Abstract P329: Exosomes Derived From Podoplanin Positive Cells Alter The Cellular Composition Of Healthy Mouse Hearts

Fibrosis and blood hypoperfusion stimulated by paracrine signals enhances the ventricular dysfunctionafter myocardial infarction (MI). We have earlier reported that within 2 days post-MI a cohort ofpodoplanin (PDPN) positive cells populate injured heart and enhance inflammatory response by physicalinteractions with monocytes. Here we explored whether exosomes from these cells could independentlyalter healthy heart physiology and structure. PDPN+ cells were isolated 2 days after MI, culture expandedand activated with TNFα and Angiotensin II. Exosomes derived from activated PDPN+cells conditionedmedia (PDPN+exo) were used in vitro for the treatment of mouse cardiac endothelial cells (mCECs) andmouse fibroblast (3T3) and in vivo for the treatment of healthy mouse hearts. In vitro, PDPN+exoinfluenced the phenotype of mCECs, stimulating their lineage into lymphatic endothelial cells andfacilitated fibroblasts transition to myofibroblast. Characterization of the protein content of PDPN+exoshowed high concentration of Notch receptors and γ-Secretase, suggesting these cellular transitions maydepend on exosome-mediated Notch translocation and cleavage. In fact, after exosomes treatmentcleaved notch (NICD) translocated in the nuclei of mCECs and 3T3 as early as 1h of treatment and eitherHes-1 or Hey-1, major transcription factors activated by NICD were enhanced within 2d of treatment.Using DAPT, a γSecretase inhibitor, notch cleavage was inhibited, and no phenotype switching in responseto exosome treatment was observed. In vivo, PDPN+exo were injected into the left ventricle of healthymouse hearts followed by boosters delivered by retro-orbital vein injection. Treated mice developed anextended epicardial fibrosis with a subsequent impairment in the contractility and increase of the enddiastolic and systolic volumes. The fibrotic area was characterized by vessels double positive toendothelial and lymphatic endothelial markers, and infiltrating CD45+ cells. Podoplanin positive cellsrepresent 80% of the scar’s cells of a chronic infarcted myocardium and the specific exosomes cargo highlyinfluence the lineage of cardiac cells altering the biology of endothelial cells and fibroblasts which mayfacilitate adverse remodeling.