Postprandial lipid and vascular responses following consumption of a commercially-relevant interesterified palmitic acid-rich spread in comparison to functionally-equivalent non-interesterified spread and spreadable butter: a randomised controlled trial in healthy adults

Background: Interesterification is an industrial processing technique used widely where hard fats are essential for functionality and consumer acceptability, e.g. margarines and lower fat spreads. Objective: The aim of this study was to compare acute cardiovascular effects of functionally equivalent spreads (similar solid fat content) made with interesterified (IE) or non-IE palm-based fats, or spreadable butter. Methods: A randomised, controlled, 4-armed crossover, double-blind study (25 men, 25 women; 35-75 years; healthy; mean BMI 24.5, SD 3.8), compared effects of mixed nutrient meals containing 50 g fat from functionally equivalent products [IE spread, non-IE spread and spreadable butter (SB), with rapeseed oil (RO) as a reference treatment: with 16.7%, 27.9%, 19.3% and 4% palmitic acid, respectively] on 8 h postprandial changes in plasma triacylglycerol (TAG) and endothelial dysfunction (flow-mediated dilatation; FMD). Circulating reactive oxygen species (estimated using a neutrophil oxidative burst assay), glucose, insulin, NEFA, lipoprotein particle profiles, inflammatory markers (glycoprotein acetylation (Glyc-A) and IL-6), and biomarkers of endotoxemia were measured. Results: Postprandial plasma TAG concentrations after test meals were similar. However following RO versus the 3 spreads, there were significantly higher postprandial apolipoprotein B concentrations, and small HDL and LDL particle concentrations, and lower postprandial extra-large, large, and medium HDL particle concentrations, as well as smaller average HDL and LDL particle sizes. There were no differences following IE compared to the other spreads. Postprandial FMD% did not decrease after high-fat test meals, and there were no differences between treatments. Postprandial serum IL-6 increased similarly after test meals, but RO provoked a greater increase in postprandial concentrations of glycoprotein acetyls (GlycA), as well as 8 h sCD14, an endotoxemia marker. All other postprandial outcomes were not different between treatments. Conclusions: In healthy adults, a commercially-available IE-based spread did not evoke a different postprandial triacylglycerol, lipoprotein subclass, oxidative stress, inflammatory or endotoxemic response to functionally-equivalent, but compositionally-distinct alternative spreads. Clinical trial registry number: NCT03438084 (https://ClinicalTrials.gov).

Inhibition of intestinal FXR activity as a possible mechanism for the beneficial effects of a probiotic mix supplementation on lipid metabolism alterations and weight gain in mice fed a high fat diet

Supplementation with probiotics has emerged as a promising therapeutic tool to manage metabolic diseases. We investigated the effects of a mix of Bifidobacterium animalis subsp. lactis LA804 and Lactobacillus gasseri LA806 on high-fat (HF) diet -induced metabolic disease in mice. Supplementation with the probiotic mix in HF diet-fed mice (HF-Pr2) reduced weight and fat mass gains, decreased hepatic lipid accumulation, and lowered plasma triglyceride peak during an oral lipid tolerance test. At the molecular level, the probiotic mix protected against HF-induced rise in mRNA levels of genes related to lipid uptake, metabolism, and storage in the liver and white adipose tissues, and strongly decreased mRNA levels of genes related to inflammation in the white adipose tissue and to oxidative stress in the liver. Regarding intestinal homeostasis, the probiotic mix did not prevent HF-induced gut permeability but slightly modified microbiota composition without correcting the dysbiosis induced by the HF diet. Probiotic supplementation also modified the cecal bile acid (BA) profile, leading to an increase in the Farnesoid-X-Receptor (FXR) antagonist/agonist ratio between BA species. In agreement, HF-Pr2 mice exhibited a strong inhibition of FXR signaling pathway in the ileum, which was associated with lipid metabolism protection. This is consistent with recent reports proposing that inhibition of intestinal FXR activity could be a potent mechanism to overcome metabolic disorders. Altogether, our results demonstrate that the probiotic mix evaluated, when administered preventively to HF diet-fed mice could limit obesity and associated lipid metabolism disorders, likely through the inhibition of FXR signaling in the intestinal tract.

Role of circulating sphingolipids in lipid metabolism: Why dietary lipids matter

Sphingolipids are structural components of cell membranes and lipoproteins but also act as signaling molecules in many pathophysiological processes. Although sphingolipids comprise a small part of the plasma lipidome, some plasma sphingolipids are recognized as implicated in the development of metabolic diseases and cardiovascular diseases. Plasma sphingolipids are mostly carried out into lipoproteins and may modulate their functional properties. Lipids ingested from the diet contribute to the plasma lipid pool besides lipids produced by the liver and released from the adipose tissue. Depending on their source, quality and quantity, dietary lipids may modulate sphingolipids both in plasma and lipoproteins. A few human dietary intervention studies investigated the impact of dietary lipids on circulating sphingolipids and lipid-related cardiovascular risk markers. On the one hand, dietary saturated fatty acids, mainly palmitic acid, may increase ceramide concentrations in plasma, triglyceride-rich lipoproteins and HDL. On the other hand, milk polar lipids may decrease some molecular species of sphingomyelins and ceramides in plasma and intestine-derived chylomicrons. Altogether, different dietary fatty acids and lipid species can modulate circulating sphingolipids vehicled by postprandial lipoproteins, which should be part of future nutritional strategies for prevention of cardiovascular diseases.

Rapeseed and Soy Lecithin As Food Additives Vectors of α-Linolenic Acid: Impacts on High-Fat Induced Adiposity, Inflammation and Gut Microbiota in Mice

Objectives

Dietary synthetic emulsifiers have recently been shown to promote metabolic syndrome and alter gut microbiota. The effects of natural emulsifiers, such as vegetable lecithin, remain, however, poorly described. Our objective was to evaluate, in mice, the impact of soy and rapeseed lecithin, both rich in essential α-linolenic acid (ALA), when incorporated in high-fat (HF) Western diets on the bioavailability of ALA, as well as on HF-induced adiposity, inflammation and gut microbiota.

Methods

For 13 weeks, male Swiss mice (n = 72) were fed either a standard Chow diet, a control semi-synthetic HF-diet (25 wt% lipids) poor in ALA (HFC), or different ALA-enriched (4.7% of total fatty acids) HF-diets containing 0% lecithin (HFA-L0), a nutritional dose of soy or rapeseed lecithin (10 wt% of lipids; HFA-SL10, HFA-RL10), or a 20 wt% supplemental dose of RL (HFA-RL20). Histomorphology of the epididymal adipose tissue (EAT) was analysed; hepatic lipid composition was determined by GC-FID, gene expression by RT-PCR, and faecal microbiota composition by 16S sequencing.

Results

Within ALA-rich HF diets, the hepatic bioavailability of ALA was similar whether ALA was vectorised as lecithin (HFA-RL10, HFA-RL20, HFA-SL10) or as oil only (HFA-L0) (yet, all higher than HFC). Similarly to HFC, HFA-SL10 and HFA-RL20, but not HFA-RL10, increased body weight gain (P < 0.001), visceral adiposity (P < 0.001) and adipocyte hypertrophy (P < 0.05), compared to Chow. The addition of lecithin in HF-diets, regardless of origin or dose, cancelled the anti-inflammatory effect of ALA observed in HFA-L0 on the expression of genes involved in macrophage infiltration in the EAT (e.g., Tnfα, Cd11c). Only HFA-RL10 increased gut microbiota α-diversity compared to HFC (P < 0.05), and altered the abundance of several gut bacterial groups, such as Lachnospiraceae and Desulfovibrionaceae.

Conclusions

Although the incorporation of neither soy nor rapeseed lecithin in HF-diets improved ALA hepatic bioavailability, the two lecithins exerted differential metabolic effects in mice. At a nutritional dose, rapeseed lecithin, unlike soy lecithin, did not significantly enhance visceral adiposity comparatively to a Chow diet, and increased gut bacterial diversity. Rapeseed lecithin may therefore be considered as a promising food ingredient.

