Endothelium Fk506 Binding Protein 12 Deficiency in Endothelial and Hematopoietic Cells Decreases Regulatory T Cells and Causes Hypertension

Patients treated with the immunosuppressive drug tacrolimus (FK506), which binds FK506 binding protein 12 (FKBP12) and then inhibits the calcium-dependent phosphatase calcineurin, exhibit decreased regulatory T cells, endothelial dysfunction, and hypertension; however, the mechanisms and whether altered T-cell polarization play a role are unknown. Tacrolimus treatment of mice for 1 week dose-dependently decreased splenic CD4 /FoxP3 (regulatory T cells), increased splenic CD4 /IL-17 (T-helper 17) cells, and caused endothelial dysfunction and hypertension. To determine the mechanisms, we crossed floxed FKBP12 mice with Tie2-Cre mice to generate offspring lacking FKBP12 in endothelial and hematopoietic cells only (FKBP12EC knockout [KO]). Given the role of FKBP12 in inhibiting transforming growth factorreceptor activation, Tie2-Cre–mediated deletion of FKBP12 increased transforming growth factorreceptor activation and SMAD2/3 signaling. FKBP12EC KO mice exhibited increased vascular expression of genes and proteins related to endothelial cell activation and inflammation. Serum levels of the proinflammatory cytokines IL-2, IL-6, interferon, IL-17a, IL-21, and IL-23 were increased significantly, suggesting a T-helper 17 cell-mediated inflammatory state. Flow cytometry studies confirmed this, because splenic levels of CD4 /IL-17 cells were increased significantly, whereas CD4 /FoxP3 cells were decreased in FKBP12EC KO mice. Furthermore, spleens from FKBP12EC KO mice showed increased signal transducer and activator of transcription 3 activation, involved in T-helper 17 cell induction, and decreased signal transducer and activator of transcription 5 activation, involved in regulatory T-cell induction. FKBP12EC KO mice also exhibited endothelial dysfunction and hypertension. These data suggest that tacrolimus, through its activation of transforming growth factorreceptors in endothelial and hematopoietic cells, may cause endothelial dysfunction and hypertension by activating endothelial cells, reducing regulatory T cells, and increasing T-helper 17 cell polarization and inflammation. (Hypertension. 2011;57:1167-1175.) ● Online Data Supplement