We will test the hypothesis that the superior cognitive abilities of humans compared to rodents is, at least in part, the result of an evolutionary increas in the ability of human astrocytes to control synapse formation and function compared to rodent astrocytes. Astrocytes are a major cell type in the brain that constitute at least one third of rodent and human brain cells. Long thought to be passive support cells, studies from many labs over the past 15 years have shown that astrocytes powerfully control the formation, function, and plasticity of synapses in the central nervous system (CNS). Could the superior cognitive abilities of humans be due to an evolutionary advance in astrocytic control of synaptic formation and/or function? We have developed new methods to purify both rodent and human astrocytes. These new methods will enable us to directly test our hypothesis. To address this hypothesis, we will take three different approaches. First we will use next generation RNA-Seq sequencing to determine and compare the transcriptomes of mouse and human astrocytes. A prediction of our hypothesis is that human astrocytes may secrete synaptic signals that are quantitatively or qualititavely different than those secreted by rodent astrocytes. The function of the human specific genes identified will therefore be further assessed for potential synaptic functions in Approach 2. Second, we will directly compare the ability of mouse and human astrocytes to stimulate synapse formation and function. We will also determine whether novel human astrocyte genes identified in approach 1 that encode for secreted proteins can stimulate synapse formation or function. Human genes that strongly control synapse formation or function will then be expressed in mouse astrocytes in transgenic mice to determine if they have enhanced cognitive abilities. In our final third approach, we will use modern metabolomics methods to elucidate the small chemical signaling molecules secreted by mouse and human astrocytes, with a focus on identifying novel astrocyte secreted chemicals that control synaptic function. The new molecular insight these studies provide about human astrocytes will also provide the foundation for investigations of pathological changes of astrocytes in human neurological disorders and reveal how malfunction of astrocytes leads to neurodevelopmental disorders such as autism and neuropsychiatric disorders with unique manifestations in human emotion and behavior, such as autism, anxiety disorder, and depression.
Our goal is to test the hypothesis that the superior cognitive abilities of humans compared with rodents is due to an evolutionary advance in the abilities of human astrocytes to control synapse formation and function. The proposed experiments will explore this using 3 different approaches (1) to use RNA---seq to determine and compare the rodent and human astrocyte transcriptomes, (2) to directly compare the effects of rodent and human astrocytes on synapse formation and function, and (3) to determine and compare the rodent and human astrocyte secreted metabolome. These experiments will advance our understanding of what it means to be human and lead to better understanding of the cause and treatment of human neurological and psychiatric diseases.
