Mitochondrial changes in fish cells in vitro in response to serum deprivation

Mitochondria are critical to cellular activity that implicated in expansive networks to maintain organismal homeostasis under external stimuli of nutrient variability, a common and severe stress to fish performance during the intensive culture conditions. In the present study, zebrafish embryonic fibroblast cells were used to investigate the fish mitochondrial changes upon serum deprivation. Results showed that mitochondrial content and membrane potential were significantly reduced with increased intracellular ROS level in the serum deprivation treated fish cells. And the impaired mitochondria were characterized by rough and fracted outer membrane, and more fused mitochondria were frequently observed with the upregulated mRNA expressions of mitochondrial fusion genes (mfn1b, mfn2, and opa1). Besides, the mitochondrial DNA (mtDNA) copy numbers of mtatp6, mtcox1, mtcytb, mtnd4, and mtnd6 were overall showing the highly significant reduction, together with the mRNA expressions of these genes significantly increased, exhibiting the compensatory effects in mitochondria. Furthermore, the methyl-cytosine of whole mtDNA was compared and the methyl-reads numbers were distinctly increased in the treatment group, reflecting the instability of fish mtDNA with mitochondrial dysfunction under nutrient fluctuations. Collectively, current findings could facilitate the integrated research between fish mitochondrial response and external variables that indicates the potentially profound and durative deficits in fish health during the aquaculture processes.

Automated summary

This study investigated the changes in fish mitochondria upon serum deprivation using zebrafish embryonic fibroblast cells. The results showed that mitochondrial content and membrane potential were reduced, and intracellular ROS levels were increased in serum deprivation treated fish cells. The impaired mitochondria had rough and fracted outer membranes, and fused mitochondria were frequently observed. The mRNA expressions of mitochondrial fusion genes (mfn1b, mfn2, and opa1) were upregulated. The mtDNA copy numbers of mtatp6, mtcox1, mtcytb, mtnd4, and mtnd6 were significantly reduced, but the mRNA expressions of these genes increased, indicating compensatory effects in mitochondria. Moreover, the methylation of whole mtDNA was found to be increased, reflecting the instability of fish mtDNA with mitochondrial dysfunction under nutrient fluctuations. Overall, these findings suggest that fish health may be significantly affected during aquaculture processes due to profound and long-lasting deficits in mitochondrial response to external variables.