Diurnal variation in inflammatory and immune function is evident in the physiology and pathology of humans and animals, but molecular mechanisms and mediating cell types that provide this gating remain unknown. By screening cytokine responses in mice to endotoxin challenge at different times of day, we reveal that the magnitude of response exhibited pronounced temporal dependence, yet only within a subset of proinflammatory cytokines. Disruption of the circadian clockwork in macrophages (primary effector cells of the innate immune system) by conditional targeting of a key clock gene ( bmal1 ) removed all temporal gating of endotoxin-induced cytokine response in cultured cells and in vivo. Loss of circadian gating was coincident with suppressed rev-erb α expression, implicating this nuclear receptor as a potential link between the clock and inflammatory pathways. This finding was confirmed in vivo and in vitro through genetic and pharmacological modulation of REV-ERB α activity. Circadian gating of endotoxin response was lost in rev-erb α ^−/− mice and in cultured macrophages from these animals, despite maintenance of circadian rhythmicity within these cells. Using human macrophages, which show circadian clock gene oscillations and rhythmic endotoxin responses, we demonstrate that administration of a synthetic REV-ERB ligand, or genetic knockdown of rev-erb α expression, is effective at modulating the production and release of the proinflammatory cytokine IL-6. This work demonstrates that the macrophage clockwork provides temporal gating of systemic responses to endotoxin, and identifies REV-ERBα as the key link between the clock and immune function. REV-ERBα may therefore represent a unique therapeutic target in human inflammatory disease.

The circadian clock in fibroblasts determines the efficiency of wound healing through rhythmic regulation of actin cytoskeletal dynamics.

Rationale: Shared symptoms and genetic architecture between coronavirus disease (COVID-19) and lung fibrosis suggest severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection may lead to progressive lung damage. Objectives: The UK Interstitial Lung Disease Consortium (UKILD) post–COVID-19 study interim analysis was planned to estimate the prevalence of residual lung abnormalities in people hospitalized with COVID-19 on the basis of risk strata. Methods: The PHOSP–COVID-19 (Post-Hospitalization COVID-19) study was used to capture routine and research follow-up within 240 days from discharge. Thoracic computed tomography linked by PHOSP–COVID-19 identifiers was scored for the percentage of residual lung abnormalities (ground-glass opacities and reticulations). Risk factors in linked computed tomography were estimated with Bayesian binomial regression, and risk strata were generated. Numbers within strata were used to estimate posthospitalization prevalence using Bayesian binomial distributions. Sensitivity analysis was restricted to participants with protocol-driven research follow-up. Measurements and Main Results: The interim cohort comprised 3,700 people. Of 209 subjects with linked computed tomography (median, 119 d; interquartile range, 83–155), 166 people (79.4%) had more than 10% involvement of residual lung abnormalities. Risk factors included abnormal chest X-ray (risk ratio [RR], 1.21; 95% credible interval [CrI], 1.05–1.40), percent predicted Dl CO less than 80% (RR, 1.25; 95% CrI, 1.00–1.56), and severe admission requiring ventilation support (RR, 1.27; 95% CrI, 1.07–1.55). In the remaining 3,491 people, moderate to very high risk of residual lung abnormalities was classified at 7.8%, and posthospitalization prevalence was estimated at 8.5% (95% CrI, 7.6–9.5), rising to 11.7% (95% CrI, 10.3–13.1) in the sensitivity analysis. Conclusions: Residual lung abnormalities were estimated in up to 11% of people discharged after COVID-19–related hospitalization. Health services should monitor at-risk individuals to elucidate long-term functional implications.

The circadian clock regulates many aspects of immunity. Bacterial infections are affected by time of day, but the mechanisms involved remain undefined. Here we show that loss of the core clock protein BMAL1 in macrophages confers protection against pneumococcal pneumonia. Infected mice show both reduced weight loss and lower bacterial burden in circulating blood. In vivo studies of macrophage phagocytosis reveal increased bacterial ingestion following Bmal1 deletion, which was also seen in vitro. BMAL1 ^−/− macrophages exhibited marked differences in actin cytoskeletal organization, a phosphoproteome enriched for cytoskeletal changes, with reduced phosphocofilin and increased active RhoA. Further analysis of the BMAL1 ^−/− macrophages identified altered cell morphology and increased motility. Mechanistically, BMAL1 regulated a network of cell movement genes, 148 of which were within 100 kb of high-confidence BMAL1 binding sites. Links to RhoA function were identified, with 29 genes impacting RhoA expression or activation. RhoA inhibition restored the phagocytic phenotype to that seen in control macrophages. In summary, we identify a surprising gain of antibacterial function due to loss of BMAL1 in macrophages, associated with a RhoA-dependent cytoskeletal change, an increase in cell motility, and gain of phagocytic function.

Pulmonary inflammatory responses lie under circadian control; however, the importance of circadian mechanisms in the underlying fibrotic phenotype is not understood. Here, we identify a striking change to these mechanisms resulting in a gain of amplitude and lack of synchrony within pulmonary fibrotic tissue. These changes result from an infiltration of mesenchymal cells, an important cell type in the pathogenesis of pulmonary fibrosis. Mutation of the core clock protein REVERBα in these cells exacerbated the development of bleomycin-induced fibrosis, whereas mutation of REVERBα in club or myeloid cells had no effect on the bleomycin phenotype. Knockdown of REVERBα revealed regulation of the little-understood transcription factor TBPL1. Both REVERBα and TBPL1 altered integrinβ1 focal-adhesion formation, resulting in increased myofibroblast activation. The translational importance of our findings was established through analysis of 2 human cohorts. In the UK Biobank, circadian strain markers (sleep length, chronotype, and shift work) are associated with pulmonary fibrosis, making them risk factors. In a separate cohort, REVERBα expression was increased in human idiopathic pulmonary fibrosis (IPF) lung tissue. Pharmacological targeting of REVERBα inhibited myofibroblast activation in IPF fibroblasts and collagen secretion in organotypic cultures from IPF patients, thus suggesting that targeting of REVERBα could be a viable therapeutic approach.