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Key Event Title
Increased, Steroidogenic acute regulatory protein (StAR)
|Level of Biological Organization|
|steroid hormone secreting cell|
Key Event Components
|increased luteinizing hormone level||StAR-related lipid transfer protein 3||increased|
|increased luteinizing hormone level||StAR-related lipid transfer protein 4||increased|
|increased luteinizing hormone level||StAR-related lipid transfer protein 5||increased|
|increased luteinizing hormone level||StAR-related lipid transfer protein 6||increased|
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP||Point of Contact||Author Status||OECD Status|
|Hypothalamic estrogen receptors inhibition leading to ovarian cancer||KeyEvent||Kalyan Gayen (send email)||Under development: Not open for comment. Do not cite||Under Development|
|Adult, reproductively mature||High|
Key Event Description
Biological state: Steroidogenic acute regulatory protein (StAR) plays important role in luteal steroidogenesis(Christenson and Devoto, 2003). Steroidogenic acute regulatory protein (StAR) controls the transport of cholesterol from the outer to inner mitochondrial membrane(Stocco, 2000). There are several pathways involved for the transport of cholesterol from different subcellular pools into the inner mitochondria(Martin et al., 2016).
Biological compartments: Cholesterol is one type of lipid which is crystalline solid with yellow colour. It is biosynthesized by animal cells and is an essential structural component of animal cell membranes (Hanukoglu, 1992). It is the precursor molecule for the synthesis all steroid hormones(Payne and Hales, 2004). Cytochrome P450 enzymes are present in most tissues of the body, and play important roles in hormone synthesis in mitochondria using cholesterol as precursor(Poderoso et al., 2013).
General role in biology: It is been reported that high in cholesterol levels in mitochondrial resulted several diseases like cancer, neurodegenerative diseases, steatohepatitis ischemia, and influence disease (Martin et al., 2016). The alteration in mitochondrial cholesterol import may change the cholesterol concentrations that may lead to proper mitochondrial function along with biophysical properties of mitochondrial membranes. In absence of StAR protein, cholesterol transport into the mitochondria did not occurs leading to no conversion of progesterone from cholesterol precursors doesn’t occur(Kiriakidou et al., 1996; Pescador et al., 1996). All Steroidogenic acute regulatory protein (StAR) promoters contain steroidogenic factor 1 binding sites which is responsible for sex hormones regulation(Manna et al., 2002).
One of the important function of the steroid hormones is maintaining reproductive capacity. For this purpose, steroidogenic cells must move large amounts of cholesterol from the outer mitochondrial membrane to the inner membrane. In the granulosa cells, this cholesterol is ultimately converted to progesterone. The initial transport of cholesterol across the mitochondrial membrane requires Steroidogenic Acute Regulatory (StAR) protein. Expression of StAR protein in preovulatory cells of the developing follicle is low. The dramatic upregulation of StAR protein expression within the dominant follicle is found after the luteinizing hormone (LH) surge. This upregulation allows the corpus luteum to produce substantial amounts of progesterone to maintain the reproductive capacity in human/animal (Men et al., 2017; Stocco, 2000).
How It Is Measured or Detected
StAR protein is measure by quantitative real time PCR (qRT-PCR):
For qRT-PCR analyses, cDNA is synthesized using reagent kit in a 20-μl reaction containing 0.5 μg of total RNA collected from human ovarian granulosa tumor cell line ( KGN cells ), mouse Leydig cells. qPCR is performed in a 25-μl reaction containing 0.5 to 1.5 μl of cDNA using fluorescein in real-time PCR detection systems. PCR was performed by initial denaturation at 95°C for 5 minutes, followed by 40 cycles of 30 seconds at 95°C, 30 seconds at 60°C, and 30 seconds at 72°C. The threshold cycle values of each sample are used to calculate mRNA levels. The PCR primers for the indicated human and mouse genes are as follows (Men et al., 2017).
Human H19 forward: 5′-GCACCTTGGACATCTGGAGT
Human H19 reverse: 5′-TTCTTTCCAGCCCTAGCTCA
Human StAR forward: 5′-GGCATCCTTAGCAACCAAGA
Human StAR reverse: 5′-TCTCCTTGACATTGGGGTTC
Mouse StAR forward: 5′-TTGGGCATACTCAACAACCA
Mouse StAR reverse: 5′-GAAACACCTTGCCCACATCT
Indirect immunohistochemistry for the detection of Steroidogenic Acute Regulatory Protein (StAR):
Ovarian or peritoneal tissues from the human patients are collected. Ovarian or peritoneal tissues from the patient are fixed using 10% paraformaldehyde. Tissues are embedded in paraffin. Serial sections of 5 µm are made using microtome. Tissue sections are prepared by microwave heating in 10× citrate buffer, pH 6.0, for 10 min. Tissues are rinsed three times in 20 mM phosphate buffered saline (PBS), pH 7.2, for 10 min each, before incubation with 1:200 dilutions of polyclonal anti-human StAR antibodies at 37°C for 60 min. Tissue sections were washed three times in 20 mM PBS, pH 7.2, for 2 min each, before incubation with a 1:1000 dilution of secondary mouse– anti-rabbit antibody at 37°C for 30 min. Indirect immunohistochemistry kits were used according to the manufacturer’s instructions to visualize StAR protein stained tissue under microscope and image collected. A pathological image analysis system is used to measure mean optical density (MOD) analysis under high-magnification (×400) microscopy. The MOD, which reflected the positive staining intensity, and the positive staining ratio (area %) of every positively stained area, are measured. The area % is calculated as ([the area of positive staining]/[total nuclear area in the field of view]) × 100. The MOD and area % are used to calculate the expression index, EI (%) = MOD × area %(Tian et al., 2009).
