TREM-1 Mediates Inflammatory Injury and Cardiac Remodeling Following Myocardial Infarction.

RATIONALE: Optimal outcome after myocardial infarction (MI) depends on a coordinated healing response in which both debris removal and repair of the myocardial extracellular matrix play a major role. However, adverse remodeling and excessive inflammation can promote heart failure, positioning leucocytes as central protagonists and potential therapeutic targets in tissue repair and wound healing after MI. OBJECTIVE: In this study, we examined the role of triggering receptor expressed on myeloid cells-1(TREM-1) in orchestrating the inflammatory response that follows MI. TREM-1, expressed by neutrophils and mature monocytes, is an amplifier of the innate immune response. METHODS AND RESULTS: After infarction, TREM-1 expression is upregulated in ischemic myocardium in mice and humans. Trem-1 genetic invalidation or pharmacological inhibition using a synthetic peptide (LR12) dampens myocardial inflammation, limits neutrophils recruitment and monocyte chemoattractant protein-1 production, thus reducing classical monocytes mobilization to the heart. It also improves left ventricular function and survival in mice (n=20-22 per group). During both permanent and transient myocardial ischemia, Trem-1 blockade also ameliorates cardiac function and limits ventricular remodeling as assessed by fluorodeoxyglucose-positron emission tomographic imaging and conductance catheter studies (n=9-18 per group). The soluble form of TREM-1 (sTREM-1), a marker of TREM-1 activation, is detectable in the plasma of patients having an acute MI (n=1015), and its concentration is an independent predictor of death. CONCLUSIONS: These data suggest that TREM-1 could constitute a new therapeutic target during acute MI.

Dexamethasone and recombinant human activated protein C improve myocardial function and efficiency during experimental septic shock.

Corticosteroids have been shown to reduce short-term mortality during septic shock and therefore recommended in the most severe patients as adjuvant therapy. Until recently, recombinant human activated protein C (APC) was also considered in the management of more severe cases. As myocardial depression has long been recognized as a manifestation of organ dysfunction during septic shock, we examined whether corticosteroids (dexamethasone, 150 µg/kg per hour) and/or APC (33 µg/kg per hour) treatments improve sepsis-induced cardiac dysfunction during cecal ligature and puncture-induced septic shock in Wistar rats. All rats received intravenous saline resuscitation (10 mL/kg per hour) and antibiotics. Eighteen hours after surgery, anesthesia was performed (isoflurane), and myocardial function was assessed using a conductance catheter introduced into the left ventricle. Rats were then killed; blood and heart were harvested for biological analysis, including radical oxygen species determination. Cecal ligature and puncture induced hypotension, depression of myocardial systolic performance (demonstrated by significant decreases in dP/dtmax [first derivative of maximal developed pressure during isovolumetric contraction], end-systolic pressure-volume relationship, and preload recruitable stroke work) and alteration of diastolic function (dP/dtmin [first derivative of minimal developed pressure during isovolumetric relaxation]), whereas dexamethasone, APC, and their combination thereof allowed correction of hemodynamic disorders and improved myocardial mechanical efficiency. Cecal ligature and puncture was associated with higher levels of nitric oxide and superoxide anion (O2) in heart (electron paramagnetic resonance studies) and consequently peroxynitrite. Dexamethasone and APC also improved cardiac dysfunction by downregulating the inducible nitric oxide synthase pathway and reducing myocardial oxidative stress.

Effects of a TREM-like transcript 1-derived peptide during hypodynamic septic shock in pigs.

The objective of this study was to determine the effects of a TREM (triggering receptor expressed on myeloid cells 1)-like transcript 1-derived peptide (LR12) administration during septic shock in pigs. Two hours after induction of a fecal peritonitis, anesthetized and mechanically ventilated adult male minipigs were randomized to receive LR12 (n = 6) or its vehicle alone (normal saline, n = 5). Two animals were operated and instrumented without the induction of peritonitis and served as controls (sham). Resuscitation was achieved using hydroxyethyl starch (up to 20 mL/kg) and norepinephrine infusion (up to 10 µg/kg per minute). Hemodynamic parameters were continuously recorded. Gas exchange, acid-base status, organ function, and plasma cytokines concentrations were evaluated at regular intervals until 24 h after the onset of peritonitis when animals were killed under anesthesia. Peritonitis induced profound hypotension, myocardial dysfunction, lactic acidosis, coagulation abnormalities, and multiple organ failure. These disorders were largely attenuated by LR12. In particular, cardiovascular failure was dampened as attested by a better mean arterial pressure, cardiac index, cardiac power index, and S(v)O(2), despite lower norepinephrine requirements. LR12, a TREM-like transcript 1-derived peptide, exhibits salutary properties during septic shock in adult minipigs.

