PMP22 transgenic dorsal root ganglia cultures show myelin abnormalities similar to those of human CMT1A

Downregulation of PMP22 ameliorates myelin defects in iPSC-derived human organoid cultures of CMT1A

Charcot-Marie-Tooth disease is the most common inherited disorder of the PNS. CMT1A accounts for 40-50% of all cases and is caused by a duplication of the PMP22 gene on chromosome 17, leading to dysmyelination in the PNS. Patient-derived models to study such myelination defects are lacking as the in vitro generation of human myelinating Schwann cells has proved to be particularly challenging. Here, we present an induced pluripotent stem cell-derived organoid culture, containing various cell types of the PNS, including myelinating human Schwann cells, which mimics the human PNS. Single-cell analysis confirmed the PNS-like cellular composition and provides insight into the developmental trajectory. We used this organoid model to study disease signatures of CMT1A, revealing early ultrastructural myelin alterations, including increased myelin periodic line distance and hypermyelination of small axons. Furthermore, we observed the presence of onion-bulb-like formations in a later developmental stage. These hallmarks were not present in the CMT1A-corrected isogenic line or in a CMT2A iPSC line, supporting the notion that these alterations are specific to CMT1A. Downregulation of PMP22 expression using short-hairpin RNAs or a combinatorial drug consisting of baclofen, naltrexone hydrochloride and D-sorbitol was able to ameliorate the myelin defects in CMT1A-organoids. In summary, this self-organizing organoid model can capture biologically meaningful features of the disease and capture the physiological complexity, forms an excellent model for studying demyelinating diseases and supports the therapeutic approach of reducing PMP22 expression.

Exploiting Sphingo- and Glycerophospholipid Impairment to Select Effective Drugs and Biomarkers for CMT1A

In Charcot-Marie-Tooth type 1A (CMT1A), Schwann cells exhibit a preponderant transcriptional deficiency of genes involved in lipid biosynthesis. This perturbed lipid metabolism affects the peripheral nerve physiology and the structure of peripheral myelin. Nevertheless, the identification and functional characterization of the lipid species mainly responsible for CMT1A myelin impairment currently lack. This is critical in the pathogenesis of the neuropathy since lipids are many and complex molecules which play essential roles in the cell, including the structural components of cellular membranes, cell signaling, and membrane trafficking. Moreover, lipids themselves are able to modify gene transcription, thereby affecting the genotype-phenotype correlation of well-defined inherited diseases, including CMT1A. Here we report for the first time a comprehensive lipid profiling in experimental and human CMT1A, demonstrating a previously unknown specific alteration of sphingolipid (SP) and glycerophospholipid (GP) metabolism. Notably, SP, and GP changes even emerge in biological fluids of CMT1A rat and human patients, implying a systemic metabolic dysfunction for these specific lipid classes. Actually, SP and GP are not merely reduced; their expression is instead aberrant, contributing to the ultrastructural abnormalities that we detailed by X-ray diffraction in rat and human internode myelin. The modulation of SP and GP pathways in myelinating dorsal root ganglia cultures clearly sustains this issue. In fact, just selected molecules interacting with these pathways are able to modify the altered geometric parameters of CMT1A myelinated fibers. Overall, we propose to exploit the present SP and GP metabolism impairment to select effective drugs and validate a set of reliable biomarkers, which remain a challenge in CMT1A neuropathy.

Targeting myelin lipid metabolism as a potential therapeutic strategy in a model of CMT1A neuropathy

In patients with Charcot-Marie-Tooth disease 1A (CMT1A), peripheral nerves display aberrant myelination during postnatal development, followed by slowly progressive demyelination and axonal loss during adult life. Here, we show that myelinating Schwann cells in a rat model of CMT1A exhibit a developmental defect that includes reduced transcription of genes required for myelin lipid biosynthesis. Consequently, lipid incorporation into myelin is reduced, leading to an overall distorted stoichiometry of myelin proteins and lipids with ultrastructural changes of the myelin sheath. Substitution of phosphatidylcholine and phosphatidylethanolamine in the diet is sufficient to overcome the myelination deficit of affected Schwann cells in vivo. This treatment rescues the number of myelinated axons in the peripheral nerves of the CMT rats and leads to a marked amelioration of neuropathic symptoms. We propose that lipid supplementation is an easily translatable potential therapeutic approach in CMT1A and possibly other dysmyelinating neuropathies.

