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Lipopolysaccharide-Induced Microglia Activation Promotes the Survival of Midbrain Dopaminergic Neurons In Vitro
Xiaolai Zhou1,2, Björn Spittau3,4
1Department of Neuroscience, Mayo Clinic Jacksonville, 4500 San Pablo Road, Jacksonville, FL, 32224, USA.
Abstract:
Microglia are the resident immune cells of the central nervous system (CNS) and respond to a variety of endogenous and exogenous stimuli in order to restore cell and tissue homeostasis. Lipopolysaccharide (LPS) is one of these exogenous stimuli, constitutes a major component of the outer membrane of Gram-negative bacteria, and binds to the microglial pattern recognition receptor Toll-like receptor 4 (TLR4). LPS-induced microglia activation is believed to promote neurodegeneration by release of neurotoxic factors such as interleukin-1β, tumor necrosis factor α, or nitric oxide. In the present study, we investigated whether the physical presence of microglia is required to promote neurotoxicity and whether microglia-derived factors are essential. Interestingly, we observed that dopaminergic (mDA) neuron survival was only affected in mixed neuron-glia cultures containing microglia but not in neuron-enriched cultures. Moreover, we clearly demonstrate that microglia-conditioned medium (MCM) after LPS treatment increased mDA neuron survival, process numbers as well as process length. The observed protective effects of MCM was rather caused by microglia-derived factors and only partially dependent on the increase in reactive astrocytes. These results indicate that LPS-induced microglia activation does not necessarily have detrimental effects on mDA neurons and further support the hypothesis that activated microglia support neuron survival by release of neurotrophic and neuroprotective factors.
Insights
Lipopolysaccharide (LPS) does not harm dopaminergic neurons when microglia are present. Instead, factors released by activated microglia, specifically in microglia-conditioned medium, promote neuron survival and growth.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglia are central nervous system immune cells crucial for homeostasis.
- Lipopolysaccharide (LPS), a bacterial component, activates microglia via Toll-like receptor 4 (TLR4).
- LPS-induced microglia activation is often linked to neurotoxicity via factors like IL-1β, TNF-α, and nitric oxide.
Purpose of the Study:
- To determine if microglia presence is necessary for LPS-induced neurotoxicity.
- To investigate the role of microglia-derived factors in neuroprotection or neurodegeneration.
- To assess the impact of LPS-activated microglia on dopaminergic (mDA) neuron survival.
Main Methods:
- Comparison of mDA neuron survival in mixed neuron-glia cultures versus neuron-enriched cultures.
- Treatment of microglia with LPS.
- Analysis of microglia-conditioned medium (MCM) effects on mDA neurons.
- Assessment of reactive astrocyte involvement.
Main Results:
- mDA neuron survival was compromised only in cultures containing microglia, not in neuron-enriched cultures.
- Microglia-conditioned medium (MCM) from LPS-treated microglia enhanced mDA neuron survival, process number, and process length.
- The protective effects of MCM were attributed to microglia-derived factors and only partially to reactive astrocytes.
Conclusions:
- LPS-induced microglia activation is not inherently detrimental to mDA neurons.
- Activated microglia can support neuron survival through the release of neurotrophic and neuroprotective factors.
- These findings challenge the notion of universally detrimental microglial responses in neuroinflammation.
