Osteoclasts are multinucleated cells formed mainly on bone surfaces in response to cytokines by fusion of bone marrow-derived myeloid lineage precursors that circulate in the blood. Major advances in understanding of the molecular mechanisms regulating osteoclast formation and functions have been made in the past 20 years since the discovery that their formation requires nuclear factor-kappa B (NF-κB) signaling and that this is activated in response to the essential osteoclastogenic cytokine, receptor activator of NF-κB ligand (RANKL), which also controls osteoclast activation to resorb (degrade) bone. These studies have revealed that RANKL and some pro-inflammatory cytokines, including tumor necrosis factor, activate NF-κB and downstream signaling, including c-Fos and nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1), and inhibition of repressors of NFATc1 signaling, to positively regulate osteoclast formation and functions. However, these cytokines also activate NF-κB signaling that can limit osteoclast formation through the NF-κB signaling proteins, TRAF3 and p100, and the suppressors of c-Fos/NFATc1 signaling, IRF8, and RBP-J. This paper reviews current understanding of how NF-κB signaling is involved in the positive and negative regulation of cytokine-mediated osteoclast formation and activation.
Citations
Relationship Between Metabolic Syndrome and Bone Health – An Evaluation of Epidemiological Studies and Mechanisms Involved
Reduced appetite and body weight loss are typical symptoms of inflammatory diseases. A number of inflammatory stimuli are responsible for the imbalance in energy homeostasis, leading to metabolic disorders. The herpes virus entry mediator (HVEM) protein plays an important role in the development of various inflammatory diseases, such as intestinal inflammation and diet-induced obesity. However, the role of HVEM in the brain is largely unknown. This study aims to investigate whether HVEM signaling in the brain is involved in inflammation-induced anorexia and body weight loss.
Food intake and body weight were measured at 24 hours after intraperitoneal injection of lipopolysaccharide (LPS) or intracerebroventricular injection of recombinant mouse LIGHT (also called tumor necrosis factor receptor superfamily 14, TNFSF14), an HVEM ligand, into 8- to 10-week-old male C57BL/6 mice and mice lacking HVEM expression (HVEM-/-). We also assessed LPS-induced change in hypothalamic expression of HVEM using immunohistochemistry.
Administration of LPS significantly reduced food intake and body weight, and moreover, increased expression of HVEM in the hypothalamic arcuate nucleus. However, LPS induced only minor decreases in food intake and body weight in HVEM-/- mice. Administration of LIGHT into the brain was very effective at decreasing food intake and body weight in wild-type mice, but was less effective in HVEM-/- mice.
Activation of brain HVEM signaling is responsible for inflammation-induced anorexia and body weight loss.
Citations
Tumor necrosis factor (TNF)-α is associated with insulin resistance and systemic inflammatory responses. The aim of this study was to investigate the relationship between TNF-α and the development of nonalcoholic fatty liver disease (NAFLD) in a longitudinal study.
Three hundred and sixty-three apparently healthy subjects (mean age, 40.5±6.1 years; male, 57.6%) without NAFLD were enrolled in 2003. Anthropometric and laboratory measurements were performed. The participants were grouped into tertiles according to their serum TNF-α levels from samples taken in 2003. At a 4-year follow-up, we compared the odds ratios (ORs) of the development of NAFLD according to the tertiles of TNF-α levels measured in 2003.
At the 4-year follow-up, the cumulative incidence of NAFLD was 29.2% (106/363). The group that developed NAFLD had higher levels of TNF-α than those in the group without NAFLD (3.65±1.79 pg/mL vs. 3.15±1.78 pg/mL;
Higher serum TNF-α levels in subjects without NAFLD were associated with the development of NAFLD. The results of study might suggest a pathologic role of inflammation in NAFLD.
Citations
Sarcopenia Is an Independent Risk Factor for NAFLD in COPD: A Nationwide Survey (KNHANES 2008–2011)