Rab32 connects ER stress to mitochondrial defects in multiple sclerosis

The neuropathobiology of multiple sclerosis

Chronic low-grade inflammation and neuronal deregulation are two components of a smoldering disease activity that drives the progression of disability in people with multiple sclerosis (MS). Although several therapies exist to dampen the acute inflammation that drives MS relapses, therapeutic options to halt chronic disability progression are a major unmet clinical need. The development of such therapies is hindered by our limited understanding of the neuron-intrinsic determinants of resilience or vulnerability to inflammation. In this Review, we provide a neuron-centric overview of recent advances in deciphering neuronal response patterns that drive the pathology of MS. We describe the inflammatory CNS environment that initiates neurotoxicity by imposing ion imbalance, excitotoxicity and oxidative stress, and by direct neuro-immune interactions, which collectively lead to mitochondrial dysfunction and epigenetic dysregulation. The neuronal demise is further amplified by breakdown of neuronal transport, accumulation of cytosolic proteins and activation of cell death pathways. Continuous neuronal damage perpetuates CNS inflammation by activating surrounding glia cells and by directly exerting toxicity on neighbouring neurons. Further, we explore strategies to overcome neuronal deregulation in MS and compile a selection of neuronal actuators shown to impact neurodegeneration in preclinical studies. We conclude by discussing the therapeutic potential of targeting such neuronal actuators in MS, including some that have already been tested in interventional clinical trials.

Temporin-GHaR Peptide Alleviates LPS-Induced Cognitive Impairment and Microglial Activation by Modulating Endoplasmic Reticulum Stress

Neuroinflammation is considered an important factor that leads to cognitive impairment. Microglia play a crucial role in neuroinflammation, which leads to cognitive impairment. This study aimed at determining whether temporin-GHaR peptide (GHaR) could improve cognitive function and at uncovering the underlying mechanisms. We found that GHaR treatment alleviated LPS-induced cognitive impairment and inhibited activation of microglia in LPS-induced mice. Furthermore, GHaR inhibited activation of endoplasmic reticulum stress (ERS) and the NF-κB signaling pathway in LPS-induced mice. In vitro, GHaR inhibited M1 polarization of BV2 cells and suppressed TNF-α and IL-6 secretion. Additionally, GHaR neuronal cell viability and apoptosis were induced by LPS-activated microglia-conditioned medium. Moreover, in LPS-induced BV2 cells, GHaR inhibited activation of ERS and the NF-κB signaling pathway. In summary, GHaR improved LPS-induced cognitive and attenuated inflammatory responses via microglial activation reversal. In conclusion, the neuroprotective effects of GHaR were mediated via the ERS signaling pathway.

V-ATPase B2 promotes microglial phagocytosis of myelin debris by inactivating the MAPK signaling pathway

Microglial phagocytosis of myelin debris is a crucial process for promoting myelin regeneration in conditions such as multiple sclerosis (MS). Vacuolar-ATPase B2 (V-ATPase B2) has been implicated in various cellular processes, but its role in microglial phagocytosis and its potential impact on MS-related responses remain unclear. In this study, we employed BV-2 murine microglial cells to investigate the influence of V-ATPase B2 on the phagocytosis of myelin debris by microglia. The results revealed that V-ATPase B2 expression increased in response to myelin debris exposure. Overexpression of V-ATPase B2 significantly enhanced BV-2 phagocytosis of myelin debris. Additionally, V-ATPase B2 overexpression shifted microglial polarization towards an anti-inflammatory M2 phenotype, coupled with decreased lysosomal pH and enhanced lysosome degradation capacity. Moreover, endoplasmic reticulum (ER) stress inhibitor, 4-PBA, reversed the effects of V-ATPase B2 silencing on ER stress, M2 polarization, and lysosomal degradation of BV-2 cells. The MAPK pathway was inhibited upon V-ATPase B2 overexpression, contributing to heightened myelin debris clearance by BV-2 cells. Notably, MAPK pathway inhibition partially attenuated the inhibitory effects of V-ATPase B2 knockdown on myelin debris clearance. In conclusion, our findings reveal a pivotal role for V-ATPase B2 in promoting microglial phagocytosis of myelin debris by regulating microglial polarization and lysosomal function via the MAPK signaling pathway, suggesting that targeting V-ATPase B2 may hold therapeutic potential for enhancing myelin debris clearance and modulating microglial responses in MS and related neuroinflammatory disorders.

The Emerging Role of Microglial Hv1 as a Target for Immunomodulation in Myelin Repair

In the central nervous system (CNS), the myelin sheath ensures efficient interconnection between neurons and contributes to the regulation of the proper function of neuronal networks. The maintenance of myelin and the well-organized subtle process of myelin plasticity requires cooperation among myelin-forming cells, glial cells, and neural networks. The process of cooperation is fragile, and the balance is highly susceptible to disruption by microenvironment influences. Reactive microglia play a critical and complicated role in the demyelination and remyelination process. Recent studies have shown that the voltage-gated proton channel Hv1 is selectively expressed in microglia in CNS, which regulates intracellular pH and is involved in the production of reactive oxygen species, underlying multifaceted roles in maintaining microglia function. This paper begins by examining the molecular mechanisms of demyelination and emphasizes the crucial role of the microenvironment in demyelination. It focuses specifically on the role of Hv1 in myelin repair and its therapeutic potential in CNS demyelinating diseases.

The Role of Rab GTPases in the development of genetic and malignant diseases

Small GTPases have been shown to play an important role in several cellular functions, including cytoskeletal remodeling, cell polarity, intracellular trafficking, cell-cycle, progression and lipid transformation. The Ras-associated binding (Rab) family of GTPases constitutes the largest family of GTPases and consists of almost 70 known members of small GTPases in humans, which are known to play an important role in the regulation of intracellular membrane trafficking, membrane identity, vesicle budding, uncoating, motility and fusion of membranes. Mutations in Rab genes can cause a wide range of inherited genetic diseases, ranging from neurodegenerative diseases, such as Parkinson's disease (PD) and Alzheimer's disease (AD) to immune dysregulation/deficiency syndromes, like Griscelli Syndrome Type II (GS-II) and hemophagocytic lymphohistiocytosis (HLH), as well as a variety of cancers. Here, we provide an extended overview of human Rabs, discussing their function and diseases related to Rabs and Rab effectors, as well as focusing on effects of (aberrant) Rab expression. We aim to underline their importance in health and the development of genetic and malignant diseases by assessing their role in cellular structure, regulation, function and biology and discuss the possible use of stem cell gene therapy, as well as targeting of Rabs in order to treat malignancies, but also to monitor recurrence of cancer and metastasis through the use of Rabs as biomarkers. Future research should shed further light on the roles of Rabs in the development of multifactorial diseases, such as diabetes and assess Rabs as a possible treatment target.

