ErbB2 receptor tyrosine kinase signaling mediates early demyelination induced by leprosy bacilli

ncRNAs: an unexplored cellular defense mechanism in leprosy

Leprosy is an infectious disease primarily caused by the obligate intracellular parasite Mycobacterium leprae. Although it has been considered eradicated in many countries, leprosy continues to be a health issue in developing nations. Besides the social stigma associated with it, individuals affected by leprosy may experience nerve damage leading to physical disabilities if the disease is not properly treated or early diagnosed. Leprosy is recognized as a complex disease wherein socioenvironmental factors, immune response, and host genetics interact to contribute to its development. Recently, a new field of study called epigenetics has emerged, revealing that the immune response and other mechanisms related to infectious diseases can be influenced by noncoding RNAs. This review aims to summarize the significant advancements concerning non-coding RNAs in leprosy, discussing the key perspectives on this novel approach to comprehending the pathophysiology of the disease and identifying molecular markers. In our view, investigations on non-coding RNAs in leprosy hold promise and warrant increased attention from researches in this field.

What happens when Schwann cells are exposed to Mycobacterium leprae - A systematic review

Mycobacterium leprae, the pathogen that causes human leprosy, has a unique affinity for infecting and persisting inside Schwann cells, the principal glia of the peripheral nervous system. Several studies have focused on this intricate host-pathogen interaction as an attempt to advance the current knowledge of the mechanisms governing nerve destruction and disease progression. However, during the chronic course of leprosy neuropathy, Schwann cells can respond to and internalize both live and dead M. leprae and bacilli-derived antigens, and this may result in divergent cellular pathobiological responses. This may also distinctly contribute to tissue degeneration, failure to repair, inflammatory reactions, and nerve fibrosis, hallmarks of the disease. Therefore, the present study systematically searched for published studies on M. leprae-Schwann cell interaction in vitro to summarize the findings and provide a focused discussion of Schwann cell dynamics following challenge with leprosy bacilli.

Perspective on receptor-associated immune response to Candida albicans single and mixed infections: Implications for therapeutics in oropharyngeal candidiasis

Oropharyngeal candidiasis (OPC), commonly known as 'thrush', is an oral infection that usually dismantles oral mucosal integrity and malfunctions local innate and adaptive immunities in compromised individuals. The major pathogen responsible for the occurrence and progression of OPC is the dimorphic opportunistic commensal Candida albicans. However, the incidence induced by non-albicans Candida species including C. glabrata, C. tropicalis, C. dubliniensis, C. parapsilosis, and C. krusei are increasing in company with several oral bacteria, such as Streptococcus mutans, S. gordonii, S. epidermidis, and S. aureus. In this review, the microbiological and infection features of C. albicans and its co-contributors in the pathogenesis of OPC are outlined. Since the invasion and concomitant immune response lie firstly on the recognition of oral pathogens through diverse cellular surface receptors, we subsequently emphasize the roles of epidermal growth factor receptor, ephrin-type receptor 2, human epidermal growth factor receptor 2, and aryl hydrocarbon receptor located on oral epithelial cells to delineate the underlying mechanism by which host immune recognition to oral pathogens is mediated. Based on these observations, the therapeutic approaches to OPC comprising conventional and non-conventional antifungal agents, fungal vaccines, cytokine and antibody therapies, and antimicrobial peptide therapy are finally overviewed. In the face of newly emerging life-threatening microbes (C. auris and SARS-CoV-2), risks (biofilm formation and interconnected translocation among diverse organs), and complicated clinical settings (HIV and oropharyngeal cancer), the research on OPC is still a challenging task.

CD11b+Gr-1low cells that accumulate in M.leprae-induced granulomas of the footpad skin of nude mice have the characteristics of monocytic-myeloid-derived suppressor cells

CD11b⁺Gr-1^low cells that are increased in the lungs of a Mycobacterium (M) tuberculosis-infection mouse model have the characteristics of monocytic (M)-myeloid-derived suppressor cells (MDSCs) and harbor M.tuberculosis. Interestingly, a high number of M-MDSCs have also been observed in skin lesions of patients with lepromatous leprosy. We hypothesized that CD11b⁺Gr-1^low cells might be involved in the pathogenesis of leprosy, as they are in tuberculosis. In the current study, we investigated the issue of whether CD11b⁺Gr-1^low cells accumulate in Mycobacterium (M) leprae-induced granulomas of the footpad skin of nude mice. Our results show that CD11b⁺Gr-1^low cells began to accumulate in the 7-month-old M.leprae-induced granulomas and were replaced by other leukocytes, including CD11b⁺Gr-1^high over time during M.leprae infections. CD11b ⁺ Gr-1^low cells expressed the surface markers of M-MDSC, Ly6C^high and Ly6G^low. In addition, CD11b⁺Gr-1^low cells have the nuclei of a mononuclear cell type and expressed higher levels of arginase 1 (Arg1) and inducible NO synthetase (iNOS). Furthermore, they showed a higher infection rate by M.leprae. Taken together, our results indicate that the inoculation with M.leprae induced an accumulation of CD11b ⁺ Gr-1^low at a relatively early stage, 7-month-old M.leprae-induced granulomas, and that CD11b⁺Gr-1^low have the characteristics of M-MDSC and may act as a reservoir for M.leprae.

Phenolic glycolipid-1 of Mycobacterium leprae is involved in human Schwann cell line ST8814 neurotoxic phenotype

Leprosy is a chronic infectious disease caused by Mycobacterium leprae infection in Schwann cells. Axonopathy is considered a hallmark of leprosy neuropathy and is associated with the irreversible motor and sensory loss seen in infected patients. Although M. leprae is recognized to provoke Schwann cell dedifferentiation, the mechanisms involved in the contribution of this phenomenon to neural damage remain unclear. In the present work, we used live M. leprae to infect the immortalized human Schwann cell line ST8814. The neurotoxicity of infected Schwann cell-conditioned medium (SCCM) was then evaluated in a human neuroblastoma cell lineage and mouse neurons. ST8814 Schwann cells exposed to M. leprae affected neuronal viability by deviating glial ¹⁴ C-labeled lactate, important fuel of neuronal central metabolism, to de novo lipid synthesis. The phenolic glycolipid-1 (PGL-1) is a specific M. leprae cell wall antigen proposed to mediate bacterial-Schwann cell interaction. Therefore, we assessed the role of the PGL-1 on Schwann cell phenotype by using transgenic M. bovis (BCG)-expressing the M. leprae PGL-1. We observed that BCG-PGL-1 was able to induce a phenotype similar to M. leprae, unlike the wild-type BCG strain. We next demonstrated that this Schwann cell neurotoxic phenotype, induced by M. leprae PGL-1, occurs through the protein kinase B (Akt) pathway. Interestingly, the pharmacological inhibition of Akt by triciribine significantly reduced free fatty acid content in the SCCM from M. leprae- and BCG-PGL-1-infected Schwann cells and, hence, preventing neuronal death. Overall, these findings provide novel evidence that both M. leprae and PGL-1, induce a toxic Schwann cell phenotype, by modifying the host lipid metabolism, resulting in profound implications for neuronal loss. We consider this metabolic rewiring a new molecular mechanism to be the basis of leprosy neuropathy.

Pathogenicity and virulence of Mycobacterium leprae

Leprosy is caused by Mycobacterium leprae (M. leprae) and M. lepromatosis, an obligate intracellular organism, and over 200,000 new cases occur every year. M. leprae parasitizes histiocytes (skin macrophages) and Schwann cells in the peripheral nerves. Although leprosy can be treated by multidrug therapy, some patients relapse or have a prolonged clinical course and/or experience leprosy reaction. These varying outcomes depend on host factors such as immune responses against bacterial components that determine a range of symptoms. To understand these host responses, knowledge of the mechanisms by which M. leprae parasitizes host cells is important. This article describes the characteristics of leprosy through bacteriology, genetics, epidemiology, immunology, animal models, routes of infection, and clinical findings. It also discusses recent diagnostic methods, treatment, and measures according to the World Health Organization (WHO), including prevention. Recently, the antibacterial activities of anti-hyperlipidaemia agents against other pathogens, such as M. tuberculosis and Staphylococcus aureus have been investigated. Our laboratory has been focused on the metabolism of lipids which constitute the cell wall of M. leprae. Our findings may be useful for the development of future treatments.

