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Huffman RG, Leduc A, Wichmann C, Di Gioia M, Borriello F, Specht H, Derks J, Khan S, Khoury L, Emmott E, Petelski AA, Perlman DH, Cox J, Zanoni I, Slavov N. Prioritized mass spectrometry increases the depth, sensitivity and data completeness of single-cell proteomics. Nat Methods 2023; 20:714-722. [PMID: 37012480 PMCID: PMC10172113 DOI: 10.1038/s41592-023-01830-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2022] [Accepted: 02/27/2023] [Indexed: 04/05/2023]
Abstract
Major aims of single-cell proteomics include increasing the consistency, sensitivity and depth of protein quantification, especially for proteins and modifications of biological interest. Here, to simultaneously advance all these aims, we developed prioritized Single-Cell ProtEomics (pSCoPE). pSCoPE consistently analyzes thousands of prioritized peptides across all single cells (thus increasing data completeness) while maximizing instrument time spent analyzing identifiable peptides, thus increasing proteome depth. These strategies increased the sensitivity, data completeness and proteome coverage over twofold. The gains enabled quantifying protein variation in untreated and lipopolysaccharide-treated primary macrophages. Within each condition, proteins covaried within functional sets, including phagosome maturation and proton transport, similarly across both treatment conditions. This covariation is coupled to phenotypic variability in endocytic activity. pSCoPE also enabled quantifying proteolytic products, suggesting a gradient of cathepsin activities within a treatment condition. pSCoPE is freely available and widely applicable, especially for analyzing proteins of interest without sacrificing proteome coverage. Support for pSCoPE is available at http://scp.slavovlab.net/pSCoPE .
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Affiliation(s)
- R Gray Huffman
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Center and Barnett Institute, Northeastern University, Boston, MA, USA
| | - Andrew Leduc
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Center and Barnett Institute, Northeastern University, Boston, MA, USA
| | - Christoph Wichmann
- Computational Systems Biochemistry Research Group, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Marco Di Gioia
- Boston Children's Hospital and Harvard Medical School, Boston, MA, USA
| | | | - Harrison Specht
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Center and Barnett Institute, Northeastern University, Boston, MA, USA
| | - Jason Derks
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Center and Barnett Institute, Northeastern University, Boston, MA, USA
| | - Saad Khan
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Center and Barnett Institute, Northeastern University, Boston, MA, USA
| | - Luke Khoury
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Center and Barnett Institute, Northeastern University, Boston, MA, USA
| | - Edward Emmott
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Center and Barnett Institute, Northeastern University, Boston, MA, USA
- Centre for Proteome Research, Department of Biochemistry and Systems Biology, University of Liverpool, Liverpool, UK
| | - Aleksandra A Petelski
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Center and Barnett Institute, Northeastern University, Boston, MA, USA
- Parallel Squared Technology Institute, Watertown, MA, USA
| | - David H Perlman
- Merck Exploratory Sciences Center, Merck Sharp and Dohme Corp., Cambridge, MA, USA
| | - Jürgen Cox
- Computational Systems Biochemistry Research Group, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Ivan Zanoni
- Boston Children's Hospital and Harvard Medical School, Boston, MA, USA
| | - Nikolai Slavov
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Center and Barnett Institute, Northeastern University, Boston, MA, USA.
- Parallel Squared Technology Institute, Watertown, MA, USA.
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Derks J, Leduc A, Wallmann G, Huffman RG, Willetts M, Khan S, Specht H, Ralser M, Demichev V, Slavov N. Increasing the throughput of sensitive proteomics by plexDIA. Nat Biotechnol 2023; 41:50-59. [PMID: 35835881 PMCID: PMC9839897 DOI: 10.1038/s41587-022-01389-w] [Citation(s) in RCA: 61] [Impact Index Per Article: 61.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Accepted: 06/13/2022] [Indexed: 01/22/2023]
Abstract
Current mass spectrometry methods enable high-throughput proteomics of large sample amounts, but proteomics of low sample amounts remains limited in depth and throughput. To increase the throughput of sensitive proteomics, we developed an experimental and computational framework, called plexDIA, for simultaneously multiplexing the analysis of peptides and samples. Multiplexed analysis with plexDIA increases throughput multiplicatively with the number of labels without reducing proteome coverage or quantitative accuracy. By using three-plex non-isobaric mass tags, plexDIA enables quantification of threefold more protein ratios among nanogram-level samples. Using 1-hour active gradients, plexDIA quantified ~8,000 proteins in each sample of labeled three-plex sets and increased data completeness, reducing missing data more than twofold across samples. Applied to single human cells, plexDIA quantified ~1,000 proteins per cell and achieved 98% data completeness within a plexDIA set while using ~5 minutes of active chromatography per cell. These results establish a general framework for increasing the throughput of sensitive and quantitative protein analysis.