Relevance of the endoplasmic reticulum-mitochondria axis in cancer diagnosis and therapy

Dynamic interactions between organelles are responsible for a variety of intercellular functions, and the endoplasmic reticulum (ER)-mitochondrial axis is recognized as a representative interorganelle system. Several studies have confirmed that most proteins in the physically tethered sites between the ER and mitochondria, called mitochondria-associated ER membranes (MAMs), are vital for intracellular physiology. MAM proteins are involved in the regulation of calcium homeostasis, lipid metabolism, and mitochondrial dynamics and are associated with processes related to intracellular stress conditions, such as oxidative stress and unfolded protein responses. Accumulating evidence has shown that, owing to their extensive involvement in cellular homeostasis, alterations in the ER-mitochondrial axis are one of the etiological factors of tumors. An in-depth understanding of MAM proteins and their impact on cell physiology, particularly in cancers, may help elucidate their potential as diagnostic and therapeutic targets for cancers. For example, the modulation of MAM proteins is utilized not only to target diverse intracellular signaling pathways within cancer cells but also to increase the sensitivity of cancer cells to anticancer reagents and regulate immune cell activities. Therefore, the current review summarizes and discusses recent advances in research on the functional roles of MAM proteins and their characteristics in cancers from a diagnostic perspective. Additionally, this review provides insights into diverse therapeutic strategies that target MAM proteins in various cancer types.

Missed diagnosis of Fabry disease: should we screen patients with multiple sclerosis?

INTRODUCTION

Fabry disease (FD) can be undiagnosed in the context of multiple sclerosis (MS) due to similar clinical and paraclinical features. Our study aimed to determine the prevalence (and the necessity of screening) of FD among patients with possible or definite MS.

METHODS

In this prospective monocentric observational study, we included consecutive patients enrolled between May 2017 and May 2019 after the first clinical event suggestive of MS. All patients underwent FD screening using dried blood spots in a stepwise manner combining genetic and enzyme testing. Patients were followed until May 2022.

RESULTS

We included 160 patients (73.1% female, mean age 33.9 years). The 2017 revised McDonald's criteria for definite MS were fulfilled by 74 (46.3%) patients at the time of study recruitment and 89 (55.6%) patients after 3-5 years of follow-up. None of the patients had a pathogenic GLA variant, and four (2.5%) had a variant of unknown significance (p.A143T, p.S126G, 2 × p.D313Y). In two of these patients, the intrathecal synthesis of oligoclonal bands was absent, and none had hyperproteinorachia or pleocytosis in cerebrospinal fluid. Detailed examination of FD organ manifestations revealed only discrete ocular and kidney involvement in two patients.

CONCLUSION

The prevalence of FD in the population of suspected or definite MS patients does not appear to be high. Our results do not support routine FD screening in all patients with a possible diagnosis of MS, but there is an urgent need to search for red flags and include FD in the differential diagnosis of MS.

Mitochondrial dysfunction in neurodegenerative disorders: Potential therapeutic application of mitochondrial transfer to central nervous system-residing cells

Mitochondrial dysfunction is reiteratively involved in the pathogenesis of diverse neurodegenerative diseases. Current in vitro and in vivo approaches support that mitochondrial dysfunction is branded by several molecular and cellular defects, whose impact at different levels including the calcium and iron homeostasis, energetic balance and/or oxidative stress, makes it difficult to resolve them collectively given their multifactorial nature. Mitochondrial transfer offers an overall solution since it contains the replacement of damage mitochondria by healthy units. Therefore, this review provides an introducing view on the structure and energy-related functions of mitochondria as well as their dynamics. In turn, we summarize current knowledge on how these features are deregulated in different neurodegenerative diseases, including frontotemporal dementia, multiple sclerosis, amyotrophic lateral sclerosis, Friedreich ataxia, Alzheimer´s disease, Parkinson´s disease, and Huntington's disease. Finally, we analyzed current advances in mitochondrial transfer between diverse cell types that actively participate in neurodegenerative processes, and how they might be projected toward developing novel therapeutic strategies.

Immunomodulatory therapy with glatiramer acetate reduces endoplasmic reticulum stress and mitochondrial dysfunction in experimental autoimmune encephalomyelitis

Endoplasmic reticulum (ER) stress and mitochondrial dysfunction are found in lesions of multiple sclerosis (MS) and animal models of MS such as experimental autoimmune encephalomyelitis (EAE), and may contribute to the neuronal loss that underlies permanent impairment. We investigated whether glatiramer acetate (GA) can reduce these changes in the spinal cords of chronic EAE mice by using routine histology, immunostaining, and electron microscopy. EAE spinal cord tissue exhibited increased inflammation, demyelination, mitochondrial dysfunction, ER stress, downregulation of NAD+ dependent pathways, and increased neuronal death. GA reversed these pathological changes, suggesting that immunomodulating therapy can indirectly induce neuroprotective effects in the CNS by mediating ER stress.

Astrocytes show increased levels of Ero1α in multiple sclerosis and its experimental autoimmune encephalomyelitis animal model

Multiple sclerosis (MS) and its animal models are characterized by cellular inflammation within the central nervous system (CNS). The sources and consequences of this inflammation are currently not completely understood. Critical signs and mediators of CNS inflammation are reactive oxygen species (ROS) that promote inflammation. ROS originate from a variety of redox-reactive enzymes, one class of which catalyses oxidative protein folding within the endoplasmic reticulum (ER). Here, the unfolded protein response and other signalling mechanisms maintain a balance between ROS producers such as ER oxidoreductin 1α (Ero1α) and antioxidants such as glutathione peroxidase 8 (GPx8). The role of ROS production within the ER has so far not been examined in the context of MS. In this manuscript, we examined how components of the ER redox network change upon MS and experimental autoimmune encephalomyelitis (EAE). We found that unlike GPx8, Ero1α increases within both MS and EAE astrocytes, in parallel with an imbalance of other oxidases such of GPx7, and that no change was observed within neurons. This imbalance of ER redox enzymes can reduce the lifespan of astrocytes, while neurons are not affected. Therefore, Ero1α induction makes astrocytes vulnerable to oxidative stress in the MS and EAE pathologies.

Nuclear and Cytoplasmatic Players in Mitochondria-Related CNS Disorders: Chromatin Modifications and Subcellular Trafficking

Aberrant mitochondrial phenotypes are common to many central nervous system (CNS) disorders, including neurodegenerative and neurodevelopmental diseases. Mitochondrial function and homeostasis depend on proper control of several biological processes such as chromatin remodeling and transcriptional control, post-transcriptional events, vesicle and organelle subcellular trafficking, fusion, and morphogenesis. Mutation or impaired regulation of major players that orchestrate such processes can disrupt cellular and mitochondrial dynamics, contributing to neurological disorders. The first part of this review provides an overview of a functional relationship between chromatin players and mitochondria. Specifically, we relied on specific monogenic CNS disorders which share features with mitochondrial diseases. On the other hand, subcellular trafficking is coordinated directly or indirectly through evolutionarily conserved domains and proteins that regulate the dynamics of membrane compartments and organelles, including mitochondria. Among these “building blocks”, longin domains and small GTPases are involved in autophagy and mitophagy, cell reshaping, and organelle fusion. Impairments in those processes significantly impact CNS as well and are discussed in the second part of the review. Hopefully, in filling the functional gap between the nucleus and cytoplasmic organelles new routes for therapy could be disclosed.

