Steroidogenesis entails processes by which cholesterol is converted to biologically active steroid hormones. Whereas most endocrine texts discuss adrenal, ovarian, testicular, placental, and other steroidogenic processes in a gland-specific fashion, steroidogenesis is better understood as a single process that is repeated in each gland with cell-type-specific variations on a single theme. Thus, understanding steroidogenesis is rooted in an understanding of the biochemistry of the various steroidogenic enzymes and cofactors and the genes that encode them. The first and rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone by a single enzyme, P450scc (CYP11A1), but this enzymatically complex step is subject to multiple regulatory mechanisms, yielding finely tuned quantitative regulation. Qualitative regulation determining the type of steroid to be produced is mediated by many enzymes and cofactors. Steroidogenic enzymes fall into two groups: cytochrome P450 enzymes and hydroxysteroid dehydrogenases. A cytochrome P450 may be either type 1 (in mitochondria) or type 2 (in endoplasmic reticulum), and a hydroxysteroid dehydrogenase may belong to either the aldo-keto reductase or short-chain dehydrogenase/reductase families. The activities of these enzymes are modulated by posttranslational modifications and by cofactors, especially electron-donating redox partners. The elucidation of the precise roles of these various enzymes and cofactors has been greatly facilitated by identifying the genetic bases of rare disorders of steroidogenesis. Some enzymes not principally involved in steroidogenesis may also catalyze extraglandular steroidogenesis, modulating the phenotype expected to result from some mutations. Understanding steroidogenesis is of fundamental importance to understanding disorders of sexual differentiation, reproduction, fertility, hypertension, obesity, and physiological homeostasis.

The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders.

The primary function of the corpus luteum is secretion of the hormone progesterone, which is required for maintenance of normal pregnancy in mammals. The corpus luteum develops from residual follic...

https://www.physiology.org/doi/pdf/10.1152/physrev.2000.80.1.1

Mechanisms Controlling the Function and Life Span of the Corpus Luteum

Steroid hormone biosynthesis is acutely regulated by pituitary trophic hormones and other steroidogenic stimuli. This regulation requires the synthesis of a protein whose function is to translocate cholesterol from the outer to the inner mitochondrial membrane in steroidogenic cells, the rate-limiting step in steroid hormone formation. The steroidogenic acute regulatory (StAR) protein is an indispensable component in this process and is the best candidate to fill the role of the putative regulator. StAR is expressed in steroidogenic tissues in response to agents that stimulate steroid production, and mutations in the StAR gene result in the disease congenital lipoid adrenal hyperplasia, in which steroid hormone biosynthesis is severely compromised. The StAR null mouse has a phenotype that is essentially identical to the human disease. The positive and negative expression of StAR is sensitive to agents that increase and inhibit steroid biosynthesis respectively. The mechanism by which StAR mediates cholesterol transfer in the mitochondria has not been fully characterized. However, the tertiary structure of the START domain of a StAR homolog has been solved, and identification of a cholesterol-binding hydrophobic tunnel within this domain raises the possibility that StAR acts as a cholesterol-shuttling protein.

StAR Protein and the Regulation of Steroid Hormone Biosynthesis

Context: The cause of declining testosterone (T) in aging men and their relationships with risk factors are unclear. Objective: The objective of the study was to investigate the relationships between lifestyle and health with reproductive hormones in aging men. Design: This was a baseline cross-sectional survey on 3200 community-dwelling men aged 40–79 yr from a prospective cohort study in eight European countries. Results: Four predictors were associated with distinct modes of altered function: 1) age: lower free T (FT; −3.12 pmol/liter·yr, P < 0.001) with raised LH, suggesting impaired testicular function; 2) obesity: lower total T (TT; −2.32 nmol/liter) and FT (−17.60 pmol/liter) for body mass index (BMI; ≥ 25 to < 30 kg/m2) and lower TT (−5.09 nmol/liter) and FT (−53.72 pmol/liter) for BMI 30 kg/m2 or greater (P < 0.001–0.01, referent: BMI < 25 kg/m2) with unchanged/decreased LH, indicating hypothalamus/pituitary dysfunction; 3) comorbidity: lower TT (−0.80 nmol/liter, P < 0.01) with unchanged LH in y...

