The involvement of specific PKC isoenzymes in phorbol ester-mediated regulation of steroidogenic acute regulatory protein expression and steroid synthesis in mouse Leydig cells

Steroidogenic acute regulatory protein mediated variations of gender-specific sex neurosteroids in Alzheimer's disease: Relevance to hormonal and neuronal imbalance

The steroidogenic acute regulatory (StAR) protein mediates the rate-liming step in neuro/steroid biosynthesis. Multifaceted and delicate changes during aging, disrupting hormonal and neuronal homeostasis, constitute human senescence, an inevitable phenomenon that attributes to increased morbidity and mortality. Aging, along with progressive decreases in bioactive neurosteroids, is the primary risk factor for Alzheimer's disease (AD), which preferentially impacts two-thirds of women and one-third of men. AD is neuropathologically characterized by the accumulation of extracellular amyloid-β and intracellular phosphorylated Tau containing neurofibrillary tangles, resulting in dementia. Postmortem brains pertaining to gender-specific AD patients exhibit varied suppression of StAR and sex neurosteroid levels compared with age-matched cognitively healthy subjects, in which the attenuation of StAR is inversely correlated with the AD pathological markers. Interestingly, retinoid signaling upregulates StAR-motivated neurosteroid biosynthesis and reinstates various neurodegenerative vulnerabilities that promote AD pathogenesis. This review summarizes current understanding of StAR-driven alterations of sex neurosteroids in gender-specific AD risks and provides biochemical and molecular insights into therapeutic interventions for preventing and/or alleviating dementia for healthy aging.

Exposure to atrazine stimulates progesterone secretion and induces oxidative stress, inflammation, and apoptosis in the ovary of pseudopregnant rats

Atrazine (ATR) is one of the most commonly used herbicides worldwide. As an endocrine disruptor, it causes ovarian dysfunction, but the mechanism is unclear. We hypothesized that ATR could affect ovarian steroidogenesis, oxidative stress, inflammation, and apoptosis. In the current study, rats aged 28 days were treated with PMSG and HCG to obtain amounts of corpora lutea. Then, rats were injected with ATR (50 mg/kg/day) or saline (0.9%) for 7 days. Sera were collected to detect biochemical indices and progesterone (P4) level, ovaries were collected for antioxidant status, HE, qPCR, and WB analysis. Results showed that ATR exposure affected growth performance as well as serum TP, GLB, and ALB levels, increased serum P4 level and ovarian mRNA and protein levels of StAR, CYP11A1, and HSD3B. ATR treatment increased ovarian mRNA and protein levels of CREB but not PKA expression. ATR treatment increased ovarian mRNA abundances of Nrf-2 and Nqo1, MDA level, and decreased SOD, GST, and T-AOC levels. ATR exposure increased the mRNA abundances of pro-inflammatory cytokines including Tnf-α, Il-1β, Il-6, Il-18, and Inos. ATR exposure increased the mRNA and protein level of Caspase 3 and the ratio of BAX/BCL-2. In conclusion, NRF-2/NQO1 signaling pathway and CREB might be involved in the regulation of ATR in luteal steroidogenesis, oxidative stress, inflammation, and apoptosis in rat ovary.

Regulation of retinoid mediated StAR transcription and steroidogenesis in hippocampal neuronal cells: Implications for StAR in protecting Alzheimer's disease

Retinoids (vitamin A and its derivatives) play pivotal roles in diverse processes, ranging from homeostasis to neurodegeneration, which are also influenced by steroid hormones. The rate-limiting step in steroid biosynthesis is mediated by the steroidogenic acute regulatory (StAR) protein. In the present study, we demonstrate that retinoids enhanced StAR expression and pregnenolone biosynthesis, and these parameters were markedly augmented by activation of the PKA pathway in mouse hippocampal neuronal HT22 cells. Deletion and mutational analyses of the 5'-flanking regions of the StAR gene revealed the importance of a retinoic acid receptor (RAR)/retinoid X receptor (RXR)-liver X receptor (LXR) heterodimeric motif at -200/-185 bp region in retinoid responsiveness. The RAR/RXR-LXR sequence motif can bind RARα and RXRα, and retinoid regulated transcription of the StAR gene was found to be influenced by the LXR pathway, representing signaling cross-talk in hippocampal neurosteroid biosynthesis. Steroidogenesis decreases during senescence due to declines in the central nervous system and the endocrine system, and results in hormone deficiencies, inferring the need for hormonal balance for healthy aging. Loss of neuronal cells, involving accumulation of amyloid beta (Aβ) and/or phosphorylated Tau within the brain, is the pathological hallmark of Alzheimer's disease (AD). HT22 cells overexpressing either mutant APP (mAPP) or mutant Tau (mTau), conditions mimetic to AD, enhanced toxicities, and resulted in attenuation of both basal and retinoid-responsive StAR and pregnenolone levels. Co-expression of StAR with either mAPP or mTau diminished cytotoxicity, and concomitantly elevated neurosteroid biosynthesis, pointing to a protective role of StAR in AD. These findings provide insights into the molecular events by which retinoid signaling upregulates StAR and steroid levels in hippocampal neuronal cells, and StAR, by rescuing mAPP and/or mTau-induced toxicities, modulates neurosteroidogenesis and restores hormonal balance, which may have important implications in protecting AD and age-related complications and diseases.

Expression and Function of StAR in Cancerous and Non-Cancerous Human and Mouse Breast Tissues: New Insights into Diagnosis and Treatment of Hormone-Sensitive Breast Cancer

Breast cancer (BC) is primarily triggered by estrogens, especially 17β-estradiol (E2), which are synthesized by the aromatase enzyme. While all steroid hormones are derived from cholesterol, the rate-limiting step in steroid biosynthesis is mediated by the steroidogenic acute regulatory (StAR) protein. Herein, we demonstrate that StAR mRNA expression was aberrantly high in human hormone-dependent BC (MCF7, MDA-MB-361, and T-47D), modest in hormone-independent triple negative BC (TNBC; MDA-MB-468, BT-549, and MDA-MB-231), and had little to none in non-cancerous mammary epithelial (HMEC, MCF10A, and MCF12F) cells. In contrast, these cell lines showed abundant expression of aromatase (CYP19A1) mRNA. Immunofluorescence displayed qualitatively similar patterns of both StAR and aromatase expression in various breast cells. Additionally, three different transgenic (Tg) mouse models of spontaneous breast tumors, i.e., MMTV-Neu, MMTV-HRAS, and MMTV-PyMT, demonstrated markedly higher expression of StAR mRNA/protein in breast tumors than in normal mammary tissue. While breast tumors in these mouse models exhibited higher expression of ERα, ERβ, and PR mRNAs, their levels were undetected in TNBC tumors. Accumulation of E2 in plasma and breast tissues, from MMTV-PyMT and non-cancerous Tg mice, correlated with StAR, but not with aromatase, signifying the importance of StAR in governing E2 biosynthesis in mammary tissue. Treatment with a variety of histone deacetylase inhibitors (HDACIs) in primary cultures of enriched breast tumor epithelial cells, from MMTV-PyMT mice, resulted in suppression of StAR and E2 levels. Importantly, inhibition of StAR, concomitant with E2 synthesis, by various HDACIs, at clinical and preclinical doses, in MCF7 cells, indicated therapeutic relevance of StAR in hormone-dependent BCs. These findings provide insights into the molecular events underlying the differential expression of StAR in human and mouse cancerous and non-cancerous breast cells/tissues, highlighting StAR could serve not only as a novel diagnostic maker but also as a therapeutic target for the most prevalent hormone-sensitive BCs.

The insulin-like growth factor and its players: their functions, significance, and consequences in all aspects of ovarian physiology

Background

Insulin-like growth factor (IGF) has unique and well-known functions in female fertility, according to documents reporting improved yield of oocytes, reinforced quality of the embryo, and enhanced live births with simultaneous reduction of miscarriage. However, there is no detailed information on the bio-mechanisms linking such clinical differences.

