CYBB-Mediated Ferroptosis Associated with Immunosuppression in Mycobacterium leprae-Infected Monocyte-Derived Macrophages.

Mycobacterium leprae-infected macrophages preferentially exhibit the regulatory M2 phenotype in vitro, which helps the immune escape unabated growth of M leprae in host cells. The mechanism that triggers macrophage polarization is still unknown. In this study, we performed single-cell RNA sequencing to determine the initial responses of human monocyte-derived macrophages against M leprae infection of 4 healthy individuals and found an increase in a major alternative-activated macrophage type that overexpressed NEAT1, CCL2, and CD163. Importantly, further functional analysis showed that ferroptosis was positively correlated with M2 polarization of macrophages, and in vitro experiments have shown that inhibition of ferroptosis promotes the survival of M leprae within macrophages. In addition, further joint analysis of our results with mutisequencing data from patients with leprosy and in vitro validation identified that CYBB was the pivotal molecule for ferroptosis that could promote the M2 polarization of M leprae-infected macrophages, resulting in the immune escape and unabated growth of pathogenic bacteria. Overall, our results suggest that M leprae facilitated its survival by inducing CYBB-mediated macrophage ferroptosis leading to its alternative activation and might reveal the potential for a new therapeutic strategy of leprosy.

Mycobacterium leprae is able to infect adipocytes, inducing lipolysis and modulating the immune response.

Leprosy is a chronic infectious disease caused by the intracellular bacillus Mycobacterium leprae (M. leprae), which is known to infect skin macrophages and Schwann cells. Although adipose tissue is a recognized site of Mycobacterium tuberculosis infection, its role in the histopathology of leprosy was, until now, unknown. We analyzed the M. leprae capacity to infect and persist inside adipocytes, characterizing the induction of a lipolytic phenotype in adipocytes, as well as the effect of these infected cells on macrophage recruitment. We evaluated 3T3-L1-derived adipocytes, inguinal adipose tissue of SWR/J mice, and subcutaneous adipose tissue biopsies of leprosy patients. M. leprae was able to infect 3T3-L1-derived adipocytes in vitro, presenting a strong lipolytic profile after infection, followed by significant cholesterol efflux. This lipolytic phenotype was replicated in vivo by M. leprae injection into mice inguinal adipose tissue. Furthermore, M. leprae was detected inside crown-like structures in the subcutaneous adipose tissue of multibacillary patients. These data indicate that subcutaneous adipose tissue could be an important site of infection, and probably persistence, for M. leprae, being involved in the modulation of the innate immune control in leprosy via the release of cholesterol, MCP-1, and adiponectin.

Single-cell sequencing analysis reveals development and differentiation trajectory of Schwann cells manipulated by M. leprae.

BACKGROUND: M. leprae preferentially infects Schwann cells (SCs) in the peripheral nerves leading to nerve damage and irreversible disability. Knowledge of how M. leprae infects and interacts with host SCs is essential for understanding mechanisms of nerve damage and revealing potential new therapeutic strategies. METHODOLOGY/PRINCIPAL FINDINGS: We performed a time-course single-cell sequencing analysis of SCs infected with M. leprae at different time points, further analyzed the heterogeneity of SCs, subpopulations associated with M. leprae infection, developmental trajectory of SCs and validated by Western blot or flow cytometry. Different subpopulations of SCs exhibiting distinct genetic features and functional enrichments were present. We observed two subpopulations associated with M. leprae infection, a stem cell-like cell subpopulation increased significantly at 24 h but declined by 72 h after M. leprae infection, and an adipocyte-like cell subpopulation, emerged at 72 h post-infection. The results were validated and confirmed that a stem cell-like cell subpopulation was in the early stage of differentiation and could differentiate into an adipocyte-like cell subpopulation. CONCLUSIONS/SIGNIFICANCE: Our results present a systematic time-course analysis of SC heterogeneity after infection by M. leprae at single-cell resolution, provide valuable information to understand the critical biological processes underlying reprogramming and lipid metabolism during M. leprae infection of SCs, and increase understanding of the disease-causing mechanisms at play in leprosy patients as well as revealing potential new therapeutic strategies.

