Faculty Bibliography

Insulin resistance plays a primary role in the development of type 2 diabetes and may be related to alterations in fat metabolism. Recent studies have suggested that local accumulation of fat metabolites inside skeletal muscle may activate a serine kinase cascade involving protein kinase C-theta (PKC-theta), leading to defects in insulin signaling and glucose transport in skeletal muscle. To test this hypothesis, we examined whether mice with inactivation of PKC-theta are protected from fat-induced insulin resistance in skeletal muscle. Skeletal muscle and hepatic insulin action as assessed during hyperinsulinemic-euglycemic clamps did not differ between WT and PKC-theta KO mice following saline infusion. A 5-hour lipid infusion decreased insulin-stimulated skeletal muscle glucose uptake in the WT mice that was associated with 40-50% decreases in insulin-stimulated tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1) and IRS-1-associated PI3K activity. In contrast, PKC-theta inactivation prevented fat-induced defects in insulin signaling and glucose transport in skeletal muscle. In conclusion, our findings demonstrate that PKC-theta is a crucial component mediating fat-induced insulin resistance in skeletal muscle and suggest that PKC-theta is a potential therapeutic target for the treatment of type 2 diabetes

The serine/threonine-specific protein kinase C (PKC)-theta is predominantly expressed in T cells and localizes to the center of the immunological synapse upon T cell receptor (TCR) and CD28 signaling. T cells deficient in PKC-theta exhibit reduced interleukin (IL)-2 production and proliferative responses in vitro, however, its significance in vivo remains unclear. We found that pkc-theta(-/-) mice were protected from pulmonary allergic hypersensitivity responses such as airway hyperresponsiveness, eosinophilia, and immunoglobulin E production to inhaled allergen. Furthermore, T helper (Th)2 cell immune responses against Nippostrongylus brasiliensis were severely impaired in pkc-theta(-/-) mice. In striking contrast, pkc-theta(-/-) mice on both the C57BL/6 background and the normally susceptible BALB/c background mounted protective Th1 immune responses and were resistant against infection with Leishmania major. Using in vitro TCR transgenic T cell-dendritic cell coculture systems and antigen concentration-dependent Th polarization, PKC-theta-deficient T cells were found to differentiate into Th1 cells after activation with high concentrations of specific peptide, but to have compromised Th2 development at low antigen concentration. The addition of IL-2 partially reconstituted Th2 development in pkc-theta(-/-) T cells, consistent with an important role for this cytokine in Th2 polarization. Taken together, our results reveal a central role for PKC-theta signaling during Th2 responses

Intestinal intraepithelial T lymphocytes (IELs) are likely to play a key role in host mucosal immunity and, unlike other T cells, have been proposed to differentiate from local precursors rather than from thymocytes. We show here that IELs expressing the alphabeta T cell receptor are derived from precursors that express RORgammat, an orphan nuclear hormone receptor detected only in immature CD4+CD8+ thymocytes, fetal lymphoid tissue-inducer (LTi) cells, and LTi-like cells in cryptopatches within the adult intestinal lamina propria. Using cell fate mapping, we found that all intestinal alphabeta T cells are progeny of CD4+CD8+ thymocytes, indicating that the adult intestine is not a significant site for alphabeta T cell development. Our results suggest that intestinal RORgammat+ cells are local organizers of mucosal lymphoid tissue

Runx family proteins have the potential for either activating or suppressing gene expression in a context-dependent manner. There are several mechanisms by which transcriptional repression can occur. A wide range of locus inactivation, that is often called gene silencing, is thought to be achieved by chromatin modifications. Recently, Runx family proteins were found to have an essential role in either temporal transcriptional repression or irreversible epigenetic silencing at the CD4 locus through binding to a CD4 silencer at different stages of development. These findings link Runx function to epigenetic gene regulation, and shed new light on the mechanisms by which Runx represses target gene expression

In this study, we analyzed the phenotypic and physiological consequences of the interaction of plasmacytoid dendritic cells (pDCs) with human immunodeficiency virus type 1 (HIV-1). pDCs are one cellular target of HIV-1 and respond to the virus by producing alpha/beta interferon (IFN-alpha/beta) and chemokines. The outcome of this interaction, notably on the function of bystander myeloid DC (CD11c+ DCs), remains unclear. We therefore evaluated the effects of HIV-1 exposure on these two DC subsets under various conditions. Blood-purified pDCs and CD11c+ DCs were exposed in vitro to HIV-1, after which maturation markers, cytokine production, migratory capacity, and CD4 T-cell stimulatory capacity were analyzed. pDCs exposed to different strains of infectious or even chemically inactivated, nonreplicating HIV-1 strongly upregulated the expression of maturation markers, such as CD83 and functional CCR7, analogous to exposure to R-848, a synthetic agonist of toll-like receptor-7 and -8. In addition, HIV-1-activated pDCs produced cytokines (IFN-alpha and tumor necrosis factor alpha), migrated in response to CCL19 and, in coculture, matured CD11c+ DCs, which are not directly activated by HIV. pDCs also acquired the ability to stimulate naive CD4+ T cells, albeit less efficiently than CD11c+ DCs. This HIV-1-induced maturation of both DC subsets may explain their disappearance from the blood of patients with high viral loads and may have important consequences on HIV-1 cellular transmission and HIV-1-specific T-cell responses

Memory T cells are long-lived antigen-experienced T cells that are generally accepted to be direct descendants of proliferating primary effector cells. However, the factors that permit selective survival of these T cells are not well established. We show that homodimeric alpha chains of the CD8 molecule (CD8alphaalpha) are transiently induced on a selected subset of CD8alphabeta+ T cells upon antigenic stimulation. These CD8alphaalpha molecules promote the survival and differentiation of activated lymphocytes into memory CD8 T cells. Thus, memory precursors can be identified among primary effector cells and are selected for survival and differentiation by CD8alphaalpha

Understanding the pathways that signal T cell tolerance versus activation is key to regulating immunity. Previous studies have linked CD28 and protein kinase C-theta (PKCtheta) as a potential signaling pathway that influences T cell activation. Therefore, we have compared the responses of T cells deficient for CD28 and PKCtheta in vivo and in vitro. Here, we demonstrate that the absence of PKCtheta leads to the induction of T cell anergy, with a phenotype that is comparable to the absence of CD28. Further experiments examined whether PKCtheta triggered other CD28-dependent responses. Our data show that CD4 T cell-B cell cooperation is dependent on CD28 but not PKCtheta, whereas CD28 costimulatory signals that augment proliferation can be uncoupled from signals that regulate anergy. Therefore, PKCtheta relays a defined subset of CD28 signals during T cell activation and is critical for the induction of activation versus tolerance in vivo

Lymphoid tissue inducer (LTi) cells are associated with early development of lymph nodes and Peyer's patches. We show here that during fetal life the nuclear hormone receptor RORgamma(t) is expressed exclusively in and is required for the generation of LTi cells. RORgamma(t+) LTi cells provide essential factors, among which lymphotoxin-alpha1beta2 is necessary but not sufficient for activation of the mesenchyma in lymph node and Peyer's patch anlagen. This early LTi cell-mediated activation of lymph node and Peyer's patch mesenchyma forms the necessary platform for the subsequent development of mature lymphoid tissues