Metabolism of 3H-dehydroepiandrosterone sulphate by subjects with steroid sulphatase deficiency

Structural distortions due to missense mutations in human formylglycine-generating enzyme leading to multiple sulfatase deficiency

The major candidate for multiple sulfatase deficiency is a defective formylglycine-generating enzyme (FGE). Though adequately produced, mutations in FGE stall the activation of sulfatases and prevent their activity. Missense mutations, viz. E130D, S155P, A177P, W179S, C218Y, R224W, N259I, P266L, A279V, C336R, R345C, A348P, R349Q and R349W associated with multiple sulfatase deficiency are yet to be computationally studied. Aforementioned mutants were initially screened through ws-SNPs&GO^3D program. Mutant R345C acquired the highest score, and hence was studied in detail. Discrete molecular dynamics explored structural distortions due to amino acid substitution. Therein, comparative analyses of wild type and mutant were carried out. Changes in structural contours were observed between wild type and mutant. Mutant had low conformational fluctuation, high atomic mobility and more compactness than wild type. Moreover, free energy landscape showed mutant to vary in terms of its conformational space as compared to wild type. Subsequently, wild type and mutant were subjected to single-model analyses. Mutant had lesser intra molecular interactions than wild type suggesting variations pertaining to its secondary structure. Furthermore, simulated thermal denaturation showed dissimilar pattern of hydrogen bond dilution. Effects of these variations were observed as changes in elements of secondary structure. Docking studies of mutant revealed less favourable binding energy towards its substrate as compared to wild type. Therefore, theoretical explanations for structural distortions of mutant R345C leading to multiple sulfatase deficiency were revealed. The protocol of the study could be useful to examine the effectiveness of pharmacological chaperones prior to experimental studies.

Role of steroid sulfatase in steroid homeostasis and characterization of the sulfated steroid pathway: Evidence from steroid sulfatase deficiency

The impact of steroid sulfatase (STS) activity in the circulating levels of both sulfated and unconjugated steroids is only partially known. In addition, the sulfated steroid pathway, a parallel pathway to the one for unconjugated steroids, which uses the same enzymes, has never been characterized in detail before. Patients with steroid sulfatase deficiency (STSD) are unable to enzymatically convert sulfated steroids into their unconjugated forms, and are a good model to elucidate how STS affects steroid biosynthesis and to study the metabolism of sulfated steroids. We quantified unconjugated and sulfated steroids in STSD serum, and compared these results with data obtained from serum of healthy controls. Most sulfated steroids were increased in STSD. However, androstenediol-3-sulfate and epiandrosterone sulfate showed similar levels in both groups, and the concentrations of androsterone sulfate were notably lower. Hydroxylated forms of DHEAS and of pregnenolone sulfate were found to be increased in STSD, suggesting a mechanism to improve the excretion of sulfated steroids. STSD testosterone concentrations were normal, but cholesterol and DHEA were significantly decreased. Additionally, serum bile acids were three-fold higher in STSD. Correlations between concentrations of steroids in each group indicate that 17α-hydroxy-pregnenolone-3-sulfate in men is mainly biosynthesized from the precursor pregnenolone sulfate and androstenediol-3-sulfate from DHEAS. These findings confirm the coexistence of two steroidogenic pathways: one for unconjugated steroids and another one for sulfated steroids. Each pathway is responsible for the synthesis of specific steroids. The equal levels of testosterone, and the reduced level of unconjugated precursors in STSD, support that testosterone is primarily synthesized from sulfated steroids. In consequence, testosterone synthesis in STSD relies on an enzyme with sulfatase activity other than STS. This study reveals that STS is a key player of steroid biosynthesis regulating the availability of circulating cholesterol.