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Affiliation(s)
- Jason Derks
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Proteomics Center, and Barnett Institute, Northeastern University, Boston, MA, USA.
| | - Andrew Leduc
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Proteomics Center, and Barnett Institute, Northeastern University, Boston, MA, USA
| | - Georg Wallmann
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Proteomics Center, and Barnett Institute, Northeastern University, Boston, MA, USA
| | - R Gray Huffman
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Proteomics Center, and Barnett Institute, Northeastern University, Boston, MA, USA
| | | | - Saad Khan
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Proteomics Center, and Barnett Institute, Northeastern University, Boston, MA, USA
| | - Harrison Specht
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Proteomics Center, and Barnett Institute, Northeastern University, Boston, MA, USA
| | - Markus Ralser
- Charité - Universitätsmedizin Berlin, Berlin, Germany
- Molecular Biology of Metabolism Laboratory, The Francis Crick Institute, London, UK
| | | | - Nikolai Slavov
- Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Proteomics Center, and Barnett Institute, Northeastern University, Boston, MA, USA.
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Leduc A, Huffman RG, Cantlon J, Khan S, Slavov N. Exploring functional protein covariation across single cells using nPOP. Genome Biol 2022; 23:261. [PMID: 36527135 PMCID: PMC9756690 DOI: 10.1186/s13059-022-02817-5] [Citation(s) in RCA: 44] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Accepted: 11/18/2022] [Indexed: 12/23/2022] Open
Abstract
BACKGROUND Many biological processes, such as cell division cycle and drug resistance, are reflected in protein covariation across single cells. This covariation can be quantified and interpreted by single-cell mass spectrometry with sufficiently high throughput and accuracy. RESULTS Here, we describe nPOP, a method that enables simultaneous sample preparation of thousands of single cells, including lysing, digesting, and labeling individual cells in volumes of 8-20 nl. nPOP uses piezo acoustic dispensing to isolate individual cells in 300 pl volumes and performs all subsequent sample preparation steps in small droplets on a fluorocarbon-coated glass slide. Protein covariation analysis identifies cell cycle dynamics that are similar and dynamics that differ between cell types, even within subpopulations of melanoma cells delineated by markers for drug resistance priming. Melanoma cells expressing these markers accumulate in the G1 phase of the cell cycle, display distinct protein covariation across the cell cycle, accumulate glycogen, and have lower abundance of glycolytic enzymes. The non-primed melanoma cells exhibit gradients of protein abundance, suggesting transition states. Within this subpopulation, proteins functioning in oxidative phosphorylation covary with each other and inversely with proteins functioning in glycolysis. This protein covariation suggests divergent reliance on energy sources and its association with other biological functions. These results are validated by different mass spectrometry methods. CONCLUSIONS nPOP enables flexible, automated, and highly parallelized sample preparation for single-cell proteomics. This allows for quantifying protein covariation across thousands of single cells and revealing functionally concerted biological differences between closely related cell states. Support for nPOP is available at https://scp.slavovlab.net/nPOP .
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Affiliation(s)
- Andrew Leduc
- grid.261112.70000 0001 2173 3359Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Proteomics Center, and Barnett Institute, Northeastern University, Boston, MA 02115 USA
| | - R. Gray Huffman
- grid.261112.70000 0001 2173 3359Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Proteomics Center, and Barnett Institute, Northeastern University, Boston, MA 02115 USA
| | | | - Saad Khan
- grid.261112.70000 0001 2173 3359Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Proteomics Center, and Barnett Institute, Northeastern University, Boston, MA 02115 USA
| | - Nikolai Slavov
- grid.261112.70000 0001 2173 3359Departments of Bioengineering, Biology, Chemistry and Chemical Biology, Single Cell Proteomics Center, and Barnett Institute, Northeastern University, Boston, MA 02115 USA
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Petelski AA, Emmott E, Leduc A, Huffman RG, Specht H, Perlman DH, Slavov N. Multiplexed single-cell proteomics using SCoPE2. Nat Protoc 2021; 16:5398-5425. [PMID: 34716448 PMCID: PMC8643348 DOI: 10.1038/s41596-021-00616-z] [Citation(s) in RCA: 81] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Accepted: 08/12/2021] [Indexed: 11/09/2022]
Abstract
Many biological systems are composed of diverse single cells. This diversity necessitates functional and molecular single-cell analysis. Single-cell protein analysis has long relied on affinity reagents, but emerging mass-spectrometry methods (either label-free or multiplexed) have enabled quantifying >1,000 proteins per cell while simultaneously increasing the specificity of protein quantification. Here we describe the Single Cell ProtEomics (SCoPE2) protocol, which uses an isobaric carrier to enhance peptide sequence identification. Single cells are isolated by FACS or CellenONE into multiwell plates and lysed by Minimal ProteOmic sample Preparation (mPOP), and their peptides labeled by isobaric mass tags (TMT or TMTpro) for multiplexed analysis. SCoPE2 affords a cost-effective single-cell protein quantification that can be fully automated using widely available equipment and scaled to thousands of single cells. SCoPE2 uses inexpensive reagents and is applicable to any sample that can be processed to a single-cell suspension. The SCoPE2 workflow allows analyzing ~200 single cells per 24 h using only standard commercial equipment. We emphasize experimental steps and benchmarks required for achieving quantitative protein analysis.
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Affiliation(s)
- Aleksandra A Petelski
- Department of Bioengineering, Northeastern University, Boston, MA, USA
- Barnett Institute, Northeastern University, Boston, MA, USA
| | - Edward Emmott
- Department of Bioengineering, Northeastern University, Boston, MA, USA
- Barnett Institute, Northeastern University, Boston, MA, USA
- Centre for Proteome Research, Department of Biochemistry & Systems Biology, University of Liverpool, Liverpool, UK
| | - Andrew Leduc
- Department of Bioengineering, Northeastern University, Boston, MA, USA
- Barnett Institute, Northeastern University, Boston, MA, USA
| | - R Gray Huffman
- Department of Bioengineering, Northeastern University, Boston, MA, USA
- Barnett Institute, Northeastern University, Boston, MA, USA
| | - Harrison Specht
- Department of Bioengineering, Northeastern University, Boston, MA, USA
- Barnett Institute, Northeastern University, Boston, MA, USA
| | - David H Perlman
- Department of Bioengineering, Northeastern University, Boston, MA, USA
- Merck Exploratory Sciences Center, Merck Sharp & Dohme Corp., Cambridge, MA, USA
| | - Nikolai Slavov
- Department of Bioengineering, Northeastern University, Boston, MA, USA.
- Barnett Institute, Northeastern University, Boston, MA, USA.
- Department of Biology, Northeastern University, Boston, MA, USA.
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Specht H, Emmott E, Petelski AA, Huffman RG, Perlman DH, Serra M, Kharchenko P, Koller A, Slavov N. Single-cell proteomic and transcriptomic analysis of macrophage heterogeneity using SCoPE2. Genome Biol 2021; 22:50. [PMID: 33504367 PMCID: PMC7839219 DOI: 10.1186/s13059-021-02267-5] [Citation(s) in RCA: 239] [Impact Index Per Article: 79.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Accepted: 01/07/2021] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND Macrophages are innate immune cells with diverse functional and molecular phenotypes. This diversity is largely unexplored at the level of single-cell proteomes because of the limitations of quantitative single-cell protein analysis. RESULTS To overcome this limitation, we develop SCoPE2, which substantially increases quantitative accuracy and throughput while lowering cost and hands-on time by introducing automated and miniaturized sample preparation. These advances enable us to analyze the emergence of cellular heterogeneity as homogeneous monocytes differentiate into macrophage-like cells in the absence of polarizing cytokines. SCoPE2 quantifies over 3042 proteins in 1490 single monocytes and macrophages in 10 days of instrument time, and the quantified proteins allow us to discern single cells by cell type. Furthermore, the data uncover a continuous gradient of proteome states for the macrophages, suggesting that macrophage heterogeneity may emerge in the absence of polarizing cytokines. Parallel measurements of transcripts by 10× Genomics suggest that our measurements sample 20-fold more protein copies than RNA copies per gene, and thus, SCoPE2 supports quantification with improved count statistics. This allowed exploring regulatory interactions, such as interactions between the tumor suppressor p53, its transcript, and the transcripts of genes regulated by p53. CONCLUSIONS Even in a homogeneous environment, macrophage proteomes are heterogeneous. This heterogeneity correlates to the inflammatory axis of classically and alternatively activated macrophages. Our methodology lays the foundation for automated and quantitative single-cell analysis of proteins by mass spectrometry and demonstrates the potential for inferring transcriptional and post-transcriptional regulation from variability across single cells.
