Desmosterolosis: an illustration of diagnostic ambiguity of cholesterol synthesis disorders

DHCR24-mediated sterol homeostasis during spermatogenesis is required for sperm mitochondrial sheath formation and impacts male fertility over time

Desmosterol and cholesterol are essential lipid components of the sperm plasma membrane. Cholesterol efflux is required for capacitation, a process through which sperm acquire fertilizing ability. In this study, using a transgenic mouse model overexpressing 24-dehydrocholesterol reductase (DHCR24), an enzyme in the sterol biosynthesis pathway responsible for the conversion of desmosterol to cholesterol, we show that disruption of sterol homeostasis during spermatogenesis led to defective sperm morphology characterized by incomplete mitochondrial packing in the midpiece, reduced sperm count and motility, and a decline in male fertility with increasing paternal age, without changes in body fat composition. Sperm depleted of desmosterol exhibit inefficiency in the acrosome reaction, metabolic dysfunction, and an inability to fertilize the egg. These findings provide molecular insights into sterol homeostasis for sperm capacitation and its impact on male fertility.

Exploiting in silico structural analysis to introduce emerging genotype-phenotype correlations in DHCR24-related sterol biosynthesis disorder: a case study

Desmosterolosis is a rare sterol biosynthesis disorder characterized by multiple congenital anomalies, failure to thrive, severe developmental delay, progressive epileptic encephalopathy, and elevated levels of desmosterol caused by biallelic mutations of DHCR24 encoding 3-β-hydroxysterol Δ-24-reductase. DHCR24 is regarded as the key enzyme of cholesterol synthesis in the metabolism of brain cholesterol as it catalyzes the reduction of the Δ-24 double bond of sterol intermediates during cholesterol biosynthesis. To date, 15 DHCR24 variants, detected in 2 related and 14 unrelated patients, have been associated with the desmosterolosis disorder. Here, we describe a proband harboring the never-described DHCR24 homozygous missense variant NM_014762.4:c.506T>C, NP_055577.1:p.M169T, whose functional validation was confirmed through biochemical assay. By using molecular dynamics simulation techniques, we investigated the impact of this variant on the protein stability and interaction network with the flavin adenine dinucleotide cofactor, thereby providing a preliminary assessment of its mechanistic role in comparison to all known pathogenic variants, the wild-type protein, and a known benign DHCR24 variant. This report expands the clinical and molecular spectra of the DHCR24-related disorder, reports on a novel DHCR24 deleterious variant associated with desmosterolosis, and gives new insights into genotype-phenotype correlations.

DHCR24 in Tumor Diagnosis and Treatment: A Comprehensive Review

As an important nutrient in the human body, cholesterol can not only provide structural components for the body's cells, but also can be transformed into a variety of active substances to regulate cell signaling pathways. As an important cholesterol synthase, DHCR24 participates in important regulatory processes in the body. The application of DHCR24 in tumor clinical diagnosis and treatment also attracts much attention. This article reviews the structure and regulatory characteristics of DHCR24, and the research of DHCR24 on tumor progression. We summarize the possible mechanisms of DHCR24 promoting tumor progression through reactive oxygen species (ROS), p53, Ras and PI3K-AKT pathways. Through our review, we hope to provide more research ideas and reference value for the application of DHCR24 in tumor prevention and treatment.

Amiodarone accumulates two cholesterol precursors in myocardium: A controlled clinical study

BACKGROUND

Amiodarone is an effective antiarrhythmic drug, which interferes with cholesterol synthesis. In the human body, it inhibits two enzymes in the cholesterol-synthesis pathway, followed by increases especially in serum desmosterol and zymostenol concentrations and a decrease in that of serum lathosterol.

OBJECTIVES

We explored whether desmosterol and zymostenol accumulate also in myocardial tissue during amiodarone treatment.

METHODS

Thirty-three patients admitted for cardiac transplantation volunteered for the study. Ten patients were on amiodarone treatment (AD group) and 23 were not (control group). The groups were matched as regards demographic and clinical variables. Myocardial samples were obtained from the removed hearts from 31 patients. Cholesterol, non-cholesterol sterols and squalene were quantified by means of gas-liquid chromatography.

