Circadian molecular clock disruption in chronic pulmonary diseases

Circadian clock disruption in the lung is associated with chronic pulmonary diseases such as asthma, chronic obstructive pulmonary disease (COPD), pulmonary fibrosis (PF), cystic fibrosis (CF), pulmonary arterial hypertension (PAH), and lung cancer.Cumulative evidence from preclinical models demonstrates the promising role of the circadian clock in modulating immune response and other associated phenotypes observed in chronic pulmonary diseases.Understanding the core molecular mechanisms contributing to circadian clock disruption in chronic lung diseases will help advance the development of novel clock-based therapeutics in the future. The circadian clock is the biochemical oscillator with a near 24-h period that is responsible for generating the circadian rhythms in peripheral organs including the lung. Mounting evidence suggests that circadian clock disruption during chronic lung diseases plays an essential role in augmented oxidative stress, inflammatory response, metabolic imbalances, hypoxia/hyperoxia, mucus secretion, dysregulated autophagy, and alters pulmonary function. Here, we review circadian clock disruption and discuss candidate clock genes that are altered at the transcriptional or translational level in chronic pulmonary diseases. This review aims to provide the current knowledge and understanding of the circadian molecular clock disruption in chronic pulmonary diseases which will further advance the development of novel clock-based therapeutics in the future. The circadian clock is the biochemical oscillator with a near 24-h period that is responsible for generating the circadian rhythms in peripheral organs including the lung. Mounting evidence suggests that circadian clock disruption during chronic lung diseases plays an essential role in augmented oxidative stress, inflammatory response, metabolic imbalances, hypoxia/hyperoxia, mucus secretion, dysregulated autophagy, and alters pulmonary function. Here, we review circadian clock disruption and discuss candidate clock genes that are altered at the transcriptional or translational level in chronic pulmonary diseases. This review aims to provide the current knowledge and understanding of the circadian molecular clock disruption in chronic pulmonary diseases which will further advance the development of novel clock-based therapeutics in the future. Circadian rhythms (see Glossary) are predictable intrinsic biological oscillations in physical, mental, and behavioral changes that follow a period near 24 h driven by the endogenous circadian clock. In mammals, the circadian clock evolved in a convergent process as a powerful tool to anticipate daily environmental changes and subsequently synchronize the internal biological functions. Accumulating evidence from literature suggests that lung function is greatly influenced by circadian rhythms. Increased night-time or early morning airway resistance in the lungs has been long appreciated in chronic inflammatory lung diseases such as asthma and chronic obstructive pulmonary disease (COPD) [1.Agusti A. et al.Night-time symptoms: a forgotten dimension of COPD.Eur. Respir. Rev. 2011; 20: 183-194Crossref PubMed Scopus (144) Google Scholar,2.Scheer F. et al.The endogenous circadian system worsens asthma at night independent of sleep and other daily behavioral or environmental cycles.Proc. Natl. Acad. Sci. U. S. A. 2021; 118e2018486118Crossref Scopus (6) Google Scholar]. During early morning hours, the lungs have an increased tolerance for carbon dioxide levels in the blood, which is evident through the diurnal variations in end-tidal carbon dioxide levels [3.Spengler C.M. et al.An endogenous circadian rhythm of respiratory control in humans.J. Physiol. 2000; 526: 683-694Crossref PubMed Google Scholar]. Prior studies have shown circadian variation in lung function is associated with differential CD4+ lymphocytes, blood, and sputum eosinophils in asthmatics [4.Kelly E.A. et al.Inflammatory changes associated with circadian variation in pulmonary function in subjects with mild asthma.Clin. Exp. Allergy. 