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Zaidi SK, Shen WJ, Cortez Y, Bittner S, Bittner A, Arshad S, Huang TT, Kraemer FB, Azhar S. SOD2 deficiency-induced oxidative stress attenuates steroidogenesis in mouse ovarian granulosa cells. Mol Cell Endocrinol 2021; 519:110888. [PMID: 32717420 PMCID: PMC8011630 DOI: 10.1016/j.mce.2020.110888] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/07/2019] [Revised: 05/27/2020] [Accepted: 06/01/2020] [Indexed: 02/06/2023]
Abstract
This study investigated the effects of SOD2 (MnSOD)-deficiency-induced excessive oxidative stress on ovarian steroidogenesis in vivo and isolated and cultured granulosa cells using WT and Sod2+/- mice. Basal and 48 h eCG-stimulated plasma progesterone levels were decreased ~50% in female Sod2+/- mice, whereas plasma progesterone levels were decreased ~70% in Sod2+/- mice after sequential stimulation with eCG followed by hCG. Sod2+/- deficiency caused about 50% reduction in SOD2 activity in granulosa cells. SOD2-deficiency also caused a marked reduction in progestins and estradiol in isolated granulosa cells. qRT-PCR measurements indicated that the mRNA expression levels of StAR protein and steroidogenic enzymes are decreased in the ovaries of Sod2+/- mice. Further studies showed a defect in the movement of mobilized cytosolic cholesterol to mitochondria. The ovarian membrane from Sod2+/- mice showed higher susceptibility to lipid peroxidation. These data indicates that SOD2-deficiency induced oxidative stress inhibits ovarian granulosa cell steroidogenesis primarily by interfering with cholesterol transport to mitochondria and attenuating the expression of Star protein gene and key steroidogenic enzyme genes.
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Affiliation(s)
- Syed Kashif Zaidi
- Geriatric Research, Education, and Clinical Center, VA Palo Alto Health Care System, Palo Alto, CA, 94304, USA; Division of Endocrinology, Gerontology and Metabolism, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Wen-Jun Shen
- Geriatric Research, Education, and Clinical Center, VA Palo Alto Health Care System, Palo Alto, CA, 94304, USA; Division of Endocrinology, Gerontology and Metabolism, Stanford University School of Medicine, Stanford, CA, 94305, USA.
| | - Yuan Cortez
- Geriatric Research, Education, and Clinical Center, VA Palo Alto Health Care System, Palo Alto, CA, 94304, USA
| | - Stefanie Bittner
- Geriatric Research, Education, and Clinical Center, VA Palo Alto Health Care System, Palo Alto, CA, 94304, USA
| | - Alex Bittner
- Geriatric Research, Education, and Clinical Center, VA Palo Alto Health Care System, Palo Alto, CA, 94304, USA
| | - Sara Arshad
- Geriatric Research, Education, and Clinical Center, VA Palo Alto Health Care System, Palo Alto, CA, 94304, USA; Division of Endocrinology, Gerontology and Metabolism, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Ting-Ting Huang
- Geriatric Research, Education, and Clinical Center, VA Palo Alto Health Care System, Palo Alto, CA, 94304, USA; Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Fredric B Kraemer
- Geriatric Research, Education, and Clinical Center, VA Palo Alto Health Care System, Palo Alto, CA, 94304, USA; Division of Endocrinology, Gerontology and Metabolism, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Salman Azhar
- Geriatric Research, Education, and Clinical Center, VA Palo Alto Health Care System, Palo Alto, CA, 94304, USA; Division of Endocrinology, Gerontology and Metabolism, Stanford University School of Medicine, Stanford, CA, 94305, USA.
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Huang Q, Liu Y, Yang Z, Xie Y, Mo Z. The Effects of Cholesterol Metabolism on Follicular Development and Ovarian Function. Curr Mol Med 2019; 19:719-730. [PMID: 31526349 DOI: 10.2174/1566524019666190916155004] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2019] [Revised: 08/21/2019] [Accepted: 09/03/2019] [Indexed: 12/23/2022]
Abstract
Cholesterol is an important substrate for the synthesis of ovarian sex hormones and has an important influence on follicular development. The cholesterol in follicular fluid is mainly derived from plasma. High-density lipoprotein (HDL) and lowdensity lipoprotein (LDL) play important roles in ovarian cholesterol transport. The knockout of related receptors in the mammalian HDL and LDL pathways results in the reduction or absence of fertility, leading us to support the importance of cholesterol homeostasis in the ovary. However, little is known about ovarian cholesterol metabolism and the complex regulation of its homeostasis. Here, we reviewed the cholesterol metabolism in the ovary and speculated that regardless of the functioning of cholesterol metabolism in the system or the ovarian microenvironment, an imbalance in cholesterol homeostasis is likely to have an adverse effect on ovarian structure and function.
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Affiliation(s)
- Qin Huang
- Clinical Anatomy & Reproductive Medicine Application Institute, Department of Histology and Embryology, Hengyang Medical school, University of South China, Hengyang 421001, China
| | - Yannan Liu
- Nursing School, Hunan University of Medicine, Huaihua 418000, China
| | - Zhen Yang
- Clinical Anatomy & Reproductive Medicine Application Institute, Department of Histology and Embryology, Hengyang Medical school, University of South China, Hengyang 421001, China
| | - Yuanjie Xie
- Clinical Anatomy & Reproductive Medicine Application Institute, Department of Histology and Embryology, Hengyang Medical school, University of South China, Hengyang 421001, China
| | - Zhongcheng Mo
- Clinical Anatomy & Reproductive Medicine Application Institute, Department of Histology and Embryology, Hengyang Medical school, University of South China, Hengyang 421001, China
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Shen WJ, Asthana S, Kraemer FB, Azhar S. Scavenger receptor B type 1: expression, molecular regulation, and cholesterol transport function. J Lipid Res 2018; 59:1114-1131. [PMID: 29720388 DOI: 10.1194/jlr.r083121] [Citation(s) in RCA: 85] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2018] [Revised: 04/26/2018] [Indexed: 12/16/2022] Open
Abstract
Cholesterol is required for maintenance of plasma membrane fluidity and integrity and for many cellular functions. Cellular cholesterol can be obtained from lipoproteins in a selective pathway of HDL-cholesteryl ester (CE) uptake without parallel apolipoprotein uptake. Scavenger receptor B type 1 (SR-B1) is a cell surface HDL receptor that mediates HDL-CE uptake. It is most abundantly expressed in liver, where it provides cholesterol for bile acid synthesis, and in steroidogenic tissues, where it delivers cholesterol needed for storage or steroidogenesis in rodents. SR-B1 transcription is regulated by trophic hormones in the adrenal gland, ovary, and testis; in the liver and elsewhere, SR-B1 is subject to posttranscriptional and posttranslational regulation. SR-B1 operates in several metabolic processes and contributes to pathogenesis of atherosclerosis, inflammation, hepatitis C virus infection, and other conditions. Here, we summarize characteristics of the selective uptake pathway and involvement of microvillar channels as facilitators of selective HDL-CE uptake. We also present the potential mechanisms of SR-B1-mediated selective cholesterol transport; the transcriptional, posttranscriptional, and posttranslational regulation of SR-B1; and the impact of gene variants on expression and function of human SR-B1. A better understanding of this unique pathway and SR-B1's role may yield improved therapies for a wide variety of conditions.
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Affiliation(s)
- Wen-Jun Shen
- Geriatric Research, Education, and Clinical Research Center (GRECC), Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94304 and Division of Endocrinology, Gerontology, and Metabolism, Stanford University School of Medicine, Stanford, CA 94305
| | - Shailendra Asthana
- Drug Discovery Research Center (DDRC), Translational Health Science and Technology Institute (THSTI), NCR Biotech Science Cluster, Faridabad 121001, Haryana, India
| | - Fredric B Kraemer
- Geriatric Research, Education, and Clinical Research Center (GRECC), Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94304 and Division of Endocrinology, Gerontology, and Metabolism, Stanford University School of Medicine, Stanford, CA 94305
| | - Salman Azhar
- Geriatric Research, Education, and Clinical Research Center (GRECC), Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94304 and Division of Endocrinology, Gerontology, and Metabolism, Stanford University School of Medicine, Stanford, CA 94305
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Lai WA, Yeh YT, Fang WL, Wu LS, Harada N, Wang PH, Ke FC, Lee WL, Hwang JJ. Calcineurin and CRTC2 mediate FSH and TGFβ1 upregulation of Cyp19a1 and Nr5a in ovary granulosa cells. J Mol Endocrinol 2014; 53:259-70. [PMID: 25057110 DOI: 10.1530/jme-14-0048] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Estrogens are essential for female reproduction and overall well-being, and estrogens in the circulation are largely synthesized in ovarian granulosa cells. Using primary cultures of ovarian granulosa cells from gonadotropin-primed immature rats, we have recently discovered that pituitary FSH and ovarian cytokine transforming growth factor beta 1 (TGFβ1) induce calcineurin-mediated dephosphorylation-activation of cAMP-response element-binding protein (CREB)-regulated transcription coactivator (CRTC2) to modulate the expression of Star, Cyp11a1, and Hsd3b leading to increased production of progesterone. This study explored the role of calcineurin and CRTC2 in FSH and TGFβ1 regulation of Cyp19a1 expression in granulosa cells. Ovarian granulosa cells treated with FSH displayed increased aromatase protein at 24 h post-treatment, which subsided by 48 h, while TGFβ1 acting through its type 1 receptor augmented the action of FSH with a greater and longer effects. It is known that the ovary-specific Cyp19a1 PII-promoter contains crucial response elements for CREB and nuclear receptor NR5A subfamily liver receptor homolog 1 (LRH1/NR5A2) and steroidogenic factor 1 (SF1/NR5A1), and that the Nr5a2 promoter also has a potential CREB-binding site. Herein, we demonstrate that FSH+TGFβ1 increased LRH1 and SF1 protein levels, and their binding to the Cyp19a1 PII-promoter evidenced, determined by chromatin immunoprecipitation analysis. Moreover, pretreatment with calcineurin auto-inhibitory peptide (CNI) abolished the FSH+TGFβ1-upregulated but not FSH-upregulated aromatase activity at 48 h, and the corresponding mRNA changes in Cyp19a1, and Nr5a2 and Nr5a1 at 24 h. In addition, FSH and TGFβ1 increased CRTC2 binding to the Cyp19a1 PII-promoter and Nr5a2 promoter at 24 h, with CREB bound constitutively. In summary, the results of this study indicate that calcineurin and CRTC2 have important roles in mediating FSH and TGFβ1 collateral upregulation of Cyp19a1 expression together with its transcription regulators Nr5a2 and Nr5a1 in ovarian granulosa cells.
