Discussion
RA represents a chronic inflammatory autoimmune disease, which leads to
irreversible destruction of the joints. The role of Treg cells in the
pathogenesis is not entirely clear, as the decrease in the number of
Treg cells in synovium and peripheral blood has been described in the
past few years[33-35]. Our FCM data also
demonstrate a significant decrease of Treg cells in PBMCs and spleen
from CIA mice. The prevailing view in the functions of Treg cells is
that they use different pathways to inhibit effector T cell
proliferation and immune responses, including immunomodulatory cytokines
such as IL-10, TGF-β and IL-35. For instance, IL-10 reporter (IL-10R)
depletion results in the selective dysregulation of Th17 immune
responses[36]. And several studies reported that
mice with IL-10 deficient Treg cells could develop autoimmune diseases,
such as spontaneous colitis[37]. Our data have
validated the inverse correlation between plasma IL-10 and DAS28 scores
in the RA patient cohort, suggesting that Treg-targeted might be an
effective and potential strategy for RA treatment.
Previous
studies have found that miRNAs play a key regulatory role in the
pathogenesis of RA[38-40], and their regulatory
role in Th cell differentiation and function has also been confirmed.
Interestingly, results from emerging studies of miR-143-3p expression in
RA patients appear to be conflicting, which has been reported to show
different expression in different individuals with
RA[17,27,28]. Hence, We conducted the clinical
research and analysis of the correlation between miR-143-3p and Th in RA
patients, and explored that miR-143-3p, with negatively correlated with
DAS28, was actively associated with IL-10 secreted by Treg cells. The
results in CIA mice were consistent with the clinical study. Meanwhile,
a recent study reported that miR-143-3p was negatively associated with
plasma inflammatory cytokines IL-6 in RA and
sepsis[41,42],
and IL-6 functions as a critical switch in inhibiting development of
TGF-β-induced Treg cells[43]. Based on the above
analyses, it is rational to hypothesize that miR-143-3p promoted the
differentiation of Treg cells and treated Treg-deficiency diseases such
as RA.
To further investigate the potential mechanisms associated with the
protective effect of miR-143-3p in RA, we verified Treg cells as the
critical node of miR-143-3p in this function. The elevated expression of
miR-143-3p was verified to inhibit the mRNA levels of Foxp3 in vitro,
which was the master transcription factor of Treg cells, indicating that
miR-143-3p is capable to facilitate Treg cells differentiation. To
further illuminate the role of miR-143-3p on the differentiation of Treg
cells during the RA progress, the overexpression of miR-143-3p was
conducted with synthetic miR-143-3p mimics in vivo. Our data
corroborated that miR-143-3p mimic treatment resulted in a higher
proportion of Treg cells in PBMC and spleen, along with the higher
levels of IL-10 in plasma and Foxp3 mRNA in lymph nodes and spleen.
These data demonstrate that miR-143-3p could upregulate Foxp3 expression
to promote Treg cells differentiation.
Nevertheless, the molecular mechanism of the effect of miR-143-3p on the
Treg cells differentiation is still unclear. In order to understand
potential mechanism of miR-143-3p in Treg-deficiency of RA, we explored
the microRNA database
(miRBase
at http://www.mirbase.org), which is the high confidence microRNA data
set to identify potential target of the
miR‐143-3p[44,45]. With the TargetScan and miRDB
miRNA target prediction tool, we have identified that Kras, c-maf,
Mapk7, Bmp5, Etv6 may be the miR-143-3p targets. It is known that c-maf
can affect the differentiation and function of CD4+T
cells through its unique regulatory mechanism, especially Treg
cells[46]. It has been recent reported that c-maf
was highly expressed in intestinal suppressive effector Treg cells
(eTreg cells)[47], which were critical enforcers
of the immune equilibrium. Moreover, Treg-derived IL-10 production was
c-maf dependent[48]. These evidence indicate that
the effect of miR-143-3p on Treg cells may be medicated by c-maf, which
requires further studies for verification.
In conclusion, our results provide the evidence that the expression of
miR-143-3p in PBMCs is negatively correlated with RA disease activity.
And miR-143-3p could act as a key regulator of Treg cells
differentiation to ameliorate CIA symptoms. These results provide a
novel strategy to treat Treg-deficiency autoimmune diseases such as RA.