Commentary
Abstract
Anorexia is one of several abnormalities characterizing chronic kidney disease (CKD) that cause cachexia, the loss of muscle and adipose stores. It has been attributed to mechanisms ranging from accumulation of toxic “middle molecules” to psychological problems. In this issue of the JCI, Cheung and coworkers used elegant techniques to demonstrate that CKD-associated anorexia is caused by defective hypothalamic regulation of appetite. They attributed the defect to an alteration in the hypothalamus’s response to leptin and inflammation. Since similar hypothalamic defects suppress appetite in inflammatory states and in cancer, it is possible that anorexia in several cachexia-inducing conditions results from a common set of hypothalamic abnormalities. The development of small molecules capable of preventing these regulatory abnormalities holds the promise of eliminating the contribution of anorexia to the development of cachexia.
Authors
William E. Mitch
Abstract
An emerging body of evidence implicates peripheral and central endocannabinoid pathways in the regulation of feeding behavior and body weight. A report in this issue of the JCI demonstrates the presence of a common endocannabinoid-regulated molecular pathway for peripheral lipogenic and central appetitive regulation. This pathway involves the activation of the transcription factor SREBP-1c and its associated enzymes, acetyl-CoA carboxylase-1 and fatty acid synthase, in the liver and hypothalamus. Activation of cannabinoid receptor 1 (CB1) in liver plays a key role in increased serum lipid production, fatty liver, and possibly diet-induced obesity. Conversely, stimulation of these receptors in the hypothalamus may lead to an increase in food consumption. Thus, targeting both of these pathways with CB1 antagonists could promote sustained weight loss and favorable serum lipid profiles in obese patients.
Authors
Aron H. Lichtman, Benjamin F. Cravatt
Abstract
Angiogenesis may be an important factor in the development of fibrotic lung disease. Prior studies have strongly suggested a role for angiogenic vascular remodeling in pulmonary fibrosis, and emerging evidence indicates that new vessel formation is critical in airway fibrosis. Bronchiolitis obliterans syndrome is a fibrotic occlusion of distal airways that is largely responsible for the morbidity and mortality of patients after lung transplantation. In this issue, Belperio et al. demonstrate a role for CXC chemokine receptor 2 in the regulation of angiogenesis-mediated airway fibroproliferation. By integrating an understanding of neovascularization into the study of events that occur between inflammation and fibrosis, it becomes increasingly possible to rationally design therapies that can halt conditions of maladaptive fibrosis.
Authors
Ivor S. Douglas, Mark R. Nicolls
Abstract
The inability of insulin to suppress hepatic glucose production (HGP) is a key defect found in type 2 diabetes. Insulin inhibits HGP through both direct and indirect means, the latter of which include inhibition of glucagon secretion, reduction in plasma nonesterified fatty acid level, decrease in the load of gluconeogenic substrates reaching the liver, and change in neural signaling to the liver. Two studies in this issue of the JCI demonstrate that selective changes in the expression of insulin receptors in mouse liver do not have a detectable effect on the ability of insulin to inhibit HGP (see the related articles beginning on pages 1306 and 1314). These provocative data suggest that the indirect effects of insulin on the liver are the primary determinant of HGP in mice.
Authors
Alan D. Cherrington
Abstract
Nonalcoholic fatty liver disease (NAFLD) is a component of the metabolic syndrome, with a clinical spectrum ranging from simple fatty liver to steatohepatitis, cirrhosis, and hepatocellular carcinoma. The primary event of NAFLD is the accumulation of triacylglycerols (TAGs) in hepatocytes. In this issue of the JCI, Donnelly et al. report on their use of stable isotope methodology to show that fatty acids stored in adipose tissue and fatty acids newly made within the liver through de novo lipogenesis are the major sources of TAGs in the liver and are secreted as lipoproteins in NAFLD.
