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Tumor necrosis factor alpha mediates lipopolysaccharide-induced microglial toxicity to developing oligodendrocytes
Jianrong Li1, E Radhika Ramenaden, Jie Peng
1Department of Neurology and the F. M. Kirby Neurobiology Center, Children's Hospital Boston, Harvard Medical School, Boston, Massachusetts 02115, USA. jrli@cvm.tamu.edu
Abstract:
Reactive microglia and astrocytes are present in lesions of white matter disorders, such as periventricular leukomalacia and multiple sclerosis. However, it is not clear whether they are actively involved in the pathogenesis of these disorders. Previous studies demonstrated that microglia, but not astrocytes, are required for lipopolysaccharide (LPS)-induced selective killing of developing oligodendrocytes (preOLs) and that the toxicity is mediated by microglia-derived peroxynitrite. Here we report that, when astrocytes are present, the LPS-induced, microglia-dependent toxicity to preOLs is no longer mediated by peroxynitrite but instead by a mechanism dependent on tumor necrosis factor-alpha (TNFalpha) signaling. Blocking peroxynitrite formation with nitric oxide synthase (NOS) inhibitors or a decomposition catalyst did not prevent LPS-induced loss of preOLs in mixed glial cultures. PreOLs were highly vulnerable to peroxynitrite; however, the presence of astrocytes prevented the toxicity. Whereas LPS failed to kill preOLs in cocultures of microglia and preOLs deficient in inducible NOS (iNOS) or gp91(phox), the catalytic subunit of the superoxide-generating NADPH oxidase, LPS caused a similar degree of preOL death in mixed glial cultures of wild-type, iNOS-/-, and gp91(phox-/-) mice. TNFalpha neutralizing antibody inhibited LPS toxicity, and addition of TNFalpha induced selective preOL injury in mixed glial cultures. Furthermore, disrupting the genes encoding TNFalpha or its receptors TNFR1/2 completely abolished the deleterious effect of LPS. Our results reveal that TNFalpha signaling, rather than peroxynitrite, is essential in LPS-triggered preOL death in an environment containing all major glial cell types and underscore the importance of intercellular communication in determining the mechanism underlying inflammatory preOL death.
Insights
Astrocytes alter inflammatory responses in white matter disorders. Tumor necrosis factor-alpha (TNFalpha) signaling, not peroxynitrite, drives oligodendrocyte death when all glial cells are present.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Reactive microglia and astrocytes are hallmarks of white matter disorders like multiple sclerosis.
- The precise role of these glial cells in disease pathogenesis remains unclear.
- Previous research indicated microglia, not astrocytes, mediate oligodendrocyte death via peroxynitrite.
Purpose of the Study:
- To investigate the mechanism of lipopolysaccharide (LPS)-induced oligodendrocyte death in the presence of astrocytes.
- To determine the role of peroxynitrite versus tumor necrosis factor-alpha (TNFalpha) signaling in this process.
Main Methods:
- Utilized mixed glial cultures containing microglia, astrocytes, and developing oligodendrocytes (preOLs).
- Assessed preOL death in response to LPS, with and without inhibitors of peroxynitrite formation.
- Examined the role of TNFalpha signaling by using neutralizing antibodies and gene disruption of TNFalpha and its receptors.
- Compared LPS-induced toxicity in wild-type and knockout mice lacking inducible nitric oxide synthase (iNOS) or gp91(phox).
Main Results:
- Astrocytes prevented peroxynitrite-mediated toxicity to preOLs.
- LPS-induced preOL death in mixed glial cultures was dependent on TNFalpha signaling, not peroxynitrite.
- Blocking TNFalpha signaling or its receptors abolished LPS-induced preOL death.
- LPS toxicity was observed in mixed glial cultures regardless of iNOS or gp91(phox) presence.
Conclusions:
- TNFalpha signaling is the critical mediator of LPS-induced preOL death in a mixed glial environment.
- Intercellular communication between glial cells significantly influences inflammatory mechanisms driving oligodendrocyte injury.
- Findings highlight the complexity of inflammatory processes in white matter disorders.
