DHEA and DHEAS are steroids synthesized in human adrenals, but their function is unclear. In addition to adrenal synthesis, evidence also indicates that DHEA and DHEAS are synthesized in the brain, further suggesting a role of these hormones in brain function and development. Despite intensifying research into the biology of DHEA and DHEAS, many questions concerning their mechanisms of action and their potential involvement in neuropsychiatric illnesses remain unanswered. We review and distill the preclinical and clinical data on DHEA and DHEAS, focusing on (i) biological actions and putative mechanisms of action, (ii) differences in endogenous circulating concentrations in normal subjects and patients with neuropsychiatric diseases, and (iii) the therapeutic potential of DHEA in treating these conditions. Biological actions of DHEA and DHEAS include neuroprotection, neurite growth, and antagonistic effects on oxidants and glucocorticoids. Accumulating data suggest abnormal DHEA and/or DHEAS concentrations in several neuropsychiatric conditions. The evidence that DHEA and DHEAS may be fruitful targets for pharmacotherapy in some conditions is reviewed.
Dehydroepiandrosterone; DHEA; DHEAS; neuroprotection; neurogenesis; apoptosis; depression; schizophrenia; dementia; cortisol
The functions for neurosteroids during development and in response to nervous system injury are beginning to be identified. We focused on a mouse model in which we believed neurosteroid production would be altered, and which had a neurodegenerative phenotype. Niemann Pick Type-C (NP-C) is an autosomal recessive neurodegenerative disease caused by mutations in NPC1 (95%) or NPC2 (5%), resulting in lysosomal accumulation of unesterified cholesterol and glycolipids. The NIH mouse model of NP-C has a mutation in the NPC1 gene, and exhibits several pathological features of the most severe NP-C patients. How lysosomal storage and trafficking defects lead to neurodegeneration is unknown. We found that these mice had normal neurosteroidogenic enzyme activity during development, but lost this activity in the early neonatal period, prior to onset of neurological symptoms. Neurons that expressed P450scc, 3ß HSD, as well as those that expressed 3α HSD and 5α reductase were lost in adult NP-C brains, resulting in diminished concentrations of allopregnanolone. We treated NP-C mice with allopregnanolone and found that a single dose in the neonatal period resulted in a doubling of lifespan, substantial delay in onset of neurological symptoms, survival of cerebellar Purkinje and granule cell neurons, and reduction in cholesterol and ganglioside accumulation. The mechanism by which allopregnanolone elicited these effects is unknown. Our in vitro studies showed that Purkinje cell survival promoted by allopregnanolone was lost by treatment with bicuculline, suggesting GABAA receptors may play a role. We treated NP-C mice with a synthetic GABAA neurosteroid, ganaxolone (3α-hydroxy-3β-methyl-5α -pregnan-20-one). Ganaxolone treatment of NP-C mice produced beneficial neurological effects, but these effects were not as robust as those obtained using allopregnanolone. Thus, allopregnanolone may elicit its effects through GABAA receptors and through other mechanisms. Additional studies also suggest that allopregnanolone may elicit its effects through pregnane-X receptors (PXR). Our data suggest that mouse models of neurodegeneration may be beneficial in establishing both physiologic and pharmacologic actions of neurosteroids. These animal models further establish the wide range of functions of these compounds, which may ultimately be useful for treatment of human diseases.
allopregnanolone; Niemann Pick Type C; GABAA receptor; pregnane-X-receptor
Neurosteroids are a relatively new class of neuroactive compounds, brought to prominence in the past two decades. Despite knowing of their presence in the nervous system of various species for over twenty years and knowing of their functions as GABAA and NMDA ligands, new and unexpected functions of these compounds are continuously being identified. Absence or reduced concentrations of neurosteroids during development and in adults may be associated with neurodevelopmental, psychiatric, or behavioral disorders. Treatment with physiologic or pharmacologic concentrations of these compounds may also promote neurogenesis, neuronal survival, myelination, increased memory, and reduced neurotoxicity. This review highlights what is currently known about the neurodevelopmental functions and mechanisms of action of four distinct neurosteroids – pregnenolone, progesterone, allopregnanolone and dehydroepiandrosterone.
