The neurosteroid allopregnanolone modulates specific functions in central and peripheral glial cells

Protection from oxygen-glucose deprivation by neurosteroid treatment in primary neurons and oligodendrocytes

Preterm birth results in an increased risk of neonatal brain injury and neurobehavioural disorders. Despite the seriousness of these adverse outcomes, there are currently no effective therapies to protect the vulnerable developing brain. We propose that neurosteroid replacement therapy may be a novel approach in reducing detrimental neurological outcomes following preterm birth. The use of guinea pig primary neuronal and oligodendrocyte cultures with relevance to late gestation allows insight into the mechanisms behind the effectiveness of these treatments. Primary neuronal and oligodendrocyte cultures were derived from fetal guinea pig frontal cortex brain tissue at gestational age 62 (GA62). Cell cultures were pre-treated with either etifoxine (5 µM) or zuranolone (1 µm) for 24 h prior to insult. Cells were then exposed to either oxygen-glucose deprivation (OGD; 0% O2 and no glucose DMEM; preterm birth insult) or sham (standard cell culture conditions; 25 mM DMEM) for 2 h. Lactate dehydrogenase assay (LDH) was performed following OGD as a measure of cytotoxicity. Relative mRNA expression of key neuronal and oligodendrocyte markers, as well as neuronal receptors and transporters, were quantified using high throughput (Fluidigm) RT-PCR. OGD significantly increased cellular cytotoxicity in both neurons and oligodendrocytes. Additionally, key neuronal marker mRNA expression was reduced following OGD, and oligodendrocytes displayed arrested mRNA expression of key markers of lineage progression. Treatment with etifoxine restored a number of parameters back to control levels, whereas treatment with zuranolone provided a robust improvement in all parameters examined. This study has demonstrated the neuroprotective potential of neurosteroid replacement therapy in a model of hypoxia related to preterm birth. Neuroprotection appears to be mediated through glutamate reduction and increased brain derived neurotrophic factor (BDNF). Future work is warranted in examining these treatments in vivo, with the overall aim to suppress preterm associated brain damage and reduce long term outcomes for affected offspring.

Local effect of allopregnanolone in rat ovarian steroidogenesis, follicular and corpora lutea development

Allopregnanolone (ALLO) is a known neurosteroid and a progesterone metabolite synthesized in the ovary, CNS, PNS, adrenals and placenta. Its role in the neuroendocrine control of ovarian physiology has been studied, but its in situ ovarian effects are still largely unknown. The aims of this work were to characterize the effects of intrabursal ALLO administration on different ovarian parameters, and the probable mechanism of action. ALLO administration increased serum progesterone concentration and ovarian 3β-HSD2 while decreasing 20α-HSD mRNA expression. ALLO increased the number of atretic follicles and the number of positive TUNEL granulosa and theca cells, while decreasing positive PCNA immunostaining. On the other hand, there was an increase in corpora lutea diameter and PCNA immunostaining, whereas the count of TUNEL-positive luteal cells decreased. Ovarian angiogenesis and the immunohistochemical expression of GABAA receptor increased after ALLO treatment. To evaluate if the ovarian GABAA receptor was involved in these effects, we conducted a functional experiment with a specific antagonist, bicuculline. The administration of bicuculline restored the number of atretic follicles and the diameter of corpora lutea to normal values. These results show the actions of ALLO on the ovarian physiology of the female rat during the follicular phase, some of them through the GABAA receptor. Intrabursal ALLO administration alters several processes of the ovarian morpho-physiology of the female rat, related to fertility and oocyte quality.

The Effects of Neuroactive Steroids on Myelin in Health and Disease

Myelin plays a pivotal role in the efficient transmission of nerve impulses. Disruptions in myelin integrity are associated with numerous neurological disorders, including multiple sclerosis. In the central nervous system (CNS), myelin is formed by oligodendrocytes. Remyelination refers to the re-formation of the damaged myelin sheath by newly formed oligodendrocytes. Steroids have gained attention for their potential modulatory effects on myelin in both health and disease. Steroids are traditionally associated with endocrine functions, but their local synthesis within the nervous system has generated significant interest. The term "neuroactive steroids" refers to steroids that can act on cells of the nervous system. In the healthy state, neuroactive steroids promote myelin formation, maintenance, and repair by enhancing oligodendrocyte differentiation and maturation. In pathological conditions, such as demyelination injury, multiple neuroactive steroids have shown promise in promoting remyelination. Understanding the effects of neuroactive steroids on myelin could lead to novel therapeutic approaches for demyelinating diseases and neurodegenerative disorders. This review highlights the potential therapeutic significance of neuroactive steroids in myelin-related health and diseases. We review the synthesis of steroids by neurons and glial cells and discuss the roles of neuroactive steroids on myelin structure and function in health and disease. We emphasize the potential promyelinating effects of the varying levels of neuroactive steroids during different female physiological states such as the menstrual cycle, pregnancy, lactation, and postmenopause.

Quantification of glucocorticoid and progestogen metabolites in bovine plasma, skimmed milk and saliva by UHPLC-HR-MS with polarity switching

Steroid metabolites are increasingly in focus when searching for novel biomarkers in physiological mechanisms and their disorders. While major steroids such as progesterone and cortisol are well-researched and routinely determined to assess the health, particularly the reproductive status of mammals, the function of potentially biologically active progestogen and glucocorticoid metabolites is widely unexplored. One of the main reasons for this is the lack of comprehensive, sensitive, and specific analytical methods. This is particularly the case when analyzing matrices like milk or saliva obtained by non-invasive sampling with steroid concentrations often below those present in plasma. Therefore, a new UHPLC-HR-MS method based on an Ultimate UHPLC system equipped with an Acquity HSS T3 reversed-phase column and a Q Exactive™ mass spectrometer was developed, enabling the simultaneous chromatographic separation, detection and quantification of eleven isobaric glucocorticoids (11-dehydrocorticosterone (A), corticosterone (B), cortisol (F), cortisone (E), the tetrahydrocortisols (THF): 3α,5α-THF, 3α,5β-THF, 3β,5α-THF, 3β,5β-THF, and the tetrahydrocortisones (THE): 3α,5α-THE, 3α,5β-THE, 3β,5α-THE) and twelve progestogens (progesterone (P4), pregnenolone (P5), the dihydroprogesterones (DHP): 20α-DHP, 20β-DHP, 3α-DHP, 3β-DHP, 5α-DHP, 5β-DHP, and the tetrahydroprogesterones (THP): 3α,5α-THP, 3α,5β-THP, 3β,5α-THP, 3β,5β-THP) in bovine plasma, skimmed milk, and saliva. A simple liquid-liquid extraction (LLE) with MTBE (methyl tert-butyl ether) was used for sample preparation of 500 μL plasma, skimmed milk, and saliva. Heated electrospray ionization (HESI) with polarity switching was applied to analyze steroids in high-resolution full scan mode (HR-FS). The method validation covered the investigation of sensitivity, selectivity, curve fitting, carry-over, accuracy, precision, recovery, matrix effects and applicability. A high sensitivity in the range of pg mL-1 was achieved for all steroids suitable for the analysis of authentic samples.

