IU Indianapolis ScholarWorks :: Browsing by Author "Fehrenbacher, Jill C."

Browsing by Author "Fehrenbacher, Jill C."

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Aromatase inhibitors produce hypersensitivity in experimental models of pain : studies in vivo and in isolated sensory neurons
(2014) Robarge, Jason Dennis; Flockhart, David A.; Fehrenbacher, Jill C.; Khanna, Rajesh; Skaar, Todd C.; Vasko, Michael R.
Aromatase inhibitors (AIs) are the current standard of care for the treatment of hormone receptor positive breast cancer in postmenopausal women. Nearly one-half of patients receiving AI therapy develop musculoskeletal toxicity that is characterized by joint and/or muscle pain and approximately one-fourth of patients discontinue their therapy as a result of musculoskeletal pain. Since there are no effective strategies for prevention or treatment, insight into the mechanisms of AI-induced pain is critical to improve treatment. However, there are few studies of AI effects in animal models of nociception. To determine whether AIs produce hypersensitivity in animal models of pain, I examined the effects of AI administration on mechanical, thermal, and chemical sensitivity in rats. The results demonstrate that (1) repeated injection of 5 mg/kg letrozole in male rats produces mechanical, but not thermal, hypersensitivity that extinguishes when drug dosing is stopped; (2) administering a single dose of 1 or 5 mg/kg letrozole in ovariectomized (OVX) rats also induces mechanical hypersensitivity, without altering thermal sensitivity and (3) a single dose of 5 mg/kg letrozole or daily dosing of letrozole or exemestane in male rats augments flinching behavior induced by intraplantar ATP injection. To determine whether the effects of AIs on nociceptive behaviors are mediated by activation or sensitization of peptidergic sensory neurons, I determined whether letrozole exposure alters release of calcitonin gene-related peptide (CGRP) from isolated rat sensory neurons and from sensory nerve endings in rat spinal cord slices. No changes in basal, capsaicin-evoked or high extracellular potassium-evoked CGRP release were observed in sensory neuronal cultures acutely or chronically exposed to letrozole. Furthermore, letrozole exposure did not alter the ability of ATP to augment CGRP release from sensory neurons in culture. Finally, chronic letrozole treatment did not augment neuropeptide release from spinal cord slices. Taken together, these results do not support altered release of this neuropeptide into the spinal cord as mediator of letrozole-induced mechanical hypersensitivity and suggest the involvement of other mechanisms. Results from this dissertation provide a new experimental model for AI-induced hypersensitivity that could be beneficial in delineating mechanisms mediating pain during AI therapy.
Challenges and opportunities identifying therapeutic targets for chemotherapy-induced peripheral neuropathy resulting from oxidative DNA damage
(Wolters Kluwer, 2017-01) Kelley, Mark R.; Fehrenbacher, Jill C.; Department of Pharmacology and Toxicology, IU School of Medicine
Characterizing Effects of Sphingosine-1-Phosphate Receptor 1 Activation in Subtypes of Central Amygdala Neurons and Effects of Prenatal Methadone Exposure on Motor Cortex Neurons in Mice
(2021-04) Mork, Briana E.; Atwood, Brady K.; Sheets, Patrick L.; Cummins, Theodore R.; Fehrenbacher, Jill C.; McKinzie, David L.
Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that mediates a wide spectrum of biological processes including apoptosis, immune response and inflammation. S1P receptor (S1PR) ligands have been utilized as an effective immunosuppressant, treatment in multiple sclerosis and studied as a treatment for pain. The primary cellular response to S1P is thought to be elicited through S1PR type 1 (S1PR1). My first goal was to understand how S1PR1 signaling affects neuronal excitability in the central amygdala (CeA), a supraspinal node of the descending pain pathway. The CeA is made up of a heterogenous population of neurons which form complex local and long-range circuits. The central lateral amygdala (CeL) consists of two major populations of inhibitory neurons identified by expression of the peptides somatostatin (Sst) and protein kinase Cδ (PKCδ). Sst neurons have been shown to maintain control over local circuits within the CeL and play a critical role in pain modulation. I utilized transgenic breeding strategies to fluorescently label Sst-expressing CeL neurons for whole-cell electrophysiology in acute brain slice. This strategy allowed me to study the effects of S1PR1 agonist SEW2871 and S1PR1 antagonist NIBR on the cellular physiology of CeL Sst neurons. My findings reveal intrinsically distinct subtypes of CeL Sst neurons that are uniquely affected by S1PR1 activation, which may have implications for how S1P alters supraspinal pain pathways. My second goal was to assess the physiology of motor cortex neurons in mice exposed to prenatal methadone. Methadone is a synthetic μ-opioid agonist used for opioid maintenance therapy and chronic pain management. Methadone treatment for opioid use disorder in pregnant women can result in structural changes within the brain of their offspring causing and developmental delays to their children, including poorer motor performance. Using a mouse model of prenatal methadone exposure (PME), whole-cell electrophysiology, and analyses of cellular morphology, I elucidated the effects of PME on primary motor cortex (M1) output layer 5 (L5) neurons, which encompass the major cortical output pathway for motor control. My findings provide the first evidence that PME disrupts neuronal firing, subthreshold properties, and strength of local inputs onto M1 L5 neurons in prepubescent mice.
The Chimeric Fusion Protein SETMAR Functions as a Chromatin Organizing Factor
(2020-08) Bates, Alison Melissa; Georgiadis, Millie M.; Mosley, Amber L.; Quilliam, Lawrence A.; Fehrenbacher, Jill C.
About 50 million years ago, an Hsmar1 transposon invaded an early primate genome and inserted itself downstream of a SET methyltransferase gene, leading to the birth of a new chimeric protein now called SETMAR. While all other Hsmar1 sequences in the human genome have suffered inactivating mutational damage, the transposase domain of SETMAR has remained remarkably intact, suggesting that it has gained a novel, evolutionarily advantageous function. While SETMAR can no longer transpose itself throughout the genome, it has retained its ancestral sequence-specific DNA binding activity, the importance of which is currently unknown. To investigate this, we performed ChIP-seq to examine SETMAR binding in the human genome. We also utilized RNA-sequencing to assess SETMAR overexpression as well as SETMAR deletion on the human transcriptome. Additionally, we explored SETMAR’s transposase-derived chromatin-looping ability using chromosome-conformation-capture-on-ChIP (4C) in the presence of SETMAR overexpression and performed genome-wide Hi-C to assess the impact of complete SETMAR silencing on global chromatin interactions. ChIP-seq revealed that SETMAR amassed 7,332 unique binding sites, 69% of which included a TIR motif. RNA-sequencing in cells overexpressing SETMAR indicated 177 differentially regulated transcripts, including repression of 17 histone transcripts, suggesting a possible role in chromatin dynamics. RNA-sequencing of parental and SETMAR knockout clones highlighted an average of 5,000 altered transcripts in each cell line, with 343 transcripts significantly differentially expressed in all three knockout clones, many of which participate in embryonic development pathways. 4C analysis in the presence of SETMAR overexpression discovered multiple intrachromosomal looping interactions, and Hi-C analysis of SETMAR knockout cell lines uncovered genome-wide loss of chromatin interactions and disruption of TAD boundaries. The prevalence of SETMAR binding in the human genome combined with its chromatin looping capability and its dramatic effects on the transcriptome suggest a previously undiscovered role for SETMAR as a novel chromatin organizing factor.
