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Platelet-dependent pulmonary recruitment of neutrophils in abdominal sepsis

Rahman, Milladur LU (2012) In Lund University, Faculty of Medicine, Doctoral Dissertation Series 2012:26.
Abstract (Swedish)
Popular Abstract in Swedish

Sepsis, blodförgiftning, är ett potentiellt allvarligt tillstånd där bakterier eller deras toxiner aktiverar immunsystemet I blodbanan. Svår sepsis är associerad med organdysfunktion och hög mortalitet (30-60%). Cirka 200 per 100 000 invånare i Sverige drabbas årligen av svår sepsis. Akut lungskada är en central komponent hos patienter med sepsis och experimentella studier har visat att aktivering och ackumulering av vita blodkroppar är ett hastighetsberoende steg i sepsis-associerad lungskada. Trombocyter är kända för sin viktiga roll vid blödning och sårläkning men nyare data indikerar också att trombocyter är också viktiga vid inflammatoriska reaktioner. Den här avhandlingen fokuserar på den... (More)
Popular Abstract in Swedish

Sepsis, blodförgiftning, är ett potentiellt allvarligt tillstånd där bakterier eller deras toxiner aktiverar immunsystemet I blodbanan. Svår sepsis är associerad med organdysfunktion och hög mortalitet (30-60%). Cirka 200 per 100 000 invånare i Sverige drabbas årligen av svår sepsis. Akut lungskada är en central komponent hos patienter med sepsis och experimentella studier har visat att aktivering och ackumulering av vita blodkroppar är ett hastighetsberoende steg i sepsis-associerad lungskada. Trombocyter är kända för sin viktiga roll vid blödning och sårläkning men nyare data indikerar också att trombocyter är också viktiga vid inflammatoriska reaktioner. Den här avhandlingen fokuserar på den potentiella betydelsen av trombocyter vid sepsis. I det första arbetet observerades att om man tog bort trombocyterna från möss minskade aktiveringen och rekrytering av vita blodkroppar, neutropfila granulocyter, till lunga med minskad vävnadsskada som följd. Inhibering av PSGL-1 fullständigt blockerade aggregat bildningen mellan trombocyter och neutrofiler vid sepsis. Det vill säga att den här trombocyt-beroende aktivering av neutrofiler visade sig vara oberoende av fysisk kontakt mellan trombocyterna och neutrofilerna. Istället kunde det konstateras att någon eller några faktorer som utsöndras i löslig form från trombocyter i sin tur aktiverade cirkulerande neutrofiler vid sepsis. I arbete nummer två observerade vi att löslig form av CD40L ökade kraftigt i blodet vid sepsis och att den här ökningen försvann helt om man tog bort trombocyterna före induktion av sepsis. I det här arbetet identifierades CD40L vara den molekyl som utsöndras från trombocyter och som aktiverar neutrofiler i blodbanan. Blockering av CD40L minskade inte bara aktivering av neutrofiler utan reducerade också sepsis inducerad lungskada. CD40L-medierad aktivering av neutrofiler visade sig vara indirekt via bildningen av MIP-2 som är en potent stimulator av neutrofiler. I det tredje arbetet visade det sig att lösligt CD40L också ökade i blodet på patienter med sepsis jämfört med friska kontroller. Löslig CD40L ökade inte bara vid septisk chock utan också vid chock orsakad av andra faktorer än bakterier. De här resultaten indikerar att fynden i de två första djurexperimentella arbetena kan vara relevanta också hos patienter med sepsis. I arbete fyra undersöktes mekanismer som kan förklara hur CD40L frisätts från trombocyter vid sepsis. Blockering av en grupp av enzym, metalloproteinaser (MMP), visade sig hindra frisättning av CD40L från trombocyter och därmed aktiveringen av neutrofiler samt minskade lungskadan vid sepsis. Efter att ha konstaterat att något MMP kan vara involverat, mättes bildningen av relevanta kandidater, MMP-2 och MMP-9, i blodet. Det visade sig att MMP-9 men inte MMP-2 ökade i blodet vid sepsis. Med hjälp av möss som saknar MMP-9 kunde det fastställas att MMP-9 reglerade CD40L frisättningen från trombocyter vid sepsis. I direkta försök på isolerade trombocyter kunde det konstateras att MMP-9 ökar på ytan av aktiverade trombocyter och spelar en direkt avgörande roll för frisättning av CD40L. Det visade sig också att patienter hade förhöjda nivåer av MMP-9 i blodet jämfört med friska kontroller vilket skulle kunna betyda att MMP-9 också spelar en funktionell roll vid sepsis. Sammanfattningsvis kan det konstateras att trombocyter spelar en viktig roll vid sepsis genom att aktivera cirkulerande neutrofiler via frisättning av CD40L. Dessutom visar den här avhandlingen att MMP-9 upregleras på aktiverade trombocyter och frisätter CD40L ligand. Mot bakgrund av att dessa molekyler också ökar vid hos patienter med sepsis skulle CD40L och MMP-9 kunna utgöra nya och mer specifika måltavlor för behandling av patienter med svår sepsis. (Less)
