Role of cholesterol in embryonic development

Non-genetic risk factors for holoprosencephaly

Holoprosencephaly (HPE) is a congenital defect of the brain characterized by incomplete cleavage of the embryonic forebrain into left and right hemispheres. Although a substantial proportion of cases of HPE can be attributed to genetic abnormalities, the etiology in many cases remains unknown, with non-genetic risk factors believed to be important contributors. Due to the low birth prevalence of this defect, it has proven difficult to conduct studies of sufficient size to identify risk factors with certainty. This article provides a summary of non-genetic risk factors for HPE that have been investigated in case reports and case series, animal studies, and epidemiologic studies, including maternal illnesses, therapeutic and non-therapeutic exposures, nutritional factors, and sociodemographic factors. The article also highlights challenges in study design and further areas for research to better understand the etiology of HPE.

Cholesterol metabolism: the main pathway acting downstream of cytochrome P450 oxidoreductase in skeletal development of the limb

Cytochrome P450 oxidoreductase (POR) is the obligate electron donor for all microsomal cytochrome P450 enzymes, which catalyze the metabolism of a wide spectrum of xenobiotic and endobiotic compounds. Point mutations in POR have been found recently in patients with Antley-Bixler-like syndrome, which includes limb skeletal defects. In order to study P450 function during limb and skeletal development, we deleted POR specifically in mouse limb bud mesenchyme. Forelimbs and hind limbs in conditional knockout (CKO) mice were short with thin skeletal elements and fused joints. POR deletion occurred earlier in forelimbs than in hind limbs, leading additionally to soft tissue syndactyly and loss of wrist elements and phalanges due to changes in growth, cell death, and skeletal segmentation. Transcriptional analysis of E12.5 mouse forelimb buds demonstrated the expression of P450s involved in retinoic acid, cholesterol, and arachidonic acid metabolism. Biochemical analysis of CKO limbs confirmed retinoic acid excess. In CKO limbs, expression of genes throughout the whole cholesterol biosynthetic pathway was upregulated, and cholesterol deficiency can explain most aspects of the phenotype. Thus, cellular POR-dependent cholesterol synthesis is essential during limb and skeletal development. Modulation of P450 activity could contribute to susceptibility of the embryo and developing organs to teratogenesis.

Plant stanol ester spreads as components of a balanced diet for pregnant and breast-feeding women: evaluation of clinical safety

Clinical safety of consuming plant stanol ester spreads during pregnancy and lactation, the impact on maternal and infant serum and breast-milk cholesterol and the ratios (μmol/mmol of cholesterol) of synthesis and absorption markers were evaluated. Pregnant women (n21) were randomised to control and dietary intervention groups, the intervention including advice to follow a balanced diet and to consume spreads enriched with plant stanol esters. Participants were followed during and after pregnancy and their infants up to 1 year of age. A mean 1·1 (sd0·4) g consumption of plant stanols during pregnancy and 1·4 (sd0·9) g 1 month post-partum increased sitostanol and the markers for cholesterol synthesis, lathosterol, lathosterol/campesterol and lathosterol/sitosterol, and reduced a marker for cholesterol absorption, campesterol, in maternal serum. In breast milk, desmosterol was lower in the intervention group, while no differences were detected between the groups in infants' serum. Plant stanol ester spread consumption had no impact on the length of gestation, infants' growth or serum β-carotene concentration at 1 and 6 months of age, but the cholesterol-adjusted serum β-carotene concentration was lowered at 1 month in the intervention group. Plant stanol ester spread consumption appeared safe in the clinical setting, except for potential lowering of infants' serum β-carotene concentration, and was reflected in the markers of cholesterol synthesis and absorption in mothers' serum, encouraging further studies in larger settings.

Key mechanisms of early lung development

Lung morphogenesis requires the integration of multiple regulatory factors, which results in a functional air-blood interface required for gas exchange at birth. The respiratory tract is composed of endodermally derived epithelium surrounded by cells of mesodermal origin. Inductive signaling between these 2 tissue compartments plays a critical role in formation and differentiation of the lung, which is mediated by evolutionarily conserved signaling families used reiteratively during lung formation, including the fibroblast growth factor, hedgehog, retinoic acid, bone morphogenetic protein, and Wnt signaling pathways. Cells coordinate their response to these signaling proteins largely through transcription factors, which determine respiratory cell fate and pattern formation via the activation and repression of downstream target genes. Gain- and loss-of-function studies in null mutant and transgenic mice models have greatly facilitated the identification and hierarchical classification of these molecular programs. In this review, we highlight select molecular events that drive key phases of pulmonary development, including specification of a lung cell fate, primary lung bud formation, tracheoesophageal septation, branching morphogenesis, and proximal-distal epithelial patterning. Understanding the genetic pathways that regulate respiratory tract development is essential to provide insight into the pathogenesis of congenital anomalies and to develop innovative strategies to treat inherited and acquired lung disease.

