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Although not a source of energy, cholesterol plays a significant role as a foundational structure for bile salts, steroid hormones, and vitamin D, as well as being a crucial component of plasma membranes. Approximately 15% of blood cholesterol is derived from our diet, with the remainder synthesized from acetyl CoA by the liver and intestines. Cholesterol is eliminated from the body through its conversion into bile salts, which are eventually discarded in the feces.
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Related Experiment Video

Updated: Aug 3, 2025

Cholesterol Efflux Assay
07:54

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Tom40 in cholesterol transport.

Himangshu S Bose1,2, Mahuya Bose3, Randy M Whittal4

  • 1Laboratory of Biochemistry and Cell Biology, Department of Biomedical Sciences, Mercer University School of Medicine, Savannah, GA 31404, USA.

Iscience
|April 10, 2023
PubMed
Summary
This summary is machine-generated.

Mitochondrial translocase of outer mitochondrial membrane (OMM), Tom40, is crucial for transporting cholesterol into mitochondria, a key step in steroidogenesis. This discovery reveals Tom40

Keywords:
BiomoleculesCell biologyProtein folding

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Area of Science:

  • Mitochondrial biology
  • Steroidogenesis
  • Cellular transport mechanisms

Background:

  • Cholesterol transport into mitochondria is essential for steroid hormone production in adrenal and gonadal tissues.
  • The precise mechanism governing mitochondrial cholesterol transport, particularly during rapid steroidogenesis under stress, remains largely unknown.
  • Steroidogenic acute regulatory (StAR) protein is known to be involved in cholesterol transport, but its precise role at the mitochondrial level is unclear.

Purpose of the Study:

  • To elucidate the mechanism of mitochondrial cholesterol transport in steroidogenesis.
  • To identify key proteins involved in facilitating cholesterol movement into the mitochondria.
  • To investigate the role of the translocase of the outer mitochondrial membrane (OMM) in this process.

Main Methods:

  • Utilized rat testicular tissue and mouse Leydig (MA-10) cells for experimental analysis.
  • Investigated the interaction between StAR protein and mitochondrial outer membrane components.
  • Examined the impact of Tom40 absence on cholesterol transport and steroidogenesis.

Main Results:

  • Identified Tom40, a component of the OMM translocase, as central to mitochondrial cholesterol transport.
  • Demonstrated that cytoplasmic cholesterol-lipid complexes containing StAR protein move from the mitochondria-associated ER membrane (MAM) to the OMM.
  • Showed that Tom40 interacts with StAR at the OMM, facilitating cholesterol entry into mitochondria.
  • Observed that the absence of Tom40 disrupts complex formation, inhibits mitochondrial cholesterol transport, and impairs steroidogenesis.

Conclusions:

  • Tom40 plays a critical role in the rapid transport of cholesterol into mitochondria, initiating and regulating steroidogenesis.
  • The interaction between Tom40 and StAR at the OMM is essential for efficient cholesterol translocation.
  • Understanding Tom40's function provides new insights into the regulation of steroid hormone production.