Lipopolysaccharide improves cardiomyocyte survival and function after serum deprivation.
Toll-like receptor-4 (TLR4) and its signaling molecule interleukin-1 receptor-associated kinase (IRAK-1) play an important role in host defense and tissue inflammation. Intriguingly, systemic administration of lipopolysaccharide (LPS), the agonist for TLR4, confers a cardio-protective effect against ischemic injury. However, the mechanisms leading to the cardiac protection remain largely unknown. The present study was designed to investigate the role of TLR4 activation by LPS in protecting cardiomyocytes (CM) against apoptosis in an in vitro model of ischemia and to explore the downstream mechanisms leading to the protective effect. Incubation with LPS led to activation of IRAK-1 and protected CMs against serum deprivation (SD)-induced apoptosis as demonstrated by DNA laddering, histone-DNA fragment enzyme-linked immunosorbent assay, and activation of caspase-3. Phosphatidylinositol 3-kinase/Akt, extracellular signal-regulated kinase 1/2, and IkappaB kinase beta appear to contribute to the anti-apoptotic effect of LPS since the specific inhibitors, wortmannin, PD98059, and dominant negative IKKbeta transgene expression reversed the LPS effect. To assess whether LPS improves CM function, we examined intracellular Ca(2+) transients and cell shortening in single adult rat CMs. SD for 6 h dramatically inhibited Ca(2+) transients and CM contractility. LPS at 500 ng/ml significantly improved the [Ca(2+)](i) transients and enhanced contractility in control CMs as well as in CMs subjected to SD. Importantly, transient ischemia led to rapid activation of IRAK-1 in cultured CMs and in adult rat myocardium. Adenovirus-mediated transgene expression of IRAK-1 but not its kinase-deficient mutant IRAK-1(K239S) protected CMs against SD-induced apoptosis. Taken together, these data suggest an important role of TLR4 signaling via IRAK-1 in protecting against SD-induced apoptosis.
Chao
Wei
W
Department of Anesthesia and Critical Care, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, Boston, MA 02114, USA. wchao@partners.org
Shen
Yan
Y
Zhu
Xinsheng
X
Zhao
Huailong
H
Novikov
Mikhail
M
Schmidt
Ulrich
U
Rosenzweig
Anthony
A
D000256:Adenoviridae / Q000235:genetics; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D004247:DNA / Q000737:chemistry; D053938:DNA Fragmentation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D005419:Flavonoids / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006657:Histones / Q000737:chemistry; D000860:Hypoxia; D047468:Immunoprecipitation; D053592:Interleukin-1 Receptor-Associated Kinases; D007511:Ischemia; D008070:Lipopolysaccharides / Q000378:metabolism / Q000494:pharmacology*; D008562:Membrane Glycoproteins / Q000378:metabolism / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000166:cytology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D019076:Transgenes; D000077191:Wortmannin
D000730:Androstadienes; D016895:Culture Media, Serum-Free; D004791:Enzyme Inhibitors; D005419:Flavonoids; D006657:Histones; D008070:Lipopolysaccharides; D008562:Membrane Glycoproteins; D011956:Receptors, Cell Surface; D011994:Recombinant Proteins; C495347:Tlr4 protein, rat; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D049452:Green Fluorescent Proteins; D004247:DNA; D011494:Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D053592:Interleukin-1 Receptor-Associated Kinases; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D002118:Calcium; D000077191:Wortmannin