Aging promotes lung function decline and susceptibility to chronic lung diseases, which are the third leading cause of death worldwide. Here, we use single cell transcriptomics and mass spectrometry-based proteomics to quantify changes in cellular activity states across 30 cell types and chart the lung proteome of young and old mice. We show that aging leads to increased transcriptional noise, indicating deregulated epigenetic control. We observe cell type-specific effects of aging, uncovering increased cholesterol biosynthesis in type-2 pneumocytes and lipofibroblasts and altered relative frequency of airway epithelial cells as hallmarks of lung aging. Proteomic profiling reveals extracellular matrix remodeling in old mice, including increased collagen IV and XVI and decreased Fraser syndrome complex proteins and collagen XIV. Computational integration of the aging proteome with the single cell transcriptomes predicts the cellular source of regulated proteins and creates an unbiased reference map of the aging lung. Aging impacts lung functionality and makes it more susceptible to chronic diseases. Combining proteomics and single cell transcriptomics, the authors chart molecular and cellular changes in the aging mouse lung, discover aging hallmarks, and predict the cellular sources of regulated proteins.

/pdf/an-atlas-of-the-aging-lung-mapped-by-single-cell-1ba1igwwvt.pdf

An atlas of the aging lung mapped by single cell transcriptomics and deep tissue proteomics.

Fluorescent tools have revolutionized our ability to probe biological dynamics, particularly at the cellular level. Fluorescent sensors have been developed on several platforms, utilizing either small-molecule dyes or fluorescent proteins, to monitor proteins, RNA, DNA, small molecules, and even cellular properties, such as pH and membrane potential. We briefly summarize the impressive history of tool development for these various applications and then discuss the most recent noteworthy developments in more detail. Particular emphasis is placed on tools suitable for single-cell analysis and especially live-cell imaging applications. Finally, we discuss prominent areas of need in future fluorescent tool development—specifically, advancing our capability to analyze and integrate the plethora of high-content data generated by fluorescence imaging.

A Critical and Comparative Review of Fluorescent Tools for Live-Cell Imaging.

Aging promotes lung function decline and susceptibility to chronic lung diseases, which are the third leading cause of death worldwide. We used single cell transcriptomics and mass spectrometry to quantify changes in cellular activity states of 30 cell types and the tissue proteome from lungs of young and old mice. Aging led to increased transcriptional noise, indicating deregulated epigenetic control. We observed highly distinct effects of aging on cell type level, uncovering increased cholesterol biosynthesis in type-2 pneumocytes and lipofibroblasts as a novel hallmark of lung aging. Proteomic profiling revealed extracellular matrix remodeling in old mice, including increased collagen IV and XVI and decreased Fraser syndrome complex proteins and Collagen XIV. Computational integration of the aging proteome and single cell transcriptomes predicted the cellular source of regulated proteins and created a first unbiased reference of the aging lung. The lung aging atlas can be accessed via an interactive user-friendly webtool at: https://theislab.github.io/LungAgingAtlas

/pdf/an-atlas-of-the-aging-lung-mapped-by-single-cell-2x1ymigfrw.pdf

An atlas of the aging lung mapped by single cell transcriptomics and deep tissue proteomics

Prodrug approaches represent an excellent solution to certain pharmaceutical issues commonly encountered in the drug discovery and development process. Along this line, the chemistry needed for the bio-reversible derivatization of drug functional groups for on-demand release is critical. In recent years, "click and release" approaches have shown great promise in the design of prodrugs because of their bioorthogonality and controlled bond-cleavage, which help ensure prodrug stability during circulation and ready cleavage at the desired site of action. This review highlights recent developments of this research field and discusses issues yet to be addressed.

Click and release: bioorthogonal approaches to "on-demand" activation of prodrugs.

Compositional diversity is a fundamental property in cell populations. Single-cell analysis promises new insight into this cellular heterogeneity on the genomic, transcriptomic, proteomic, and metabolomic levels. Mass spectrometry (MS) is a label-free technique that enables the multiplexed analysis of proteins, peptides, lipids, and metabolites in individual cells. The abundances of these molecular classes are correlated with the physiological states and environmental responses of the cells. In this Minireview, we discuss recent advances in single-cell MS techniques with an emphasis on sampling and ionization methods developed for volume-limited samples. Strategies for sample treatment, separation methods, and data analysis require special considerations for single cells. Ongoing analytical challenges include subcellular heterogeneity, non-normal statistical distributions of cellular properties, and the need for high-throughput, high molecular coverage and minimal perturbation.

Single-Cell Mass Spectrometry Approaches to Explore Cellular Heterogeneity.

Most current approaches for quantification of RNA species in their natural spatial contexts in single cells are limited by a small number of parallel analyses. Here we report a strategy to dramatically increase the multiplexing capacity for RNA analysis in single cells in situ. In this method, transcripts are detected by fluorescence in situ hybridization (FISH). After imaging and data storage, the fluorescence signal is efficiently removed by photobleaching. This enables the reinitiation of FISH to detect other RNA species in the same cell. Through reiterative cycles of hybridization, imaging and photobleaching, the identities, positions and copy numbers of a large number of varied RNA species can be quantified in individual cells in situ. Using this approach, we analyzed seven different transcripts in single HeLa cells with five reiterative RNA FISH cycles. This approach has the potential to detect over 100 varied RNA species in single cells in situ, which will have wide applications in studies of systems biology, molecular diagnosis and targeted therapies.