A specific inhibitor of cholesterol biosynthesis, BM15.766, reduces the expression of ?-secretase and the production of amyloid-?in vitro

We have previously shown that statins reduce the production of amyloid-beta (Abeta) by both isoprenoid- and cholesterol-dependent mechanisms. These pathways contribute to the regulation of the dimerisation of BACE into its physiologically active form. Statins reduce cellular cholesterol levels by 20-40%; therefore, it is possible that the remaining cholesterol within the cell may play a significant role in the production of Abeta. Incubation of cells with the specific cholesterol biosynthesis inhibitor BM15.766 together with 50 micromol/L simvastatin and 400 micromol/L mevalonate reduced cellular cholesterol levels in a dose-dependent manner with increasing BM15.766 concentration (r = -0.9736, p = 0.0264). Furthermore, decreases in cellular cholesterol levels correlated with reductions in total Abeta production (r = 0.9683, p = 0.0317). A total of 2.5 micromol/L BM15.766 inhibited the dimerisation of BACE, whilst the expression of BACE monomer was reduced by 5 micromol/L BM15.766. BM15.766 treatment localised BACE predominantly within the Golgi, and reduced total BACE expression per cell. Similar changes were observed in the expression of the Golgi marker golgin-97, suggesting that reduced BACE expression may arise from a decrease in protein trafficking and an increase in degradation. By targeting cholesterol synthesis using specific cholesterol biosynthesis inhibitors, it is possible to reduce Abeta production without reducing protein isoprenylation.

Functional analysis of cholesterol biosynthesis by RNA interference

Inborn errors of cholesterol biosynthesis caused by dysfunctionality of single enzymes are known to cause severe malformation syndromes like X-linked chondrodysplasia punctata (CDPX2), CHILD syndrome or Smith-Lemli-Opitz-syndrome (SLOS). In this study we established the method of RNA interference (RNAi) for analyzing the molecular mechanisms underlying disrupted cholesterol biosynthesis. For different genes involved in the cholesterol biosynthesis pathway-NAD(P) dependent steroid dehydrogenase-like (NSDHL), 17-beta hydroxysteroid dehydrogenase type 7 (HSD17B7) and emopamil binding protein (EBP)-shRNA sequences were designed and tested for their effectiveness. For a better comparability of the experiments and to avoid different transfection efficiencies, examined shRNA sequences which reached a knock down of at least 80% were stably transfected in a HeLa cell line with a tetracycline-regulated expression (HeLa T-REx). These stable transfected cell lines represent novel tools for the analysis of cholesterol biosynthesis.

Brain neutral lipids mass is increased in alpha-synuclein gene-ablated mice

Because alpha-synuclein (Snca) has a role in brain lipid metabolism, we determined the impact that Snca deletion had on whole brain lipid composition. We analysed masses of individual phospholipid (PL) classes and neutral lipid mass as well as PL acyl chain composition in brains from wild-type and Snca-/- mice. Although total brain PL mass was not altered, cardiolipin and phosphatidylglycerol mass decreased 16% and 27%, respectively, in Snca-/- mice. In addition, no changes were observed in plasmalogen or polyphosphoinositide mass. In ethanolamine glycerophospholipids and phosphatidylserine, docosahexaenoic acid (22 : 6n-3) was decreased 7%, while 16 : 0 was increased 1.1-fold and 1.4-fold, respectively. Surprisingly, brain cholesterol, cholesteryl ester, and triacylglycerol mass were increased 1.1-fold, 1.6-fold, and 1.4-fold, respectively in Snca-/- mice. In isolated myelin, cholesterol mass was also increased 1.3-fold, but because there was also a net increase in myelin PL mass, the cholesterol to PL ratio was unaltered. No changes in the expression of cholesterogenic enzymes were observed, suggesting these did not account for the observed changes in cholesterol. These data extend our previous results in astrocytes and kinetic studies in vivo demonstrating a role for Snca in brain lipid metabolism and demonstrate a clear impact on brain neutral lipid metabolism.

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.

[Biochemical profile of fetal blood sampled by cordocentesis in 35 pregnancies complicated by growth retardation]

AIM OF THE STUDY

Intra-uterine growth retardation (IUGR) is a frequent pathology in obstetrics characterized by high heterogeneity. Fetal smallness is sometimes constitutional, but can also be accompanied by fetal distress and vital risks for the infant. In 35 pregnancies complicated by IUGR of different etiologies, we measured on fetal blood obtained by cordocentesis, biochemical variables characteristic of the fetuses' respiratory and metabolic status. The aim of the study was to identify the discriminative biological alterations, related to growth retardation and fetal distress.

PATIENTS AND METHODS

The studied population includes 27 cases of severe IUGR, of gestational age 30,2+/-4,6 weeks of gestation (WG) (divided into 20 cases of isolated IUGR and 7 cases of IUGR associated with malformative syndrome), as well as 8 cases of moderate IUGR, of gestational age 26+/-4,5 WG; all fetuses had normal karyotypes. A group of 73 normal fetuses, of gestational age 26,3+/-5,7 WG, constituted a reference population. PH, pCO(2), bicarbonate concentration, pO(2) and SaO(2), as well as glucose, pyruvate, lactate, free fatty acids, aceto-acetate, beta-hydroxybutyrate and cholesterol concentrations were measured on umbilical venous blood (UVB).

