The Effect of Lighting and Diet on Macrophage Activation in Liver

Abstract

Abstract

Introduction:

Modern lifestyles characterized by high-fat diets and disrupted circadian rhythms contribute to liver inflammation and metabolic disorders such as non-alcoholic steatohepatitis (NASH). The progression of NASH can lead to fibrosis, cirrhosis, and hepatocellular carcinoma. Emerging evidence implicates the circadian clock protein Bmal1 in regulating lipid synthesis and macrophage polarization, thereby linking environmental factors to liver pathology. Shifts in macrophage phenotype—from anti-inflammatory (M2) to pro-inflammatory (M1)—may exacerbate NASH progression.

Aim. This study examined the effects of diet and circadian rhythm on NASH progression in an animal model by assessing liver tissue morphology. It aimed to clarify the relationship between Bmal1 expression and macrophage activity, particularly its association with macrophage M1 and M2 biomarkers.

Methods:

In this study, we established a NASH animal model using C57BL/6 mice, divided into four groups: CL (sham-control light), BL (blue LED light), WD (Western diet with control light), and WDBL (Western diet with blue light). Interventions were administered for four weeks. Liver tissue was analyzed using hematoxylin and eosin (HE) staining, with NASH severity evaluated via the NAS scoring system, while Masson’s trichrome staining was employed to assess fibrosis and evaluated with the Brunt Scoring System. Immunohistochemistry was performed to quantify Bmal1 expression and macrophage markers—iNOS (M1) and CD163 (M2). Statistical analyses were used to compare differences among groups.

Results:

HE staining revealed that mice subjected to WD and/or BL exhibited a significant increase in fat vacuole accumulation and higher NAS scores compared with controls. Mild fibrosis, detected by Masson’s trichrome staining, was apparent exclusively in the WDBL group. Immunohistochemical analysis demonstrated a significant upregulation of Bmal1 and the pro-inflammatory marker iNOS in both the WD and BL groups, whereas the anti-inflammatory marker CD163 was correspondingly reduced. These findings indicate that both a high-fat diet and circadian disruption promote a shift towards a pro-inflammatory macrophage phenotype in the liver.

Conclusion:

The results suggest that lipid accumulation, driven by a Western diet and circadian rhythm disruption, aggravates liver steatosis, ballooning, and inflammation. Upregulation of Bmal1 and iNOS under these conditions, alongside decreased CD163 expression, implies that Bmal1 may modulate macrophage polarization to favor an M1-dominant state, thereby contributing to NASH progression. Future studies in human NASH samples will be necessary to validate these mechanisms and assess the potential of Bmal1 as a therapeutic target.

Keywords: Western diet, circadian rhythm, NASH, macrophage, inflammation