General questions

(i) How does the extracellular microenvironment regulate cellular behaviour?

(ii) How do organelles achieve their intracellular position and mechanical stability in cells?

(iii) How do pathogens hijack the principles of the cell-to-matrix interplay?

Immune cells are very fast-moving cells. On their journey, these migratory cells have to find their way through crowded three-dimensional mazes (Kameritsch & Renkawitz, Trends in Cell Biology). Whereas some cell types such as mesenchymal cells proteolytically digest the environment on their path, immune cells typically migrate without digesting or remodelling their environment. Given the cumulative distance of all immune cells in the human body of more than 100,000 km per hour, they otherwise would perforate the body with more than two million kilometers of tunnels per day. To discover how these extremely fast cells navigate through the dense meshwork of interstitial tissue fibres without harming other cells, we built obstacle courses for immune cells in reconstituted environments (Kroll et al, Current Protocols). Thereby, we discovered that immune cells use their nucleus as a ruler to probe their surroundings for the largest pores — and thereby find the path of least resistance (Renkawitz et al, Nature). Further, we discovered that microtubules are functionally important to coordinate the exploratory fronts of dendritic cells that are simultaneously probing the 3D microenvironments (Kopf et al, Journal of Cell Biology; Renkawitz et al, Nature).

Selected Literature:

Schmitt et al, bioRxiv 2024

Kroll & Renkawitz, EMBO reports 2024

Kroll et al, EMBO J  2023

Kameritsch & Renkawitz, Trends in Cell Biology 2020

Renkawitz et al, Nature 2019

Whereas in vivo experiments are truly physiological, they do not allow for precise manipulation of environmental parameters and are elaborate for the discovery of detailed molecular mechanisms. In contrast, in vitro  experiments on two-dimensional (2D) substrates (e.g. cell culture dishes) enable faster manipulations, but increasing knowledge points to substantial differences in cellular mechanisms in 2D and three-dimensional (3D) environments. To bridge this gap, we and others developed micro-engineered tissue-mimetic assays to combine the advantage of precise manipulations in 2D assays with the presence of complex 3D microenvironments. Specifically, we implemented the methodology of micro-engineered ”pillar forests’ to study cell migration in vitro in 3D with precisely defined microenvironmental parameters (Renkawitz et al., Methods in Cell Biology). Shortly, these devices provide a 3D migration environment made of PDMS (polydimethylsiloxane), in which two closely adjacent surfaces are interconnected by micron-sized structures such as pillars (or microchannels). Thereby, these devices represent a flattened approximation of complex 3D environments with the advantage of cellular confinement in one plane (XY) close to the imaging surface, enabling high-resolution single-cell imaging. We complement these assays with experimentation in collagen matrices, ex vivo tissue explants, and in vivo approaches.

Selected Literature:

Ruiz et al, bioRxiv 2024

Kroll et al, Current Protocols 2022

Clausen et al, Eur J Immunology 2022

Renkawitz et al, Methods in Cell Biology 2018

Almost all moving cells employ the actin cytoskeleton as an intracellular force generator to move forward. We discovered that amoeboid cells (such as dendritic cells) adapt their actin cytoskeleton dynamics to the adhesiveness of the migratory substrate (Renkawitz et al, Nature Cell Biology). Thereby we could show that not tracks of adhesive substrates but gradients of chemoattractants dictate the path of amoeboid cells, endowing these cells with extraordinary flexibility and enabling them to traverse almost every type of tissue (Renkawitz & Sixt, EMBOreports).

Selected Literature:

Braun et al, researchsquare (preprint) 2024

Hons et al, Nature Immunology 2018

Renkawitz & Sixt, EMBOreports 2010

Lämmermann et al, Blood  2009

Renkawitz et al, Nature Cell Biology 2009

Current knowledge on the molecular mechanisms and cell biological principles of immune cell biology (such  as  cell migration) is often based on studies utilizing knockout mice, which however hampers screening of large numbers of candidate components due to its time and resource consuming nature. To circumvent this bottleneck, conditionally immortalised hematopoietic precursor cells (Hoxb8 cells) with myeloid and lymphoid potential have been established by the Häcker Lab (Redecke et al, Nature Methods 2013). We recently contributed in showing that Hoxb8 cells can be differentiated into migratory DCs functionally indistinguishable from their primary counterparts (bone-marrow derived DCs) (Leithner et al, Eur J Immunol). Importantly, Hoxb8-FL cells can be efficiently targeted via CRISPR mediated gene editing (Leithner et al, Eur J Immunol). Thus, we employ immortalised hematopoietic precursor cells (Hoxb8 cells) as an accessible cellular model for genetic engineering, including genetic knockouts and fluorescent tagging.

Selected Literature:

Leithner et al, Eur J Immunol 2018