Immunology of leprosy.

Leprosy is a disease caused by Mycobacterium leprae (ML) with diverse clinical manifestations, which are strongly correlated with the host's immune response. Skin lesions may be accompanied by peripheral neural damage, leading to sensory and motor losses, as well as deformities of the hands and feet. Both innate and acquired immune responses are involved, but the disease has been classically described along a Th1/Th2 spectrum, where the Th1 pole corresponds to the most limited presentations and the Th2 to the most disseminated ones. We discuss this dichotomy in the light of current knowledge of cytokines, Th subpopulations and regulatory T cells taking part in each leprosy presentation. Leprosy reactions are associated with an increase in inflammatory activity both in limited and disseminated presentations, leading to a worsening of previous symptoms or the development of new symptoms. Despite the efforts of many research groups around the world, there is still no adequate serological test for diagnosis in endemic areas, hindering the eradication of leprosy in these regions.

The expression of FOXP3 in lesions of several forms of leprosy in patients co-infected with HIV.

BACKGROUND: Brazil remains endemic for infection by the human immunodeficiency virus (HIV) and leprosy, having a major impact on public health and the life quality of affected patients. Although the relevance of this co-infection is recognized, several aspects, such as the immune response, are not yet fully understood. The objective of this study was to investigate the expression of FOXP3+ Treg cells in leprosy skin lesions and to correlate their clinical forms, laboratory characteristics (CD4, CD8, and CV), and the immune reconstitution syndrome in HIV-leprosy co-infection. METHODOLOGY/PRINCIPAL FINDINGS: An observational, cross-sectional, and analytical study was carried out comparing four groups of patients: those with concomitant diagnosis of leprosy and HIV infection without a leprosy reaction, those with leprosy and HIV co-infection patients with a reverse reaction (RR), those with leprosy without HIV and without reaction, and those with leprosywithout HIV and with RR. The patients were diagnosed at a dermatology outpatient clinic located in Belém, Pará, Brazil, from 2003 to 2017. In the sample studied, there was a positive correlation between FOXP3+ cell density and viral load, negative correlation with blood CD4+ (not statistically significant), significant positive correlation in CD8 count in patients with leprosy reaction, and positive relationship in patients with IRIS. The density of cells expressing FOXP3 was higher in the BL/LL forms in patients without HIV, although the difference was not statistically significant. However, the cell mean was higher in the TT/BT forms in patients co-infected with leprosy and HIV, showing contradictory results. CONCLUSIONS/SIGNIFICANCE: These findings support that higher activity of the HIV may stimulate or result in a higher expression of FOXP3-Tregs and that they may be involved in active immunosuppression observed at the infection site at the tissue level. This supports the need to expand studies on FOXP3+ Treg cells in co-infected patients.

Leprosy in children in Cuba: Epidemiological and clinical description of 50 cases from 2012-2019.

