Structure and alternative splicing of the rat 7-dehydrocholesterol reductase gene

Integrated Transcriptome and 16S rDNA Analyses Reveal That Transport Stress Induces Oxidative Stress and Immune and Metabolic Disorders in the Intestine of Hybrid Yellow Catfish (Tachysurus fulvidraco♀ × Pseudobagrus vachellii♂)

Live fish are often transported in aquaculture. To explore the effects of transport stress, hybrid yellow catfish (Tachysurus fulvidraco♀ × Pseudobagrus vachellii♂) were subjected to simulated transport treatments (0–16 h) with 96 h of recovery after the 16-h transport treatment, and intestinal biochemical parameters, the transcriptome, and gut microbiota were analyzed. Transportation affected the number of mucus cells and led to oxidative stress in the intestine, which activated immune responses. Changes in lipid metabolism reflected metabolic adaptation to oxidative stress. Toll-like receptor signaling, peroxisome proliferator-activated receptor signaling, and steroid biosynthesis pathways were involved in the transport stress response. Gene expression analyses indicated that transport-induced local immune damage was reversible, whereas disordered metabolism recovered more slowly. A 16S rDNA analysis revealed that transport stress decreased the alpha diversity of the gut microbiota and disrupted its homeostasis. The dominant phyla (Fusobacteria, Bacteroidetes) and genera (Cetobacterium, Barnesiellaceae) were involved in the antioxidant, immune, and metabolic responses of the host to transportation stress. Correlation analyses suggested that gut microbes participate in the transport stress response and the host–microbiota interaction may trigger multiple events in antioxidant, immune, and metabolic pathways. Our results will be useful for optimizing transport processes.

Protein disulfide isomerase A3 might be involved in the regulation of 24-dehydrocholesterol reductase via vitamin D equilibrium in primary cortical neurons

Vitamin D is a secosteroid hormone mediating its functions via vitamin D receptor (VDR) and an endoplasmic reticulum chaperone, protein disulfide isomerase A3 (PDIA3). From a physiological perspective, there is also a well-established association of cholesterol and vitamin D synthesis, since both share a common metabolic substrate, 7 dehydrocholesterol (7-DHC). Yet, the potential basic pathways, of the biological interplay of DHCR24 and vitamin D equilibrium, on neuronal level, are yet to be determined. In this study, we aimed to investigate the relation between vitamin D pathways and DHCR24 in primary cortical neuron cultures. The neocortex of Sprague-Dawley rat embryos (E16) was used for the preparation of primary cortical neuron cultures. DHCR24 mRNA and protein expression levels were determined by qRT-PCR, Western blotting, and immunofluorescent labeling in 1,25-dihydroxyvitamin D3-treated or VDR/PDIA3-silenced primary cortical neurons. The mRNA expression of DHCR24 was significantly decreased in the cortical neurons treated with 10-8M 1,25-dihydroxyvitamin D3 (p<0.001). In parallel with the mRNA results, DHCR24 protein expression in cortical neurons treated with 10-8M 1,25-dihydroxyvitamin D3 was also significantly lower than untreated neurons (p<0.05). These data were also confirmed with immunofluorescent labeling and fluorescence intensity measurements of DHCR24 (p<0.001). Finally, DHCR24 mRNA expression level was significantly increased in PDIA3 siRNA-treated neurons (p<0.05). Similar to the mRNA results, the DHCR24 protein expression of PDIA3 siRNA-treated neurons was also statistically higher than the other groups (p<0.05). Results of this mechanistic experimental basic study demonstrate that DHCR24 mRNA expression and protein concentrations attenuated in response to vitamin D treatment. Furthermore, we observed that PDIA3 might be involved in this modulatory effect. Our findings indicate a complex interaction of DHCR24 and vitamin D equilibrium, through the involvement of PDIA3 and vitamin D in the modulation of cholesterol metabolism in neuronal cells, requiring future studies on the field.

