Enhanced PDE4B expression augments LPS-inducible TNF expression in ethanol-primed monocytes: relevance to alcoholic liver disease
ABSTRACT Increased plasma and hepatic TNF-alpha expression is well documented in patients with alcoholic hepatitis and is implicated in the pathogenesis of alcoholic liver disease. We have previously shown that monocytes from patients with alcoholic hepatitis show increased constitutive and LPS-induced NF-kappaB activation and TNF-alpha production. Our recent studies showed that chronic ethanol exposure significantly decreased cellular cAMP levels in both LPS-stimulated and unstimulated monocytes and Kupffer cells, leading to an increase in LPS-inducible TNF-alpha production by affecting NF-kappaB activation and induction of TNF mRNA expression. Accordingly, the mechanisms underlying this ethanol-induced decrease in cellular cAMP leading to an increase in TNF expression were examined in monocytes/macrophages. In this study, chronic ethanol exposure was observed to significantly increase LPS-inducible expression of cAMP-specific phosphodiesterase (PDE)4B that degrades cellular cAMP. Increased PDE4B expression was associated with enhanced NF-kappaB activation and transcriptional activity and subsequent priming of monocytes/macrophages leading to enhanced LPS-inducible TNF-alpha production. Selective inhibition of PDE4 by rolipram abrogated LPS-mediated TNF-alpha expression at both protein and mRNA levels in control and ethanol-treated cells. Notably, PDE4 inhibition did not affect LPS-inducible NF-kappaB activation but significantly decreased NF-kappaB transcriptional activity. These findings strongly support the pathogenic role of PDE4B in the ethanol-mediated priming of monocytes/macrophages and increased LPS-inducible TNF production and the subsequent development of alcoholic liver disease (ALD). Since enhanced TNF expression plays a significant role in the evolution of clinical and experimental ALD, its downregulation via selective PDE4B inhibitors could constitute a novel therapeutic approach in the treatment of ALD.
SourceAvailable from: Jeanette N Mcclintick[Show abstract] [Hide abstract]
ABSTRACT: Phosphodiesterase-4 (PDE4) and neuroimmune signaling have been posited to regulate alcohol drinking. This study evaluated the involvement of PDE4 and Il22ra2 on ethanol (EtOH) intake by alcohol-preferring (P) and high-alcohol-drinking (HAD1) rats. Exp 1 determined the dose-response effects of PDE4 inhibitors, rolipram, and Ro 20-1724, on 2 h/day free-choice EtOH intake by adult P and HAD1 rats. Exps 2-3 examined the effects of repeated administration with the PDE4 inhibitors on EtOH or sucrose intake and locomotor behavior. Exp 4 determined Pde4-associated gene expression differences in subregions of the extended amygdala, between high- and low-alcohol-consuming rat lines. Exp 5 evaluated the effects of infusing short hairpin RNA to knock down Il22ra2 in the nucleus accumbens (NAc) shell on a 24-h free-choice EtOH drinking by P rats. Administration of rolipram or Ro 20-1724 reduced EtOH intake by P rats; Ro 20-1724 reduced EtOH intake by HAD1 rats. Repeated rolipram or Ro 20-1724 exposure reduced EtOH intake by P and HAD1 rats. PDE4 inhibition induced motor impairment during the first hour of EtOH intake by P rats. Higher gene expression levels for PDE4A were found in the NAc shell of P vs NP rats. ShRNAs targeting Il22ra2 in the NAc shell significantly reduced chronic EtOH intake. PDE4 and neuroinflammatory/immune signaling pathways could represent molecular targets for the treatment of alcohol use disorders in genetically predisposed subjects. This study underscores the importance of testing compounds over multiple days and rat lines when determining efficacy to disrupt excessive alcohol intake.Psychopharmacology 01/2015; DOI:10.1007/s00213-014-3852-3 · 3.99 Impact Factor
