SYNCRIP-dependent Nox2 mRNA destabilization impairs ROS formation in M2-polarized macrophages.
OBJECTIVE
During sepsis, macrophages are alternatively activated toward an M2-like phenotype on contact with apoptotic cells (ACs) or their secretion products. Simultaneously, NADPH oxidase-dependent reactive oxygen species (ROS) formation is attenuated, thus contributing to immune paralysis. However, the exact mechanism remains elusive. Here, we provide mechanistic insights into diminished mRNA stability of the NADPH oxidase Nox2 on macrophage M2 polarization and therefore reduced ROS formation in sepsis.


RESULTS
Murine J774A.1 macrophages were stimulated with conditioned medium (CM) of apoptotic T cells, which reduced Nox2 mRNA and protein expression, consequently decreasing ROS production. An mRNA pulldown approach coupled to mass spectrometry analysis identified the RNA-binding protein SYNCRIP attached to the Nox2 mRNA 3' untranslated region (3'UTR). The binding of SYNCRIP to the 3'UTR of Nox2 mRNA is attenuated after treatment with CM of apoptotic T cells, followed by Nox2 mRNA destabilization. In in vivo models of polymicrobial sepsis such as cecal ligation and puncture, SYNCRIP was strongly downregulated, which was associated with a decreased Nox2 expression in peritoneal macrophages.


METHODS
Downregulation of SYNCRIP in macrophages after contact to material of ACs destabilized Nox2 mRNA and impaired ROS formation, thereby contributing to an M2 phenotype shift of macrophages in sepsis.


CONCLUSIONS
M2 polarization of macrophages in sepsis results in an attenuated SYNCRIP binding to the 3'UTR of Nox2 mRNA, destabilizing Nox2 mRNA abundance and expression. Consequently, ROS formation needed to fight against recurrent infections is impaired. In conclusion, SYNCRIP-regulated Nox2 mRNA degradation mediates the hypoinflammatory phase of sepsis.
1 Faculty of Medicine, Institute of Biochemistry I-Pathobiochemistry, Goethe-University Frankfurt , Frankfurt, Germany .
Laura
L
Kuchler
Annika Klara
AK
Giegerich
Lisa Katharina
LK
Sha
Tilo
T
Knape
Michael Sze Ka
MS
Wong
Katrin
K
Schröder
Ralf P
RP
Brandes
Heinrich
H
Heide
Ilka
I
Wittig
Bernhard
B
Brüne
Andreas
A
von Knethen
D000818:Animals; D017209:Apoptosis / Q000235:genetics; D005786:Gene Expression Regulation; D034441:Heterogeneous-Nuclear Ribonucleoproteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008264:Macrophages / Q000378:metabolism* / Q000473:pathology; D008562:Membrane Glycoproteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000235:genetics* / Q000378:metabolism; D020871:RNA Stability; D012333:RNA, Messenger / Q000235:genetics; D017382:Reactive Oxygen Species / Q000378:metabolism; D018805:Sepsis / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D015398:Signal Transduction
D034441:Heterogeneous-Nuclear Ribonucleoproteins; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; C486049:Syncrip protein, mouse; C488842:Cybb protein, mouse; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases