Microglia and Central Nervous System-Associated Macrophages-From Origin to Disease Modulation.

The immune system of the central nervous system (CNS) consists primarily of innate immune cells. These are highly specialized macrophages found either in the parenchyma, called microglia, or at the CNS interfaces, such as leptomeningeal, perivascular, and choroid plexus macrophages. While they were primarily thought of as phagocytes, their function extends well beyond simple removal of cell debris during development and diseases. Brain-resident innate immune cells were found to be plastic, long-lived, and host to an outstanding number of risk genes for multiple pathologies. As a result, they are now considered the most suitable targets for modulating CNS diseases. Additionally, recent single-cell technologies enhanced our molecular understanding of their origins, fates, interactomes, and functional cell statesduring health and perturbation. Here, we review the current state of our understanding and challenges of the myeloid cell biology in the CNS and treatment options for related diseases.

Mechanisms of myeloid cell entry to the healthy and diseased central nervous system.

Myeloid cells in the central nervous system (CNS), such as microglia, CNS-associated macrophages (CAMs), dendritic cells and monocytes, are vital for steady-state immune homeostasis as well as the resolution of tissue damage during brain development or disease-related pathology. The complementary usage of multimodal high-throughput and high-dimensional single-cell technologies along with recent advances in cell-fate mapping has revealed remarkable myeloid cell heterogeneity in the CNS. Despite the establishment of extensive expression profiles revealing myeloid cell multiplicity, the local anatomical conditions for the temporal- and spatial-dependent cellular engraftment are poorly understood. Here we highlight recent discoveries of the context-dependent mechanisms of myeloid cell migration and settlement into distinct subtissular structures in the CNS. These insights offer better understanding of the factors needed for compartment-specific myeloid cell recruitment, integration and residence during development and perturbation, which may lead to better treatment of CNS diseases.

Author Correction: Novel Hexb-based tools for studying microglia in the CNS.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Novel Hexb-based tools for studying microglia in the CNS.

Microglia and central nervous system (CNS)-associated macrophages (CAMs), such as perivascular and meningeal macrophages, are implicated in virtually all diseases of the CNS. However, little is known about their cell-type-specific roles in the absence of suitable tools that would allow for functional discrimination between the ontogenetically closely related microglia and CAMs. To develop a new microglia gene targeting model, we first applied massively parallel single-cell analyses to compare microglia and CAM signatures during homeostasis and disease and identified hexosaminidase subunit beta (Hexb) as a stably expressed microglia core gene, whereas other microglia core genes were substantially downregulated during pathologies. Next, we generated HexbtdTomato mice to stably monitor microglia behavior in vivo. Finally, the Hexb locus was employed for tamoxifen-inducible Cre-mediated gene manipulation in microglia and for fate mapping of microglia but not CAMs. In sum, we provide valuable new genetic tools to specifically study microglia functions in the CNS.

A Subset of Skin Macrophages Contributes to the Surveillance and Regeneration of Local Nerves.

The skin comprises tissue macrophages as the most abundant resident immune cell type. Their diverse tasks including resistance against invading pathogens, attraction of bypassing immune cells from vessels, and tissue repair require dynamic specification. Here, we delineated the postnatal development of dermal macrophages and their differentiation into subsets by adapting single-cell transcriptomics, fate mapping, and imaging. Thereby we identified a phenotypically and transcriptionally distinct subset of prenatally seeded dermal macrophages that self-maintained with very low postnatal exchange by hematopoietic stem cells. These macrophages specifically interacted with sensory nerves and surveilled and trimmed the myelin sheath. Overall, resident dermal macrophages contributed to axon sprouting after mechanical injury. In summary, our data show long-lasting functional specification of macrophages in the dermis that is driven by stepwise adaptation to guiding structures and ensures codevelopment of ontogenetically distinct cells within the same compartment.

Specification of CNS macrophage subsets occurs postnatally in defined niches.

