Identification and characterization of a constitutively expressed Ctenopharyngodon idella ADAR1 splicing isoform (CiADAR1a)

Cloning and expression of Malabar grouper (Epinephelus malabaricus) ADAR1 gene in response to immune stimulants and nervous necrosis virus

ADARs are RNA editing catalysts that bind double-stranded RNA and convert adenosine to inosine, a process that can lead to destabilization of dsRNA structures and suppression of mRNA translation. In mammals, ADAR1 genes are involved in various cellular pathways, including interferon (IFN)-mediated response. However, the function of fish ADAR1 remains unclear. We report here the cloning of ADAR1 in Malabar grouper (Epinephelus malabaricus) (MgADAR1) and its response to various immune stimulants. The MgADAR1 cDNA is 5371-bp long, consisting of an open reading frame encoding a putative protein of 1381 amino acids, a 235-nt 5'-terminal untranslated region (UTR), and a 990-nt 3'-UTR. The deduced amino acid sequence exhibits signature features of a chitin synthesis regulation domain, two Z-DNA-binding domains (Z alpha), three dsRNA binding motifs (DSRM) and one tRNA-specific and dsRNA adenosine deaminase domain (ADEAMc). MgADAR1 mRNA expressed ubiquitously in tissues of healthy Malabar grouper, with elevated levels in the brain, gills and eyes. In response to poly (I: C), the MgADAR1 mRNA level was significantly up-regulated in the brain and spleen, but not head kidney. Upon nervous necrosis virus (NNV) infection the level of MgADAR1 increased in the brain, whereas Mx increased in the brain, spleen and head kidney. Induction of MgADAR1 by poly (I: C) and NNV was also observed in vitro. Additionally, the expression of MgADAR1 was upregulated by recombinant grouper IFN in grouper cells. These data indicate an intricate interplay between ADAR1 and NNV infection in grouper as MgADAR1 might be regulated in a tissue-specific manner.

Inhibition of PKR protects against H2O2-induced injury on neonatal cardiac myocytes by attenuating apoptosis and inflammation

Reactive oxygenation species (ROS) generated from reperfusion results in cardiac injury through apoptosis and inflammation, while PKR has the ability to promote apoptosis and inflammation. The aim of the study was to investigate whether PKR is involved in hydrogen peroxide (H₂O₂) induced neonatal cardiac myocytes (NCM) injury. In our study, NCM, when exposed to H₂O₂, resulted in persistent activation of PKR due to NCM endogenous RNA. Inhibition of PKR by 2-aminopurine (2-AP) or siRNA protected against H₂O₂ induced apoptosis and injury. To elucidate the mechanism, we revealed that inhibition of PKR alleviated H₂O₂ induced apoptosis companied by decreased caspase3/7 activity, BAX and caspase-3 expression. We also revealed that inhibition of PKR suppressed H₂O₂ induced NFκB pathway and NLRP3 activation. Finally, we found ADAR1 mRNA and protein expression were both induced after H₂O₂ treatment through STAT-2 dependent pathway. By gain and loss of ADAR1 expression, we confirmed ADAR1 modulated PKR activity. Therefore, we concluded inhibition of PKR protected against H₂O₂-induced injury by attenuating apoptosis and inflammation. A self-preservation mechanism existed in NCM that ADAR1 expression is induced by H₂O₂ to limit PKR activation simultaneously. These findings identify a novel role for PKR/ADAR1 in myocardial reperfusion injury.