Oxidative stress, serotonergic changes and decreased ultrasonic vocalizations in a mouse model of Smith-Lemli-Opitz syndrome.

Smith-Lemli-Opitz syndrome is an inherited monogenic disorder in which mutations to the 7-dehydrocholesterol (7-DHC) reductase (Dhcr7) gene lead to deficits in cholesterol synthesis. As a result, many patients suffer from gross physiological and neurological deficits. The purpose of this study was to identify a potential abnormal behavioral phenotype in a compound mutant mouse model for Smith-Lemli-Opitz disease (Dhcr7 Δ3-5/T93M ) to further validate the model and to provide potential targets for future therapeutic interventions. We also sought to identify some of the underlying changes in brain function that may be responsible for behavioral differences among groups. The Dhcr7 compound mutant mice were smaller than their single mutant littermates. Both single and compound heterozygous mice made fewer ultrasonic vocalizations when separated from the dam, which may suggest a communication deficit in these animals. Striking increases of the highly oxidizable 7-DHC were observed in the compound mutant mice. 7-Dehydrocholesterol is the precursor to cholesterol and builds up because of decreased function of the mutated Dhcr7 enzyme. Additionally, several differences were noted in the serotonergic system including increased expression of the serotonin transporter and increased uptake of serotonin by isolated synaptosomes. We propose that changes to the oxidative environment during development can have a significant impact on the development of serotonergic function and that this contributes to behavioral differences observed in the mutant mice.

Fibroblasts from patients with major depressive disorder show distinct transcriptional response to metabolic stressors.

Major depressive disorder (MDD) is increasingly viewed as interplay of environmental stressors and genetic predisposition, and recent data suggest that the disease affects not only the brain, but the entire body. As a result, we aimed at determining whether patients with major depression have aberrant molecular responses to stress in peripheral tissues. We examined the effects of two metabolic stressors, galactose (GAL) or reduced lipids (RL), on the transcriptome and miRNome of human fibroblasts from 16 pairs of patients with MDD and matched healthy controls (CNTR). Our results demonstrate that both MDD and CNTR fibroblasts had a robust molecular response to GAL and RL challenges. Most importantly, a significant part (messenger RNAs (mRNAs): 26-33%; microRNAs (miRNAs): 81-90%) of the molecular response was only observed in MDD, but not in CNTR fibroblasts. The applied metabolic challenges uncovered mRNA and miRNA signatures, identifying responses to each stressor characteristic for the MDD fibroblasts. The distinct responses of MDD fibroblasts to GAL and RL revealed an aberrant engagement of molecular pathways, such as apoptosis, regulation of cell cycle, cell migration, metabolic control and energy production. In conclusion, the metabolic challenges evoked by GAL or RL in dermal fibroblasts exposed adaptive dysfunctions on mRNA and miRNA levels that are characteristic for MDD. This finding underscores the need to challenge biological systems to bring out disease-specific deficits, which otherwise might remain hidden under resting conditions.

Behavioral and serotonergic response changes in the Dhcr7-HET mouse model of Smith-Lemli-Opitz syndrome.

Smith-Lemli-Opitz syndrome (SLOS) is a developmental disorder resulting from mutations to the Dhcr7 gene, which is required for cholesterol synthesis. Patients with SLOS typically exhibit a number of severe behavioral deficits and many are diagnosed with autistic spectrum disorder. Although the molecular pathophysiology underlying behavioral changes in SLOS and autism spectrum disorders is poorly understood, there is evidence for the involvement of the serotonergic system in SLOS and autism in general. Behavioral testing was undertaken to ascertain the basal behavioral differences between Dhcr7-heterozygous (HET) and wild-type control mice and explore the utility of a Dhcr7-HET mouse line in the development of new treatments for this disorder. Dhcr7-HET mice did not differ from wild-type control mice on basic measures of locomotor activity, anxiety and neuromuscular ability. However, female Dhcr7-HET mice at 6 months of age or older were significantly more likely to win on the social dominance tube test against an unfamiliar mouse. Pharmacological testing, using the 5-HT2A agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), showed increased head-twitch response in Dhcr7-HET mice, which was apparent from 6 months of age. No differences were found between the genotypes in testing for 5-HT1A agonist 8-OH-DPAT-induced hypothermia. These data indicate an underlying dysfunction of the 5-HT2A receptors in Dhcr7-HET mice that warrants further investigation to establish how this may relate to behavioral disturbances in human patients carrying Dhcr7 mutations.

Restriction in cell fates of developing spinal cord cells transplanted to neural crest pathways.

At early neural tube stages, individual stem cells can generate neural crest cells as well as dorsal or ventral spinal cord cells. To determine whether this pluripotency is lost as development proceeds, we back-transplanted quail spinal cells from different developmental stages and different spinal locations into the crest migratory pathways of st 16-20 chicken host embryos. The transplanted spinal cells from st 27 dorsal cord and st 18 ventral cord differentiated within the new crest environment into sensory and sympathetic neurons, satellite and Schwann cells, and melanocytes. St 27 ventral cells still generated several crest derivatives but not sensory or sympathetic neurons. This loss in ability to produce neurons correlates with the end of neurogenesis in ventral cord. The end of neurogenesis in the cord, therefore, results from an intrinsic change in the potential of spinal neuroepithelial cells to generate neurons.

Late-migrating neuroepithelial cells from the spinal cord differentiate into sensory ganglion cells and melanocytes.

During embryonic development, neural crest cells give rise to many structures in peripheral tissues. Other neural tube cells are thought to contribute only to structures within the CNS. In contrast to this idea, we report a second wave of migration of cells away from the spinal cord occurring after the emigration of crest cells is complete. Neuroepithelial cells from spinal cords in E5 chicken embryos migrate into the periphery and differentiate into neurons and satellite cells within sensory ganglia and into melanocytes in skin and feathers. These results show that some cell types previously considered to be the descendants exclusively of neural crest cells are also derived from neuroepithelial cells in the spinal cord.

Development of specific muscle and cutaneous sensory projections in cultured segments of spinal cord.

Development of sensory projections was studied in cultured spinal segments with attached dorsal root ganglia. In spinal segments from stage 30 (E6.5) and older chicken embryos, prelabeled muscle and cutaneous afferents established appropriate projections. Cutaneous afferents terminated solely within the dorsolateral laminae, whereas some muscle afferents (presumably Ia afferents) projected ventrally towards motoneurons. Development of appropriate projections suggests that sufficient cues are preserved in spinal segments to support the formation of modality-specific sensory projections. Further, because these projections developed in the absence of muscle or skin, these results show that the continued presence of peripheral targets is not required for the formation of specific central projections after stage 29 (E6.0). Development of the dorsal horn in cultured spinal segments was assessed using the dorsal midline as a marker. In ovo, this midline structure appears at stage 29. Lack of midline formation in stage 28 and 29 cultured spinal segments suggests that the development of the dorsal horn is arrested in this preparation. This is consistent with earlier reports suggesting that dorsal horn development may be dependent on factors outside the spinal cord. Because dorsal horn development is blocked in cultured spinal segments, this preparation makes it possible to study the consequences of premature ingrowth of sensory axons into the spinal cord. In chicken embryos sensory afferents reach the spinal cord at stage 25 (E4.5) but do not arborize within the gray matter until stage 30. During this period dorsal horn cells are still being generated. In spinal segments, only those segments that have developed a midline at the time of culture support the formation of midline at the time of culture support the formation of specific sensory projections.(ABSTRACT TRUNCATED AT 250 WORDS)