Hydrogel-Based Artificial Cells for Energy Generation and Communication

Natural cells are highly complex microreactors that can be regarded as the basic building blocks of life. They serve as inspiration for artificial cells (ACs) in which certain structural and functional features are mimicked with the goal of creating ACs that mimic life-like properties¹. The focus is often on a single key property that assists to support or interact with their natural role models, here mammalian cells. Functions can be implemented using a variety of building blocks, either natural or synthetic. Further, hydrogels are a relevant option to serve as a structural scaffold since it creates an ‘intracellular’ environment akin to the dense cytosolic environment found in mammalian cells.<br/>In this project, two essential cellular functions are explored: Energy generation and cellular communication.<br/>Energy generation is essential for creating a self-sustaining system that can work out of equilibrium and to facilitate a wide array of functions that requires energy. In mammalian cells, mitochondria are responsible for the chemically driven adenosine triphosphate (ATP) synthesis. Here, mitochondria are used as a natural ATP producing subunit in gelatin methacryloyl (GelMA)-based ACs². Specifically, hepatocytes are employed as donor cells to isolate mitochondria. The maintained inner membrane potential, respiration and ATP production is confirmed in buffer and upon encapsulation in GelMA disks of the isolated mitochondria. Additionally, mitochondria are co-encapsulated with the ATP dependent enzyme firefly luciferase in GelMA particles to demonstrate the utilization of mitochondrially produced ATP in a cell-sized carrier, exemplified by the bioluminescent decarboxylation of D-luciferin.<br/>Communication is ubiquitous amongst multicellular assemblies and on the tissue level to moderate collective behaviour. Here, communication is explored between alginate-based ACs and HepG2 cells.³ First, a one-way signal transfer is established by equipping two different types of ACs with catalytic function by the use of metalloporphyrins as artificial enzymes that mimic cytochrome P450 enzyme (CYP450) activity. Metalloporphyrins are employed to catalyse a dealkylation and hydroxylation, exemplified by the conversion of resorufin ethyl ether to resorufin and coumarin to 7-hydroxycoumarin. The two fluorescent products diffuse into the neighbouring HepG2 cells, establishing a one way signal transfer as an important first step in communication.<br/>Taken together, these efforts work toward expanding the enzymatic functions that can be implemented in ACs by supplying energy to the system, here as mitochondrially produced ATP, moving towards a metabolically active AC. Further, the interaction between alginate-based ACs and HepG2 cells is explored, in one approach by utilizing metalloporphyrins as enzyme mimics as a synthetic approach to achieve catalytically active ACs.<br/>¹X. Qian<b>, I.N. Westense</b>e et al. (2020) <i>WIREs Nanomed Nanobiotechnol</i>. <b>13:</b> e1683<br/>²<b>I.N. Westensee</b>, E. Brodszkij et al. (2021) <i>Small</i> <b>17</b>:2007959.<br/>³X. Qian, <b>I.N. Westensee</b> et al. (2021) Angew. <i>Chem. Int. Ed., </i>DOI: 10.1002/ange.202104904.