In vivo partial reprogramming by bacteria promotes adult liver organ growth without fibrosis and tumorigenesis

Ideal therapies for regenerative medicine or healthy aging require healthy organ growth and rejuvenation, but no organ-level approach is currently available. Using Mycobacterium leprae (ML) with natural partial cellular reprogramming capacity and its animal host nine-banded armadillos, we present an evolutionarily refined model of adult liver growth and regeneration. In infected armadillos, ML reprogram the entire liver and significantly increase total liver/body weight ratio by increasing healthy liver lobules, including hepatocyte proliferation and proportionate expansion of vasculature, and biliary systems. ML-infected livers are microarchitecturally and functionally normal without damage, fibrosis, or tumorigenesis. Bacteria-induced reprogramming reactivates liver progenitor/developmental/fetal genes and upregulates growth-, metabolism-, and anti-aging-associated markers with minimal change in senescence and tumorigenic genes, suggesting bacterial hijacking of homeostatic, regeneration pathways to promote de novo organogenesis. This may facilitate the unraveling of endogenous pathways that effectively and safely re-engage liver organ growth, with broad therapeutic implications including organ regeneration and rejuvenation.

Peripheral mechanisms of chronic pain

Acutely, pain serves to protect us from potentially harmful stimuli, however damage to the somatosensory system can cause maladaptive changes in neurons leading to chronic pain. Although acute pain is fairly well controlled, chronic pain remains difficult to treat. Chronic pain is primarily a neuropathic condition, but studies examining the mechanisms underlying chronic pain are now looking beyond afferent nerve lesions and exploring new receptor targets, immune cells, and the role of the autonomic nervous system in contributing chronic pain conditions. The studies outlined in this review reveal how chronic pain is not only confined to alterations in the nervous system and presents findings on new treatment targets and for this debilitating disease.

Kynurenines in the Pathogenesis of Peripheral Neuropathy During Leprosy and COVID-19

Inflammatory disorders are associated with the activation of tryptophan (TRYP) catabolism via the kynurenine pathway (KP). Several reports have demonstrated the role of KP in the immunopathophysiology of both leprosy and coronavirus disease 19 (COVID-19). The nervous system can be affected in infections caused by both Mycobacterium leprae and SARS-CoV-2, but the mechanisms involved in the peripheral neural damage induced by these infectious agents are not fully understood. In recent years KP has received greater attention due the importance of kynurenine metabolites in infectious diseases, immune dysfunction and nervous system disorders. In this review, we discuss how modulation of the KP may aid in controlling the damage to peripheral nerves and the effects of KP activation on neural damage during leprosy or COVID-19 individually and we speculate its role during co-infection.

Metabolic Control of Sensory Neuron Survival by the p75 Neurotrophin Receptor in Schwann Cells

We report that the neurotrophin receptor p75 contributes to sensory neuron survival through the regulation of cholesterol metabolism in Schwann cells. Selective deletion of p75 in mouse Schwann cells of either sex resulted in a 30% loss of dorsal root ganglia (DRG) neurons and diminished thermal sensitivity. P75 regulates Schwann cell cholesterol biosynthesis in response to BDNF, forming a co-receptor complex with ErbB2 and activating ErbB2-mediated stimulation of sterol regulatory element binding protein 2 (SREBP2), a master regulator of cholesterol synthesis. Schwann cells lacking p75 exhibited decreased activation of SREBP2 and a reduction in 7-dehydrocholesterol (7-DHC) reductase (DHCR7) expression, resulting in accumulation of the neurotoxic intermediate, 7-dehyrocholesterol in the sciatic nerve. Restoration of DHCR7 in p75 null Schwann cells in mice significantly attenuated DRG neuron loss. Together, these results reveal a mechanism by which the disruption of lipid metabolism in glial cells negatively influences sensory neuron survival, which has implications for a wide range of peripheral neuropathies.SIGNIFICANCE STATEMENT Although expressed in Schwann cells, the role of p75 in myelination has remained unresolved in part because of its dual expression in sensory neurons that Schwann cells myelinate. When p75 was deleted selectively among Schwann cells, myelination was minimally affected, while sensory neuron survival was reduced by 30%. The phenotype is mainly due to dysregulation of cholesterol biosynthesis in p75-deficient Schwann cells, leading to an accumulation of neurotoxic cholesterol precursor, 7-dehydrocholesterol (7-DHC). Mechanism-wise, we discovered that in response to BDNF, p75 recruits and activates ErbB2 independently of ErbB3, thereby stimulating the master regulator, sterol regulatory element binding protein 2 (SREBP2). These results together highlight a novel role of p75 in Schwann cells in regulating DRG neuron survival by orchestrating proper cholesterol metabolism.

Lapatinib alleviates TOCP-induced axonal damage in the spinal cord of mouse

Neuregulin-1 (NRG1), a family of EGF-like factors that activates ErbB receptors, can regulate the proliferation, migration, and myelinating of Schwann cells. We previously reported that NRG1/ErbB signal is responsible for organophosphate (OP)-induced delayed neuropathy (OPIDN) in hens, a susceptive animal model to neuropathic organophosphorous compounds. Our previous study discovered that a neuropathic OP, tri-o-cresyl phosphate (TOCP) activated NRG1/ErbB signaling pathway in both spinal cord and sciatic nerves of hens during the formation of OPIDN and lapatinib, a non-selective antagonist of ErbB1 and ErbB2 receptors, alleviated the toxicity. In this study, we intended to further look into the potential role of NRG1 in the pathogenesis of TOCP-induced axon damage in spinal cord and sciatic nerves and whether lapatinib could also rescue this damage in mice, an OPIDN-resistant animal model. The results revealed that no obvious toxic signs were observed after single TOCP exposure. However, slight histopathological wreck in lumbar spinal cord and sciatic nerves was found following TOCP intoxication, and the damage in sciatic nerves was characterized by axon degeneration of myelin sheath but not the loss of neural skeleton. Only histopathological damage induced by TOCP in spinal cord could be prevented by lapatinib. The translational expression of NRG1/ErbB signaling molecules was analyzed by both in vivo and in vitro studies. In general, NRG1/ErbB pathway was activated by TOCP while combined treatment with lapatinib attenuated TOCP-induced NRG1/ErbB signaling cascade. The results implied that NRG1/ErbB system may predominately play functional role in spinal cord (central nervous system) but not in sciatic nerves (peripheral nervous system) of mouse subjected to neurotoxic OP, which was confirmed by the study in vitro that lapatinib was not able to attenuate TOCP-induced neurotoxicity in rodent Schwann cell line RSC 96 cells.

Pathogenesis and Host Immune Response in Leprosy

Leprosy is an ancient insidious disease caused by Mycobacterium leprae, where the skin and peripheral nerves undergo chronic granulomatous infections, leading to sensory and motor impairment with characteristic deformities. Susceptibility to leprosy and its disease state are determined by the manifestation of innate immune resistance mediated by cells of monocyte lineage. Due to insufficient innate resistance, granulomatous infection is established, influencing the specific cellular immunity. The clinical presentation of leprosy ranges between two stable polar forms (tuberculoid to lepromatous) and three unstable borderline forms. The tuberculoid form involves Th1 response, characterized by a well demarcated granuloma, infiltrated by CD4⁺ T lymphocytes, containing epitheloid and multinucleated giant cells. In the lepromatous leprosy, there is no characteristic granuloma but only unstructured accumulation of ineffective macrophages containing engulfed pathogens. Th1 response, characterised by IFN-γ and IL-2 production, activates macrophages in order to kill intracellular pathogens. Conversely, a Th2 response, characterized by the production of IL-4, IL-5 and IL-10, helps in antibody production and consequently downregulates the cell-mediated immunity induced by the Th1 response. M. lepare has a long generation time and its inability to grow in culture under laboratory conditions makes its study challenging. The nine-banded armadillo still remains the best clinical and immunological model to study host-pathogen interaction in leprosy. In this chapter, we present cellular morphology and the genomic uniqueness of M. leprae, and how the pathogen shows tropism for Schwann cells, macrophages and dendritic cells.

