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Direct Reprogramming from Blood to Brain May Boost Complex Genetic Studies of Disease

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Review of “Transdifferentiation of human adult peripheral blood T cells into neurons” from PNAS by Stuart P. Atkinson

While the generation and differentiation of induced pluripotent stem cells (iPSCs) from patient samples may seem like an excellent approach to study complex genetic backgrounds in disease modeling [1], problems including line-to-line variability in differentiation potential, karyotypic instability, labor-intensive culture, and a lack of scalability. The direct conversion of patient-derived somatic cells to induced neuronal cells (iN cells) [2] may provide a means to avoid these problems and research led by Thomas C. Südhof and Marius Wernig (Stanford University, CA, USA) recently demonstrated the efficient and safe generation of iN cells from adult peripheral T cells employing non-integrating episomal vectors [3]. Can direct reprogramming from blood to brain boost the study of complex genetic effects on neuro-related diseases and disorders?

Tanabe et al. employed non-integrating episomal vectors encoding Brn2, Ascl1, Myt1l, and Ngn2 (“BAMN”) transcription factors shown to generate iN cells from human fibroblasts [4]. Initial reprogramming efforts with peripheral blood mononuclear cells (PBMCs) demonstrated that fresh and frozen cells from healthy adult donors of various ages, ethnicities all gave rise to morphologically complex iN cells, although with different reprogramming efficiencies. Inhibition of BMP- and TGF-β-signaling and activation of PKA-signaling improved reprogramming efficiency to a maximum to 6.2%, with the resultant iN cells displaying both passive and active neuronal membrane properties. While ROCK inhibition further improved neuron morphology, this did not provide for improved functional properties, with the stable neuronal identity of the iN cells not requiring the continued expression of the exogenous BAMN reprogramming factors. Overall, this reprogramming strategy permits the generation of over 50 thousand iN cells from just one milliliter of peripheral blood in a single step without the need for initial expansion

Following these optimization steps, the authors then studied direct reprogramming of the more defined CD3+ T cell population, discovering that their efficient reprogramming strategy generated cells expressing multiple pan-neuronal markers, displaying passive and active neuronal membrane properties, with the added potential to make synaptic connections. The team evidenced this claim by demonstrating prominent neurotransmitter receptor-mediated inhibitory and excitatory postsynaptic currents (PSCs), the formation of a synaptic network when cultured with human iPSC-derived neurons, and the production of evoked PSCs by the activating surrounding axons via extracellular field stimulation.

Overall, this study describes an easy and efficient method to generate induced neural cells from CD3+ T cells, a defined, homogeneous, and readily accessible donor cell population, in a strategy the authors hope will aid the construction of informative disease models through the analysis of patient-derived genetic backgrounds in relevant cell types.

For more on direct reprogramming from blood to brain and complex genetic studies of disease, stay tuned to the Stem Cells Portal!

References

  1. Takahashi K, Tanabe K, Ohnuki M, et al., Induction of pluripotent stem cells from adult human fibroblasts by defined factors. Cell 2007;131:861-72.
  2. Vierbuchen T, Ostermeier A, Pang ZP, et al., Direct conversion of fibroblasts to functional neurons by defined factors. Nature 2010;463:1035-41.
  3. Tanabe K, Ang CE, Chanda S, et al., Transdifferentiation of human adult peripheral blood T cells into neurons. Proceedings of the National Academy of Sciences 2018;115:6470-6475.
  4. Pang ZP, Yang N, Vierbuchen T, et al., Induction of human neuronal cells by defined transcription factors. Nature 2011;476:220-3.