The blood brain barrier is a chemical and physical interface that separates the central nervous system from systemic blood circulation. Dysfunction of the blood brain barrier is implicated in multiple neurodegenerative diseases including Alzheimer’s disease and dementia. Evidence shows consumption of a Western diet can downregulate tight-junction protein expression within the blood brain barrier and may be pivotal to the reduced integrity of the blood brain barrier. Recent studies also suggest a sex-dependent effect on the integrity of the blood brain barrier; however, these sex-dependent effects are not well-established. Moreover, it remains to be seen the interaction of both sex and diet on blood brain barrier integrity. Therefore, the purpose of this study was to determine the effects of diet and sex on the expression of tight-junction proteins in the blood brain barrier. We hypothesized that consumption of a Western diet reduced the expression of tight-junction proteins and that female mice showed protective effects against the downregulation of these proteins. To evaluate these hypotheses, male and female senescence-accelerated mouse-prone 8 (SAMP8) mice were assigned to either a Western diet (45% kcal fat) or a control diet for 32-weeks after a 16-week acclimation period. Following this 32-week intervention, quantitative RT-PCR was used to determine cortical tissue mRNA for tight-junction protein genes claudin-3, claudin-5, claudin-12, occludin, and JAM-A. Additionally, blood brain barrier maintenance genes ZO-1 and Mfsd2a were quantified, as well as, neurotrophic factor BDNF. Sex differences and diet main effects were identified using a two-way (2 × 2) factor ANOVA with statistical significance set at p < 0.05. Following 32-weeks, we observed no significant sex or diet effects for body mass, although the male western diet (MWD) group was significantly heavier than all other groups.
A significant sex (p < 0.001) and diet (p < 0.001) effect were observed for plasma cholesterol concentrations. Male mice and WD-fed mice had greater cholesterol concentrations than female mice and SD-fed mice, respectively. The MWD group were significantly higher compared to the male standard diet (MSD) and female western diet (FWD); moreover, the FWD was higher than the FSD. No sex or diet differences, nor differences between groups was observed for plasma triglyceride concentrations. A sex effect (p < 0.001) was observed for basal glucose concentrations were male mice were higher when compared to female mice. In addition, a diet effect (p = 0.021) was observed for plasma glucose were WD-fed mice were greater that when compared to SD mice. After a glucose tolerance test (GTT), a significant sex effect was observed where male mice had a higher total AUC than female mice; however, no diet effect was observed. Significant interactions were seen with MWD having higher total AUC compared to FWD (p < 0.001) and MSD (p = 0.004).
A significant sex effect was observed for tight-junction proteins claudin-1 (p = 0.035), claudin-5 (p = 0.002), claudin-12 (p < 0.001), occludin (p = 0.003), and JAM-A (p = 0.049); female mice had greater mRNA expression compared to male mice. Additionally, a significant diet effect was observed for tight-junction proteins claudin-1 (p = 0.027) claudin-12 (p < 0.001), occludin (p = 0.002), and JAM-A (p = 0.043); SD-fed mice had greater mRNA expression compared to male mice. A significant interaction was observed between sex and diet for occludin (p = 0.006). When examining pairwise comparisons, the FSD group had significantly expression of claudin-1 (p = 0.004), claudin-5 (p = 0.005), claudin-12 (p < 0.001), occludin (p < 0.001), and JAM-A (p = 0.007) compared to MSD group. Furthermore, the FSD group had significantly higher expression of claudin-1 (p = 0.001) claudin-12 (p < 0.001), occludin (p < 0.001), and JAM-A (p = 0.006) compared to the FWD group. Lastly, the MSD (p < 0.001) and FWD (p = 0.004) groups possessed significantly higher expression of claudin-12 when compared to the MWD group.
A significant sex effect was seen for the associated genes ZO-1 (p = 0.004), Mfsd2a (p = 0.002), and BDNF (p = 0.003); female mice had greater expression compared to male mice. Additionally, a significant diet effect was observed for ZO-1 (p < 0.001), Mfsd2a (p = 0.001), and BDNF (p = 0.001); SD-fed mice had greater expression compared to WD-fed mice. A significant interaction between sex and diet was observed for Mfsd2a (p = 0.014). When examining pairwise comparisons, the FSD possessed significantly greater expression of ZO-1 (p = 0.002), Mfsd2a (p < 0.001), and BDNF (p = 0.006) when compared to MSD. The FSD also possessed significantly greater expression of ZO-1 (p = 0.006), Mfsd2a (p < 0.001), and BDNF (p < 0.001) when compared to FWD. Lastly, the MSD group had significantly greater expression of ZO-1 when compared to the MWD (p = 0.027).
This research supports the hypothesis that the WD induces downregulations in tight-junction protein expression and leads us to believe that female mice are protected against both downregulation in expression both from aging and from the consumption of a WD. No differences were observed for body mass, although male mice displayed hypercholesterolemia and impaired glucose tolerance when compared to female mice. Moreover, consumption of a WD promoted hypercholesterolemia.
Male mice demonstrated significantly lower expression of tight-junction proteins, structural proteins, vesicular movement proteins, and neurotrophic factors when compared to female mice, possibly indicating a protective measure against aging in female mice. Differences in plasma chemistries, specifically cholesterol may be a key effect to conduct further research on as well as directly measuring BBB integrity using molecular tracers. Consumption of a WD reduced expression of these proteins in both sexes, although this effect was more exacerbated in male mice. Overall, reduced expression of tight-junction proteins, structural proteins, movement proteins, and neurotrophic factors may point to decreased integrity of TJs and in turn the BBB. Future research hopes to directly measure protein expression and BBB integrity in vivo.
|Advisor:||Wooten, Joshua S.|
|Commitee:||Guilford, Brianne L., Witt, Ken A.|
|School:||Southern Illinois University at Edwardsville|
|School Location:||United States -- Illinois|
|Source:||MAI 58/06M(E), Masters Abstracts International|
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