Pregnenolone; Progesterone; Allopregnanolone; Dehydroepiandrosterone; neurogenesis; neurotoxicity; neurodegeneration; Niemann Pick Type C
Current methods for studying central nervous system myelination necessitate permissive axonal substrates conducive for myelin wrapping by oligodendrocytes. We have developed a neuron-free culture system in which electron-spun nanofibers of varying sizes substitute for axons as a substrate for oligodendrocyte myelination, thereby allowing manipulation of the biophysical elements of axonal-oligodendroglial interactions. To investigate axonal regulation of myelination, this system effectively uncouples the role of molecular (inductive) cues from that of biophysical properties of the axon. We use this method to uncover the causation and sufficiency of fiber diameter in the initiation of concentric wrapping by rat oligodendrocytes. We also show that oligodendrocyte precursor cells display sensitivity to the biophysical properties of fiber diameter and initiate membrane ensheathment prior to differentiation. The use of nanofiber scaffolds will enable screening for potential therapeutic agents that promote oligodendrocyte differentiation and myelination as well as provide valuable insight into the processes involved in remyelination.
fiber diameter; oligodendrocyte; myelination
Oligogenesis plays an important role in functional recovery after ischemic stroke. We tested the hypothesis that oligogenesis and the maturation of oligodendrocyte progenitor cells (OPCs) vary in different brain regions using a rat transient middle cerebral artery occlusion (tMCAO) model. Compared to Day 1, olig2+ OPCs and oligodendrocytes (OLGs) increased in the peri-infarct basal ganglia (BG) 7 (44%) and 14 (61%) days after 2 hours of MCAO; OPCs (PDGFRα+) and OLGs (CC1+) increased in this region 14 days after tMCAO by 139% and 126%, respectively. Although the olig2+ cells and OLGs did not increase significantly in the peri-infarct cortex (CTX), the OPCs increased in this region by 95% at Day 14 vs. Day 1 after tMCAO. The numbers of OPCs and OLGs remained low after an initial reduction at Day 1 in the peri-infarct corpus callosum (CC). Correlation analyses showed that the numbers of olig2+ cells (r=0.73, P=0.03) and OLGs (r=0.74, P=0.02) correlated with local vessel density; however, the number of OPCs did not correlate with vessel density (r=0.43, P=0.24). Our data show that oligogenesis and the maturation of OPCs differ in various brain regions and the difference in regional angiogenic response is one of the potential reasons.
Transient middle cerebral artery occlusion; Rat model; Olig2 positive cells; CC1 positive cells; PDGFRα positive cells
The “neurotrophin hypothesis” of depression posits a role of brain-derived neurotrophic factor (BDNF) in depression, although it is unknown whether BDNF is more involved in the etiology of depression or in the mechanism of action of antidepressants. . It is also unknown whether pre-treatment serum BDNF levels predict antidepressant response.
Thirty un-medicated depressed subjects were treated with escitalopram (N=16) or sertraline (N=14) for eight weeks. Twenty-five of the depressed subjects completed 8 weeks of antidepressant treatment and had analyzable data. Twenty-eight healthy controls were also studied. Serum for BDNF assay was obtained at baseline in all subjects and after 8 weeks of treatment in the depressed subjects. Depression ratings were obtained at baseline and after 8 weeks of treatment in the depressed subjects.
Pre-treatment BDNF levels were lower in the depressed subjects than the controls (p= 0.001) but were not significantly correlated with pre-treatment depression severity. Depression ratings improved with SSRI treatment (p< 0.001), and BDNF levels increased with treatment (p= 0.005). Changes in BDNF levels were not significantly correlated with changes in depression ratings. However, pre-treatment BDNF levels were directly correlated with antidepressant responses (p<0.01), and “Responders” to treatment (≥ 50% improvement in depression ratings) had higher pre-treatment BDNF levels than did “Non-responders” (p< 0.05).
These results confirm low serum BDNF levels in unmedicated depressed subjects and confirm antidepressant-induced increases in BDNF levels, but they suggest that antidepressants do not work simply by correcting BDNF insufficiency. Rather, these findings are consistent with a permissive or facilitatory role of BDNF in the mechanism of action of antidepressants.
Depression; brain-derived neurotrophic factor (BDNF); neurotrophin; antidepressant; SSRI
Some studies have found that antidepressants increase serum brain-derived neurotrophic factor (BDNF) levels in patients with major depression and the expression of BDNF mRNA in limbic structures of rats.
This study addressed whether the SSRI escitalopram increases serum BDNF levels in subjects with PTSD and whether BDNF levels are associated with treatment response.
Medically healthy male subjects (N=16) with chronic PTSD completed a 12-week open label trial of flexible dose (5–20mg/day) escitalopram monotherapy. BDNF levels were obtained at baseline, and at weeks 4, 8 and 12.
