MyD88 and NOS2 are essential for Toll-like receptor 4-mediated survival effect in cardiomyocytes

• Published in: American journal of physiology. Heart and circulatory physiology 2006-10, Vol.291 (4), p.H1900-H1909
• Main Authors: Zhu, Xinsheng, Zhao, Huailong, Graveline, Amanda R, Buys, Emmanuel S, Schmidt, Ulrich, Bloch, Kenneth D, Rosenzweig, Anthony, Chao, Wei
• Format: Article
• Language: English
• Subjects: Adaptor Proteins, Signal Transducing - genetics; Adaptor Proteins, Signal Transducing - physiology; Animals; Apoptosis; Apoptosis - drug effects; Apoptosis - physiology; Calcium - metabolism; Cardiovascular system; Cell Survival - drug effects; Cell Survival - physiology; Gene Expression Regulation; Heart; Immune system; Lipopolysaccharides - pharmacology; Mice; Mice, Inbred C57BL; Mice, Knockout; Myeloid Differentiation Factor 88; Myocytes, Cardiac - cytology; Myocytes, Cardiac - drug effects; Myocytes, Cardiac - physiology; Nitric Oxide Synthase Type II - genetics; Nitric Oxide Synthase Type II - physiology; Signal transduction; Signal Transduction - physiology; Toll-Like Receptor 4 - physiology
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.00112.2006

1 Department of Anesthesia and Critical Care, Massachusetts General Hospital, Harvard Medical School, Boston; 2 Cardiovascular Research Center, Massachusetts General Hospital, Charlestown; and 3 Division of Cardiology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts Submitted 31 January 2006 ; accepted in final form 20 April 2006 Innate immune system such as Toll-like receptor 4 (TLR4) represents the first line of defense against infection. In addition to its pivotal role in host immunity, recent studies have suggested that TLR4 may play a broader role in mediating tissue inflammation and cell survival in response to noninfectious injury. We and other investigators have reported that cardiac TLR4 signaling is dynamically modulated in ischemic myocardium and that activation of TLR4 confers a survival benefit in the heart and in isolated cardiomyocytes. However, the signaling pathways leading to these effects are not completely understood. Here, we investigate the role of MyD88, an adaptor protein of TLR4 signaling, and inducible nitric oxide synthase (NOS2) in mediating TLR4-induced cardiomyocyte survival in an in vitro model of apoptosis. Serum deprivation induced a significant increase in the number of apoptotic cardiomyocytes as demonstrated by transferase-mediated dUTP nick-end labeling (TUNEL) assay, nuclear morphology, DNA laddering, and DNA-histone ELISA. Lipopolysaccharide (LPS), a TLR4 agonist, activated TLR4 signaling and led to significant reduction in apoptotic cardiomyocytes and improved cellular function of surviving cardiomyocytes with enhanced Ca 2+ transients and cell shortening. We found that both TLR4 and MyD88 are required for the LPS-induced beneficial effects as demonstrated by improved survival and function in wild-type but not in TLR4 –/– or MyD88 –/– cardiomyocytes. Moreover, genetic deletion or pharmacological inhibition of NOS2 abolished survival and functional rescue of cardiomyocytes treated with LPS. Taken together, these data suggest that TLR4 protects cardiomyocytes from stress-induced injury through MyD88- and NOS2-dependent mechanisms. signal transduction; cardiac; apoptosis; inducible nitric oxide synthase Address for reprint requests and other correspondence: W. Chao, Dept. of Anesthesia & Critical Care, MGH, GRJ-4-462, 55 Fruit St., Boston, MA 02114 (e-mail: wchao{at}partners.org )