Periodic Reporting for period 4 - MECHEMGUI (The integration of mechanical and chemical signals in neuronal guidance)
Reporting period: 2022-12-01 to 2023-12-31
During the development of the brain, neurons extend long processes called “axons” through a crowded environment along well-defined pathways to connect to distant cells. These connections eventually give rise to highly complex neuronal networks, along which information is transmitted and processed throughout the body. Past research has identified a variety of small signalling molecules that cells in the brain secrete to tell developing neurons where to grow. However, these molecules alone cannot explain the complex neuronal growth patterns we see.
We previously showed that neurons also respond to mechanical cues, such as local tissue stiffness, suggesting that mechanical signals are likely an important missing part of the puzzle. However, how neurons feel tissue stiffness, and how mechanical (tissue stiffness) and chemical (small signalling molecules) signals work together to guide growing neurons during development is currently unknown. As defects in axon guidance can lead to a variety of so-called neurodevelopmental disorders, understanding how neuronal growth is regulated is crucial not only for our understanding of brain development but also for illuminating new facets of human diseases.
This project aimed to close this comprehension gap. By developing and combining state-of-the-art approaches in physics, engineering and biology, we investigated mechanosensitive molecular mechanisms that regulate neuronal growth and guidance. In particular, we developed new methods that allowed us to investigate how tissue stiffness impacts neuronal growth directly (through regulation of the forces exerted by neurons on their environment) and indirectly (by modulating chemical signalling pathways). Furthermore, we developed a mathematical model based on our findings, which illuminated the role of stiffness gradients in guiding axons through developing brain tissue.
We identified an intense cross-talk between chemical and mechanical signals. Changes in tissue stiffness led to changes in the chemical landscape in the developing brain and vice versa. Also, the way in which neurons responded to certain chemical signals was regulated by tissue stiffness. We identified molecular signalling pathways enabling neurons to integrate mechanical and chemical signals and confirmed their cross-talk in an in vivo system. Hence, our project unveiled new mechanisms of axon guidance with importance to brain development and potentially disease. The integration of mechanical and chemical signals by neurons identified here is likely also taking place in many other cell types, tissues and organ systems, thus opening many new avenues of future research.
We previously showed that neurons also respond to mechanical cues, such as local tissue stiffness, suggesting that mechanical signals are likely an important missing part of the puzzle. However, how neurons feel tissue stiffness, and how mechanical (tissue stiffness) and chemical (small signalling molecules) signals work together to guide growing neurons during development is currently unknown. As defects in axon guidance can lead to a variety of so-called neurodevelopmental disorders, understanding how neuronal growth is regulated is crucial not only for our understanding of brain development but also for illuminating new facets of human diseases.
This project aimed to close this comprehension gap. By developing and combining state-of-the-art approaches in physics, engineering and biology, we investigated mechanosensitive molecular mechanisms that regulate neuronal growth and guidance. In particular, we developed new methods that allowed us to investigate how tissue stiffness impacts neuronal growth directly (through regulation of the forces exerted by neurons on their environment) and indirectly (by modulating chemical signalling pathways). Furthermore, we developed a mathematical model based on our findings, which illuminated the role of stiffness gradients in guiding axons through developing brain tissue.
We identified an intense cross-talk between chemical and mechanical signals. Changes in tissue stiffness led to changes in the chemical landscape in the developing brain and vice versa. Also, the way in which neurons responded to certain chemical signals was regulated by tissue stiffness. We identified molecular signalling pathways enabling neurons to integrate mechanical and chemical signals and confirmed their cross-talk in an in vivo system. Hence, our project unveiled new mechanisms of axon guidance with importance to brain development and potentially disease. The integration of mechanical and chemical signals by neurons identified here is likely also taking place in many other cell types, tissues and organ systems, thus opening many new avenues of future research.
We have developed new experimental techniques and data analysis software to investigate how neurons feel and respond to the mechanical properties of their environment. These enabled us now to investigate how neurons and neural tissue respond to the stiffness of their environment.
We found that neurons and other cells do not adapt their own stiffness to that of their environment, which contradicts a long-standing paradigm in the field. However, neuronal forces increase on stiffer substrate, and so does the activity of the mechanosensitive ion channel Piezo1. We investigated how Piezo1 is activated and what its activity triggers inside of cells. We identified molecules that are involved in both chemical and mechanical signalling, which serve as interface between the two different types of signals.
Exploiting this knowledge, we showed that changes in tissue mechanics lead to changes in the chemical landscape of the developing brain and vice versa. Hence, the formation of functional neuronal circuits is not only regulated by chemical signals, as widely believed, but equally also by mechanical signals, and molecular signalling pathways triggered by chemical and mechanical signals are intimately linked. These complex interactions are likely also found in many other cell types, indicating that chemical and mechanical signals should not be considered in isolation.
We have disseminated our results so far in 22 peer-reviewed publications, 3 further manuscripts are currently found on bioRxiv. We published all codes and data analysis pipelines in open access platforms, facilitating their use by the wider community. Experimental approaches developed in this project have been picked up by the community. Furthermore, we contributed to the dissemination of this project by presenting its results in ~70 talks at international meetings and by organizing 7 international meetings about the topic. Finally, we actively participated in the education of undergraduate and graduate students through lectures, seminars, outreach events and lab placements, exciting them about the topic and getting them in touch with interdisciplinary research.
We found that neurons and other cells do not adapt their own stiffness to that of their environment, which contradicts a long-standing paradigm in the field. However, neuronal forces increase on stiffer substrate, and so does the activity of the mechanosensitive ion channel Piezo1. We investigated how Piezo1 is activated and what its activity triggers inside of cells. We identified molecules that are involved in both chemical and mechanical signalling, which serve as interface between the two different types of signals.
Exploiting this knowledge, we showed that changes in tissue mechanics lead to changes in the chemical landscape of the developing brain and vice versa. Hence, the formation of functional neuronal circuits is not only regulated by chemical signals, as widely believed, but equally also by mechanical signals, and molecular signalling pathways triggered by chemical and mechanical signals are intimately linked. These complex interactions are likely also found in many other cell types, indicating that chemical and mechanical signals should not be considered in isolation.
We have disseminated our results so far in 22 peer-reviewed publications, 3 further manuscripts are currently found on bioRxiv. We published all codes and data analysis pipelines in open access platforms, facilitating their use by the wider community. Experimental approaches developed in this project have been picked up by the community. Furthermore, we contributed to the dissemination of this project by presenting its results in ~70 talks at international meetings and by organizing 7 international meetings about the topic. Finally, we actively participated in the education of undergraduate and graduate students through lectures, seminars, outreach events and lab placements, exciting them about the topic and getting them in touch with interdisciplinary research.
We have advanced the field by providing new experimental tools and AI-based data analysis software to the community. Also, we have accumulated new knowledge in diverse areas of science, which we published in highly visible, cross-disciplinary journals. We identified mechanotransduction pathways in neurons, figured out how neurons integrate mechanical and chemical signals, and corroborated a strong link between chemical and mechanical signalling in an in vivo context. We showed that both the availability of key chemical signals in the developing brain and the response of neurons to these chemical signals are strongly influenced by the mechanical properties of the brain tissue. Similar phenomena are likely encountered in many other organ systems, opening many new avenues for future research.