Astrocyte Homeostatic Gene Expression Is Altered Across Pain States

Astrocytes provide homeostatic support for the CNS environment. In pathology such as chronic pain, astrocytes become “reactive”; however, little is known about how this reactive state alters astrocytic homeostatic functions. We have previously observed that spinal cord astrocytes increase expression of glial fibrillary acidic protein (GFAP) in a preclinical model of post-fracture pain, which is thought to indicate a reactive astrocyte state. In contrast, depletion of microglia increases GFAP but reduces pain. Such findings highlight a disconnect between GFAP levels and astrocyte function. We hypothesized that microglia depletion may alter astrocyte homeostasis differently than an injury response, even if GFAP is increased in both conditions. In this study, we used qPCR of lumbar spinal cord to track the expression of genes related to astrocytic homeostatic functions following fracture. We find significant increases in RNA for glutamate transporters (Slc1a3), potassium channels (Kcnj10), and gap junctions (Gja1) by 24 hours post-fracture compared to uninjured mice as well as increases in RNA for GFAP. In contrast, we found that 24 hours after microglia depletion there are increases in RNA for GFAP and Kcnj10 but not for Gja1 or Slc1a3. When we looked at a chronic injury timepoint, 5 weeks post-fracture, we instead saw decreases in Slc1a3 and Kcnj10 compared to controls. These decreases were not seen in 5-week post-fracture mice where microglia were depleted at 3 weeks, indicating microglia depletion may normalize astrocyte functions. These results indicate that astrocyte function is differentially altered in acute and chronic pain, and with microglia depletion.