Tolerability and efficacy study of P2X7 inhibition in experimental Charcot-Marie-Tooth type 1A (CMT1A) neuropathy

Charcot-Marie-Tooth 1A (CMT1A) is a demyelinating hereditary neuropathy for which pharmacological treatments are not yet available. An abnormally high intracellular Ca(2+) concentration was observed in Schwann cells (SC) from CMT1A rats, caused by the PMP22-mediated overexpression of the P2X7 purinoceptor. The purpose of this study was to investigate the tolerability and therapeutic potential of a pharmacological antagonist of the P2X7 receptor (A438079) in CMT1A. A438079 ameliorated in vitro myelination of organotypic DRG cultures from CMT1A rats. Furthermore, we performed an experimental therapeutic trial in PMP22 transgenic and in wild-type rats. A preliminary dose-escalation trial showed that 3mg/kg A438079 administered via intraperitoneal injection every 24h for four weeks was well tolerated by wild type and CMT1A rats. Affected rats treated with 3mg/kg A438079 revealed a significant improvement of the muscle strength, when compared to placebo controls. Importantly, histologic analysis revealed a significant increase of the total number of myelinated axons in tibial nerves. Moreover, a significant decrease of the hypermyelination of small caliber axons and a significant increase of the frequency and diameter of large caliber myelinated axons was highlighted. An improved distal motor latencies was recorded, whereas compound muscle action potentials (CMAP) remained unaltered. A438079 reduced the SC differentiation defect in CMT1A rats. These results show that pharmacological inhibition of the P2X7 receptor is well tolerated in CMT1A rats and represents a proof-of-principle that antagonizing this pathway may correct the molecular derangements and improve the clinical phenotype in the CMT1A neuropathy.

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.

A novel transgenic mouse model of Chinese Charcot-Marie-Tooth disease type 2L

We previously found that the K141N mutation in heat shock protein B8 (HSPB8) was responsible for Charcot-Marie-Tooth disease type 2L in a large Chinese family. The objective of the present study was to generate a transgenic mouse model bearing the K141N mutation in the human HSPB8 gene, and to determine whether this ^K141NHSPB8 transgenic mouse model would manifest the clinical phenotype of Charcot-Marie-Tooth disease type 2L, and consequently be suitable for use in studies of disease pathogenesis. Transgenic mice overexpressing ^K141NHSPB8 were generated using K141N mutant HSPB8 cDNA cloned into a pCAGGS plasmid driven by a human cytomegalovirus expression system. PCR and western blot analysis confirmed integration of the ^K141NHSPB8 gene and widespread expression in tissues of the transgenic mice. The ^K141NHSPB8 transgenic mice exhibited decreased muscle strength in the hind limbs and impaired motor coordination, but no obvious sensory disturbance at 6 months of age by behavioral assessment. Electrophysiological analysis showed that the compound motor action potential amplitude in the sciatic nerve was significantly decreased, but motor nerve conduction velocity remained normal at 6 months of age. Pathological analysis of the sciatic nerve showed reduced myelinated fiber density, notable axonal edema and vacuolar degeneration in ^K141NHSPB8 transgenic mice, suggesting axonal involvement in the peripheral nerve damage in these animals. These findings indicate that the ^K141NHSPB8 transgenic mouse successfully models Charcot-Marie-Tooth disease type 2L and can be used to study the pathogenesis of the disease.