Funding Sources

ANRT CIFRE PhD grant (UMT ACTIA BALI).

Human milk pasteurisation reduces pre-lipolysis but not digestive lipolysis and moderately decreases intestinal lipid uptake in a combination of preterm infant in vitro models

Donor human milk, pasteurised for safety reasons, is the first alternative for feeding preterm infants when mothers' own milk is unavailable. Breastmilk pasteurisation impact on lipid digestion and absorption was evaluated by a static in vitro digestion model for preterm infants coupled with intestinal absorption using Caco-2/TC7 cells. Lipid absorption was quantified by digital image analysis of lipid droplets, by measurement of basolateral triglyceride concentration and by analysing the expression of major genes involved. After in vitro digestion, lipolysis extent was 13% lower in pasteurised human milk (PHM) than in raw human milk (RHM). In Caco-2/TC7 cells, the number of lipid droplets was identical for both milk types, while the mean droplet area was 17% smaller with PHM. Altogether, pasteurisation decreased the pre-lipolysis of human milk. This initial difference in free fatty acid amount was only partially buffered by the subsequent processes of in vitro digestion and cellular lipid absorption.

Dietary emulsifiers from milk and soybean differently impact adiposity and inflammation in association with modulation of colonic goblet cells in high-fat fed mice

SCOPE

Enhanced adiposity and metabolic inflammation are major features of obesity that could be impacted by dietary emulsifiers. We investigated in high-fat fed mice the effects of using a new polar lipid (PL) emulsifier from milk (MPL) instead of soybean lecithin (soybean PL [SPL]) on adipose tissue and intestinal mucosa function.

METHODS AND RESULTS

Four groups of C57BL6 mice received for 8 wks a low-fat (LF) diet or a high-fat diet devoid of PLs or an high-fat diet including MPL (high-fat-MPL) or SPL (high-fat-SPL). Compared with high-fat diet, high-fat-SPL diet increased white adipose tissue (WAT) mass (p < 0.05), with larger adipocytes (p < 0.05) and increased expression of tumor necrosis factor alpha, monochemoattractant protein-1, LPS-binding protein, and leptin (p < 0.05). This was not observed with high-fat-MPL diet despite similar dietary intakes and increased expression of fatty acid transport protein 4 and microsomal TG transfer protein, involved in lipid absorption, in upper intestine (p < 0.05). High-fat-MPL mice had a lower expression in WAT of cluster of differentiation 68, marker of macrophage infiltration, versus high-fat and high-fat-SPL mice (p < 0.05), and more goblet cells in the colon (p < 0.05).

CONCLUSIONS

Unlike SPL, MPL in the high-fat diet did not induce WAT hypertrophy and inflammation but increased colonic goblet cells. This supports further clinical exploration of different sources of dietary emulsifiers in the frame of obesity outbreak.

Milk Polar Lipids Affect In Vitro Digestive Lipolysis and Postprandial Lipid Metabolism in Mice

BACKGROUND

Polar lipid (PL) emulsifiers such as milk PLs (MPLs) may affect digestion and subsequent lipid metabolism, but focused studies on postprandial lipemia are lacking.

OBJECTIVE

We evaluated the impact of MPLs on postprandial lipemia in mice and on lipid digestion in vitro.

METHODS

Female Swiss mice were gavaged with 150 μL of an oil-in-water emulsion stabilized with 5.7 mg of either MPLs or soybean PLs (SPLs) and killed after 1, 2, or 4 h. Plasma lipids were quantified and in the small intestine, gene expression was analyzed by reverse transcriptase-quantitative polymerase chain reaction. Emulsions were lipolyzed in vitro using a static human digestion model; triglyceride (TG) disappearance was followed by thin-layer chromatography.

RESULTS

In mice, after 1 h, plasma TGs tended to be higher in the MPL group than in the SPL group (141 μg/mL vs. 90 μg/mL; P = 0.07) and nonesterified fatty acids (NEFAs) were significantly higher (64 μg/mL vs. 44 μg/mL; P < 0.05). The opposite was observed after 4 h with lower TGs (21 μg/mL vs. 35 μg/mL; P < 0.01) and NEFAs (20 μg/mL vs. 32 μg/mL; P < 0.01) in the MPL group compared with the SPL group. This was associated at 4 h with a lower gene expression of apolipoprotein B (Apob) and Secretion Associated, Ras related GTPase 1 gene homolog B (Sar1b), in the duodenum of MPL mice compared with SPL mice (P < 0.05). In vitro, during the intestinal phase, TGs were hydrolyzed more in the MPL emulsion than in the SPL emulsion (decremental AUCs were 1750%/min vs. 180%/min; P < 0.01). MPLs enhance lipid intestinal hydrolysis and promote more rapid intestinal lipid absorption and sharper kinetics of lipemia.

CONCLUSIONS

Postprandial lipemia in mice can be modulated by emulsifying with MPLs compared with SPLs, partly through differences in chylomicron assembly, and TG hydrolysis rate as observed in vitro. MPLs may thereby contribute to the long-term regulation of lipid metabolism.

A gut-brain neural circuit controlled by intestinal gluconeogenesis is crucial in metabolic health

Objectives

Certain nutrients positively regulate energy homeostasis via intestinal gluconeogenesis (IGN). The objective of this study was to evaluate the impact of a deficient IGN in glucose control independently of nutritional environment.

Methods

We used mice deficient in the intestine glucose-6 phosphatase catalytic unit, the key enzyme of IGN (I-G6pc^−/− mice). We evaluated a number of parameters involved in energy homeostasis, including insulin sensitivity (hyperinsulinemic euglycaemic clamp), the pancreatic function (insulin secretion in vivo and in isolated islets) and the hypothalamic homeostatic function (leptin sensitivity).

Results

Intestinal-G6pc^−/− mice exhibit slight fasting hyperglycaemia and hyperinsulinemia, glucose intolerance, insulin resistance and a deteriorated pancreatic function, despite normal diet with no change in body weight. These defects evoking type 2 diabetes (T2D) derive from the basal activation of the sympathetic nervous system (SNS). They are corrected by treatment with an inhibitor of α-2 adrenergic receptors. Deregulation in a key target of IGN, the homeostatic hypothalamic function (highlighted here through leptin resistance) is a mechanistic link. Hence the leptin resistance and metabolic disorders in I-G6pc^−/− mice are corrected by rescuing IGN by portal glucose infusion. Finally, I-G6pc^−/− mice develop the hyperglycaemia characteristic of T2D more rapidly under high fat/high sucrose diet.

Conclusions

Intestinal gluconeogenesis is a mandatory function for the healthy neural control of glucose homeostasis.

Intestinal gluconeogenesis is crucial to maintain a physiological fasting glycemia in the absence of hepatic glucose production in mice

OBJECTIVE

Similar to the liver and kidneys, the intestine has been strongly suggested to be a gluconeogenic organ. However, the precise contribution of the intestine to endogenous glucose production (EGP) remains to be determined. To define the quantitative role of intestinal gluconeogenesis during long-term fasting, we compared changes in blood glucose during prolonged fasting in mice with a liver-deletion of the glucose-6 phosphatase catalytic (G6PC) subunit (LKO) and in mice with a combined deletion of G6PC in both the liver and the intestine (ILKO).

MATERIALS/METHODS

The LKO and ILKO mice were studied after 6h and 40 h of fasting by measuring metabolic and hormonal plasmatic parameters, as well as the expression of gluconeogenic enzymes in the liver, kidneys and intestine.

RESULTS

After a transient hypoglycemic episode (approximately 60 mg/dL) because of their incapacity to mobilize liver glycogen, the LKO mice progressively re-increased their plasma glucose to reach a glycemia comparable to that of wild-type mice (90 mg/dL) from 30 h of fasting. This increase was associated with a rapid induction of renal and intestinal gluconeogenic gene expression, driven by glucagon, glucocorticoids and acidosis. The ILKO mice exhibited a similar induction of renal gluconeogenesis. However, these mice failed to re-increase their glycemia and maintained a plasma glucose level of only 60 mg/dL throughout the 48 h-fasting period.

