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Primary Culture of Rat Adrenocortical Cells and Assays of Steroidogenic Functions
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Orexins stimulate steroidogenic acute regulatory protein expression through multiple signaling pathways in human

Manjunath Ramanjaneya1, Alex C Conner, Jing Chen

  • 1Warwick Medical School, Warwick University, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom.

Endocrinology
|May 3, 2008
PubMed

Insights

Orexins A and B significantly increase steroidogenic acute regulatory protein (StAR) expression in adrenal cells. This study elucidates the complex signaling pathways, including G protein-coupled and MAPK pathways, involved in orexin-mediated steroid biosynthesis.

Area of Science:

  • Endocrinology
  • Neuroendocrinology
  • Molecular Biology

Background:

  • Orexins regulate diverse physiological functions, including feeding and cortisol secretion.
  • Steroidogenesis, a key process in hormone production, relies on the steroidogenic acute regulatory protein (StAR) for cholesterol transport.
  • The precise mechanisms by which orexins influence steroid biosynthesis remain incompletely understood.

Purpose of the Study:

  • To investigate the effect of orexins A and B on steroidogenic acute regulatory protein (StAR) expression in H295R adrenocortical cells.
  • To characterize the dose- and time-dependent regulation of StAR by orexins.
  • To elucidate the specific G protein-coupled and MAPK signaling pathways mediating orexin-induced StAR expression.

Main Methods:

  • Treatment of H295R cells with varying concentrations and durations of orexins A and B.
  • Analysis of StAR protein levels.
  • Dominant-negative G protein analysis and inhibition of protein kinase A, protein kinase C, ERK1/2, and p38 pathways.
  • Orexin receptor antagonist analysis.

Main Results:

  • Orexins A and B significantly up-regulated StAR expression in H295R cells.
  • StAR up-regulation was observed at nanomolar concentrations after 4 hours, with dose- and time-dependent effects.
  • Signaling pathways involving G protein-coupled receptors, protein kinase A, protein kinase C, ERK1/2, p38, and primarily orexin receptor type 1 were identified.

Conclusions:

  • Orexins A and B stimulate StAR expression, a critical step in steroidogenesis.
  • Multiple G protein-coupled and MAPK-mediated signaling pathways are fundamentally involved in orexin-regulated StAR expression.
  • Orexin receptor type 1 plays a primary role in mediating these effects on hormone biosynthesis.

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