The diadenosine homodinucleotide P18 improves in vitro myelination in experimental Charcot-Marie-Tooth type 1A

Charcot-Marie-Tooth 1A (CMT1A) is a demyelinating hereditary neuropathy whose pathogenetic mechanisms are still poorly defined and an etiologic treatment is not yet available. An abnormally high intracellular Ca(2+) concentration ([Ca(2+)]i) occurs in Schwann cells from CMT1A rats (CMT1A SC) and is caused by overexpression of the purinoceptor P2X7. Normalization of the Ca(2+) levels through down-regulation of P2X7 appears to restore the normal phenotype of CMT1A SC in vitro. We recently demonstrated that the diadenosine 5',5'''-P1, P2-diphosphate (Ap2A) isomer P18 behaves as an antagonist of the P2X7 purinergic receptor, effectively blocking channel opening induced by ATP. In addition, P18 behaves as a P2Y11 agonist, inducing cAMP overproduction in P2Y11-overexpressing cells. Here we investigated the in vitro effects of P18 on CMT1A SC. We observed that basal levels of intracellular cAMP ([cAMP]i), a known regulator of SC differentiation and myelination, are significantly lower in CMT1A SC than in wild-type (wt) cells. P18 increased [cAMP]i in both CMT1A and wt SC, and this effects was blunted by NF157, a specific P2Y11 antagonist. Prolonged treatment of organotypic dorsal root ganglia (DRG) cultures with P18 significantly increased expression of myelin protein zero, a marker of myelin production, in both CMT1A and wt cultures. Interestingly, P18 decreased the content of non-phosphorylated neurofilaments, a marker of axonal damage, only in CMT1A DRG cultures. These results suggest that P2X7 antagonists, in combination with [cAMP]i-increasing agents, could represent a therapeutic strategy aimed at correcting the molecular derangements causing the CMT1A phenotype.

Hyccin, the molecule mutated in the leukodystrophy hypomyelination and congenital cataract (HCC), is a neuronal protein

“Hypomyelination and Congenital Cataract”, HCC (MIM #610532), is an autosomal recessive disorder characterized by congenital cataract and diffuse cerebral and peripheral hypomyelination. HCC is caused by deficiency of Hyccin, a protein whose biological role has not been clarified yet. Since the identification of the cell types expressing a protein of unknown function can contribute to define the physiological context in which the molecule is explicating its function, we analyzed the pattern of Hyccin expression in the central and peripheral nervous system (CNS and PNS). Using heterozygous mice expressing the b-galactosidase (LacZ) gene under control of the Hyccin gene regulatory elements, we show that the gene is primarily expressed in neuronal cells. Indeed, Hyccin-LacZ signal was identified in CA1 hippocampal pyramidal neurons, olfactory bulb, and cortical pyramidal neurons, while it did not colocalize with oligodendroglial or astrocytic markers. In the PNS, Hyccin was detectable only in axons isolated from newborn mice. In the brain, Hyccin transcript levels were higher in early postnatal development (postnatal days 2 and 10) and then declined in adult mice. In a model of active myelinogenesis, organotypic cultures of rat Schwann cells (SC)/Dorsal Root Ganglion (DRG) sensory neurons, Hyccin was detected along the neurites, while it was absent from SC. Intriguingly, the abundance of the molecule was upregulated at postnatal days 10 and 15, in the initial steps of myelinogenesis and then declined at 30 days when the process is complete. As Hyccin is primarily expressed in neurons and its mutation leads to hypomyelination in human patients, we suggest that the protein is involved in neuron-to-glia signalling to initiate or maintain myelination.

Dorsal Root Ganglia Sensory Neuronal Cultures: a tool for drug discovery for peripheral neuropathies

BACKGROUND: Peripheral neuropathies affect many people worldwide and are caused by or associated with a wide range of conditions, both genetic and acquired. Current therapies are directed at symptomatic control because no effective regenerative treatment exists. Primary challenge is that mechanisms that lead to distal axonal degeneration, a common feature of all peripheral neuropathies, are largely unknown. OBJECTIVE/METHODS: To address the role and specific characteristics of dorsal root ganglia (DRG) derived sensory neuron culture system as a useful model in evaluating the pathogenic mechanisms of peripheral neuropathies and examination and validation of potential therapeutic compounds. A thorough review of the recent literature was completed and select examples of the use of DRG neurons in different peripheral neuropathy models were chosen to highlight the utility of these cultures. CONCLUSION: Many useful models of different peripheral neuropathies have been developed using DRG neuronal culture and potential therapeutic targets have been examined, but so far none of the potential therapeutic compounds have succeeded in clinical trials. In recent years, focus has changed to evaluation of axon degeneration as the primary outcome measure advocating a drug development strategy starting with phenotypic drug screening, followed by validation in primary complex co-cultures and animal models.

