Effects of heat stress on histomorphology antioxidant capacity, and transcriptomic frofiles in the liver of Gymnocypris przewalskii

Weifeng Fan¹Zhenshuo Bai¹Fuju Chen^1*Jiaoyang Du¹Changzhong Li²HongMei Qi¹MingYue Zhao¹ChangZhen An³YanHong Wu³Yang Wang³ShengYun Fu³Lian Zhang⁴

• ¹Qinghai University, Xining, China
• ²College of Eco-Environmental Engineering, Qinghai University, Xining, 810016, China
• ³The Rescue and Rehabilitation Center of Naked Carps in Qinghai Lake, Xining 810000, China
• ⁴Agriculture and Rural Affairs Bureau of Chengzhong District, Xining 810012, Qinghai Province, China

The cold-water scaleless carp (Gymnocypris przewalskii) is highly vulnerable to rising temperatures, yet the mechanisms underlying its thermal adaptation under global climate change remain poorly understood. To elucidate these mechanisms, juvenile G. przewalskii were exposed to 22°C heat stress, and liver samples were collected at 6, 12, 24, and 48 h post-exposure for integrated histopathological, oxidative stress, and transcriptomic analyses. Histopathological examination showed no significant tissue alterations after the initial 6 h of exposure. In contrast, prolonged exposure (24 to 48 h) resulted in conspicuous liver damage induced by oxidative stress, characterized by hepatocellular fatty degeneration, hepatic hyperemia and inflammatory cell infiltration. Biochemically, the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and total antioxidant capacity (T-AOC), as well as the content of malondialdehyde (MDA), were significantly elevated across multiple time points, indicating an activated oxidative stress responses and concomitant induction of antioxidant defenses. Transcriptomic analysis identified 3,589 up-regulated and 3,828 down-regulated genes at 6 h, along with 2,810 up-regulated and 1,990 down-regulated genes at 48 h. Notably, key genes including heat shock proteins (HSC70, HSPA8, DNAJB5, HSP90AA1.2), energy metabolism-related factors (NDUFA5, FABP6, SLC2A1a), and immune-related pathways components (C4, TRIM39, RNF14, ETHE1, IL4) were significantly altered. These findings suggest that acute heat stress induces hepatic structural injury and disrupts energy metabolism, while G. przewalskii mobilizes a comprehensive defense strategy involving enhanced heat shock protein expression, augmented antioxidative capacity, activation of immune pathways, and metabolism regulation to mitigate hepatic damage. Overall, this study provides molecular insights into the heat stress response mechanisms of cold-water fish.