The 20 S proteasome core, active within apoptotic exosome-like vesicles, induces autoantibody production and accelerates rejection

Abstract

Autoantibodies to components of apoptotic cells, such as anti-perlecan antibodies, contribute to rejection in organ transplant recipients. However, mechanisms of immunization to apoptotic components remain largely uncharacterized. We used large-scale proteomics, with validation by electron microscopy and biochemical methods, to compare the protein profiles of apoptotic bodies and apoptotic exosome-like vesicles, smaller extracellular vesicles released by endothelial cells downstream of caspase-3 activation. We identified apoptotic exosome-like vesicles as a central trigger for production of anti-perlecan antibodies and acceleration of rejection. Unlike apoptotic bodies, apoptotic exosome-like vesicles triggered the production of anti-perlecan antibodies in naïve mice and enhanced anti-perlecan antibody production and allograft inflammation in mice transplanted with an MHC (major histocompatibility complex)-incompatible aortic graft. The 20S proteasome core was active within apoptotic exosome-like vesicles and controlled their immunogenic activity. Finally, we showed that proteasome activity in circulating exosome-like vesicles increased after vascular injury in mice. These findings open new avenues for predicting and controlling maladaptive humoral responses to apoptotic cell components that enhance the risk of rejection after transplantation.

Antigen Presentation in Transplantation

“…Serum-deprived endothelial cells release, besides apoptotic cell-derived vesicles, exosome-like EVs enriched in the LG3 fragment of the vascular extracellular matrix protein perlecam [90]. Repetitive injection of these endothelial-derived exosome-like EVs, unlike infusion of apoptotic cell vesicles from the same parent cells, triggers production of antibodies against the auto-antigen LG3 and aggravate vascular rejection in mice [90]. …”

Immunoproteasome in the blood plasma of children with acute appendicitis, and its correlation with proteasome and UCHL1 measured by SPR imaging biosensors

“…The release of proteasome in the blood plasma may be a result of membrane disruption. Some authors postulate that the release of active 20S proteasome is regulated [13]. In-vitro studies have shown that proteasome is released by injured endothelial cells, smooth muscle cells of the vessels and tubular epithelial cells [13].…”

“…Some authors postulate that the release of active 20S proteasome is regulated [13]. In-vitro studies have shown that proteasome is released by injured endothelial cells, smooth muscle cells of the vessels and tubular epithelial cells [13]. A study by Ito et al [14] demonstrated that extracellular 20S proteasome is not only released from cells but also plays a functional role in physiological processes.…”

Revealing the diversity of extracellular vesicles using high-dimensional flow cytometry analyses

“…Apoptotic bodies are released by apoptotic cells and generally possess dimensions larger than 1000 nm123. However, it should be noted that these definitions are still subject to change, as larger exosomes (up to 250 nm) have been described, and apoptotic cells also release exosome-like vesicles34. Hence, the term EV is increasingly utilized, as it more liberally encompasses all vesicle types released by cells.…”

“…EV subpopulations may contain active proteasome, organelles ( e.g . mitochondria), and may undergo post-translational modification in disease, such as citrullination in inflammatory arthritis41623252627. Furthermore, EVs are decorated with autoantibodies in autoimmune diseases such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA)162328, and different platelet stimuli were shown to trigger release of different EV subpopulations1824.…”