Impaired expression of ciliary neurotrophic factor in Charcot-Marie-Tooth type 1A neuropathy

We investigated the contribution of Schwann cell-derived ciliary neurotrophic factor (CNTF) to the pathogenesis of Charcot-Marie-Tooth disease type 1A (CMT1A) and addressed the question as to whether it plays a role in the development of axonal damage observed in the disease, with aging. Ciliary neurotrophic factor was underexpressed in experimental CMT1A but not in other models of hereditary neuropathies. Sciatic nerve crush experiments and dosage of CNTF at different time points showed that expression of this trophic factor remained significantly lower in CMT1A rats than in normal controls; moreover, in uninjured CMT1A sciatic nerves CNTF levels further decreased with ageing, thus paralleling the molecular signs of axonal impairment, that is increased expression of non-phosphorylated neurofilaments and amyloid precursor protein. Administration of CNTF to dorsal root ganglia cultures reduced dephosphorylation of neurofilaments in CMT1A cultures, without improving demyelination. Taken together, these results provide further evidence that the production of CNTF by Schwann cells is markedly reduced in CMT1A. Moreover, the observations suggest that trophic support to the axon is impaired in CMT1A and that further studies on the therapeutic use of trophic factors or their derivatives in experimental and human CMT1A are warranted.

P2X7-mediated increased intracellular calcium causes functional derangement in Schwann cells from rats with CMT1A neuropathy

Charcot-Marie-Tooth (CMT) is the most frequent inherited neuromuscular disorder, affecting 1 person in 2500. CMT1A, the most common form of CMT, is usually caused by a duplication of chromosome 17p11.2, containing the PMP22 (peripheral myelin protein-22) gene; overexpression of PMP22 in Schwann cells (SC) is believed to cause demyelination, although the underlying pathogenetic mechanisms remain unclear. Here we report an abnormally high basal concentration of intracellular calcium ([Ca(2+)](i)) in SC from CMT1A rats. By the use of specific pharmacological inhibitors and through down-regulation of expression by small interfering RNA, we demonstrate that the high [Ca(2+)](i) is caused by a PMP22-related overexpression of the P2X7 purinoceptor/channel leading to influx of extracellular Ca(2+) into CMT1A SC. Correction of the altered [Ca(2+)](i) in CMT1A SC by small interfering RNA or with pharmacological inhibitors of P2X7 restores functional parameters of SC (migration and release of ciliary neurotrophic factor), which are typically defective in CMT1A SC. More significantly, stable down-regulation of the expression of P2X7 restores myelination in co-cultures of CMT1A SC with dorsal root ganglion sensory neurons. These results establish a pathogenetic link between high [Ca(2+)](i) and impaired SC function in CMT1A and identify overexpression of P2X7 as the molecular mechanism underlying both abnormalities. The development of P2X7 inhibitors is expected to provide a new therapeutic strategy for treatment of CMT1A neuropathy.

Nonmyelinating Schwann cell involvement with well-preserved unmyelinated axons in Charcot-Marie-Tooth disease type 1A

Electron microscopic examination was performed to compare morphologic changes of nonmyelinating Schwann cells and unmyelinated axons in patients with Charcot-Marie-Tooth disease type 1A (CMT1A) with peripheral myelin protein 22 duplication (n = 27) and normal control individuals (n = 14). Complete transverse sural nerve cross-sections were obtained in 16 patients and the total number of axons and Schwann cells in each cross-section was estimated. In patients with CMT1A, the number of myelinated axons was significantly decreased, whereas unmyelinated axons were well-preserved and did not show any marked changes. The numbers of nuclei, subunits, and profiles of nonmyelinating Schwann cells were all increased significantly in patients with CMT1A, whereas the numbers of axons per unmyelinated axon-containing subunit were significantly decreased. Schwann cell subunits consisted of layers of flattened cytoplasmic profiles wrapped around unmyelinated axons in the patient with CMT1A. The numbers of nonmyelinating Schwann cell profiles were increased and the numbers of axons per unmyelinated axon-containing subunit were reduced even in young patients with well-preserved myelinated fibers. In conclusion, there is marked alteration of the population and morphology of nonmyelinating Schwann cells, and axon-Schwann cell interactions seem to be regulated differently between myelinated and unmyelinated fibers in CMT1A.