Endoplasmic Reticulum Stress-Associated Neuronal Death and Innate Immune Response in Neurological Diseases

Neuronal death and inflammatory response are two common pathological hallmarks of acute central nervous system injury and chronic degenerative disorders, both of which are closely related to cognitive and motor dysfunction associated with various neurological diseases. Neurological diseases are highly heterogeneous; however, they share a common pathogenesis, that is, the aberrant accumulation of misfolded/unfolded proteins within the endoplasmic reticulum (ER). Fortunately, the cell has intrinsic quality control mechanisms to maintain the proteostasis network, such as chaperone-mediated folding and ER-associated degradation. However, when these control mechanisms fail, misfolded/unfolded proteins accumulate in the ER lumen and contribute to ER stress. ER stress has been implicated in nearly all neurological diseases. ER stress initiates the unfolded protein response to restore proteostasis, and if the damage is irreversible, it elicits intracellular cascades of death and inflammation. With the growing appreciation of a functional association between ER stress and neurological diseases and with the improved understanding of the multiple underlying molecular mechanisms, pharmacological and genetic targeting of ER stress are beginning to emerge as therapeutic approaches for neurological diseases.

Rab32 uses its effector reticulon 3L to trigger autophagic degradation of mitochondria-associated membrane (MAM) proteins

BACKGROUND

Rab32 is a small GTPase associated with multiple organelles but is particularly enriched at the endoplasmic reticulum (ER). Here, it controls targeting to mitochondria-ER contacts (MERCs), thus influencing composition of the mitochondria-associated membrane (MAM). Moreover, Rab32 regulates mitochondrial membrane dynamics via its effector dynamin-related protein 1 (Drp1). Rab32 has also been reported to induce autophagy, an essential pathway targeting intracellular components for their degradation. However, no autophagy-specific effectors have been identified for Rab32. Similarly, the identity of the intracellular membrane targeted by this small GTPase and the type of autophagy it induces are not known yet.

RESULTS

To investigate the target of autophagic degradation mediated by Rab32, we tested a large panel of organellar proteins. We found that a subset of MERC proteins, including the thioredoxin-related transmembrane protein TMX1, are specifically targeted for degradation in a Rab32-dependent manner. We also identified the long isoform of reticulon-3 (RTN3L), a known ER-phagy receptor, as a Rab32 effector.

CONCLUSIONS

Rab32 promotes degradation of mitochondrial-proximal ER membranes through autophagy with the help of RTN3L. We propose to call this type of selective autophagy "MAM-phagy".

Modelling the functional genomics of Parkinson's disease in Caenorhabditis elegans: LRRK2 and beyond

For decades, Parkinson's disease (PD) cases have been genetically categorised into familial, when caused by mutations in single genes with a clear inheritance pattern in affected families, or idiopathic, in the absence of an evident monogenic determinant. Recently, genome-wide association studies (GWAS) have revealed how common genetic variability can explain up to 36% of PD heritability and that PD manifestation is often determined by multiple variants at different genetic loci. Thus, one of the current challenges in PD research stands in modelling the complex genetic architecture of this condition and translating this into functional studies. Caenorhabditis elegans provide a profound advantage as a reductionist, economical model for PD research, with a short lifecycle, straightforward genome engineering and high conservation of PD relevant neural, cellular and molecular pathways. Functional models of PD genes utilising C. elegans show many phenotypes recapitulating pathologies observed in PD. When contrasted with mammalian in vivo and in vitro models, these are frequently validated, suggesting relevance of C. elegans in the development of novel PD functional models. This review will discuss how the nematode C. elegans PD models have contributed to the uncovering of molecular and cellular mechanisms of disease, with a focus on the genes most commonly found as causative in familial PD and risk factors in idiopathic PD. Specifically, we will examine the current knowledge on a central player in both familial and idiopathic PD, Leucine-rich repeat kinase 2 (LRRK2) and how it connects to multiple PD associated GWAS candidates and Mendelian disease-causing genes.

Mitochondrial dynamics and mitophagy in lung disorders

Mitochondria are biosynthetic, bioenergetic, and signaling organelles which are critical for physiological adaptations and cellular stress responses to the environment. Various endogenous and environmental stress affects critical processes in mitochondrial homeostasis such as oxidative phosphorylation, biogenesis, mitochondrial redox system which leads to the formation of reactive oxygen species (ROS) and free radicals. The state of function of the mitochondrion is particularly dependent on the dynamic balance between mitochondrial biogenesis, fusion and fission, and degradation of damaged mitochondria by mitophagy. Increasing evidence has suggested a prominent role of mitochondrial dysfunction in the onset and progression of various lung pathologies, ranging from acute to chronic disorders. In this comprehensive review, we discuss the emerging findings of multifaceted regulations of mitochondrial dynamics and mitophagy in normal lung homeostasis as well as the prominence of mitochondrial dysfunction as a determining factor in different lung disorders such as lung cancer, COPD, IPF, ALI/ARDS, BPD, and asthma. The review will contribute to the existing understanding of critical molecular machinery regulating mitochondrial dynamic state during these pathological states. Furthermore, we have also highlighted various molecular checkpoints involved in mitochondrial dynamics, which may serve as hopeful therapeutic targets for the development of potential therapies for these lung disorders.

miR‑367‑3p downregulates Rab23 expression and inhibits Hedgehog signaling resulting in the inhibition of the proliferation, migration, and invasion of prostate cancer cells

MicroRNAs play an important role in tumor cell proliferation, invasion, and Rab23 is a member of the Ras-related small GTPase family and plays a critical role in the progression of may types of tumors. The present study was designed to investigate the inhibitory effect of microRNA (miR)-367-3p on the proliferation, invasion, and metastasis of prostate cancer cells. qRT-PCR was used to detect the expression of miR-367-3p in prostate cancer and adjacent tissues. Cell proliferation, scratch, and Transwell assays were performed to verify the inhibitory effect of miR-367-3p overexpression or Ras-related protein Rab 23 (Rab23) knockdown on prostate cancer. Double luciferase reporter assay was utilized to verify whether miR-367-3p could target the Rab23 3′-untranslated region (UTR). The expression levels of Rab23, Gli1, and Gli2 in prostate cancer cells transfected with the miR-367-3p mimic were detected via qRT-PCR analysis. miR-367-3p expression in the prostate cancer tissues was downregulated compared with that in the para-cancer control tissues. miR-367-3p expression in DU145 and PC3 cells was also downregulated compared with that in the human prostate epithelial cell line RWPE-1. The overexpression of miR-367-3p or the knockdown of Rab23 inhibited the proliferation, invasion, and metastasis of prostate cancer cells. The results of the luciferase reporter assay confirmed that Rab23 was a target gene that was regulated by miR-367-3p. miR-367-3p specifically bound to the 3′-UTR of Rab23 mRNA. The overexpression of miR-367-3p inhibited Rab23 expression and the Hedgehog pathway. Cell function experiments confirmed that the overexpression of Rab23 reversed the anticancer effect of miR-367-3p. miR-367-3p was able to inhibit the Hedgehog pathway by targeting the expression of the Rab23 gene, thus inhibiting the proliferation, invasion, and metastasis of prostate cancer cells.

