Aeromonas hydrophila infection activates death receptor apoptosis pathway in the red blood cells of grass carp (Ctenopharyngodon idellus)

Abstract

Fish blood contains RBCs (Red blood cells) as the major cells. Unlike the absence of nucleus in mammalian RBC, fish RBC contains a nucleus. Previous researches have indicated that fish RBCs have a significant function in immune responses. However, the mechanism underlying the immune responses against bacterial infection of teleost RBCs remains enigmatic. To decipher the mechanisms, after the infection of Aeromonas hydrophila, transcriptomic profiling of grass carp RBCs was analyzed. Outcomes demonstrated that there were 2144 altogether DEGs (Differently Expressed Genes) between the A. hydrophila-infected and non-infected groups, which includes 817 up-regulated and 1327 down-regulated DEGs. Differently Expressed Genes were allocated to 45 GO terms, including 20 natural procedure terms, 14 cell related element, and 11 terms related to molecular functions. In addition, to validate our transcriptomic data, the expression levels of cytokines by Quantitative Reverse Transcription Polymerase Chain Reaction showed that they (e.g. CCL4, CCL11, CCL20, IL-4, IL-12, and IFNα) were significantly increased after A. hydrophila infection, which was identical to the expression patterns of transcriptomic data. The infection could cause the apoptosis of RBCs which was confirmed by annexin V/PI assay. To further elucidate the apoptosis pathway, the expression levels of genes by mRNA included in cellular apoptosis were monitored. The outcomes indicated that the expressions of mRNA of p53, Fas, Leucine-rich repeats, death domain-containing (LRDD) and caspase 8 were all significantly increased, respectively. Our results support the notion that A. hydrophila infection could activate Fas-related death receptor apoptosis pathway in grass carp RBCs, which will reveal another insight on the mechanisms underlying the antibacterial immunity of teleost fish RBCs.