Felix Meissner

Inflammasome activation in NADPH oxidase defective mononuclear phagocytes from patients with chronic granulomatous disease

Chronic granulomatous disease (CGD) is an inherited disorder characterized by recurrent infections and deregulated inflammatory responses. CGD is caused by mutations in subunits of the NADPH oxidase, an enzyme that generates reactive oxygen species in phagocytes. To elucidate the contribution of the proinflammatory protease caspase-1 to aberrant inflammatory reactions in CGD, we analyzed cells isolated from patients with defects in the phagocyte oxidase subunits p22phox, p47phox or gp91phox. We report that mononuclear phagocytes from CGD patients activated caspase-1 and produced biologically active interleukin-1beta (IL-1beta) in response to danger signals. Notably, caspase-1 activation and IL-1beta secretion from CGD monocytes was elevated in asymptomatic patients and strongly increased in patients with noninfectious inflammatory conditions. Treatment with IL-1 receptor antagonist reduced IL-1 production in monocytes ex vivo and during medical therapy. Our results identify phagocyte oxidase defective monocytes as a source of elevated IL-1 and provide a potential therapeutic option to ameliorate inflammatory conditions associated with CGD.

Mutant superoxide dismutase 1-induced IL-1β accelerates ALS pathogenesis

ALS is a fatal motor neuron disease of adult onset. Neuroinflammation contributes to ALS disease progression; however, the inflammatory trigger remains unclear. We report that ALS–linked mutant superoxide dismutase 1 (SOD1) activates caspase-1 and IL-1β in microglia. Cytoplasmic accumulation of mutant SOD1 was sensed by an ASC containing inflammasome and antagonized by autophagy, limiting caspase-1–mediated inflammation. Notably, mutant SOD1 induced IL-1β correlated with amyloid-like misfolding and was independent of dismutase activity. Deficiency in caspase-1 or IL-1β or treatment with recombinant IL-1 receptor antagonist (IL-1RA) extended the lifespan of G93A-SOD1 transgenic mice and attenuated inflammatory pathology. These findings identify microglial IL-1β as a causative event of neuroinflammation and suggest IL-1 as a potential therapeutic target in ALS.

Cytoplasmic protein aggregates interfere with nucleocytoplasmic transport of protein and RNA

Location, location, location Aggregates of certain disease-associated proteins are involved in neurodegeneration. Woerner et al. now show that the exact location of these aggregates in the cell may be the key to their pathology (see the Perspective by Da Cruz and Cleveland). An artificial aggregate-prone protein caused problems when expressed in the cytoplasm but not when expressed in the nucleus. Cytoplasmic aggregates interfered with nucleocytoplasmic import and export. Perhaps if we can shunt pathological aggregates to the nucleus in the future, we will be able to ameliorate some forms of degenerative disease. Science, this issue p. 173; see also p. 125 Protein aggregates in the cytoplasm soak up accessory factors needed for transport of other proteins and RNA across the nuclear envelope. [Also see Perspective by Da Cruz and Cleveland] Amyloid-like protein aggregation is associated with neurodegeneration and other pathologies. The nature of the toxic aggregate species and their mechanism of action remain elusive. Here, we analyzed the compartment specificity of aggregate toxicity using artificial β-sheet proteins, as well as fragments of mutant huntingtin and TAR DNA binding protein–43 (TDP-43). Aggregation in the cytoplasm interfered with nucleocytoplasmic protein and RNA transport. In contrast, the same proteins did not inhibit transport when forming inclusions in the nucleus at or around the nucleolus. Protein aggregation in the cytoplasm, but not the nucleus, caused the sequestration and mislocalization of proteins containing disordered and low-complexity sequences, including multiple factors of the nuclear import and export machinery. Thus, impairment of nucleocytoplasmic transport may contribute to the cellular pathology of various aggregate deposition diseases.