Amyotrophic Lateral Sclerosis (ALS): Stressed by Dysfunctional Mitochondria-Endoplasmic Reticulum Contacts (MERCs)

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease for which there is currently no cure. Progress in the characterization of other neurodegenerative mechanisms has shifted the spotlight onto an intracellular structure called mitochondria-endoplasmic reticulum (ER) contacts (MERCs) whose ER portion can be biochemically isolated as mitochondria-associated membranes (MAMs). Within the central nervous system (CNS), these structures control the metabolic output of mitochondria and keep sources of oxidative stress in check via autophagy. The most relevant MERC controllers in the ALS pathogenesis are vesicle-associated membrane protein-associated protein B (VAPB), a mitochondria-ER tether, and the ubiquitin-specific chaperone valosin containing protein (VCP). These two systems cooperate to maintain mitochondrial energy output and prevent oxidative stress. In ALS, mutant VAPB and VCP take a central position in the pathology through MERC dysfunction that ultimately alters or compromises mitochondrial bioenergetics. Intriguingly, both proteins are targets themselves of other ALS mutant proteins, including C9orf72, FUS, or TDP-43. Thus, a new picture emerges, where different triggers cause MERC dysfunction in ALS, subsequently leading to well-known pathological changes including endoplasmic reticulum (ER) stress, inflammation, and motor neuron death.

Hippocampal CA3 transcriptional modules associated with granule cell alterations and cognitive impairment in refractory mesial temporal lobe epilepsy patients

In about a third of the patients with epilepsy the seizures are not drug-controlled. The current limitation of the antiepileptic drug therapy derives from an insufficient understanding of epilepsy pathophysiology. In order to overcome this situation, it is necessary to consider epilepsy as a disturbed network of interactions, instead of just looking for changes in single molecular components. Here, we studied CA3 transcriptional signatures and dentate gyrus histopathologic alterations in hippocampal explants surgically obtained from 57 RMTLE patients submitted to corticoamygdalohippocampectomy. By adopting a systems biology approach, integrating clinical, histopathological, and transcriptomic data (weighted gene co-expression network analysis), we were able to identify transcriptional modules highly correlated with age of disease onset, cognitive dysfunctions, and granule cell alterations. The enrichment analysis of transcriptional modules and the functional characterization of the highly connected genes in each trait-correlated module allowed us to unveil the modules’ main biological functions, paving the way for further investigations on their roles in RMTLE pathophysiology. Moreover, we found 15 genes with high gene significance values which have the potential to become novel biomarkers and/or therapeutic targets in RMTLE.

Bi-phasic dose response in the preclinical and clinical developments of sigma-1 receptor ligands for the treatment of neurodegenerative disorders

Introduction: The sigma-1 receptor (S1R) is attracting much attention for disease-modifying therapies in neurodegenerative diseases. It is a conserved protein, present in plasma and endoplasmic reticulum (ER) membranes and enriched in mitochondria-associated ER membranes (MAMs). It modulates ER-mitochondria Ca2+ transfer and ER stress pathways. Mitochondrial and MAM dysfunctions contribute to neurodegenerative processes in diseases such as Alzheimer, Parkinson, Huntington or Amyotrophic Lateral Sclerosis. Interestingly, the S1R can be activated by small druggable molecules and accumulating preclinical data suggest that S1R agonists are effective protectants in these neurodegenerative diseases.Area covered: In this review, we will present the data showing the high therapeutic potential of S1R drugs for the treatment of neurodegenerative diseases, focusing on pridopidine as a potent and selective S1R agonist under clinical development. Of particular interest is the bi-phasic (bell-shaped) dose-response effect, representing a common feature of all S1R agonists and described in numerous preclinical models in vitro, in vivo and in clinical trials.Expert opinion: S1R agonists modulate inter-organelles communication altered in neurodegenerative diseases and activate intracellular survival pathways. Research will continue growing in the future. The particular cellular nature of this chaperone protein must be better understood to facilitate the clinical developement of promising molecules.

Use of Immunohistochemistry to Determine Expression of Rab5 Subfamily of GTPases in Mature and Developmental Brains

Rab GTPases are essentially molecular switches. They serve as master regulators in intracellular membrane trafficking from the formation and transport of vesicles at the originating organelle to its fusion to the membrane at the target organelle. Their functions are diversified and each has their specific subcellular location. Their expression may vary significantly in the same cell when the level of protein production is significantly different in different physiologic status. One of the best examples is the transition from fetal to mature status of cells. Expression and localization of Rab GTPases in mature and developing brains have not been well studied. Immunohistochemistry is an efficient way in the detection, semiquantitation, and localization of Rab GTPases in tissue sections. It is inexpensive and fast which allow efficient mass screening of many sections. In this chapter, we describe the immunohistochemical assay protocol for analyzing several Rab protein expressions of the Rab5 subfamily, including Rab5, Rab17, Rab22, and Rab31, in developmental (fetal) and mature human brains.

MAMs Protect Against Ectopic Fat Deposition and Lipid-Related Kidney Damage in DN Patients

Ectopic fat deposition (EFD) in the kidney plays a key role in the development of diabetic nephropathy (DN). Mitochondria-associated ER membranes (MAMs) are structures that connect to the endoplasmic reticulum (ER) and are involved in lipid metabolism. However, there are few studies on MAMs in the field of kidney disease, and the relationship between EFD and MAMs in DN is still unclear. In this study, increased EFD in the kidneys of DN patients was observed, and analysis showed that the degree of EFD was positively correlated with renal damage. Then, the MAMs were quantified by an in situ proximity ligation assay (PLA). The MAMs in the kidneys were found to gradually decrease through the different stages of DN, while the expression of ADRP (a marker of lipid droplets) and tubulointerstitial damage increased. Moreover, correlation analysis showed that the MAMs were negatively correlated with serum lipid levels, the EFD in the kidney and renal damage. Finally, we observed decreased expression of MAM-control proteins (DsbA-L, PACS-2, and MFN-2) in different stages of DN and they were associated with lipid deposition and renal damage. These data showed that the destruction of MAMs in DN might be the cause of EFD and interstitial damage in the kidney.

