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Kennedy BE, Charman M, Karten B. Measurement of Mitochondrial Cholesterol Import Using a Mitochondria-Targeted CYP11A1 Fusion Construct. Methods Mol Biol 2018; 1583:163-184. [PMID: 28205173 DOI: 10.1007/978-1-4939-6875-6_12] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/13/2023]
Abstract
All animal membranes require cholesterol as an essential regulator of biophysical properties and function, but the levels of cholesterol vary widely among different subcellular compartments. Mitochondria, and in particular the inner mitochondrial membrane, have the lowest levels of cholesterol in the cell. Nevertheless, mitochondria need cholesterol for membrane maintenance and biogenesis, as well as oxysterol, steroid, and hepatic bile acid production. Alterations in mitochondrial cholesterol have been associated with a range of pathological conditions, including cancer, hepatosteatosis, cardiac ischemia, Alzheimer's, and Niemann-Pick Type C Disease. The mechanisms of mitochondrial cholesterol import are not fully elucidated yet, and may vary in different cell types and environmental conditions. Measuring cholesterol trafficking to the mitochondrial membranes is technically challenging because of its low abundance; for example, traditional pulse-chase experiments with isotope-labeled cholesterol are not feasible. Here, we describe improvements to a method first developed by the Miller group at the University of California to measure cholesterol trafficking to the inner mitochondrial membrane (IMM) through the conversion of cholesterol to pregnenolone. This method uses a mitochondria-targeted, ectopically expressed fusion construct of CYP11A1, ferredoxin reductase and ferredoxin. Pregnenolone is formed exclusively from cholesterol at the IMM, and can be analyzed with high sensitivity and specificity through ELISA or radioimmunoassay of the medium/buffer to reflect mitochondrial cholesterol import. This assay can be used to investigate the effects of genetic or pharmacological interventions on mitochondrial cholesterol import in cultured cells or isolated mitochondria.
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Affiliation(s)
- Barry E Kennedy
- Department of Biochemistry and Molecular Biology, Dalhousie University, Sir Charles Tupper Medical Building 9G, 5850 College Street, Halifax, NS, Canada, B3H 4R2
| | - Mark Charman
- Department of Biochemistry and Molecular Biology, Dalhousie University, Sir Charles Tupper Medical Building 9G, 5850 College Street, Halifax, NS, Canada, B3H 4R2
| | - Barbara Karten
- Department of Biochemistry and Molecular Biology, Dalhousie University, Sir Charles Tupper Medical Building 9G, 5850 College Street, Halifax, NS, Canada, B3H 4R2.
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Lin Y, Hou X, Shen WJ, Hanssen R, Khor VK, Cortez Y, Roseman AN, Azhar S, Kraemer FB. SNARE-Mediated Cholesterol Movement to Mitochondria Supports Steroidogenesis in Rodent Cells. Mol Endocrinol 2016; 30:234-47. [PMID: 26771535 DOI: 10.1210/me.2015-1281] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Vesicular transport involving soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) proteins is known to be responsible for many major cellular activities. In steroidogenic tissues, chronic hormone stimulation results in increased expression of proteins involved in the steroidogenic pathway, whereas acute hormone stimulation prompts the rapid transfer of cholesterol to the inner mitochondrial membrane to be utilized as substrate for steroid hormone production. Several different pathways are involved in supplying cholesterol to mitochondria, but mobilization of stored cholesteryl esters appears to initially constitute the preferred source; however, the mechanisms mediating this cholesterol transfer are not fully understood. To study the potential contribution of SNARE proteins in steroidogenesis, we examined the expression levels of various SNARE proteins in response to hormone stimulation in steroidogenic tissues and cells and established an in vitro mitochondria reconstitution assay system to assess the contribution of various SNARE proteins on cholesterol delivery for steroidogenesis. Our results from reconstitution experiments along with knockdown studies in rat primary granulosa cells and in a Leydig cell line show that soluble N-ethylmaleimide sensitive factor attachment protein-α, synaptosomal-associated protein of 25 kDa, syntaxin-5, and syntaxin-17 facilitate the transport of cholesterol to mitochondria. Thus, although StAR is required for efficient cholesterol movement into mitochondria for steroidogenesis, specific SNAREs participate and are necessary to mediate cholesterol movement to mitochondria.