INTRODUCTION: In 1993, Cuba achieved leprosy elimination according to the World Health Organization's (WHO) indicator of less than one case per 10,000 population. Despite this achievement, detection of new cases occurs every year among all age groups including children. Detection of new cases in children reveals persistent transmission of the infection. OBJECTIVE: To describe the clinical and epidemiological features of leprosy in individuals younger than 15 years (childhood leprosy) reported to the Cuban National Leprosy Control Program (NLCP) between 2012 and 2019. METHODS: We conducted a retrospective descriptive study between 2012 and 2019 to assess the clinical and epidemiologic features of individuals under the age of 15 years with a confirmed diagnosis of leprosy reported to the NLCP. We reviewed the NLCP database and collected data to better define the total number of cases of leprosy in adults, children (younger than 15 years). We assessed socio-demographic variables (age, gender, and province of residence) as well as variables of clinical interest including operational classification and staging at diagnosis, bacillary index, grade of disability by WHO staging. Additionally, we evaluated epidemiological variables including passive versus active surveillance of cases, contact investigation focusing specifically in household transmission, and the degree of kinship as well as standing of the child within the focus of transmission when there were additional cases. RESULTS: We identified fifty children during the study period corresponding to 3% of the overall cases of leprosy comprising all age groups in Cuba. In the age group younger than 15 years, the majorities of cases was from the Granma province and most were between the ages of 10 and 14 years. Clinically, multibacillary/lepromatous forms were the most common type identified with positive bacillary index. The majority of children diagnosed with leprosy during our study period had a history of a relative with a confirmed diagnosis of leprosy. CONCLUSIONS: Detection of cases of leprosy in individuals younger than 15 years of age in Cuba demonstrates ongoing transmission of M. leprae in specific geographic hotspots. Its frequency in the early adolescence, the predominant clinical forms, and the mode of detection associated with sources of suspected familiar infection demonstrated that there is a need for further efforts by the NLCP to conduct active surveillance activities among affected communities to identify cases of leprosy earlier with the goal of preventing further household and community transmission.

Innovative tracking, active search and follow-up strategies for new leprosy cases in the female prison population.

BACKGROUND: Regarding the leprosy transmission through the upper airways, overcrowded locations such as prisons can become a risk to get sick. Like the leprosy hidden endemic demonstrated in male prison population, being interesting to assess the leprosy scene also among confined women. METHODS: A prospective descriptive study conducted at Female Penitentiary, Brazil. Leprosy Suspicion Questionnaire (LSQ) were applied to the participants, and submitted to specialized dermatoneurological exam, peripheral nerve ultrasonography, and anti-PGL-I serology. FINDINGS: 404 female inmates were evaluated, 14 new cases were diagnosed (LG-leprosy group), a new case detection rate (NCDR) of 3.4%, 13 multibacillary, while another 390 constituted the Non-Leprosy group (NLG). Leprosy cases were followed up during multidrug therapy with clinical improvement. The confinement time median was 31 months in LG, similar to NLG, less than the time of leprosy incubation. Regarding LSQ, the neurological symptoms reached the highest x2 values as Q1-numbness (5.6), Q3-anesthetizes areas in the skin (7.5), Q5-Stinging sensation (5.8), and Q7-pain in the nerves (34.7), while Q4-spots on the skin was 4.94. When more than one question were marked in the LSQ means a 12.8-fold higher to have the disease than a subject who marked only one or none. The high 34% rate of anti-PGL-I seropositivity in the penitentiary, higher levels in LG than NLG. Three additional leprosy cases each were diagnosed on the second (n = 66) and third (n = 14) reevaluations 18 and 36 months after the initial one. Semmes-Weinstein monofilaments demonstrated lower limbs (32.2%) more affected than the upper limbs (25%) with improvement during the follow-up. INTERPRETATION: The NCDR in this population showed an hidden endemic of leprosy as well as the efficacy of a search action on the part of a specialized team with the aid of the LSQ and anti-PGL-I serology as an auxiliary tracking tools.

Mycobacterium leprae transmission characteristics during the declining stages of leprosy incidence: A systematic review.

