Rac1 regulates platelet shedding of CD40L in abdominal sepsis

Abstract

Matrix metalloproteinase-9 (MMP-9) regulates platelet shedding of CD40L in abdominal sepsis. However, the signaling mechanisms controlling sepsis-induced shedding of CD40L from activated platelets remain elusive. Rac1 has been reported to regulate diverse functions in platelets; we hypothesized herein that Rac1 might regulate platelet shedding of CD40L in sepsis. The specific Rac1 inhibitor NSC23766 (N6-[2-[[4-(diethylamino)-1-methylbutyl] amino]-6-methyl-4-pyrimidinyl]-2 methyl-4, 6-quinolinediamine trihydrochloride) was administered to mice undergoing cecal ligation and puncture (CLP). Levels of CD40L and MMP-9 in plasma, platelets, and neutrophils were determined by use of ELISA, western blot, and confocal microscopy. Platelet depletion abolished the CLP-induced increase in plasma levels of CD40L. Rac1 activity was significantly increased in platelets from septic animals. Administration of NSC23766 abolished the CLP-induced enhancement of soluble CD40L levels in the plasma. Moreover, Rac1 inhibition completely inhibited proteinase-activated receptor-4-induced surface mobilization and secretion of CD40L in isolated platelets. CLP significantly increased plasma levels of MMP-9 and Rac1 activity in neutrophils. Treatment with NSC23766 markedly attenuated MMP-9 levels in the plasma from septic mice. In addition, Rac1 inhibition abolished chemokine-induced secretion of MMP-9 from isolated neutrophils. Finally, platelet shedding of CD40L was significantly reduced in response to stimulation with supernatants from activated MMP-9-deficient neutrophils compared with supernatants from wild-type neutrophils, indicating a direct role of neutrophil-derived MMP-9 in regulating platelet shedding of CD40L. Our novel data suggest that sepsis-induced platelet shedding of CD40L is dependent on Rac1 signaling. Rac1 controls surface mobilization of CD40L on activated platelets and MMP-9 secretion from neutrophils. Thus, our findings indicate that targeting Rac1 signaling might be a useful way to control pathologic elevations of CD40L in the systemic circulation in abdominal sepsis.

Rac1-dependent secretion of platelet-derived CCL5 regulates neutrophil recruitment via activation of alveolar macrophages in septic lung injury

“…Numerous studies have pointed to a functional role of platelets in regulating pathologic aspects of the inflammatory response in severe infections [10,26,34]. For example, there is evidence in the literature showing that platelets are important for the development of dysfunctional coagulation in sepsis [35].…”

“…For example, there is evidence in the literature showing that platelets are important for the development of dysfunctional coagulation in sepsis [35]. Moreover, accumulating evidence has demonstrated that platelets are potent regulators of neutrophil accumulation in septic lung damage [10,26]. One apparent key mechanism is secretion of potent proinflammatory mediators, such as CD40L, harboring in platelets [10,26].…”

“…The intracellular signaling cascades triggering platelet secretion of CCL5 are not well understood. We have recently observed that Rac1, a member of the Rho family, not only plays an important role in septic lung injury [25] but also regulates platelet secretion of CD40L in sepsis [26]. Moreover, it has been reported that Rac1 is essential for lamellipodia formation, granule secretion, clot retraction, and phospholipase Cg2 activation in platelets [27][28][29][30].…”

Inhibition of prostate smooth muscle contraction and prostate stromal cell growth by the inhibitors of Rac, NSC23766 and EHT1864

“…At lower concentrations and shorter exposure, cytotoxicity appeared to be remarkably low. Although cytotoxicity of both inhibitors may be additionally relevant in non-prostatic cells and may limit clinical use, NSC23766 and EHT1864 have been recently applied repeatedly in animal models, where no severe side effects became apparent (Desire et al, 2005;Kawarazaki et al, 2012;Zhang et al, 2013;Hwaiz et al, 2014;Liao et al, 2014;Yoshida et al, 2014).…”

Platelet‐derived microparticles regulates thrombin generation via phophatidylserine in abdominal sepsis

“…Accumulating data suggest that platelets promote pathological inflammation in sepsis (Asaduzzaman et al, 2009;Hwaiz et al, 2014Hwaiz et al, , 2015Rahman et al, 2009). In the present study, it was observed that platelet depletion not only reduced CLP-induced pulmonary levels of MPO but also attenuated lung levels of CXCL2…”