Domain of Applicability
In Granulosa cells
Baker, B. Y., Epand, R. F., Epand, R. M., & Miller, W. L. (2007). Cholesterol binding does not predict activity of the steroidogenic acute regulatory protein, StAR. J Biol Chem, 282(14), 10223-32. doi:S0021-9258(19)57693-1 [pii]
Chaffin, C., Dissen, G., & Stouffer, R. (2000). Hormonal regulation of steroidogenic enzyme expression in granulosa cells during the peri-ovulatory interval in monkeys. Molecular human reproduction, 6(1), 11-18.
Christenson, L. K., & Devoto, L. (2003). Cholesterol transport and steroidogenesis by the corpus luteum. Reproductive Biology and Endocrinology, 1(1), 1-9.
Hanukoglu, I. (1992). Steroidogenic enzymes: structure, function, and role in regulation of steroid hormone biosynthesis. The Journal of steroid biochemistry and molecular biology, 43(8), 779-804.
Hasegawa, T., Zhao, L., Caron, K. M., Majdic, G., Suzuki, T., Shizawa, S., et al. (2000). Developmental roles of the steroidogenic acute regulatory protein (StAR) as revealed by StAR knockout mice. Mol Endocrinol, 14(9), 1462-71. doi:10.1210/mend.14.9.0515.
Kiriakidou, M., Mcallister, J. M., Sugawara, T., & Strauss 3rd, J. (1996). Expression of steroidogenic acute regulatory protein (StAR) in the human ovary. The Journal of Clinical Endocrinology & Metabolism, 81(11), 4122-4128.
Manna, P. R., Dyson, M. T., Eubank, D. W., Clark, B. J., Lalli, E., Sassone-Corsi, P., et al. (2002). Regulation of steroidogenesis and the steroidogenic acute regulatory protein by a member of the cAMP response-element binding protein family. Molecular Endocrinology, 16(1), 184-199.
Martin, L. A., Kennedy, B. E., & Karten, B. (2016). Mitochondrial cholesterol: mechanisms of import and effects on mitochondrial function. Journal of bioenergetics and biomembranes, 48(2), 137-151.
Men, Y., Fan, Y., Shen, Y., Lu, L., & Kallen, A. N. (2017). The Steroidogenic Acute Regulatory Protein (StAR) Is Regulated by the H19/let-7 Axis. Endocrinology, 158(2), 402-409. doi:10.1210/en.2016-1340.
Payne, A. H., & Hales, D. B. (2004). Overview of steroidogenic enzymes in the pathway from cholesterol to active steroid hormones. Endocrine reviews, 25(6), 947-970.
Pescador, N., Soumano, K., Stocco, D. M., Price, C. A., & Murphy, B. D. (1996). Steroidogenic acute regulatory protein in bovine corpora lutea. Biology of reproduction, 55(2), 485-491.
Poderoso, C., Duarte, A., Cooke, M., Orlando, U., Gottifredi, V., Solano, A. R., et al. (2013). The spatial and temporal regulation of the hormonal signal. Role of mitochondria in the formation of a protein complex required for the activation of cholesterol transport and steroids synthesis. Molecular and cellular endocrinology, 371(1-2), 26-33.
Sreerangaraja Urs, D. B., Wu, W.-H., Komrskova, K., Postlerova, P., Lin, Y.-F., Tzeng, C.-R., et al. (2020). Mitochondrial function in modulating human granulosa cell steroidogenesis and female fertility. International journal of molecular sciences, 21(10), 3592.
Stocco, D. (2000). The role of the StAR protein in steroidogenesis: challenges for the future. Journal of Endocrinology, 164(3), 247-253.
Tian, Y., Kong, B., Zhu, W., Su, S., & Kan, Y. (2009). Expression of steroidogenic factor 1 (SF-1) and steroidogenic acute regulatory protein (StAR) in endometriosis is associated with endometriosis severity. J Int Med Res, 37(5), 1389-95. doi:10.1177/147323000903700513.