Delayed CO₂ postconditioning promotes neurological recovery after cryogenic traumatic brain injury by downregulating...

Few treatments are available in the subacute phase of traumatic brain injury (TBI) except rehabilitation training. We previously reported that transient CO₂ inhalation applied within minutes after reperfusion has neuroprotective effects against cerebral ischemia/reperfusion injury. In this study, it was hypothesized that delayed CO₂ postconditioning (DCPC) starting at the subacute phase may promote neurological recovery of TBI.

Using a cryogenic TBI (cTBI) model, mice received DCPC daily by inhaling 5%/10%/20% CO₂ for various time-courses (one/two/three cycles of 10-min inhalation/10-min break) at Days 3-7, 3-14 or 7-18 after cTBI. Beam walking and gait tests were used to assess the effect of DCPC. Lesion size, expression of GAP-43 and synaptophysin, amoeboid microglia number and glia scar area were detected. Transcriptome and recombinant interferon regulatory factor 7 (Irf7) adeno-associated virus were applied to investigate the molecular mechanisms.

DCPC significantly promoted recovery of motor function in a concentration and time-course dependent manner with a wide therapeutic time window of at least 7 days after cTBI. The beneficial effects of DCPC were blocked by intracerebroventricular injection of NaHCO₃ . DCPC also increased puncta density of GAP-43 and synaptophysin, and reduced amoeboid microglia number and glial scar formation in the cortex surrounding the lesion. Transcriptome analysis showed many inflammation-related genes and pathways were altered by DCPC, and Irf7 was a hub gene, while overexpression of IRF7 blocked the motor function improvement of DCPC.

We first showed that DCPC promoted functional recovery and brain tissue repair, which opens a new therapeutic time window of postconditioning for TBI. Inhibition of IRF7 is a key molecular mechanism for the beneficial effects of DCPC, and IRF7 may be a potential therapeutic target for rehabilitation after TBI.