Development of new biophysical approaches

Although less familiar than genetic or biochemical aspects, physical forces have in the last two decades emerged as key regulators of cellular processes. We are interested in mechanical regulation of cell functions, specifically in our immune system, where immune cells use forces to guide target selection and enhance target killing. Understanding the role of forces in cellular functions (mechanobiology) critically depends on tools to measure cellular forces and modulate the mechanical signals received by cells. We developed deformable microspheres, which greatly expand the range of physiological contexts where such biophysical measurements can be made. This includes immune cell-target interactions, but also multicellular tissue and even live animals (in vivo). Multiple technological challenges lie ahead to realize this full potential: more detailed and complete mechanical measurements can be achieved and will be required to measure force exertion by single cells in the native tissue context.

Dynamics of immune cell effector functions:

Interactions between immune cells and their targets often require rapid and large-scale changes of cellular shape and organization. We aim to understand the organizational principles behind such complex and dynamic behavior. Our approach is to make quantitative measurements of immune cell dynamics (force exertion & cytoskeletal reorganization), and how they change over time. By combining these measurements with cellular perturbations (KO of single genes), we can precisely determine how, where and when individual molecules regulate immune cell behavior. Moreover, by making controlled changes of our synthetic model targets (ligands, size, shape) we study how immune cell behavior is governed by chemical and physical properties of targets. So far, we mostly focused on phagocytosis by macrophages, and we revealed multiple new aspects of this behavior (e.g. the occurrence of teeth shown in the movie). Currently, we are particularly focused on the mechanisms of apoptotic cell removal by macrophages (see below). In the future, and in collaborations, we will expand our approach to other (innate and adaptive) immune cell types.

Molecular regulation of efferocytosis:

A strong current focus is on how macrophages clean up dead cells from tissues. They do this by engulfing and subsequently degrading them in a process called efferocytosis. This process is increasingly recognized as a target for therapeutic intervention in the context of atherosclerosis, neurodegenerative disease, and cancer. This form of engulfment is particularly challenging for immune cells, because dying cells are close in their surface chemistry and physical properties to healthy tissue cells. We recently showed that phosphatidylserine, the key trigger for sinking phagocytosis, induces unique phagocytic dynamics, including partial uptake of targets. We further performed a genome-wide CRISPR screen to identify regulators of this process. Now, we aim to reveal how known and novel regulators, including receptors, precisely function in efferocytosis.