Blue light improves survival after pneumonia by augmenting circadian protein expression

John Griepentrog; Xianghong Zhang; Anthony Lewis; Zeyu Xiong; Gianmarino Gianfrate; Janet Lee; Matthew Rosengart

Pneumonia is a major cause of sepsis and acute lung injury, with three million cases reported annually in the US; it is the sixth most common cause of death. The causal mechanisms of acute alveolar damage include an excessive accumulation of neutrophils in the lung and subsequent production of inflammatory mediators and neutrophil-mediated oxidant damage. Light has been shown to influence an organism’s response to stress. Circadian proteins, including REV-ERB, are known to attenuate inflammation and regulate mitochondrial biogenesis.

We hypothesize that blue light enhances regional control of a septic focus and that modulating circadian protein expression will augment lung innate immunity and bacterial clearance.

Male C57BL/6 mice were intratracheally administered Klebsiella pneumoniae (6000 CFUs) and immediately exposed to 36 hours followed by 12 hours daily of bright (1400 lux) blue (442nm), bright red (617nm); or ambient white (400 lux) light. In parallel experiments, mice were subjected to pneumonia and then administered the REV-ERBα agonist, SR9009. Mice were euthanized at 72 hours, the lungs lavaged, and the blood/organs harvested. Tissue and blood were analyzed for bacterial CFUs. Tissue expression of REV-ERBα was analyzed by immunofluorescence and immunoblot. Cytokine concentrations were quantified by ELISA. Statistical analysis was performed by Wilcoxon rank-sum, and a p<0.05 was considered significant.

Mice exposed to blue light survived longer than red or ambient light (log-rank p = 0.02). They exhibited faster bacterial clearance (p = 0.06), but did so with reduced neutrophil counts (p = 0.0001) and tissue cytokine concentrations. Blue light induced elevated expression of REV-ERB in the lungs, alveolar macrophages, and spleen. Mice administered the REV-ERB agonist SR9009 survived longer than the control group. Similar to blue light, SR9009 enhanced bacterial clearance and reduced bacterial dissemination (p = 0.14), while reducing neutrophil influx into the lung (p = 0.001). This appeared to be due to an inhibition of pulmonary chemokines, as SR9009 reduced KC, MIP-1α, MIP-2 within the lung, as well as TNFα and IL-6.

Blue light functions through a visual and cholinergic pathway and the spleen to augment lung innate immunity and bacterial clearance, while reducing neutrophilic inflammation. The mechanisms involve an augmentation in REV-ERB expression in alveolar macrophages and lung tissue, whereby the REV-ERB agonist SR9009 yielded similar results to blue light. Further studies are required to determine how altering REV-ERB affects macrophage phagocytic function.