2004; 34: 227-233Crossref PubMed Scopus (44) Google Scholar, 5.Bates M.E. et al.Relationship of plasma epinephrine and circulating eosinophils to nocturnal asthma.Am. J. Respir. Crit. Care Med. 1994; 149: 667-672Crossref PubMed Google Scholar, 6.Durrington H.J. et al.Time of day affects eosinophil biomarkers in asthma: implications for diagnosis and treatment.Am. J. Respir. Crit. Care Med. 2018; 198: 1578-1581Crossref PubMed Scopus (29) Google Scholar, 7.Panzer S.E. et al.Circadian variation of sputum inflammatory cells in mild asthma.J. Allergy Clin. Immunol. 2003; 111: 308-312Abstract Full Text Full Text PDF PubMed Scopus (55) Google Scholar]. Higher plasma concentrations of histamine are also observed during the night and early morning hours than in the evening, which contributes to airflow obstruction in patients with nocturnal asthma [8.Szefler S.J. et al.Plasma histamine, epinephrine, cortisol, and leukocyte beta-adrenergic receptors in nocturnal asthma.Clin. Pharmacol. Ther. 1991; 49: 59-68Crossref PubMed Google Scholar]. Proper entrainment and maintenance of the circadian rhythms in the lung are essential for normal lung function. Circadian clock disruption, either through genetic or environmental factors, is perceived as stress by the organism and affects the health either in the short- or long-term, leading to an increased risk for pulmonary diseases and metabolic syndromes [9.Nosal C. et al.Why lungs keep time: circadian rhythms and lung immunity.Annu. Rev. Physiol. 2020; 82: 391-412Crossref PubMed Scopus (14) Google Scholar]. Recent understanding of the molecular mechanisms controlling the circadian rhythms earned the 2017 Nobel Prize in Physiology or Medicine and changed the field of circadian biology into a highly dynamic thrust area for basic and translational research. Notably, the National Institute of Health (NIH) has taken great initiatives foreseeing the translational value of circadian research in medicine. The 2021 NIH Sleep Research Plan, ‘Advancing the science of sleep and circadian biology research’, highlights several key aspects of the circadian mechanism underlying health and disease, including the need to improve treatment of sleep and circadian disorders, reduce risks associated with circadian misalignment, and identify gaps and opportunities to accelerate the clinical implementation of circadian research. Critical opportunities (CO) are related to the strategic goals; CO5 emphasized the need to ‘develop chronotherapeutic approaches to prevent and treat chronic diseases’, which discusses adjusting the timing of treatments to circadian rhythms (‘chronotherapy’) (https://www.nhlbi.nih.gov/sleep-research-plan/critical-opportunities). However, there was no mention of the pharmacological approaches to target core clock molecules that have been recently shown to possess enormous potential in the development of novel clock-based therapeutics tested in preclinical models against chronic lung diseases. Circadian molecular clock disruption has been strongly implicated in the pathophysiology of several chronic lung diseases. Here, we provide an updated account of the circadian clock disruption in the pathophysiology of chronic lung diseases and finally highlight the knowledge gap, challenges, and limitations in circadian medicine that will help advance the development of novel clock-based therapeutics for the treatment and management of chronic lung diseases. The circadian machinery in mammals comprises a hierarchical network of oscillators that work in synchrony with one another at the cellular, tissue, and organ system level. Endogenous circadian clock consists of the central or the ‘master clock’ that resides in the suprachiasmatic nucleus (SCN) of the brain and regulates the ‘peripheral clocks’ (an independent clock residing in the peripheral organs such as the lungs, heart, liver, stomach, intestine, and kidneys) that is present virtually in every cell. Light is considered the most potent zeitgeber (or ‘time cue’) for the human body. The SCN primarily receives input in the form of light signals from the external environment via the intrinsically photosensitive retinal ganglion cells of the eye, which allow the master clock to synchronize with the external environment. Prior studies suggest that it is either through neuronal (sympathetic or parasympathetic) or hormonal signals (e.g., the release of melatonin from the pineal gland that induces sleep or glucocorticoids and catecholamines from the adrenal cortex via the hypothalamus–pituitary–adrenal axis) [10.Curtis A.M. et al.Circadian clock proteins and immunity.Immunity. 