BACKGROUND: Leprosy is an infectious disease caused by Mycobacterium leprae. As incidence begins to decline, the characteristics of new cases shifts away from those observed in highly endemic areas, revealing potentially important insights into possible ongoing sources of transmission. We aimed to investigate whether transmission is driven mainly by undiagnosed and untreated new leprosy cases in the community, or by incompletely treated or relapsing cases. METHODOLOGY/PRINCIPAL FINDINGS: A literature search of major electronic databases was conducted in January, 2020 with 134 articles retained out of a total 4318 records identified (PROSPERO ID: CRD42020178923). We presented quantitative data from leprosy case records with supporting evidence describing the decline in incidence across several contexts. BCG vaccination, active case finding, adherence to multidrug therapy and continued surveillance following treatment were the main strategies shared by countries who achieved a substantial reduction in incidence. From 3950 leprosy case records collected across 22 low endemic countries, 48.3% were suspected to be imported, originating from transmission outside of the country. Most cases were multibacillary (64.4%) and regularly confirmed through skin biopsy, with 122 cases of suspected relapse from previous leprosy treatment. Family history was reported in 18.7% of cases, while other suspected sources included travel to high endemic areas and direct contact with armadillos. None of the countries included in the analysis reported a distinct increase in leprosy incidence in recent years. CONCLUSIONS/SIGNIFICANCE: Together with socioeconomic improvement over time, several successful leprosy control programmes have been implemented in recent decades that led to a substantial decline in incidence. Most cases described in these contexts were multibacillary and numerous cases of suspected relapse were reported. Despite these observations, there was no indication that these cases led to a rise in new secondary cases, suggesting that they do not represent a large ongoing source of human-to-human transmission.

Loop-mediated isothermal amplification (LAMP) assay targeting RLEP for detection of Mycobacterium leprae in leprosy patients.

OBJECTIVE: Leprosy is a chronic infectious disease caused by Mycobacterium leprae and it remains a significant health problem in several parts of the world. Early and accurate diagnosis of this disease is therefore essential. Previously published loop-mediated isothermal amplification (LAMP) protocols for detecting mycobacterial species used conventional primers targeting the 16S rRNA, gyrB and insertion sequence genes. METHODS: In this study, we conducted a LAMP assay for leprosy and compared it with quantitative polymerase chain reaction (q-PCR) and conventional PCR assays to determine the efficiency, sensitivity and specificity of each technique. We chose conserved sequence RLEP as a suitable molecular target for assays. RESULTS: The LAMP assay provided rapid and accurate results, confirming leprosy in 91/110 clinical skin tissue samples from leprosy patients and amplifying the target pathogen in <60 min at 65 °C. The assay was more sensitive than conventional PCR and more straightforward and faster than the q-PCR assay. CONCLUSIONS: The LAMP assay has the potential for developing quicker, more accessible visual methods for the detection of M. leprae, which will enable early diagnosis and treatment and prevent further infection in endemic areas.

Mycobacterium leprae-helminth co-infections and vitamin D deficiency as potential risk factors for leprosy: A case-control study in south-eastern Brazil.

BACKGROUND: Evidence suggests that biological mechanisms involved in helminth infections and vitamin deficiencies increase susceptibility to other infections. The aim of this study was to investigate the associations of helminth co-infection and select micronutrient deficiencies with leprosy using a case-control design. METHODS: From 2016 to 2018, individuals aged ≥3 years were recruited at clinics in and around Governador Valadares, Minas Gerais, Brazil in three groups: cases of leprosy, household contacts and community-matched (non-contact) controls. Helminths were diagnosed through stool Kato Katz examination and serum reactivity to anti-soluble adult worm antigen preparation IgG4. Serum ferritin, 25-OH vitamin D and retinol concentrations were measured. Multi-variate logistic regression was conducted to identify associations with active leprosy. RESULTS: Seventy-nine cases of leprosy, 96 household contacts and 81 non-contact controls were recruited; 48.1% of participants were male with a median age of 40 years. Helminths were found in 7.1% of participants on Kato Katz test, all but one of which were Schistosoma mansoni, and 32.3% of participants were positive for S. mansoni serology. On multi-variate analysis, cases were more likely to be infected with helminths (diagnosed by stool) than household contacts [adjusted odds ratio (aOR) 8.69, 95% confidence interval (CI) 1.50-50.51]. Vitamin D deficiency was common, and was more likely in cases compared with non-contact controls (aOR 4.66, 95% CI 1.42,-15.33). Iron deficiency was not associated with leprosy, and vitamin A deficiency was not detected. CONCLUSION: These associations suggest that the immune consequences of schistosomiasis and vitamin D deficiency may increase the risk of active leprosy. Comorbid conditions of poverty deserve further study as addressing co-infections and nutritional deficiencies could be incorporated into programmes to improve leprosy control.