RESULTS

In case of severe but isolated growth retardation, UVB analysis showed the frequency of acid-base and gasometric disturbances: acidemia and hypoxemia (65% of cases), hypercapnia (60% of cases). Metabolic abnormalities were shown: decrease in glycemia (35% of cases), increase in pyruvatemia and lactatemia (40% of cases), increased free fatty acids serum concentration; a diminution of umbilical venous cholesterol level, the most frequent abnormality, can be seen in 70% of fetuses. In case of severe IUGR associated with malformative syndrome, UVB acid-base and metabolic changes were rarely seen; however, UVB cholesterol level is low in some cases. In case of growth retardation classified as moderate, modifications are relatively not frequent and essentially gasometric.

CONCLUSION

In about 60% of cases of severe and isolated IUGR, there is a risk of fetal distress, related to an alteration of the transplacental transfer of respiratory gases and nutritional substrates; chronic fetal malnutrition can be involved, with an impact on the growth of the fetus. In case of IUGR associated with malformative syndrome, fetal smallness is probably a result of intrinsic fetal damage, without nutritional origin.

The use of the Dhcr7 knockout mouse to accurately determine the origin of fetal sterols

Mice with a targeted mutation of 3beta-hydroxysterol Delta(7)-reductase (Dhcr7) that cannot convert 7-dehydrocholesterol to cholesterol were used to identify the origin of fetal sterols. Because their heterozygous mothers synthesize cholesterol normally, virtually all sterols found in a Dhcr7 knockout fetus having a Delta(7) or a Delta(8) double bond must have been synthesized by the fetus itself but any cholesterol had to have come from the mother. Early in gestation, most fetal sterols were of maternal origin, but at approximately E13-14, in situ synthesis became increasingly important, and by birth, 55-60% of liver and lung sterols had been made by the fetus. In contrast, at E10-11, upon formation of the blood-brain barrier, the brain rapidly became the source of almost all of its own sterols (90% at birth). New, rapid, de novo sterol synthesis in brain was confirmed by the observation that concentrations of C24,25-unsaturated sterols were low in the brains of all very young fetuses but increased rapidly beginning at approximately E11-12. Reduced activity of sterol C24,25-reductase (Dhcr24) in brain, suggested by the abundance of C24,25-unsaturated compounds, seems to be the result of suppressed Dhcr24 expression. The early fetal brain also appears to conserve cholesterol by keeping cholesterol 24-hydroxylase expression low until approximately E18.

DHCR24 gene knockout mice demonstrate lethal dermopathy with differentiation and maturation defects in the epidermis

Desmosterolosis is an autosomal recessive disorder due to mutations in the 3beta-hydroxysterol-Delta24 reductase (DHCR24) gene that encodes an enzyme catalyzing the conversion of desmosterol to cholesterol. To date, only two patients have been reported with severe developmental defects including craniofacial abnormalities and limb malformations. We employed mice with targeted disruption of DHCR24 to understand the pathophysiology of desmosterolosis. All DHCR24-/- mice died within a few hours after birth. Their skin was wrinkleless and less pliant, leading to restricted movement and inability to suck (empty stomach). DHCR24 gene was expressed abundantly in the epidermis of control but not of DHCR24-/- mice. Accordingly, cholesterol was not detected whereas desmosterol was abundant in the epidermis of DHCR24-/- mice. Skin histology revealed thickened epidermis with few and smaller keratohyaline granules. Aberrant expression of keratins such as keratins 6 and 14 suggested hyperproliferative hyperkeratosis with undifferentiated keratinocytes throughout the epidermis. Altered expression of filaggrin, loricrin, and involcrin were also observed in the epidermis of DHCR24-/-. These findings suggested impaired skin barrier function. Indeed, increased trans-epidermal water loss and permeability of Lucifer yellow were observed in DHCR24-/- mice. DHCR24 thus plays crucial role for skin development and its proper function.

Another observation with VATER association and a complex IV respiratory chain deficiency

The VATER association of vertebral anomalies (V), anal atresia (A), esophageal atresia and/or tracheo-esophageal fistula (TE), radial and renal anomalies (R) is a common congenital association of unknown origin with probably heterogeneous causes. Here, we report on a girl presenting with pre- and postnatal growth retardation, esophageal atresia, vertebral and costal anomalies and a unilateral radial defect, consistent with the diagnosis of VATER association. In the first month of life, she presented with failure to thrive, severe episodes of hypoglycemia, liver dysfunction and high levels of lactate, which prompted us to perform metabolic screening. A complex IV respiratory chain deficiency (RCD) was diagnosed on a liver biopsy. The respiratory chain defect was not observed in skin fibroblasts. No mtDNA point mutation or deletion was identified. The girl is now 9 years old and has a normal mental development but persistent feeding difficulties and moderate hyperlactatemia. To our knowledge, this is the second report of VATER association with mitochondrial disorder. In a previous report, a VACTERL association was observed in a girl with the mitochondrial A3243G point mutation. The association of VATER phenotype with a mitochondrial disorder may be coincidental but could also suggest that the presence of multiple malformations is the result of the antenatal expression of RCD.

