UC Riverside UCR Honors Capstones 2020-2021
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UC Riverside UCR Honors Capstones 2020-2021 Title Transcriptomic Analysis of Molecular Mechanisms of Neuroprotection by Neuregulin-1 Following Ischemic Stroke Permalink https://escholarship.org/uc/item/1c89b11s Author Bennett, Kimberly R. Publication Date 2021-08-13 Data Availability The data associated with this publication are within the manuscript. eScholarship.org Powered by the California Digital Library University of California TRANSCRIPTOMIC ANALYSIS OF MOLECULAR MECHANISMS OF NEUROPROTECTION BY NERUEGULIN-1 FOLLOWING ISCHEMIC STROKE By Kimberly R. Bennett A capstone project submitted for graduation with University Honors May 06, 2021 University Honors University of California, Riverside APPROVED Dr. Victor G. J. Rodgers Department of Bioengineering Dr. Byron D. Ford Department of Biomedical Sciences Dr. Richard Cardullo, Howard H Hays Jr. Chair University Honors ABSTRACT Ischemic stroke is a global health problem that is characterized by early neuronal death, apoptosis, inflammation, and oxidative stress following an obstruction of the blood supply to the brain. Previous studies have shown that ischemic stroke causes a release of pro-inflammatory cytokines that produce changes in gene expression, primarily in inflammation and cell death. Neuregulin-1 (NRG-1) is growth factor that has been investigated for its neuroprotective properties and ability to delay neuronal death following ischemic stroke. While NRG-1 has shown significant promise in preventing brain damage and stimulating post-injury repair following stroke, the mechanisms behind its neuroprotective effects are unclear. The goal of this research was to investigate the effects of NRG-1 treatment on ischemia-induced gene expression profiles following a permanent middle cerebral artery occlusion (pMCAO) in rat models. Rats were sacrificed twelve hours following vehicle or NRG-1 treatment. From the total RNA extracted from the rat brains, mRNA from the peri-infarct cortex was used to generate microarrays, which were then hybridized to an Affymetrix Rat Genome 2.0st Gene Chip and analyzed using the Affymetrix Transcriptome Analysis Console (TAC) Software. Our results show that NRG-1 delivery increases the regulation of pro-survival genes. Most notably, NRG-1 treatment upregulates the CREB1 and FOXO1 transcription factors, which are involved in increasing anti-inflammatory and cell proliferation responses and decreasing apoptosis and oxidative stress responses, respectively. These findings provide novel insight into the molecular mechanisms involved in neuregulin-1 neuroprotection. Further region-specific research is necessary to elucidate the importance of these genes in stroke and the significance of their regulation by NRG-1. 2 ACKNOWLEDGEMENTS I would like to thank my principal investigator and my faculty mentor, Dr. Victor Rodgers, for his enthusiastic support and mentorship throughout my entire time in the B2K Group. I would also like to thank our collaborating mentor, Dr. Byron Ford, for his consistent dedication towards providing me with an engaging and enriching experience in the laboratory. I also express special thanks to two graduate students, Jennifer Yang and Catherine Augello, for being dependable mentors and being open to any questions I had. Having experiments of their own, as well as other commitments, their patience and willingness to explain various concepts, techniques, and assays was instrumental to my success. Lastly, I would express my appreciation for all members of the B2K Group and the Ford Lab. I would not have been able to conduct this project, or any research for that matter, without the supportive environment and collaborative team effort put forth by everyone. Additionally, I would like to recognize the Bourns College of Engineering, the UC Riverside School of Medicine, the MARC U-STAR program, and the University Honors Program for granting me the opportunity to accomplish scientific research and share my findings with the academic community, as well as nurturing my interest in the pursuit for novel discovery. Overall, I am positive the skills and experiences I have learned from my time in the B2K Group will serve me well in the near future, as I will attend the Harvard-MIT Health Sciences and Technology PhD Program. 3 TABLE OF CONTENTS Abstract…………………..………………………………………………………………………. 2 Acknowledgements………………………………………………………………………………. 3 Table of Contents………………………………………………………………………………… 4 Introduction………………………………………………………………………………………. 5 Methodology……………………………………………………………………………………... 7 Animals.……………………………………………………………………………….…. 7 Microarray Analysis.………………………………………………..………..…….……. 8 Multiplex Transcription Factor Array…………………………….…………………...… 9 Immunohistochemistry...……...……………………………………..