Discussion
Previous studies has shown the noticeable anti-inflammatory effects of
NR4a1. In this study, we explored the mechanism of NR4a1 through
bioinformatics analysis. We employed the GSE68167 dataset and selected
108 DEGs to be analyzed using DAVID and KEGG pathway and GO term
analysis. BP analysis mainly shows signal transduction, positive
regulation of chemokine production and inflammatory response. CC terms
displayed enrichment of DEGs mainly in cytoplasm, membrane, and cytosol;
while MF indicated the protein binding, calcium ion binding and callagen
binding. KEGG showed the enrichment of DEGs mainly in cytokine-cytokine
receptor, JAK-STAT signaling pathway and cAMP signaling pathway. We used
STRING and Cytoscape to construct the gene network, where 49 DEGs were
mapped and top Hub gene
IFNG, IL10, Fos, IL19, PDE4B, Cnr1, MMP13, NPY, Rtn1, UCHL1 were ranked
by CytoHubba. Among these Hub genes, IFNG encodes IFNγ, IL10 and IFNγ
are considered the important inflammatory cytokine and NR4a1 defects
macrophage showed the decreased IL10 while the increased IFNγ
production [10,33,34]. NR4a1 regulates the expression of early gene,
including Fos in cancer [35]. Fos together with c-jun forms AP-1
plays a key role in inflammatory type macrophage [36]. UCHL1 has
been reported to exert the anti-inflammatory effects via MAPK and NFκB
signaling pathway in LPS stimulated macrophage [37].
Phosphodiesterase 4B(PDE4B), a member of the phosphodiesterase (PDEs)
family, serving as a selectively hydrolytic enzyme of the second signal
messenger cyclic adenosine monophosphate (cAMP) to play a crucial role
in cAMP signaling pathway [15,25]. PDE4B, NPY and FOS were found to
be enriched in cAMP signaling pathway, where the former is critical in
signal transduction of inflammation [15,25,30]. The inhibitor of
PDE4B has been shown exert an effective validity in treating various
inflammatory diseases [15]. PED4B defected macrophage shows the
decreased LPS induced NFκB activation and reactive oxygen species
level [30,38].
Our data demonstrated that NR4a1 showed the effects of increasing cAMP
and p-PKA levels through down-regulating PED4B expression. We also found
that NR4a1 can inhibit LPS induced NF-κB signaling activation and the
mRNA level of IL-6 and IL-1β by down-regulating PED4B expression. The
anti-inflammatory function of NR4a1 has been proved to be related to
restrict NFκB signaling pathway [33,39] Interestingly, cAMP
activated PKA could effectively inhibit the NFκB regulated gene
transcription [10,27].Thus, we hypothesized that NR4a1 may regulates
the NFκB signaling pathway through PDE4B-cAMP-PKA signaling, which is
also worthy to further detecting. In addition, bioinformatics analysis
showed that the effect of NR4a1 in macrophage may be related to Fos,
UCHL1, MMP13. JAK-STAT signaling pathway and cytokine-cytokine
interaction may be regulated by NR4a1.