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Submitted on November 26, 2001
Accepted on June 14, 2002
1 Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390-8857; Institute of Molecular Biology, Academia Sinica, Nankang, Taipei, Taiwan 115, Republic of China; Department of Biological Chemistry, The Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
* To whom correspondence should be addressed. E-mail: kparke{at}mednet.swmed.edu.
The steroidogenic acute regulatory protein (StAR) is essential for the regulated production of steroid hormones, mediating the translocation of intracellular cholesterol to the inner mitochondrial membrane where steroidogenesis commences. Steroidogenic cells lacking StAR have impaired steroidogenesis and progressively accumulate lipid, ultimately causing cytopathic changes and deterioration of steroidogenic capacity. Developmental studies of StAR knockout (KO) mice have correlated gonadal lipid deposits with puberty, suggesting that trophic hormones contribute to this lipid accumulation. To delineate the role of gonadotropins in this process, we examined double mutant mice deficient in both StAR and gonadotropins (StAR KO/hpg). Lipid accumulation was ameliorated considerably in StAR KO/hpg mice but was restored by treatment with exogenous gonadotropins, directly linking trophic hormones with gonadal lipid accumulation. To define the relative roles of exogenous vs. endogenous cholesterol in the lipid accumulation, we also examined mice lacking both StAR and apolipoprotein A-I (StAR KO/Apo A-I KO). Steroidogenic tissues of StAR KO/Apo A-I KO mice had markedly decreased lipid deposits, supporting the predominant role of HDL-derived cholesterol in the lipid accumulation caused by StAR deficiency. Finally, we used electron microscopy to compare mitochondrial ultrastructure in StAR KO and cholesterol side-chain cleavage enzyme (Cyp11a1) KO mice; despite comparable lipid accumulation within adrenocortical cells, the effects of StAR deficiency and Cyp11a1 deficiency on mitochondrial ultrastructure were markedly different. These findings extend our understanding of steroidogenic cell dysfunction in StAR KO mice and highlight key roles of trophic hormones and HDL-derived cholesterol in lipid deposits within StAR deficient steroidogenic cells.
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