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Affiliation(s)
- Wei-An Lai
- Institute of PhysiologySchool of Medicine, National Yang-Ming University, 155 Linong Street, Section 2, Taipei 11221, TaiwanDepartment of NursingHsin-Sheng College of Medical Care and Management, Taoyuan, TaiwanDepartment of Animal Science and TechnologyCollege of Bio-Resources and Agriculture, National Taiwan University, Taipei, TaiwanDepartment of BiochemistrySchool of Medicine, Fujita Health University, Aichi, JapanDepartment of Obstetrics and GynecologyTaipei Veterans General Hospital, Taipei, TaiwanDepartment of Obstetrics and GynecologyNational Yang-Ming University, Taipei, TaiwanInstitute of Molecular and Cellular BiologyCollege of Life Science, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 10617, TaiwanDepartment of MedicineCheng Hsin General Hospital, 45 Jhensing Street, Taipei 11220, TaiwanDepartment of NursingOriental Institute of Technology, New Taipei City, Taiwan
| | - Yi-Ting Yeh
- Institute of PhysiologySchool of Medicine, National Yang-Ming University, 155 Linong Street, Section 2, Taipei 11221, TaiwanDepartment of NursingHsin-Sheng College of Medical Care and Management, Taoyuan, TaiwanDepartment of Animal Science and TechnologyCollege of Bio-Resources and Agriculture, National Taiwan University, Taipei, TaiwanDepartment of BiochemistrySchool of Medicine, Fujita Health University, Aichi, JapanDepartment of Obstetrics and GynecologyTaipei Veterans General Hospital, Taipei, TaiwanDepartment of Obstetrics and GynecologyNational Yang-Ming University, Taipei, TaiwanInstitute of Molecular and Cellular BiologyCollege of Life Science, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 10617, TaiwanDepartment of MedicineCheng Hsin General Hospital, 45 Jhensing Street, Taipei 11220, TaiwanDepartment of NursingOriental Institute of Technology, New Taipei City, Taiwan
| | - Wei-Ling Fang
- Institute of PhysiologySchool of Medicine, National Yang-Ming University, 155 Linong Street, Section 2, Taipei 11221, TaiwanDepartment of NursingHsin-Sheng College of Medical Care and Management, Taoyuan, TaiwanDepartment of Animal Science and TechnologyCollege of Bio-Resources and Agriculture, National Taiwan University, Taipei, TaiwanDepartment of BiochemistrySchool of Medicine, Fujita Health University, Aichi, JapanDepartment of Obstetrics and GynecologyTaipei Veterans General Hospital, Taipei, TaiwanDepartment of Obstetrics and GynecologyNational Yang-Ming University, Taipei, TaiwanInstitute of Molecular and Cellular BiologyCollege of Life Science, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 10617, TaiwanDepartment of MedicineCheng Hsin General Hospital, 45 Jhensing Street, Taipei 11220, TaiwanDepartment of NursingOriental Institute of Technology, New Taipei City, Taiwan Institute of PhysiologySchool of Medicine, National Yang-Ming University, 155 Linong Street, Section 2, Taipei 11221, TaiwanDepartment of NursingHsin-Sheng College of Medical Care and Management, Taoyuan, TaiwanDepartment of Animal Science and TechnologyCollege of Bio-Resources and Agriculture, National Taiwan University, Taipei, TaiwanDepartment of BiochemistrySchool of Medicine, Fujita Health University, Aichi, JapanDepartment of Obstetrics and GynecologyTaipei Veterans General Hospital, Taipei, TaiwanDepartment of Obstetrics and GynecologyNational Yang-Ming University, Taipei, TaiwanInstitute of Molecular and Cellular BiologyCollege of Life Science, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 10617, TaiwanDepartment of MedicineCheng Hsin General Hospital, 45 Jhensing Street, Taipei 11220, TaiwanDepartment of NursingOriental Institute of Technology, New Taipei City, Taiwan
| | - Leang-Shin Wu
- Institute of PhysiologySchool of Medicine, National Yang-Ming University, 155 Linong Street, Section 2, Taipei 11221, TaiwanDepartment of NursingHsin-Sheng College of Medical Care and Management, Taoyuan, TaiwanDepartment of Animal Science and TechnologyCollege of Bio-Resources and Agriculture, National Taiwan University, Taipei, TaiwanDepartment of BiochemistrySchool of Medicine, Fujita Health University, Aichi, JapanDepartment of Obstetrics and GynecologyTaipei Veterans General Hospital, Taipei, TaiwanDepartment of Obstetrics and GynecologyNational Yang-Ming University, Taipei, TaiwanInstitute of Molecular and Cellular BiologyCollege of Life Science, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 10617, TaiwanDepartment of MedicineCheng Hsin General Hospital, 45 Jhensing Street, Taipei 11220, TaiwanDepartment of NursingOriental Institute of Technology, New Taipei City, Taiwan
| | - Nobuhiro Harada
- Institute of PhysiologySchool of Medicine, National Yang-Ming University, 155 Linong Street, Section 2, Taipei 11221, TaiwanDepartment of NursingHsin-Sheng College of Medical Care and Management, Taoyuan, TaiwanDepartment of Animal Science and TechnologyCollege of Bio-Resources and Agriculture, National Taiwan University, Taipei, TaiwanDepartment of BiochemistrySchool of Medicine, Fujita Health University, Aichi, JapanDepartment of Obstetrics and GynecologyTaipei Veterans General Hospital, Taipei, TaiwanDepartment of Obstetrics and GynecologyNational Yang-Ming University, Taipei, TaiwanInstitute of Molecular and Cellular BiologyCollege of Life Science, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 10617, TaiwanDepartment of MedicineCheng Hsin General Hospital, 45 Jhensing Street, Taipei 11220, TaiwanDepartment of NursingOriental Institute of Technology, New Taipei City, Taiwan
| | - Peng-Hui Wang
- Institute of PhysiologySchool of Medicine, National Yang-Ming University, 155 Linong Street, Section 2, Taipei 11221, TaiwanDepartment of NursingHsin-Sheng College of Medical Care and Management, Taoyuan, TaiwanDepartment of Animal Science and TechnologyCollege of Bio-Resources and Agriculture, National Taiwan University, Taipei, TaiwanDepartment of BiochemistrySchool of Medicine, Fujita Health University, Aichi, JapanDepartment of Obstetrics and GynecologyTaipei Veterans General Hospital, Taipei, TaiwanDepartment of Obstetrics and GynecologyNational Yang-Ming University, Taipei, TaiwanInstitute of Molecular and Cellular BiologyCollege of Life Science, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 10617, TaiwanDepartment of MedicineCheng Hsin General Hospital, 45 Jhensing Street, Taipei 11220, TaiwanDepartment of NursingOriental Institute of Technology, New Taipei City, Taiwan Institute of PhysiologySchool of Medicine, National Yang-Ming University, 155 Linong Street, Section 2, Taipei 11221, TaiwanDepartment of NursingHsin-Sheng College of Medical Care and Management, Taoyuan, TaiwanDepartment of Animal Science and TechnologyCollege of Bio-Resources and Agriculture, National Taiwan University, Taipei, TaiwanDepartment of BiochemistrySchool of Medicine, Fujita Health University, Aichi, JapanDepartment of Obstetrics and GynecologyTaipei Veterans General Hospital, Taipei, TaiwanDepartment of Obstetrics and GynecologyNational Yang-Ming University, Taipei, TaiwanInstitute of Molecular and Cellular BiologyCollege of Life Science, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 10617, TaiwanDepartment of MedicineCheng Hsin General Hospital, 45 Jhensing Street, Taipei 11220, TaiwanDepartment of NursingOriental Institute of Technology, New Taipei City, Taiwan
| | - Ferng-Chun Ke
- Institute of PhysiologySchool of Medicine, National Yang-Ming University, 155 Linong Street, Section 2, Taipei 11221, TaiwanDepartment of NursingHsin-Sheng College of Medical Care and Management, Taoyuan, TaiwanDepartment of Animal Science and TechnologyCollege of Bio-Resources and Agriculture, National Taiwan University, Taipei, TaiwanDepartment of BiochemistrySchool of Medicine, Fujita Health University, Aichi, JapanDepartment of Obstetrics and GynecologyTaipei Veterans General Hospital, Taipei, TaiwanDepartment of Obstetrics and GynecologyNational Yang-Ming University, Taipei, TaiwanInstitute of Molecular and Cellular BiologyCollege of Life Science, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 10617, TaiwanDepartment of MedicineCheng Hsin General Hospital, 45 Jhensing Street, Taipei 11220, TaiwanDepartment of NursingOriental Institute of Technology, New Taipei City, Taiwan
| | - Wen-Ling Lee
