CXCL12 Engages Cortical Inhibitory Neurons to Enhance Dendritic Spine Plasticity and Structured Network Activity

The chemokine CXCL12 is a highly conserved peptide that regulates homeostatic processes in the brain throughout life. Recent work shows that CXCL12 increases dendritic spine density in cortical neurons, which requires activation of CXCL12's receptor CXCR4. This same pathway reverses cortical dendritic spine deficits and cognitive impairment in an animal model of neuroHIV. However, it remained unclear if CXCL12 simply preserved existing spines or also engaged spine plasticity processes that drove network-level adaptations. We therefore tested if CXCL12 could regulate dendritic spine turnover, maturation, clustering, and neuronal network activity in primary rat cortical neurons of either sex using live-cell imaging, confocal microscopy, and multielectrode arrays. Intriguingly, CXCL12-treated neurons formed significantly more new spines than controls, and this outcome was blocked by the CXCR4 antagonist AMD3100. CXCL12 also increased the density of thin spines expressing postsynaptic markers, including postsynaptic density protein 95 (PSD-95), phospho-PSD-95^Ser295, and GluA1, and allowed neurons to better maintain synaptic PSD-95 puncta size. Thin spines were modestly closer together after CXCL12 treatment, suggesting a possible effect on anatomical spine clustering. These effects translated to structured network activity, as CXCL12 increased spike frequency within network bursts in multielectrode array cultures. Finally, a targeted knockdown of CXCR4 in inhibitory neurons, which mostly lack dendritic spines, prevented CXCL12 from increasing spine density on excitatory neurons. Overall, our findings suggest CXCL12/CXCR4 signaling engages inhibitory neurons along with multiple aspects of spine dynamics and remodeling to shape how broader neuronal networks function.