The function of peroxisome proliferator-activated receptors PPAR-γ and PPAR-δ in Mycobacterium leprae-induced foam cell formation in host macrophages.

Leprosy is a chronic infectious disease caused by Mycobacterium leprae (M. leprae). In lepromatous leprosy (LL), skin macrophages, harboring extensive bacterial multiplication, gain a distinctive foamy appearance due to increased intracellular lipid load. To determine the mechanism by which M. leprae modifies the lipid homeostasis in host cells, an in vitro M. leprae infection system, using human macrophage precursor THP-1 cells and M. leprae prepared from the footpads of nude mice, was employed. RNA extracted from skin smear samples of patients was used to investigate host gene expressions before and after multidrug therapy (MDT). We found that a cluster of peroxisome proliferator-activated receptor (PPAR) target genes associated with adipocyte differentiation were strongly induced in M. leprae-infected THP-1 cells, with increased intracellular lipid accumulation. PPAR-δ and PPAR-γ expressions were induced by M. leprae infection in a bacterial load-dependent manner, and their proteins underwent nuclear translocalization after infection, indicating activation of PPAR signaling in host cells. Either PPAR-δ or PPAR-γ antagonist abolished the effect of M. leprae to modify host gene expressions and inhibited intracellular lipid accumulation in host cells. M. leprae-specific gene expressions were detected in the skin smear samples both before and after MDT, whereas PPAR target gene expressions were dramatically diminished after MDT. These results suggest that M. leprae infection activates host PPAR signaling to induce an array of adipocyte differentiation-associated genes, leading to accumulation of intracellular lipids to accommodate M. leprae parasitization. Certain PPAR target genes in skin lesions may serve as biomarkers for monitoring treatment efficacy.

Macrophage Polarization in Leprosy-HIV Co-infected Patients.

In HIV-infected individuals, a paradoxical clinical deterioration may occur in preexisting leprosy when highly active antiretroviral therapy (HAART)-associated reversal reaction (RR) develops. Leprosy-HIV co-infected patients during HAART may present a more severe form of the disease (RR/HIV), but the immune mechanisms related to the pathogenesis of leprosy-HIV co-infection remain unknown. Although the adaptive immune responses have been extensively studied in leprosy-HIV co-infected individuals, recent studies have described that innate immune cells may drive the overall immune responses to mycobacterial antigens. Monocytes are critical to the innate immune system and play an important role in several inflammatory conditions associated with chronic infections. In leprosy, different tissue macrophage phenotypes have been associated with the different clinical forms of the disease, but it is not clear how HIV infection modulates the phenotype of innate immune cells (monocytes or macrophages) during leprosy. In the present study, we investigated the phenotype of monocytes and macrophages in leprosy-HIV co-infected individuals, with or without RR. We did not observe differences between the monocyte profiles in the studied groups; however, analysis of gene expression within the skin lesion cells revealed that the RR/HIV group presents a higher expression of macrophage scavenger receptor 1 (MRS1), CD209 molecule (CD209), vascular endothelial growth factor (VEGF), arginase 2 (ARG2), and peroxisome proliferator-activated receptor gamma (PPARG) when compared with the RR group. Our data suggest that different phenotypes of tissue macrophages found in the skin from RR and RR/HIV patients could differentially contribute to the progression of leprosy.

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.

PGL-1 and LID-1 antibody levels in HIV-infected and HIV-uninfected individuals in a Hansen's disease (leprosy) endemic area of Brazil.

