β-Actin shows limited mobility and is required only for supraphysiological insulin-stimulated glucose transport in young adult soleus muscle

Am J Physiol Endocrinol Metab. 2018 Jul 1;315(1):E110-E125. doi: 10.1152/ajpendo.00392.2017. Epub 2018 Mar 13.

Abstract

Studies in skeletal muscle cell cultures suggest that the cortical actin cytoskeleton is a major requirement for insulin-stimulated glucose transport, implicating the β-actin isoform, which in many cell types is the main actin isoform. However, it is not clear that β-actin plays such a role in mature skeletal muscle. Neither dependency of glucose transport on β-actin nor actin reorganization upon glucose transport have been tested in mature muscle. To investigate the role of β-actin in fully differentiated muscle, we performed a detailed characterization of wild type and muscle-specific β-actin knockout (KO) mice. The effects of the β-actin KO were subtle; however, we confirmed the previously reported decline in running performance of β-actin KO mice compared with wild type during repeated maximal running tests. We also found insulin-stimulated glucose transport into incubated muscles reduced in soleus but not in extensor digitorum longus muscle of young adult mice. Contraction-stimulated glucose transport trended toward the same pattern, but the glucose transport phenotype disappeared in soleus muscles from mature adult mice. No genotype-related differences were found in body composition or glucose tolerance or by indirect calorimetry measurements. To evaluate β-actin mobility in mature muscle, we electroporated green fluorescent protein (GFP)-β-actin into flexor digitorum brevis muscle fibers and measured fluorescence recovery after photobleaching. GFP-β-actin showed limited unstimulated mobility and no changes after insulin stimulation. In conclusion, β-actin is not required for glucose transport regulation in mature mouse muscle under the majority of the tested conditions. Thus, our work reveals fundamental differences in the role of the cortical β-actin cytoskeleton in mature muscle compared with cell culture.

Keywords: actin cytoskeleton; glucose transport; insulin; skeletal muscle; β-actin.

Publication types

  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin Cytoskeleton / metabolism
  • Actins / genetics
  • Actins / metabolism*
  • Actins / physiology*
  • Aminoimidazole Carboxamide / analogs & derivatives
  • Aminoimidazole Carboxamide / pharmacology
  • Animals
  • Biological Transport, Active / drug effects
  • Female
  • Glucose / metabolism*
  • Glucose Tolerance Test
  • Hypoglycemic Agents / pharmacology*
  • In Vitro Techniques
  • Insulin / pharmacology*
  • Male
  • Mice
  • Mice, Knockout
  • Muscle Contraction / drug effects
  • Muscle Fibers, Skeletal / metabolism
  • Muscle, Skeletal / drug effects*
  • Muscle, Skeletal / metabolism*
  • Ribonucleotides / pharmacology
  • Running / physiology

Substances

  • Actins
  • Hypoglycemic Agents
  • Insulin
  • Ribonucleotides
  • Aminoimidazole Carboxamide
  • AICA ribonucleotide
  • Glucose