DNA damage mediates changes in neuronal sensitivity induced by the inflammatory mediators, MCP-1 and LPS, and can be reversed by enhancing the DNA repair function of APE1
(Elsevier, 2017) Fehrenbacher, Jill C.; Guo, Chunlu; Kelley, Mark R.; Vasko, Michael R.; Pharmacology and Toxicology, School of Medicine
Although inflammation-induced peripheral sensitization oftentimes resolves as an injury heals, this sensitization can be pathologically maintained and contribute to chronic inflammatory pain. Numerous inflammatory mediators increase the production of reactive oxygen (ROS) and nitrogen species (RNS) during inflammation and in animal models of chronic neuropathic pain. Our previous studies demonstrate that ROS/RNS and subsequent DNA damage mediate changes in neuronal sensitivity induced by anticancer drugs and by ionizing radiation in sensory neurons, thus we investigated whether inflammation and inflammatory mediators also could cause DNA damage in sensory neurons and whether that DNA damage alters neuronal sensitivity. DNA damage was assessed by pH2A.X expression and the release of the neuropeptide, calcitonin gene-related peptide (CGRP), was measured as an index of neuronal sensitivity. Peripheral inflammation or exposure of cultured sensory neurons to the inflammatory mediators, LPS and MCP-1, elicited DNA damage. Moreover, exposure of sensory neuronal cultures to LPS or MCP-1 resulted in changes in the stimulated release of CGRP, without altering resting release or CGRP content. Genetically enhancing the expression of the DNA repair enzyme, apurinic/apyrimidinic endonuclease (APE1) or treatment with a small-molecule modulator of APE1 DNA repair activity, both which enhance DNA repair, attenuated DNA damage and the changes in neuronal sensitivity elicited by LPS or MCP-1. In conclusion, our studies demonstrate that inflammation or exposure to inflammatory mediators elicits DNA damage in sensory neurons. By enhancing DNA repair, we demonstrate that this DNA damage mediates the alteration of neuronal function induced by inflammatory mediators in peptidergic sensory neurons.
Exploiting the Ref-1-APE1 node in cancer signaling and other diseases: from bench to clinic
(Springer NPG, 2017-06-08) Shah, Fenil; Logsdon, Derek; Messmann, Richard A.; Fehrenbacher, Jill C.; Fishel, Melissa L.; Kelley, Mark R.; Department of Pediatrics, School of Medicine
Reduction-oxidation factor 1-apurinic/apyrimidinic endonuclease (Ref-1/APE1) is a critical node in tumor cells, both as a redox regulator of transcription factor activation and as part of the DNA damage response. As a redox signaling protein, Ref-1/APE1 enhances the transcriptional activity of STAT3, HIF-1α, nuclear factor kappa B, and other transcription factors to promote growth, migration, and survival in tumor cells as well as inflammation and angiogenesis in the tumor microenvironment. Ref-1/APE1 is activated in a variety of cancers, including prostate, colon, pancreatic, ovarian, lung and leukemias, leading to increased aggressiveness. Transcription factors downstream of Ref-1/APE1 are key contributors to many cancers, and Ref-1/APE1 redox signaling inhibition slows growth and progression in a number of tumor types. Ref-1/APE1 inhibition is also highly effective when paired with other drugs, including standard-of-care therapies and therapies targeting pathways affected by Ref-1/APE1 redox signaling. Additionally, Ref-1/APE1 plays a role in a variety of other indications, such as retinopathy, inflammation, and neuropathy. In this review, we discuss the functional consequences of activation of the Ref-1/APE1 node in cancer and other diseases, as well as potential therapies targeting Ref-1/APE1 and related pathways in relevant diseases. APX3330, a novel oral anticancer agent and the first drug to target Ref-1/APE1 for cancer is entering clinical trials and will be explored in various cancers and other diseases bringing bench discoveries to the clinic.
