Disruption of Sirtuin 1-Mediated Control of Circadian Molecular Clock and Inflammation in Chronic Obstructive Pulmonary Disease

Asymmetric expression level of clock genes in left vs. right nasal mucosa in humans with and without allergies and in rats: Circadian characteristics and possible contribution to nasal cycle

Numerous peripheral tissues possess self-sustaining daily biologic rhythms that are regulated at the molecular level by clock genes such as PER1, PER2, CLOCK, and BMAL1. Physiological function of nasal mucosa exhibits rhythmic variability to a day-night environmental cycle. Nevertheless, little is known of the expression and distribution pattern of clock genes in nasal mucosa. The present study investigates the expression level and distribution pattern of PER1, PER2, CLOCK, and BMAL1 genes in nasal mucosa of healthy controls, allergic rhinitis patients, and normal rats. In human and rat nasal mucosa, the levels of these genes are asymmetrically expressed in nasal mucosa derived from right and left cavities in normal controls, allergic patients, and rat. In human nasal mucosa, the expression levels of these genes were higher in the decongested side than the congested mucosa. In rat nasal mucosa, these clock genes are expressed in a rhythmic circadian manner under the regular light/dark cycles. The expression levels of MUC5AC, a key mucin genes produced in superficial epithelium, are higher in decongested side than that congested side in human nasal mucosa. In rat nasal mucosa, MUC5AC levels showed a circadian rhythm which was associated with different expression levels in nasal mucosa derived from the right and left nasal cavities. Taken together with these results, the present study shows that the clock genes such as PER1, PER2, CLOCK, and BMAL1 are present in human and rat nasal mucosa, and suggest that these clock genes may control the pathophysiological function of nasal mucosa as circadian oscillators and affect the maintenance of the nasal cycle.

Timing Matters: Circadian Rhythm in Sepsis, Obstructive Lung Disease, Obstructive Sleep Apnea, and Cancer

Physiological and cellular functions operate in a 24-hour cyclical pattern orchestrated by an endogenous process known as the circadian rhythm. Circadian rhythms represent intrinsic oscillations of biological functions that allow for adaptation to cyclic environmental changes. Key clock genes that affect the persistence and periodicity of circadian rhythms include BMAL1/CLOCK, Period 1, Period 2, and Cryptochrome. Remarkable progress has been made in our understanding of circadian rhythms and their role in common medical conditions. A critical review of the literature supports the association between circadian misalignment and adverse health consequences in sepsis, obstructive lung disease, obstructive sleep apnea, and malignancy. Circadian misalignment plays an important role in these disease processes and can affect disease severity, treatment response, and survivorship. Normal inflammatory response to acute infections, airway resistance, upper airway collapsibility, and mitosis regulation follows a robust circadian pattern. Disruption of normal circadian rhythm at the molecular level affects severity of inflammation in sepsis, contributes to inflammatory responses in obstructive lung diseases, affects apnea length in obstructive sleep apnea, and increases risk for cancer. Chronotherapy is an underused practice of delivering therapy at optimal times to maximize efficacy and minimize toxicity. This approach has been shown to be advantageous in asthma and cancer management. In asthma, appropriate timing of medication administration improves treatment effectiveness. Properly timed chemotherapy may reduce treatment toxicities and maximize efficacy. Future research should focus on circadian rhythm disorders, role of circadian rhythm in other diseases, and modalities to restore and prevent circadian disruption.

Development and Therapeutic Potential of Small-Molecule Modulators of Circadian Systems

Circadian timekeeping systems drive oscillatory gene expression to regulate essential cellular and physiological processes. When the systems are perturbed, pathological consequences ensue and disease risks rise. A growing number of small-molecule modulators have been reported to target circadian systems. Such small molecules, identified via high-throughput screening or derivatized from known scaffolds, have shown promise as drug candidates to improve biological timing and physiological outputs in disease models. In this review, we first briefly describe the circadian system, including the core oscillator and the cellular networks. Research progress on clock-modulating small molecules is presented, focusing on development strategies and biological efficacies. We highlight the therapeutic potential of small molecules in clock-related pathologies, including jet lag and shiftwork; various chronic diseases, particularly metabolic disease; and aging. Emerging opportunities to identify and exploit clock modulators as novel therapeutic agents are discussed.

The nuclear receptor and clock gene REV-ERBα regulates cigarette smoke-induced lung inflammation

REV-ERBα is a nuclear heme receptor, transcriptional repressor and critical component of the molecular clock that drives daily rhythms of metabolism. Evidence reveals that REV-ERBα also plays an important regulatory role in clock-dependent lung physiology and inflammatory responses. We hypothesize that cigarette smoke (CS) exposure influences REV-ERBα abundance in the lungs, facilitating a pro-inflammatory phenotype. To determine the impact of REV-ERBα activation in the CS-induced inflammatory response we treated primary human small airway epithelial cells (SAECs) with CS extract (CSE) or lipopolysaccharide (LPS) in the absence or presence of pre-treatment with the REV-ERBα agonist GSK 4112. We also exposed adult C57BL/6J (WT) and Rev-erbα global KO mice to CS (10 and 30 days) and measured pro-inflammatory cytokine release. Our data reveal that pre-treatment with GSK 4112 reduced CSE/LPS induced pro-inflammatory cytokines release from both SAECs and mouse lung fibroblasts (MLFs). Furthermore, REV-ERBα KO mice show a greater inflammatory response to 10 and 30 days of CS, including increased neutrophil lung influx, pro-inflammatory cytokine (IL-6, MCP-1 and KC) release, and pro-senescence marker (p16) when compared to WT mice. These data demonstrate that REV-ERBα is a critical regulator of CS-induced lung inflammatory responses.

