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Catestatin (CST) is a bioactive cleavage product of the neuroendocrine prohormone chromogranin A (CgA). Recent findings show that CST can exert anti-inflammatory and antiadrenergic effects by suppressing the inflammatory actions of mammalian macrophages. However, recent findings also suggest that macrophages themselves are major CST producers. Here, we hypothesize that macrophages produce CST in an inflammation-dependent manner and thereby might self-regulate inflammation in an autocrine fashion. CST is associated with pathological conditions hallmarked by chronic inflammation, including autoimmune, cardiovascular, and metabolic disorders. Since intraperitoneal injection of CST in mouse models of diabetes and inflammatory bowel disease has been reported to be beneficial for mitigating disease, we posit that CST should be further investigated as a candidate target for treating certain inflammatory diseases.

AimsAging is associated with the development of insulin resistance and hypertension which may stem from inflammation induced by accumulation of toxic bacterial DNA crossing the gut barrier. The aim of this study was to identify factors counter-regulating these processes. Taking advantage of the Chromogranin A (CgA) knockout (CgA-KO) mouse as a model for healthy aging, we have identified Vsig4 (V-set and immunoglobulin domain containing 4) as the critical checkpoint gene in offsetting age-associated hypertension and diabetes.Methods and resultsThe CgA-KO mice display two opposite aging phenotypes: hypertension but heightened insulin sensitivity at young age, whereas the blood pressure normalizes at older age and insulin sensitivity further improves. In comparison, aging WT mice gradually lost glucose tolerance and insulin sensitivity and developed hypertension. The gut barrier, compromised in aging WT mice, was preserved in CgA KO mice leading to major 35-fold protection against bacterial DNA-induced inflammation. Similarly, RNA sequencing showed increased expression of the Vsig4 gene (which removes bacterial DNA) in the liver of 2-yr-old CgA-KO mice, which may account for the very low accumulation of microbial DNA in the heart. The reversal of hypertension in aging CgA-KO mice likely stems from (i) low accumulation of microbial DNA, (ii) decreased spillover of norepinephrine in the heart and kidneys, and (iii) reduced inflammation.ConclusionWe conclude that healthy aging relies on protection from bacterial DNA and the consequent low inflammation afforded by CgA-KO. Vsig4 also plays a crucial role in "healthy aging" by counteracting age-associated insulin resistance and hypertension.

AimA "leaky" gut barrier has been implicated in the initiation and progression of a multitude of diseases, for example, inflammatory bowel disease (IBD), irritable bowel syndrome and celiac disease. Here we show how pro-hormone Chromogranin A (CgA), produced by the enteroendocrine cells, and Catestatin (CST: hCgA352-372 ), the most abundant CgA-derived proteolytic peptide, affect the gut barrier.MethodsColon tissues from region-specific CST-knockout (CST-KO) mice, CgA-knockout (CgA-KO) and WT mice were analysed by immunohistochemistry, western blot, ultrastructural and flowcytometry studies. FITC-dextran assays were used to measure intestinal barrier function. Mice were supplemented with CST or CgA fragment pancreastatin (PST: CgA250-301 ). The microbial composition of cecum was determined. CgA and CST levels were measured in blood of IBD patients.ResultsPlasma levels of CST were elevated in IBD patients. CST-KO mice displayed (a) elongated tight, adherens junctions and desmosomes similar to IBD patients, (b) elevated expression of Claudin 2, and (c) gut inflammation. Plasma FITC-dextran measurements showed increased intestinal paracellular permeability in the CST-KO mice. This correlated with a higher ratio of Firmicutes to Bacteroidetes, a dysbiotic pattern commonly encountered in various diseases. Supplementation of CST-KO mice with recombinant CST restored paracellular permeability and reversed inflammation, whereas CgA-KO mice supplementation with CST and/or PST in CgA-KO mice showed that intestinal paracellular permeability is regulated by the antagonistic roles of these two peptides: CST reduces and PST increases permeability.ConclusionThe pro-hormone CgA regulates the intestinal paracellular permeability. CST is both necessary and sufficient to reduce permeability and primarily acts by antagonizing PST.