Furanocoumarins are a novel class of modulators for the transient receptor potential vanilloid type 1 (TRPV1) channel
(ASBMB, 2014-04-04) Chen, Xingjuan; Sun, Weiyang; Ginaris, Nicholas G.; Riley, Ashley M.; Cummins, Theodore R.; Fehrenbacher, Jill C.; Obukhov, Alexander G.; Department of Cellular & Integrative Physiology, IU School of Medicine
Furanocoumarin imperatorin is the major active component of Angelica dahurica root extracts, widely used in traditional medicine to treat headache, toothache, and orbital eye pain. In this study, we investigated the mechanisms that may underlie the pain-relieving effects of the compound. We found that imperatorin significantly inhibited formalin- and capsaicin-induced nocifensive responses but did not alter baseline thermal withdrawal thresholds in the rat. We established that imperatorin is a weak agonist of TRPV1, a channel implicated in detecting several noxious stimuli, exhibiting a 50% effective concentration (EC50) of 12.6 ± 3.2 μM. A specific TRPV1 antagonist, JNJ-17203212 (0.5 μM), potently inhibited imperatorin-induced TRPV1 activation. Site-directed mutagenesis studies revealed that imperatorin most likely acted via a site adjacent to or overlapping with the TRPV1 capsaicin-binding site. TRPV1 recovery from desensitization was delayed in the presence of imperatorin. Conversely, imperatorin sensitized TRPV1 to acid activation but did not affect the current amplitude and/or the activation-inactivation properties of Na(v)1.7, a channel important for transmission of nociceptive information. Thus, our data indicate that furanocoumarins represent a novel group of TRPV1 modulators that may become important lead compounds in the drug discovery process aimed at developing new treatments for pain management.
An in vitro study of the mechanisms that underlie changes in neuronal sensitivity and neurite morphology following treatment with microtubule targeting agents
(2014-11) Pittman, Sherry Kathleen; Fehrenbacher, Jill C.; Cummins, Theodore R.; Hingtgen, Cynthia M.; Hudmon, Andrew; Vasko, Michael R.
Microtubule targeting agents (MTAs) are chemotherapeutics commonly used in the treatment of breast, ovarian, lung, and lymphoma cancers. There are two main classes of MTAs based upon their effects on microtubule stability. The two classes are the destabilizing agents, which include the drug vincristine, and the stabilizing agents, which include paclitaxel and epothilone B. These drugs are highly effective antineoplastics, but their use is often accompanied by several side effects, one of which is peripheral neuropathy. Peripheral neuropathy can be characterized by burning pain, tingling, loss of proprioception, or numbness in the hands and feet. In some patients, the MTA-induced peripheral neuropathy is debilitating and dose-limiting; however, there are no effective prevention strategies or treatment options for peripheral neuropathy as the mechanisms mediating this side effect are unknown. The goal of this work was to investigate MTA-induced effects on neuronal activity and morphology in order to elucidate the underlying mechanisms involved in the development of MTA-induced peripheral neuropathy. As an indicator of sensory neuronal activity, the basal and stimulated release of the putative nociceptive peptide, calcitonin gene-related peptide (CGRP), was measured from sensory neurons in culture after exposure to the MTAs paclitaxel, epothilone B, and vincristine. Neurite length and branching were also measured in sensory neuronal cultures after treatment with these MTAs. The results described in this thesis demonstrate that MTAs alter the stimulated release of CGRP from sensory neurons in differential ways depending on the MTA agent employed, the CGRP evoking-stimulus used, the concentration of the MTA agent, the duration of exposure to the MTA agent, and the presence of NGF. It was also observed that MTA agents decrease neurite length and branching, independent of the concentration of NGF in the culture media. Thus, this thesis describes MTA-induced alterations of sensory neuronal sensitivity and neurite morphology and begins to elucidate the underlying mechanisms involved in MTA-induced alterations of sensory neurons. These findings will undoubtedly be used to help elucidate the mechanisms underlying MTA-induced peripheral neuropathy.