………..…….…... 10 Results………………………………………………………………………………………...… 11 Microarray Analysis.………………………………………………..………..…….…... 11 Multiplex Transcription Factor Array…………………………….…………………......17 Immunohistochemistry...……...……………………………………..………..…….…... 18 Discussion……………..………………………………………………………………………... 21 Conclusion……………………………………………………………………………………… 23 References……………………………………………………………………………………… 24 Supplementary……………..…………………………………………………………………… 26 4 INTRODUCTION Stroke is the 5th leading cause of death worldwide, with about 87% of cases being ischemic stroke (1). Differing from hemorrhagic stroke, which occurs due to internal blood loss, ischemic stroke occurs when the brain blood supply is obstructed. Ischemic stroke is characterized by cell death, inflammation, and oxidative stress, that occur through molecular cascades and changes in regulatory gene expression (2,3). The only approved treatment for ischemic stroke is tPA, a limited and time-sensitive treatment aimed at restoring blood flow that only 3-5% of patients qualify for (4). Given the wide-spread and dire need for an effective ischemic stroke treatment that can be administered outside the three-hour therapeutic window of tPA, a better understanding of the pathophysiology associated with ischemic stroke is necessary to develop effective therapeutic treatments aimed at reducing the progression of the associated cell death. Previous studies have shown that ischemic stroke causes a release of pro-inflammatory cytokines that produce changes in gene expression, primarily in inflammation and cell death (5,6). The initial area of injury, known as the infarct core, develops within minutes of stroke onset and develops up to three hours after stroke. The infarct core is characterized by low cerebral blood flow, oxidative stress, and excitotoxicity, which is accompanied by an increased production of inflammatory molecules. The resulting inflammation begins to affect a larger area of brain tissue, known as the ischemic penumbra, where neurons can survive up to twenty-four hours after stroke onset, prolonging the therapeutic window for ischemic stroke treatment (7–9). Neuregulin-1 has been investigated as a potential therapeutic for ischemic stroke for its various roles in the nervous system. Neuregulin-1 is a small protein first discovered by several laboratories researching cancer biology mechanisms, cancer biology mechanisms, neuromuscular 5 junction function and Schwann cell proliferation. Multiple reports from our laboratory have demonstrated that the exogenous delivery of NRG-1 reduces neuronal damage in the penumbral region of rats that underwent middle cerebral artery occlusion in an extended therapeutic window (10–13). While NRG-1 has shown significant promise in preventing brain damage and stimulating post-injury repair following stroke, the regulatory mechanisms behind its neuroprotective effects are unclear. The investigation of ischemia-induced gene expression profiles following NRG-1 administration will provide valuable insight into the transcriptional regulation of these processes. In this study, we performed a computational transcriptomic analysis to identify gene expression profiles and their associated transcriptional mechanisms affected by NRG-1 treatment twelve hours following permanent MCAO using the Transcriptome Analysis Console (TAC) software. TAC software allows for the statistical analysis of differential gene expression. To investigate mechanisms involved in the inflammatory and cell death responses that occur in the penumbra, we identified genes that were significantly regulated following NRG-1 treatment at twelve hours following ischemic stroke and the transcription factors that regulated the expression of these genes. Additionally, we verified transcriptional regulation activity of these factors through a Multiplex Transcription Factor Array. Cellular processes were investigated through literature search and STRING database analysis, and the brain cell types involved in these processes were visually displayed using immunohistochemistry (which remains incomplete due to COVID-19). Understanding the mechanisms regulated by the NRG-1 phosphorylation cascade may explain the neuroprotective effects of NRG-1 on a molecular level. These findings could support the development of clinical studies using NRG-1 to treat patients with ischemic stroke. 6 METHODS Animals All animals were treated humanely with regard for the alleviation of pain and suffering. All surgical protocols involving animals were performed by aseptic techniques and were approved by the Institutional Animal Care and Use Committee at Morehouse School of Medicine prior to the experiment. Male adult Sprague-Dawley rattus norvegucis (250-300g; Charles River Laboratory International, Inc., USA) were housed in standard cages in a temperature-controlled