SIRT1 is required for mitochondrial biogenesis reprogramming in hypoxic human pulmonary arteriolar smooth muscle cells

Although recent studies have reported that mitochondria are putative oxygen sensors underlying hypoxic pulmonary vasoconstriction, little is known concerning the sirtuin 1 (SIRT1)-mediated mitochondrial biogenesis regulatory program in pulmonary arteriolar smooth muscle cells (PASMCs) during hypoxia/reoxygenation (H/R). We investigated the epigenetic regulatory mechanism of mitochondrial biogenesis and function in human PASMCs during H/R. Human PASMCs were exposed to hypoxia of 24–48 h and reoxygenation of 24–48 h. The expression of SIRT1 was reduced in a time-dependent manner. Mitochondrial transcription factor A (TFAM) expression was increased during hypoxia and decreased during reoxygenation, while the release of TFAM was increased in a time-dependent manner. Lentiviral overexpression of SIRT1 preserved SIRT3 deacetylase activity in human PASMCs exposed to H/R. Knockdown of PGC-1α suppressed the effect of SIRT1 on SIRT3 activity. Knockdown of SIRT3 abrogated SIRT1-mediated deacetylation of cyclophilin D (CyPD). Notably, knockdown of SIRT3 or PGC-1α suppressed the incremental effect of SIRT1 on mitochondrial TFAM, mitochondrial DNA (mtDNA) content and cellular ATP levels. Importantly, polydatin restored SIRT1 levels in human PASMCs exposed to H/R. Knockdown of SIRT1 suppressed the effect of polydatin on mitochondrial TFAM, mtDNA content and cellular ATP levels. In conclusion, SIRT1 expression is decreased in human PASMCs during H/R. TFAM expression in mitochondria is reduced and the release of TFAM is increased by H/R. PGC-1α/SIRT3/CyPD mediates the protective effect of SIRT1 on expression and release of TFAM and mitochondrial biogenesis and function. Polydatin improves mitochondrial biogenesis and function by enhancing SIRT1 expression in hypoxic human PASMCs.

Circadian clock-coupled lung cellular and molecular functions in chronic airway diseases

Airway diseases are associated with abnormal circadian rhythms of lung function, reflected in daily changes of airway caliber, airway resistance, respiratory symptoms, and abnormal immune-inflammatory responses. Circadian rhythms are generated at the cellular level by an autoregulatory feedback loop of interlocked transcription factors collectively referred to as clock genes. The molecular clock is altered by cigarette smoke, LPS, and bacterial and viral infections in mouse and human lungs and in patients with chronic airway diseases. Stress-mediated post-translational modification of molecular clock proteins, brain and muscle aryl hydrocarbon receptor nuclear translocator-like 1 (BMAL1) and PERIOD 2, is associated with a reduction in the activity/level of the deacetylase sirtuin 1 (SIRT1). Similarly, the levels of the nuclear receptor REV-ERBα and retinoic acid receptor-related orphan receptor α (ROR α), critical regulators of Bmal1 expression, are altered by environmental stresses. Molecular clock dysfunction is implicated in immune and inflammatory responses, DNA damage response, and cellular senescence. The molecular clock in the lung also regulates the timing of glucocorticoid sensitivity and phasic responsiveness to inflammation. Herein, we review our current understanding of clock-controlled cellular and molecular functions in the lungs, the impact of clock dysfunction in chronic airway disease, and the response of the pulmonary clock to different environmental perturbations. Furthermore, we discuss the evidence for candidate signaling pathways, such as the SIRT1-BMAL1-REV-ERBα axis, as novel targets for chronopharmacological management of chronic airway diseases.

Circadian molecular clock in lung pathophysiology

Disrupted daily or circadian rhythms of lung function and inflammatory responses are common features of chronic airway diseases. At the molecular level these circadian rhythms depend on the activity of an autoregulatory feedback loop oscillator of clock gene transcription factors, including the BMAL1:CLOCK activator complex and the repressors PERIOD and CRYPTOCHROME. The key nuclear receptors and transcription factors REV-ERBα and RORα regulate Bmal1 expression and provide stability to the oscillator. Circadian clock dysfunction is implicated in both immune and inflammatory responses to environmental, inflammatory, and infectious agents. Molecular clock function is altered by exposomes, tobacco smoke, lipopolysaccharide, hyperoxia, allergens, bleomycin, as well as bacterial and viral infections. The deacetylase Sirtuin 1 (SIRT1) regulates the timing of the clock through acetylation of BMAL1 and PER2 and controls the clock-dependent functions, which can also be affected by environmental stressors. Environmental agents and redox modulation may alter the levels of REV-ERBα and RORα in lung tissue in association with a heightened DNA damage response, cellular senescence, and inflammation. A reciprocal relationship exists between the molecular clock and immune/inflammatory responses in the lungs. Molecular clock function in lung cells may be used as a biomarker of disease severity and exacerbations or for assessing the efficacy of chronotherapy for disease management. Here, we provide a comprehensive overview of clock-controlled cellular and molecular functions in the lungs and highlight the repercussions of clock disruption on the pathophysiology of chronic airway diseases and their exacerbations. Furthermore, we highlight the potential for the molecular clock as a novel chronopharmacological target for the management of lung pathophysiology.