L-Arginine Modulates T Cell Metabolism and Enhances Survival and Anti-tumor Activity

Summary Metabolic activity is intimately linked to T cell fate and function. Using high-resolution mass spectrometry, we generated dynamic metabolome and proteome profiles of human primary naive T cells following activation. We discovered critical changes in the arginine metabolism that led to a drop in intracellular L-arginine concentration. Elevating L-arginine levels induced global metabolic changes including a shift from glycolysis to oxidative phosphorylation in activated T cells and promoted the generation of central memory-like cells endowed with higher survival capacity and, in a mouse model, anti-tumor activity. Proteome-wide probing of structural alterations, validated by the analysis of knockout T cell clones, identified three transcriptional regulators (BAZ1B, PSIP1, and TSN) that sensed L-arginine levels and promoted T cell survival. Thus, intracellular L-arginine concentrations directly impact the metabolic fitness and survival capacity of T cells that are crucial for anti-tumor responses.

η-Secretase processing of APP inhibits neuronal activity in the hippocampus

Alzheimer disease (AD) is characterized by the accumulation of amyloid plaques, which are predominantly composed of amyloid-β peptide. Two principal physiological pathways either prevent or promote amyloid-β generation from its precursor, β-amyloid precursor protein (APP), in a competitive manner. Although APP processing has been studied in great detail, unknown proteolytic events seem to hinder stoichiometric analyses of APP metabolism in vivo. Here we describe a new physiological APP processing pathway, which generates proteolytic fragments capable of inhibiting neuronal activity within the hippocampus. We identify higher molecular mass carboxy-terminal fragments (CTFs) of APP, termed CTF-η, in addition to the long-known CTF-α and CTF-β fragments generated by the α- and β-secretases ADAM10 (a disintegrin and metalloproteinase 10) and BACE1 (β-site APP cleaving enzyme 1), respectively. CTF-η generation is mediated in part by membrane-bound matrix metalloproteinases such as MT5-MMP, referred to as η-secretase activity. η-Secretase cleavage occurs primarily at amino acids 504–505 of APP695, releasing a truncated ectodomain. After shedding of this ectodomain, CTF-η is further processed by ADAM10 and BACE1 to release long and short Aη peptides (termed Aη-α and Aη-β). CTFs produced by η-secretase are enriched in dystrophic neurites in an AD mouse model and in human AD brains. Genetic and pharmacological inhibition of BACE1 activity results in robust accumulation of CTF-η and Aη-α. In mice treated with a potent BACE1 inhibitor, hippocampal long-term potentiation was reduced. Notably, when recombinant or synthetic Aη-α was applied on hippocampal slices ex vivo, long-term potentiation was lowered. Furthermore, in vivo single-cell two-photon calcium imaging showed that hippocampal neuronal activity was attenuated by Aη-α. These findings not only demonstrate a major functionally relevant APP processing pathway, but may also indicate potential translational relevance for therapeutic strategies targeting APP processing.

Direct proteomic quantification of the secretome of activated immune cells

Tracking Secreted Proteins The proteins secreted by cells provide a flow of information within tissues and are thus of particular interest. However, systematic detection of secreted proteins is tricky because they tend to be present in small amounts within complex mixtures of proteins where other components are very abundant. Meissner et al. (p. 475) developed a method for screening the secreted proteins from cultured mouse macrophages in response to cues that cause inflammation. The amount of contaminating proteins was reduced by culturing the cells without added serum and then sensitive mass spectrometry techniques were used to detect and quantify secretion of nearly 800 different proteins. Secretion was compared from cells lacking the signaling adaptor proteins MyD88 or TRIF, or both. Secretion of some proteins were regulated redundantly and were secreted without one of the adaptors, but others required both signals for release. Some anti-inflammatory proteins were released at later times in response to synergistic signals from both adaptor proteins, perhaps as a fail-safe mechanism to prevent excessive inflammation. A mass spectrometry–based method detects picogram quantities of proteins secreted by macrophages. Protein secretion allows communication of distant cells in an organism and controls a broad range of physiological functions. We describe a quantitative, high-resolution mass spectrometric workflow to detect and quantify proteins that are released from immune cells upon receptor ligation. We quantified the time-resolved release of 775 proteins, including 52 annotated cytokines from only 150,000 primary Toll-like receptor 4–activated macrophages per condition. Achieving low picogram sensitivity, we detected secreted proteins whose abundance increased by a factor of more than 10,000 upon stimulation. Secretome to transcriptome comparisons revealed the transcriptionally decoupled release of lysosomal proteins. From genetic models, we defined secretory profiles that depended on distinct intracellular signaling adaptors and showed that secretion of many proinflammatory proteins is safeguarded by redundant mechanisms, whereas signaling adaptor synergy promoted the release of anti-inflammatory proteins.

