Single-Cell Proteomics

Exploring the Protein Landscape One Cell at a Time

Introduction

Proteomics has transformed our understanding of biology by enabling scientists to study the full complement of proteins expressed in cells and tissues. Traditionally, proteomic studies analyzed bulk tissue samples, which provide averaged information from thousands or millions of cells. While useful, this approach masks the cell-to-cell variability that drives many important biological processes. Recent advances in technology have allowed scientists to study proteins at the level of individual cells, giving rise to the field of single-cell proteomics (SCP). This approach reveals the diversity and complexity of cellular behavior in unprecedented detail, providing insights into development, disease progression, immune responses, and potential personalized therapeutic strategies.

What is Single-Cell Proteomics?

Single-cell proteomics is the study of proteins in individual cells, as opposed to bulk populations of cells. Each cell in a tissue or organism can express proteins differently, reflecting its unique state, function, or response to its environment. Studying proteins at the single-cell level allows researchers to detect rare cell types, transient cell states, and subtle changes that would otherwise be invisible in averaged bulk data. SCP provides a high-resolution view of biological processes, enabling scientists to understand how heterogeneity among cells influences overall tissue function, disease progression, or treatment response. By quantifying protein abundance, modifications, and interactions in individual cells, SCP bridges the gap between molecular biology and systems biology, offering a more precise understanding of life at the cellular level.

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What’s New in Single-Cell Proteomics

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Published in final edited form as:
Curr Opin Biotechnol. 2024 April ; 86: 103077. doi:10.1016/j.copbio.2024.103077
HHS Public Access
Figure 1
In recent years, single-cell proteomics has undergone significant evolution, enabling the analysis of thousands of proteins within single cells. This progress is driven by advances in experimental design, with maturing label-free and multiplexed methods, optimized sample preparation, and innovations in separation techniques, including ultra-low-flow nanoLC. These factors collectively contribute to improved sensitivity, throughput and reproducibility. Cutting-edge mass spectrometry platforms and data acquisition approaches continue to play a critical role in enhancing data quality. Furthermore, the exploration of spatial proteomics with single-cell resolution offers significant promise for understanding cellular interactions giving rise to various phenotypes. Single-cell proteomics has far-reaching applications in cancer research, biomarker discovery and developmental biology. Here we provide a critical review recent advances in the field of single-cell proteomics.

Importance of Single-Cell Proteomics

Single-cell proteomics is transforming multiple areas of research because it reveals heterogeneity within seemingly uniform cell populations. In cancer research, for example, tumors are rarely homogeneous; they contain subpopulations of cells that may resist therapy or drive metastasis. SCP can identify these rare subpopulations, enabling more targeted treatments. In immunology, individual immune cells can respond differently to infections or vaccines. Single-cell studies allow researchers to map these variations and understand immune system function at a detailed level. Similarly, in developmental biology, cells undergo highly dynamic changes during differentiation. SCP can capture transient protein states that indicate cell fate decisions, helping scientists map the progression of development with high temporal resolution. Overall, SCP provides insights into how cells function individually and collectively, offering opportunities for precision medicine and novel therapeutic strategies.

Figure 2

Key Technologies in Single-Cell Proteomics

Recent technological innovations have made single-cell proteomics possible by overcoming the challenge of extremely low protein amounts per cell. One of the most prominent techniques is SCoPE-MS (Single-Cell Proteomics by Mass Spectrometry), which leverages a “carrier” proteome to amplify signals from low-abundance proteins, allowing hundreds of proteins to be identified and quantified in single cells. Another approach, nanoPOTS (Nanodroplet Processing in One Pot for Trace Samples), minimizes sample loss during protein extraction and preparation, enabling highly sensitive detection of proteins from individual cells. Other emerging methods include CyTOF (Cytometry by Time-of-Flight), which uses metal-labeled antibodies to measure dozens of proteins simultaneously, and microfluidic-based workflows that allow high-throughput single-cell sample handling. Together, these technologies provide researchers with the ability to explore the proteome at single-cell resolution, uncovering patterns and interactions that were previously inaccessible.

Figure 3
          Figure : Validating SCoPE-MS by classifying single cancer cells based on their proteomes.

Applications of Single-Cell Proteomics

The applications of SCP are wide-ranging and have already begun to reshape our understanding of biology. In cancer research, SCP allows scientists to uncover tumor heterogeneity, detect therapy-resistant cells, and map the signaling networks that drive metastasis. In immunology, single-cell proteomics provides insight into immune cell activation, communication, and diversity, revealing rare populations that orchestrate immune responses. Developmental biology also benefits from SCP, as it enables the study of dynamic protein changes during differentiation, mapping transient states that influence cell fate. Moreover, SCP supports drug discovery and precision medicine by identifying protein markers for rare or disease-relevant cells, monitoring responses to treatment, and guiding therapeutic strategies tailored to individual cellular landscapes. By capturing protein-level variation at single-cell resolution, SCP is transforming how scientists approach complex biological questions.

Challenges and Future Perspectives

Despite its transformative potential, single-cell proteomics faces several challenges. The small amount of protein in a single cell means that sample loss and sensitivity are critical issues. High variability in sample preparation and measurement can affect reproducibility, and the resulting datasets are large and complex, requiring advanced computational tools for analysis. However, ongoing technological advancements promise to overcome these limitations. Integration with single-cell transcriptomics and multi-omics approaches is providing a more holistic view of cellular states, while improvements in mass spectrometry, microfluidics, and machine learning are enabling higher throughput, deeper proteome coverage, and more precise quantification. In the coming years, SCP is expected to become a routine tool in research and clinical applications, helping scientists explore cellular heterogeneity, disease mechanisms, and personalized treatment strategies in unprecedented detail.

https://www.nature.com/articles/s41592-023-01828-9

Conclusion

Single-cell proteomics is a revolutionary approach that allows scientists to study proteins at the resolution of individual cells. By revealing cellular heterogeneity, mapping dynamic protein networks, and uncovering rare cell populations, SCP is transforming research in cancer, immunology, development, and precision medicine. As technologies continue to advance and integration with computational biology improves, single-cell proteomics will provide deeper insights into the complexity of life, enabling new discoveries and therapeutic innovations that were previously impossible to achieve with bulk analyses.

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