This study was designed to determine the effects and underlying mechanism of
honokiol (HNK) on
traumatic brain injury (TBI). A rat TBI model was constructed using the modified Feeney free-fall percussion method and treatment with HNK via
intraperitoneal injection. The brain tissues of the rats in each group were assessed using the
terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay to detect the level of neuronal apoptosis. Western blots were used to detect the expression levels of apoptosis-related
proteins (Bcl-2 and Bax), and ELISAs were used to measure the levels of pro-inflammatory
cytokines (IL-18 and IL-1β) and the activity of caspase-1. In addition, the mitochondrial membrane potential,
reactive oxygen species (ROS), and
adenosine 5'-triphosphate (
ATP) were also measured. Western blots and qRT-PCRs were used to determine the relative expression levels of the mitochondrial unfolded protein response (UPRmt)-related
proteins and mRNAs. Based on the experimental results, treatment with HNK was associated with a decrease in the number of TUNEL-positive cells, downregulated Bax expression levels, elevated Bcl-2 expression levels, and inhibition of neuronal apoptosis in the brain tissue of TBI rats. HNK also suppressed
neuroinflammation by decreasing IL-1β and
IL-18 levels and caspase-1 activity. Additionally, HNK lowered the mitochondrial membrane potential and ROS levels, increased
ATP levels, and improved
mitochondrial dysfunction in neural cells. Furthermore, in the investigation of the mechanism of HNK on TBI, we observed that HNK could activate UPRmt by upregulating the
mRNA and
protein expression levels of HSPA9, CLPP, and HSP60 in the brain tissues of TBI rats. Collectively, HNK reduced
mitochondrial dysfunction, inhibited the apoptosis of nerve cells, and attenuated
inflammation in the brains of TBI rats. The protective effect of HNK may be achieved through the activation of UPRmt.