Abstract
Sepsis and subsequent multiple organ failure remain the major cause of mortality in intensive care units. Leukocyte-mediated tissue damage is a key feature in septic lung injury. Accumulating data suggest that platelets play a role in inflammation and tissue injury. However, the role of platelets in sepsis-induced leukocyte recruitment and lung edema formation in abdominal sepsis is not demonstrated yet. We hypothesized that platelets may play a significant role in pulmonary neutrophil recruitment and tissue damage in abdominal sepsis. For this purpose, we used the mice cecal ligation and puncture (CLP) model of abdominal sepsis. CLP causes significant pulmonary damage characterized by neutrophil infiltration, increased levels of CXC... (More)
Sepsis and subsequent multiple organ failure remain the major cause of mortality in intensive care units. Leukocyte-mediated tissue damage is a key feature in septic lung injury. Accumulating data suggest that platelets play a role in inflammation and tissue injury. However, the role of platelets in sepsis-induced leukocyte recruitment and lung edema formation in abdominal sepsis is not demonstrated yet. We hypothesized that platelets may play a significant role in pulmonary neutrophil recruitment and tissue damage in abdominal sepsis. For this purpose, we used the mice cecal ligation and puncture (CLP) model of abdominal sepsis. CLP causes significant pulmonary damage characterized by neutrophil infiltration, increased levels of CXC chemokines and increased edema formation in the lung. CLP also provoked Mac-1 expression on circulating neutrophils. Interestingly, depletion of platelets reduced CLP-induced lung damage, neutrophil recruitment in the bronchoalveolar space and edema formation as well as up-regulation of Mac-1 on neutrophils. However, blocking of platelet-neutrophil aggregates formation did not attenuate CLP-induced lung damage and neutrophil activation suggesting that platelets regulate sepsis-induced lung damage via up-regulation of Mac-1 in a contact independent manner. We also found that plasma levels of soluble CD40L was significantly increased in septic mice. Use of CD40L-deficient mice confirmed that platelet-derived CD40L is a pivotal mediator of neutrophil activation and recruitment in abdominal sepsis and this platelet mediated neutrophil activation was indirect and mediated via formation of MIP-2 and CXCR2 signaling. In addition, we observed a significant increase of soluble CD40L levels in septic patients. Interestingly, we found that inhibition of matrix MMPs reduced Mac-1 up-regulation on neutrophils and CXC chemokine formation in the septic lung injury. We also found that MMP-9 levels are significantly increased in septic mice but not MMP-2. In vitro studies revealed that activated platelets up-regulate surface expression of MMP-9 and that inhibition of MMP-9 decreased platelet shedding of CD40L. Use of MMP-9-deficient mice suggested that MMP-9 regulates platelet CD40L shedding in abdominal sepsis. Moreover, pulmonary infiltration of neutrophils as well as edema formation and lung injury were markedly decreased in septic animals lacking MMP-9. Plasma levels of MMP-9 were significantly increased in patients with septic shock compared to healthy controls. Taken together, platelets regulate neutrophil activation in abdominal sepsis via MMP-9-dependent shedding of platelet-derived CD40L. Thus, MMP-9 and CD40L may constitute novel and effective therapeutic targets in abdominal sepsis. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Sund, Malin, Department of Surgical and Perioperative Sciences, University of Umeå, Sweden
organization
publishing date
type
Thesis
publication status
published
subject
keywords
abdominal sepsis, neutrophil recruitment, platelet, lung injury
in
Lund University, Faculty of Medicine, Doctoral Dissertation Series
volume
2012:26
pages
118 pages
publisher
Section for Surgery, Dept of Clinical Sciences, Malmö, Lund University
defense location
Clinical Research Centre (CRC) Aula, Entrance 72, Skåne University Hospital, Malmö
defense date
2012-03-23 13:00
ISBN
978-91-86671-88-8
1652-8220
language
English
LU publication?
