Fig 2: Illustration of ApoE4 in astrocytes and neurons inducing greater cPLA2 activation than ApoE3 through p38 MAPK pathway, leading to more LTB4, iNOS, and ROS production, increased oxidative stress and neuroinflammation

Fig 3: Signaling pathway overview. Hyperglycemia stimulates mesangial production of IL-1β which activates PDGF-BB secretion. In turn, PDGF-BB promotes IL-1β secretion, sustaining and boosting the pathway activation. IL-1β and PDGF-BB stimulation give rise to the production of phosphorylated sphingoid bases, activating COX-2 transcription. At the same time, IL-1β and PDGF-BB stimulate cPLA2 activation. Arachidonic acid (AA) released by cPLA2 is converted into prostanoids by COX-2 and downstream enzymes. The other product of cPLA2, lysophosphatidylcholine (LPC), is converted into lysophosphatidic acid (LPA) by autotaxin. Thus, hyperglycemia triggered the activation of an interplay between IL-1β and PDGF-BB which stimulates the secretion of lipid hormones (prostanoids PGE2, PGI2, but also lysophosphatidic acid) with hemodynamic, proliferative, and migratory effects at glomerular level. Inhibition of the cPLA2 reaction with AACOCF3 blocks the supply of AA for the COX-2 reaction, thus resolving the inflammatory stimulus. In addition, LPC is not produced, and this blocks the supply for the autotaxin reaction and LPA mediated proliferative response.

Fig 4: cPLA2 activity is greater in brains of ApoE4-TR mice compared with ApoE3-TR mice. The cortex of 8-month old ApoE3 and ApoE4-TR mice was collected to extract RNA and proteins. A cPLA2 mRNA level in the cortex was detected by qPCR. B Phosphorylated-cPLA2 and total cPLA2 protein levels in the cortex were detected by western blot. Densitometric quantification from B. D cPLA2 activity in mouse cortex homogenates were measured by cPLA2 activity assay kit. E LTB4 levels in mouse cortical homogenates were measured by an LTB4 assay kit. (n = 5 for each genotype for A-E, 3 males and 2 females). LTB4: leukotriene B4. Data are represented as mean ± SEM and analyzed by Student’s t-test (two-tailed). *p < 0.05

Fig 5: Inhibition of cPLA2 with AACOCF3 1 μM reduces IL-1β, PDGF-BB induced PGE2 secretion. **P < 0.01. Data are reported as mean ± SEM.