Serological tests for subclinical Mycobacterium leprae infection based on antibodies to phenolic glycolipid-1 (PGL-1) and leprosy IDRI diagnostic-1 (LID-1) have not been compared in HIV-infected and uninfected individuals. PGL-1 seropositivity by ELISA was 6.0 % (21/350) in HIV-infected compared with 29.1 % (102/350) in HIV-uninfected individuals (p < 0.001); LID-1 seropositivity was 45.4 % (159/350) in HIV-infected compared with 50.3 % (153/304) in HIV-uninfected individuals (p = 0.21). In HIV-infected individuals, LID-1 but not PGL-1 antibody levels were inversely associated with CD4+ cell count (p = 0.02). These differential associations of HIV infection and CD4 count with PGL-1 and LID-1 have implications for M leprae immunodiagnostic tools and require replication.

Intracellular Mycobacterium leprae Utilizes Host Glucose as a Carbon Source in Schwann Cells.

New approaches are needed to control leprosy, but understanding of the biology of the causative agent Mycobacterium leprae remains rudimentary, principally because the pathogen cannot be grown in axenic culture. Here, we applied 13C isotopomer analysis to measure carbon metabolism of M. leprae in its primary host cell, the Schwann cell. We compared the results of this analysis with those of a related pathogen, Mycobacterium tuberculosis, growing in its primary host cell, the macrophage. Using 13C isotopomer analysis with glucose as the tracer, we show that whereas M. tuberculosis imports most of its amino acids directly from the host macrophage, M. leprae utilizes host glucose pools as the carbon source to biosynthesize the majority of its amino acids. Our analysis highlights the anaplerotic enzyme phosphoenolpyruvate carboxylase required for this intracellular diet of M. leprae, identifying this enzyme as a potential antileprosy drug target.IMPORTANCE Leprosy remains a major problem in the world today, particularly affecting the poorest and most disadvantaged sections of society in the least developed countries of the world. The long-term aim of research is to develop new treatments and vaccines, and these aims are currently hampered by our inability to grow the pathogen in axenic culture. In this study, we probed the metabolism of M. leprae while it is surviving and replicating inside its primary host cell, the Schwann cell, and compared it to a related pathogen, M. tuberculosis, replicating in macrophages. Our analysis revealed that unlike M. tuberculosis, M. leprae utilized host glucose as a carbon source and that it biosynthesized its own amino acids, rather than importing them from its host cell. We demonstrated that the enzyme phosphoenolpyruvate carboxylase plays a crucial role in glucose catabolism in M. leprae Our findings provide the first metabolic signature of M. leprae in the host Schwann cell and identify novel avenues for the development of antileprosy drugs.

Effectiveness of single-dose rifampicin after BCG vaccination to prevent leprosy in close contacts of patients with newly diagnosed leprosy: A cluster randomized controlled trial.

OBJECTIVE: To assess the effectiveness of single-dose rifampicin (SDR) after bacillus Calmette-Guérin (BCG) vaccination in preventing leprosy in contacts. METHODS: This was a single-centre, cluster-randomized controlled trial at a leprosy control programme in northwest Bangladesh. Participants were the 14988 contacts of 1552 new leprosy patients who were randomized into the SDR-arm (n=7379) and the SDR+arm (n=7609). In the intervention group, BCG vaccination was followed by SDR 8-12 weeks later. In the control group, BCG vaccination only was given. Follow-up was performed at 1year and 2 years after intake. The main outcome measure was the occurrence of leprosy. RESULTS: The incidence rate per 10000 person-years at risk was 44 in the SDR-arm and 31 in the SDR+arm at 1year; the incidence rate was 34 in the SDR-arm and 41 in the SDR+arm at 2 years. There was a statistically non-significant (p=0.148; 42%) reduction for paucibacillary (PB) leprosy in the SDR+ arm at 1 year. Of all new cases, 33.6% appeared within 8-12 weeks after BCG vaccination. CONCLUSIONS: In the first year, SDR after BCG vaccination reduced the incidence of PB leprosy among contacts by 42%. This was a statistically non-significant reduction due to the limited number of cases after SDR was administered. To what extent SDR suppresses excess leprosy cases after BCG vaccination is difficult to establish because many cases appeared before the SDR intervention. TRIAL REGISTRATION: Netherlands Trial Register: NTR3087.

