Effects of preconditioned mesenchymal stem cells secretome intranasal administration on perinatal asphyxia-induced mitochondrial dysfunction and cell death in rat hippocampus : role of nrf2 activation

Abstract

Perinatal asphyxia (PA) is a severe condition that can lead to long-lasting neurological impairments affecting the surviving newborns. This thesis aims to investigate the effects of PA on mitochondrial dynamics in the rat hippocampus at early (P1) and late (P7) neo-natal stages and to explore the potential therapeutic benefits of intranasal mesenchymal stem cell secretome (MSC-S) administration. It is hypothesised that PA increases mito-chondrial fission, inducing delayed cell death in the rat hippocampus, and that these al-terations can be prevented by neonatal intranasal administration of secretome derived from preconditioned human mesenchymal stem cells via Nrf2 pathway activation. The study provides evidence for a transient activation of the Nrf2 pathway following MSC-S administration on a rat model of PA. Nevertheless, the precise role of Nrf2 activa-tion in the effect of MSC-S remains to be fully elucidated. PA-induced changes in mito-chondrial dynamics proteins, with increased fission proteins Drp1 at P1 and Fis1 at P7, and increased fusion protein S-OPA1 isoform at P1 and L-OPA at P7. Furthermore, PA decreased mitochondrial density and mass by decreasing the D-Loop region expression of mitochondrial DNA at P1 but not at P7. Expansion microscopy analysis revealed de-creased mitochondria density in the CA1 and dentate gyrus (DG) regions of PA-exposed animals at P1, with smaller mitochondria in the DG than in CA1. Sex-specific differences were identified in response to PA. Female PA-rats exhibited altered OPA1 expression at P1 and P7, suggesting a potential upregulation of mitochondrial fission at P1 and in-creased fusion at P7, whose impact on mitochondrial bioenergetics requires further stud-ies. Treatment with MSC-S derived from preconditioned human MSC normalised fission pro-teins to control levels, but did not modify the effect of PA on OPA1 levels, either at P1 or at P7, nor on mitochondrial density. These findings contribute to our understanding of the pathophysiology of PA and emphasise the importance of considering sex as a biolog-ical variable. Future research should focus on unravelling the molecular mechanisms be-hind these sex-specific differences.