Single-Cell RNA Sequencing of Microglia throughout the Mouse Lifespan and in the Injured Brain Reveals Complex Cell-State Changes.

Microglia, the resident immune cells of the brain, rapidly change states in response to their environment, but we lack molecular and functional signatures of different microglial populations. Here, we analyzed the RNA expression patterns of more than 76,000 individual microglia in mice during development, in old age, and after brain injury. Our analysis uncovered at least nine transcriptionally distinct microglial states, which expressed unique sets of genes and were localized in the brain using specific markers. The greatest microglial heterogeneity was found at young ages; however, several states-including chemokine-enriched inflammatory microglia-persisted throughout the lifespan or increased in the aged brain. Multiple reactive microglial subtypes were also found following demyelinating injury in mice, at least one of which was also found in human multiple sclerosis lesions. These distinct microglia signatures can be used to better understand microglia function and to identify and manipulate specific subpopulations in health and disease.

Targeted evolution of adeno-associated virus capsids for systemic transgene delivery to microglia and tissue-resident macrophages.

Tissue macrophages, including microglia, are notoriously resistant to genetic manipulation. Here, we report the creation of Adeno-associated viruses (AAV) variants that efficiently and widely transduce microglia and tissue macrophages in vivo following intravenous delivery, with transgene expression of up to 80%. We use this technology to demonstrate manipulation of microglia gene expression and microglial ablation, thereby providing invaluable research tools for the study of these important cells.

Niche stiffness underlies the ageing of central nervous system progenitor cells.

Ageing causes a decline in tissue regeneration owing to a loss of function of adult stem cell and progenitor cell populations1. One example is the deterioration of the regenerative capacity of the widespread and abundant population of central nervous system (CNS) multipotent stem cells known as oligodendrocyte progenitor cells (OPCs)2. A relatively overlooked potential source of this loss of function is the stem cell 'niche'-a set of cell-extrinsic cues that include chemical and mechanical signals3,4. Here we show that the OPC microenvironment stiffens with age, and that this mechanical change is sufficient to cause age-related loss of function of OPCs. Using biological and synthetic scaffolds to mimic the stiffness of young brains, we find that isolated aged OPCs cultured on these scaffolds are molecularly and functionally rejuvenated. When we disrupt mechanical signalling, the proliferation and differentiation rates of OPCs are increased. We identify the mechanoresponsive ion channel PIEZO1 as a key mediator of OPC mechanical signalling. Inhibiting PIEZO1 overrides mechanical signals in vivo and allows OPCs to maintain activity in the ageing CNS. We also show that PIEZO1 is important in regulating cell number during CNS development. Thus we show that tissue stiffness is a crucial regulator of ageing in OPCs, and provide insights into how the function of adult stem and progenitor cells changes with age. Our findings could be important not only for the development of regenerative therapies, but also for understanding the ageing process itself.

Neuronal vulnerability and multilineage diversity in multiple sclerosis.

Multiple sclerosis (MS) is a neuroinflammatory disease with a relapsing-remitting disease course at early stages, distinct lesion characteristics in cortical grey versus subcortical white matter and neurodegeneration at chronic stages. Here we used single-nucleus RNA sequencing to assess changes in expression in multiple cell lineages in MS lesions and validated the results using multiplex in situ hybridization. We found selective vulnerability and loss of excitatory CUX2-expressing projection neurons in upper-cortical layers underlying meningeal inflammation; such MS neuron populations exhibited upregulation of stress pathway genes and long non-coding RNAs. Signatures of stressed oligodendrocytes, reactive astrocytes and activated microglia mapped most strongly to the rim of MS plaques. Notably, single-nucleus RNA sequencing identified phagocytosing microglia and/or macrophages by their ingestion and perinuclear import of myelin transcripts, confirmed by functional mouse and human culture assays. Our findings indicate lineage- and region-specific transcriptomic changes associated with selective cortical neuron damage and glial activation contributing to progression of MS lesions.

Author Correction: Niche stiffness underlies the ageing of central nervous system progenitor cells.