- Institute of PhysiologySchool of Medicine, National Yang-Ming University, 155 Linong Street, Section 2, Taipei 11221, TaiwanDepartment of NursingHsin-Sheng College of Medical Care and Management, Taoyuan, TaiwanDepartment of Animal Science and TechnologyCollege of Bio-Resources and Agriculture, National Taiwan University, Taipei, TaiwanDepartment of BiochemistrySchool of Medicine, Fujita Health University, Aichi, JapanDepartment of Obstetrics and GynecologyTaipei Veterans General Hospital, Taipei, TaiwanDepartment of Obstetrics and GynecologyNational Yang-Ming University, Taipei, TaiwanInstitute of Molecular and Cellular BiologyCollege of Life Science, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 10617, TaiwanDepartment of MedicineCheng Hsin General Hospital, 45 Jhensing Street, Taipei 11220, TaiwanDepartment of NursingOriental Institute of Technology, New Taipei City, Taiwan Institute of PhysiologySchool of Medicine, National Yang-Ming University, 155 Linong Street, Section 2, Taipei 11221, TaiwanDepartment of NursingHsin-Sheng College of Medical Care and Management, Taoyuan, TaiwanDepartment of Animal Science and TechnologyCollege of Bio-Resources and Agriculture, National Taiwan University, Taipei, TaiwanDepartment of BiochemistrySchool of Medicine, Fujita Health University, Aichi, JapanDepartment of Obstetrics and GynecologyTaipei Veterans General Hospital, Taipei, TaiwanDepartment of Obstetrics and GynecologyNational Yang-Ming University, Taipei, TaiwanInstitute of Molecular and Cellular BiologyCollege of Life Science, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 10617, TaiwanDepartment of MedicineCheng Hsin General Hospital, 45 Jhensing Street, Taipei 11220, TaiwanDepartment of NursingOriental Institute of Technology, New Taipei City, Taiwan
| | - Jiuan-Jiuan Hwang
- Institute of PhysiologySchool of Medicine, National Yang-Ming University, 155 Linong Street, Section 2, Taipei 11221, TaiwanDepartment of NursingHsin-Sheng College of Medical Care and Management, Taoyuan, TaiwanDepartment of Animal Science and TechnologyCollege of Bio-Resources and Agriculture, National Taiwan University, Taipei, TaiwanDepartment of BiochemistrySchool of Medicine, Fujita Health University, Aichi, JapanDepartment of Obstetrics and GynecologyTaipei Veterans General Hospital, Taipei, TaiwanDepartment of Obstetrics and GynecologyNational Yang-Ming University, Taipei, TaiwanInstitute of Molecular and Cellular BiologyCollege of Life Science, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 10617, TaiwanDepartment of MedicineCheng Hsin General Hospital, 45 Jhensing Street, Taipei 11220, TaiwanDepartment of NursingOriental Institute of Technology, New Taipei City, Taiwan
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Hu Z, Hu J, Zhang Z, Shen WJ, Yun CC, Berlot CH, Kraemer FB, Azhar S. Regulation of expression and function of scavenger receptor class B, type I (SR-BI) by Na+/H+ exchanger regulatory factors (NHERFs). J Biol Chem 2013; 288:11416-35. [PMID: 23482569 DOI: 10.1074/jbc.m112.437368] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Scavenger receptor class B, type I (SR-BI) binds HDL and mediates selective delivery of cholesteryl esters (CEs) to the liver, adrenals, and gonads for product formation (bile acids and steroids). Because relatively little is known about SR-BI posttranslational regulation in steroidogenic cells, we examined the roles of Na(+)/H(+) exchanger regulatory factors (NHERFs) in regulating SR-BI expression, SR-BI-mediated selective CE uptake, and steroidogenesis. NHERF1 and NHERF2 mRNA and protein are expressed at varying levels in model steroidogenic cell lines and the adrenal, with only low expression of PDZK1 (NHERF3) and NHERF4. Dibutyryl cyclic AMP decreased NHERF1 and NHERF2 and increased SR-BI mRNA expression in primary rat granulosa cells and MLTC-1 cells, whereas ACTH had no effect on NHERF1 and NHERF2 mRNA levels but decreased their protein levels in rat adrenals. Co-immunoprecipitation, colocalization, bimolecular fluorescence complementation, and mutational analysis indicated that SR-BI associates with NHERF1 and NHERF2. NHERF1 and NHERF2 down-regulated SR-BI protein expression through inhibition of its de novo synthesis. NHERF1 and NHERF2 also inhibited SR-BI-mediated selective CE transport and steroidogenesis, which were markedly attenuated by partial deletions of the PDZ1 or PDZ2 domain of NHERF1, the PDZ2 domain of NHERF2, or the MERM domains of NHERF1/2 or by gene silencing of NHERF1/2. Moreover, an intact COOH-terminal PDZ recognition motif (EAKL) in SR-BI is needed. Transient transfection of hepatic cell lines with NHERF1 or NHERF2 caused a significant reduction in endogenous protein levels of SR-BI. Collectively, these data establish NHERF1 and NHERF2 as SR-BI protein binding partners that play a negative role in the regulation of SR-BI expression, selective CE transport, and steroidogenesis.
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Affiliation(s)
- Zhigang Hu
- Geriatric Research, Education and Clinical Center, Veterans Affairs Palo Alto Health Care System, Palo Alto, California 94304, USA
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Twiddy AL, Cox ME, Wasan KM. Knockdown of scavenger receptor class B type I reduces prostate specific antigen secretion and viability of prostate cancer cells. Prostate 2012; 72:955-65. [PMID: 22025344 DOI: 10.1002/pros.21499] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/29/2011] [Accepted: 09/19/2011] [Indexed: 01/22/2023]
Abstract
BACKGROUND Scavenger Receptor Class B Type I (SR-BI) facilitates influx of cholesterol to the cell from lipoproteins in the circulation. This influx of cholesterol may be important for many cellular functions, including synthesis of androgens. Castration-resistant prostate cancer tumors are able to synthesize androgens de novo in order to supplement the loss of exogenous sources often induced by androgen deprivation therapy. Silencing of SR-BI may impact the ability of prostate cancer cells, particularly those of castration-resistant state, to maintain the intracellular supply of androgens by removing a supply of cholesterol. METHODS SR-BI expression was knocked down using small interfering RNA in LNCaP and C4-2 cells. The effect of down-regulation of SR-BI on PSA production, cell toxicity, and cell viability was measured in both cell types. In addition, compensatory cholesterol synthesis activity was measured using the radiolabeled precursor, (14) C-acetate. RESULTS SR-BI protein expression is higher basally in C4-2 cells than LNCaP cells. Silencing of SR-BI expression to greater than 85% reduced PSA production in LNCaP and C4-2 SRBI-KD cells by 55% and 58% compared to negative control cells, respectively. SR-BI-KD C4-2 cells demonstrated significantly reduced cell viability (>25%) compared the NC cells. CONCLUSIONS The down-regulation of SR-BI significantly impacts PSA production of prostate cancer cells, as well as the viability of C4-2 cells in the presence and absence of HDL. This may indicate a deficiency in cholesterol availability to the androgen synthesis pathway or may implicate a role for SR-BI in prostate cancer signal transduction pathways.
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Affiliation(s)
- Alexis L Twiddy
- Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, British Columbia, Canada
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Twiddy AL, Leon CG, Wasan KM. Cholesterol as a Potential Target for Castration-Resistant Prostate Cancer. Pharm Res 2010; 28:423-37. [DOI: 10.1007/s11095-010-0210-y] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2010] [Accepted: 06/28/2010] [Indexed: 01/15/2023]
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Jiménez LM, Binelli M, Bertolin K, Pelletier RM, Murphy BD. Scavenger receptor-B1 and luteal function in mice. J Lipid Res 2010; 51:2362-71. [PMID: 20404351 DOI: 10.1194/jlr.m006973] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
During luteinization, circulating high-density lipoproteins supply cholesterol to ovarian cells via the scavenger receptor-B1 (SCARB1). In the mouse, SCARB1 is expressed in cytoplasm and periphery of theca, granulosa, and cumulus cells of developing follicles and increases dramatically during formation of corpora lutea. Blockade of ovulation in mice with meloxicam, a prostaglandin synthase-2 inhibitor, resulted in follicles with oocytes entrapped in unexpanded cumulus complexes and with granulosa cells with luteinized morphology and expressing SCARB1 characteristic of luteinization. Mice bearing null mutation of the Scarb1 gene (SCARB1(-/-)) had ovaries with small corpora lutea, large follicles with hypertrophied theca cells, and follicular cysts with blood-filled cavities. Plasma progesterone concentrations were decreased 50% in mice with Scarb1 gene disruption. When SCARB1(-/-) mice were treated with a combination of mevinolin [an inhibitor of 3-hydroxy-3-methylglutaryl CoA reductase (HMGR)] and chloroquine (an inhibitor of lysosomal processing of low-density lipoproteins), serum progesterone was further reduced. HMGR protein expression increased in SCARB1(-/-) mice, independent of treatment. It was concluded that theca, granulosa, and cumulus cells express SCARB1 during follicle development, but maximum expression depends on luteinization. Knockout of SCARB1(-/-) leads to ovarian pathology and suboptimal luteal steroidogenesis. Therefore, SCARB1 expression is essential for maintaining normal ovarian cholesterol homeostasis and luteal steroid synthesis.
