Molecular Crowding – (in Cell Culture)

Macromolecular crowding (MMC) is an intrinsic and ubiquitous feature in biological cells. We find MMC in the first bacterial cell and see it culminating in the intricate extracellular matrix (ECM) that evolved in multicellular organisms. Research work on MMC started with the observation that biological cellular systems are crammed with macromolecules. The interior of cells is teeming with enzymes, transport systems, and nucleotide assemblies. In addition, eukaryotic cells possess a three-layered cytoskeleton adding confinement to an already packed cytoplasm. Likewise, the extracellular space of multicellular organisms comprises an ECM consisting of fibrillar proteins, such as collagen or elastin, surrounded by an amorphous gel-like ground substance glycoproteins and proteoglycans and their hydration shells. Together, they provide mechanical resilience to the tissues of vertebrates while forming a crowded and structural microenvironment that in turn creates confinement for other macromolecules. Surprisingly, most biochemical and cell culture experiments are still done in non-crowded, highly aqueous solutions. Here, we shall discuss the shortcomings of contemporary cell culture and emphasize the benefits of applying MMC to cell culture models of tissues. MMC can be achieved by adding water-soluble macromolecules to the culture medium. Not only is this technically feasible, it also moves in vitro biology toward a higher physiological level, allowing the design of more meaningful cell-based assays and enabling tissue engineering of matured and physiologically relevant tissue-like assemblies