Glenn T. Barnes

Insulin resistance arises from the inability of insulin to act normally in regulating nutrient metabolism in peripheral tissues. Increasing evidence from human population studies and animal research has established correlative as well as causative links between chronic inflammation and insulin resistance. However, the underlying molecular pathways are largely unknown. In this report, we show that many inflammation and macrophage-specific genes are dramatically upregulated in white adipose tissue (WAT) in mouse models of genetic and high-fat diet-induced obesity (DIO). The upregulation is progressively increased in WAT of mice with DIO and precedes a dramatic increase in circulating-insulin level. Upon treatment with rosiglitazone, an insulin-sensitizing drug, these macrophage-originated genes are downregulated. Histologically, there is evidence of significant infiltration of macrophages, but not neutrophils and lymphocytes, into WAT of obese mice, with signs of adipocyte lipolysis and formation of multinucleate giant cells. These data suggest that macrophages in WAT play an active role in morbid obesity and that macrophage-related inflammatory activities may contribute to the pathogenesis of obesity-induced insulin resistance. We propose that obesity-related insulin resistance is, at least in part, a chronic inflammatory disease initiated in adipose tissue.

Insulin resistance arises from the inability of insulin to act normally in regulating nutrient metabolism in peripheral tissues. Increasing evidence from human population studies and animal research has established correlative as well as causative links between chronic inflammation and insulin resistance. However, the underlying molecular pathways are largely unknown. In this report, we show that many inflammation and macrophage-specific genes are dramatically upregulated in white adipose tissue (WAT) in mouse models of genetic and high-fat diet-induced obesity (DIO). The upregulation is progressively increased in WAT of mice with DIO and precedes a dramatic increase in circulating-insulin level. Upon treatment with rosiglitazone, an insulin-sensitizing drug, these macrophage-originated genes are downregulated. Histologically, there is evidence of significant infiltration of macrophages, but not neutrophils and lymphocytes, into WAT of obese mice, with signs of adipocyte lipolysis and formation of multinucleate giant cells. These data suggest that macrophages in WAT play an active role in morbid obesity and that macrophage-related inflammatory activities may contribute to the pathogenesis of obesity-induced insulin resistance. We propose that obesity-related insulin resistance is, at least in part, a chronic inflammatory disease initiated in adipose tissue.

Huntington's disease (HD) is a dominant neurodegenerative disorder caused by expansion of a CAG repeat in the gene encoding huntingtin, a protein of unknown function. To distinguish between "loss of function" and "gain of function" models of HD, the murine HD homolog Hdh was inactivated by gene targeting. Mice heterozygous for Hdh inactivation were phenotypically normal, whereas homozygosity resulted in embryonic death. Homozygotes displayed abnormal gastrulation at embryonic day 7.5 and were resorbing by day 8.5. Thus, huntingtin is critical early in embryonic development, before the emergence of the nervous system. That Hdh inactivation does not mimic adult HD neuropathology suggests that the human disease involves a gain of function.

CAG repeat expansion in the Huntington's disease gene (HD) was examined in postmortem brains from 310 clinically diagnosed and 15 'at risk' individuals. Presence of an expanded CAG allele (>37 units) was the cause of the disorder in almost all cases (307 of 310). Despite a diversity of reporting clinicians, neurological and psychiatric onset and age at death all displayed significant inverse correlations with CAG number indicating that diagnosis of onset is reasonably accurate, and that most patients die from the disease and its complications. Neuronal changes before clinical onset are not detected by conventional microscopic examination as three out of 15 'at risk' brains had an expanded CAG allele but no neuropathology. The cause of HD-like neuropathology in three exceptional brains from clinically diagnosed individuals is unclear. The disorder in these cases could be an HD phenocopy or result from alternative mutational mechanisms at the HD locus.