TNFR1 Expressing Exosomes are Critical Mediators of Pathological Immune Activation in the Spleen post-Myocardial Infarction

Project Summary
Immune activation is a hallmark of myocardial infarction (MI) and dictate infarct healing and left ventricular (LV)
remodeling. It is established, both in preclinical and clinical studies, that immediately after infarction immune
cells from the spleen and the bone-marrow (BM) egress into the systemic circulation and traffic to the ischemic
hearts. This suggests that the damage signals from the injured hearts are communicated to the lymphoid and
the hematopoietic tissues to initiate cardiac-specific immune responses. However, the mechanisms by which
these signals are transferred to the immune-rich niches such as the spleen are not known.
Recent studies have shown that exosomes, membranous vesicles of 30-100 nm size, are potent
intercellular communication vehicles that can shuttle mRNA, miRNA, and proteins to the distant tissues for
physiological and pathological immune activation. It is also known that circulating exosomal levels increase
during myocyte damage and contain sarcomeric, cytosolic and mitochondrial proteins in their cargo. Despite
this understanding, it is not known if exosomes also serve as the antigenic vehicles to carry damage-
associated protein signals from the ischemic myocardium to the spleen for subsequent immune activation.
Indeed, our preliminary results clearly show that intravenous administration of exosomes released by the
ischemic hearts (as compared to sham) into the naïve mice induce i) systolic dysfunction (increased end-
diastolic and end-systolic volumes and decreased ejection fraction), ii) gene expression of damage associated
signals (S100A8, S100A9 and eotaxin) in the left-ventricles, iii) splenic remodeling, and iv) infiltration of innate
and adaptive immune cells in the myocardium. Moreover, MI exosomes expressed tumor necrosis factor
receptor-1 (TNFR1; and not TNFR2) on their membranes, a classical pro-inflammatory signaling molecule that
have been shown to correlate with HF severity and cardiac dysfunction clinically. Importantly, intravenous
injection of exosomes isolated from 1d MI TNFR1-/- mice failed to induce cardiac dysfunction in naïve mice
suggesting a potent, and previously unknown, role of exosomal TNFR1 in mediating immune activation post-MI
and cardiac dysfunction. Therefore, this led us to hypothesize that exosomes carry cardiac antigens to mediate
splenic immune cell activation during MI, are critical for immune cell mediated pathological LV remodeling, and
these effects are dependent upon the exosomal TNFR1 expression. Importantly, these are key cellular targets
for immunomodulation. We will test this hypothesis by i) determining the pathophysiological role of the spleen
in mediating exosomal processing post-MI, ii) defining the source and role of vesicular TNFR1 in exosome
mediated cardiac dysfunction, and iii) determining the role of exosomal TNFR1 in mediating immunogenic
signaling.

Grant Number: 5R01HL153164-06
NIH Institute/Center: NIH
Principal Investigator: Shyam Bansal