A role for translational regulation by S6 kinase and a downstream target in inflammatory pain

Abstract

Background and Purpose Translational controls pervade neurobiology. Nociceptors play an integral role in the detection and propagation of pain signals. Nociceptors can undergo persistent changes in their intrinsic excitability. Pharmacological disruption of nascent protein synthesis diminishes acute and chronic forms of pain‐associated behaviours. However, the targets of translational controls that facilitate plasticity in nociceptors are unclear. Experimental Approach We used ribosome profiling to probe the translational landscape in dorsal root ganglion (DRG) neurons from male Swiss‐Webster mice, after treatment with nerve growth factor and IL‐6. Expression dynamics of c‐Fos were followed with immunoblotting and immunohistochemistry. The involvement of ribosomal protein S6 kinase 1 (S6K1), a downstream component of mTOR signalling, in the control of c‐Fos levels was assessed with low MW inhibitors of S6K1 (DG2) or c‐Fos (T‐5224), studying their effects on nociceptor activity in vitro using multielectrode arrays (MEAs) and pain behaviour in vivo in Swiss‐Webster mice using the hyperalgesic priming model. Key Results c‐Fos was expressed in sensory neurons. Inflammatory mediators that promote pain in both humans and rodents promote c‐Fos translation. The mTOR effector S6K1 is essential for c‐Fos biosynthesis. Inhibition of S6K1 or c‐Fos with low MW compounds diminished mechanical and thermal hypersensitivity in response to inflammatory cues. Additionally, both inhibitors reduced evoked nociceptor activity. Conclusion and implications Our data show a novel role of S6K1 in modulating the rapid response to inflammatory mediators, with c‐Fos being one key downstream target. Targeting the S6 kinase pathway or c‐Fos is an exciting new avenue for pain‐modulating compounds.

A compendium of validated pain genes

“…A third report found that deletion of TRPC5 increased mechanical sensitivity following partial meniscectomy and intraarticular injection of monoiodoacetate (MIA)—the latter of which was used to induce a model of osteoarthritis (de Sousa Valente et al, 2020). The increased sensitivity following MIA injection was also correlated with increased c‐Fos expression in cultured neurons, which is significant given that c‐Fos has been implicated as playing a key role in the transition to chronic forms of inflammatory and neuropathic pain via the downstream expression of dynorphin (Ahmad & Ismail, 2002; Marvaldi et al, 2020; de la Peña, Kunder, et al, 2021).…”

“…Taken together, these results point to future avenues of osteoarthritic pharmaceutical development that could jointly address pain management and joint morphology through combined targeting of NGF, MMP13, and IL‐1B. In addition to these genetic models, local injection of NGF has been used as a key inflammatory mediator in behavioral models given that NGF serves as a potentiator of protein synthesis (Barragan‐Iglesias et al, 2021; Melemedjian et al, 2010; de la Peña, Barragan‐Iglesias, et al, 2021; de la Peña, Kunder, et al, 2021).…”

“…Hyperalgesia may be further classified as either primary or secondary, with primary hyperalgesia referring to hypersensitivity at the site of injury and secondary hyperalgesia extending to the surrounding areas (Sarkar et al, 2000; Treede et al, 1992). Primary hyperalgesia is caused by a process called peripheral sensitization through which inflammatory mediators and local factors trigger intracellular signaling pathways in primary afferents, thereby altering the function or expression of receptor molecules and voltage‐gated ion channels (Barragan‐Iglesias et al, 2021; de la Peña, Kunder, et al, 2021; Gangadharan & Kuner, 2013; Melemedjian et al, 2010; Prescott & Ratté, 2017; Woolf & Thompson, 1991). At the same time, peptidergic C fibers can release pro‐inflammatory neuropeptides to initiate a biochemical signaling cascade known as neurogenic inflammation.…”

Global analyses of mRNA expression in human sensory neurons reveal eIF5A as a conserved target for inflammatory pain

“…While the initiation phase of protein synthesis has garnered substantial attention, relatively little is known regarding elongation. Inhibitors that prevent translation elongation diminish pain amplification behaviors 26,29,98 . Given that inflammatory mediators increase ribosome occupancy in 5′UTRs, it would be interesting to determine what effects eIF5A inhibition has on translation start sites and if they mirror those increased by inflammatory cues 30 .…”

“…The consequences of inflammatory mediators on translation have recently been reported using ribosome profiling 28 . Within 20 min, translation of immediate early genes such as Arc and c‐Fos is increased as is the utilization of cryptic open reading frames situated in the 5′ untranslated region of numerous transcripts including calca/CGRP 28–30 . Despite the pervasive roles of translational regulation in preclinical murine models, it remains somewhat tenuous if translational regulation is a broadly conserved pathway for nociceptor sensitization.…”