Description:
<jats:p>
<jats:bold>Introduction:</jats:bold>
Exosomes are cell-derived vesicles in the extracellular environment present in biological fluids. Exosomal content is actively assembled containing mRNA, miRNA and proteins. Exosomal-derived molecules have messenger function on target cells.
</jats:p>
<jats:p>
<jats:bold>Hypothesis:</jats:bold>
The serum-derived exosomal proteome is altered in acute cardiac allograft rejection allowing a distinction between non-rejection and acute rejection episodes with specifics for the type of rejection.
</jats:p>
<jats:p>
<jats:bold>Methods:</jats:bold>
Serum samples were collected from heart transplant (HTx) recipients with no rejection (n=10), acute cellular rejection (n=10) and antibody-mediated rejection (n=8) confirmed by myocardial biopsy and histopathology report. Exosome isolation was performed using an isolation kit (Invitrogen). Proteomic analyses were performed by LC-MS/MS analysis using the Fusion Tribrid Orbitrap Mass Spectrometer. To confirm these findings, one of the proteins found by proteomic analysis, C1Q, was compared across samples with ELISA (Abcam).
</jats:p>
<jats:p>
<jats:bold>Results:</jats:bold>
A distinct pattern was detectable separating each group by clustering analysis. A exosomal protein signature totaling 24 proteins (FDR<2%) was found in the rejection group compared to the no rejection group. Further, patients with ACR had a distinctly different exosomal protein signature compared to patients with AMR. Of note, complement factor components such as C1QA (-53%), C1QB (-36%) and immunoglobulin subfractions such as IGHM (+42%) were the most significantly regulated proteins. Confirmatory ELISA testing of exosomal C1Q levels revealed a trend (p=0.077) towards decreased levels of C1Q in the AMR group but no significant difference in the ACR group.
</jats:p>
<jats:p>
<jats:bold>Conclusions:</jats:bold>
These data suggest a distinct exosomal proteome signature in cardiac allograft rejection patients as compared to patients without rejection, mainly involving complement cascade proteins, immunoglobulin fractions and structural proteins. Exosomal proteome analysis shows potential for non-invasive characterization of cardiac allograft rejection with distinct profiles in patients with ACR and AMR.
</jats:p>