2014; 40: 178-186Abstract Full Text Full Text PDF PubMed Scopus (333) Google Scholar] that the SCN entrains the peripheral clocks [11.Honma S. The mammalian circadian system: a hierarchical multi-oscillator structure for generating circadian rhythm.J. Physiol. Sci. 2018; 68: 207-219Crossref PubMed Scopus (80) Google Scholar]. Although the central clock helps align the peripheral clock with the external environment, ablation of the SCN does not abolish the circadian rhythms in the peripheral clock completely, highlighting the endogenous, self-sustaining nature of the peripheral clocks [12.Yoo S.H. et al.PERIOD2::LUCIFERASE real-time reporting of circadian dynamics reveals persistent circadian oscillations in mouse peripheral tissues.Proc. Natl. Acad. Sci. U. S. A. 2004; 101: 5339-5346Crossref PubMed Scopus (1639) Google Scholar]. Prior reports have also highlighted the role of other zeitgebers, such as food intake time, exercise, or stress, that modulate the peripheral clock independently, thus further adding to the complexity of the overall circadian machinery [13.Mohawk J.A. et al.Central and peripheral circadian clocks in mammals.Annu. Rev. Neurosci. 2012; 35: 445-462Crossref PubMed Scopus (1231) Google Scholar]. The circadian molecular clock machinery that operates at the cellular level and generates circadian rhythms in peripheral organs such as the lung is summarized in Box 1 and Figure 1.Box 1Overview of the circadian clock in the lungAt a cellular level, circadian rhythms are generated by an autoregulatory negative feedback loop of interlocked transcription factors, collectively referred to as the clock genes. In mammals, important genes that regulate the circadian machinery are the Periods (Per1/2/3) and the Cryptochromes (Cry1/2). Transcription of the Per and Cry genes is tightly regulated by three feedback loops that operate in conjuncture with one another ensuring that a new cycle resets approximately every 24 h. The first core loop comprises the circadian locomotor output cycles kaput (CLOCK) and its paralog NPAS2. During the day, CLOCK teams up to form a heterodimer with Brain and Muscle ARNT-Like 1 (BMAL1) and drives the expression of the Per and Cry genes by direct binding to the E-box enhancer region. Later during the day, as PERs and CRYs reach a critical level, the proteins dimerize in the cytosol and translocate to the nucleus, where they interact with the CLOCK:BMAL1 complex to suppress their own transcriptional activity. Meanwhile, the cytosolic PER and the CRY proteins are also targeted for ubiquitination and subsequent degradation, which ensures the gradual decline of PER and CRY. With this continual decline, there is lesser inhibition of the CLOCK:BMAL1 complex and the transcriptional activity of the Per and Cry genes are restored (Figure 1).The second loop comprises the circadian oscillation of Bmal1, which is both negatively and positively regulated by two families of nuclear receptors namely, REV-ERBs (α and β) and RAR-related orphan receptors (RORs α, β, and γ) respectively, that are transcribed from the same E-box promoter driven by the CLOCK:BMAL1 complex and help stabilize the core loop. Both REV-ERBs and RORs compete to bind to the RORE in the Bmal1 promoter region and together fine-tune the expression of Bmal1 and ensure the antiphase oscillation of Bmal1 and the Per genes (Figure 1).The third loop comprises the D-box binding protein (DBP), Thyrotroph Embryonic Factor (TEF), and Hepatic Leukemia Factor (HLF), which are driven by the CLOCK:BMAL1 complex from the first loop and the repressor E4 promoter-binding protein 4 (E4BP4/NFIL3) regulated via the RORE as discussed in the second loop. Both DBP and NFIL3 competitively bind to the D-box promoter region to regulate the expression of D-box genes, including the Per and Ror genes [84.Yoshitane H. et al.Functional D-box sequences reset the circadian clock and drive mRNA rhythms.Commun Biol. 2019; 2: 300Crossref PubMed Scopus (17) Google Scholar]. In addition to this trilateral feedback system, the biological clock is also maintained