Injury causes a systemic inflammatory response syndrome (SIRS) that is clinically much like sepsis. Microbial pathogen-associated molecular patterns (PAMPs) activate innate immunocytes through pattern recognition receptors. Similarly, cellular injury can release endogenous 'damage'-associated molecular patterns (DAMPs) that activate innate immunity. Mitochondria are evolutionary endosymbionts that were derived from bacteria and so might bear bacterial molecular motifs. Here we show that injury releases mitochondrial DAMPs (MTDs) into the circulation with functionally important immune consequences. MTDs include formyl peptides and mitochondrial DNA. These activate human polymorphonuclear neutrophils (PMNs) through formyl peptide receptor-1 and Toll-like receptor (TLR) 9, respectively. MTDs promote PMN Ca(2+) flux and phosphorylation of mitogen-activated protein (MAP) kinases, thus leading to PMN migration and degranulation in vitro and in vivo. Circulating MTDs can elicit neutrophil-mediated organ injury. Cellular disruption by trauma releases mitochondrial DAMPs with evolutionarily conserved similarities to bacterial PAMPs into the circulation. These signal through innate immune pathways identical to those activated in sepsis to create a sepsis-like state. The release of such mitochondrial 'enemies within' by cellular injury is a key link between trauma, inflammation and SIRS.

/pdf/circulating-mitochondrial-damps-cause-inflammatory-responses-l5nblb4vre.pdf

Circulating mitochondrial DAMPs cause inflammatory responses to injury

Introduction Neutrophil accumulation in a tissue is characteristic of inflammation and is observed in a variety of pathological conditions as disparate as infection, trauma, ischemia, and cancer. The process of tissue infiltration is best understood in bacterial infection, where neutrophils are selectively attracted in large numbers to phagocytose and kill the invaders. In other conditions neutrophils are presumably recruited as scavengers of damaged tissue or unwanted extracellular deposits like immune complexes or fibrin. Phagocytosis is accompanied by the release of granule enzymes, superoxide, H202, and a variety of bioactive lipids. Several of these products are required for the killing and digestion of microorganisms. They also induce inflammation and tissue damage, however, which is normally observed after neutrophil accumulation. Several neutrophil chemoattractants have been characterized in recent years; the best known are the anaphylatoxin C5a (1), formylmethionyl peptides of bacterial origin (2), plateletactivating factor (PAF; 3),1 and leukotriene B4 (LTB4; 4). These stimuli have different origins and modes of formation, and their occurrence in disease must thus be expected to vary in accord with the underlying pathophysiological process. C5a is formed upon complement activation via the classical pathway after interaction of microorganisms with antibodies or the formation of immune complexes, or via the alternative pathway after the nonimmune recognition of foreign materials. In bacterial infections, on the other hand, formylmethionyl peptides (which are released by the microorganisms) are likely to be the major attractants. PAFand LTB4 are of special interest because they can be generated by the neutrophils themselves and may thus function as autoor paracrine amplifiers of the responses elicited by other stimuli (5). It has been shown that CSa, formylmethionyl peptides, PAF, and LTB4 act via unrelated receptors, suggesting that neutrophil recruitment can result from the concerted action of multiple stimuli.

/pdf/neutrophil-activating-peptide-1-interleukin-8-a-novel-1qfpxlltik.pdf

Neutrophil-activating peptide-1/interleukin 8, a novel cytokine that activates neutrophils.

https://depositonce.tu-berlin.de/bitstream/11303/5674/1/c2np20085f.pdf

Ribosomally synthesized and post-translationally modified peptide natural products: Overview and recommendations for a universal nomenclature

The study of endocytosis has traditionally focused on the contents of endocytic vacuoles, i.e., extracellular fluid, dissolved solutes, and macromolecules or particles which specifically or nonspecifically bind to the plasma membrane (PM). Substances that are endocytosed include important nutrients, toxins, effector molecules (growth factors, hormones, antibodies), enzymes, and pathogens. This article centers on the properties and dynamics of the endocytic vacuole membrane. In many instances we will stress observations on cultured mouse macrophages with which we are most familier. We will emphasize four points: (a) Movement of vesicles is rapid such that endocytosed membrane and contents move from one cellular compartment to another in seconds to minutes. (b) Vesicular movement requires the interiorization and flow of large amounts of PM) (c) In many instances, internalized PM must recycle or return intact to the cell surface. (d) During recycling, contents and membrane components can be sorted from one another; e.g., endocytosed contents can accumulate within the cell while the container (membrane) can move into and out of the cell after one or more fusion events with other endocytic vacuoles, lysosomes (Ly), or Golgi apparatus. While it has been difficult to obtain direct evidence, the literature is replete with examples in which rapid membrane flow and recycling readily explains the data. Two of the more striking examples derive from studies of pinocytosis in cultured ceils. Fibroblasts, for instance, interiorize the equivalent of 50% of their surface area and 5-10% of their cell volume during each hour of pinocytic activity. Yet, the overall dimensions of the cells and the vacuolar system remain constant throughout hours, even days, of endocytic activity. Since it is unlikely that internalized PM is rapidly degraded, it was proposed that

/pdf/endocytosis-and-the-recycling-of-plasma-membrane-ivaf90oe9b.pdf

Endocytosis and the recycling of plasma membrane.

