Rab27b is Involved in Lysosomal Exocytosis and Proteolipid Protein Trafficking in Oligodendrocytes

Activation of P2X7R Inhibits Proliferation and Promotes the Migration and Differentiation of Schwann Cells

In the vertebrate nervous system, myelination of nerve fibers is crucial for the rapid propagation of action potentials through saltatory conduction. Schwann cells-the main glial cells and myelinating cells of the peripheral nervous system-play a crucial role in myelination. Following injury during the repair of peripheral nerve injuries, a significant amount of ATP is secreted. This ATP release acts to trigger the dedifferentiation of myelinating Schwann cells into repair cells, an essential step for axon regeneration. Subsequently, to restore nerve function, these repair cells undergo redifferentiate into myelinating Schwann cells. Except for P2X4R, purine receptors such as P2X7R also play a significant role in this process. In the current study, decreased expression of P2X7R was observed after sciatic nerve injury, followed by a gradual increase to the normal level of P2X7R expression. In vivo experiments showed that the activation of P2X7R using an agonist injection promoted remyelination, while the antagonists hindered remyelination. Further, in vitro experiments supported these findings and demonstrated that P2X7R activation inhibited the proliferation of Schwann cells, but it promoted the migration and differentiation of the Schwann cells. Remyelination is a prominent feature of the nerve regeneration. In the current study, it was proposed that the manipulation of P2X7R expression in Schwann cells after nerve injury could be effective in facilitating nerve remyelination.

Vesicular Trafficking, a Mechanism Controlled by Cascade Activation of Rab Proteins: Focus on Rab27

Vesicular trafficking is essential for the cell to internalize useful proteins and soluble substances, for cell signaling or for the degradation of pathogenic elements such as bacteria or viruses. This vesicular trafficking also enables the cell to engage in secretory processes for the elimination of waste products or for the emission of intercellular communication vectors such as cytokines, chemokines and extracellular vesicles. Ras-related proteins (Rab) and their effector(s) are of crucial importance in all of these processes, and mutations/alterations to them have serious pathophysiological consequences. This review presents a non-exhaustive overview of the role of the major Rab involved in vesicular trafficking, with particular emphasis on their involvement in the biogenesis and secretion of extracellular vesicles, and on the role of Rab27 in various pathophysiological processes. Therefore, Rab and their effector(s) are central therapeutic targets, given their involvement in vesicular trafficking and their importance for cell physiology.

Superresolution live-cell imaging reveals that the localization of TMEM106B to filopodia in oligodendrocytes is compromised by the hypomyelination-related D252N mutation

Hypomyelination leukodystrophies constitute a group of heritable white matter disorders exhibiting defective myelin development. Initially identified as a lysosomal protein, the TMEM106B D252N mutant has recently been associated with hypomyelination. However, how lysosomal TMEM106B facilitates myelination and how the D252N mutation disrupts that process are poorly understood. We used superresolution Hessian structured illumination microscopy (Hessian-SIM) and spinning disc-confocal structured illumination microscopy (SD-SIM) to find that the wild-type TMEM106B protein is targeted to the plasma membrane, filopodia, and lysosomes in human oligodendrocytes. The D252N mutation reduces the size of lysosomes in oligodendrocytes and compromises lysosome changes upon starvation stress. Most importantly, we detected reductions in the length and number of filopodia in cells expressing the D252N mutant. PLP1 is the most abundant myelin protein that almost entirely colocalizes with TMEM106B, and coexpressing PLP1 with the D252N mutant readily rescues the lysosome and filopodia phenotypes of cells. Therefore, interactions between TMEM106B and PLP1 on the plasma membrane are essential for filopodia formation and myelination in oligodendrocytes, which may be sustained by the delivery of these proteins from lysosomes via exocytosis.