CONCLUSIONS

These data indicate that intestinal glucose production is essential to maintain glucose homeostasis in the absence of hepatic glucose production during fasting. These data provide a definitive quantitative estimate of the capacity of intestinal gluconeogenesis to sustain EGP during long-term fasting.

Targeted deletion of liver glucose-6 phosphatase mimics glycogen storage disease type 1a including development of multiple adenomas

BACKGROUND AND AIMS

Glycogen storage disease type 1a (GSD1a) is an inherited disease caused by a deficiency in the catalytic subunit of the glucose-6 phosphatase enzyme (G6Pase). GSD1a is characterized by hypoglycaemia, hyperlipidemia, and lactic acidosis with associated hepatic (including hepatocellular adenomas), renal, and intestinal disorders. A total G6pc (catalytic subunit of G6Pase) knock-out mouse model has been generated that mimics the human pathology. However, these mice rarely live longer than 3 months and long-term liver pathogenesis cannot be evaluated. Herein, we report the long-term characterization of a liver-specific G6pc knock-out mouse model (L-G6pc(-/-)).

METHODS

We generated L-G6pc(-/-) mice using an inducible CRE-lox strategy and followed up the development of hepatic tumours using magnetic resonance imaging.

RESULTS

L-G6pc(-/-) mice are viable and exhibit normoglycemia in the fed state. They develop hyperlipidemia, lactic acidosis, and uricemia during the first month after gene deletion. However, these plasmatic parameters improved after 6 months. L-G6pc(-/-) mice develop hepatomegaly with glycogen accumulation and hepatic steatosis. Using an MRI approach, we could detect hepatic nodules with diameters of less than 1 mm, 9 months after induction of deficiency. Hepatic nodules (1 mm) were detected in 30-40% of L-G6pc(-/-) mice at 12 months. After 18 months, all L-G6pc(-/-) mice developed multiple hepatocellular adenomas of 1-10 mm diameter.

CONCLUSIONS

This is the first report of a viable animal model of the hepatic pathology of GSD1a, including the late development of hepatocellular adenomas.

Expression of the human melanocortin-2 receptor in different eukaryotic cells

The human melanocortin-2 receptor (hMC2R) is mainly present in the adrenal cortex and has been difficult to express in heterologous cells. The hMC2R fused to the EGFP at its C-terminus has been stably transfected in the murine M3 melanoma and HEK293 cells. In the M3 cells, the hMC2R-EGFP was well-addressed to the cell membrane and functional whereas in the HEK293 cells, the hMC2R-EGFP was retained intracellularly. These results suggest that some specific factors, missing in cells, which do not express any melanocortin receptor, are involved in the correct addressing of the hMC2R to the cell membrane.

Volume-sensitive Cl- current in bovine adrenocortical cells: comparison with the ACTH-induced Cl- current

In a previous study performed on zona fasciculata (ZF) cells isolated from calf adrenal glands, we identified an ACTH-induced Cl- current involved in cell membrane depolarization. In the present work, we describe a volume-sensitive Cl- current and compare it with the ACTH-activated Cl- current. Experiments were performed using the whole-cell patch-clamp recording method, video microscopy and cortisol-secretion measurements. In current-clamp experiments, hypotonic solutions induced a membrane depolarization to -22 mV. This depolarization, correlated with an increase in the membrane conductance, was sensitive to different Cl- channel inhibitors. In voltage-clamp experiments, hypotonic solution induced a membrane current that slowly decayed and reversed at -21 mV. This ionic current displayed no time dependence and showed a slight outward rectification. It was blocked to variable extent by different conventional Cl- channel inhibitors. Under hypotonic conditions, membrane depolarizations were preceded by an increase in cell volume that was not detected under ACTH stimulation. It was concluded that hypotonic solution induced cell swelling, which activated a Cl- current involved in membrane depolarization. Although cell volume change was not observed in the presence of ACTH, biophysical properties and pharmacological profile of the volume-sensitive Cl- current present obvious similarities with the ACTH-activated Cl- current. As compared to ACTH, hypotonic solutions failed to trigger cortisol production that was weakly stimulated in the presence of high-K+ solution. This shows that in ZF cells, membrane depolarization is not a sufficient condition to fully activate secretory activities.

Inactivation and intracellular retention of the human I183N mutated melanocortin 3 receptor associated with obesity

Melanocortins are known to be involved in the regulation of feeding behavior. These hormones mediate their effects through G protein-coupled receptors (GPCRs) by stimulating adenylate cyclase. The melanocortin 3 receptor (MC3R) in the melanocortin receptor (MCR) family has been identified as a neural receptor subtype mainly expressed in the brain in mammals. Until now, only one heterozygous mutation (I183N) has been identified in the coding region of this receptor in two obese patients of the same family. In this study, we reported the functional characterization of the I183N mutated MC3R compared with that of the wild-type MC3R after transfection in HEK293 cells. Our results showed that the I183N mutation totally abolished the activity of the mutated receptor to generate intracellular cAMP. Furthermore, confocal microscopy observation revealed that the mutation induced an intracellular retention of the mutated receptor. Moreover, we demonstrated for the first time by co-transfection studies that the mutated receptor could reduce the wild-type receptor activity through a dominant negative effect.

Stable expression of human melanocortin 3 receptor fused to EGFP in the HEK293 cells

Among the melanocortins alpha-MSH is known to be involved in feeding behavior. These hormones mediate their effects through G protein-coupled receptors by stimulating adenylate cyclase. In this study, we have developed an in vitro expression model for human melanocortin 3 receptor (hMC3R) tagged at its C terminus with EGFP. The corresponding chimeric cDNA was stably expressed in HEK293 cells. The selected clones expressing the hMC3R-EGFP exhibited cell surface fluorescence and responded to NDP-MSH stimulation by producing cAMP in a dose-dependent manner (EC(50): 0.3 nM). Binding studies revealed a single class of binding sites with a K(D) of 2.24 nM. Moreover, Agouti-related protein was also demonstrated to be an antagonist of the hMC3R-EGFP. Thus, the hMC3R tagged with EGFP stably expressed in HEK293 cells, exhibiting the same characteristics than the wild-type hMC3R, is the only model of expression of this receptor allowing its direct localization inside living cells.

Familial glucocorticoid deficiency type 2 in two neonates

Familial glucocorticoid deficiency (FGD) is a rare autosomal recessive disorder characterized by glucocorticoid deficiency, elevated plasma adrenocorticotropic hormone (ACTH) levels and preserved aldosterone/renin secretion. Adrenocorticotropic receptor mutations occur in about 40% of patients (FGD type 1), whereas the rest of the cases are associated with a normal receptor (FGD type 2). More than 50 cases have been reported in the literature so far. We report two cases of type 2 FGD from two related families who presented in the newborn period with varying clinical features. Direct sequencing of the genomic DNA of the patients failed to reveal mutations or other defects in the coding sequence of the ACTH receptor. Linkage analysis excluded mutations on the MC2-R gene outside the coding region. To our knowledge, these are the first two cases of FGD reported from the Middle East.

The human MC2-R gene expression: different aspects of its control

Expression of the adrenocorticotropin receptor (MC2-R) is restricted to adrenocortical cells and is up-regulated by both adrenocorticotropin and angiotensin II through the activation of protein kinase A and protein kinase C pathways, respectively. After cloning of the promoter region of the human MC2-R gene (hMC2-R), we have shown that cyclic AMP-induced regulation of transcriptional activity of the gene is achieved through two SF1 binding elements located in the proximal promoter. On the other hand, regulation by angiotensin II partly involved two AP1 binding sites. Using different primary cell cultures, we have also been able to delineate a region inside the promoter which is responsible for part of the tissue-specific expression of the gene.

