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Tracing of pulmonary neuro-immune networks

Periodic Reporting for period 1 - TOPNIN (Tracing of pulmonary neuro-immune networks)

Reporting period: 2018-03-14 to 2020-03-13

The immune and nervous systems are the body’s main sensory systems that process and respond to environmental stimuli. Both systems can recall earlier challenges and events, leading to responses that are tailored to everchanging conditions. Immune responses are at the basis of keeping organisms healthy and protect them from outside aggressors. For instance, vaccines activate the immune system to mount a protective response against infectious diseases. Similarly, the brain allows us to learn from dangerous situations, so that they can be avoided later to avoid harm. Recent studies revealed that neuronal cells dialogue with immune cells in many of our organs that are exposed to the outside world, such as the lungs. These findings provoke a change in our understanding of how our body works to preserve health, but also lays the foundation for the discovery of new therapeutic strategies by taking advantages of this system. However, we currently lack the knowledge of how these “neuroimmune” networks look like, and how these two complex systems communicate.

In this project, entitled “Tracing of pulmonary neuro-immune networks” (TOPNIN), we focused on group 2 innate lymphoid cells (ILC2). These immune cells are strategically positioned at mucosal surfaces, regulating mucosal defense, tissue homeostasis and inflammation. In the lung, ILC2 contribute to the pathogenesis of allergic airway diseases, such as asthma. The host laboratory and other researchers have previously shown that ILC2 exert their function in the context of neuro-immune cell units that respond to environmental signals, steering mucosal immunity and repair. Nevertheless, the identity of the neuronal circuits innervating neuro-immune cell units and the nature of the bidirectional neuron-immune signals steering mucosal physiology remain elusive.

Therefore, in this Marie Skłodowska-Curie action, we developed new tools that allow us to discover the architecture of the system. We made use of the latest knowledge and tools from neuroscience and immunology, and combined this to develop a technology platform that we call KISS: Kindle of Intercellular Signals and Synapses. We used a combination of viruses that are labeled with fluorescent proteins to specifically label the neurons that communicate with immune cell subsets. By using light sheet microscopy, we were able to generate a three-dimensional atlas of the neurons that innervate these immune cells.
In addition, we combined advanced genetic and molecular approaches to determine how the neurons that innervate neuro-immune cell units in the lung, influence immune cell functions. We found that modulation of the neurons that connect to pulmonary immune cells leads to an altered function of the latter. This is a first step toward understanding how neuro-immune pathways steer homeostasis at the level of organs and the whole organism.

We are currently further exploring the interactions between other immune cells and neuronal networks, not only in the lung, but also in other organs. We seek to unravel the ‘language’ of neuro-immune communication and to discover the different dialects in various organs. In this way, we will gain a better understanding of this new paradigm in mammalian physiology, paving the way for the development of new strategies to promote health, and to prevent disease.
We aimed to elucidate the architecture of neuro-immune cell units, focusing on the communication between immune cells and neurons in the mouse lung. Furthermore, we wanted to functionally map the bidirectional signals in these neuro-immune cell units.

In TOPNIN, we developed a versatile platform that we call KISS: Kindle of Intercellular Signals and Synapses. It consists of a flexible combination of genetic tools used as tracers and molecular tools that can be used to study the architecture of neuro-immune cell units using high-resolution microscopy. In addition, it is easily extended with neuronal-specific genetic tools that allow the specific expression of proteins in defined subsets of neurons that have established a connection with immune cells. By doing so, the activity of these neurons can be controlled, and these neurons can be temporarily or permanently tagged to allow for further downstream analyses of the molecular identity of these neurons.

More specifically, in this project we generated a three-dimensional, high-resolution atlas of the neurons that connect to immune cell subsets in the mouse lung. We also revealed the molecular identity of these neurons. By controlling the activity of these neurons, we were able to determine how neuronal activity impacts on the function of these immune cells. In addition, we are currently addressing how immune cell activation impacts on neuronal functions. Together, these interdisciplinary approaches are the basis of an atlas of neuro-immune interactions, revealing the architecture and interactome of these recently described networks.

The results of this action have not been published in a peer-reviewed journal yet, as not all analyses that we deem necessary for a full report are finished. However, we secured additional competitive funding that will support the completion of the project. The procurement of this funding was already widely covered by national media in Portugal. Once the results have been published in a peer-reviewed journal, the results will also be shared with the general public through the various channels available at the Champalimaud Foundation.

Furthermore, this project serves as an important stepping stone for the researcher. During the development of this interdisciplinary project, various technical difficulties were overcome, new international scientific collaborations were established and additional competitive funding at various levels (personal, supervisor, laboratory) was secured.
In TOPNIN, we developed a platform that allows us to decipher neuro-immune crosstalk between pulmonary neurons and local immune cells. However, this platform is versatile and can directly be applied to other instances of neuro-immune units, comprising other cell types and located in other tissues. Therefore, TOPNIN will importantly contribute to the emerging body of knowledge on neuro-immune interaction.

Altogether, fundamental understanding of this new paradigm in mammalian physiology will pave the way for the development of much needed new treatment strategies of various chronic conditions and mucosal disorders.
Light sheet imaging of murine lung neurons