title: Mouse model of testosterone-induced muscle fiber hypertrophy: involvement of p38 mitogen-activated protein kinase-mediated Notch signaling.
abstract: As a prerequisite for studies using mutant mice, we established a mouse model for investigating the molecular mechanisms by which testosterone (T) promotes muscle growth. Groups of six adult male mice (C57BL/6) received one of the following treatments: 1) vehicle (sterile distilled water; normal control) and 2) GnRH antagonist with empty (sham control) or 2 cm T- filled implant. Mice were killed 2, 6, and 8 weeks after treatment. T treatment for 8 weeks resulted in a significant (P<0.001) increase in fiber area of gastrocnemius muscles. T-induced fiber-hypertrophy was accompanied by up-regulation of the Notch ligand Delta 1 and activation of Notch signaling, as evidenced by increase in activated forms of Notch 1 and Notch 2. Consistent with this, we also observed an increase in the number of proliferating cell nuclear antigen (PCNA)-positive nuclei in muscles of T-treated mice, indicating that activation of Notch signaling enhanced cell proliferation. T supplementation not only triggered p38 mitogen-activated protein kinase (MAPK) activation but also concurrently inhibited c-Jun NH(2)-terminal kinase (JNK) activation within 2 weeks of treatment. Concomitant administration of SB203580, a p38 MAPK inhibitor, effectively blocked T-induced activation of Notch signaling and significantly (P<0.001) suppressed PCNA levels. Together, our results indicate that T induces muscle fiber hypertrophy through activation of Notch signaling and the inactivation of JNK together with the activation of p38 MAPK may be critical for T-induced activation of Notch signaling and, as a consequence, muscle fiber hypertrophy.
authors.affiliation: Division of Endocrinology, Charles Drew University, Los Angeles, California 90059, USA.
authors.forename: Danielle
authors.initials: D
authors.lastname: Brown
authors.forename: Amiya P Sinha
authors.initials: AP
authors.lastname: Hikim
authors.forename: Ekaterina L
authors.initials: EL
authors.lastname: Kovacheva
authors.forename: Indrani
authors.initials: I
authors.lastname: Sinha-Hikim
mesh_terms: D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D004195:Disease Models, Animal; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006984:Hypertrophy; D007093:Imidazoles / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000473:pathology* / Q000502:physiology; D009135:Muscular Diseases / Q000139:chemically induced* / Q000378:metabolism / Q000473:pathology; D018008:Myogenin / Q000378:metabolism; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D051880:Receptors, Notch / Q000378:metabolism* / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013739:Testosterone; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*
chemical_list: D004791:Enzyme Inhibitors; D007093:Imidazoles; C503801:Myog protein, mouse; D018008:Myogenin; D018809:Proliferating Cell Nuclear Antigen; D011725:Pyridines; D051880:Receptors, Notch; D013739:Testosterone; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580