Expression of purine metabolism-related enzymes by microglial cells in the developing rat brain

Abstract

The nucleoside triphosphatase (NTPase), nucleoside diphosphatase (NDPase), 5'-nucleotidase (5'-Nase), and purine nucleoside phosphorylase (PNPase) activity has been examined in the cerebral cortex, subcortical white matter, and hippocampus from embryonic day (E)16 to postnatal day (P)18. Microglia display all four purine-related enzymatic activities, but the expression of these enzymatic activities differed depending on the distinct microglial typologies observed during brain development. We have identified three main morphologic typologies during the process of microglial differentiation: ameboid microglia (parenchymatic precursors), primitive ramified microglia (intermediate forms), and resting microglia (differentiated cells). Ameboid microglia, which were encountered from E16 to P12, displayed the four enzymatic activities. However, some ameboid microglial cells lacked 5'-Nase activity in gray matter, and some were PNPase-negative in both gray and white matter. Primitive ramified microglia were already observed in the embryonic period but mostly distributed during the first 2 postnatal weeks. These cells expressed NTPase, NDPase, 5'-Nase, and PNPase. Similar to ameboid microglia, we found primitive ramified microglia lacking the 5'-Nase and PNPase activities. Resting microglia, which were mostly distinguishable from the third postnatal week, expressed NTPase and NDPase, but they lacked or displayed very low levels of 5'-Nase activity, and only a subpopulation of resting microglia was PNPase-positive. Apart from cells of the microglial lineage, GFAP-positive astrocytes and radial glia cells were also labeled by the PNPase histochemistry. As shown by our results, the differentiation process from cell precursors into mature microglia is accompanied by changes in the expression of purine-related enzymes. We suggest that the enzymatic profile and levels of the different purine-related enzymes may depend not only on the differentiation stage but also on the nature of the cells. The use of purine-related histoenzymatic techniques as a microglial markers and the possible involvement of microglia in the control of extracellular purine levels during development are also discussed.

Evidence for functional adenosine A3 receptors in microglia cells

“…The fact that microglia cells express high levels of enzymes on the extracellular side of the membrane that participate in the nucleotide breakdown (Dalmau et al . 1998; Braun et al .…”

Physiology of Microglia

“…Furthermore, microglia are endowed with ectonucleotidases, which degrade ATP and its derivatives. Microglial cells were shown to express nucleoside triphosphatase (NTPase), nucleoside diphosphatase (NDPase), 5=-nucleotidase (5=-Nase), and purine nucleoside phosphorylase (PNPase), with this expression being dependent on the activation and developmental stage (186). Microglial cells also express CD39 ectonucleotidase, which is critical for ATP-mediated signaling.…”

Microglia during development and aging

“…The physiological effects of purines and pyrimidines are mediated through purinoceptors classified as metabotropic P1 adenosine receptors, metabotropic P2Y purinoceptors, and ionotropic P2X purinoceptors (Fredholm et al, 2007; North, 2002; Surprenant and North, 2009). Receptor expression is abundant in glia with microglia expressing P2X 4 , P2X 7 , P2Y 2 , P2Y 4 , P2Y 6 , P2Y 12 , and P2Y 14 receptors (Verkhratsky et al, 2009) and purine metabolism-related enzymes are expressed by microglia in the developing brain (Dalmau et al, 1998). In the case of neuropathic pain, one such signaling molecule is the chemokine, CCL2 (monocyte chemoattractant protein 1, MCP-1).…”