Functional and expression analysis of ovine steroid 11 beta-hydroxylase (cytochrome P450 11 beta)

Elaboration of the Corticosteroid Synthesis Pathway in Primates through a Multistep Enzyme

Metabolic networks are complex cellular systems dependent on the interactions among, and regulation of, the enzymes in the network. Although there is great diversity of types of enzymes that make up metabolic networks, the models meant to understand the possible evolutionary outcomes following duplication neglect specifics about the enzyme, pathway context, and cellular constraints. To illuminate the mechanisms that shape the evolution of biochemical pathways, I functionally characterize the consequences of gene duplication of an enzyme family that performs multiple subsequent enzymatic reactions (a multistep enzyme) in the corticosteroid pathway in primates. The products of the corticosteroid pathway (aldosterone and cortisol) are steroid hormones that regulate metabolism and stress response in tetrapods. These steroid hormones are synthesized by a multistep enzyme Cytochrome P450 11B (CYP11B) that performs subsequent steps on different carbon atoms of the steroid derivatives. Through ancestral state reconstruction and in vitro characterization, I find that the primate ancestor of the CYP11B1 and CYP11B2 paralogs had moderate ability to synthesize both cortisol and aldosterone. Following duplication in Old World primates, the CYP11B1 homolog specialized on the production of cortisol, whereas its paralog, CYP11B2, maintained its ability to perform multiple subsequent steps as in the ancestral pathway. Unlike CYP11B1, CYP11B2 could not specialize on the production of aldosterone because it is constrained to perform earlier steps in the corticosteroid synthesis pathway to achieve the final product aldosterone. These results suggest that enzyme function, pathway context, along with tissue-specific regulation, both play a role in shaping potential outcomes of metabolic network elaboration.

Identification of functional consequence of a novel selection signature in CYP11b1 gene for milk fat content in Bubalus bubalis

Genomic selection for traits of economic importance is an emerging approach carrying tremendous potentials. Many of polygenic traits as milk fat, protein and yield have been characterize at genomic level and important selection signatures have been identified. Cytochrome P450 enzymes are potential loci for affecting many of dairy capabilities. Present study was conducted for genomic dissection of CYP11b1 gene in riverine buffaloes and seven genetic variations were identified. Out of these, one novel polymorphism (p.A313T) was found well associated with milk fat %age. AB genotyped buffaloes were found to have higher milk fat %age (8.9%) for this loci. p.A313T was further validated at larger data set by restriction digestion using CviAII enzyme. Functional consequences of this locus were also predicted by studying three dimensional structure of CYP11b1 protein. For this purpose, 3D protein model was predicted by homology modeling, secondary structural attributes were determined, signal peptide was predicted and a transmembrane helix was also identified. One of polymorphism (p.Y205L) was found in the vicinity of functionally significant F-G loop region, which is the part of protein gets attached to the inner mitochondrial membrane. But this variation could not be associated and needs further investigation. p.A30V, a popular selection marker in cattle, was found in buffaloes as well but could not be associated and might need further confirmation on larger data set. Results of this study illustrate the impending potential of this gene in determining dairy capabilities of buffaloes and might have a role in selection of superior dairy buffaloes.

Relative contribution of P450c17 towards the acute cortisol response: Lessons from sheep and goats

The rapid release of cortisol from the adrenal cortex upon ACTH receptor activation plays an integral role in the stress response. It has been suggested that the quantitative control over adrenal steroidogenesis (quantity of total steroids produced) depends on the activities of cytochrome P450 side-chain cleavage and steroidogenic acute regulatory protein that supplies pregnenolone precursor to the pathway. The qualitative control (which steroids) then depends on the downstream steroidogenic enzymes, including cytochrome P450 17α-hydroxylase/17,20-lyase (P450c17). In this review we focus on the relative contribution of P450c17 in the qualitative control of cortisol production with data collected from studies on South African Angora and Boer goats, as well as Merino sheep. Unique P450c17 genotypes were identified in these breeds with isoforms differing only with a couple of single amino acid residue substitutions. This review demonstrates how molecular and cellular differences relating to P450c17 activity can affect physiological and behavioural responses.