VARP and Rab9 Are Dispensable for the Rab32/BLOC-3 Dependent Salmonella Killing

Salmonella enterica serovar Typhi (S. Typhi) is the causative agent of typhoid fever, a disease that kills an estimated 200,000 people annually. Previously, we discovered an antimicrobial pathway dependent on Rab32 and BLOC-3 (BRAM) that is critical to kill S. Typhi in murine macrophages. The BLOC-3 complex is comprised of the two sub-units HPS1 and HPS4 and exhibits guanine-nucleotide exchange factor (GEF) activity to Rab32. In melanocytes, Rab9 has been shown to interact with HPS4 and RUTBC1, a Rab32 GTPase activating (GAP) protein, and regulate the Rab32-mediated melanosome biogenesis. Intriguingly, Rab9-deficient melanocytes exhibit hypopigmentation, a similar phenotype to Rab32 or BLOC-3 deficient melanocytes. Additionally, VPS9-ankyrin-repeat-protein (VARP) has been shown to regulate melanocytic enzyme trafficking into the melanosomes through interaction with Rab32. Although Rab32, Rab9 and VARP are a part of melanogenesis in melanocytes, whether Rab9 and VARP are required for the BRAM mediated killing in macrophages is currently unknown. Here we showed that HPS4 is recruited to the Salmonella-containing vacuoles (SCV) and over-expression of BLOC-3 significantly increased Rab32-positive bacteria vacuoles. We found that SCV acquire Rab9, however over-expressing Rab9 did not change HPS4 localization on bacteria vacuoles. Importantly, we used shRNA to knock-down Rab9 and VARP in macrophages and showed that these proteins are dispensable for Rab32 recruitment to the SCV. Furthermore, we assessed the survival of S. Typhimurium in macrophages deficient for Rab9 or VARP and demonstrated that these proteins are not essential for BRAM pathway-dependent killing.

Proteolysis of Rab32 by Salmonella GtgE induces an inactive GTPase conformation

Rab GTPases are central regulators of intracellular vesicular trafficking. They are frequently targeted by bacterial pathogens through post-translational modifications. Salmonella typhimurium secretes the cysteine protease GtgE during infection, leading to a regioselective proteolytic cleavage of the regulatory switch I loop in the small GTPases of the Rab32 subfamily. Here, using a combination of biochemical methods, molecular dynamics simulations, NMR spectroscopy, and single-pair Förster resonance energy transfer, we demonstrate that the cleavage of Rab32 causes a local increase of conformational flexibility in both switch regions. Cleaved Rab32 maintains its ability to interact with the GDP dissociation inhibitor (GDI). Interestingly, the Rab32 cleavage enables GDI binding also with an active GTP-bound Rab32 in vitro. Furthermore, the Rab32 proteolysis provokes disturbance in the interaction with its downstream effector VARP. Thus, the proteolysis of Rab32 is not a globally degradative mechanism but affects various biochemical and structural properties of the GTPase in a diverse manner.

"The Loss of Golden Touch": Mitochondria-Organelle Interactions, Metabolism, and Cancer

Mitochondria represent the energy hub of cells and their function is under the constant influence of their tethering with other subcellular organelles. Mitochondria interact with the endoplasmic reticulum, lysosomes, cytoskeleton, peroxisomes, and nucleus in several ways, ranging from signal transduction, vesicle transport, and membrane contact sites, to regulate energy metabolism, biosynthetic processes, apoptosis, and cell turnover. Tumorigenesis is often associated with mitochondrial dysfunction, which could likely be the result of an altered interaction with different cell organelles or structures. The purpose of the present review is to provide an updated overview of the links between inter-organellar communications and interactions and metabolism in cancer cells, with a focus on mitochondria. The very recent publication of several reviews on these aspects testifies the great interest in the area. Here, we aim at (1) summarizing recent evidence supporting that the metabolic rewiring and adaptation observed in tumors deeply affect organelle dynamics and cellular functions and vice versa; (2) discussing insights on the underlying mechanisms, when available; and (3) critically presenting the gaps in the field that need to be filled, for a comprehensive understanding of tumor cells’ biology. Chemo-resistance and druggable vulnerabilities of cancer cells related to the aspects mentioned above is also outlined.

The Fabp5/calnexin complex is a prerequisite for sensitization of mice to experimental autoimmune encephalomyelitis

We previously showed that calnexin (Canx)-deficient mice are desensitized to experimental autoimmune encephalomyelitis (EAE) induction, a model that is frequently used to study inflammatory demyelinating diseases, due to increased resistance of the blood-brain barrier to immune cell transmigration. We also discovered that Fabp5, an abundant cytoplasmic lipid-binding protein found in brain endothelial cells, makes protein-protein contact with the cytoplasmic C-tail domain of Canx. Remarkably, both Canx-deficient and Fabp5-deficient mice commonly manifest resistance to EAE induction. Here, we evaluated the importance of Fabp5/Canx interactions on EAE pathogenesis and on the patency of a model blood-brain barrier to T-cell transcellular migration. The results demonstrate that formation of a complex comprised of Fabp5 and the C-tail domain of Canx dictates the permeability of the model blood-brain barrier to immune cells and is also a prerequisite for EAE pathogenesis.

RAB7 GTPase regulates actin dynamics for DRP1-mediated mitochondria function and spindle migration in mouse oocyte meiosis

RAB7 is a small GTPase that belongs to the Rab family, and as a vesicle trafficking factor it is shown to regulate the transport to late endocytic compartments, autophagosome maturation and organelle function. In present study, we showed the critical roles of RAB7 GTPase on actin dynamics and mitochondria function in oocyte meiosis. RAB7 mainly accumulated at cortex and spindle periphery during oocyte maturation. RAB7 depletion caused the failure of polar body extrusion and asymmetric division, and Rab7 exogenous mRNA supplement could rescue the defects caused by RAB7 RNAi. Based on mass spectrometry analysis, we found that RAB7 associated with several actin nucleation factors and mitochondria-related proteins in oocytes. The depletion of RAB7 caused the decrease of actin dynamics, which further affected meiotic spindle migration to the oocyte cortex. In addition, we found that RAB7 could maintain mitochondrial membrane potential and the mitochondrial distribution in mouse oocytes, and this might be due to its effects on the phosphorylation of DRP1 at Ser616 domain. Taken together, our data indicated that RAB7 transported actin nucleation factor for actin polarization, which further affected the phosphorylation of DRP1 for mitochondria dynamics and the meiotic spindle migration in mouse oocytes.

Vesicular transport mediates the uptake of cytoplasmic proteins into mitochondria in Drosophila melanogaster

Mitochondrial aging, which results in mitochondrial dysfunction, is strongly linked to many age-related diseases. Aging is associated with mitochondrial enlargement and transport of cytosolic proteins into mitochondria. The underlying homeostatic mechanisms that regulate mitochondrial morphology and function, and their breakdown during aging, remain unclear. Here, we identify a mitochondrial protein trafficking pathway in Drosophila melanogaster involving the mitochondria-associated protein Dosmit. Dosmit induces mitochondrial enlargement and the formation of double-membraned vesicles containing cytosolic protein within mitochondria. The rate of vesicle formation increases with age. Vesicles originate from the outer mitochondrial membrane as observed by tracking Tom20 localization, and the process is mediated by the mitochondria-associated Rab32 protein. Dosmit expression level is closely linked to the rate of ubiquitinated protein aggregation, which are themselves associated with age-related diseases. The mitochondrial protein trafficking route mediated by Dosmit offers a promising target for future age-related mitochondrial disease therapies.