Main body

IGF and its receptors are expressed in a variety of tissues in the reproductive system such as granulosa cells, oocytes, and theca cells. Hence, the development of female gametes may be directly regulated by IGF, thereby affecting gamete quality and so its competence for implantation. IGF is a central player in changing the fate of cells during survival and proliferation through the modulation of leading signaling pathways, including Jak/STAT, MAP kinase/ERK, and PI3K/Akt, and subsequent impacts on steroidogenesis and cell division.

Conclusion

The current review aims to scrutinize the performance of IGF to regulate the normal ovarian, and its impacts on cell signaling pathways and resulting alterations in steroidogenesis and cell proliferation. The function of IGF and its receptor has been reviewed in female fertility at both molecular and biochemical levels.

Exogenous cholesterol acquisition signaling in LH-responsive MA-10 Leydig cells and in adult mice

MA-10 cells, established 4 decades ago from a murine Leydig cell tumor, has served as a key model system for studying steroidogenesis. Despite a precipitous loss in their innate ability to respond to luteinizing hormone (LH), the use of a cell-permeable cAMP analog for induction ensured their continued use. In parallel, a paradigm that serum-free conditions are essential for trophic steroidogenic stimulation was rationalized. Through the selection of LH-responsive single-cell MA-10Slip clones, we uncovered that Leydig cells remain responsive in the presence of serum in vitro and that exogenous cholesterol delivery by lipoproteins provided a significantly elevated steroid biosynthetic response (>2-fold). In scrutinizing the underlying regulation, systems biology of the MA-10 cell proteome identified multiple Rho-GTPase signaling pathways as highly enriched. Testing Rho function in steroidogenesis revealed that its modulation can negate the specific elevation in steroid biosynthesis observed in the presence of lipoproteins/serum. This signaling modality primarily linked to the regulation of endocytic traffic is evident only in the presence of exogenous cholesterol. Inhibiting Rho function in vivo also decreased hCG-induced testosterone production in mice. Collectively, our findings dispel a long-held view that the use of serum could confound or interfere with trophic stimulation and underscore the need for exogenous lipoproteins when dissecting physiological signaling and cholesterol trafficking for steroid biosynthesis in vitro. The LH-responsive MA-10Slip clones derived in this study present a reformed platform enabling biomimicry to study the cellular and molecular basis of mammalian steroidogenesis.

Gigantol Improves Cholesterol Metabolism and Progesterone Biosynthesis in MA-10 Leydig Cells

In aging males, androgen production by testicular Leydig cells decreases at a rate of approximately 1% per year. Phenolic compounds may enhance testosterone biosynthesis and delay the onset of male hypogonadism. Gigantol is a bibenzyl compound isolated from several types of orchids of the genus Dendrobium. This compound has various biological activities, including antioxidant activity. However, its capacity to regulate gene expression and steroid production in testicular Leydig cells has never been evaluated. We investigated the effect of gigantol on MA-10 Leydig cells' gene expression using an RNA-Seq approach. To further investigate the structure-function relationship of the hydroxy-methoxyphenyl moiety of gigantol, experiments were also performed with ferulic acid and isoferulic acid. According to transcriptomic analysis, all genes coding for cholesterol biosynthesis-related enzymes are increased in response to gigantol treatment, resulting in increased lipid droplets accumulation. Moreover, treatments with 10 μM gigantol increased StAR protein levels and progesterone production from MA-10 Leydig cells. However, neither ferulic acid nor isoferulic acid influenced StAR protein synthesis and progesterone production in MA-10 Leydig cells. Thus, our findings indicate that gigantol improves cholesterol and steroid biosynthesis within testicular Leydig cells.

The AP-1 family of transcription factors are important regulators of gene expression within Leydig cells

PURPOSE

Members of the AP-1 family of transcription factors are immediate early genes being modulated by different extracellular signals. The aim of this review is to highlight the important roles of AP-1 members in transcriptional regulation of genes important for testicular Leydig cell function and male testosterone production.

METHODS

A search of the relevant literature was performed in Google Scholar and NCBI Pubmed for AP-1 members and Leydig cells. Additional information was accessed from references of relevant articles. Only primary data from original peer-reviewed articles was considered for this review.

RESULTS

Different signaling pathways important for Leydig cells' functions are involved in the regulation of the activity of AP-1 members. These transcription factors participate in the regulation of genes related to different biological processes important for Leydig cells.

CONCLUSIONS

We conclude that members of the AP-1 family of transcription factors play critical roles in the regulation of Leydig cell proliferation, steroidogenesis, and cell-to-cell communication.

Regulation of lipid droplets via the PLCβ2-PKCα-ADRP pathway in granulosa cells exposed to cadmium

In steroidogenic cells, steroids are synthesized de novo from cholesterol stored in lipid droplets (LDs). The size of LDs regulated by adipose differentiation-related protein (ADRP) is closely related to cholesterol ester hydrolysis. Many studies reported that cadmium (Cd) had dual effects on steroidogenesis in granulosa cells (GCs). However, the role of LD and its regulation in abnormal steroidogenesis caused by Cd exposure remain unknown. In current study, female rats were exposed to CdCl₂ during gestation and lactation, and influence of such exposure was investigated in ovarian GCs of female offspring. The size of LDs was found much smaller than normal in GCs; ADRP was down-regulated and hormone-sensitive lipase (HSL) phosphorylation was increased, followed by up-regulation of steroidogenic acute regulatory protein (StAR) and cholesterol side-chain cleavage enzyme (CYP11A1); the expression of 1-phosphatidylinositol 4,5-bisphosphate phosphodiesterase beta-2 (PLCβ2) and protein kinase C alpha type (PKCα) were both decreased accompanying the ADRP down-regulation. This series of events resulted in a high level of progesterone in serum. Similar results were demonstrated in GCs treated with 20 μM CdCl₂ for 24 h in vitro. The protein level of ADRP was decreased after gene silencing of PLCβ2/PKCα, and the knockdown of PLCβ2/PKCα/ADRP led to micro-sized LD formation. We found that Cd exposure down-regulated ADRP by inhibiting the PLCβ2-PKCα signaling pathway, reduced the size of LDs, and promoted HSL phosphorylation. StAR and CYP11A1 were both up-regulated following the hydrolysis of cholesterol ester, which led to a high production of progesterone. LD thereby is a target subcellular organelle for Cd to affect steroid hormone synthesis in ovarian GCs. These findings might help to uncover the mechanism of ovarian dysfunction and precocious puberty caused by Cd pollution.

Involvement of CREB-regulated transcription coactivators (CRTC) in transcriptional activation of steroidogenic acute regulatory protein (Star) by ACTH

Studies in vivo have suggested the involvement of CREB-regulated transcription coactivator (CRTC)2 on ACTH-induced transcription of the key steroidogenic protein, Steroidogenic Acute Regulatory (StAR). The present study uses two ACTH-responsive adrenocortical cell lines, to examine the role of CRTC on Star transcription. Here we show that ACTH-induced Star primary transcript, or heteronuclear RNA (hnRNA), parallels rapid increases in nuclear levels of the 3 isoforms of CRTC; CRTC1, CRTC2 and CRTC3. Furthermore, ACTH promotes recruitment of CRTC2 and CRTC3 by the Star promoter and siRNA knockdown of either CRTC3 or CRTC2 attenuates the increases in ACTH-induced Star hnRNA. Using pharmacological inhibitors of PKA, MAP kinase and calcineurin, we show that the effects of ACTH on Star transcription and CRTC nuclear translocation depend predominantly on the PKA pathway. The data provides evidence that CRTC2 and CRTC3, contribute to activation of Star transcription by ACTH, and that PKA/CRTC-dependent pathways are part of the multifactorial mechanisms regulating Star transcription.

Endoplasmic Reticulum Stress-Induced Upregulation of STARD1 Promotes Acetaminophen-Induced Acute Liver Failure

BACKGROUND & AIMS

Acetaminophen (APAP) overdose is a major cause of acute liver failure (ALF). Mitochondrial SH3BP5 (also called SAB) and phosphorylation of c-Jun N-terminal kinase (JNK) mediate the hepatotoxic effects of APAP. We investigated the involvement of steroidogenic acute regulatory protein (STARD1), a mitochondrial cholesterol transporter, in this process and sensitization by valproic acid (VPA), which depletes glutathione and stimulates steroidogenesis.