Soluble TREM-like transcript-1 regulates leukocyte activation and controls microbial sepsis.

The triggering receptor expressed on myeloid cells (TREM)-1 plays a crucial role during the onset of sepsis by amplifying the host immune response. The TREM-like transcript-1 (TLT-1) belongs to the TREM family, is selectively expressed on activated platelets, and is known to facilitate platelet aggregation through binding to fibrinogen. In this study, we show that a soluble form of TLT-1 is implicated in the regulation of inflammation during sepsis by dampening leukocyte activation and modulating platelet-neutrophil crosstalk. A 17-aa sequence of the TLT-1 extracellular domain (LR17) is responsible for this activity through competition with the TREM-1 ligand. Whereas early or late LR17 treatment of septic mice improves survival, treml-1(-/-) animals are highly susceptible to polymicrobial infection. The present findings identify platelet-derived soluble TLT-1 as a potent endogenous regulator of sepsis-associated inflammation and open new therapeutic perspectives. We anticipate soluble TLT-1 to be important in regulating leukocyte activation during other noninfectious inflammatory disorders.

Myeloid-derived suppressor cells control microbial sepsis.

PURPOSE: To investigate the role of myeloid-derived suppressor cells (MDSCs) during sepsis in mice. MDSCs are a heterogeneous population of cells that expand during cancer, inflammation and infection. These cells, by their ability to suppress T lymphocyte proliferation, regulate immune responses during various diseases. Their role during microbial infections is scarcely known. METHODS: Septic shock was induced by caecal ligation and puncture in adult male BALB/c mice; sham-operated animals served as controls. Animals were killed under anaesthesia to harvest blood and organs. RESULTS: Polymicrobial sepsis induced a progressive accumulation of MDSCs in spleens that were found to be enlarged in surviving mice. MDSCs harvested at day 10 after the onset of infection were highly responsive to LPS in terms of cytokines secretion, NF-kB activation, ROS production and arginase I activity, whereas early-appearing (day 3) MDSCs poorly responded to this stimulus. By contrast, both day 3 and day 10 MDSCs were able to inhibit T cell proliferation. Adoptive transfer of day 10 MDSCs to septic mice attenuated peritoneal cytokine production, increased bacterial clearance and dramatically improved survival rate. CONCLUSION: These results provide new information on the role of MDSCs, suggesting a protective effect during sepsis. Pharmacologic agents known to promote the expansion of MDSCs should thus be further studied for sepsis treatment.

Comparative effects of recombinant human activated protein C and dexamethasone in experimental septic shock.

PURPOSE: To compare the effects of recombinant human activated protein C (APC) and glucocorticoids alone and in combination in non-anesthetized resuscitated septic shock induced by cecal ligation and puncture (CLP) on (a) survival, (b) hemodynamics, and (c) vascular reactivity. The effects of treatments on major cellular pathways likely implicated were also studied. METHODS: Four hours after CLP, rats were continuously infused with either saline (10 ml/kg/h), saline + APC, saline + dexamethasone (Dexa), or saline + APC + Dexa. Eighteen hours after CLP, arterial pressure, cardiac output, nitrite/nitrate ratio, and lactate concentrations were measured. Aortic rings and mesenteric arteries were isolated and mounted in a myograph, after which arterial contractility and endothelium-dependent relaxation were measured in the presence or absence of nitric oxide synthase (NOS) or cyclooxygenase (COX) inhibitors. Protein expression was assessed by Western blotting. Aorta NO and superoxide anion content were measured by electron paramagnetic resonance. RESULTS: All treatments improved hemodynamic parameters and vascular reactivity and decreased lactate and nitrite/nitrate levels. In treated aorta and mesenteric arteries, contractility and endothelial dysfunction were improved. This effect was associated with an increase in the phosphorylated form of protein kinase B as well as an increase in COX vasodilatory pathways and a decrease in iNOS expression suggesting that these pathways are implicated in the vascular effect of the treatments. CLP was associated with a marked increase in aortic NO and superoxide anion content (p < 0.05), which were decreased by APC and Dexa and totally abolished by APC + Dexa (p < 0.01). Survival length was significantly increased by the APC-Dexa combination. CONCLUSIONS: Both APC and Dexa improve arterial contractility and endothelial dysfunction resulting from septic shock in rats. Moreover, their combination increased the length of survival. These findings provide important insights into the mechanisms underlying APC- and/or Dexa-induced improvements of arterial dysfunction during septic shock.

Caspase-dependent protein phosphatase 2A activation contributes to endotoxin-induced cardiomyocyte contractile dysfunction.