All tissue-resident macrophages of the central nervous system (CNS)-including parenchymal microglia, as well as CNS-associated macrophages (CAMs1) such as meningeal and perivascular macrophages2-7-are part of the CNS endogenous innate immune system that acts as the first line of defence during infections or trauma2,8-10. It has been suggested that microglia and all subsets of CAMs are derived from prenatal cellular sources in the yolk sac that were defined as early erythromyeloid progenitors11-15. However, the precise ontogenetic relationships, the underlying transcriptional programs and the molecular signals that drive the development of distinct CAM subsets in situ are poorly understood. Here we show, using fate-mapping systems, single-cell profiling and cell-specific mutants, that only meningeal macrophages and microglia share a common prenatal progenitor. By contrast, perivascular macrophages originate from perinatal meningeal macrophages only after birth in an integrin-dependent manner. The establishment of perivascular macrophages critically requires the presence of arterial vascular smooth muscle cells. Together, our data reveal a precisely timed process in distinct anatomical niches for the establishment of macrophage subsets in the CNS.

Direct neuronal conversion of microglia/macrophages reinstates neurological function after stroke.

Although generating new neurons in the ischemic injured brain would be an ideal approach to replenish the lost neurons for repairing the damage, the adult mammalian brain retains only limited neurogenic capability. Here, we show that direct conversion of microglia/macrophages into neurons in the brain has great potential as a therapeutic strategy for ischemic brain injury. After transient middle cerebral artery occlusion in adult mice, microglia/macrophages converge at the lesion core of the striatum, where neuronal loss is prominent. Targeted expression of a neurogenic transcription factor, NeuroD1, in microglia/macrophages in the injured striatum enables their conversion into induced neuronal cells that functionally integrate into the existing neuronal circuits. Furthermore, NeuroD1-mediated induced neuronal cell generation significantly improves neurological function in the mouse stroke model, and ablation of these cells abolishes the gained functional recovery. Our findings thus demonstrate that neuronal conversion contributes directly to functional recovery after stroke.

Mapping the origin and fate of myeloid cells in distinct compartments of the eye by single-cell profiling.

Similar to the brain, the eye is considered an immune-privileged organ where tissue-resident macrophages provide the major immune cell constituents. However, little is known about spatially restricted macrophage subsets within different eye compartments with regard to their origin, function, and fate during health and disease. Here, we combined single-cell analysis, fate mapping, parabiosis, and computational modeling to comprehensively examine myeloid subsets in distinct parts of the eye during homeostasis. This approach allowed us to identify myeloid subsets displaying diverse transcriptional states. During choroidal neovascularization, a typical hallmark of neovascular age-related macular degeneration (AMD), we recognized disease-specific macrophage subpopulations with distinct molecular signatures. Our results highlight the heterogeneity of myeloid subsets and their dynamics in the eye that provide new insights into the innate immune system in this organ which may offer new therapeutic targets for ophthalmological diseases.

Author Correction: Spatial and temporal heterogeneity of mouse and human microglia at single-cell resolution.

In this Letter, Dominic Grün and Sagar have been added to the author list (affiliated with Max-Planck-Institute of Immunology and Epigenetics (MPI-IE), Freiburg, Germany). The author list, 'Author contribution' and 'Acknowledgements' sections have been corrected online. See accompanying Amendment.

Spatial and temporal heterogeneity of mouse and human microglia at single-cell resolution.

Microglia have critical roles not only in neural development and homeostasis, but also in neurodegenerative and neuroinflammatory diseases of the central nervous system1-4. These highly diverse and specialized functions may be executed by subsets of microglia that already exist in situ, or by specific subsets of microglia that develop from a homogeneous pool of cells on demand. However, little is known about the presence of spatially and temporally restricted subclasses of microglia in the central nervous system during development or disease. Here we combine massively parallel single-cell analysis, single-molecule fluorescence in situ hybridization, advanced immunohistochemistry and computational modelling to comprehensively characterize subclasses of microglia in multiple regions of the central nervous system during development and disease. Single-cell analysis of tissues of the central nervous system during homeostasis in mice revealed specific time- and region-dependent subtypes of microglia. Demyelinating and neurodegenerative diseases evoked context-dependent subtypes of microglia with distinct molecular hallmarks and diverse cellular kinetics. Corresponding clusters of microglia were also identified in healthy human brains, and the brains of patients with multiple sclerosis. Our data provide insights into the endogenous immune system of the central nervous system during development, homeostasis and disease, and may also provide new targets for the treatment of neurodegenerative and neuroinflammatory pathologies.