Allopregnanolone pleiotropic action in neurons and astrocytes: calcium signaling as a unifying mechanism

Objective

Allopregnanolone (Allo) is a neurosteroid with pleiotropic action in the brain that includes neurogenesis, oligogenesis, human and rodent neural stem cell regeneration, increased glucose metabolism, mitochondrial respiration and biogenesis, improved cognitive function, and reduction of both inflammation and Alzheimer's disease (AD) pathology. Because the breadth of Allo-induced responses requires activation of multiple systems of biology in the absence of an Allo-specific nuclear receptor, analyses were conducted in both neurons and astrocytes to identify unifying systems and signaling pathways.

Methods

Mechanisms of Allo action were investigated in embryonic hippocampal neurons and astrocytes cultured in an Aging Model (AM) media. Cellular morphology, mitochondrial function, and transcriptomics were investigated followed by mechanistic pathway analyses.

Results

In hippocampal neurons, Allo significantly increased neurite outgrowth and synaptic protein expression, which were paralleled by upregulated synaptogenesis and long-term potentiation gene expression profiles. Mechanistically, Allo induced Ca2+/CREB signaling cascades. In parallel, Allo significantly increased maximal mitochondrial respiration, mitochondrial membrane potential, and Complex IV activity while reducing oxidative stress, which required both the GABAA and L-type Ca2+ channels. In astrocytes, Allo increased ATP generation, mitochondrial function and dynamics while reducing oxidative stress, inflammasome indicators, and apoptotic signaling. Mechanistically, Allo regulation of astrocytic mitochondrial function required both the GABAA and L-type Ca2+ channels. Furthermore, Allo activated NRF1-TFAM signaling and increased the DRP1/OPA1 protein ratio, which led to increased mitochondrial biogenesis and dynamics.

Conclusion

Collectively, the cellular, mitochondrial, transcriptional, and pharmacological profiles provide evidence in support of calcium signaling as a unifying mechanism for Allo pleiotropic actions in the brain.

Protein kinase C epsilon activation regulates proliferation, migration, and epithelial to mesenchymal-like transition in rat Schwann cells

Introduction

Protein kinase type C-ε (PKCε) plays an important role in the sensitization of primary afferent nociceptors, promoting mechanical hyperalgesia. In accordance, we showed that PKCε is present in sensory neurons of the peripheral nervous system (PNS), participating in the control of pain onset and chronification. Recently, it was found that PKCε is also implicated in the control of cell proliferation, promoting mitogenesis and metastatic invasion in some types of cancer. However, its role in the main glial cell of the PNS, the Schwann cells (SCs), was still not investigated.

Methods

Rat primary SCs culture were treated with different pharmacologic approaches, including the PKCε agonist dicyclopropyl-linoleic acid (DCP-LA) 500 nM, the human recombinant brain derived neurotrophic factor (BDNF) 1 nM and the TrkB receptor antagonist cyclotraxin B 10 nM. The proliferation (by cell count), the migration (by scratch test and Boyden assay) as well as some markers of SCs differentiation and epithelial-mesenchymal transition (EMT) process (by qRT-PCR and western blot) were analyzed.

Results

Overall, we found that PKCε is constitutively expressed in SCs, where it is likely involved in the switch from the proliferative toward the differentiated state. Indeed, we demonstrated that PKCε activation regulates SCs proliferation, increases their migration, and the expression of some markers (e.g., glycoprotein P0 and the transcription factor Krox20) of SCs differentiation. Through an autocrine mechanism, BDNF activates TrkB receptor, and controls SCs proliferation via PKCε. Importantly, PKCε activation likely promoted a partial EMT process in SCs.

Discussion

PKCε mediates relevant actions in the neuronal and glial compartment of the PNS. In particular, we posit a novel function for PKCε in the transformation of SCs, assuming a role in the mechanisms controlling SCs' fate and plasticity.

Exploring Novel Therapeutic Approaches for Depressive Disorders: The Role of Allopregnanolone Agonists

Depressive disorders are caused due to the impaired functioning of important brain networks. Recent studies have also shown that it is caused by a significant reduction in the levels of allopregnanolone, which is a progesterone metabolite. Newer treatment modalities are now focusing on the usage of neuroactive steroids, such as allopregnanolone, in various depressive disorders. Our aim was to provide a comprehensive literature review on the clinical aspects of the allopregnanolone agonists brexanolone and zuranolone with reference to the physiological role of allopregnanolone. Brexanolone was approved by the FDA in 2019 for the treatment of postpartum depression and has greatly influenced further research into potential drugs such as zuranolone, which is currently undergoing phase 3 of clinical trials. Although these drugs exhibit improvement in symptoms of depressive disorders along with notable side effects, further research is required for their future clinical use.

Lack of placental neurosteroid alters cortical development and female somatosensory function

Placental endocrine function is essential to fetal brain development. Placental hormones include neurosteroids such as allopregnanolone (ALLO), a regulator of neurodevelopmental processes via positive allosteric modulation of the GABAA receptor (GABAA-R). Using a mouse model (plKO) in which the gene encoding the ALLO synthesis enzyme is specifically deleted in trophoblasts, we previously showed that placental ALLO insufficiency alters cerebellar white matter development and leads to male-specific autistic-like behavior. We now demonstrate that the lack of placental ALLO causes female-predominant alterations of cortical development and function. Placental ALLO insufficiency disrupts cell proliferation in the primary somatosensory cortex (S1) in a sex-linked manner. Early changes are seen in plKO embryos of both sexes, but persist primarily in female offspring after birth. Adolescent plKO females show significant reduction in pyramidal neuron density, as well as somatosensory behavioral deficits as compared with plKO males and control littermates. Assessment of layer-specific markers in human postmortem cortices suggests that preterm infants may also have female-biased abnormalities in cortical layer specification as compared with term infants. This study establishes a novel and fundamental link between placental function and sex-linked long-term neurological outcomes, emphasizing the importance of the growing field of neuroplacentology.

