Proceedings of the National Academy of Sciences, 2016
Significance Chemotherapy-induced peripheral neuropathic pain (CIPNP) is a severe side effect tha... more Significance Chemotherapy-induced peripheral neuropathic pain (CIPNP) is a severe side effect that affects up to 80% of patients during cancer treatment. Pharmacological treatment options are poor, as CIPNP differs mechanistically from other chronic pain states. Here, we describe a mechanism by which pronociceptive oxidized lipid mediators are generated by the cytochrome P 450 -epoxygenase CYP2J2 in sensory neurons during CIPNP. Blocking the synthesis of these oxidized lipids with telmisartan, which we identified as a potent CYP2J2 inhibitor in a large drug repurposing screen, caused a robust reduction of paclitaxel-induced pain in mice in vivo. We therefore consider targeting CYP2J2 with telmisartan as a treatment option for chemotherapy-induced peripheral neuropathic pain in patients.
T50 Abstract: The past few decades have witnessed a huge leap forward in our understanding of the... more T50 Abstract: The past few decades have witnessed a huge leap forward in our understanding of the mechanistic underpinnings of pain, in normal stateswhere it helps protect from injury, and also in pathological stateswhere pain evolves from a symptom reflecting tissue injury to become the disease itself. However, despite these scientific advances, chronic pain remains extremely challenging tomanage clinically. Although the number of potential treatment targets has grown substantially and a strong case has beenmade for amechanism-based and individualized approach to pain therapy, arguably clinicians are not much more advanced now than 20 years ago, in their capacity to either diagnose or effectively treat their patients. Thegulf betweenpain researchandpainmanagement is aswide as ever.Weare still currently unable to apply an evidence-based approach to chronic painmanagement that reflectsmechanistic understanding, and instead, clinical practice remains an empirical and often unsatisfact...
SummaryCNS neurons do not regenerate after injury, leading to permanent functional deficits. Alth... more SummaryCNS neurons do not regenerate after injury, leading to permanent functional deficits. Although sensory and motor neuron axons do regrow after peripheral nerve injury, functional outcome is limited due to the incomplete and slow regrowth. The lack of human-relevant assays suitable for large-scale drug screens has limited neuro-repair therapy discovery. To address this we developed a phenotypic screening strategy using human induced pluripotent stem cell-derived motor neurons to identify axon-regeneration promoting compounds and targets. The screens involve both re-plating human motor neurons on chondroitin sulfate proteoglycans and measuring regeneration responses to laser axotomy in spot cultures, and from them we identified multiple hits that promote injured axon regrowth. The top hit blebbistatin, a non-muscle myosin II inhibitor, accelerated axon regeneration and functional recovery after sciatic nerve injury in vivo. Human “injury in a dish” assays are suitable, therefore...
SummaryPrimary somatosensory neurons are specialized to transmit specific types of sensory inform... more SummaryPrimary somatosensory neurons are specialized to transmit specific types of sensory information through differences in cell size, myelination, and the expression of distinct receptors and ion channels, which together define their transcriptional and functional identity. By transcriptionally profiling sensory ganglia at single-cell resolution, we find that different somatosensory neuronal subtypes undergo a remarkably consistent and dramatic transcriptional response to peripheral nerve injury that both promotes axonal regeneration and suppresses cell identity. Successful axonal regeneration leads to a restoration of neuronal cell identity and the deactivation of the growth program. This injury-induced transcriptional reprogramming requires Atf3, a transcription factor which is induced rapidly after injury and is necessary for axonal regeneration and functional recovery. While Atf3 and other injury-induced transcription factors are known for their role in reprogramming cell fat...
Axotomy results in permanent loss of function after brain and spinal cord injuries due to the min... more Axotomy results in permanent loss of function after brain and spinal cord injuries due to the minimal regenerative propensity of the adult central nervous system (CNS). To identify pharmacological enhancers of axon regeneration, 960 compounds were screened for cortical neuron axonal regrowth using an in vitro cortical scrape assay. Diltiazem, verapamil, and bromopride were discovered to facilitate axon regeneration in rat cortical cultures, in the presence of chondroitin sulfate proteoglycans (CSPGs). Diltiazem, an L-type calcium channel blocker (L-CCB), also promotes axon outgrowth in adult primary mouse dorsal root ganglion (DRG) and induced human sensory (iSensory) neurons.
