Roles of Mitochondrial Fusion and Division in Harmine Derivative H-2-168-Induced Neurotoxicity.

Harmine (HM) has several pharmacological effects; however, severe neurotoxicity limits its clinical application and development. HM neurotoxicity is associated with abnormal energy metabolism. This study aimed to explore the roles and underlying mechanisms of mitochondrial fusion and division in HM derivative H-2-168-induced neurotoxicity. PC12 cells were treated with H-2-168, Mdivi-1 (an inhibitor of mitochondrial division), or a combination of both. Cell viability, levels of reactive oxygen species (ROS), adenosine triphosphate (ATP), lactic dehydrogenase (LDH), mitochondrial morphology, and membrane potential were measured. Immunofluorescence (IF) and western blotting were used to determine the expression of apoptosis-, mitochondrial fusion-, and division-related proteins. Additionally, PC12 cells with Drp1 knockdown or Mfn2 overexpression were generated to explore their effects. H-2-168 alone or in combination with Mdivi-1 significantly reduced PC12 cell viability, induced apoptosis, and impaired mitochondrial function. These effects were accompanied by increased levels of ROS and LDH, reduced ATP levels, upregulation of caspase-3, cytochrome c (Cyt-c), Drp1, and Fis1, and downregulation of Mfn2 and OPA1. Additionally, Drp1 knockdown or Mfn2 overexpression further enhanced the H-2-168-induced reduction in cell viability. These data implied that H-2-168 may initiate apoptosis in PC12 cells by influencing the balance between mitochondrial fusion and division, accompanied by changes in energy metabolism, which may induce neurotoxicity.