Decreased cholesterol synthesis as a possible aetiological factor in malformations of trisomy 18

We report a series of neonates and foetuses with trisomy 18 and abnormally low cholesterol levels and propose that down regulation of cholesterol synthesis in trisomy 18 is, in part, responsible for its phenotype. Cholesterol is a major structural lipid of cell membranes, as well as the precursor of steroid hormones and bile acids. Several human malformation syndromes have been identified biochemically as disorders of cholesterol biosynthesis. Trisomy 18, a multi-system malformation syndrome, has clinical features that overlap with those of disorders of cholesterol biosynthesis and dysregulation of this pathway may have a role in the developmental pathology.

Sterol profiling of amniotic fluid: a routine method for the detection of distal cholesterol synthesis deficit

OBJECTIVES

Smith Lemli Opitz syndrome (SLOS) caused by a deficit of 3beta-hydroxysterol-Delta7 reductase was the first sterol deficit described with multiple malformations. The lack of specificity of many morphological abnormalities detected by ultrasound and their frequency have justified routine screening of amniotic fluid (AF) for sterols by GC-MS. The examination contributes to an improved knowledge of the sterol status in the fluid.

METHODS

A series of sterol profiles is collated here. Accumulation of 7- and 8-dehydrocholesterol are diagnostic for SLOS. However, a number of other sterols have also been detected by GC-MS in control AF and their presence may be confusing.

RESULTS AND CONCLUSIONS

In addition to cholesterol, the level of which varies as function of the gestational age, lathosterol is present together with trace amounts of 7- and 8-dehydrocholesterol and other precursors such as desmosterol, lanosterol, and dimethylsterol. Phytosterols are also present in 70% of AF samples that have been tested. Besides SLOS, GC-MS examination of amniotic fluid can detect various sterol deficits associated with malformations (lathosterolosis, desmosterolosis, X-linked chondrodysplasia, and particular Antley-Bixler syndrome). Practical conclusions support GC-MS as a routine method to investigate skeletal and central nervous system malformations.

Expression and role of cubilin in the internalization of nutrients during the peri-implantation development of the rodent embryo

Histiotrophic nutrition is essential during the peri-implantation development in rodents, but little is known about receptors involved in protein and lipid endocytosis derived from the endometrium and the uterine glands. Previous studies suggested that cubilin, a multiligand receptor for vitamin, iron, and protein uptake in the adult, might be important in this process, but the onset of its expression and function is not known. In this study, we analyzed the expression of cubilin in the pre- and early post-implantation rodent embryo and tested its potential function in protein and cholesterol uptake. Using morphological and Western blot analysis, we showed that cubilin first appeared at the eight-cell stage. It was expressed by the maternal-fetal interfaces, trophectoderm and visceral endoderm, but also by the future neuroepithelial cells and the developing neural tube. At all these sites, cubilin was localized at the apical pole of the cells exposed to the maternal environment or to the amniotic and neural tube cavities, and had a very similar distribution to megalin, a member of the LDLR gene family and a coreceptor for cubilin in adult tissues. To analyze cubilin function, we followed endocytosis of apolipoprotein A-I and HDL cholesterol, nutrients normally present in the uterine glands and essential for embryonic growth. We showed that internalization of both ligands was cubilin dependent during the early rodent gestation. In conclusion, the early cubilin expression and its function in protein and cholesterol uptake suggest an important role for cubilin in the development of the peri-implantation embryo.

Maternal nutritional status and the risk for orofacial cleft offspring in humans

Periconceptional folate and folic acid intake prevents orofacial clefts (OFC) in the offspring. It has been suggested that other nutrients also play a role. We investigated the preconceptional intake of macronutrients (protein, fat, carbohydrate, fiber, and cholesterol), vitamins (vitamin A, retinol, beta-carotene, ascorbic acid, and alpha-tocopherol), minerals (calcium, phosphorus, iron, magnesium, and zinc) and food groups in mothers of OFC children and controls. At approximately 14 mo after the index pregnancy, 206 mothers of a child with a nonsyndromic OFC and 203 control mothers completed a FFQ on current food intake and a general questionnaire. After exclusion of pregnant and lactating mothers, mothers who reported a change in diet compared with the preconceptional period, and those for whom periconceptional folic acid supplement use was unclear, 182 OFC mothers and 173 control mothers were evaluated. Macronutrient, vitamin, mineral, and food group intakes were compared. After adjustment for energy, quintiles of dietary nutrient intake and odds ratios with 95% CI were calculated. The preconceptional intake of all macronutrients, vitamins, minerals, and food groups with the exception of milk (products), potatoes, pies/cookies were lower in OFC mothers than in controls. The energy-adjusted intakes of vegetable protein, fiber, beta-carotene, ascorbic acid, alpha-tocopherol, iron, and magnesium were significantly lower in cases compared with controls. Increasing intakes of vegetable protein, fiber, ascorbic acid, iron, and magnesium decreased OFC risk. In conclusion, a higher preconceptional intake of nutrients predominantly present in fruits and vegetables reduces the risk of offspring affected by OFC.

