Advances in Single-Cell Biology Using Mass Spectrometry

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Single-cell measurement science has numerous applications across the chemical, biomedical and life science fields. Understanding how seemingly homogeneous cell populations can differ at the metabolomic and proteomic level is possible using mass spectrometry, coupled with techniques such as capillary electrophoresis and fluorescent microscopy. Attempting to probe cells to such a high degree of detail poses a number of challenges: detectability is often low, as metabolites and proteins are present in miniscule quantities, so a highly sensitive technique such as MS is required. Because sampling large populations of cells also remains a challenge, attention is focused on developing higher-throughput techniques to obtain more and improved data.

The metabolome is particularly fascinating because it reflects the nature of a cell’s reactions to its dynamic environment.¹ Single cells provide a limited volume of product for analysis: in DNA or RNA analysis, this problem is overcome by amplification, which is not possible for molecules such as metabolites.

Single-cell analysis by MS has proven extremely valuable in discovering unique neuropeptides in a broad range of animal models, from complex mammalian species to simpler organisms such as sea slugs. Studies are able to combine information on novel peptides with the blueprint of the cell that produced it, formulating a unique profile.

Single-cell analysis

Matrix-assisted laser-desorption ionization (MALDI)-MS is widely used to characterize peptides and generate peptide profiles directly from an individual cell. However, detection limits can be low, so new methods have been devised using capillary electrophoresis-electrospray ionization (CE-ESI)-MS to achieve robust metabolomic measurements from isolated neurons.² Regardless of the technique used, single-cell analysis technology has undergone unprecedented advances to improve automation and detection capabilities. Traditional single-cell analysis techniques such as imaging and flow cytometry are making way for new methods using MALDI-MS, representing a convergence between technology and biology.

Conclusion

Techniques like MALDI-MS and FTMS lead the way in single-cell biology. Molecules involved in cell-to-cell signaling are particularly challenging to characterize, because early signaling events often take place within seconds of the stimulus.³ Instrument sensitivity is therefore critical for obtaining accurate and robust data. Solutions to the challenges surrounding single-cell measurements have evolved over the past few years. The creation of increasingly high-quality mass spectrometers has allowed the single-cell community to advance research into new areas. MS techniques are now combined with other chemically information-rich approaches, such as vibrational spectroscopy (infrared or Raman). Combining these data sets presents a new challenge, as there is currently no robust method for integrating data from MS-based platforms with non-MS-based platforms.

For more information on mass spectrometry instruments, please visit https://www.bruker.com/products/mass-spectrometry-and-separations.html. For more information about Professor Sweedler’s group, please visit http://www.chemistry.illinois.edu/faculty/Jonathan_Sweedler.html.

References

1. Fassenden, M. Metabolomics: small molecules, single cells. Nature2016, 540, 153–4.
2. Lapainis, T. Capillary electrophoresis with electrospray ionization mass spectrometric detection for single-cell metabolomics. Anal. Chem.2009, 81, 5858–64.
3. Spiller, D.G.; Wood, C.D. et al. Measurement of single-cell dynamics. Nature2010, 465, 736–45.

Rohan Thakur is executive vice president at Bruker Daltonics, 40 Manning Rd., Manning Park, Billerica, Mass. 01821, U.S.A.; tel.: 978-663-3660; e-mail:  [email protected]; www.bruker.com