Differential Regulation of the Muscle-specific GLUT4 Enhancer in Regenerating and Adult Skeletal Muscle

Abstract

We have reported a novel functional co-operation among MyoD, myocyte enhancer factor-2 (MEF2), and the thyroid hormone receptor in a muscle-specific enhancer of the rat GLUT4 gene in muscle cells. Here, we demonstrate that the muscle-specific enhancer of the GLUT4 gene operates in skeletal muscle and is muscle fiber-dependent and innervation-independent. Under normal conditions, both in soleus and in extensor digitorum longus muscles, the activity of the enhancer required the integrity of the MEF2-binding site. Cancellation of the binding site of thyroid hormone receptor enhanced its activity, suggesting an inhibitory role. Muscle regeneration of the soleus and extensor digitorum longus muscles caused a marked induction of GLUT4 and stimulation of the enhancer activity, which was independent of innervation. During muscle regeneration, the enhancer activity was markedly inhibited by cancellation of the binding sites of MEF2, MyoD, or thyroid hormone receptors. Different MEF2 isoforms expressed in skeletal muscle (MEF2A, MEF2C, and MEF2D) and all members of the MyoD family had the capacity to participate in the activity of the GLUT4 enhancer as assessed by transient transfection in cultured cells. Our data indicate that the GLUT4 enhancer operates in muscle fibers and its activity contributes to the differences in GLUT4 gene expression between oxidative and glycolytic muscle fibers and to the GLUT4 up-regulation that occurs during muscle regeneration. The activity of the enhancer is maintained in adult muscle by MEF2, whereas during regeneration the operation of the enhancer depends on MEF2, myogenic transcription factors of the MyoD family, and thyroid hormone receptors.

Evidence for a Mitochondrial Regulatory Pathway Defined by Peroxisome Proliferator–Activated Receptor-γ Coactivator-1α, Estrogen-Related Receptor-α, and Mitofusin 2

“…Mouse embryonic fibroblasts were cultured in Dulbecco's modified Eagle's medium containing 10% calf serum. Myotube differentiation was induced as previously reported (22). Nuclear and mitochondrial fractions were obtained by differential centrifugation of L6E9 cell homogenates (21).…”

The Effect of Passive Movement on Denervated Soleus Highlights a Differential Nerve Control on SERCA and MyHC Isoforms

“…In accordance with this, inactivation of Ras (Zádor and Wuytack 2003) or calcineurin (Zádor et al 2005) in the regenerating soleus induced a decline in the expression of MyHC1 but left the expression of SERCA2a unchanged. Although the nervous control of muscle gene expression may differ in the regenerating vs normal muscle (Moreno et al 2003), a number of studies have shown that the expression of the corresponding SERCA and MyHC isoforms are also dissociated in paralyzed cat and rat soleus Talmadge and Paalani 2007), in overloaded soleus (Awede et al 1999), and in denervated soleus muscles (Leberer et al 1986;Hämäläinen and Pette 2001;Roy et al 2002).…”

Epigenetics of Glucose Metabolism and the Basis for T2DM Interventions

“…These two proteins synergistically enhance skeletal muscle GLUT4 transcriptions and gene expression (Moreno et al, 2003).…”