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Fujimoto VY, Kane JP, Ishida BY, Bloom MS, Browne RW. High-density lipoprotein metabolism and the human embryo. Hum Reprod Update 2010; 16:20-38. [PMID: 19700490 DOI: 10.1093/humupd/dmp029] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND High-density lipoprotein (HDL) appears to be the dominant lipoprotein particle in human follicular fluid (FF). The reported anti-atherogenic properties of HDL have been attributed in part to reverse cholesterol transport. The discoveries of the scavenger receptor class B type I (SR-BI) and the ATP-binding cassette A1 lipid (ABCA1) transporter have generated studies aimed at unraveling the pathways of HDL biogenesis, remodeling and catabolism. The production of SR-BI and ABCA1 knockout mice as well as other lipoprotein metabolism-associated mutants has resulted in reduced or absent fertility, leading us to postulate the existence of a human hepatic-ovarian HDL-associated axis of fertility. Here, we review an evolving literature on the role of HDL metabolism on mammalian fertility and oocyte development. METHODS An extensive online search was conducted of published articles relevant to the section topics discussed. All relevant English language articles contained in Pubmed/Medline, with no specific time frame for publication, were considered for this narrative review. Cardiovascular literature was highly cited due to the wealth of relevant knowledge on HDL metabolism, and the dearth thereof in the reproductive field. RESULTS Various vertebrate models demonstrate a role for HDL in embryo development and fertility. In our clinical studies, FF levels of HDL cholesterol and apolipoprotein AI levels were negatively associated with embryo fragmentation, but not with embryo cell cleavage rate. However, the HDL component, paraoxonase 1 arylesterase activity, was positively associated with embryo cell cleavage rate. CONCLUSIONS HDL contributes to intra-follicular cholesterol homeostasis which appears to be important for successful oocyte and embryo development.
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Affiliation(s)
- Victor Y Fujimoto
- Department of Obstetrics, Gynecology and Reproductive Sciences, University of California at San Francisco, San Francisco, CA 94115-0916, USA.
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Abstract
Dysregulation of cholesterol balance contributes significantly to atherosclerotic cardiovascular disease (ASCVD), the leading cause of death in the United States. The intestine has the unique capability to act as a gatekeeper for entry of cholesterol into the body, and inhibition of intestinal cholesterol absorption is now widely regarded as an attractive non-statin therapeutic strategy for ASCVD prevention. In this chapter we discuss the current state of knowledge regarding sterol transport across the intestinal brush border membrane. The purpose of this work is to summarize substantial progress made in the last decade in regards to protein-mediated sterol trafficking, and to discuss this in the context of human disease.
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Affiliation(s)
| | - Liqing Yu
- Address correspondence to: Liqing Yu, M.D., Ph.D., Department of Pathology Section on Lipid Sciences, Wake Forest University School of Medicine, Medical Center Blvd, Winston-Salem, NC 27157-1040, Tel: 336-716-0920, Fax: 336-716-6279,
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11
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Connelly MA. SR-BI-mediated HDL cholesteryl ester delivery in the adrenal gland. Mol Cell Endocrinol 2009; 300:83-8. [PMID: 18840501 DOI: 10.1016/j.mce.2008.09.011] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/19/2008] [Accepted: 09/04/2008] [Indexed: 10/21/2022]
Abstract
In adrenocortical cells, scavenger receptor class B, type I (SR-BI) is localized in specialized plasma membrane compartments, called microvillar channels, that retain high density lipoprotein particles (HDL) and are sites for the selective uptake of cholesteryl esters (CE). Formation of microvillar channels is regulated by adrenocorticotropic hormone (ACTH) and requires SR-BI expression. Subsequent to SR-BI-mediated delivery to the plasma membrane, HDL-CE is metabolized to free cholesterol by hormone sensitive lipase and transported to the mitochondria for steroid synthesis via START domain proteins. The relevance of SR-BI to adrenal steroidogenesis is evident by the impairment of glucocorticoid-mediated stress response in the absence of SR-BI-mediated HDL-CE uptake in mice. On the molecular level, SR-BI mediates HDL-CE selective uptake by forming a hydrophobic channel. In addition, SR-BI facilitates bi-directional flux of cholesterol by modifying the phospholipid content of the plasma membrane. SR-BI most likely accomplishes these functions by forming homo-oligomers in the plasma membrane. Examination of SR-BI oligomerization using fluorescence resonance energy transfer spectroscopy revealed that SR-BI multimerizes via its C-terminal region. Overall, SR-BI is the cell surface receptor responsible for selective uptake of lipoprotein cholesterol and its ultimate delivery to sites of hormone synthesis in steroidogenic tissues.
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Affiliation(s)
- Margery A Connelly
- Metabolic Diseases, Johnson & Johnson Pharmaceutical Research and Development, LLC, Welsh & McKean Roads, Spring House, PA 19477-0776, United States.
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12
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Cherian-Shaw M, Puttabyatappa M, Greason E, Rodriguez A, VandeVoort CA, Chaffin CL. Expression of scavenger receptor-BI and low-density lipoprotein receptor and differential use of lipoproteins to support early steroidogenesis in luteinizing macaque granulosa cells. Endocrinology 2009; 150:957-65. [PMID: 18832102 PMCID: PMC2646541 DOI: 10.1210/en.2008-0619] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
An ovulatory hCG stimulus to rhesus macaques undergoing controlled ovarian stimulation protocols results in a rapid and sustained increase in progesterone synthesis. The use of lipoproteins as a substrate for progesterone synthesis remains unclear, and the expression of lipoprotein receptors [very-low-density lipoprotein receptor (VLDLR), low-density lipoprotein receptor (LDLR), and scavenger receptor-BI (SR-BI)] soon after human chorionic gonadotropin (hCG) (<12 h) has not been characterized. This study investigated lipoprotein receptor expression and lipoprotein (VLDL, LDL, and HDL) support of steroidogenesis during luteinization of macaque granulosa cells. Granulosa cells were aspirated from rhesus monkeys undergoing controlled ovarian stimulation before or up to 24 h after an ovulatory hCG stimulus. The expression of VLDLR decreased within 3 h of hCG, whereas LDLR and SR-BI increased at 3 and 12 h, respectively. Granulosa cells isolated before hCG were cultured for 24 h in the presence of FSH or FSH plus hCG with or without VLDL, LDL, or HDL. Progesterone levels increased in the presence of hCG regardless of lipoprotein addition, although LDL, but not HDL, further augmented hCG-induced progesterone. Other cells were cultured with FSH or FSH plus hCG without an exogenous source of lipoprotein for 24 h, followed by an additional 24 h culture with or without lipoproteins. Cells treated with hCG in the absence of any lipoprotein were unable to maintain progesterone levels through 48 h, whereas LDL (but not HDL) sustained progesterone synthesis. These data suggest that an ovulatory stimulus rapidly mobilizes stored cholesterol esters for use as a progesterone substrate and that as these are depleted, new cholesterol esters are obtained through an LDLR- and/or SR-BI-mediated mechanism.
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Affiliation(s)
- Mary Cherian-Shaw
- Department of Obstetrics, Gynecology, & Reproductive Sciences, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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13
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Shimada M, Hernandez-Gonzalez I, Gonzalez-Robanya I, Richards JS. Induced Expression of Pattern Recognition Receptors in Cumulus Oocyte Complexes: Novel Evidence for Innate Immune-Like Functions during Ovulation. Mol Endocrinol 2006; 20:3228-39. [PMID: 16931571 DOI: 10.1210/me.2006-0194] [Citation(s) in RCA: 110] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Ovulation is the complex, inflammatory-like process by which the cumulus oocyte complex (COC) is released from a mature, preovulatory follicle through a rupture site at the ovarian surface and requires expression of genes that generate and stabilize the expanded extracellular COC matrix. Gene profiling analyses of COCs at selected time intervals during ovulation revealed that many genes associated with immune related surveillance functions were also induced in cumulus cells. Specifically, cell surface signaling molecules known as pattern recognition receptors that act as sensors of the external environment important for the innate immune system to detect self from nonself or altered self are induced and/or expressed in cumulus cells as well as granulosa cells. These include the complement factor q1, CD14, and the Toll-like receptors (TLRs) 4, 8, and 9 as well as mediators of TLR activation, myeloid differentiation primary response gene 88 and interferon regulatory factor 3. COCs exposed to bacterial lipopolysaccharide exhibit enhanced phosphorylation of p38MAPK, ERK1/2 and nuclear factor-kappaB and increased expression of Il6 and Tnfa target genes, documenting that the TLR pathway is functional. Cumulus cells and granulosa cells also express the scavenger receptors CD36 and scavenger receptor type B1 and exhibited phagocytic uptake of fluorescently tagged bacterial particles. Collectively, these results provide novel evidence that cumulus cells as well as granulosa cells express innate immune related genes that may play critical roles in surveillance and cell survival during the ovulation process.
