Nicotine containing products such as cigarettes, nicotine gums, chewing tobacco, and e-cigarettes have a high probability of causing wide ranging harmful effects on different organs of the developing embryo. Investigation is important to provide a basis for educating the public, of the effects, especially those who are pregnant, to avoid smoking when pregnant or considering having a family.
In addition to being a known risk for birth defects smoking is linked to adverse neurobehavioural, respiratory, cardiovascular, endocrine, and metabolic outcomes that can extend into adulthood. Nicotine is primarily responsible for these elevated risks, and the advent of e-cigarettes is reversing progress made towards reduction of tobacco use, according to the researchers.
Animals studies of maternal exposure to nicotine has been been well documented as demonstrating many detrimental effects on aspects of fetal development such as oxidative stress, increcreased inflammation, cellular damage, and impaired cell replication. Conducting such detailed investigations in humans is not feasible and effects of nicotine on the developing embryo has been poorly understood.
Advent of microdroplet based scRNA sequencing technology enables analyzing transcriptomes at the single cell levels within heterogeneous cell populations; integrated analysis of control and nicotine exposed EBs at this level enables quantitative assessment of cell type specific responses to nicotine.
To analyze effects of nicotine exposure on the transcriptomes of 12,500 cells generated from human embryonic stem cell derived embryoid bodies over 21 days scRNA sequencing was utilized.
Neural, liver, stromal, muscle, endothelial, and epithelial progenitors were included in analysis; results showed exposure to nicotine reduced cell viability, increased ROS, and decreased the size of embryoid bodies resulting in aberrant formation and differentiation. Exposure also altered cell cycling in various progenitor cells, and caused dysregulated cell to cell communication. Quantification showed an association with 5% reduction in epithelial cells after nicotine exposure; 4% increase in liver cells after nicotine exposure; and a considerable difference in relative proportion of genes that were affected by nicotine in each cell type, with muscle cells exhibiting the greatest number of differentially expressed genes.
Cell type specific changes in expression of genes implicated in metal toxicity, mitochondrial function, brain malformations, intellectual disability, muscle development and disease, lung disease, and Ca2+ associated arrhythmias affecting contractility of heart muscle cells were revealed with scRNA sequencing.
Nicotine exposure resulted in up or downregulation of certain genes in neural progenitor cells known to lead to amyloid formation, increased synaptic transmission, brain malformations, and intellectual disability; most upregulated genes in response were myosin chaperone protein genes involved in muscle development and disease.
Genes known to regulate amino acid acetylation and nutrient levels were downgraded in stromal cells after exposure, and liver cells demonstrated downregulation of genes related to lipid metabolism. Epithelial cells had reduced expression of genes associated with chronic obstructive pulmonary disease, cell type specific alterations in expression of genes related to suppression of glycolysis and endothelial cell dysfunction, and endothelial lumen formation during angiogenesis.
DEG patterns from progenitor cell populations indicated effects on cells derived from all three germ lines. The team plans to continue studying the mechanisms of nicotine induced fetal defects, hoping to discover biomarkers that can help to prevent, diagnose, and treat these diseases. In the future their hESC derived embryoid body model and single cell sequencing technology will be utilized to investigate wider effects of other harmful conditions on human embryonic development, as well as being used to optimize drug and environmental toxicity screening.
