Congratulations Jenna Gollihue, PhD
On Friday, June 16th, 2017 Jenna Gollihue, mentored by Dr. Sasha Rabchevsky, successfully defended her dissertation and earned her PhD.
Contusion spinal cord injury (SCI) results in devastating life-long debilitation in which there are currently no effective treatments. The primary injury site presents a complex environment marked by subsequent secondary pathophysiological cascades involving excessive reactive oxygen and nitrogen species (ROS/RNS) production, glutamate-induced excitotoxicity, calcium dysregulation, and delayed neuronal apoptosis. Many of these cascades involve mitochondrial dysfunction, thus a single mitochondrial-centric therapy that targets a variety of these factors could be far reaching in its potential benefits after SCI. As such, this dissertation examines whether transplantation of exogenous mitochondria after SCI can attenuate secondary injury cascades to decrease the spread and severity of the injury.
Our first experiment tested the dose-dependent effects of mitochondrial transplantation on the ability to maintain acute overall bioenergetics after SCI. We compared transplantation of mitochondria originating from two different sources- cultured PC12 cells or rat soleus leg muscle. 24 hours after injury, State III oxygen consumption rates were maintained to over 80% of sham levels when 100ug of mitochondria was transplanted, regardless of the origin of the mitochondria. Complex I enzyme activity assays corroborated our findings that the 100ug dosage gave optimal benefits compared to vehicle injection.
We also analyzed the rostral-caudal distribution and cell-type colocalization of transplanted transgenically-labeled tGFP mitochondria after SCI. There were greater volumes and rostral-caudal spread of tGFP mitochondria at the 24 hour time point compared to 7 days post injection. tGFP mitochondria had the greatest propensity to colocalize with macrophages and pericytes and was evident in endothelial cells, oligodendrocytes and astrocytes, though no such co-labeling was present in neurons. Further, colocalization of tGFP was always greater at the 24 hour time compared to 48 hour or 7days post injection time points. These data indicate that there is a cell-type difference in incorporation potential of exogenous mitochondria which changes over time.
Finally, we tested the effects of mitochondrial transplantation on long term functional recovery. Animals were injected with either vehicle, 100ug cell-derived mitochondria, or 100ug muscle-derived mitochondria immediately after contusion SCI. Functional analyses including BBB overground locomotor scale and von Frey mechanical sensitivity tests did not show any differences between treatment groups. Likewise, there were no differences in tissue sparing when mitochondria were transplanted compared to vehicle injections.
These studies present the potential of mitochondrial transplantation for therapeutic intervention after SCI. While our acute measures do not correspond into long term recovery, we show that at 24 hours transplanted mitochondria do have an effect on bioenergetics and that they are taken into host cells. We believe that further investigation into caveats and technical refinement is necessary at this time to translate the evident acute bioenergetic recovery into long term functional recovery.
Dr. Alexander “Sasha” Rabchevsky
Department of Physiology, Mentor
Dr. Steve Estus
Department of Physiology
Dr. Bret Smith
Department of Physiology
Dr. John Gensel
Department of Physiology
Dr. Patrick Sullivan
Department of Neuroscience
Dr. Daniel Pack
Department of Chemical and Materials Engineering
Acknowledgments from Dr. Gollihue
My gratitude goes to my mentor, Dr. Alexander “Sasha” Rabchevsky for taking me in as a graduate student in his lab. Sasha’s passion for the research we are doing continually inspires me to work harder, and his mentoring has taught me to be a scientist that is always critical to find the truth. Thank you for instilling in me a drive to be the best scientist I can be. Secondly, I would like to thank the members of the Rabchevsky lab. Dr. Samir Patel, who spent many exhausting “mito days” working beside me in the lab; your friendship, support, and cheerfulness made the long experimental days much more enjoyable. Khalid Eldahan and David Cox, thank you for all of your help over the years, especially with the surgeries that started at dawn and didn’t end until after dark.
I would also like to thank my committee members, who have given me invaluable advice and encouragement whenever I hit a roadblock. Dr. Bret Smith, Dr. Steve Estus, Dr. John Gensel, and Dr. Pat Sullivan, thank you for always giving me your valuable help and guidance, whether it be science related or not. Our discussions taught me the importance of thinking both critically and creatively.
The Physiology department and the Spinal Cord and Brain Injury Research Center at the University of Kentucky has been a vital part of my education. Thank you to all of the faculty, administrators, lab techs, post docs, grad students, and undergrads. It really does take a village, and without such a great network none of this would have been possible. From you I have found great role models, great friends, and had experiences I wouldn’t change for anything.
My family’s love and support has gotten me through the ups and downs that come with graduate school. All my life, my parents believed in me and pushed me to excel. They gave me the confidence to never doubt that I could do and be whatever I wanted as long as I tried. And thank you for always pushing me to try. My brothers, Alex and Jason, are the best siblings a girl could ask for. Just a phone call away, talking to you guys always made me feel better whenever I was homesick. Which sometimes was a lot.
Thank you to my friends, Erica Littlejohn, Stacy Webb, Caitlyn Reidmann and many others- your friendship has meant the world to me. From hanging out first year to the parades and festivals, craft nights with lots of glitter, coffee breaks and dinners, thank you for the times we just needed a break from science. Even though we all inevitably just ended up talking science anyways.
And last but certainly, definitely, not least- thank you to my amazing husband, Jarrad Gollihue. You have been my rock and my best friend, the shoulder I lean on. After a long day in the lab, you always just know whether I need a hug, a high five, or a jumbo margarita. I am so thankful to have you as my partner through these important life experiences.