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Affiliation(s)
- Masayuki Shimada
- Department of Molecular Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
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14
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Azhar S, Medicherla S, Shen WJ, Fujioka Y, Fong LG, Reaven E, Cooper AD. LDL and cAMP cooperate to regulate the functional expression of the LRP in rat ovarian granulosa cells. J Lipid Res 2006; 47:2538-50. [PMID: 16929031 PMCID: PMC1855269 DOI: 10.1194/jlr.m600349-jlr200] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Rat ovarian granulosa rely heavily on lipoprotein-derived cholesterol for steroidogenesis, which is principally supplied by the LDL receptor- and scavenger receptor class B type I (SR-BI)-mediated pathways. In this study, we characterized the hormonal and cholesterol regulation of another member of the LDL receptor superfamily, low density lipoprotein receptor-related protein (LRP), and its role in granulosa cell steroidogenesis. Coincubation of cultured granulosa cells with LDL and N6,O2'-dibutyryl adenosine 3',5'-cyclic monophosphate (Bt2cAMP) greatly increased the mRNA/protein levels of LRP. Bt2cAMP and Bt2cAMP plus human hLDL also enhanced SR-BI mRNA levels. However, there was no change in the expression of receptor-associated protein, a chaperone for LRP, or another lipoprotein receptor, LRP8/apoER2, in response to Bt2cAMP plus hLDL, whereas the mRNA expression of LDL receptor was reduced significantly. The induced LRP was fully functional, mediating increased uptake of its ligand, alpha2-macroglobulin. The level of binding of another LRP ligand, chylomicron remnants, did not increase, although the extent of remnant degradation that could be attributed to the LRP doubled in cells with increased levels of LRP. The addition of lipoprotein-type LRP ligands such as chylomicron remnants and VLDL to the incubation medium significantly increased the progestin production under both basal and stimulated conditions. In summary, our studies demonstrate a role for LRP in lipoprotein-supported ovarian granulosa cell steroidogenesis.
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Affiliation(s)
- Salman Azhar
- Geriatric Research, Education, and Clinical Center, Department of Veterans Affairs Palo Alto Health Care System, Palo Alto, CA, USA.
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15
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Abstract
Scavenger receptor class B, type I (SR-BI) is the receptor for high density lipoprotein (HDL) that mediates cellular uptake of HDL cholesteryl ester (CE) and is a major route for cholesterol delivery to steroidogenic pathways. SR-BI is localized in specialized microvillar channel plasma membrane compartments that retain HDL and are sites for HDL CE selective uptake. In fact, adrenal gland microvillar channel formation is regulated by adrenocorticotropin hormone and requires SR-BI expression. SR-BI-mediated uptake of HDL CE is a two-step process requiring high affinity HDL binding followed by transfer of CE to the membrane. SR-BI delivers HDL CE to sites in the membrane where it is readily metabolized to free cholesterol by cell type-specific neutral CE hydrolases. The most likely candidate for the hydrolysis of HDL CE delivered via SR-BI in the adrenal gland is hormone sensitive lipase. New data in adrenocortical cells as well as the study of a mutant SR-BI receptor lend insight into the mechanism of cholesterol transfer from plasma HDL to the steroidogenic pathway in endocrine cells.
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Affiliation(s)
- Margery A Connelly
- Department of Pharmacological Sciences, University Medical Center, State University of New York at Stony Brook, Stony Brook, NY 11794-8651, USA.
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16
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Rhainds D, Brissette L. The role of scavenger receptor class B type I (SR-BI) in lipid trafficking. defining the rules for lipid traders. Int J Biochem Cell Biol 2004; 36:39-77. [PMID: 14592533 DOI: 10.1016/s1357-2725(03)00173-0] [Citation(s) in RCA: 158] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The scavenger receptor class B type I (SR-BI) is a 509-amino acid, 82 kDa glycoprotein, with two cytoplasmic C- and N-terminal domains separated by a large extracellular domain. The aim of this review is to define the role of SR-BI as a lipoprotein receptor responsible for selective uptake of cholesteryl esters (CE) from high density lipoprotein (HDL) and low density lipoprotein (LDL) and free cholesterol (FC) efflux to lipoprotein acceptors. These activities depend on lipoprotein binding to its extracellular domain and subsequent lipid exchange at the plasma membrane. CE selective uptake supplies cholesterol to liver and steroidogenic tissues, for biliary cholesterol secretion and steroid hormone synthesis. Genetically modified mice have confirmed SR-BI's major role in tissue cholesterol uptake and in reverse cholesterol transport, i.e. cholesterol turnover. Accordingly, cellular cholesterol level, estrogens and trophic hormones regulate SR-BI expression by both transcriptional and post-transcriptional mechanisms. Importantly, mouse SR-BI overexpression has both corrective and preventive effects on atherosclerosis. Human SR-BI has very similar tissue distribution, binding properties and lipid transfer activities compared to rodent SR-BI. However, human plasma has most of its cholesterol in LDL. Thus, there is considerable interest to develop anti-atherogenic strategies involving human SR-BI-mediated increases in reverse cholesterol transport through HDL and/or LDL.
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MESH Headings
- Amino Acid Sequence
- Animals
- Biological Transport, Active
- CD36 Antigens
- Cell Membrane/chemistry
- Cell Membrane/genetics
- Cell Membrane/metabolism
- Cell Membrane/physiology
- Humans
- Lipid Metabolism
- Lipoproteins/metabolism
- Models, Biological
- Promoter Regions, Genetic
- Protein Structure, Tertiary
- Receptors, Immunologic/chemistry
- Receptors, Immunologic/genetics
- Receptors, Immunologic/metabolism
- Receptors, Immunologic/physiology
- Receptors, Scavenger
- Scavenger Receptors, Class B
- Tissue Distribution
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Affiliation(s)
- David Rhainds
- Département des Sciences Biologiques, Université du Québec à Montréal, C.P. 8888, Succ. Centre-Ville, Montreal, Que., Canada H3C 3P8.
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17
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Abstract
Scavenger receptor class B, type I (SR-BI) is a receptor for high-density lipoprotein (HDL) that mediates cellular uptake of HDL cholesteryl ester (HDL CE) and is the major route for cholesterol delivery to the steroidogenic pathway. SR-BI is localized in specialized microvillar channels in the plasma membrane that retain HDL and are sites of selective uptake of HDL CE. The formation of microvillar channels in the adrenal gland requires SR-BI and is regulated by adrenocorticotropin hormone. SR-BI-mediated uptake of HDL CE is a two-step process that requires high-affinity binding of HDL followed by transfer of CE to the membrane. CE uptake is followed by hydrolysis to free cholesterol by a neutral CE hydrolase. In this review, we describe new information on the mechanism of transfer of cholesterol from plasma HDL to the steroidogenic pathway in endocrine cells.
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Affiliation(s)
- Margery A Connelly
- Department of Pharmacological Sciences, University Medical Center, State University of New York at Stony Brook, Stony Brook, New York 11794-8651, USA
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18
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Rigotti A, Miettinen HE, Krieger M. The role of the high-density lipoprotein receptor SR-BI in the lipid metabolism of endocrine and other tissues. Endocr Rev 2003; 24:357-87. [PMID: 12788804 DOI: 10.1210/er.2001-0037] [Citation(s) in RCA: 313] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Because cholesterol is a precursor for the synthesis of steroid hormones, steroidogenic tissues have evolved multiple pathways to ensure adequate supplies of cholesterol. These include synthesis, storage as cholesteryl esters, and import from lipoproteins. In addition to endocytosis via members of the low-density lipoprotein receptor superfamily, steroidogenic cells acquire cholesterol from lipoproteins by selective lipid uptake. This pathway, which does not involve lysosomal degradation of the lipoprotein, is mediated by the scavenger receptor class B type I (SR-BI). SR-BI is highly expressed in steroidogenic cells, where its expression is regulated by various trophic hormones, as well as in the liver. Studies of genetically manipulated strains of mice have established that SR-BI plays a key role in regulating lipoprotein metabolism and cholesterol transport to steroidogenic tissues and to the liver for biliary secretion. In addition, analysis of SR-BI-deficient mice has shown that SR-BI expression is important for alpha-tocopherol and nitric oxide metabolism, as well as normal red blood cell maturation and female fertility. These mouse models have also revealed that SR-BI can protect against atherosclerosis. If SR-BI plays similar physiological and pathophysiological roles in humans, it may be an attractive target for therapeutic intervention in cardiovascular and reproductive diseases.
