Molecular Mechanism Based on Histopathology, Antioxidant System and Transcriptomic Profiles in Heat Stress Response in the Gills of Japanese Flounder

Abstract

As an economically important flatfish in Asia, Japanese flounder is threatened by continuously rising temperatures due to global warming. To understand the molecular responses of this species to temperature stress, adult Japanese flounder individuals were treated with two kinds of heat stress—a gradual temperature rise (GTR) and an abrupt temperature rise (ATR)—in aquaria under experimental conditions. Changes in histopathology, programmed cell death levels and the oxidative stress status of gills were investigated. Histopathology showed that the damage caused by ATR stress was more serious. TUNEL signals confirmed this result, showing more programmed cell death in the ATR group. In addition, reactive oxygen species (ROS) levels and the 8-O-hDG contents of both the GTR and ATR groups increased significantly, and the total superoxide dismutase (T-SOD) activities and total antioxidant capacity (T-AOC) levels decreased in the two stressed groups, which showed damage to antioxidant systems. Meanwhile, RNA-seq was utilized to illustrate the molecular mechanisms underyling gill damage. Compared to the control group of 18 °C, 507 differentially expressed genes (DEGs) were screened in the GTR group; 341 were up-regulated and 166 were down-regulated, and pathway enrichment analysis indicated that they were involved in regulation and adaptation, including chaperone and folding catalyst pathways, the mitogen-activated protein kinase signaling (MAPK) pathway and DNA replication protein pathways. After ATR stress, 1070 DEGs were identified, 627 were up-regulated and 423 were down-regulated, and most DEGs were involved in chaperone and folding catalyst and DNA-related pathways, such as DNA replication proteins and nucleotide excision repair. The annotation of DEGs showed the great importance of heat shock proteins (HSPs) in protecting Japanese flounder from heat stress injury; 12 hsp genes were found after GTR, while 5 hsp genes were found after ATR. In summary, our study records gill dysfunction after heat stress, with different response patterns observed in the two experimental designs; chaperones were activated to defend heat stress after GTR, while replication was almost abandoned due to the severe damage consequent on ATR stress.

Probing the Potential Mechanism of Quercetin and Kaempferol against Heat Stress-Induced Sertoli Cell Injury: Through Integrating Network Pharmacology and Experimental Validation

“…At the same time, heat stress causes testicular SCs to rapidly accumulate a large amount of ROS. In normal testes, ROS are maintained at an acceptable level due to a balance with antioxidants [ 49 , 50 , 51 ]. The production of ROS is important for the apoptosis of germ cells and DNA damage [ 52 ].…”

Dietary antarctic krill improves antioxidant capacity, immunity and reduces lipid accumulation, insights from physiological and transcriptomic analysis of Plectropomus leopardus

“…The analysis of antioxidant enzyme activities was performed as described previously [ 39 ]. The frozen intestinal and liver samples were homogenized with 0.9% saline using an electronic homogenizer and centrifugated at 12,000 rpm at 4 ℃, then the supernatant was used for further antioxidant enzyme activities analysis.…”

Transcriptomic Networks Reveal the Tissue-Specific Cold Shock Responses in Japanese Flounder (Paralichthys olivaceus)

“…Then, the tissue samples were transparentized with xylene and ethanol mixture, embedded into paraffin, and sliced into a thickness of 5 µm. The samples were further dewaxed and stained with hematoxylin and eosin (H&E) (Solarbio, Beijing, China) following the traditional method [ 14 ]. Finally, the samples, which were sealed with neutral gum, were observed and photographed with a Nikon Eclipse TiU microscope (Nikon, Tokyo, Japan) for histological examination.…”

“…The spleen is mainly composed of lymph nodes and plays important roles in the hematopoietic, immune, and blood storage of fish [ 13 ]. Moreover, there are many functional pathways, including mitochondrial function, antioxidation, apoptosis, carbohydrate/lipid metabolism, DNA/RNA processing, and protein catabolism, that show temperature-dependent regulation [ 14 , 15 , 16 , 17 ]. Therefore, investigating the molecular mechanisms among the various tissues of fish that are affected by low temperature could provide a better understanding of how organisms adapt or respond to aquatic environmental challenges.…”

“…Japanese flounder ( Paralichthys olivaceus ) is an economically important aquaculture teleost species broadly cultivated in east Asia, mainly along the coast of the Bohai and Yellow Seas in China, as well as along the coast of Korea and east Japan [ 14 ]. Many studies have illustrated the effect of heat stress on the mechanisms of sexual differentiation, energy metabolism, neurosecretion, and stress-related gene regulation in P. olivaceus [ 14 , 20 , 21 , 22 , 23 ]. However, as a temperate water fish, nowadays, temperature decline has also influenced the survival, growth, distribution, and reproduction of this species [ 24 ].…”