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      An extensive phenotypic characterization of the hTNFα transgenic mice

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          Abstract

          Background

          Tumor necrosis factor alpha (TNFα) is implicated in a wide variety of pathological and physiological processes, including chronic inflammatory conditions, coronary artery disease, diabetes, obesity, and cachexia. Transgenic mice expressing human TNFα (hTNFα) have previously been described as a model for progressive rheumatoid arthritis. In this report, we describe extensive characterization of an hTNFα transgenic mouse line.

          Results

          In addition to arthritis, these hTNFα transgenic mice demonstrated major alterations in body composition, metabolic rate, leptin levels, response to a high-fat diet, bone mineral density and content, impaired fertility and male sexual function. Many phenotypes displayed an earlier onset and a higher degree of severity in males, pointing towards a significant degree of sexual dimorphism in response to deregulated expression of TNFα.

          Conclusion

          These results highlight the potential usefulness of this transgenic model as a resource for studying the progressive effects of constitutively expressed low levels of circulating TNFα, a condition mimicking that observed in a number of human pathological conditions.

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          Most cited references48

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          Leptin inhibits bone formation through a hypothalamic relay: a central control of bone mass.

          Gonadal failure induces bone loss while obesity prevents it. This raises the possibility that bone mass, body weight, and gonadal function are regulated by common pathways. To test this hypothesis, we studied leptin-deficient and leptin receptor-deficient mice that are obese and hypogonadic. Both mutant mice have an increased bone formation leading to high bone mass despite hypogonadism and hypercortisolism. This phenotype is dominant, independent of the presence of fat, and specific for the absence of leptin signaling. There is no leptin signaling in osteoblasts but intracerebroventricular infusion of leptin causes bone loss in leptin-deficient and wild-type mice. This study identifies leptin as a potent inhibitor of bone formation acting through the central nervous system and therefore describes the central nature of bone mass control and its disorders.
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            Estrogen deficiency induces bone loss by enhancing T-cell production of TNF-alpha.

            Estrogen deficiency induces bone loss by upregulating osteoclastogenesis by mechanisms not completely defined. We found that ovariectomy-enhanced T-cell production of TNF-alpha, which, acting through the TNF-alpha receptor p55, augments macrophage colony-stimulating factor-induced (M-CSF-induced) and RANKL-induced osteoclastogenesis. Ovariectomy failed to induce bone loss, stimulate bone resorption, or increase M-CSF- and RANKL-dependent osteoclastogenesis in T-cell deficient mice, establishing T cells as essential mediators of the bone-wasting effects of estrogen deficiency in vivo. These findings demonstrate that the ability of estrogen to target T cells, suppressing their production of TNF-alpha, is a key mechanism by which estrogen prevents osteoclastic bone resorption and bone loss.
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              Rheumatoid cachexia: cytokine-driven hypermetabolism accompanying reduced body cell mass in chronic inflammation.

              The cytokines IL-1 beta and TNF-alpha cause cachexia and hypermetabolism in animal models, but their role in human inflammation remains controversial. The relationship between in vitro cytokine production and metabolism was examined in 23 adults with RA and 23 healthy control subjects matched on age, sex, race, and weight. Body composition was measured by multicompartmental analysis of body cell mass, water, fat, and bone mass. Resting energy expenditure (REE) was measured by indirect calorimetry. Cytokine production by PBMC was measured by radioimmunoassay. Usual energy intake, physical activity, disability scores, medication use, and other confounders were also measured. Body cell mass was 13% lower (P < 0.00001), REE was 12% higher (P < 0.008), and physical activity was much lower (P < 0.001) in subjects with RA. Production of TNF-alpha was higher in RA than controls, both before and after stimulation with endotoxin (P < 0.05), while production of IL-1 beta was higher with endotoxin stimulation (P < 0.01). In multivariate analysis, cytokine production was directly associated with REE (P < 0.001) in patients but not in controls. While energy and protein intake were similar in the two groups and exceeded the Recommended Dietary Allowances, energy intake in subjects with RA was inversely associated with IL-1 beta production (P < 0.005). In this study we conclude that: loss of body cell mass is common in RA; cytokine production in RA is associated with altered energy metabolism and intake, despite a theoretically adequate diet; and TNF-alpha and IL-1 beta modulate energy metabolism and body composition in RA.
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                Author and article information

                Journal
                BMC Physiol
                BMC Physiology
                BioMed Central
                1472-6793
                2007
                10 December 2007
                : 7
                : 13
                Affiliations
                [1 ]Caliper Discovery Alliances & Services (Xenogen Biosciences), 5 Cedar Brook Drive, Cranbury, NJ 08512, USA
                Article
                1472-6793-7-13
                10.1186/1472-6793-7-13
                2222242
                18070349
                d9f6d273-12f8-474b-a371-f7def017d624
                Copyright © 2007 Hayward et al; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 2 February 2007
                : 10 December 2007
                Categories
                Research Article

                Anatomy & Physiology
                Anatomy & Physiology

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