Microglial purinergic receptor regulation by physiological factors and role in TNFalpha production

As the primary resident immune cell population in the CNS, microglia react to injury or infection and produce immunomodulatory factors. Uncontrolled microglial activation is thought to contribute to the pathology of several neurodegenerative disorders, many with incidence rates that vary by age and sex. Purinergic receptors (P2Rs) have been shown to modulate microglial activity, however prior to this study, alterations in P2R expression as a result of sex or aging had not been investigated. The expression of the rodent P2Rs and select associated genes was examined in microglia freshly-isolated from mice ranging in age from three days to 12 months-old. Many P2Rs showed increased expression in older mice, and the expression of some was sexually dimorphic at certain ages. Similarly, basal expression of many proinflammatory and neuroprotective genes in microglia was highest in adult mice. It was also observed that culturing microglia dramatically alters gene expression: ten P2Rs were affected; four changed by 90-fold or greater.;Neuronal populations vary across the CNS, but it was unknown if different local environments also resulted in microglial heterogeneity. Microglia isolated from five different CNS regions displayed differences in the expression of P2Rs and other genes. Levels were often lowest in spinal cord microglia, while the inverse was observed for TNFalpha. The pattern of microglial gene expression across the CNS sometimes changed with animal age or differed between males and females.;The presence of sexual dimorphisms in microglial gene expression suggests regulation by gonadal hormones. Treatment of mice with estrogen altered microglial expression of several P2Rs, often in a manner that was sex-dependent or influenced by gonadectomy. In addition, P2R activation with ADP resulted in decreased expression and release of TNFalpha from LPS-treated microglia in a manner consistent with P2Y13 signaling - the first identified function of this receptor in microglia.;The novel research presented here addresses unexplored areas necessary for a more complete understanding of microglial biology, and will form the foundation for future studies examining microglial contributions to normal and pathological CNS function.