Amphiregulin Regulates Phagocytosis-Induced Cell Death in Monocytes via EGFR and Matrix Metalloproteinases

Abstract

Neonates are highly susceptible to microbial infections which is partially attributable to fundamental phenotypic and functional differences between effector cells of the adult and neonatal immune system. The resolution of the inflammation is essential to return to tissue homeostasis, but given that various neonatal diseases, such as periventricular leukomalacia, necrotizing enterocolitis, or bronchopulmonary dysplasia, are characterized by sustained inflammation, newborns seem predisposed to a dysregulation of the inflammatory response. Targeted apoptosis of effector cells is generally known to control the length and extent of the inflammation, and previous studies have demonstrated that phagocytosis-induced cell death (PICD), a special type of apoptosis in phagocytic immune cells, is less frequently triggered in neonatal monocytes than in adult monocytes. We concluded that a rescue of monocyte PICD could be a potential therapeutic approach to target sustained inflammation in neonates. The EGFR ligand amphiregulin (AREG) is shed in response to bacterial infection and was shown to mediate cellular apoptosis resistance. We hypothesized that AREG might contribute to the reduced PICD of neonatal monocytes by affecting apoptosis signaling. In this study, we have examined a cascade of signaling events involved in extrinsic apoptosis by using a well-established in vitro E. coli infection model in monocytes from human peripheral blood (PBMO) and cord blood (CBMO). We found that CBMO shows remarkably higher pro-AREG surface expression as well as soluble AREG levels in response to infection as compared to PBMO. AREG increases intracellular MMP-2 and MMP-9 levels and induces cleavage of membrane-bound FasL through engagement with the EGF receptor. Our results demonstrate that loss of AREG rescues PICD in CBMO to the level comparable to adult monocytes. These findings identify AREG as a potential target for the prevention of prolonged inflammation in neonates.

Amphiregulin Regulates Phagocytosis-Induced Cell Death in Monocytes via EGFR and the Bcl-2 Protein Family

“…By contrast stimulation with AREG did not show a significant effect ( Table 1). This is in line with previous results showing that EGFR density (MFI) significantly increases after infection with E. coli [38].…”

“…In the first step, we investigated whether infection with E. coli or AREG stimulation would affect the number of EGFRpositive cells in our PBMO and CBMO populations. As previously reported, infection with E. coli increased the number of EGFR-expressing PBMO and CBMO [38]. By contrast stimulation with AREG did not show a significant effect ( Table 1).…”

“…In a previous study, we demonstrated that CBMO have a higher pro-AREG surface expression compared to PBMO. Hence, upon E. coli infection-induced cleavage of pro-AREG, CBMO show an 11-fold higher level of soluble AREG compared to PBMO [38]. We further showed that AREG increases intracellular MMP-2 and MMP-9 levels and induces cleavage of membrane-bound FasL through engagement with the EGF receptor, pointing towards involvement of the extrinsic apoptosis pathway.…”

“…We further showed that AREG increases intracellular MMP-2 and MMP-9 levels and induces cleavage of membrane-bound FasL through engagement with the EGF receptor, pointing towards involvement of the extrinsic apoptosis pathway. Reduction of AREG levels was found to diminish PICD in CBMO and PBMO [38].…”

“…We had previously demonstrated that AREG regulates matrix metalloprotease-2-and matrix metalloprotease-9-mediated extrinsic FAS-mediated apoptosis via activation of EGFR downstream signaling [38]. Since EGFR is also capable of mediating intrinsic apoptosis through MAPK (ERK, p38, and JNK) and PI3K/Akt signaling [27][28][29], we wanted to examine whether AREG affects intrinsic apoptosis in PBMO and CBMO through EGFR.…”