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

Fatigue in early rheumatoid arthritis: data from the Early Rheumatoid Arthritis Network.

OBJECTIVES: Fatigue is a disabling symptom in people with RA. This study aims to describe the prevalence, risk factors and longitudinal course of fatigue in early RA. METHODS: Demographic, clinical, quality of life (QoL), comorbidities and laboratory data were from the Early RA Network (ERAN), a UK multicentre inception cohort of people with RA. Fatigue was measured using the vitality subscale of the 36-item Short Form Health Survey, where higher values represent better QoL. Baseline prevalences of fatigue classifications were age and sex standardized. Linear regression, hierarchical growth curve modelling and group-based trajectory modelling (GBTM) were utilized. RESULTS: At baseline (n = 1236, 67% female, mean age 57 years), the mean vitality was 41 (s.d. 11) and disease duration was 11 months (interquartile range 7-18). Age- and sex-standardized prevalence rates of fatigue and severe fatigue were 44% (95% CI 39, 50) and 19% (95% CI 15, 23), respectively. Fatigue changed little over 3 years and five measurement occasions ß = -0.13 (95% CI -0.23, -0.02). GBTM identified two subgroups, which we named 'Fatigue' (53%) and 'No-fatigue' (47%). Female sex, worse pain, mental health and functional ability were associated with greater fatigue and predicted Fatigue group membership (area under the receiver operating characteristics curve = 0.81). Objective measures of inflammation-swollen joint count and ESR-were not significantly associated with fatigue. CONCLUSIONS: Fatigue is prevalent and persistent in early RA. Diverse characteristics indicative of central mechanisms are associated with persistent fatigue. Management of fatigue might require interventions targeted at central mechanisms in addition to inflammatory disease modification. People who require such interventions might be identified at presentation with early RA.

Predictors of poor function in RA based on two prospective UK inception cohorts. Do comorbidities matter?

OBJECTIVES: Evidence suggests that factors beyond disease activity associate with functional disability in RA. The primary study objective was to explore associations between comorbidities, sociodemographic factors and functional outcomes at five and 10 years. METHODS: RA patients from two UK prospective cohorts were grouped into low (<1.5) and high (≥1.5) five- and 10-year health assessment questionnaire (HAQ) score. Clinical variables (e.g. disease activity, rheumatoid nodules, erosions) and sociodemographic factors (e.g. ethnicity, deprivation) were recorded at baseline and yearly thereafter. Comorbidity was measured using the Rheumatic Diseases Comorbidity Index (RDCI). Binary logistic regression models were fitted using multiple imputation. RESULTS: In total, 2701 RA patients were recruited (mean age 56.1 years, 66.9% female). A total of 1718 (63.4%) had five-year and 820 (30.4%) 10-year follow-up data. In multivariable analysis, no association was found between RDCI and HAQ ≥ 1.5 at five or 10 years. Sociodemographic factors (increased age at disease onset, female gender, minority ethnicity) were associated with higher odds of HAQ ≥ 1.5 at five and 10 years, with worse deprivation additionally associated with HAQ ≥ 1.5 at 10 years (OR 0.79, 95% CI: 0.69, 0.90). CONCLUSION: Comorbidities at baseline have not been found to be associated with worse RA functional outcome in the long-term. On the other hand, sociodemographic factors, independently of disease measures, are associated with worse functional outcome in RA at five and 10 years, in models adjusting for comorbidity burden. Tailoring management interventions according to not only clinical disease parameters but also patient sociodemographic factors may improve long-term outcomes including functional disability.

The role of comorbidities alongside patient and disease characteristics in long-term disease activity in RA using UK inception cohort data.

