One sentence summary: Bench to bedside translation using iPSC to characterise phenotype and pharmacology in primary erythromelalgia, an inherited chronic pain condition. ABSTRACTIn common with other chronic pain conditions, inherited erythromelalgia (IEM) represents a significant unmet medical need. The peripherally expressed SCN9A encoded sodium channel Nav1.7 plays a critical role in IEM with gain-of-function leading to aberrant sensory neuronal activity and extreme pain, particularly in response to heat. In five carefully phenotyped IEM patients, a novel highly potent and selective Nav1.7 blocker reduced heat-induced pain in the majority of subjects. In four of the five subjects we used induced pluripotent stem cell (iPSC) technology to create sensory neurons which uniquely emulated the clinical phenotype of hyperexcitability and aberrant responses to heat stimuli. When we compared the severity of the clinical phenotype with the iPSC-derived sensory neuron hyperexcitability we saw a trend towards a correlation for individual mutations. The in vitro IEM phenotype was sensitive to Nav1.7 blockers, including the clinical test agent. Given the importance of peripherally expressed sodium channels in many pain conditions, this translational approach is likely to have broader utility to a wide range of pain and sensory conditions. This emphasizes the use of iPSC approaches to bridge between clinical and preclinical studies, enabling greater understanding of a disease and the response to a therapeutic agent in defined patient populations.
Induced pluripotent stem cells (iPSCs), and cells derived from them, have become key tools to model biological processes, particularly in cell types that are difficult to access from living donors. We present the first map of regulatory variants in iPSC-derived neurons, based on 123 differentiations of iPSCs to a sensory neuronal fate. Gene expression was more variable across cultures than in primary dorsal root ganglion, particularly in genes related to nervous system development. Using single-cell RNA-sequencing, we found that the fraction of neuronal vs. contaminating cells was influenced by iPSC culture conditions prior to differentiation. Despite high differentiation-induced variability, using an allele-specific method we detected thousands of quantitative trait loci (QTLs) influencing gene expression, chromatin accessibility, and RNA splicing. Based on our QTLs, we estimate that recall-by-genotype studies using iPSC-derived cells will require at least 20-80 individuals to detect the effects of regulatory variants with moderately large effect sizes.
Induced pluripotent stem cells (iPSCs), and cells derived from them, have become key tools to model biological processes and disease mechanisms, particularly in cell types such as neurons that are difficult to access from living donors. Here, we present the first map of regulatory variants in an iPSC-derived cell type. To investigate genetic contributions to human sensory function, we performed 123 differentiations of iPSCs from 103 unique donors to a sensory neuronal fate, and measured gene expression, chromatin accessibility, and neuronal excitability. Compared with primary dorsal root ganglion, where sensory nerves collect near the spinal cord, gene expression was more variable across iPSC-derived neuronal cultures, particularly in genes related to differentiation and nervous system development. Single cell RNA-sequencing revealed that although the majority of cells are neuronal and express the expected marker genes, a substantial fraction have a fibroblast-like expression profile. By applying an allele-specific method we identify 3,778 quantitative trait loci influencing gene expression, 6,318 for chromatin accessibility, and 2,097 for RNA splicing at FDR 10%. A number of these overlap with common disease associations, and suggest candidate causal variants and target genes. These include known causal variants at SNCA for Parkinson's disease and TNFRSF1A for multiple sclerosis, as well as new candidates for migraine, Parkinson's disease, and schizophrenia.
BACKGROUND AND PURPOSENaV1.8 ion channels have been highlighted as important molecular targets for the design of low MW blockers for the treatment of chronic pain. Here, we describe the effects of PF-01247324, a new generation, selective, orally bioavailable Nav1.8 channel blocker of novel chemotype. EXPERIMENTAL APPROACHThe inhibition of Nav1.8 channels by PF-01247324 was studied using in vitro patch-clamp electrophysiology and the oral bioavailability and antinociceptive effects demonstrated using in vivo rodent models of inflammatory and neuropathic pain. KEY RESULTSPF-01247324 inhibited native tetrodotoxin-resistant (TTX-R) currents in human dorsal root ganglion (DRG) neurons (IC50: 331 nM) and in recombinantly expressed h Nav1.8 channels (IC50: 196 nM), with 50-fold selectivity over recombinantly expressed TTX-R hNav1.5 channels (IC50: ∼10 μM) and 65-100-fold selectivity over TTX-sensitive (TTX-S) channels (IC50: ∼10-18 μM). Native TTX-R currents in small-diameter rodent DRG neurons were inhibited with an IC50 448 nM, and the block of both human recombinant Nav1.8 channels and TTX-R from rat DRG neurons was both frequency and state dependent. In vitro current clamp showed that PF-01247324 reduced excitability in both rat and human DRG neurons and also altered the waveform of the action potential. In vivo experiments n rodents demonstrated efficacy in both inflammatory and neuropathic pain models. CONCLUSIONS AND IMPLICATIONSUsing PF-01247324, we have confirmed a role for Nav1.8 channels in both inflammatory and neuropathic pain. We have also demonstrated a key role for Nav1.8 channels in action potential upstroke and repetitive firing of rat and human DRG neurons.
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