Current models of somatosensory perception emphasize transmission from primary sensory neurons to... more Current models of somatosensory perception emphasize transmission from primary sensory neurons to the spinal cord and on to the brain. Mental influence on perception is largely assumed to occur locally within the brain. Here we investigate whether sensory inflow through the spinal cord undergoes direct top-down control by the cortex. Although the corticospinal tract (CST) is traditionally viewed as a primary motor pathway, a subset of corticospinal neurons (CSNs) originating in the primary and secondary somatosensory cortex directly innervate the spinal dorsal horn via CST axons. Either reduction in somatosensory CSN activity or transection of the CST in mice selectively impairs behavioural responses to light touch without altering responses to noxious stimuli. Moreover, such CSN manipulation greatly attenuates tactile allodynia in a model of peripheral neuropathic pain. Tactile stimulation activates somatosensory CSNs, and their corticospinal projections facilitate light-touch-evok...
Chemotherapy-induced peripheral neuropathic pain (CIPN) is a common and severe debilitating side ... more Chemotherapy-induced peripheral neuropathic pain (CIPN) is a common and severe debilitating side effect of many widely used cytostatics. However, there is no approved pharmacological treatment for CIPN available. Among other substances, oxaliplatin causes CIPN in up to 80% of treated patients. Here, we report the involvement of the G-protein coupled receptor G2A (GPR132) in oxaliplatin-induced neuropathic pain in mice. We found that mice deficient in the G2A-receptor show decreased mechanical hypersensitivity after oxaliplatin treatment. Lipid ligands of G2A were found in increased concentrations in the sciatic nerve and dorsal root ganglia of oxaliplatin treated mice. Calcium imaging and patch-clamp experiments show that G2A activation sensitizes the ligand-gated ion channel TRPV1 in sensory neurons via activation of PKC. Based on these findings, we conclude that targeting G2A may be a promising approach to reduce oxaliplatin-induced TRPV1-sensitization and the hyperexcitability of...
HSN2is a nervous system predominant exon of the gene encoding the kinase WNK1 and is mutated in a... more HSN2is a nervous system predominant exon of the gene encoding the kinase WNK1 and is mutated in an autosomal recessive, inherited form of congenital pain insensitivity. The HSN2-containing splice variant is referred to as WNK1/HSN2. We created a knockout mouse specifically lacking theHsn2exon ofWnk1 Although these mice had normal spinal neuron and peripheral sensory neuron morphology and distribution, the mice were less susceptible to hypersensitivity to cold and mechanical stimuli after peripheral nerve injury. In contrast, thermal and mechanical nociceptive responses were similar to control mice in an inflammation-induced pain model. In the nerve injury model of neuropathic pain, WNK1/HSN2 contributed to a maladaptive decrease in the activity of the K(+)-Cl(-)cotransporter KCC2 by increasing its inhibitory phosphorylation at Thr(906)and Thr(1007), resulting in an associated loss of GABA (γ-aminobutyric acid)-mediated inhibition of spinal pain-transmitting nerves. Electrophysiologi...
The somatosensory nervous system is critical for the organism's ability to respond to mechani... more The somatosensory nervous system is critical for the organism's ability to respond to mechanical, thermal, and nociceptive stimuli. Somatosensory neurons are functionally and anatomically diverse but their molecular profiles are not well-defined. Here, we used transcriptional profiling to analyze the detailed molecular signatures of dorsal root ganglion (DRG) sensory neurons. We used two mouse reporter lines and surface IB4 labeling to purify three major non-overlapping classes of neurons: 1)IB4(+)SNS-Cre/TdTomato(+), 2)IB4(-)SNS-Cre/TdTomato(+), and 3)Parv-Cre/TdTomato(+) cells, encompassing the majority of nociceptive, pruriceptive, and proprioceptive neurons. These neurons displayed distinct expression patterns of ion channels, transcription factors, and GPCRs. Highly parallel qRT-PCR analysis of 334 single neurons selected by membership of the three populations demonstrated further diversity, with unbiased clustering analysis identifying six distinct subgroups. These data si...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 18, 2009
Partial peripheral nerve injury in adult rats results in neuropathic pain-like hypersensitivity, ... more Partial peripheral nerve injury in adult rats results in neuropathic pain-like hypersensitivity, while that in neonatal rats does not, a phenomenon also observed in humans. We therefore compared gene expression profiles in the dorsal horn of adult and neonatal rats in response to the spared nerve injury (SNI) model of peripheral neuropathic pain. The 148 differentially regulated genes in adult, but not young, rat spinal cords indicate a greater microglial and T-cell response in adult than in young animals. T-cells show a large infiltration in the adult dorsal horn but not in the neonate after SNI. T-cell-deficient Rag1-null adult mice develop less neuropathic mechanical allodynia than controls, and central expression of cytokines involved in T-cell signaling exhibits large relative differences between young and adult animals after SNI. One such cytokine, interferon-gamma (IFNgamma), is upregulated in the dorsal horn after nerve injury in the adult but not neonate, and we show that I...
