Animal Studies

To investigate the role of IL-33 in gouty arthritis.

Hyperalgesic priming is characterized by enhanced nociceptor sensitization by pronociceptive mediators, prototypically PGE . Priming has gained interest as a mechanism underlying the transition to chronic pain. Which stimuli induce priming and what cellular mechanisms are employed remains incompletely understood. In adult male rats, we present the cytokine Oncostatin M (OSM), a member of the IL-6 family, as an inducer of priming by a novel mechanism. We used a high content microscopy based approach to quantify the activation of endogenous PKA-II and ERK of thousands sensory neurons in culture. Incubation with OSM increased and prolonged ERK activation by agents that increase cAMP production such as PGE , forskolin, and cAMP analogs. These changes were specific to IB4/CaMKIIα positive neurons, required protein translation, and increased cAMP-to-ERK signaling. In both, control and OSM-treated neurons, cAMP/ERK signaling involved RapGEF2 and PKA but not Epac. Similar enhancement of cAMP-to-ERK signaling could be induced by GDNF, which acts mostly on IB4/CaMKIIα-positive neurons, but not by NGF, which acts mostly on IB4/CaMKIIα-negative neurons. In vitro, OSM pretreatment rendered baseline TTX-R currents ERK-dependent and switched forskolin-increased currents from partial to full ERK-dependence in small/medium sized neurons. In summary, priming induced by OSM uses a novel mechanism to enhance and prolong coupling of cAMP/PKA to ERK1/2 signaling without changing the overall pathway structure.

Genetic ablation or pharmacological inhibition of the heat-activated cation channel TRPM3 alleviates inflammatory heat hyperalgesia, but the underlying mechanisms are unknown. We induced unilateral inflammation of the hind paw in mice, and directly compared expression and function of TRPM3 and two other heat-activated TRP channels (TRPV1 and TRPA1) in sensory neurons innervating the ipsilateral and contralateral paw. We detected increased mRNA levels in dorsal root ganglion neurons innervating the inflamed paw, and augmented TRP channel-mediated calcium responses, both in the cell bodies and the intact peripheral endings of nociceptors. In particular, inflammation provoked a pronounced increase in nociceptors with functional co-expression of TRPM3, TRPV1 and TRPA1. Finally, pharmacological inhibition of TRPM3 dampened TRPV1- and TRPA1-mediated responses in nociceptors innervating the inflamed paw, but not in those innervating healthy tissue. These insights into the mechanisms underlying inflammatory heat hypersensitivity provide a rationale for developing TRPM3 antagonists to treat pathological pain.

Stinging trees from Australasia produce remarkably persistent and painful stings upon contact of their stiff epidermal hairs, called trichomes, with mammalian skin. -induced acute pain typically lasts for several hours, and intermittent painful flares can persist for days and weeks. Pharmacological activity has been attributed to small-molecule neurotransmitters and inflammatory mediators, but these compounds alone cannot explain the observed sensory effects. We show here that the venoms of Australian species contain heretofore unknown pain-inducing peptides that potently activate mouse sensory neurons and delay inactivation of voltage-gated sodium channels. These neurotoxins localize specifically to the stinging hairs and are miniproteins of 4 kDa, whose 3D structure is stabilized in an inhibitory cystine knot motif, a characteristic shared with neurotoxins found in spider and cone snail venoms. Our results provide an intriguing example of inter-kingdom convergent evolution of animal and plant venoms with shared modes of delivery, molecular structure, and pharmacology.

Pulsed radiofrequency stimulation at the dorsal root ganglion is used for treatment of radicular pain; however, its mechanism for neuropathic pain treatment has not been fully elucidated. Here, we investigated whether pulsed radiofrequency stimulation affects the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, which play a critical role in synaptic plasticity.

We aimed to demonstrate the effects of microRNA (miR)-101 on neuropathic pain and explore the underlying mechanisms. Rat spinal microglia cells were isolated and inflammatory condition was stimulated by 24-h incubation with lipopolysaccharide (LPS). Rats were divided into 4 groups: sham, chronic constriction injury (CCI), CCI + miR-negative control (miR-NC) and CCI + miR-101 mimics. Paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) tests were conducted. The mRNA levels of key genes were determined by quantitative real-time polymerase chain reaction. Mammalian target of rapamycin (mTOR) protein level was detected by Western blot. Concentrations of interleukin (IL)-6, IL-1β and tumor necrosis factor (TNF)-α were examined by ELISA. MiR-101 was downregulated and mTOR was upregulated in lumbar spinal dorsal horns from CCI rats. Targetscan and luciferase reporter assay confirmed that mTOR was direct target of miR101. MiR-101 mimics inhibited LPS-stimulated increase in the levels of IL-6, IL-1β and TNF-α in primary microglial cells in vitro. In the rat CCI model, miR-101 mimics also suppressed CCI-induced decrease in PWT and PWL and inhibited CCI-induced increase in mRNA and protein levels of IL-6, IL-1β and TNF-α. In addition, miR-101 downregulated mTOR mRNA and protein expressions in CCI rats. Besides, CCI operation resulted in miR-101 downregulation and mTOR mRNA upregulation in spinal microglia cells in a time-dependent manner. In conclusion, miR-101 had neuropathic pain-attenuating activity through targeting mTOR.