Early life injury alters spinal astrocyte development

Neonatal injury alters synaptic transmission and plasticity in the spinal superficial dorsal horn (SDH), resulting in aberrant amplification of ascending nociceptive transmission. Astrocytes orchestrate synapse development and function across the CNS and have been shown to play a critical role in the emergence and maintenance of persistent pain. However, very little is currently known about the postnatal development of spinal astrocytes, nor about how the maturation of SDH astrocytes is impacted by early life injury. Here, we used a hindpaw incision model of postsurgical pain in postnatal day (P) 3 mice to elucidate the effects of neonatal injury on the maturation of SDH astrocytes. Three-dimensional morphological analysis of individual astrocytes revealed that incision elicits age-dependent changes to astrocyte structure. At P4, spinal astrocytes in incised mice show increased size and complexity compared to naïve controls. This is reversed at P10 and P24, as astrocytes from incised mice are smaller and less ramified compared to their naïve counterparts. Transcriptomic analysis of spinal astrocytes demonstrated that injury-evoked changes to astrocyte gene expression occur acutely. We found 76 differentially expressed genes (DEGs) at P4, many of which are related to cell motility and cytoskeletal organization (Thbs1, Efemp1, Acta1, Acta2, Tpm2, Fgf14) but very few DEGs at P10 and P24. Lastly, we identified that microglial engulfment of astrocytes occurs in the developing dorsal horn, and that this process is altered by neonatal injury in a sex-dependent manner. These data illustrate, for the first time, that neonatal injury alters the postnatal development of spinal astrocytes.