We show that transsynaptic apoptosis is induced in the superficial dorsal horn (laminas I-III) of... more We show that transsynaptic apoptosis is induced in the superficial dorsal horn (laminas I-III) of the spinal cord by three distinct partial peripheral nerve lesions: spared nerve injury, chronic constriction, and spinal nerve ligation. Ongoing activity in primary afferents of the injured nerve and glutamatergic transmission cause a caspase-dependent degeneration of dorsal horn neurons that is slow in onset and persists for several weeks. Four weeks after spared nerve injury, the cumulative loss of dorsal horn neurons, determined by stereological analysis, is >20%. GABAergic inhibitory interneurons are among the neurons lost, and a marked decrease in inhibitory postsynaptic currents of lamina II neurons coincides with the induction of apoptosis. Blocking apoptosis with the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone (zVAD) prevents the loss of GABAergic interneurons and the reduction of inhibitory currents. Partial peripheral nerve injury results in pai...
We used a mouse with deletion of exons 4, 5, and 6 of the SCN11A (sodium channel, voltage-gated, ... more We used a mouse with deletion of exons 4, 5, and 6 of the SCN11A (sodium channel, voltage-gated, type XI, α) gene that encodes the voltage-gated sodium channel Nav1.9 to assess its contribution to pain. Nav1.9 is present in nociceptor sensory neurons that express TRPV1, bradykinin B2, and purinergic P2X3receptors. InNav1.9−/−mice, the non-inactivating persistent tetrodotoxin-resistant sodium TTXr-Per current is absent, whereas TTXr-Slow is unchanged. TTXs currents are unaffected by the mutation of Nav1.9. Pain hypersensitivity elicited by intraplantar administration of prostaglandin E2, bradykinin, interleukin-1β, capsaicin, and P2X3and P2Y receptor agonists, but not NGF, is either reduced or absent inNav1.9−/−mice, whereas basal thermal and mechanical pain sensitivity is unchanged. Thermal, but not mechanical, hypersensitivity produced by peripheral inflammation (intraplanatar complete Freund's adjuvant) is substantially diminished in the null allele mutant mice, whereas hypers...
Proceedings of the National Academy of Sciences, 1999
Brain-derived neurotrophic factor (BDNF) is expressed in nociceptive sensory neurons and transpor... more Brain-derived neurotrophic factor (BDNF) is expressed in nociceptive sensory neurons and transported anterogradely to the dorsal horn of the spinal cord where it is located in dense core vesicles in C-fiber terminals. Peripheral inflammation substantially up-regulates BDNF mRNA and protein in the dorsal root ganglion (DRG) in a nerve growth factor-dependent fashion and results in novel expression of BDNF by DRG neurons with myelinated axons. C-fiber electrical activity also increases BDNF expression in the DRG, and both inflammation and activity increase full-length TrkB receptor levels in the dorsal horn. Sequestration of endogenous BDNF/neurotrophin 4 by intraspinal TrkB-Fc fusion protein administration does not, in noninflamed animals, change basal pain sensitivity nor the mechanical hypersensitivity induced by peripheral capsaicin administration, a measure of C fiber-mediated central sensitization. TrkB-Fc administration also does not modify basal inflammatory pain hypersensitiv...
