Infusion of the chemotherapeutic agent oxaliplatin leads to an acute and a chronic form of peripheral neuropathy. Acute oxaliplatin neuropathy is characterized by sensory paresthesias and muscle cramps that are notably exacerbated by cooling. Painful dysesthesias are rarely reported for acute oxaliplatin neuropathy, whereas a common symptom of chronic oxaliplatin neuropathy is pain. Here we examine the role of the sodium channel isoform Na V 1.6 in mediating the symptoms of acute oxaliplatin neuropathy. Compound and single-action potential recordings from human and mouse peripheral axons showed that cooling in the presence of oxaliplatin (30-100 μM; 90 min) induced bursts of action potentials in myelinated A, but not unmyelinated C-fibers. Whole-cell patch-clamp recordings from dissociated dorsal root ganglion (DRG) neurons revealed enhanced tetrodotoxin-sensitive resurgent and persistent current amplitudes in large, but not small, diameter DRG neurons when cooled (22°C) in the presence of oxaliplatin. In DRG neurons and peripheral myelinated axons from Scn8a med/med mice, which lack functional Na V 1.6, no effect of oxaliplatin and cooling was observed. Oxaliplatin significantly slows the rate of fast inactivation at negative potentials in heterologously expressed mNa V 1.6r in ND7 cells, an effect consistent with prolonged Na V open times and increased resurgent and persistent current in native DRG neurons. This finding suggests that Na V 1.6 plays a central role in mediating acute cooling-exacerbated symptoms following oxaliplatin, and that enhanced resurgent and persistent sodium currents may provide a general mechanistic basis for cold-aggravated symptoms of neuropathy.chemotherapy | peripheral nerve | abnormal axonal excitability | repetitive action potential discharge C linical use of the highly effective chemotherapeutic oxaliplatin is compromised by an acute and a chronic form of peripheral neuropathy. Acutely, 85-90% of patients exhibit muscle fasciculations (1, 2), sensory paresthesias, and occasional dysesthesias (3), all triggered by mild cooling. Although chronic oxaliplatin-induced neuropathy has been recently linked to changes in the expression and sensitivity of transient receptor potential (TRP) channels TRPM8 and TRPA1 (4, 5), two-pore domain potassium channels (TREK1, TRAAK) and the hyperpolarization-activated channel HCN1 (6), the mechanism underlying acute oxaliplatin neuropathy remains unresolved. Several candidate mechanisms have been proposed including potassium channel blockade (7), calcium chelation (8), and alterations in voltage-gated sodium channel (Na V ) kinetics (9, 10), but none adequately account for motor and sensory symptoms nor their exacerbation by cooling.

Detection and adaptation to cold temperature is crucial to survival. Cold sensing in the innocuous range of cold (>10-15°C) in the mammalian peripheral nervous system is thought to rely primarily on transient receptor potential (TRP) ion channels, most notably the menthol receptor, TRPM8. Here we report that TRP cation channel, subfamily C member 5 (TRPC5), but not TRPC1/TRPC5 heteromeric channels, are highly cold sensitive in the temperature range 37-25°C. We found that TRPC5 is present in mouse and human sensory neurons of dorsal root ganglia, a substantial number of peripheral nerves including intraepithelial endings, and in the dorsal lamina of the spinal cord that receives sensory input from the skin, consistent with a potential TRPC5 function as an innocuous cold transducer in nociceptive and thermosensory nerve endings. Although deletion of TRPC5 in 129S1/SvImJ mice resulted in no temperature-sensitive behavioral changes, TRPM8 and/or other menthol-sensitive channels appear to underpin a much larger component of noxious cold sensing after TRPC5 deletion and a shift in mechanosensitive C-fiber subtypes. These findings demonstrate that highly cold-sensitive TRPC5 channels are a molecular component for detection and regional adaptation to cold temperatures in the peripheral nervous system that is distinct from noxious cold sensing.pain | single-fiber | thermo-transient receptor potential | nociception | temperature sensing N ociceptors and thermoreceptive neurons, such as cold and heat receptors, innervate the skin and deep tissues. The cell bodies of sensory nerve endings are clustered in ganglia located in the vertebral column and cranium. Their projections extend to the skin where they arborize in terminals embedded between keratinocytes. Although nociceptors are polymodal and respond to stimuli (cold, heat, pressure, and noxious chemicals) that are capable of producing tissue damage and pain (1), cold receptors are unimodal and specialized to detect cool and cold temperatures (2). Transient receptor potential (TRP) ion channels are principal transducers of thermal stimuli that depolarize nerve terminals to the action potential threshold. Action potentials then relay the sensory information to integrative centers in the spinal cord and brain.All proteins are temperature sensitive, but most ion channels exhibit two-to threefold increases in gating with a 10°C change in temperature (Q 10 = 2-3). Certain ion channels exhibit dramatic temperature sensitivity in gating over physiologically relevant ranges (Q 10 = 10-30). Mammalian ion channels with such high Q 10 values include particular two-pore K + channels (3), the voltage-gated proton channel (4), transient receptor potential cation channel subfamily V members 1-3 (TRPV1-3) (5-7), transient receptor potential menthol receptor 8 (TRPM8) (8), and in some reports, TRP cation channel subfamily A member 1 (TRPA1) (9, 10). There is no a priori requirement for cold encoding by high Q 10 channels-action potential firing rates are affected perforce by temperature,...

