title: Human skeletal myotubes display a cell-autonomous circadian clock implicated in basal myokine secretion.
abstract: OBJECTIVE
  Circadian clocks are functional in all light-sensitive organisms, allowing an adaptation to the external world in anticipation of daily environmental changes. In view of the potential role of the skeletal muscle clock in the regulation of glucose metabolism, we aimed to characterize circadian rhythms in primary human skeletal myotubes and investigate their roles in myokine secretion.
  
  
  METHODS
  We established a system for long-term bioluminescence recording in differentiated human myotubes, employing lentivector gene delivery of the Bmal1-luciferase and Per2-luciferase core clock reporters. Furthermore, we disrupted the circadian clock in skeletal muscle cells by transfecting siRNA targeting CLOCK. Next, we assessed the basal secretion of a large panel of myokines in a circadian manner in the presence or absence of a functional clock.
  
  
  RESULTS
  Bioluminescence reporter assays revealed that human skeletal myotubes, synchronized in vitro, exhibit a self-sustained circadian rhythm, which was further confirmed by endogenous core clock transcript expression. Moreover, we demonstrate that the basal secretion of IL-6, IL-8 and MCP-1 by synchronized skeletal myotubes has a circadian profile. Importantly, the secretion of IL-6 and several additional myokines was strongly downregulated upon siClock-mediated clock disruption.
  
  
  CONCLUSIONS
  Our study provides for the first time evidence that primary human skeletal myotubes possess a high-amplitude cell-autonomous circadian clock, which could be attenuated. Furthermore, this oscillator plays an important role in the regulation of basal myokine secretion by skeletal myotubes.
authors.affiliation: Division of Endocrinology, Diabetes and Nutrition, Department of Clinical Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Laurent
authors.initials: L
authors.lastname: Perrin
authors.affiliation: Division of Endocrinology, Diabetes and Nutrition, Department of Clinical Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Ursula
authors.initials: U
authors.lastname: Loizides-Mangold
authors.affiliation: Division of Endocrinology, Diabetes and Nutrition, Department of Clinical Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Svetlana
authors.initials: S
authors.lastname: Skarupelova
authors.affiliation: Division of Endocrinology, Diabetes and Nutrition, Department of Clinical Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Pamela
authors.initials: P
authors.lastname: Pulimeno
authors.affiliation: CarMeN Laboratory, INSERM U1060, INRA 1397, University Lyon 1, Oullins, France.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Chanon
authors.affiliation: Department of Digestive and Bariatric Surgery, Edouard Herriot Hospital, Lyon, France.
authors.forename: Maud
authors.initials: M
authors.lastname: Robert
authors.affiliation: Department of Genetic Medicine and Development, Faculty of Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Karim
authors.initials: K
authors.lastname: Bouzakri
authors.affiliation: Division of Immunology and Allergy, Department of Medical Specialties, University Hospital and Faculty of Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Christine
authors.initials: C
authors.lastname: Modoux
authors.affiliation: Division of Immunology and Allergy, Department of Medical Specialties, University Hospital and Faculty of Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Pascale
authors.initials: P
authors.lastname: Roux-Lombard
authors.affiliation: CarMeN Laboratory, INSERM U1060, INRA 1397, University Lyon 1, Oullins, France.
authors.forename: Hubert
authors.initials: H
authors.lastname: Vidal
authors.affiliation: CarMeN Laboratory, INSERM U1060, INRA 1397, University Lyon 1, Oullins, France.
authors.forename: Etienne
authors.initials: E
authors.lastname: Lefai
authors.affiliation: Division of Endocrinology, Diabetes and Nutrition, Department of Clinical Medicine, Faculty of Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Charna
authors.initials: C
authors.lastname: Dibner
keywords: Circadian bioluminescence recording; Circadian clock; Human skeletal myotube; Interleukin-6; Myokine