Effects of dietary cholesterol on plasma lipoproteins in Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome is a condition of impaired cholesterol synthesis that is caused by mutations in DHCR7 encoding 7-dehydrocholesterol-Delta7 reductase. Birth defects and mental retardation are characteristic. Deficient plasma and tissue cholesterol and excess cholesterol precursors 7 and 8 dehydrocholesterol (7DHC and 8DHC) contribute to the pathogenesis. Cholesterol is transported to tissues via lipoproteins. We measured the effect of dietary cholesterol (egg yolk) on plasma lipoproteins to evaluate this potential treatment. We used the enzymatic method to measure total sterols in lipoproteins (n=12) and plasma (n=16). In addition, we analyzed individual plasma sterols by a gas chromatographic method. Samples were evaluated after 3 wk of a cholesterol-free diet and after 6-19 mo of dietary cholesterol. We also analyzed the distribution of sterols in lipoproteins and the apolipoprotein E genotype. Dietary cholesterol significantly increased the total sterols in plasma (2.22 +/- 0.13 to 3.10 +/- 0.22; mean +/- SEM; p < 0.002), in LDL (0.98 +/- 0.13 to 1.52 +/- 0.17 mM), and in HDL (0.72 +/- 0.04 to 0.92 +/- 0.07). Plasma cholesterol increased (1.78 +/- 0.16 to 2.67 +/- 0.25 mM; p < 0.007) and plasma 7DHC decreased in 10 children, but the mean decrease was not significant. The distribution of individual sterols in each lipoprotein fraction was similar to the distribution in plasma. The baseline cholesterol and the response to dietary cholesterol was the same in children with 3/3 and 3/4 apolipoprotein E genotypes. Dietary cholesterol increased total sterols in plasma, LDL, and HDL in children with Smith-Lemli-Opitz syndrome. These favorable increases in the lipoproteins are potentially therapeutic for this condition.

Cholesterol supplementation does not improve developmental progress in Smith-Lemli-Opitz syndrome

OBJECTIVE

Smith-Lemli-Opitz syndrome (SLOS) results in multiple malformations, growth deficiency, and mental retardation. Cholesterol supplementation has been used for several years to treat symptoms of SLOS. We assessed the developmental progress of children and adolescents with SLOS over a 6-year period.

STUDY DESIGN

Patients with SLOS (n=14) received continuous cholesterol supplementation as part of a longitudinal study. Assessment of their developmental progress in the areas of cognitive, motor, and adaptive skills occurred every 6 to 12 months. The progress of each subject over time and the progress of the group as a whole were analyzed by using a repeated-measures design and multiple t tests.

RESULTS

Developmental quotients did not improve over time for children with SLOS receiving cholesterol. In addition, baseline cholesterol levels, rather than age when supplementation began or increase in cholesterol levels, best predicted developmental outcome.

CONCLUSIONS

These results suggest that cholesterol supplementation in its current form does not improve the developmental progress of children and adolescents with SLOS.

Multidimensional separations in the pharmaceutical arena

The introduction of novel, powerful and rapid multidimensional separation and characterization methods has produced revolutionary global changes at the genome, proteome and metabolome level, bringing about a radical transition in our views of living systems, at the molecular level. The age of proteomics and metabolomics demands high-resolution multidimensional separation techniques. Multidimensional gas and liquid chromatography techniques, in addition to capillary and microchip electrophoresis methods, offer increased resolution and sensitivity, while also affording adequate throughput and reproducibility to meet the demands of the modern pharmaceutical industry. Coupled with MS, these techniques provide not only separation but also reliable identification of the sample components. The resolving power of these methods has proved to be superior over individual one-dimensional approaches, enabling the comprehensive separation of complex biological mixtures, with excellent resolution and reproducibility. High capacity computer systems that are capable of rigorous qualitative and quantitative analysis of the separation profiles allow the establishment and mining of large databases. Examples of various modern multidimensional separation techniques, and their integration with MS, are reviewed, here, with respect to pharmaceutical analysis.

Role ofSonic hedgehog in patterning of tracheal-bronchial cartilage and the peripheral lung

Sonic hedgehog (Shh) was conditionally deleted in respiratory epithelial cells of the embryonic lung in vivo. Deletion of Shh before embryonic day (E) 13.5 resulted in respiratory failure at birth. While lobulation was not perturbed, the lungs were hypoplastic, with reduced branching of peripheral lung tubules, evident from E13.5. Smooth muscle and endothelial cells were absent or reduced, the latter in relationship to the loss of peripheral lung parenchyma. Tracheal-bronchial ring abnormalities occurred when Shh was deleted between E8.5 and E12.5. Deletion of Shh later in gestation (after E13.5) caused mild abrogation of peripheral branching morphogenesis but did not disrupt tracheal-bronchial development. Defects in branching morphogenesis and vascularization seen in Shh null mutant (Shh(-/-)) mice were substantially corrected when SHH was ectopically expressed in the respiratory epithelium; however, peripheral expression of SHH failed to correct cartilage abnormalities in the trachea and bronchi, indicating a spatial requirement for SHH expression near sites of cartilage formation. Expression of SHH by the respiratory epithelium plays an important role in the patterning of tracheal-bronchial mesenchyme required for formation of cartilage rings in conducting airways. SHH regulates branching morphogenesis and influences differentiation of the peripheral lung mesenchyme required for formation of bronchial and vascular smooth muscle.