yes
id
f2d05196-08e6-4357-af8f-b704b362a558 (old id 2364989)
date added to LUP
2012-03-07 09:41:10
date last changed
2016-09-19 08:45:12
@phdthesis{f2d05196-08e6-4357-af8f-b704b362a558,
  abstract     = {Sepsis and subsequent multiple organ failure remain the major cause of mortality in intensive care units. Leukocyte-mediated tissue damage is a key feature in septic lung injury. Accumulating data suggest that platelets play a role in inflammation and tissue injury. However, the role of platelets in sepsis-induced leukocyte recruitment and lung edema formation in abdominal sepsis is not demonstrated yet. We hypothesized that platelets may play a significant role in pulmonary neutrophil recruitment and tissue damage in abdominal sepsis. For this purpose, we used the mice cecal ligation and puncture (CLP) model of abdominal sepsis. CLP causes significant pulmonary damage characterized by neutrophil infiltration, increased levels of CXC chemokines and increased edema formation in the lung. CLP also provoked Mac-1 expression on circulating neutrophils. Interestingly, depletion of platelets reduced CLP-induced lung damage, neutrophil recruitment in the bronchoalveolar space and edema formation as well as up-regulation of Mac-1 on neutrophils. However, blocking of platelet-neutrophil aggregates formation did not attenuate CLP-induced lung damage and neutrophil activation suggesting that platelets regulate sepsis-induced lung damage via up-regulation of Mac-1 in a contact independent manner. We also found that plasma levels of soluble CD40L was significantly increased in septic mice. Use of CD40L-deficient mice confirmed that platelet-derived CD40L is a pivotal mediator of neutrophil activation and recruitment in abdominal sepsis and this platelet mediated neutrophil activation was indirect and mediated via formation of MIP-2 and CXCR2 signaling. In addition, we observed a significant increase of soluble CD40L levels in septic patients. Interestingly, we found that inhibition of matrix MMPs reduced Mac-1 up-regulation on neutrophils and CXC chemokine formation in the septic lung injury. We also found that MMP-9 levels are significantly increased in septic mice but not MMP-2. In vitro studies revealed that activated platelets up-regulate surface expression of MMP-9 and that inhibition of MMP-9 decreased platelet shedding of CD40L. Use of MMP-9-deficient mice suggested that MMP-9 regulates platelet CD40L shedding in abdominal sepsis. Moreover, pulmonary infiltration of neutrophils as well as edema formation and lung injury were markedly decreased in septic animals lacking MMP-9. Plasma levels of MMP-9 were significantly increased in patients with septic shock compared to healthy controls. Taken together, platelets regulate neutrophil activation in abdominal sepsis via MMP-9-dependent shedding of platelet-derived CD40L. Thus, MMP-9 and CD40L may constitute novel and effective therapeutic targets in abdominal sepsis.},
  author       = {Rahman, Milladur},
  isbn         = {978-91-86671-88-8},
  keyword      = {abdominal sepsis,neutrophil recruitment,platelet,lung injury},
  language     = {eng},
  pages        = {118},
  publisher    = {Section for Surgery, Dept of Clinical Sciences, Malmö, Lund University},
  school       = {Lund University},
  series       = {Lund University, Faculty of Medicine, Doctoral Dissertation Series},
  title        = {Platelet-dependent pulmonary recruitment of neutrophils in abdominal sepsis},
  volume       = {2012:26},
  year         = {2012},
}