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Affiliation(s)
- Harrison Specht
- Department of Bioengineering and Barnett Institute, Northeastern University, Boston, MA, 02115, USA.
| | - Edward Emmott
- Department of Bioengineering and Barnett Institute, Northeastern University, Boston, MA, 02115, USA
- Present Address: Department of Biochemistry, Centre for Proteome Research, University of Liverpool, Liverpool, L69 7ZB, UK
| | - Aleksandra A Petelski
- Department of Bioengineering and Barnett Institute, Northeastern University, Boston, MA, 02115, USA
| | - R Gray Huffman
- Department of Bioengineering and Barnett Institute, Northeastern University, Boston, MA, 02115, USA
| | - David H Perlman
- Department of Bioengineering and Barnett Institute, Northeastern University, Boston, MA, 02115, USA
- Present Address: Merck Exploratory Sciences Center, Merck Sharp & Dohme Corp., 320 Bent St., Cambridge, MA, 02141, USA
| | - Marco Serra
- Department of Biomedical Informatics, Harvard Medical School, Boston, MA, 02115, USA
| | - Peter Kharchenko
- Department of Biomedical Informatics, Harvard Medical School, Boston, MA, 02115, USA
| | - Antonius Koller
- Department of Bioengineering and Barnett Institute, Northeastern University, Boston, MA, 02115, USA
| | - Nikolai Slavov
- Department of Bioengineering and Barnett Institute, Northeastern University, Boston, MA, 02115, USA.
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Specht H, Emmott E, Petelski AA, Huffman RG, Perlman DH, Serra M, Kharchenko P, Koller A, Slavov N. Single-cell proteomic and transcriptomic analysis of macrophage heterogeneity using SCoPE2. Genome Biol 2021; 22:50. [PMID: 33504367 DOI: 10.1101/665307] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Accepted: 01/07/2021] [Indexed: 05/27/2023] Open
Abstract
BACKGROUND Macrophages are innate immune cells with diverse functional and molecular phenotypes. This diversity is largely unexplored at the level of single-cell proteomes because of the limitations of quantitative single-cell protein analysis. RESULTS To overcome this limitation, we develop SCoPE2, which substantially increases quantitative accuracy and throughput while lowering cost and hands-on time by introducing automated and miniaturized sample preparation. These advances enable us to analyze the emergence of cellular heterogeneity as homogeneous monocytes differentiate into macrophage-like cells in the absence of polarizing cytokines. SCoPE2 quantifies over 3042 proteins in 1490 single monocytes and macrophages in 10 days of instrument time, and the quantified proteins allow us to discern single cells by cell type. Furthermore, the data uncover a continuous gradient of proteome states for the macrophages, suggesting that macrophage heterogeneity may emerge in the absence of polarizing cytokines. Parallel measurements of transcripts by 10× Genomics suggest that our measurements sample 20-fold more protein copies than RNA copies per gene, and thus, SCoPE2 supports quantification with improved count statistics. This allowed exploring regulatory interactions, such as interactions between the tumor suppressor p53, its transcript, and the transcripts of genes regulated by p53. CONCLUSIONS Even in a homogeneous environment, macrophage proteomes are heterogeneous. This heterogeneity correlates to the inflammatory axis of classically and alternatively activated macrophages. Our methodology lays the foundation for automated and quantitative single-cell analysis of proteins by mass spectrometry and demonstrates the potential for inferring transcriptional and post-transcriptional regulation from variability across single cells.
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Affiliation(s)
- Harrison Specht
- Department of Bioengineering and Barnett Institute, Northeastern University, Boston, MA, 02115, USA.