Proceedings of the National Academy of Sciences, 2016
Significance Chemotherapy-induced peripheral neuropathic pain (CIPNP) is a severe side effect tha... more Significance Chemotherapy-induced peripheral neuropathic pain (CIPNP) is a severe side effect that affects up to 80% of patients during cancer treatment. Pharmacological treatment options are poor, as CIPNP differs mechanistically from other chronic pain states. Here, we describe a mechanism by which pronociceptive oxidized lipid mediators are generated by the cytochrome P 450 -epoxygenase CYP2J2 in sensory neurons during CIPNP. Blocking the synthesis of these oxidized lipids with telmisartan, which we identified as a potent CYP2J2 inhibitor in a large drug repurposing screen, caused a robust reduction of paclitaxel-induced pain in mice in vivo. We therefore consider targeting CYP2J2 with telmisartan as a treatment option for chemotherapy-induced peripheral neuropathic pain in patients.
T50 Abstract: The past few decades have witnessed a huge leap forward in our understanding of the... more T50 Abstract: The past few decades have witnessed a huge leap forward in our understanding of the mechanistic underpinnings of pain, in normal stateswhere it helps protect from injury, and also in pathological stateswhere pain evolves from a symptom reflecting tissue injury to become the disease itself. However, despite these scientific advances, chronic pain remains extremely challenging tomanage clinically. Although the number of potential treatment targets has grown substantially and a strong case has beenmade for amechanism-based and individualized approach to pain therapy, arguably clinicians are not much more advanced now than 20 years ago, in their capacity to either diagnose or effectively treat their patients. Thegulf betweenpain researchandpainmanagement is aswide as ever.Weare still currently unable to apply an evidence-based approach to chronic painmanagement that reflectsmechanistic understanding, and instead, clinical practice remains an empirical and often unsatisfact...
SummaryCNS neurons do not regenerate after injury, leading to permanent functional deficits. Alth... more SummaryCNS neurons do not regenerate after injury, leading to permanent functional deficits. Although sensory and motor neuron axons do regrow after peripheral nerve injury, functional outcome is limited due to the incomplete and slow regrowth. The lack of human-relevant assays suitable for large-scale drug screens has limited neuro-repair therapy discovery. To address this we developed a phenotypic screening strategy using human induced pluripotent stem cell-derived motor neurons to identify axon-regeneration promoting compounds and targets. The screens involve both re-plating human motor neurons on chondroitin sulfate proteoglycans and measuring regeneration responses to laser axotomy in spot cultures, and from them we identified multiple hits that promote injured axon regrowth. The top hit blebbistatin, a non-muscle myosin II inhibitor, accelerated axon regeneration and functional recovery after sciatic nerve injury in vivo. Human “injury in a dish” assays are suitable, therefore...
SummaryPrimary somatosensory neurons are specialized to transmit specific types of sensory inform... more SummaryPrimary somatosensory neurons are specialized to transmit specific types of sensory information through differences in cell size, myelination, and the expression of distinct receptors and ion channels, which together define their transcriptional and functional identity. By transcriptionally profiling sensory ganglia at single-cell resolution, we find that different somatosensory neuronal subtypes undergo a remarkably consistent and dramatic transcriptional response to peripheral nerve injury that both promotes axonal regeneration and suppresses cell identity. Successful axonal regeneration leads to a restoration of neuronal cell identity and the deactivation of the growth program. This injury-induced transcriptional reprogramming requires Atf3, a transcription factor which is induced rapidly after injury and is necessary for axonal regeneration and functional recovery. While Atf3 and other injury-induced transcription factors are known for their role in reprogramming cell fat...
Axotomy results in permanent loss of function after brain and spinal cord injuries due to the min... more Axotomy results in permanent loss of function after brain and spinal cord injuries due to the minimal regenerative propensity of the adult central nervous system (CNS). To identify pharmacological enhancers of axon regeneration, 960 compounds were screened for cortical neuron axonal regrowth using an in vitro cortical scrape assay. Diltiazem, verapamil, and bromopride were discovered to facilitate axon regeneration in rat cortical cultures, in the presence of chondroitin sulfate proteoglycans (CSPGs). Diltiazem, an L-type calcium channel blocker (L-CCB), also promotes axon outgrowth in adult primary mouse dorsal root ganglion (DRG) and induced human sensory (iSensory) neurons.
