Review of cellular and molecular pathways linking thrombosis and innate immune system during sepsis

Abstract

Cellular and molecular pathways link thrombosis and innate immune system during sepsis. Extrinsic pathway activation of protease thrombin through FVIIa and tissue factor (TF) in sepsis help activate its endothelial cell (EC) membrane Protease Activated Receptor 1 (PAR-1). Thrombin adjusts the EC cycle through activation of G proteins (G12/13), and later through Rho GEFs (guanine nucleotide exchange factors), and provides a path for Rho GTPases mediated cytoskeletal responses involved in shape change and permeability of the EC membrane leading to an increase of leakage of plasma proteins.

At the same time, thrombin stimulates spontaneous mitogenesis by inducing activation of the cell cycle from G0-G1 to S by down-regulation of p27Kip1, a negative regulator of the cell cycle, in association with the up-regulation of S-phase kinase associated protein 2 (Skp2). After transport in cytoplasm, p27 Kip1 binds to RhoA thus prevent activation of RhoA by GEFs, thus inhibit GDP-GTP exchange mediated by GEFs. In cytoplasm, releasing factor (RF) p27-RF-Rho is able to free RhoA. P27 RF-Rho binds p27kip1 and prevents p27kip1 from binding to RhoA. Exposed RhoA is later able to increase the expression of the F-box protein Skp2, after its Akt triggered 14-3-3-β-dependent cytoplasm relocation. Skp2 increases cytoplasm ubiquitination-dependent degradation of p27Kip1. Additionally, after septic induction of canonical NF-kB pathway in EC through TLR4/IRAK4/TRAF/IkB, an IKKα dimer phosphorylates the p52 precursor NF-kB2/p100, leading to p100 processing and translocation of RelB/p52 to the nucleus. By controlling the NF-kB-RelB complex, IKKα signaling regulates the transcription of the Skp2 and correspondingly p27Kip1.