METHODS

Nonfasted C57BL/6J mice (control) and mice with liver-specific deletion of STARD1 (Stard1^ΔHep), SAB (Sab^ΔHep), or JNK1 and JNK2 (Jnk1+2^ΔHep) were given VPA with or without APAP. Liver tissues were collected and analyzed by histology and immunohistochemistry and for APAP metabolism, endoplasmic reticulum (ER) stress, and mitochondrial function. Adult human hepatocytes were transplanted into Fah^-/-/Rag2^-/-/Il2rg^-/-/NOD (FRGN) mice to create mice with humanized livers.

RESULTS

Administration of VPA before administration of APAP increased the severity of liver damage in control mice. The combination of VPA and APAP increased expression of CYP2E1, formation of NAPQI-protein adducts, and depletion of glutathione from liver tissues of control mice, resulting in ER stress and the upregulation of STARD1. Livers from control mice given VPA and APAP accumulated cholesterol in the mitochondria and had sustained mitochondrial depletion of glutathione and mitochondrial dysfunction. Inhibition of ER stress, by administration of tauroursodeoxycholic acid to control mice, prevented upregulation of STARD1 in liver and protected the mice from hepatoxicity following administration of VPA and APAP. Administration of N-acetylcysteine to control mice prevented VPA- and APAP-induced ER stress and liver injury. Stard1^ΔHep mice were resistant to induction of ALF by VPA and APAP, despite increased mitochondrial levels of glutathione and phosphorylated JNK; we made similar observations in fasted Stard1^ΔHep mice given APAP alone. Sab^ΔHep mice or Jnk1+2^ΔHep mice did not develop ALF following administration of VPA and APAP. The ability of VPA to increase the severity of APAP-induced liver damage was observed in FRGN mice with humanized liver.

CONCLUSIONS

In studies of mice, we found that upregulation of STARD1 following ER stress mediates APAP hepatoxicity via SH3BP5 and phosphorylation of JNK1 and JNK2.

Genomic Profiling of the Steroidogenic Acute Regulatory Protein in Breast Cancer: In Silico Assessments and a Mechanistic Perspective

Cancer is a multifactorial condition with aberrant growth of cells. A substantial number of cancers, breast in particular, are hormone sensitive and evolve due to malfunction in the steroidogenic machinery. Breast cancer, one of the most prevalent form of cancers in women, is primarily stimulated by estrogens. Steroid hormones are made from cholesterol, and regulation of steroid/estrogen biosynthesis is essentially influenced by the steroidogenic acute regulatory (StAR) protein. Although the impact of StAR in breast cancer remains a mystery, we recently reported that StAR protein is abundantly expressed in hormone sensitive breast cancer, but not in its non-cancerous counterpart. Herein, we analyzed genomic profiles, hormone receptor expression, mutation, and survival for StAR and steroidogenic enzyme genes in a variety of hormone sensitive cancers. These profiles were specifically assessed in breast cancer, exploiting The Cancer Genome Atlas (TCGA) datasets. Whereas StAR and key steroidogenic enzyme genes evaluated (CYP11A1, HSD3B, CYP17A1, CYP19A1, and HSD17B) were altered to varying levels in these hormone responsive cancers, amplification of the StAR gene was correlated with poor overall survival of patients afflicted with breast cancer. Amplification of the StAR gene and its correlation to survival was also verified in a number of breast cancer studies. Additionally, TCGA breast cancer tumors associated with aberrant high expression of StAR mRNA were found to be an unfavorable risk factor for survival of patients with breast cancer. Further analyses of tumors, nodal status, and metastases of breast cancer tumors expressing StAR mRNA displayed cancer deaths in stage specific manners. The majority of these tumors were found to express estrogen and progesterone receptors, signifying a link between StAR and luminal subtype breast cancer. Collectively, analyses of genomic and molecular profiles of key steroidogenic factors provide novel insights that StAR plays an important role in the biologic behavior and/or pathogenesis of hormone sensitive breast cancer.

Growth Hormone and Insulin-Like Growth Factor Action in Reproductive Tissues

The role of growth hormone (GH) in human fertility is widely debated with some studies demonstrating improvements in oocyte yield, enhanced embryo quality, and in some cases increased live births with concomitant decreases in miscarriage rates. However, the basic biological mechanisms leading to these clinical differences are not well-understood. GH and the closely-related insulin-like growth factor (IGF) promote body growth and development via action on key metabolic organs including the liver, skeletal muscle, and bone. In addition, their expression and that of their complementary receptors have also been detected in various reproductive tissues including the oocyte, granulosa, and testicular cells. Therefore, the GH/IGF axis may directly regulate female and male gamete development, their quality, and ultimately competence for implantation. The ability of GH and IGF to modulate key signal transduction pathways such as the MAP kinase/ERK, Jak/STAT, and the PI3K/Akt pathway along with the subsequent effects on cell division and steroidogenesis indicates that these growth factors are centrally located to alter cell fate during proliferation and survival. In this review, we will explore the function of GH and IGF in regulating normal ovarian and testicular physiology, while also investigating the effects on cell signal transduction pathways with subsequent changes in cell proliferation and steroidogenesis. The aim is to clarify the role of GH in human fertility from a molecular and biochemical point of view.

Molecular Mechanisms of Action of FSH

The glycoprotein follicle-stimulating hormone (FSH) acts on gonadal target cells, hence regulating gametogenesis. The transduction of the hormone-induced signal is mediated by the FSH-specific G protein-coupled receptor (FSHR), of which the action relies on the interaction with a number of intracellular effectors. The stimulatory Gαs protein is a long-time known transducer of FSH signaling, mainly leading to intracellular cAMP increase and protein kinase A (PKA) activation, the latter acting as a master regulator of cell metabolism and sex steroid production. While in vivo data clearly demonstrate the relevance of PKA activation in mediating gametogenesis by triggering proliferative signals, some in vitro data suggest that pro-apoptotic pathways may be awakened as a "dark side" of cAMP/PKA-dependent steroidogenesis, in certain conditions. P38 mitogen-activated protein kinases (MAPK) are players of death signals in steroidogenic cells, involving downstream p53 and caspases. Although it could be hypothesized that pro-apoptotic signals, if relevant, may be required for regulating atresia of non-dominant ovarian follicles, they should be transient and counterbalanced by mitogenic signals upon FSHR interaction with opposing transducers, such as Gαi proteins and β-arrestins. These molecules modulate the steroidogenic pathway via extracellular-regulated kinases (ERK1/2), phosphatidylinositol-4,5-bisphosphate 3-kinases (PI3K)/protein kinase B (AKT), calcium signaling and other intracellular signaling effectors, resulting in a complex and dynamic signaling network characterizing sex- and stage-specific gamete maturation. Even if the FSH-mediated signaling network is not yet entirely deciphered, its full comprehension is of high physiological and clinical relevance due to the crucial role covered by the hormone in regulating human development and reproduction.

Calretinin Participates in Regulating Steroidogenesis by PLC-Ca2+-PKC Pathway in Leydig Cells

Calretinin, a Ca²⁺-binding protein, participates in many cellular events. Our previous studies found the high expression of calretinin in testicular Leydig cells. In this study, (MLTC-1 cells were infected with LV-calb2, R2C cells with LV-siRNA-calb2. The primary mouse Leydig cells were also used to confirm those data from cell lines. Testosterone level was significantly higher in the MLTC-1 cells with over-expressed calretinin than in the control, while progesterone was lower in the R2C cells in which down-regulated calretinin. The expressions of StAR changed in synchrony with hormones. Cytoplasmic Ca²⁺ level was significantly increased when calretinin was over-expressed. When MLTC-1 cells were infected with LV-calb2 and then stimulated using Clopiazonic, a Ca²⁺-releasing agent, testosterone was significantly increased. Interestingly, the expression levels of PLC, p-PKCµ (PKD), p-MARCKS and CREB, were significantly increased in the MLTC-1 cells with over-expressed calretinin, while PLC, p-PKD, p-MARCKS, MARCKS and CREB were decreased in the R2C cells with down-regulated calretinin. We also observed the increased expression of calretinin up-regulated testosterone production and the expressions of StAR and PLC in primary mouse Leydig cells. So, calretinin as a Ca²⁺-binding protein participates in the regulation of steroidogenesis via the PLC-Ca²⁺-PKC pathway in Leydig cells.