Mitochondrial dynamics change during ageing, with larger mitochondria and altered protein import in older animals. Here the authors show that Dosmit protein mediates mitochondrial morphology with Rab32 by inducing double-membraned vesicles that regulate protein trafficking into mitochondria.

Oxidative Stress in Autism Spectrum Disorder

According to the United States Centers for Disease Control and Prevention (CDC), as of July 11, 2016, the reported average incidence of children diagnosed with an autism spectrum disorder (ASD) was 1 in 68 (1.46%) among 8-year-old children born in 2004 and living within the 11 monitoring sites' surveillance areas in the United States of America (USA) in 2012. ASD is a multifaceted neurodevelopmental disorder that is also considered a hidden disability, as, for the most part; there are no apparent morphological differences between children with ASD and typically developing children. ASD is diagnosed based upon a triad of features including impairment in socialization, impairment in language, and repetitive and stereotypic behaviors. The increasing incidence of ASD in the pediatric population and the lack of successful curative therapies make ASD one of the most challenging disorders for medicine. ASD neurobiology is thought to be associated with oxidative stress, as shown by increased levels of reactive oxygen species and increased lipid peroxidation, as well as an increase in other indicators of oxidative stress. Children with ASD diagnosis are considered more vulnerable to oxidative stress because of their imbalance in intracellular and extracellular glutathione levels and decreased glutathione reserve capacity. Several studies have suggested that the redox imbalance and oxidative stress are integral parts of ASD pathophysiology. As such, early assessment and treatment of antioxidant status may result in a better prognosis as it could decrease the oxidative stress in the brain before it can induce more irreversible brain damage. In this review, many aspects of the role of oxidative stress in ASD are discussed, taking into account that the process of oxidative stress may be a target for therapeutic interventions.

Engagement of people with multiple sclerosis to enhance research into the physiological effect of hyperbaric oxygen therapy

BACKGROUND

Thousands of people with multiple sclerosis (MS) have used self-administered oxygen therapy in the UK. Clinical trials have been performed, with scant evidence that people with MS have been consulted to explore how they benefit from or how to optimize this treatment. The conventional MS disease disability scores used in trials seldom reflect the effects individuals report when using oxygen therapy to treat their symptoms.

METHODS

Three people with MS and the manager of an MS Centre formed a public involvement group and collaborated with clinicians and scientists to inform a lab-based study to investigate the physiological effects of oxygen therapy on microvascular brain endothelial cells.

RESULTS

People with MS often use oxygen therapy at a later stage when their symptoms worsen and only after using other treatments. The frequency of oxygen therapy sessions and hyperbaric pressure is individualized and varies for people with MS. Despite direct comparisons of efficacy proving difficult, most individuals are exposed to 100% O₂ at 1.5 atmosphere absolute (ATA; 1140 mmHg absolute) for 60 min. In a laboratory-based study human brain endothelial cells were exposed in vitro to 152 mmHg O₂ for 60 min with and without pressure, as this equates to 20% O₂ achievable via hyperbarics, which was then replicated at atmospheric pressure. A significant reduction in endothelial cells ICAM-1 (CD54) implicated in inflammatory cell margination across the blood brain barrier was observed under oxygen treatment.

CONCLUSIONS

By collaborating with people living with MS, we were able to design laboratory-based experimental protocols that replicate their treatment regimens to advance our understanding of the physiological effects of hyperbaric oxygen treatment on brain cells and their role in neuroinflammation.

The balance of protein farnesylation and geranylgeranylation during the progression of nonalcoholic fatty liver disease

Protein prenylation is an essential posttranslational modification and includes protein farnesylation and geranylgeranylation using farnesyl diphosphate or geranylgeranyl diphosphate as substrates, respectively. Geranylgeranyl diphosphate synthase is a branch point enzyme in the mevalonate pathway that affects the ratio of farnesyl diphosphate to geranylgeranyl diphosphate. Abnormal geranylgeranyl diphosphate synthase expression and activity can therefore disrupt the balance of farnesylation and geranylgeranylation and alter the ratio between farnesylated and geranylgeranylated proteins. This change is associated with the progression of nonalcoholic fatty liver disease (NAFLD), a condition characterized by hepatic fat overload. Of note, differential accumulation of farnesylated and geranylgeranylated proteins has been associated with differential stages of NAFLD and NAFLD-associated liver fibrosis. In this review, we summarize key aspects of protein prenylation as well as advances that have uncovered the regulation of associated metabolic patterns and signaling pathways, such as Ras GTPase signaling, involved in NAFLD progression. Additionally, we discuss unique opportunities for targeting prenylation in NAFLD/hepatocellular carcinoma with agents such as statins and bisphosphonates to improve clinical outcomes.

High fat diet consumption results in mitochondrial dysfunction, oxidative stress, and oligodendrocyte loss in the central nervous system

Metabolic syndrome is a key risk factor and co-morbidity in multiple sclerosis (MS) and other neurological conditions, such that a better understanding of how a high fat diet contributes to oligodendrocyte loss and the capacity for myelin regeneration has the potential to highlight new treatment targets. Results demonstrate that modeling metabolic dysfunction in mice with chronic high fat diet (HFD) consumption promotes loss of oligodendrocyte progenitors across the brain and spinal cord. A number of transcriptomic and metabolomic changes in ER stress, mitochondrial dysfunction, and oxidative stress pathways in HFD-fed mouse spinal cords were also identified. Moreover, deficits in TCA cycle intermediates and mitochondrial respiration were observed in the chronic HFD spinal cord tissue. Oligodendrocytes are known to be particularly vulnerable to oxidative damage, and we observed increased markers of oxidative stress in both the brain and spinal cord of HFD-fed mice. We additionally identified that increased apoptotic cell death signaling is underway in oligodendrocytes from mice chronically fed a HFD. When cultured under high saturated fat conditions, oligodendrocytes decreased both mitochondrial function and differentiation. Overall, our findings show that HFD-related changes in metabolic regulators, decreased mitochondrial function, and oxidative stress contribute to a loss of myelinating cells. These studies identify HFD consumption as a key modifiable lifestyle factor for improved myelin integrity in the adult central nervous system and in addition new tractable metabolic targets for myelin protection and repair strategies.

