This meeting report is co-authored by Dayna Loyd Averitt and Shivani Ruparel (Media Committee Co-Chairs).
On August 24, 2017, the Texas Pain Research Consortium hosted its second biennial scientific meeting beachfront at the historic Hotel Galvez in Galveston, Texas. The meeting was organized by the consortium’s co-chairs, Ted Price and Jin Mo Chung, and hosted by the University of Texas Medical Branch with support from the UT system, the Gulf Coast Consortia, and Purdue Pharma. Despite the looming Hurricane Harvey, there was an impressive turnout of 133 attendees including basic scientists, clinicians, postdoctoral trainees, and graduate students from 19 universities across Texas.
The meeting commenced with welcome remarks from David Niesel, PhD (chief research officer and dean of the Graduate School of Biomedical Sciences at UTMB) and Jin Mo Chung, PhD (UTMB). Chung designated the meeting in honor of the late William Darrell Willis Jr., MD, PhD (UTMB) with a heartwarming photographic trip down memory lane, and announced the added support of the Texas Pain Research Consortium by the UTMB Willis Research Endowment. Leslie Carruth and Matt Sorenson (UT System) then addressed the group to voice their support for the consortium and highlight research funding opportunities out of the UT System Office of Health Affairs and Office of Innovation and Strategic Investment, respectively.
The meeting was organized in data blitz, platform talk style to update the consortium members of current research with the aims of fostering discussion and encouraging new collaboration. The first session covered research on sex differences in pain. Kenneth Hargreaves, DDS, PhD (UT Health San Antonio), introduced his newly founded company, Vindalor, which will focus on developing novel non-opioid analgesics that will be effective for pain in both sexes. He then presented his team’s latest findings on identification of serotonin-dependent complement release from human tissue in a sex-dependent manner. He reported that a specific complement factor is released following serotonin treatment of human tooth pulp extracted from females, but not from males. The released complement factor then sensitizes TRPV1 on sensory neurons, further elucidating the sexually dimorphic mechanism of sensory neuron activation and TRPV1 regulation.
The discussion of sex-dependent differences of serotonin on TRPV1 continued with a presentation from Dayna Averitt, PhD (Texas Woman’s University) on the effects of estrogen on serotonin-induced nociceptive hypersensitivity. Her study showed that 5HT evokes an increase in thermal hypersensitivity in female rats that are in the proestrus and estrus phases of the estrous cycle, and this effect is absent in males and ovariectomized females. In cultured trigeminal sensory neurons, the presence of estrogen enhances serotonin- and capsaicin-evoked inflammatory peptide release, further corroborating a sex difference in the effects of serotonin on TRPV1.
Phillip Kramer, PhD (Texas A&M Dentistry), next described his work on sex differences in post-herpetic neuralgia (PHN), which is 65 percent more common in women. His group has developed a rat model of orofacial PHN and confirmed that specific viral proteins were expressed in trigeminal neurons after virus injection. They report that neuropathic pain behaviors were greater in females compared to males, with the highest pain behaviors observed during the diestrus and proestrus phases of the estrous cycle, implicating a role of gonadal hormones in PHN in females.
The session was then concluded with a presentation by Greg Dussor, PhD (UT Dallas), on the novel role of prolactin in migraine. The study, conducted in collaboration with Armen Akopian, DDS (UT Health San Antonio), reported that prolactin application to the dura triggers nocifensive behaviors in females, but not males, in their rodent model of migraine. They report that this may be due to higher prolactin receptor expression in the dura of females. In support of this, they reported that dural application of prolactin induced CGRP release from dura extracted from females but not males, indicating that sex differences in the effects of prolactin on dura may be a mechanism underlying the prevalence of migraine in women.
Following a Hurricane Harvey location update from Jin Mo Chung, the meeting pushed on with a session on neuroimmune interactions in pain. The session was kicked off by Michelle Hook, PhD (Texas A&M University), who presented data on the role of opioid-immune interactions occurring during pain management in a rodent model of spinal cord injury. Her group reported that morphine treatment slowed motor recovery with evidence of increased cell death at the injury site, similar to humans. One underlying mechanism is that morphine-treated rats displayed higher levels of immune cells and activated microglia.