Functional relationships between three novel homozygous mutations in the ACTH receptor gene and familial glucocorticoid deficiency

Familial glucocorticoid deficiency (FGD) is an autosomal recessive disorder characterized by a glucocorticoid adrenal insufficiency without mineralocorticoid deficiency. Mutations of the ACTH receptor (MC2-R) gene have been reported in some FGD cases, but only a few of them have been functionally studied. We reported clinical features and MC2-R gene analysis in three families. For each proband, an homozygous mutation was identified after amplification and sequencing of the whole intronless MC2-R gene. One mutation converted Val-142 located in the second intracellular loop to Leu. Another mutation in the sixth transmembrane domain converted Ala-233 to Pro. The last mutation converted the negatively charged Asp-103 in the first extracellular loop to an uncharged Asn. Functional studies of these mutations as well as the S120R mutation were performed after stable transfection of M3 cells and measurement of ACTH-induced cAMP production. For the S120R, V142L, and A233P mutated MC2-R, cAMP production curves were similar to that obtained with M3 parental cells, confirming that these mutations are responsible for the FGD in the affected patients. The D103N-mutated MC2-R had an impaired cAMP response to physiological doses of ACTH, but the maximal response at very high concentrations of ACTH was similar to that obtained for the wild-type MC2-R. All these results demonstrated clear relationships based on functional studies between MC2-R homozygous mutations and FGD phenotype.

ACTH-induced Cl(-) current in bovine adrenocortical cells: correlation with cortisol secretion

ACTH has been shown to depolarize bovine adrenal zona fasciculata cells by inhibiting a K(+) current. The effects of this hormone on such cells have been reexamined using perforated and standard patch recording methods. In current clamp experiments, ACTH (10 nM) induced a membrane depolarization to -36 +/- 1 mV (n = 56), which was mimicked by forskolin (10 microM) or by 8-(4-chlorophenylthio)-cAMP (8 mM). ACTH-induced membrane depolarizations were associated in the majority of cells with an increase in membrane conductance. In the other cells, these membrane responses could occur without change or could be correlated with a transient or with a continuous Cs(+)-sensitive decrease in membrane conductance. The depolarizations associated with an increase in membrane conductance were depressed by Cl(-) current inhibitors diphenylamine-2-carboxylic acid (DPC; 1 mM), anthracene-9-carboxylic acid (9-AC; 1 mM), DIDS (400 microM), verapamil (100 microM), and glibenclamide (20 microM). In voltage-clamped Cs(+)-loaded cells, ACTH activated a time-independent current that displayed an outward rectification and reversed at -21.5 mV +/- 2 (n = 6). This current, observed in the presence of internal EGTA (5 mM), was depressed in low Cl(-) external solution and was inhibited by DPC, 9-AC, DIDS, 5-nitro-2-(3-phenylpropylamino)benzoic acid, verapamil, and glibenclamide. ACTH-stimulated cortisol secretion was blocked by Cl(-) channel inhibitors DIDS (400 microM) and DPC (1 mM). The present results reveal that, in addition to inhibiting a K(+) current, ACTH activates in bovine zona fasciculata cells a Ca(2+)-insensitive, cAMP-dependent Cl(-) current. This Cl(-) current is involved in the ACTH-induced membrane depolarization, which seems to be a crucial step in stimulating steroidogenesis.

Syndrome of congenital adrenocortical unresponsiveness to ACTH. Report of six patients

Familial glucocorticoid deficiency (FGD) or unresponsiveness to ACTH at the receptor level is a rare autosomal recessive hereditary syndrome characterized by a low cortisol level despite high serum ACTH concentration. Aldosterone levels are normal. The clinical entity generally presents in the first year of life with skin hyperpigmentation and hypoglycemic convulsions. Cortisol response to exogenous ACTH is also absent. Unresponsiveness to ACTH may be due to a mutation in the ACTH receptor; sometimes no mutation is found. We discuss the clinical and laboratory findings and genetic studies in six patients with a diagnosis of FGD. A homozygous V142L mutation was detected in three of the patients and a homozygous D103N mutation was detected in two patients.

Functional expression of the human ACTH receptor gene

The ACTH receptor is the type 2 (MC2R) among the melanocortin receptor family and is expressed almost exclusively in the adrenal cortex. The human MC2R (hMC2R) was very difficult to express in heterologous cell lines. We have succeeded in transient and stable expression of hMC2R using the M3 melanoma cells. Moreover, we have found that the expressed hMC2R in M3 cells showed similar ACTH binding affinity and coupling to adenylate cyclase as the MC2R of normal human adrenal cells, contrarily to most of the other expression cell models. In these conditions, we have been able to test several mutant hMC2R described in patients with the familial glucocorticoid deficiency syndrome (FGD) using this cell line.

[ACTH resistance syndromes]

ACTH resistance syndromes consist of a group of rare disorders with three various molecular etiologies. However, all these diseases share the feature of severe glucocorticoid adrenal insufficiency. The simplest disorder is the isolated familial glucocorticoid deficiency (FGD) which could be divided in two different types. In FGD type 1, ACTH receptor mutations have been described and are responsible for the loss of function of the receptor, leading to the ACTH unresponsiveness. Patients with FGD type 2 show the same phenotype as in the previous syndrome but no mutation of the ACTH receptor has been reported in these cases. It has been proposed that morbidity of one or several other gene(s) could be responsible for this syndrome although there is no information about their chromosomal localization. The third molecular form of the disease corresponds to the Triple A syndrome for the triad of association "ACTH resistance, Achalasia, Alacrima", thus reflecting a large spectrum of additional symptoms. It has recently been reported that the morbid gene in this last syndrome maps to chromosome 12q13. The aim of this review is to examine the clinical aspect as well as the current knowledge of the molecular and genetic aspects of the different forms of the disease.

Bovine thrombospondin-2: complete complementary deoxyribonucleic acid sequence and immunolocalization in the external zones of the adrenal cortex

Given the variety of biological functions in the adrenal cortex that are controlled by ACTH, we hypothesized that some extracellular proteins act as biological relays for this systemic hormone. One candidate protein [corticotropin-induced secreted protein (CISP)] was purified from the conditioned medium of bovine adrenocortical cells on the basis of a 5- to 14-fold increase in its synthesis after the addition of ACTH. We report here the cloning of overlapping complementary DNAs that span the sequence encoding the full-length protein (1170 amino acids). The deduced CISP protein sequence is 89% identical to that of human thrombospondin-2 (TSP2), but only 61% identical to that of bovine TSP1, confirming that CISP is the bovine ortholog of TSP2. The bovine TSP2 sequence aligned perfectly with human, mouse, and chicken TSP2 sequences, except for a gap of 2 amino acids located in a linker region. All 58 cysteine residues that are conserved in other species were present in the bovine sequence as well as most of the functional domains. Most endocrine tissues (adrenal cortex, testis, ovary, and placenta) appeared to express TSP2, as determined by Western blot analysis. The highest levels of TSP2 protein were found in the adrenal cortex, followed by the heart, spleen, brain, and kidney. A differential extent of N-glycosylation or tissular proteolytic maturation may be responsible for the mol wt differences observed between bovine TSP2 detected in the medium from primary cultures and that in fresh tissue extracts. The immunohistochemical analysis of the distribution of TSP2 in the bovine adrenal gland revealed that the protein is much more abundant in the external zones (zona glomerulosa and zona fasciculata) than in the internal reticularis zone, a pattern similar to that reported for ACTH receptors. This distribution clearly suggests that TSP2 is a candidate relay protein for a subset of ACTH actions in the adrenal cortex.

