Intranasal delivery of an antisense oligonucleotide to the RNA-binding protein HuR relieves nerve injury-induced neuropathic pain

Neuropathic pain remains an undertreated condition and there is a medical need to develop effective treatments. Accumulating evidence indicates that post-transcriptional regulation of gene expression is involved in neuropathic pain; however, RNA processing is not clearly investigated. Our study investigated the role of HuR, an RNA binding protein, in promoting neuropathic pain and trauma-induced microglia activation in the spared nerve injury (SNI) mouse model. To this aim, an antisense oligonucleotide (ASO) knockdown of HuR gene expression was used. ASOs poorly cross the blood brain barrier and an intranasal (i.n.) administration was employed to achieve CNS penetration through a noninvasive delivery. The efficacy of i.n. ASO administration was compared to an intrathecal (i.t.) delivery. I.n. administered ASO reduced spinal HuR protein and relieved pain hypersensitivity with a similar efficacy to i.t. administration. Immunofluorescence studies showed that HuR was expressed in activated microglia, co-localized with p38 and, partially, with extracellular signal-regulated kinase (ERK)1/2 within the spinal cord dorsal horn. An anti-HuR ASO inhibited the activation of spinal microglia by reducing the levels of pro-inflammatory cytokines, inducible nitric oxide synthase (iNOS), the activation of nuclear factor-κB (NF-κB), and suppressed the SNI-induced overphosphorylation of spinal p38, ERK1/2 and c-Jun-N-terminal kinase (JNK)-1. In addition, HuR silencing increased the expression of the anti-inflammatory cytokine IL-10, promoting the shift of microglial M1 to M2 phenotype. Targeting HuR by i.n. anti-HuR ASO might represent a noninvasive promising perspective for neuropathic pain management by its powerful inhibition of microglia-mediated spinal neuroinflammation and promotion of an anti-inflammatory and neuroprotectant response.