Animal models of Charcot-Marie-Tooth disease type 1A

The most frequent genetic subtype of Charcot-Marie-Tooth disease is CMT1A, linked to chromosome 17p11.2. In the majority of cases, CMT1A is a gene dosage disease associated with a 1.5 Mb large genomic duplication. Transgenic models with extra copies of the Pmp22 gene have provided formal proof that overexpression of only this candidate gene is sufficent to cause peripheral demyelination, onion bulb formation, secondary axonal loss, and progressive muscle atrophy, the pathological hallmarks of CMT1A. The transgenic CMT rat with about 1.6-fold PMP22 overexpression exhibits clinical abnormalities, such as reduced nerve conduction velocity and lower grip strength that mimick findings in CMT1A patients. Also transgenic mice, carrying yeast artifical chromosomes as Pmp22 transgenes, demonstrate the variability of disease expression as a function of increased gene dosage. Recently, the first rational experimental therapies of CMT1A were tested, using transgenic animal models. In one proof-of-principle study with the CMT rat, a synthetic antagonist of the nuclear progesterone receptor was shown to reduce PMP22 overexpression and to ameliorate the clinical severity. In another study, administration of ascorbic acid, an essential factor of in vitro myelination, prolonged the survival and restored myelination of a dysmyelinated mouse model. Application of gene expression analysis to nerve biopsies that are readily available from such CMT1A animal models might identify additional pharmacological targets.

Axonal damage and demyelination in long-term dorsal root ganglia cultures from a rat model of Charcot-Marie-Tooth type 1A disease

Clinical progression in hereditary and acquired demyelinating disorders of both the central and peripheral nervous system is mainly due to a time-dependent axonal impairment. We established 90-day dorsal root ganglia (DRG) cultures from a rat model of Charcot-Marie-Tooth type 1A (CMT1A) neuropathy to evaluate the structure of myelin and axons, and the expression of myelin-related proteins and cytoskeletal components, by morphological and molecular techniques. Both wild-type and CMT1A cultures were rich in myelinated fibres. Affected cultures showed dysmyelinated internodes and focal myelin swellings. Furthermore, uncompacted myelin and smaller axons with increased neurofilament (NF) density were found by electron microscopy, and Western blots showed higher levels of nonphosphorylated NF. Confocal microscopy demonstrated an abnormal distribution of the myelin-associated glycoprotein which, instead of being expressed at the noncompact myelin level, showed focal accumulation along the internodes while other myelin proteins were normally distributed. These findings suggest that CMT1A DRG cultures, similarly to the animal model and human disease, undergo axonal atrophy over a period of time. This model may be utilized to study the molecular changes underlying demyelination and secondary axonal impairment. As axonal damage may occur after just 3 months and tissue cultures represent a strictly controlled environment, this model may be ideal for testing neuroprotective therapies.

Early abnormalities in sciatic nerve function and structure in a rat model of Charcot-Marie-Tooth type 1A disease

