The transcription factor Myc controls metabolic reprogramming upon T lymphocyte activation.

To fulfill the bioenergetic and biosynthetic demand of proliferation, T cells reprogram their metabolic pathways from fatty acid ß-oxidation and pyruvate oxidation via the TCA cycle to the glycolytic, pentose-phosphate, and glutaminolytic pathways. Two of the top-ranked candidate transcription factors potentially responsible for the activation-induced T cell metabolic transcriptome, HIF1α and Myc, were induced upon T cell activation, but only the acute deletion of Myc markedly inhibited activation-induced glycolysis and glutaminolysis in T cells. Glutamine deprivation compromised activation-induced T cell growth and proliferation, and this was partially replaced by nucleotides and polyamines, implicating glutamine as an important source for biosynthetic precursors in active T cells. Metabolic tracer analysis revealed a Myc-dependent metabolic pathway linking glutaminolysis to the biosynthesis of polyamines. Therefore, a Myc-dependent global metabolic transcriptome drives metabolic reprogramming in activated, primary T lymphocytes. This may represent a general mechanism for metabolic reprogramming under patho-physiological conditions.

A unified model of mammalian BCL-2 protein family interactions at the mitochondria.

During apoptosis, the BCL-2 protein family controls mitochondrial outer membrane permeabilization (MOMP), but the dynamics of this regulation remain controversial. We employed chimeric proteins composed of exogenous BH3 domains inserted into a tBID backbone that can activate the proapoptotic effectors BAX and BAK to permeabilize membranes without being universally sequestered by all antiapoptotic BCL-2 proteins. We thus identified two "modes" whereby prosurvival BCL-2 proteins can block MOMP, by sequestering direct-activator BH3-only proteins ("MODE 1") or by binding active BAX and BAK ("MODE 2"). Notably, we found that MODE 1 sequestration is less efficient and more easily derepressed to promote MOMP than MODE 2. Further, MODE 2 sequestration prevents mitochondrial fusion. We provide a unified model of BCL-2 family function that helps to explain otherwise paradoxical observations relating to MOMP, apoptosis, and mitochondrial dynamics.

Catalytic activity of the caspase-8-FLIP(L) complex inhibits RIPK3-dependent necrosis.

Caspase-8 has two opposing biological functions--it promotes cell death by triggering the extrinsic pathway of apoptosis, but also has a survival activity, as it is required for embryonic development, T-lymphocyte activation, and resistance to necrosis induced by tumour necrosis factor-α (TNF-α) and related family ligands. Here we show that development of caspase-8-deficient mice is completely rescued by ablation of receptor interacting protein kinase-3 (RIPK3). Adult animals lacking both caspase-8 and RIPK3 display a progressive lymphoaccumulative disease resembling that seen with defects in CD95 or CD95-ligand (also known as FAS and FASLG, respectively), and resist the lethal effects of CD95 ligation in vivo. We have found that caspase-8 prevents RIPK3-dependent necrosis without inducing apoptosis by functioning in a proteolytically active complex with FLICE-like inhibitory protein long (FLIP(L), also known as CFLAR), and this complex is required for the protective function.

Transduced monocyte/macrophages targeted to murine skin by UV light.

We have selectively targeted monocyte/macrophages overexpressing an immunomodulatory molecule, latency-associated peptide (LAP), a naturally occurring antagonist for transforming growth factor-beta1, to murine skin utilizing UV light to produce a cutaneous influx of transduced monocyte/macrophages. Bone marrow (BM) cells from BALB/c mice were transduced in vitro with a retroviral construct containing green fluorescent protein (GFP) for detection and human LAP (hLAP) as a test molecule. The transduced BM cells were then cultured in vitro with granulocyte-macrophage colony-stimulating factor (GM-CSF) to produce differentiation to monocyte/macrophages. More than 80% of transduced BM cells were CD11b-positive and MOMA-positive by fluorescence-activated cell-sorter analysis and secreted LAP by ELISA after 10 days of culture in granulocyte-macrophage colony-stimulating factor (GM-CSF). Transduced monocyte/macrophages containing either GFP or hLAP-GFP were then injected intravenously into BALB/c mice. One-half of recipients in each group were exposed to UVB (72 mJ) to induce monocyte/macrophage infiltration into skin. Recipients were sacrificed 60 h after UV irradiation. We found transduced cutaneous macrophages expressing GFP by examining with fluorescence microscopy frozen skin sections of recipient mice immunostained with antibodies to GFP and to macrophage marker F4/80. We identified hLAP sequences by polymerase chain reaction (PCR) of total DNA in recipient blood and UV-irradiated skin but not in unirradiated skin. LAP sequences were also detected at much lower levels in other organs (lung, spleen, and liver) by PCR. Therefore, we have shown that genetically altered monocytic cells can be injected intravenously and targeted to mouse skin by UV exposure. This macrophage-based gene-transfer method may be a potentially useful immunotherapeutic approach for delivering monocyte/macrophage-derived products to skin.

