Sirtuin 1 Regulates SREBP-1c Expression in a LXR-Dependent Manner in Skeletal Muscle

International audienceSirtuin 1 (SIRT1), a NAD +-dependent protein deacetylase, has emerged as a main determinant of whole body homeostasis in mammals by regulating a large spectrum of transcriptional regulators in metabolically relevant tissue such as liver, adipose tissue and skeletal muscle. Sterol regulatory element binding protein (SREBP)-1c is a transcription factor that controls the expression of genes related to fatty acid and triglyceride synthesis in tissues with high lipid synthesis rates such as adipose tissue and liver. Previous studies indicate that SIRT1 can regulate the expression and function of SREBP-1c in liver. In the present study, we determined whether SIRT1 regulates SREBP-1c expression in skeletal muscle. SREBP-1c mRNA and protein levels were decreased in the gastrocnemius muscle of mice harboring deletion of the catalytic domain of SIRT1 (SIRT1 Dex4/Dex4 mice). By contrast, adenoviral expression of SIRT1 in human myotubes increased SREBP-1c mRNA and protein levels. Importantly, SREBP-1c promoter transactivation, which was significantly increased in response to SIRT1 overexpression by gene electrotransfer in skeletal muscle, was completely abolished when liver X receptor (LXR) response elements were deleted. Finally, our in vivo data from SIRT1 Dex4/Dex4 mice and in vitro data from human myotubes overexpressing SIRT1 show that SIRT1 regulates LXR acetylation in skeletal muscle cells. This suggests a possible mechanism by which the regulation of SREBP-1c gene expression by SIRT1 may require the deacetylation of LXR transcription factors

Association between combination antibiotic therapy as opposed as monotherapy and outcomes of ICU patients with Pseudomonas aeruginosa ventilator-associated pneumonia: an ancillary study of the iDIAPASON trial

Abstract Background The optimal treatment duration and the nature of regimen of antibiotics (monotherapy or combination therapy) for Pseudomonas aeruginosa ventilator‑associated pneumonia (PA-VAP) remain debated. The aim of this study was to evaluate whether a combination antibiotic therapy is superior to a monotherapy in patients with PA-VAP in terms of reduction in recurrence and death, based on the 186 patients included in the iDIAPASON trial, a multicenter, randomized controlled trial comparing 8 versus 15 days of antibiotic therapy for PA-VAP. Methods Patients with PA-VAP randomized in the iDIAPASON trial (short-duration—8 days vs. long-duration—15 days) and who received appropriate antibiotic therapy were eligible in the present study. The main objective is to compare mortality at day 90 according to the antibiotic therapy received by the patient: monotherapy versus combination therapy. The primary outcome was the mortality rate at day 90. The primary outcome was compared between groups using a Chi-square test. Time from appropriate antibiotic therapy to death in ICU or to censure at day 90 was represented using Kaplan–Meier survival curves and compared between groups using a Log-rank test. Results A total of 169 patients were included in the analysis. The median duration of appropriate antibiotic therapy was 14 days. At day 90, among 37 patients (21.9%) who died, 17 received monotherapy and 20 received a combination therapy (P = 0.180). Monotherapy and combination antibiotic therapy were similar for the recurrence rate of VAP, the number of extra pulmonary infections, or the acquisition of multidrug-resistant (MDR) bacteria during the ICU stay. Patients in combination therapy were exposed to mechanical ventilation for 28 ± 12 days, as compared with 23 ± 11 days for those receiving monotherapy (P = 0.0243). Results remain similar after adjustment for randomization arm of iDIAPASON trial and SOFA score at ICU admission. Conclusions Except longer durations of antibiotic therapy and mechanical ventilation, potentially related to increased difficulty in achieving clinical cure, the patients in the combination therapy group had similar outcomes to those in the monotherapy group. Trial registration: NCT02634411 , Registered 15 December 2015

Sterol regulatory element binding protein (SREBP)-1c expression.

<p>(A) SREBP-1c mRNA level in the <i>gastrocnemius</i> muscle of SIRT1^+/Δex4 and SIRT1^Δex4/Δex4 mice. (B) SREBP-1c protein level in the <i>gastrocnemius</i> muscle of SIRT1^+/Δex4 and SIRT1^Δex4/Δex4 mice. (C) SREBP-1c mRNA level in human myotubes (7 days of differentiation) infected for 48 hours with recombinant adenovirus expressing either green fluorescent protein (AdGFP) or sirtuin 1 (AdSIRT1). (D) SREBP-1c protein level in human myotubes (7 days of differentiation) infected for 48 hours with AdGFP or AdSIRT1. For western blot analyses, equal protein loading was controlled by measuring total protein content and α-tubulin expression by western blot. Data are expressed as means ± SE (n = 4/group for animal study; n = 5/group for <i>in vitro</i> study). ** <i>P</i><0.01 and * <i>P</i><0.05: significantly different from the corresponding control condition.</p

Liver X receptor (LXR)-α and LXR-β expression.

