Alzheimer’s disease alters astrocytic functions related to neuronal support and transcellular internalization of mitochondria

Under physiological conditions in vivo astrocytes internalize and degrade neuronal mitochondria in a process called transmitophagy. Mitophagy is widely reported to be impaired in neurodegeneration but it is unknown whether and how transmitophagy is altered in Alzheimer’s disease (AD). Here we report that the internalization and degradation of neuronal mitochondria are significantly increased in astrocytes isolated from aged AD mouse brains. We also demonstrate for the first time a similar phenomenon between human neurons and AD astrocytes, and in murine hippocampi in vivo. The results suggest the involvement of S100a4 in impaired mitochondrial transfer between neurons and aged AD astrocytes. Significant increases in the mitophagy regulator Ambra1 were observed in the aged AD astrocytes. These findings demonstrate altered neuron-supporting functions of aged AD astrocytes and provide a starting point for studying the molecular mechanisms of transmitophagy in AD.