PARP3 SHAPES NEUROINFLAMMATORY AND SYNAPTIC RESPONSES IN NEONATAL HYPOXIC-ISCHEMIC BRAIN INJURY

Perinatal hypoxic-ischemic encephalopathy (HIE) is a leading cause of neonatal brain injury, contributing to approximately 25% of childhood neurodevelopmental disorders. Poly(ADP-ribose) polymerases (PARPs), key mediators of the HIE-induced DNA damage response (DDR), influence chromatin remodeling and transcriptional regulation. Among them, PARP-3, a less-studied isoform, catalyzes mono(ADP-ribosylation).
In this study, we investigated the role of PARP3 in immune responses to HIE using Parp3^-/- mouse and human microglia cell (CHME3) models. Parp3^-/- mice exhibited greater acute brain damage, particularly in the striatum, 24 hours post-insult. Single-nucleus RNA sequencing of P9 striatum three hours after HIE revealed that wild-type brains showed a robust induction of TNFα/NFκB signaling, heat-shock/chaperone programs, and hypoxia-responsive pathways across major cell types. In contrast, Parp3^-/- brains showed broad enrichment of synaptic membrane, ion-channel, and neurotransmitter receptor programs extending beyond neurons to astrocytes, oligodendrocytes, pericytes, and ependymal cells, alongside suppression of inflammatory cytokine pathways. Microglia in Parp3^-/- brains adopted a proliferative, less inflammatory state with reduced TYROBP-associated phagocytic programs and diminished chemokine expression (Ccl3/Ccl4), while gaining synaptic localization and microautophagy signatures. Immunohistochemical studies confirmed uncontrolled microglia proliferation and impaired migration in the PARP3-deficient striatum after HI. Similarly, Parp3^-/-human CHME3 cells displayed abnormal activation and reduced migration ability even under resting conditions. These findings indicate that PARP3 coordinates neuroinflammatory and synaptic responses to hypoxic-ischemic injury, and its loss disrupts immune signaling and cellular communication across multiple brain cell types, exacerbating tissue damage. Targeting PARP3 may offer a novel therapeutic strategy to modulate neuroinflammation and improve outcomes in neonatal HIE.