Engineering Light- and Pharmacologically Triggered Extracellular Biological Switches

Synthetic molecular switches are the key components to obtain control of mammalian cells. While the majority of the developed switches focuses on intracellular processes we now transfer concepts of synthetic biology out of the cell. In this context, we (i) engineered pharmacologically switchable viral vectors enabling precise control of the transfer of genetic information into cells and (ii) a synthetic extracellular matrix the mechanical properties of which can be modulated by light.

For the chemical switch controlling viral infectivity we used adeno-associated viral particles (AAV) due to their high relevance in gene-therapeutic approaches. We engineered the system in such a way that infection of the target cells occurs only in the presence of the rapamycin structural analog AP21967.

The development of the light-tunable extracellular matrix was realized by combining light-gated molecular switches from the field of optogenetics with cell-compatible polymers from material sciences. To this aim, we covalently coupled the cyanobacterial phytochrome Cph1 to an eight-arm polyethylene glycol forming a biohybrid hydrogel. Illumination with red light triggers dimerization of Cph1, thereby increasing the number of crosslinks within the hydrogel and thus enhancing its stiffness. Vice versa, far-red light illumination induces Cph1 monomerization and decreases hydrogel stiffness. Due to the fast switching properties of Cph1, the stiffness can be modulated reversibly within seconds. By incorporation of RGD cell adhesion motifs our hydrogel serves as suitable matrix for primary cells as well as cell lines. Since variations in matrix stiffness can modulate cellular signaling pathways and even direct cell differentiation, we propose that our engineered light-tunable extracellular matrix will be a unique tool for studying matrix-cell interactions.