Innate immunity and remodelling

A wide variety of cardiac disease states can induce remodelling and lead to the functional consequence of heart failure. These complex disease states involve a plethora of parallel signal transduction events, which may be associated with tissue injury or tissue repair. Innate immunity is activated in hearts injured in different ways, evident as cytokine release from the heart, activation of toll-like receptors involved in recognizing danger, and activation of the transcription factor nuclear factor kappa B. Nuclear factor kappa B regulates gene programmes involved in inflammation as well as the resolution of inflammation. The impact of this is an enigma; while cytokines, toll-like receptors, and nuclear factor kappa B appear to elicit myocardial protection in studies of preconditioning, the literature strongly indicates a detrimental role for activation of innate immunity in studies of acute ischaemia–reperfusion injury. The impact of activation of cardiac innate immunity on the long-term outcome in in vivo models of hypertrophy and remodelling is less clear, with conflicting results as to whether it is beneficial or detrimental. More research using genetically engineered mice as tools, different models of evoking remodelling, and long-term follow-up is required for us to conclude whether activation of the innate immune system is good, bad, or unimportant in chronic injury models

Endotoxin and ischemic preconditioning: TNF-α concentration and myocardial infarct development in rabbits

Ischemic preconditioning (IP) and prior exposure to lipopolysaccharides (LPS) reduce infarct size (IS) and serum tumor necrosis factor-α (TNF-α) concentration resulting from myocardial ischemia-reperfusion in rabbits. The decrease in TNF-α might relate to an induced TNF-α inhibitory serum activity (TNF-α-ISA). We analyzed TNF-α and TNF-α-ISA during 30 and 180 min ischemia and reperfusion, respectively, in anesthetized rabbits either untreated ( group 1, n = 7), preconditioned (5 and 10 min ischemia and reperfusion, respectively, group 2, n = 9), or exposed to LPS 72 h before ischemia ( group 3, n = 9). TNF-α-ISA was assessed by coincubating LPS-stimulated rabbit blood with serum of groups 1–3 and measuring TNF-α (WEHI assay). With a comparable area at risk, IS in group 1 was 36.9 ± 11.1 (SD)%, and it was reduced to 13.1 ± 11.6% and 17.3 ± 11.3% (both P &lt; 0.05) in groups 2 and 3, respectively. TNF-α was increased during ischemia-reperfusion in group 1 but remained unchanged in rabbits subjected to IP or LPS. TNF-α-ISA was detected during ischemia-reperfusion in group 2 (29% and 38% of maximum inhibition, respectively) and during baseline, ischemia and reperfusion in group 3 (51%, 46%, 48% of maximum inhibition, respectively) but was absent in group 1. Cardioprotection by IP and LPS is associated with a reduced TNF-α and an induced TNF-α-ISA during ischemia-reperfusion. </jats:p

Deletion of the innate immune NLRP3 receptor abolishes cardiac ischemic preconditioning and is associated with decreased Il-6/STAT3 signaling

Contains fulltext : 110810.pdf (publisher's version ) (Open Access)OBJECTIVE: Recent studies indicate that the innate immune system is not only triggered by exogenous pathogens and pollutants, but also by endogenous danger signals released during ischemia and necrosis. As triggers for the innate immune NLRP3 inflammasome protein complex appear to overlap with those for cardiac ischemia-reperfusion (I/R) and ischemic preconditioning (IPC), we explored the possibility that the NLRP3 inflammasome is involved in IPC and acute I/R injury of the heart. PRINCIPAL FINDINGS: Baseline cardiac performance and acute I/R injury were investigated in isolated, Langendorff-perfused hearts from wild-type (WT), ASC(-/-) and NLRP3(-/-) mice. Deletion of NLRP3 inflammasome components ASC(-/-) or NLRP3(-/-) did not affect baseline performance. The deletions exacerbated I/R-induced mechanical dysfunction, but were without effect on I/R-induced cell death. When subjected to IPC, WT and ASC(-/-) hearts were protected against I/R injury (improved function and less cell death). However, IPC did not protect NLRP3(-/-) hearts against I/R injury. NLRP3(-/-) hearts had significantly decreased cardiac IL-6 levels with a trend towards lower IL-1beta levels at end reperfusion, suggesting abrogation of IPC through diminished IL-6 and/or IL-1beta signaling. Subsequent experiments showed that neutralising IL-6 using an antibody against IL-6 abrogated IPC in WT hearts. However, inhibition of the IL-1r receptor with the IL-1 receptor inhibitor Anakinra (100 mg/L) did not abrogate IPC in WT hearts. Analysis of survival kinases after IPC demonstrated decreased STAT3 expression in NLRP3(-/-) hearts when compared to WT hearts. CONCLUSIONS: The data suggest that the innate immune NLRP3 protein, in an NLRP3-inflammasome-independent fashion, is an integral component of IPC in the isolated heart, possibly through an IL-6/STAT3 dependent mechanism