Michael Burton, PhD (UT Dallas), then pointed to a dichotomy in neuroimmune crosstalk by reporting that long-term plastic changes in mechanical hypersensitivity are brought about by TLR4 on macrophages in males, whereas TLR4 on nociceptors plays this role in females. His conclusions were based on the findings from differential ablation of TLR4 in sensory neurons versus macrophages showing sex-specific differences of TLR4 contribution to neuropathic pain.
Next, Pooja Singhmar, PhD (MD Anderson), unraveled the role of a fibroblast-secreted protein, which is a peptidase inhibitor, in the regulation of neuropathic pain. She reported that this protein is upregulated under neuropathic pain conditions in dorsal root ganglia (DRG) and that knockouts for this gene have a reduced pain phenotype. Interestingly, this gene, which was previously thought to be fibroblast specific, is expressed in the meningeal sheath of the DRG/sciatic nerve, a novel finding implicating a role of the epineurium in neuropathic pain.
Blaine Jacobs, PhD (UT Dallas), then discussed a novel neurovascular mechanism in migraine involving communication between endothelial cells and dura via VEGF. She reported that dural epithelial cells release VEGF when stimulated by IL-6. This leads to activation of trigeminal neurons as measured by calcium accumulation and evoked craniofacial nociceptive behavior in rodents.
The session wrapped up with a presentation from Alan Prossin, MBBS (UT Health Houston), on evidence of expectation-related placebo analgesia and neuroimmune interactions. His current studies report that hypotonic saline injection into the masseter muscle evokes greater affective pain in females, while no differences in sensory pain were observed. The increased affective pain and placebo treatment were both unexpectedly correlated with a decrease in IL-18, but not sensory pain, indicating a sex difference in the physiological effects of affective pain and placebo.
The session was followed by an interactive lunch break that included almost 30 trainees presenting and discussing their latest findings in poster format. Lunch was followed with a keynote presentation from external advisory board member Cheryl Stucky, PhD (Medical College of Wisconsin). She provided an overview of the latest research in her lab utilizing cell-specific optogenetics in combination with electrophysiology and behavior testing to dissect distinct roles of specific subsets of sensory neurons in touch and pain. Her group is finding that optogenetic silencing of CGRP-positive neurons reverses neuropathy-induced allodynia, hypersensitivity, and ongoing pain behaviors measured by place preference. Single-fiber recordings revealed sensitization of CGRP-positive neurons from SNI mice, which was reversed by optogenetic silencing. Interestingly, this was not the case for CGRP fibers from CFA-inflamed or postsurgical mice, indicating that CGRP fiber sensitization might be specific to neuropathic pain and not inflammatory to pain. Stucky was then rushed to the airport to board the last plane out of Houston to return home safely to Wisconsin.
Our scheduled two-day meeting then became a one-day meeting as Jin Mo Chung announced that Hurricane Harvey had developed into a Category 2 hurricane and was going to land somewhere along the Texas Gulf Coast. Following some schedule rearranging, and some humorous comments from the peanut gallery (in particular, from Cobi Heijnen, PhD, and Annemieke Kavelaars, PhD [MD Anderson]), the consortium continued on with a third session on pain associated with chemotherapy and HIV.
Shao-Jun Tang, PhD (UTMB), started the session with a report on work aiming to uncover why astrocytes but not microglia are highly activated in HIV patients with chronic pain. His group found evidence that the Wnt5a protein may be a neuron-to-astrocyte signal involved in HIV pain, as knocking out Wnt5a blocked allodynia in a mouse model of HIV. This reduction in pain behavior was corroborated by the observation that infected neurons release Wnt5a, which activates astrocytes, and potentially triggers pain in HIV patients.
Yogesh Wairkar, PhD (UTMB), added to this topic with research modeling HIV drug-induced neuropathy in Drosophila larvae. The antiretroviral Zidovudine (AZT), an HIV/AIDS medication, triggered a dose-dependent writhing response in Drosophila larvae. Sensory neurons from these larvae then showed signs of neurodegeneration, much like Wallerian degeneration. However, genes involved in Wallerian degeneration have thus far not shown involvement in AZT-induced neurodegeneration, suggesting discovery of a new mechanism.
