Astrocyte Senescence Disrupts the Extracellular Mitochondrial Compartment and Compromises Bioenergetic Support to Human Neurons

Astrocyte senescence is a recognized feature of brain aging, but its impact on neuronal mitochondrial homeostasis remains poorly defined, particularly in human cells. Here we show that doxorubicin-induced senescence disrupts mitochondrial function in primary human astrocytes and compromises their capacity to sustain neuronal bioenergetics. Senescent astrocytes accumulated a denser population of smaller, ultrastructurally damaged mitochondria together with increased levels of fission, fusion and biogenesis-associated proteins. Despite this apparent expansion of the mitochondrial compartment, these cells displayed reduced mitochondrial membrane potential, intracellular ATP and cellular metabolic activity, indicating accumulation of a functionally impaired mitochondrial population. Senescence also remodeled the extracellular mitochondrial compartment: conditioned medium from senescent astrocytes contained fewer mitochondrial particles with lower membrane potential and reduced ATP. Functionally, conditioned medium from control astrocytes increased TOMM20 and PGC-1α levels in human postmitotic neurons, whereas medium from senescent astrocytes failed to elicit this response and instead promoted hydrogen peroxide accumulation, ATP depletion and reduced cellular metabolic activity in the absence of overt cytotoxicity. Neurons acquired an astrocyte-derived MitoTracker signal from both conditions. Our data indicate that factors released by senescent human astrocytes are sufficient to induce neuronal mitochondrial and redox dysfunction.