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The adenosine generating enzymes CD39/CD73 control microglial processes ramification in the mouse brain
Marina Matyash1, Oleksandr Zabiegalov1, Stefan Wendt1
1Cellular Neurosciences, Max-Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.
Abstract:
Microglial cells invade the brain as amoeboid precursors and acquire a highly ramified morphology in the postnatal brain. Microglia express all essential purinergic elements such as receptors, nucleoside transporters and ecto-enzymes, including CD39 (NTPDase1) and CD73 (5'-nucleotidase), which sequentially degrade extracellular ATP to adenosine. Here, we show that constitutive deletion of CD39 and CD73 or both caused an inhibition of the microglia ramified phenotype in the brain with a reduction in the length of processes, branching frequency and number of intersections with Sholl spheres. In vitro, unlike wild-type microglia, cd39-/- and cd73-/- microglial cells were less complex and did not respond to ATP with the transformation into a more ramified phenotype. In acute brain slices, wild-type microglia retracted approximately 50% of their processes within 15 min after slicing of the brain, and this phenomenon was augmented in cd39-/- mice; moreover, the elongation of microglial processes towards the source of ATP or towards a laser lesion was observed only in wild-type but not in cd39-/- microglia. An elevation of extracellular adenosine 1) by the inhibition of adenosine transport with dipyridamole, 2) by application of exogenous adenosine or 3) by degradation of endogenous ATP/ADP with apyrase enhanced spontaneous and ATP-induced ramification of cd39-/- microglia in acute brain slices and facilitated the transformation of cd39-/- and cd73-/- microglia into a ramified process-bearing phenotype in vitro. These data indicate that under normal physiological conditions, CD39 and CD73 nucleotidases together with equilibrative nucleoside transporter 1 (ENT1) control the fate of extracellular adenosine and thereby the ramification of microglial processes.
Insights
The study reveals that CD39 and CD73 enzymes are crucial for microglia
Area of Science:
- Neuroscience
- Cell Biology
- Immunology
Background:
- Microglia, the brain's immune cells, develop a complex, branched structure postnatally.
- These cells utilize purinergic signaling, involving enzymes like CD39 and CD73 that break down ATP into adenosine.
- The role of these enzymes in microglial morphology and function remains incompletely understood.
Purpose of the Study:
- To investigate the impact of CD39 and CD73 deletion on microglial morphology and behavior.
- To elucidate the role of extracellular adenosine in regulating microglial ramification.
Main Methods:
- Utilized knockout mouse models lacking CD39, CD73, or both.
- Performed in vitro studies on isolated microglial cells.
- Analyzed microglial morphology and process extension in acute brain slices and cell cultures.
- Manipulated extracellular adenosine levels using pharmacological inhibitors and enzymatic degradation.
Main Results:
- Mice lacking CD39 and/or CD73 exhibited impaired microglial ramification, with reduced process length and complexity.
- In vitro, CD39/CD73-deficient microglia failed to ramify in response to ATP.
- CD39 deficiency exacerbated microglial process retraction in brain slices and impaired directed process extension.
- Elevating extracellular adenosine levels rescued the ramification defects in CD39/CD73-deficient microglia.
Conclusions:
- CD39 and CD73 nucleotidases are essential regulators of microglial process ramification.
- Extracellular adenosine, controlled by CD39/CD73 and ENT1, dictates microglial morphology.
- These findings highlight a novel mechanism controlling microglial structure and potentially function in the brain.