/pdf/multiplexed-single-cell-in-situ-rna-analysis-by-reiterative-34k0zkxca5.pdf

Multiplexed single-cell in situ RNA analysis by reiterative hybridization

Comprehensive RNA analyses in individual cells in their native spatial contexts promise to transform our understanding of normal physiology and disease pathogenesis. Here we report a single-cell in situ RNA analysis approach using switchable fluorescent oligonucleotides (SFO). In this method, transcripts are first hybridized by pre-decoding oligonucleotides. These oligonucleotides subsequently recruit SFO to stain their corresponding RNA targets. After fluorescence imaging, all the SFO in the whole specimen are simultaneously removed by DNA strand displacement reactions. Through continuous cycles of target staining, fluorescence imaging, and SFO removal, a large number of different transcripts can be identified by unique fluorophore sequences and visualized at the optical resolution. To demonstrate the feasibility of this approach, we show that the hybridized SFO can be efficiently stripped by strand displacement reactions within 30 min. We also demonstrate that this SFO removal process maintains the integrity of the RNA targets and the pre-decoding oligonucleotides, and keeps them hybridized. Applying this approach, we show that transcripts can be restained in at least eight hybridization cycles with high analysis accuracy, which theoretically would enable the whole transcriptome to be quantified at the single molecule sensitivity in individual cells. This in situ RNA analysis technology will have wide applications in systems biology, molecular diagnosis, and targeted therapies.

/pdf/single-cell-in-situ-rna-analysis-with-switchable-fluorescent-31tm8jbf1y.pdf

Single-Cell in Situ RNA Analysis With Switchable Fluorescent Oligonucleotides.

Understanding the composition, regulation, and function of complex biological systems requires tools that quantify multiple transcripts at their native cellular locations. However, the current multiplexed RNA imaging technologies are limited by their relatively low sensitivity or specificity, which hinders their applications in studying highly autofluorescent tissues, such as formalin-fixed paraffin-embedded (FFPE) tissues. To address this issue, here we develop a multiplexed in situ RNA profiling approach with a high sensitivity and specificity. In this approach, transcripts are first hybridized by target-specific oligonucleotide probes in pairs. Only when these two independent probes hybridize to the target in tandem will the subsequent signal amplification by oligonucleotide hybridization occur. Afterwards, horseradish peroxidase (HRP) is applied to further amplify the signal and stain the target with cleavable fluorescent tyramide (CFT). After imaging, the fluorophores are chemically cleaved and the hybridized probes are stripped by DNase and formamide. Through cycles of RNA staining, fluorescence imaging, signal cleavage, and probe stripping, many different RNA species can be profiled at the optical resolution. In applying this approach, we demonstrated that multiplexed in situ RNA analysis can be successfully achieved in both fixed, frozen, and FFPE tissues.

https://www.mdpi.com/2073-4409/10/6/1277/pdf

Highly Sensitive and Multiplexed In Situ RNA Profiling with Cleavable Fluorescent Tyramide.

The ability to comprehensively profile nucleic acids in individual cells in their natural spatial contexts is essential to advance our understanding of biology and medicine. Here, we report a novel method for spatial transcriptomics and genomics analysis. In this method, every nucleic acid molecule is detected as a fluorescent spot at its natural cellular location throughout the cycles of consecutive fluorescence in situ hybridization (C-FISH). In each C-FISH cycle, fluorescent oligonucleotide probes hybridize to the probes applied in the previous cycle, and also introduce the binding sites for the next cycle probes. With reiterative cycles of hybridization, imaging and photobleaching, the identities of the varied nucleic acids are determined by their unique color sequences. To demonstrate the feasibility of this method, we show that transcripts or genomic loci in single cells can be unambiguously quantified with 2 fluorophores and 16 C-FISH cycles or with 3 fluorophores and 9 C-FISH cycles. Without any error correction, the error rates obtained using the raw data are close to zero. These results indicate that C-FISH potentially enables tens of thousands (216 = 65,536 or 39 = 19,683) of different transcripts or genomic loci to be precisely profiled in individual cells in situ.

https://www.mdpi.com/1420-3049/25/21/4900/pdf

Highly Multiplexed Single-Cell In Situ RNA and DNA Analysis by Consecutive Hybridization

Provided herein are methods for multiplexed in situ analysis of biomolecules in a tissue. In particular, provided herein are methods for multiplexed single-cell in situ protein and nucleic acid profiling in fixed or fresh tissues, and also allows the investigation of the different cell compositions and their spatial organizations in intact tissues through consecutive cycles of probe hybridization, fluorescence imaging, and signal removal.

Cleavable fluorescent tyramide for sensitive and multiplexed analysis of biological samples

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