Three steroidogenic factor-1 binding elements are required for constitutive and cAMP-regulated expression of the human adrenocorticotropin receptor gene

In the present study, we characterized two new SF-1 binding sites, SF-209 and SF-98, in the promoter of the human ACTH receptor (hACTH-R) gene. Both sites, together with the previously described SF-35 site, are required for full constitutive activity of this gene. This was demonstrated by the use of constructs containing part of the promoter upstream of the luciferase gene and carrying mutation in one of these sites, to transiently transfect H295R cells. Mutations of either SF-35, SF-98, or SF-209 induced a decrease of luciferase activity. This effect was amplified when two or three elements were mutated together in the same construct. Only SF-35 and SF-98 seem to play a major role in the cAMP-induced regulation of the hACTH-R gene, since mutation of either one of these sites reduced the forskolin induction of luciferase activity by 50%. When both elements were mutated, no stimulation was obtained over the control. This indicates that SF-1 protein must bind to both sites for the cAMP response.

SF-1 and the transcriptional regulation of the human ACTH receptor gene

The adrenocorticotropin receptor or ACTH-R which is the type 2 among the melanocortin receptor family is almost exclusively expressed in the adrenal cortex, reflecting a high degree of tissue specificity. In human cultured adrenocortical cells, we have previously reported that ACTH in contrast to most of the peptide hormones, is able to up-regulate the number of its own receptors through an increase of the transcriptional activity of the encoding gene. Three putative SF-1 binding sites are present in the sequence of the human ACTH-R gene promoter at -35 (SF-35), -98 (SF-98) and -209 (SF-209). By EMSA studies, we demonstrated that these sites effectively bind SF-1 protein. After transient transfection of H295R cells using a construct containing the first 263 bp upstream of the transcriptional start site, in front of the luciferase gene in the pGL3 vector, we demonstrated the involvement of all three SF-1 sites to confer maximal constitutive activity to a proximal region of the hACTH-R gene promoter. Only SF-35 and SF-98 play a role in cAMP-induced regulation of this gene.

A steroidogenic factor-1 binding element is essential for basal human ACTH receptor gene transcription

We have previously shown that the promoter of the human ACTH receptor (ACTH-R) contains, at -35 bp, a binding site for the steroidogenic factor 1 (SF-1), an orphan nuclear receptor which could be responsible for the transcriptional activity of this promoter. In the present study, electrophoretic mobility shift assays demonstrated that the sequence -43/-19 bound the SF-1 protein present in the nuclear extracts of adrenocortical cells. Mutation of the SF-1 binding site markedly reduced (40%) the basal transcription of the reporter gene in Y-1 cells transfected with the mutated p(-56/+22)GH construct compared to the wild-type construct. These results demonstrate that the SF-1 binding element present in this fragment is required for the basal promoter activity of the human ACTH-R gene. In addition, other binding elements located upstream from this characterized SF-1 binding site are involved in the full basal promoter activity of the human ACTH-R since transfection studies with a longer p(-1017/+22)GH construct resulted in a higher GH release than with the p(-56/+22)GH construct.

Autocrine role of TGFbeta1 in adrenal

Three main criteria are required to postulate that a factor has an autocrine action in any cell: presence of receptors and biological effects of the factor; local production which must be regulated by physiological signals and the inhibition of its secretion or action should cause effects opposite to those caused by the exogenous factor. In adrenal cells, transforming growth factor beta1 (TGFbeta1) fulfilled these criteria: 1) Adrenal cells possess TGFbeta1 receptors and this factor regulates the expression of adrenal cell specific genes, including ACTH and angiotensin II (AngII) receptors and several steroidogenic enzymes, leading to changes in the steroidogenic responsiveness; 2) Adrenal cells express and secrete TGFbeta1 and its secretion is regulated by the two adrenal specific hormones ACTH and AngII; 3) The blockade of TGFbeta1 protein synthesis by an antisense oligonucleotide produces changes in adrenal cell functions opposed to those induced by the exogenous factor.

Is there a local IGF-system in human adrenocortical cells?

There is increasing evidence that in the fetal and postnatal development of the adrenal gland, trophic and differentiating effects of ACTH are locally modulated by a species-specific pattern of growth factors. As we have shown previously in human adult adrenocortical cells (HAC) in culture, IGF-I and, even more, IGF-II enhance the steroidogenesis and ACTH responsiveness. We now examined the secretion of IGFs and their binding proteins (IGFBP) in the medium of 12 serum free primary cultures of HAC by specific RIAs and [125I]IGF ligand blot or by immunoblot, and their long-term regulation by ACTH. HAC secrete 0.41 and 0.91 ng IGF-I and IGF-II/5 x 10(5) cells per day, respectively, and their secretion is significantly stimulated 2- and 1.6-fold, respectively, by ACTH. HAC secrete at least three IGFBPs. The 43-46 kDa and the 29 kDa proteins correspond to glycosylated and fragmented forms of IGFBP-3, and the 36 kDa protein to IGFBP-2. The most abundant protein is the 24 kDa IGFBP, with identical electrophoretic mobility to IGFBP-4. IGFBP-3, as measured by RIA, is in the range of 1 ng/day. None of the IGFBPs is significantly changed by ACTH. Thus, we have evidence for a local IGF system, and the IGF-levels are in a range compatible with a physiological auto or paracrine action on steroidogenesis.

Glucocorticoids enhance corticotropin receptor mRNA levels in ovine adrenocortical cells

We have shown previously that chronic treatment with glucocorticoids enhances both ACTH-induced cAMP production and ACTH- or 8Br-cAMP-induced steroidogenesis of cultured ovine adrenocortical cells. This treatment has been shown to involve an increase in the number of ACTH receptors. The present study aimed to explore the mechanism of this effect of glucocorticoids on ACTH receptors. Ovine adrenocortical cells expressed one major ACTH receptor transcript of 3.6 kb and three minor ones of 4.2, 1.8 and 1.3 kb. Dexamethasone treatment of cultured cells increased the levels of all these transcripts in a time- and dose-dependent manner, with an EC50 of (1.5 +/- 0.6) x 10(-8) M. The mean increase over control with 10(-6) M dexamethasone was 144 +/- 11% (n = 14). This enhancing effect was specific for glucocorticosteroids. The antiglucocorticoid Ru38486 blocked the effect of dexamethasone. Testosterone did not modify, while high concentrations of 17 beta-estradiol decreased, ACTH receptor mRNA levels. Treatment of cells with aminoglutethimide (an inhibitor of steroidogenesis) resulted in a dose-dependent decrease in ACTH receptor mRNA levels, which was prevented by concomitant treatment with dexamethasone. Treatment with ACTH also increased ACTH receptor mRNA levels more than twofold. Addition of aminoglutethimide together with ACTH resulted in a smaller increase than that achieved with ACTH alone. Neither dexamethasone nor ACTH modified ACTH receptor mRNA half-lives. However, these two hormones enhanced the levels of both newly synthesized and total ACTH receptor mRNAs. These results indicate that the positive trophic effect of glucocorticoids on ovine adrenocortical cells involves an enhancement of the transcription rate of the ACTH receptor gene. In addition, they suggest that part of the trophic action of ACTH on ACTH receptors may be mediated by ACTH-induced steroidogenesis.

Presence of multiple functional polyadenylation signals in the 3'-untranslated region of human corticotropin receptor cDNA

We present 2.59 kb of the 3'-non-coding region of the ACTH receptor cDNA that contains seven potential polyadenylation signals. Among these signals, five are functional as detected by 3'-RACE and are consistent with the transcripts of 1.8, 3.4 and 4 kb visualized on Northern blots. We propose that the most likely molecular mechanism for the multiple ACTH-R mRNA transcripts is the alternative use of polyadenylation signals.

