Chronic Volume Overload Caused by Abdominal Aorto-Venocaval Shunt Provides Arrhythmogenic Substrates in the Rat Atrium.

Atrial enlargement is thought to provide arrhythmogenic substrates, leading to the induction of atrial fibrillation (AF). In this study, we investigated the anatomical, molecular biological, and electrophysiological characteristics of remodeled atria in an animal model with chronic volume overload. We used rats that underwent abdominal aorto-venocaval shunt (AVS) surgery. In the in vivo studies, marked changes in electrocardiogram parameters, such as the P-wave duration, PR interval, and QRS width, as well as prolongation of the atrial effective refractory period were observed 12 weeks after the creation of AVS (AVS-12W), which were undetected at 8 weeks postoperative (AVS-8W) despite obvious atrial and ventricular enlargement. Moreover, the duration of AF induced by burst pacing in the AVS-12W rats was significantly longer than that in the Sham and AVS-8W rats. In the isolated atria, a longer action potential duration at 90% repolarization was detected in the AVS-12W rats compared with that in the Sham group. The mRNA levels of the Kv and Kir channels in the right atrium were mostly upregulated in the AVS-8W rats but were downregulated in the AVS-12W rats. These results show that chronic volume overload caused by abdominal AVS provides arrhythmogenic substrates in the rat atrium. The difference in gene expression in the right atrium between the AVS-8W and AVS-12W rats may partly explain the acquisition of arrhythmogenicity.

HSP70/DNAJA3 chaperone/cochaperone regulates NF-κB activity in immune responses.

Nuclear factor kappa B (NF-κB) controls the transcription of various genes in response to immune stimuli. Our previous study revealed that the Droj2/DNAJA3 cochaperone contributes to the NF-κB pathway in Drosophila and humans. In general, the cochaperone is associated with the 70-kDa heat shock protein (HSP70) chaperone and the complex supports the folding of diverse target proteins. The cochaperone/chaperone functions in the NF-κB pathway, however, are not clearly understood. Here, we report that HSP70 proteins are involved in activating canonical NF-κB signaling during immune responses. In human cultured cells, HSP70 inhibitor destabilized the IKKß/IκBα/NF-κB p65 complex and dampened the phosphorylation of NF-κB p65 in response to flagellin stimulation. We identified HSPA1A and HSPA8 as the HSP70 family proteins that physically interact with DNAJA3, and established their requirement for the phosphorylation of NF-κB p65. Furthermore, as in flies with knockdown of Droj2, flies with knockdown of Hsc70-4, a Drosophila homolog of HSPA8, were more susceptible to infection. Our results suggest that the chaperone/cochaperone complex regulates NF-κB immune signaling in an evolutionarily conserved manner.

The Role of the Phylogenetically Conserved Cochaperone Protein Droj2/DNAJA3 in NF-κB Signaling.

The NF-κB pathway is a phylogenetically conserved signaling pathway with a central role in inflammatory and immune responses. Here we demonstrate that a cochaperone protein, Droj2/DNAJA3, is involved in the activation of canonical NF-κB signaling in flies and in human cultured cells. Overexpression of Droj2 induced the expression of an antimicrobial peptide in Drosophila. Conversely, Droj2 knockdown resulted in reduced expression of antimicrobial peptides and higher susceptibility to Gram-negative bacterial infection in flies. Similarly, Toll-like receptor-stimulated IκB phosphorylation and NF-κB activation were suppressed by DNAJA3 knockdown in HEK293 cells. IκB kinase overexpression-induced NF-κB phosphorylation was also compromised in DNAJA3 knockdown cells. Our study reveals a novel conserved regulator of the NF-κB pathway acting at the level of IκB phosphorylation.

Evaluation of hepatic damage by reactive metabolites--with consideration of circadian variation of murine hepatic glutathione levels.

Generally, reactive metabolites are detoxified by conjugation with glutathione (GSH). A GSH-depleted model was prepared by administering L-buthionine-(S,R)-sulfoximine (BSO), which can be used to detect hepatic damage by reactive metabolites. However, BSO may cause adverse effects on other organs, such as renal damage by reactive metabolites because it depletes GSH in the whole body. The present study was designed to examine whether it was possible to specifically detect hepatic damage by reactive metabolites without reducing renal GSH levels by administering BSO in a time course when hepatic GSH levels are naturally reduced. Male BALB/c mice were administered reverse osmosis (RO) water or 20 mmol/l BSO in drinking water for 4 days. Subsequently, animals in the RO water group were orally administered 500 mg/kg acetaminophen (APAP) at 9:00 or 15:00 and in the BSO group at 9:00 for 4 days. As a result, severe hepatic damage and necrosis of the renal proximal tubules were observed in the BSO/APAP administration at 9:00 group, and all animals died on 1 or 2 days after APAP administration. Hepatic damage was clearly increased in the RO water/APAP administration at 15:00 group compared with the RO water/APAP administration at 9:00 group. However, renal damage and deaths were not observed. This BSO administration model may detect renal damage induced by reactive metabolites. Using an administration time course, whereby hepatic GSH levels were naturally reduced, hepatic damage by reactive metabolites can be detected without secondary renal effects.