The transcription factor Stat-1 is essential for Schwann cell differentiation, myelination and myelin sheath regeneration

BACKGROUND

Myelin sheath is a crucial accessory to the functional nerve-fiber unit, its disruption or loss can lead to axonal degeneration and subsequent neurodegenerative diseases (NDs). Notwithstanding of substantial progress in possible molecular mechanisms underlying myelination, there is no therapeutics that prevent demyelination in NDs. Therefore, it is crucial to seek for potential intervention targets. Here, we focused on the transcriptional factor, signal transducer and activator of transcription 1 (Stat1), to explore its effects on myelination and its potential as a drug target.

METHODS

By analyzing the transcriptome data obtained from Schwann cells (SCs) at different stages of myelination, it was found that Stat1 might be involved in myelination. To test this, we used the following experiments: (1) In vivo, the effect of Stat1 on remyelination was observed in an in vivo myelination mode with Stat1 knockdown in sciatic nerves or specific knockdown in SCs. (2) In vitro, the RNA interference combined with cell proliferation assay, scratch assay, SC aggregate sphere migration assay, and a SC differentiation model, were used to assess the effects of Stat1 on SC proliferation, migration and differentiation. Chromatin immunoprecipitation sequencing (ChIP-Seq), RNA-Seq, ChIP-qPCR and luciferase activity reporter assay were performed to investigate the possible mechanisms of Stat1 regulating myelination.

RESULTS

Stat1 is important for myelination. Stat1 knockdown in nerve or in SCs reduces the axonal remyelination in the injured sciatic nerve of rats. Deletion of Stat1 in SCs blocks SC differentiation thereby inhibiting the myelination program. Stat1 interacts with the promoter of Rab11-family interacting protein 1 (Rab11fip1) to initiate SC differentiation.

CONCLUSION

Our findings demonstrate that Stat1 regulates SC differentiation to control myelinogenic programs and repair, uncover a novel function of Stat1, providing a candidate molecule for clinical intervention in demyelinating diseases.

Role of SNAREs and Rabs in Myelin Regulation

The myelin sheath is an insulating layer around the nerves of the brain and spinal cord which allows a fast and efficient nerve conduction. Myelin is made of protein and fatty substances and gives protection for the propagation of the electrical impulse. The myelin sheath is formed by oligodendrocytes in the central nervous system (CNS) and by Schwann cells in the peripheral nervous system (PNS). The myelin sheath presents a highly organized structure and expands both radially and longitudinally, but in a different way and with a different composition. Myelin alterations determine the onset of several neuropathies, as the electrical signal can be slowed or stopped. Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) and ras (rat sarcoma)-associated binding proteins (rabs) have been proved to contribute to several aspects regarding the formation of myelin or dysmyelination. Here, I will describe the role of these proteins in regulating membrane trafficking and nerve conduction, myelin biogenesis and maintenance.

Deletion in chromosome 6 spanning alpha-synuclein and multimerin1 loci in the Rab27a/b double knockout mouse

We report an incidental 358.5 kb deletion spanning the region encoding for alpha-synuclein (αsyn) and multimerin1 (Mmrn1) in the Rab27a/Rab27b double knockout (DKO) mouse line previously developed by Tolmachova and colleagues in 2007. Western blot and RT-PCR studies revealed lack of αsyn expression at either the mRNA or protein level in Rab27a/b DKO mice. PCR of genomic DNA from Rab27a/b DKO mice demonstrated at least partial deletion of the Snca locus using primers targeted to exon 4 and exon 6. Most genes located in proximity to the Snca locus, including Atoh1, Atoh2, Gm5570, Gm4410, Gm43894, and Grid2, were shown not to be deleted by PCR except for Mmrn1. Using whole genomic sequencing, the complete deletion was mapped to chromosome 6 (60,678,870–61,037,354), a slightly smaller deletion region than that previously reported in the C57BL/6J substrain maintained by Envigo. Electron microscopy of cortex from these mice demonstrates abnormally enlarged synaptic terminals with reduced synaptic vesicle density, suggesting potential interplay between Rab27 isoforms and αsyn, which are all highly expressed at the synaptic terminal. Given this deletion involving several genes, the Rab27a/b DKO mouse line should be used with caution or with appropriate back-crossing to other C57BL/6J mouse substrain lines without this deletion.