Development of neuroactive steroids for the treatment of postpartum depression

Postpartum depression (PPD) is a common major depressive episode surrounding childbirth, with estimated rates ranging from 5.5% to 23.5% of all live births across Europe and the USA based on the presence of key symptoms. PPD has been associated with significant impairments in both maternal functioning and mother-infant attachment, and these impairments can have lasting effects on the emotional and cognitive development of children. Although the precise pathophysiology of PPD is unknown, preclinical findings suggest that large fluctuations in neurosteroid hormone levels can induce physiological plasticity in the expression of functional GABA_A receptors during pregnancy and the postpartum period, and that deficits in this plasticity may underpin a biological mechanism that contributes to the manifestation of depressive symptoms. Here, we review the controlled clinical trials to date that have assessed the efficacy of pharmacological treatments for PPD, including oestradiol, selective serotonin reuptake inhibitors, brexanolone (an iv formulation of allopregnanolone) and an investigational neuroactive steroid and GABA_A positive allosteric modulator, zuranolone. Coupled with the GABAergic deficits implicated in major depressive disorder, these findings highlight not only the potential role of GABA_A receptor plasticity in the pathophysiology of PPD, but also the novel therapeutic approach of using positive allosteric modulators targeting GABAergic transmission to treat women affected by PPD.

Superior mesenteric ganglion neural modulation of ovarian angiogenesis, apoptosis and proliferation by the neuroactive steroid allopregnanolone

Allopregnanolone (ALLO), a potent neuroactive steroid, is synthesized and active in the peripheral nervous system. Previous studies have shown that ALLO participates in the central regulation of reproduction with effects on ovarian physiology, although there is little evidence for its ability to modulate peripheral tissues. The present study aimed to determine whether ALLO, administered to an ex vivo system that comprises the superior mesenteric ganglion (SMG), the ovarian nervous plexus (ONP) and the ovary (O), or to the denervated ovary (DO), was able to modify ovarian apoptosis, proliferation and angiogenesis. For this purpose, the SMG-ONP-O system and DO were incubated during 120 min at 37°C, in the presence of two ALLO doses (0.06 µm and 6 µm). The intrinsic and extrinsic pathways of apoptosis were analyzed. Incubation of the SMG-ONP-O system with ALLO 0.06 µm led to an increase in the BAX/BCL-2 ratio and a reduction of FAS-L mRNA levels. ALLO 6 µm induced a decrease of FAS-L levels. Incubation of DO with ALLO 0.06 µm reduced FAS-L, whereas ALLO 6 µm significantly increased it. Cyclin D1 mRNA was measured to evaluate proliferation. Treatment with ALLO 6 µm increased proliferation in both SMG-ONP-O and DO. ALLO 0.06 µm produced an increase of Cyclin D1 in DO only. Administration of either ALLO dose led to a higher ovarian expression of vascular endothelial growth factor in the SMG-ONP-O system, but a lower one in the DO system. ALLO 6 µm induced ovarian sensitization to GABA by increasing GABA_A receptor expression. In conclusion, ALLO participates in the peripheral neural modulation of ovarian physiology. It can also interact directly with the ovarian tissue, modulating key mechanisms involved in normal and pathological processes in a dose-dependent manner.

Allopregnanolone Improves Locomotor Activity and Arousal in the Aged CGG Knock-in Mouse Model of Fragile X-Associated Tremor/Ataxia Syndrome

Carriers of the fragile X premutation (PM) can develop a variety of early neurological symptoms, including depression, anxiety and cognitive impairment as well as being at risk for developing the late-onset fragile X-associated tremor/ataxia syndrome (FXTAS). The absence of effective treatments for FXTAS underscores the importance of developing efficacious therapies to reduce the neurological symptoms in elderly PM carriers and FXTAS patients. A recent preliminary study reported that weekly infusions of Allopregnanolone (Allop) may improve deficits in executive function, learning and memory in FXTAS patients. Based on this study we examined whether Allop would improve neurological function in the aged CGG knock-in (CGG KI) dutch mouse, B6.129P2(Cg)-Fmr1^tm2Cgr/Cgr, that models much of the symptomatology in PM carriers and FXTAS patients. Wild type and CGG KI mice received 10 weekly injections of Allop (10 mg/kg, s.c.), followed by a battery of behavioral tests of motor function, anxiety, and repetitive behavior, and 5-bromo-2'-deoxyuridine (BrdU) labeling to examine adult neurogenesis. The results provided evidence that Allop in CGG KI mice normalized motor performance and reduced thigmotaxis in the open field, normalized repetitive digging behavior in the marble burying test, but did not appear to increase adult neurogenesis in the hippocampus. Considered together, these results support further examination of Allop as a therapeutic strategy in patients with FXTAS.

Membrane progesterone receptor α (mPRα/PAQR7) promotes migration, proliferation and BDNF release in human Schwann cell-like differentiated adipose stem cells

Membrane progesterone receptors (mPRs) were recently found to be present and active in Schwann cells, where they have a potentially pro-regenerative activity. In this study, we investigated the role of mPRs in human adipose stem cells (ASC) differentiated into Schwann cell-like cells (SCL-ASC), which represent a promising alternative to Schwann cells for peripheral nerve regeneration. Our findings show that mPRs are present both in undifferentiated and differentiated ASC, and that the differentiation protocol upregulates mPR expression. Activation of mPRα promoted cell migration and differentiation in SCL-ASC, alongside with changes in cell morphology and mPRα localization. Moreover, it increased the expression and release of BDNF, a neurotrophin with pro-regenerative activity. Further analysis showed that Src and PI3K-Akt signaling pathways are involved in mPRα activity in SCL-ASC. These findings suggest that mPRα could play a pro-regenerative role in SCL-ASC and may be a promising target for the promotion of peripheral nerve regeneration.

The Aging GABAergic System and Its Nutritional Support

Aging is associated with a decline in hormones and an associated decline in GABAergic function and calcium and ion current dysregulation. Neurosteroid hormones act as direct calcium channel blockers, or they can act indirectly on calcium channels through their interaction with GABA receptors. The calcium channel dysfunction associated with hormone loss further leads to an excitatory cell state, which can ultimately lead to cell death. The calcium theory of aging posits that cellular mechanisms, which maintain the homeostasis of cytosol Ca2+ concentration, play a key role in brain aging and that sustained changes in Ca2+ homeostasis provide the final common pathway for age-associated brain changes. There is a link between hormone loss and calcium dysregulation. Loss of calcium regulation associated with aging can lead to an excitatory cell state, primarily in the mitochondria and nerve cells, which can ultimately lead to cell death if not kept in check. A decline in GABAergic function can also be specifically tied to declines in progesterone, allopregnanolone, and DHEA levels associated with aging. This decline in GABAergic function associated with hormone loss ultimately affects GABAergic inhibition or excitement and calcium regulation throughout the body. In addition, declines in GABAergic function can also be tied to vitamin status and to toxic chemicals in the food supply. The decline in GABAergic function associated with aging has an effect on just about every body organ system. Nutritional support of the GABAergic system with supportive foods, vitamins, and GABA or similar GABA receptor ligands may address some of the GABAergic dysfunction associated with aging.