The Regulation of Steroid Action by Sulfation and Desulfation

Steroid sulfation and desulfation are fundamental pathways vital for a functional vertebrate endocrine system. After biosynthesis, hydrophobic steroids are sulfated to expedite circulatory transit. Target cells express transmembrane organic anion-transporting polypeptides that facilitate cellular uptake of sulfated steroids. Once intracellular, sulfatases hydrolyze these steroid sulfate esters to their unconjugated, and usually active, forms. Because most steroids can be sulfated, including cholesterol, pregnenolone, dehydroepiandrosterone, and estrone, understanding the function, tissue distribution, and regulation of sulfation and desulfation processes provides significant insights into normal endocrine function. Not surprisingly, dysregulation of these pathways is associated with numerous pathologies, including steroid-dependent cancers, polycystic ovary syndrome, and X-linked ichthyosis. Here we provide a comprehensive examination of our current knowledge of endocrine-related sulfation and desulfation pathways. We describe the interplay between sulfatases and sulfotransferases, showing how their expression and regulation influences steroid action. Furthermore, we address the role that organic anion-transporting polypeptides play in regulating intracellular steroid concentrations and how their expression patterns influence many pathologies, especially cancer. Finally, the recent advances in pharmacologically targeting steroidogenic pathways will be examined.

High levels of oxysterol sulfates in serum of patients with steroid sulfatase deficiency

Steroid sulfatase (STS) deficiency is the underlying cause of the skin condition known as recessive X-linked ichthyosis (RXLI). RXLI patients show scales on their skin caused by high concentrations of cholesterol sulfate (CS), as they are not capable of releasing the sulfate group from its structure to obtain free cholesterol. CS has been reported, so far, as the sole sulfated steroid with increased concentrations in the blood of RXLI patients. A non-targeted LC-MS approach in negative mode detection (LC-MS precursor ion scan mode) was applied to serum samples of 12 RXLI patients and 19 healthy males. We found that CS was not the only sulfated compound consistently elevated in RXLI patients, because a group of compounds with a m/z of 481 was found in high concentrations too. Further LC-MS/MS demonstrated that the main contributor to the m/z 481 signal in RXLI serum is 27-hydroxycholesterol-3-sulfate (27OHC3S). Accordingly, a new method for 27OHC3S quantification in the context of RXLI has been developed and validated. Other hydroxycholesterol sulfate compounds were elevated as well in RXLI patients.

Role of cholesterol sulfate in epidermal structure and function: lessons from X-linked ichthyosis

X-linked ichthyosis is a relatively common syndromic form of ichthyosis most often due to deletions in the gene encoding the microsomal enzyme, steroid sulfatase, located on the short area of the X chromosome. Syndromic features are mild or unapparent unless contiguous genes are affected. In normal epidermis, cholesterol sulfate is generated by cholesterol sulfotransferase (SULT2B1b), but desulfated in the outer epidermis, together forming a 'cholesterol sulfate cycle' that potently regulates epidermal differentiation, barrier function and desquamation. In XLI, cholesterol sulfate levels my exceed 10% of total lipid mass (≈1% of total weight). Multiple cellular and biochemical processes contribute to the pathogenesis of the barrier abnormality and scaling phenotype in XLI. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Pathogenesis-based therapies in ichthyoses

During the past 20 years, tremendous progress has been made in our understanding of the molecular basis of many genetic skin conditions. The translation of these laboratory findings into effective therapies for affected individuals has been slow, however, in large part due to the risk of carcinogenesis from random viral genomic integration and the lack of efficacy of topically applied genetic material and most proteins. As intervention at the gene level still appears remote for most genetic disorders, increased knowledge about the cellular and biochemical pathogenesis of disease allows specific targeting of pathways with existing and/or novel drugs and molecules. In contrast to the requirement for personalization of most gene-based approaches, pathogenesis-based therapy is pathway specific, and in theory, it should have broader applicability. In this chapter, we provide an overview of the pathoetiology of the various types of ichthyoses and demonstrate how a pathogenesis-based approach can potentially lead to innovative treatments for these conditions. Notably, this strategy has been successfully validated for the treatment of the rare X-linked dominant condition, CHILD syndrome, in which topical applications of cholesterol and lovastatin together to affected skin resulted in marked improvement of the skin phenotype.

