Obesity is highly associated with insulin resistance and is the biggest risk factor for non-insulin-dependent diabetes mellitus. The molecular basis of this common syndrome, however, is poorly understood. It has been suggested that tumour necrosis factor (TNF)-alpha is a candidate mediator of insulin resistance in obesity, as it is overexpressed in the adipose tissues of rodents and humans and it blocks the action of insulin in cultured cells and whole animals. To investigate the role of TNF-alpha in obesity and insulin resistance, we have generated obese mice with a targeted null mutation in the gene encoding TNF-alpha and those encoding the two receptors for TNF-alpha. The absence of TNF-alpha resulted in significantly improved insulin sensitivity in both diet-induced obesity and that resulting for the ob/ob model of obesity. The TNFalpha-deficient obese mice had lower levels of circulating free fatty acids, and were protected from the obesity-related reduction in the insulin receptor signalling in muscle and fat tissues. These results indicate that TNF-alpha is an important mediator of insulin resistance in obesity through its effects on several important sites of insulin action.

Although tumor necrosis factor (TNF) initially came to prominence because of its anti-tumor activity, most attention is now focused on its proinflammatory actions. TNF appears to play a critical role in both early and late events involved in inflammation, from localizing the noxious agent and amplifying the cellular and mediator responses at the local site and systemically, to editing (e.g., apoptosis) injured cells or effete immune cells and repairing inflammatory damage. We have generated mice deficient in TNF (TNF ؊/؊ mice) and have begun to examine the multiple functions attributed to TNF. TNF

The two genetically established antimicrobial mechanisms of macrophages are production of reactive oxygen intermediates by phagocyte oxidase (phox) and reactive nitrogen intermediates by inducible nitric oxide synthase (NOS2). Mice doubly deficient in both enzymes (gp91(phox-/-)/NOS2(-/-)) formed massive abscesses containing commensal organisms, mostly enteric bacteria, even when reared under specific pathogen-free conditions with antibiotics. Neither parental strain showed such infections. Thus, phox and NOS2 appear to compensate for each other's deficiency in providing resistance to indigenous bacteria, and no other pathway does so fully. Macrophages from gp91(phox-/-)/NOS2(-/-) mice could not kill virulent Listeria. Their killing of S. typhimurium, E. coli, and attenuated Listeria was markedly diminished but demonstrable, establishing the existence of a mechanism of macrophage antibacterial activity independent of phox and NOS2.

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS) characterized by localized areas of demyelination. Although the etiology and pathogenesis of MS remain largely unknown, it is generally assumed that immune responses to myelin antigens contribute to the disease process. The exact sequence of events, as well as the molecular mediators that lead to myelin destruction, is yet to be defined. As a potent mediator of inflammation, the cytopathic cytokine, tumor necrosis factor (TNF) has been considered to be a strong candidate in the pathogenesis of MS and its animal model, experimental autoimmune encephalomyelitis (EAE). However, its role in immune-mediated demyelination remains to be elucidated. To determine the contribution of TNF to the pathogenesis of the MS-like disease provoked by the myelin oligodendrocyte glycoprotein (MOG), we have tested mice with an homologous disruption of the gene encoding TNF. Here we report that upon immunization with MOG, mice lacking TNF develop severe neurological impairment with high mortality and extensive inflammation and demyelination. We show further that inactivation of the TNF gene converts MOG-resistant mice to a state of high susceptibility. Furthermore, treatment with TNF dramatically reduces disease severity in both TNF-/- mice and in other TNF+/+ mice highly susceptible to the MOG-induced disease. These findings indicate that TNF is not essential for the induction and expression of inflammatory and demyelinating lesions, and that it may limit the extent and duration of severe CNS pathology.

Cytokines, in particular tumor necrosis factor-alpha (TNF-␣ ), have significant effects on energy metabolism and appetite although their mechanisms of action are largely unknown. Here, we examined whether TNF-␣ modulates the production of leptin, the recently identified fat-specific energy balance hormone, in cultured adipocytes and in mice. TNF-␣ treatment of 3T3-L1 adipocytes resulted in rapid stimulation of leptin accumulation in the media, with a maximum effect at 6 h. This stimulation was insensitive to cycloheximide, a protein synthesis inhibitor, but was completely inhibited by the secretion inhibitor brefeldin A, indicating a posttranslational effect. Treatment of mice with TNF-␣ also caused a similar increase in plasma leptin levels. Finally, in obese TNF-␣ -deficient mice, circulating leptin levels were significantly lower, whereas adipose tissue leptin was higher compared with obese wild-type animals. These data provide evidence that TNF-␣ can act directly on adipocytes to regulate the release of a preformed pool of leptin. Furthermore, they suggest that the elevated adipose tissue expression of TNF-␣ that occurs in obesity may contribute to obesity-related hyperleptinemia. (

The present study evaluated behavioral and histopathological outcome after controlled cortical impact (CCI) brain injury in mice deficient in tumor necrosis factor [TNF(؊/؊)] and their wild-type (wt) littermates. Mice were subjected to CCI brain injury [TNF(؊/؊), n ‫؍‬ 10; wt, n ‫؍‬ 10] or served as uninjured controls [TNF(؊/؊), n ‫؍‬ 10; wt, n ‫؍‬ 10] and were evaluated for deficits in memory retention at 7 days postinjury. Although both brain-injured wt and TNF(؊/؊) mice exhibited significant memory dysfunction compared to uninjured controls (P < 0.02), the deficits in memory retention in injured TNF(؊/؊) mice were significantly less severe than in injured wt mice (P < 0.02). A second group of mice was subjected to CCI brain injury [TNF(؊/؊), n ‫؍‬ 20; wt, n ‫؍‬ 20] or served as uninjured controls [TNF(؊/؊), n ‫؍‬ 15; wt, n ‫؍‬ 15] and were evaluated over a 4-week period for neurological motor function. In the acute posttraumatic period (48 h postinjury), braininjured TNF(؊/؊) mice were significantly less impaired than injured wt mice on composite neuroscore (P < 0.001), rotarod (P < 0.05), and beam balance (P < 0.02) tests. However, wt mice recovered from brain injury by 2-3 weeks postinjury, whereas TNF(؊/؊) mice continued to demonstrate persistent motor deficits up to 4 weeks postinjury. Histopathological analysis at 2 and 4 weeks postinjury revealed that brain-injured TNF(؊/؊) mice had significantly more cortical tissue loss than wt mice (P < 0.02). Our results suggest that although the presence of TNF in the acute posttraumatic period may be deleterious, this cytokine may play a role in facilitating long-term behavioral recovery and histological repair after brain injury.

Mice lacking the RelA (p65) subunit of NF-κB die between days 14 and 15 of embryogenesis because of massive liver destruction. Fibroblasts and macrophages isolated from relA −/− embryos were found to be highly sensitive to tumor necrosis factor (TNF) cytotoxicity, raising the possibility that endogenous TNF is the cause of liver cell apoptosis. To test this idea, we generated mice lacking both TNF and RelA. Embryogenesis proceeds normally in such mice, and TNF/RelA double-deficient mice are viable and have normal livers. Thus, the RelA-mediated antiapoptotic signal that protects normal cells from TNF injury in vitro can be shown to be operative in vivo .

Tumor necrosis factor-␣ (TNF-␣