Researchers at the Icahn School of Medicine at Mount Sinai have shed valuable light on the nuanced functions and intricate regulatory methods of RNA editing, a critical mechanism underlying brain development and disease.
In a study published June 26 in Nature Communications, the team reported finding important differences between postmortem and live brain tissues of the prefrontal cortex when it comes to one of the most abundant RNA modifications in the brain, known as adenosine-to-inosine (A to I) editing. . This discovery will play an important role in shaping the development of diagnostics and therapies for brain diseases.
While DNA contains the genetic blueprint for humans, RNA actually carries out its instructions to create functional proteins that play important roles in the functioning of the body, including the complex functions of the central nervous system. The function and stability of RNA is controlled by many modifications, each of which serves a specific purpose. These modifications, known as RNA editing, are a continuous process that occurs in all of our cells and tissues, facilitated by enzymes known as ADAR. This process may continue to occur in individual cells for some time after the death of the person whose tissues the cells were a part of.
The conversion of adenosine nucleosides to inosine (A to I) is a common and well-studied RNA modification and is orchestrated by ADAR family proteins, primarily ADAR1 and ADAR2. In the mammalian brain, thousands of highly regulated A-to-I editing sites have been discovered in anatomical regions and cell types, some of them by Mount Sinai researchers. These sites are known to be involved in neuronal maturation and brain development. Aberrant regulation of A-to-I editing has been linked to neurological disorders.
“Until now, investigation of A-to-I editing and its biological importance in the mammalian brain has been restricted to the analysis of postmortem tissues. Using fresh samples from living individuals, we were able to discover significant differences in A-to-I editing activity. RNA. that previous studies, which relied solely on postmortem samples, may have missed,” said Michael Breen, PhD, co-senior author of the study and assistant professor of Psychiatry, Genetics and Genomic Sciences at Icahn Mount Sinai. “We were especially surprised to find that levels of RNA editing were significantly higher in postmortem brain tissue compared to living tissue, which is likely due to postmortem changes such as inflammation and hypoxia that do not occur in living brains. Furthermore , we found that RNA editing was significantly greater in postmortem brain tissue compared to living tissue. “In living tissue it tends to involve evolutionarily conserved and functionally important sites that are also dysregulated in human diseases, emphasizing the need to study. “both live and postmortem samples for a comprehensive understanding of brain biology.”
After death, oxygen deprivation rapidly damages brain cells, causing an irreversible cascade of damage that can alter ADAR expression and A to I editing. “We hypothesize that the molecular responses to hypoxic and immune responses induced postmortem “can significantly alter the landscape of A-to-I editing. This may lead to misunderstandings about RNA editing in the brain if we only study postmortem tissues,” said Miguel Rodríguez de los Santos, PhD, co-first author of the study and fellow. postdoctoral fellow in the Department of Psychiatry at Mount Sinai. “Studying living brain tissue gives us a clearer picture of the biology of RNA editing in the human brain.”
To investigate, the research team based their study on the Living Brain Project, in which dorsolateral prefrontal cortex (DLPFC) tissues are obtained from living people during neurosurgical procedures for deep brain stimulation, an elective treatment for neurological diseases. For comparison, a cohort of postmortem DLPFC tissues was assembled from three brain banks to match the live cohort on key demographic and clinical variables. The team investigated multiple types of genomic data from the Living Brain Project, including bulk tissue RNA sampling, single-nucleus RNA sequencing, and whole-genome sequencing. The generation of this data is described in several upcoming Living Brain Project manuscripts.
The researchers identified more than 72,000 locations where A to I editing occurs more frequently or differently in postmortem brain tissue than in living DLPFC brain tissue. They found higher levels of the enzymes ADAR and ADARB1, which are responsible for elevated editing patterns in postmortem brain tissues. Interestingly, they also found hundreds of sites with higher levels of A-to-I editing in living brain tissue. These sites are primarily found at connections between neurons (called synapses) and are typically conserved throughout evolution, suggesting that they play important roles in brain activity. Some well-known A-to-I editing sites were highly edited in living brains, indicating that they may be involved in critical neural processes such as synaptic plasticity, which is essential for learning and memory. However, many other A-to-I editing sites found in living brain tissues have unclear functions and more research is needed to understand their impact on brain health.
“Using fresh brain tissue from living human donors has provided us with the opportunity to investigate the brain without the confounding factors inherent in postmortem tissue analysis,” said Alexander W. Charney, MD, PhD, co-senior author of the study and associate professor of Psychiatry, Genetic and Genomic Sciences, Neuroscience, and Neurosurgery at Icahn Mount Sinai and co-director of the Living Brain Project. “We thereby reveal more precise insights into the prevalence and functions of AaI editing in the human brain. Critically, our findings do not negate, but rather provide, missing context for the use of postmortem brain tissues in AaI regulation research. Understanding these differences helps advance our understanding of brain function and disease through the lens of RNA editing modifications, which can potentially lead to better diagnostic and therapeutic approaches.”
The research team will further analyze the RNA editing data to better understand its implications and identify potential therapeutic targets for Parkinson’s disease. They are also expanding the research to include emerging work from this cohort that focuses on gene expression, proteomics, and multiomics of the living brain.
“By leveraging the unique, transdisciplinary nature of the Living Brain Project, we can turn a cutting-edge clinical care modality like deep brain stimulation into a platform to gain unprecedented insights into the biology of the human brain that will lead to new therapeutic opportunities,” said Brian Kopell, MD, co-senior author of the study, director of the Center for Neuromodulation at Mount Sinai and co-director of the Living Brain Project.