Role of cholesterol in the regulation of growth plate chondrogenesis and longitudinal bone growth

Inborn errors of cholesterol synthesis are associated with multiple systemic abnormalities, including skeletal malformations. The regulatory role of cholesterol during embryogenesis appears to be mediated by Shh, a signaling molecule in which activity depends on molecular events involving cholesterol. Based on this evidence, we hypothesized that cholesterol, by modifying the activity of Ihh (another of the Hedgehog family proteins) in the growth plate, regulates longitudinal bone growth. To test this hypothesis, we treated rats with AY 9944, an inhibitor of the final reaction of cholesterol synthesis. After 3 weeks, AY 9944 reduced the cumulative growth, tibial growth, and the tibial growth plate height of the rats. To determine whether cholesterol deficiency affects bone growth directly at the growth plate, we then cultured fetal rat metatarsal bones in the presence of AY 9944. After 4 days, AY 9944 suppressed metatarsal growth and growth plate chondrocyte proliferation and hypertrophy. The inhibitory effect on chondrocyte hypertrophy was confirmed by the AY 9944-mediated decreased expression of collagen X. Lastly, AY 9944 decreased the expression of Ihh in the metatarsal growth plate. We conclude that reduced cholesterol synthesis in the growth plate, possibly by altering the normal activity of Ihh, results in suppressed longitudinal bone growth and growth plate chondrogenesis.

Differential effects of polyunsaturated fatty acids on sterol synthesis rates in adult and fetal tissues of the hamster: consequence of altered sterol balance

Cholesterol is necessary for the proper growth and development of the fetus. Consequently, disruptions in cholesterol biosynthesis lead to abnormal fetal development. It has been shown that in cells exposed to polyunsaturated fatty acids (PUFA), the expressions of genes and activities of enzymes involved in cholesterol synthesis are reduced. Similarly, we found that adult male hamsters fed PUFA-enriched diets had an approximately 60% reduction in in vivo hepatic sterol synthesis rates. If fetal tissues respond to PUFA in the same manner as do adult livers, then maternal dietary PUFA could lead to a reduction in fetal sterol synthesis rates and possibly abnormal development. To investigate the impact of maternal dietary fatty acids on fetal sterol synthesis rates, female hamsters were fed diets enriched in various fatty acids before and throughout gestation. In vivo sterol synthesis rates were measured in fetuses at mid- and late gestation. At both gestational stages, dietary PUFA had no effect on fetal sterol synthesis rates. This lack of effect was not a consequence of a lack of PUFA enrichment in fetal fatty acids or the lack of PUFA receptor expression in the fetus. We hypothesize that the fetus may experience a dysregulation of sterol synthesis as the result of the fetus being in a negative sterol balance; the PUFA-induced suppression of sterol synthesis in the adult male hamster liver was ablated by creating a net negative sterol balance across the adult hepatocyte.

Diagnosis of Smith-Lemli-Opitz syndrome by ultraviolet spectrophotometry

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder due to an inborn error of cholesterol metabolism, characterized by congenital malformations, dysmorphism of multiple organs, mental retardation and delayed neuropsychomotor development resulting from cholesterol biosynthesis deficiency. A defect in 3 -hydroxysteroid-delta7-reductase (delta7-sterol-reductase), responsible for the conversion of 7-dehydrocholesterol (7-DHC) to cholesterol, causes an increase in 7-DHC and frequently reduces plasma cholesterol levels. The clinical diagnosis of SLOS cannot always be conclusive because of the remarkable variability of clinical expression of the disorder. Thus, confirmation by the measurement of plasma 7-DHC levels is needed. In the present study, we used a simple, fast, and selective method based on ultraviolet spectrophotometry to measure 7-DHC in order to diagnose SLOS. 7-DHC was extracted serially from 200 l plasma with ethanol and n-hexane and the absorbance at 234 and 282 nm was determined. The method was applied to negative control plasma samples from 23 normal individuals and from 6 cases of suspected SLOS. The method was adequate and reliable and 2 SLOS cases were diagnosed.

Transport of cholesterol across a BeWo cell monolayer: implications for net transport of sterol from maternal to fetal circulation

The placental transport of various compounds, such as glucose and fatty acids, has been well studied. However, the transport of cholesterol, a sterol essential for proper fetal development, remains undefined in the placenta. Therefore, the purpose of these studies was to examine the transport of cholesterol across a placental monolayer and its uptake by various cholesterol acceptors. BeWo cells, which originated from a human choriocarcinoma, were grown on transwells for 3 days to form a confluent monolayer. The apical side of the cells was radiolabeled with either free cholesterol or LDL cholesteryl ester. After 24 h, the radiolabel was removed and cholesterol acceptors were added to the basolateral chamber. Cholesterol was found to be taken up by the apical surface of the placental monolayer, transported to the basolateral surface of the cell, and effluxed to fetal human serum, fetal HDL, or phospholipid vesicles, but not to apolipoprotein A-I. In addition, increasing the cellular cholesterol concentration further increased the amount of cholesterol transported to the basolateral acceptors. These are the first studies to demonstrate the movement of cholesterol across a placental cell from the maternal circulation (apical side) to the fetal circulation (basolateral side).

