Enriched endogenous omega-3 fatty acids in mice protect against global ischemia injury

Abstract

Transient global cerebral ischemia, one of the consequences of cardiac arrest and cardiovascular surgery, usually leads to delayed death of hippocampal cornu Ammonis1 (CA1) neurons and cognitive deficits. Currently, there are no effective preventions or treatments for this condition. Omega-3 (ω-3) PUFAs have been shown to have therapeutic potential in a variety of neurological disorders. Here, we report that the transgenic mice that express the fat-1 gene encoding for ω-3 fatty acid desaturase, which leads to an increase in endogenous ω-3 PUFAs and a concomitant decrease in ω-6 PUFAs, were protected from global cerebral ischemia injury. The results of the study show that the hippocampal CA1 neuronal loss and cognitive deficits induced by global ischemia insult were significantly less severe in fat-1 mice than in WT mice controls. The protection against global cerebral ischemia injury was closely correlated with increased production of resolvin D1, suppressed nuclear factor-kappa B activation, and reduced generation of pro-inflammatory mediators in the hippocampus of fat-1 mice compared with WT mice controls. Our study demonstrates that fat-1 mice with high endogenous ω-3 PUFAs exhibit protective effects on hippocampal CA1 neurons and cognitive functions in a global ischemia injury model.

Fig. 1.

Improved spatial learning and memory in fat-1 mice after 2-VO. The latency per testing session represents the average of four trials of all animals in each group. A: In hidden platform trial, the escape latency(s) of fat-1 mice (n = 6) was significantly lower than that of WT mice on a high ω-6 PUFAs diet (n = 6; P < 0.05) or normal diet (n = 6; P < 0.05) on days 5 and 7 after 2-VO. B: In the space probe trial, the number of platform crossings was significantly increased in the fat-1 mice as compared with their WT counterparts at 7 days after 2-VO (P < 0.05).

Fig. 2.

Evaluation of neuronal survival in the hippocampus CA1 region on day 7 after 2-VO. A: Representative images of Nissl staining on CA1 pyramidal cells. B: Quantitative analyses showed that more surviving neurons were found in the hippocampus CA1 region of fat-1 mice compared with their WT counterparts at day 7 after 2-VO. Values were expressed as mean ± SEM (n = 6 per group, fat-1 mice vs.WT mice on the high ω-6 PUFAs diet, P < 0.05). C: Representative images of double staining of NeuN and TUNEL on CA1 pyramidal cells. D: Quantitative analyses showed that significantly less TUNEL-positive cells were found in the CA1 region of the fat-1 mice compared with their WT counterparts on day 7 after 2-VO. Values were expressed as mean ± SEM (n = 6 per group, fat-1 mice vs.WT mice on the high ω-6 PUFAs diet, P < 0.05). Scale bar: 100 µm for A and 200 µm for C.

Fig. 3.

Inhibited NF-κB activation, reduced production of pro-inflammatory factors, and elevated generation of Resolvin D1 in the hippocampus CA1 region of fat-1 mice after 2-VO. A: The relative expression of GPR120 mRNA in hippocampus on days 1, 3, and 7 after 2-VO using QPCR analyses. No difference was found at any time point between the fat-1 mice group and the WT group (n = 4 per group, P > 0.05). B: Representative images of Western blot taken from the hippocampus CA1 region. C: Quantification of nuclear P65 showed that the level of nuclear p65 was markedly increased in WT mice and pronouncedly decreased in fat-1 mice on days 3 and 7 after 2-VO. D: The protein levels of TNF-α, IL-1β, IL-6, and MCP-1 in the hippocampus of fat-1 mice were significantly decreased compared with those in WT mice on day 7 after 2-VO using ELISA analyses (n = 4 per group, P < 0.05). E: The level of Resolvin D1 in the hippocampus of fat-1 mice was greatly increased on days 1 and 3 after transient global ischemia compared with the expression level in WT mice (n = 4 per group, P < 0.05).

Fig. 4.

Attenuated glial activation in the hippocampus CA1 region of fat-1 mice after 2-VO. A: Representative images taken from the hippocampus CA1 region showed the glial activation was significantly suppressed in the hippocamus CA1 region of fat-1 mice compared with their WT counterparts. B: Quantitative analyses of Iba-1 immunoreactivity confirmed that Iba-1 immunoreactivity in the hippocampus CA1 region of fat-1 mice was significantly suppressed compared with the WT group on day 7 after 2-VO (n = 6 per group, P < 0.05). C: Quantitative analyses of GFAP immunoreactivity confirmed that GFAP immunoreactivity in the hippocampus CA1 region of fat-1 mice was significantly suppressed compared with the WT group on day 7 after 2-VO (n = 6 per group, P < 0.05). Scale bar: 150 µm.