Differential gene expression in skeletal muscle cells after membrane depolarization

Abstract

Skeletal muscle is a highly plastic tissue with a remarkable capacity to adapt itself to challenges imposed by contractile activity. Adaptive response, that include hypertrophy and activation of oxidative mechanisms have been associated with transient changes in transcriptional activity of specific genes. To define the set of genes regulated by a depolarizing stimulus, we used 22 K mouse oligonucleotide microarrays. Total RNA from C2C12 myotubes was obtained at 2, 4, 18, and 24 h after high K+ stimulation. cDNA from control and depolarized samples was labeled with cyanine 3 or 5 dyes prior to microarray hybridization. Loess normalization followed by statistical analysis resulted in 423 differentially expressed genes using an unadjusted P-value < or = 0.01 as cut off. Depolarization affects transcriptional activity of a limited number of genes, mainly associated with metabolism, cell communication and response to stress. A number of genes related to Ca2+ signaling pathways are induced at 4 h, reinforcing the potential role of Ca2+ in early steps of signal transduction that leads to gene expression. Significant changes in the expression of molecules involved in muscle cell structure were observed; K+-depolarization increased Tnni1 and Acta1 mRNA levels in both differentiated C2C12 and rat skeletal muscle cells in primary culture. Of these two, depolarization induced slow Ca2+ transients appear to have a role only in the regulation of Tnni1 transcriptional activity. We suggest that depolarization induced expression of a small set of genes may underlie Ca2+ dependent plasticity of skeletal muscle cells.

Electrical stimulation induces IL-6 in skeletal muscle through extracellular ATP by activating Ca2+signals and an IL-6 autocrine loop

“…Membrane depolarization is the primary event for excitation-transcription coupling (9,22) that triggers Cav1.1 activation and the IP 3 -dependent Ca 2ϩ pathway (6,24). Previous results from our laboratory have placed the activation of gene expression, particularly of IL-6, as an event downstream of the myotube membrane depolarization (15,45,46). Depolarization of cultured myotubes using a high K ϩ solution induces the expression of IL-6 (45).…”

NFAT activation by membrane potential follows a calcium pathway distinct from other activity-related transcription factors in skeletal muscle cells

“…8). In addition, the slow Ca 2ϩ signal in cultured muscle cells also regulates the expression of genes such as IL-6 (22) and troponin I (23), whereas other genes with Ca 2ϩ -dependent elements within their promoters, such as the ␣-actin 1 gene, appear not to be regulated by this particular Ca 2ϩ transient (23). For skeletal muscle, both the frequency and duration of electrical stimuli (or even lack of stimuli) have a meaning in terms of genes that will be upregulated or downregulated.…”

Cav1.1 controls frequency-dependent events regulating adult skeletal muscle plasticity

“…In addition to this canonical signal, sustained depolarization stimulates inositol 1,4,5-trisphosphate receptor [Ins(1,4,5)P 3 R]-mediated Ca 2+ release that generates slow, long-lasting Ca 2+ transients (Jaimovich et al, 2000). These slow transients, not related to muscle contraction, regulate several transcription-related events following membrane depolarization (Carrasco et al, 2003;Juretić et al, 2007). The signaling pathway activated by depolarization of muscle cells and triggered by Cav1.1 includes the sequential activation of G protein, phosphatidylinositide 3-kinase (PI3K) and phospholipase C (PLC) to produce inositol (1,4,5)-trisphosphate [Ins(1,4,5)P 3 ] that causes Ca 2+ release via Ins(1,4,5)P 3 R present in the SR membrane as well as in the nucleus (Cárdenas et al, 2005;Eltit et al, 2006).…”