The SET protein promotes androgen production in testicular Leydig cells

Approximately 40% of middle‐aged men exhibit symptoms of late‐onset hypogonadism (LOH). However, the mechanism of androgen deficiency is still currently unclear. As shown in our previous studies, the SET protein is expressed in testicular Leydig cells and ovarian granule cells. This study was designed to investigate the effect of the SET protein on androgen production in Leydig cells. The AdCMV/SET and AdH1siRNA/SET adenoviruses were individually transduced into a cultured mouse Leydig cell line (mLTC‐1) with or without human chorionic gonadotropin (HCG) stimulation in vitro. The primary mouse Leydig cells were used to confirm the main data from mLTC‐1 cells. The SET protein was expressed in the cytoplasm and nucleus of mLTC‐1 cells. Testosterone production was significantly increased in mLTC‐1 cells overexpressing the SET protein compared with the control group (p < 0.05), whereas testosterone production was significantly decreased in the SET knockdown mLTC‐1 cells (p < 0.05). Consistent with the testosterone levels, the expression levels of the steroidogenic acute regulatory (StAR) and cytochrome P450c17α‐hydroxylase (CYP17a1) mRNAs and proteins synchronously changed according to the expression level of the SET protein. Interestingly, the expression of the SET protein was significantly increased in the mLTC‐1 cells stimulated with 0.04 and 0.1 U/mL hCG. In the mLTC‐1 cells transfected with AdH1siRNA/SET and concurrently stimulated with 0.1 U/mL hCG, both testosterone production and StAR expression were significantly lower than in the cells without SET knockdown (p < 0.05). In conclusion, the SET protein participates in regulating testosterone production by increasing the expression of StAR and CYP17a1, and it may be a downstream factor of the classic luteinizing hormone (LH)/luteinizing hormone receptor (LHR) signaling pathway. This study improves our understanding of the intracellular mechanism of testicular steroidogenesis and the pathophysiological mechanism of LOH in the aging male.

The Renin-Angiotensin-Aldosterone System as a Therapeutic Target in Late Injury Caused by Ischemia-Reperfusion

Ischemia-reperfusion (I/R) injury is a well-known phenomenon that involves different pathophysiological processes. Connection in diverse systems of survival brings about cellular dysfunction or even apoptosis. One of the survival systems of the cells, to the assault caused by ischemia, is the activation of the renin-angiotensin-aldosterone system (also known as an axis), which is focused on activating diverse signaling pathways to favor adaptation to the decrease in metabolic supports caused by the hypoxia. In trying to adapt to the I/R event, great changes occur that unchain cellular dysfunction with the capacity to lead to cell death, which translates into a poor prognosis due to the progression of dysfunction of the cellular activity. The search for the understanding of the diverse therapeutic alternatives in molecular coupling could favor the prognosis and evolution of patients who are subject to the I/R process.

Mitochondrial Cholesterol and the Paradox in Cell Death

Mitochondria are considered cholesterol-poor organelles, and obtain their cholesterol load by the action of specialized proteins involved in its delivery from extramitochondrial sources and trafficking within mitochondrial membranes. Although mitochondrial cholesterol fulfills vital physiological functions, such as the synthesis of bile acids in the liver or the formation of steroid hormones in specialized tissues, recent evidence indicates that the accumulation of cholesterol in mitochondria may be a key event in prevalent human diseases, in particular in the development of steatohepatitis (SH) and its progression to hepatocellular carcinoma (HCC). Mitochondrial cholesterol accumulation promotes the transition from simple steatosis to SH due to the sensitization to oxidative stress and cell death. However, mitochondrial cholesterol loading in HCC determines apoptosis resistance and insensitivity to chemotherapy. These opposing functions of mitochondrial cholesterol in SH and HCC define its paradoxical role in cell death as a pro- and anti-apoptotic factor. Further understanding of this conundrum may be useful to modulate the progression from SH to HCC by targeting mitochondrial cholesterol trafficking.

Primary Aldosteronism: Changing Definitions and New Concepts of Physiology and Pathophysiology Both Inside and Outside the Kidney

In the 60 years that have passed since the discovery of the mineralocorticoid hormone aldosterone, much has been learned about its synthesis (both adrenal and extra-adrenal), regulation (by renin-angiotensin II, potassium, adrenocorticotrophin, and other factors), and effects (on both epithelial and nonepithelial tissues). Once thought to be rare, primary aldosteronism (PA, in which aldosterone secretion by the adrenal is excessive and autonomous of its principal regulator, angiotensin II) is now known to be the most common specifically treatable and potentially curable form of hypertension, with most patients lacking the clinical feature of hypokalemia, the presence of which was previously considered to be necessary to warrant further efforts towards confirming a diagnosis of PA. This, and the appreciation that aldosterone excess leads to adverse cardiovascular, renal, central nervous, and psychological effects, that are at least partly independent of its effects on blood pressure, have had a profound influence on raising clinical and research interest in PA. Such research on patients with PA has, in turn, furthered knowledge regarding aldosterone synthesis, regulation, and effects. This review summarizes current progress in our understanding of the physiology of aldosterone, and towards defining the causes (including genetic bases), epidemiology, outcomes, and clinical approaches to diagnostic workup (including screening, diagnostic confirmation, and subtype differentiation) and treatment of PA.

Analysis of specific RNA in cultured cells through quantitative integration of q-PCR and N-SIM single cell FISH images: Application to hormonal stimulation of StAR transcription

The steroidogenic acute regulatory protein (StAR) has been proposed to serve as the switch that can turn on/off steroidogenesis. We investigated the events that facilitate dynamic StAR transcription in response to cAMP stimulation in MA-10 Leydig cells, focusing on splicing anomalies at StAR gene loci. We used 3' reverse primers in a single reaction to respectively quantify StAR primary (p-RNA), spliced (sp-RNA/mRNA), and extended 3' untranslated region (UTR) transcripts, which were quantitatively imaged by high-resolution fluorescence in situ hybridization (FISH). This approach delivers spatio-temporal resolution of initiation and splicing at single StAR loci, and transfers individual mRNA molecules to cytoplasmic sites. Gene expression was biphasic, initially showing slow splicing, transitioning to concerted splicing. The alternative 3.5-kb mRNAs were distinguished through the use of extended 3'UTR probes, which exhibited distinctive mitochondrial distribution. Combining quantitative PCR and FISH enables imaging of localization of RNA expression and analysis of RNA processing rates.

Calcium-dependent Nr4a1 expression in mouse Leydig cells requires distinct AP1/CRE and MEF2 elements

The nuclear receptor NR4A1 is expressed in steroidogenic Leydig cells where it plays pivotal roles by regulating the expression of several genes involved in steroidogenesis and male sex differentiation including Star, HSD3B2, and Insl3 Activation of the cAMP and Ca(2+) signaling pathways in response to LH stimulation leads to a rapid and robust activation of Nr4a1 gene expression that requires the Ca(2+)/CAMKI pathway. However, the downstream transcription factor(s) have yet to be characterized. To identify potential Ca(2+)/CaM effectors responsible for hormone-induced Nr4a1 expression, MA-10 Leydig cells were treated with forskolin to increase endogenous cAMP levels, dantrolene to inhibit endoplasmic reticulum Ca(2+) release, and W7 to inhibit CaM activity. We identified Ca(2+)-responsive elements located in the discrete regions of the Nr4a1 promoter, which contain binding sites for several transcription factors such as AP1, CREB, and MEF2. We found that one of the three AP1/CRE sites located at -255 bp is the most responsive to the Ca(2+) signaling pathway as are the two MEF2 binding sites at -315 and -285 bp. Furthermore, we found that the hormone-induced recruitment of phospho-CREB and of the co-activator p300 to the Nr4a1 promoter requires the Ca(2+) pathway. Lastly, siRNA-mediated knockdown of CREB impaired NR4A1 expression and steroidogenesis. Together, our data indicate that the Ca(2+) signaling pathway increases Nr4a1 expression in MA-10 Leydig cells, at least in part, by enhancing the recruitment of coactivator most likely through the MEF2, AP1, and CREB transcription factors thus demonstrating an important interplay between the Ca(2+) and cAMP pathways in regulating Nr4a1 expression.