Drug Delivery Systems on Leprosy Therapy: Moving Towards Eradication?

Leprosy disease remains an important public health issue as it is still endemic in several countries. Mycobacterium leprae, the causative agent of leprosy, presents tropism for cells of the reticuloendothelial and peripheral nervous system. Current multidrug therapy consists of clofazimine, dapsone and rifampicin. Despite significant improvements in leprosy treatment, in most programs, successful completion of the therapy is still sub-optimal. Drug resistance has emerged in some countries. This review discusses the status of leprosy disease worldwide, providing information regarding infectious agents, clinical manifestations, diagnosis, actual treatment and future perspectives and strategies on targets for an efficient targeted delivery therapy.

Functional Impairment of Skin Appendages Due to Peripheral Nerve Involvement by Mycobacterium leprae

In the earliest stage of Mycobacterium leprae infection, bacteria parasitize fine fiber twigs of autonomic peripheral nerves supplying efferent impulses to appendages of the skin. This obligate intracellular pathogen invades Schwann cells, the glial cells of peripheral nerves. Intracellular events inhibit Schwann cell physiology in complex ways, which include demyelination and dedifferentiation. Ultimately, axons embraced by their surrounding dysfunctional glia are damaged by poorly understood mechanisms. Loss of nerve conduction impairs the functions of skin appendages including hair growth, sebaceous gland secretion, sweating, and skin pigmentation. At the clinical level, these changes may be subtle and may precede the more obvious anesthetic skin lesions associated with Hansen’s disease. Recognizing the early signs of skin appendage malfunction may aid in diagnosis leading to initiation of antimycobacterial treatment. Effective therapy administered early during infection may prevent irreversible peripheral nerve destruction, the presage for morbid complications of leprosy.

Mechanisms of Schwann cell plasticity involved in peripheral nerve repair after injury

The great plasticity of Schwann cells (SCs), the myelinating glia of the peripheral nervous system (PNS), is a critical feature in the context of peripheral nerve regeneration following traumatic injuries and peripheral neuropathies. After a nerve damage, SCs are rapidly activated by injury-induced signals and respond by entering the repair program. During the repair program, SCs undergo dynamic cell reprogramming and morphogenic changes aimed at promoting nerve regeneration and functional recovery. SCs convert into a repair phenotype, activate negative regulators of myelination and demyelinate the damaged nerve. Moreover, they express many genes typical of their immature state as well as numerous de-novo genes. These genes modulate and drive the regeneration process by promoting neuronal survival, damaged axon disintegration, myelin clearance, axonal regrowth and guidance to their former target, and by finally remyelinating the regenerated axon. Many signaling pathways, transcriptional regulators and epigenetic mechanisms regulate these events. In this review, we discuss the main steps of the repair program with a particular focus on the molecular mechanisms that regulate SC plasticity following peripheral nerve injury.

HER2-mediated enhancement of Ebola virus entry

Multiple cell surface molecules including TAM receptors (TYRO3, AXL, and MERTK), a family of tyrosine kinase receptors, can serve as attachment receptors for Ebola virus (EBOV) entry into cells. The interaction of these receptors with EBOV particles is believed to trigger the initial internalization events that lead to macropinocytosis. However, the details of how these interactions lead to EBOV internalization have yet to be elucidated. Here, we screened receptor tyrosine kinase (RTK) inhibitors for anti-EBOV activity by using our previously established biologically contained Ebola virus that lacks the VP30 gene (EBOVΔVP30) and identified several RTKs, including human epidermal growth factor receptor 2 (HER2), as potential targets of anti-EBOV inhibitors and as novel host factors that have a role in EBOV infection. Of these identified RTKs, it was only HER2 whose knockdown by siRNAs impaired EBOVΔVP30-induced AKT1 phosphorylation, an event that is required for AKT1 activation and subsequent macropinocytosis. Stable expression of HER2 resulted in constitutive activation of AKT1, resulting in the enhancement of EBOVΔVP30 growth, EBOV GP-mediated entry, and macropinocytosis. Moreover, we found that HER2 interacts with the TAM receptors, and in particular forms a complex with TYRO3 and EBOVΔVP30 particles on the cell surface. Interestingly, HER2 was required for EBOVΔVP30-induced TYRO3 and AKT1 activation, but the other TAM receptors (TYRO3 and MERTK) were not essential for EBOVΔVP30-induced HER2 and AKT1 activation. Our findings demonstrate that HER2 plays an important role in EBOV entry and provide novel insights for the development of therapeutics against the virus.

Mycobacterium leprae: Pathogenesis, diagnosis, and treatment options

Mycobacterium leprae is known to cause leprosy, a neurological and dermatological disease. In the past 20 years, 16 million leprosy cases have been recorded and more than 200,000 new cases were registered each year, indicating that the disease is still progressing without hindrance. M. leprae, an intracellular bacterium, infects the Schwann cells of the peripheral nervous system. Several types of leprosy have been described, including indeterminate, tuberculoid, borderline tuberculoid, mid-borderline, borderline lepromatous and lepromatous, and three different forms of leprosy reactions, namely type 1, 2 and 3, have been designated. Microscopic detection, serological diagnostic test, polymerase chain reaction and flow tests are employed in the diagnosis of leprosy. The recommended treatment for leprosy consists of rifampicin, dapsone, clofazimine, ofloxacin and minocycline and vaccines are also available. However, relapse may occur after treatment has been halted and hence patients must be educated on the signs of relapse to allow proper treatment and reduce severity. In this review, we depict the current understanding of M. leprae pathogenicity, clinical aspects and manifestations. Transmission of leprosy, diagnosis and treatment are also discussed.

Notch Signaling Pathway Expression in the Skin of Leprosy Patients: Association With Skin and Neural Damage

Introduction: Leprosy is an infectious disease caused by Mycobacterium leprae, a debilitating disease that affects the skin and peripheral nerves. It is possible that tissue changes during infection with leprosy are related to alterations in the activity of the Notch signaling pathway, an innate signaling pathway in the physiology of the skin and peripheral nerves.

Methods: This is a descriptive observational study. Thirty skin biopsies from leprosy patients and 15 from individuals with no history of this disease were evaluated. In these samples, gene expressions of cellular components associated with the Notch signaling pathway, Hes-1, Hey-1, Runx-1 Jagged-1, Notch-1, and Numb, were evaluated using q-PCR, and protein expression was evaluated using immunohistochemistry of Runx-1 and Hes-1.

Results: Changes were observed in the transcription of Notch signaling pathway components; Hes-1 was downregulated and Runx-1 upregulated in the skin of infected patients. These results were confirmed by immunohistochemistry, where reduction of Hes-1 expression was found in the epidermis, eccrine glands, and hair follicles. Increased expression of Runx-1 was found in inflammatory cells in the dermis of infected patients; however, it is not related to tissue changes. With these results, a multivariate analysis was performed to determine the causes of transcription factor Hes-1 reduction. It was concluded that tissue inflammation was the main cause.

Conclusions: The tissue changes found in the skin of infected patients could be associated with a reduction in the expression of Hes-1, a situation that would promote the survival and proliferation of M. leprae in this tissue.