| | - Edward Emmott
- Department of Bioengineering and Barnett Institute, Northeastern University, Boston, MA, 02115, USA
- Present Address: Department of Biochemistry, Centre for Proteome Research, University of Liverpool, Liverpool, L69 7ZB, UK
| | - Aleksandra A Petelski
- Department of Bioengineering and Barnett Institute, Northeastern University, Boston, MA, 02115, USA
| | - R Gray Huffman
- Department of Bioengineering and Barnett Institute, Northeastern University, Boston, MA, 02115, USA
| | - David H Perlman
- Department of Bioengineering and Barnett Institute, Northeastern University, Boston, MA, 02115, USA
- Present Address: Merck Exploratory Sciences Center, Merck Sharp & Dohme Corp., 320 Bent St., Cambridge, MA, 02141, USA
| | - Marco Serra
- Department of Biomedical Informatics, Harvard Medical School, Boston, MA, 02115, USA
| | - Peter Kharchenko
- Department of Biomedical Informatics, Harvard Medical School, Boston, MA, 02115, USA
| | - Antonius Koller
- Department of Bioengineering and Barnett Institute, Northeastern University, Boston, MA, 02115, USA
| | - Nikolai Slavov
- Department of Bioengineering and Barnett Institute, Northeastern University, Boston, MA, 02115, USA.
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Abstract
The performance of ultrasensitive liquid chromatography and tandem mass spectrometry (LC-MS/MS) methods, such as single-cell proteomics by mass spectrometry (SCoPE-MS), depends on multiple interdependent parameters. This interdependence makes it challenging to specifically pinpoint the sources of problems in the LC-MS/MS methods and approaches for resolving them. For example, a low signal at the MS2 level can be due to poor LC separation, ionization, apex targeting, ion transfer, or ion detection. We sought to specifically diagnose such problems by interactively visualizing data from all levels of bottom-up LC-MS/MS analysis. Many software packages, such as MaxQuant, already provide such data, and we developed an open source platform for their interactive visualization and analysis: Data-driven Optimization of MS (DO-MS). We found that in many cases DO-MS not only specifically diagnosed LC-MS/MS problems but also enabled us to rationally optimize them. For example, by using DO-MS to optimize the sampling of the elution peak apexes, we increased ion accumulation times and apex sampling, which resulted in a 370% more efficient delivery of ions for MS2 analysis. DO-MS is easy to install and use, and its GUI allows for interactive data subsetting and high-quality figure generation. The modular design of DO-MS facilitates customization and expansion. DO-MS v1.0.8 is available for download from GitHub: https://github.com/SlavovLab/DO-MS . Additional documentation is available at https://do-ms.slavovlab.net .
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Affiliation(s)
- R Gray Huffman
- Department of Bioengineering , Northeastern University , Boston , Massachusetts 02115 , United States.,Barnett Institute , Northeastern University , Boston , Massachusetts 02115 , United States
| | - Albert Chen
- Department of Bioengineering , Northeastern University , Boston , Massachusetts 02115 , United States.,Barnett Institute , Northeastern University , Boston , Massachusetts 02115 , United States
| | - Harrison Specht
- Department of Bioengineering , Northeastern University , Boston , Massachusetts 02115 , United States.,Barnett Institute , Northeastern University , Boston , Massachusetts 02115 , United States
| | - Nikolai Slavov
- Department of Bioengineering , Northeastern University , Boston , Massachusetts 02115 , United States.,Barnett Institute , Northeastern University , Boston , Massachusetts 02115 , United States.,Department of Biology , Northeastern University , Boston , Massachusetts 02115 , United States
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Li AK, Schattenkerk ME, Huffman RG, Ross JS, Malt RA. Hypersecretion of submandibular saliva in male mice: trophic response in small intestine. Gastroenterology 1983; 84:949-55. [PMID: 6187621] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
The submandibular salivary gland of the male mouse and its secretions contain growth-promoting factors that accelerate cell proliferation in vitro and also have effects on the gastrointestinal tract in vivo. We therefore stimulated salivary secretion with isoproterenol for studies of the effects of submandibular saliva on intestinal cell proliferation; only submandibular glands respond to isoproterenol by releasing epidermal growth factors and other growth factors into the saliva. Submandibular sialadenectomized and sham sialadenectomized male mice on pair-feeding schedules were given isoproterenol intraperitoneally for 1 wk. A 44% increase in ribonucleic acid and a 13% increase in deoxyribonucleic acid were observed in the jejunum of animals with intact submandibular glands (p less than 0.001). In the ileum, there was a 26% increase in ribonucleic acid, a 47% increase in deoxyribonucleic acid, and a 28% increase in deoxyribonucleic acid specific activity (p less than 0.001). Morphometric measurements showed a 28% increase in villous height (p less than 0.001). No differences were found in colonic mucosa. Submandibular saliva increases the nucleic-acid content of mucosal cells and the villous height in the small intestine of male mice, presumably in part because of the growth factors it contains; a systemic metabolic change could also be present.
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