Discussion
In this study, we used EAN mice to explore the effects of M2 macrophages
and BAY11-7082 as an NF-κB inhibitor on this disease. Our results
displayed that M2 macrophages ameliorated the clinical signs and reduced
the duration of symptoms of EAN in mice by inhibiting pro-inflammatory
M1 macrophages and cytokines accumulation. Additionally, the M2
macrophage polarization was increased in M2 treatment group, which was
related to inhibition of NF-κB signaling pathway. BAY11-7082 could also
diminish EAN symptoms by reducing the expression of TNF-α, IL-6 and
IL-12, delaying the onset of EAN in preventive group. Further,
BAY11-7082 greatly increased the percentage of M2 macrophage and reduced
the percentage of M1 macrophage in preventive group. In vitro,
BAY11-7082 inhibited the activity and proliferation of M1 macrophages.
Overall, these results demonstrated the NF-κB signaling pathway may be
involved in the pathogenesis of EAN by regulating the polarization of
macrophages and inhibiting the expression of inflammatory cytokines. The
results of adoptive transfer of M2 macrophages into EAN mice displayed
the marked beneficial effects on EAN by inhibiting the activation of
NF-κB.
Macrophages are broadly divided into two phenotypes: pro-inflammatory
macrophages (M1) and anti-inflammatory macrophages (M2)
[14]. M1 macrophages secrete
pro-inflammatory cytokines that cause tissue damage and disease
development, whereas M2 macrophages express high levels of
anti-inflammatory molecule to reduce inflammation and promote disease
recovery [14,
16]. Macrophages play either a
pro-inflammatory or anti-inflammatory role in the different stages of
GBS [17]. M1 cells promote the
expression of major histocompatibility complex-II (MHC-II), adhesion
molecules, reactive oxygen intermediates (ROI), and inflammatory
cytokines, resulting inflammation, broken brood–nerve barrier (BNB),
and demyelination [3]. In contrast, M2
macrophages exert a neuroprotective role in the pathogenicity of EAN
[18]. M2 macrophages may contribute
to the spontaneous re-myelination and regeneration of the axon
[19,
20] by promoting T cell apoptosis,
suppressing inflammatory responses[9],
clearing myelin and axonal debris
[16], and inducing the secretion of
anti-inflammatory cytokines such as IL-10 and
TGF-β[21].
In agreement with those findings, the present study showed that the
improved outcome of EAN was associated with the higher proportion of M2
macrophages and the M2 macrophage polarization was increased in M2
treatment group. In addition, the role of BAY11-7082 inhibiting EAN
clearly is related to shift macrophages from M1 to M2 type as the
evidence with higher percentage of M2 macrophages and lower percentage
of M1 macrophages in EAN treated by BAY11-7082.
NF-κB is an inducible transcription factor expressed in a large number
of cells and involved in immune and inflammatory responses. It plays a
critical role of cell differentiation, apoptosis as well as oncogenesis.
NF-κB as a pro-inflammatory signaling pathway, facilitate the
inflammatory reaction by up-regulation of NF-κB target genes encoding
pro-inflammatory cytokines, chemokines and adhesion molecules. These
signals lead to the recruitment and activation of
neutrophils,macrophages and leukocytes to sites of inflammation
[22].
NF-κB can modulate the inflammatory response in EAN as the several
studies demonstrated that the the activated p65 of NF-κB was observed in
peripheral nerve macrophages in the patients with AIDP or CIDP and EAN
[23,
24]. The activated p65 of NF-κB in T
cells and macrophages has higher intensity at the peak of EAN than
control. The activation of NF-κB is induced by a large number of potent
stimuli such as LPS, TNF-α and IL-1. Activated NF-κB is responsible for
the expression of many pro-inflammatory cytokines (TNF, IL-1, IL-6 and
IL-8), chemokines [25], adhesion
molecules, prostaglandins, reactive oxygen species
[26] and matrix
metalloproteinases[27]. P65 is
required for the leukocyte recruitment and the macrophages activation
during the onset of inflammation
[28]. However, recent studies have
found that NF-κB activation promotes neuronal survival by inducing the
transcription of anti-apoptotic genes and a number of growth factors
[29-31]. P65/RelA over-expression
induces the expression of anti-apoptotic gene and protects neurons from
death. NF-κB protects neurons against amyloid β-peptide toxicity,
glutamate-induced toxicity, and excitotoxic or oxidative stress
[32].
In this work, we found that BAY11-7082 can improve EAN outcome by
suppressing M1 macrophages and the expression of TNF-α, IL-6 and IL-12.
Although our results indicated that inhibiting NF-κB enhanced
polarization of M2 macrophages and repressed M1 macrophages, the
underlying mechanisms are still unknown. In addition, previous studies
have reported that inhibition of NF-κB can prolong the inflammatory
process and maintain leukocyte activation
[33]. Therefore, the possible effects
that NF-κB mediate macrophages polarization in EAN, warrant further
studies.