We investigated early peripheral nervous system impairment in PMP22-transgenic rats ("CMT rat"), an established animal model for Charcot-Marie-Tooth disease 1A, at postnatal day 30 (P30), when the clinical phenotype is not yet apparent. Hemizygous CMT1A rats and wildtype littermates were studied by means of behavioral examination, electrophysiology, molecular biology, and light microscopy analysis. Behavioral studies only showed, a mild, but significant, decrease in toe spread 1-5, suggesting a weakness of distal foot muscles in CMT1A rats compared with normal littermates. Nerve conduction studies disclosed a severe slowing in motor conduction velocity, a temporal dispersion and a dramatic decrease of amplitude of motor waves in P30 transgenic animals. Coherently with a demyelinating process, affected nerves showed a significant thinning of myelin. Interestingly, axonal diameter and area were unchanged, but expression of non-phosphorylated neurofilaments was increased in CMT1A rats compared with normal controls. Our results confirm the fidelity of this animal model to human disease. Similarly, in young CMT1A patients, the MCV is significantly reduced and the muscle weakness is confined to distal segments, whereas morphological and morphometrical signs of axonal atrophy are absent. However, the presence of a molecular and functional damage of the axons suggests that this may be the correct moment to start neuroprotective therapies.

Impairment of PMP22 transgenic Schwann cells differentiation in culture: implications for Charcot-Marie-Tooth type 1A disease

Charcot-Marie-Tooth type 1A (CMT1A) is a hereditary demyelinating neuropathy due to an increased genetic dosage of the peripheral myelin protein 22 (PMP22). The mechanisms leading from PMP22 overexpression to impairment of myelination are still unclear. We evaluated expression and processing of PMP22, viability, proliferation, migration, motility and shaping properties, and ability of forming myelin of PMP22 transgenic (PMP22(tg)) Schwann cells in culture. In basal conditions, PMP22(tg) Schwann cells, although expressing higher PMP22 levels than control ones, show normal motility, migration and shaping properties. Addition of forskolin to the media induces an additional stimulation of PMP22 expression and results in an impairment of cells migration and motility, and a reduction of cell area and perimeter. Similarly, co-culturing transgenic Schwann cells with neurons causes an altered cells differentiation and an impairment of myelin formation. In conclusion, exposure of PMP22(tg) Schwann to the axon or to axonal-mimicking stimuli significantly affects the transition of transgenic Schwann cells to the myelinating phenotype.

Mifepristone (RU 38486) influences expression of glycoprotein Po and morphological parameters at the level of rat sciatic nerve: in vivo observations

The observations here reported indicate that, in vivo, the expression of an important protein of peripheral myelin, the glycoprotein Po, is influenced by mifespristone (RU 38486), that is, an antagonist of progesterone (PR) and glucocorticoid (GR) receptor. In our experimental model, male rats have been treated at the first day of life with this antagonist and after repeated treatments, we have analyzed in the sciatic nerve of 20- (20d) and 30-day-old rats (30d) the mRNA and protein levels of Po. Moreover, expression of Po has also been analyzed in the sciatic nerve of animals treated during the first 30 days of postnatal life and then sacrificed at 90th day of life (90d). The results obtained have indicated that both mRNA and protein levels of Po decrease at 20d. Apparently, these effects seem to be transient because no changes are evident at the other two times of analysis. As shown by morphometric analysis, the treatment with RU 38486 is also able to induce morphological changes at the level of sciatic nerve. However, at variance to what is expected by an alteration of an important component of the myelin membranes like Po, no changes are evident at the level of the myelin compartment. On the contrary, a significant reduction of axon diameter in parallel to an increase in neurofilament (NF) density occurs since 30d. In conclusion, the present data seem to suggest that progestin and/or glucocorticoid signals are not only involved in the control of myelin compartment but also on the axon maintenance.

Epithelial membrane protein-2 is expressed in discrete anatomical regions of the eye

Epithelial membrane protein-2 (EMP2) is a member of the four transmembrane superfamily (TM4SF) and is thought to mediate trafficking of diverse proteins such as alpha6beta1 integrin and MHC class I to lipid raft microdomains. EMP2 has also recently been recognized as a putative tumor suppressor gene in certain model systems. Normally, EMP2 is expressed at discrete locations in the body including high levels in the eye, lung, heart, thyroid, and uterus. Here we examine in detail the subanatomic distribution of EMP2 in murine and human ocular tissue. We observe that EMP2 is localized to epithelial layers of the cornea, ciliary body, and retinal pigmented epithelium-choroid, the stromal layers of the sclera, and the nerve fiber layer of the retina and optic nerve. This distribution is distinct from other TM4SF proteins and may relate to a role in apical membrane recycling.