Cell Biology of Intracellular Adaptation of Mycobacterium leprae in the Peripheral Nervous System

The mammalian nervous system is invaded by a number of intracellular bacterial pathogens which can establish and progress infection in susceptible individuals. Subsequent clinical manifestation is apparent with the impairment of the functional units of the nervous system, i.e., the neurons and the supporting glial cells that produce myelin sheaths around axons and provide trophic support to axons and neurons. Most of these neurotrophic bacteria display unique features, have coevolved with the functional sophistication of the nervous system cells, and have adapted remarkably to manipulate neural cell functions for their own advantage. Understanding how these bacterial pathogens establish intracellular adaptation by hijacking endogenous pathways in the nervous system, initiating myelin damage and axonal degeneration, and interfering with myelin maintenance provides new knowledge not only for developing strategies to combat neurodegenerative conditions induced by these pathogens but also for gaining novel insights into cellular and molecular pathways that regulate nervous system functions. Since the pathways hijacked by bacterial pathogens may also be associated with other neurodegenerative diseases, it is anticipated that detailing the mechanisms of bacterial manipulation of neural systems may shed light on common mechanisms, particularly of early disease events. This chapter details a classic example of neurodegeneration, that caused by Mycobacterium leprae, which primarily infects glial cells of the peripheral nervous system (Schwann cells), and how it targets and adapts intracellularly by reprogramming Schwann cells to stem cells/progenitor cells. We also discuss implications of this host cell reprogramming by leprosy bacilli as a model in a wider context.

Myelin breakdown favours Mycobacterium leprae survival in Schwann cells

Leprosy neuropathy is a chronic degenerative infectious disorder of the peripheral nerve caused by the intracellular obligate pathogen Mycobacterium leprae (M. leprae). Among all nonneuronal cells that constitute the nerve, Schwann cells are remarkable in supporting M. leprae persistence intracellularly. Notably, the success of leprosy infection has been attributed to its ability in inducing the demyelination phenotype after contacting myelinated fibres. However, the exact role M. leprae plays during the ongoing process of myelin breakdown is entirely unknown. Here, we provided evidence showing an unexpected predilection of leprosy pathogen for degenerating myelin ovoids inside Schwann cells. In addition, M. leprae infection accelerated the rate of myelin breakdown and clearance leading to increased formation of lipid droplets, by modulating a set of regulatory genes involved in myelin maintenance, autophagy, and lipid storage. Remarkably, the blockage of myelin breakdown significantly reduced M. leprae content, demonstrating a new unpredictable role of myelin dismantling favouring M. leprae physiology. Collectively, our study provides novel evidence that may explain the demyelination phenotype as an evolutionarily conserved mechanism used by leprosy pathogen to persist longer in the peripheral nerve.

Toxic Peripheral Neuropathies: Agents and Mechanisms

Toxic peripheral neuropathies are an important form of acquired polyneuropathy produced by a variety of xenobiotics and different exposure scenarios. Delineating the mechanisms of neurotoxicants and determining the degenerative biological pathways triggered by peripheral neurotoxicants will facilitate the development of sensitive and specific biochemical-based methods for identifying neurotoxicants, designing therapeutic interventions, and developing structure-activity relationships for predicting potential neurotoxicants. This review presents an overview of the general concepts of toxic peripheral neuropathies with the goal of providing insight into why certain agents target the peripheral nervous system and produce their associated lesions. Experimental data and the main hypotheses for the mechanisms of selected agents that produce neuronopathies, axonopathies, or myelinopathies including covalent or noncovalent modifications, compromised energy or protein biosynthesis, and oxidative injury and disruption of ionic gradients across membranes are presented. The relevance of signaling between the main components of peripheral nerve, that is, glia, neuronal perikaryon, and axon, as a target for neurotoxicants and the contribution of active programmed degenerative pathways to the lesions observed in toxic peripheral neuropathies is also discussed.

Apolipoprotein E Homozygous ε4 Allele Status: A Deteriorating Effect on Visuospatial Working Memory and Global Brain Structure

Theoretical background: The Apolipoprotein E (APOE) ε4 genotype is known to be one of the strongest single-gene predictors for Alzheimer disease, which is characterized by widespread brain structural degeneration progressing along with cognitive impairment. The ε4 allele status has been associated with brain structural alterations and lower cognitive ability in non-demented subjects. However, it remains unclear to what extent the visuospatial cognitive domain is affected, from what age onward changes are detectable and if alterations may interact with cognitive deficits in major depressive disorder (MDD). The current work investigated the effect of APOE ε4 homozygosity on visuospatial working memory (vWM) capacity, and on hippocampal morphometry. Furthermore, potential moderating roles of age and MDD were assessed.

Methods: A sample of n = 31 homozygous ε4 carriers was contrasted with n = 31 non-ε4 carriers in a cross-sectional design. The sample consisted of non-demented, young to mid-age participants (mean age = 34.47; SD = 13.48; 51.6% female). Among them were n = 12 homozygous ε4 carriers and n = 12 non-ε4 carriers suffering from MDD (39%). VWM was assessed using the Corsi block-tapping task. Region of interest analyses of hippocampal gray matter density and volume were conducted using voxel-based morphometry (CAT12), and Freesurfer, respectively.

Results: Homozygous ε4 carriers showed significantly lower Corsi span capacity than non-ε4 carriers did, and Corsi span capacity was associated with higher gray matter density of the hippocampus. APOE group differences in hippocampal volume could be detected but were no longer present when controlling for total intracranial volume. Hippocampal gray matter density did not differ between APOE groups. We did not find any interaction effects of age and MDD diagnosis on hippocampal morphometry.

Conclusion: Our results point toward a negative association of homozygous ε4 allele status with vWM capacity already during mid-adulthood, which emerges independently of MDD diagnosis and age. APOE genotype seems to be associated with global brain structural rather than hippocampus specific alterations in young- to mid-age participants.

Mycobacterium leprae-induced nerve damage: direct and indirect mechanisms

Leprosy is a chronic infectious disease caused by Mycobacterium leprae. This disease is characterized by skin and peripheral nerve trunk damage. The mechanisms responsible for the observed nerve damage in leprosy could be directly related to the ability of M. leprae to infect Schwann cells, leading to triggering of signaling events. Therefore, we hypothesize that in response to M. leprae infection, activation of the Notch signaling pathway in Schwann cells could play a crucial role in glial cell dedifferentiation. On the other hand, nerve damage evidenced in this disease may be additionally explained by indirect mechanisms such as the immune response and genetic susceptibility of the host. The understanding of the mechanisms leading to nerve damage induced by M. leprae infection will allow us to generate valuable tools for the early detection of leprosy as well as for the mitigation of the effects of this disabling disease.

Activation of Neuregulin 1/ErbB Signaling Is Involved in the Development of TOCP-Induced Delayed Neuropathy

Organophosphate-induced delayed neuropathy (OPIDN) is characterized by progressive axonal degeneration and demyelination of the spinal cord and sciatic nerves. The neuregulin 1/epidermal growth factor receptor (ErbB) signaling pathway is crucial for axonal myelination. In this study, we investigated whether the neuregulin 1/ErbB signaling pathway mediated the progression of OPIDN. Adult hens were given tri-o-cresyl phosphate (TOCP), a typical neuropathic organophosphorus compound, to induce OPIDN. The ErbB inhibitor lapatinib was administered to hens 4 h prior to and 4 days after TOCP exposure. The neuregulin 1/ErbB signaling pathway was examined for their role in maintaining spinal cord and sciatic nerve fiber integrity. Schwann cell line sNF96.2 was used as the in vitro cell model. The in vivo results showed that TOCP (750 mg/kg body weight, p.o.) induced prominent ataxia and significant axon degeneration in the spinal cord and sciatic nerves. Lapatinib (25 mg/kg body weight, p.o.) treatment attenuated OPIDN clinically and histopathlogically and partially prevented the TOCP-induced activation of neuregulin 1/ErbB signaling pathway. Lapatinib also prevented the TOCP-induced inhibition of neuropathy target esterase (NTE), a key enzyme during the development of OPIDN, and the disturbed metabolism of phosphatidylcholine in sciatic nerves. In addition, lapatinib was shown, in vitro, to protect sNF96.2 cells from TOCP-induced dedifferentiation through neuregulin 1/ErbB signaling. Our results suggest that neuregulin 1/ErbB, through regulation of NTE activity in the peripheral nervous system, mediates the progression of OPIDN. Thus, this signal may serve as a potential target for the treatment of OPIDN.

