Effect of MALT1 inhibition by MI‑2 on the microglial phenotype switch, inflammatory cytokine secretion, neuronal loss and oxidative stress in Alzheimer's disease

Mucosa‑associated lymphoid tissue lymphoma translocation protein 1 (MALT1) is a key paracaspase enzyme regulating immune responses, inflammation and oxidative stress. The present study aimed to investigate the effect of MALT1 inhibition on neuroinflammation, neuronal loss and oxidative stress in Alzheimer's disease (AD). A co‑culture system involving microglia and neuron cells under β‑amyloid (Aβ) intervention was used to establish AD cellular models using human microglia HMC3 cells and neuroblastoma SH‑SY5Y cells and mouse microglia BV‑2 and hippocampal neuron HT‑22 cells. The inhibition of MALT1 proteolytic activity was achieved by MALT1 inhibitor 2 (MI‑2) treatment, and the NF‑κB pathway was activated by phorbol 12‑myristate 13‑acetate (PMA) treatment in HMC3 and BV‑2 cells. Western blotting, ELISA, Cell Counting Kit‑8, EdU staining, reactive oxygen species (ROS) detection and reduced glutathione (GSH) assays were performed to evaluate molecular changes, inflammatory responses, neuronal viability and oxidative stress. MALT1 expression was upregulated following Aβ treatment in HMC3 and BV‑2 cells. MALT1 inhibition by MI‑2 suppressed the microglial M1 phenotype but enhanced the M2 phenotype, reduced the levels of the proinflammatory cytokines TNF‑α and IL‑1β and inactivated the NF‑κB pathway in HMC3 and BV‑2 cells. Moreover, microglial MALT1 inhibition elevated cell viability (verified by Cell Counting Kit‑8 and EdU assays), increased the level of reduced glutathione and decreased the levels of reactive oxygen species in SH‑SY5Y and HT‑22 cells. NF‑κB activation by PMA attenuated the effects of MALT1 inhibition on the microglial phenotype switch and proinflammatory cytokine secretion in HMC3 and BV‑2 cells, as well as cell viability and oxidative stress in SH‑SY5Y and HT‑22 cells. The present study reveals that MALT1 inhibition may suppress microglial M1 phenotype, neuroinflammation, neuronal loss and oxidative stress by inactivating the NF‑κB pathway in AD.