Chronic Akt Activation Attenuated Lipopolysaccharide-Induced Cardiac Dysfunction via Akt/GSK3β-Dependent Inhibition of Apoptosis and ER Stress

摘要

Sepsis is characterized by systematic inflammation and contributes to cardiac dysfunction. This study was designed to examine the effect of Akt activation on LPS-induced cardiac anomalies and underlying mechanism(s) involved. Mechanical and intracellular Ca²⁺ properties were examined in myocardium from wild-type and transgenic mice with cardiac-specific chronic Akt overexpression following LPS (4 mg/kg, i.p.) challenge. Akt signaling cascade (Akt, PTEN, GSK3β), stress signal (ERK, JNK, p38), apoptotic markers (BAX, caspase-3/-9), ER stress markers (GRP78, GADD153, eIF2α), inflammatory markers (TNFα, IL-1β, IL-6) and autophagic markers (Beclin-1, LC3B, Atg7 and p62) were evaluated. Our results revealed that LPS induced marked decrease in ejection fraction, fractional shortening, cardiomyocyte contractile capacity with dampened intracellular Ca²⁺ release and clearance, elevated ROS generation and decreased GSH/GSSG ratio, increased ERK, JNK, p38, GRP78, GADD153, eIF2α, BAX, caspase-3 and - 9, downregulated Bcl-2, the effects of which were significantly attenuated or obliterated by Akt activation. Akt activation itself did not affect cardiac contractile and intracellular Ca²⁺ properties, ROS production, oxidative stress, apoptosis and ER stress. In addition, LPS upregulated levels of Beclin-1, LC3B and Atg7, while suppressing p62 accumulation. Akt activation did not affect Beclin-1, LC3B, Atg7 and p62 in the presence or absence of LPS. Akt overexpression promoted phosphorylation of Akt and GSK3β. In vitro study using the GSK3β inhibitor SB216763 mimicked the response elicited by chronic Akt activation. Taken together, these data showed that Akt activation ameliorated LPS-induced cardiac contractile and intracellular Ca²⁺ anomalies through inhibition of apoptosis and ER stress, possibly involving an Akt/GSK3β-dependent mechanism.