Microglial Cytokines Mediate Plasticity Induced by 10 Hz Repetitive Magnetic Stimulation.

Microglia, the resident immune cells of the CNS, sense the activity of neurons and regulate physiological brain functions. They have been implicated in the pathology of brain diseases associated with alterations in neural excitability and plasticity. However, experimental and therapeutic approaches that modulate microglia function in a brain region-specific manner have not been established. In this study, we tested for the effects of repetitive transcranial magnetic stimulation (rTMS), a clinically used noninvasive brain stimulation technique, on microglia-mediated synaptic plasticity; 10 Hz electromagnetic stimulation triggered a release of plasticity-promoting cytokines from microglia in mouse organotypic brain tissue cultures of both sexes, while no significant changes in microglial morphology or microglia dynamics were observed. Indeed, substitution of tumor necrosis factor α (TNFα) and interleukin 6 (IL6) preserved synaptic plasticity induced by 10 Hz stimulation in the absence of microglia. Consistent with these findings, in vivo depletion of microglia abolished rTMS-induced changes in neurotransmission in the mPFC of anesthetized mice of both sexes. We conclude that rTMS affects neural excitability and plasticity by modulating the release of cytokines from microglia.SIGNIFICANCE STATEMENT Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive brain stimulation technique that induces cortical plasticity. Despite its wide use in neuroscience and clinical practice (e.g., depression treatment), the cellular and molecular mechanisms of rTMS-mediated plasticity remain not well understood. Herein, we report an important role of microglia and plasticity-promoting cytokines in synaptic plasticity induced by 10 Hz rTMS in organotypic slice cultures and anesthetized mice, thereby identifying microglia-mediated synaptic adaptation as a target of rTMS-based interventions.

Redefining the ontogeny of hyalocytes as yolk sac-derived tissue-resident macrophages of the vitreous body.

BACKGROUND: The eye is a highly specialized sensory organ which encompasses the retina as a part of the central nervous system, but also non-neural compartments such as the transparent vitreous body ensuring stability of the eye globe and a clear optical axis. Hyalocytes are the tissue-resident macrophages of the vitreous body and are considered to play pivotal roles in health and diseases of the vitreoretinal interface, such as proliferative vitreoretinopathy or diabetic retinopathy. However, in contrast to other ocular macrophages, their embryonic origin as well as the extent to which these myeloid cells might be replenished by circulating monocytes remains elusive. RESULTS: In this study, we combine transgenic reporter mice, embryonic and adult fate mapping approaches as well as parabiosis experiments with multicolor immunofluorescence labeling and confocal laser-scanning microscopy to comprehensively characterize the murine hyalocyte population throughout development and in adulthood. We found that murine hyalocytes express numerous well-known myeloid cell markers, but concomitantly display a distinct immunophenotype that sets them apart from retinal microglia. Embryonic pulse labeling revealed a yolk sac-derived origin of murine hyalocytes, whose precursors seed the developing eye prenatally. Finally, postnatal labeling and parabiosis established the longevity of hyalocytes which rely on Colony Stimulating Factor 1 Receptor (CSF1R) signaling for their maintenance, independent of blood-derived monocytes. CONCLUSION: Our study identifies hyalocytes as long-living progeny of the yolk sac hematopoiesis and highlights their role as integral members of the innate immune system of the eye. As a consequence of their longevity, immunosenescence processes may culminate in hyalocyte dysfunction, thereby contributing to the development of vitreoretinal diseases. Therefore, myeloid cell-targeted therapies that convey their effects through the modification of hyalocyte properties may represent an interesting approach to alleviate the burden imposed by diseases of the vitreoretinal interface.

Lineage tracing identifies in vitro microglia-to-neuron conversion by NeuroD1 expression.

