Bone marrow stromal cells (BMSCs) produce long-lasting attenuation of
pain hypersensitivity. This effect involves BMSC's ability to interact with the immune system and activation of the endogenous
opioid receptors in the
pain modulatory circuitry. The
nuclear factor kappa B (NF-κB)
protein complex is a key
transcription factor that regulates gene expression involved in immunity. We tested the hypothesis that the NF-κB signaling plays a role in BMSC-induced
pain relief. We focused on the rostral ventromedial medulla (RVM), a key structure in the descending
pain modulatory pathway, that has been shown to play an important role in BMSC-produced antihyperalgesia. In Sprague-Dawley rats with a
ligation injury of the masseter muscle tendon (TL), BMSCs (1.5 M/rat) from donor rats were infused i.v. at 1 week post-TL. P65 exhibited predominant neuronal localization in the RVM with scattered distribution in glial cells. At 1 week, but not 8 weeks after BMSC infusion, western blot and immunostaining showed that p65 of NF-κB was significantly increased in the RVM. Given that
chemokine signaling is critical to BMSCs'
pain-relieving effect, we further evaluated a role of
chemokine signaling in p65 upregulation. Prior to infusion of BMSCs, we transduced BMSCs with Ccl4
shRNA, incubated BMSCs with
RS 102895, a CCR2b antagonist, or
maraviroc, a CCR5 antagonist. The antagonism of
chemokines significantly reduced BMSC-induced upregulation of p65, suggesting that upregulation of p65 was related to BMSCs'
pain-relieving effect. We then tested the effect of a selective NF-κB activation inhibitor,
BAY 11-7082. The
mechanical hyperalgesia of the rat was assessed with the von Frey method. In the pre-treatment experiment,
BAY 11-7082 (2.5 and 25 pmol) was injected into the RVM at 2 h prior to BMSC infusion. Pretreatment with
BAY 11-7082 attenuated BMSCs' antihyperalgesia, but post-treatment at 5 weeks post-BMSC was not effective. On the contrary, in TL rats receiving
BAY 11-7082 without BMSCs, TL-induced
hyperalgesia was attenuated, consistent with dual roles of NF-κB in
pain hypersensitivity and BMSC-produced
pain relief. These results indicate that the NF-κB signaling pathway in the descending circuitry is involved in initiation of BMSC-produced behavioral antihyperalgesia.