The interplay between P2 and P1 receptors to control microglial function
Final Report Abstract
Microglial cells are the immunocompetent cells of the central nervous system and are activated by any pathologic event. Activated microglial cells can influence the pathologic process. The activation of microglial cells is controlled by a plethora of factors among which purinergic signaling plays a prominent role. The activated microglia cells can release a number of factors such as cytokines and are the professional phagocytes of the brain. Purinergic signaling plays a major role in the regulation of phagocytosis in microglia. Interplay between P2 and P1 receptor activation is controlled by a cascade of extracellular enzymes which dephosphorylate purines resulting in the formation of adenosine. The ATP and ADP degrading capacity of cultured microglia depends on the expression of E-NTPDase1 (CD39) and is several times higher when compared to astrocytes which lack this enzyme. In brain slices, deletion of CD39 resulted in a 50% decrease of ADP-degrading ability, while the degradation of ATP was decreased to about 75% of the values measured in wild type brain tissue. Microglia in acute slices from cd39-/- animals had increased constitutive phagocytic activity which could not be further enhanced by ATP in contrast to control animals. Pharmacological blockage of P2 receptors decreased the constitutive phagocytic activity to a similar base level in wildtype and cd39-/- microglia. Activation of P1 receptors by non-hydrolysable adenosine analog significantly decreased phagocytic activity. Deletion of CD73, an enzyme expressed by microglia which converts AMP to adenosine, did not affect phagocytic activity. Deletion of CD39 results in a reduction of microglia density in adult mice and a less ramified morphology with less-branched processes, increase in length of process segments between branch points, but a decreased cumulative process length. Upon brain injury, mimicked by brain slicing, the CD39-/- microglia more rapidly transforms into an amoeboid morphological phenotype. Inhibition of P2Y12 receptors enhances the transformation into the ameboid phenotype in wild type but not in CD39-/- microglia. Enlargements of processes appear during slice maintenance and are more prominent in CD39-/- microglia. In response to a local injury, microglial cells rapidly extend their processes to the lesion site and this function is impaired in CD39-/- microglia. In cell culture experiments we found that Cd39-/- microglia has diminished ability to degrade extracellular ATP after autocrine release or exogenous addition. While microglia can release ATP, the release by astrocytes is much more prominent. The astrocyte calcium wave spreads to a larger area in CD39 deleted microglia–astrocyte co-cultures. Thus Cd39 is an autocrine regulator of the microglial phenotype. Taken together, these data show that CD39 plays a prominent role in controlling ATP levels and thereby microglial phagocytosis.
Publications
- Physiology of microglia. Physiol Rev. 2011; 91: 461–553
Kettenmann H, Hanisch UK, Noda M, Verkhratsky A
(See online at https://doi.org/10.1152/physrev.00011.2010) - Microglia: New roles for the synaptic stripper. Neuron. 2013; 77: 10–18
Kettenmann H, Kirchhoff F, Verkhratsky A
(See online at https://doi.org/10.1016/j.neuron.2012.12.023) - NTPDase1 activity attenuates microglial phagocytosis. Purinergic Signal. 2013; 9: 199–205
Bulavina L, Szulzewsky F, Rocha A, Krabbe G, Robson SC, Matyash V, Kettenmann H
(See online at https://doi.org/10.1007/s11302-012-9339-y) - Altered microglial phagocytosis in GPR34-deficient mice. Glia. 2015; 63: 206–15
Preissler J, Grosche A, Lede V, Le Duc D, Krügel K, Matyash V, Szulzewsky F, Kallendrusch S, Immig K, Kettenmann H, Bechmann I, Schöneberg T, Schulz A
(See online at https://doi.org/10.1002/glia.22744)
