Drp1-Mediated Mitochondrial Fission Controls Cortical Astrocyte Organization During Development

Dysfunctional mitochondria are implicated in multiple neurodevelopmental disorders, and the role of mitochondria in brain development has historically been studied through the lens of neurons. However, neurons are surrounded by glial cells, which make up over half the brain parenchyma, and the role of mitochondria in the development of glia is still unclear. Astrocytes are glial cells characterized by their complex branched morphology that allows them to perform many functions such as inducing synaptogenesis in the developing cortex. Cortical astrocytes are organized in equidistant nonoverlapping, which is thought to enable them to form a network and communicate over long distances by gap junction coupling. However, the molecular mechanisms of how astrocytes establish this phenotype are not well understood. Past research in the Eroglu Lab has shown that early postnatal knockdown (KD) of Drp1, the regulator of mitochondrial fission, in astrocytes in the mouse cortex leads to astrocytes clustering. Therefore, we hypothesized that Drp1-induced mitochondrial fission regulates astrocyte organization in the mouse cortex. We uncovered that Drp1 KD astrocyte clusters are multi-cell clusters and have disorganized cell somas, confirming Drp1 controls the organization of astrocytes. Furthermore, we found that sparse Drp1 KD in astrocytes induces clustering into adulthood up to 6-month-old mice, indicating Drp1 control of astrocyte organization persists into adulthood. Additionally, Drp1 KD astrocyte clusters have decreased Connexin 43 gap junction protein expression, suggesting they have impaired gap junction coupling. Lastly, we found that astrocyte-specific conditional KO of Drp1 results in reduced astrocyte coverage in the cortex and astrocyte network disorganization, coupled with heterogeneous upregulation of GFAP, a marker of astrocyte dysfunction. These findings indicate that Drp1 controls astrocyte organization and function and underscore the importance and therapeutic potential of mitochondrial fission in the proper development of astrocytes.