Abstract: Objective To elucidate the role of programmed cell death factor 4 (PDCD4) in mitochondrial dysfunction caused by sepsis-related vascular endothelial damage. Methods Cultured human umbilical vein endothelial cells (HUVECs) and mouse vascular endothelial cells (C166 cells) were transfected with a small interfering RNA targeting PDCD4 followed by treatment with lipopolysaccharide (LPS) alone or in combination with carbonyl cyanide 3-chlorophenylhydrazone (FCCP). The proteomic changes in the cells after PDCD4 knockdown were analyzed using LC-MS/MS technique. The mRNA expressions of PDCD4 and the genes associated with cell inflammation and apoptosis were detected with RT-PCR, and the expressions of FIS1, DRP1 and OPA1 proteins key to mitochondrial fission and fusion were determined using Western blotting. JC-1 and MitoSOX fluorescent probes were used to observe the changes in mitochondrial membrane potential and mitochondrial reactive oxygen species levels under by a laser confocal microscope. Results LPS stimulation of the cells significantly increased the mRNA expressions of interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and monocyte chemoattractant protein 1 (MCP1) and enhanced the cellular expression of PDCD4 (P<0.05). Proteomic analysis suggested a correlation between PDCD4 knockdown and changes in mitochondrial dynamics in the cells. LPS treatment significantly increased the expressions of mitochondrial fission proteins FIS1 and DRP1 and lowered the expression of the fusion protein OPA1 in the cells (P<0.05), causing also mitochondrial oxidative stress and reduction of the mitochondrial membrane potential (P<0.05). In HUVECs, treatment with FCCP significantly attenuated the protective effect of PDCD4 knockdown, which inhibited LPS-induced inflammation and oxidative stress and restored the balance between mitochondrial fission and fusion. Conclusion PDCD4 knockdown protects vascular endothelial cells against LPS- induced damages by repressing mitochondrial fission and oxidative stress, promoting mitochondrial fusion, and maintaining normal mitochondrial function.

Key words: sepsis; vascular endothelial cells; mitochondrial dynamics; PDCD4; inflammation