Abstract 16837: Exosomes Derived From Podoplanin Positive Cells Induce Serum Amyloid A3 Amyloidosis in Healthy Mouse Heart

The extra-cellular-matrix (ECM) composition of scar tissue after myocardial infarction (MI)has been largely investigated; although fibronectin and collagen are favorable for newmyocyte formation there is a missing component that increase the stiffness and reducethe remodeling of the ischemic area. We identified a primary Serum Amyloid A3 (Saa3)extracellular accumulation that contribute to the chronic alteration of the tissue. Serumamyloid amyloidosis (AA) are characterized by deposition of hepatic misfolded protein,Saa3 is the only amyloid protein that is released locally after inflammation, mostly bymesenchymal progenitor cells. We already described that two days after MI,mesenchymal and endothelial progenitor cells express Podoplanin (PDPN) a plateletaggregation-inducing type I transmembrane glycoprotein as a signal of activation. Exosomes derived from this cohort of cells actively release Saa3 in the ECM affecting thebiology of fibrosis beyond the inflammation. Specific histological staining such asthioflavin t and Congo red, showed amyloid deposition in mouse hearts 1 month after MI;furthermore, immunohistochemistry for Saa3 detected the deposition of the misfoldedprotein alongside fibronectin and collagen. PDPN+ cells were isolated 2 days after MI,cultured expanded and activated with TNFα and AngiotensinII. Activated PDPN positivecells highly expressed Saa3 and exosomes derived from activated PDPN+ cellsconditioned media were used in vivo for the treatment of healthy mouse hearts. Treatedmice developed an extended epicardial fibrosis and amyloidosis with a subsequentimpairment in the contractility and increase of the end diastolic and systolic volumes. Thefibrotic area was characterized by infiltrating CD45+ cells. Novel therapies aimed atpromoting clearance of existing amyloid deposits may be an effective approach in thenear future in the treatment of scar remodeling after MI.