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Immune responses are initiated by the interactions between antigen-presenting cells (APCs), such as dendritic cells (DCs), with responder cells, such as T cells, via a tight cellular contact interface called the immunological synapse. The immunological synapse is a highly organized subcellular structure that provides a platform for the presentation of antigen in major histocompatibility class I and II complexes (MHC class I and II) on the surface of the APC to receptors on the surface of the responder cells. In T cells, these contacts lead to highly polarized membrane trafficking that results in the local release of lytic granules and in the delivery and recycling of T cell receptors at the immunological synapse. Localized trafficking also occurs at the APC side of the immunological synapse, especially in DCs where antigen loaded in MHC class I and II is presented and cytokines are released specifically at the synapse. Whereas the molecular mechanisms underlying polarized membrane trafficking at the T cell side of the immunological synapse are increasingly well understood, these are still very unclear at the APC side. In this review, we discuss the organization of the APC side of the immunological synapse. We focus on the directional trafficking and release of membrane vesicles carrying MHC molecules and cytokines at the immunological synapses of DCs. We hypothesize that the specific delivery of MHC and the release of cytokines at the immunological synapse mechanistically resemble that of lytic granule release from T cells.

Aims: Aging is associated with the development of insulin resistance and hypertension which may stem from inflammation induced by accumulation of toxic bacterial DNA crossing the gut barrier. The aim of this study was to identify factors counter-regulating these processes. Taking advantage of the Chromogranin A (CgA) knockout (CgA-KO) mouse as a model for healthy aging, we have identified Vsig4 (V-set and immunoglobulin domain containing 4) as the critical checkpoint gene in offsetting age-associated hypertension and diabetes. Methods and Results: The CgA-KO mice display two opposite aging phenotypes: hypertension but heightened insulin sensitivity at young age, whereas the blood pressure normalizes at older age and insulin sensitivity further improves. In comparison, aging WT mice gradually lost glucose tolerance and insulin sensitivity and developed hypertension. The gut barrier, compromised in aging WT mice, was preserved in CgA KO mice leading to major 35-fold protection against bacterial DNA-induced inflammation. Similarly, RNA sequencing showed increased expression of the Vsig4 gene (which removes bacterial DNA) in the liver of 2-yr-old CgA-KO mice, which may account for the very low accumulation of microbial DNA in the heart. The reversal of hypertension in aging CgA-KO mice likely stems from (i) low accumulation of microbial DNA, (ii) decreased spillover of norepinephrine in the heart and kidneys, and (iii) reduced inflammation. Conclusion: We conclude that healthy aging relies on protection from bacterial DNA and the consequent low inflammation afforded by CgA-KO. Vsig4 also plays a crucial role in "healthy aging" by counteracting age-associated insulin resistance and hypertension. [ABSTRACT FROM AUTHOR]

Increased levels of the anti‐inflammatory peptide Catestatin (CST), a cleavage product of the pro‐hormone chromogranin A, correlate with less severe outcomes in hypertension, colitis, and diabetes. However, it is unknown how CST reduces the infiltration of monocytes and macrophages (Mϕs) in inflamed tissues. Here, it is reported that CST blocks leukocyte migration toward inflammatory chemokines. By in vitro and in vivo migration assays, it is shown that although CST itself is chemotactic, it blocks migration of monocytes and neutrophils to inflammatory attracting factor CC‐chemokine ligand 2 (CCL2) and C‐X‐C motif chemokine ligand 2 (CXCL2). Moreover, it directs CX3CR1+ Mϕs away from pancreatic islets. These findings suggest that the anti‐inflammatory actions of CST are partly caused by its regulation of chemotaxis. [ABSTRACT FROM AUTHOR]

Neuronal exocytosis is catalysed by the SNAP receptor protein syntaxin-lA (1), which is clustered in the plasma membrane at sites where synaptic vesicles undergo exocytosis (2,3). However, how syntaxin-1A is sequestered is unknown. Here we show that syntaxin clustering is mediated by electrostatic interactions with the strongly anionic lipid phosphatidylinositol-4,5-bisphosphate (PIP2). Using super-resolution stimulated-emission depletion microscopy on the plasma membranes of PC12 cells, we found that PIP2 is the dominant inner-leaflet lipid in microdomains about 73 nanometres in size. This high accumulation of PIP2 was required for syntaxin-1A sequestering, as destruction of PIP2 by the phosphatase synaptojanin-1 reduced syntaxin-1A clustering. Furthermore, co-reconstitution of PIP2 and the carboxy-terminal part of syntaxin-1A in artificial giant unilamellar vesicles resulted in segregation of PIP2 and syntaxin-1A into distinct domains even when cholesterol was absent. Our results demonstrate that electrostatic protein-lipid interactions can result in the formation of microdomains independently of cholesterol or lipid phases., Phosphoinositides are lipids that contain an inositol head group conjugated to one to three phosphate groups. With ~ 1% of total lipids in the inner leaflet of the plasma membrane [...]