OBJECTIVE: Several studies report calcium mishandling, sarcomere disarray, and caspase activation during heart failure. Although active caspases have been shown to cleave myofibrillar proteins, little is known regarding their effects on calcium handling proteins. Therefore, we aimed to explore how endotoxin-induced caspase activation disrupts intracellular calcium regulation. DESIGN: Randomized controlled trial. SETTING: Small animal research laboratory. SUBJECTS: Adult male Sprague-Dawley rats. INTERVENTIONS: Sepsis was induced by injection of endotoxin (10 mg/kg, intravenously). Caspase inhibition was achieved by coinjection with zVAD.fmk (3 mg/kg, intravenously). We first isolated adult rat ventricular myocytes from control, endotoxin, and (endotoxin + zVAD)-treated rats to characterize contractile parameters and cellular calcium homeostasis. Underlying molecular mechanisms responsible for calcium mishandling were explored on sarcoplasmic reticulum vesicles and mitochondria prepared from treated animals. All experiments were performed 4 hrs postendotoxin treatment. MEASUREMENTS AND MAIN RESULTS: zVAD normalized reductions in fractional cell shortening and relaxation rate triggered by endotoxin treatment. Both sarco-/endoplasmic reticulum Ca-ATPase and mitochondria-dependent calcium uptakes were impaired after endotoxin treatment and prevented when myocytes were isolated from zVAD-treated endotoxinic rat hearts. zVAD blocked endotoxin-induced phospholamban dephosphorylation, protein phosphatase 2A activation, and mitochondrial calcium retention capacity reduction. To strengthen these results, control sarcoplasmic reticulum vesicles and mitochondria were incubated with active recombinant caspase-3. Although no effects were observed on mitochondria, caspase-3 directly exerts detrimental effects on sarcoplasmic reticulum calcium uptake capacity by activating protein phosphatase 2A, leading to phospholamban dephosphorylation. CONCLUSIONS: Caspase inhibition protects from endotoxin-induced sarcoplasmic reticulum calcium uptake capacity reduction and mitochondrial dysfunction.

Prevention of endotoxin-induced sarcoplasmic reticulum calcium leak improves mitochondrial and myocardial dysfunction.

OBJECTIVE: Growing evidence suggests that mitochondria function is impaired in sepsis. Here, we tested the hypothesis that lipopolysaccharide would induce mitochondrial Ca2+ overload and oxygen utilization abnormalities as consequences of sarcoplasmic reticulum Ca2+ handling derangements that are typically observed in sepsis. As lipopolysaccharide-induced sarcoplasmic reticulum dysfunction was mainly characterized by reduced sarcoplasmic reticulum Ca2+ uptake and Ca2+ leak, we tested whether dantrolene, a sarco(endo)plasmic reticulum calcium ATPase leak inhibitor, would prevent mitochondrial and cardiac contractile dysfunction. DESIGN: Randomized controlled trial. SETTING: Experimental laboratory. SUBJECTS: Male Sprague Dawley rats. INTERVENTIONS: Sepsis was induced by injection of endotoxin lipopolysaccharide (10 mg/kg/intravenously). Assessment of contractile function and Ca2+ handling was performed 4 hr after lipopolysaccharide. The relative contribution of the different Ca2+ transporters to relaxation in intact cardiomyocytes was studied during successive electrically evoked twitches and caffeine stimulation. Sarcoplasmic reticulum vesicles and mitochondria from ventricles of rats treated or not with lipopolysaccharide were prepared to evaluate Ca2+ uptake-release and oxygen fluxes, respectively. Effects of dantrolene (10 mg/kg) treatment in rats were evaluated in sarcoplasmic reticulum vesicles, mitochondria, and isolated hearts. MEASUREMENTS AND MAIN RESULTS: Lipopolysaccharide challenge elicited cardiac contractile dysfunction that was accompanied by severe derangements in sarcoplasmic reticulum function, i.e., reduced Ca2+ uptake and increased sarcoplasmic reticulum Ca2+ leak. Functional sarcoplasmic reticulum changes were associated with modification in the status of phospholamban phosphorylation whereas SERCA was unchanged. Rises in mitochondrial Ca2+ content observed in lipopolysaccharide-treated rats coincided with derangements in mitochondrial oxygen efficacy, i.e., reduced respiratory control ratio. Administration of dantrolene in lipopolysaccharide-treated rats prevented mitochondrial Ca2+ overload and mitochondrial oxygen utilization abnormalities. Moreover, dantrolene treatment in lipopolysaccharide rats improved heart mitochondrial redox state and myocardial dysfunction. CONCLUSION: These experiments suggest that sarcoplasmic reticulum Ca2+ handling dysfunction is an early event during endotoxemia that could be responsible for, or contribute to, mitochondrial Ca2+ overload, metabolic failure, and cardiac dysfunction.