Exposure to low-intensity noise exacerbates nonalcoholic fatty liver disease by activating hypothalamus pituitary adrenal axis

Noise exposure induces metabolic disorders, in a latent, chronic and complex way. However, there is no direct evidence elucidating the relationship between low-intensity noise exposure and nonalcoholic fatty liver disease (NAFLD). Male mice (n = 5) on high-fat diet (HFD) were exposed to an average of 75 dB SPL noise for 3 months to reveal the effect of noise exposure on NAFLD, where the potential mechanisms were explored. In vivo (n = 5) and in vitro models challenged with dexamethasone (DEX) were used to verify the role of hypothalamus pituitary adrenal (HPA) axis activation in hepatic lipid metabolism. Typical chronic-restraint stress (CRS, n = 8) was used to explore the role of depression in modifying activity of HPA axis. Finally, animal experiment (n = 8) was repeated to validate the roles of depression and HPA axis activation in NAFLD development. Chronic low-intensity noise exposure exacerbated NAFLD in mice on HFD characterized by hepatocyte steatosis, modified lipid metabolism and inflammation level. Plasma ACTH in H + N group was 1.5-fold higher than that in HFD group. Transcription of glucocorticoid receptor target genes was increased by chronic low-intensity noise exposure in HFD-treated mice. Excessive glucocorticoids mimicking HPA axis activation induced NAFLD in vivo and in vitro. Plasma ACTH increase and lipid storage also occurred in depressive mice stressed by CRS. More interestingly, the same noise exposure simultaneously induced depression in mice, disrupted the HPA axis homeostasis and exacerbated NAFLD in a repeated experiment. Thus, three-month exposure to 75 dB SPL noise was sufficient to exacerbate NAFLD progress in mice, where activation of HPA axis played a critical role. Depression played an intermediate role and contributed to HPA axis activation up-stream of the exacerbation.