2025 Theses Doctoral

Glucocorticoid stress hormones in the regulation of small extracellular vesicle biogenesis and secretion in brain cells

Burke, Mia

Chronic stress, characterized by long-term elevation of glucocorticoid (GC) stress hormones, is a major risk factor for Alzheimer’s disease (AD). Stress and high GC levels stimulate AD cellular mechanisms in the brain, including tau hyperphosphorylation and accumulation, Aβ peptide production, activation of pro-inflammatory pathways, and the dramatic acceleration of these pathologies in AD mouse models. One reported accelerator of AD pathology and disease progression is the secretion of small extracellular vesicles (sEVs) carrying pathogenic proteins and signaling molecules between brain regions.

However, the role of GCs in sEV biogenesis and secretion remains poorly understood. Using total internal reflection fluorescence (TIRF) microscopy and the pH-sensitive fluorescent marker mCh-CD63-pHluorin to visualize sEV release, we show that GCs stimulate sEV secretion in a neuronal cell line. We also find that sEVs produced by these same neuronal cells, when stably expressing the familial P301L mutation of tau, can carry oligomeric tau which underscores the potential for amplified sEV release by GCs to enhance spread of disease-associated molecules.

This GC-dependent secretion requires the small GTPase Rab27a and neutral sphingomyelinase 2 (nSMase2), an enzyme that catalyzes ceramide production and drives sEV biogenesis. Moreover, we find that GCs promote sEV release by activating nSMase2, and that this event requires mitochondrial reactive oxygen species (mROS) and opening of the mitochondrial permeability transition pore (mPTP). These findings link GC-induced mitochondrial damage, specifically mPTP opening, to nSMase2 activation and the release of sEVs by neuronal cells.