MiRNAs are a class of endogenous and evolutionarily conserved noncoding short RNA molecules that post-transcriptionally regulate gene expression through sequence-specific interactions with mRNAs and are capable of controlling gene expression by binding to miRNA targets and interfering with the final protein output. The miRNAs of teleost were firstly reported in zebrafish development, but there are recent studies on the characteristics and functions of miRNAs in fish, especially when compared with mammals. Environmental factors including salinity, oxygen concentration, temperature, feed, pH, environmental chemicals and seawater metal elements may affect the transcriptional and posttranscriptional regulators of miRNAs, contributing to nearly all biological processes. The survival of aquatic fish is constantly challenged by the changes in these environmental factors. Environmental factors can influence miRNA expression, the functions of miRNAs and their target mRNAs. Progress of available information is reported on the environmental effects of the identified miRNAs, miRNA targets and the use of miRNAs in fish.

This study attempted to evaluate the possible impact and mechanism of leucine (Leu) on fish intestinal barrier function. One hundred and five hybrid Pelteobagrus vachelli ♀ × Leiocassis longirostris ♂ catfish were fed with six diets in graded levels of Leu 10.0 (control group), 15.0, 20.0, 25.0, 30.0, 35.0, and 40.0 g/kg diet for 56 days. Results showed that the intestinal activities of LZM, ACP, and AKP and contents of C3, C4, and IgM had positive linear and/or quadratic responses to dietary Leu levels. The mRNA expressions of itnl1, itnl2, c-LZM, g-LZM, and β-defensin increased linearly and/or quadratically (p < 0.05). The ROS, PC, and MDA contents had a negative linear and/or quadratic response, but GSH content and ASA, AHR, T-SOD, and GR activities had positive quadratic responses to dietary Leu levels (p < 0.05). No significant differences on the CAT and GPX activities were detected among treatments (p > 0.05). Increasing dietary Leu level linearly and/or quadratically increased the mRNA expressions of CuZnSOD, CAT, and GPX1α. The GST mRNA expression decreased linearly while the GCLC and Nrf2 mRNA expressions were not significantly affected by different dietary Leu levels. The Nrf2 protein level quadratically increased, whereas the Keap1 mRNA expression and protein level decreased quadratically (p < 0.05). The translational levels of ZO-1 and occludin increased linearly. No significant differences were indicated in Claudin-2 mRNA expression and protein level. The transcriptional levels of Beclin1, ULK1b, ATG5, ATG7, ATG9a, ATG4b, LC3b, and P62 and translational levels of ULK1, LC3Ⅱ/Ⅰ, and P62 linearly and quadratically decreased. The Beclin1 protein level was quadratically decreased with increasing dietary Leu levels. These results suggested that dietary Leu could improve fish intestinal barrier function by increasing humoral immunity, antioxidative capacities, and tight junction protein levels.

MicroRNAs (miRNAs) play important roles in adipogenesis that is closely linked to obesity and energy homeostasis. Thus far, only a few miRNAs have been identified to regulate adipocyte development, arousing interest in the detailed function of miRNAs during adipogenesis. In this study, we found that the miR-26b expression showed an increasing trend during 3T3-L1 cells differentiation. To investigate the role of miR-26b in adipogenesis, the synthetic miR-26b agomirs and antagomirs were used to perform overexpression and knockdown experiment, respectively. Our data revealed that overexpression of miR-26b significantly accelerated the mRNA expression of the adipogenic markers, peroxisome proliferator-activated receptor gamma (PPARγ), fatty acid synthase (FAS), CCAAT/enhancer binding protein alpha (C/EBPα), and lipoprotein lipase, and the protein level of PPARγ and FAS. miR-26b overexpression also resulted in a significant increase in lipid accumulation. In contrast, inhibition of miR-26b expression decreased differentiation of 3T3-L1 cells. By target gene prediction and luciferase reporter assay, we demonstrated that miR-26b may directly bind to the 3′ UTR of phosphatase and tensin homolog (PTEN). Taken together, these results demonstrate that miR-26b might participate in regulating adipogenic differentiation in 3T3-L1 cells by inhibiting the PTEN expression, further highlighting the importance of miRNA in adipogenesis.

Ferroptosis is a form of regulated cell death characterized by iron-dependent lipid peroxidation, affecting physiological and pathological processes. Fatty liver disease associated with metabolic dysfunction is a common pathological condition in aquaculture. However, the exact role and mechanism of ferroptosis in its pathogenesis and progression remains unclear. In this study, an experiment was conducted using different dietary lipid levels in the feeding of largemouth bass (Micropterus salmoides) for 11 weeks. The results revealed that the growth performance and whole-body protein content significantly increased with the elevation of dietary lipid levels up to 12%. The activities of antioxidant enzymes as well as the content of GSH (glutathione) in the liver initially increased but later declined as the lipid levels increased; the contents of MDA (malondialdehyde) and GSSG (oxidized glutathione) demonstrated an opposite trend. Moreover, elevating lipid levels in the diet significantly increased liver Fe²⁺ content, as well as the expressions of TF (Transferrin), TFR (Transferrin receptor), ACSL4 (acyl-CoA synthetase long-chain family member 4), LPCAT3 (lysophosphatidylcholine acyltransferase 3), and LOX12 (Lipoxygenase-12), while decreasing the expressions of GPX4 (glutathione peroxidase 4) and SLC7A11 (Solute carrier family 7 member 11). In conclusion, the optimal lipid level is 12.2%, determined by WG-based linear regression. Excess lipid-level diets can up-regulate the ACSL4/LPCAT3/LOX12 axis, induce hepatic oxidative stress and cell death through a ferroptotic-like program, and decrease growth performance.

Fish primary cell culture has emerged as a valuable tool for investigating the physiological roles and responses of various cell types found in fish species. This review aims to provide an overview of the advancements and applications of fish primary cell culture techniques, focusing on the profiling of physiological roles exhibited by fish cells in vitro. Fish primary cell culture involves the isolation and cultivation of cells directly derived from fish tissues, maintaining their functional characteristics and enabling researchers to study their behavior and responses under controlled conditions. Over the years, significant progress has been made in optimizing the culture conditions, establishing standardized protocols, and improving the characterization techniques for fish primary cell cultures. The review highlights the diverse cell types that have been successfully cultured from different fish species, including gonad cells, pituitary cells, muscle cells, hepatocytes, kidney and immune cells, adipocyte cells and myeloid cells, brain cells, primary fin cells, gill cells, and other cells. Each cell type exhibits distinct physiological functions, contributing to vital processes such as metabolism, tissue regeneration, immune response, and toxin metabolism. Furthermore, this paper explores the pivotal role of fish primary cell culture in elucidating the mechanisms underlying various physiological processes. Researchers have utilized fish primary cell cultures to study the effects of environmental factors, toxins, pathogens, and pharmaceutical compounds on cellular functions, providing valuable insights into fish health, disease pathogenesis, and drug development. The paper also discusses the application of fish primary cell cultures in aquaculture research, particularly in investigating fish growth, nutrition, reproduction, and stress responses. By mimicking the in vivo conditions in vitro, primary cell culture has proven instrumental in identifying key factors influencing fish health and performance, thereby contributing to the development of sustainable aquaculture practices.