MCA/MR syndrome with hypocholesterolemia related to familial dominant hypobetalipoproteinemia

Recent reports have emphasized the role of cholesterol in vertebrate embryonic development. The RSH or so-called Smith-Lemli-Opitz syndrome (SLOS) was the first multiple congenital anomalies/mental retardation syndrome related to a cholesterol synthesis disturbance. Familial hypobetalipoproteinemia is a well-known dominantly inherited entity in which affected individuals usually are free of symptoms. We report on the unusual association of a malformation syndrome with mental retardation resembling SLOS and profound hypocholesterolemia related to familial hypobetalipoproteinemia. We discuss the possible causal relationship between the two conditions and the current understanding of the role of cholesterol in normal embryogenesis.

Embryonic expression of cholesterogenic genes is restricted to distinct domains and colocalizes with apoptotic regions in mice

Cholesterol biosynthesis has been assumed to be an ubiquitous process in vertebrate organisms. Here we present data demonstrating that expression of key enzymes of cholesterol biosynthesis is restricted to specific tissues during embryonic development. Distinct expression starts in the dorsal neural tube at embryonic day 8 and is later detected in dorsal root and cephalic ganglia, in the pharyngeal pouches and limb buds. In the limb, expression becomes progressively restricted to interdigital regions during differentiation. Caspase3 whole mount immunostaining revealed that cholesterol biosynthesis colocalizes with apoptotic regions that are targets of the morphogenic signal Sonic hedgehog. This expression pattern correlates closely with the shared phenotypic features of cholesterol biosynthesis and hedgehog mutants.

Role of cholesterol in synapse formation and function

Cholesterol is a multifaceted molecule, which serves as essential membrane component, as cofactor for signaling molecules and as precursor for steroid hormones. Consequently, defects in cholesterol metabolism cause devastating diseases. So far, the role of cholesterol in the nervous system is less well understood. Recent studies showed that cultured neurons from the mammalian central nervous system (CNS) require glia-derived cholesterol to form numerous and efficient synapses. This suggests that the availability of cholesterol in neurons limits the extent of synaptogenesis. Here, I will summarize the experimental evidence for this hypothesis, describe what is known about the structural and functional role of cholesterol at synapses, and discuss how cholesterol may influence synapse development and stability.

Outsourcing in the brain: do neurons depend on cholesterol delivery by astrocytes?

Brain function depends on the cooperation between highly specialized cells. Neurons generate electrical signals and glial cells provide structural and metabolic support. Here, I propose a new kind of job-sharing between neurons and astrocytes. Recent studies on primary cultures of highly purified neurons from the rodent central nervous system (CNS) suggest that, during development, neurons reduce or even abandon cholesterol synthesis to save energy and import cholesterol from astrocytes via lipoproteins. The cholesterol shuttle may be restricted to compartments distant from the soma including synapses and may be regulated by electrical activity. Testing these hypotheses will help to improve our still insufficient understanding of brain cholesterol metabolism and its role in neurodegeneration.

Lipid metabolism in pregnancy and its consequences in the fetus and newborn

During early pregnancy there is an increase in body fat accumulation, associated with both hyperphagia and increased lipogenesis. During late pregnancy there is an accelerated breakdown of fat depots, which plays a key role in fetal development. Besides using placental transferred fatty acids, the fetus benefits from two other products: glycerol and ketone bodies. Although glycerol crosses the placenta in small proportions, it is a preferential substrate for maternal gluconeogenesis, and maternal glucose is quantitatively the main substrate crossing the placenta. Enhanced ketogenesis under fasting conditions and the easy transfer of ketones to the fetus allow maternal ketone bodies to reach the fetus, where they can be used as fuels for oxidative metabolism as well as lipogenic substrates. Although maternal cholesterol is an important source of cholesterol for the fetus during early gestation, its importance becomes minimal during late pregnancy, owing to the high capacity of fetal tissues to synthesize cholesterol. Maternal hypertriglyceridemia is a characteristic feature during pregnancy and corresponds to an accumulation of triglycerides not only in very low-density lipoprotein but also in low- and high-density lipoprotein. Although triglycerides do not cross the placental barrier, the presence of lipoprotein receptors in the placenta, together with lipoprotein lipase, phospholipase A2, and intracellular lipase activities, allows the release to the fetus of polyunsaturated fatty acids transported as triglycerides in maternal plasma lipoproteins. Normal fetal development needs the availability of both essential fatty acids and long chain polyunsaturated fatty acids, and the nutritional status of the mother during gestation has been related to fetal growth. However, excessive intake of certain long chain fatty acids may cause both declines in arachidonic acid and enhanced lipid peroxidation, reducing antioxidant capacity.

