Astrocytic pyruvate dehydrogenase kinase-lactic acid axis involvement in glia-neuron crosstalk contributes to morphine-induced hyperalgesia in mice

The activation of spinal astrocytes accounts for opioid-induced hyperalgesia(OIH),but the underlying mechanisms remain elusive.The presence of astrocyte-neuron lactate shuttle(ANLS)makes astrocytes necessary for some neural function and communication.The aim of this study was to explore the role of ANLS in the occurrence and maintenance of OIH.After 7 days consecutive morphine injection,a mice OIH model was established and astrocytic pyruvate dehydrogenase kinase 4(PDK4),phosphorylated pyruvate dehydrogenase(p-PDH)and accumulation of L-lactate was elevated in the spinal dorsal horn.Intrathecally administration of inhibitors of PDK,lactate dehydrogenase 5 and monocarboxylate transporters to decrease the supply of L-lactate on neurons was observed to attenuate hypersensitivity behaviors induced by repeated morphine administration and downregulate the expression of markers of central sensitization in the spinal dorsal horns.The astrocyte line and the neuronal line were co-cultured to investigate the mechanisms in vitro.In this study,we demonstrated that morphine-induced hyperalgesia was sustained by lactate overload consequent upon aberrant function of spinal ANLS.In this process,PDK-p-PDH-lactate axis serves a pivotal role,which might therefore be a new target to improve long-term opioid treatment strategy in clinical practice.

Deficiency of pyruvate dehydrogenase kinase 4 sensitizes mouse liver to diethylnitrosamine and arsenic toxicity through inducing apoptosis

Background and Aim:Pyruvate dehydrogenase kinase 4(PDK4)is a metabolism switch that regulates glucose oxidation and the tricarboxylic acid cycle(TCA cycle)in the mitochondria.Liver detoxifies xenobiotics and is constantly challenged by various injuries.This study aims at understanding how the loss of the metabolism regulator PDK4 contributes to liver injuries.Methods:Wild-type(WT)and Pdk4 knockout(Pdk4-/-)mice of different ages were examined for spontaneous hepatic apoptosis.Juvenile or adult mice of two genotypes were insulted by diethylnitrosamine(DEN),arsenic,galactosamine(GalN)/lipopolysaccharide(LPS),anti-CD95(Jo2)antibody or carbon tetrachloride(CCl4).Liver injury was monitored by blood biochemistry test.Apoptosis was determined by terminal deoxynucleotidyl transferase dUTP nick end labeling(TUNEL)staining,poly(ADP-ribose)polymerase(PARP)cleavage,and caspase activity assay.Inflammatory response was determined by nuclear factor(NF)-kB activation and the activation of NF-kB target genes.Primary hepatocytes were isolated and cell viability was evaluated by MTS assay.Results:We showed that systematic Pdk4-/-in mice resulted in age-dependent spontaneous hepatic apoptosis.PDK4-deficiency increased the toxicity of DEN in juvenile mice,which correlated with a lethal consequence and massive hepatic apoptosis.Similarly,chronic arsenic administration induced more severe hepatic apoptosis in Pdk4-/-mice compared to WT control mice.An aggravated hepatic NF-kB mediated-inflammatory response was observed in Pdk4-/-mice livers.In vitro,Pdk4-deficient primary hepatocytes were more vulnerable to DEN and arsenic challenges and displayed higher caspase activity than wild type cells.Notably,hepatic PDK4 mRNA level was remarkably reduced during acute liver failure induced by GalN/LPS or Jo2 antibody.The diminished PDK4 expression was also observed in CCl4-induced acute liver injury.Conclusions:PDK4 may contribute to the protection from apoptotic injury in mouse liver.