Transcranial magnetic stimulation neurophysiology of patients with major depressive disorder: a systematic review and meta-analysis

Major depressive disorder (MDD) is a mental illness with high socio-economic burden, but its pathophysiology has not been fully elucidated. Recently, the cortical excitatory and inhibitory imbalance hypothesis and neuroplasticity hypothesis have been proposed for MDD. Although several studies have examined the neurophysiological profiles in MDD using transcranial magnetic stimulation (TMS), a meta-analysis of TMS neurophysiology has not been performed. The objective of this study was to compare TMS-electromyogram (TMS-EMG) findings between patients with MDD and healthy controls (HCs). To this end, we examined whether patients with MDD have lower short-interval cortical inhibition (SICI) which reflects gamma-aminobutyric acid (GABA)A receptor-mediated activity, lower cortical silent period (CSP) which represents GABAB receptor-mediated activity, higher intracortical facilitation (ICF) which reflects glutamate N-methyl-D-aspartate receptor-mediated activity, and the lower result of paired associative stimulation (PAS) paradigm which shows the level of neuroplasticity in comparison with HC. Further, we explored the effect of clinical and demographic factors that may influence TMS neurophysiological indices. We first searched and identified research articles that conducted single- or paired-pulse TMS-EMG on patients with MDD and HC. Subsequently, we extracted the data from the included studies and meta-analyzed the data with the comprehensive meta-analysis software. Patients with MDD were associated with lower SICI, lower CSP, potentially higher ICF, and lower PAS compared with HC. Our results confirmed the proposed hypotheses, suggesting the usefulness of TMS neurophysiology as potential diagnostic markers of MDD.

Interleukin 6 reduces allopregnanolone synthesis in the brain and contributes to age-related cognitive decline in mice

Cognitive decline with age is a harmful process that can reduce quality of life. Multiple factors have been established to contribute to cognitive decline, but the overall etiology remains unknown. Here, we hypothesized that cognitive dysfunction is mediated, in part, by increased levels of inflammatory cytokines that alter allopregnanolone (AlloP) levels, an important neurosteroid in the brain. We assessed the levels and regulation of AlloP and the effects of AlloP supplementation on cognitive function in 4-month-old and 24-month-old male C57BL/6 mice. With age, the expression of enzymes involved in the AlloP synthetic pathway was decreased and corticosterone (CORT) synthesis increased. Supplementation of AlloP improved cognitive function. Interestingly, interleukin 6 (IL-6) infusion in young animals significantly reduced the production of AlloP compared with controls. It is notable that inhibition of IL-6 with its natural inhibitor, soluble membrane glycoprotein 130, significantly improved spatial memory in aged mice. These findings were supported by in vitro experiments in primary murine astrocyte cultures, indicating that IL-6 decreases production of AlloP and increases CORT levels. Our results indicate that age-related increases in IL-6 levels reduce progesterone substrate availability, resulting in a decline in AlloP levels and an increase in CORT. Furthermore, our results indicate that AlloP is a critical link between inflammatory cytokines and the age-related decline in cognitive function.

Expression and Function of GABA Receptors in Myelinating Cells

Myelin facilitates the fast transmission of nerve impulses and provides metabolic support to axons. Differentiation of oligodendrocyte progenitor cells (OPCs) and Schwann cell (SC) precursors is critical for myelination during development and myelin repair in demyelinating disorders. Myelination is tightly controlled by neuron-glia communication and requires the participation of a wide repertoire of signals, including neurotransmitters such as glutamate, ATP, adenosine, or γ-aminobutyric acid (GABA). GABA is the main inhibitory neurotransmitter in the central nervous system (CNS) and it is also present in the peripheral nervous system (PNS). The composition and function of GABA receptors (GABARs) are well studied in neurons, while their nature and role in glial cells are still incipient. Recent studies demonstrate that GABA-mediated signaling mechanisms play relevant roles in OPC and SC precursor development and function, and stand out the implication of GABARs in oligodendrocyte (OL) and SC maturation and myelination. In this review, we highlight the evidence supporting the novel role of GABA with an emphasis on the molecular identity of the receptors expressed in these glial cells and the possible signaling pathways involved in their actions. GABAergic signaling in myelinating cells may have potential implications for developing novel reparative therapies in demyelinating diseases.

Schwann Cell Autocrine and Paracrine Regulatory Mechanisms, Mediated by Allopregnanolone and BDNF, Modulate PKCε in Peripheral Sensory Neurons

Protein kinase type C-ε (PKCε) plays important roles in the sensitization of primary afferent nociceptors, such as ion channel phosphorylation, that in turn promotes mechanical hyperalgesia and pain chronification. In these neurons, PKCε is modulated through the local release of mediators by the surrounding Schwann cells (SCs). The progesterone metabolite allopregnanolone (ALLO) is endogenously synthesized by SCs, whereas it has proven to be a crucial mediator of neuron-glia interaction in peripheral nerve fibers. Biomolecular and pharmacological studies on rat primary SCs and dorsal root ganglia (DRG) neuronal cultures were aimed at investigating the hypothesis that ALLO modulates neuronal PKCε, playing a role in peripheral nociception. We found that SCs tonically release ALLO, which, in turn, autocrinally upregulated the synthesis of the growth factor brain-derived neurotrophic factor (BDNF). Subsequently, glial BDNF paracrinally activates PKCε via trkB in DRG sensory neurons. Herein, we report a novel mechanism of SCs-neuron cross-talk in the peripheral nervous system, highlighting a key role of ALLO and BDNF in nociceptor sensitization. These findings emphasize promising targets for inhibiting the development and chronification of neuropathic pain.

Genomic and Non-genomic Action of Neurosteroids in the Peripheral Nervous System

Since the former evidence of biologic actions of neurosteroids in the central nervous system, also the peripheral nervous system (PNS) was reported as a structure affected by these substances. Indeed, neurosteroids are synthesized and active in the PNS, exerting many important actions on the different cell types of this system. PNS is a target for neurosteroids, in their native form or as metabolites. In particular, old and recent evidence indicates that the progesterone metabolite allopregnanolone possesses important functions in the PNS, thus contributing to its physiologic processes. In this review, we will survey the more recent findings on the genomic and non-genomic actions of neurosteroids in nerves, ganglia, and cells forming the PNS, focusing on the mechanisms regulating the peripheral neuron-glial crosstalk. Then, we will refer to the physiopathological significance of the neurosteroid signaling disturbances in the PNS, in to identify new molecular targets for promising pharmacotherapeutic approaches.