via different post-translational modifications, including phosphorylation mediated by kinases such as casein kinase CKIα, CKIβδ, and CKIε, phosphatases like PP1 and PP5, and through histone modification via the histone acetyltransferase activity of the CLOCK [85.Doi M. et al.Circadian regulator CLOCK is a histone acetyltransferase.Cell. 2006; 125: 497-508Abstract Full Text Full Text PDF PubMed Scopus (631) Google Scholar] (Figure 1). At a cellular level, circadian rhythms are generated by an autoregulatory negative feedback loop of interlocked transcription factors, collectively referred to as the clock genes. In mammals, important genes that regulate the circadian machinery are the Periods (Per1/2/3) and the Cryptochromes (Cry1/2). Transcription of the Per and Cry genes is tightly regulated by three feedback loops that operate in conjuncture with one another ensuring that a new cycle resets approximately every 24 h. The first core loop comprises the circadian locomotor output cycles kaput (CLOCK) and its paralog NPAS2. During the day, CLOCK teams up to form a heterodimer with Brain and Muscle ARNT-Like 1 (BMAL1) and drives the expression of the Per and Cry genes by direct binding to the E-box enhancer region. Later during the day, as PERs and CRYs reach a critical level, the proteins dimerize in the cytosol and translocate to the nucleus, where they interact with the CLOCK:BMAL1 complex to suppress their own transcriptional activity. Meanwhile, the cytosolic PER and the CRY proteins are also targeted for ubiquitination and subsequent degradation, which ensures the gradual decline of PER and CRY. With this continual decline, there is lesser inhibition of the CLOCK:BMAL1 complex and the transcriptional activity of the Per and Cry genes are restored (Figure 1). The second loop comprises the circadian oscillation of Bmal1, which is both negatively and positively regulated by two families of nuclear receptors namely, REV-ERBs (α and β) and RAR-related orphan receptors (RORs α, β, and γ) respectively, that are transcribed from the same E-box promoter driven by the CLOCK:BMAL1 complex and help stabilize the core loop. Both REV-ERBs and RORs compete to bind to the RORE in the Bmal1 promoter region and together fine-tune the expression of Bmal1 and ensure the antiphase oscillation of Bmal1 and the Per genes (Figure 1). The third loop comprises the D-box binding protein (DBP), Thyrotroph Embryonic Factor (TEF), and Hepatic Leukemia Factor (HLF), which are driven by the CLOCK:BMAL1 complex from the first loop and the repressor E4 promoter-binding protein 4 (E4BP4/NFIL3) regulated via the RORE as discussed in the second loop. Both DBP and NFIL3 competitively bind to the D-box promoter region to regulate the expression of D-box genes, including the Per and Ror genes [84.Yoshitane H. et al.Functional D-box sequences reset the circadian clock and drive mRNA rhythms.Commun Biol. 2019; 2: 300Crossref PubMed Scopus (17) Google Scholar]. In addition to this trilateral feedback system, the biological clock is also maintained via different post-translational modifications, including phosphorylation mediated by kinases such as casein kinase CKIα, CKIβδ, and CKIε, phosphatases like PP1 and PP5, and through histone modification via the histone acetyltransferase activity of the CLOCK [85.Doi M. et al.Circadian regulator CLOCK is a histone acetyltransferase.Cell. 2006; 125: 497-508Abstract Full Text Full Text PDF PubMed Scopus (631) Google Scholar] (Figure 1). The importance of the peripheral clock in lung health and disease has expanded exponentially in the past decade. A critical review of the current literature reveals a strong association between circadian clock disruption and severe health consequences. In this section, we aim to provide an updated summary of the circadian clock regulation that underpins the pathophysiology of various chronic lung diseases including preclinical in vitro and in vivo studies (Table 1).Table 1Circadian clock in preclinical models of lung diseasesAgents that cause circadian disruptionExperimental models and conditionsKey findingsRefsHouse dust mite (HDM)WT and Rev-erbα KO mice exposed to HDM for 5 days/week for 3 weeks at ZT11 or ZT23Time-of-day differences in airway hyper-responsiveness (in vivo in mice and ex vivo in precision-cut lung slices) were observed in WT but not in Rev-erbα KO mice (possible role of muscarinic receptors Chrm1 and Chrm3 genes)[20.Durrington H.J. et al.Circadian asthma airway responses are gated by REV-ERBalpha.Eur. Respir. J. 2020; 561902407PubMed Google Scholar]Sendai and influenza A virus (IAV)Bmal1 KO mice exposed to viral agentBmal1 KO mice develop more asthma-like airway remodeling, inflammation, and hyperproduction of mucus[21.Ehlers A. et al.BMAL1 links the circadian clock to viral airway pathology and asthma phenotypes.Mucosal Immunol. 