Abnormal barrier function in the pathogenesis of ichthyosis: therapeutic implications for lipid metabolic disorders

Ichthyoses, including inherited disorders of lipid metabolism, display a permeability barrier abnormality in which the severity of the clinical phenotype parallels the prominence of the barrier defect. The pathogenesis of the cutaneous phenotype represents the consequences of the mutation for epidermal function, coupled with a "best attempt" by affected epidermis to generate a competent barrier in a terrestrial environment. A compromised barrier in normal epidermis triggers a vigorous set of metabolic responses that rapidly normalizes function, but ichthyotic epidermis, which is inherently compromised, only partially succeeds in this effort. Unraveling mechanisms that account for barrier dysfunction in the ichthyoses has identified multiple, subcellular, and biochemical processes that contribute to the clinical phenotype. Current treatment of the ichthyoses remains largely symptomatic: directed toward reducing scale or corrective gene therapy. Reducing scale is often minimally effective. Gene therapy is impeded by multiple pitfalls, including difficulties in transcutaneous drug delivery, high costs, and discomfort of injections. We have begun to use information about disease pathogenesis to identify novel, pathogenesis-based therapeutic strategies for the ichthyoses. The clinical phenotype often reflects not only a deficiency of pathway end product due to reduced-function mutations in key synthetic enzymes but often also accumulation of proximal, potentially toxic metabolites. As a result, depending upon the identified pathomechanism(s) for each disorder, the accompanying ichthyosis can be treated by topical provision of pathway product (eg, cholesterol), with or without a proximal enzyme inhibitor (eg, simvastatin), to block metabolite production. Among the disorders of distal cholesterol metabolism, the cutaneous phenotype in Congenital Hemidysplasia with Ichthyosiform Erythroderma and Limb Defects (CHILD syndrome) and X-linked ichthyosis reflect metabolite accumulation and deficiency of pathway product (ie, cholesterol). We validated this therapeutic approach in two CHILD syndrome patients who failed to improve with topical cholesterol alone, but cleared with dual treatment with cholesterol plus lovastatin. In theory, the ichthyoses in other inherited lipid metabolic disorders could be treated analogously. This pathogenesis (pathway)-driven approach possesses several inherent advantages: (1) it is mechanism-specific for each disorder; (2) it is inherently safe, because natural lipids and/or approved drugs often are utilized; and (3) it should be inexpensive, and therefore it could be used widely in the developing world.

Pathogenesis of the cutaneous phenotype in inherited disorders of cholesterol metabolism: Therapeutic implications for topical treatment of these disorders

Molecular geneticists tend to conceptualize disease pathogenesis from the mutated gene outward, an approach that does not take into account the impact of barrier requirements in determining disease phenotype. An ‘outside-to-inside’ perspective has provided quite different explanations for the ichthyoses, including several of the disorders of distal cholesterol metabolism. Elucidation of responsible pathogenic mechanisms also is pointing to appropriate, pathogenesis (pathway)-based therapeutic strategies. In the case of the lipid metabolic disorders, it takes full advantage of new molecular, genetic and cellular pathogenesis information to correct or bypass the metabolic abnormality. This approach fully exploits the unique accessibility of the skin to a topical approach. Moreover, since it will utilize topical lipids and lipid-soluble, and often generic, lipid-soluble drugs, these treatments should be readily transported across the stratum corneum. If successful, this approach could initiate an entirely new departure for the therapy of the ichthyoses. Finally, because these agents are relatively safe and inexpensive, this form of treatment has the potential to be widely-deployed, even in the developing world.

