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Updated: Aug 16, 2026
Isolation of Cortical Microglia with Preserved Immunophenotype and Functionality From Murine Neonates
Published on: January 30, 2014
Apolipoprotein J (clusterin) activates rodent microglia in vivo and in vitro
Z Xie1, M E Harris-White, P A Wals
1Andrus Gerontology Center and Department of Biological Sciences, University of Southern California, Los Angeles, 90089, USA.
Abstract:
Apolipoprotein J (apoJ; also known as clusterin and sulfated glycoprotein (SGP)-2) is associated with senile plaques in degenerating regions of Alzheimer's disease brains, where activated microglia are also prominent. We show a functional link between apoJ and activated microglia by demonstrating that exogenous apoJ activates rodent microglia in vivo and in vitro. Intracerebroventricular infusion of purified human plasma apoJ ( approximately 4 microg over 28 days) activated parenchymal microglia to a phenotype characterized by enlarged cell bodies and processes (phosphotyrosine immunostaining). In vitro, primary rat microglia were also activated by apoJ, with changes in morphology and induction of major histocompatibility complex class II (MHCII) antigen. ApoJ increased the secretion of reactive nitrogen intermediates in a dose-dependent manner (EC(50) 112 nm), which was completely blocked by aminoguanidine (AG), a nitric oxide synthase inhibitor. However, AG did not block the increased secretion of tumor necrosis factor-alpha by apoJ (EC(50) 55 nm). Microglial activation by apoJ was also blocked by an anti-apoJ monoclonal antibody (G7), and by chemical cleavage of apoJ with 2-nitro-5-thiocyanobenzoate. The mitogen-activated protein kinase kinase and protein kinase C inhibitors PD98059 and H7 inhibited apoJ-mediated induction of reactive nitrogen intermediate secretion from cultured microglia. As a functional measure, apoJ-activated microglia secreted neurotoxic agents in a microglia-neuron co-culture model. We hypothesize that ApoJ contributes to chronic inflammation and neurotoxicity through direct effects on microglia.
Insights
Apolipoprotein J (apoJ) directly activates microglia, brain immune cells, in Alzheimer's disease models. This apoJ-induced microglial activation releases neurotoxic agents, potentially contributing to chronic neuroinflammation.
Area of Science:
- Neuroscience
- Immunology
- Biochemistry
Background:
- Apolipoprotein J (apoJ) is found in senile plaques in Alzheimer's disease (AD) brains alongside activated microglia.
- Microglia play a crucial role in neuroinflammation and AD pathogenesis.
Purpose of the Study:
- To investigate the functional link between apoJ and microglial activation.
- To determine if apoJ directly activates microglia and contributes to neurotoxicity.
Main Methods:
- Administered purified human plasma apoJ intracerebroventricularly in rodents.
- Cultured primary rat microglia and treated with apoJ in vitro.
- Assessed microglial activation markers (morphology, MHCII expression, phosphotyrosine staining).
- Measured secretion of reactive nitrogen intermediates and tumor necrosis factor-alpha.
- Utilized specific inhibitors (aminoguanidine, PD98059, H7) and an anti-apoJ antibody.
- Co-cultured activated microglia with neurons to assess neurotoxicity.
Main Results:
- Exogenous apoJ activated rodent microglia in vivo and in vitro, inducing morphological changes and MHCII expression.
- ApoJ dose-dependently increased secretion of reactive nitrogen intermediates and tumor necrosis factor-alpha.
- Inhibition of nitric oxide synthase blocked reactive nitrogen intermediate secretion but not TNF-alpha secretion.
- Microglial activation by apoJ was inhibited by an anti-apoJ antibody and chemical cleavage.
- Signaling pathways involving MAPK kinase and PKC were implicated in apoJ-mediated activation.
- ApoJ-activated microglia secreted neurotoxic agents in a microglia-neuron co-culture model.
Conclusions:
- Apolipoprotein J directly activates microglia, suggesting a role in neuroinflammation.
- ApoJ-induced microglial activation may contribute to neurotoxicity and Alzheimer's disease progression.
- Targeting apoJ-microglia interactions could be a therapeutic strategy for AD.