RESULTS

In serum and myocardium, desmosterol was 19- and 18-fold higher and zymostenol 4- and 2-fold higher in the AD group versus the control group (p < 0.001 for all). In contrast, myocardial cholesterol, squalene and lathosterol levels were lower in the AD group than in the control group (p < 0.05 for all). Levels of phytosterols and cholestanol were similar in the serum and myocardium in the two groups. Levels of myocardial and serum desmosterol, zymostenol, lathosterol and phytosterols correlated with each other in both groups (p < 0.05 for all).

CONCLUSION

Amiodarone treatment caused the accumulation of desmosterol and zymostenol in myocardium. In particular, myocardial desmosterol concentrations were substantially elevated, which may play a part in some of the therapeutic and adverse effects of amiodarone treatment.

First case of desmosterolosis diagnosed by prenatal whole exome sequencing

Desmosterolosis is a rare autosomal recessive disorder of cholesterol biosynthesis resulting in multiple congenital abnormalities and syndromic intellectual disability. It is caused by defects in DHCR24, the gene encoding 3-β-hydroxysterol-24-reductase (24-dehydrocholesterol reductase), which acts in conversion of cholesterol precursor desmosterol, hence resulting in elevated plasma desmosterol levels. To date, desmosterolosis has been reported in 10 patients. Here we report an eleventh patient with desmosterolosis, and the first one to be diagnosed antenatally. Diagnosis was made on whole exome sequencing after amniocentesis due to complex antenatal abnormalities including cerebellar hypoplasia, microgyria, aortic stenosis, and renal tract abnormalities. Sterol quantitation was subsequently done postnatally, which supported the diagnosis. Although the nonspecific features make desmosterolosis difficult to suspect, we demonstrate that disorders of cholesterol synthesis can be considered as a differential diagnosis antenatally.

High Bone Mass Disorders: New Insights From Connecting the Clinic and the Bench

Monogenic high bone mass (HBM) disorders are characterized by an increased amount of bone in general, or at specific sites in the skeleton. Here, we describe 59 HBM disorders with 50 known disease-causing genes from the literature, and we provide an overview of the signaling pathways and mechanisms involved in the pathogenesis of these disorders. Based on this, we classify the known HBM genes into HBM (sub)groups according to uniform Gene Ontology (GO) terminology. This classification system may aid in hypothesis generation, for both wet lab experimental design and clinical genetic screening strategies. We discuss how functional genomics can shape discovery of novel HBM genes and/or mechanisms in the future, through implementation of omics assessments in existing and future model systems. Finally, we address strategies to improve gene identification in unsolved HBM cases and highlight the importance for cross-laboratory collaborations encompassing multidisciplinary efforts to transfer knowledge generated at the bench to the clinic. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Sterol regulation of developmental and oncogenic Hedgehog signaling

The Hedgehog (Hh) family of lipid-modified signaling proteins directs embryonic tissue patterning and postembryonic tissue homeostasis, and dysregulated Hh signaling drives familial and sporadic cancers. Hh ligands bind to and inhibit the tumor suppressor Patched and allow the oncoprotein Smoothened (SMO) to accumulate in cilia, which in turn activates the GLI family of transcription factors. Recent work has demonstrated that endogenous cholesterol and oxidized cholesterol derivatives (oxysterols) bind and modulate SMO activity. Here we discuss the myriad sterols that activate or inhibit the Hh pathway, with emphasis on endogenous 24(S),25-epoxycholesterol and 3β,5α-dihydroxycholest-7-en-6-one, and propose models of sterol regulation of SMO. Synthetic inhibitors of SMO have long been the focus of drug development efforts. Here, we discuss the possible utility of steroidal SMO ligands or inhibitors of enzymes involved in sterol metabolism as cancer therapeutics.