2018; 11: 97-111Crossref PubMed Scopus (61) Google Scholar]Ovalbumin-induced allergyBmal1 KO mice were exposed to allergens using ovalbuminBmal1 KO increased lung eosinophilia associated with a marked increase in Th2 cytokines[22.Zaslona Z. et al.The circadian protein BMAL1 in myeloid cells is a negative regulator of allergic asthma.Am. J. Phys. Lung Cell. Mol. Phys. 2017; 312: L855-L860Crossref PubMed Scopus (32) Google Scholar]Cigarette smoke (CS)Tumor-resistant C57 and tumor-susceptible AJ mice exposed to CS for 18 daysLevels of Nr1d1, Per1, Arntl, and Clock were suppressed by CS exposure[31.Vasu V.T. et al.Nr1d1, an important circadian pathway regulatory gene, is suppressed by cigarette smoke in murine lungs.Integr. Cancer Ther. 2009; 8: 321-328Crossref PubMed Scopus (26) Google Scholar]CSC57, Sirt1 KO, Sirt1 transgenic, and Bmal1-CreCC10 KO mice were exposed to CS for 3 days, 10 days, or 6 monthsCS exposure reduced SIRT1-BMAL1 activity/abundance, resulting in reduced locomotor activity, enhanced lung inflammation, and altered lung function[29.Hwang J.W. et al.Circadian clock function is disrupted by environmental tobacco/cigarette smoke, leading to lung inflammation and injury via a SIRT1-BMAL1 pathway.FASEB J. 2014; 28: 176-194Crossref PubMed Scopus (93) Google Scholar]CSC57 and Rev-erbα KO mice were exposed to CS for 10 days and 1 monthRev-erbα KO mice showed exaggerated inflammatory responses associated with an increase in cellular senescence markers[34.Sundar I.K. et al.The nuclear receptor and clock gene REV-ERBalpha regulates cigarette smoke-induced lung inflammation.Biochem. Biophys. Res. Commun. 2017; 493: 1390-1395Crossref PubMed Scopus (17) Google Scholar]CSC57 and Rev-erbα KO mice were exposed to CS for 1 month; C57 exposed to CS for 10 days with and without Rev-erbα agonist (SR9009)Rev-erbα deletion alters clock gene expression and CS-induced epithelial-mesenchymal transition and Rev-erbα agonist shows attenuation of that response[32.Wang Q. et al.Molecular clock REV-ERBalpha regulates cigarette smoke-induced pulmonary inflammation and epithelial-mesenchymal transition.JCI Insight. 2021; 6e145200Crossref Scopus (4) Google Scholar]BleomycinC57 and Clock Δ19 mutant mice were treated with bleomycinRedox-sensitive transcription factor NRF2 is regulated by BMAL1/CLOCK heterodimer in bleomycin-induced lung fibrosis[55.Pekovic-Vaughan V. et al.The circadian clock regulates rhythmic activation of the NRF2/glutathione-mediated antioxidant defense pathway to modulate pulmonary fibrosis.Genes Dev. 2014; 28: 548-560Crossref PubMed Scopus (158) Google Scholar]BleomycinRev-erbα fl/fl and Rev-erbα Pdgfrβ (fibroblast-specific KO) mice were treated with bleomycinRev-erbα Pdgfrβ KO mice show augmented fibrotic response compared with Rev-erbαfl/fl mice. Rev-erbα agonist (GSK4112) reduced the TGFβ-induced fibrogenesis in primary lung fibroblast via transcription factor TBPL1.[54.Cunningham P.S. et al.The circadian clock protein REVERBalpha inhibits pulmonary fibrosis development.Proc. Natl. Acad. Sci. U. S. A. 2020; 117: 1139-1147Crossref PubMed Scopus (21) Google Scholar]TGF-β1C57 mice were infected with TGF-β1 adenovirus (AdvTGF-β1)Bmal1 mRNA and protein levels were increased in AdvTGF-β1-infected mice associated with profibrotic response (increased collagen and reduced acetylated BMAL1) in the lungs[58.Dong C. et al.Regulation of transforming growth factor-beta1 (TGF-beta1)-induced pro-fibrotic activities by circadian clock gene BMAL1.Respir. Res. 2016; 17: 4Crossref PubMed Scopus (37) Google Scholar]Intermittent hypoxia (IH)C57 mice were exposed to normoxia (controls) or intermittent episodes of hypoxia (21–6% oxygen saturation) followed by recovery to 21% oxygen over the entire 12 h inactivity phase for 9 daysChanges circadian rhythms and immune pathways in the lungs. Nr1d1, Nr1d2, Bhlhe40, and Per3 were significantly upregulated in the IH group compared with the control[65.Wu G. et al.Short-term exposure to intermittent hypoxia leads to changes in gene expression seen in chronic pulmonary disease.Elife. 