Hypothalamic-pituitary-testicular axis disruptions in older men are differentially linked to age and modifiable risk factors: the European Male Aging Study.

In Westernized societies, average consumption of n-6 polyunsaturated fatty acids (PUFAs) far exceeds nutritional requirements. The ratio of n-6 to n-3 PUFAs is generally >10:1 whereas on a primitive human diet it was closer to 1:1. Diets fed to intensively farmed livestock have followed a similar trend. Both n-6 and n-3 PUFAs can influence reproductive processes through a variety of mechanisms. They provide the precursors for prostaglandin synthesis and can modulate the expression patterns of many key enzymes involved in both prostaglandin and steroid metabolism. They are essential components of all cell membranes. The proportions of different PUFAs in tissues of the reproductive tract reflect dietary consumption. PUFA supplements (particularly n-3 PUFAs in fish oil) are promoted for general health reasons. Fish oils may also benefit fertility in cattle and reduce the risk of preterm labor in women, but in both cases current evidence to support this is inconclusive. Gamma-linolenic acid containing oils can alter the types of prostaglandins produced by cells in vitro, but published data to support claims relating to effects on reproductive health are lacking. Spermatozoa require a high PUFA content to provide the plasma membrane with the fluidity essential at fertilization. However, this makes spermatozoa particularly vulnerable to attack by reactive oxygen species, and lifestyle factors promoting oxidative stress have clear associations with reduced fertility. Adequately powered trials that control for the ratios of different PUFAs consumed are required to determine the extent to which this aspect of our diets does influence our fertility.

https://bioone.org/journals/biology-of-reproduction/volume-77/issue-2/biolreprod.107.060558/Polyunsaturated-Fatty-Acids-in-Male-and-Female-Reproduction1/10.1095/biolreprod.107.060558.pdf

Polyunsaturated Fatty Acids in Male and Female Reproduction

Steroid hormone biosynthesis in steroidogenic cells is regulated through trophic hormone activation of protein kinase A (PKA) signaling pathways. However, many examples of the regulation of steroid synthesis via pathways other than the PKA pathway have been documented. In some cases these pathways act independently of PKA activation whereas in other cases, they act synergistically with it. The current understanding of additional signaling pathways and factors, such as the protein kinase C pathway, arachidonic acid metabolites, growth factors, chloride ion, the calcium messenger system, and others capable of regulating/modulating steroid hormone biosynthesis, and in many cases steroidogenic acute regulatory protein expression, are discussed in this review.

/pdf/multiple-signaling-pathways-regulating-steroidogenesis-and-3yqev428ss.pdf

Multiple Signaling Pathways Regulating Steroidogenesis and Steroidogenic Acute Regulatory Protein Expression: More Complicated than We Thought

The role of arachidonic acid in steroidogenesis and steroidogenic acute regulatory (StAR) gene and protein expression.

Involvement of multiple transcription factors in the regulation of steroidogenic acute regulatory protein gene expression.