Bromodomains in Human-Immunodeficiency Virus-Associated Neurocognitive Disorders: A Model of Ferroptosis-Induced Neurodegeneration

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) comprise a group of illnesses marked by memory and behavioral dysfunction that can occur in up to 50% of HIV patients despite adequate treatment with combination antiretroviral drugs. Iron dyshomeostasis exacerbates HIV-1 infection and plays a major role in Alzheimer's disease pathogenesis. In addition, persons living with HIV demonstrate a high prevalence of neurodegenerative disorders, indicating that HAND provides a unique opportunity to study ferroptosis in these conditions. Both HIV and combination antiretroviral drugs increase the risk of ferroptosis by augmenting ferritin autophagy at the lysosomal level. As many viruses and their proteins exit host cells through lysosomal exocytosis, ferroptosis-driving molecules, iron, cathepsin B and calcium may be released from these organelles. Neurons and glial cells are highly susceptible to ferroptosis and neurodegeneration that engenders white and gray matter damage. Moreover, iron-activated microglia can engage in the aberrant elimination of viable neurons and synapses, further contributing to ferroptosis-induced neurodegeneration. In this mini review, we take a closer look at the role of iron in the pathogenesis of HAND and neurodegenerative disorders. In addition, we describe an epigenetic compensatory system, comprised of bromodomain-containing protein 4 (BRD4) and microRNA-29, that may counteract ferroptosis by activating cystine/glutamate antiporter, while lowering ferritin autophagy and iron regulatory protein-2. We also discuss potential interventions for lysosomal fitness, including ferroptosis blockers, lysosomal acidification, and cathepsin B inhibitors to achieve desirable therapeutic effects of ferroptosis-induced neurodegeneration.

Pierre C, Bimschleger H, Gao J, Cheng R, Polesskaya O, Solberg Woods LC, Palmer AA, Chen H. Genome-Wide Association Study on Three Behaviors Tested in an Open Field in Heterogeneous Stock Rats Identifies Multiple Loci Implicated in Psychiatric Disorders

Many personality traits are influenced by genetic factors. Rodents models provide an efficient system for analyzing genetic contribution to these traits. Using 1,246 adolescent heterogeneous stock (HS) male and female rats, we conducted a genome-wide association study (GWAS) of behaviors measured in an open field, including locomotion, novel object interaction, and social interaction. We identified 30 genome-wide significant quantitative trait loci (QTL). Using multiple criteria, including the presence of high impact genomic variants and co-localization of cis-eQTL, we identified 17 candidate genes (Adarb2, Ankrd26, Cacna1c, Cacng4, Clock, Ctu2, Cyp26b1, Dnah9, Gda, Grxcr1, Eva1a, Fam114a1, Kcnj9, Mlf2, Rab27b, Sec11a, and Ube2h) for these traits. Many of these genes have been implicated by human GWAS of various psychiatric or drug abuse related traits. In addition, there are other candidate genes that likely represent novel findings that can be the catalyst for future molecular and genetic insights into human psychiatric diseases. Together, these findings provide strong support for the use of the HS population to study psychiatric disorders.

Lysosomal Functions in Glia Associated with Neurodegeneration

Lysosomes are cellular organelles that contain various acidic digestive enzymes. Despite their small size, they have multiple functions. Lysosomes remove or recycle unnecessary cell parts. They repair damaged cellular membranes by exocytosis. Lysosomes also sense cellular energy status and transmit signals to the nucleus. Glial cells are non-neuronal cells in the nervous system and have an active role in homeostatic support for neurons. In response to dynamic cues, glia use lysosomal pathways for the secretion and uptake of regulatory molecules, which affect the physiology of neighboring neurons. Therefore, functional aberration of glial lysosomes can trigger neuronal degeneration. Here, we review lysosomal functions in oligodendrocytes, astrocytes, and microglia, with emphasis on neurodegeneration.