2021; 10e63003Crossref Scopus (4) Google Scholar]HypoxiaCultured cells exposed to low levels of oxygenTranscript levels of Rev-erbα, Rorα, Per1, Per2, and Cry2 are significantly upregulated[68.Adamovich Y. et al.Rhythmic oxygen levels reset circadian clocks through HIF1alpha.Cell Metab. 2017; 25: 93-101Abstract Full Text Full Text PDF PubMed Scopus (143) Google Scholar]HypoxiaWT and Per1/2 KO mice were exposed to 4 h hypoxia (6% O2) or normoxia (21% O2) at ZT 4–8 (light) or ZT 16–20 (dark) phaseHypoxia phase-shifted the expression of clock genes in a tissue-dependent manner causing inter-tissue circadian clock misalignment[69.Manella G. et al.Hypoxia induces a time- and tissue-specific response that elicits intertissue circadian clock misalignment.Proc. Natl. Acad. Sci. U.S.A. 2020; 117: 779-786Crossref PubMed Scopus (40) Google Scholar]Natural killer (NK) cell deficiencyNfil3 KO mice without NK cellsNfil3 KO mice spontaneously develop pulmonary arterial hypertension as they get older[71.Ratsep M.T. et al.Spontaneous pulmonary hypertension in genetic mouse models of natural killer cell deficiency.Am. J. Phys. Lung Cell. Mol. Phys. 2018; 315: L977-L990Crossref PubMed Scopus (15) Google Scholar]Lipopolysaccharide (LPS)WT and LysM-Bmal1–/– (PER2:luc background) and Rev-erbα KO were administered LPS intraperitoneally at CT0 or CT12Peritoneal exudate cells from LysM-Bmal1–/– showed nonrhythmic expression of Per2, Cry1, and Dbp and suppressed expression of Rev-erbα and Rev-erbβ. LPS-induced cytokine gating (IL-6) release was significantly higher at CT12 versus CT0 in WT but it was abolished in Rev-erbα KO mice.[87.Gibbs J.E. et al.The nuclear receptor REV-ERBalpha mediates circadian regulation of innate immunity through selective regulation of inflammatory cytokines.Proc. Natl. Acad. Sci. U. S. A. 2012; 109: 582-587Crossref PubMed Scopus (386) Google Scholar]LPSC57 and Bmal1 KO mice were challenged with LPS (2 or 3 days)Altered circadian clock gene expression in LPS-induced lung inflammation; Bmal1 role in recruiting granulocytes rhythmically in LPS-induced lung inflammation.[93.Haspel J.A. et al.Circadian rhythm reprogramming during lung inflammation.Nat. Commun. 2014; 5: 4753Crossref PubMed Scopus (83) Google Scholar]LPSBmal1 fl/fl, conditional club cell Bmal1 KO (Ccsp-Bmal1–/–), and myeloid cell Bmal1 KO (LysM-Bmal1–/–) mice were exposed to aerosolized LPS (~20 min)Ccsp-Bmal1–/– show disruption in rhythmic expression of Cxcl5 gene associated with an exaggerated inflammatory response to LPS and impaired host immune response to Streptococcus pneumonia infection. LysM-Bmal1–/– showed increased amplitude and phasing of neutrophils and cytokines as observed in Bmal1 fl/fl mice.[89.Gibbs J. et al.An epithelial circadian clock controls pulmonary inflammation and glucocorticoid action.Nat. Med. 2014; 20: 919-926Crossref PubMed Scopus (243) Google Scholar]LPSConditional club cell and myeloid cell Rev-erbα-DBD mutant, Rev-erbα global KO, and WT mice were exposed to aerosolized LPS (~20 min)Rev-erbα deletion in club cells and myeloid cells promotes augmented inflammation responses and chemokine activation following LPS exposure.[88.Pariollaud M. et al.Circadian clock component REV-ERBalpha controls homeostatic regulation of pulmonary inflammation.J. Clin. Invest. 2018; 128: 2281-2296Crossref PubMed Scopus (74) Google Scholar]IAVWT and Bmal1 KO mice were infected with IAVBmal1 deletion showed increased morbidity and mortality following IAV infection compared with WT[94.Sundar I.K. et al.Influenza A virus-dependent remodeling of pulmonary clock function in a mouse model of COPD.Sci. Rep. 2015; 4: 9927Crossref PubMed Scopus (38) Google Scholar]Respiratory syncytial virus (RSV)WT and Bmal1 KO mice were infected with RSVBmal1 KO mice infected with RSV show a higher mortality rate and significantly reduced body weight compared with WT[95.Majumdar T. et al.Circadian transcription factor BMAL1 regulates innate immunity against select RNA viruses.Innate Immun. 