It has been proposed that the steroidogenic acute regulatory (StAR) protein controls hormone-stimulated steroid production by mediating cholesterol transfer to the mitochondrial inner membrane. This study was conducted to determine the effect of wild-type StAR and several modified forms of StAR on intramitochondrial cholesterol transfer. Forty-seven N-terminal or 28 C-terminal amino acids of the StAR protein were removed, and COS-1 cells were transfected with pCMV vector only, wild-type StAR, N-47, or the C-28 constructs. Lysates from the transfected COS-1 cells were then incubated with mitochondria from MA-10 mouse Leydig tumor cells that were preloaded with [3H]cholesterol. After incubation, mitochondria were collected and fractionated on sucrose gradients into outer membranes, inner membranes, and membrane contact sites, and [3H]cholesterol content was determined in each membrane fraction. Incubation of MA-10 mitochondria with wild-type StAR containing cell lysate resulted in a significant 34.9% increase in [3H]cholesterol content in contact sites and a significant 32.8% increase in inner mitochondrial membranes. Incubations with cell lysate containing N-47 StAR protein also resulted in a 16.4% increase in [3H]cholesterol in contact sites and a significant 26.1% increase in the inner membrane fraction. In contrast, incubation with the C-28 StAR protein had no effect on cholesterol transfer. The cholesterol-transferring activity of the N-47 truncation, in contrast to that of the C-28 mutant, was corroborated when COS-1 cells were cotransfected with F2 vector (containing cytochrome P450 side-chain cleavage enzyme, ferridoxin, and ferridoxin reductase) and either pCMV empty vector or the complementary DNAs of wild-type StAR, N-47 StAR, or C-28 StAR. Pregnenolone production was significantly increased in both wild-type and N-47-transfected cells, whereas that in C-28-transfected cells was similar to the control value. Finally, immunolocalization studies with confocal image and electron microscopy were performed to determine the cellular location of StAR and its truncated forms in transfected COS-1 cells. The results showed that wild-type and most of the C-28 StAR protein were imported into the mitochondria, whereas most of N-47 protein remained in the cytosol. These studies demonstrate a direct effect of StAR protein on cholesterol transfer to the inner mitochondrial membrane, that StAR need not enter the mitochondria to produce this transfer, and the importance of the C-terminus of StAR in this process.

/pdf/effect-of-truncated-forms-of-the-steroidogenic-acute-tjdcweg3ck.pdf

Effect of truncated forms of the steroidogenic acute regulatory protein on intramitochondrial cholesterol transfer.

The age-related decline in testosterone biosynthesis in testicular Leydig cells has been well documented, but the mechanisms involved in the decline are not clear Recent studies have described a cyclooxygenase-2 (COX2)-dependent tonic inhibition of Leydig cell steroidogenesis and expression of the steroidogenic acute regulatory protein (StAR) The present study was conducted to determine whether COX2 protein increases with age in rat Leydig cells and whether COX2 plays a role in the age-related decline in testosterone biosynthesis Our results indicate that from 3 months of age to 30 months, COX2 protein in aged rat Leydig cells increased by 346% over that of young Leydig cells, StAR protein decreased to 33%, and blood testosterone concentration and testosterone biosynthesis in Leydig cells decreased to 41 and 33%, respectively Further experiments demonstrated that overexpressing COX2 in MA-10 mouse Leydig cells inhibited StAR gene expression and steroidogenesis and that the inhibitory effects of COX2 could be reversed by blocking COX2 activity Notably, incubation of aged Leydig cells with the COX2 inhibitor NS398 enhanced their testosterone biosynthesis Blood testosterone concentrations in aged rats fed the COX2 inhibitor DFU, at doses of 5, 10, 15, and 20 mg/kg body weight per day were increased by 15, 23, 56, and 120%, respectively, over the levels in the rats receiving no DFU The present study suggests a novel mechanism in male aging involving COX2 and a potential application of the mechanism to delay the age-related decline in testosterone biosynthesis

/pdf/cyclooxygenase-2-regulation-of-the-age-related-decline-in-3coqio3wxw.pdf

XingJia Wang

Papers

Multiple Signaling Pathways Regulating Steroidogenesis and Steroidogenic Acute Regulatory Protein Expression: More Complicated than We Thought

The role of arachidonic acid in steroidogenesis and steroidogenic acute regulatory (StAR) gene and protein expression.

Involvement of multiple transcription factors in the regulation of steroidogenic acute regulatory protein gene expression.

Effect of truncated forms of the steroidogenic acute regulatory protein on intramitochondrial cholesterol transfer.

Cyclooxygenase-2 regulation of the age-related decline in testosterone biosynthesis.