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Affiliation(s)
- Attilio Rigotti
- Departamento de Gastroenterología, Facultad de Medicina, Pontificia Universidad Católica, Santiago, Chile
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19
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Wu Q, Sucheta S, Azhar S, Menon KMJ. Lipoprotein enhancement of ovarian theca-interstitial cell steroidogenesis: relative contribution of scavenger receptor class B (type I) and adenosine 5'-triphosphate- binding cassette (type A1) transporter in high-density lipoprotein-cholesterol transport and androgen synthesis. Endocrinology 2003; 144:2437-45. [PMID: 12746305 DOI: 10.1210/en.2002-221110] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The theca-interstitial cells take up plasma high-density lipoprotein (HDL)- and low-density-lipoprotein-derived cholesterol to convert into steroid hormones. The uptake of HDL-derived cholesterol is mediated by the scavenger receptor, class B, type I (SR-BI). In nonsteroidogenic cells, HDL-stimulated efflux of cholesterol has been shown to be mediated by the ATP-binding cassette A1 (ABCA1) transporter. Its expression has not been documented in steroidogenic cells. The goal of the present study was to determine: 1) the role of SR-BI in theca-interstitial cell androgen production; 2) whether theca-interstitial cells express ABCA1 transporter mRNA; and 3) the relative roles of SR-BI and ABCA1 transporter in androgen production. The ABCA1 transporter mRNA expression in rat theca-interstitial cells was shown using RT-PCR and Northern blot analyses. The role of SR-BI and ABCA1 in androstenedione production was also examined by treating cells with anti-SR-BI and 2-hydroxypropyl-beta-cyclodextrin in the presence and absence of human chorionic gonadotropin and/or human HDL(3). The treatment of theca-interstitial cells with anti-SR-BI antibody blocked more than 90% of HDL plus human chorionic gonadotropin-stimulated androstenedione production, and selective HDL-CE uptake. On the other hand, the use of inhibitors of ABCA1 transporter function had no discernible effect on HDL-supported androgen production. These data demonstrate that, although theca-interstitial cells express both SR-BI and ABCA1 transporter mRNA, the SR-BI pathway supplies the majority of the cholesterol required for androgen production. Furthermore, the present study presents evidence for a crucial role for SR-BI in HDL-mediated androgen production.
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Affiliation(s)
- Qian Wu
- Department of Obstetrics/Gynecology, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA
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20
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Briand O, Lestavel S, Pilon A, Torpier G, Fruchart JC, Clavey V. SR-BI does not require raft/caveola localisation for cholesteryl ester selective uptake in the human adrenal cell line NCI-H295R. BIOCHIMICA ET BIOPHYSICA ACTA 2003; 1631:42-50. [PMID: 12573448 DOI: 10.1016/s1388-1981(02)00354-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Class B type I scavenger receptor (SR-BI) mediates the selective uptake of high-density lipoprotein (HDL)-derived cholesteryl esters (HDL-CE) in steroidogenic cells and hepatocytes. SR-BI is enriched in the caveolae of some cell types, genetically modified or not, and these domains have already been shown to constitute primary acceptors for HDL-CE. Nevertheless, the fate of caveola-free cell types has not yet been discussed.NCI-H295R, a human adrenal cell line, highly active in HDL-CE uptake via SR-BI, does not display any morphologically defined caveolae and expresses caveolin at a very low level. Using two different fractionation protocols, we have shown, in this cell type, that SR-BI is homogeneously distributed along the plasma membrane and consists principally of a non-raft membrane-associated pool. Raft destabilisation and caveolin-1 displacement from plasma membrane did not modify the SR-BI-mediated HDL-CE selective uptake. Moreover, the induction of SR-BI expression that is associated with increased CE selective uptake was not associated with any modification in caveolin-1 expression or any raft-targeting mechanism of SR-BI in NCI-H295R. In conclusion, we provide evidence that SR-BI does not require raft/caveola localisation to be implicated in CE selective uptake either in basal or in induced conditions.
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Affiliation(s)
- Olivier Briand
- Inserm UR545, Institut Pasteur de Lille and Faculté des Sciences Pharmaceutiques et Biologiques, Université de Lille 2, 1 rue du Professeur Calmette BP245, 59019, Lille, France
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21
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Azhar S, Reaven E. Scavenger receptor class BI and selective cholesteryl ester uptake: partners in the regulation of steroidogenesis. Mol Cell Endocrinol 2002; 195:1-26. [PMID: 12354669 DOI: 10.1016/s0303-7207(02)00222-8] [Citation(s) in RCA: 142] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The steroidogenic tissues have a special requirement for cholesterol, which is used as a substrate for steroid hormone biosynthesis. In many species this cholesterol is obtained from plasma lipoproteins by a unique pathway in which circulating lipoproteins bind to the surface of the steroidogenic cells and contribute their cholesteryl esters to the cells by a 'selective' process in which the whole lipoprotein particle does not enter the cell. This review describes the lipoprotein selective cholesteryl ester uptake process and its specific partnership with the HDL receptor, scavenger receptor class BI (SR-BI). It describes the characteristics of the selective pathway, and the molecular properties, localization, regulation, anchoring sites and potential mechanisms of action of SR-BI in facilitating cholesteryl ester uptake by steroidogenic cells.
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Affiliation(s)
- Salman Azhar
- Geriatric Research, Education and Clinical Center, GRECC-182B, VA Palo Alto Health Care System, 3801 Miranda Avenue, Palo Alto, CA 94304, USA.
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22
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23
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Johnson MSC, Svensson PA, Borén J, Billig H, Carlsson LMS, Carlsson B. Expression of scavenger receptor class B type I in gallbladder columnar epithelium. J Gastroenterol Hepatol 2002; 17:713-20. [PMID: 12100619 DOI: 10.1046/j.1440-1746.2002.02776.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/09/2022]
Abstract
BACKGROUND The lipid content of bile may be modified by the gallbladder epithelium. Recent studies indicate that cholesterol can be absorbed from bile and that this can be enhanced by apolipoprotein (apo) A-I. SR-BI is a multifunctional receptor capable of binding a wide array of native or modified lipoproteins, phospholipid or bile acid micelles. As apo A-I is a ligand for scavenger receptor class B type I (SR-BI) we have characterized the expression of this receptor in murine gallbladder. METHODS Reverse transcription-polymerase chain reaction (RT-PCR), immunoblotting and immunohistochemistry were used to study SR-BI expression in murine gallbladders. SR-BI expression was also used to examine gallbladders from high-fat-fed wild-type and apo B-100 transgenic mice. RESULTS SR-BI and SR-BII mRNA are expressed in gallbladder. SR-BI immunoreactivity was localized to the columnar epithelium of the gallbladder. Immunoreactive SR-BI in gallbladder had an estimated molecular weight of 57 kDa, in contrast to the expected 82 kDa. Deglycosylation experiments indicated that the size difference between the two forms of the receptor is due to post-translational modification. Fat feeding of apo B transgenic mice resulted in gallstone formation but had no effect on the abundance of SR-BI. CONCLUSIONS Gallbladder epithelial cells express SR-BI. This opens the possibility that SR-BI may influence the modification of bile in the gallbladder.
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Affiliation(s)
- Magnus S C Johnson
- Department of Internal Medicine Vita Stråket 12, Research Center for Endocrinology & Metabolism (RCEM), Pav. 8:3 Sahlgrenska University Hospital, S-413 45 Göteborg, Sweden.
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24
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Medicherla R, Leers-Sucheta S, Luo Y, Azhar S. Age-dependent modulation of NF-kappaB expression in rat adrenal gland. Mech Ageing Dev 2002; 123:1211-27. [PMID: 12020944 DOI: 10.1016/s0047-6374(02)00015-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The current studies were initiated to examine the expression and regulation of an oxidative stress-responsive transcription factor, NF-kappa B, in rat adrenals during aging. NF- kappa B DNA-binding activity and expression of constituent proteins (Rel family of proteins and I kappa Bs) was measured in adrenal nuclear and cytoplasmic extracts from young mature (5 month) and old (24 month) Sprague-Dawley rats before and after treatment with LPS; the latter was used to further invoke oxidative stress. Administration of LPS to either young or old rats induced a dramatic activation of NF- kappa B DNA binding activity as assayed by EMSA. NF- kappa B hetero-dimers, RelA/NF- kappa B1 (p65/p50) accounted for the majority of proteins that bound to consensus NF- kappa B sequences in LPS-treated young and old animals. The intensity of DNA binding complexes was significantly reduced in old animals. The age-related decline in the activation of NF- kappa B could not be attributed to an alteration in the composition of constituent subunits or degradation of NF- kappa B inhibitory proteins (I kappa B alpha and I kappa B beta) but rather was due to selective down-regulation of RelA/p65 and NF- kappa B2/p52 proteins. No age-related or LPS-induced changes in the constitutively active transcription factors SP-1 and OCT-1 were detected. These data suggest that aberrancies in the activation of NF- kappa B DNA-binding activity may contribute to the excessive oxidative damage observed in adrenal tissue with aging and may adversely affect cellular processes crucial for intracellular cholesterol transport and steroid hormone production.
