ABSTRACT
BACKGROUND: The outcomes of traumatic brain injury (TBI) exhibit variance contingent upon biological sex. Although female sex hormones exert neuroprotective effects, the administration of estrogen and progesterone has not yielded conclusive results. Hence, it is conceivable that additional mediators, distinct from female sex hormones, merit consideration due to their potential differential impact on TBI outcomes. Calcitonin gene-related peptide (CGRP) exhibits sexually dimorphic expression and demonstrates neuroprotective effects in acute brain injuries. In this study, we aimed to examine sex-based variations in TBI structural and functional outcomes with respect to CGRP expression. METHODS: Male and female Sprague Dawley rats were exposed to controlled cortical impact to induce severe TBI, followed by interventions with and without CGRP inhibition. In the acute phase of TBI, the study centered on elucidating the influence of CGRP on oxidative stress, nuclear factor erythroid 2-related factor 2 (Nrf2) and endothelial nitric oxide synthase (eNOS) signaling in the peri-impact tissue. Subsequently, during the chronic phase of TBI, the investigation expanded to evaluate CGRP expression in relation to lesion volume, microvascular dysfunction, and white matter injury, as well as working and spatial memory, anxiety-like, and depression-like behaviors in subjects of both sexes. RESULTS: Female rats exhibited elevated levels of CGRP in the peri-impact brain tissue during both baseline conditions and in the acute and chronic phases of TBI, in comparison to age-matched male counterparts. Enhanced CGRP levels in specific brain sub-regions among female rats correlated with superior structural and functional outcomes following TBI compared to their male counterparts. CGRP inhibition induced heightened oxidative stress and a reduction in the expression of Nrf2 and eNOS in both male and female rats, with the observed alteration being more pronounced in females than in males. CONCLUSIONS: This study marks the inaugural identification of CGRP as a downstream mediator contributing to the sexually dimorphic response observed in TBI outcomes.
Investigating sex disparities in traumatic brain injury (TBI) is crucial for the advancement of precision therapeutics. Despite the neuroprotective effects demonstrated by female sex hormones, the administration of estrogen and progesterone has not produced conclusive results. Therefore, it is conceivable that additional mediators, separate from female sex hormones, warrant consideration due to their potential differential influence on TBI outcomes. In this study, we examined sex-related variations in calcitonin gene-related peptide (CGRP) expression in peri-impact brain tissue and investigated its potential implications on associated TBI outcomes. CGRP exhibits sexually dimorphic expression and exerts a multifaceted influence on diverse physiological processes that contribute to the pathophysiology of TBI. Our findings reveal that female rats exhibit heightened CGRP levels at both baseline and post-TBI within specific brain sub-regions, thereby contributing to superior structural and functional outcomes compared to their age-matched male counterparts. Additionally, we identified substantial sex-based variations in mechanisms modulated by CGRP pertaining to oxidative stress and microvascular dysfunction. The disparities in CGRP levels may be crucial for comprehending the advantageous outcomes noted in female TBI. Therefore, elucidating the sex-related distinctions in CGRP within TBI brains could pave the way for improved management and treatment strategies for TBI in both male and female individuals.