[Influence of family with sequence similarity 134, member B-mediated reticulophagy on lipopolysaccharide-induced apoptosis of mouse dendritic cells]

Objective: To investigate the influence of family with sequence similarity 134, member B (FAM134B)-mediated reticulophagy on lipopolysaccharide (LPS)-induced apoptosis of mouse dendritic cells (DCs), so as to provide a basis for improving the immune suppression of sepsis caused by wound infection and other factors. Methods: The experimental research methods were used. The DC line DC2.4 of the 3^rd to 10^th passage in the logarithmic growth stage was collected for experiments. DCs were divided into LPS stimulation 0 h (no stimulation) group, LPS stimulation 6 h group, LPS stimulation 12 h group, LPS stimulation 24 h group, and LPS stimulation 72 h group, which were cultured with 1 μg/mL LPS (the same concentration below) for the corresponding time. The protein expressions of FAM134B, microtubule-associated protein 1 light chain 3B (LC3B), and transporter protein SEC61B were determined by Western blotting, and the ratio of LC3B-Ⅱ/LC3B-Ⅰ was calculated (n=3). DCs were divided into phosphate buffer solution (PBS) group and LPS group for corresponding treatment. After 24 hours of culture, the expression of FAM134B and its co-localization with lysosomal probes and LC3B were detected using immunofluorescence method, while the number of autolysosomes in cells were observed through transmission electron microscope. DCs were divided into the FAM134B-knockdown group that were transfected with lentivirus containing small interfering RNA (siRNA) sequence of FAM134B gene and the empty vector group with empty lentivirus transfected. At post transfection hour 72, the fluorescence expression of cells was observed under the inverted fluorescence phase contrast microscope, meanwhile, the normally cultured DCs were set as blank control group, and the same observation was performed at the corresponding time point. DCs were divided into PBS alone group and LPS alone group, DCs successfully transfected with lentivirus containing siRNA sequence of FAM134B gene were divided into FAM134B-knockdown+PBS group and FAM134B-knockdown+LPS group, and DCs successfully transfected with empty lentivirus were divided into empty vector+PBS group and empty vector+LPS group. These cells were stimulated correspondingly and cultured for 24 hours. The protein expression of FAM134B was detected using Western blotting (n=3); the apoptotic rate of cells was determined by flow cytometry (n=3); the situation of apoptosis was observed by Hoechst staining, and the apoptotic rate was calculated (n=5); the protein expressions of cleaved cysteine aspartic acid specific protease-3 (caspase-3), B cell lymphoma 2 (Bcl-2), and Bcl-2-associated X protein (Bax) were detected using Western blotting, and the ratio of Bax/Bcl-2 was calculated (n=5). Data were statistically analyzed with one-way analysis of variance (ANOVA), least significant difference test, and ANOVA for factorial design. Results: Compared with those in LPS stimulation 0 h group, the protein expressions of FAM134B of cells in LPS stimulation 12 h group and LPS stimulation 24 h group were significantly increased (P<0.05), the protein expressions of SEC61B of cells in LPS stimulation 6 h group, LPS stimulation 12 h group, LPS stimulation 24 h group, and LPS stimulation 72 h group were significantly decreased (P<0.05), and the ratios of LC3B-Ⅱ/LC3B-Ⅰ of cells in LPS stimulation 24 h group and LPS stimulation 72 h group were obviously increased (P<0.05). As the most significant changes of three proteins were seen in the cells of LPS stimulation 24 h group, 24 h was used as the duration of subsequent LPS stimulation. After 24 hours of culture, the expression of FAM134B and its co-localization with LC3B and lysosomal probes in the cells of LPS group were all significantly enhanced, with a significant increase in the number of autolysosomes in comparison with those in PBS group. Both the empty vector group and the FAM134B-knockdown group showed high intensity fluorescence in the cells at post transfection hour 72, but the blank control group showed no fluorescence in the cells at the corresponding time point. After 24 hours of culture, the protein expression of FAM134B of cells in FAM134B-knockdown+PBS group was significantly lower than the expressions in PBS alone group and empty vector+PBS group (with P values all <0.05), the protein expression of FAM134B of cells in FAM134B-knockdown+LPS group was significantly lower than the expressions in LPS alone group and empty vector+LPS group (with P values all <0.05), the protein expression of FAM134B of cells in LPS alone group was significantly higher than that in PBS alone group (P<0.05), while the protein expression of FAM134B of cells in empty vector+LPS group was significantly higher than that in empty vector+PBS group (P<0.05). After 24 hours of culture, flow cytometry assay revealed that the apoptotic rate of cells in PBS alone group, LPS alone group, empty vector+PBS group, empty vector+LPS group, FAM134B-knockdown+PBS group, and FAM134B-knockdown+LPS group were (13.3±0.8)%, (32.6±4.3)%, (17.0±1.5)%, (51.7±3.3)%, (52.4±3.1)%, and (62.3±2.6)%, respectively. After 24 hours of culture, compared with those in LPS alone group and empty vector+LPS group, the protein expression of cleaved caspase-3, the ratio of Bax/Bcl-2, and the apoptotic rates of cells detected by flow cytometry and Hoechst staining were significantly increased in FAM134B-knockdown+LPS group (P<0.05); compared with those in the corresponding PBS treatment group, namely, PBS alone group, empty vector+PBS group, and FAM134B-knockdown+PBS group, the protein expression of cleaved caspase-3, the ratio of Bax/Bcl-2, and the apoptotic rates of cells detected by flow cytometry and Hoechst staining were significantly increased in LPS alone group, empty vector+LPS group, and FAM134B-knockdown+LPS group (P<0.05). Conclusions: The activation of reticulophagy mediated by FAM134B in mouse DCs is enhanced and peaked in 24 hours under LPS stimulation, and the activated reticulophagy has a significant inhibitory effect on cell apoptosis.