Intrathecal injection of bone marrow stromal cells attenuates neuropathic pain via inhibition of P2X4R in spinal cord microglia

Abstract

BackgroundNeuropathic pain is one of the most debilitating of all chronic pain syndromes. Intrathecal (i.t.) bone marrow stromal cell (BMSC) injections have a favorable safety profile; however, results have been inconsistent, and complete understanding of how BMSCs affect neuropathic pain remains elusive.MethodsWe evaluated the analgesic effect of BMSCs on neuropathic pain in a chronic compression of the dorsal root ganglion (CCD) model. We analyzed the effect of BMSCs on microglia reactivity and expression of purinergic receptor P2X4 (P2X4R). Furthermore, we assessed the effect of BMSCs on the expression of transient receptor potential vanilloid 4 (TRPV4), a key molecule in the pathogenesis of neuropathic pain, in dorsal root ganglion (DRG) neurons.ResultsI.t. BMSC transiently but significantly ameliorated neuropathic pain behavior (37.6% reduction for 2 days). We found no evidence of BMSC infiltration into the spinal cord parenchyma or DRGs, and we also demonstrated that intrathecal injection of BMSC-lysates provides similar relief. These findings suggest that the analgesic effects of i.t. BMSC were largely due to the release of BMSC-derived factors into the intrathecal space. Mechanistically, we found that while i.t. BMSCs did not change TRPV4 expression in DRG neurons, there was a significant reduction of P2X4R expression in the spinal cord microglia. BMSC-lysate also reduced P2X4R expression in activated microglia in vitro. Coadministration of additional pharmacological interventions targeting P2X4R confirmed that modulation of P2X4R might be a key mechanism for the analgesic effects of i.t. BMSC.ConclusionAltogether, our results suggest that i.t. BMSC is an effective and safe treatment of neuropathic pain and provides novel evidence that BMSC’s analgesic effects are largely mediated by the release of BMSC-derived factors resulting in microglial P2X4R downregulation.

The Role of the Kynurenine Signaling Pathway in Different Chronic Pain Conditions and Potential Use of Therapeutic Agents

“…Individuals may complain of concomitant positive (allodynia, paresthesias) and/or negative (impaired perception to various stimuli) somatosensory symptoms. Spinal cord microglia, a non-neuronal cell population, are in close neuroanatomical and neurochemical proximity with spinal cord neurons in terms of initiating and maintaining the neuropathic pain-associated hypersensitivity [ 39 , 40 , 41 ]. The relationship between the activity of several kynurenine pathway enzymes (IDO1/2, TDO, KMO, KYNU, and HAOO) and the development of neuropathic pain has been explored in a chronic constriction injury (CCI) rat model at the spinal cord and dorsal root ganglia (DRG) levels [ 42 ].…”

Critical roles of sphingosine kinase 1 in the regulation of neuroinflammation and neuronal injury after spinal cord injury

“…Then, cellular samples containing 30 μg of protein and tissue samples containing 60 μg of protein were separated by SDS-PAGE before being transferred to PVDF membranes. Western blot was performed using standard protocols as we previously described [ 29 ]. Membranes were blocked with 5% (w/v) milk (Bio-Rad) in TBS with 0.05% Tween 20 (TBST) for 2 h at room temperature and then incubated with the appropriate primary antibodies overnight.…”

Stem Cells in the Treatment of Neuropathic Pain: Research Progress of Mechanism

“…In their experiment, stem cells inhibited the core pain signal pathway of P2X4R in microglia and reduced the expression of P2X4R. However, it was found that the number of activated microglia was not affected by IBA labeling of microglia [ 66 ]. Compared to the previous three-week studies, the results from Teng et al were taken from the chronic compression of the dorsal root ganglion model (CCD) six days after stem cell therapy.…”