miRNome Expression Analysis Reveals New Players on Leprosy Immune Physiopathology

Leprosy remains as a public health problem and its physiopathology is still not fully understood. MicroRNAs (miRNA) are small RNA non-coding that can interfere with mRNA to regulate gene expression. A few studies using DNA chip microarrays have explored the expression of miRNA in leprosy patients using a predetermined set of genes as targets, providing interesting findings regarding the regulation of immune genes. However, using a predetermined set of genes restricted the possibility of finding new miRNAs that might be involved in different mechanisms of disease. Thus, we examined the miRNome of tuberculoid (TT) and lepromatous (LL) patients using both blood and lesional biopsies from classical leprosy patients (LP) who visited the Dr. Marcello Candia Reference Unit in Sanitary Dermatology in the State of Pará and compared them with healthy subjects. Using a set of tools to correlate significantly differentially expressed miRNAs with their gene targets, we identified possible interactions and networks of miRNAs that might be involved in leprosy immunophysiopathology. Using this approach, we showed that the leprosy miRNA profile in blood is distinct from that in lesional skin as well as that four main groups of genes are the targets of leprosy miRNA: (1) recognition and phagocytosis, with activation of immune effector cells, where the immunosuppressant profile of LL and immunoresponsive profile of TT are clearly affected by miRNA expression; (2) apoptosis, with supportive data for an antiapoptotic leprosy profile based on BCL2, MCL1, and CASP8 expression; (3) Schwann cells (SCs), demyelination and epithelial–mesenchymal transition (EMT), supporting a role for different developmental or differentiation gene families, such as Sox, Zeb, and Hox; and (4) loss of sensation and neuropathic pain, revealing that RHOA, ROCK1, SIGMAR1, and aquaporin-1 (AQP1) may be involved in the loss of sensation or leprosy pain, indicating possible new therapeutic targets. Additionally, AQP1 may also be involved in skin dryness and loss of elasticity, which are well known signs of leprosy but with unrecognized physiopathology. In sum, miRNA expression reveals new aspects of leprosy immunophysiopathology, especially on the regulation of the immune system, apoptosis, SC demyelination, EMT, and neuropathic pain.

Postinjury Induction of Activated ErbB2 Selectively Hyperactivates Denervated Schwann Cells and Promotes Robust Dorsal Root Axon Regeneration

Following nerve injury, denervated Schwann cells (SCs) convert to repair SCs, which enable regeneration of peripheral axons. However, the repair capacity of SCs and the regenerative capacity of peripheral axons are limited. In the present studies we examined a potential therapeutic strategy to enhance the repair capacity of SCs, and tested its efficacy in enhancing regeneration of dorsal root (DR) axons, whose regenerative capacity is particularly weak. We used male and female mice of a doxycycline-inducible transgenic line to induce expression of constitutively active ErbB2 (caErbB2) selectively in SCs after DR crush or transection. Two weeks after injury, injured DRs of induced animals contained far more SCs and SC processes. These SCs had not redifferentiated and continued to proliferate. Injured DRs of induced animals also contained far more axons that regrew along SC processes past the transection or crush site. Remarkably, SCs and axons in uninjured DRs remained quiescent, indicating that caErbB2 enhanced regeneration of injured DRs, without aberrantly activating SCs and axons in intact nerves. We also found that intraspinally expressed glial cell line-derived neurotrophic factor (GDNF), but not the removal of chondroitin sulfate proteoglycans, greatly enhanced the intraspinal migration of caErbB2-expressing SCs, enabling robust penetration of DR axons into the spinal cord. These findings indicate that SC-selective, post-injury activation of ErbB2 provides a novel strategy to powerfully enhance the repair capacity of SCs and axon regeneration, without substantial off-target damage. They also highlight that promoting directed migration of caErbB2-expressing SCs by GDNF might be useful to enable axon regrowth in a non-permissive environment.SIGNIFICANCE STATEMENT Repair of injured peripheral nerves remains a critical clinical problem. We currently lack a therapy that potently enhances axon regeneration in patients with traumatic nerve injury. It is extremely challenging to substantially increase the regenerative capacity of damaged nerves without deleterious off-target effects. It was therefore of great interest to discover that caErbB2 markedly enhances regeneration of damaged dorsal roots, while evoking little change in intact roots. To our knowledge, these findings are the first demonstration that repair capacity of denervated SCs can be efficaciously enhanced without altering innervated SCs. Our study also demonstrates that oncogenic ErbB2 signaling can be activated in SCs but not impede transdifferentiation of denervated SCs to regeneration-promoting repair SCs.

Effectiveness of 32 versus 20 weeks of prednisolone in leprosy patients with recent nerve function impairment: A randomized controlled trial

BACKGROUND

While prednisolone is commonly used to treat recent nerve function impairment (NFI) in leprosy patients, the optimal treatment duration has not yet been established. In this "Treatment of Early Neuropathy in Leprosy" (TENLEP) trial, we evaluated whether a 32-week prednisolone course is more effective than a 20-week course in restoring and improving nerve function.

METHODS

In this multi-centre, triple-blind, randomized controlled trial, leprosy patients who had recently developed clinical NFI (<6 months) were allocated to a prednisolone treatment regimen of either 20 weeks or 32 weeks. Prednisolone was started at either 45 or 60 mg/day, depending on the patient's body weight, and was then tapered. Throughout follow up, NFI was assessed by voluntary muscle testing and monofilament testing. The primary outcome was the proportion of patients with improved or restored nerve function at week 78. As secondary outcomes, we analysed improvements between baseline and week 78 on the Reaction Severity Scale, the SALSA Scale and the Participation Scale. Serious Adverse Events and the need for additional prednisolone treatment were monitored and reported.

RESULTS

We included 868 patients in the study, 429 in the 20-week arm and 439 in the 32-week arm. At 78 weeks, the proportion of patients with improved or restored nerve function did not differ significantly between the groups: 78.1% in the 20-week arm and 77.5% in the 32-week arm (p = 0.821). Nor were there any differences in secondary outcomes, except for a significant higher proportion of Serious Adverse Events in the longer treatment arm.

CONCLUSION

In our study, a 20-week course of prednisolone was as effective as a 32-week course in improving and restoring recent clinical NFI in leprosy patients. Twenty weeks is therefore the preferred initial treatment duration for leprosy neuropathy, after which likely only a minority of patients require further individualized treatment.

The Tyrosine Kinase Inhibitor Gefitinib Restricts Mycobacterium tuberculosis Growth through Increased Lysosomal Biogenesis and Modulation of Cytokine Signaling

Host-directed therapeutics have the potential to combat the global tuberculosis pandemic. We previously identified gefitinib, an inhibitor of EGFR, as a potential host-targeted therapeutic effective against Mycobacterium tuberculosis infection of macrophages and mice. Here we examine the functional consequences of gefitinib treatment on M. tuberculosis infected macrophages. Using phosphoproteomic and transcriptional profiling, we identify two mechanisms by which gefitinib influences macrophage responses to infection to affect cytokine responses and limit replication of M. tuberculosis in macrophages. First, we find that gefitinib treatment of M. tuberculosis infected macrophages inhibits STAT3, a transcription factor known to repress effective immune responses to M. tuberculosis in vivo. Second, we find that gefitinib treatment of M. tuberculosis infected macrophages leads to increased expression of genes involved in lysosomal biogenesis and function and an increase of functional lysosomes in gefitinib treated cells. Furthermore, we show that gefitinib treatment increases the targeting of bacteria to lysosomes, providing an explanation for the cell intrinsic effects of gefitinib treatment on M. tuberculosis infection. Our data provide novel insights into the effects of gefitinib on mammalian cells and into the possible roles for EGFR signaling in macrophages.

