Multiscale imaging of organ-specific inflammation – our scientific concept

Innate immune responses in vivo

Figure 1: Inflammation is a common, fast, and innate response of the immune system to sterile or infectious tissue damage or autoimmune triggers aiming at tissue repair and maintaining organ function. Such innate immune responses involve different bone marrow-derived and tissue-resident immune cells that interact with each other, with the local endothelium and with the inflamed tissue microenvironment. In principle, these cellular and molecular mechanisms define organ specificity of innate immune responses and the effect on organ function.

However, while a substantial number of mechanisms involved in the regulation of inflammation has been described in the past, their relevance for the individual course and outcome of inflammation and of organspecific differences in vivo is not clear due to a lack of research tools to monitor inflammation in situ, locally and systemically.

Fundamental questions remain concerning the dynamics of distinct innate immune cell populations, their sequence of occurrence, activation and interaction at inflammatory sites, the heterogeneity and specificity of immune cell responses in different organs, and their individual contribution to the decision between curative and destructive inflammation.

To address this unmet challenge our interdisciplinary team develops and applies a novel multiscale imaging strategy that uniquely will cover the continuum from the behaviour of individual immune, endothelial and tissueforming cells to functional consequences of inflammation in various organs to the entire organisms (mouse and man) in vivo.

Dynamics and outcome of inflammatory responses

Figure 2: Innate immune cell responses (orange curves) are initiated by various triggers in multiple diseases (A) followed by (B) acute inflammation, impairing organ function (blue curves). If neutralisation of the inflammatory triggers is successful, the immune response will be terminated and the organ function will be restored (D). However, overshooting inflammation can lead to fatal loss of organ function (C) while other mechanisms may lead to chronic inflammation associated with organ dysfunction (E).

While such mechanisms have been partly described in vitro it is now important to monitor their molecular and cellular dynamics, organ-specificity and relevance for organ function in vivo. This is our major scientific aim and we will develop and employ a novel and unique multiscale imaging strategy to study the interplay of organspecific innate immune responses and organ function in vivo.

Biomedical imaging

Figure 3: Imaging is well suited to analyse biological processes such as the innate immune response addressed here. However, each imaging modality can only record a limited set of parameters in a given ‘biological volume’ (cell vs. tissue vs. whole-body) with a specific maximal spatial and temporal resolution. Therefore, a holistic spatiotemporal analysis of molecular and cellular processes in the living organism across scales, from cells to tissues to organs, and from minutes to days, is needed to permit a higher level of understanding of organ-specific innate immune cell dynamics and their impact on organ function in different diseases.

This can only be achieved by the development of a novel imaging paradigm – multiscale imaging – that uniquely integrates emergent molecular and cellular information from different temporal and spatial scales in a single experimental or clinical setup in vivo. We will integrate information from optical, intravital and whole-body imaging modalities through technological, chemical biology, mathematical and computational strategies to visualise the behaviour of individual cells, cells in tissues and organs and cells in whole organisms. Importantly, our multiscale imaging strategy allows for translation of information from basic research in disease models to clinical research in patients and vice versa.

Chemical biology strategy

Figure 4: In addition to the bioorthogonal targeting strategy, we will also develop several other chemical biology-based strategies to target and label specific cells and assess their inflammatory and metabolic activity. Notable examples include (1) small molecules binding to alarmins or serving as metabolic substrates, (2) classical genetically encoded fluorescent proteins, (3) the aforementioned genetically encoded uptake mechanisms for substrates such as radioactive iodine and (4) hypoxia-sensors, allowing us to image oxygen-depleted tissues. Within the context of inflammation, our interest is not limited to immune cells, but we will also label bacteria by synthesizing selectively labelled oligosaccharides that are preferentially taken up and metabolized by certain bacteria. Finally, we will use nanostructures to assess endothelial permeability during inflammation.

In summary, we will develop and apply biochemical and chemical strategies to target immune cells, bacteria, and the endothelial barrier. Our strategy relies on a modular chemical approach, allowing to switch between different labels and thus imaging modalities, ranging from fluorescence microscopy to PET and MRI.

Mathematical & computational strategy

Figure 5: The mathematical/computational techniques used for bridging scales will not be restricted to those projects in which they are developed. On the contrary, using joint software platforms and additional support by WWU in our INF project to facilitate the application of the developed computational tools, all CRC projects are supposed to benefit from the novel machine learning, pattern recognition, interactive visualization and multiscale data analysis and
management tools, which will help to create and test new biomedical hypotheses.

Vice versa, these tools will be designed and adapted to optimally answer biomedical questions and to fully exploit the associated imaging and experimental data. We expect a mutual stimulation of the biomedical research (which is raised to a new level by the availability of multiscale data analysis) and the development of novel mathematical/computational concepts (which are triggered by biomedical ideas).

Deliverables and perspectives

Figure 6: Beyond our immediate aim to apply multiscale strategies in order to solve important biomedical questions in inflammation, we have a clear translational long-term goal, which is the introduction of novel clinical imaging protocols into the diagnostics of inflammatory diseases to monitor and guide existing and emerging immunemodulatory therapies.

Our concept will be established in phases where initially (a) a tight cooperation between CRC projects driving biomedical questions (left) and those developing multiscale strategies (right) will set the basis for a dynamic interaction between models and methods, disciplines and individual research groups. Deliverables from this initial phase will be new hypotheses and methodologies (b), that will in turn pose new questions and challenges for the respective discipline/field, but also drive other disciplines and fields (re-cycling and cross-over). Longterm (c), all fields together aim at clinical translation of novel biological concepts and imaging strategies.

This process will by no means be a one way street from mouse to man. Instead, we expect clinical data and findings to feed back into basic science leading to new hypotheses that again require preclinical testing (reverse translation). Our framework will consequently stimulate the development of novel methodologies requiring the design of fresh mathematical algorithms, imaging tracers and chemical approaches.