OBJECTIVES: Control of disease activity in RA is a crucial part of its management to prevent long-term joint damage and disability. This study aimed to identify early predictors of poor disease activity at 5 and 10 years, focusing on comorbidities and clinical/sociodemographic factors at first presentation. METHODS: Patients from two UK-based RA cohorts were classified into two groups; low (<3.2) and moderate/high (≥3.2) DAS using 28 joint counts (DAS28) at 5/10 years. Clinical variables (e.g. rheumatoid nodules, erosions), sociodemographic factors (e.g. ethnicity, deprivation) and comorbidities were recorded at baseline and yearly thereafter. The Rheumatic Diseases Comorbidity Index quantified patient comorbidity burden. Binary logistic regression models (outcome low vs moderate/high DAS28) were fitted using multiple imputation. RESULTS: A total of 2701 patients living with RA were recruited (mean age 56.1 years, 66.9% female); 5-year data were available for 1718 (63.4%) patients and 10-year data for 820 (30.4%). Baseline Rheumatic Diseases Comorbidity Index was not associated with DAS28 at 5 [odds ratio (OR) 1.05, 95% CI 0.91, 1.22] or 10 years (OR 0.99, 95% CI 0.75, 1.31) in multivariable analyses. Sociodemographic factors (female gender, worse deprivation) and poorer baseline HAQ-Disability Index were associated with DAS28 ≥3.2 at both timepoints. Being seropositive was associated with 5-year DAS28 ≥3.2. CONCLUSION: This study demonstrates an association between sociodemographic and clinical factors and long-term RA disease activity, in models adjusting for comorbidity burden. The findings call for more holistic and targeted patient management in patients with RA and provide insights for more individualized management plans even on first presentation to rheumatology.

Exploring the disparity between inflammation and disability in the 10-year outcomes of people with rheumatoid arthritis.

OBJECTIVES: To identify groups of people with RA with different disability trajectories over 10 years, despite comparable levels of inflammation. METHODS: Data for this analysis came from three European prospective cohort studies of people with RA [Norfolk Arthritis Register (NOAR), Early RA Network (ERAN), Étude et Suivi des Polyarthrites Indifférenciées Récentes (ESPOIR)]. Participants were assessed regularly over 8 (ERAN) to 10 (NOAR/ESPOIR) years. Inclusion criteria were: recruited after 1 January 2000, <24 months baseline symptom duration, and disability (HAQ) and inflammation [two-component DAS28 (DAS28-2C)] recorded at baseline and at one other follow-up. People in each cohort also completed patient-reported outcome measures at each assessment (pain, fatigue, depressive symptoms). Group-based trajectory models were used to identify distinct groups of people with similar HAQ and DAS28-2C trajectories over follow-up. RESULTS: This analysis included 2500 people with RA (NOAR: 1000, ESPOIR: 766, ERAN: 734). ESPOIR included more women and the participants were younger [mean (standard deviation) age: NOAR: 57.1 (14.6), ESPOIR: 47.6 (12.5), ERAN: 56.8 (13.8); women: NOAR: 63.9%, ESPOIR: 76.9%, ERAN: 69.1%). Within each cohort, two pairs of trajectories following the hypothesized pattern (comparable DAS28-2Cs but different HAQs) were identified. Higher pain, fatigue and depressive symptoms were associated with increased odds of being in the high HAQ trajectories. CONCLUSION: Excess disability is persistent in RA. Controlling inflammation may not be sufficient to alleviate disability in all people with RA, and effective pain, fatigue and mood management may be needed in some groups to improve long-term function.

Large joints are progressively involved in rheumatoid arthritis irrespective of rheumatoid factor status-results from the early rheumatoid arthritis study.

This study aimed to examine the progression of large joint involvement from early to established RA in terms of range of movement (ROM) and time to joint surgery, according to the presence of rheumatoid factor (RF). We used a historical longitudinal cohort of early RA patients. Patients were deemed RF negative if all repeated assessments were negative. The rate of progression from normal to any loss of range of movement (ROM) from years 3 to 14 were modelled using generalized estimating equations, for elbows, wrists, hips, knees and ankle, adjusting for confounders. Time to joint surgery was analysed using multivariable Cox models. A total of 1458 patients were included (66% female, mean age 55 years) and 74% were RF-positive. The prevalence of any loss of ROM, from year 3 through to 14 was highest in the wrist followed by ankle, knee, elbow and hip. Odds of loss of ROM increased over time in all joint regions assessed, at around 7-13% per year from year 3 to 14. Time to surgery was similar according to RF-status for the wrist and ankle, but RF-positive cases had a lower hazard of surgery at the elbow (HR 0.37, 0.15-0.90), hip (HR 0.69, 0.48-0.99) and after 10 years at the knee (HR 0.41, 0.25-0.68). Large joints become progressively involved in RA, most frequently affecting the wrist followed by ankle, which is overlooked in composite disease activity indices. RF-negative and positive cases progressed similarly. Treat-to-target approaches should be followed irrespective of RF status.

