Nerve-responsive troponin I slow promoter does not respond to unloading

J Appl Physiol (1985). 1998 Mar;84(3):1083-7. doi: 10.1152/jappl.1998.84.3.1083.

Abstract

We examined the regulation of the troponin I slow (TnIs) promoter during skeletal muscle unloading-induced protein isoform transition, by using a transgenic mouse line harboring the -4,200 to +12 base pairs region of the human TnIs promoter. Eighteen female transgenic mice ( approximately 30 g body mass) were randomly divided into two groups: weight-bearing (WB) controls (n = 9) and hindlimb unloaded (HU; n = 9). The HU mice were tail suspended for 7 days. Body mass was unchanged in the WB group but was reduced (-6%; P < 0.05) after the HU treatment. Absolute soleus muscle mass (-25%) and soleus mass relative to body mass (-16%) were both lower (P < 0.05) in the HU group compared with the WB mice. Northern blot analyses indicate that 7 days of HU result in a 64% decrease (P < 0.05) in the abundance of endogenous TnIs mRNA (microg/mg muscle) in the mouse soleus. Furthermore, there is a trend for the abundance of the fast troponin I mRNA to be increased (+34%). Analysis of transgenic chloramphenicol acetyltransferase activity in the soleus muscle revealed no difference (P > 0.05) between WB and HU groups. We conclude that additional elements are necessary for the TnIs gene to respond to an unloading-induced, slow-to-fast isoform transition stimulus.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Blotting, Northern
  • Body Weight / physiology
  • Chloramphenicol O-Acetyltransferase / biosynthesis
  • Chloramphenicol O-Acetyltransferase / genetics
  • Chloramphenicol O-Acetyltransferase / metabolism
  • DNA Probes
  • Female
  • Hindlimb Suspension / physiology*
  • Humans
  • Mice
  • Mice, Transgenic
  • Muscle, Skeletal / enzymology
  • Muscle, Skeletal / physiology*
  • Organ Size / physiology
  • RNA / biosynthesis
  • Transcription, Genetic
  • Troponin I / genetics
  • Troponin I / physiology*

Substances

  • DNA Probes
  • Troponin I
  • RNA
  • Chloramphenicol O-Acetyltransferase