Excessive production of eicosanoids is characteristic of many inflammatory diseases. In this study we show that ceramide, which is an early messenger of inflammatory cytokine action, exerts a dual effect on the cytosolic phospholipase A ₂ (cPLA ₂ ), the rate‐limiting enzyme in arachidonic acid release and subsequent eicosanoid formation. Stimulation of renal mesangial cells with exogenous short‐chain ceramide analogs for 30 and 60 min leads to a concentration‐dependent increase in arachidonic acid release that is not blocked by specific inhibitors of mitogen‐activated protein kinase pathways. This suggests that these established upstream activators of cPLA ₂ are not involved in ceramide‐induced arachidonic acid release. By use of photoactivatable ceramide analogs, D‐ and L‐ [ ¹²⁵ I]3‐trifluoromethyl‐3‐( m ‐iodophenyl)diazirineceramides (TID‐ceramides), we observed a direct interaction of ceramide with cPLA ₂ . This interaction was independent of the absolute configuration as D‐ and L‐TID‐ceramide were equally effective in binding to cPLA ₂ . Moreover, recombinant CaLB domain of cPLA ₂ as well as a mutant deficient in the connecting ‘hinge’ domain of cPLA ₂ , efficiently bound D‐ and L‐TID‐ceramides, whereas the catalytic domain did not interact with TID‐ceramides. In vitro binding assays reveal that stearoyl‐arachidonyl‐phosphatidylcholine (SAPC)‐liposomes containing increasing mol% of ceramide lead to an increased association of recombinant cPLA ₂ to the liposomes. Furthermore, measurement of cPLA ₂ activity in vitro shows that the presence of SAPC‐liposomes resulted in only weak cPLA ₂ activity. However, the activity dramatically increases by addition of ceramide to the liposomes. Furthermore, liposomes containing SAPC and sphingomyelin resulted in no better substrate than SAPC liposomes, unless bacterial sphingomyelinase was added to generate ceramide, which then causes a marked increase in cPLA ₂ activity. These results demonstrate that ceramide can interact directly with cPLA ₂ via the CaLB domain and thereby serves as a membrane‐docking device that facilitates cPLA ₂ action in inflammatory diseases.

Expression of the inducible nitric oxide synthase (iNOS) gene in rat mesangial cells is differentially triggered by IL-1β and cAMP predominantly at the transcriptional level. The 5′-flanking region of the rat iNOS gene contains several binding sites for transcription factors potentially involved in cytokine and cAMP signaling such as nuclear factor-κB/Rel, CCAAT/enhancer-binding protein (C/EBP), and cyclic AMP-responsive element-binding protein/ATF. We tested promoter activities of serial and site-directed deletion mutants of iNOS-chloramphenicol acetyltransferase reporter genes after transient transfection and stimulation of mesangial cells. A region between bp −277 and −111 bearing a CCAAT/enhancer-binding protein-response element was found to be critical for cAMP-mediated gene induction but dispensable for IL-1β inducibility. Moreover, a minimal promoter ranging from the transcriptional start site up to −111 containing a κB site is sufficient to confer IL-1β-mediated iNOS promoter activation. Consistent with these findings, an electrophoretic mobility shift assay shows the appearance of an IL-1β-inducible nuclear factor-κB p50/p65 heterodimeric complex. Using probes containing C/EBP-binding sites from the iNOS gene revealed further binding of different complexes, all of which were strongly inducible by cAMP and to a lower extent also by IL-1β. Abs against cyclic AMP-responsive element-binding protein, C/EBPβ, and C/EBPδ were able to partially supershift single complexes, suggesting the participation of these transcription factors in the regulation of iNOS gene expression by cAMP and IL-1β. Finally, we show that both cAMP and IL-1β strongly induce steady-state levels of C/EBPβ and C/EBPδ mRNA levels. These data demonstrate that IL-1β and cAMP use distinct as well as partially overlapping sets of transcriptional activators to modulate iNOS gene expression in rat mesangial cells.

Sphingosine 1-phosphate (S1P), derived from membrane sphingolipids, is a pleiotropic bioactive lipid mediator capable of evoking complex immune phenomena. Studies have highlighted its importance regarding intracellular signaling cascades as well as membrane-bound S1P receptor (S1PR) engagement in various clinical conditions. In neurological disorders, the S1P–S1PR axis is acknowledged in neurodegenerative, neuroinflammatory, and cerebrovascular disorders. Modulators of S1P signaling have enabled an immense insight into fundamental pathological pathways, which were pivotal in identifying and improving the treatment of human diseases. However, its intricate molecular signaling pathways initiated upon receptor ligation are still poorly elucidated. In this review, the authors highlight the current evidence for S1P signaling in neurodegenerative and neuroinflammatory disorders as well as stroke and present an array of drugs targeting the S1P signaling pathway, which are being tested in clinical trials. Further insights on how the S1P–S1PR axis orchestrates disease initiation, progression, and recovery may hold a remarkable potential regarding therapeutic options in these neurological disorders.

Interleukin-22 (IL-22), recently identified as a crucial parameter of pathology in experimental liver damage, may determine survival in clinical end-stage liver disease. Systematic analysis of serum IL-22 in relation to morbidity and mortality of patients with advanced liver cirrhosis has not been performed so far. This is a prospective cohort study including 120 liver cirrhosis patients and 40 healthy donors to analyze systemic levels of IL-22 in relation to survival and hepatic complications. A total of 71% of patients displayed liver cirrhosis-related complications at study inclusion. A total of 23% of the patients died during a mean follow-up of 196 ± 165 days. Systemic IL-22 was detectable in 74% of patients but only in 10% of healthy donors (P < 0.001). Elevated levels of IL-22 were associated with ascites (P = 0.006), hepatorenal syndrome (P < 0.0001), and spontaneous bacterial peritonitis (P = 0.001). Patients with elevated IL-22 (>18 pg/ml, n = 57) showed significantly reduced survival compared to patients with regular (≤18 pg/ml) levels of IL-22 (321 days versus 526 days, P = 0.003). Other factors associated with reduced overall survival were high CRP (≥2.9 mg/dl, P = 0.005, hazard ratio (HR) 0.314, confidence interval (CI) (0.141 to 0.702)), elevated serum creatinine (P = 0.05, HR 0.453, CI (0.203 to 1.012)), presence of liver-related complications (P = 0.028, HR 0.258, CI (0.077 to 0.862)), model of end stage liver disease (MELD) score ≥20 (P = 0.017, HR 0.364, CI (0.159 to 0.835)) and age (P = 0.011, HR 0.955, CI (0.922 to 0.989)). Adjusted multivariate Cox proportional-hazards analysis identified elevated systemic IL-22 levels as independent predictors of reduced survival (P = 0.007, HR 0.218, CI (0.072 to 0.662)). In patients with liver cirrhosis, elevated systemic IL-22 levels are predictive for reduced survival independently from age, liver-related complications, CRP, creatinine and the MELD score. Thus, processes that lead to a rise in systemic interleukin-22 may be relevant for prognosis of advanced liver cirrhosis.