Macrophage epigenetic memories of early life injury drive neonatal nociceptive priming. [ATAC-Seq]

The developing peripheral nervous and immune systems are functionally distinct from adults. These systems are vulnerable to effects of early life injury which can influence outcomes related to nociception following subsequent injury later in life (i.e. “neonatal nociceptive priming”). The underpinnings of this phenomenon are largely unknown, although critical periods in macrophages can be epigenetically trained by injury. We found that macrophages are both necessary and partially sufficient to drive neonatal nociceptive priming possibly due to a long-lasting epigenetic remodeling of peripheral macrophages. The p75 neurotrophic factor receptor (NTR) was found to be an important effector in regulating this “nociceptive trained immunity”. p75NTR modulates the inflammatory profile and responses of rodent and human macrophages and this “pain memory” was able to be transferred to a naive host to alter sex-specific pain-related behaviors. This study reveals a novel mechanism by which acute post-surgical pain may transition to chronic pain in children. Overall design: Samples are macrophages isolated from the peritoneum and sorted by LysM+ cells. Groups included naïve P7 isolated, naïve P35 isolated and P35 isolated from animals that had received a hind paw incision at P7.