Negative regulation of diacylglycerol kinase θ mediates adenosine-dependent hepatocyte preconditioning

Abstract

In liver ischemic preconditioning (IP), stimulation of adenosine A2a receptors (A2aR) prevents ischemia/reperfusion injury by promoting diacylglycerol-mediated activation of protein kinase C (PKC). By concerting diacylglycerol to phosphatidic acid, diacylglycerol kinases (DGKs) act as terminator of diacylglycerol signalling. This study investigates the role of DGK in the development of hepatocyte IP. DGK activity and cell viability were evaluated in isolated rat hepatocytes preconditioned by 10 min hypoxia followed by 10 min re-oxygenation or by the treatment with the A2aR agonist, CGS21680, and subsequently exposed to prolonged hypoxia. We observed that after IP or A2aR activation, a decrease in DGK activity was associated with the onset of hepatocyte tolerance to hypoxia. CGS21680-induced stimulation of A2aR specifically inhibited DGK isoform h by activating RhoA-GTPase. Consistently, both siRNA-mediated downregulation of DGK h and hepatocyte pretreatment with the DGK inhibitor R59949 induced cell tolerance to hypoxia. The pharmacological inhibition of DGK was associated with the diacylglyceroldependent activation of PKC d and e and of their downstream target p38 MAPK. In conclusion, we unveil a novel signalling pathway contributing to the onset of hepatocyte preconditioning, which through RhoA-GTPase, couples A2aR to the downregulation of DGK. Such an inhibition is essential for the sustained accumulation of diacylglycerol required for triggering PKC-mediated survival signals.

The Role of Diacylglycerol Kinase ζ and Phosphatidic Acid in the Mechanical Activation of Mammalian Target of Rapamycin (mTOR) Signaling and Skeletal Muscle Hypertrophy

“…To begin this analysis, we first took advantage of the DGK inhibitor R59949. Before describing our results, it is important to mention that the DGK family of enzymes is composed of at least 10 different isoforms, and currently available inhibitors of DGK (R59949 and its weaker analog R59902) preferentially inhibit only the ␣, ␤, ␥, and isoforms of DGK (34,35). Consistent with these points, we found that R59949 (100 M) induces a partial, but significant, inhibition of basal DGK activity (Fig.…”

Molecular mechanisms of liver preconditioning

“…However, it is now clear that the accumulation of cellular diacylglycerol also depends on the rate of its metabolism to phosphatidic acid by diacylglycerol kinases (DGKs) [36] . In this regard, we recently observed that following IP or A2aR activation, the onset of hepatocyte tolerance to hypoxia was associated with a decrease in DGK activity [37] . Moreover, stimulation of A2aR specifically inhibited DGK isoform θ by activating RhoA-GTPase [37] .…”

“…Diacylglycerol kinase theta (DGKθ) and the phosphatase tensin-homologues-deleted from chromosome 10 (PTEN) which metabolize diacyglycerol and phosphatidylinositol, respectively, are inhibited during preconditioning to sustain activation of the diacylglycerol (DAG)-dependent PKC δ and ε and the PI3K-dependent signals. See text and Refs [21,25,27,28,32,35,37,43] represents an important pathway in the development of liver IP. Interestingly, PKB/AKT activation in connection with the development of tolerance to I/R was evident in rat hepatocytes and mouse livers [32,34] undergoing IP, as well as in preconditioned human liver grafts immediately after transplantation [35] .…”

Activation of the δ-opioid receptor inhibits serum deprivation-induced apoptosis of human liver cells via the activation of PKC and the mitochondrial pathway

“…The PKC signaling pathway is implicated in a wide range of biological activities and specifically mediates the proliferation and differentiation of a variety of cells. Studies have found that PKC is involved in the preconditioning protection of hepatic ischemia (18). The proliferation and apoptosis of normal cells and hepatic tumor cells closely correlate with PKC (19)(20)(21)(22).…”