Cyclic nucleotides suppress tumor necrosis factor alpha-mediated apoptosis by inhibiting caspase activation and cytochrome c release in primary hepatocytes via a mechanism independent of Akt activation
ABSTRACT Cyclic nucleotides have been previously shown to modulate cell death processes in many cell types; however, the mechanisms by which cyclic nucleotides regulate apoptosis are unclear. In this study, we demonstrated that cAMP as well as cGMP analogs suppressed tumor necrosis factor alpha (TNFalpha) plus actinomycin D (ActD)-induced apoptosis in a dose-dependent manner in cultured primary hepatocytes. Furthermore, forskolin, which increases intracellular cAMP levels, also effectively suppressed TNFalpha+ActD-induced apoptosis. Activation of multiple caspases was suppressed in cells exposed to TNFalpha+ActD in the presence of cAMP or cGMP analogs. TNFalpha+ActD-induced cytochrome c release from mitochondria was also inhibited by cAMP or cGMP, reinforcing our conclusion that cyclic nucleotides interfere with the early signaling events of TNFalpha-mediated apoptosis. We evaluated the possibility that cAMP and cGMP inhibit apoptosis by activating the serine/threonine kinase Akt, which is known to promote cell survival. Both cAMP- and cGMP-elevating agents led to marked increases in Akt activation that was inhibited by the phosphatidylinositol 3'-kinase inhibitors, LY294002 and wortmannin. However, complete inhibition of cyclic nucleotide-induced Akt activation had little effect on cyclic nucleotide-mediated cell survival, indicating the existence of other survival pathways. Interestingly, the specific inhibitor of protein kinase A (PKA), KT5720, blocked cGMP-mediated protection but only partially prevented the anti-apoptotic effect of cAMP, indicating that both PKA-dependent and -independent mechanisms are involved in cAMP-mediated suppression of apoptosis signaling. Our data suggest that multiple survival signaling pathways coexist in cells and that cyclic nucleotides delay apoptosis by interfering with apoptosis signaling by both PKA-dependent and -independent mechanisms.
SourceAvailable from: Leila Gobejishvili[Show abstract] [Hide abstract]
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 · 3.86 Impact Factor
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ABSTRACT: The reverse micellar peroxotitanium-containing catalyst [C18H37N(CH3)3]7[PW10Ti2O38(O2)2] was assembled in the organic solvent and the structure was characterized by Fourier transform infrared spectroscopy(FT-IR), Diffuse reflectance UV–vis spectrum (DR-UV–vis), X-ray photoelectron spectrum (XPS), transmission electron microscopy (TEM), Energy dispersive X-ray analysis (EDAX), and Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. Direct oxidation of dibenzothiophene (DBT) using O2 was performed by this reverse micellar catalyst with ∼100% selectivity in the oxidation of DBT to sulfone. By this catalyst, it could catalytically decrease sulfur level in diesel from 500ppm to 1.0ppm at ambient pressure and moderate temperature.Applied Catalysis B Environmental 08/2011; 106(3):343-349. DOI:10.1016/j.apcatb.2011.05.038 · 6.01 Impact Factor
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ABSTRACT: While a number of extrinsic factors are known to promote the survival of plasma cells (PCs), the signaling intermediates involved remain poorly characterized. Here we identified inducible nitric oxide synthase (iNOS) as an intermediate that supported the survival of PCs. PCs deficient in iNOS (Nos2(-/-) PCs) showed enhanced death in vitro, after transfer into congenic adoptive hosts, and in chimeras made with wild-type and Nos2(-/-) bone marrow. The iNOS-mediated protection involved activation of protein kinase G and modulation of endoplasmic reticulum stress components. Activation of caspases was also diminished. We found that iNOS was required for PCs to respond to some prosurvival mediators associated with bone marrow stromal cells and that at least one mediator, interleukin 6, fed directly into this pathway by inducing iNOS.Nature Immunology 01/2014; 16(2). DOI:10.1038/ni.2806 · 24.97 Impact Factor