Data from: Down-regulation of CXCL12/CXCR4 expression alleviates ischemia-reperfusion-induced inflammatory pain via inhibiting glial TLR4 activation in the spinal cord

Toll-like receptor 4 (TLR4) is important for the pathogenesis of
inflammatory reactions and the promotion of pain processing after
ischemia/reperfusion (IR) in spinal cord. Recently, C-X-C chemokine ligand
12 (CXCL12) and its receptor, C-X-C chemokine receptor 4 (CXCR4), were
demonstrated to be simultaneously critical for inflammatory reactions,
thereby facilitating glial activation. However, whether CXCL12/CXCR4
expression can contribute to IR-induced inflammatory pain via spinal TLR4
remained unclear. A rat model was established by 8 min of aortic arch
occlusion. The effects of CXCL12/CXCR4 expression and TLR4 activation on
inflammatory hyperalgesia were investigated by pretreatments with
CXCL12-neutralizing antibody, CXCR4 antagonist (AMD3100) and TLR4
antagonist (TAK-242) for 5 consecutive days before surgery. The results
indicated that IR induced significant and sustained inflammatory pain,
observed as decreases in paw withdrawal threshold (PWT) and paw withdrawal
latency (PWL), throughout the post-injury period. The increased levels of
TLR4 and proinflammatory chemokine CXCL12, as well as its receptor, CXCR4,
were closely correlated with the PWT and PWL trends. Double immunostaining
further suggested that TLR4, which is mainly expressed on astrocytes and
microglia, was closely co-localized with CXCL12 and CXCR4 in spinal dorsal
horn. As expected, intrathecal pretreatment with the TLR4 antagonist,
TAK-242 markedly ameliorated pain by inhibiting astrocytic and microglial
activation, as shown by decreases in TLR4 immunoreactivity and the
percentage of double-labeled cells. These protective effects were likely
due in part to the reduced production of the downstream cytokines IL-1β
and TNF-α, as well as for the recruitment of CXCL12 and CXCR4.
Additionally, intrathecal pretreatment with CXCL12-neutralizing antibody
and AMD3100 resulted in similar analgesic and anti-inflammatory effects as
those receiving TAK-242 pretreatment. These results suggest that
intrathecal blockade of CXCL12/CXCR4 expression may attenuate IR-induced
pain sensation and the release of inflammatory cytokines by limiting glial
TLR4 activation in spinal cord.