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Type: Journal article
Title: Attenuated platelet aggregation in patients with septic shock is independent from the activity state of myosin light chain phosphorylation or a reduction in Rho kinase-dependent inhibition of myosin light chain phosphatase
Author: Reddi, B.
Iannella, S.
O'Connor, S.
Deane, A.
Willoughby, S.
Wilson, D.
Citation: Intensive Care Medicine Experimental, 2015; 3(1):37-1-37-17
Publisher: SpringerOpen
Issue Date: 2015
ISSN: 2197-425X
Statement of
Benjamin AJ Reddi, Samantha M Iannella, Stephanie N O, Connor, Adam M Deane, Scott R Willoughby, and David P Wilson
Abstract: BACKGROUND: Impaired coagulation contributes to the morbidity and mortality associated with septic shock. Whether abnormal platelet contraction adds to the bleeding tendency is unknown. Platelets contract when Ca(2+)-dependent myosin light chain kinase (MLCK) phosphorylates Ser19 of myosin light chain (MLC20), promoting actin-myosin cross-bridge cycling. Contraction is opposed when myosin light chain phosphatase (MLCP) dephosphorylates MLC20. It is thought that Rho kinase (ROK) inhibits MLCP by phosphorylating Thr855 of the regulatory subunit MYPT, favouring platelet contraction. This study tested the hypotheses that in septic shock, (i) platelet function is inversely correlated with illness severity and (ii) ROK-dependent MLCP inhibition and myosin light chain phosphorylation are reduced. METHODS: Blood was sampled from non-septic shock patients and patients in the first 24 h of septic shock. Platelet function was assessed using whole blood impedance aggregation induced by 1) ADP (1.6 and 6.5 μM), 2) thrombin receptor-activating protein (TRAP; 32 μM), 3) arachidonic acid (500 μM) and 4) collagen (3.2 μg/ml). Arachidonic acid-induced aggregation was measured in the presence of the ROK inhibitor Y27632. Illness severity was evaluated using sequential organ failure assessment (SOFA) and acute physiology and chronic health evaluation (APACHE) II scores. Western blot analysis of [Ser19]MLC20 and [Thr855]MYPT phosphorylation quantified activation and inhibition of platelet MLC20 and MLCP, respectively. Data were analysed using Spearman's rank correlation coefficient, Student's t-test and Mann-Whitney test; p < 0.05 was considered significant. RESULTS: Agonist-induced aggregation was attenuated in septic shock patients (n = 22 to 34; p < 0.05). Aggregation correlated inversely with SOFA and APACHE II scores (n = 34; p < 0.05). Thr855 phosphorylation of MYPT from unstimulated platelets was not decreased in patients with septic shock (n = 22 to 24). Both septic shock and ROK inhibition attenuated arachidonic acid-induced platelet aggregation independent of changes in [Ser19]MLC20 and [Thr855]MYPT phosphorylation (n = 14). CONCLUSIONS: Impairment of whole blood aggregation in patients within the first 24 h of septic shock was correlated with SOFA and APACHE II scores. Attenuated aggregation was independent of molecular evidence of diminished platelet contraction or reduced ROK inhibition of MLCP. Efforts to restore platelet function in septic shock should therefore focus on platelet adhesion and degranulation.
Keywords: Platelets; Sepsis; Shock; Aggregation; Rho kinase; Myosin phosphatase; Whole blood impedance aggregometry; Illness severity score
Rights: © 2015 Reddi et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.
RMID: 0030032205
DOI: 10.1186/s40635-014-0037-7
Appears in Collections:Medicine publications

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