Perioperative acute renal failure (ARF) is a frequent clinical problem with high financial costs and mortality but there is no effective therapy. Ischemia and reperfusion (IR) injury is the #1 cause of perioperative ARF. We demonstrated during the first funding period that several clinically used volatile anesthetics protect against renal IR injury in rats and mice by directly reducing renal proximal tubule necrotic cell death and inflammation and by attenuating the influx of pro-inflammatory neutrophils, macrophages and lymphocytes after renal IR. The mechanisms involve the externalization of phosphatidylserine (PS) on the plasma membrane of kidney proximal tubule cells initiating the synthesis of the anti-inflammatory cytokine TGF-b1 which in turn activates cytoprotective proteins (i.e. ERK, Akt and HSP70) in renal proximal tubule cells. However, mechanistic questions with therapeutic potential remain with regard to the proximal and distal cellular signaling events linking PS and TGF-b1 signaling and the mechanisms by which volatile anesthetics reduce leukocyte influx into the kidney. In the current proposal, we aim to identify the downstream signaling events of volatile anesthetic- mediated PS externalization and TGF-b1 signaling that mediate the anti-necrotic and anti-inflammatory effects against renal IR injury utilizing physiological, cellular and molecular techniques. Exciting and novel preliminary data generated for this proposal show that sphingosine kinase (SK) is activated by isoflurane in vivo as well as in vitro to increase the generation of a sphingolipid molecule sphingosine-1-phosphate (S1P). Moreover, inhibition of S1P signaling via S1P1 receptor antagonism or SK enzyme inhibition significantly attenuated the renal protective effects of isoflurane in mice. Additionally, isoflurane enhanced the co-localization of SK and TGF-b1 receptors in caveolae lipid rafts and externalized PS via inhibition of flippase by increasing ROS generation. We therefore hypothesize that volatile anesthetics via ROS generation and flippase inhibition externalize PS and release TGF-b1 which activates sphingosine kinase to release S1P following co- localization of signaling molecules in caveolae. This liberated S1P protects renal function by a direct reduction in necrosis of proximal tubule cells and by a direct reduction of leukocyte activation and renal influx. We propose the following specific aims:
Aim #1 : To confirm preliminary findings that the volatile anesthetics cause SK activation and increase S1P in renal proximal tubules to produce renal protection.
Aim #2 : To identify the cellular mechanisms of increased SK activity with volatile anesthetic treatment.
Aim #3 : To determine whether volatile anesthetic-mediated S1P receptor activation in leukocytes reduces intrarenal leukocyte activation and influx and lymphocyte cytokine synthesis after renal IR injury. To test these aims, we will use in vitro [immortalized human proximal tubule cells, primary mouse proximal tubule cultures, freshly isolated renal proximal tubules] as well as in vivo studies in genetically-modified mice. Our findings of volatile anesthetic mediated modulation of cytoprotective sphingolipid signaling clearly have implications beyond renal protection.
We propose that volatile anesthetics protect against renal ischemia reperfusion injury via TGF-beta1-mediated sphingosine kinase activation and S1P release. Our studies will mechanistically advance our understanding of volatile anesthetic-mediated renal tubule protection, leukocyte modulation and improved outcome after renal IR injury.
Showing the most recent 10 out of 32 publications
