Grouper KCNE2 Restricts RGNNV Replication and Attenuates Virus-Induced Mitochondrial Depolarization and Apoptosis

Groupers (Epinephelus spp.) are economically important marine aquaculture species in China; however, recurrent outbreaks of red-spotted grouper nervous necrosis virus (RGNNV) severely constrain sustainable production. RGNNV induces host-cell apoptosis through mitochondrial membrane-potential dissipation, and ion-channel proteins are important regulators of mitochondrial membrane potential and apoptotic signaling. Our previous single-cell RNA-seq analysis identified marked upregulation of the ion-channel auxiliary-subunit gene kcne2 in RGNNV-infected target cells. Here, we cloned the full-length open reading frame of orange-spotted grouper ((Epinephelus coioides) kcne2. Phylogenetic analysis showed that kcne2 was most closely related to the Epinephelus moara ortholog, and tissue-expression analysis showed highest kcne2 expression in the heart and brain. In GS cells, kcne2 overexpression alleviated RGNNV-induced cytopathic effects and reduced RGNNV replication, whereas kcne2 knockdown exacerbated cell lesions and increased viral replication. kcne2 overexpression also attenuated RGNNV-induced loss of mitochondrial membrane potential and cellular apoptosis, whereas kcne2 silencing enhanced mitochondrial depolarization and apoptotic cell death. In addition, kcne2 overexpression increased the transcription of interferon-related genes (ifp35, irf3, isg15 and irf7) and pro-inflammatory cytokines (il-1β, il-6, il-8 and tnf-α), while KCNE2 silencing produced the opposite effects. Collectively, these findings indicate that KCNE2 contributes to the antiviral response against RGNNV by preserving mitochondrial homeostasis and promoting host interferon and inflammatory responses. This study provides insight into the role of piscine KCNE2 during viral infection.