Insulin-like growth factors enhance steroidogenic enzyme and corticotropin receptor messenger ribonucleic acid levels and corticotropin steroidogenic responsiveness in cultured human adrenocortical cells

In several species, including the human fetus, insulin-like growth factors (IGF-I and IGF-II) have been reported to modulate adrenal steroidogenesis, thus contributing to adrenal cortical differentiation. In the present study, we examined the long term effects of IGF-I and -II on human adult adrenal fasciculata-reticularis cells cultured in a chemically defined medium and compared them to the effects of insulin, human GH, and ACTH. Treatment for 3 days with IGF-I or -II at nanomolar concentrations or with insulin at micromolar concentrations slightly increased the production of androstenedione, cortisol, and dehydroepiandrosterone about 1.5-fold over that by control cells. Moreover, the acute steroidogenic response to ACTH of cells pretreated with IGF-I, IGF-II, or insulin was 3- to 6-fold higher than that of control cells. For each hormone, these effects of IGF-I and -II were dose dependent between 0.1-26 nmol/L (1-200 ng/mL). The secretion of androstenedione was more potently stimulated than that of dehydroepiandrosterone and cortisol, and this effect was more clearly yielded by pretreatment with IGF-II than with IGF-I or insulin. Human GH had no effect on these cells. In cells treated with IGF-I or -II, the messenger ribonucleic acid (mRNA) levels of cytochrome P450 17 alpha-hydroxylase and of 3 beta-hydroxysteroid dehydrogenase were increased, and the abundance of ACTH receptor mRNA was also slightly enhanced, but the mRNA of cytochrome P450 cholesterol side-chain cleavage enzyme was unchanged. In conclusion, IGFs enhance the steroidogenesis and ACTH responsiveness of human adrenocortical cells in culture. We speculate, that by this mechanism, IGFs may contribute to clinical states with hyperandrogenemia.

Characterization of the human ACTH receptor gene and in vitro expression

The coding sequence of the human ACTH receptor, cloned in 1992, contains no intron, but the presence of one intron (of about 18 kb) separating the coding exon from an upstream exon has been demonstrated. One major transcription start site was located in this first exon. Northern blot analysis of cultured human adrenocortical cells revealed several transcripts that can be partly explained by the use of different polyadenylation sites. We have isolated a 1 kb fragment of genomic DNA upstream of exon 1 and studied its basal promoter activity. The sequence of this region shows several putative CREs that could be responsible for the stimulation by ACTH of its own receptors as demonstrated on human adrenocortical cells. To functionally characterize the human ACTH receptor, we have prepared cells stably transfected with either the normal receptor or a mutant receptor. This model allows the study of both binding to ACTH and coupling to adenylate cyclase. Two naturally mutated receptors, described in patients with Familial Glucocorticoid Deficiency, have been studied. Both mutations (C251F and D107N) strongly impaired the binding of ACTH to its receptors and are then responsible for the absence of biological response to ACTH.

Cycloheximide enhances ACTH-receptor mRNA through transcriptional and post-transcriptional mechanisms in bovine adrenocortical cells

We have previously shown that ACTH is one of the few polypeptide hormones having a positive trophic effect, not only on the number, but also on the expression of its own receptors. In the present study, we investigated whether the constitutive and ACTH-induced expression of ACTH-receptor (ACTH-R) mRNA in bovine adrenocortical cells (BAC) requires new protein synthesis. The results show that cycloheximide alone, an inhibitor of protein synthesis, induced a time- and dose-dependent increase in the constitutive level of the ACTH-R major transcript of 3.6 kb in BAC. The maximal stimulation (5.17 +/- 1.15 fold, n = 4) was obtained after 24 h treatment with 5 micrograms/ml cycloheximide. The effect of cycloheximide was specific and not directly related to translational arrest since other protein synthesis inhibitors acting through different mechanisms, emetine and puromycin, were unable to reproduce such an effect at concentrations inhibiting protein synthesis. The effect of cycloheximide involved an increase in the half-life and the transcription rate of the major transcript of ACTH-R (2- and 8.4-fold respectively). In addition, the results also demonstrated that neither the constitutive nor the ACTH-induced expression of ACTH-R require new protein synthesis.

Regulation of primary response and specific genes in adrenal cells by peptide hormones and growth factors

Using cultured bovine adrenal fasciculata cells (BAC), we investigated the effects of two hormones, corticotropin (ACTH) and angiotensin II (Ang-II) and two growth factors, insulin-like growth factors I (IGF-I) and transforming growth factor beta 1 (TGF beta 1), on the mRNA levels of nuclear proto-oncogenes of the Fos and Jun families and on the mRNA levels of genes expressed in BAC coding for ACTH and AT1 receptors, cytochrome P450scc and P450 17 alpha and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD). ACTH and IGF-1 increased c-fos and jun-B mRNA levels early with later increases in the levels of mRNA for the ACTH receptor and the three steroidogenic enzymes, and enhanced steroidogenic responses to both ACTH and Ang-II. In contrast, Ang-II increased mRNA coding for the three proto-oncogenes (cfos, c-jun, and jun-B), decreased those for P450 17 alpha and 3 beta-HSD, and caused marked homologous and heterologous steroidogenic desensitization. TGF beta 1 increased only jun-B mRNA and markedly reduced BAC-differentiated functions and steroidogenic responsiveness to both ACTH and Ang-II. The long-term effects of ACTH on human adrenal fasciculata cells were comparable with those observed in BAC, whereas the long term effects of Ang-II and TGF beta 1 were different from those observed in BAC. Whether these species-specific differences are related to a different effect of these factors on proto-oncogene expression is not yet known.

Regulation of ACTH receptor mRNA and binding sites by ACTH and angiotensin II in cultured human and bovine adrenal fasciculata cells

Human (HAC) and bovine (BAC) adrenal fasciculata cells express ACTH and angiotensin-II (A-II) receptors. In the present work, we have studied the effects of both hormones on ACTH receptor (ACTH-R) mRNA and binding sites. Both HAC and BAC expressed several ACTH-R transcripts. Although in both cell types, ACTH and A-II increased ACTH-R transcripts in a time- and dose-dependent manner, the maximal effects were different. Thus, ACTH at 10(-9) M enhanced 21- and 5-fold the level of ACTH-R mRNA and binding sites in HAC, whereas in BAC both parameters were enhanced only 3-fold. A-II at 10(-7) M increased 17- and 3.5-fold ACTH-R mRNA and binding sites in HAC, whereas in BAC, it caused only a 2-fold increase in ACTH-R mRNA and a small decrease in receptor number. In HAC, the stimulatory effects of both hormones on ACTH-R mRNA are mainly transcriptional, whereas in BAC they are mainly post-transcriptional, by decreasing the rate of degradation of ACTH-R mRNA. The stimulatory effects of ACTH on ACTH-R in both HAC and BAC were associated with an enhanced steroidogenic response to further hormonal stimulation. In contrast, specific species differences were observed with A-II. Thus, in HAC A-II increased ACTH-R mRNA and binding sites and the ACTH-induced cortisol production, whereas in BAC, A-II caused a slight decrease of ACTH binding sites and steroidogenic desensitization.

Peptide hormone and growth factor regulation of nuclear proto-oncogenes and specific functions in adrenal cells

Among the large number of immediate early genes, nuclear proto-oncogenes of the Fos and Jun families, have been postulated to be involved in the long-term effects of several growth factors on cell differentiation and/or multiplication. Since adrenal cell differentiated functions appear to be regulated by specific hormones and growth factors, the effects of these factors on proto-oncogene mRNA levels were analysed in bovine adrenal fasciculata cells (BAC) in culture. Corticotropin (ACTH) and insulin-like growth factor I increased c-fos and jun-B mRNA, but had no effect on c-jun mRNA and these early changes were associated with a later increase in BAC specific function [ACTH receptors, cytochrome P450 17 alpha) and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD)] and an enhanced steroidogenic responsiveness to both ACTH and angiotensin-II (A-II). On the other hand, A-II increased the three proto-oncogene (c-fos, c-jun and jun-B) mRNAs, induced a decrease of P450 17 alpha and 3 beta-HSD and caused a marked homologous and heterologous (ACTH) densitization. Transforming growth factor beta 1 which only increased jun-B mRNA, markedly reduced BAC differentiated functions and the steroidogenic responsiveness to both ACTH and A-II. Thus, it is postulated that the proto-oncoproteins encoded by the immediate early genes may play a role in the long-term effects of peptide hormones and growth factors on BAC differentiated functions.

