Abstract
OBJECTIVE: This study aims to elucidate the apoptotic mechanism induced by doxycycline (Dox) in human microglial clone 3 (HMC3) cells infected with the Brucella suis S2 strain, with the goal of identifying potential therapeutic targets for neurobrucellosis. METHODS: The expression of calreticulin (CALR) at both the protein and mRNA levels was assessed using Western blot analysis and reverse transcription-quantitative polymerase chain reaction (RT-qPCR), respectively, following exposure of HMC3 cells to varying concentrations and treatment durations of Dox. Apoptosis rates were determined via flow cytometry. To investigate the involvement of the inositol-requiring enzyme-1 (IRE1)/Caspase-12/Caspase-3 pathway, CALR protein levels were analyzed through Western blot after a 12-hour treatment with 160 μM Dox. Endoplasmic reticulum (ER) stress and intracellular calcium (Ca²⁺) concentrations were evaluated using fluorescent staining. The same parameters were measured in B. suis S2-infected HMC3 cells following treatment with 160 μM Dox. RESULTS: Treatment with 160 μM Dox for 12 hours resulted in a reduction in CALR protein levels and the induction of apoptosis in HMC3 cells. The downregulation of CALR activated the IRE1/Caspase-12/Caspase-3 signaling pathway, leading to apoptosis. Similar apoptotic effects were observed in B. suis S2-infected HMC3 cells following Dox treatment. CONCLUSION: Dox promotes apoptosis in B. suis S2-infected HMC3 cells by suppressing CALR expression and activating the IRE1/Caspase-12/Caspase-3 signaling pathway. These findings suggest that CALR regulation may serve as a potential therapeutic target for neurobrucellosis.