CD47 does not mediate amyloid-β(1–42) protofibril-stimulated microglial cytokine release

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.

Peptide analogues PKHB1 and 4N1K induce cell death through CD47‐independent mechanisms

“…Another group working on microglia biology has since corroborated our results on 4N1K. 10 Given that 4N1K is known to have substantial CD47independent effects, it is conceivable that PKHB1 may as well.…”

CD47-ligation induced cell death in T-acute lymphoblastic leukemia

“…The TSP-derivative C-terminal peptides, 4N1K and 7N3, were similarly shown to induce cell death in a number of cell lines in solution 38 , 49 , 50 . However, questions arose concerning the specificity of these peptides since 4N1K appears to bind cells and stimulate activities in a CD47-independent manner 51 , 52 . As the only commercially available CD47-antibody able to induce cell death in solution, CC2C6 should enable further studies that enhance understanding of a 'don’t eat me' tumour cell antigen that can be exploited to turn on itself.…”

Microglial phagocytosis in aging and Alzheimer's disease

“…In another report, Floden et al found an age‐dependent loss of CD47 expression (Floden & Combs, ), a molecule involved in recognition of fibrillary Aβ in a complex with the co‐receptor molecules alpha 6 beta 1 integrin and CD36 (Koenigsknecht & Landreth, ). The role of CD47 in controlling microglia function seems to be restricted to phagocytosis, as the levels of pro‐inflammatory cytokines produced by CD47‐deficient microglia exposed to Aβ were comparable to control cells (Karki & Nichols, ).…”