Inflammatory processes play an important role in the pathogenesis of vascular diseases, and insulin-resistant diabetes mellitus type 2 represents an important risk factor for the development of atherosclerosis. To directly address the role of insulin resistance in myeloid lineage cells in the development of atherosclerosis, we have created mice with myeloid lineage-specific inactivation of the insulin receptor gene. On an ApoE-deficient background, MphIRKO mice developed smaller atherosclerotic lesions. There was a dramatic decrease in LPS-stimulated IL-6 and IL-1beta expression in the presence of macrophage autonomous insulin resistance. Consistently, while insulin-resistant IRS-2-deficient mice on an ApoE-deficient background display aggravated atherosclerosis, fetal liver cell transplantation of IRS-2(-/-) ApoE(-/-) cells ameliorated atherosclerosis in Apo-E-deficient mice. Thus, systemic versus myeloid cell-restricted insulin resistance has opposing effects on the development of atherosclerosis, providing direct evidence that myeloid lineage autonomous insulin signaling provides proinflammatory signals predisposing to the development of atherosclerosis.

Development of obesity-associated insulin resistance and diabetes mellitus type 2 has been linked to activation of proinflammatory pathways in the liver, leading to impaired insulin signal transduction. To further define the role of hepatic NF-B activation in this process, we have analyzed glucose metabolism in mice with liver-specific inactivation of the NF-B essential modulator gene (NEMO L-KO mice) exposed to a high-fat diet (HFD). These animals are protected from the development of obesity-associated insulin resistance, highlighting the importance of hepatic NF-B activation in this context. However, hepatic NEMO deficiency synergizes with HFD in the development of liver steatosis as a consequence of decreased peroxisome proliferator-activated receptor (PPAR-␣) and increased PPAR-␥ expression. Steatosis interacts with increased inflammation, causing elevated apoptosis in the livers of these mice under HFD. These changes result in liver tumorigenesis of NEMO L-KO mice under normal diet, a process that is largely aggravated when these mice are exposed to HFD. These data directly demonstrate the interaction of hepatic inflammation, dietary composition, and metabolism in the development of liver tumorigenesis.insulin sensitivity ͉ spontaneous hepatic carcinoma ͉ steatosis ͉ hepatic NEMO deficiency E xcessive weight gain is associated with a chronic inflammatory state in white adipose tissue that releases proinflammatory cytokines such as TNF and IL-6 into circulation (1). While adipocytes have also been demonstrated to exhibit increased expression of proinflammatory cytokines in obesity (1), more recent studies have revealed that increased macrophage infiltration of white adipose tissue contributes to the proinflammatory state under conditions of obesity (2). These cytokines inhibit insulin action in classical insulin target tissues such as skeletal muscle, liver, and adipose cells, thereby resulting in alterations of glucose homeostasis (3). More recently, TNFstimulated activation of the JNK and NF-B signaling pathways has been demonstrated to inhibit insulin action in a tissuespecific manner (3-5). With respect to NF-B signaling, TNF binding induces activation of the IKK-1 and -2 kinases that are released from a multiproteincomplex containing the regulatory subunit NF-B essential modulator (NEMO), thereby mediating phosphorylation and subsequent proteasomal degradation of I-Bs liberating the transcription factor NF-B.In addition to predisposing to insulin resistance and diabetes, obesity also represents a major risk factor for the development of the malignant neoplasias (4-8). It has been clearly demonstrated that metabolic syndrome is a key factor leading to sequential development of hepatic steatosis, steatohepatitis, hepatic fibrosis, cirrhosis, and finally increased frequency of hepatocellular carcinoma (HCC) (10). Thus, steatohepatitis represents a key feature of this particular tumor entity. Recent work has also demonstrated that the NF-B signaling pathway plays a crucial role in the development of malign...

The inhibitor of NF-kappaB (IkappaB) kinases (IKK1[alpha] and IKK2[beta]), the catalytic subunits of the IKK complex, phosphorylate IkappaB proteins on serine residues, targeting them for degradation and thus activating the transcription factor NF-kappaB. More recently, IKK2 has been implicated in mediation of insulin resistance caused by obesity, lipid infusion, and TNF-alpha stimulation, since salicylate and aspirin, known inhibitors of IKK activity, can reverse insulin resistance in obese mouse models. To further genetically elucidate the role of IKK2 in obesity-mediated insulin resistance, we have conditionally inactivated the mouse IKK2 gene in adult myocytes by Cre-loxP-mediated recombination in vivo. We have investigated the development of obesity-induced insulin resistance in muscle-specific IKK2 knockout mice and mice exhibiting a 50% reduction of IKK2 expression in every tissue and have found that, after gold thioglucose treatment, wild-type and mutant mice developed obesity to a similar extent. Surprisingly, no difference in obesity-induced insulin resistance was detectable, either at a physiological or at a molecular level. Moreover, impaired glucose tolerance resulting from a high-fat diet occurred to the same degree in control and IKK2 mutant mice. These data argue against a substantial role for muscular IKK2 in mediating obesity-induced insulin resistance in these models in vivo.

Figure 4. Impaired inflammatory response in insulin-resistant macrophages A) Northern blot analysis of MCP1, TNF-a, IL-1b, and IL-6 expression in IR flox/flox immortalized macrophage cell lines treated without (WT) or with HNTC-Cre (KO), which have been cultured either in the absence or presence of 10 ng/ml LPS for 24 hr.

The IGF-1 receptor (IGF-1R) is expressed on T and B lymphocytes, and the expression of the insulin- and IGF-1-signaling machinery undergoes defined changes throughout lineage differentiation, offering a putative role for IGF-1 in the regulation of immune responses. To study the role of the IGF-1R in lymphocyte differentiation and function in vivo, we have reconstituted immunodeficient RAG2-deficient mice with IGF-1R−/− fetal liver cells. Despite the absence of IGF-1Rs, the development and ex vivo activation of B and T lymphocytes were unaltered in these chimeric mice. By contrast, the humoral immune response to the T cell-independent type 2 Ag 4-hydroxy-3-nitrophenyl acetyl-Ficoll was significantly reduced in mice reconstituted with IGF-1R-deficient fetal liver cells, whereas responses to the T cell-dependent Ag 4-hydroxy-3-nitrophenyl acetyl-chicken globulin were normal. Moreover, in an in vitro model of T cell-independent type 2 responses, IGF-1 promoted Ig production potently upon polyvalent membrane-IgD cross-linking. These data indicate that functional IGF-1R signaling is required for T cell-independent B cell responses in vivo, defining a novel regulatory mechanism for the immune response against bacterial polysaccharides.