Retinoid regulated macrophage cholesterol efflux involves the steroidogenic acute regulatory protein

Elimination of excess cholesteryl esters from macrophage-derived foam cells is known to be a key process in limiting plaque stability and progression of atherosclerotic lesions. We have recently demonstrated that regulation of retinoid mediated cholesterol efflux is influenced by liver X receptor (LXR) signaling in mouse macrophages (Manna, P.R. et al., 2015, Biochem. Biophys. Res. Commun., 464:312-317). The data presented in this article evaluate the importance of the steroidogenic acute regulatory protein (StAR) in retinoid mediated macrophage cholesterol efflux. Overexpression of StAR in mouse RAW 264.7 macrophages increased the effects of both all-trans retinoic acid (atRA) and 9-cis RA on cholesterol efflux, suggesting StAR enhances the efficacy of retinoic acid receptor (RAR) and/or retinoid X receptor (RXR) ligands. Additional data revealed that atRA enhances (Bu)₂cAMP induced StAR and ATP-binding cassette transporter A1 protein levels. Treatment of macrophages transfected with an LXRE reporter plasmid (pLXREx3-Luc) was found to induce the effects of RAR and RXR analogs on LXR activity.

Steroidogenesis and early response gene expression in MA-10 Leydig tumor cells following heterologous receptor down-regulation and cellular desensitization

The Leydig tumor cell line, MA-10, expresses the luteinizing hormone receptor, a G protein-coupled receptor that, when activated with luteinizing hormone or chorionic gonadotropin (CG), stimulates cAMP production and subsequent steroidogenesis, notably progesterone. These cells also respond to epidermal growth factor (EGF) and phorbol esters with increased steroid biosynthesis. In order to probe the intracellular pathways along with heterologous receptor down-regulation and cellular desensitization, cells were preincubated with EGF or phorbol esters and then challenged with CG, EGF, dibutryl-cyclic AMP, and a phorbol ester. Relative receptor numbers, steroid biosynthesis, and expression of the early response genes, JUNB and c-FOS, were measured. It was found that in all cases but one receptor down-regulation and decreased progesterone production were closely coupled under the conditions used; the exception involved preincubation of the cells with EGF followed by addition of CG where the CG-mediated stimulation of steroidogenesis was considerably lower than the level of receptor down-regulation. In a number of instances JUNB and c-FOS expression paralleled the decreases in receptor number and progesterone production, while in some cases these early response genes were affected little if at all by the changes in receptor number. This finding may indicate that even low levels of activated signaling kinases, e.g. protein kinase A, protein kinase C, or receptor tyrosine kinase, may suffice to yield good expression of JUNB and c-FOS, or it may suggest alternative pathways for regulating expression of these two early response genes.

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Leydig tumor cells respond to hCG, cAMP, EGF, and phorbol esters with increased steroidogenesis.

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These same agents increase expression of the early response genes JUNB and c-FOS.

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Down-regulation of EGF receptors reduced hCG receptors and steroidogenesis.

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Desensitization of the PKC pathway reduced hCG receptors and steroidogenesis.

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Often expression of JUNB and c-FOS paralleled receptor loss, but not always.

Intratesticular alpha1-adrenergic receptors mediate stress-disturbed transcription of steroidogenic stimulator NUR77 as well as steroidogenic repressors DAX1 and ARR19 in Leydig cells of adult rats

The aim of the present study was to define the role of testicular α1-adrenergic receptors (α1-ADRs) in stress-triggered adaptation of testosterone-producing Leydig cells of adult rats. Results showed that in vivo blockade of testicular α1-ADRs prevented partial recovery of circulating androgen levels registered after 10× repeated immobilization stress (10 × IMO). Moreover, α1-ADR-blockade diminished 10 × IMO-triggered recovery of Leydig cell androgen production, and abolished mitochondrial membrane potential recovery. In the same cells, 10 × IMO-induced increase in Star transcript was abolished, Lhcgr transcript decreased, while transcription of other steroidogenic proteins was not changed. α1-ADR-blockade recovered stress-induced decrease of Nur77, one of the main steroidogenic stimulator, while significantly reduced 10 × IMO-increased in the transcription of the main steroidogenic repressors, Arr19 and Dax1. In vitro experiments revealed an adrenaline-induced α1-ADR-mediated decrease in Nur77 transcription in Leydig cells. Adrenaline-induced increase of repressor Dax1 also involves ADRs in Leydig cells. Accordingly, α1-ADRs participate in some of the stress-triggered effects on the steroidogenic machinery of Leydig cells.

Up-regulation of steroid biosynthesis by retinoid signaling: Implications for aging

Retinoids (vitamin A and its derivatives) are critical for a spectrum of developmental and physiological processes, in which steroid hormones also play indispensable roles. The StAR protein predominantly regulates steroid biosynthesis in steroidogenic tissues. We have reported that regulation of retinoid, especially atRA and 9-cis RA, responsive StAR transcription is largely mediated by an LXR-RXR/RAR heterodimeric motif in the mouse StAR promoter. Herein we demonstrate that retinoids are capable of enhancing StAR protein, P-StAR, and steroid production in granulosa, adrenocortical, glial, and epidermal cells. Whereas transient expression of RARα and RXRα enhanced 9-cis RA induced StAR gene transcription, silencing of RXRα with siRNA, decreased StAR and steroid levels. An oligonucleotide probe encompassing an LXR-RXR/RAR motif bound to adrenocortical and epidermal keratinocyte nuclear proteins in EMSAs. ChIP studies revealed association of RARα and RXRα with the StAR proximal promoter. Further studies demonstrated that StAR mRNA levels decreased in diseased and elderly men and women skin tissues and that atRA could restore steroidogenesis in epidermal keratinocytes of aged individuals. These findings provide novel insights into the relevance of retinoid signaling in the up-regulation of steroid biosynthesis in various target tissues, and indicate that retinoid therapy may have important implications in age-related complications and diseases.

Regulation of retinoid mediated cholesterol efflux involves liver X receptor activation in mouse macrophages

Removal of cholesterol from macrophage-derived foam cells is a critical step to the prevention of atherosclerotic lesions. We have recently demonstrated the functional importance of retinoids in the regulation of the steroidogenic acute regulatory (StAR) protein that predominantly mediates the intramitochondrial transport of cholesterol in target tissues. In the present study, treatment of mouse macrophages with retinoids, particularly all-trans retinoic acid (atRA) and 9-cis RA, resulted in increases in cholesterol efflux to apolipoprotein AI (Apo-A1). Activation of the PKA pathway by a cAMP analog, (Bu)2cAMP, markedly augmented retinoid mediated cholesterol efflux. Macrophages overexpressing hormone-sensitive lipase increased the hydrolysis of cholesteryl esters and concomitantly enhanced the efficacy of retinoic acid receptor and liver X receptor (LXR) ligands on StAR and ATP-binding cassette transporter A1 (ABCA1) protein levels. RAs elevated StAR promoter activity in macrophages, and an increase in StAR levels augmented cholesterol efflux to Apo-A1, suggesting retinoid-mediated efflux of cholesterol involves enhanced oxysterol production. Further studies revealed that retinoids activate the LXR regulated genes, sterol receptor-element binding protein-1c and ABCA1. These findings provide insights into the regulatory events in which retinoid signaling effectively enhances macrophage cholesterol efflux and indicate that retinoid therapy may have important implications in limiting and/or regressing atherosclerotic cardiovascular disease.