PTSD symptoms significantly declined over the course of the 12 week escitalopram treatment. Despite a substantial improvement in PTSD symptoms, there was virtually no change in BDNF levels over time. Nevertheless, mean BDNF levels across the trial were strongly correlated with the slope of PTSD symptoms over the 12 weeks (r = 0.58, p= 0.018). Lower mean BDNF was associated with a greater decrease in PTSD symptoms over the course of the trial.
PTSD subjects with low BDNF levels demonstrated the largest treatment response from an agent with putative neurotrophic effects.
BDNF; biomarker; escitalopram; posttraumatic stress disorders; predictor of response
Depression is associated with an unusually high rate of aging-related illnesses and early mortality. One aspect of “accelerated aging” in depression may be shortened leukocyte telomeres. When telomeres critically shorten, as often occurs with repeated mitoses or in response to oxidation and inflammation, cells may die. Indeed, leukocyte telomere shortening predicts early mortality and medical illnesses in non-depressed populations. We sought to determine if leukocyte telomeres are shortened in Major Depressive Disorder (MDD), whether this is a function of lifetime depression exposure and whether this is related to putative mediators, oxidation and inflammation.
Leukocyte telomere length was compared between 18 unmedicated MDD subjects and 17 controls and was correlated with lifetime depression chronicity and peripheral markers of oxidation (F2-isoprostane/Vitamin C ratio) and inflammation (IL-6). Analyses were controlled for age and sex.
The depressed group, as a whole, did not differ from the controls in telomere length. However, telomere length was significantly inversely correlated with lifetime depression exposure, even after controlling for age (p<0.05). Average telomere length in the depressed subjects who were above the median of lifetime depression exposure (≥9.2 years' cumulative duration) was 281 base pairs shorter than that in controls (p<0.05), corresponding to approximately seven years of “accelerated cell aging.” Telomere length was inversely correlated with oxidative stress in the depressed subjects (p<0.01) and in the controls (p<0.05) and with inflammation in the depressed subjects (p<0.05).
These preliminary data indicate that accelerated aging at the level of leukocyte telomeres is proportional to lifetime exposure to MDD. This might be related to cumulative exposure to oxidative stress and inflammation in MDD. This suggest that telomere shortening does not antedate depression and is not an intrinsic feature. Rather, telomere shortening may progress in proportion to lifetime depression exposure.
Niemann Pick C disease (NPC) is an autosomal recessive neurodegenerative disorder caused by the abnormal function of NPC1 or NPC2 proteins, leading to an accumulation of unesterified cholesterol and glycosphingolipids (GSLs) in the lysosomes. The mechanisms underlying the pathophysiology in NPC disease are not clear. Oxidative damage is implicated in the pathophysiology of different neurological disorders and the effect of GSL accumulation on the intracellular redox state has been documented. Therefore, we determined whether the intracellular redox state might contribute to the NPC disease pathophysiology. Since the treatment of NPC mice with allopregnanolone (ALLO) increases their lifespan and delays the onset of neurological impairment, we analyzed the effect of ALLO on the oxidative damage in human NPC fibroblasts.
Concentrations of reactive oxygen species (ROS) and lipid peroxidation were higher in fibroblasts from NPC patients than in fibroblasts from normal subjects. Fibroblasts from NPC patients were more susceptible to cell death through apoptosis after an acute oxidative insult. This process is mediated by activation of the NF-κB signaling pathway. Knockdown of NPC1 mRNA both in normal fibroblasts and in human SH-SY5Y neuroblastoma cells, caused increased ROS concentrations. ALLO treatment of fibroblasts from NPC patients or NPC1 knockdown cells reduced the levels of ROS and lipid peroxidation, and prevented peroxide-induced apoptosis and NF-kB activation.
Thus, these findings suggest that oxidative stress might contribute to the NPC disease and ALLO might be beneficial in the treatment of the disease, at least in part, due to its ability to restore the intracellular redox state.