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Affiliation(s)
- Rajeshwari Medicherla
- Geriatric Research, Education and Clinical Center (GRECC, 182B), VA Palo Alto Health Care System, 3801 Miranda Ave, Palo Alto, CA 94304, USA
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25
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Tsuruoka H, Khovidhunkit W, Brown BE, Fluhr JW, Elias PM, Feingold KR. Scavenger receptor class B type I is expressed in cultured keratinocytes and epidermis. Regulation in response to changes in cholesterol homeostasis and barrier requirements. J Biol Chem 2002; 277:2916-22. [PMID: 11707442 DOI: 10.1074/jbc.m106445200] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cholesterol is a key lipid in the stratum corneum, where it is critical for permeability barrier homeostasis. The epidermis is an active site of cholesterol synthesis, but inhibition of epidermal cholesterol synthesis with topically applied statins only modestly affects epidermal permeability barrier function, suggesting a possible compensatory role for extraepidermal cholesterol. Scavenger receptor class B type I (SR-BI) is a recently described cell surface receptor for high density lipoproteins (HDL) that mediates the selective uptake of cholesterol esters from circulating HDL. In the present study, we demonstrate that SR-BI is present in cultured human keratinocytes and that calcium-induced differentiation markedly decreases SR-BI levels. Additionally, the cell association of [(3)H]cholesterol-labeled HDL decreased in differentiated versus undifferentiated keratinocytes. Furthermore, the inhibition of cholesterol synthesis with simvastatin resulted in a 3-4-fold increase in both SR-BI mRNA and protein levels, whereas conversely, addition of 25-hydroxycholesterol suppressed SR-BI levels by approximately 50%. SR-BI mRNA is also expressed in murine epidermis, increasing by 50% in parallel with cholesterol requirements following acute barrier disruption. Because the increase is completely blocked by occlusion with a vapor-impermeable membrane, changes in epidermal SR-BI expression are regulated specifically by barrier requirements. Lastly, using immunofluorescence we demonstrated that SR-BI is present in human epidermis predominantly in the basal layer and increases following barrier disruption. In summary, the present study demonstrates first that SR-BI is expressed in keratinocytes and regulated by cellular cholesterol requirements, suggesting that it plays a role in keratinocyte cholesterol homeostasis. Second, the increase in SR-BI following barrier disruption suggests that SR-BI expression increases to facilitate cholesterol uptake leading to barrier restoration.
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MESH Headings
- Anticholesteremic Agents/pharmacology
- Blotting, Northern
- Blotting, Western
- CD36 Antigens/biosynthesis
- CD36 Antigens/metabolism
- Cell Differentiation
- Cells, Cultured
- Cholesterol/metabolism
- Dose-Response Relationship, Drug
- Down-Regulation
- Electrophoresis, Polyacrylamide Gel
- Epidermis/metabolism
- Humans
- Keratinocytes/metabolism
- Lipoproteins, HDL/metabolism
- Membrane Proteins
- Microscopy, Fluorescence
- Poly A
- RNA/metabolism
- RNA, Messenger/metabolism
- Receptors, Immunologic
- Receptors, Lipoprotein
- Receptors, Scavenger
- Scavenger Receptors, Class B
- Simvastatin/pharmacology
- Sterols/metabolism
- Time Factors
- Up-Regulation
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Affiliation(s)
- Hiroki Tsuruoka
- Dermatology and Medical (Metabolism) Services, Department of Veterans Affairs Medical Center, San Francisco, California 94121, USA
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26
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Cherradi N, Bideau M, Arnaudeau S, Demaurex N, James RW, Azhar S, Capponi AM. Angiotensin II promotes selective uptake of high density lipoprotein cholesterol esters in bovine adrenal glomerulosa and human adrenocortical carcinoma cells through induction of scavenger receptor class B type I. Endocrinology 2001; 142:4540-9. [PMID: 11564720 DOI: 10.1210/endo.142.10.8412] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Angiotensin II is one of the main physiological regulators of aldosterone biosynthesis in the zona glomerulosa of the adrenal cortex. The hormone stimulates intracellular cholesterol mobilization to the mitochondrion for steroid biosynthesis. Here we have examined whether angiotensin II also modulates exogenous lipoprotein cholesterol ester supply to the steroidogenic machinery and whether this control is exerted on the selective transport of high density lipoprotein-derived cholesterol ester to intracellular lipid droplets through the scavenger receptor class B type I. In bovine adrenal glomerulosa and human NCI H295R adrenocortical carcinoma cells, high density lipoprotein stimulated steroid production. Angiotensin II pretreatment for 24 h potentiated this response. Fluorescence microscopy of cellular uptake of reconstituted high density lipoprotein containing a fluorescent cholesterol ester revealed an initial, time-dependent narrow labeling of the cell membrane followed by an intense accumulation of the fluorescent cholesterol ester within lipid droplets. At all time points, labeling was more pronounced in cells that had been treated for 24 h with angiotensin II. Fluorescence incorporation into cells was prevented by a monoclonal antibody directed against apolipoprotein A-I. Upon quantitative fluorometric determination, cholesterol ester uptake in angiotensin II-treated bovine cells was increased to 175 +/- 15% of controls after 2 h and to 260 +/- 10% after 4 h of exposure to fluorescent high density lipoprotein. The amount of scavenger receptor class B type I protein detected in cells treated with angiotensin II for 24 h reached 203 +/- 12% of that measured in control cells (n = 3, P < 0.01). In contrast, low density lipoprotein receptors were only minimally affected by angiotensin II treatment. This increase in scavenger receptor class B type I protein was associated with a 3-fold induction of scavenger receptor class B type I mRNA, which could be prevented by actinomycin D but not by cycloheximide. Similar results were obtained in the human adenocarcinoma cell line H295R. These observations show that angiotensin II regulates the scavenger receptor class B type I-mediated selective transport of lipoprotein cholesterol ester across the cell membrane as a major source of precursor for mineralocorticoid biosynthesis in both human and bovine adrenal cells.
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Affiliation(s)
- N Cherradi
- Division of Endocrinology and Diabetology, Faculty of Medicine, University Hospital, CH-1211 Geneva, Switzerland
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27
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Swarnakar S, Beers J, Strickland DK, Azhar S, Williams DL. The apolipoprotein E-dependent low density lipoprotein cholesteryl ester selective uptake pathway in murine adrenocortical cells involves chondroitin sulfate proteoglycans and an alpha 2-macroglobulin receptor. J Biol Chem 2001; 276:21121-8. [PMID: 11274190 DOI: 10.1074/jbc.m101691200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cells acquire lipoprotein cholesterol by receptor-mediated endocytosis and selective uptake pathways. In the latter case, lipoprotein cholesteryl ester (CE) is transferred to the plasma membrane without endocytosis and degradation of the lipoprotein particle. Previous studies with Y1/E/tet/2/3 murine adrenocortical cells that were engineered to express apolipoprotein (apo) E demonstrated that apoE expression enhances low density lipoprotein (LDL) CE uptake by both selective and endocytic pathways. The present experiments test the hypothesis that apoE-dependent LDL CE selective uptake is mediated by scavenger receptor, class B, type I (SR-BI). Surprisingly, SR-BI expression was not detected in the Y1/E/tet/2/3 clone of Y1 adrenocortical cells, indicating the presence of a distinct apoE-dependent pathway for LDL CE selective uptake. ApoE-dependent LDL CE selective uptake in Y1/E/tet/2/3 cells was inhibited by receptor-associated protein and by activated alpha(2)-macroglobulin (alpha(2)M), suggesting the participation of the LDL receptor-related protein/alpha(2)M receptor. Reagents that inhibited proteoglycan synthesis or removed cell surface chondroitin sulfate proteoglycan completely blocked apoE-dependent LDL CE selective uptake. None of these reagents inhibited SR-BI-mediated LDL CE selective uptake in the Y1-BS1 clone of Y1 cells in which LDL CE selective uptake is mediated by SR-BI. We conclude that LDL CE selective uptake in adrenocortical cells occurs via SR-BI-independent and SR-BI-dependent pathways. The SR-BI-independent pathway is an apoE-dependent process that involves both chondroitin sulfate proteoglycans and an alpha(2)M receptor.
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Affiliation(s)
- S Swarnakar
- Department of Pharmacological Sciences, University Medical Center, State University of New York, Stony Brook, New York 11794, USA
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28
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Reaven E, Leers-Sucheta S, Nomoto A, Azhar S. Expression of scavenger receptor class B type 1 (SR-BI) promotes microvillar channel formation and selective cholesteryl ester transport in a heterologous reconstituted system. Proc Natl Acad Sci U S A 2001; 98:1613-8. [PMID: 11171999 PMCID: PMC29305 DOI: 10.1073/pnas.98.4.1613] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In the "selective" cholesteryl ester (CE) uptake process, surface-associated lipoproteins [high density lipoprotein (HDL) and low density lipoprotein] are trapped in the space formed between closely apposed surface microvilli (microvillar channels) in hormone-stimulated steroidogenic cells. This is the same location where an HDL receptor (SR-BI) is found. In the current study, we sought to understand the relationship between SR-BI and selective CE uptake in a heterologous insect cell system. Sf9 (Spodoptera frugiperda) cells overexpressing recombinant SR-BI were examined for (i) SR-BI protein by Western blot analysis and light or electron immunomicroscopy, and (ii) selective lipoprotein CE uptake by the use of radiolabeled or fluorescent (BODIPY-CE)-labeled HDL. Noninfected or infected control Sf9 cells do not express SR-BI, show microvillar channels, or internalize CEs. An unexpected finding was the induction of a complex channel system in Sf9 cells expressing SR-BI. SR-BI-expressing cells showed many cell surface double-membraned channels, immunogold SR-BI, apolipoprotein (HDL) labeling of the channels, and high levels of selective HDL-CE uptake. Thus, double-membraned channels can be induced by expression of recombinant SR-BI in a heterologous system, and these specialized structures facilitate both the binding of HDL and selective HDL-CE uptake.