Vitamin D equilibrium affects sex-specific changes in lipid concentrations during Christian Orthodox fasting

We aimed to evaluate sex differences in changes of lipid profiles in a cohort of metabolically healthy adults following Orthodox fasting (OF), as well as to assess a potential role of vitamin D status in mediating these variations. 45 individuals (24 premenopausal females, 53.3 %) with mean age 48.3 ± 9.1 years and mean Body Mass Index 28.7 ± 5.8 kg/m² were prospectively followed for 12 weeks. Anthropometry, dietary and biochemical data regarding serum lipids, and vitamin D status were collected at baseline, 7 weeks after the implementation of OF, and 5 weeks after fasters returned to their standard dietary habits (12 weeks from baseline). According to 25-hydroxy-vitamin D [25(OH)D] measurements, participants were divided into two groups: those with concentrations above and below the median of values. Females with 25(OH)D concentrations below the median manifested a non-significant reduction by approximately 15 % in total and low-density lipoprotein cholesterol during the fasting period, followed by a significant increase 5 weeks after OF cessation (170.7 vs. 197.5 and 99.6 vs. 121.0 mg/dl respectively, p < 0.001). In contrast, males with 25(OH)D levels below the median demonstrated an inverse, non-significant trend of increase in lipid concentrations during the whole study period. Our findings suggest strikingly different inter-gender lipid responses to a dietary model of low-fat, mediated by vitamin D status. Further studies are necessary to reveal the underlying mechanisms and assess the importance of these differences with respect to cardiovascular health and the benefit of vitamin D supplementation strategies.

DHCR7: A vital enzyme switch between cholesterol and vitamin D production

The conversion of 7-dehydrocholesterol to cholesterol, the final step of cholesterol synthesis in the Kandutsch-Russell pathway, is catalyzed by the enzyme 7-dehydrocholesterol reductase (DHCR7). Homozygous or compound heterozygous mutations in DHCR7 lead to the developmental disease Smith-Lemli-Opitz syndrome, which can also result in fetal mortality, highlighting the importance of this enzyme in human development and survival. Besides serving as a substrate for DHCR7, 7-dehydrocholesterol is also a precursor of vitamin D via the action of ultraviolet light on the skin. Thus, DHCR7 exerts complex biological effects, involved in both cholesterol and vitamin D production. Indeed, we argue that DHCR7 can act as a switch between cholesterol and vitamin D synthesis. This review summarizes current knowledge about the critical enzyme DHCR7, highlighting recent findings regarding its structure, transcriptional and post-transcriptional regulation, and its links to vitamin D synthesis. Greater understanding about DHCR7 function, regulation and its place within cellular metabolism will provide important insights into its biological roles.

Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive, multiple congenital malformation and intellectual disability syndrome, with clinical characteristics that encompass a wide spectrum and great variability. Elucidation of the biochemical and genetic basis for SLOS, specifically understanding SLOS as a cholesterol deficiency syndrome caused by mutation in DHCR7, opened up enormous possibilities for therapeutic intervention. When cholesterol was discovered to be the activator of sonic hedgehog, cholesterol deficiency with inactivation of this developmental patterning gene was thought to be the cause of SLOS malformations, yet this explanation is overly simplistic. Despite these important research breakthroughs, there is no proven treatment for SLOS. Better animal models are needed to allow potential treatment testing and the study of disease pathophysiology, which is incompletely understood. Creation of human cellular models, especially models of brain cells, would be useful, and in vivo human studies are also essential. Biomarker development will be crucial in facilitating clinical trials in this rare condition, because the clinical phenotype can change over many years. Additional research in these and other areas is critical if we are to make headway towards ameliorating the effects of this devastating condition.

Cholesterol homeostasis in development: the role of Xenopus 7-dehydrocholesterol reductase (Xdhcr7) in neural development

7-dehydrocholesterol reductase (7-Dhcr) catalyses the final step in the pathway of cholesterol biosynthesis. Human patients with inborn errors of 7-Dhcr (Smith-Lemli-Opitz-Syndrome) have elevated serum levels of 7-dehydrocholesterol but low levels of cholesterol, which in phenotypical terms can result in growth retardation, craniofacial abnormalities including cleft palate, and reduced metal abilities. This study reports the isolation and molecular characterisation of 7-dehydrocholesterol reductase (Xdhcr7) from Xenopus laevis. During early embryonic development, the expression of Xdhcr7 is first of all spatially restricted to the Spemann's organizer and later to the notochord. In both tissues, Xdhcr7 is coexpressed with Sonic hedgehog (Shh), which itself is cholesterol-modified during autoproteolytic cleavage. Data from Xdhcr7 overexpression and knockdown experiments reveals that a tight control of cholesterol synthesis is particularly important for proper development of the central and peripheral nervous system.