KIAA1199: A novel regulator of MEK/ERK-induced Schwann cell dedifferentiation

The molecular mechanisms that regulate Schwann cell (SC) plasticity and the role of the Nrg1/ErbB-induced MEK1/ERK1/2 signalling pathway in SC dedifferentiation or in myelination remain unclear. It is currently believed that different levels of MEK1/ERK1/2 activation define the state of SC differentiation. Thus, the identification of new regulators of MEK1/ERK1/2 signalling could help to decipher the context-specific aspects driving the effects of this pathway on SC plasticity. In this perspective, we have investigated the potential role of KIAA1199, a protein that promotes ErbB and MEK1/ERK1/2 signalling in cancer cells, in SC plasticity. We depleted KIAA1199 in the SC-derived MSC80 cell line with RNA-interference-based strategy and also generated Tamoxifen-inducible and conditional mouse models in which KIAA1199 is inactivated through homologous recombination, using the Cre-lox technology. We show that the invalidation of KIAA1199 in SC decreases the expression of cJun and other negative regulators of myelination and elevates Krox20, driving them towards a pro-myelinating phenotype. We further show that in dedifferentiation conditions, SC invalidated for KIAA1199 exhibit lower myelin clearance as well as increased myelination capacity. Finally, the Nrg1-induced activation of the MEK/ERK/1/2 pathway is severely reduced when KIAA1199 is absent, indicating that KIAA1199 promotes Nrg1-dependent MEK1 and ERK1/2 activation in SCs. In conclusion, this work identifies KIAA1199 as a novel regulator of MEK/ERK-induced SC dedifferentiation and contributes to a better understanding of the molecular control of SC dedifferentiation.

Laminin 211 inhibits protein kinase A in Schwann cells to modulate neuregulin 1 type III-driven myelination

Myelin is required for proper nervous system function. Schwann cells in developing nerves depend on extrinsic signals from the axon and from the extracellular matrix to first sort and ensheathe a single axon and then myelinate it. Neuregulin 1 type III (Nrg1III) and laminin α2β1γ1 (Lm211) are the key axonal and matrix signals, respectively, but how their signaling is integrated and if each molecule controls both axonal sorting and myelination is unclear. Here, we use a series of epistasis experiments to show that Lm211 modulates neuregulin signaling to ensure the correct timing and amount of myelination. Lm211 can inhibit Nrg1III by limiting protein kinase A (PKA) activation, which is required to initiate myelination. We provide evidence that excessive PKA activation amplifies promyelinating signals downstream of neuregulin, including direct activation of the neuregulin receptor ErbB2 and its effector Grb2-Associated Binder-1 (Gab1), thereby elevating the expression of the key transcription factors Oct6 and early growth response protein 2 (Egr2). The inhibitory effect of Lm211 is seen only in fibers of small caliber. These data may explain why hereditary neuropathies associated with decreased laminin function are characterized by focally thick and redundant myelin.

Wallerian demyelination: chronicle of a cellular cataclysm

Wallerian demyelination is characteristic of peripheral nerve degeneration after traumatic injury. After axonal degeneration, the myelinated Schwann cell undergoes a stereotypical cellular program that results in the disintegration of the myelin sheath, a process termed demyelination. In this review, we chronologically describe this program starting from the late and visible features of myelin destruction and going backward to the initial molecular steps that trigger the nuclear reprogramming few hours after injury. Wallerian demyelination is a wonderful model for myelin degeneration occurring in the diverse forms of demyelinating peripheral neuropathies that plague human beings.

The Role of ErbB Receptors in Infection

Members of the epidermal growth factor receptor family (ErbB family) possess a wide distribution and diverse functions ranging from cellular growth to migration and apoptosis. Though highly implicated in a variety of cancers, their involvement in infectious disease is less recognised. A growing body of evidence now highlights the importance of the ErbB family in a variety of infections. Their role as growth factor receptors, along with other characteristics, such as surface expression and continuous intracellular trafficking, make this receptor family ideally placed for exploitation by pathogens. Herein, we review our current understanding of the role of the ErbB family in the context of infectious disease, exploring the mechanisms that govern pathogen exploitation of this system.

A wide and diverse variety of microbes have each evolved distinct mechanisms to exploit ErbB receptors, highlighting this receptor kinase family as a critical factor in initiation and maintenance of pathogen infections.

ErbB family members are utilised by pathogens attempting to gain cellular entry, subvert immune responses, and manipulate the cell cycle of infected host cells. These events support and are necessary for pathogen persistence.

Pathogen-mediated ErbB-exploitation may contribute to cellular transformation and oncogenesis in a variety of cancers.

The use of existing FDA-approved drugs that target ErbB receptors and associated signalling components may offer potential future therapies against infection.

Axon contact-driven Schwann cell dedifferentiation

Mature Schwann cells (SCs) retain dedifferentiation potential throughout adulthood. Still, how dedifferentiation occurs remains uncertain. Results from a variety of cell-based assays using in vitro cultured cAMP-differentiated and myelinating SCs revealed the existence of a novel dedifferentiating activity expressed on the surface of dorsal root ganglion (DRG) axons. This activity had the capacity to prevent SC differentiation and elicit dedifferentiation through direct SC-axon contact. Evidence is provided showing that a rapid loss of myelinating SC markers concomitant to proliferation occurred even in the presence of elevated cAMP, a signal that is required to drive and maintain a differentiated state. The dedifferentiating activity was a membrane-bound protein found exclusively in DRG neurons, as judged by its subcellular partitioning, sensitivity to proteolytic degradation and cell-type specificity, and remained active even after disruption of cellular organization. It differed from the membrane-anchored neuregulin-1 isoforms that are responsible for axon contact-induced SC proliferation and exerted its action independently of mitogenic signaling emanating from receptor tyrosine kinases and mitogen-activated protein kinases such as ERK and JNK. Interestingly, dedifferentiation occurred without concomitant changes in the expression of Krox-20, a transcriptional enhancer of myelination, and c-Jun, an inhibitor of myelination. In sum, our data indicated the existence of cell surface axon-derived signals that override pro-differentiating cues, drive dedifferentiation and allow SCs to proliferate in response to axonal mitogens. This axonal signal may negatively regulate myelination at the onset or reversal of the differentiated state. GLIA 2017;65:851-863.

Molecular Mechanisms Involved in Schwann Cell Plasticity

Schwann cell incredible plasticity is a hallmark of the utmost importance following nerve damage or in demyelinating neuropathies. After injury, Schwann cells undergo dedifferentiation before redifferentiating to promote nerve regeneration and complete functional recovery. This review updates and discusses the molecular mechanisms involved in the negative regulation of myelination as well as in the reprogramming of Schwann cells taking place early following nerve lesion to support repair. Significant advance has been made on signaling pathways and molecular components that regulate SC regenerative properties. These include for instance transcriptional regulators such as c-Jun or Notch, the MAPK and the Nrg1/ErbB2/3 pathways. This comprehensive overview ends with some therapeutical applications targeting factors that control Schwann cell plasticity and highlights the need to carefully modulate and balance this capacity to drive nerve repair.

