Systemic Inflammation Decreases Initial Brain Injury but Attenuates Neurite Extension and Synapse Formation during the Repair of Injured Brains

In this study, we explored the impact of systemic inflammation on initial brain injury and repair processes, including neurite extension and synapse formation. For this purpose, we established a brain injury model by administering adenosine triphosphate (ATP), a component of damage-associated molecular patterns (DAMPs), through stereotaxic injection into the striatum of mice. Systemic inflammation was induced by intraperitoneal injection of lipopolysaccharide (LPS-ip). Bulk RNA-sequencing (RNA-seq) analyses and immunostaining for microtubule-associated protein 2 (MAP2) and tyrosine hydroxylase (TH) showed that LPS-ip led to a reduction in initial brain injury, but inhibited neurite extension into the damaged brain. LPS-ip upregulated expression of defense response genes and anti-apoptotic genes, but decreased expression of genes associated with repair and regeneration. In addition, LPS-ip reduced levels of vGlut1 and PSD95 (markers for excitatory pre and post synapses, respectively), but had little effect on vGAT and gephyrin (markers for inhibitory pre and post synapses, respectively). Taken together, these findings suggest that systemic inflammation reduce initial damage but impede subsequent repair process.