Depletion of T lymphocytes ameliorates cardiac fibrosis in streptozotocin-induced diabetic cardiomyopathy

• Diabetic myocardium exhibited profibrotic milieu manifested by increased T cell infiltration with enhanced expression of TGF-β1 and CD34-expressing fibrocytes.
• FTY720 inhibited profibrotic milieu in diabetic myocardium and exerted cardioprotection in diabetic C57BL/6 mice.
• FTY720 augmented cardiac fibrosis in diabetic Rag1 knockout mice.

T cell infiltration has been associated with increased coronary heart disease risk in patients with diabetes mellitus. Effect of modulation of T cell trafficking on diabetes-induced cardiac fibrosis has yet to be determined. Therefore, our aim was to investigate the circulatory T cell depletion-mediated cardioprotection in streptozotocin-induced diabetic cardiomyopathy. Fingolimod (FTY720), an immunomodulatory drug, was tested in wild-type (WT) C57BL/6 and recombination activating gene 1 (Rag1) knockout (KO) mice without mature lymphocytes in streptozotocin-induced type 1 diabetic model. FTY720 (0.3 mg/kg/day) was administered intraperitoneally daily for the first 4 weeks with interim 3 weeks then resumed for another 4 weeks in 11 weeks study period. T lymphocyte counts, cardiac histology, function, and fibrosis were examined in diabetic both WT and KO mice. FTY720 reduced both CD4+ and CD8+ T cells in diabetic WT mice. FTY720-treated diabetic WT mouse myocardium showed reduction in CD3 T cell infiltration and decreased expression of S1P1 and TGF-β1 in cardiac tissue. Fibrosis was reduced after FTY720 treatment in diabetic WT mice. Rag1 KO mice exhibited no CD4+ and CD8+ T cells in the blood and CD3 T cells in the heart. Diabetic Rag1 KO mouse hearts appeared no fibrosis and exhibited preserved myocardial contractility. FTY720-induced antifibrosis was abolished in diabetic Rag1 KO mice. These findings demonstrate that chronic administration with FTY720 induces lymphopenia and protects diabetic hearts in WT mice whereas FTY720 increases cardiac fibrosis and myocardial dysfunction in diabetic Rag1 KO mice without mature lymphocytes.