MicroRNA–mediated downregulation of potassium-chloride-cotransporter and vesicular γ-aminobutyric acid transporter expression in spinal cord contributes to neonatal cystitis–induced visceral pain in rats

Abstract

Loss of GABAergic inhibition in pain pathways has been considered to be a key component in the development of chronic pain. In the present study, we intended to examine whether miR-92b–mediated posttranscriptional dysregulation of spinal potassium chloride cotransporter (KCC2) and vesicular γ-aminobutyric acid transporter (VGAT) plays a major role in the development and maintenance of long-term visceral hyperalgesia in neonatal zymosan–treated rats. Neonatal cystitis was induced by transurethral zymosan administration from postnatal (P) days 14 to 16 (protocol 1). Two other zymosan protocols were also used: adult rechallenge on P57 to 59 following neonatal P14 to 16 exposures (protocol 2), and adult zymosan exposures on P57 to 59 (protocol 3). Both neonatal and adult bladder inflammation protocols demonstrated an increase in spinal miR-92b-3p expression and subsequent decrease in KCC2 and VGAT expression in spinal dorsal horn neurons. In situ hybridization demonstrated a significant upregulation of miR-92b-3p in the spinal dorsal horn neurons of neonatal cystitis rats compared with saline-treated controls. In dual in situ hybridization and immunohistochemistry studies, we further demonstrated coexpression of miR-92b-3p with targets KCC2 and VGAT in spinal dorsal horn neurons, emphasizing a possible regulatory role both at pre- and post-synaptic levels. Intrathecal administration of lentiviral pLSyn-miR-92b-3p sponge (miR-92b-3p inhibitor) upregulated KCC2 and VGAT expression in spinal dorsal horn neurons. In behavioral studies, intrathecal administration of lentiviral miR-92b-3p sponge attenuated an increase in visceromotor responses and referred viscerosomatic hypersensitivity following the induction of cystitis. These findings indicate that miR-92b-3p–mediated posttranscriptional regulation of spinal GABAergic system plays an important role in sensory pathophysiology of zymosan-induced cystitis.

Substance P and pain chronicity

“…Knockdown of KCC2 by intrathecal administration of KCC2-siRNA reduces inhibitory synaptic transmission (Lin et al 2017 ). mRNA-mediated downregulation of KCC2 and vesicular GABA transporter expression in the spinal cord contribute to visceral pain in rats (Zhang et al 2017 ). Dynamic changes in the mRNA profile revealed multiple regulatory mechanisms in spinofugal projection neurons (von Schack et al 2011 ).…”

Stress-Induced Chronic Visceral Pain of Gastrointestinal Origin

“…As a negative regulator of transient receptor potential cation channel subfamily V member 1 (TRPV1) expression, miR-199 expression in colonic biopsies was negatively correlated with visceral pain scores and TRPV1 expression in diarrhea-predominate IBS patients (Zhou Q. et al, 2016 ). Preclinical studies in rat models examined miRNA expression in the spinal cord and identified miR-17-5p as a possible mediator of water avoidance stress-induced colonic hypersensitivity (Sengupta et al, 2013 ; Bradesi et al, 2015 ; Zhang et al, 2017 ). In summary, life experiences along with a person's genetic make-up determines their vulnerability or resilience to developing chronic stress-induced pain disorders such as IBS.…”

Targeting epigenetic mechanisms for chronic visceral pain: A valid approach for the development of novel therapeutics

“…Loss of these two ion transport channels interfered with GABA-mediated inhibition of pain signaling 112. Administration of a miR-92-3p sponge (a miRNA inhibitor) to the spinal cord of these animals reversed visceral hypersensitivity, highlighting the importance of miR-mediated mechanisms 112. Detrimental effects of prenatal, neonatal, and adult stress (top-down mechanism) on spinal cord neurons have been described by other investigators.…”

“…For instance, the upregulation of miR-92-3p caused the downregulation of KCC2 and VGAT in the lumbosacral spinal cord. Loss of these two ion transport channels interfered with GABA-mediated inhibition of pain signaling 112. Administration of a miR-92-3p sponge (a miRNA inhibitor) to the spinal cord of these animals reversed visceral hypersensitivity, highlighting the importance of miR-mediated mechanisms 112.…”