Recent studies have focused on the potential role of transforming growth factor type beta (TGF-beta) as an immunoregulatory peptide. In this context, we demonstrate that TGF-beta is a potent chemoattractant for human peripheral blood monocytes. At concentrations from 0.1 to 10 pg/ml, TGF-beta induces directed monocyte migration in vitro. Consistent with this observation is the expression of high-affinity TGF-beta receptors on the monocytes with a Kd of 1-10 pM. At higher concentrations of TGF-beta (greater than or equal to 1 ng/ml), monocytes are stimulated to generate biologically active mediator(s) that enhance fibroblast growth. Gene expression for one of these growth factors, interleukin 1, is induced in monocytes within hours after exposure to TGF-beta. Thus, TGF-beta may provide an important signal for monocyte recruitment and for regulation of their synthesis of mediators of fibroblast growth and activity in wound healing.

https://www.pnas.org/content/pnas/84/16/5788.full.pdf

Transforming growth factor type beta induces monocyte chemotaxis and growth factor production

Leucocytes such as neutrophils are attracted by N-formylmethionine, but not by methionine. Di- and tripeptides containing formylmethionine are strong attractants for both neutrophils and macrophages, whereas the corresponding nonacylated compounds are not chemotactic. The formylated peptides may be related to an incompletely characterized chemotactic material normally produced by bacteria which attract the same animal cells.

https://www.pnas.org/content/pnas/72/3/1059.full.pdf

N-formylmethionyl peptides as chemoattractants for leucocytes.

Demonstration of a receptor on rabbit neutrophils for chemotactic peptides.

When rabbit peritoneal leukocytes were treated with chemoattractants such as fMet-Leu-Phe, an apparent decrease of [3H]methyl incorporation into the lipid fraction from L-[methyl-3H]methionine was observed. This decrease was a result of increased degradation of methylated phospholipids, not of decreased synthesis. Chemotactic peptides did not affect the metabolism of the phospholipids in which [methyl-14C]choline was incorporated. The disappearance of the [3H]methyl group was associated with the release of [1-14C]arachidonic acid from phospholipids prelabeled with these compounds. These findings suggested the activation by chemoattractants of phospholipase A2, an enzyme that removes an unsaturated fatty acid from phospholipids. The order of potency of chemoattractants for the stimulated degradation of phospholipids was in good agreement with that for chemotaxis. Mepacrine (quinacrine) and hydrocortisone inhibited and a phorbol ester enhanced both chemotaxis and phospholipase A2 activity. These results, taken together, suggest close association of the metabolism of methylated phospholipids with chemotaxis in rabbit peritoneal leukocytes.

Chemoattractants stimulate degradation of methylated phospholipids and release of arachidonic acid in rabbit leukocytes.

Heat-stable, chemotactically active peptides have been obtained from Escherichia coli culture filtrates. They range in size between 150 and 1500 daltons and are anionic at neutral pH. Free carboxyl groups but not free amino groups appear to be required for activity. The N-terminal group may be blocked. There do not appear to be internal aromatic or basic residues in the chemotactically active fractions. A highly purified, not completely characterized, fraction was found to contain aspartic acid, serine, glutamic acid, alanine, and glycine.

The isolation and partial characterization of neutrophil chemotactic factors from Escherichia coli.

THERE has been considerable interest recently in protein carboxylmethyltransferase, and in its possible role in secretory1 and chemotactic mechanisms2,3. Using S-adenosyl-L-methionine as the methyl donor, this enzyme catalyses the formation of protein methyl esters4,5 which undergo rapid spontaneous hydrolysis at physiological pH to liberate methanol6,7. The enzyme is widely distributed in mammalian tissues, especially in endocrine organs and brain7,8. Escherichia coli and Salmonella typhimurium appear to require methylation for chemotaxis2,3. Eukaryotic cells, such as leukocytes (neutrophils, polymorphonuclear cells), have been shown to respond chemotactically to a variety of peptides derived from complement9, to crude bacterial factors10, and more recently to welldefined synthetic formylated peptides11. We wish to report here the presence in leukocytes of a protein carboxylmethyltransferase system, whose activity is specifically stimulated by synthetic peptides, which may be related to chemoattractants produced by bacteria12.

Barbara A. Corcoran

Papers

N-formylmethionyl peptides as chemoattractants for leucocytes.

Demonstration of a receptor on rabbit neutrophils for chemotactic peptides.

Chemoattractants stimulate degradation of methylated phospholipids and release of arachidonic acid in rabbit leukocytes.

The isolation and partial characterization of neutrophil chemotactic factors from Escherichia coli.

Raipid stimulation of protein carboxymethylation in leukocytes by a chemotatic peptide.