[Spinal transcription factor GATA4 mediated adenosine A1 receptor activation contributes to electroacupuncture analgesia in neuropathic pain rats]

Abstract

Objective: To investigate the effect of electroacupuncture (EA) on pain behaviors and expression of spinal transcription factor GATA-binding Protein 4 (GATA4) and adenosine A1 receptor in neuropathic pain rats, so as to explore its mechanism underlying pain relief.

Methods: The present study includes 2 parts. In the first part, 18 SD rats were randomly divided into control, adenovirus short-hairpin interference RNA for GATA4 (AV-shGATA4 RNA) and adenovirus empty vector (AV-control short-hairpin RNA, AV-shCTRL) groups, with 6 rats in each group. The expression of GATA4 protein in the lumbar spinal cord (L4-L6) was detected to evaluate the transfection efficiency of AV-shGATA4 RNA (silencing GATA4 expression). In the second part, thirty SD rats were randomly divided into 5 groups, namely sham operation, CCI model, EA, EA+AV-shGATA4 RNA, and EA+AV-shCTRL groups, with 6 rats in each group. The neuropathic pain model was established by chronic constriction injury (CCI) of the right sciatic nerve. On the 7th day following modeling, EA was applied to the right "Zusanli"(ST36) and "Taichong"(LR3) (1 mA，2 Hz /100 Hz) for 30 min. Rats of the EA+AV-shGATA4 RNA and EA+AV-shCTRL groups received intrathecal injection of AV-shGATA4 RNA and AV-shCTRL(1×10¹¹ PFU/mL，10 μL)at the spinal L4-L6 segments, separately, 48 h before EA intervention. The mechanical pain threshold and thermal pain threshold of the affected limb were detected before molding, 7 days following molding and 60 min after EA. The expressions of adenosine A1 receptor and GATA4 protein in the spinal cord (L4-L6) were detected by Western blot.

Results: Outcomes of the first part showed that compared with the control group, no significant changes were found in the mechanical and thermal pain thresholds in both AV-shCTRL and AV-shGATA4 RNA groups and in the expression of spinal GATA4 protein of the AV-shCTRL group (P＞0.05). The expression of spinal GATA4 protein of the AV-shGATA4 RNA group was significantly lower than that of the AV-shCTRL group (P<0.05). In the second part of the study, before CCI modeling, there were no significant differences among the five groups in the mechanical and thermal pain thre-sholds (P> 0.05). On the 7th day following modeling, the mechanical and thermal pain thresholds were significantly lowered in compa-rison with their own pre-modeling of each group and with the sham operation group (P<0.05). At 60 min after EA and compared with the model group, the mechanical and thermal pain thresholds were significantly increased in both the EA and EA+AV-shCTRL groups (P<0.05) but not in the EA+AV-shGATA4 RNA group (P>0.05), suggesting a critical involvement of GATA4 in EA analgesia. The expression levels of adenosine A1 receptor and GATA4 protein were significantly increased in the model group than in the sham operation group (P<0.05), and considerably further up-regulated in both EA and EA+AV-shCTRL groups (P< 0.05), rather than in the EA+AV-shGATA4 RNA group (P>0.05), suggesting that the effects of EA in up-regulating the expression of A1 receptor and GATA4 were eliminated after silencing GATA4 protein.

Conclusion: EA of ST36 and LR3 can relieve pain by increasing the expression of adenosine A1 receptor of the lumbar spinal cord in neuropathic pain rats, which is probably mediated by GATA4 protein.

Keywords: Adenosine A1 receptor; Electroacupuncture analgesia; Neuropathic pain; Transcription factor GATA4.