Unraveling GLUT-mediated transcytosis pathway of glycosylated nanodisks

Glucose transporter (GLUT)-mediated transcytosis has been validated as an efficient method to cross the blood-brain barrier and enhance brain transport of nanomedicines. However, the transcytosis process remains elusive. Glycopeptide-modified nanodisks (Gly-A7R-NDs), which demonstrated high capacity of brain targeting via GLUT-mediated transcytosis in our previous reports, were utilized to better understand the whole transcytosis process. Gly-A7R-NDs internalized brain capillary endothelial cells mainly via GLUT-mediated/clathrin dependent endocytosis and macropinocytosis. The intracellular Gly-A7R-NDs remained intact, and the main excretion route of Gly-A7R-NDs was lysosomal exocytosis. Glycosylation of nanomedicine was crucial in GLUT-mediated transcytosis, while morphology did not affect the efficiency. This study highlights the pivotal roles of lysosomal exocytosis in the process of GLUT-mediated transcytosis, providing a new impetus to development of brain targeting drug delivery by accelerating lysosomal exocytosis.

Genetic Evidence that Dorsal Spinal Oligodendrocyte Progenitor Cells are Capable of Myelinating Ventral Axons Effectively in Mice

In the developing spinal cord, the majority of oligodendrocyte progenitor cells (OPCs) are induced in the ventral neuroepithelium under the control of the Sonic Hedgehog (Shh) signaling pathway, whereas a small subset of OPCs are generated from the dorsal neuroepithelial cells independent of the Shh pathway. Although dorsally-derived OPCs (dOPCs) have been shown to participate in local axonal myelination in the dorsolateral regions during development, it is not known whether they are capable of migrating into the ventral region and myelinating ventral axons. In this study, we confirmed and extended the previous study on the developmental potential of dOPCs in the absence of ventrally-derived OPCs (vOPCs). In Nestin-Smo conditional knockout (cKO) mice, when ventral oligodendrogenesis was blocked, dOPCs were found to undergo rapid amplification, spread to ventral spinal tissue, and eventually differentiated into myelinating OLs in the ventral white matter with a temporal delay, providing genetic evidence that dOPCs are capable of myelinating ventral axons in the mouse spinal cord.

A founder RAB27A variant causes Griscelli syndrome type 2 with phenotypic heterogeneity in Qatari families

Griscelli syndrome type 2 (GS2) is a rare autosomal recessive disorder caused by pathogenic variants in the RAB27A gene and characterized by partial albinism, immunodeficiency, and occasional hematological and neurological involvement. We reviewed and analyzed the medical records of 12 individuals with GS2 from six families belonging to a highly consanguineous Qatari tribe and with a recurrent pathogenic variant in the RAB27A gene (NM_004580.4: c.244C > T, p.Arg82Cys). Detailed demographic, clinical, and molecular data were collected. Cutaneous manifestations were the most common presentation (42%), followed by neurological abnormalities (33%) and immunodeficiency (25%). The most severe manifestation was HLH (33%). Among the 12 patients, three patients (25%) underwent HSCT, and four (33%) died. The cause of death in all four patients was deemed HLH, providing evidence for this complication's fatal nature. Interestingly, two affected patients (16%) were asymptomatic. This report highlights the broad spectrum of clinical presentations of GS2 associated with a founder variant in the RAB27A gene (c.244C > T, p.Arg82Cys). Early suspicion of GS2 among Qatari patients with cutaneous manifestations, neurological findings, immunodeficiency, and HLH would shorten the diagnostic odyssey, guide early and appropriate treatment, and prevent fatal outcomes.

