Forward programming of hiPSCs via the transcription factor ETV2: rapid, reproducible, and cost-effective generation of highly enriched, functional endothelial cells.

AIMS: Endothelial cell (EC) dysfunction plays a key role in the initiation and progression of cardiovascular disease. However, studying these disorders in ECs from patients is challenging, hence the use of human induced pluripotent stem cells (hiPSCs) and their in vitro differentiation into ECs represents a very promising approach. Still, the generation of hiPSC-derived ECs (hECs) remains demanding as a cocktail of growth factors and an intermediate purification step are required for hEC enrichment. Therefore, we probed the utility of a forward programming approach using transgenic hiPSC lines. METHODS AND RESULTS: We have used the transgenic hiPSC line PGP1 ETV2 iso2 to explore the in vitro differentiation of hECs via doxycycline-dependent induction of the transcription factor ETV2 and compared these with a standard differentiation protocol for hECs using non-transgenic control hiPSCs. The transgenic hECs were highly enriched without an intermediate purification step and expressed - as non-transgenic hECs and HUVECs - characteristic EC markers. The viability and yield of transgenic hECs were strongly improved by applying EC growth medium during differentiation. This protocol was successfully applied in two more transgenic hiPSC lines yielding reproducible results with low line-to-line variability. Transgenic hECs displayed typical functional properties, such as tube formation and LDL uptake, and a more mature phenotype than non-transgenic hECs. Transgenic hiPSCs preferentially differentiated into the arterial lineage, this was further enhanced by adding a high VEGF concentration to the medium. We also demonstrate that complexing lentivirus with magnetic nanoparticles and application of a magnetic field enables efficient transduction of transgenic hECs. CONCLUSIONS: We have established a highly efficient, cost-effective, and reproducible differentiation protocol for the generation of functional hECs via forward programming. The transgenic hECs can be genetically modified and are a powerful tool for disease modelling, tissue engineering, and translational purposes.

Trigeminal ganglion and sensory nerves suggest tactile specialization of elephants.

Sensory nerves are information bottlenecks giving rise to distinct sensory worlds across animal species.1 Here, we investigate trigeminal ganglion2,3 and sensory nerves4 of elephants. The elephant trigeminal ganglion is very large. Its maxillary branch, which gives rise to the infraorbital nerve innervating the trunk, has a larger diameter than the animal's spinal cord, i.e., trunk innervation is more substantive than connections of the brain to the rest of the body. Hundreds of satellite cells surround each trigeminal neuron, an indication of exceptional glial support to these large projection neurons.5-7 Fiber counts of Asian elephant infraorbital nerves of averaged 4,00,000 axons. The infraorbital nerve consists of axons that are ∼10 µm thick and it has a large diameter of 17 mm, roughly 3 times as thick as the optic and 6 times as thick as the vestibulocochlear nerve. In most mammals (including tactile specialists) optic nerve fibers8-10 greatly outnumber infraorbital nerve fibers,11,12 but in elephants the infraorbital nerve fiber count is only slightly lower than the optic nerve fiber count. Trunk innervation (nerves and ganglia) weighs ∼1.5 kg in elephant cows. Our findings characterize the elephant trigeminal ganglion as one of the largest known primary sensory structures and point to a high degree of tactile specialization in elephants.