University of Kentucky UKnowledge Theses and Dissertations--Physiology Physiology 2014 TRPA1 CHANNELS IN COCHLEAR SUPPORTING CELLS REGULATE HEARING SENSITIVITY AFTER NOISE EXPOSURE Alejandra C. Velez-Ortega University of Kentucky, [email protected] Right click to open a feedback form in a new tab to let us know how this document benefits ou.y Recommended Citation Velez-Ortega, Alejandra C., "TRPA1 CHANNELS IN COCHLEAR SUPPORTING CELLS REGULATE HEARING SENSITIVITY AFTER NOISE EXPOSURE" (2014). Theses and Dissertations--Physiology. 20. https://uknowledge.uky.edu/physiology_etds/20 This Doctoral Dissertation is brought to you for free and open access by the Physiology at UKnowledge. It has been accepted for inclusion in Theses and Dissertations--Physiology by an authorized administrator of UKnowledge. For more information, please contact [email protected]. STUDENT AGREEMENT: I represent that my thesis or dissertation and abstract are my original work. Proper attribution has been given to all outside sources. I understand that I am solely responsible for obtaining any needed copyright permissions. I have obtained needed written permission statement(s) from the owner(s) of each third-party copyrighted matter to be included in my work, allowing electronic distribution (if such use is not permitted by the fair use doctrine) which will be submitted to UKnowledge as Additional File. I hereby grant to The University of Kentucky and its agents the irrevocable, non-exclusive, and royalty-free license to archive and make accessible my work in whole or in part in all forms of media, now or hereafter known. I agree that the document mentioned above may be made available immediately for worldwide access unless an embargo applies. I retain all other ownership rights to the copyright of my work. I also retain the right to use in future works (such as articles or books) all or part of my work. I understand that I am free to register the copyright to my work. REVIEW, APPROVAL AND ACCEPTANCE The document mentioned above has been reviewed and accepted by the student’s advisor, on behalf of the advisory committee, and by the Director of Graduate Studies (DGS), on behalf of the program; we verify that this is the final, approved version of the student’s thesis including all changes required by the advisory committee. The undersigned agree to abide by the statements above. Alejandra C. Velez-Ortega, Student Dr. Gregory I. Frolenkov, Major Professor Dr. Bret N. Smith, Director of Graduate Studies TRPA1 CHANNELS IN COCHLEAR SUPPORTING CELLS REGULATE HEARING SENSITIVITY AFTER NOISE EXPOSURE DISSERTATION A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the College of Medicine at the University of Kentucky By Alejandra Catalina Vélez-Ortega Lexington, Kentucky Director: Dr. Gregory I. Frolenkov, Associate Professor of Physiology Lexington, Kentucky 2014 Copyright © A. Catalina Vélez-Ortega 2014 ABSTRACT TRPA1 CHANNELS IN COCHLEAR SUPPORTING CELLS REGULATE HEARING SENSITIVITY AFTER NOISE EXPOSURE TRPA1 channels are sensors for noxious stimuli in a subset of nociceptive neurons. TRPA1 channels are also expressed in cells of the mammalian inner ear, but their function in this tissue remains unknown given that Trpa1–/– mice exhibit normal hearing, balance and sensory mechanotransduction. Here we show that non-sensory (supporting) cells of the hearing organ in the cochlea detect tissue damage via the activation of TRPA1 channels and subsequently modulate cochlear amplification through active cell- shape changes. We found that cochlear supporting cells of wild type but not Trpa1–/– mice generate inward currents and robust long-lasting Ca2+ responses after stimulation with TRPA1 agonists. These Ca2+ responses often propagated between different types of supporting cells and were accompanied by prominent tissue displacements. The most prominent shape changes were observed in pillar cells which here we show possess Ca2+-dependent contractile machinery. Increased oxidative stress following acoustic overstimulation leads to the generation of lipid peroxidation byproducts such as 4-hydroxynonenal (4-HNE) that could directly activate TRPA1. Therefore, we exposed mice to mild noise and found a longer-lasting inhibition of cochlear amplification in wild type than in Trpa1–/– mice. Our results suggest that TRPA1-dependent changes in pillar cell shape can alter the tissue geometry and affect cochlear amplification. We believe this novel mechanism of cochlear regulation may protect or fine-tune the organ of Corti after noise exposure or other cochlear injuries. KEYWORDS: Transient receptor potential A1 channel, cochlear supporting cells, reactive oxygen species, cochlear amplification, 4-hydroxynonenal Alejandra Catalina