Loss of TMEM106B leads to myelination deficits: implications for frontotemporal dementia treatment strategies

Genetic variants that define two distinct haplotypes at the TMEM106B locus have been implicated in multiple neurodegenerative diseases and in healthy brain ageing. In frontotemporal dementia (FTD), the high expressing TMEM106B risk haplotype was shown to increase susceptibility for FTD with TDP-43 inclusions (FTD-TDP) and to modify disease penetrance in progranulin mutation carriers (FTD-GRN). To elucidate the biological function of TMEM106B and determine whether lowering TMEM106B may be a viable therapeutic strategy, we performed brain transcriptomic analyses in 8-month-old animals from our recently developed Tmem106b-/- mouse model. We included 10 Tmem106b+/+ (wild-type), 10 Tmem106b+/- and 10 Tmem106-/- mice. The most differentially expressed genes (153 downregulated and 60 upregulated) were identified between Tmem106b-/- and wild-type animals, with an enrichment for genes implicated in myelination-related cellular processes including axon ensheathment and oligodendrocyte differentiation. Co-expression analysis also revealed that the most downregulated group of correlated genes was enriched for myelination-related processes. We further detected a significant loss of OLIG2-positive cells in the corpus callosum of Tmem106b-/- mice, which was present already in young animals (21 days) and persisted until old age (23 months), without worsening. Quantitative polymerase chain reaction revealed a reduction of differentiated but not undifferentiated oligodendrocytes cellular markers. While no obvious changes in myelin were observed at the ultrastructure levels in unchallenged animals, treatment with cuprizone revealed that Tmem106b-/- mice are more susceptible to cuprizone-induced demyelination and have a reduced capacity to remyelinate, a finding which we were able to replicate in a newly generated Tmem106b CRISPR/cas9 knock-out mouse model. Finally, using a TMEM106B HeLa knock-out cell line and primary cultured oligodendrocytes, we determined that loss of TMEM106B leads to abnormalities in the distribution of lysosomes and PLP1. Together these findings reveal an important function for TMEM106B in myelination with possible consequences for therapeutic strategies aimed at lowering TMEM106B levels.

The GTPase Rab27b regulates the release, autophagic clearance, and toxicity of α-synuclein

α-Synuclein (αsyn) is the primary component of proteinaceous aggregates termed Lewy bodies that pathologically define synucleinopathies including Parkinson's disease (PD) and dementia with Lewy bodies (DLB). αsyn is hypothesized to spread through the brain in a prion-like fashion by misfolded protein forming a template for aggregation of endogenous αsyn. The cell-to-cell release and uptake of αsyn are considered important processes for its prion-like spread. Rab27b is one of several GTPases essential to the endosomal-lysosomal pathway and is implicated in protein secretion and clearance, but its role in αsyn spread has yet to be characterized. In this study, we used a paracrine αsyn in vitro neuronal model to test the impact of Rab27b on αsyn release, clearance, and toxicity. shRNA-mediated knockdown (KD) of Rab27b increased αsyn-mediated paracrine toxicity. Rab27b reduced αsyn release primarily through nonexosomal pathways, but the αsyn released after Rab27b KD was of higher-molecular-weight species, as determined by size-exclusion chromatography. Rab27b KD increased intracellular levels of insoluble αsyn and led to an accumulation of endogenous light chain 3 (LC3)-positive puncta. Rab27b KD also decreased LC3 turnover after treatment with an autophagosome-lysosome fusion inhibitor, chloroquine, indicating that Rab27b KD induces a defect in autophagic flux. Rab27b protein levels were increased in brain lysates obtained from postmortem tissues of individuals with PD and DLB compared with healthy controls. These data indicate a role for Rab27b in the release, clearance, and toxicity of αsyn and, ultimately, in the pathogenesis of synucleinopathies.