Regulation of bovine adrenal cell corticotropin receptor mRNA levels by corticotropin (ACTH) and angiotensin-II (A-II)

Bovine adrenal fasciculata-reticularis cells (BAC) expressed at least four ACTH receptor (ACTH-R) mRNA transcripts, one major of 3.6 kb and three minor of 4.2, 1.8 and 1.3 kb. ACTH and A-II increased ACTH-R mRNA levels in a time- and dose-dependent manner. At maximal concentrations, ACTH caused a 2.7-fold increase in the level of the major transcript of 3.6 kb with an ED50 = 10(-11) M and A-II produced a 2.4-fold increase with an ED50 = 5 x 10(-8) M. Under our experimental conditions, the stimulatory effects of both hormones appeared to be due to post-transcriptional changes rather than to transcriptional regulation since the hormonal effects were also observed in actinomycin-treated cells. The results indicate that regulation of ACTH-R mRNA levels may be one mechanism by which ACTH and A-II regulate adrenocortical functions.

Regulation of adrenal cell-differentiated functions by growth factors

Adrenal cell-differentiated functions and, therefore, their steroidogenic capacity can be regulated in an opposite direction by insulin-like growth factor I (IGF-I) and transforming growth factor-beta 1 (TGF beta 1). The enhanced steroidogenic responsiveness of bovine and ovine adrenal cells treated with IGF-I can be explained by its positive effects on the number of corticotropin (ACTH) and angiotensin II (A-II) receptors associated with an increase in the alpha s and alpha i subunits of G proteins but also by its effects on several steps of the steroidogenic pathway. In contrast, TGF beta 1 is a potent inhibitor of differentiated functions of both bovine and ovine adrenal cells. TGF beta 1 reduces ACTH and A-II receptor number, inhibits cAMP formation, and decreases several steroidogenic enzyme activities. The physiological role of these peptides in adrenal cells is strengthened by the fact that both are synthetized and secreted by these cells and that their secretion can be regulated by the specific hormones, ACTH and A-II.

Identification and characterization of corticotropin receptors in bovine and human adrenals

Corticotropin (ACTH) receptors have been characterized by covalent cross-linking of radiolabeled ACTH ([125I]ACTH) with the bifunctional cross-linking reagent disuccinimidyl suberate to cultured bovine adrenal fasciculata reticularis cells (BAC), and to crude plasma membrane fractions prepared from both human and bovine adrenals. Incubation of BAC with [125I]ACTH at 20 degrees C followed by cross-linking resulted in the specific labeling of two binding proteins with apparent M(r) of 154,000 and 43,000 as measured by SDS-PAGE under reducing and non-reducing conditions. In addition, in some experiments another band with an apparent M(r) of 124,000 was observed. All of these bands disappeared when the incubation was performed in the presence of an excess of unlabeled ACTH. When BAC were incubated with [125I]ACTH in the presence of 100 microM phenylarsine oxide at 20 degrees C, a condition which prevents the internalization of the ACTH-receptor complex, the bulk of the radioactivity was present in the 43,000 band. After [125I]ACTH cross-linking to BAC, subcellular preparations followed by SDS-PAGE revealed that the 20,000 g fraction contained mainly the 43,000 M(r) form. Cross-linking of [125I]ACTH to plasma membrane-enriched fractions prepared from human and bovine adrenals resulted only in the labeling of the 43,000 protein. These results indicate that the ACTH receptor present at the cell surface is a macromolecule of 43,000, and suggest that the 154,000 form probably represents association of the ACTH-receptor complex to another macromolecule. The 154,000 protein would be formed during or after internalization of the ACTH-receptor complex.

Characterization and coupling of angiotensin-II receptor subtypes in cultured bovine adrenal fasciculata cells

Angiotensin-II (A-II) receptor subtypes and their potential coupling mechanisms were investigated in bovine adrenal fasciculata cells (BAC) in culture, by the use of selective antagonists for AT1 (DUP 753 or Losartan) and AT2 (PD 123177 and CGP 42112A) sites. Competition for [125I]A-II specific binding with AT1 or AT2 selective ligands produced a biphasic displacement curve, suggesting two distinct A-II binding sites. In the presence of PD 123177 (10(-5) M), a concentration at which most of the AT2 sites were saturated, DUP 753 displaced [125I]A-II specific binding in a monophasic manner with an IC50 of 6.2 +/- 1.4 x 10(-7) M. In the presence of DUP 753 (10(-5) M), the displacement produced by CGP 42112A and PD 123177 was also monophasic, with IC50s of 8 +/- 3 x 10(-10) and 4.6 +/- 2.1 x 10(-7) M, respectively. The reducing agent dithio-1,4-erythritol inhibited the binding of [125I]A-II to AT1 (DUP 753 sensitive) sites, but increased its binding to AT2 sites 2-fold. The IC50 values for these two effects were about 0.5 and 3 mM, respectively. The biological effects of A-II in BAC, phosphoinositide hydrolysis and cortisol production, were inhibited in a dose-dependent manner by DUP 753, but not by AT2 antagonists. Similarly, the potentiating action of A-II on corticotropin-induced cAMP production was blocked by DUP 753, but not by AT2 antagonists. These data indicate that BAC contain both receptor subtypes, but that all the known effects of A-II in BAC were induced via the AT1 receptor subtype.

ACTH and angiotensin II regulation of insulin-like growth factor-I and its binding proteins in cultured bovine adrenal cells

Insulin-like growth factor-I (IGF-I) is required for the maintenance of differentiated functions of bovine adrenal fasciculata cells in culture. We have investigated, by immunocytochemistry, the presence of IGF-I in cells cultured in the absence or presence of ACTH and angiotensin II (AII), as well as the secretion of IGF-I and its binding proteins (IGFBPs). In control cultures, very few cells were specifically stained with the anti-IGF-I serum. Following 2 days of treatment with AII (1 microM) or ACTH (10 nM) the number of stained cells increased by 5- and 14-fold respectively. In all cases the staining was specific, since it was abolished when non-immune rabbit serum replaced the anti-IGF serum or when the anti-IGF-I serum was preincubated with saturating concentrations of the peptide. Under the same experimental conditions the secretion of IGF-I into the medium, evaluated by a specific radioimmunoassay, was increased two- and sevenfold by AII and ACTH respectively. Using the method of Western ligand blotting, the major form of IGFBP secreted by control adrenal cells was found to be a 38-42 kDa doublet protein. Two minor forms with apparent molecular weights of 28-31 kDa and 24 kDa have also been identified. Following acid-ethanol extraction of the conditioned medium, all the IGFBPs were recovered in the pellet, whereas most of the IGF-I was in the supernatant. ACTH and, to a lesser extent, AII pretreatment increased the 38-42 kDa IGFBP by several fold, decreased the 28-31 kDa IGFBP and had no effect on the 24 kDa IGFBP. In conclusion, these results demonstrate (i) that bovine adrenal cells contain IGF-I-like immunoreactive material, (ii) that the stimulatory effects of ACTH and AII on IGF-I secretion by bovine adrenal cells are due mainly to an increase in the number of IGF-I-producing cells and (iii) that ACTH and AII modulate the secretion of IGFBP by adrenal cells. Although the roles of IGFBPs have not been defined in adrenal cells, they are capable of modulating the biological action of IGFs in other cell cultures. Regulation of both IGF-I and its binding proteins by the two specific hormones ACTH and AII suggests important roles for these binding proteins in modulating the action of IGF-I in bovine adrenal cell function.

