title: Targeted gene silencing of tumor necrosis factor attenuates the negative inotropic effects of lipopolysaccharide in isolated contracting cardiac myocytes.
abstract: Bacterial endotoxin (lipopolysaccharide) depresses cardiovascular function; however, the mediators and signaling pathways that are responsible for the negative inotropic effects of lipopolysaccharide are not fully known. We used RNA interference to determine the relative role of tumor necrosis factor with respect to mediating the negative inotropic effects of lipopolysaccharide in isolated cardiac myocytes. Cardiac myocyte cultures were treated with lipopolysaccharide in the presence or absence of small interfering RNAs (siRNA) for tumor necrosis factor. We examined the effects of tumor necrosis factor siRNA on lipopolysaccharide-induced tumor necrosis factor messenger RNA (mRNA) and protein biosynthesis, as well as the negative inotropic effects of lipopolysaccharide in isolated contracting cardiac myocytes. Treatment of adult cardiac myocyte cultures with tumor necrosis factor siRNA significantly attenuated lipopolysaccharide-induced tumor necrosis factor mRNA and protein biosynthesis, whereas transfection with a double-stranded RNA that does not target mammalian mRNA had no effect. Pretreatment with tumor necrosis factor siRNA significantly attenuated, but did not abrogate, the lipopolysaccharide-induced decrease in sarcomere shortening in isolated contracting cardiac myocytes. In contrast, tumor necrosis factor siRNA had a comparatively smaller effect on improving sarcomere shortening once the negative inotropic effects of lipopolysaccharide were fully established. These results suggest that tumor necrosis factor plays an important upstream role in lipopolysaccharide-induced negative inotropic effects in isolated contracting cardiac myocytes and that other molecular mechanisms are responsible for the decrease in sarcomere shortening after sustained lipopolysaccharide signaling.
authors.affiliation: Winters Center for Heart Failure Research, Section of Cardiology, Department of Medicine, Baylor College of Medicine and the Texas Heart Institute at St. Luke's Episcopal Hospital, Houston, Texas 77030, USA.
authors.forename: R S
authors.initials: RS
authors.lastname: Ramabadran
authors.forename: Amanda
authors.initials: A
authors.lastname: Chancey
authors.forename: Jesus G
authors.initials: JG
authors.lastname: Vallejo
authors.forename: Philip M
authors.initials: PM
authors.lastname: Barger
authors.forename: Natarajan
authors.initials: N
authors.lastname: Sivasubramanian
authors.forename: Douglas L
authors.initials: DL
authors.lastname: Mann
mesh_terms: D002478:Cells, Cultured; D006801:Humans; D008070:Lipopolysaccharides / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000502:physiology*; D034622:RNA Interference / Q000502:physiology*; D034741:RNA, Small Interfering / Q000502:physiology; D012518:Sarcomeres / Q000187:drug effects / Q000502:physiology; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology
chemical_list: D008070:Lipopolysaccharides; D034741:RNA, Small Interfering; D014409:Tumor Necrosis Factor-alpha