"Rapid actions of the neurosteroid allopregnanolone on ovarian and hypothalamic steroidogenesis: Central and peripheral modulation"

The present study aimed to determine whether an i.c.v. administration of allopregnanolone (ALLO) rapidly modifies the hypothalamic and ovarian 3β-hydroxysteroid dehydrogenase (3β-HSD) enzymatic activity and gene expression in in vivo and ex vivo systems in pro-oestrus (PE) and dioestrus I (DI) rats. Animals were injected with vehicle, ALLO, bicuculline or bicuculline plus ALLO and were then killed. In the in vivo experiment, the hypothalamus, ovaries and serum were extracted and analysed. In the ex vivo experiment, the superior mesenteric ganglion - ovarian nerve plexus - ovary system was extracted and incubated during 120 minutes at 37 ºC. The serum and ovarian compartment fluids were used to determine progesterone by radioimmunoanalysis. In the in vivo experiments, ALLO caused a decrease in hypothalamic and ovarian 3β-HSD enzymatic activity during PE. During DI, ALLO increased hypothalamic and ovarian 3β-HSD activity and gene expression. The ovarian 3β-HSD activity increased in both stages in the ex vivo system; gene expression increased only during DI. ALLO induced an increase in serum progesterone only in D1 and in the ovarian incubation liquids in both stages. All findings were reversed by an injection of bicuculline before ALLO. Ovarian steroidogenic changes could be attributed to signals coming from ganglion neurones, which are affected by the acute central neurosteroid stimulation. The i.c.v. administration of ALLO via the GABAergic system altered 3β-HSD activity and gene expression, modulating the neuroendocrine axis. The present study reveals the action that ALLO exerts on the GABAA receptor in both the central and peripheral nervous system and its relationship with hormonal variations. ALLO is involved in the "fine tuning" of neurosecretory functions as a potent modulator of reproductive processes in female rats.

CYP17A1 Maintains the Survival of Glioblastomas by Regulating SAR1-Mediated Endoplasmic Reticulum Health and Redox Homeostasis

Cytochrome P450 (CYP) 17A1 is an important steroidogenic enzyme harboring 17α-hydroxylase and performing 17,20 lyase activities in multiple steps of steroid hormone synthesis, including dehydroepiandrosterone (DHEA) biosynthesis. Previously, we showed that CYP17A1-mediated DHEA production clearly protects glioblastomas from temozolomide-induced apoptosis, leading to drug resistance. Herein, we attempt to clarify whether the inhibition of CYP17A1 has a tumor-suppressive effect, and to determine the steroidogenesis-independent functions of CYP17A1 in glioblastomas. Abiraterone, an inhibitor of CYP17A1, significantly inhibits the proliferation of A172, T98G, and PT#3 (the primary glioblastoma cells) by inducing apoptosis. In parallel, abiraterone potently suppresses tumor growth in mouse models through transplantation of PT#3 cells to the back or to the brain. Based on evidence that abiraterone induces endoplasmic reticulum (ER) stress, followed by the accumulation of reactive oxygen species (ROS), CYP17A1 is important for ER health and redox homeostasis. To confirm our hypothesis, we showed that CYP17A1 overexpression prevents the initiation of ER stress and attenuates ROS production by regulating SAR1a/b expression. Abiraterone dissociates SAR1a/b from ER-localized CYP17A1, and induces SAR1a/b ubiquitination, leading to degradation. Furthermore, SAR1 overexpression rescues abiraterone-induced apoptosis and impairs redox homeostasis. In addition to steroid hormone synthesis, CYP17A1 associates with SAR1a/b to regulate protein processing and maintain ER health in glioblastomas.

Multiple functional neurosteroid binding sites on GABAA receptors

Neurosteroids are endogenous modulators of neuronal excitability and nervous system development and are being developed as anesthetic agents and treatments for psychiatric diseases. While gamma amino-butyric acid Type A (GABA_A) receptors are the primary molecular targets of neurosteroid action, the structural details of neurosteroid binding to these proteins remain ill defined. We synthesized neurosteroid analogue photolabeling reagents in which the photolabeling groups were placed at three positions around the neurosteroid ring structure, enabling identification of binding sites and mapping of neurosteroid orientation within these sites. Using middle-down mass spectrometry (MS), we identified three clusters of photolabeled residues representing three distinct neurosteroid binding sites in the human α₁β₃ GABA_A receptor. Novel intrasubunit binding sites were identified within the transmembrane helical bundles of both the α₁ (labeled residues α₁-N⁴⁰⁸, Y⁴¹⁵) and β₃ (labeled residue β₃-Y⁴⁴²) subunits, adjacent to the extracellular domains (ECDs). An intersubunit site (labeled residues β₃-L²⁹⁴ and G³⁰⁸) in the interface between the β₃(+) and α₁(−) subunits of the GABA_A receptor pentamer was also identified. Computational docking studies of neurosteroid to the three sites predicted critical residues contributing to neurosteroid interaction with the GABA_A receptors. Electrophysiological studies of receptors with mutations based on these predictions (α₁-V²²⁷W, N⁴⁰⁸A/Y⁴¹¹F, and Q²⁴²L) indicate that both the α₁ intrasubunit and β₃-α₁ intersubunit sites are critical for neurosteroid action.

Novel neurosteroid analogue photolabeling reagents identify three specific neurosteroid binding sites on α1β3 GABAA receptors, showing that a site between the α and β subunits, as well as a site within the α-subunit, contribute to neurosteroid-mediated enhancement of GABAA currents.

Neurosteroids are cholesterol metabolites produced by neurons and glial cells that participate in central nervous system (CNS) development, regulate neuronal excitability, and modulate complex behaviors such as mood. Exogenously administered neurosteroid analogues are effective sedative hypnotics and are being developed as antidepressants and anticonvulsants. Gamma amino-butyric acid Type A (GABA_A) receptors, the principal ionotropic inhibitory neurotransmitter receptors in the brain, are the primary functional target of neurosteroids. Understanding the molecular details of neurosteroid interactions with GABA_A receptors is critical to understanding their mechanism of action and developing specific and effective therapeutic agents. In the current study, we developed a suite of neurosteroid analogue affinity labeling reagents, which we used to identify three distinct binding sites on GABA_A receptors and to determine the orientation of neurosteroid binding in each site. Electrophysiological studies performed on receptors with mutations designed to disrupt the identified binding sites showed that two of the three sites contribute to neurosteroid modulation of GABA_A currents. The distinct patterns of neurosteroid affinity, binding orientation, and effect provide the potential for the development of isoform-specific agonists, partial agonists, and antagonists with targeted therapeutic effects.