Expression and p75 neurotrophin receptor dependence of cholesterol synthetic enzymes in adult mouse brain

Normal brain function depends critically on cholesterol. Although cholesterol is synthesized locally in the adult brain, the precise anatomical localization of cholesterogenic enzymes is not known. Here we show that 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoAred) and 7-dehydrocholesterol reductase (7dhcred), the first and last enzymes, respectively, in the cholesterol biosynthesis pathway, are co-expressed in neurons throughout adult murine brain. Co-localization is most prominent in cortical, hippocampal, and cholinergic neurons. Since adult hippocampal and cholinergic neurons express p75 neurotrophin receptors (p75NTR) we hypothesized that p75NTR regulates expression of cholesterogenic enzymes. Treatment of Neuro2a neuroblastoma cells or primary cerebellar cultures with siRNA downregulates p75NTR and decreases the expression level of HMG-CoAred and 7dhcred. Native neuroblastoma cell lines with differential expression of p75NTR differentially express 7dhcred; 7dhcred expression correlates with p75NTR expression. This suggests that, in p75NTR-expressing cells, p75NTR regulates cholesterol synthesis through regulation of HMG-CoAred and 7dhcred expression. The unexpected localization of cholesterogenic enzymes in adult neurons suggests that at least some adult neurons retain the ability to synthesize cholesterol.

Development and characterization of a hypomorphic Smith–Lemli–Opitz syndrome mouse model and efficacy of simvastatin therapy

Smith-Lemli-Opitz syndrome (SLOS) is a genetic syndrome caused by mutations in the 3beta-hydroxysterol Delta(7)-reductase gene (DHCR7). SLOS patients have decreased cholesterol and increased 7-dehydrocholesterol (7-DHC) levels. Dietary cholesterol supplementation improves systemic biochemical abnormalities; however, because of the blood-brain barrier, the central nervous system (CNS) is not treated. Simvastatin therapy has been proposed as a means to treat the CNS. Mice homozygous for a null disruption of Dhcr7, Dhcr7(Delta3-5/Delta3-5), die soon after birth, thus they cannot be used to study postnatal development or therapy. To circumvent this problem, we produced a hypomorphic SLOS mouse model by introducing a mutation corresponding to DHCR7(T93M). Both Dhcr7(T93M/T93M) and Dhcr7(Delta3-5/T93M) mice are viable. Phenotypic findings in Dhcr7(T93M/Delta3-5) mice include CNS ventricular dilatation and two to three syndactyly. Biochemically, both Dhcr7(T93M/T93M) and Dhcr7(T93M/Delta3-5) mice have elevated tissue 7-DHC levels; however, the biochemical defect improved with age. This has not been observed in human patients, and is due to elevated Dhcr7 expression in mouse tissues. Dietary cholesterol therapy improved sterol profiles in peripheral, but not CNS tissues. However, treatment of Dhcr7(T93M/Delta3-5) mice with simvastatin decreased 7-DHC levels in both peripheral and brain tissues. Expression of Dhcr7 increased in Dhcr7(T93M/Delta3-5) tissues after simvastatin therapy, consistent with the hypothesis that simvastatin therapy improves the biochemical phenotype by increasing the expression of a Dhcr7 allele with residual enzymatic activity. We conclude that simvastatin treatment is efficacious in improving the SLOS-associated sterol abnormality found in the brain, and thus has the potential to be an effective therapeutic intervention for behavioral and learning problems associated with SLOS.

3beta-hydroxysterol Delta7-reductase and the Smith-Lemli-Opitz syndrome

In the final step of cholesterol synthesis, 7-dehydrocholesterol reductase (DHCR7) reduces the double bond at C7-8 of 7-dehydrocholesterol to yield cholesterol. Mutations of DHCR7 cause Smith-Lemli-Opitz syndrome (SLOS). Over 100 different mutations of DHCR7 have been identified in SLOS patients. SLOS is a classical multiple malformation, mental retardation syndrome, and was the first human malformation syndrome shown to result from an inborn error of cholesterol synthesis. This paper reviews the biochemical, molecular, and mutational aspects of DHCR7.