Current models of somatosensory perception emphasize transmission from primary sensory neurons to... more Current models of somatosensory perception emphasize transmission from primary sensory neurons to the spinal cord and on to the brain. Mental influence on perception is largely assumed to occur locally within the brain. Here we investigate whether sensory inflow through the spinal cord undergoes direct top-down control by the cortex. Although the corticospinal tract (CST) is traditionally viewed as a primary motor pathway, a subset of corticospinal neurons (CSNs) originating in the primary and secondary somatosensory cortex directly innervate the spinal dorsal horn via CST axons. Either reduction in somatosensory CSN activity or transection of the CST in mice selectively impairs behavioural responses to light touch without altering responses to noxious stimuli. Moreover, such CSN manipulation greatly attenuates tactile allodynia in a model of peripheral neuropathic pain. Tactile stimulation activates somatosensory CSNs, and their corticospinal projections facilitate light-touch-evok...
Chemotherapy-induced peripheral neuropathic pain (CIPN) is a common and severe debilitating side ... more Chemotherapy-induced peripheral neuropathic pain (CIPN) is a common and severe debilitating side effect of many widely used cytostatics. However, there is no approved pharmacological treatment for CIPN available. Among other substances, oxaliplatin causes CIPN in up to 80% of treated patients. Here, we report the involvement of the G-protein coupled receptor G2A (GPR132) in oxaliplatin-induced neuropathic pain in mice. We found that mice deficient in the G2A-receptor show decreased mechanical hypersensitivity after oxaliplatin treatment. Lipid ligands of G2A were found in increased concentrations in the sciatic nerve and dorsal root ganglia of oxaliplatin treated mice. Calcium imaging and patch-clamp experiments show that G2A activation sensitizes the ligand-gated ion channel TRPV1 in sensory neurons via activation of PKC. Based on these findings, we conclude that targeting G2A may be a promising approach to reduce oxaliplatin-induced TRPV1-sensitization and the hyperexcitability of...
HSN2is a nervous system predominant exon of the gene encoding the kinase WNK1 and is mutated in a... more HSN2is a nervous system predominant exon of the gene encoding the kinase WNK1 and is mutated in an autosomal recessive, inherited form of congenital pain insensitivity. The HSN2-containing splice variant is referred to as WNK1/HSN2. We created a knockout mouse specifically lacking theHsn2exon ofWnk1 Although these mice had normal spinal neuron and peripheral sensory neuron morphology and distribution, the mice were less susceptible to hypersensitivity to cold and mechanical stimuli after peripheral nerve injury. In contrast, thermal and mechanical nociceptive responses were similar to control mice in an inflammation-induced pain model. In the nerve injury model of neuropathic pain, WNK1/HSN2 contributed to a maladaptive decrease in the activity of the K(+)-Cl(-)cotransporter KCC2 by increasing its inhibitory phosphorylation at Thr(906)and Thr(1007), resulting in an associated loss of GABA (γ-aminobutyric acid)-mediated inhibition of spinal pain-transmitting nerves. Electrophysiologi...
The somatosensory nervous system is critical for the organism's ability to respond to mechani... more The somatosensory nervous system is critical for the organism's ability to respond to mechanical, thermal, and nociceptive stimuli. Somatosensory neurons are functionally and anatomically diverse but their molecular profiles are not well-defined. Here, we used transcriptional profiling to analyze the detailed molecular signatures of dorsal root ganglion (DRG) sensory neurons. We used two mouse reporter lines and surface IB4 labeling to purify three major non-overlapping classes of neurons: 1)IB4(+)SNS-Cre/TdTomato(+), 2)IB4(-)SNS-Cre/TdTomato(+), and 3)Parv-Cre/TdTomato(+) cells, encompassing the majority of nociceptive, pruriceptive, and proprioceptive neurons. These neurons displayed distinct expression patterns of ion channels, transcription factors, and GPCRs. Highly parallel qRT-PCR analysis of 334 single neurons selected by membership of the three populations demonstrated further diversity, with unbiased clustering analysis identifying six distinct subgroups. These data si...