Cobi Heijnen, PhD (MD Anderson), then wrapped up the session by presenting data from her lab on nasal application of mesenchymal stem cells following cisplatin. These stem cells reverse cisplatin-triggered cognitive impairment, mechanical allodynia, and ongoing pain as measured by conditioned place preference. Interestingly, the therapy was ineffective in the absence of T cells, indicating that mesenchymal stem cells migrate to the meninges and educate T cells, which then travel to the DRG and stimulate repair to potentially reverse neuropathy.
The next session was focused on pain mechanisms within the DRG. Terry Walters, PhD (UT Health Houston), was the first to speak about his group’s research on the role of hyperalgesic priming of the cell soma, not only terminals and synapses, in the acute-to-chronic pain transition. He reported that ongoing activity was observed in cells extracted from nerve injury models but not in naïve rat cells. Ongoing activity was observed in IB4-positive and capsaicin-sensitive neurons as far as six months after injury and required the guanine-nucleotide exchange factor Epac.
Yu Shin Kim, PhD (UTMB), next spoke on his research developing in vivo imaging techniques to look at spontaneous activation in the spinal cord, DRG, and central terminals. Using a mouse line generated with a genetically encoded calcium indicator combined with in vivo imaging and behavior testing, his group could report that inflammation of the mouse temporomandibular joint activates approximately 2,800 neurons, while an mGluR5 receptor antagonist reduces this activation corresponding with a reduction in pain behaviors.
Next up, Zachary Campbell, PhD (UT Dallas), presented his research on using an RNA mimic to inhibit Poly(A)-binding proteins (PABPs) to reduce pain sensitization in mice. His group has found that PABP is expressed throughout DRG neurons and that co-administration of an RNA mimic with NGF inhibited NGF-evoked hyperalgesia. Similar findings were also reported with IL-6, capsaicin and in the postsurgical pain model.
The session was then concluded with a report from Lucas Rodriguez, PhD, the chief executive officer of the Texas startup CerSci Therapeutics, on a novel pain therapeutic. CT-044, a peroxynitrite neutralizer that is peripherally restricted, prevents the development of mechanical allodynia in a rodent model of incisional pain. The drug is also able to reverse incisional pain, block opioid-induced hyperalgesia, and reduce the development of tolerance to opioids.
Updates on Hurricane Harvey’s then-impending landfall on the south central Texas Gulf Coast spurred acceleration in the presentations for the rest of the afternoon and into the early evening. The next afternoon session covered models and methods of studying sensitization. Michael Galko, PhD (MD Anderson), asked what genetic targets are relevant to responding to noxious stimuli. Using Drosophila larvae, his group studies noxious stimuli as writhing responses to wounds, UV light radiation, acid, and noxious heat and cold. Wounded larvae display robust sensitization that is not altered by knockdown of TNF and Hedgehog. The researchers are developing and utilizing a custom von Frey method to test thermal and cold allodynia.
Carmen Dessauer, PhD (UT Health Houston), next spoke on novel methodology to determine how spinal cord injury induces spontaneous activity in nociceptors. Their group isolates DRG following spinal cord injury, cultures them for 24 hours, stimulates them, and then fixes and stains them to perform cluster analysis to look at what type of signaling pathways are being utilized for various types of cells. They have measured adenylyl cyclase activity in DRG membranes from naïve and injured rodents and found activity to be refractory to G protein signaling and opioids.
Perry Fuchs, PhD (UT Arlington), wrapped up the session with a thought-provoking discussion on the important issue of lack of translation from preclinical testing to clinical utility, stressing the need to focus on the emotional component of pain. He argued that areas of focus for pain scientists should include comorbidity (with substance abuse, depression, and anxiety), age in terms of psychological and cultural influences, and not only sex as a factor but the cultural influence of gender as well.
