Daily oscillations of pulmonary function depend on the rhythmic activity of the circadian timing system. Environmental tobacco/cigarette smoke (CS) disrupts circadian clock leading to enhanced inflammatory responses. Infection with influenza A virus (IAV) increases hospitalization rates and death in susceptible individuals, including patients with Chronic Obstructive Pulmonary Disease (COPD). We hypothesized that molecular clock disruption is enhanced by IAV infection, altering cellular and lung function, leading to severity in airway disease phenotypes. C57BL/6J mice exposed to chronic CS, BMAL1 knockout (KO) mice and wild-type littermates were infected with IAV. Following infection, we measured diurnal rhythms of clock gene expression in the lung, locomotor activity, pulmonary function, inflammatory, pro-fibrotic and emphysematous responses. Chronic CS exposure combined with IAV infection altered the timing of clock gene expression and reduced locomotor activity in parallel with increased lung inflammation, disrupted rhythms of pulmonary function, and emphysema. BMAL1 KO mice infected with IAV showed pronounced detriments in behavior and survival, and increased lung inflammatory and pro-fibrotic responses. This suggests that remodeling of lung clock function following IAV infection alters clock-dependent gene expression and normal rhythms of lung function, enhanced emphysematous and injurious responses. This may have implications for the pathobiology of respiratory virus-induced airway disease severity and exacerbations. I nfluenza virus, rhinovirus, coronavirus, respiratory syncytial virus, parainfluenza, adenovirus and metapeumovirus are among the respiratory viruses known to cause exacerbations in Chronic Obstructive Pulmonary Disease (COPD) and asthma 1-4 . In fact, respiratory viral infections account for about 50-70% of acute exacerbations in patients with COPD 5 . COPD exacerbations are often followed by subsequent clinical pulmonary deterioration, including significant declines in forced expiratory volume at 1 second (FEV 1 ) and increased hospitalization or mortality 6 . This is associated with worsening of COPD phenotypes, such as cough, fever and mucus production; the timing of which depends on the activity of the biological clock. Circadian rhythms are biological oscillations that occur with a near-24-h period and are synchronized or entrained to environmental cues, such as the day-night cycle 7 . These rhythms are the manifestation of an autoregulatory molecular oscillator of interlocked positive and negative transcription factors collectively referred to as clock genes 8 . In mammals, the central pacemaker, localized to the suprachiasmatic nucleus (SCN) of the anterior hypothalamus, drives rhythms of physiology and behavior, and synchronizes internal timing with the external environment 7 . Apart from the central clock, peripheral tissues such as the liver, heart and the lung also contain autonomous circadian oscillators that coordinate tissue specific cellular functions and responses to environmental stimuli 7-12 . As an example, circadian rhythms in pulmonary function have been demonstrated in animal models and healthy individuals (highest at noon time and low during the early morning hours) [13] [14] [15] . The coordinated and synchronized activity of central and peripheral oscillators is referred to as the circadian timing system 9,12 . It has been shown that recruitment of leukocytes to tissues following infection is also regulated by the circadian timing system 16, 17 . For example, macrophages and mast cells exhibit robust rhythms of circadian clock and proinflammatory cytokine gene expression 18, 19 . The magnitude of immune and inflammatory parameters varies with time of day, and disruption of circadian rhythms (chronodisruption) has been implicated in cellular dysfunction, and in the pathogenesis of chronic metabolic disease, infection, and inflammatory diseases 20-22 .
Output: Influenza A virus-dependent remodeling of pulmonary clock function in a mouse model of COPD