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.

M. leprae interacts with the human epidermal keratinocytes, neonatal (HEKn) via the binding of laminin-5 with α-dystroglycan, integrin-ß1, or -ß4.

Although Mycobacterium leprae (M.leprae) is usually found in macrophages and nerves of the dermis of patients with multibacillary leprosy, it is also present in all layers of the epidermis, basal, suprabasal, prickle cells, and keratin layers. However, the mechanism by which M.leprae invades the dermis remains unknown, whereas the underlying mechanism by which M.leprae invades peripheral nerves, especially Schwann cells, is well defined. M. leprae binds to the α-dystroglycan (DG) of Schwann cells via the interaction of α-DG and laminin (LN) -α2 in the basal lamina, thus permitting it to become attached to and invade peripheral nerves. In the current study, we investigated the issue of how M.leprae is phagocytosed by human epidermal keratinocytes, neonatal (HEKn). LN-5 is the predominant form of laminin in the epidermis and allows the epidermis to be stably attached to the dermis via its interaction with α/ß-DG as well as integrins that are produced by keratinocytes. We therefore focused on the role of LN-5 when M. leprae is internalized by HEKn cells. Our results show that M.leprae preferentially binds to LN-5-coated slides and this binding to LN-5 enhances its binding to HEKn cells. The findings also show that pre-treatment with an antibody against α-DG, integrin-ß1, or -ß4 inhibited the binding of LN-5-coated M.leprae to HEKn cells. These results suggest that M. leprae binds to keratinocytes by taking advantage of the interaction of LN-5 in the basal lamina of the epidermis and a surface receptor of keratinocytes, such as α-DG, integrin-ß1, or -ß4.

Mycobacterium leprae's evolution and environmental adaptation.

Leprosy is an ancient disease caused by the acid-fast bacillus Mycobacterium leprae, also known as Hansen's bacillus. M. leprae is an obligate intracellular microorganism with a marked Schwann cell tropism and is the only human pathogen capable of invading the superficial peripheral nerves. The transmission mechanism of M. leprae is not fully understood; however, the nasal mucosa is accepted as main route of M. leprae entry to the human host. The complete sequencing and the comparative genome analysis show that M. leprae underwent a genome reductive evolution process, as result of lifestyle change and adaptation to different environments; some of lost genes are homologous to those of host cells. Thus, M. leprae reduced its genome size to 3.3 Mbp, contributing to obtain the lowest GC content (approximately 58%) among mycobacteria. The M. leprae genome contains 1614 open reading frames coding for functional proteins, and 1310 pseudogenes corresponding to 41% of the genome, approximately. Comparative analyses to different microorganisms showed that M. leprae possesses the highest content of pseudogenes among pathogenic and non-pathogenic bacteria and archaea. The pathogen adaptation into host cells, as the Schwann cells, brought about the reduction of the genome and induced multiple gene inactivation. The present review highlights the characteristics of genome's reductive evolution that M. leprae experiences in the genetic aspects compared with other pathogens. The possible mechanisms of pseudogenes formation are discussed.

Life history tradeoffs in humans: increased life expectancy with sperm count reduction.

Although not without controversy, as a general trend, the human sperm count is declining world-wide. One major reason for such a decline is an increase in the human life-span.  According to the life history tradeoff theory, fecundity is inversely related to the lifespan; the longer the lifespan, the lower the fecundity. This is essential to the maintainance of diversity and balance of different species. Such a corrleation validated by experimental data that show that the extension of life in Caenorhabditis elegans, Drosophila and Rodents is  associated with reduction in fecundity. The demographic data from a public data source, shows that the total fertility rate is positively correlated with the infant death rate, it is inversely correlated with the life expectancy. We postulate that the fall in spermatogenesis might be regulated by the neuroendocrine system that underlie human longevity.