Sex differences in a murine model of Cerebral Amyloid Angiopathy

Abstract

Cerebral amyloid angiopathy (CAA) is one of the common causes of lobar intracerebral hemorrhage and vascular cognitive impairment (VCI) in the aging population. Increased amyloid plaque deposition within cerebral blood vessels, specifically the smooth muscle layer, is linked to increased cerebral microbleeds (CMBs) and impaired cognition in CAA. Studies in Alzheimer's disease (AD) have shown that amyloid plaque pathology is more prevalent in the brains of elderly women (2/3rd of the dementia population) compared with men, however, there is a paucity of studies on sex differences in CAA. The objective of this study was to discern the sexual dichotomies in CAA. We utilized male and female Tg-SwDI mice (mouse model of CAA) at 12-14 months of age for this study. We evaluated sex differences in CMBs, cognitive function and inflammation. Cognition was assessed using Y-maze (spatial working memory) and Fear Conditioning (contextual memory). CMBs were quantified by ex vivo brain MRI scans. Inflammatory cytokines in brain were quantified using ELISA. Our results demonstrated that aging Tg-SwDI female mice had a significantly higher burden of CMBs on MRI as compared to males. Interestingly, these aging Tg-SwDI female mice also had significantly impaired spatial and contextual memory on Y maze and Fear Conditioning respectively. Furthermore, female mice had significantly lower circulating inflammatory cytokines, IL-1α, IL-2, IL-9, and IFN-γ, as compared to males. Our results demonstrate that aging female Tg-SwDI mice are more cognitively impaired and have higher number of CMBs, as compared to males at 12-14 months of age. This may be secondary to reduced levels of neural repair cytokines (IL-1α, IL-2, IL-9 and IFN-γ) involved in sex specific inflammatory signaling in CAA.

Keywords: Cerebral amyloid angiopathy; Cerebral microbleeds; Cognition; MRI.

Fig. 1

Spatial working memory test using Y-maze for Tg-SwDI female (n ​= ​9) vs Tg-SwDI male (n ​= ​9) at 12–14 months of age, A) Total Arm Entry and B) % Alternation. Total testing time per trial of 5 ​minutes demonstrated no difference in Total Arm Entry between female and male mice (A), but female mice demonstrated a significant reduction in % Alternations, or inability to distinguish the novel arm versus familiar arm, compared to male mice. This suggests a more impaired spatial working memory in females, ∗ indicates p ​= ​0.03.

Fig. 2

Fear Conditioning to test contextual memory for Tg-SwDI female (n ​= ​9) vs Tg-SwDI male (n ​= ​14) at 12–14 months of age. Delta Inactive State was calculated using first 60 ​seconds of Training (pre-shock) – Testing (post-shock) to determine “freezing” behavior. Female mice demonstrated a significant reduction in Delta Inactive State or decreased freezing time compared to male mice, suggesting deficits in contextual memory. ∗ indicates p ​< ​0.01.

Fig. 3

A. MRI for cerebral microbleeds (CMBs) in Tg-SwDI female (n ​= ​4) vs Tg-SwDI male (n ​= ​8) at 12–14 months age. Female mice had significantly more total CMBs compared to male mice. ∗∗∗ indicates p ​= ​0.009. Fig. 3 B. Top panel- Females, Bottom panel-males. Left panel: T2 anatomy scan (A and C), Right panel showing T2 star sequence on MRI (B and D). Arrows demonstrate the cerebral microbleeds (CMBs).

Fig. 4

Inflammatory cytokines identified by ELISA from whole brain tissue lysate in Tg-SwDI female (n ​= ​8) vs male (n ​= ​10) mice at 12–14 months of age. Concentrations are represented in pg/ml. Sex differences were identified in four inflammatory cytokine markers with male Tg-SwDI mice having significantly higher concentrations of A) IL-1α, B) IL-2, C) IL-9, and D) IFN-γ, when compared to female Tg-SwDI mice. ∗ IL-1α, p ​= ​0.007∗∗; IL-2, p ​= ​0.01; IL-9, p ​= ​0.01, and IFN-γ, p ​= ​0.012.