<p>(A) LXR-α and LXR-β mRNA level in the <i>gastrocnemius</i> muscle of SIRT1^+/Δex4 and SIRT1^Δex4/Δex4 mice. (B) LXR-α and LXR-β protein level in the <i>gastrocnemius</i> muscle of SIRT1^+/Δex4 and SIRT1^Δex4/Δex4 mice. (C) LXR-α and LXR-β mRNA level in human myotubes (7 days of differentiation) infected for 48 hours with recombinant adenovirus expressing either green fluorescent protein (AdGFP) or sirtuin 1 (AdSIRT1). For western blot analysis, equal protein loading was controlled by measuring total protein content and α-tubulin expression by western blot. Data are expressed as means ± SE (n = 4/group for animal study; n = 8/group for <i>in vitro</i> study). * <i>P</i><0.05: significantly different from SIRT1^+/Δex4 mice.</p

Sirtuin 1 (SIRT1) regulates liver X receptor (LXR)-α and LXR-β acetylation.

<p>(A) Immunoblot representing the acetylation profile of <i>gastrocnemius</i> muscle lysates of SIRT1^+/Δex4 and SIRT1^Δex4/Δex4 mice. Expected LXR band is indicated by a grey arrow. (B) Immunoblots showing LXR-α immunoprecipitates probed either with an acetyl-Lysine antibody (upper left) or a LXR-α antibody (lower left) and LXR-β immunoprecipitates probed either with an acetyl-Lysine antibody (upper right) or a LXR-β antibody (lower right). (C) Acetylation level of LXR-α and LXR-β normalized to the amount of LXR-α and LXR-β in the immunoprecipitate. (D) Acetylation level of LXR-β in human myotubes (7 days of differentiation) infected for 48 hours with recombinant adenovirus expressing either green fluorescent protein (AdGFP) or SIRT1 (AdSIRT1). Proteins were immunoprecipitated with a LXR-β antibody and then probed with an acetyl-lysine antibody. Data were normalized to the amount of LXR-β in the immunoprecipitate. Data are expressed as means ± SE (n = 4/group for animal study; n = 8/group for <i>in vitro</i> study). * <i>P</i><0.05: significantly different from the corresponding control condition.</p

Comparison of 8 versus 15 days of antibiotic therapy for Pseudomonas aeruginosa ventilator-associated pneumonia in adults: a randomized, controlled, open-label trial

International audiencePurpose: Duration of antibiotic therapy for ventilator-associated pneumonia (VAP) due to non-fermenting Gram-negative bacilli (NF-GNB), including Pseudomonas aeruginosa (PA) remains uncertain. We aimed to assess the non-inferiority of a short duration of antibiotics (8 days) vs. prolonged antibiotic therapy (15 days) in VAP due to PA (PA-VAP).Methods: We conducted a nationwide, randomized, open-labeled, multicenter, non-inferiority trial to evaluate optimal duration of antibiotic treatment in PA-VAP. Eligible patients were adults with diagnosis of PA-VAP and randomly assigned in 1:1 ratio to receive a short-duration treatment (8 days) or a long-duration treatment (15 days). A pre-specified analysis was used to assess a composite endpoint combining mortality and PA-VAP recurrence rate during hospitalization in the intensive care unit (ICU) within 90 days.Results: The study was stopped after 24 months due to slow inclusion rate. In intention-to-treat population (n = 186), the percentage of patients who reached the composite endpoint was 25.5% (N = 25/98) in the 15-day group versus 35.2% (N = 31/88) in the 8-day group (difference 9.7%, 90% confidence interval (CI) -1.9%-21.2%). The percentage of recurrence of PA-VAP during the ICU stay was 9.2% in the 15-day group versus 17% in the 8-day group. The two groups had similar median days of mechanical ventilation, of ICU stay, number of extra pulmonary infections and acquisition of multidrug-resistant (MDR) pathogens during ICU stay.Conclusions: Our study failed to show the non-inferiority of a short duration of antibiotics in the treatment of PA-VAP, compared to a long duration. The short duration strategy may be associated to an increase of PA-VAP recurrence. However, the lack of power limits the interpretation of this study