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Published on: November 9, 2018
CD47 does not mediate amyloid-β(1-42) protofibril-stimulated microglial cytokine release
Sanjib Karki1, Michael R Nichols1
1Department of Chemistry and Biochemistry and Center for Nanoscience, University of Missouri-St. Louis, United States.
Abstract:
Neuroinflammation triggered by accumulation of amyloid-β protein (Aβ) is a significant component of the Alzheimer's disease (AD) brain. Senile plaques composed of Aβ attract and activate microglia cells resulting in cytokine secretion and a proinflammatory environment. The mechanism by which Aβ activates microglia is complex and involves numerous cellular components. One receptor potentially involved in Aβ recognition and the ensuing microglia proinflammatory response is CD47. Since there is significant interest in soluble aggregated Aβ species, we sought to determine if CD47 plays a key role in microglia cytokine release stimulated by soluble Aβ(1-42) protofibrils. Pretreatment of primary murine microglia with the CD47 antagonist peptide 4N1K significantly and potently inhibited both tumor necrosis factor-α (TNFα) and interleukin-1β (IL-1β) secretion stimulated by Aβ(1-42) protofibrils. 4N1K displayed toxicity to the microglia but only at concentrations much higher than the observed inhibition. Surprisingly, 4N1K also potently inhibited TNFα secretion triggered by lipopolysaccharide which is not known to signal through CD47. Treatment of the microglia with a neutralizing anti-CD47 antibody failed to block the Aβ protofibril response even though comparable samples were completely inhibited by 4N1K. Finally, Aβ(1-42) protofibrils stimulated similar levels of secreted TNFα production in both wild-type and CD47(-/-) microglia and 4N1K still potently inhibited the Aβ protofibril response even in the CD47(-/-) microglia. The overall findings demonstrated that the microglial proinflammatory response to Aβ(1-42) protofibril is not dependent on CD47 and that 4N1K exhibits CD47-independent inhibitory activity.
Insights
The CD47 antagonist peptide 4N1K inhibits microglial cytokine release stimulated by amyloid-beta (Aβ) in Alzheimer's disease models. However, this inhibition is independent of CD47 signaling, suggesting alternative mechanisms are at play.
Area of Science:
- Neuroscience
- Immunology
- Alzheimer's Disease Research
Background:
- Neuroinflammation, driven by amyloid-beta (Aβ) accumulation, is central to Alzheimer's disease (AD) pathology.
- Microglia activation by Aβ leads to a pro-inflammatory environment via cytokine secretion.
- The receptor CD47 is a potential mediator of Aβ recognition and microglial activation.
Purpose of the Study:
- To investigate the role of CD47 in microglia cytokine release stimulated by soluble Aβ(1-42) protofibrils.
- To determine if the CD47 antagonist peptide 4N1K modulates Aβ-induced microglial responses.
Main Methods:
- Primary murine microglia were treated with Aβ(1-42) protofibrils and the CD47 antagonist peptide 4N1K.
- Tumor necrosis factor-α (TNFα) and interleukin-1β (IL-1β) secretion were measured.
- Experiments included CD47(-/-) microglia and anti-CD47 antibody neutralization.
Main Results:
- 4N1K significantly inhibited Aβ(1-42) protofibril-induced TNFα and IL-1β secretion.
- 4N1K also inhibited lipopolysaccharide-induced TNFα secretion, independent of CD47.
- Neither anti-CD47 antibody nor CD47 deficiency blocked Aβ protofibril responses, while 4N1K retained inhibitory activity in CD47(-/-) microglia.
Conclusions:
- The microglial pro-inflammatory response to Aβ(1-42) protofibrils is not CD47-dependent.
- The peptide 4N1K exerts CD47-independent inhibitory effects on microglial cytokine release.
- These findings suggest novel therapeutic targets beyond CD47 for modulating neuroinflammation in Alzheimer's disease.