Activated spinal astrocytes contribute to the later phase of carrageenan-induced prostatitis pain

Background

Prostatodynia is the main symptom of chronic prostatitis and the main reason that patients go to the hospital for treatment. Although a variety of factors, including inflammatory immune response, nervous system sensitization, and psychological factors, have been shown to play important roles in the induction and development of chronic pain in prostatitis, the underlying cause of chronic prostatodynia maintenance in prostatitis patients remains unclear.

Methods

A mouse model of chronic prostatitis induced by carrageenan injection was used. The von Frey test was used to measure pain behavior. The microglial and astrocyte activations were immunohistochemically demonstrated with antibodies against Iba1 and GFAP. The expression of cytokine or signaling pathway was detected by enzyme-linked immunosorbent assay (ELISA) and Western blotting.

Results

In this study, we provide several lines of evidence to demonstrate that activated spinal astrocytes contribute to the later phase (5 weeks after carrageenan injection) of carrageenan-induced prostatitis pain. First, activation of spinal astrocytes but not microglia was found in the spinal cord dorsal horn at 5 weeks. Second, intrathecal injection of the astroglial toxin L-2-Aminoadipate acid (L-AA) but not microglial inhibitor minocycline reduced mechanical allodynia at 5 weeks. Third, chronic prostatitis induced a profound and persistent upregulation of connexin-43 hemichannels in spinal astrocytes, and spinal injection of the connexin-43 inhibitor carbenoxolone (CBX) effectively reduced pain symptoms. Fourth, increased expression and release of chemokine C-X-C motif ligand 1 (CXCL1) in the spinal dorsal horn and intrathecal injection of a CXCL1 neutralizing antibody or the CXCR2 (a major receptor of CXCL1) antagonist SB225002 significantly reduced mechanical allodynia at 5 weeks.

Conclusions

In this study, we found that a novel mechanism of activated spinal astrocytes plays a crucial role in maintaining chronic prostatitis-induced persistent pain via connexin-43-regulated CXCL1 production and secretion.

17β-Estradiol Enhances Schwann Cell Differentiation via the ERβ-ERK1/2 Signaling Pathway and Promotes Remyelination in Injured Sciatic Nerves

Remyelination is critical for nerve regeneration. However, the molecular mechanism involved in remyelination is poorly understood. To explore the roles of 17β-estradiol (E2) for myelination in the peripheral nervous system, we used a co-culture model of rat dorsal root ganglion (DRG) explants and Schwann cells (SCs) and a regeneration model of the crushed sciatic nerves in ovariectomized (OVX) and non-ovariectomized (non-OVX) rats for in vitro and in vivo analysis. E2 promoted myelination by facilitating the differentiation of SCs in vitro, which could be inhibited by the estrogen receptors (ER) antagonist ICI182780, ERβ antagonist PHTPP, or ERK1/2 antagonist PD98059. This suggests that E2 accelerates SC differentiation via the ERβ-ERK1/2 signaling. Furthermore, E2 promotes remyelination in crushed sciatic nerves of both OVX and non-OVX rats. Interestingly, E2 also significantly increased the expression of the lysosome membrane proteins LAMP1 and myelin protein P0 in the regenerating nerves. Moreover, P0 has higher degree of colocalization with LAMP1 in the regenerating nerves. Taking together, our results suggest that E2 enhances Schwann cell differentiation and further myelination via the ERβ-ERK1/2 signaling and that E2 increases the expression of myelin proteins and lysosomes in SCs to promotes remyelination in regenerating sciatic nerves.

