Lipotoxicity reduces DDX58/Rig-1 expression and activity leading to impaired autophagy and cell death.

Nonalcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease globally. NAFLD is a consequence of fat accumulation in the liver leading to lipotoxicity. Increasing evidence has demonstrated the critical role of autophagy in NAFLD. This study uncovers the unexpected role of immune surveillance protein DDX58/Rig-1 (DExD/H box helicase 58) in activating macroautophagy/autophagy and protecting from lipotoxicity associated with NAFLD. Here we show for the first time that DDX58 protein is significantly reduced in nonalcoholic steatohepatitis (NASH) mouse model, an aggressive form of NAFLD characterized by inflammation and fibrosis of the liver. In addition to decreased expression of DDX58, we found that DDX58 activity can be attenuated by treatments with palmitic acid (PA), a saturated fatty acid. To investigate whether PA inhibition of DDX58 is harmful to the cell, we characterized DDX58 function in hepatocytes when exposed to high doses of PA in the presence and/or absence of DDX58. We show that siRNA knockdown of DDX58 promotes apoptosis. Importantly, we show that stable overexpression of DDX58 is protective against toxic levels of PA and stimulates autophagy. This study begins to demonstrate the regulation of the autophagy receptor protein SQSTM1/p62 through DDX58. DDX58 expression directly influences SQSTM1 mRNA and protein levels. This work proposes a model in which activating DDX58 increases an autophagic response and this aids in clearing toxic lipid inclusion bodies, which leads to inflammation and apoptosis. Activating a DDX58-induced autophagy response may be a strategy for treating NAFLD.Abbreviations:5'pppdsRNA: 5' triphosphate double-stranded RNA; CDAHFD: choline-deficient, L-amino acid defined high-fat diet; CEBPB: CCAAT/enhancer binding protein (C/EBP), beta; CQ: chloroquine; DDX58/retinoic acid inducible gene 1/Rig-1: DExD/H box helicase 58; h: hours; IFIH1/MDA5: interferon induced with helicase C domain 1; IFNB/IFN-ß: interferon beta 1, fibroblast; KO: knockout; MAVS: mitochondrial antiviral signaling protein; NAFLD: nonalcoholic fatty liver disease; NASH: nonalcoholic steatohepatitis; NFKB/NF-κB: nuclear factor of kappa light polypeptide gene enhancer in B cells; PA: palmitic acid; poly:IC: polyinosinic:polycytidylic acid; PRR: pattern recognition receptors; PSR: picrosirus red; RAP: rapamycin; RLR: RIG-I-like receptor; SQSTM1/p62: sequestosome 1; STING1: stimulator of interferon response cGAMP interactor 1; TBK1: TANK-binding kinase 1.

Major vault protein in cardiac and smooth muscle.

Major vault protein (MVP) is the major component of the vault particle whose functions are not well understood. One proposed function of the vault is to serve as a mechanism of drug transport, which confers drug resistance in cancer cells. We show that MVP can be found in cardiac and smooth muscle. In human airway smooth muscle cells, knocking down MVP was found to cause cell death, suggesting that MVP serves as a cell survival factor. Further, our laboratory found that MVP is S-glutathionylated in response to ligand/receptor-mediated cell signaling. The S-glutathionylation of MVP appears to regulate protein-protein interactions between MVP and a protein called myosin heavy chain 9 (MYH9). Through MYH9 and Vsp34, MVP may form a complex with Beclin-1 that regulates autophagic cell death. In pulmonary vascular smooth muscle, proteasome inhibition promotes the ubiquitination of MVP, which may function as a mechanism of proteasome inhibition-mediated cell death. Investigating the functions and the regulatory mechanisms of MVP and vault particles is an exciting new area of research in cardiovascular/pulmonary pathophysiology.

Carfilzomib reverses pulmonary arterial hypertension.