Characterization and regulation of angiotensin and corticotropin receptors on cultured bovine adrenal cells

Cultured bovine adrenal fasciculata cells were used to characterize angiotensin II (A-II) and corticotropin (ACTH) receptors and to study their homologous and heterologous regulation. These cells contain one type of high affinity binding sites for A-II (KD congruent to 2.4 +/- 0.3 10(-9) M) and about 100000 sites/cell. Photoaffinity labeling followed by SDS-PAGE under reducing conditions revealed a single macromolecule of apparent MR 65,000. Treatment of cells with increasing concentrations of A-II produced down-regulation of its own receptors and marked homologous and heterologous (ACTH) steroidogenic desensitization. However, the desensitization was not correlated with receptor loss and was mainly due to alterations of the steroidogenic pathway. Pretreatment of cells with ACTH also reduced A-II receptors, but this was not associated with steroidogenic desensitization. Bovine fasciculata cells contain two binding sites for ACTH: one of high affinity (KD congruent to 2.6 +/- 0.4 10(-10) M) and low capacity (2030 +/- 390 sites/cell) and the other of low affinity and high capacity. Affinity cross-linking of ACTH to plasma membranes prepared from adrenal cells revealed a labeled macromolecule of apparent MR 43000. However, cross-linking experiments to intact cells revealed, both under reducing and non-reducing conditions, two labeled macromolecules of apparent MR of 123000 and 43000. Pretreatment of cells with ACTH enhanced its receptor and the cAMP and cortisol responses to further ACTH stimulation. These effects were time- and dose-dependent. The maximal effects were observed at 10(-10) to 10(-9) M. A-II alone had no effect but it blocked partially the stimulatory action of ACTH.

Human proopiomelanocortin-(79-96), a proposed cortical androgen-stimulating hormone, does not affect steroidogenesis in cultured human adult adrenal cells

The existence of a cortical androgen-stimulating hormone (CASH), distinct from ACTH, regulating the secretion of human adrenal androgens has long been postulated. Recently, it has been reported that an 18-amino acid peptide, corresponding to the first part of the joining peptide of proopiomelanocortin [POMC-(79-96)], was able to stimulate the secretion of dehydroepiandrosterone from cultured human adult adrenocortical cells, but had no effect on cortisol production. We have studied the acute and long term effects of ACTH (10(-11) and 10(-9) M), CASH-18 (10(-8) M), or both on cortisol and dehydroepiandrosterone sulfate by human adult adrenocortical cells. Although ACTH increased steroid secretion and enhanced the steroidogenic responsiveness to further ACTH stimulation, CASH-18 alone or together with ACTH (10(-11) or 10(-9) M) had no effect. In addition, we were unable to demonstrate any specific binding of [125I]CASH-18 to human adrenocortical cells, although [125I] ACTH-(1-39) binds specifically to the same cell preparation.

Synergistic effects of corticotropin and insulin-like growth factor I on corticotropin receptors and corticotropin responsiveness in cultured bovine adrenocortical cells

Pretreatment of bovine adrenocortical cells with increasing concentrations of insulin-like growth factor I (IGF-I) for 3 days resulted in a dose dependent (ED50 congruent to 5 ng/ml) increment in Corticotropin (ACTH) receptors. Moreover, IGF-I pretreatment potentiated the effects of maximal active concentration of ACTH (10(-9) M) on its own receptors. Whereas ACTH (10(-9) M) or IGF-I (50 ng/ml) alone induced a 3- and 2.5-fold increase respectively in ACTH receptors, there was a 7.5 fold increase in the presence of the two peptides. This synergism between ACTH and IGF-I was also observed for the ACTH-induced cortisol response with an increase of 9-, 3- and 20-fold for cells pretreated with ACTH, IGF-I and the two peptides, respectively. However, the effects of both peptides on ACTH-induced cAMP production was only additive. The present results show that ACTH and IGF-I are potent stimulating factors on bovine adrenal cell differentiated functions and that the effects of both peptides are synergistic.

Regulation of IGF-I receptors by corticotropin and angiotensin-II in cultured bovine adrenocortical cells

The effects of angiotensin II (A-II) and corticotropin (ACTH) on insulin-like growth factor-I (IGF-I) receptors of bovine adrenocortical cells were investigated. Pretreatment of cells for 48 h with ACTH or A-II induced in a dose-dependent manner an increase in [125I]IGF-I binding (ED50 congruent to 10(-11)M, Vmax = 10(-10) M with ACTH; ED50 congruent to 3.10(-9) M, Vmax = 10(-7) M with A-II). This resulted from an increase in the number of binding sites without modification of the binding affinity. Pretreatment with 8-Bromo-cAMP (10(-3) M), a phorbol ester (PMA 10(-7) M) + ionophore A23187 (10(-7) M) produced a positive regulation of IGF-I receptors. Glucocorticoids did not mediate the effect of A-II and ACTH on IGF-I receptors. Since previous studies have shown that IGF-I increased ACTH and A-II receptors the present data indicate the existence of a reciprocal positive trophic effect between IGF-I and the two hormones on the regulation of their specific membrane-bound receptors.

Corticotropin positively regulates its own receptors and cAMP response in cultured bovine adrenal cells

Bovine fasciculata adrenal cells contain specific high-affinity (KD approximately 2.3 +/- 0.4 x 10(-10) M) and low-capacity (1910 +/- 300 sites per cell) corticotropin (ACTH) receptors. Pretreatment of cells with ACTH, caused in a time-(maximum effect at 48 hr) and dose-(ED50 approximately 10(-11) M, Vmax = 10(-10) to 10(-9) M) dependent manner an increase in ACTH binding. This was due to a 4-fold increase in the number of binding sites without modification of the binding affinity. The same pretreatment also enhanced the cAMP response to further ACTH stimulation in a dose-dependent manner (ED50 approximately 10(-11) M) and to a lesser extent the response to forskolin. However, pretreatment with higher concentrations of ACTH (10(-8) M) reduced the binding and the cAMP response when compared to the effect of 10(-9) M. These ACTH effects, which were mimicked by 8-bromoadenosine 3',5'-cyclic monophosphate, required de novo protein synthesis. Pretreatment with 10(-13) to 10(-11) M ACTH also enhanced the steroidogenic responsiveness to further hormonal stimulation. However, at higher concentrations the hormone induced an apparent steroidogenic desensitization that was probably related to a depletion of endogenous cholesterol, since cortisol production in the presence of 22-(R)-hydroxycholesterol was increased. Neither angiotensin-II nor atrial natriuretic factor alone modified ACTH receptors, but angiotensin-II partially blocked the stimulatory effect of ACTH. Thus, ACTH is one of the few polypeptide hormones having a positive trophic effect on its own receptors and target-cell responsiveness.

Hormonal regulation of insulin-like growth factor I secretion by bovine adrenal cells

The role of insulin-like growth factor I (IGF-I) on the specific function of several steroidogenic cells has been recently reported. Since IGF-I is produced by several tissues, we have investigated whether bovine adrenal cells secrete this peptide. Purification of conditioned medium from adrenal cells incubated with [35S]methionine through affinity chromatography (monoclonal anti-IGF-I antibody), high pressure liquid chromatography, and polyacrylamide gel electrophoresis revealed a single band of similar Mr as pure recombinant IGF-I. Moreover, the purified adrenal-secreted IGF-I displaced bound 125I-IGF-I to its adrenal receptors, and pretreatment of adrenal cells with the purified peptide enhanced the acute corticotropin (ACTH)-induced cAMP production as recombinant IGF-I. The basal secretion of IGF-I (6 +/- 1 ng/48 h/10(6) cells) was stimulated 3-, 4.5-, and 9.5-fold by fibroblast growth factor, angiotensin II (A-II), and ACTH, respectively, but not by growth hormone. The stimulatory effects of A-II and ACTH were dose-dependent (ED50 congruent to 2.5 x 10(-8) and 1.5 x 10(-10) M, respectively), and the effects of both hormones were additive. Glucocorticoids were not the mediators of the effect of the two hormones on IGF-I secretion, since inhibition of their steroidogenic action by aminoglutethimide did not significantly modify IGF-I secretion. An immunoreactive IGF-I material was also secreted by mouse adrenal tumor cell line Y-1, but the stimulatory effect of ACTH was only 2-fold, and there was no effect of A-II. Since bovine adrenal cells contain specific IGF-I receptors and this peptide is required for the maintenance of some adrenal cell-specific function, the present data suggest that IGF-I may act in an autocrine fashion to stimulate adrenal cell differentiation stimulated by ACTH and A-II.