Natural products (NPs) from microorganisms have been important sources for discovering new therapeutic and chemical entities. While their corresponding biosynthetic gene clusters (BGCs) can be easily identified by gene‐sequence‐similarity‐based bioinformatics strategies, the actual access to these NPs for structure elucidation and bioactivity testing remains difficult. Deletion of the gene encoding the RNA chaperone, Hfq, results in strains losing the production of most NPs. By exchanging the native promoter of a desired BGC against an inducible promoter in Δhfq mutants, almost exclusive production of the corresponding NP from the targeted BGC in Photorhabdus, Xenorhabdus and Pseudomonas was observed including the production of several new NPs derived from previously uncharacterized non‐ribosomal peptide synthetases (NRPS). This easyPACId approach (easy Promoter Activated Compound Identification) facilitates NP identification due to low interference from other NPs. Moreover, it allows direct bioactivity testing of supernatants containing secreted NPs, without laborious purification.

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Ceramides are mediators of inflammatory processes. In experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS), we observed that CerS6 mRNA expression was upregulated 15-fold in peripheral blood leukocytes before the onset of EAE symptoms. In peripheral blood leukocytes from MS patients, a 3.9-fold upregulation was found. Total genetic deletion of CerS6 and the selective deletion of CerS6 in peripheral blood leucocytes exacerbated the progression of clinical symptoms in EAE mice. This was associated with enhanced leukocyte, predominantly neutrophil infiltration and enhanced demyelination in the lumbar spinal cord of EAE mice. Interferon-gamma/tumor necrosis factor alpha (IFN-γ/TNF-α) and granulocyte colony-stimulating factor (G-CSF) both drive EAE development and induce expression of the integrin CD11b and the chemokine receptor C-X-C motif chemokine receptor 2 (CXCR2), and we found they also induce CerS6 expression. In vivo, the genetic deletion of CerS6 enhanced the activation/migration of neutrophils, as reflected by an enhanced upregulation of CD11b and CXCR2. In vitro, the genetic deletion of CerS6 enhanced the activation status of IFN-γ/TNF-α-stimulated neutrophils, as shown by increased expression of nitric oxide and CD11b and an increased adhesion capacity. In G-CSF-stimulated neutrophils, the migration status was enhanced, as reflected by an elevated level of CXCR2 and an increased migration capacity. These data suggest that CerS6/C16-Cer mediates feedback regulation by inhibiting the formation of CD11b and CXCR2, which are induced either by IFN-γ/TNF-α or by G-CSF, respectively. We conclude that CerS6/C16-Cer mediates anti-inflammatory effects during the development of EAE and MS possibly by suppressing the migration and deactivation of neutrophils.

A major immunological response during neuroinflammation is the activation of microglia, which subsequently release proinflammatory mediators such as prostaglandin E 2 (PGE 2 ). Besides its proinflammatory properties, cyclooxygenase-2 (COX-2)-derived PGE 2 has been shown to exhibit anti-inflammatory effects on innate immune responses. Here, we investigated the role of microsomal PGE 2 synthase-1 (mPGES-1), which is functionally coupled to COX-2, in immune responses using a model of lipopolysaccharide (LPS)-induced spinal neuroinflammation. Interestingly, we found that activation of Eprostanoid (EP)2 and EP4 receptors, but not EP1, EP3, PGI 2 receptor (IP), thromboxane A 2 receptor (TP), PGD 2 receptor (DP), and PGF 2 receptor (FP), efficiently blocked LPS-induced tumor necrosis factor ␣ (TNF␣) synthesis and COX-2 and mPGES-1 induction as well as prostaglandin synthesis in spinal cultures. In vivo, spinal EP2 receptors were up-regulated in microglia in response to intrathecally injected LPS. Accordingly, LPS priming reduced spinal synthesis of TNF␣, interleukin 1␤ (IL-1␤), and prostaglandins in response to a second intrathecal LPS injection. Importantly, this reduction was only seen in wild-type but not in mPGES-1-deficient mice. Furthermore, intrathecal application of EP2 and EP4 agonists as well as genetic deletion of EP2 significantly reduced spinal TNF␣ and IL-1␤ synthesis in mPGES-1 knock-out mice after LPS priming. These data suggest that initial inflammation prepares the spinal cord for a negative feedback regulation by mPGES-1-derived PGE 2 followed by EP2 activation, which limits the synthesis of inflammatory mediators during chronic inflammation. Thus, our data suggest a role of mPGES-1-derived PGE 2 in resolution of neuroinflammation.Neurodegenerative disorders, including Alzheimer and Parkinson disease, multiple sclerosis, and spinal cord or peripheral nerve injury, are associated with neuroinflammation (1, 2). Its initiation, maintenance and resolution are regulated by various cell types, including resident microglia, astroglia, and oligodendrocytes as well as invading blood leukocytes. Lipopolysaccharide (LPS) has traditionally been used to simulate innate immune responses in the central nervous system (CNS) by activating toll-like receptor-4 of microglia (3). Upon activation, microglia release inflammatory mediators such as cytokines, chemokines, free radicals, nitric oxide, or prostaglandins (4). One of the earliest events during LPS-induced neuroinflammation is the synthesis and release of the proinflammatory cytokine TNF␣ by microglia, which reaches maximum concentrations 2-8 h after the initial inflammatory stimulus (5). In effector cells, TNF␣ induces the expression of multiple proteins that further enhance the inflammatory response, including cyclooxygenase-2 (COX-2) and the functionally coupled microsomal PGE 2 synthase-1 (mPGES-1) 2 (6, 7). After 24 h, TNF␣ levels decrease to base-line levels whereas the activation of glia persists for several days (8). The mechanisms controlling the precise...

Ceramide synthases (CerS) synthesize chain length specific ceramides (Cer), which mediate cellular processes in a chain length-dependent manner. In experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS), we observed that the genetic deletion of CerS2 suppresses EAE pathology by interaction with granulocyte-colony stimulating factor (G-CSF) signaling and CXC motif chemokine receptor 2 (CXCR2) expression, leading to impaired neutrophil migration. In the present study, we investigated the importance of Cers and their synthesizing/metabolizing enzymes in MS. For this purpose, a longitudinal study with 72 MS patients and 25 healthy volunteers was performed. Blood samples were collected from healthy controls and MS patients over 1- or 3-year periods, respectively. Immune cells were counted using flow cytometry, ceramide levels were determined using liquid chromatography-tandem mass spectrometry, and mRNA expression was analyzed using quantitative PCR. In white blood cells, C16-LacCer and C24-Cer were down-regulated in MS patients in comparison with healthy controls. In plasma, C16-Cer, C24:1-Cer, C16-GluCer, and C24:1-GluCer were up-regulated and C16-LacCer was down-regulated in MS patients in comparison with healthy controls. Blood samples from MS patients were characterized by an increased B-cell number. However, there was no correlation between B-cell number and Cer levels. mRNA expression of Cer metabolizing enzymes and G-CSF signaling enzymes was significantly increased in MS patients. Interestingly, G-CSF receptor (G-CSFR) and CXCR2 mRNA expression correlated with CerS2 and UDP-glucose Cer glucosyltransferase (UGCG) mRNA expression. In conclusion, our results indicate that Cer metabolism is linked to G-CSF signaling in MS.