Long-term exposure to PGE2 causes homologous desensitization of receptor-mediated activation of protein kinase A
(Springer (Biomed Central Ltd.), 2016-07-11) Malty, Ramy Habashy; Hudmon, Andy; Fehrenbacher, Jill C.; Vasko, Michael R.; Department of Pharmacology and Toxicology, IU School of Medicine
BACKGROUND: Acute exposure to prostaglandin E2 (PGE2) activates EP receptors in sensory neurons which triggers the cAMP-dependent protein kinase A (PKA) signaling cascade resulting in enhanced excitability of the neurons. With long-term exposure to PGE2, however, the activation of PKA does not appear to mediate persistent PGE2-induced sensitization. Consequently, we examined whether homologous desensitization of PGE2-mediated PKA activation occurs after long-term exposure of isolated sensory neurons to the eicosanoid. METHODS: Sensory neuronal cultures were harvested from the dorsal root ganglia of adult male Sprague-Dawley rats. The cultures were pretreated with vehicle or PGE2 and used to examine signaling mechanisms mediating acute versus persistent sensitization by exposure to the eicosanoid using enhanced capsaicin-evoked release of immunoreactive calcitonin gene-related peptide (iCGRP) as an endpoint. Neuronal cultures chronically exposed to vehicle or PGE2 also were used to study the ability of the eicosanoid and other agonists to activate PKA and whether long-term exposure to the prostanoid alters expression of EP receptor subtypes. RESULTS: Acute exposure to 1 μM PGE2 augments the capsaicin-evoked release of iCGRP, and this effect is blocked by the PKA inhibitor H-89. After 5 days of exposure to 1 μM PGE2, administration of the eicosanoid still augments evoked release of iCGRP, but the effect is not attenuated by inhibition of PKA or by inhibition of PI3 kinases. The sensitizing actions of PGE2 after acute and long-term exposure were attenuated by EP2, EP3, and EP4 receptor antagonists, but not by an EP1 antagonist. Exposing neuronal cultures to 1 μM PGE2 for 12 h to 5 days blocks the ability of PGE2 to activate PKA. The offset of the desensitization occurs within 24 h of removal of PGE2 from the cultures. Long-term exposure to PGE2 also results in desensitization of the ability of a selective EP4 receptor agonist, L902688 to activate PKA, but does not alter the ability of cholera toxin, forskolin, or a stable analog of prostacyclin to activate PKA. CONCLUSIONS: Long-term exposure to PGE2 results in homologous desensitization of EP4 receptor activation of PKA, but not to neuronal sensitization suggesting that activation of PKA does not mediate PGE2-induced sensitization after chronic exposure to the eicosanoid.
Men with acute cholecystitis have higher tissue-based cytokine levels than women: a cross-sectional study
(2015-04) Fehrenbacher, Jill C.; Bingener, J.; Aho, J. M.; Wasky, P. R.; Locke, E. E.; Schwesinger, W. H.; Van Sickle, K. R.; Hargreaves, K. M.; Department of Pharmacology and Toxicology, IU School of Medicine
Aim. Sex-based differences in surgical outcomes may be related to socioeconomic, behavioral, or physiologic factors. Estrogenreceptor-related modulation is a proposed mechanism for sex-based differences in reaction to inflammation. We evaluated sex-based differences in gallbladder tissue-levels of inflammatory cytokines using a novel method to collect interstitial fluid from cholecystectomy samples. Methods. Patients undergoing laparoscopic cholecystectomy for acute or chronic cholecystitis were prospectively enrolled from August 1, 2006, through August 1, 2009. Immediately after gallbladder removal, interstitial fluid from the gallbladder fundus and infundibulum was collected. Tissue-level cytokines were determined using a multiplex cytometric bead assay. Messenger RNA levels of estrogen receptors and aromatase (ESR1, GPER, CYP19A1) were analyzed with real-time reverse transcriptasepolymerase chain reaction. Results. Interstitial fluid from gallbladder tissue of 78 patients (48 women) was analyzed. All patients with acute cholecystitis had higher levels of interleukin (IL)-6 and IL-10 than patients with chronic cholecystitis. Men with acute disease had higher tissue levels of IL-6 and IL-8 than women. IL-1β and IL-10 were increased only in men with acute cholecystitis. Tumor necrosis factor-α levels did not vary by sex or disease status. Tissues from acutely inflamed gallbladders had higher expression of a G protein-coupled estrogen receptor (GPER) and aromatase (CYP19A1). Conclusion. Tissue-level proinflammatory cytokines differ between men and women with acute cholecystitis. Mechanistic studies are needed to determine whether changes in cytokine levels or estrogen function contribute to local tissue inflammation and whether these influence surgical outcomes.

Browsing by Author "Fehrenbacher, Jill C."

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