Role of actin filaments in allodynia induced by chronic compression of the dorsal root ganglion

Effect of cGMP-activated aquaporin 1 on TRPV4 in rats with allodynia induced by chronic compression of the dorsal root ganglion

BACKGROUND

The aim of this study was to investigate the effects of aquaporin 1 (AQP1) knockdown on allodynia in rats with chronic compression of the dorsal root ganglia (DRG) and the role of TRPV4 in these effects.

METHODS

Adult male Wistar rats were subjected to chronic compression of the dorsal root ganglia (CCD) via surgery. Behavioral tests were performed to calculate the paw withdrawal mechanical threshold (PWMT). Gene silence was induced by injecting rats with lentivirus expressing AQP1 short hairpin RNA (shRNA, Lv-shAQP1). Western blot analyses were performed to examine AQP1 and TRPV4 protein expression. The concentration of cyclic guanosine monophosphate (cGMP) was determined via enzyme-linked immunosorbent assay.

RESULTS

AQP1 protein levels in DRG neurons were significantly increased in CCD rats and were accompanied by a decrease in the PWMT. Lentivirus-mediated RNA interference of AQP1 decreased AQP1 protein expression in CCD rats and normalized their PWMT, but not in rats infected with lentivirus-expressing negative control short hairpin RNA. Furthermore, AQP1 was identified as a cGMP-gated channel. cGMP concentration was upregulated in CCD rats. This effect was attenuated by treatment with a cGMP inhibitor. Additionally, the cGMP inhibitor decreased the mechanical allodynia and AQP1 protein expression in CCD rats. Finally, levels of TRPV4 expression were upregulated in DRG neurons and the L4/L5 spinal cord following surgery, and these effects were reversed by treatment with Lv-shAQP1 or a cGMP inhibitor.

CONCLUSION

AQP1 plays a vital role in CCD-induced allodynia as Lv-shAQP1 significantly reduced the allodynia in CCD rats by inhibiting TRPV4 expression.

Gene therapy by lentivirus-mediated RNA interference targeting extracellular-regulated kinase alleviates neuropathic pain in vivo

BACKGROUNDS

Neuropathic pain is an abnormal pain, which is related to the activation of extracellular-regulated kinase (ERK) signaling. This study was to investigate the effects of ERK knockdown via lentivirus-mediated RNA interference on allodynia in rats with chronic compression of the dorsal root ganglia (DRG) and to uncover the potential mechanisms.

METHODS

The model of chronic compression of the dorsal root ganglia (CCD) was established in rats by surgery. Gene silence was induced by injecting rats with lentivirus expressing ERK short hairpin RNA (shRNA). Behavioral test was performed by calculating paw withdrawal mechanical threshold (PWMT) and thermal paw withdrawal latency (TPWL).

RESULTS

We firstly generated lentivirus expressing ERK shRNA to downregulate ERK gene expression both in vitro and in vivo by using Western blot analysis and quantitative reverse transcription polymerase chain reaction. In CCD, ERK mRNA, and protein levels in DRG neurons were dramatically increased, accompanied with decreased PWMT and TPWL. Lentivirus-mediated RNA interference decreased ERK gene expression in DRG neurons and normalized the PWMT and TPWL in CCD rats, but not in rats infected with lentivirus expressing negative control shRNA. Further, calcium responses of DRG neurons to the hypotonic solution and 4α-phorbol 12,13-didecanoate were enhanced in CCD rats, which were suppressed by lentivirus-mediated ERK gene silence. Finally, the levels of transient receptor potential vanilloid 4 gene expressions in DRG neurons and L4 to L5 spinal cord isolated from CCD rats were dramatically upregulated, which were reversed by lentivirus-mediated ERK gene knockdown.

CONCLUSION

Lentivirus-mediated RNA interference (RNAi) silencing targeting ERK might reverse CCD-induced neuropathic pain in rats through transient receptor potential vanilloid 4.

The potential role of Piezo2 in the mediation of visceral sensation

Piezo2 is an important mechano-gated ion channel that is involved in light touch sensitivity and inflammatory allodynia. However, current research has focused on the function of Piezo2 in somatic sensation but not in visceral sensation. The present study aimed to investigate the role of Piezo2 in visceral sensation of mechanically innocuous and noxious stimuli under physiological and hyperalgesic conditions using rats as a model organism. Neonatal enema with acetic acid induced visceral hypersensitivity. Intrathecal administration of Piezo2-short hairpin RNA (shRNA) reduced Piezo2 expression in lumbosacral dorsal root ganglia (DRG) at both the mRNA and protein levels. Piezo2 knock-down in DRG attenuated visceral sensation to innocuous stimuli in control rats and to both innocuous and noxious stimuli in rats with neonatal irritation. Compared with control rats, Piezo2 was not up-regulated in irritated rats at the mRNA or protein levels in thoracolumbar or lumbosacral DRGs, while TRPV1 was up-regulated in lumbosacral DRGs. These data suggest a potential role of Piezo2 in the mediation of visceral sensation.