The transcription factor Nrf2 is a key regulator of the cellular stress response, and pharmacological Nrf2 activation is a promising strategy for skin protection and cancer prevention. We show here that prolonged Nrf2 activation in keratinocytes causes sebaceous gland enlargement and seborrhea in mice due to upregulation of the growth factor epigen, which we identified as a novel Nrf2 target. This was accompanied by thickening and hyperkeratosis of hair follicle infundibula. These abnormalities caused dilatation of infundibula, hair loss, and cyst development upon aging. Upregulation of epigen, secretory leukocyte peptidase inhibitor (Slpi), and small proline-rich protein 2d (Sprr2d) in hair follicles was identified as the likely cause of infundibular acanthosis, hyperkeratosis, and cyst formation. These alterations were highly reminiscent to the phenotype of chloracne/“metabolizing acquired dioxin-induced skin hamartomas” (MADISH) patients. Indeed, SLPI, SPRR2, and epigen were strongly expressed in cysts of MADISH patients and upregulated by dioxin in human keratinocytes in an NRF2-dependent manner. These results identify novel Nrf2 activities in the pilosebaceous unit and point to a role of NRF2 in MADISH pathogenesis.

Glycoprotein 130 (gp130) is the signal transducing receptor subunit for cytokines of the interleukin-6 (IL-6) family, and it is expressed in a multitude of cell types of the immune and nervous system. IL-6-like cytokines are not only key regulators of innate immunity and inflammation but are also essential factors for the differentiation and development of the somatosensory system. Mice with a null mutation of gp130 in primary nociceptive afferents (SNS-gp130 ؊/؊ ) are largely protected from hypersensitivity to mechanical stimuli in mouse models of pathological pain. Therefore, we set out to investigate how neuronal gp130 regulates mechanonociception. SNSgp130 ؊/؊ mice revealed reduced mechanosensitivity to high mechanical forces in the von Frey assay in vivo, and this was associated with a reduced sensitivity of nociceptive primary afferents in vitro. Together with these findings, transient receptor potential ankyrin 1 (TRPA1) mRNA expression was significantly reduced in DRG from SNS-gp130 ؊/؊ mice. This was also reflected by a reduced number of neurons responding with calcium transients to TRPA1 agonists in primary DRG cultures. Downregulation of Trpa1 expression was predominantly discovered in nonpeptidergic neurons, with the deficit becoming evident during stages of early postnatal development. Regulation of Trpa1 mRNA expression levels downstream of gp130 involved the classical Janus kinase family-signal transducer and activator of transcription pathway. Our results closely link proinflammatory cytokines to the expression of TRPA1, both of which have been shown to contribute to hypersensitive pain states. We suggest that gp130 has an essential role in mechanonociception and in the regulation of TRPA1 expression.

SummaryHuman pluripotent stem cells (hPSCs) offer the opportunity to generate neuronal cells, including nociceptors. Using a chemical-based approach, we generated nociceptive sensory neurons from HUES6 embryonic stem cells and retrovirally reprogrammed induced hPSCs derived from fibroblasts. The nociceptive neurons expressed respective markers and showed tetrodotoxin-sensitive (TTXs) and -resistant (TTXr) voltage-gated sodium currents in patch-clamp experiments. In contrast to their counterparts from rodent dorsal root ganglia, TTXr currents of hPSC-derived nociceptors unexpectedly displayed a significantly more hyperpolarized voltage dependence of activation and fast inactivation. This apparent discrepancy is most likely due to a substantial expression of the developmentally important sodium channel NAV1.5. In view of the obstacles to recapitulate neuropathic pain in animal models, our data advance hPSC-derived nociceptors as a better model to study developmental and pathogenetic processes in human nociceptive neurons and to develop more specific small molecules to attenuate pain.