Dietary restriction in the periconceptional period in normal-weight or obese ewes results in increased abundance of angiotensin-converting enzyme (ACE) and angiotensin type 1 receptor (AT1R) in the absence of changes in ACE or AT1R methylation in the adrenal of the offspring

Exposure to dietary restriction during the periconceptional period in either normal or obese ewes results in increased adrenal growth and a greater cortisol response to stress in the offspring, but the mechanisms that programme these changes are not fully understood. Activation of the angiotensin type 1 receptor (AT1R) has been demonstrated to stimulate adrenal growth and steroidogenesis. We have used an embryo transfer model in the sheep to investigate the effects of exposure to dietary restriction in normal or obese mothers from before and 1 week after conception on the methylation status, expression, abundance and localisation of key components of the renin–angiotensin system (RAS) in the adrenal of post-natal lambs. Maternal dietary restriction in normal or obese ewes during the periconceptional period resulted in an increase in angiotensin-converting enzyme (ACE) and AT1R abundance in the absence of changes in the methylation status or mRNA expression ofACEandAT1Rin the adrenal of the offspring. Exposure to maternal obesity alone also resulted in an increase in adrenal AT1R abundance. There was no effect of maternal dietary restriction or obesity on ACE2 and AT2R or on ERK, calcium/calmodulin-dependent kinase II abundance, and their phosphorylated forms in the lamb adrenal. Thus, weight loss around the time of conception, in both normal-weight and obese ewes, results in changes within the intra-adrenal RAS consistent with increased AT1R activation. These changes within the intra-adrenal RAS system may contribute to the greater adrenal stress response following exposure to signals of adversity in the periconceptional period.

Exploration of the Hypothalamic-Pituitary-Adrenal Axis to Improve Animal Welfare by Means of Genetic Selection: Lessons from the South African Merino

It is a difficult task to improve animal production by means of genetic selection, if the environment does not allow full expression of the animal's genetic potential. This concept may well be the future for animal welfare, because it highlights the need to incorporate traits related to production and robustness, simultaneously, to reach sustainable breeding goals. This review explores the identification of potential genetic markers for robustness within the hypothalamic-pituitary-adrenal axis (HPAA), since this axis plays a vital role in the stress response. If genetic selection for superior HPAA responses to stress is possible, then it ought to be possible to breed robust and easily managed genotypes that might be able to adapt to a wide range of environmental conditions whilst expressing a high production potential. This approach is explored in this review by means of lessons learnt from research on Merino sheep, which were divergently selected for their multiple rearing ability. These two selection lines have shown marked differences in reproduction, production and welfare, which makes this breeding programme ideal to investigate potential genetic markers of robustness. The HPAA function is explored in detail to elucidate where such genetic markers are likely to be found.

Joint analysis of the influence of CYP11B1 and DGAT1 genetic variation on milk production, somatic cell score, conformation, reproduction, and productive lifespan in German Holstein cattle1

Recent publications indicate genetic variation in milk production traits on proximal BTA14, which cannot be explained solely with genetic variation in the DGAT1 gene. To elucidate these QTL effects, animals from a German Holstein granddaughter design (18 families, 1,291 sons) were genotyped for CYP11B1 (V30A) and DGAT1 (K232A) polymorphisms. Frequencies of alleles of maternal descent were estimated for CYP11B1(V) (0.776) and DGAT1(K) (0.549). Allele substitution effects (alpha/2) were first calculated for both alleles in separate models and then in a joint model. From the joint analysis, CYP11B1(V) effects on fat content (+0.04%) and protein content (+0.01%) were positive. Effects on milk yield (-82 kg), fat yield (-0.5 kg), and protein yield (-1.9 kg) were negative. Compared with the individual analysis, DGAT1(K) effects on fat content (+0.28%), protein content (+0.06%), and milk yield (-258 kg) were reduced; fat yield (+10.8 kg) was enhanced; and protein yield (-3.8 kg) was reduced. In the joint analysis, allele substitution effects of CYP11B1(V) and DGAT1(K) together explained more of the variation in milk production traits than DGAT1(K) alone. Further significant effects were found for CYP11B1(V) and DGAT1(K) among 6 reproduction traits and 14 conformational traits. These observations indicate a possible negative influence of DGAT1(K) on maternal nonreturn rate, and thus, on length of productive life.

Molecular identity and gene expression of aldosterone synthase cytochrome P450

11Beta-hydroxylase (CYP11B1) of bovine adrenal cortex produced corticosterone as well as aldosterone from 11-deoxycorticosterone in the presence of the mitochondrial P450 electron transport system. CYP11B1s of pig, sheep, and bullfrog, when expressed in COS-7 cells, also performed corticosterone and aldosterone production. Since these CYP11B1s are present in the zonae fasciculata and reticularis as well as in the zona glomerulosa, the zonal differentiation of steroid production may occur by the action of still-unidentified factor(s) on the enzyme-catalyzed successive oxygenations at C11- and C18-positions of steroid. In contrast, two cDNAs, one encoding 11beta-hydroxylase and the other encoding aldosterone synthase (CYP11B2), were isolated from rat, mouse, hamster, guinea pig, and human adrenals. The expression of CYP11B1 gene was regulated by cyclic AMP (cAMP)-dependent signaling, whereas that of CYP11B2 gene by calcium ion-signaling as well as cAMP-signaling. Salt-inducible protein kinase, a cAMP-induced novel protein kinase, was one of the regulators of CYP11B2 gene expression.

