Insulin activation of the phosphatidylinositol 3-kinase/protein kinase B (Akt) pathway reduces lipopolysaccharide-induced inflammation in mice.

Insulin is used to control pro-inflammatory hyperglycemia in critically ill patients. However, recent studies suggest that insulin-induced hypoglycemia may negate its beneficial effects in these patients. It is noteworthy that recent evidence indicates that insulin has anti-inflammatory effects that are independent of controlling hyperglycemia. To date, the mechanism by which insulin directly reduces inflammation has not been elucidated. It is well established that insulin activates phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling in many cell types. We and others have shown that this pathway negatively regulates LPS-induced signaling and pro-inflammatory cytokine production in monocytic cells. We hypothesized that insulin inhibits inflammation during endotoxemia by activation of the PI3K/Akt pathway. We used a nonhyperglycemic mouse model of endotoxemia to determine the effect of continuous administration of a low dose of human insulin on inflammation and survival. It is noteworthy that insulin treatment induced phosphorylation of Akt in muscle and adipose tissues but did not exacerbate lipopolysaccharide (LPS)-induced hypoglycemia. Insulin decreased plasma levels of interleukin-6, tumor necrosis factor-alpha, monocyte chemotactic protein 1 (MCP1)/JE, and keratinocyte chemoattractant, and decreased mortality. The PI3K inhibitor wortmannin abolished the insulin-mediated activation of Akt and the reduction of chemokine and interleukin-6 levels. We conclude that insulin reduces LPS-induced inflammation in mice in a PI3K/Akt-dependent manner without affecting blood glucose levels.

TLR2 is constitutively expressed within the kidney and participates in ischemic renal injury through both MyD88-dependent and -independent pathways.

TLRs are an evolutionarily conserved family of cell membrane proteins believed to play a significant role in innate immunity and the response to tissue injury, including that induced by ischemia. TLR signaling pathways activate transcription factors that regulate expression of prosurvival proteins, as well as proinflammatory cytokines and chemokines through one of two proximal adapter proteins, MyD88 or Toll/IL-1R domain-containing adaptor-inducing IFN-beta (Trif). Our study defines the constitutive protein expression of TLR2 in kidneys of humans and mice, and provides insight into the signaling mechanisms by which a deficiency of TLR2 protects from ischemic organ injury. Our study compared and contrasted the effects of renal ischemia in wild-type mice and mice deficient in TLR2, MyD88, Trif, and MyD88xTrif. TLR2 protein was evident in many cell types in the kidney, including renal tubules of the outer stripe of the medulla, glomeruli, and in the renal vasculature. The pattern of protein expression was similar in humans and mice. The absence of TLR2, MyD88, and MyD88xTrif conferred both physiologic and histologic protection against sublethal ischemia at 24 h. Interestingly, TLR2-deficient mice were better protected from ischemic renal injury than those deficient for the adapter protein MyD88, raising the intriguing possibility that TLR-2-dependent/MyD88-independent pathways also contribute to kidney injury. We conclude that TLR2 protein is constitutively expressed in the kidney and plays an important role in the pathogenesis of acute ischemic injury by signaling both MyD88-dependent and MyD88-independent pathways.

Repeated stress in young and old 5-HT(2C) receptor knockout mice.

Serotonin (5-HT)(2C) receptor null mutant (knockout, KO) mice develop hyperphagia and midlife obesity. Based upon previous observations indicating altered responsiveness to stressful environmental conditions in these mice, we hypothesized that this KO mouse was hyperresponsive to repeated stress. To test this, we examined the effect of two intensities of repeated stress on food intake and body weight in 5-HT(2C) receptor KO and wild-type (WT) mice. The stressors involved daily cage change (including handling) for 3 days then daily restraint for 4 days. On the final day, mice were immediately decapitated after restraint to assess levels of plasma hormones. Two ages were used: young (12 weeks) and old (32-34 weeks). Basally, young KO were prehyperphagic and weighed the same as WT. In the old mice, KO were frankly hyperphagic and heavier than WT. In response to repeated cage change alone, the genotype-specific difference in food intake in the young group was enhanced, whereas in the old group it was diminished. This stressor did not significantly affect body weight change or caloric efficiency with respect to age or genotype. Repeated restraint had little effect on the young mice. However, in the old mice, KO had decreases in relative body weight and caloric efficiency compared with WT. In the old KO mice, adrenocorticotrophic hormone (ACTH), corticosterone and insulin were increased compared with WT mice. Together, these findings indicate that 5-HT(2C) receptor KO mice are hyperresponsive to repeated stress and this effect is influenced by stressor intensity and initial metabolic state of the mouse.

Compulsive behavior in the 5-HT2C receptor knockout mouse.

The efficacy of serotonergic pharmacotherapy indicates that serotonin (5-HT) plays a role in the treatment, if not the etiology, of obsessive-compulsive disorder (OCD). While some clinical evidence implicates 5-HT(2C) receptors in this disorder, a definitive function has yet to be validated. We hypothesized that 5-HT(2C) receptor knockout (KO) mice may display compulsive-like behavior. This paper describes characterization of several distinct, highly organized behaviors in mice lacking functional 5-HT(2C) receptors, which supports a compulsive-like syndrome.Compulsive-like behavior was assessed in male 5-HT(2C) receptor KO and wildtype (WT) mice. Chewing of non-nutritive clay, chewing patterns on plastic-mesh screens, and the frequency of head dipping were measured. 5-HT(2C) receptor KO mice chewed more clay, produced a distinct pattern of "neat" chewing of plastic screens and exhibited reduced habituation of head dipping activity compared to WT mice. We conclude that the 5-HT(2C) receptor null mutant mouse provides a promising model of compulsive behavior and a means to further explore the role of 5-HT in OCD.