Scientists have described the mechanisms, unknown to date, involved in maintaining embryonic stem cells in the best possible state for their use in regenerative medicine. Their results, published in Nature Communications, will help to find novel stem-cell therapies for brain stroke, heart disease or neurodegenerative conditions like Alzheimer's or Parkinson's disease.
Embryonic stem cells (ESCs) are pluripotent cells that can grow into all somatic cell types - a characteristic that is extremely useful for researchers and regenerative medicine. There are two types of pluripotency: naïve and primed. The naïve state comes before the primed one during embryonic development. Naïve ESCs have the potential to differentiate into any cell types. Thus, they are more relevant in research. However, the naïve state is unstable, because naïve ESCs are constantly receiving signals that regulate the transition to the primed state and their self-renewal. Understanding the mechanisms that regulate the pluripotent states is important because they might help achieve long-term maintenance of stable naïve pluripotent stem cells in ESC cultures.
Traditionally, maintenance of naïve ESC cultures is based on the inhibition of two of the signalling pathways that regulate cell differentiation - aka as the 2i culture method. Recently, naïve ESCs have been maintained adopting a totally different approach, namely, the inhibition of Cdk8/19, a protein that regulates the expression of numerous genes, including the genes that help maintain the naïve state. "While the two approaches are used to culture naïve cells, little is known about the mechanisms involved," says the study lead.
Now, using proteomics, the large-scale characterisation of proteins coded in a genome, scientists have described a large number of the molecular events that help stabilise these valuable ESC. "This is the first time proteomics has been used in this context," says the first author of the article. "We analysed the mechanisms at a number of levels. First, we conducted phosphoproteomic analyses, studying phosphorylated proteins. Phosphorylation regulates protein functions (by activating or inhibiting them). Second, we analysed the expression of these proteins. Finally, we identified changes in metabolites (reaction intermediates or end products). With our integrated approach, we got an accurate picture of the causes of the high degree of plasticity of ESC," the author explains.
The results of the study might have implications for research on some types of cancer. We know that "the inhibition of Cdk8 leads to reduced cell proliferation in acute myeloid leukaemia by enhancing tumour suppressors", and that "Cdk8 is a colorectal cancer oncogene." "Cdk8 activity is somehow enigmatic, since its functions vary considerably with the cell environment," says the author. "We have identified a number of Cdk8 targets that were unknown until now. This can help understand the function this protein regulates in other biological contexts."
The study by the CNIO team shows the need for a greater focus on proteomics in cancer research strategies.
Dissection of two routes to na´ve pluripotency using different kinase inhibitors
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