Authors
Shinji Tamura, Iichiro Shimomura
Abstract
Infantile cortical hyperostosis (also known as Caffey disease) is characterized by hyperirritability, acute inflammation of soft tissues, and profound alterations of the shape and structure of the underlying bones, particularly the long bones, mandible, clavicles, or ribs. In this issue of the JCI, Gensure et al. undertook fine mapping of the genetic locus for this disease in a large kindred of individuals with the autosomal dominant form of the condition. The authors found a novel missense mutation in COL1A1, the gene encoding the α1 chain of type I collagen, in all affected individuals in 3 discrete pedigrees. This is a surprising finding, as all other reported mutations affecting the synthesis of type I collagen lead to conditions such as osteogenesis imperfecta and Ehlers-Danlos syndrome, in which quantitative or qualitative defects in type I collagen synthesis give rise to bone fragility and/or connective tissue hyperextensibility. The deleterious effect of the mutation on collagen fibril morphology is demonstrated; however, the precise functional link between the reported missense mutation and the localized inflammation and hyperostosis seen in Caffey disease awaits future studies.
Authors
Francis H. Glorieux
Abstract
Almost a quarter of a century ago, Oldstone and colleagues proposed that infection of cells by noncytopathic viruses may lead to an alteration of the cells’ ability to produce certain products or perform certain tasks, i.e., inhibition of “luxury function.” In this issue of the JCI, this topic has been revisited by Yamano et al., who demonstrate that human T cell lymphotropic virus type I (HTLV-I) infection of CD4+CD25+ Tregs in patients with HTLV-I–associated myelopathy/tropical spastic paraparesis (HAM/TSP) results in a decrease in FOXP3 mRNA and protein expression. This leads to the inability of HTLV-I–infected CD4+CD25+ Tregs to inhibit the proliferation of CD4+CD25− Tregs, due to the effect of the HTLV-I tax gene. Defects in the Treg population could be responsible for the large numbers of virus-specific T cells and occurrence of lymphoproliferation and inflammatory autoimmune disease in HAM/TSP patients.
Authors
Robert S. Fujinami
Abstract
T and NK cells collaborate to control viral infections, discerning minute differences between infected and uninfected cells. At the same time, viruses have evolved to escape this discovery. In this issue of the JCI, Ganem and colleagues show that Kaposi sarcoma–associated herpesvirus (KSHV) inhibits CD1d presentation to T cells. This novel immune evasion strategy highlights the importance of CD1d-restricted T cells in controlling viral infection and raises an interesting question: how do T cells recognize viruses in the context of CD1 molecules that bind lipids? In the case of herpesviruses, alterations in endosomal trafficking might trigger redistribution of CD1/lipid complexes to cell surfaces, thereby promoting recognition by CD1d-restricted T cells.
Authors
Nagendra R. Hegde, David C. Johnson
Abstract
Knowledge of the pathophysiology of immunobullous diseases has been advanced by the demonstration that passive transfer of antibodies against skin autoantigens can induce blisters in experimental animals with clinical, histologic, and immunopathologic features similar to those seen in human patients. In this issue of the JCI, Liu et al. extend their earlier observations regarding an experimental murine model of bullous pemphigoid by showing that the plasminogen/plasmin signaling cascade synergizes with MMP-9 during the early phase of antibody-induced blister formation in vivo. In a separate study, Sitaru et al. show for the first time to my knowledge that passive transfer of experimental antibodies against type VII collagen create subepidermal blisters in mice that mimic those seen in patients with epidermolysis bullosa acquisita (see the related article beginning on page 870). While the articles by Liu, Sitaru, and their colleagues identify pathways of inflammation and tissue injury that, if interrupted, may abrogate blister formation, in a third study, Payne et al. utilized phage display technologies to isolate human anti-desmoglein monoclonal antibodies from a patient with pemphigus vulgaris and show that such antibodies have restricted patterns of heavy and light chain gene usage — findings suggesting that autoantibodies may represent an additional target for therapeutic interventions in patients with immunobullous diseases (see the related article beginning on page 888).
Authors
Kim B. Yancey
Abstract
Every cell in the body expresses a set of proteins designed to trigger permeabilization of the mitochondria and cell death. Inactivation or inappropriate triggering of these pathways is increasingly recognized as a contributor to human disease. A study in this issue of the JCI demonstrates that IL-6 exerts its protective effect against the development of lung injury following exposure of mice to 95% O2 by increasing the expression of a Bcl-2–related protein, A1. This protein acts to prevent mitochondrial membrane permeabilization and cell death following exposure to hyperoxia. The data in this study lend support to the hypothesis that inappropriate triggering of cell-death pathways may contribute to the development of hyperoxic pulmonary edema, lung injury, and respiratory failure.
Authors
G.R. Scott Budinger, Jacob I. Sznajder
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