Vélez-Ortega Student’s Signature December 10, 2014 Date TRPA1 CHANNELS IN COCHLEAR SUPPORTING CELLS REGULATE HEARING SENSITIVITY AFTER NOISE EXPOSURE By Alejandra Catalina Vélez-Ortega Dr. Gregory I. Frolenkov Director of Dissertation Dr. Bret N. Smith Director of Graduate Studies December 10, 2014 Date To my father, whose creativity kept my curiosity from fading (a curiosity that now fuels a career in research). PREFACE AND ACKNOWLEDGEMENTS Almost 10 years ago, in a course for advanced English writing, I was asked to write an essay about the perfect career pattern for myself. I wrote about my passion for research and my desire to return to school to obtain a graduate degree. Now that I see ‘the light at the end of the PhD tunnel’, I am glad that I still feel the same level of passion and curiosity I felt 10 years ago. This further confirms my desire to pursue a career in research. Interestingly, back then I was absolutely convinced that “…it (was) not part of my (career) scheme to create my own research group”. I did not feel I was creative enough or that I had the critical thinking required to develop my own research ideas. So, I went on and obtained a Master’s degree and subsequently joined a PhD program, all while thinking that a career in academia was not the option for me. I thank my advisor, Dr. Gregory I. Frolenkov, for his guidance throughout the development and execution of this research project. At occasions, my curiosity led me off track, but he always brought me back by providing a clear distinction between the main experiments that were required to test our hypothesis vs. the additional experiments that only provided extra support (or, as he called them, the ‘icing on the cake’). Gregory often made me think like an independent investigator. For instance, he allowed me set up the imaging/electrophysiological system that was used for most experiments presented here. For about three months, I read countless manuals, made dozens of cable connections, calibrated and tested individual components, and configured the system’s software. Gregory knew that by allowing me to do this I would be able to easily troubleshoot “technical problems” encountered during the experiments. Additionally, I knew the full capabilities of the system and therefore was able to plan experiments to take full advantage of them. This process indeed facilitated the standardization phase of new experiments. But most importantly, as Gregory knew and eventually told me, those 3 iii months provided a glimpse of what one day setting up my own laboratory could feel like. And I must confess, this took some of the fear I had away. Together with this, our long discussions over the results of experiments, grant proposals, publication strategies and career options, allowed me to feel like a colleague more than a student. Nowadays, I often think about my career options and I find myself contemplating a career in academia and wanting to start my own laboratory. Therefore, I feel most grateful to Gregory for boosting my own confidence and believing I have what it takes to become an independent investigator. I want to thank Dr. Timothy S. McClintock, Dr. Bradley K. Taylor, Dr. Kenneth S. Campbell and Dr. Olivier Thibault for serving on my PhD committee. Their constructive criticism in each of our meetings has truly improved the quality of this work. I also thank Dr. Douglas A. Andres for agreeing to be the outside examiner for my dissertation defense. I also wish to express my gratitude to all members in the Frolenkov laboratory. When I first joined the laboratory, the former members, Dr. Ruben S. Stepanyan, Dr. Artur A. Indzhykulian and Dr. Mircea Anghelescu (a.k.a. ‘the boys’), provided training for several techniques, a welcoming work environment, and even a ‘big brother’-like behavior since they often walked me to my car when I would leave the laboratory in the late night. I feel truly lucky to have met Ms. Stephanie E. Edelmann as well. Her kind heart and unselfish nature mean the world to me. In addition, Stephanie provided significant help with the in vivo experiments in this project. In addition to the people mentioned above, I also thank Dr. Ghanshyam P. Sinha, Mr. Mike Grossheim, Ms. Diana Syam and Ms. Shadan Hadi for their valuable comments during laboratory meetings. Throughout this and other projects, I had the privilege to mentor several students: Ms. Weisi Fu, Ms. Brianna D. Harfmann, Ms. Shaniya Maimaiti, Mr. Julián Vergara and Ms. Kathryn M. Toner. I enjoyed the time they spent in the laboratory and I look forward to continue training more students in the years ahead. I also had the pleasure to mentor Dr. Channy Park. Her help was crucial for some of the experiments presented here. I am extremely thankful