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ABSTRACT: Anti-inflammatory and anti-fibrotic effects of the broad spectrum PDE inhibitor Pentoxifylline have suggested an important role for cyclic nucleotides in the pathogenesis of hepatic fibrosis; however studies examining the role of specific PDEs are lacking. Endotoxemia and Toll-like receptor 4 (TLR4) mediated inflammatory and pro-fibrotic signaling play a major role in the development of hepatic fibrosis. Since cAMPspecific PDE4 critically regulates LPS-TLR4 induced inflammatory cytokine expression, its pathogenic role in bile duct ligation induced hepatic injury and fibrogenesis in Sprague Dawley rats was examined. Initiation of cholestatic liver injury and fibrosis was accompanied by a significant induction of PDE4A, B and D expression and activity. Treatment with the PDE4-specific inhibitor, rolipram, significantly decreased liver PDE4 activity, hepatic inflammatory and pro-fibrotic cytokine expression, injury and fibrosis. At the cellular level, in relevance to endotoxemia and inflammatory cytokine production, PDE4B was observed to play a major regulatory role in the LPS-inducible TNF production by isolated Kupffer cells. Moreover, PDE4 expression was also involved in the in vitro activation and transdifferentiation of isolated hepatic stellate cells (HSCs). Particularly, PDE4A, B and D up-regulation preceded induction of the HSC activation marker α-SMA. In vitro treatment of HSCs with rolipram effectively attenuated α-SMA, collagen expression and accompanying morphological changes. Overall, these data strongly suggest that up-regulation of PDE4 expression during cholestatic liver injury plays a potential pathogenic role in the development of inflammation, injury and fibrosis.Journal of Pharmacology and Experimental Therapeutics 07/2013; 347(1). DOI:10.1124/jpet.113.204933 · 3.89 Impact Factor
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ABSTRACT: Chronic alcohol exposure results in liver injury that is driven in part by inflammatory cytokines such as tumor necrosis factor-α (TNF). Hepatocytes are normally resistant to the cytotoxic effects of TNF, but they become sensitized to TNF by chronic alcohol exposure. Recently, we reported that the decrease in the ratio of S-adenosylmethionine (SAM) to S-adenosylhomocysteine (SAH) that occurs with alcoholic liver injury renders hepatocytes sensitive to TNF cytotoxicity. The purpose of this study was to determine whether inhibition of the transcription factor nuclear factor-kappaB (NF-κB) contributed to TNF-induced cell death in hepatocytes with high levels of SAH. Primary human hepatocytes or HepG2 cells were pre-incubated with a combination of adenosine plus homocysteine to increase SAH levels. Following exposure to TNF, viability was determined by the MTT assay, and activation of the NF-κB pathway was assessed by measuring degradation of cytosolic IκB-α, phosphorylation and translocation of NF-κB to the nucleus, and expression of NF-κB-dependent genes. TNF-induced apoptotic signaling pathways were assessed by monitoring levels of the anti-apoptotic protein, A20, and cleavage products of the caspase-8 substrate, RIP1. NF-κB-mediated gene expression was inhibited in cells with high SAH, despite the fact that TNF-induced degradation of the cytoplasmic inhibitor IκB-α and accumulation of NF-κB in the nucleus persisted for much longer. In contrast to control cells, the NF-κB that accumulated in the nucleus of cells with high SAH levels was not phosphorylated at serine 536, a modification associated with activation of the transactivation potential of this transcription factor. The inhibition of transactivation by NF-κB resulted in lower mRNA and protein levels of the anti-apoptotic protein A20 and increased cleavage of RIP1. High SAH levels inhibited NF-κB-mediated gene expression and sensitized primary hepatocytes and HepG2 cells to the cytotoxic effects of TNF. It is likely that crosstalk with other transcription factors is perturbed under these conditions, resulting in still other changes in gene expression.Alcoholism Clinical and Experimental Research 11/2013; 38(4). DOI:10.1111/acer.12315 · 3.31 Impact Factor