p38 MAP kinase is a mediator of ischemic preconditioning in pigs

OBJECTIVE: The role of p38MAPK in ischemic preconditioning (IP) is still equivocal, insofar as the p38MAPK-inhibitor SB203580 abolished IP in rats, rabbits and dogs, but not in pigs. Blockade of p38MAPK prior to the sustained ischemia also generated contradictory findings, insofar as p38MAPK acted as trigger in dogs but as mediator in rats. We have now tested whether the two structurally unrelated p38MAPK-inhibitors, BIX-645 and SB203580, abolished infarct size (IS) reduction by IP in pigs and whether their effects depended on the time of administration. METHODS: Sixty-five enflurane-anesthetized pigs underwent 90 min low-flow ischemia and 120 min reperfusion without or with one preceding cycle of 10 min preconditioning ischemia and 15 min reperfusion. Pigs received BIX-645 (1 mg/kg, i.v.) or SB203580 (10 microM, i.c.) prior to either IP or the sustained ischemia. RESULTS: IS (% TTC-staining) was reduced by IP [4.8+/-3.1(S.E.M.), P <0.05] compared to placebo (25.8+/-5.5). BIX-645 or SB203580 per se had no effect on IS (23.5+/-5.2 and 21.8+/-4.4, respectively). IS reduction by IP was abolished by BIX-645 (26.2+/-6.4 or 25.5+/-4.7) and SB203580 (19.9+/-4.3 or 16.7+/-4.7), given either prior to IP or the sustained ischemia, respectively. The supernatant of homogenized myocardial biopsies taken during the sustained ischemia from preconditioned pigs receiving either BIX-645 or SB203580 inhibited the anisomycin-stimulated ATF-2 phosphorylation in cultured Rat1 fibroblasts. This in vitro inhibition of ATF-2 phosphorylation correlated to the actual IS. CONCLUSION: The attenuation of the IS-reducing effect of IP depends on the effectiveness of blockade of p38MAPK activity. p38MAPK is a mediator of IP in pig

Serum but not myocardial TNF-α concentration is increased in pacing-induced heart failure in rabbits

In animals and patients with severe heart failure (HF), the serum tumor necrosis factor-α (TNF-α) concentration is increased. It is, however, still controversial whether or not such increased serum TNF-α originates from the heart itself or is of peripheral origin secondary to gastrointestinal congestion and increased endotoxin concentration. We therefore now examined TNF-α in serum, myocardium, and liver of sham-operated and HF rabbits. In nine rabbits in which HF was induced by left ventricular (LV) pacing at 400 beats/min for 3 wk, LV end-diastolic diameter was increased and systolic shortening fraction (9.4 ± 1.0 vs. 28.5 ± 1.3%, echocardiography, P &lt; 0.05) was reduced. Serum TNF-α was higher in HF than in sham-operated rabbits (240 ± 24 vs. 150 ± 22 U/ml, WEHI-cell assay, P &lt; 0.05). In the heart, TNF-α was located mainly in the vascular endothelium (immunohistochemistry), and TNF-α protein (920 ± 160 vs. 900 ± 95 U/g) did not differ between groups. In the liver of HF rabbits, hepatocytes expressed TNF-α, and TNF-α protein was increased compared with sham-operated rabbits (2,390 ± 310 vs. 1,220 ± 135 U/g, P &lt; 0.05) and correlated to the number of hepatic leukocytes ( r = 0.85) and serum TNF-α ( r = 0.69). The intestinal endotoxin concentration was 24.5 ± 1.2 vs. 17.0 ± 3.1 endotoxin units/g wet wt ( P &lt; 0.05) in HF compared with sham-operated rabbits. In this HF model, serum but not myocardial TNF-α is increased. The increased serum TNF-α originates from peripheral sources. </jats:p

Inconsistent relation of MAPK activation to infarct size reduction by ischemic preconditioning in pigs

The importance of the activation of mitogen-activated protein kinases (MAPK) for the cardioprotection achieved by ischemic preconditioning (IP) is still controversial. We therefore measured infarct size and p38, extracellular signal-regulated kinase (ERK), and c-Jun NH2-terminal kinase (JNK) MAPK phosphorylation (by biopsies) in enflurane-anesthetized pigs. After 90 min low-flow ischemia and 120 min reperfusion, infarct size averaged 18.3 ± 12.4 (SD)% ( group 1, n = 14). At similar subendocardial blood flows, IP by 10 min ischemia and 15 min reperfusion ( group 2, n = 14) reduced infarct size to 6.2 ± 5.1% ( P &lt; 0.05). An inconsistent increase in p38, ERK, and p54 JNK phosphorylation (by Western blot) was found during IP; p46 JNK phosphorylation increased with the subsequent reperfusion. At 8 min of the sustained ischemia, p38, ERK, and p54 JNK phosphorylation were increased with no difference between groups (medians: p38: 207% of baseline in group 1vs. 153% in group 2; ERK: 142 vs. 144%; p54 JNK: 171 vs. 155%, respectively). MAPK phosphorylation and reduction of infarct size by IP were not correlated, thus not supporting the concept of a causal role of MAPK in mediating cardioprotection by IP. </jats:p