Elucidating PAR1 as a therapeutic target for delayed traumatic brain injury: Unveiling the PPAR-γ/Nrf2/HO-1/GPX4 axis to suppress ferroptosis and alleviate NLRP3 inflammasome activation in rats

Repetitive traumatic brain injury (RTBI) is acknowledged as a silent overlooked public health crisis, with an incomplete understanding of its pathomechanistic signaling pathways. Mounting evidence suggests the involvement of thrombin and its receptor, the protease-activated receptor (PAR)1, in the development of secondary injury in TBI; however, the consequences of PAR1 modulation and its impact on ferroptosis-redox signaling, and NLRP3 inflammasome activation in RTBI, remain unclear. Further, the utilitarian function of PAR1 as a therapeutic target in RTBI has not been elucidated. To study this crosstalk, RTBI was induced in Wistar rats by daily weight drops on the right frontal region for five days. Three groups were included: normal control, untreated RTBI, and RTBI+SCH79797 (a PAR1 inhibitor administered post-trauma at 25 μg/kg/day). The concomitant treatment of PAR1 antagonism improved altered behavior function, cortical histoarchitecture, and neuronal cell survival. Moreover, the receptor blockade downregulated mRNA expression of PAR1 but upregulatedthat of the neuroprotective receptor PPAR-γ. The anti-inflammatory impact of SCH79797 was signified by the low immune expression/levels of NF-κB p65,TNF-α, IL-1β, and IL-18. Consequently, the PAR1 blocker hindered the formation of inflammasome components NLRP3, ASC, and activated caspase-1. Ultimately, SCH79797 treatment abated ferroptosis-dependent iron redox signaling through the activation of the antioxidant Nrf2/HO-1 axis and its subsequent antioxidant machinery (GPX4, SOD) to limit lipid peroxidation, iron accumulation, and transferrin serum increment. Collectively, SCH79797 offered putative preventive mechanisms against secondary RTBI consequences in rats by impeding ferroptosis and NLRP3 inflammasome through activating the PPAR-γ/Nrf2 antioxidant cue.