The role of primary infection of Schwann cells in the aetiology of infective inflammatory neuropathies

Numerous different pathogens are responsible for infective peripheral neuropathies and this is generally the result of the indirect effects of pathogen infection, namely anti pathogen antibodies cross reacting with epitopes on peripheral nerve, auto reactive T cells attacking myelin, circulating immune complexes and complement fixation. Primary infection of Schwann cells (SC) associated with peripheral nerve inflammation is rare requiring pathogens to cross the Blood Peripheral Nerve Barrier (BPNB) evade anti-pathogen innate immune pathways and invade the SC. Spirochetes Borrelia bourgdorferi and Trepomema pallidum are highly invasive, express surface lipo proteins, but despite this SC are rarely infected. However, Trypanosoma cruzi (Chaga's disease) and Mycobacterium leprae. Leprosy are two important causes of peripheral nerve infection and both demonstrate primary infection of SC. This is due to two novel strategies; T. cruzi express a trans-silalidase that mimics host neurotrophic factors and infects SC via tyrosine kinase receptors. M. leprae demonstrates multi receptor SC tropism and subsequent infection promotes nuclear reprogramming and dedifferentiation of host SC into progenitor stem like cells (pSLC) that are vulnerable to M. leprae infection. These two novel pathogen evasion strategies, involving stem cells and receptor mimicry, provide potential therapeutic targets relevant to the prevention of peripheral nerve inflammation by inhibiting primary SC infection.

Ion mobility-enhanced MS(E)-based label-free analysis reveals effects of low-dose radiation post contextual fear conditioning training on the mouse hippocampal proteome

Recent advances in the field of biodosimetry have shown that the response of biological systems to ionizing radiation is complex and depends on the type and dose of radiation, the tissue(s) exposed, and the time lapsed after exposure. The biological effects of low dose radiation on learning and memory are not well understood. An ion mobility-enhanced data-independent acquisition (MS(E)) approach in conjunction with the ISOQuant software tool was utilized for label-free quantification of hippocampal proteins with the goal of determining protein alteration associated with low-dose whole body ionizing radiation (X-rays, 1Gy) of 5.5-month-old male C57BL/6J mice post contextual fear conditioning training. Global proteome analysis revealed deregulation of 73 proteins (out of 399 proteins). Deregulated proteins indicated adverse effects of irradiation on myelination and perturbation of energy metabolism pathways involving a shift from the TCA cycle to glutamate oxidation. Our findings also indicate that proteins associated with synaptic activity, including vesicle recycling and neurotransmission, were altered in the irradiated mice. The elevated LTP and decreased LTD suggest improved synaptic transmission and enhanced efficiency of neurotransmitter release which would be consistent with the observed comparable contextual fear memory performance of the mice following post-training whole body or sham-irradiation.

SIGNIFICANCE

This study is significant because the biological consequences of low dose radiation on learning and memory are complex and not yet well understood. We conducted a IMS-enhanced MS(E)-based label-free quantitative proteomic analysis of hippocampal tissue with the goal of determining protein alteration associated with low-dose whole body ionizing radiation (X-ray, 1Gy) of 5.5-month-old male C57BL/6J mice post contextual fear conditioning training. The IMS-enhanced MS(E) approach in conjunction with ISOQuant software was robust and accurate with low median CV values of 0.99% for the technical replicates of samples from both the sham and irradiated group. The biological variance was as low as 1.61% for the sham group and 1.31% for the irradiated group. The applied data generation and processing workflow allowed the quantitative evaluation of 399 proteins. The current proteomic analysis indicates that myelination is sensitive to low dose radiation. The observed protein level changes imply modulation of energy metabolism pathways in the radiation exposed group, specifically changes in protein abundance levels suggest a shift from TCA cycle to glutamate oxidation to satisfy energy demands. Most significantly, our study reveals deregulation of proteins involved in processes that govern synaptic activity including enhanced synaptic vesicle cycling, and altered long-term potentiation (LTP) and depression (LTD). An elevated LTP and decreased LTD suggest improved synaptic transmission and enhanced efficiency of neurotransmitter release which is consistent with the observed comparable contextual fear memory performance of the mice following post-training whole body or sham-irradiation. Overall, our results underscore the importance of low dose radiation experiments for illuminating the sensitivity of biochemical pathways to radiation, and the modulation of potential repair and compensatory response mechanisms. This kind of studies and associated findings may ultimately lead to the design of strategies for ameliorating hippocampal and CNS injury following radiation exposure as part of medical therapies or as a consequence of occupational hazards.

Dysregulation of ErbB Receptor Trafficking and Signaling in Demyelinating Charcot-Marie-Tooth Disease

Charcot-Marie-Tooth (CMT) disease is the most common inherited peripheral neuropathy with the majority of cases involving demyelination of peripheral nerves. The pathogenic mechanisms of demyelinating CMT remain unclear, and no effective therapy currently exists for this disease. The discovery that mutations in different genes can cause a similar phenotype of demyelinating peripheral neuropathy raises the possibility that there may be convergent mechanisms leading to demyelinating CMT pathogenesis. Increasing evidence indicates that ErbB receptor-mediated signaling plays a major role in the control of Schwann cell-axon communication and myelination in the peripheral nervous system. Recent studies reveal that several demyelinating CMT-linked proteins are novel regulators of endocytic trafficking and/or phosphoinositide metabolism that may affect ErbB receptor signaling. Emerging data have begun to suggest that dysregulation of ErbB receptor trafficking and signaling in Schwann cells may represent a common pathogenic mechanism in multiple subtypes of demyelinating CMT. In this review, we focus on the roles of ErbB receptor trafficking and signaling in regulation of peripheral nerve myelination and discuss the emerging evidence supporting the potential involvement of altered ErbB receptor trafficking and signaling in demyelinating CMT pathogenesis and the possibility of modulating these trafficking and signaling processes for treating demyelinating peripheral neuropathy.

Methylcobalamin promotes the differentiation of Schwann cells and remyelination in lysophosphatidylcholine-induced demyelination of the rat sciatic nerve

Schwann cells (SCs) are constituents of the peripheral nervous system. The differentiation of SCs in injured peripheral nerves is critical for regeneration after injury. Methylcobalamin (MeCbl) is a vitamin B12 analog that is necessary for the maintenance of the peripheral nervous system. In this study, we estimated the effect of MeCbl on SCs. We showed that MeCbl downregulated the activity of Erk1/2 and promoted the expression of the myelin basic protein in SCs. In a dorsal root ganglion neuron–SC coculture system, myelination was promoted by MeCbl. In a focal demyelination rat model, MeCbl promoted remyelination and motor and sensory functional regeneration. MeCbl promoted the in vitro differentiation of SCs and in vivo myelination in a rat demyelination model and may be a novel therapy for several types of nervous disorders.

Myelination of the nervous system: mechanisms and functions

Myelination of axons in the nervous system of vertebrates enables fast, saltatory impulse propagation, one of the best-understood concepts in neurophysiology. However, it took a long while to recognize the mechanistic complexity both of myelination by oligodendrocytes and Schwann cells and of their cellular interactions. In this review, we highlight recent advances in our understanding of myelin biogenesis, its lifelong plasticity, and the reciprocal interactions of myelinating glia with the axons they ensheath. In the central nervous system, myelination is also stimulated by axonal activity and astrocytes, whereas myelin clearance involves microglia/macrophages. Once myelinated, the long-term integrity of axons depends on glial supply of metabolites and neurotrophic factors. The relevance of this axoglial symbiosis is illustrated in normal brain aging and human myelin diseases, which can be studied in corresponding mouse models. Thus, myelinating cells serve a key role in preserving the connectivity and functions of a healthy nervous system.

Reprogramming of human somatic cells by bacteria

In general, it had been believed that the cell fate restriction of terminally differentiated somatic cells was irreversible. In 1952, somatic cell nuclear transfer (SCNT) was introduced to study early embryonic development in frogs. So far, various mammalian species have been successfully cloned using the SCNT technique, though its efficiency is very low. Embryonic stem (ES) cells were the first pluripotent cells to be isolated from an embryo and have a powerful potential to differentiate into more than 260 types of cells. The generation of induced pluripotent stem (iPS) cells was a breakthrough in stem cell research, and the use of these iPS cells has solved problems such as low efficiency and cell fate restriction. These cells have since been used for clinical application, disease investigation, and drug selection. As it is widely accepted that the endosymbiosis of Archaea into eukaryotic ancestors resulted in the generation of eukaryotic cells, we examined whether bacterial infection could alter host cell fate. We previously showed that when human dermal fibroblast (HDF) cells were incorporated with lactic acid bacteria (LAB), the LAB-incorporated HDF cells formed clusters and expressed a subset of common pluripotent markers. Moreover, LAB-incorporated cell clusters could differentiate into cells derived from each of the three germinal layers both in vivo and in vitro, indicating successful reprogramming of host HDF cells by LAB. In the current review, we introduce the existing examples of cellular reprogramming by bacteria and discuss their nuclear reprogramming mechanisms.