Quantitative shotgun proteomics: considerations for a high-quality workflow in immunology

Proteomics based on high-resolution mass spectrometry has become a powerful tool for the analysis of protein abundance, modifications and interactions. Here we describe technical aspects of proteomics workflows, instrumentation as well as computational considerations to obtain high-quality proteomics data.

Functional classification of memory CD8(+) T cells by CX3CR1 expression.

Localization of memory CD8+ T cells to lymphoid or peripheral tissues is believed to correlate with proliferative capacity or effector function. Here we demonstrate that the fractalkine-receptor/CX3CR1 distinguishes memory CD8+ T cells with cytotoxic effector function from those with proliferative capacity, independent of tissue-homing properties. CX3CR1-based transcriptome and proteome-profiling defines a core signature of memory CD8+ T cells with effector function. We find CD62LhiCX3CR1+ memory T cells that reside within lymph nodes. This population shows distinct migration patterns and positioning in proximity to pathogen entry sites. Virus-specific CX3CR1+ memory CD8+ T cells are scarce during chronic infection in humans and mice but increase when infection is controlled spontaneously or by therapeutic intervention. This CX3CR1-based functional classification will help to resolve the principles of protective CD8+ T-cell memory.

Evidence of Extrapancreatic Glucagon Secretion in Man.

Glucagon is believed to be a pancreas-specific hormone, and hyperglucagonemia has been shown to contribute significantly to the hyperglycemic state of patients with diabetes. This hyperglucagonemia has been thought to arise from α-cell insensitivity to suppressive effects of glucose and insulin combined with reduced insulin secretion. We hypothesized that postabsorptive hyperglucagonemia represents a gut-dependent phenomenon and subjected 10 totally pancreatectomized patients and 10 healthy control subjects to a 75-g oral glucose tolerance test and a corresponding isoglycemic intravenous glucose infusion. We applied novel analytical methods of plasma glucagon (sandwich ELISA and mass spectrometry–based proteomics) and show that 29–amino acid glucagon circulates in patients without a pancreas and that glucose stimulation of the gastrointestinal tract elicits significant hyperglucagonemia in these patients. These findings emphasize the existence of extrapancreatic glucagon (perhaps originating from the gut) in man and suggest that it may play a role in diabetes secondary to total pancreatectomy.

A new class of carriers that transport selective cargo from the trans Golgi network to the cell surface.

We have isolated a membrane fraction enriched in a class of transport carriers that form at the trans Golgi network (TGN) and are destined for the cell surface in HeLa cells. Protein kinase D (PKD) is required for the biogenesis of these carriers that contain myosin II, Rab6a, Rab8a, and synaptotagmin II, as well as a number of secretory and plasma membrane‐specific cargoes. Our findings reveal a requirement for myosin II in the migration of these transport carriers but not in their biogenesis per se. Based on the cargo secreted by these carriers we have named them CARTS for CARriers of the TGN to the cell Surface. Surprisingly, CARTS are distinct from the carriers that transport vesicular stomatitis virus (VSV)‐G protein and collagen I from the TGN to the cell surface. Altogether, the identification of CARTS provides a valuable means to understand TGN to cell surface traffic.