Downregulation of GRK6 in arcuate nucleus promotes chronic visceral hypersensitivity via NF-κB upregulation in adult rats with neonatal maternal deprivation

Thalamic Nucleus Reuniens Glutamatergic Neurons Mediate Colorectal Visceral Pain in Mice via 5-HT2B Receptors

Irritable bowel syndrome (IBS) is a common functional bowel disorder characterized by abdominal pain and visceral hypersensitivity. Reducing visceral hypersensitivity is the key to effectively relieving abdominal pain in IBS. Increasing evidence has confirmed that the thalamic nucleus reuniens (Re) and 5-hydroxytryptamine (5-HT) neurotransmitter system play an important role in the development of colorectal visceral pain, whereas the exact mechanisms remain largely unclear. In this study, we found that high expression of the 5-HT2B receptors in the Re glutamatergic neurons promoted colorectal visceral pain. Specifically, we found that neonatal maternal deprivation (NMD) mice exhibited visceral hyperalgesia and enhanced spontaneous synaptic transmission in the Re brain region. Colorectal distension (CRD) stimulation induced a large amount of c-Fos expression in the Re brain region of NMD mice, predominantly in glutamatergic neurons. Furthermore, optogenetic manipulation of glutamatergic neuronal activity in the Re altered colorectal visceral pain responses in CON and NMD mice. In addition, we demonstrated that 5-HT2B receptor expression on the Re glutamatergic neurons was upregulated and ultimately promoted colorectal visceral pain in NMD mice. These findings suggest a critical role of the 5HT2B receptors on the Re glutamatergic neurons in the regulation of colorectal visceral pain.

The Role of G Protein-Coupled Receptor Kinase 6 Regulation in Inflammation and Pain

The G protein-coupled receptor kinase 6 is associated with inflammation and pathological pain. Impairment of GRK6 expression was described in chronic inflammatory diseases such as rheumatoid arthritis and this was shown to be accompanied by an imbalance of downstream signaling pathways. Here, we discuss novel aspects of GRK6 interaction and its impact upon hyperalgesia and inflammatory processes. In this review, we compile important findings concerning GRK6 regulation for a better pathophysiological understanding of the intracellular interaction in the context of inflammation and show clinical implications-for example, the identification of possible therapy goals in the treatment of chronic inflammatory hyperalgesia.

Overexpression of GRK6 alleviates chronic visceral hypersensitivity through downregulation of P2Y6 receptors in anterior cingulate cortex of rats with prenatal maternal stress

Aims

Visceral hypersensitivity is a major clinic symptom in patients with irritable bowel syndrome (IBS). Anterior cingulate cortex (ACC) is involved in processing the information of pain. Both G protein‐coupled receptor kinase 6 (GRK6) and P2Y purinoceptor 6 (P2Y6) are associated with neuroinflammation and pathological pain. The aim of this study was to investigate the interaction between GRK6 and P2Y6 in ACC in the development of visceral hypersensitivity of adult offspring rats with prenatal maternal stress (PMS).

Methods

Visceral hypersensitivity was quantified by abdominal withdrawal reflex threshold to colorectal distension (CRD). The expression and cellular distribution of GRK6 and P2Y6 were determined by Western blotting, qPCR, and fluorescence immunohistochemistry. Co‐immunoprecipitation was used to evaluate the interaction between GRK6 and P2Y6.

Results

The mRNA and protein levels of GRK6 were significantly decreased in ACC of PMS rats. The injection of GRK6 overexpression virus significantly attenuated visceral hypersensitivity of PMS rats. P2Y6’s mRNA level, protein level, and ratio of membrane protein over total protein expression was markedly increased in PMS rats. P2Y6 antagonist MRS2578 microinjection reversed visceral hypersensitivity of PMS rats. GRK6 overexpression significantly reduced P2Y6’s expression in membrane proteins and P2Y6’s ratio of membrane protein over total protein expression.

Conclusions

These results indicate that decreased GRK6 leads to the accumulation of P2Y6 at neuron membrane in ACC, thereby contributing to visceral hypersensitivity of PMS rats.

Upregulation of Spinal ASIC1 and NKCC1 Expression Contributes to Chronic Visceral Pain in Rats

Aims: To determine whether acid-sensing ion channel 1 (ASIC1)–sodium-potassium-chloride cotransporter 1 (NKCC1) signaling pathway participates in chronic visceral pain of adult rats with neonatal maternal deprivation (NMD).

Methods: Chronic visceral pain was detected by colorectal distension (CRD). Western blotting and Immunofluorescence were performed to detect the expression and location of ASIC1 and NKCC1. Whole-cell patch-clamp recordings were performed to record spinal synaptic transmission.

Results: The excitatory synaptic transmission was enhanced and the inhibitory synaptic transmission was weakened in the spinal dorsal horn of NMD rats. ASIC1 and NKCC1 protein expression in the spinal dorsal horn was significantly up-regulated in NMD rats. Incubation of Amiloride reduced the amplitude of mEPSCs. Incubation of Bumetanide (BMT) increased the amplitude of mIPSCs. Intrathecal injection of ASIC1 or NKCC1 inhibitors reversed the threshold of CRD in NMD rats. Also, Amiloride treatment significantly reversed the expression of NKCC1 in the spinal dorsal horn of NMD rats.

Conclusion: Our data suggest that the ASIC1-NKCC1 signaling pathway is involved in chronic visceral pain in NMD rats.

Upregulation of spinal ASIC1 by miR-485 mediates enterodynia in adult offspring rats with prenatal maternal stress

Aims

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disease characterized by abdominal pain. Our recent study has shown that the acid‐sensitive ion channel 1 (ASIC1) in dorsal root ganglion (DRG) is involved in stomachache of adult offspring rats subjected with prenatal maternal stress (PMS). MiR‐485 is predicted to target the expression of ASIC1. The aim of the present study was designed to determine whether miR‐485/ASIC1 signaling participates in enterodynia in the spinal dorsal horn of adult offspring rats with PMS.

Methods

Enterodynia was measured by colorectal distension (CRD). Western blotting, qPCR, and in situ hybridization were performed to detect the expression of ASICs and related miRNAs. Spinal synaptic transmission was also recorded by patch clamping.

Results

PMS offspring rats showed that spinal ASIC1 protein expression and synaptic transmission were significantly enhanced. Administration of ASICs antagonist amiloride suppressed the synaptic transmission and enterodynia. Besides, PMS induced a significant reduction in the expression of miR‐485. Upregulating the expression markedly attenuated enterodynia, reversed the increase in ASIC1 protein and synaptic transmission. Furthermore, ASIC1 and miR‐485 were co‐expressed in NeuN‐positive spinal dorsal horn neurons.

Conclusions

Overall, these data suggested that miR‐485 participated in enterodynia in PMS offspring, which is likely mediated by the enhanced ASIC1 activities.