Sphingosine kinase-2 inhibition improves mitochondrial function and survival after hepatic ischemia–reperfusion

Abstract

Background/Aims The mitochondrial permeability transition (MPT) and inflammation play important roles in liver injury caused by ischemia-reperfusion (IR). This study investigated the roles of sphingosine kinase-2 (SK2) in mitochondrial dysfunction and inflammation after hepatic IR. Methods Mice were gavaged with vehicle or ABC294640 (50 mg/kg), a selective inhibitor of SK2, 1 h before surgery and subjected to 1 h-warm ischemia to ~70% of the liver followed by reperfusion. Results Following IR, hepatic SK2 mRNA and sphingosine-1-phosphate (S1P) levels increased ~25-fold and 3-fold, respectively. SK2 inhibition blunted S1P production and liver injury by 54% to 91%, and increased mouse survival from 28% to 100%. At 2 h after reperfusion, mitochondrial depolarization was observed in 74% of viable hepatocytes, and mitochondrial voids excluding calcein disappeared, indicating MPT onset in vivo. SK2 inhibition decreased mitochondrial depolarization and prevented MPT onset. Inducible nitric oxide synthase, phosphorylated NFκB-p65, TNFα mRNA, and neutrophil infiltration all increased markedly after hepatic IR, and these increases were blunted by SK2 inhibition. In cultured hepatocytes, anoxia/reoxygenation resulted in increases of SK2 mRNA, S1P levels and cell death. SK2 siRNA and ABC294640 each substantially decreased S1P production and cell death in cultured hepatocytes. Conclusions SK2 plays an important role in mitochondrial dysfunction, inflammation responses, hepatocyte death and survival after hepatic IR and represents a new target for the treatment of IR injury.

Regulation of the Sphingosine Kinase/Sphingosine 1-Phosphate Pathway

“…Moreover, siRNA-mediated downregulation of SK2 was shown to inhibit proliferation and migration in tumor cells (Gao and Smith 2011). Another recently identified role for SK2 is in precondition-mediated protection from cerebral ischemic injury (Shi et al 2012). SK2 inhibition prevented preconditioninduced tolerance to ischemic injury in a rodent stroke model (Garofalo et al 2012).…”

Regulation of Mitochondrial Function by Bioactive Sphingolipids

“…Furthermore, SphK2 is required for the downstream protective modulation of permeability transition as an effector of preconditioning protection [63]. On the contrary, SphK2 generated S1P is detrimental in hepatic ischemia, and inhibition of SphK2 activity improves mitochondrial function and survival in mice after hepatic ischemiareperfusion [64]. [65].…”

“…Besides ATP synthesis, mitochondria are also involved in key cellular functions such as Ca 2+ homeostasis, heme biosynthesis, nutrient metabolism], and signaling pathways for cell death and autophagy [9][10][11]. Mitochondrial dysfunction also leads to many human maladies, such as cancer [12][13][14], aging [15], neurodegenerative disease [16,17], hepatic ischemiareperfusion [18], diabetes [19], cardio-protection [20], and liver injury [21]. Multiple studies show intimate connections between ceramide signaling and the functioning of mitochondria, which play a central role in the integration of cellular signals to determine the outcome among apoptosis, necrosis, or proliferation [22][23][24][25].…”

Divergent Role of Sphingosine 1-Phosphate on Insulin Resistance

“…This is consistent with studies indicating that S1P diminished regeneration of liver injury caused by ischemia-reperfusion. In this model mouse survival increases from 28% to 100%, when S1P formation is inhibited [40]. However it should be noted that another study indicates that repeated injection of S1P decreases hepatic and renal injury after hepatic ischemia-reperfusion, possibly through activation of S1P 1 receptors [41].…”