MicroRNA-141-5p Acts as a Tumor Suppressor via Targeting RAB32 in Chronic Myeloid Leukemia

MicroRNA-141-5p (miR-141-5p), an important member of the miR-200 family, has been reported to be involved in cellular proliferation, migration, invasion, and drug resistance in different kinds of human malignant tumors. However, the role and function of miR-141-5p in chronic myeloid leukemia (CML) are unclear. In this current study, we found that the level of miR-141-5p was significantly decreased in peripheral blood cells from CML patients compared with normal blood cells and human leukemic cell line (K562 cells) compared with normal CD34⁺ cells, but was remarkably elevated in patients after treatment with nilotinib or imatinib. Suppression of miR-141-5p promoted K562 cell proliferation and migration in vitro. As expected, overexpression of miR-141-5p weakened K562 cell proliferation, migration, and promoted cell apoptosis. A xenograft model in nude mice showed that overexpression of miR-141-5p markedly suppressed tumor growth in vivo. Mechanistic studies suggested that RAB32 was the potential target of miR-141-5p, and silencing of RAB32 suppressed the proliferation and migration of K562 cells and promoted cell apoptosis. Taken together, our study demonstrates that miR-141-5p plays an important role in the activation of K562 cells in vitro and may act as a tumor suppressor via targeting RAB32 in the development of CML.

Different functions of biogenesis of lysosomal organelles complex 3 subunit 1 (Hps1) and adaptor-related protein complex 3, beta 1 subunit (Ap3b1) genes on spermatogenesis and male fertility

Hermansky-Pudlak syndrome (HPS) is an autosomal recessive disorder in humans and mice. Pale ear (ep) and pearl (pe) mice, bearing mutations in the biogenesis of lysosomal organelles complex 3 subunit 1 (Hps1) and adaptor-related protein complex 3, beta 1 subunit (Ap3b1) genes respectively, are mouse models of human HPS Type 1 (HPS1) and Type 2 (HPS2) respectively. In the present study we investigated and compared the reduced fertilities of ep and pe male mice. Both ep and pe males exhibited lower abilities to impregnate C57BL/6J (B6) females, and B6 females mated with ep males produced smaller litters than those mated with pe males. Delayed testis development, reduced sperm count and lower testosterone concentrations were observed in the pe but not ep male mice. However, the reduction in sperm motility was greater in ep than pe males, likely due to the mitochondrial and fibrous sheath abnormalities observed by electron microscopy in the sperm tails of ep males. Together, the results indicate that the Hps1 and Ap3b1 genes play distinct roles in male reproductive system development and spermatogenesis in mice, even though ep and pe males share common phenotypes, including reduced lysosomes in Sertoli cells and dislocated Zn2+ in sperm heads.

Sural nerve pathology in TFG-associated motor neuron disease with sensory neuropathy

The tropomyosin-receptor kinase fused gene (TFG) functions in vesicles formation and egress at the endoplasmic reticulum (ER). A heterozygous missense mutation c.854C > T (p.Pro285Leu) within TFG has been reported as causative for hereditary motor and sensory neuropathy with proximal predominance. Here, we describe two unrelated Chinese pedigrees with 13 affected members harboring the same variant. The clinical, electrophysiological and pathological findings are consistent with motor neuron disease with sensory neuropathy. The main symptoms were painful muscle cramps, slowly progressive proximal predominant weakness, muscle atrophy, fasciculation and distal sensory disturbance. Electromyography revealed widespread denervation and reinnervation. Sural nerve biopsy revealed severe loss of myelinated fibers. Electron microscopy revealed aggregation of ER with enlarged lumen and small vesicles in the remaining myelinated and unmyelinated axons. The mitochondria are smaller in Schwann cells and axons. Some unmyelinated axons showed disappearance of neurofilament and microtubular structures. This is the first report of c.854C > T mutation within TFG in Chinese population. Our findings not only extend the geographical and phenotypic spectrum of TFG-related neurological disorders, but also confirm the abnormalities of ER and mitochondria in sural nerves.

Targeting Microglia and Macrophages: A Potential Treatment Strategy for Multiple Sclerosis

Multiple sclerosis (MS) is a chronic inflammatory neurodegenerative disease of the central nervous system (CNS). The early stage is characterized by relapses and the later stage, by progressive disability. Results from experimental and clinical investigations have demonstrated that microglia and macrophages play a key part in the disease course. These cells actively initiate immune infiltration and the demyelination cascade during the early phase of the disease; however, they promote remyelination and alleviate disease in later stages. This review aims to provide a comprehensive overview of the existing knowledge regarding the neuromodulatory function of macrophages and microglia in the healthy and injured CNS, and it discusses the feasibility of harnessing microglia and macrophage physiology to treat MS. The review encourages further investigations into macrophage-targeted therapy, as well as macrophage-based drug delivery, for realizing efficient treatment strategies for MS.

The physiology of foamy phagocytes in multiple sclerosis

Multiple sclerosis (MS) is a chronic disease of the central nervous system characterized by massive infiltration of immune cells, demyelination, and axonal loss. Active MS lesions mainly consist of macrophages and microglia containing abundant intracellular myelin remnants. Initial studies showed that these foamy phagocytes primarily promote MS disease progression by internalizing myelin debris, presenting brain-derived autoantigens, and adopting an inflammatory phenotype. However, more recent studies indicate that phagocytes can also adopt a beneficial phenotype upon myelin internalization. In this review, we summarize and discuss the current knowledge on the spatiotemporal physiology of foamy phagocytes in MS lesions, and elaborate on extrinsic and intrinsic factors regulating their behavior. In addition, we discuss and link the physiology of myelin-containing phagocytes to that of foamy macrophages in other disorders such atherosclerosis.

The role of oligodendrocytes and their progenitors on neural interface technology: A novel perspective on tissue regeneration and repair

Oligodendrocytes and their precursors are critical glial facilitators of neurophysiology, which is responsible for cognition and behavior. Devices that are used to interface with the brain allow for a more in-depth analysis of how neurons and these glia synergistically modulate brain activity. As projected by the BRAIN Initiative, technologies that acquire a high resolution and robust sampling of neural signals can provide a greater insight in both the healthy and diseased brain and support novel discoveries previously unobtainable with the current state of the art. However, a complex series of inflammatory events triggered during device insertion impede the potential applications of implanted biosensors. Characterizing the biological mechanisms responsible for the degradation of intracortical device performance will guide novel biomaterial and tissue regenerative approaches to rehabilitate the brain following injury. Glial subtypes which assist with neuronal survival and exchange of electrical signals, mainly oligodendrocytes, their precursors, and the insulating myelin membranes they produce, are sensitive to inflammation commonly induced from insults to the brain. This review explores essential physiological roles facilitated by oligodendroglia and their precursors and provides insight into their pathology following neurodegenerative injury and disease. From this knowledge, inferences can be made about the impact of device implantation on these supportive glia in order to engineer effective strategies that can attenuate their responses, enhance the efficacy of neural interfacing technology, and provide a greater understanding of the challenges that impede wound healing and tissue regeneration during pathology.

