A long noncoding RNA contributes to neuropathic pain by silencing Kcna2 in primary afferent neurons

Xiuli Zhao, Zongxiang Tang, Hongkang Zhang, Fidelis E Atianjoh, Jian-Yuan Zhao, Lingli Liang, Wei Wang, Xiaowei Guan, Sheng-Chin Kao, Vinod Tiwari, Yong-Jing Gao, Paul N Hoffman (+4 others)
2013 Nature Neuroscience  
nature neurOSCIenCe advance online publication a r t I C l e S Neuropathic pain is a major public health problem. Treatment for this disorder has had limited success owing to our incomplete understanding of the mechanisms that underlie the induction of neuropathic pain 1 . Nerve injury-induced neuropathic pain is thought to be triggered by abnormal spontaneous activity that arises in neuromas and first-order sensory neurons of the DRG 2,3 . The abnormal excitability may result from maladaptive
more » ... hanges in gene transcription and translation of receptors, enzymes and voltage-dependent ion channels in the DRG 4 . Voltage-dependent potassium channels govern cell excitability. Peripheral nerve injury downregulates expression of mRNA and protein for these channels in the DRG 5-10 , a phenomenon that may contribute to induction of neuropathic pain 11-14 . However, the molecular mechanisms that underlie this downregulation are still unknown. Recent studies suggest that the mechanism for gene regulation involves widespread noncoding RNAs, including lncRNAs 15-17 . The study of lncRNAs is still in its infancy 18, 19 . A few lncRNAs have been identified in mammalian cells and implicated in gene-regulatory roles such as transcription and translation 18, 19 . Their expression is associated with some physiological and pathological processes, but how they are causally linked to disease development is elusive 18, 19 . Here, we report a new native lncRNA that is expressed in mammalian DRG neurons. Because most of its sequence is complementary to Kcna2 RNA, we named it Kcna2 antisense RNA. We found that Kcna2 antisense RNA may act as a biologically active regulator and participate in induction and maintenance of neuropathic pain by specifically silencing Kcna2 expression in the DRG. RESULTS Identification of natural Kcna2 antisense RNA in DRG neurons To detect Kcna2 antisense RNA, we first searched a database using the complete published Kcna2 cDNA sequence. Although many of the expressed sequence tags reflected portions of Kcna2 transcript, a few were in the antisense direction. Using strand-specific primers for reverse transcription, we identified Kcna2 antisense transcript in the DRGs of rat, mouse, monkey and human (Fig. 1a) , although the sequences were not identical among species. We also detected this transcript in spinal cord, various brain regions and other body organs of rats (Supplementary Fig. 1a) . Using rapid amplification of cDNA ends for directional sequencing of 5′ and 3′ ends, we identified a 2.52-kb Kcna2 antisense RNA in rat DRG ( Supplementary Fig. 1b) . Most of its sequence overlapped that of Kcna2 RNA, including the coding sequence, the 3′ untranslated region and part of the 5′ untranslated region, but Kcna2 antisense RNA had unique regions at the 5′ and 3′ ends (Fig. 1b) . It had no apparent open reading frame (Supplementary Fig. 1b) , indicating that Kcna2 antisense RNA is noncoding RNA. We further confirmed the Kcna2 antisense RNA at the expected size by northern blot analysis of RNA from adult rat DRG and spinal cord, Neuropathic pain is a refractory disease characterized by maladaptive changes in gene transcription and translation in the sensory pathway. Long noncoding RNAs (lncRNAs) are emerging as new players in gene regulation, but how lncRNAs operate in the development of neuropathic pain is unclear. Here we identify a conserved lncRNA, named Kcna2 antisense RNA, for a voltage-dependent potassium channel mRNA, Kcna2, in first-order sensory neurons of rat dorsal root ganglion (DRG). Peripheral nerve injury increased Kcna2 antisense RNA expression in injured DRG through activation of myeloid zinc finger protein 1, a transcription factor that binds to the Kcna2 antisense RNA gene promoter. Mimicking this increase downregulated Kcna2, reduced total voltage-gated potassium current, increased excitability in DRG neurons and produced neuropathic pain symptoms. Blocking this increase reversed nerve injury-induced downregulation of DRG Kcna2 and attenuated development and maintenance of neuropathic pain. These findings suggest endogenous Kcna2 antisense RNA as a therapeutic target for the treatment of neuropathic pain.
doi:10.1038/nn.3438 pmid:23792947 pmcid:PMC3742386 fatcat:27htnypaujhzpj4swqboyjaej4