Expression of membrane progesterone receptors (mPRs) in rat peripheral glial cell membranes and their potential role in the modulation of cell migration and protein expression

The role played by progestogens in modulating Schwann cell pathophysiology is well established. Progestogens exert their effects in these cells through both classical genomic and non-genomic mechanisms, the latter mediated by the GABA-A receptor. However, there is evidence that other receptors may be involved. Membrane progesterone receptors (mPRs) are novel 7-transmembrane receptors coupled to G proteins that have been characterized in different tissues and cells, including the central nervous system (CNS). The mPRs were shown to mediate some of progestogens' neuroprotective effects in the CNS, and to be upregulated in glial cells after traumatic brain injury. Based on this evidence, this paper investigated the possible involvement of mPRs in mediating progestogen actions in S42 Schwann cells. All five mPR isoforms and progesterone receptor membrane component 1 (PGRMC1) were detected in Schwann cells, and were present on the cell membrane. Progesterone and the mPR-specific agonist, Org-OD-02-0 (02) bound to these membranes, indicating the presence of functional mPRs. The mPR agonist 02 rapidly increased cell migration in an in vitro assay, suggesting a putative role of mPRs in the nerve regeneration process. Treatment with pertussis toxin and 8-Br-cAMP blocked 02-induced cell migration, suggesting this progestogen action is mediated by activation of an inhibitory G protein, leading to a decrease in intracellular cAMP levels. In contrast, long-term mPR activation led to increased expression levels of myelin associated glycoprotein (MAG). Taken together, these findings show that mPRs are present and active in Schwann cells and have a role in modulating their physiological processes.

GABA-B1 Receptor-Null Schwann Cells Exhibit Compromised In Vitro Myelination

GABA-B receptors are important for Schwann cell (SC) commitment to a non-myelinating phenotype during development. However, the P0-GABA-B1^fl/fl conditional knockout mice, lacking the GABA-B1 receptor specifically in SCs, also presented axon modifications, suggesting SC non-autonomous effects through the neuronal compartment. In this in vitro study, we evaluated whether the specific deletion of the GABA-B1 receptor in SCs may induce autonomous or non-autonomous cross-changes in sensory dorsal root ganglia (DRG) neurons. To this end, we performed an in vitro biomolecular and transcriptomic analysis of SC and DRG neuron primary cultures from P0-GABA-B1^fl/fl mice. We found that cells from conditional P0-GABA-B1^fl/fl mice exhibited proliferative, migratory and myelinating alterations. Moreover, we found transcriptomic changes in novel molecules that are involved in peripheral neuron-SC interaction.

Allopregnanolone alters follicular and luteal dynamics during the estrous cycle

BACKGROUND

Allopregnanolone is a neurosteroid synthesized in the central nervous system independently of steroidogenic glands; it influences sexual behavior and anxiety. The aim of this work is to evaluate the indirect effect of a single pharmacological dose of allopregnanolone on important processes related to normal ovarian function, such as folliculogenesis, angiogenesis and luteolysis, and to study the corresponding changes in endocrine profile and enzymatic activity over 4 days of the rat estrous cycle. We test the hypothesis that allopregnanolone may trigger hypothalamus - hypophysis - ovarian axis dysregulation and cause ovarian failure which affects the next estrous cycle stages.

METHODS

Allopregnanolone was injected during the proestrous morning and then, the animals were sacrificed at each stage of the estrous cycle. Ovarian sections were processed to determine the number and diameter of different ovarian structures. Cleaved caspase 3, proliferating cell nuclear antigen, α-actin and Von Willebrand factor expressions were evaluated by immunohistochemistry. Luteinizing hormone, prolactin, estrogen and progesterone serum levels were measured by radioimmunoassay. The enzymatic activities of 3β-hydroxysteroid dehydrogenase, 3α-hydroxysteroid oxidoreductase and 20α-hydroxysteroid dehydrogenase were determined by spectrophotometric assays. Two-way ANOVA followed by Bonferroni was performed to determine statistical differences between control and treated groups along the four stages of the cycle.

RESULTS

The results indicate that allopregnanolone allopregnanolone decreased the number of developing follicles, while atretic follicles and cysts increased with no effects on normal cyclicity. Some cysts in treated ovaries showed morphological characteristics similar to luteinized unruptured follicles. The apoptosis/proliferation balance increased in follicles from treated rats. The endocrine profile was altered at different stages of the estrous cycle of treated rats. The angiogenic markers expression increased in treated ovaries. As regards corpora lutea, the apoptosis/proliferation balance and 20α-hydroxysteroid dehydrogenase enzymatic activity decreased significantly. Progesterone levels and 3β-hydroxysteroid dehydrogenase enzymatic activity increased in treated rats. These data suggest that allopregnanolone interferes with steroidogenesis and folliculogenesis at different stages of the cycle.

CONCLUSION

Allopregnanolone interferes with corpora lutea regression, which might indicate that this neurosteroid exerts a protective role over the luteal cells and prevents them from luteolysis. Allopregnanolone plays an important role in the ovarian pathophysiology.

Allopregnanolone Alters the Gene Expression Profile of Human Glioblastoma Cells

Glioblastomas (GBM) are the most frequent and aggressive brain tumors. In these malignancies, progesterone (P4) promotes proliferation, migration, and invasion. The P4 metabolite allopregnanolone (3α-THP) similarly promotes cell proliferation in the U87 human GBM cell line. Here, we evaluated global changes in gene expression of U87 cells treated with 3α-THP, P4, and the 5α-reductase inhibitor, finasteride (F). 3α-THP modified the expression of 137 genes, while F changed 90. Besides, both steroids regulated the expression of 69 genes. After performing an over-representation analysis of gene ontology terms, we selected 10 genes whose products are cytoskeleton components, transcription factors, and proteins involved in the maintenance of DNA stability and replication to validate their expression changes by RT-qPCR. 3α-THP up-regulated six genes, two of them were also up-regulated by F. Two genes were up-regulated by P4 alone, however, such an effect was blocked by F when cells were treated with both steroids. The remaining genes were regulated by the combined treatments of 3α-THP + F or P4 + F. An in-silico analysis revealed that promoters of the six up-regulated genes by 3α-THP possess cyclic adenosine monophosphate (cAMP) responsive elements along with CCAAT/Enhancer binding protein alpha (CEBPα) binding sites. These findings suggest that P4 and 3α-THP regulate different sets of genes that participate in the growth of GBMs.

In vitro and in vivo evaluation of silk fibroin functionalized with GABA and allopregnanolone for Schwann cell and neuron survival

AIM

This in vitro and in vivo study reports on silk fibroin (SF) scaffold, functionalized for in situ delivery of GABA and/or allopregnanolone (ALLO), as biomaterial for potential application in tissue engineering and nerve regeneration.

