1A), the ligand for DR3, exacerbated disease in a dose-and DR3-dependent fashion. Analysis of osteoclast number within AIA joint revealed a reduction in areas susceptible to bone erosion in DR3 ko mice, whereas in vitro osteoclastogenesis assays showed that TL1A could directly promote osteoclastogenesis in mouse and man. Treatment with antagonistic anti-TL1A mAb protected animals in a systemic model of RA disease collagen-induced arthritis. We therefore conclude that the DR3 -TL1A pathway regulates joint destruction in two murine models of arthritis and represents a potential novel target for therapeutic intervention in infl ammatory joint disease.

This study describes the previously uncharacterized ontogeny and regulation of truncal adipose reserves in the profoundly GH-deficient dwarf (dw/dw) rat. We show that, despite normal proportionate food intake, dw/dw rats develop abdominal leanness and hypoleptinemia (circulating leptin halved in dw/dw males, P Ͻ 0.05) during puberty. This contrasts with the hyperleptinemia seen in moderately GH-deficient Tgr rats (circulating leptin doubled at 6 wk of age, P Ͻ 0.05) and in GH receptor-binding protein (GHR/BP)-null mice (circulating leptin doubled; P Ͻ 0.05). This lean/hypoleptinemic phenotype was not completely normalized by GH treatment, but dw/dw rats developed abdominal obesity in response to neonatal MSG treatment or maintenance on a high-fat diet. Unlike Tgr rats, dw/dw rats did not become obese with age; plasma leptin levels and fat pad weights became similar to those in wild-type rats. In contrast with truncal leanness, tibial marrow adiposity was normal in male and doubled in female dwarves (P Ͻ 0.01), this increase being attributable to increased adipocyte number (P Ͻ 0.01). Neonatal MSG treatment and high-fat feeding elevated marrow adiposity in dw/dw rats by inducing adipocyte enlargement (P Ͻ 0.05). These results demonstrate that, despite lipolytic influence of GH, severe GH deficiency in dw/dw rats is accompanied by a paradoxical leanness. This lean/hypoleptinemic phenotype is not solely attributable to reduced GH signaling and does not appear to result from a reduction in nutrient intake or the ability of dw/dw adipocytes to accumulate lipid. Disruption of preadipocyte differentiation or adipocyte proliferation in the dw/dw rat may lead to the development of this unusually lean/hypoleptinemic phenotype. adipose tissue; bone marrow fat; leptin; dwarfism IT IS WELL ESTABLISHED that growth hormone (GH) deficiency is usually accompanied by an increase in fat accumulation, whereas conditions of GH excess are normally associated with leanness. However, recent studies have revealed that the relationship between GH status and the degree of adiposity is far from simple. For example, although it is assumed that obesity results from the removal of the lipolytic influence of GH (37), it is also recognized that abdominal obesity results in a secondary reduction in GH secretion (35). Similarly, whereas GH replacement in patients with primary GH deficiency leads to specific depletion of intra-abdominal fat (2, 12), the administration of GH to treat obesity in GH-replete individuals does not elicit a consistent reduction or redistribution in body fat (31). Some of these apparent contradictions may be explained by the depot-specific sensitivity of adipose tissue to the lipolytic action of GH (19). The relationship between GH status and adiposity in rodent models of GH deficiency is similarly complex. In the profoundly GH-deficient lit/lit mouse a significant elevation in total proportionate fat mass (14) is reflected in increased inguinal and retroperitoneal fat, whereas parametrial fat is unaffected (26). In addit...

Death receptor 3 is a proinflammatory member of the immunomodulatory tumor necrosis factor receptor superfamily, which has been implicated in several inflammatory diseases such as arthritis and inflammatory bowel disease. Intriguingly however, constitutive DR3 expression has been detected in the brains of mice, rats, and humans, although its neurological function remains unknown. By mapping the normal brain expression pattern of DR3, we found that DR3 is expressed specifically by cells of the neuron lineage in a developmentally regulated and region-specific pattern. Behavioral studies on DR3-deficient (DR3 ko ) mice showed that constitutive neuronal DR3 expression was required for stable motor control function in the aging adult. DR3 ko mice progressively developed behavioral defects characterized by altered gait, dyskinesia, and hyperactivity, which were associated with elevated dopamine and lower serotonin levels in the striatum. Importantly, retrograde tracing showed that absence of DR3 expression led to the loss of corticostriatal innervation without significant neuronal loss in aged DR3 ko mice. These studies indicate that DR3 plays a key nonredundant role in the retention of normal motor control function during aging in mice and implicate DR3 in progressive neurological disease.

Mice prematurely expressing human CR2 (hCR2) in the B cell lineage have a defective B cell ontogeny and immune response. Our recent analysis of this phenotype suggested that signalling through hCR2 and presumably mouse CD19 on the B cell surface, during bone marrow development, could result in the observed changes in B cell function in these mice. To test this hypothesis, we back crossed hCR2 high transgenic mice onto the CD19 −/− background. CD19 −/− hCR2 high mice were found to possess even fewer mature B cells than their CD19 +/+ hCR2 high littermates, demonstrating that loss of CD19 exascerbated the effects elicited through hCR2. This data suggests that CD19 provides a survival signal during B cell development in this model. Next, we examined if the removal of the main ligand for CR2, namely C3d, through back-crossing onto the C3 −/− background could restore normal B cell development. However, we found only minor recovery in peripheral B cell numbers and no obvious change in function. This was despite a 3-fold increase in the level of hCR2 expression on B cells isolated from the spleen or bone marrow of C3 −/− hCR2 high mice when compared with C3 sufficient littermates. These data demonstrate that hCR2 is integrated in mouse B cell signalling and that the downstream effects of hCR2 expression during early B cell development are partially but not completely due to interaction with C3 fragments and signaling through CD19 in the bone marrow environment.

The relationship between the degree of GH deficiency and impaired bone integrity is not simple and may be influenced by related endocrine variables. To test the hypothesis that elevated adiposity and hyperleptinaemia are contributory factors, we quantified femoral trabecular organisation in two models of GH deficiency with divergent degrees of adiposity -the moderately GH-deficient/hyperleptinaemic transgenic growth retarded (Tgr) rat and the profoundly GH-deficient/ hypoleptinaemic dw/dw rat. Trabecular density (bone volume/total volume) and surface were reduced by 16% in dw/dw males, with a more fragmented trabecular lattice. This impairment was more pronounced in Tgr rats, with trabecular number and density further reduced (by an additional 21%) and relative surface (bone surface/bone volume), trabecular convexity (structural modal index) and fragmentation (pattern factor) increased. To establish whether the presence of obesity/hyperleptinaemia exacerbates bone impairment in GH deficiency, trabecular structure was assessed in dw/dw rats following diet-induced obesity (DIO). DIO had minimal effect on trabecular architecture, the increased concavity of trabecular surfaces being the only observable effect. Similarly, infusion of leptin into the tibial bone marrow cavity had no effect on trabecular organisation or tibial growth in wild-type rats. However, while this procedure also failed to affect trabecular architecture or osteoclast number in dw/dw rats, distal osteoblast surface was increased by 23%, marrow adipocyte number and epiphyseal plate width being reduced (by 40 and 5% respectively), without increasing caspase-3 immunoreactivity. These findings suggest that while leptin may directly inhibit adipocyte differentiation and favour osteoblast production, hyperleptinaemia makes only a minimal contribution to the impairment of bone structure in GH deficiency.