HMGB1 in traumatic brain injury– the effects of hmgb1 isoforms on total cell count, neurogenesis and astrogliogenesis in cortical rat tissue

Abstract

Background: Traumatic brain injury (TBI) is amongst the leading causes of mortality and morbidity globally. Neuroinflammation is heavily implicated in TBI pathophysiology. High mobility group box-1 (HMGB1) protein is a master initiator of this process, resulting in secretion of key pro-inflammatory cytokines involved in secondary injury to the brain. Three HMGB1-isoforms have been identified, as determined by redox-status. Despite extensive research into HMGB1 as a therapeutic target, the differential effects of each isoform remain unknown. This study aims to investigate the effect of different HMGB1-isoforms on cortical neurogenesis in vitro. Methods: Neural stem cell cultures generated from postnatal rat cortical tissue were plated on 24-well plates. Neurogenesis in presence or absence of different 100ng/mL HMGB1-isoforms (ds-HMGB1, fr-HMGB1, and ox-HMGB1) was quantified using immunohistochemistry at 3DIV and 7DIV time-points. Results: Administration of ds-HMGB1 resulted in a significant reduction in the counts of total number of cells (DAPI+), neurons (Tuj1+) cells and astrocytes (GFAP+) at 7DIV, however there was no change in proportions of either cell phenotypes. Exposure to ox-HMGB1 resulted in a significant reduction in the proportion of astrocytic (GFAP+/DAPI) and neuronal (Tuj1+/DAPI) cells at 7DIV with no effect on total cell counts or the number of each phenotype. No significant effect was noted with fr-HMGB1 treatment. Conclusion: Exposure to ds-HMGB1 results in a decreased total cell count, consistent with anti-trophic or anti-survival effect, particularly of neurons and astrocytes. but there was no fate determining effect. Exposure to ox-HMGB1 showed an anti-neurogenic effect and a reduction in astrogliogenesis. Future experiments investigating the exact mechanisms leading to those observations are needed.