Neuronal regeneration to replenish lost neurons after injury is critical for brain repair. Microglia, brain-resident macrophages that have the propensity to accumulate at the site of injury, can be a potential source for replenishing lost neurons through fate conversion into neurons, induced by forced expression of neuronal lineage-specific transcription factors. However, it has not been strictly demonstrated that microglia, rather than central nervous system-associated macrophages, such as meningeal macrophages, convert into neurons. Here, we show that NeuroD1-transduced microglia can be successfully converted into neurons in vitro using lineage-mapping strategies. We also found that a chemical cocktail treatment further promoted NeuroD1-induced microglia-to-neuron conversion. NeuroD1 with loss-of-function mutation, on the other hand, failed to induce the neuronal conversion. Our results indicate that microglia are indeed reprogrammed into neurons by NeuroD1 with neurogenic transcriptional activity.

Macrophages at CNS interfaces: ontogeny and function in health and disease.

The segregation and limited regenerative capacity of the CNS necessitate a specialized and tightly regulated resident immune system that continuously guards the CNS against invading pathogens and injury. Immunity in the CNS has generally been attributed to neuron-associated microglia in the parenchyma, whose origin and functions have recently been elucidated. However, there are several other specialized macrophage populations at the CNS borders, including dural, leptomeningeal, perivascular and choroid plexus macrophages (collectively known as CNS-associated macrophages (CAMs)), whose origins and roles in health and disease have remained largely uncharted. CAMs are thought to be involved in regulating the fine balance between the proper segregation of the CNS, on the one hand, and the essential exchange between the CNS parenchyma and the periphery, on the other. Recent studies that have been empowered by major technological advances have shed new light on these cells and suggest central roles for CAMs in CNS physiology and in the pathogenesis of diseases.

Factors associated with death, hospitalization, resignation, and sick leave from work among patients with schizophrenia in Japan: a nested case-control study using a large claims database.

BACKGROUND: Premature mortality, frequent relapse that easily leads to hospitalization, and discontinuous employment are key challenges for the treatment of schizophrenia. We evaluated risk factors for important clinical outcomes (death, hospitalization, resignation, and sick leave from work) in patients with schizophrenia in Japan. METHODS: A nested case-control study was conducted for patients with schizophrenia identified in a Japanese claims database. For each outcome, the case was matched with up to four controls of the same age, sex, index year, and enrollment status (employee or dependent family). Potential risk factors were defined by prescriptions or diagnoses within 3 months prior to or in the month of the event. The association among potential risk factors and each outcome was evaluated using multivariable conditional logistic regression analysis with stepwise variable selection. RESULTS: The number of cases and eligible patients for each outcome were 144 and 38,451 (death), 1,520 and 35,225 (hospitalization), 811 and 18,770 (resignation), and 4,590 and 18,770 (sick leave), respectively. Depression was a risk factor for death (odds ratio [OR]: 1.92; 95% confidence interval [CI]: 1.12, 3.29), hospitalization (OR: 1.22; 95% CI: 1.05, 1.42), and sick leave from work (OR: 1.46; 95% CI: 1.36, 1.57). Other risk factors for death were hospitalization history, Charlson Comorbidity Index (CCI) score, and prescription for laxatives. Prescriptions for hypnotics, laxatives, and anticholinergics were risk factors for hospitalization. Prescriptions for hypnotics and anticholinergics were risk factors for resignation. CCI score, prescription for hypnotics, laxatives, and antidiabetics were risk factors for sick leave from work. CONCLUSIONS: Our findings suggest that depression and some physical symptoms, such as constipation and extrapyramidal symptoms, are risk factors for important clinical outcomes in patients with schizophrenia. Attention should be paid to both depression and physical symptoms for the treatment of schizophrenia.

Prognostic significance of preoperative osteosarcopenia on patient' outcomes after emergency surgery for gastrointestinal perforation.

