Investigations into Serum Components Which Support Proliferation in Culture: The Crucial Role of Albumin-Associated Lipids

Abstract

Serum is a ubiquitous additive to culture media despite its complex and heterogeneous composition, which can affect experimental reproducibility. Development of a defined serum-free culture medium would improve experimental consistency; however, the environmental requirements for proliferation which are provided by serum remain unclear. To determine how serum supports growth of cells in culture, I used a combination of live-cell imaging and liquid chromatography-mass spectrometry (LC-MS) to investigate serum components that enable sustained proliferation in culture. Importantly, the primary serum components that enable proliferation were identified as trace metals and serum lipids. Moreover, despite access to a broad range of lipid species, albumin-bound lipids were selectively depleted from media during cell proliferation, and a combination of these lipid classes with essential soluble serum components was sufficient to support cell proliferation in the absence of serum. Utilizing the serum-free media as a tool to investigate variables which influence consumption, I found that lipid scavenging occurs through a mass action mechanism, independent of FA structure and non-competitive with other albumin-associated lipid classes. The critical role of lipid scavenging in sustaining cell proliferation in culture was further supported by the finding that impairments to lipid synthesis had minimal effects on proliferation, while disruption of exogenous FA utilization effectively reduced cell proliferation in culture. These results advance our knowledge of serum components that support proliferation in culture, particularly the role of environmental lipids, and provide a serum-free culture medium that may be applied to various cell lines.