Niemann Pick C; oxidative stress; allopregnanolone
Estrogens are used extensively to treat hot flashes in menopausal women. Some of the beneficial effects of estrogens in hormone therapy on the brain might be due to nongenomic effects in neurons such as the rapid stimulation of calcium oscillations. Most studies have examined the nongenomic effects of estrogen receptors (ER) in primary neurons or brain slices from the rodent brain. However, these cells can not be maintained continuously in culture because neurons are post-mitotic. Neurons derived from embryonic stem cells could be a potential continuous, cell-based model to study nongenomic actions of estrogens in neurons if they are responsive to estrogens after differentiation. In this study ER-subtype specific estrogens were used to examine the role of ERα and ERβ on calcium oscillations in neurons derived from human (hES) and mouse embryonic stem cells. Unlike the undifferentiated hES cells the differentiated cells expressed neuronal markers, ERβ, but not ERα. The non-selective ER agonist 17β-estradiol (E2) rapidly increased [Ca2+]i oscillations and synchronizations within a few minutes. No change in calcium oscillations was observed with the selective ERα agonist 4,4′,4″-(4-Propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT). In contrast, the selective ERβ agonists, 2,3-bis(4-Hydroxyphenyl)-propionitrile (DPN), MF101, and 2-(3-fluoro-4-hydroxyphenyl)-7-vinyl-1,3 benzoxazol-5-ol (ERB-041; WAY-202041) stimulated calcium oscillations similar to E2. The ERβ agonists also increased calcium oscillations and phosphorylated PKC, AKT and ERK1/2 in neurons derived from mouse ES cells, which was inhibited by nifedipine demonstrating that ERβ activates L-type voltage gated calcium channels to regulate neuronal activity. Our results demonstrate that ERβ signaling regulates nongenomic pathways in neurons derived from ES cells, and suggest that these cells might be useful to study the nongenomic mechanisms of estrogenic compounds.
Dehydroepiandrosterone (DHEA), a 19-carbon precursor of sex steroids, is abundantly produced in the human but not the mouse adrenal. However, mice produce DHEA and DHEA-sulfate (DHEAS) in the fetal brain. DHEA stimulates axonal growth from specific populations of mouse neocortical neurons in vitro, while DHEAS stimulates dendritic growth from those cells. The synthesis of DHEA and sex steroids, but not mouse glucocorticoids and mineralocorticoids, requires P450c17, which catalyzes both 17α-hydroxylase and 17,20-lyase activities. We hypothesized that P450c17-knockout mice would have disordered sex steroid synthesis and disordered brain DHEA production and thus provide phenotypic clues about the functions of DHEA in mouse brain development. We deleted the mouse P450c17 gene in 127/SvJ mice and obtained several lines of mice from two lines of targeted embryonic stem cells. Heterozygotes were phenotypically and reproductively normal, but in all mouse lines, P450c17−/− zygotes died by embryonic day 7, prior to gastrulation. The cause of this early lethality is unknown, as there is no known function of fetal steroids at embryonic day 7. Immunocytochemistry identified P450c17 in embryonic endoderm in E7 wild-type and heterozygous embryos, but its function in these cells is unknown. Enzyme assays of wild-type embryos showed a rapid rise in 17-hydroxylase activity between E6 and E7 and the presence of C17,20-lyase activity at E7. Treatment of pregnant females with subcutaneous pellets releasing DHEA or 17-OH pregnenolone at a constant rate failed to rescue P450c17−/− fetuses. Treatment of normal pregnant females with pellets releasing pregnenolone or progesterone did not cause fetal demise. These data suggest that steroid products of P450c17 have heretofore-unknown essential functions in early embryonic mouse development.
Tumor necrosis factor alpha (TNF-α) has been demonstrated to inhibit steroidogenesis in Leydig cells at the transcriptional level of steroidogenic enzymes. However, the molecular mechanism of this observed gene repression is not well understood. We now demonstrate that nuclear factor κB (NF-κB) activated by TNF-α inhibits the transactivation of orphan nuclear receptors, which regulate the expression of steroidogenic-enzyme genes. TNF-α treatment suppressed the luteinizing-hormone-induced or Nur77/SF-1-stimulated promoter activity of steroidogenic-enzyme genes in Leydig cells. The TNF-α-mediated gene suppression was blocked by treatment with an inhibitor of NF-κB. In addition, overexpression of the p65 (RelA) subunit of NF-κB showed the same effect as TNF-α and inhibited Nur77 transactivation, suggesting the involvement of NF-κB activation in the observed gene repression. Physical association of Nur77 with p65 was revealed by mammalian two-hybrid, GST pull-down, and coimmunoprecipitation analyses. The NF-κB inhibition of Nur77 transactivation was likely due to the competition of p65 for Nur77 binding with coactivators. Finally, chromatin immunoprecipitation assays revealed that TNF-α treatment caused the recruitment of NF-κB to the promoter of the steroidogenic-enzyme P450c17 gene, supporting the hypothesis that the TNF-α-mediated gene repression involves NF-κB inhibition of the transcriptional activity of Nur77 and other orphan nuclear receptors. These findings provide a molecular mechanism underlying the inhibition of testicular steroidogenesis by proinflammatory cytokines.