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 18, 2009
Partial peripheral nerve injury in adult rats results in neuropathic pain-like hypersensitivity, ... more Partial peripheral nerve injury in adult rats results in neuropathic pain-like hypersensitivity, while that in neonatal rats does not, a phenomenon also observed in humans. We therefore compared gene expression profiles in the dorsal horn of adult and neonatal rats in response to the spared nerve injury (SNI) model of peripheral neuropathic pain. The 148 differentially regulated genes in adult, but not young, rat spinal cords indicate a greater microglial and T-cell response in adult than in young animals. T-cells show a large infiltration in the adult dorsal horn but not in the neonate after SNI. T-cell-deficient Rag1-null adult mice develop less neuropathic mechanical allodynia than controls, and central expression of cytokines involved in T-cell signaling exhibits large relative differences between young and adult animals after SNI. One such cytokine, interferon-gamma (IFNgamma), is upregulated in the dorsal horn after nerve injury in the adult but not neonate, and we show that I...
We show that transsynaptic apoptosis is induced in the superficial dorsal horn (laminas I-III) of... more We show that transsynaptic apoptosis is induced in the superficial dorsal horn (laminas I-III) of the spinal cord by three distinct partial peripheral nerve lesions: spared nerve injury, chronic constriction, and spinal nerve ligation. Ongoing activity in primary afferents of the injured nerve and glutamatergic transmission cause a caspase-dependent degeneration of dorsal horn neurons that is slow in onset and persists for several weeks. Four weeks after spared nerve injury, the cumulative loss of dorsal horn neurons, determined by stereological analysis, is >20%. GABAergic inhibitory interneurons are among the neurons lost, and a marked decrease in inhibitory postsynaptic currents of lamina II neurons coincides with the induction of apoptosis. Blocking apoptosis with the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone (zVAD) prevents the loss of GABAergic interneurons and the reduction of inhibitory currents. Partial peripheral nerve injury results in pai...
We used a mouse with deletion of exons 4, 5, and 6 of the SCN11A (sodium channel, voltage-gated, ... more We used a mouse with deletion of exons 4, 5, and 6 of the SCN11A (sodium channel, voltage-gated, type XI, α) gene that encodes the voltage-gated sodium channel Nav1.9 to assess its contribution to pain. Nav1.9 is present in nociceptor sensory neurons that express TRPV1, bradykinin B2, and purinergic P2X3receptors. InNav1.9−/−mice, the non-inactivating persistent tetrodotoxin-resistant sodium TTXr-Per current is absent, whereas TTXr-Slow is unchanged. TTXs currents are unaffected by the mutation of Nav1.9. Pain hypersensitivity elicited by intraplantar administration of prostaglandin E2, bradykinin, interleukin-1β, capsaicin, and P2X3and P2Y receptor agonists, but not NGF, is either reduced or absent inNav1.9−/−mice, whereas basal thermal and mechanical pain sensitivity is unchanged. Thermal, but not mechanical, hypersensitivity produced by peripheral inflammation (intraplanatar complete Freund's adjuvant) is substantially diminished in the null allele mutant mice, whereas hypers...
Proceedings of the National Academy of Sciences, 1999
Brain-derived neurotrophic factor (BDNF) is expressed in nociceptive sensory neurons and transpor... more Brain-derived neurotrophic factor (BDNF) is expressed in nociceptive sensory neurons and transported anterogradely to the dorsal horn of the spinal cord where it is located in dense core vesicles in C-fiber terminals. Peripheral inflammation substantially up-regulates BDNF mRNA and protein in the dorsal root ganglion (DRG) in a nerve growth factor-dependent fashion and results in novel expression of BDNF by DRG neurons with myelinated axons. C-fiber electrical activity also increases BDNF expression in the DRG, and both inflammation and activity increase full-length TrkB receptor levels in the dorsal horn. Sequestration of endogenous BDNF/neurotrophin 4 by intraspinal TrkB-Fc fusion protein administration does not, in noninflamed animals, change basal pain sensitivity nor the mechanical hypersensitivity induced by peripheral capsaicin administration, a measure of C fiber-mediated central sensitization. TrkB-Fc administration also does not modify basal inflammatory pain hypersensitiv...
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