RIPK3 activation of CaMKII triggers mitochondrial apoptosis in NIBV-infected renal tubular epithelial cells.

The purpose of this study was to investigate whether RIPK3-mediated programmed cell death can promote the replication and transmission of renal infectious bronchitis virus in renal tubular epithelial cells. Primary renal tubular epithelial cells were extracted from 1 to 7 day old Hy-Line Brown chicks, cultured in vitro by type I collagenase digestion, and infected with 1MOI SX9 strain. Cell samples were collected at 12 hpi, 24 hpi, 36 hpi and 48 hpi for experimental exploration. Our results showed that NIBV infection could lead to programmed necrosis and mitochondrial apoptosis, and the expression levels of programmed necrosis-related genes TNFR1, TRADD, FADD, RIPK1, RIPK3 and MLKL increased significantly with the extension of infection time, the expression levels of mitochondrial apoptosis-related genes Cyt-C, APAF-1, Caspase-9 and Csapase-3 were significantly increased at 36 hpi. While, after 36 hpi of virus infection, apoptosis decreased and necrosis increased, and virus replication peaked. In order to further explore the effect of necroptosis on the amplification of renal infectious virus, the RIPK3 was inhibited at 36 hpi. Inhibition of necroptosis could reduce viral replication and cell death, programmed necrosis occurred in the cells, and cell membrane perforation led to virus diffusion and replication. NIBV-induced necroptosis depends on RIPK3, and RIPK3 activates CAMKII and interacts to cause abnormal opening of mitochondrial membrane permeability transition pore, promotes Ca2 + influx into mitochondria, initiates mitochondrial apoptosis. While, inhibition of RIPK3 significantly inhibited the programmed necrosis of cells caused by NIBV infection, making excessive necrosis into moderate necrosis, thereby inhibiting the replication of the virus in cells.