Pharmacological Inhibition of Amyloidogenic APP Processing and Knock-Down of APP in Primary Human Macrophages Impairs the Secretion of Cytokines

Abstract

It has been previously shown that the amyloid precursor protein (APP) support the innate immune defense as an immune receptor. Amyloid β (Aβ) peptides seem to have properties of an antimicrobial peptide and can act as opsonines. In APP-deficient mouse models, a reduced secretion of cytokines has been observed. Still, it is unclear whether this can be attributed to the lack of APP or to the missing secretion of Aβ peptides. We inhibited the secretion of Aβ peptides in primary human monocyte derived macrophages with the γ-secretase inhibitor N-[N-(3,5-Difluorophenacetyl)-L-alanyl]-Sphenylglycine-t-butyl-ester (DAPT) or the β-secretase inhibitor GL-189. Alternatively, we knocked down APP by transfection with siRNA. We measured tumor necrosis factor α (TNFα), interleukin 6 (IL-6) and interleukin (IL-10) by enzyme linked immunosorbent assay (ELISA) and evaluated the phagocytotic activity by flow cytometry. We observed reduced concentrations of TNFα and IL-6 in the media of APP k/d macrophages and after inhibition of the β-, or γ-secretase, especially after additional immunological activation with lipopolysaccharide (LPS). Secretion of IL-10 was increased after pharmacological inhibition of APP processing when the macrophages were not immunologically activated but was decreased during LPS-induced inflammation in APP k/d macrophages. No changes of the phagocytotic activity were observed. We conclude that macrophage APP and Aβ peptides support the initiation of an immune response and are involved in the regulation of TNFα, IL-6, and IL-10 secretion by human monocyte-derived macrophages.

Identification of the key genes in chronic obstructive pulmonary disease by weighted gene co-expression network analysis

“…However, APP has not been thoroughly investigated in pulmonary disease etiology. Spitzer et al have reported that APP is hydrolyzed to β-amyloid (Aβ) in macrophage lineages, and stimulated pro-inflammatory cytokine secretion from macrophages (32). APP also regulates tumor necrosis factor-α (TNF-α), IL-6, and IL-10 secretion from human monocyte-derived macrophages.…”

“…APP also regulates tumor necrosis factor-α (TNF-α), IL-6, and IL-10 secretion from human monocyte-derived macrophages. APP knockdown in macrophages decreased TNF-α and IL-6 levels and increased the IL-10 level (32). However, IL-10 secretion was diminished during lipopolysaccharide (LPS)-induced inflammation.…”

“…After APP was scavenged by a specific antibody, the pro-fibrotic phenotype in the macrophage subsets was increased (40). IL-10 is an important anti-inflammatory cytokine and anti-fibrotic factor, LPS-induced secretion of IL-10 was also suppressed in APP knockout macrophages (32). Lung fibrosis can develop in some patients with advanced COPD, SPP1 and APP may contribute to this change.…”

Distinct human stem cell subpopulations drive adipogenesis and fibrosis in musculoskeletal injury

“…TGFβ signaling both to and from FAPs and multiple other cell types was elevated in muscle from partial tears and even more so in full thickness tears 4,46,47 . Immunomodulatory signaling such as APP and THY1 signaling from FAPs to macrophages and T-cells increased with injury severity [48][49][50] . We also found pro-fibrotic (tenascin) signaling from FAPs and pro-adipogenic (visfatin) signaling to FAPs were significantly increased with injury 51,52 .…”

Physiological Roles of Monomeric Amyloid-β and Implications for Alzheimer’s Disease Therapeutics

“…Instead of exhibiting intended clinical benefits such as improved cognitive abilities, the rates of infection elevated in the subjects. Another study demonstrated the regulative effect of different β-secretase and γ-secretase inhibitors, GL-189 and N-[N-(3,5-Difluorophenacetyl)-L-alanyl]-S-phenylglycine-t-butyl-ester (DAPT), on secretion levels of tumor necrosis factor α, interleukin (IL) 6 and 10, which are involved in immune response by macrophages [ 36 ]. Intriguingly, these results are in agreement with another in vivo studies demonstrating that Aβ may act as an innate defense system against pathogens in case of skin damage and thrombosis as the elevated level of Aβ40 peptides around brain and dermal blood vessels in mice were observed [ 37 , 38 ].…”