MATERIALS & METHODS

We evaluated the feasibility to design 2D scaffolds (films) made of regenerated Bombyx mori SF, functionalized with GABA and/or ALLO to enhance in vitro biological functions, health, survival and growth of Schwann cells and sensitive neurons of the dorsal root ganglia.

RESULTS & CONCLUSION

Our 2D-SF film showed an efficient loading and controllable release of drugs promoting nerve regeneration. SF functionalized film may be helpful for the development of bioengineered conduits and, in principle, have great potential for long-gap nerve injury repair.

Allopregnanolone promotes proliferation and differential gene expression in human glioblastoma cells

Allopregnanolone (3α-THP) is one of the main reduced progesterone (P₄) metabolites that is recognized as a neuroprotective and myelinating agent. 3α-THP also induces proliferation of different neural cells. It has been shown that P₄ favors the progression of glioblastomas (GBM), the most common and aggressive primary brain tumors. However, the role of 3α-THP in the growth of GBMs is unknown. Here, we studied the effects of 3α-THP on the number of cells, proliferation and gene expression in U87 cell line derived from a human GBM. 3α-THP (10, 100nM and 1μM) increased the number of U87 cells, and at 10nM exerted a similar increase in both the number of total and proliferative U87 cells as compared with P₄ (10nM). Interestingly, finasteride (F; 100nM), an inhibitor of 5α-reductase (5αR), an enzyme necessary to metabolize P₄ and produce 3α-THP, blocked the increase in the number of U87 cells induced by P₄. By using RT-qPCR, we determined that U87 cells express 5α-R isoenzymes 1 and 2 (5αR1 and 5αR2), being 5αR1 the predominant one in these cells. 3α-THP (10nM) increased the expression of TGFβ1, EGFR, VEGF and cyclin D1 genes. P₄ increased TGFβ1 and EGFR expression, and this effect was blocked by F. These data provide evidence that P₄, through its metabolite 3α-THP, can promote in part cell proliferation of human GBM cells by changing the expression of genes involved in tumor progression.

Src and phospho-FAK kinases are activated by allopregnanolone promoting Schwann cell motility, morphology and myelination

Schwann cells' (SCs) development and maturation require coordinate and complementary activation of several signals and intracellular pathways. Among factors controlling these processes, the signalling intermediates Src tyrosine kinase and focal adhesion kinase (FAK) are relevant for SCs', participating in regulation of their adhesion, motility and migration. Recently, the progesterone metabolite allopregnanolone (ALLO) was proved to be synthesized by SCs, whereas it acts autocrinally on SCs motility and proliferation, which are crucial processes for nerve development, maturation and regeneration. Herein, we investigate the hypothesis that the molecular mechanisms behind the ALLO's action on SCs involve the signalling intermediates Src and FAK. We first demonstrated that ALLO 10^-6  M regulates SCs morphology, motility and myelination, also increasing the internode distance in the in vitro myelination model of neuron/SCs co-culture. ALLO's actions were mediated by the modulation of Src/FAK pathway, since they were counteracted by PP2 10^-5  M, a selective inhibitor of Src kinase. Then, we proved that Src/FAK activation in SCs involves GABA-A dependent mechanisms and actin re-arrangements. In conclusion, our findings are the first to corroborate the importance of the neuroactive steroid ALLO in regulating SCs development and maturation via the Src and phospho-FAK signalling activation. Cover Image for this issue: doi: 10.1111/jnc.13795.

Schwann cell development, maturation and regeneration: a focus on classic and emerging intracellular signaling pathways

The development, maturation and regeneration of Schwann cells (SCs), the main glial cells of the peripheral nervous system, require the coordinate and complementary interaction among several factors, signals and intracellular pathways. These regulatory molecules consist of integrins, neuregulins, growth factors, hormones, neurotransmitters, as well as entire intracellular pathways including protein-kinase A, C, Akt, Erk/MAPK, Hippo, mTOR, etc. For instance, Hippo pathway is overall involved in proliferation, apoptosis, regeneration and organ size control, being crucial in cancer proliferation process. In SCs, Hippo is linked to merlin and YAP/TAZ signaling and it seems to respond to mechanic/physical challenges. Recently, among factors regulating SCs, also the signaling intermediates Src tyrosine kinase and focal adhesion kinase (FAK) proved relevant for SC fate, participating in the regulation of adhesion, motility, migration and in vitro myelination. In SCs, the factors Src and FAK are regulated by the neuroactive steroid allopregnanolone, thus corroborating the importance of this steroid in the control of SC maturation. In this review, we illustrate some old and novel signaling pathways modulating SC biology and functions during the different developmental, mature and regenerative states.

Neurosteroids Involvement in the Epigenetic Control of Memory Formation and Storage

Memory is our ability to store and remember past experiences; it is the result of changes in neuronal circuits of specific brain areas as the hippocampus. During memory formation, neurons integrate their functions and increase the strength of their connections, so that synaptic plasticity is improved and consolidated. All these processes recruit several proteins at the synapses, whose expression is highly regulated by DNA methylation and histone tails posttranslational modifications. Steroids are known to influence memory process, and, among them, neurosteroids are implicated in neurodegenerative disease related to memory loss and cognitive impairment. The epigenetic control of neurosteroids involvement in memory formation and maintenance could represent the basis for neuroregenerative therapies.

Novel analogs of allopregnanolone show improved efficiency and specificity in neuroprotection and stimulation of proliferation

The natural neurosteroid allopregnanolone exerts beneficial effects in animal models of neurodegenerative diseases, nervous system injury and peripheral neuropathies. It not only has anti-apoptotic activity, but also promotes proliferation of progenitor cells. With respect to using it as a therapeutic tool, such pleiotropic actions might create unwanted side effects. Therefore, we have synthesized allopregnanolone analogs and analyzed their neuroprotective and proliferative effects to identify compounds with higher efficiency and less ambiguous biological actions. Proliferation-promoting effects of 3α and 3β isomers of 3-O-allyl-allopregnanolone and 12 oxo-allopregnanolone were studied in adult subventricular zone stem cell cultures and in primary hippocampal cultures by measuring 5-ethynyl-2'-deoxyuridine incorporation. Neuroprotective activity against amyloid beta 42-induced cell death was determined by quantifying caspase 3/7 activity. The 3α isomers significantly stimulated proliferation in all culture systems, whereas the 3β isomers were ineffective. The stimulatory effect of 3α-O-allyl-allopregnanolone was significantly higher than that of allopregnanolone. In neural stem cell cultures, 3α-O-allyl-allopregnanolone specifically enhanced proliferation of Nestin-positive progenitors. In addition, it promoted the differentiation of doublecortin-positive neurons. In neural stem cell cultures treated with amyloid beta 42, both the α and β isomers of O-allyl- allopregnanolone showed increased neuroprotective activity as compared to allopregnanolone, completely preventing amyloid-induced caspase 3/7 activation. The 12 oxo-allopregnanolone analogs were ineffective. These results identify structural allopregnanolone analogs with higher anti-apoptotic and proliferation-promoting activity than the natural neurosteroid. Interestingly, stereoisomers of the analogs were found to have distinct profiles of activity raising the possibility of exploiting the neuroprotective properties of neurosteroids with or without simultaneously stimulating neurogenesis. Cover Image for this issue: doi: 10.1111/jnc.13344.