PURPOSE: Sarcopenia is a prognostic predictor in emergency surgery. However, there are no reports on the relationship between osteopenia and in-hospital mortality. This study clarified the effect of preoperative osteosarcopenia on patients with gastrointestinal perforation after emergency surgery. METHODS: We included 216 patients with gastrointestinal perforations who underwent emergency surgery between January 2013 and December 2022. Osteopenia was evaluated by measuring the pixel density in the mid-vertebral core of the 11th thoracic vertebra. Sarcopenia was evaluated by measuring the area of the psoas muscle at the level of the third lumbar vertebra. Osteosarcopenia is defined as the combination of osteopenia and sarcopenia. RESULTS: Osteosarcomas were identified in 42 patients. Among patients with osteosarcopenia, older and female patients and those with an American Society of Anesthesiologists Physical Status of ≥ 3 were significantly more common, and the body mass index, hemoglobin value, and albumin level were significantly lower in these patients than in patients without osteosarcopenia. Furthermore, the osteosarcopenia group presented with more postoperative complications than patients without osteosarcopenia (P < 0.01). In the multivariate analysis, age ≥ 74 years old (P = 0.04) and osteosarcopenia (P = 0.04) were independent and significant predictors of in-hospital mortality. CONCLUSION: Preoperative osteosarcopenia is a risk factor of in-hospital mortality in patients with gastrointestinal perforation after emergency surgery.

Prognostic significance of the preoperative C-reactive protein-albumin-lymphocyte (CALLY) index on outcomes after gastrectomy for gastric cancer.

PURPOSE: Systemic inflammatory response markers are reported to be prognostic for patients with cancer. The C-reactive protein (CRP)-albumin-lymphocyte (CALLY) index has been established as an immuno-nutritional scoring system. The aim of this study was to clarify the impact of the preoperative CALLY index on the outcome of patients undergoing gastrectomy for gastric cancer. METHODS: We analyzed the data of 826 patients who underwent gastrectomy for stage I, II, or III gastric cancer between 2010 and 2017. The CALLY index was defined as (albumin × lymphocyte)/(CRP × 104). RESULTS: The cut-off of the CALLY index was 2. The 147 patients with a preoperative CALLY index < 2 had significantly worse overall survival (OS) and relapse-free survival (RFS) than those with a CALLY index ≥ 2 (P < 0.01, P < 0.01, respectively). Multivariate analysis identified that a CALLY index < 2 (P = 0.02), intraoperative blood loss (P < 0.01), and stage II or III disease (P < 0.01) were independent and significant predictors of worse RFS. A CALLY index < 2 (P = 0.01), intraoperative blood loss (P < 0.01), postoperative complications (P = 0.02), and stage II or III disease (P < 0.01) were independent and significant predictors of worse OS. CONCLUSION: The preoperative CALLY index was independently associated with a poor prognosis for patients after gastrectomy for gastric cancer.

Is it meaningful to add mesh reinforcement to laparoscopic fundoplication for esophageal hiatal hernias in the patients with high risk of hiatal hernia recurrence?

BACKGROUND: While laparoscopic fundoplication is a standard surgical procedure for patients with esophageal hiatal hernias, the postoperative recurrence of esophageal hiatal hernias is a problem for patients with giant hernias, elderly patients, or obese patients. Although there are some reports indicating that reinforcement with mesh is effective, there are differing opinions regarding the use thereof. The aim of this study is to investigate whether mesh reinforcement is effective for laparoscopic fundoplication in patients with esophageal hiatus hernias. METHODS: The subjects included 280 patients who underwent laparoscopic fundoplication as the initial surgery for giant esophageal hiatal hernias, elderly patients aged 75 years or older, and obese patients with a BMI of 28 or higher, who were considered at risk of recurrent hiatal hernias based on the previous reports. Of the subject patients, 91 cases without mesh and 86 cases following the stabilization of mesh use were extracted to compare the postoperative course including the pathology, symptom scores, surgical outcome, and recurrence of esophageal hiatus hernias. RESULTS: The preoperative conditions indicated that the degree of esophageal hiatal hernias was high in the mesh group (p = 0.0001), while the preoperative symptoms indicated that the score of heartburn was high in the non-mesh group (p = 0.0287). Although the surgical results indicated that the mesh group underwent a longer operation time (p < 0.0001) and a higher frequency of intraoperative complications (p = 0.037), the rate of recurrence of esophageal hiatal hernia was significantly low (p = 0.049), with the rate of postoperative reflux esophagitis also tending to be low (p = 0.083). CONCLUSIONS: Mesh reinforcement in laparoscopic fundoplication for esophageal hiatal hernias contributes to preventing the recurrence of esophageal hiatal hernias when it comes to patient options based on these criteria.

