Thymic medullar conduits-associated podoplanin promotes natural regulatory T cells

Podoplanin, a mucin-like plasma membrane protein, is expressed by lymphatic endothelial cells and responsible for separation of blood and lymphatic circulation through activation of platelets. Here we show that podoplanin is also expressed by thymic fibroblastic reticular cells (tFRC), a novel thymic medulla stroma cell type associated with thymic conduits, and involved in development of natural regulatory T cells (nTreg). Young mice deficient in podoplanin lack nTreg owing to retardation of CD4+CD25+ thymocytes in the cortex and missing differentiation of Foxp3+ thymocytes in the medulla. This might be due to CCL21 that delocalizes upon deletion of the CCL21-binding podoplanin from medullar tFRC to cortex areas. The animals do not remain devoid of nTreg but generate them delayed within the first month resulting in Th2-biased hypergammaglobulinemia but not in the death-causing autoimmune phenotype of Foxp3-deficient Scurfy mice

Thymic medullar conduits-associated podoplanin promotes natural regulatory T cells

Podoplanin, a mucin-like plasma membrane protein, is expressed by lymphatic endothelial cells and responsible for separation of blood and lymphatic circulation through activation of platelets. Here we show that podoplanin is also expressed by thymic fibroblastic reticular cells (tFRC), a novel thymic medulla stroma cell type associated with thymic conduits, and involved in development of natural regulatory T cells (nTreg). Young mice deficient in podoplanin lack nTreg owing to retardation of CD4+CD25+ thymocytes in the cortex and missing differentiation of Foxp3+ thymocytes in the medulla. This might be due to CCL21 that delocalizes upon deletion of the CCL21-binding podoplanin from medullar tFRC to cortex areas. The animals do not remain devoid of nTreg but generate them delayed within the first month resulting in Th2-biased hypergammaglobulinemia but not in the death-causing autoimmune phenotype of Foxp3-deficient Scurfy mice

Indirubin-3'-Monoxime Blocks Vascular Smooth Muscle Cell Proliferation by Inhibition of Signal Transducer and Activator of Transcription 3 Signaling and Reduces Neointima Formation In Vivo.

Objective-Our goal was to examine the influence of indirubin-3 '-monoxime (I3MO), a natural product-derived cyclin-dependent kinase inhibitor, on vascular smooth muscle cell (VSMC) proliferation in vitro, experimentally induced neointima formation in vivo, and related cell signaling pathways. Methods and Results-I3MO dose-dependently inhibited platelet-derived growth factor (PDGF)-BB-induced VSMC proliferation by arresting cells in the G(0)/G(1) phase of the cell cycle as assessed by 5-bromo-2 '-deoxyuridine incorporation and flow cytometry. PDGF-induced activation of the kinases Akt, Erk1/2, and p38(MAPK) was not affected. In contrast, I3MO specifically blocked PDGF-, interferon-gamma-, and thrombin-induced phosphorylation of signal transducer and activator of transcription 3 (STAT3). Human endothelial cells (EA.hy926) responded to I3MO with increased endothelial nitric oxide synthase activity as assessed via [C-14]L-arginine/[C-14]L-citrulline conversion. The specific STAT3 inhibitor Stattic led to decreased VSMC proliferation, and transient expression of a constitutively active form of STAT3 overcame the I3MO-induced cell cycle arrest in mouse embryonic fibroblasts. In a murine femoral artery cuff model, I3MO prevented neointima formation while reducing STAT3 phosphorylation and the amount of proliferating Ki67-positive cells. Conclusion-I3MO represses PDGF-and thrombin-induced VSMC proliferation and, in vivo, neointima formation, likely because it specifically blocks STAT3 signaling. This profile and its positive effect on endothelial NO production turns I3MO into a promising lead compound to prevent restenosis. (Arterioscler Thromb Vasc Biol. 2010;30:2475-2481.

Pulmonary Vein, Dorsal Atrial Wall and Atrial Septum Abnormalities in Podoplanin Knockout Mice With Disturbed Posterior Heart Field Contribution

The developing sinus venosus myocardium, derived from the posterior heart field, contributes to the atrial septum, the posterior atrial wall, the sino-atrial node, and myocardium lining the pulmonary and cardinal veins, all expressing podoplanin, a coelomic and myocardial marker. . We compared development and differentiation of the myocardium and vascular Wall of the pulmonary veins (PV), left atrial dorsal wall, and atrial septum in wild type with podoplanin knockout mouse embryos (E10.5-E18.5) by 3D reconstruction and immunohistochemistry. Expression of Nkx2.5 in the pulmonary venous myocardium changes from mosaic to positive during development pointing Out a high proliferative rate compared with Nkx2.5 negative myocardium of the sino-atrial node and cardinal veins. In Mutants, myocardium of the PVs, dorsal atrial wall and atrial septum was hypoplastic. The atrial septum and right-sided wall of the PV almost lacked interposed mesenchyme. Extension of smooth muscle cells into the left atrial body was diminished. We conclude that myocardium of the PVs, dorsal atrial wall, and atrial septum, as well as the smooth Muscle cells, are derived from the posterior heart field regulated by podoplanin. (Pediatr Res 65: 27-32, 2009