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MESH Headings
- Animals
- Biological Transport
- Blotting, Western/methods
- Boron Compounds
- CD36 Antigens/biosynthesis
- CD36 Antigens/genetics
- Cell Line
- Cholesterol Esters/metabolism
- Fluorescent Dyes
- Iodine Radioisotopes
- Isotope Labeling
- Lipoproteins, HDL/metabolism
- Lipoproteins, HDL3
- Membrane Proteins
- Microscopy, Electron/methods
- Microscopy, Fluorescence/methods
- Microvilli/metabolism
- Protein Binding
- Rats
- Receptors, Immunologic
- Receptors, Lipoprotein/biosynthesis
- Receptors, Lipoprotein/genetics
- Receptors, Scavenger
- Scavenger Receptors, Class B
- Spodoptera
- Tritium
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Affiliation(s)
- E Reaven
- Geriatric Research, Education, and Clinical Center, Department of Veterans Affairs, Palo Alto Health Care System, Palo Alto, CA 94304, USA.
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29
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Williams DL, de La Llera-Moya M, Thuahnai ST, Lund-Katz S, Connelly MA, Azhar S, Anantharamaiah GM, Phillips MC. Binding and cross-linking studies show that scavenger receptor BI interacts with multiple sites in apolipoprotein A-I and identify the class A amphipathic alpha-helix as a recognition motif. J Biol Chem 2000; 275:18897-904. [PMID: 10858447 DOI: 10.1074/jbc.m002411200] [Citation(s) in RCA: 91] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Scavenger receptor, class B, type I (SR-BI) mediates the selective uptake of high density lipoprotein (HDL) cholesteryl ester without the uptake and degradation of the particle. In transfected cells SR-BI recognizes HDL, low density lipoprotein (LDL) and modified LDL, protein-free lipid vesicles containing anionic phospholipids, and recombinant lipoproteins containing apolipoprotein (apo) A-I, apoA-II, apoE, or apoCIII. The molecular basis for the recognition of such diverse ligands by SR-BI is unknown. We have used direct binding analysis and chemical cross-linking to examine the interaction of murine (m) SR-BI with apoA-I, the major protein of HDL. The results show that apoA-I in apoA-I/palmitoyl-oleoylphosphatidylcholine discs, HDL(3), or in a lipid-free state binds to mSR-BI with high affinity (K(d) congruent with 5-8 microgram/ml). ApoA-I in each of these forms was efficiently cross-linked to cell surface mSR-BI, indicating that direct protein-protein contacts are the predominant feature that drives the interaction between HDL and mSR-BI. When complexed with dimyristoylphosphatidylcholine, the N-terminal and C-terminal CNBr fragments of apoA-I each bound to SR-BI in a saturable, high affinity manner, and each cross-linked efficiently to mSR-BI. Thus, mSR-BI recognizes multiple sites in apoA-I. A model class A amphipathic alpha-helix, 37pA, also showed high affinity binding and cross-linking to mSR-BI. These studies identify the amphipathic alpha-helix as a recognition motif for SR-BI and lead to the hypothesis that mSR-BI interacts with HDL via the amphipathic alpha-helical repeat units of apoA-I. This hypothesis explains the interaction of SR-BI with a wide variety of apolipoproteins via a specific secondary structure, the class A amphipathic alpha-helix, that is a common structural motif in the apolipoproteins of HDL, as well as LDL.
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Affiliation(s)
- D L Williams
- Department of Pharmacological Sciences, University Medical Center, State University of New York, Stony Brook, New York 11794, USA.
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30
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Abstract
The HDL receptor scavenger receptor class B type I (SR-BI), which mediates selective HDL cholesterol uptake, plays a role in murine HDL metabolism, reverse cholesterol transport and whole-body cholesterol homeostasis. SR-BI is found in the liver, where its expression is regulated by estrogen, dietary cholesterol and fat, and controls murine plasma HDL cholesterol levels and bile cholesterol secretion. SR-BI is also highly expressed in rodent steroidogenic cells, where it facilitates cholesterol uptake for storage or steroid hormone synthesis and where its expression is regulated by trophic hormones. The detailed mechanism(s) underlying SR-BI-mediated selective cholesterol uptake have not yet been elucidated. Further analysis of the molecular and cellular bases of SR-BI regulation and function should provide new insights into the physiology and pathophysiology of cholesterol metabolism.
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Affiliation(s)
- B Trigatti
- Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA
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31
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Abstract
The scavenger receptor class B, type I (SR-BI) is an HDL receptor that mediates selective cholesterol uptake from HDL to cells. In rodents, SR-BI has a critical influence on plasma HDL-cholesterol concentration and structure, the delivery of cholesterol to steroidogenic tissues, female fertility, and biliary cholesterol concentration. SR-BI can also serve as a receptor for non-HDL lipoproteins and appears to play an important role in reverse cholesterol transport. Recent studies involving the manipulation of SR-BI expression in mice, either using adenovirus-mediated or transgenic hepatic overexpression or using homologous recombination for complete functional ablation, indicate that the expression of SR-BI protects against atherosclerosis. If SR-BI has a similar activity in humans, it may become an attractive target for therapeutic intervention.
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Affiliation(s)
- M Krieger
- Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA.
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32
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Azhar S, Luo Y, Medicherla S, Reaven E. Upregulation of selective cholesteryl ester uptake pathway in mice with deletion of low-density lipoprotein receptor function. J Cell Physiol 1999; 180:190-202. [PMID: 10395289 DOI: 10.1002/(sici)1097-4652(199908)180:2<190::aid-jcp7>3.0.co;2-z] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
This study examines the effect of mutation of the low-density lipoprotein receptor (LDLR) on cholesterol metabolism, and especially lipoprotein-derived cholesteryl ester uptake, in murine ovarian granulosa cells. Although the tests were conducted on cells prepared by two different procedures, the results are similar. Deletion of LDLR function did not noticeably affect key enzymes of the steroidogenic pathway or affect progestin production and secretion in granulosa cells. No change was found in expression of LDL-related protein (LRP). These data suggested that cholesterol turnover in cells from the knockout animals is within normal limits and that the cells are not stressed to acquire more cholesterol. Both biochemical and morphological data indicate that unstimulated granulosa cells from LDLR-/- mice are nonetheless programmed to take in double the amount of lipoprotein-derived cholesteryl ester (via the selective cholesteryl ester uptake pathway) and to process (hydrolyze, re-esterify, or utilize) more than twofold the cholesteryl ester processed by cells from wildtype (LDLR+/+) animals. Bt2cAMP stimulation of the murine granulosa cells increases the mass of cholesteryl ester taken up by the selective pathway by an additional 38%. To determine to what extent this increase is related to high-density lipoprotein (HDL) scavenger receptor protein (SR-BI) or caveolin function, Western blots and immunohistochemical studies were performed under a variety of conditions. SR-BI levels are found to be low in unstimulated cells of both LDLR+/+ and LDLR-/- animals, but highly expressed (approximately 20-fold increase over basal levels) in stimulated (Bt2cAMP) cells of both animal models. Thus, the functional relationship between selective cholesteryl ester uptake and SR-BI receptor protein is not as tight as in previously reported studies, suggesting a requirement for other tissue factors. Caveolin expression did not change under any of the conditions tested and appears not to be functionally involved in this process.
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MESH Headings
- Animals
- Biological Transport/drug effects
- Biological Transport/physiology
- Boron Compounds/pharmacokinetics
- Bucladesine/pharmacology
- CD36 Antigens/analysis
- CD36 Antigens/genetics
- Caveolin 1
- Caveolins
- Cells, Cultured
- Cholesterol Esters/pharmacokinetics
- Cholesterol, HDL/pharmacokinetics
- Female
- Fluorescent Antibody Technique
- Gene Expression/physiology
- Granulosa Cells/chemistry
- Granulosa Cells/drug effects
- Granulosa Cells/metabolism
- Humans
- Iodine Radioisotopes
- Lipoproteins/metabolism
- Male
- Membrane Proteins/analysis
- Membrane Proteins/genetics
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Oligonucleotide Probes
- RNA, Messenger/analysis
- Receptors, Immunologic
- Receptors, LDL/genetics
- Receptors, LDL/metabolism
- Receptors, Lipoprotein
- Receptors, Scavenger
- Reverse Transcriptase Polymerase Chain Reaction
- Scavenger Receptors, Class B
- Up-Regulation/genetics
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Affiliation(s)
- S Azhar
- Geriatric Research, Education and Clinical Center, VA Palo Alto Health Care System, California 94304, USA
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33
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Williams DL, Connelly MA, Temel RE, Swarnakar S, Phillips MC, de la Llera-Moya M, Rothblat GH. Scavenger receptor BI and cholesterol trafficking. Curr Opin Lipidol 1999; 10:329-39. [PMID: 10482136 DOI: 10.1097/00041433-199908000-00007] [Citation(s) in RCA: 141] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Scavenger receptor BI (SR-BI) mediates the selective uptake of HDL cholesteryl ester into steroidogenic cells and the liver and is a major determinant of the plasma HDL concentration in the mouse. Recent studies indicate that SR-BI also alters the metabolism of apolipoprotein B-containing particles and influences the development of atherosclerosis in several animal models. These results and the similar pattern of SR-BI expression in humans emphasize that it is important to learn how this receptor influences lipoprotein metabolism and atherosclerosis in people.
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Affiliation(s)
- D L Williams
- Department of Pharmacological Sciences, University Medical Centre, State University of New York at Stony Brook, 11794, USA.
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