Chronic treatment with the S1P modulator FTY can induce fibrosis through S1PR3 signaling leading to systolic heart failure

Background: Fingolimod (FTY) is a commonly used S1P modulator in the treatment of multiple sclerosis. Besides its effect on inflammation, FTY also affects the cardiovascular system. Recent studies have shown an acute effect of FTY on the cardiovascular system, including reduced blood pressure (BP), cardioprotective effects after myocardial infarction (MI) and prevention of perivascular inflammation. However, the effect of chronic administration remains unclear in detail.

Methods: In vivo: Wildtype (WT) and S1PR3 deficient mice (S1PR3^-/-) as well as corresponding littermates were treated with FTY via drinking water (10 mg/L) for 16 weeks. Cardiac function was assessed by echocardiography every four weeks. After the treatment, catheter-based blood pressure measurement was conducted, heart failure markers were analyzed via qPCR from heart tissue (ANP, myosin) and via ELISA from blood samples (NTproBNP). The ratio of fibrosis in heart tissue was determined by histological analyses using Picrosirius red staining. In vitro: Human cardiac fibroblasts (HCFs) were incubated with S1P and FTY for 72h. The percentage of myofibroblasts differentiated from HCFs was evaluated by immunohistological analyses using representative fluorescent markers.

Results: In vivo: WT mice treated with FTY (16 weeks) showed decreased ejection fraction (EF) and stroke volume (SV) as compared to control mice (EF: Con 49.32±3.50% [n=11], FTY 41.91±6.12% [n=11], p=0.0024; SV: Con 38.52±2.85 µl [n=11], FTY 34.80±4.93 µl [n=11], p=0.0425). In addition, a larger left ventricle end-systolic volume (LV-ESV) could be observed in FTY treated animals (LV-ESV: Con 39.80±5.23 µl [n=11], FTY 48.52±7.36 µl [n=11], p=0.0044). Correspondingly, LV internal dimension in systole (LVID, s) was enlarged, but not in diastole (LVID, s: Con 3.20±0.29 mm [n=11], FTY 3.63±0.31 mm [n=11], p=0.0032). Chronic treatment with FTY increased systolic BP (SBP), but not diastolic BP (DBP) (SBP: Con 91.91±3.60 mmHg [n=6], FTY 100.70±3.70 mmHg [n=6], p=0.0019). Furthermore, chronic treatment with FTY augmented fibrosis levels determined by Picrosirius red staining (Con 0.283±0.114% [n=9], FTY 0.408±0.094% [n=10], p=0.0181). Gene expression analysis showed an upregulation of myosin (Myh-7) and heart failure markers ANP in cardiomyocytes of FTY treated animals (Myosin: Con 1.067±0.378 [n=9], FTY 2.018±1.154 [n=9] , p=0.0320; ANP: Con 1.037±0.224 [n=9], FTY 1.476±0.295 [n=9], p=0.0026). These mice also showed elevated biomarker of heart failure in plasma (NTproBNP: Ctrl 127.7±15.4 pg/ml [n=8], FTY 208.7±30.7 pg/ml [n=8], p<0.0001). FTY effects were eliminated in the S1PR3^-/- mice. In Vitro: Treatment with FTY increased the percentage of myofibroblasts differentiated from HCFs (Con: 8.83±2.14% [n=6], S1P: 16.83±3.55% [n=6], p=0.0006, FTY: 17.00±2.68% [n=6] p=0.0005).

Summary: Our study demonstrated that chronic treatment with FTY induces fibrosis through S1PR3 signaling, leading to systolic heart failure, even in the absence of myocardial infarction. Future studies have to show, whether other S1P modulators, such as Ozanimod and Ponesimod, which do not bind to S1PR3, also impact the cardiovascular system.