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Affiliation(s)
- Ye Lin
- Division of Endocrinology, Gerontology, and Metabolism (Y.L., X.H., W.-J.S., R.H., V.K.K., S.A., F.B.K.), Stanford University, and Veterans Affairs Palo Alto Health Care System (Y.L., X.H., W.-J.S., R.H., V.K.K., Y.C., A.N.R., S.A., F.B.K.), Palo Alto, California 94304
| | - Xiaoming Hou
- Division of Endocrinology, Gerontology, and Metabolism (Y.L., X.H., W.-J.S., R.H., V.K.K., S.A., F.B.K.), Stanford University, and Veterans Affairs Palo Alto Health Care System (Y.L., X.H., W.-J.S., R.H., V.K.K., Y.C., A.N.R., S.A., F.B.K.), Palo Alto, California 94304
| | - Wen-Jun Shen
- Division of Endocrinology, Gerontology, and Metabolism (Y.L., X.H., W.-J.S., R.H., V.K.K., S.A., F.B.K.), Stanford University, and Veterans Affairs Palo Alto Health Care System (Y.L., X.H., W.-J.S., R.H., V.K.K., Y.C., A.N.R., S.A., F.B.K.), Palo Alto, California 94304
| | - Ruth Hanssen
- Division of Endocrinology, Gerontology, and Metabolism (Y.L., X.H., W.-J.S., R.H., V.K.K., S.A., F.B.K.), Stanford University, and Veterans Affairs Palo Alto Health Care System (Y.L., X.H., W.-J.S., R.H., V.K.K., Y.C., A.N.R., S.A., F.B.K.), Palo Alto, California 94304
| | - Victor K Khor
- Division of Endocrinology, Gerontology, and Metabolism (Y.L., X.H., W.-J.S., R.H., V.K.K., S.A., F.B.K.), Stanford University, and Veterans Affairs Palo Alto Health Care System (Y.L., X.H., W.-J.S., R.H., V.K.K., Y.C., A.N.R., S.A., F.B.K.), Palo Alto, California 94304
| | - Yuan Cortez
- Division of Endocrinology, Gerontology, and Metabolism (Y.L., X.H., W.-J.S., R.H., V.K.K., S.A., F.B.K.), Stanford University, and Veterans Affairs Palo Alto Health Care System (Y.L., X.H., W.-J.S., R.H., V.K.K., Y.C., A.N.R., S.A., F.B.K.), Palo Alto, California 94304
| | - Ann N Roseman
- Division of Endocrinology, Gerontology, and Metabolism (Y.L., X.H., W.-J.S., R.H., V.K.K., S.A., F.B.K.), Stanford University, and Veterans Affairs Palo Alto Health Care System (Y.L., X.H., W.-J.S., R.H., V.K.K., Y.C., A.N.R., S.A., F.B.K.), Palo Alto, California 94304
| | - Salman Azhar
- Division of Endocrinology, Gerontology, and Metabolism (Y.L., X.H., W.-J.S., R.H., V.K.K., S.A., F.B.K.), Stanford University, and Veterans Affairs Palo Alto Health Care System (Y.L., X.H., W.-J.S., R.H., V.K.K., Y.C., A.N.R., S.A., F.B.K.), Palo Alto, California 94304
| | - Fredric B Kraemer
- Division of Endocrinology, Gerontology, and Metabolism (Y.L., X.H., W.-J.S., R.H., V.K.K., S.A., F.B.K.), Stanford University, and Veterans Affairs Palo Alto Health Care System (Y.L., X.H., W.-J.S., R.H., V.K.K., Y.C., A.N.R., S.A., F.B.K.), Palo Alto, California 94304
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Charman M, Kennedy BE, Osborne N, Karten B. MLN64 mediates egress of cholesterol from endosomes to mitochondria in the absence of functional Niemann-Pick Type C1 protein. J Lipid Res 2009; 51:1023-34. [PMID: 19965586 DOI: 10.1194/jlr.m002345] [Citation(s) in RCA: 137] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Niemann-Pick Type C (NPC) disease is a fatal, neurodegenerative disorder, caused in most cases by mutations in the late endosomal protein NPC1. A hallmark of NPC disease is endosomal cholesterol accumulation and an impaired cholesterol homeostatic response, which might affect cholesterol transport to mitochondria and, thus, mitochondrial and cellular function. This study aimed to characterize mitochondrial cholesterol homeostasis in NPC disease. Using wild-type and NPC1-deficient Chinese hamster ovary cells, stably transfected with a CYP11A1 complex to assess mitochondrial cholesterol import by pregnenolone production, we show that cholesterol transport to the mitochondrial inner membrane is not affected by loss of NPC1. However, mitochondrial cholesterol content was higher in NPC1-deficient than in wild-type cells. Cholesterol transport to the mitochondrial inner membrane increased markedly upon exposure of cholesterol-deprived cells to lipoproteins, indicating transport of endosomal cholesterol to mitochondria. Reduction of endosomal metastatic lymph node protein 64 (MLN64) by RNA interference decreased cholesterol transport to the mitochondrial inner membrane and reduced mitochondrial cholesterol levels in NPC1-deficient cells, suggesting that MLN64 transported cholesterol to mitochondria even in the absence of NPC1. In summary, this study describes a transport pathway for endosomal cholesterol to mitochondria that requires MLN64, but not NPC1, and that may be responsible for increased mitochondrial cholesterol in NPC disease.
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Affiliation(s)
- Mark Charman
- Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia, B3H 1X5, Canada
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