Prolonged in vivo administration of testosterone-enanthate, the widely used and abused anabolic androgenic steroid, disturbs prolactin and cAMP signaling in Leydig cells of adult rats

This study was designed to systematically analyze and define the effects of 1-day, 2-weeks, 10-weeks intramuscular administration of testosterone-enanthate, widely used and abused anabolic androgenic steroid (AAS), on main regulators of steroidogenesis and steroidogenic genes expression in testosterone-producing Leydig cells of adult rats. The results showed that prolonged (10-weeks) intramuscular administration of testosterone-enanthate, in clinically relevant dose, significantly increased prolactin, but decreased Prlr2 and Gnrhr in pituitary of adult rat. The levels of testosterone, Insl3, cAMP and mitochondrial membrane potential of Leydig cells were significantly reduced. This was followed by decreased expression of some steroidogenic enzymes and regulatory proteins such as Lhcgr, Prlr1/2, Tspo, Star, Cyp11a1, Cyp17a1, Dax1. Oppositely, Hsd3b1/2, Hsd3b5, Hsd17b4, Ar, Arr19 increased. In the same cells, transcriptional milieu of cAMP signaling elements was disturbed with remarkable up-regulation of PRKA (the main regulator of steroidogenesis). Increased prolactin together with stimulated transcription of Jak2/Jak3 could account for increased Hsd3b1/2 and Hsd3b5 in Leydig cells following 10-weeks in vivo treatment with testosterone-enanthate. In vitro studies revealed that testosterone is capable to increase level of Prlr1, Prlr2, Hsd3b1/2, Hsd3b5 in Leydig cells. Accordingly, testosterone-induced changes in prolactin receptor signaling together with up-regulation of PRKA, Hsd3b1/2, Hsd3b5, Ar in Leydig cells, could be the possible mechanism that contribute to the establishment of a new adaptive response to maintain homeostasis and prevent loss of steroidogenic function. Presented data provide new molecular insights into the relationship between disturbed testosterone homeostasis and mammalian reproduction and are important in terms of wide use and abuse of AASs and human reproductive health.

Molecular adaptations of testosterone-producing Leydig cells during systemic in vivo blockade of the androgen receptor

This study systematically evaluates the effects of androgen receptor (AR) blockade on molecular events in Leydig cells. Results showed that intramuscular administration of testosterone-enanthate, at clinically relevant dose, decreased testosterone in interstitial fluid and Leydig cells from adult rats. AR-blocker (Androcur) prevented this effect and testosterone-reduced Leydig cells steroidogenic capacity/activity. Testosterone-reduced expression of some steroidogenic enzymes/proteins (Tspo,StAR,Hsd3b1/2) and transcription factors (Nur77,Gata4,Dax1) was completely abrogated, while decreased expression of Star,Cyp11a1,Cyp17a1,Hsd17b4,Creb1a was partially prevented. In the same cells, increased expression of Hsd3b5/HSD3B and Ar/AR was abolished. Androcur-treatment abolished testosterone-reduced cAMP, coupled with a changed expressional milieu of cAMP signaling elements. Results from in vitro experiments suggest that some of these effects are testosterone-AR dependent, while others could be due to disturbed LH and/or other signals. Presented data provide new molecular insight into Leydig cells function and are important in terms of human reproductive health and the wide-spread use of Androcur as well as use/abuse of testosterone-enanthate.

Mitochondrial cholesterol accumulation in alcoholic liver disease: Role of ASMase and endoplasmic reticulum stress

Alcoholic liver disease (ALD) is a major cause of chronic liver disease and a growing health concern in theworld. While the pathogenesis of ALD is poorly characterized key players identified in experimental models and patients, such as perturbations in mitochondrial structure and function, selective loss of antioxidant defense and susceptibility to inflammatory cytokines, contribute to ALD progression. Both oxidative stress and mitochondrial dysfunction compromise essential cellular functions and energy generation and hence are important pathogenic mechanisms of ALD. An important process mediating the mitochondrial disruption induced by alcohol intake is the trafficking of cholesterol to mitochondria, mediated by acid sphingomyelinase-induced endoplasmic reticulum stress, which contributes to increased cholesterol synthesis and StARD1upregulation. Mitochondrial cholesterol accumulation not only sensitizes to oxidative stress but it can contribute to the metabolic reprogramming in ALD, manifested by activation of the hypoxia inducible transcription factor 1 and stimulation of glycolysis and lactate secretion. Thus, a better understanding of the mechanisms underlying alcohol-mediated mitochondrial impairment and oxidative stress may lead to the identification of novel treatments for ALD. The present review briefly summarizes current knowledge on the cellular and molecular mechanisms contributing to alcohol-induced mitochondrial dysfunction and cholesterol accumulation and provides insights for potential therapeutic targets in ALD.

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Alcohol perturbs mitochondria function, which modulates ROS generation and alcohol metabolism.

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Alcohol stimulates mitochondrial cholesterol (mChol) accumulation.

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MChol accumulation impairs mitochondrial function and mediates alcohol-induced lipotoxicity.

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ASMase promotes mitochondrial dysfunction by stimulating mChol loading.

Phospholipase D activity underlies very-low-density lipoprotein (VLDL)-induced aldosterone production in adrenal glomerulosa cells

Aldosterone is the mineralocorticoid responsible for sodium retention, thus increased blood volume and pressure. Excessive production of aldosterone results in high blood pressure as well as renal disease, stroke, and visual loss via both direct effects and effects on blood pressure. Weight gain is often associated with increased blood pressure, but it remains unclear how obesity increases blood pressure. Obese patients typically have higher lipoprotein levels; moreover, some studies have suggested that aldosterone levels are also elevated and represent a link between obesity and hypertension. Very-low-density lipoprotein (VLDL) functions to transport triglycerides from the liver to peripheral tissues. Although previous studies have demonstrated that VLDL can stimulate aldosterone production, the mechanisms underlying this effect are largely unclear. Here we show for the first time that phospholipase D (PLD) is involved in VLDL-induced aldosterone production in both a human adrenocortical cell line (HAC15) and primary cultures of bovine zona glomerulosa cells. Our data also reveal that PLD mediates steroidogenic acute regulatory (StAR) protein and aldosterone synthase (CYP11B2) expression via increasing the phosphorylation (activation) of their regulatory transcription factors. Finally, by using selective PLD inhibitors, our studies suggest that both PLD1 and PLD2 isoforms play an important role in VLDL-induced aldosterone production.

Estradiol modulates translocator protein (TSPO) and steroid acute regulatory protein (StAR) via protein kinase A (PKA) signaling in hypothalamic astrocytes

The ability of the central nervous system to synthesize steroid hormones has wide-ranging implications for physiology and pathology. Among the proposed roles of neurosteroids is the regulation of the LH surge. This involvement in the estrogen-positive feedback demonstrates the integration of peripheral steroids with neurosteroids. Within the female hypothalamus, estradiol from developing follicles stimulates progesterone synthesis in astrocytes, which activate neural circuits regulating gonadotropin (GnRH) neurons. Estradiol acts at membrane estrogen receptor-α to activate cellular signaling that results in the release of inositol trisphosphate-sensitive calcium stores that are sufficient to induce neuroprogesterone synthesis. The purpose of the present studies was to characterize the estradiol-induced signaling leading to activation of steroid acute regulatory protein (StAR) and transporter protein (TSPO), which mediate the rate-limiting step in steroidogenesis, ie, the transport of cholesterol into the mitochondrion. Treatment of primary cultures of adult female rat hypothalamic astrocytes with estradiol induced a cascade of phosphorylation that resulted in the activation of a calcium-dependent adenylyl cyclase, AC1, elevation of cAMP, and activation of both StAR and TSPO. Blocking protein kinase A activation with H-89 abrogated the estradiol-induced neuroprogesterone synthesis. Thus, together with previous results, these experiments completed the characterization of how estradiol action at the membrane leads to the augmentation of neuroprogesterone synthesis through increasing cAMP, activation of protein kinase A, and the phosphorylation of TSPO and StAR in hypothalamic astrocytes.