AIMS: Pulmonary arterial hypertension (PAH) remains a lethal disease with pronounced narrowing of pulmonary vessels due to abnormal cell growth. Agents that can reduce the pulmonary vascular thickness thus have therapeutic potential. The present study investigated the efficacy of carfilzomib (CFZ), a proteasome inhibitor and a cancer chemotherapeutic drug, on reversing PAH. METHODS AND RESULTS: In two rat models of PAH, SU5416/hypoxia and SU5416/ovalbumin, CFZ effectively reversed pulmonary vascular remodelling with the promotion of apoptosis and autophagy. In human pulmonary artery smooth muscle cells, knocking down mediators of autophagy attenuated CFZ-induced cell death. The cell death role of autophagy was promoted by the participation of tumour protein p53-inducible nuclear protein 1. CFZ increased the protein ubiquitination, and siRNA knockdown of ubiquitin inhibited cell death, suggesting that CFZ-induced cell death is ubiquitin-dependent. Mass spectrometry demonstrated the ubiquitination of major vault protein and heat shock protein 90 in response to CFZ. The siRNA knockdown of these proteins enhanced CFZ-induced cell death, revealing that they are cell survival factors. CFZ reduced right-ventricular pressure and enhanced the efficacy of a vasodilator, sodium nitroprusside. While no indications of CFZ toxicity were observed in the right ventricle of PAH rats, apoptosis was promoted in the left ventricle. Apoptosis was prevented by dexrazoxane or by pifithrin-α without interfering with the efficacy of CFZ to reverse pulmonary vascular remodelling. CONCLUSION: The addition of anti-tumour agents such as CFZ along with cardioprotectants to currently available vasodilators may be a promising way to improve PAH therapy.

Major vault protein regulates cell growth/survival signaling through oxidative modifications.

Major vault protein forms a hollow, barrel-like structure in the cell called the vault, whose functions and regulation are not well understood. The present study reports that major vault protein regulates growth/survival signaling in human airway smooth muscle cells through oxidative modifications. The promotion of protein S-glutathionylation by asthma mediators such as interleukin-22 and platelet-derived growth factor or by knocking down glutaredoxin-1 or thioredoxin activated cell growth signaling. Mass spectrometry identified that major vault protein is glutathionylated. Major vault protein knockdown enhanced cell death and inhibited STAT3 and Akt signaling. We identified a protein partner of major vault protein that is regulated by glutaredoxin-1, namely myosin-9, which was found to serve as a cell death factor. Knocking down myosin-9 or promoting protein S-glutathionylation by knocking down glutaredoxin-1 inhibited the death of airway smooth muscle cells by heating to simulate bronchial thermoplasty, a clinically successful procedure for the treatment of severe asthma. These results establish a novel signaling pathway in which ligand/receptor-mediated oxidation promotes the S-glutathionylation of major vault protein, which in turn binds to myosin-9 to suppress the heating-induced death of airway smooth muscle cells.

IL-22 activates oxidant signaling in pulmonary vascular smooth muscle cells.

Reactive oxygen species (ROS) mediate cell-signaling processes in response to various ligands and play important roles in the pathogenesis of cardiovascular diseases. The present study reports that interleukin-22 (IL-22) elicits signal transduction in vascular smooth muscle cells (SMCs) through a ROS-dependent mechanism. We find that pulmonary artery SMCs express IL-22 receptor alpha 1 and that IL-22 activates STAT3 through this receptor. IL-22-induced signaling is found to be mediated by NADPH oxidase, as indicated by the observations that the inhibition and siRNA knock-down of this enzyme inhibit IL-22 signaling. IL-22 triggers the oxidative modifications of proteins through protein carbonylation and protein glutathionylation. Mass spectrometry identified some proteins that are carbonylated in response to IL-22 stimulation, including α-enolase, heat shock cognate 71kDa protein, mitochondrial 60kDa heat shock protein, and cytoplasmic 2 actin and determined that α-tubulin is glutathionylated. Protein glutathionylation and STAT3 phosphorylation are enhanced by the siRNA knock-down of glutaredoxin, while IL-22-mediated STAT3 phosphorylation is suppressed by knocking down thioredoxin interacting protein, an inhibitor of thioredoxin. IL-22 is also found to promote the growth of SMCs via NADPH oxidase. In rats, pulmonary hypertension is found to be associated with increased smooth muscle IL-22 expression. These results show that IL-22 promotes the growth of pulmonary vascular SMCs via a signaling mechanism that involves NADPH oxidase-dependent oxidation.

