Proteomic Evaluation and Immunosuppression in Sepsis Derived Circulating Exosomes

Author(s):
Jon Wisler; Kanhaiya SIngh; Helen Hou; Chandan Sen

Background:

During Sepsis systemic immune dysregulation and immunosuppression is a poor prognostic marker and may predispose survivors to increased infection risk and worse outcomes. During this process, gene expression is significantly altered with subsequent persistent derangement of the pro- and anti-inflammatory responses. During sepsis, circulating exosomes are known to transport cellular cargo and participate is systemic signal amplification.  Exosomes have been implicated in potentiating endothelial dysfunction and gene regulation via microRNA transfer. Despite these advances in knowledge, our understanding of the role of circulating exosomes during sepsis remains limited.

Hypothesis:

We hypothesize that circulating exosomes contain protein cargo important in the regulatory processes involved in the immune response.

Methods:

Circulating exosomes were isolated from plasma of patients with sepsis and septic shock within 24 hours of diagnosis and subjected to 1D liquid chromatography/mass spectrometry and pathway analysis was performed using Gene Ontology Enrichment Analysis and Ingenuity Pathway Analysis.

Results:

Exosomes were isolated from patients with septic shock(n=5) and critical illness without sepsis(n=5). Exosomal origin was predomiinately with monocyte derived in patients with sepsis and controls (64% vs. 72%).  198 total proteins were detected. 18 were differentially expressed with 17 downregulated and 1 upregulated(p<0.05). Gene ontology identified several key downregulated biological process including the immune system and response to stimuli. These downregulated process were largely focused on the immune response and the defense response to bacteria. Ingenuity Pathway Analysis identified several involved networks including primary immunodeficiency signaling, hematopoiesis from pluripotent stem cells, and communication between innate and adaptive immune cells. Taken together, these pathway analyses suggest a significant role for sepsis derived circulating exosomes in relation to immunomodulation and immunosuppression.

Conclusions:

Sepsis-derived exosomes are rich in protein networks involved in key regulatory components of the immune response.  Several networks identified are important in the anti-inflammatory response suggesting an immunosuppresive effect.  These data are important because they offer new insights into the regulatory mechanisms involved in the septic response.  Additionally, existing data suggests that a heightened anti-inflammatory response is associated with worse outcomes in patients with sepsis, and circulating exosomes may be used as a novel therapeutic target to maintain immune function.