THE OCCURRENCE OF MITOCHONDRIAL AUTOPHAGY AND NLRP3 INFLAMMATORY CORTICES AFTER CRANIOCEREBRAL TRAUMA AND THEIR CORRELATION WITH NEUROINFLAMMATORY RESPONSES

Mu He¹, Han Li¹, Xiaoli Min^{2, *}

¹Sichuan Province Forest Center Hospital, Chengdu 610081, PR China - ²Department of Cerebrovascular Disease, The Second Affiliated Hospital, Kunming Medical

Objective: To analyze mitochondrial autophagy and nod-like receptor protein 3 (NLRP3) inflammidas after traumatic brain injury and their correlation with neuroinflammatory responses.

Methods: Five cases of craniocerebral injury (the observation group) and 5 cases of non-craniocerebral injury (control group) were randomly selected. The expressions of autophagy-related proteins and mitochondrial marker proteins in brain tissues of each group were determined. Then 36 clean healthy male SD rats were randomly selected and divided evenly into a sham operation group and a model group. The rat model of brain injury was established. The autophagy inhibitor 3-methyladenine (3-MA), mitochondrial autophagy agent Mdivi-1, and autophagy agonist RAPA were used to regulate the mitochondrial autophagy after brain injury. The expression levels of LC3-Ⅱ, interleukin 1β (IL-1β), and caspase-1 expression were determined in each group. The expression levels of NLRP3, IL-1β, IL-18, and caspase-1 in the brain tissues of each group were measured by using 3-MA and Mdivi-1 to inhibit mitochondrial autophagy. The expression levels of NLRP3, IL-1β, and caspase-1 in the NLRP3 down-regulated group and the NLRP3 down-regulated control group were measured. Six rats to be knockouts of NLRP3, caspase-1, and IL-1βR were selected and bred with C57/B6-J mice. Another six wild-type mice in the same nest were selected as the control group.

Results: Compared with the control group, in the observation group the brain tissue p62, COXIV, TOM40, and MnSOD expression levels clearly declined and the LC3-Ⅱ expression level increased significantly (P<0.01). Compared with the model group, model group rats LC3-Ⅱ and caspase-1, IL-1β expression level increased significantly (P<0.05). Compared with the model group, the expression levels of LC3-Ⅱ in the 3-MA group significantly declined, but the IL-1β and caspase-1 expression levels increased significantly. The LC3-Ⅱ expression level increased significantly and the IL-1β and caspase-1 expression level clearly declined in both the Mdivi-1 and RAPA groups (P<0.05). Compared with the sham operation group, there was no significant difference in the time the rats were on the balance beam before injury (P>0.05). Starting from 1 day after the injury, the time the rats in the Mdivi-1 group stayed on the balance beam was significantly shortened, and the time to find the hidden platform was significantly prolonged starting from 12 days after injury (P<0.01). Compared with the control group, NLRP3, IL-1β, IL-18, and caspase-1 significantly declined in the brain tissue of the observation group (P<0.05). Compared with the NLRP3 down-regulated control group, the expression levels of NLRP3, IL-1β investment, and caspase-1 in the brain tissue of the NLRP3 down-regulated group were significantly reduced (P<0.01). There was no significant difference in the time the rats stayed on the balance beam before injury (P>0.01). From 2 days after injury, compared with the wild-type control group, the NLRP3, IL-1β, and caspase-1 knockout group rats spent significantly more time on the balance beam. From 11 days after injury, rats in the NLRP3, IL-1β, and caspase-1 knockout group took significantly more time to find the hidden platform (P<0.01). 

Conclusion: NLRP3 expression and mitochondrial autophagy were significantly increased after craniocerebral injury. Mitochondrial autophagy has a protective effect on nerve function, and inhibiting mitochondrial autophagy will significantly aggravate the neuroinflammatory response and hinder the recovery of nerve function. However, the NLRP3-mediated neuroinflammatory response is significantly enhanced, and down-regulation of NLRP3 expression can significantly reduce the neuroinflammatory response caused by craniocerebral injury, which is conducive to the recovery of nerve function.