Current opinion in toxicology最新文献

Reproduction is a remarkably intricate process involving the interaction of multiple cell types and organ systems unfolding over long periods of time and that culminates with the production of gametes. The initiation of germ cell development takes place during embryogenesis but only completes decades later in humans. The complexity inherent to reproduction and its study has long hampered our ability to decipher how environmental agents disrupt this process. Single-cell approaches provide an opportunity for a deeper understanding of the action of toxicants on germline function and analyze how the response to their exposure is differentially distributed across tissues and cell types. In addition to single-cell RNA sequencing, other single-cell or nucleus level approaches such as ATAC-sequencing and multi-omics have expanded the strategies that can be implemented in reproductive toxicological studies to include epigenomic and the nuclear transcriptomic data. Here we will discuss the current state of single-cell technologies and how they can best be utilized to advance reproductive toxicological studies. We will then discuss case studies in two model organisms (Caenorhabditis elegans and rat) studying different environmental exposures (alcohol and e-cigarettes respectively) to highlight the value of single-cell and single-nucleus approaches for reproductive biology and reproductive toxicology.

Human exposure to the metal lead (Pb) is prevalent and associated with adverse neurodevelopmental and neurodegenerative outcomes. Pb disrupts normal brain function by inducing oxidative stress and neuroinflammation, altering cellular metabolism, and displacing essential metals. Prior studies on the molecular impacts of Pb have examined bulk tissues, which collapse information across all cell types, or in targeted cells, which are limited to cell autonomous effects. These approaches are unable to represent the complete biological implications of Pb exposure because the brain is a cooperative network of highly heterogeneous cells, with cellular diversity and proportions shifting throughout development, by brain region, and with disease. New technologies are necessary to investigate whether Pb and other environmental exposures alter cell composition in the brain and whether they cause molecular changes in a cell-type-specific manner. Cutting-edge, single-cell approaches now enable research resolving cell-type-specific effects from bulk tissues. This article reviews existing Pb neurotoxicology studies with genome-wide molecular signatures and provides a path forward for the field to implement single-cell approaches with practical recommendations.

The utilization of transcriptomic studies identifying profiles of gene expression, especially in toxicogenomics, has catapulted next-generation sequencing to the forefront of reproductive toxicology. An innovative yet underutilized RNA sequencing technique emerging into this field is single-cell RNA sequencing (scRNA-seq), which provides sequencing at the individual cellular level of gonad tissue. ScRNA-seq provides a novel and unique perspective for identifying distinct cellular profiles, including identification of rare cell subtypes. The specificity of scRNA-seq is a powerful tool for reproductive toxicity research, especially for translational animal models including zebrafish. Studies to date not only have focused on ‘tissue atlassing’ or characterizing what cell types make up different tissues but have also begun to include toxicant exposure as a factor that this review aims to explore. Future scRNA-seq studies will contribute to understanding exposure-induced outcomes; however, the trade-offs with traditional methods need to be considered.

The European Chemicals Strategy for Sustainability requests to include a mixture assessment factor (MAF) into the safety assessment of chemicals, in order to account for the elevated risks of chemical mixtures. This text first reflects on the conceptual background of the MAF, and then provides an overview of current stakeholder positions and of the studies attempting to quantify an appropriate size of the MAF.

Stakeholders from industry, civil society organizations (NGOs), and regulatory authorities have already put forth statements regarding the perceived advantages and disadvantages of the MAF approach, sometimes without providing detailed arguments. A consensus seems to emerge that the so-called MAF_factor is not a suitable instrument, due to its indiscriminatory nature that penalizes even chemicals that contribute only marginally to the mixture risk. Members of the larger MAF_ceiling family, in particular the MAF_exact, overcome this limitation and are therefore suggested as the way forward.

The advanced single-cell RNA sequencing (scRNA-seq) technology enables the measurement of gene expression levels and identification of cell-specific markers in individual cells, and the revealing of cell types, providing valuable insights into cell behavior. ScRNA-seq has emerged as an effective method for detecting rare cell populations, cellular heterogeneity, and cell-to-cell crosstalk under physiology and pathology conditions, thereby advancing the revolution of toxicology research. In this review, we first briefly introduce the concept of hepatotoxicity and nephrotoxicity, along with their underlying mechanisms. We then summarize the single-cell sequencing technology, with an emphasis on single-cell isolation techniques, particularly for the most used droplet-based methods. Finally, we review the recent advances in the application of single-cell RNA sequencing in studying hepatotoxicity and nephrotoxicity. Overall, this review provides a comprehensive understanding of the recent advances in hepatotoxicity and nephrotoxicity studies at a single-cell resolution.

Defining mechanisms of immunotoxicity is complicated by the many cell types that comprise the immune system, their phenotypic heterogeneity, distribution in tissues throughout the body, and complexity of in vivo interactions. Single-cell RNA-sequencing (scRNA-seq) methods hold promise for determining how chemical exposures alter gene expression and phenotype of individual immune cell phenotypes, leading to adverse effects on immune function. Using arsenic as a case study, this review will examine challenges in defining mechanisms of immunotoxicity and highlight findings from recent studies that have addressed immunotoxicological questions with scRNA-seq. Advancements in immunotherapeutic development driven by single-cell sequencing technologies will be discussed, along with how these state-of-the art methods may be applied to accelerate immunotoxicity testing in future studies. We will finally consider how cell-type-specific gene expression data can be leveraged to glean immune profiles from existing gene expression data, improving our understanding of immunotoxicity and ability to assess the health impacts of immunotoxic chemicals.

Breast cancer is a heterogeneous suite of diseases, with likely strong, but still poorly understood, environmental etiologies. New advances in single cell methods are now poised to help us understand how environmental exposures, such as air and water pollutants, diet, personal and consumer care products, and social factors, may promote the development of aggressive breast cancers. In this review, we describe how dissociated and spatial single cell transcriptomic analyses can be used to advance our understanding how our environment impacts breast carcinogenesis through the view of frameworks such as the Hallmarks of Cancer and the Key Characteristics of Carcinogens.

Neurotoxicological research faces the challenge of linking biological changes resulting from exposures to neuronal function. An additional challenge is understanding cell-type-specific differences and selective vulnerabilities of distinct neuronal populations to toxic insults. Single-cell RNA-sequencing (scRNA-seq) allows for measurement of the transcriptome of individual cells. This makes it a valuable tool for validating and characterizing cell types present in multi-cell type samples in complex tissue or cell culture models, but also for understanding how different cell types respond to toxic insults. Pathway analysis of differentially expressed genes can provide in-depth insights into underlying cell-type-specific mechanisms of neurotoxicity. Toxicological data often has to be translated to outcomes for human health which requires an understanding of inter-species differences. Transcriptomic data aids in understanding these differences, including understanding the developmental timelines of different species. We believe that scRNA-seq holds exciting promises for future neurotoxicological research.