2017; 23: 147-154Crossref PubMed Scopus (31) Google Scholar]Tumor cell lineCancer cells with Per2 and Bmal1 deletionsEnhanced cell proliferation, increased expression of c-Myc, and upregulation of metabolic activity[105.Papagiannakopoulos T. et al.Circadian rhythm disruption promotes lung tumorigenesis.Cell Metab. 2016; 24: 324-331Abstract Full Text Full Text PDF PubMed Google Scholar]Lung cancerBmal1 KO and overexpression of Bmal1 in lung cancerBmal1 KO promotes cancer cell invasion while overexpression inhibits[110.Jung C.H. et al.Bmal1 suppresses cancer cell invasion by blocking the phosphoinositide 3-kinase-Akt-MMP-2 signaling pathway.Oncol. Rep. 2013; 29: 2109-2113Crossref PubMed Scopus (59) Google Scholar]Lung cancerOverexpression of casein kinase 2 (CK2)Overexpression of CK2 associated with tumor progression and metastasis[111.Oshima T. et al.Cell-based screen identifies a new potent and highly selective CK2 inhibitor for modulation of circadian rhythms and cancer cell growth.Sci. Adv. 2019; 5eaau9060Crossref PubMed Scopus (54) Google Scholar]IAVInducible Bmal1 knockout (iKO), Bmal1 fl/fl ERCre+, Bmal1+/+LysM-Cre+/+ mice were infected with PR8 or X31 strain of influenza virus at CT23 and CT11IAV-infected WT mice showed time-of-day differences in morbidity and mortality (increased at ZT11 versus ZT23), which was lost in Bmal1 KO mice. Bmal1fl/fl ERCre+ and Bmal1+/+LysM-Cre+/+ showed influenza virus-induced severe lung inflammation and injury, suggesting the role of NKT, NK, and Ly6Chi cell-mediated temporal gating.[96.Sengupta S. et al.Circadian control of lung inflammation in influenza infection.Nat. Commun. 2019; 10: 4107Crossref PubMed Scopus (51) Google Scholar]Influenza virus infection and hyperoxiaC57 mice (newborn pups <12 h old) were exposed to ≥95% oxygen between postnatal days 0 and 5. Bmal1 fl/fl and Bmal1 SftpcCre-ERT2/+ (AT2 cell-specific Bmal1 KO) mice were infected with PR8 (IAV) at ZT11 and ZT23.Neonatal hyperoxia abolishes the time-of-day response in circadian regulation caused by IAV infection observed in adult mice. Bmal1 deletion in AT2 cells shows increased mortality, loss of temporal gating seen in adult mice exposed to neonatal hyperoxia.[97.Issah Y. et al.Loss of circadian protection against influenza infection in adult mice exposed to hyperoxia as neonates.Elife. 2021; 10e61241Crossref PubMed Scopus (5) Google Scholar]SARS-CoV-2Silencing Bmal1 expression in lung epithelial cells in vitroReduction of ACE2 expression and inhibition of SARS-CoV-2 entry[100.Zhuang X. et al.The circadian clock component BMAL1 regulates SARS-CoV-2 entry and replication in lung epithelial cells.iScience. 2021; 24103144Abstract Full Text Full Text PDF Scopus (4) Google Scholar]SARS-CoV-2Human monocyte viral infection initiated at CT6 and CT17 corresponding to acrophase and bathyphase of BMAL1, respectivelyInfection at CT6 resulted in higher viral load and significantly increased production of inflammatory cytokine (IL-6, IL-1β, and IL-10) level at CT6 compared with CT17.[115.Diallo A.B. et al.Daytime variation in SARS-CoV-2 infection and cytokine production.Microb. Pathog. 2021; 158105067Crossref PubMed Scopus (4) Google Scholar] Open table in a new tab Approximately 75% of people suffering from asthma report worsening of symptoms/severity at night or early morning hours [2.Scheer F. et al.The endogenous circadian system worsens asthma at night independent of sleep and other daily behavioral or environmental cycles.Proc. Natl. Acad. Sci. U. S. A. 2021; 118e2018486118Crossref Scopus (6) Google Scholar]. Few studies have shown that the dose of allergens needed to trigger bronchospasms varies with time of day, with allergens being most potent at night [14.Mohiuddin A.A. Martin R.J. Circadian basis of the late asthmatic response.Am. Rev. Respir. Dis. 1990; 142: 1153-1157Crossref PubMed Google Scholar,15.Ferraz E. et al.Comparison of 4 AM and 4 PM bronchial responsiveness to hypertonic saline in asthma.Lung. 2006; 184: 341-346Crossref PubMed Scopus (17) Google Scholar]. Inflammatory molecules, including chemokine signaling ligands such as CXCL2, show circadian-like oscillation in the lung, suggesting that