Spinal astrocytes hardly proliferate following peripheral nerve injury: Evidence from adult Aldh1l1-GFP reporter mice

Peripheral nerve injury (PNI) induces neuroinflammatory responses in the spinal cord that contribute to neuropathic pain. While microglial proliferation is a well-established feature of this process, whether spinal astrocytes undergo proliferation after PNI seems to be controversial. In this study, we examined astrocytic proliferative responses using Aldh1l1-GFP transgenic mice subjected to spinal nerve ligation (SNL), combined with immunohistochemical and transcriptomic analyses. SNL elicited a temporally organized glial reaction, characterized by early microglial reactivity followed by delayed astrocytic reactivity marked by increased GFAP expression. Despite pronounced astrocytic reactivity, the number of Aldh1l1-GFP⁺ astrocytes in the spinal dorsal horn remained unchanged across all examined time points, and only negligible colocalization with proliferation markers (Ki67 and EdU) was detected. Consistently, transcriptomic analyses revealed extensive astrocyte-associated transcriptional reprogramming without activation of cell-cycle gene programs after PNI. Minimally proliferative astrocytic responses were observed in additional cranial nerve injury model, partial infraorbital nerve transection (pIONT), in which proliferative responses in medullary dorsal horn were also restricted to microglia. Together, these findings demonstrate that spinal or medullary astrocytes respond to PNI with minimal proliferation (rare colocalization with proliferation markers) and primarily through reactive remodeling rather than cell division, providing direct evidence addressing previous inconsistencies and highlighting astrocytic functional plasticity as a key mechanism contributing to neuropathic pain.