Generation and validation of a conditional knockout mouse model for desmosterolosis

The enzyme 3β-hydroxysterol-Δ24 reductase (DHCR24, EC 1.3.1.72) catalyzes the conversion of desmosterol to cholesterol and is obligatory for post-squalene cholesterol synthesis. Genetic loss of this enzyme results in desmosterolosis (MIM #602398), a rare disease that presents with multiple congenital anomalies, features of which overlap with subjects with the Smith-Lemli-Opitz syndrome (another post-squalene cholesterol disorder). Global knockout (KO) of Dhcr24 in mice recapitulates the biochemical phenotype, but pups die within 24 h from a lethal dermopathy, limiting its utility as a disease model. Here, we report a conditional KO mouse model (Dhcr24^flx/flx) and validate it by generating a liver-specific KO (Dhcr24^{flx/flx,Alb-Cre}). Dhcr24^{flx/flx,Alb-Cre} mice showed normal growth and fertility, while accumulating significantly elevated levels of desmosterol in plasma and liver. Of interest, despite the loss of cholesterol synthesis in the liver, hepatic architecture, gene expression of sterol synthesis genes, and lipoprotein secretion appeared unchanged. The increased desmosterol content in bile and stool indicated a possible compensatory role of hepatobiliary secretion in maintaining sterol homeostasis. This mouse model should now allow for the study of the effects of postnatal loss of DHCR24, as well as role of tissue-specific loss of this enzyme during development and adulthood.

Male pseudohermaphroditism: A case study of 46,XY disorder of sexual development using whole-exome sequencing

The study shows that whole-exome sequencing is a promising approach to detect novel variants-and gene candidates in DSD, that, as a future direction, may improve the diagnostic gene panels for this heterogeneous disorder.

Desmosterol accumulation in users of amiodarone

BACKGROUND

Amiodarone is an effective and widely used antiarrhythmic drug with many possible adverse effects including hypercholesterolaemia and hepatotoxicity.

OBJECTIVE

Our aim was to evaluate how long-term amiodarone treatment affects cholesterol metabolism.

METHODS

The study population consisted of 56 cardiac patients, of whom 20 were on amiodarone (amiodarone + group) and 36 did not use the drug (amiodarone - group). We also studied a control group of 124 individuals selected randomly from the population. Cholesterol metabolism was evaluated by analysis of serum noncholesterol sterols by gas-liquid chromatography and gas chromatography-mass spectrometry.

RESULTS

Comparisons of serum lipids and noncholesterol sterols across the three groups showed increased serum triglyceride in users of amiodarone but no statistically significant group differences in total, LDL or HDL cholesterol or serum proprotein convertase subtilisin/kexin type 9 concentrations. Nor did the groups differ in the ratios of cholestanol or plant sterols to cholesterol in serum, suggesting that cholesterol absorption was unaltered. However, all users of amiodarone had very markedly elevated serum desmosterol concentrations: the desmosterol-to-cholesterol ratio (10² × μmol mmol^-1 ) averaged 1030.7 ± 115.7 (mean ± SE) in the amiodarone + group versus 82.7 ± 3.4 and 75.9 ± 1.4 in the amiodarone - and the population control groups (P < 0.001), respectively.

CONCLUSION

Use of amiodarone was associated with on average 12-fold serum desmosterol concentrations compared with the control groups. This observation is fully novel and suggests that amiodarone interferes with the conversion of desmosterol to cholesterol in the cholesterol synthesis pathway. Whether accumulation of desmosterol plays a role in amiodarone-induced hepatotoxicity deserves to be studied in the future.

Desmosterolosis presenting with multiple congenital anomalies

Desmosterolosis is a rare multiple congenital anomaly syndrome caused by a defect in the enzyme 3-beta-hydroxysterol delta-24-reductase (DHCR24) in the cholesterol biosynthesis pathway. Defects in this enzyme cause increased level of the cholesterol precursor desmosterol while disrupting development of cholesterol, impacting embryogenesis. A total of 9 cases of desmosterolosis have been reported to date. We report a 20-month-old male from consanguineous parents with multiple congenital anomalies including corpus callosum hypoplasia, facial dysmorphism, cleft palate, pectus deformity, short and wide neck and distal contractures. On analysis of the regions of homozygosity found by microarray, we identified DHCR24 as a candidate gene. Sterol quantitation showed a desmosterol level of 162 μg/mL (nl: 0.82 ± 0.48). Genetic testing confirmed the diagnosis with a homozygous likely pathogenic mutation (p.Glu191Lys) in the DHCR24 gene. Our case expands the known diagnostic spectrum for Desmosterolosis. We suggest considering Desmosterolosis in the differential diagnosis of patients who present with concurrent agenesis of the corpus callosum with white matter atrophy and ventriculomegaly, retromicrognathia with or without cleft palate, hand contractures, and delay of growth and development. Children of consanguineous mattings may be at higher risk for rare recessive disorders and testing for cholesterol synthesis defect should be a consideration for affected children. Initial evaluation can be performed using sterol quantitation, followed by genetic testing.