Pathogenesis of permeability barrier abnormalities in the ichthyoses: inherited disorders of lipid metabolism

Many of the ichthyoses are associated with inherited disorders of lipid metabolism. These disorders have provided unique models to dissect physiologic processes in normal epidermis and the pathophysiology of more common scaling conditions. In most of these disorders, a permeability barrier abnormality "drives" pathophysiology through stimulation of epidermal hyperplasia. Among primary abnormalities of nonpolar lipid metabolism, triglyceride accumulation in neutral lipid storage disease as a result of a lipase mutation provokes a barrier abnormality via lamellar/nonlamellar phase separation within the extracellular matrix of the stratum corneum (SC). Similar mechanisms account for the barrier abnormalities (and subsequent ichthyosis) in inherited disorders of polar lipid metabolism. For example, in recessive X-linked ichthyosis (RXLI), cholesterol sulfate (CSO(4)) accumulation also produces a permeability barrier defect through lamellar/nonlamellar phase separation. However, in RXLI, the desquamation abnormality is in part attributable to the plurifunctional roles of CSO(4) as a regulator of both epidermal differentiation and corneodesmosome degradation. Phase separation also occurs in type II Gaucher disease (GD; from accumulation of glucosylceramides as a result of to beta-glucocerebrosidase deficiency). Finally, failure to assemble both lipids and desquamatory enzymes into nascent epidermal lamellar bodies (LBs) accounts for both the permeability barrier and desquamation abnormalities in Harlequin ichthyosis (HI). The barrier abnormality provokes the clinical phenotype in these disorders not only by stimulating epidermal proliferation, but also by inducing inflammation.

Basis For Abnormal Desquamation And Permeability Barrier Dysfunction in RXLI

Mutations in the gene for steroid sulfatase (SSase), are responsible for recessive x-linked ichthyosis (RXLI). As a consequence of SSase deficiency, its substrate, cholesterol sulfate (CSO4), accumulates in the epidermis. Accumulation of this amphipathic lipid in the outer epidermis provokes both a typical scaling phenotype and permeability barrier dysfunction. Research on RXLI has illuminated several, potentially overlapping pathogenic mechanisms and provided insights about the role of SSase and CSO4 in normal differentiation, barrier maintenance, and desquamation. We now show here that SSase is concentrated in lamellar bodies (LB), and secreted into the SC interstices, along with other LB-derived lipid hydrolases. There, it degrades CSO4, generating some cholesterol for the barrier, while the progressive decline in CSO4 (a serine protease (SP) inhibitor) permits corneodesmosome (CD) degradation leading to normal desquamation. Two molecular pathways contribute to disease pathogenesis in RXLI: 1) excess CSO4 produces nonlamellar phase separation in the stratum corneum (SC) interstices, explaining the barrier abnormality. 2) The increased CSO4 in the SC interstices inhibit activity sufficiently to delay CD degradation, leading to corneocyte retention. We also show here that increased Ca++ in the SC interstices in RXLI could contribute to corneocyte retention, by increasing CD and interlamellar cohesion. RXLI represents one of the best understood diseases in dermatology--from the gene to the SC interstices, its etiology and pathogenesis are becoming clear, and assessment of disease mechanisms in RXLI led to new insights about the role of SSase and CSO4 in epidermis terminal differentiation.

Molecular and biochemical characterisation of a novel sulphatase gene: Arylsulfatase G (ARSG)

Molecular analysis has provided important insights into the biochemistry and genetics of the sulphatase family of enzymes. Through bioinformatic searches of the EST database, we have identified a novel gene consisting of 11 exons and encoding a 525 aa protein that shares a high degree of sequence similarity with all sulphatases and in particular with arylsulphatases, hence the tentative name Arylsulfatase G (ARSG). The highest homology is shared with Arylsulfatase A, a lysosomal sulphatase which is mutated in metachromatic leukodistrophy, particularly in the amino-terminal region. The 10 amino acids that form the catalytic site are strongly conserved. The murine homologue of Arylsulfatase G gene product shows 87% identity with the human protein. To test the function of this novel gene we transfected the full-length cDNA in Cos7 cells, and detected an Arylsulfatase G precursor protein of 62 kDa. After glycosylation the precursor is maturated in a 70 kDa form, which localises to the endoplasmic reticulum. Northern blot analysis of Arylsulfatase G revealed a ubiquitous expression pattern. We tested the sulphatase activity towards two different artificial substrates 4-methylumbelliferyl (4-MU) sulphate and p-nitrocatechol sulphate, but no arylsulphatase activity was detectable. Further studies are needed to characterise the function of Arylsulfatase G, possibly revealing a novel metabolic pathway.