Role of modified Glasgow Prognostic Score in patients with achalasia who underwent laparoscopic Heller-myotomy with Dor-fundoplication.

BACKGROUND: Systemic inflammatory response is significant prognostic indicator in patients with various diseases. The relationship between prognostic scoring systems based on the modified Glasgow Prognostic Score (mGPS) and achalasia in patients treated with laparoscopic Heller­myotomy with Dor­fundoplication (LHD) remains uninvestigated. This study aimed to examine the role of mGPS in patients with achalasia. METHODS: 457 patients with achalasia who underwent LHD as the primary surgery between September 2005 and December 2020 were included. We divided patients into the mGPS 0 and mGPS 1 or 2 groups and compared the patients' background, pathophysiology, symptoms, surgical outcomes, and postoperative course. RESULTS: mGPS was 0 in 379 patients and 1 or 2 in 78 patients. Preoperative vomiting and pneumonia were more common in patients with mGPS of 1 or 2. There were no differences in surgical outcomes. Postoperative upper gastrointestinal endoscopy revealed that severe esophagitis was more frequently observed in patients with mGPS of 1 or 2 (P < 0.01). The clinical success was 91% and 99% in the mGPS 0 and mGPS 1 or 2 groups, respectively (P < 0.01). CONCLUSIONS: Although severe reflux esophagitis was more common in patients with achalasia with a high mGPS, good clinical success was obtained regardless of the preoperative mGPS.

Improving the Diagnostic Yield of High-Resolution Esophageal Manometry for GERD: The "Straight Leg-Raise" International Study.

BACKGROUND & AIMS: The straight leg raise (SLR) maneuver during high-resolution manometry (HRM) can assess esophagogastric junction (EGJ) barrier function by measuring changes in intraesophageal pressure (IEP) when intra-abdominal pressure is increased. We aimed to determine whether increased esophageal pressure during SLR predicts pathologic esophageal acid exposure time (AET). METHODS: Adult patients with persistent gastroesophageal reflux disease (GERD) symptoms undergoing HRM and pH-impedance or wireless pH study off proton pump inhibitor were prospectively studied between July 2021 and March 2022. After the HRM Chicago 4.0 protocol, patients were requested to elevate 1 leg at 45º for 5 seconds while supine. The SLR maneuver was considered effective when intra-abdominal pressure increased by 50%. IEPs were recorded 5 cm above the lower esophageal sphincter at baseline and during SLR. GERD was defined as AET greater than 6%. RESULTS: The SLR was effective in 295 patients (81%), 115 (39%) of whom had an AET greater than 6%. Hiatal hernia (EGJ type 2 or 3) was seen in 135 (46%) patients. Compared with patients with an AET less than 6%, peak IEP during SLR was significantly higher in the GERD group (29.7 vs 13.9 mm Hg; P < .001). Using receiver operating characteristic analysis, an increase of 11 mm Hg of peak IEP from baseline during SLR was the optimal cut-off value to predict an AET greater than 6% (area under the receiver operating characteristic curve, 0.84; sensitivity, 79%; and specificity, 85%), regardless of the presence of hiatal hernia. On multivariable analysis, an IEP pressure increase during the SLR maneuver, EGJ contractile integral, EGJ subtype 2, and EGJ subtype 3, were found to be significant predictors of AET greater than 6% CONCLUSIONS: The SLR maneuver can predict abnormal an AET, thereby increasing the diagnostic value of HRM when GERD is suspected. CLINICALTRIALS: gov ID: NCT04813029.