Neurosteroids; potential underpinning roles in maintaining homeostasis

The neuroactive steroids which are synthesized in the brain and nervous system are known as "Neurosteroids". These steroids have crucial functions such as contributing to the myelination and organization of the brain connectivity. Under the stressful circumstances, the concentrations of neurosteroid products such as allopregnanolone (ALLO) and allotetrahydrodeoxycorticosterone (THDOC) alter. It has been suggested that these stress-derived neurosteroids modulate the physiological response to stress. Moreover, it has been demonstrated that the hypothalamic-pituitary-adrenal (HPA) axis mediates the physiological adaptation following stress in order to maintain homeostasis. Although several regulatory pathways have been introduced, the exact role of neurosteroids in controlling HPA axis is not clear to date. In this review, we intend to discern specific pathways associated with regulation of HPA axis in which neuroactive steroids have the main role. In this respect, we propose pathways that may be initiated after neurosteroidogenesis in different brain subregions following acute stress which are potentially capable of activating or inhibiting the HPA axis.

Peripheral nerve regeneration: experimental strategies and future perspectives

Peripheral nerve injuries represent a substantial clinical problem with insufficient or unsatisfactory treatment options. This review summarises all the events occurring after nerve damage at the level of the cell body, the site of injury and the target organ. Various experimental strategies to improve neuronal survival, axonal regeneration and target reinnervation are described including pharmacological approaches and cell-based therapies. Given the complexity of nerve regeneration, further studies are needed to address the biology of nerve injury, to improve the interaction with implantable scaffolds, and to implement cell-based therapies in nerve tissue engineering.

Protective actions of 17β-estradiol and progesterone on oxidative neuronal injury induced by organometallic compounds

Steroid hormones synthesized in and secreted from peripheral endocrine glands pass through the blood-brain barrier and play a role in the central nervous system. In addition, the brain possesses an inherent endocrine system and synthesizes steroid hormones known as neurosteroids. Increasing evidence shows that neuroactive steroids protect the central nervous system from various harmful stimuli. Reports show that the neuroprotective actions of steroid hormones attenuate oxidative stress. In this review, we summarize the antioxidative effects of neuroactive steroids, especially 17β-estradiol and progesterone, on neuronal injury in the central nervous system under various pathological conditions, and then describe our recent findings concerning the neuroprotective actions of 17β-estradiol and progesterone on oxidative neuronal injury induced by organometallic compounds, tributyltin, and methylmercury.

Polytherapy with a combination of three repurposed drugs (PXT3003) down-regulates Pmp22 over-expression and improves myelination, axonal and functional parameters in models of CMT1A neuropathy

Charcot-Marie-Tooth disease type 1A (CMT1A) is the most common inherited sensory and motor peripheral neuropathy. It is caused by PMP22 overexpression which leads to defects of peripheral myelination, loss of long axons, and progressive impairment then disability. There is no treatment available despite observations that monotherapeutic interventions slow progression in rodent models. We thus hypothesized that a polytherapeutic approach using several drugs, previously approved for other diseases, could be beneficial by simultaneously targeting PMP22 and pathways important for myelination and axonal integrity. A combination of drugs for CMT1A polytherapy was chosen from a group of authorised drugs for unrelated diseases using a systems biology approach, followed by pharmacological safety considerations. Testing and proof of synergism of these drugs were performed in a co-culture model of DRG neurons and Schwann cells derived from a Pmp22 transgenic rat model of CMT1A. Their ability to lower Pmp22 mRNA in Schwann cells relative to house-keeping genes or to a second myelin transcript (Mpz) was assessed in a clonal cell line expressing these genes. Finally in vivo efficacy of the combination was tested in two models: CMT1A transgenic rats, and mice that recover from a nerve crush injury, a model to assess neuroprotection and regeneration. Combination of (RS)-baclofen, naltrexone hydrochloride and D-sorbitol, termed PXT3003, improved myelination in the Pmp22 transgenic co-culture cellular model, and moderately down-regulated Pmp22 mRNA expression in Schwannoma cells. In both in vitro systems, the combination of drugs was revealed to possess synergistic effects, which provided the rationale for in vivo clinical testing of rodent models. In Pmp22 transgenic CMT1A rats, PXT3003 down-regulated the Pmp22 to Mpz mRNA ratio, improved myelination of small fibres, increased nerve conduction and ameliorated the clinical phenotype. PXT3003 also improved axonal regeneration and remyelination in the murine nerve crush model. Based on these observations in preclinical models, a clinical trial of PTX3003 in CMT1A, a neglected orphan disease, is warranted. If the efficacy of PTX3003 is confirmed, rational polytherapy based on novel combinations of existing non-toxic drugs with pleiotropic effects may represent a promising approach for rapid drug development.

Sex steroids and neuroprotection in spinal cord injury: a review of preclinical investigations

Spinal cord injury (SCI) is a debilitating condition that affects motor, sensory and autonomic functions. Subsequent to the first mechanical trauma, secondary events, which include inflammation and glial activation, exacerbate tissue damage and worsen functional deficits. Although these secondary injury mechanisms are amenable to therapeutic interventions, the efficacy of current approaches is inadequate. Further investigations are necessary to implement new therapies that can protect neural cells and attenuate some of the detrimental effects of inflammation while promoting regeneration. Studies on different animal models of SCI indicated that sex steroids, especially 17β-estradiol and progesterone, exert neuroprotective, anti-apoptotic and anti-inflammatory effects, ameliorate tissue sparing and improve functional deficits in SCI. As sex steroid receptors are expressed in a variety of cells including neurons, glia and immune system-related cells which infiltrate the injury epicenter, sex steroids could impact multiple processes simultaneously and in doing so, influence the outcomes of SCI. However, the translation of these pre-clinical findings into the clinical setting presents challenges such as the narrow therapeutic time window of sex steroid administration, the diversity of treatment regimens that have been employed in animal studies and the lack of sufficient information regarding the persistence of the effects in chronic SCI. The current review will summarize some of the major findings in this field and will discuss the challenges associated with the implementation of sex steroids as a promising treatment in human SCI.