Protein kinase C and Src family kinases mediate angiotensin II-induced protein kinase D activation and acute aldosterone production

Recent evidence has shown a role for the serine/threonine protein kinase D (PKD) in the regulation of acute aldosterone secretion upon angiotensin II (AngII) stimulation. However, the mechanism by which AngII activates PKD remains unclear. In this study, using both pharmacological and molecular approaches, we demonstrate that AngII-induced PKD activation is mediated by protein kinase C (PKC) and Src family kinases in primary bovine adrenal glomerulosa cells and leads to increased aldosterone production. The pan PKC inhibitor Ro 31-8220 and the Src family kinase inhibitors PP2 and Src-1 inhibited both PKD activation and acute aldosterone production. Additionally, like the dominant-negative serine-738/742-to-alanine PKD mutant that cannot be phosphorylated by PKC, the dominant-negative tyrosine-463-to-phenylalanine PKD mutant, which is not phosphorylatable by the Src/Abl pathway, inhibited acute AngII-induced aldosterone production. Taken together, our results demonstrate that AngII activates PKD via a mechanism involving Src family kinases and PKC, to underlie increased aldosterone production.

Angiotensin II-induced protein kinase D activates the ATF/CREB family of transcription factors and promotes StAR mRNA expression

Aldosterone synthesis is initiated upon the transport of cholesterol from the outer to the inner mitochondrial membrane, where the cholesterol is hydrolyzed to pregnenolone. This process is the rate-limiting step in acute aldosterone production and is mediated by the steroidogenic acute regulatory (StAR) protein. We have previously shown that angiotensin II (AngII) activation of the serine/threonine protein kinase D (PKD) promotes acute aldosterone production in bovine adrenal glomerulosa cells, but the mechanism remains unclear. Thus, the purpose of this study was to determine the downstream signaling effectors of AngII-stimulated PKD activity. Our results demonstrate that overexpression of the constitutively active serine-to-glutamate PKD mutant enhances, whereas the dominant-negative serine-to-alanine PKD mutant inhibits, AngII-induced StAR mRNA expression relative to the vector control. PKD has been shown to phosphorylate members of the activating transcription factor (ATF)/cAMP response element binding protein (CREB) family of leucine zipper transcription factors, which have been shown previously to bind the StAR proximal promoter and induce StAR mRNA expression. In primary glomerulosa cells, AngII induces ATF-2 and CREB phosphorylation in a time-dependent manner. Furthermore, overexpression of the constitutively active PKD mutant enhances the AngII-elicited phosphorylation of ATF-2 and CREB, and the dominant-negative mutant inhibits this response. Furthermore, the constitutively active PKD mutant increases the binding of phosphorylated CREB to the StAR promoter. Thus, these data provide insight into the previously reported role of PKD in AngII-induced acute aldosterone production, providing a mechanism by which PKD may be mediating steroidogenesis in primary bovine adrenal glomerulosa cells.

Synergistic activation of steroidogenic acute regulatory protein expression and steroid biosynthesis by retinoids: involvement of cAMP/PKA signaling

Both retinoic acid receptors (RARs) and retinoid X receptors (RXRs) mediate the action of retinoids that play important roles in reproductive development and function, as well as steroidogenesis. Regulation of steroid biosynthesis is principally mediated by the steroidogenic acute regulatory protein (StAR); however, the modes of action of retinoids in the regulation of steroidogenesis remain obscure. In this study we demonstrate that all-trans retinoic acid (atRA) enhances StAR expression, but not its phosphorylation (P-StAR), and progesterone production in MA-10 mouse Leydig cells. Activation of the protein kinase A (PKA) cascade, by dibutyrl-cAMP or type I/II PKA analogs, markedly increased retinoid-responsive StAR, P-StAR, and steroid levels. Targeted silencing of endogenous RARα and RXRα, with small interfering RNAs, resulted in decreases in 9-cis RA-stimulated StAR and progesterone levels. Truncation of and mutational alterations in the 5'-flanking region of the StAR gene demonstrated the importance of the -254/-1-bp region in retinoid responsiveness. An oligonucleotide probe encompassing an RXR/liver X receptor recognition motif, located within the -254/-1-bp region, specifically bound MA-10 nuclear proteins and in vitro transcribed/translated RXRα and RARα in EMSAs. Transcription of the StAR gene in response to atRA and dibutyrl-cAMP was influenced by several factors, its up-regulation being dependent on phosphorylation of cAMP response-element binding protein (CREB). Chromatin immunoprecipitation studies revealed the association of phosphorylation of CREB, CREB binding protein, RXRα, and RARα to the StAR promoter. Further studies elucidated that hormone-sensitive lipase plays an important role in atRA-mediated regulation of the steroidogenic response that involves liver X receptor signaling. These findings delineate the molecular events by which retinoids influence cAMP/PKA signaling and provide additional and novel insight into the regulation of StAR expression and steroidogenesis in mouse Leydig cells.

Sustained in vivo blockade of α₁-adrenergic receptors prevented some of stress-triggered effects on steroidogenic machinery in Leydig cells

This study was designed to systematically analyze and evaluate the effects of in vivo blockade of α₁-adrenergic receptors (α₁-ADRs) on the stress-induced disturbance of steroidogenic machinery in Leydig cells. Parameters followed 1) steroidogenic enzymes/proteins, transcription factors, and cAMP/testosterone production; 2) the main hallmarks of stress (epinephrine, glucocorticoids); and 3) transcription profiles of ADRs and oxidases with high affinity to inactivate glucocorticoids. Results showed that sustained blockade of α₁-ADRs prevented stress-induced 1) decrease of the transcripts/proteins for main steroidogenic CYPs (CYP11A1, CYP17A1); 2) decrease of Scarb1 and Hsd3b1 transcripts; 3) decrease of transcript for Nur77, one of the main activator of the steroidogenic expression; and 4) increase of Dax1 and Arr19, the main steroidogenic repressors in Leydig cells. In the same cells, the expression of steroidogenic stimulatory factor Creb1, StAR, and androgen receptor increased. In this signaling scenario, stress-induced stimulation of Adra1a/Adra1b/Adrbk1 and Hsd11b2 (the unidirectional oxidase with high affinity to inactivate glucocorticoids) was not changed. Blockade additionally stimulated stress-increased transcription of the most abundantly expressed ADRs Adra1d/Adrb1/Adrb2 in Leydig cells. In the same cells, stress-decreased testosterone production, the main marker of Leydig cells functionality, was completely prevented, while reduction of cAMP, the main regulator of androgenesis, was partially prevented. Accordingly, the presented data provide a new molecular/transcriptional base for "fight/adaptation" of steroidogenic cells and new molecular insights into the role of α₁-ADRs in stress-impaired Leydig cell steroidogenesis. The results are important in term of wide use of α₁-ADR selective antagonists, alone/in combination, to treat high blood pressure, nightmares associated with posttraumatic stress disorder, and disrupted sexual health.

Regulation of adrenocortical steroid hormone production by RhoA-diaphanous 1 signaling and the cytoskeleton

The production of glucocorticoids and aldosterone in the adrenal cortex is regulated at multiple levels. Biosynthesis of these hormones is initiated when cholesterol, the substrate, enters the inner mitochondrial membrane for conversion to pregnenolone. Unlike most metabolic pathways, the biosynthesis of adrenocortical steroid hormones is unique because some of the enzymes are localized in mitochondria and others in the endoplasmic reticulum (ER). Although much is known about the factors that control the transcription and activities of the proteins that are required for steroid hormone production, the parameters that govern the exchange of substrates between the ER and mitochondria are less well understood. This short review summarizes studies that have begun to provide insight into the role of the cytoskeleton, mitochondrial transport, and the physical interaction of the ER and mitochondria in the production of adrenocortical steroid hormones.