Unfolded Protein Response-Dependent Communication and Contact among Endoplasmic Reticulum, Mitochondria, and Plasma Membrane

The function of the endoplasmic reticulum (ER) can be impaired by changes to the extra- and intracellular environment, such as disruption of calcium homeostasis, expression of mutated proteins, and oxidative stress. In response to disruptions to ER homeostasis, eukaryotic cells activate canonical branches of signal transduction cascades, collectively termed the unfolded protein response (UPR). The UPR functions to remove or recover the activity of misfolded proteins that accumulated in the ER and to avoid irreversible cellular damage. Additionally, the UPR plays unique physiological roles in the regulation of diverse cellular events, including cell differentiation and development and lipid biosynthesis. Recent studies have shown that these important cellular events are also regulated by contact and communication among organelles. These reports suggest strong involvement among the UPR, organelle communication, and regulation of cellular homeostasis. However, the precise mechanisms for the formation of contact sites and the regulation of ER dynamics by the UPR remain unresolved. In this review, we summarize the current understanding of how the UPR regulates morphological changes to the ER and the formation of contact sites between the ER and other organelles. We also review how UPR-dependent connections between the ER and other organelles affect cellular and physiological functions.

Neuronal microRNA regulation in Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is an autoimmune, neurodegenerative disease but the molecular mechanisms underlying neurodegenerative aspects of the disease are poorly understood. microRNAs (miRNAs) are powerful regulators of gene expression that regulate numerous mRNAs simultaneously and can thus regulate programs of gene expression. Here, we describe miRNA expression in neurons captured from mice subjected to experimental autoimmune encephalomyelitis (EAE), a model of central nervous system (CNS) inflammation. Lumbar motor neurons and retinal neurons were laser captured from EAE mice and miRNA expression was assessed by next-generation sequencing and validated by qPCR. We describe 14 miRNAs that are differentially regulated in both neuronal subtypes and determine putative mRNA targets though in silico analysis. Several upregulated neuronal miRNAs are predicted to target pathways that could mediate repair and regeneration during EAE. This work identifies miRNAs that are affected by inflammation and suggests novel candidates that may be targeted to improve neuroprotection in the context of pathological inflammation.

Oligodendrocyte Bioenergetics in Health and Disease

The human brain weighs approximately 2% of the body; however, it consumes about 20% of a person’s total energy intake. Cellular bioenergetics in the central nervous system involves a delicate balance between biochemical processes engaged in energy conversion and those responsible for respiration. Neurons have high energy demands, which rely on metabolic coupling with glia, such as with oligodendrocytes and astrocytes. It has been well established that astrocytes recycle and transport glutamine to neurons to make the essential neurotransmitters, glutamate and GABA, as well as shuttle lactate to support energy synthesis in neurons. However, the metabolic role of oligodendrocytes in the central nervous system is less clear. In this review, we discuss the energetic demands of oligodendrocytes in their survival and maturation, the impact of altered oligodendrocyte energetics on disease pathology, and the role of energetic metabolites, taurine, creatine, N-acetylaspartate, and biotin, in regulating oligodendrocyte function.

The effect of Tmem135 overexpression on the mouse heart

Tissues with high-energy demand including the heart are rich in the energy-producing organelles, mitochondria, and sensitive to mitochondrial dysfunction. While alterations in mitochondrial function are increasingly recognized in cardiovascular diseases, the molecular mechanisms through which changes in mitochondria lead to heart abnormalities have not been fully elucidated. Here, we report that transgenic mice overexpressing a novel regulator of mitochondrial dynamics, transmembrane protein 135 (Tmem135), exhibit increased fragmentation of mitochondria and disease phenotypes in the heart including collagen accumulation and hypertrophy. The gene expression analysis showed that genes associated with ER stress and unfolded protein response, and especially the pathway involving activating transcription factor 4, are upregulated in the heart of Tmem135 transgenic mice. It also showed that gene expression changes in the heart of Tmem135 transgenic mice significantly overlap with those of aged mice in addition to the similarity in cardiac phenotypes, suggesting that changes in mitochondrial dynamics may be involved in the development of heart abnormalities associated with aging. Our study revealed the pathological consequence of overexpression of Tmem135, and suggested downstream molecular changes that may underlie those disease pathologies.

Role of Mitochondria-Associated ER Membranes in Calcium Regulation in Cancer-Specific Settings

Mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) are highly specialized subcellular compartments that are shaped by ER subdomains juxtaposed to mitochondria but are biochemically distinct from pure ER and pure mitochondria. MAMs are enriched in enzymes involved in lipid synthesis and transport, channels for calcium transfer, and proteins with oncogenic/oncosuppressive functions that modulate cell signaling pathways involved in physiological and pathophysiological processes. The term "cancer" denotes a group of disorders that result from uncontrolled cell growth driven by a mixture of genetic and environmental components. Alterations in MAMs are thought to account for the onset as well as the progression and metastasis of cancer and have been a focus of investigation in recent years. In this review, we present the current state of the art regarding MAM-resident proteins and their relevance, alterations, and deregulating functions in different types of cancer from a cell biology and clinical perspective.

Calnexin is necessary for T cell transmigration into the central nervous system

In multiple sclerosis (MS), a demyelinating inflammatory disease of the CNS, and its animal model (experimental autoimmune encephalomyelitis; EAE), circulating immune cells gain access to the CNS across the blood-brain barrier to cause inflammation, myelin destruction, and neuronal damage. Here, we discovered that calnexin, an ER chaperone, is highly abundant in human brain endothelial cells of MS patients. Conversely, mice lacking calnexin exhibited resistance to EAE induction, no evidence of immune cell infiltration into the CNS, and no induction of inflammation markers within the CNS. Furthermore, calnexin deficiency in mice did not alter the development or function of the immune system. Instead, the loss of calnexin led to a defect in brain endothelial cell function that resulted in reduced T cell trafficking across the blood-brain barrier. These findings identify calnexin in brain endothelial cells as a potentially novel target for developing strategies aimed at managing or preventing the pathogenic cascade that drives neuroinflammation and destruction of the myelin sheath in MS.

Expression of a T39N mutant Rab32 protein arrests mitochondria movement within neurites of differentiated SH-SY5Y cells

We have shown that multiple sclerosis (MS) and endoplasmic reticulum (ER) stress induce Rab32, an ER/mitochondria-localized small GTPase. High levels of both dominant-active (Q85L) or dominant-inactive (T39N) Rab32 are toxic to neurons. While Rab32Q85L interacts with its effector Drp1 to promote mitochondria fission, it is unclear how Rab32T39N could result as toxic to neurons. Given the perinuclear clustering of mitochondria observed upon transfection of inactive Rab32, we hypothesized Rab32T39N could stall mitochondria within neurites. The movement of mitochondria depends on kinesin-binding Miro proteins. High cytosolic [Ca²⁺] is bound by an EF hand motif within Miro proteins, resulting in mitochondrial arrest. Consistent with increased cytosolic [Ca²⁺], expression of Rab32T39N arrests mitochondria movement within neurites.