Continuous Monochromatic Blue Light Exacerbates High-Fat Diet-Induced Kidney Injury via Corticosterone-Mediated Oxidative Stress

Excessive illumination is one of the most severe environmental factors that impacts the organism. There is growing evidence that obesity significantly contributes to the onset of chronic kidney disease. However, the effect of continuous light on the kidney and which color can produce an apparent phenomenon remains elusive. In this study, C57BL/6 mice given either a normal diet (LD-WN) or a high-fat diet (LD-WF) were subjected to a light cycle of 12 h of illumination followed by 12 h of darkness for 12 weeks. Meanwhile, 48 high-fat diet mice were given a 24 h monochromatic light exposure of varying colors (white, LL-WF; blue, LL-BF; green, LL-GF) for 12 weeks. As expected, the LD-WF mice showed significant obesity, kidney injury, and renal dysfunction compared with the LD-WN group. LL-BF mice had worse kidney injury than LD-WF mice, including higher Kim-1 and Lcn2. The kidney of the LL-BF group showed marked glomerular and tubular injury, with decreased levels of Nephrin, Podocin, Cd2ap, and a-Actinin-4 compared to LD-WF. LL-BF also reduced the antioxidant capacity, including GSH-Px, CAT, and T-AOC, increased the production of MDA, and inhibited the activation of the NRF2/HO-1 signaling pathway. Furthermore, LL-BF upregulated the mRNA levels of the pro-inflammatory factors Tnf-a, Il-6, and Mcp-1, decreasing the inhibitory inflammatory Il-4 expression. We observed increased plasma corticosterone (CORT), renal glucocorticoid receptors (GR) expression, Hsp90, Hsp70, and P23 mRNA levels. These findings suggested that LL-BF increased CORT secretion and affected glucocorticoid receptors (GR) in comparison to the LD-WF group. Moreover, in vitro research demonstrated that CORT treatment increased oxidative stress and inflammation, which was counteracted by adding a GR inhibitor. Thus, the sustained blue light worsened kidney damage, possibly by inducing elevated CORT and increasing oxidative stress and inflammation via GR.