An international project that began in 2017 and aims to study brain cell types and their functions in humans, non-human primates and rodents has achieved an unprecedented scientific milestone: the first atlas of human brain cells. This map will allow scientists to study how the neural circuits that intervene in the complex behaviors that make us human work: from getting excited when listening to music, to making ethical decisions or being creative.
The brain is made up of almost one hundred billion neurons and a similar number of non-neuronal cells, such as astrocytes and oligodendrocytes. In 2017, the Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative-Cell Census Network (BICCN) or research network for the census of brain cells was created, which includes more than 30 laboratories from different fields, and which aimed to identify, characterize and map every type of brain cell in humans, non-human primates and mice.
Now, a series of 24 scientific articles that have been mostly published in the scientific journals Science and Science advances have shown the first relevant results: the detailed cellular composition of the human brain, both in adulthood and during its development. Thanks to the use of the most advanced technologies that until now were only applied to animal models, almost 3,000 types of human brain cells have been characterized.
“These studies could be a gateway to understanding the causes of diseases such as autism, or neurodegenerative diseases such as dementia, Parkinson’s, or Alzheimer’s”
These findings will help scientists identify which cell types are most affected by certain mutations that lead to neurological diseases. In the opinion of Javier Morante Oria, senior scientist of the CSIC at the Institute of Neurosciences (CSIC-UMH): “These studies represent a milestone in the history of biology, on par with the sequencing of the human genome in the year 2000, and “They could represent a gateway to understanding the causes of diseases such as autism or psychiatric disorders with an embryonic origin, or neurodegenerative diseases such as dementia, Parkinson’s, or Alzheimer’s, whose manifestation takes place in old age,” he told SMC. Spain.
They could also help develop new drugs against brain tumors, as indicated by two of the studies, which were carried out at the Karolinska Institute (Sweden).
Differences between each person’s brains
As Francisco José Esteban Ruiz, Professor of Cellular Biology at the University of Jaén, explains in an article published in Theconversation.com, the new map of brain cells has been carried out at “three different levels of study: the transcriptional, which indicates the function of cells through the expression of their genes; the epigenetic, which reveals how these genes are activated or deactivated by age and environmental factors; and the functional level, which refers, for example, to whether neurons excite or inhibit other neurons.”
The researchers, he points out, have not only found variations between brain regions, but also between the brains of each person, something that was expected and confirms that “there is not a single prototype of the human brain, but rather a wide genetic and response range.” to the environment, both in healthy individuals and in different disease states.”
According to this expert, the findings indicate that the brain is not at all homogeneous and that, although all brain cells share the same DNA, each of them uses different genes in different quantities, which gives rise to a level of diversity and specialization. amazing cell phone. Each brain area contains a specific set of cell types and in different functional states. In addition to helping us understand how the brain works, knowing them will help treat diseases whose brain alteration may be different depending on the person who suffers from it, such as brain tumors, epilepsy or multiple sclerosis, among others.
Other research reveals that although we share a basic brain cell structure with chimpanzees and gorillas, our neurons use different genes to connect and form circuits in the brain. A finding that means that small changes in neural connections could evolutionarily boost our cognitive abilities, such as complex reasoning and the creation of advanced languages.
Implications in disorders such as autism
The research project includes the study of the development of the human cerebral cortex from the prenatal stage and for many years after birth. More than 700,000 cells from 169 tissue samples from 106 donors have been analyzed in detail, which has allowed us to understand how various cells develop and differentiate in the brain, including the neurons that are responsible for emitting electrical signals.
These findings may have important implications in developmental disorders such as autism, as they indicate how small changes in complex cellular development can lead to conditions that profoundly affect social and communicative interaction. For example, by better understanding how neurons and glial cells develop and communicate with each other, we can begin to unravel why, in some people, this process differs and how this may impact the way they perceive and interact with others. the world.
The study also illuminates the subtle but significant differences in gene expression between girls and boys with respect to autism, providing a prism through which to examine why this disorder shows different rates of incidence and manifestation between genders.
“Regardless of the enormous value of each of the published results, the interdisciplinary effort demonstrated here allows us to move forward towards the common goal of knowing the development and functioning of the brain that makes us human. In addition to opening the doors to a new era of research into the origin of neurological diseases,” concludes Professor Ruiz.