The microbiota regulates murine inflammatory responses to toxin-induced CNS demyelination but has minimal impact on remyelination.

The microbiota is now recognized as a key influence on the host immune response in the central nervous system (CNS). As such, there has been some progress toward therapies that modulate the microbiota with the aim of limiting immune-mediated demyelination, as occurs in multiple sclerosis. However, remyelination-the regeneration of myelin sheaths-also depends upon an immune response, and the effects that such interventions might have on remyelination have not yet been explored. Here, we show that the inflammatory response during CNS remyelination in mice is modulated by antibiotic or probiotic treatment, as well as in germ-free mice. We also explore the effect of these changes on oligodendrocyte progenitor cell differentiation, which is inhibited by antibiotics but unaffected by our other interventions. These results reveal that high combined doses of oral antibiotics impair oligodendrocyte progenitor cell responses during remyelination and further our understanding of how mammalian regeneration relates to the microbiota.

Seasonal variation in the canopy color of temperate evergreen conifer forests.

Evergreen conifer forests are the most prevalent land cover type in North America. Seasonal changes in the color of evergreen forest canopies have been documented with near-surface remote sensing, but the physiological mechanisms underlying these changes, and the implications for photosynthetic uptake, have not been fully elucidated. Here, we integrate on-the-ground phenological observations, leaf-level physiological measurements, near surface hyperspectral remote sensing and digital camera imagery, tower-based CO2 flux measurements, and a predictive model to simulate seasonal canopy color dynamics. We show that seasonal changes in canopy color occur independently of new leaf production, but track changes in chlorophyll fluorescence, the photochemical reflectance index, and leaf pigmentation. We demonstrate that at winter-dormant sites, seasonal changes in canopy color can be used to predict the onset of canopy-level photosynthesis in spring, and its cessation in autumn. Finally, we parameterize a simple temperature-based model to predict the seasonal cycle of canopy greenness, and we show that the model successfully simulates interannual variation in the timing of changes in canopy color. These results provide mechanistic insight into the factors driving seasonal changes in evergreen canopy color and provide opportunities to monitor and model seasonal variation in photosynthetic activity using color-based vegetation indices.

The use and context of the term 'multimorbidity' in rheumatoid arthritis: a systematic literature review.

This systematic literature review aimed to analyse terms describing coexisting conditions in the RA literature, informing the need for an operationalized definition of multimorbidity. Articles discussing RA with multimorbidity, published 1946 until August 2020, were identified. The primary outcome was the use and/or definition of 'multimorbidity' in RA. Information extracted included terms defining coexisting conditions, the use of a comorbidity/multimorbidity score and the use of 'index disease' to describe RA (more applicable to comorbidity than multimorbidity). Thirty-nine articles were included. Eight articles used the term 'multimorbidity', 18 used 'comorbidity' and 12 used both terms, 7 synonymously. One used no term. Fourteen articles fully defined the term. The number of co-existing conditions described in included studies was one-121. Twelve articles used a comorbidity/multimorbidity score. Four articles described RA as the 'index disease'. Our results demonstrate inconsistent use of the term multimorbidity. Improved assessment of multimorbidity is indicated in RA patients, including an operationalized use and definition.

Rheumatoid arthritis related interstitial lung disease - improving outcomes over 25 years: a large multicentre UK study.

