The Mechanism Of Action Of Phospholipase And Lipidomics In Traumatic Brain Injury

Part ⅠThe Effects of i PLA_2γ and mitochondrial oxidative stress after traumatic brain injury.The i PLA_2γ is calcium-independent phospholipase A2γ enzyme that selectively hydrolyses glycerophospholipids to release free fatty acids.i PLA_2γ-deficient have been associated with abnormal mitochondrial function,more importantly,PLA₂ family was identified as the causative protein in mitochondrial central nervous system disorder such as parkinsonian disorders and spine injury.Here we show that decrease of i PLA_2γ activity,aggravates organismal hypersensitivity to oxidative stress after Traumatic Brain Injury.Furthermore,we demonstrate that decrease of i PLA_2γ activity leads to an elevated number of mitochondrial abnormalities,including mitochondrial ROS generation,caspase-3 activity and abnormal mitochondrial morphology.Moreover,we show that decrease of i PLA_2γ activity is strongly associated with increased lipid peroxidation levels and mitochondrial membrane defects after mechanical stretch.In neuronal mitochondrial lipid metabolism and membrane structure,these results confirmed the obligatory role of i PLA_2γ demonstrating that decrease of i PLA_2γ activity aggravates a mitochondrial neuron disorder characterized by degenerating mitochondria after Traumatic Brain Injury.Part Ⅱ Disentangling oxidation/hydrolysis reactions of brain mitochondrial cardiolipins in pathogenesis of traumatic injuryMechanical injury to the brain triggers multiple biochemical events whose specific contributions to the pathogenesis define clinical manifestations and the overall outcome.Among many factors,mitochondrial injury has recently attracted much attention due to the importance of the organelle for bioenergetics as well as intra-and extra-cellular signaling and cell death.Assuming the essentiality of a mitochondria unique phospholipid,cardiolipin（CL）,for the structural and functional organization of mitochondria,here we applied global（phospho）lipidomics and redox lipidomics to reveal and identify CL modifications during controlled cortical impact（CCI）.We revealed two major pathways activated in the CCI-injured brain as time-specific responses: early accumulation of oxidized CL（CLox）products was followed by the hydrolytic reactions yielding mono-lyso-CLs and free fatty acids（FFA）.To quantitatively assess possible specific roles of peroxidation and hydrolysis of mitochondrial CL,we performed comparative studies of CL modifications using an animal model of Barth syndrome where deficiency of CL re-acylation（Tafazzin（Taz）-deficiency）was associated exclusively with the accumulation of mono-lyso-CLs（but not CLox）.By comparing the in vivo results with the responses to in vitro neuronal injury by mechanical stretch in Taz-deficient neurons and i PLA₂-deficient neurons,we conclude that the two processes-CL oxidation and CL hydrolysis-act as mutually synergistically enhancing components of the pathogenic mechanism of mitochondrial injury in TBI.Part Ⅲ Activation of Bradykinin B2 Receptor induced the Inflammatory Responses of Cytosolic Phospholipase A2 after the early Traumatic Brain InjuryPhospholipase A2 is a known1111 aggravator of inflammation and deteriorates neurological outcomes after traumatic brain injury（TBI）,however the exact inflammatory mechanisms remain unknown.This study investigated the role of bradykinin and bradykinin receptors,which are known initial mediators within inflammation activation,as well as the mechanisms of the cytosolic phospholipase A2（c PLA₂）-related inflammatory responses that occur after TBI.We found that the c PLA₂ and the bradykinin B2 receptor were upregulated after a TBI.Rats treated with the bradykinin B2 receptor inhibitor LF 16-0687 exhibited significantly less c PLA₂ expression and related inflammatory responses in the brain cortex after sustaining a controlled cortical impact（CCI）injury.Both the c PLA₂ inhibitor and the LF16-0687 improved CCI rat outcomes by decreasing neuron death and reducing brain edema.The following TBI model utilized both primary astrocytes and primary neurons in order to gain further understanding of the inflammation mechanisms of the B2 bradykinin receptor and the c PLA₂ in the central nervous system.There was a stronger reaction from the astrocytes as well as a protective effect of LF16-0687 after the stretch injury and bradykinin treatment.The protein kinase C pathway was thought to be involved in the B2 bradykinin receptor as well as the c PLA₂-related inflammatory responses.Rottlerin,a PKCδ inhibitor,decreased the activity of the c PLA₂ activity post-injury,and LF16-0687 suppressed both the PKC pathway and the c PLA₂ activity within the astrocytes.These results indicated that the bradykinin B2receptor-mediated pathway is involved in the c PLA₂-related inflammatory response from the PKC pathway.