Central role of peroxisomes in isoprenoid biosynthesis

Peroxisomes contain enzymes catalyzing a number of indispensable metabolic functions mainly related to lipid metabolism. The importance of peroxisomes in man is stressed by the existence of genetic disorders in which the biogenesis of the organelle is defective, leading to complex developmental and metabolic phenotypes. The purpose of this review is to emphasize some of the recent findings related to the localization of cholesterol biosynthetic enzymes in peroxisomes and to discuss the impairment of cholesterol biosynthesis in peroxisomal deficiency diseases.

Inborn errors of sterol biosynthesis

The known disorders of cholesterol biosynthesis have expanded rapidly since the discovery that Smith-Lemli-Opitz syndrome is caused by a deficiency of 7-dehydrocholesterol. Each of the six now recognized sterol disorders-mevalonic aciduria, Smith-Lemli-Opitz syndrome, desmosterolosis, Conradi-Hünermann syndrome, CHILD syndrome, and Greenberg dysplasia-has added to our knowledge of the relationship between cholesterol metabolism and embryogenesis. One of the most important lessons learned from the study of these disorders is that abnormal cholesterol metabolism impairs the function of the hedgehog class of embryonic signaling proteins, which help execute the vertebrate body plan during the earliest weeks of gestation. The study of the enzymes and genes in these several syndromes has also expanded and better delineated an important class of enzymes and proteins with diverse structural functions and metabolic actions that include sterol biosynthesis, nuclear transcriptional signaling, regulation of meiosis, and even behavioral modulation.

A chronic model of atypical absence seizures: studies of developmental and gender sensitivity

Treatment of Long Evans hooded rats during post-natal brain development with the cholesterol synthesis inhibitor, AY-9944 (AY) results in the occurrence of atypical absence seizures, which are frequent, recurrent, and life-long. AY induced slow spike-and-wave discharges (SSWD) are significantly more frequent and prolonged in female Long Evans rats than males. Three groups of experiments were performed in order to characterize further the AY model of atypical absence seizures, (1) a developmental study was performed to ascertain whether AY-induced seizures appear before or after the onset of puberty; (2) male/female differences in severity of response to AY was determined in order to answer the question whether the gender specificity was a pre- or postpubertal phenomenon; (3) a time course study was done to determine the minimum number of postnatal AY doses needed to induce the life-long atypical absence seizure state. The data indicate that AY-induced atypical absence seizures emerge before the onset of puberty. Further, we show that the gender difference in severity of AY-induced seizures also is a pre-pubertal phenomenon. Finally, a single dose of AY (7.5 mg/kg) administered on post-natal day (P) 5 was sufficient to induce SSWD on the electrocorticogram (ECoG). Our results suggest that sex hormones are important in the AY model, although the exact role of cholesterol derived steroid hormones in the regulation and maintenance of AY induced atypical absence seizures remains to be determined.

Semilobar holoprosencephaly in a 46,XY female fetus

We report the prenatal echographic diagnosis of holoprosencephaly (HPE) at 11 weeks' gestation. Fetopathological examination revealed an unusual variant of semilobar HPE with middle interhemispheric fusion associated with sex-reversal: 46,XY normal male karyotype, normal external and internal female genitalia and streak gonads.

The origins and roles of cholesterol and fatty acids in the fetus

The fetus grows at a rate that is unparalleled by that at any other stage of life. Significant amounts of cholesterol and fatty acids are required to maintain membrane growth. Recent studies have shown that these lipids are also necessary mediators of processes that are essential for proper development.

Some distal limb structures develop in mice lacking Sonic hedgehog signaling

Patterning of the limb is coordinated by the complex interplay of three signaling regions: the apical ectodermal ridge (AER), the zone of polarizing activity (ZPA), and the non-ridge limb ectoderm. Complex feedback loops exist between Shh in the ZPA, Bmps and their antagonists in the adjacent mesenchyme, Wnt7a in the dorsal ectoderm and Fgfs in the AER. In contrast to the previously reported complete absence of digits in Shh(-/-) mice, we show that one morphologically distinct digit, with a well-delineated nail and phalanges, forms in Shh(-/-) hindlimbs, while intermediate structures are severely truncated and fused. The presence of distal autopod elements is consistent with weak expression of Hoxd13 in Shh(-/-) hindlimbs. Shh(-/-) forelimbs in contrast have one distal cartilage element, a less-well differentiated nail and fused intermediate bones. Interestingly, Ihh is expressed at the tip of Shh mutant limbs and could account for formation of distal structures. In contrast to previous studies we also demonstrate that Shh signaling is required for maintenance of normal Fgf8 expression, since expression of Fgf8, unlike some other AER marker genes, is rapidly lost from anterior to posterior after E10.5, with only a small domain of Fgf8 expression remaining posteriorly. Furthermore, loss of expanded Fgf8 expression is paralleled by a collapse of the handplate. Our data show that development of most intermediate elements of the hindlimb skeleton are Shh-dependent, and that Shh signaling is required for anterior-posterior expansion of the AER in both limbs and for the subsequent branching of zeugopod and autopod elements. Finally, we show that Shh is also required for outgrowth of the limb ectoderm and thus for the formation of a distinct limb compartment.