BackgroundLuteolin, a plant derived flavonoid, exerts a variety of pharmacological activities and anti-oxidant properties associated with its capacity to scavenge oxygen and nitrogen species. Luteolin also shows potent anti-inflammatory activities by inhibiting nuclear factor kappa B (NFkB) signaling in immune cells. To better understand the immuno-modulatory effects of this important flavonoid, we performed a genome-wide expression analysis in pro-inflammatory challenged microglia treated with luteolin and conducted a phenotypic and functional characterization.MethodsResting and LPS-activated BV-2 microglia were treated with luteolin in various concentrations and mRNA levels of pro-inflammatory markers were determined. DNA microarray experiments and bioinformatic data mining were performed to capture global transcriptomic changes following luteolin stimulation of microglia. Extensive qRT-PCR analyses were carried out for an independent confirmation of newly identified luteolin-regulated transcripts. The activation state of luteolin-treated microglia was assessed by morphological characterization. Microglia-mediated neurotoxicity was assessed by quantifying secreted nitric oxide levels and apoptosis of 661W photoreceptors cultured in microglia-conditioned medium.ResultsLuteolin dose-dependently suppressed pro-inflammatory marker expression in LPS-activated microglia and triggered global changes in the microglial transcriptome with more than 50 differentially expressed transcripts. Pro-inflammatory and pro-apoptotic gene expression was effectively blocked by luteolin. In contrast, mRNA levels of genes related to anti-oxidant metabolism, phagocytic uptake, ramification, and chemotaxis were significantly induced. Luteolin treatment had a major effect on microglial morphology leading to ramification of formerly amoeboid cells associated with the formation of long filopodia. When co-incubated with luteolin, LPS-activated microglia showed strongly reduced NO secretion and significantly decreased neurotoxicity on 661W photoreceptor cultures.ConclusionsOur findings confirm the inhibitory effects of luteolin on pro-inflammatory cytokine expression in microglia. Moreover, our transcriptomic data suggest that this flavonoid is a potent modulator of microglial activation and affects several signaling pathways leading to a unique phenotype with anti-inflammatory, anti-oxidative, and neuroprotective characteristics. With the identification of several novel luteolin-regulated genes, our findings provide a molecular basis to understand the versatile effects of luteolin on microglial homeostasis. The data also suggest that luteolin could be a promising candidate to develop immuno-modulatory and neuroprotective therapies for the treatment of neurodegenerative disorders.

Portal vein ligation (PVL) induces liver growth prior to resection. Associating liver partition and portal vein ligation (pVL plus transection=ALppS) or the addition of the prolyl-hydroxylase inhibitor dimethyloxalylglycine (DMOG) to PVL both accelerate growth via stabilization of HIF-α subunits. This study aims at clarifying the crosstalk of hepatocytes (HC), hepatic stellate cells (HSC) and liver sinusoidal endothelial cells (LSEC) in accelerated liver growth. In vivo, liver volume, HC proliferation, vascular density and HSC activation were assessed in PVL, ALPPS, PVL+DMOG and DMOG alone. Proliferation of HC, HSC and LSEC was determined under DMOG in vitro. Conditioned media experiments of DMOG-exposed cells were performed. ALPPS and PVL+DMOG accelerated liver growth and HC proliferation in comparison to PVL. DMOG alone did not induce HC proliferation, but led to increased vascular density, which was also observed in ALPPS and PVL+DMOG. Activated HSC were detected in ALPPS, PVL+DMOG and DMOG, again not in PVL. In vitro, DMOG had no proliferative effect on HC, but conditioned supernatant of DMOG-treated HSC induced VEGF-dependent proliferation of LSEC. Transcriptome analysis confirmed activation of proangiogenic factors in hypoxic HSC. Hypoxia signaling in HSC induces VEGF-dependent angiogenesis. HSC play a crucial role in the cellular crosstalk of rapid liver regeneration. The liver proliferates after rerouting portal vein blood flow without removal of liver mass, likely because portal vein blood contains trophic factors 1,2 to maintain hepatocyte number and function 3. Portal vein blood rerouting is used by surgeons to induce liver growth prior to liver resection in cases of small prospective (future) liver remnants (FLR) since 1986 4-6. Portal vein branch embolization (PVE) of the hemi-liver with or without segment 4 is performed by interventional radiologists 7 to increase volume by about 38% of the total liver volume within 4 to 6 weeks 6. Portal vein ligation (PVL) by surgeons induces similar volume growth like PVE. However, volume increase with PVE or PVL is remarkably slow 8. Recently, Associating Liver Partition and Portal vein ligation for Staged hepatectomy (ALPPS) was introduced as a surgical procedure in two stages, which combines PVL with parenchymal transection in a first stage, followed by hepatectomy in a second stage after only 7-10 days 9,10. In animals models, ALPPS has been shown to increase portal venous blood flow per unit tissue just like PVL, but unlike PVL, the formation of portal collaterals over time is abrogated because of the parenchymal transection 11. The consequence is persistent high portal flow in the small growing liver 12. This high portal flow after ALPPS

These data suggest that liver hypertrophy following PVL is inversely proportional to the development of collaterals. Hypertrophy after ALPPS is likely more rapid due to reduction of collaterals through transection.