BackgroundHeat stress in laying hens negatively affects egg production and shell quality by disrupting the homeostasis of plasma calcium and phosphorus levels. Although the kidney plays an important role in calcium and phosphorus homeostasis, evidence regarding the effect of heat stress on renal injury in laying hens is yet to be elucidated. Therefore, the aim of this study was to evaluate the effects of chronic heat stress on renal damage in hens during laying periods.MethodsA total of 16 white-leghorn laying hens (32 weeks old) were randomly assigned to two groups (n= 8). One group was exposed to chronic heat stress (33 °C for 4 weeks), whereas the other group was maintained at 24 °C.ResultsChronic heat exposure significantly increased plasma creatinine and decreased plasma albumin levels (P< 0.05). Heat exposure also increased renal fibrosis and the transcription levels of fibrosis-related genes (COLA1A1,αSMA, andTGF-β) in the kidney. These results suggest that renal failure and fibrosis were induced by chronic heat exposure in laying hens. In addition, chronic heat exposure decreased ATP levels and mitochondrial DNA copy number (mtDNA-CN) in renal tissue, suggesting that renal mitochondrial dysfunction occurs under conditions of heat stress. Damaged mitochondria leak mtDNAs into the cytosol and mtDNA leakage may activate the cyclic GMP-AMP synthase (cGAS) stimulator of interferon genes (STING) signaling pathway. Our results showed that chronic heat exposure activated the cGAS-STING pathway as indicated by increased expression ofMDA5,STING,IRF7,MAVS, andNF-κBlevels. Furthermore, the expression of pro-inflammatory cytokines (IL-12) and chemokines (CCL4andCCL20) was upregulated in heat-stressed hens.ConclusionsThese results suggest that chronic heat exposure induces renal fibrosis and mitochondrial damage in laying hens. Mitochondrial damage by heat stress may activate the mtDNA-cGAS-STING signaling and cause subsequent inflammation, which contributes to the progression of renal fibrosis and dysfunction.