Mechanism of protein decarbonylation.

Ligand/receptor stimulation of cells promotes protein carbonylation that is followed by the decarbonylation process, which might involve thiol-dependent reduction (C.M. Wong et al., Circ. Res. 102:301-318; 2008). This study further investigated the properties of this protein decarbonylation mechanism. We found that the thiol-mediated reduction of protein carbonyls is dependent on heat-labile biologic components. Cysteine and glutathione were efficient substrates for decarbonylation. Thiols decreased the protein carbonyl content, as detected by 2,4-dinitrophenylhydrazine, but not the levels of malondialdehyde or 4-hydroxynonenal protein adducts. Mass spectrometry identified proteins that undergo thiol-dependent decarbonylation, which include peroxiredoxins. Peroxiredoxin-2 and -6 were carbonylated and subsequently decarbonylated in response to the ligand/receptor stimulation of cells. siRNA knockdown of glutaredoxin inhibited the decarbonylation of peroxiredoxin. These results strengthen the concept that thiol-dependent decarbonylation defines the kinetics of protein carbonylation signaling.

TGF-beta1-Induced MAPK activation promotes collagen synthesis, nodule formation, redox stress and cellular senescence in porcine aortic valve interstitial cells.

BACKGROUND AND AIM OF THE STUDY: Aortic valve stenosis is a major cause of valve replacement, particularly in the elderly. TGF-beta1 is upregulated in stenotic valves and induces calcification and collagen synthesis in cultured valve interstitial cells. It has been shown previously that TGF-beta1 increases reactive oxygen species (ROS) in these cells in association with calcifying nodule formation, but the cellular signaling pathways responsible for these TGF-beta1-induced effects are not well defined. METHODS: Cultured porcine aortic valve interstitial cells were used to investigate the effects of inhibitors of TGF-beta1 signaling pathways on 3H-proline incorporation into the extracellular matrix, the peak number of calcifying nodules formed, redox stress as dichlorofluorescein diacetate (DCF-DA) fluorescence, and senescence-associated beta-galactosidase staining. RESULTS: Nodule formation and proline incorporation were inhibited by SB431542, implicating the Smad pathway, by SB203580, implicating the P38 MAPK pathway, and by U0126, implicating the Mekl/2/Erk1/2 pathway in both processes. Fasudil, an inhibitor of the Rho kinase pathway, was selective in inhibiting nodule formation but not proline incorporation. It was verified that Smad2 phosphorylation, Erk1/2 phosphorylation and p38 MAPK phosphorylation were all induced by TGF-beta1, with Smad 2 phosphorylation peaking at 1-2 h and MAPK phosphorylation at 24-48 h. The effect of TGF-beta1 on phosphorylation of Smad 2 was inhibited by SB431542, on the phosphorylation of p38 MAPK was inhibited by SB203580, and on the phosphorylation of Erk1/2 was inhibited by U0126. ROS generation in response to TGF-beta1, measured as 2,7-dichlorofluorescein-diacetate fluorescence, was inhibited significantly by SB203580 and U0126, implicating both the p38 MAPK and Mekl/2/Erk1/2 signaling pathways. Both pathways also mediated TGF-beta1-induced cellular senescence which was localized to cellular aggregates and mature nodules. CONCLUSION: These data imply that the inhibition of either Smad or MAPK signaling pathways may have a therapeutic benefit in ameliorating the adverse pathological changes associated with aortic valve stenosis.