Pro- and Anti-inflammatory Effects of High Cholesterol Diet on Aged Brain - PubMed (original) (raw)

Pro- and Anti-inflammatory Effects of High Cholesterol Diet on Aged Brain

Yali Chen et al. Aging Dis. 2018.

Abstract

Both hypercholesterolemia and aging are related to cognitive decline or Alzheimer's disease. However, their interactive influence on the neurodegenerative progress remains unclear. To address this issue, 6-month-old and 16-month-old female mice were fed a 3% cholesterol diet for 8 weeks, followed by hippocampus-related functional, pathological, biochemical and molecular analyses. The high cholesterol diet did not exacerbate age-dependent cognitive decline and hippocampal neuronal death, and even greatly mitigated decreases of synaptophysin and growth associated protein 43 expression in the hippocampus of aged mice. Compared with young controls, aged mice fed normal diet showed mild activation of hippocampal microglia with increased expression of CD68, a marker of the microglial M1 phenotype, and decreased expression of CD206, a marker of the microglial M2 phenotype. More interestingly, the high cholesterol diet not only improved NLRP3 inflammasome activation and IL-1β expression, but also increased levels of anti-inflammatory cytokines IL-4 and IL-6 in the hippocampus of old mice, suggesting playing pro- and anti-neuroinflammatory effects. In addition, the cholesterol rich diet resulted in a defect of the blood-brain barrier of aged hippocampus, as revealed by increased brain albumin content. These results have revealed both harmful and protective effects of high cholesterol diet on aged brain, which helps us to understand that hypercholesterolemia in the aged population is not associated with dementia and cognitive impairment.

Keywords: aging; brain; high cholesterol diet; neuroinflammation; synaptic proteins.

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Figures

Figure 1.

Figure 1.

Serum cholesterol analysis of young and aged female mice fed a normal or high-cholesterol diet for 8 weeks. (A) Total cholesterol (TC). (B) High-density lipoprotein cholesterol (HDL-C). (C) Low-density lipoprotein cholesterol (LDL-C). Results were expressed as mean ± SEM. Tests were performed in duplicate on 8 serum samples per group. *P < 0.05, **P < 0.01, ***P < 0.001, high cholesterol diet (HC) mice versus normal control (ctrl) diet mice; #P < 0.05, ##P < 0.01, ###P < 0.001, aged mice versus young mice.

Figure 2.

Figure 2.

Cognitive analysis of young and aged female mice fed a normal or high-cholesterol diet for 8 weeks. (A) The percentage of time spent in the novel arm of the Y-maze. (B) The numbers of entries into the novel arm of the Y-maze. (C) The mean escape latency during the hidden platform training period of the Morris water maze test. (D) Swimming speed. (E) The percentage of time spent in the target quadrant. (F) The number of crossing the platform area. Results were expressed as mean ± SEM from 8 mice per group. #P < 0.05, aged mice versus young mice.

Figure 3.

Figure 3.

Pathological analysis of hippocampal neurons of young and aged female mice fed a normal or high-cholesterol diet for 8 weeks. (A) Nissl staining. Degenerative (dark) neurons were densely stained (arrowheads). (B) The percentage of dark neurons. (C) Immunostaining for cleaved-caspase 3. A few apoptotic neurons were marked by arrowheads. (D) The percentage of cleaved-caspase 3 positive neurons. Results were expressed as mean ± SEM of tests in duplicate on 4 hippocampal samples per group. ##P < 0.01, aged mice versus young mice.

Figure 4.

Figure 4.

Analyses of synapse-related protein levels in the hippocampus of young and aged female mice fed a normal or high-cholesterol diet for 8 weeks. (A) Representative immunoblot bands of SYP, GAP43, PSD-95 and CAMKII. (B) The corresponding densitometry analysis. Results were expressed as mean ± SEM of tests in duplicate on 4 hippocampal samples per group. *P < 0.05, **P < 0.01, high cholesterol diet (HC) mice versus normal control (ctrl) diet mice; #P < 0.05, ## P < 0.01. ### P < 0.001, aged mice versus young mice.

Figure 5.

Figure 5.

Analyses of glial activation and levels of pro-inflammatory and anti-inflammatory factors in the hippocampus of young and aged female mice fed a normal or high-cholesterol diet for 8 weeks. (A) Immunohistochemical staining for GFAP. (B) Immunohistochemical staining for Iba-1. (C) Cellular surface of GFAP positive astrocytes and Iba-1 positive microglia. (D) Cell counts of GFAP positive astrocytes and Iba-1 positive microglia. (E) The quantitative real-time PCR analysis of mRNA levels of IL-1β, IL-6 and TNF-α. (F) The quantitative real-time PCR analysis of mRNA levels of IL-4 and IL-10. Results were expressed as mean ± SEM of tests in duplicate on 4 hippocampal samples per group. *P < 0.05, ***P < 0.001, high cholesterol diet (HC) mice versus normal control (ctrl) diet mice; #P < 0.05, ###P < 0.001, aged mice versus young mice.

Figure 6.

Figure 6.

Levels of CD68 and CD206 in the hippocampus of young and aged female mice fed a normal or high-cholesterol diet for 8 weeks. (A) Representative immunoblot for CD68 and CD206. (B) The corresponding densitometry analysis. Results were expressed as mean ± SEM of tests in duplicate on 4 hippocampal samples per group. *P < 0.05, high cholesterol diet (HC) mice versus normal control (ctrl) diet mice; #P < 0.05, aged mice versus young mice.

Figure 7.

Figure 7.

Activation of NLRP3 inflammasomes in the hippocampus of young and aged female mice fed a normal or high-cholesterol diet for 8 weeks. (A and B) Representative immunoblot of proteins involved in the first and second signal pathways of NLRP3 inflammasome activation. (C and D) The corresponding densitometry analysis. Results were expressed as mean ± SEM of tests in duplicate on 4 hippocampal samples per group. *P < 0.05, **P < 0.01, high cholesterol diet (HC) mice versus normal control (ctrl) diet mice; #P < 0.05, ##P < 0.01, ###P < 0.001, aged mice versus young mice.

Figure 8.

Figure 8.

Analyses of BBB related protein levels in the hippocampus of young and aged female mice fed a normal or high-cholesterol diet for 8 weeks. (A) Representative immunoblot bands of ZO-1, serum albumin and CD31. (B) The corresponding densitometry analysis. Results were expressed as mean ± SEM of tests in duplicate on 4 hippocampal samples per group. *P < 0.05, high cholesterol diet (HC) mice versus normal control (ctrl) diet mice; #P < 0.05, ###P < 0.01, aged mice versus young mice.

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