Analyses of the CYP11B gene family in the guinea pig suggest the existence of a primordial CYP11B gene with aldosterone synthase activity

In this study we describe the isolation of three genes of the CYP11B family of the guinea pig. CYP11B1 codes for the previously described 11beta-hydroxylase [Bülow, H.E.,Möbius, K., Bähr, V. & Bernhardt, R. (1996) Biochem. Biophys. Res. Commun. 221, 304-312] while CYP11B2 represents the aldosterone synthase gene. As no expression for CYP11B3 was detected this gene might represent a pseudogene. Transient transfection assays show higher substrate specificity for its proper substrate for CYP11B1 as compared to CYP11B2, which could account for the zone-specific synthesis of mineralocorticoids and glucocorticoids, respectively. Thus, CYP11B2 displayed a fourfold higher ability to perform 11beta-hydroxylation of androstenedione than CYP11B1, while this difference is diminished with the size of the C17 substituent of the substrate. Furthermore, analyses with the electron transfer protein adrenodoxin indicate differential sensitivity of CYP11B1 and CYP11B2 as well as the three hydroxylation steps catalysed by CYP11B2 to the availability of reducing equivalents. Together, both mechanisms point to novel protein intrinsic modalities to achieve tissue-specific production of mineralocorticoids and glucocorticoids in the guinea pig. In addition, we conducted phylogenetic analyses. These experiments suggest that a common CYP11B ancestor gene that possessed both 11beta-hydroxylase and aldosterone synthase activity underwent a gene duplication event before or shortly after the mammalian radiation with subsequent independent evolution of the system in different lines. Thus, a differential mineralocorticoid and glucocorticoid synthesis might be an exclusive achievement of mammals.

Ontogeny of angiotensin II type 1 receptor and cytochrome P450(c11) in the sheep adrenal gland

In the present study we investigated the ontogeny of the expression of the type 1 angiotensin receptor (AT(1)R mRNA) and the zonal localization of AT(1)R immunoreactivity (AT(1)R-ir) and cytochrome P450(c11) (CYP11B-ir) in the sheep adrenal gland. In the adult sheep and in the fetus from as early as 90 days gestation, intense AT(1)R-ir was observed predominantly in the zona glomerulosa and to a lesser extent in the zona fasciculata, and it was not detectable in the adrenal medulla. AT(1)R mRNA decreased 4-fold between 105 days and 120 days, whereas AT(1)R mRNA levels remained relatively constant between 120 days and the newborn period. In contrast, both in the adult sheep and in the fetal sheep from as early as 90 days gestation, intense CYP11B-ir was consistently detected throughout the adrenal cortex and in steroidogenic cells that surround the central adrenal vein. In conclusion, we speculate that the presence of AT(1)R in the zona fasciculata, and the higher levels of expression of AT(1)R at around 100 days gestation, may suggest that suppression of CYP17 is mediated via AT(1)R at this time. The abundant expression of AT(1)R-ir and CYP11B-ir in the zona glomerulosa of the fetal sheep adrenal gland would also suggest that lack of angiotensin II stimulation of aldosterone secretion is not due to an absence of AT(1)R or CYP11B in the zona glomerulosa.

Late steps of aldosterone biosynthesis: sheep are not rats

1. The last three steps of aldosterone biosynthesis have been demonstrated to be catalysed by a single enzyme, referred to as CYP11B (or P450(11) beta) in cow, pig, sheep and bullfrog and as CYP11B2 (or P450aldo) in rat, human, mouse and hamster. 2. The related enzyme CYP11B1 (also referred to as P450(11) beta) in rat, human, mouse and hamster does not have aldosterone synthesis activity, but no such enzyme has been reported in the cow, pig or sheep to date. 3. Exclusive aldosterone secretion in the zona glomerulosa (ZG) of the adrenal cortex in species such as rat, human, mouse and hamster could be ascribed to the restricted distribution of CYP11B2 to the same region in the adrenal cortex. 4. In other species, such as cow, pig and sheep, the CYP11B enzyme is expressed throughout the adrenal cortex and, thus, the exclusive aldosterone biosynthesis in the ZG could not be explained simply by the distribution of the enzyme. 5. We have shown in the sheep that potassium loading and acute sodium depletion stimulate the CYP11B transcript levels, which are not further increased by chronic sodium depletion. 6. The predominant CYP11B in the sheep adrenal cortex catalyses the synthesis of aldosterone from deoxycorticosterone (DOC) in vitro, is expressed throughout the adrenal cortex and the corresponding transcript levels are increased by K+ loading or sodium depletion. In short, as far as the last step of aldosterone biosynthesis is concerned, sheep are different from rats. In the rat, the CYP11B2 transcript or protein is elevated by K+ loading or sodium depletion, but not the CYP11B1 transcript or protein. 7. We propose that during severe sodium deficiency there is a switch in the aldosterone pathway to one preferentially involving 18-OH-DOC and not corticosterone.

