Immunosuppression With FTY720 Reverses Cardiac Dysfunction in Hypomorphic ApoE Mice Deficient in SR-BI Expression That Survive Myocardial Infarction Caused by Coronary Atherosclerosis

Abstract

Aims: We recently reported that immunosuppression with FTY720 improves cardiac function and extends longevity in Hypomorphic ApoE mice deficient in scavenger receptor Type-BI expression, also known as the HypoE/SR-BI(–/–) mouse model of diet-induced coronary atherosclerosis and myocardial infarction (MI). In this study, we tested the impact of FTY720 on cardiac dysfunction in HypoE/SR-BI(–/–) mice that survive MI and subsequently develop chronic heart failure.

Methods/results: HypoE/SR-BI(–/–) mice were bred to Mx1-Cre transgenic mice, and offspring were fed a high-fat diet (HFD) for 3.5 weeks to provoke hyperlipidemia, coronary atherosclerosis, and recurrent MIs. In contrast to our previous study, hyperlipidemia was rapidly reversed by inducible Cre-mediated gene repair of the HypoE allele and switching mice to a normal chow diet. Mice that survived the period of HFD were subsequently given oral FTY720 in drinking water or not, and left ventricular (LV) function was monitored using serial echocardiography for up to 15 weeks. In untreated mice, LV performance progressively deteriorated. Although FTY720 treatment did not initially prevent a decline of heart function among mice 6 weeks after Cre-mediated gene repair, it almost completely restored normal LV function in these mice by 15 weeks. Reversal of heart failure did not result from reduced atherosclerosis as the burden of aortic and coronary atherosclerosis actually increased to similar levels in both groups of mice. Rather, FTY720 caused systemic immunosuppression as assessed by reduced numbers of circulating T and B lymphocytes. In contrast, FTY720 did not enhance the loss of T cells or macrophages that accumulated in the heart during the HFD feeding period, but it did enhance the loss of B cells soon after plasma lipid lowering. Moreover, FTY720 potently reduced the expression of matrix metalloproteinase-2 and genes involved in innate immunity-associated inflammation in the heart.

Conclusions: Our data demonstrate that immunosuppression with FTY720 prevents postinfarction myocardial remodeling and chronic heart failure.

Figure 1

A. Survival curves of HypoE/SRB1^−/− MX1-Cre mice (n=37–39) fed HFD followed by a chow diet with and without FTY720 for up to 15 weeks. B. Plasma cholesterol levels (n=4–16) were measured after 3.5 weeks HFD (0) and at 3, 6, 10, and 15 weeks after start of FTY720 treatment. Data are mean ± SEM. *P<0.05 versus control.

Figure 2

A. Quantification of aortic root lesion area from HypoE/SRB1^−/− MX1-Cre mice fed HFD for 3.5 weeks followed by 15 weeks chow diet with or without FTY720 (n=6–8). *P<0.05 versus both + and − FTY720. B. Representative images of aortic root lesions stained with ORO from HypoE/SRB1^−/− MX1-Cre mice fed HFD for 3.5 weeks followed by 15 weeks chow diet with or without FTY720.

Figure 3

A. Quantification of occluded coronary arteries from HypoE/SRB1^−/− MX1-Cre mice fed HFD for 3.5 weeks followed by 15 weeks chow diet with or without FTY720 (n=8–13). No, non-occluded (0–5%); Partial (5–50%); Severe (50–95%); Complete (100%). B. Representative images of occluded coronary arteries stained with Picro Sirius Red and counterstained with Fast Green. No, non-occluded (0–5%); Partial (5–50%); Severe (50–95%); Complete (95–100%).

Figure 4

Echocardiographic measures of left ventricular performance (n=13–39). Ejection fraction (A) and fractional shortening (B), left ventricular end-diastolic volume (LVEDV) (C) and left ventricular end-systolic volume (LVESV) (D) in HypoE/SRB1^−/− MX1-Cre mice at baseline, fed a HFD for 3.5 weeks, or fed a chow diet with and without FTY720 for up to 15 weeks following HFD. Data are mean ± SEM. *P<0.05 (− FTY720 versus + FTY720).

Figure 5

Absolute numbers (n=5–13) of T cells (CD3⁺ B220⁻) (A), B cells (CD3⁻ B220⁺) (B), neutrophils (Ly6G⁺ CD11b⁺) (C) and monocytes (Ly6G⁻ CD11b⁺) (D) in peripheral blood in HypoE/SRB1^−/− MX1-Cre mice fed a HFD for 3.5 weeks and in mice at 1, 3, 6, and 15 weeks on a chow diet with or without FTY720 treatment. Data are mean ± SEM. *P<0.05, − FTY720 versus + FTY720.

Figure 6

Relative mRNA expression levels (n=7) of CD45⁺ Leukocytes (A), B220⁺ B cells (B), CD4⁺ T cells, and F4/80⁺ macrophages in hearts from mice before HFD, immediately after HFD, and at 6 and 15 weeks post-HFD with or without FTY720. The relative quantity of mRNA was compared to baseline (Base, before HFD). Data are mean ± SEM. *P<0.05, **P<0.01

Figure 7

Relative mRNA expression levels (n=7) of full length (A), truncated (B) MMP-2, (C) MMP-9, and (D) MMP-14 in hearts from mice at baseline (base), immediately after high-fat diet (HFD), and 6 and 15 weeks post-HFD on a chow diet with or without FTY720. Relative mRNA expression was compared to baseline (Base, before HFD). Data are mean ± SEM. *P<0.05

Figure 8

Relative mRNA expression levels (n=7) of IL-6 (A), CCL7 (B), OAS1A (C), IRF-7 (D), and IFTI1 (E) in hearts from mice before HFD, immediately after HFD, and at 6 and 15 weeks post-HFD with or without FTY720. The relative quantity of mRNA was compared to baseline (Base). Data are mean ± SEM. *P<0.05, **P<0.01