Probes for protein adduction in cholesterol biosynthesis disorders: Alkynyl lanosterol as a viable sterol precursor

The formation of lipid electrophile-protein adducts is associated with many disorders that involve perturbations of cellular redox status. The identities of adducted proteins and the effects of adduction on protein function are mostly unknown and an increased understanding of these factors may help to define the pathogenesis of various human disorders involving oxidative stress. 7-Dehydrocholesterol (7-DHC), the immediate biosynthetic precursor to cholesterol, is highly oxidizable and gives electrophilic oxysterols that adduct proteins readily, a sequence of events proposed to occur in Smith-Lemli-Opitz syndrome (SLOS), a human disorder resulting from an error in cholesterol biosynthesis. Alkynyl lanosterol (a-Lan) was synthesized and studied in Neuro2a cells, Dhcr7-deficient Neuro2a cells and human fibroblasts. When incubated in control Neuro2a cells and control human fibroblasts, a-Lan completed the sequence of steps involved in cholesterol biosynthesis and alkynyl-cholesterol (a-Chol) was the major product formed. In Dhcr7-deficient Neuro2a cells or fibroblasts from SLOS patients, the biosynthetic transformation was interrupted at the penultimate step and alkynyl-7-DHC (a-7-DHC) was the major product formed. When a-Lan was incubated in Dhcr7-deficient Neuro2a cells and the alkynyl tag was used to ligate a biotin group to alkyne-containing products, protein-sterol adducts were isolated and identified. In parallel experiments with a-Lan and a-7-DHC in Dhcr7-deficient Neuro2a cells, a-7-DHC was found to adduct to a larger set of proteins (799) than a-Lan (457) with most of the a-Lan protein adducts (423) being common to the larger a-7-DHC set. Of the 423 proteins found common to both experiments, those formed from a-7-DHC were more highly enriched compared to a DMSO control than were those derived from a-Lan. The 423 common proteins were ranked according to the enrichment determined for each protein in the a-Lan and a-7-DHC experiments and there was a very strong correlation of protein ranks for the adducts formed in the parallel experiments.

Protective Effect of DHT on Apoptosis Induced by U18666A via PI3K/Akt Signaling Pathway in C6 Glial Cell Lines

Various useful animal models, such as Alzheimer's disease and Niemann-Pick disease, were provided by U18666A. However, the pathogenesis of U18666A-induced diseases, including U18666A-mediated apoptosis, remains incompletely elucidated, and therapeutic strategies are still limited. Dihydrotestosterone (DHT) has been reported to contribute to the prevention and treatment of neurodegenerative disorders. Our study investigated the neuroprotective activity of DHT in U18666A-related diseases. Apoptosis of C6 cells was detected by Hoechst 33258 fluorescent staining and flow cytometry with annexin V-FITC/PI dual staining. Cell viability was assessed using Cell Counting Kit-8. Expression of apoptosis-related proteins, such as Akt, seladin-1, Bcl-2 family proteins, and caspase-3, was determined using Western blot. Our results demonstrated that the apoptotic rate of C6 cells significantly increased after U18666A addition, but was remarkably reduced after DHT treatment. Pretreatment with DHT attenuated U18666A-induced cell viability loss. PI3K inhibitor LY294002 could suppress DHT anti-apoptotic effect. Furthermore, we discovered that U18666A could significantly downregulate seladin-1 expression in a dose-dependent manner, but no significant change was observed in Bcl-xL, Bax, and P-Akt protein expressions. Compared with U18666A-treated group, the expression of P-Akt, seladin-1, and Bcl-xL significantly increased, and the expression of Bax and caspase-3 remarkably reduced after DHT treatment. However, in the presence of LY294002, the effect of DHT was reversed. In conclusion, we found that seladin-1 may take part in U18666A-induced apoptosis. DHT may inhibit U18666A-induced apoptosis by regulating downstream apoptosis-related proteins including seladin-1, caspase-3, Bcl-xL, and Bax through activation of the PI3K/Akt signal pathway.