Mechanisms of action of hormone-sensitive lipase in mouse Leydig cells: its role in the regulation of the steroidogenic acute regulatory protein

Hormone-sensitive lipase (HSL) catalyzes the hydrolysis of cholesteryl esters in steroidogenic tissues and, thus, facilitates cholesterol availability for steroidogenesis. The steroidogenic acute regulatory protein (StAR) controls the rate-limiting step in steroid biosynthesis. However, the modes of action of HSL in the regulation of StAR expression remain obscure. We demonstrate in MA-10 mouse Leydig cells that activation of the protein kinase A (PKA) pathway, by a cAMP analog Bt2cAMP, enhanced expression of HSL and its phosphorylation (P) at Ser-660 and Ser-563, but not at Ser-565, concomitant with increased HSL activity. Phosphorylation and activation of HSL coincided with increases in StAR, P-StAR (Ser-194), and progesterone levels. Inhibition of HSL activity by CAY10499 effectively suppressed Bt2cAMP-induced StAR expression and progesterone synthesis. Targeted silencing of endogenous HSL, with siRNAs, resulted in increased cholesteryl ester levels and decreased cholesterol content in MA-10 cells. Depletion of HSL affected lipoprotein-derived cellular cholesterol influx, diminished the supply of cholesterol to the mitochondria, and resulted in the repression of StAR and P-StAR levels. Cells overexpressing HSL increased the efficacy of liver X receptor (LXR) ligands on StAR expression and steroid synthesis, suggesting HSL-mediated steroidogenesis entails enhanced oxysterol production. Conversely, cells deficient in LXRs exhibited decreased HSL responsiveness. Furthermore, an increase in HSL was correlated with the LXR target genes, steroid receptor element-binding protein 1c and ATP binding cassette transporter A1, demonstrating HSL-dependent regulation of steroidogenesis predominantly involves LXR signaling. LXRs interact/cooperate with RXRs and result in the activation of StAR gene transcription. These findings provide novel insight and demonstrate the molecular events by which HSL acts to drive cAMP/PKA-mediated regulation of StAR expression and steroidogenesis in mouse Leydig cells.

Luteinizing hormone/human chorionic gonadotropin-mediated activation of mTORC1 signaling is required for androgen synthesis by theca-interstitial cells

LH triggers the biosynthesis of androgens in the theca-interstitial (T-I) cells of ovary through the activation of a cAMP-dependent pathway. We have previously shown that LH/human chorionic gonadotropin (hCG) activates mammalian target of rapamycin complex 1 (mTORC1) signaling network, leading to cell proliferation. In the present study, we provide evidence that the LH/hCG-mediated activation of the mTORC1 signaling cascade is involved in the regulation of steroidogenic enzymes in androgen biosynthesis. Treatment with LH/hCG increased the expression of downstream targets of mTORC1, ribosomal protein S6 kinase 1, and eukaryotic initiation factor 4E as well as steroidogenic enzymes. LH/hCG-mediated stimulation of the steroidogenic enzyme mRNA was blocked by the mTORC1 inhibitor, rapamycin. This inhibitory effect was selective because rapamycin failed to block hCG-mediated increase in the expression of Star mRNA levels. Furthermore, pharmacological targeting of mTORC1 with rapamycin also blocked LH/hCG- or forskolin-induced expression of cAMP response element-binding protein (CREB) and steroidogenic enzymes (P450 side-chain cleavage enzyme, 3β-hydroxysteroid dehydrogenase type 1, and 17α-hydroxylase/17,20 lyase) but produced no effect on steroidogenic acute regulatory protein levels. These results were further confirmed by demonstrating that the knockdown of mTOR using small interfering RNA selectively abrogated the LH/hCG-induced increase in steroidogenic enzyme expression, without affecting steroidogenic acute regulatory protein expression. LH/hCG-stimulated androgen production was also blocked by rapamycin. Furthermore, the pharmacological inhibition of mTORC1 or ribosomal protein S6 kinase 1 signaling prevented the LH/hCG-induced phosphorylation of CREB. Chromatin immunoprecipitation assays revealed the association of CREB with the proximal promoter of the Cyp17a1 gene in response to hCG, and this association was reduced by rapamycin treatment. Taken together, our findings show for the first time that LH/hCG-mediated activation of androgen biosynthesis is regulated by the mTORC1 signaling pathway in T-I cells.

Repeated immobilization stress disturbed steroidogenic machinery and stimulated the expression of cAMP signaling elements and adrenergic receptors in Leydig cells

This study was designed to evaluate the effect of acute (2 h daily) and repeated (2 h daily for 2 or 10 consecutive days) immobilization stress (IMO) on: 1) the steroidogenic machinery homeostasis; 2) cAMP signaling; and the expression of receptors for main markers of 3) adrenergic and 4) glucocorticoid signaling in Leydig cells of adult rats. The results showed that acute IMO inhibited steroidogenic machinery in Leydig cells by downregulation of Scarb1 (scavenger receptor class B), Cyp11a1 (cholesterol side-chain cleavage enzyme), Cyp17a1 (17α-hydroxylase/17,20 lyase), and Hsd17b3 (17β-hydroxysteroid dehydrogenase) expression. In addition to acute IMO effects, repeated IMO increased transcription of Star (steroidogenic acute regulatory protein) and Arr19 (androgen receptor corepressor 19 kDa) in Leydig cells. In the same cells, the transcription of adenylyl cyclases (Adcy7, Adcy9, Adcy10) and cAMP-specific phosphodiesterases (Pde4a, Pde4b, Pde4d, Pde7a, Pde8a) was stimulated, whereas the expression of the genes encoding protein kinase A subunits were unaffected. Ten times repeated IMO increased the levels of all adrenergic receptors and β-adrenergic receptor kinase (Adrbk1) in Leydig cells. The transcription analysis was supported by cAMP/testosterone production. In this signaling scenario, partial recovery of testosterone production in medium/content was detected. The physiological significance of the present results was proven by ex vivo application of epinephrine, which increased cAMP/testosterone production by Leydig cells from control rats in greater fashion than from stressed. IMO did not affect the expression of transcripts for Crhr1/Crhr2 (corticotropin releasing hormone receptors), Acthr (adrenocorticotropin releasing hormone receptor), Gr (glucocorticoid receptor), and Hsd11b1 [hydroxysteroid (11-β) dehydrogenase 1], while all types of IMO stimulated the expression of Hsd11b2, the unidirectional oxidase with high affinity to inactivate glucocorticoids. Thus, presented data provide new molecular/transcriptional base for "fight/adaptation" of Leydig cells and new insights into the role of cAMP, epinephrine, and glucocorticoid signaling in recovery of stress-impaired Leydig cell steroidogenesis.

Acute and chronic regulation of aldosterone production

Aldosterone is the major mineralocorticoid synthesized by the adrenal and plays an important role in the regulation of systemic blood pressure through the absorption of sodium and water. Aldosterone production is regulated tightly by selective expression of aldosterone synthase (CYP11B2) in the adrenal outermost zone, the zona glomerulosa. Angiotensin II (Ang II), potassium (K(+)) and adrenocorticotropin (ACTH) are the main physiological agonists which regulate aldosterone secretion. Aldosterone production is regulated within minutes of stimulation (acutely) through increased expression and phosphorylation of the steroidogenic acute regulatory (StAR) protein and over hours to days (chronically) by increased expression of the enzymes involved in the synthesis of aldosterone, particularly CYP11B2. Imbalance in any of these processes may lead to several disorders of aldosterone excess. In this review we attempt to summarize the key molecular events involved in the acute and chronic phases of aldosterone secretion.

Sphingosine-1-phosphate rapidly increases cortisol biosynthesis and the expression of genes involved in cholesterol uptake and transport in H295R adrenocortical cells

In the acute phase of adrenocortical steroidogenesis, adrenocorticotrophin (ACTH) activates a cAMP/PKA-signaling pathway that promotes the transport of free cholesterol to the inner mitochondrial membrane. We have previously shown that ACTH rapidly stimulates the metabolism of sphingolipids and the secretion of sphingosine-1-phosphate (S1P) in H295R cells. In this study, we examined the effect of S1P on genes involved in the acute phase of steroidogenesis. We show that S1P increases the expression of steroidogenic acute regulatory protein (StAR), 18-kDa translocator protein (TSPO), low-density lipoprotein receptor (LDLR), and scavenger receptor class B type I (SR-BI). S1P-induced StAR mRNA expression requires Gα(i) signaling, phospholipase C (PLC), Ca(2+)/calmodulin-dependent kinase II (CamKII), and ERK1/2 activation. S1P also increases intracellular Ca(2+), the phosphorylation of hormone sensitive lipase (HSL) at Ser(563), and cortisol secretion. Collectively, these findings identify multiple roles for S1P in the regulation of glucocorticoid biosynthesis.