OBJECTIVE: This study explores whether the prognosis of interstitial lung disease in rheumatoid arthritis (RA-ILD) has improved over time and assesses the potential influence of drug therapy in a large multicentre UK network. METHODS: We analysed data from 18 UK centres on patients meeting criteria for both RA and ILD diagnosed over a 25-year period. Data included age, disease duration, outcome and cause of death. We compared all cause and respiratory mortality between RA controls and RA-ILD patients, assessing the influence of specific drugs on mortality in four quartiles based on year of diagnosis. RESULTS: A total of 290 RA-ILD patients were identified. All cause (respiratory) mortality was increased at 30% (18%) compared with controls 21% (7%) (P =0.02). Overall, prognosis improved over quartiles with median age at death rising from 63 years to 78 years (P =0.01). No effect on mortality was detected as a result of DMARD use in RA-ILD. Relative risk (RR) of death from any cause was increased among patients who had received anti-TNF therapy [2.09 (1.1-4.0)] P =0.03, while RR was lower in those treated with rituximab [0.52(0.1-2.1)] or mycophenolate [0.65 (0.2-2.0)]. Patients receiving rituximab as their first biologic had longer three (92%), five (82%) and seven year (80%) survival than those whose first biologic was an anti-TNF agent (82%, 76% and 64%, respectively) (P =0.037). DISCUSSION: This large retrospective multicentre study demonstrates survival of patients with RA-ILD has improved. This may relate to the increasing use of specific immunosuppressive and biologic agents.

Secular changes in the progression of clinical markers and patient-reported outcomes in early rheumatoid arthritis.

OBJECTIVES: To examine secular trends in the progression of clinical and patient-reported outcomes in early RA. METHODS: A total of 2701 patients recruited to the Early Rheumatoid Arthritis Study or Early Rheumatoid Arthritis Network with year of diagnosis from 1986 to 2011. The 5-year progression rates for patients diagnosed at different points in time were modelled using mixed-effects regression; 1990, 2002 and 2010, were compared. Clinical markers of disease included the 28-joint count DAS and the ESR. Patient-reported markers included the HAQ, visual analogue scale of pain and global health, and the Short-Form 36. RESULTS: Statistically significant improvements in both 28-joint count DAS and ESR were seen over the 5 years in patients diagnosed with RA compared with those diagnosed earlier. By 5 years, 59% of patients with diagnosis in 2010 were estimated to reach low disease activity compared with 48% with diagnosis in 2002 and 32% with diagnosis in 1990. Whilst HAQ demonstrated statistically significant improvements, these improvements were small, with similar proportions of patients achieving HAQ scores of ≤1.0 by 5 years with a diagnosis in 1990 compared with 2010. Levels of the visual analogue scale and the Mental Component Scores of the Short-Form 36 indicated similar, statistically non-significant levels over the 5 years, irrespective of year diagnosed. CONCLUSION: This study demonstrates improvements in inflammatory markers over time in early RA, in line with improved treatment strategies. These have not translated into similar improvements in patient-reported outcomes relating to either physical or mental health.

Remission vs low disease activity: function, quality of life and structural outcomes in the Early Rheumatoid Arthritis Study and Network.

OBJECTIVES: To examine associations between function, quality of life and structural outcomes in patients achieving remission vs low disease activity in early RA. METHODS: Demographic, clinical and radiographic variables were collected at baseline and then annually from the Early Rheumatoid Arthritis Study (ERAS) and Early Rheumatoid Arthritis Network (ERAN) inception cohorts in routine care from 1986 to 2012. Disease activity was categorized: mean DAS28 score between years 1 and 5: remission [mean remission DAS (mRDAS) <2.6] or low [mean low DAS (mLDAS) 2.6-3.2]; sustained low/remission DAS28 (sLDAS/sRDAS) at years 1 and 2; and sustained Boolean remission (sBR) at years 1 and 2. Changes in HAQ and Short Form 36 Health Survey Questionnaire [SF-36; physical (PCS) and mental (MCS) component score]) and total Sharp van der Heijde (SvdH) scores for each disease activity category were modelled using multi-level models. Covariates included year of onset, age, gender and DMARD use at first visit. RESULTS: Of 2701 patients, 562 (21%) were categorized mRDAS, 330 (12%) mLDAS, 279 (10%) sRDAS, 203 (7.5%) sLDAS and 93 (3%) sBR. Patients categorized as mRDAS had increasingly divergent improved HAQ, SF-36 PCS, MCS and total SvdH scores compared with mLDAS (P-values 0.001 to <0.0001, all time points). Patients categorized as sRDAS had better HAQ, SF-36 PCS and MCS scores (P-values 0.05 to <0.0001, all time points) and SvdH scores (P = 0.05, years 3-5) over sLDAS. sBR was associated with better HAQ, and SF-36 PCS and MCS scores over sLDAS (P-values 0.002 to <0.0001, all time points). CONCLUSION: These findings from routine care support ACR/EULAR guidelines that remission is a preferable goal over low disease activity in early RA.