X-linked ichthyosis: relation between cholesterol sulphate, dehydroepiandrosterone sulphate and patient's age

Steroid sulphatase deficiency is a feature of recessive X-linked ichthyosis (RXLI) that causes the accumulation of sulphated steroids (SS) in various organs and cells. In a previous study, we detected elevated cholesterol sulphate (CS) and dehydroepiandrosterone sulphate (DHEAS) serum levels in a group of 15 RXLI patients selected in a narrow age range. In the present study both CS and DHEAS serum levels were qualitatively and quantitatively determined using gas-chromatographic analysis in a group of 33 RXLI patients ranging in age from 3 to 70 years. The levels of CS and DHEAS were significantly increased in all patients. Variations in SS were related both to patients' ages and clinical course of the disease; Serum SS levels start to increase in early infancy, peak at puberty, remain elevated in adults and decrease slightly in the elderly.

Identification by shotgun sequencing, genomic organization, and functional analysis of a fourth arylsulfatase gene (ARSF) from the Xp22.3 region

We recently reported the isolation of two new members of the sulfatase gene family, arylsulfatase D (ARSD) and E (ARSE), located approximately 50 kb from each other in the Xp22.3 region. Mutation analysis indicated ARSE as the gene responsible for X-linked recessive chondrodysplasia punctata. Expression of the ARSE gene in COS cells resulted in a heat-labile arylsulfatase activity that was inhibited by warfarin. At the same time, we detected the presence of a 1.2-kb fragment located at approximately 60 kb from ARSD and ARSE with significant homology to these two genes, suggesting the existence of another sulfatase gene, arylsulfatase F (ARSF), in Xp22.3. We have used a combined approach of long-range genomic sequencing and screening of cDNA libraries to isolate the ARSF gene. Expression of the ARSF cDNA in COS cells resulted in a heat-labile arylsulfatase activity that is not inhibited by warfarin, supporting our hypothesis that only ARSE is specifically inhibited by warfarin and is most likely involved in warfarin embryopathy. Genomic analysis revealed that ARSF has an intron/exon organization highly similar to those of ARSD and ARSE, which is also shared by another Xp22.3 sulfatase gene, ARSC (arylsulfatase C, also known as steroid sulfatase), with the splice sites occurring at the same position in all four genes. The data obtained from sequence analysis and presented in this paper indicate that the ARSC, ARSD, ARSE, and ARSF genes are more similar to each other than to other members of the sulfatase gene family, supporting our hypothesis that they represent a subfamily of related proteins created through duplication events that occurred in an ancestral pseudoautosomal region.

Increased levels of DHEAS in serum of patients with X-linked ichthyosis

The metabolic basis of X-linked ichthyosis is a deficiency of steroid sulphatase, a microsomal enzyme which removes sulphate groups from sulphated steroids. We report on a carefully controlled group of 15 patients with recessive X-linked ichthyosis, selected in a narrow age range (22-33 years), in whom, through the use of gas chromatographic analysis and conventional radioimmunoassay, we have measured not only elevated serum cholesterol sulphate levels but also significantly elevated serum dehydroepiandrosterone sulphate levels. The latter finding has been controversial in previous reports. We believe that the radioimmunoassay procedure generally used should be held responsible for such controversy since it often gives rise to false positive and/or false negative values. Gas chromatography, although more exacting, appears to be far more reliable for the assessment of elevated serum dehydroepiandrosterone.