The phosphatidylinositol 3-kinase (PI3K) pathway has been shown to play a central role in regulating the host inflammatory response. Recent studies characterizing the downstream effector molecules within the PI3K pathway have identified that the serine/threonine kinase, glycogen synthase kinase 3 (GSK3), plays a pivotal role in regulating the production of pro-and antiinflammatory cytokines. In innate immune cells, GSK3 inactivation augments anti-inflammatory cytokine production while concurrently suppressing the production of pro-inflammatory cytokines. The role of GSK3 in T cell biology has also been studied in detail and is involved in regulating multiple downstream signaling processes mediated by the T cell receptor (TCR), the costimulatory molecule CD28, and the IL-17 receptor. In vivo studies assessing the therapeutic properties of GSK3 inhibitors have shown that the inactivation of GSK3 can protect the host from immune-mediated pathology and death. This review will highlight the immunological importance GSK3 plays within different signal transduction pathways of the immune system, the cellular mechanisms regulating the activity of GSK3, the role of GSK3 in innate and adaptive immune responses, and the in vivo use of GSK3 inhibitors to treat inflammatory mediated diseases in animals.

Toll-like receptors play a critical role in innate immunity by detecting invading pathogens. The ability of TLRs to engage different intracellular signaling molecules and cross talk with other regulatory pathways are important factors in shaping the type, magnitude, and duration of the inflammatory response. The present review will cover the fundamental signaling pathways utilized by TLRs and how these pathways regulate the innate immune response to pathogens.

Activation of the PI3K pathway plays a pivotal role in regulating the inflammatory response. The loss of mTORC2 has been shown to abrogate the activation of Akt, a critical downstream component of PI3K signaling. However, the biological importance of mTORC2 in innate immunity is currently unknown. Here we demonstrate that rictor, a key component of mTORC2, plays a critical role in controlling the innate inflammatory response via its ability to regulate FoxO1. Upon LPS stimulation, both rictor-deficient mouse embryonic fibroblasts (MEFs) and rictor knockdown dendritic cells exhibited a hyperinflammatory phenotype. The hyperinflammatory phenotype was due to a defective Akt signaling axis, because both rictor-deficient MEFs and rictor knockdown dendritic cells exhibited attenuated Akt phosphorylation and kinase activity. Analysis of downstream Akt targets revealed that phosphorylation of FoxO1 was impaired in rictor-deficient cells, resulting in elevated nuclear FoxO1 levels and diminished nuclear export of FoxO1 upon LPS stimulation. Knockdown of FoxO1 attenuated the hyperinflammatory phenotype exhibited by rictor-deficient MEFs. Moreover, FoxO1 deletion in dendritic cells attenuated the capacity of LPS to induce inflammatory cytokine expression. These findings identify a novel signaling pathway by which mTORC2 regulates the TLR-mediated inflammatory response through its ability to regulate FoxO1.PI3K is a heterodimeric enzyme that consists of a regulatory (p85) and a catalytic (p110) subunit (1). PI3K has the ability to phosphorylate both lipids and proteins. The activation of PI3K drives the generation of phosphatidylinositol 3,4,5-trisphosphate. A major downstream target of PI3K is the AGC family member and kinase Akt (Protein Kinase B). Upon the generation of phosphatidylinositol 3,4,5-trisphosphate, Akt is recruited to the plasma membrane through its pleckstrin homology domain. Sequential phosphorylation of Akt on both serine 473 and threonine 308 are required for full activation. Phosphorylation of Akt on threonine 308 is mediated by PDK1 (2, 3). Several kinases including DNA-activated Protein Kinase, integrin-linked kinase, and PKC-␤ have been proposed to be involved in the phosphorylation of Akt on serine 473 (4 -6). Studies utilizing cells deficient in rictor, a component of the mammalian target of rapamycin complex 2 (mTORC2), 4 have shown that mTORC2 is the primary kinase involved in phosphorylation of serine 473 on Akt. Upon insulin or serum stimulation, rictor-deficient MEFs displayed defective Akt Ser-473 phosphorylation compared with wild type cells (7-9).mTOR can be present in two distinct complexes, mTORC1 and mTORC2 (8, 10). The mTORC1 complex consists of mTOR, raptor, mLST8, and Deptor, which is a negative regulator mTOR (11-13). mTORC1 is the target of the immunosuppressant macrolide drug rapamycin and functions in a wide variety of cellular processes including cell growth via its phosphorylation of two downstream targets, S6 kinase 1, and eIF-4E-binding protein (14). mTORC1 has been shown to p...

AMP-activated protein kinase, AMPK, is a conserved serine/threonine kinase with a critical function in the regulation of metabolic pathways in eukaryotic cells. Recently, AMPK has been shown to play an additional role as a regulator of inflammatory activity in leukocytes. Treatment of macrophages with chemical AMPK activators, or forced expression of a constitutively active form of AMPK, results in polarization to an antiinflammatory phenotype. Additionally, we reported previously that stimulation of macrophages with antiinflammatory cytokines such as IL-10, IL-4 and TGF-β results in rapid activation of AMPK, suggesting that AMPK contributes to the suppressive function of these cytokines. In the current study we investigated the role of AMPK in IL-10-induced gene expression and antiinflammatory function. IL-10-stimulated wild-type macrophages displayed rapid activation of PI3K and its downstream targets Akt and mTORC1, an effect that was not seen in macrophages generated from AMPKα1-deficient mice. AMPK activation was not impacted by treatment with either the PI3K inhibitor LY294002 or the JAK inhibitor CP-690550, suggesting that IL-10-mediated activation of AMPK is independent of PI3K and JAK activity. IL-10 induced phosphorylation of both Tyr705 and Ser727 residues of STAT3 in an AMPKα1-dependent manner, and these phosphorylation events were blocked by inhibition of CaMKKβ, an upstream activator of AMPK, and by the mTORC1 inhibitor rapamycin, respectively. The impaired STAT3 phosphorylation in response to IL-10 observed in AMPKα1-deficient macrophages was accompanied by reduced SOCS3 expression and an inadequacy of IL-10 to suppress LPS-induced proinflammatory cytokine production. Overall, our data demonstrate that AMPKα1 is required for IL-10 activation of the PI3K/Akt/mTORC1 and STAT3-mediated antiinflammatory pathways regulating macrophage functional polarization.

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