The renin-angiotensin system and the development of the kidney and adrenal in sheep

1. The earliest form of the kidney, the pronephros, does not really occur in the ovine embryo; instead, a giant glomerulus forms at the anterior end of the mesonephros. 2. In the sheep, the mesonephros is present from 11-38% of total gestation (150 days) and produces a dilute urine, as well as expressing the genes for erythropoietin, renin, angiotensinogen, angiotensin-converting enzyme and the angiotensin II (AngII) receptors AT1 and AT2. 3. The ovine metanephros begins to develop at 18% of gestation and nephrogenesis is complete several weeks before birth. All components of the renin-angiotensin system (RAS) are expressed from at least 27% of gestation. 4. Both AT1 and AT2 receptors are expressed by the adrenocortical cells early in gestation but, at mid-gestation, exogenous AngII does not stimulate aldosterone secretion in vivo. 5. Preliminary results suggest that AngII has important roles in renal development in the ovine foetus but the role(s), if any, in adrenal development, remains to be investigated.

Ontogeny of innervation of rat and ovine fetal adrenals

The formation of adrenocortical zonation occurs in rats during late gestation. Since adult cortical function is modulated by neural mediators, it is possible that the development of differentiated function is dependent on cortical innervation. The goal of this study was to compare the pattern and timing of rodent and ovine adrenal innervation during late organogenesis by staining with antibodies directed against the neuropeptides vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP) and neuropeptide tyrosine (NPY) and the catecholamine biosynthetic enzyme, tyrosine hydroxylase (TOH). Rat adrenals were collected from fetal days 17-21 (term=21 days) and ovine adrenals from fetal days 101-136 (term=145 days). Adrenals were fixed, cryosectioned at 100 microns and immunostained using Cy3-conjugated secondary antibodies. In both species, staining of VIP, CGRP, NPY and TOH fibers was observed in the capsule and subcapsular layers of the cortex during gestation. In late gestation, VIP- and NPY-positive ganglions cells were observed near the medulla extending processes toward the outer cortex; in ovine adrenals, fibers from ganglion cells appeared to surround nests of outer cortical (presumably, zona glomerulosa) cells. These data show that phenotypically distinct neural elements appear at different stages of adrenocortical development. The presence of neural elements in contact with adrenal cortical cells supports the possibility for neural control of adrenocortical development.

Hypothesis: aldosterone is synthesized by an alternative pathway during severe sodium depletion. 'A new wine in an old bottle'

1. The last three steps of aldosterone biosynthesis, 11 beta-hydroxylation, 18-hydroxylation and 18-oxidation, have been demonstrated to be catalysed by one enzyme, which is the cytochrome P450(11 beta) (CYP11B) in cow, pig, sheep and bullfrog or cytochrome P450aldo (CYP11B2) in rat, human, mouse and hamster. 2. The related enzyme P450(11 beta) (CYP11B1) from rat, human, mouse and hamster adrenals displays 11 beta-hydroxylation and 18-hydroxylation activities, but not 18-oxidation activity in vitro. No such enzyme has been reported in the cow, pig or sheep to date. 3. Data showing the dissociation of aldosterone secretion from plasma angiotensin II (AngII) levels indicate the presence of other factor(s) that regulate aldosterone biosynthesis in response to changes in body sodium status. Thus, we propose the existence of a 'sodium status factor' that regulates aldosterone biosynthesis in addition to AngII, K+, adrenocorticotropic hormone and atrial natriuretic peptide. 4. We propose that during severe sodium deficiency there is a switch in the aldosterone pathway to a pathway using 18-hydroxy-deoxycorticosterone (18-OH-DOC) rather than corticosterone as an intermediate. This switch may be mediated via the putative 'sodium status factor'. 5. Two models of the hypothesis will be discussed in this paper: (i) a 'one-enzyme' model; and (ii) a 'two-enzyme' model. 6. The one-enzyme model proposes that P450aldo (P450(11 beta) as in the case of the cow, sheep and pig) changes its enzymatic activity during severe sodium deficiency (i.e. switching to the alternative aldosterone biosynthesis pathway). 7. The two-enzyme model proposes that, under normal circumstances, P450aldo synthesizes aldosterone from deoxycorticosterone, while during severe sodium deficiency the P450(11 beta) provides the substrate (i.e. 18-OH-DOC) for the P450aldo.