Correction to: Niacin-mediated rejuvenation of macrophage/microglia enhances remyelination of the aging central nervous system.

The article Niacin­mediated rejuvenation of macrophage/microglia enhances remyelination of the aging central nervous system, written by Khalil S. Rawji, Adam M.H. Young, Tanay Ghosh, Nathan J. Michaels, Reza Mirzaei, Janson Kappen, Kathleen L. Kolehmainen, Nima Alaeiilkhchi, Brian Lozinski, Manoj K. Mishra, Annie Pu, Weiwen Tang, Salma Zein, Deepak K. Kaushik, Michael B. Keough, Jason R. Plemel, Fiona Calvert, Andrew J. Knights, Daniel J. Gaffney, Wolfram Tetzlaff, Robin J. M. Franklin and V. Wee Yong, was originally published electronically on the publisher's internet.

Niacin-mediated rejuvenation of macrophage/microglia enhances remyelination of the aging central nervous system.

Remyelination following CNS demyelination restores rapid signal propagation and protects axons; however, its efficiency declines with increasing age. Both intrinsic changes in the oligodendrocyte progenitor cell population and extrinsic factors in the lesion microenvironment of older subjects contribute to this decline. Microglia and monocyte-derived macrophages are critical for successful remyelination, releasing growth factors and clearing inhibitory myelin debris. Several studies have implicated delayed recruitment of macrophages/microglia into lesions as a key contributor to the decline in remyelination observed in older subjects. Here we show that the decreased expression of the scavenger receptor CD36 of aging mouse microglia and human microglia in culture underlies their reduced phagocytic activity. Overexpression of CD36 in cultured microglia rescues the deficit in phagocytosis of myelin debris. By screening for clinically approved agents that stimulate macrophages/microglia, we have found that niacin (vitamin B3) upregulates CD36 expression and enhances myelin phagocytosis by microglia in culture. This increase in myelin phagocytosis is mediated through the niacin receptor (hydroxycarboxylic acid receptor 2). Genetic fate mapping and multiphoton live imaging show that systemic treatment of 9-12-month-old demyelinated mice with therapeutically relevant doses of niacin promotes myelin debris clearance in lesions by both peripherally derived macrophages and microglia. This is accompanied by enhancement of oligodendrocyte progenitor cell numbers and by improved remyelination in the treated mice. Niacin represents a safe and translationally amenable regenerative therapy for chronic demyelinating diseases such as multiple sclerosis.

Dynamic Electric Field Alignment of Metal-Organic Framework Microrods.

Alignment of metal-organic framework (MOF) crystals has previously been performed via careful control of oriented MOF growth on substrates, as well as by dynamic magnetic alignment. We show here that bromobenzene-suspended microrod crystals of the MOF NU-1000 can also be dynamically aligned via electric fields, giving rise to rapid electrooptical responses. This method of dynamic MOF alignment opens up new avenues of MOF control which are important for integration of MOFs into switchable electronic devices as well as in other applications such as reconfigurable sensors or optical systems.

Correction: Modelling outcomes after paediatric brain injury with admission laboratory values: a machine-learning approach.

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