Itraconazole-Induced Inhibition on Human Esophageal Cancer Cell Growth Requires AMPK Activation

We here evaluated the antiesophageal cancer cell activity by the antifungal drug itraconazole. Our results show that μg/mL concentrations of itraconazole potently inhibited survival and proliferation of established (TE-1 and Eca-109) and primary human esophageal cancer cells. Itraconazole activated AMPK signaling, which was required for subsequent esophageal cancer cell death. Pharmacologic AMPK inhibition, AMPKα1 shRNA, or dominant negative mutation (T172A) almost completely abolished itraconazole-induced cytotoxicity against esophageal cancer cells. Significantly, itraconazole induced AMPK-dependent autophagic cell death (but not apoptosis) in esophageal cancer cells. Furthermore, AMPK activation by itraconazole induced multiple receptor tyrosine kinases (RTKs: EGFR, PDGFRα, and PDGFRβ), lysosomal translocation, and degradation to inhibit downstream Akt activation. In vivo, itraconazole oral gavage potently inhibited Eca-109 tumor growth in SCID mice. It was yet ineffective against AMPKα1 shRNA-expressing Eca-109 tumors. The in vivo growth of the primary human esophageal cancer cells was also significantly inhibited by itraconazole administration. AMPK activation, RTK degradation, and Akt inhibition were observed in itraconazole-treated tumors. Together, itraconazole inhibits esophageal cancer cell growth via activating AMPK signaling. Mol Cancer Ther; 17(6); 1229-39. ©2018 AACR.

Consequences of Rab GTPase dysfunction in genetic or acquired human diseases

Rab GTPases are important regulators of intracellular membrane trafficking in eukaryotes. Both activating and inactivating mutations in Rab genes have been identified and implicated in human diseases ranging from neurological disorders to cancer. In addition, altered Rab expression is often associated with disease prognosis. As such, the study of diseases associated with Rabs or Rab-interacting proteins has shed light on the important role of intracellular membrane trafficking in disease etiology. In this review, we cover recent advances in the field with an emphasis on cellular mechanisms.

Microglia: Housekeeper of the Central Nervous System

Microglia, of myeloid origin, play fundamental roles in the control of immune responses and the maintenance of central nervous system homeostasis. These cells, just like peripheral macrophages, may be activated into M1 pro-inflammatory or M2 anti-inflammatory phenotypes by appropriate stimuli. Microglia do not respond in isolation, but form part of complex networks of cells influencing each other. This review addresses the complex interaction of microglia with each cell type in the brain: neurons, astrocytes, cerebrovascular endothelial cells, and oligodendrocytes. We also highlight the participation of microglia in the maintenance of homeostasis in the brain, and their roles in the development and progression of age-related neurodegenerative disorders.

Consequences of Rab GTPase dysfunction in genetic or acquired human diseases

Rab GTPases are important regulators of intracellular membrane trafficking in eukaryotes. Both activating and inactivating mutations in Rab genes have been identified and implicated in human diseases ranging from neurological disorders to cancer. In addition, altered Rab expression is often associated with disease prognosis. As such, the study of diseases associated with Rabs or Rab-interacting proteins has shed light on the important role of intracellular membrane trafficking in disease etiology. In this review, we cover recent advances in the field with an emphasis on cellular mechanisms.

Rab27a/Slp2-a complex is involved in Schwann cell myelination

Myelination of Schwann cells in the peripheral nervous system is an intricate process involving myelin protein trafficking. Recently, the role and mechanism of the endosomal/lysosomal system in myelin formation were emphasized. Our previous results demonstrated that a small GTPase Rab27a regulates lysosomal exocytosis and myelin protein trafficking in Schwann cells. In this present study, we established a dorsal root ganglion (DRG) neuron and Schwann cell co-culture model to identify the signals associated with Rab27a during myelination. First, Slp2-a, as the Rab27a effector, was endogenously expressed in Schwann cells. Second, Rab27a expression significantly increased during Schwann cell myelination. Finally, Rab27a and Slp2-a silencing in Schwann cells not only reduced myelin protein expression, but also impaired formation of myelin-like membranes in DRG neuron and Schwann cell co-cultures. Our findings suggest that the Rab27a/Slp2-a complex affects Schwann cell myelination in vitro.