title: Retinoblastoma Protein Knockdown Favors Oxidative Metabolism and Glucose and Fatty Acid Disposal in Muscle Cells.
abstract: Deficiency in the retinoblastoma protein (Rb) favors leanness and a healthy metabolic profile in mice largely attributed to activation of oxidative metabolism in white and brown adipose tissues. Less is known about Rb modulation of skeletal muscle metabolism. This was studied here by transiently knocking down Rb expression in differentiated C2C12 myotubes using small interfering RNAs. Compared with control cells transfected with non-targeting RNAs, myotubes silenced for Rb (by 80-90%) had increased expression of genes related to fatty acid uptake and oxidation such as Cd36 and Cpt1b (by 61% and 42%, respectively), increased Mitofusin 2 protein content (∼2.5-fold increase), increased mitochondrial to nuclear DNA ratio (by 48%), increased oxygen consumption (by 65%) and decreased intracellular lipid accumulation. Rb silenced myotubes also displayed up-regulated levels of glucose transporter type 4 expression (∼5-fold increase), increased basal glucose uptake, and enhanced insulin-induced Akt phosphorylation. Interestingly, exercise in mice led to increased Rb phosphorylation (inactivation) in skeletal muscle as evidenced by immunohistochemistry analysis. In conclusion, the silencing of Rb enhances mitochondrial oxidative metabolism and fatty acid and glucose disposal in skeletal myotubes, and changes in Rb status may contribute to muscle physiological adaptation to exercise.
authors.affiliation: Laboratory of Molecular Biology, Nutrition and Biotechnology-Nutrigenomics, Universitat de les Illes Balears, Palma de Mallorca, CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Spain.
authors.forename: Petar D
authors.initials: PD
authors.lastname: Petrov
authors.affiliation: Laboratory of Molecular Biology, Nutrition and Biotechnology-Nutrigenomics, Universitat de les Illes Balears, Palma de Mallorca, CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Spain.
authors.forename: Joan
authors.initials: J
authors.lastname: Ribot
authors.affiliation: Department of Physiology, Université de Lausanne, Switzerland.
authors.forename: Isabel C
authors.initials: IC
authors.lastname: López-Mejía
authors.affiliation: Department of Physiology, Université de Lausanne, Switzerland.
authors.forename: Lluís
authors.initials: L
authors.lastname: Fajas
authors.affiliation: Laboratory of Molecular Biology, Nutrition and Biotechnology-Nutrigenomics, Universitat de les Illes Balears, Palma de Mallorca, CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Spain.
authors.forename: Andreu
authors.initials: A
authors.lastname: Palou
authors.affiliation: Laboratory of Molecular Biology, Nutrition and Biotechnology-Nutrigenomics, Universitat de les Illes Balears, Palma de Mallorca, CIBER Fisiopatología de la Obesidad y Nutrición (CIBERobn), Spain.
authors.forename: M Luisa
authors.initials: ML
authors.lastname: Bonet
mesh_terms: D000818:Animals; D005227:Fatty Acids / Q000378:metabolism*; D055785:Gene Knockdown Techniques / Q000379:methods; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology; D051379:Mice; D024510:Muscle Development / Q000187:drug effects / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects; D016160:Retinoblastoma Protein / Q000172:deficiency / Q000378:metabolism*
chemical_list: D005227:Fatty Acids; D007328:Insulin; D016160:Retinoblastoma Protein; D005947:Glucose