Following a short break, Jin Mo Chung then announced that Hurricane Harvey had rapidly developed into a Category 3 hurricane with the expectation that it would be a Category 4 by the time it hit land somewhere between Corpus Christi and Galveston. The wine bar opened and the next two sessions were combined to cover central pain mechanisms and chemotherapy-induced pain mechanisms.
Feng Tao, PhD (Texas A&M Dentistry), then talked about the descending dopaminergic signaling involved in trigeminal neuralgia. His group found that optogenetic excitation of D1 dopamine receptor-expressing neurons in the trigeminal nucleus caudalis in a rodent model of trigeminal neuralgia enhanced mechanical allodynia and ongoing pain behaviors, while the opposite was true of excitation of neurons expressing D2 receptors. This relationship was also observed following chemogenetic activation of the dopamine receptor-expressing neurons. He also reported that D1, but not D2, colocalizes with glutaminase in the trigeminal nucleus caudalis, and lesioning A11 dopaminergic neurons exacerbates trigeminal neuropathic pain.
Next up, Salim Megat, PhD (UT Dallas), reported on his recent findings utilizing a translating ribosome affinity purification (TRAP) methodology that expresses GFP-tagged ribosomes specifically in nociceptors to look at RNAs being translated during chemotherapy-induced neuropathy in mice. He reported that the lipid transfer protein Esyt1 is highly translated in DRG neurons after paclitaxel, with a corresponding upregulation in mTOR and its downstream effectors.
Ted Price, PhD (UT Dallas), then spoke on a key role of dopaminergic descending modulation in priming. Knockout of D5 receptors reduced pain behaviors and hyperalgesic priming in male mice but not females. In support, fewer D5 receptors were observed in females. cFos labeling of spinal neurons primed by dopamine was observed mostly in deep dorsal horn GABAergic interneurons. Overall, his data indicate that the role of D5 in priming is highly specific to males.
Next, Sung II Park, PhD (Texas A&M Engineering), presented the development of a novel technique to measure cortical spreading depression in freely behaving rodents. The device is an ultraminiaturized, fully implantable wireless telemetry device that can record and report measurements of changes in potassium concentrations, with data reported in mV as a function of potassium concentration.
Jun-Ho La, PhD, DVM (UTMB), then presented current findings on the role of reactive oxygen species in chemotherapy-induced neuropathic pain. He reported that the radical scavenger PBN attenuated cisplatin-induced allodynia with local and systemic administration, but not with intrathecal administration, while spinal cord oxidative stress did play a role in paclitaxel-induced allodynia. Overall, his data illustrated that peripheral and central oxidative stress play an important role in chemotherapy-induced pain, but their roles will vary with different chemotherapeutics.
Last up, Geoffroy Laumet, PhD (MD Anderson), presented his latest findings on using educated CD8+ T cells to prevent chemotherapy-induced periphery neuropathy. He reported that T cell-deficient mice developed stronger neuropathic pain and that CD8+ T cells were required for resolution of cisplatin-induced spontaneous pain, allodynia, and numbness. Interestingly, injection of educated T cells from injured and recovered mice prevented the transition to chronic pain in an antigen-independent mechanism.
The two-day-turned-one-day scientific meeting then adjourned. Most of the meeting attendees headed home that evening as Hurricane Harvey, now at Category 4, approached. The devastation to the Houston area, as has been widely reported, was unprecedented. Unfortunately, many of our TPRC colleagues were adversely affected by flooding and are still recovering. This second meeting of the TPRC reflects the tightknit scientific community in pain research in Texas. Our thoughts are with our friends in Houston as they continue to recover from Hurricane Harvey.
The Third Biennial Meeting of the Texas Pain Research Consortium is tentatively planned for San Antonio in 2019—well inland.
Please follow the Texas Pain Research Consortium on Twitter @TXPainResearch and Facebook.
Image: Prefrontal cortex neurons stained with a marker for axon initial segments. This image is part of a study led by Stephanie Shiers in Ted Price's lab, who presented her work on prefrontal cortex changes in late neuropathic pain at the meeting. Image courtesy of Ted Price’s lab at the University of Texas at Dallas.