Latency-associated peptide prevents skin fibrosis in murine sclerodermatous graft-versus-host disease, a model for human scleroderma.

Murine sclerodermatous graft-versus-host disease (Scl GVHD), produced by transplanting B10.D2 bone marrow and spleen cells to lethally irradiated BALB/cJ mice, is a model for human scleroderma. Mice with Scl GVHD have skin thickening, lung fibrosis, cutaneous mononuclear cell infiltration, and upregulation of cutaneous transforming growth factor beta1 (TGF-beta1) and type I collagen mRNAs by day 21 after bone marrow transplantation. Elevated TGF-beta1 appears to be the critical cytokine driving fibrosis in Scl GVHD, which can be prevented with antibodies to TGF-beta administered early in disease. Here we demonstrate that we can also prevent skin thickening in mice with Scl GVHD with a naturally occurring antagonist to TGF-beta1, human latency-associated peptide (LAP). By quantitative real-time PCR analysis and immunostaining, LAP treatment also abrogates the upregulation of cutaneous TGF-beta1 and connective tissue growth factor mRNAs and type I collagen synthesis in Scl GVHD. In contrast to anti-TGF-beta antibodies, LAP at 4 ng total per mouse has no significant suppressive effect on cutaneous influx of T cells and monocytes or immune cell activation. LAP may be a potential new therapy in scleroderma and other TGF-beta-driven fibrosing disease that targets TGF-beta more specifically, without affecting systemic critical roles of TGF-beta on immune cell function.

Murine sclerodermatous graft-versus-host disease, a model for human scleroderma: cutaneous cytokines, chemokines, and immune cell activation.

Murine sclerodermatous graft-vs-host disease (Scl GVHD) models human scleroderma, with prominent skin thickening, lung fibrosis, and up-regulation of cutaneous collagen mRNA. Fibrosis in Scl GVHD may be driven by infiltrating TGF-beta1-producing mononuclear cells. Here we characterize the origin and types of those cutaneous effector cells, the cytokine and chemokine environments, and the effects of anti-TGF-beta Ab on skin fibrosis, immune cell activation markers, and collagen and cytokine synthesis. Donor cells infiltrating skin in Scl GVHD increase significantly at early time points post-transplantation and are detectable by PCR analysis of Y-chromosome sequences when female mice are transplanted with male cells. Cutaneous monocyte/macrophages and T cells are the most numerous cells in Scl GVHD compared with syngeneic controls. These immune cells up-regulate activation markers (MHC class II I-A(d) molecules and class A scavenger receptors), suggesting Ag presentation by cutaneous macrophages in early fibrosing disease. Early elevated cutaneous mRNA expression of TGF-beta1, but not TGF-beta2 or TGF-beta3, and elevated C-C chemokines macrophage chemoattractant protein-1, macrophage inflammatory protein-1alpha, and RANTES precede subsequent skin and lung fibrosis. Therefore, TGF-beta1-producing donor mononuclear cells may be critical effector cells, and C-C chemokines may play important roles in the initiation of Scl GVHD. Abs to TGF-beta prevent Scl GVHD by effectively blocking the influx of monocyte/macrophages and T cells into skin and by abrogating up-regulation of TGF-beta1, thereby preventing new collagen synthesis. The Scl GVHD model is valuable for testing new interventions in early fibrosing diseases, and chemokines may be new potential targets in scleroderma.