The armadillo as a model for peripheral neuropathy in leprosy

Leprosy (also known as Hansen's Disease) is a chronic infectious disease caused by Mycobacterium leprae that primarily targets the peripheral nervous system; skin, muscle, and other tissues are also affected. Other than humans, nine-banded armadillos (Dasypus novemcinctus) are the only natural hosts of M. leprae, and they are the only laboratory animals that develop extensive neurological involvement with this bacterium. Infection in the armadillo closely recapitulates many of the structural, physiological, and functional aspects of leprosy seen in humans. Armadillos can be useful models of leprosy for basic scientific investigations into the pathogenesis of leprosy neuropathy and its associated myopathies, as well as for translational research studies in piloting new diagnostic methods or therapeutic interventions. Practical and ethical constraints often limit investigation into human neuropathies, but armadillos are an abundant source of leprotic neurologic fibers. Studies with these animals may provide new insights into the mechanisms involved in leprosy that also might benefit the understanding of other demyelinating neuropathies. Although there is only a limited supply of armadillo-specific reagents, the armadillo whole genomic sequence has been completed, and gene expression studies can be employed. Clinical procedures, such as electrophysiological nerve conduction testing, provide a functional assessment of armadillo nerves. A variety of standard histopathological and immunopathological procedures including Epidermal Nerve Fiber Density (ENFD) analysis, Schwann Cell Density, and analysis for other conserved cellular markers can be used effectively with armadillos and will be briefly reviewed in this text.

The role of ERBB2 gene polymorphisms in leprosy susceptibility

Mycobacterium leprae infects skin and peripheral nerves causing deformities and disability. The M. leprae bacterium binds to ErbB2 on the Schwann cell surface causing demyelination and favoring spread of the bacilli and causing nerve injury. Polymorphisms at the ERBB2 gene were previously investigated as genetic risk factors for leprosy in two Brazilian populations but with inconsistent results. Herein we extend the analysis of ERBB2 variants to a third geographically distinct population in Brazil. Our results show that there is no association between the genotyped SNPs and the disease (p > 0.05) in this population. A gene set or pathway analysis under the genomic region of ERBB2 will be necessary to clarify its regulation under M. leprae stimulus.

Bacterial-induced cell reprogramming to stem cell-like cells: new premise in host-pathogen interactions

Bacterial pathogens employ a myriad of strategies to alter host tissue cell functions for bacterial advantage during infection. Recent advances revealed a fusion of infection biology with stem cell biology by demonstrating developmental reprogramming of lineage committed host glial cells to progenitor/stem cell-like cells by an intracellular bacterial pathogen Mycobacterium leprae. Acquisition of migratory and immunomodulatory properties of such reprogrammed cells provides an added advantage for promoting bacterial spread. This presents a previously unseen sophistication of cell manipulation by hijacking the genomic plasticity of host cells by a human bacterial pathogen. The rationale for such extreme fate conversion of host cells may be directly linked to the exceedingly passive obligate life style of M. leprae with a degraded genome and host cell dependence for both bacterial survival and dissemination, particularly the use of host-derived stem cell-like cells as a vehicle for spreading infection without being detected by immune cells. Thus, this unexpected link between cell reprogramming and infection opens up a new premise in host-pathogen interactions. Furthermore, such bacterial ingenuity could also be harnessed for developing natural ways of reprogramming host cells for repairing damaged tissues from infection, injury and diseases.

Mice lacking GD3 synthase display morphological abnormalities in the sciatic nerve and neuronal disturbances during peripheral nerve regeneration

The ganglioside 9-O-acetyl GD3 is overexpressed in peripheral nerves after lesioning, and its expression is correlated with axonal degeneration and regeneration in adult rodents. However, the biological roles of this ganglioside during the regenerative process are unclear. We used mice lacking GD3 synthase (Siat3a KO), an enzyme that converts GM3 to GD3, which can be further converted to 9-O-acetyl GD3. Morphological analyses of longitudinal and transverse sections of the sciatic nerve revealed significant differences in the transverse area and nerve thickness. The number of axons and the levels of myelin basic protein were significantly reduced in adult KO mice compared to wild-type (WT) mice. The G-ratio was increased in KO mice compared to WT mice based on quantification of thin transverse sections stained with toluidine blue. We found that neurite outgrowth was significantly reduced in the absence of GD3. However, addition of exogenous GD3 led to neurite growth after 3 days, similar to that in WT mice. To evaluate fiber regeneration after nerve lesioning, we compared the regenerated distance from the lesion site and found that this distance was one-fourth the length in KO mice compared to WT mice. KO mice in which GD3 was administered showed markedly improved regeneration compared to the control KO mice. In summary, we suggest that 9-O-acetyl GD3 plays biological roles in neuron-glia interactions, facilitating axonal growth and myelination induced by Schwann cells. Moreover, exogenous GD3 can be converted to 9-O-acetyl GD3 in mice lacking GD3 synthase, improving regeneration.

Mitogen Activated Protein Kinase Family Proteins and c-jun Signaling in Injury-induced Schwann Cell Plasticity

Schwann cells (SCs) in the peripheral nerves myelinate axons during postnatal development to allow saltatory conduction of nerve impulses. Well-organized structures of myelin sheathes are maintained throughout life unless nerves are insulted. After peripheral nerve injury, unidentified signals from injured nerves drive SC dedifferentiation into an immature state. Dedifferentiated SCs participate in axonal regeneration by producing neurotrophic factors and removing degenerating nerve debris. In this review, we focus on the role of mitogen activated protein kinase family proteins (MAP kinases) in SC dedifferentiation. In addition, we will highlight neuregulin 1 and the transcription factor c-jun as upstream and downstream signals for MAP kinases in SC responses to nerve injury.

Examining ERBB2 as a candidate gene for susceptibility to leprosy (Hansen's disease) in Brazil

Leprosy remains prevalent in Brazil. ErbB2 is a receptor for leprosy bacilli entering Schwann cells, which mediates Mycobacterium leprae-induced demyelination and the ERBB2 gene lies within a leprosy susceptibility locus on chromosome 17q11-q21. To determine whether polymorphisms at the ERBB2 locus contribute to this linkage peak, three haplotype tagging single nucleotide polymorphisms (tag-SNPs) (rs2517956, rs2952156, rs1058808) were genotyped in 72 families (208 cases; 372 individuals) from the state of Pará (PA). All three tag-SNPs were associated with leprosy per se [best SNP rs2517959 odds ratio (OR) = 2.22; 95% confidence interval (CI) 1.37-3.59; p = 0.001]. Lepromatous (LL) (OR = 3.25; 95% CI 1.37-7.70; p = 0.007) and tuberculoid (TT) (OR = 1.79; 95% CI 1.04-3.05; p = 0.034) leprosy both contributed to the association, which is consistent with the previous linkage to chromosome 17q11-q21 in the population from PA and supports the functional role of ErbB2 in disease pathogenesis. To attempt to replicate these findings, six SNPs (rs2517955, rs2517956, rs1810132, rs2952156, rs1801200, rs1058808) were genotyped in a population-based sample of 570 leprosy cases and 370 controls from the state of Rio Grande do Norte (RN) and the results were analysed using logistic regression analysis. However, none of the associations were replicated in the RN sample, whether analysed for leprosy per se, LL leprosy, TT leprosy, erythema nodosum leprosum or reversal reaction conditions. The role of polymorphisms at ERBB2 in controlling susceptibility to leprosy in Brazil therefore remains unclear.