Plateau hypoxia-induced upregulation of reticulon 4 pathway mediates altered autophagic flux involved in blood–brain barrier disruption after traumatic brain injury

This study aimed to examine reticulon 4 (RTN4), neurite outgrowth inhibitor protein expression that changes in high-altitude traumatic brain injury (HA-TBI) and affects on blood-brain barrier's (BBB) function. C57BL/6J 6-8-week-old male mice were used for TBI model induction and randomized into the normal altitude group and the 5000-m high-altitude (HA) group, each group was divided into control (C) and 8h/12h/24h/48h-TBI according to different times post-TBI. Brain water content (BWC) and modified Neurological Severity Score were measured, RTN4 and autophagy-related indexes (Beclin1, LC3B, and SQSTM1/p62) were detected by western blot, immunofluorescence technique, and PCR in peri-injury cortical tissues. The expression of NgR1, Lingo-1, TROY, P75, PirB, S1PR2, and RhoA receptors' downstream of RTN4 was detected by PCR. HA-TBI caused increased neurological deficits including motor, sensory, balance and reflex deficits, increased BWC, earlier peak RTN4 expression and a longer duration of high expression in peri-injury cortical tissues, and enhanced levels of Beclin1, LC3B, and SQSTM1/p62 to varying degrees. Concurrently, the transcription of S1PR2 and PirB, the main signaling molecules downstream of RTN4, was significantly increased. In HA-TBI's early stages, the increased RTN4 may regulate enhanced autophagic initiation and impaired autolysosome degradation in vascular endothelial cells via S1PR2 receptor activation, thereby reducing BBB function. This suggests that autophagy could be a new target using RTN4 intervention as a clinical HA-TBI mechanism.