Abstract
Promoting brain recovery after stroke is challenging as a plethora of inhibitory molecules are produced in the brain preventing it from full healing. Moreover, the full scope of inhibitory molecules produced is not well understood. Here, using a high-sensitivity UPLC-MS-based shotgun lipidomics strategy, we semiquantitively measured the differential lipid contents in the mouse cerebral cortex recovering from a transient middle cerebral artery occlusion (MCAO). The lipidomic data were interrogated using the soft independent modeling of class analogy (SIMCA) method involving principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA). Statistics of the 578 confirmed lipids revealed 84 species were differentially changed during MCAO/reperfusion. The most dynamic changes in lipids occurred between 1 and 7 days post-MCAO, whereas concentrations had subsided to the Sham group level at 14 and 28 days post-MCAO. Quantitative analyses revealed a strong monotonic relationship between the reduction in phosphatidylcholine (PC)(16:0/16:0) and the increase in lysophosphatidylcholine (LPC)(16:0) levels (Spearman’s Rs = −0.86) during the 1 to 7 days reperfusion period. Inhibition of cPLA2 prevented changes in the ratio between PC(16:0/16:0) and LPC(16:0), indicating altered Land’s cycle of PC. A series of in vitro studies showed that LPC(16:0), but not PC(16:0/16:0), was detrimental to the integrity of neuronal growth cones and neuronal viability through evoking intracellular calcium influx. In contrast, PC(16:0/16:0) significantly suppressed microglial secretion of IL-1β and TNF-α, limiting neuroinflammation pathways. Together, these data support the role of the imbalanced ratio between PC(16:0/16:0) and LPC(16:0), maintained by Lands’ cycle, in neuronal damage and microglia-mediated inflammatory response during ischemic recovery.
Highlights
Cerebral ischemia is caused by the transient or permanent occlusion of blow flow to the brain, which leads to severe brain damage and long-term functional impairments [1, 2]
tetrazolium chloride (TTC) staining of coronal brain sections showed ischemic infarction in the cerebral cortex close to the middle cerebral artery and part of the striatum (Fig. 1C), affecting both motor and sensory cortices of the brain
CPLA2-specific inhibitor arachidonyl trifluoromethyl ketone (ATK) successfully inhibited the flux of conversion from PC(16:0/16:0) to LPC(16:0) during the recovery of middle cerebral artery occlusion (MCAO), as shown in Figure 4F, which strongly supports the role of the Lands cycle in the ischemic injury
Summary
Cerebral ischemia is caused by the transient or permanent occlusion of blow flow to the brain, which leads to severe brain damage and long-term functional impairments [1, 2]. To identify lipid changes in ischemic brains, we used a wellcharacterized mouse long-term recovery model with a 30 min transient occlusion of the middle cerebral artery (MCAO), followed by up to 28 day long-term reperfusion. The volume of ischemic infarction increased significantly in 1- and 3-day groups and decreased to the Sham group level in the 14 and 28 day post-MCAO groups (Fig. 1E).
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