Effect of cholecystokinin octapeptide on diacylglycerol-PKC signaling pathway in rat pulmonary interstitial macrophages stimulated by lipopolysaccharide

Gastrin producing syngeneic mesenchymal stem cells protect non-obese diabetic mice from type 1 diabetes

Progressive destruction of pancreatic islet β-cells by immune cells is a primary feature of type 1 diabetes (T1D) and therapies that can restore the functional β-cell mass are needed to alleviate disease progression. Here, we report the use of mesenchymal stromal/stem cells (MSCs) for the production and delivery of Gastrin, a peptide hormone that is produced by intestinal cells and foetal islets and can increase β-Cell mass, to promote protection from T1D. A single injection of syngeneic MSCs that were engineered to express Gastrin (Gastrin-MSCs) caused a significant delay in hyperglycaemia in non-obese diabetic (NOD) mice compared to engineered control-MSCs. Similar treatment of early-hyperglycaemic mice caused the restoration of euglycemia for a considerable duration, and these therapeutic effects were associated with the protection of, and/or higher frequencies of, insulin-producing islets and less severe insulitis. While the overall immune cell phenotype was not affected profoundly upon treatment using Gastrin-MSCs or upon in vitro culture, pancreatic lymph node cells from Gastrin-MSC treated mice, upon ex vivo challenge with self-antigen, showed a Th2 and Th17 bias, and diminished the diabetogenic property in NOD-Rag1 deficient mice suggesting a disease protective immune modulation under Gastrin-MSC treatment associated protection from hyperglycaemia. Overall, this study shows the potential of production and delivery of Gastrin in vivo, by MSCs, in protecting insulin-producing β-cells and ameliorating the disease progression in T1D.

CCK8 negatively regulates the TLR9-induced activation of human peripheral blood pDCs by targeting TRAF6 signaling

Plasmacytoid dendritic cells (pDCs) are specialized in rapid and massive secretion of type I interferon in response to foreign nuclei acids. Combined with their antigen presentation capacity, this powerful functionality enables pDCs to orchestrate innate and adaptive immune responses. Cholecystokinin octapeptide (CCK8) is a potent immunomodulator, whose role in pDCs function is unknown. In this study, we found that two different cholecystokinin receptors, CCK1R and CCK2R, are expressed on human peripheral blood pDCs. Exogenous CCK8 was able to modulate the TLR-induced activation of pDCs, including phenotypic maturation, IFN-α synthesis and secretion, and could also regulate the potential of pDCs to induce adaptive immune responses in vitro. CCK8 inhibited TLR9-induced activation of tumor-necrosis factor receptor-associated factor 6, which is an important adapter protein in activation of interferon-regulatory factor (IRF)5 and IRF7, possibly through CCK2R, by evoking the activity of protein kinase (PK)A and reducing the activity of PKC. All these results indicate that CCK8 can inhibit the TLR9-induced phenotypic maturation and activation of pDCs, acting through CCK2R by modulating the tumor-necrosis factor receptor-associated factor 6 signaling pathways.

TLR4 activation of TRPC6-dependent calcium signaling mediates endotoxin-induced lung vascular permeability and inflammation

Lung vascular endothelial barrier disruption and the accompanying inflammation are primary pathogenic features of acute lung injury (ALI); however, the basis for the development of both remains unclear. Studies have shown that activation of transient receptor potential canonical (TRPC) channels induces Ca(2+) entry, which is essential for increased endothelial permeability. Here, we addressed the role of Toll-like receptor 4 (TLR4) intersection with TRPC6-dependent Ca(2+) signaling in endothelial cells (ECs) in mediating lung vascular leakage and inflammation. We find that the endotoxin (lipopolysaccharide; LPS) induces Ca(2+) entry in ECs in a TLR4-dependent manner. Moreover, deletion of TRPC6 renders mice resistant to endotoxin-induced barrier dysfunction and inflammation, and protects against sepsis-induced lethality. TRPC6 induces Ca(2+) entry in ECs, which is secondary to the generation of diacylglycerol (DAG) induced by LPS. Ca(2+) entry mediated by TRPC6, in turn, activates the nonmuscle myosin light chain kinase (MYLK), which not only increases lung vascular permeability but also serves as a scaffold to promote the interaction of myeloid differentiation factor 88 and IL-1R-associated kinase 4, which are required for NF-κB activation and lung inflammation. Our findings suggest that TRPC6-dependent Ca(2+) entry into ECs, secondary to TLR4-induced DAG generation, participates in mediating both lung vascular barrier disruption and inflammation induced by endotoxin.

The scaffold MyD88 acts to couple protein kinase Cepsilon to Toll-like receptors

Mice lacking protein kinase Cepsilon (PKCepsilon) are hypersensitive to both Gram-positive and Gram-negative bacterial infections; however, the mechanism of PKCepsilon coupling to the Toll-like receptors (TLRs), responsible for pathogen detection, is poorly understood. Here we sought to investigate the mechanism of PKCepsilon involvement in TLR signaling and found that PKCepsilon is recruited to TLR4 and phosphorylated on two recently identified sites in response to lipopolysaccharide (LPS) stimulation. Phosphorylation at both of these sites (Ser-346 and Ser-368) resulted in PKCepsilon binding to 14-3-3beta. LPS-induced PKCepsilon phosphorylation, 14-3-3beta binding, and recruitment to TLR4 were all dependent on expression of the scaffold protein MyD88. In mouse embryo fibroblasts and activated macrophages from MyD88 knock-out mice, LPS-stimulated PKCepsilon phosphorylation was reduced compared with wild type cells. Acute knockdown of MyD88 in LPS-responsive 293 cells also resulted in complete loss of Ser-346 phosphorylation and TLR4/PKCepsilon association. By contrast, MyD88 overexpression in 293 cells resulted in constitutive phosphorylation of PKCepsilon. A general role for MyD88 was evidenced by the finding that phosphorylation of PKCepsilon was induced by the activation of all TLRs tested that signal through MyD88 (i.e. all except TLR3) both in RAW cells and in primary human macrophages. Functionally, it is established that phosphorylation of PKCepsilon at these two sites is required for TLR4- and TLR2-induced NFkappaB reporter activation and IkappaB degradation in reconstituted PKCepsilon(-/-) cells. This study therefore identifies the scaffold protein MyD88 as the link coupling TLRs to PKCepsilon recruitment, phosphorylation, and downstream signaling.