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Nirnath Sah1, Zhi Zhang2, Alicia Chime1
1Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Abstract:
We have previously shown that maternal endotoxin exposure leads to a phenotype of cerebral palsy and pro-inflammatory microglia in the brain in neonatal rabbits. "Activated" microglia overexpress the enzyme glutamate carboxypeptidase II (GCPII) that hydrolyzes N-acetylaspartylglutamate to N-acetylaspartate and glutamate, and we have shown previously that inhibiting microglial GCPII is neuroprotective. Glutamate-induced injury and associated immune signaling can alter microglial responses including microglial process movements for surveillance and phagocytosis. We hypothesize that inhibition of GCPII activity could alter microglial phenotype and normalize microglial process movement/dynamics. Newborn rabbit kits exposed to endotoxin in utero, when treated with dendrimer-conjugated 2-(phosphonomethyl)-pentanedioic acid (D-2PMPA), a potent and selective inhibitor of microglial GCPII, showed profound changes in microglial phenotype within 48 h of treatment. Live imaging of hippocampal microglia in ex vivo brain slice preparations revealed larger cell body and phagocytic cup sizes with less stable microglia processes in CP kits compared to healthy controls. D-2PMPA treatment led to significant reversal of microglial process stability to healthy control levels. Our results emphasize the importance of microglial process dynamics in determining the state of microglial function in the developing brain and demonstrate how GCPII inhibition specifically in microglia can effectively change the microglial process motility to healthy control levels, potentially impacting migration, phagocytosis, and inflammatory functions.
Insights
Maternal endotoxin exposure causes cerebral palsy in rabbits. Inhibiting microglial glutamate carboxypeptidase II (GCPII) with D-2PMPA normalized microglial process dynamics, offering a potential therapeutic strategy.
Area of Science:
- Neuroscience
- Immunology
- Developmental Biology
Background:
- Maternal endotoxin exposure induces cerebral palsy (CP) and pro-inflammatory microglia in neonatal rabbits.
- Activated microglia overexpress glutamate carboxypeptidase II (GCPII), an enzyme hydrolyzing N-acetylaspartylglutamate to glutamate.
- GCPII inhibition has previously shown neuroprotective effects.
Purpose of the Study:
- To investigate if GCPII inhibition alters microglial phenotype and normalizes microglial process dynamics.
- To assess the therapeutic potential of D-2PMPA, a selective GCPII inhibitor, in a neonatal rabbit model of CP.
Main Methods:
- Newborn rabbit kits exposed to endotoxin in utero were treated with D-2PMPA.
- Live imaging of hippocampal microglia in ex vivo brain slices was performed.
- Microglial cell body size, phagocytic cup size, and process stability were analyzed.
Main Results:
- D-2PMPA treatment significantly altered microglial phenotype within 48 hours.
- CP microglia exhibited larger cell bodies, larger phagocytic cups, and less stable processes compared to controls.
- D-2PMPA treatment reversed microglial process instability to healthy control levels.
Conclusions:
- Microglial process dynamics are crucial for microglial function in the developing brain.
- Targeting microglial GCPII with D-2PMPA effectively normalizes microglial process motility.
- GCPII inhibition holds potential for impacting microglial migration, phagocytosis, and inflammatory functions in CP.
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