Progesterone induction of tau phosphorylation during the differentiation of human embryonic stem cells into...

Tau phosphorylation is associated with neuronal division and differentiation in the fetal brain, in neuroblastoma cells, in the hibernating brains of ground squirrels and black bears, and in post-mitotic neurons in the Alzheimer's disease (AD) brain. The disassembly of the rigid microtubule structure of neurons for neuronal division and neurite remodeling requires the removal of the microtubule stabilizing protein tau via its phosphorylation.

To determine if tau phosphorylation is required during neural embryogenesis.

Using an in vitro human model of early embryonic development, human embryonic stem cells (hESC) were differentiated into embryoid bodies (EBs; akin to an early blastocyst) and then into neuroectodermal rosettes (akin to a rudimentary neural tube containing neuroectodermal precursor cells) upon treatment with progesterone. The neuroectodermal rosettes were then treated with and without LiCl (Cdk5 inhibitor) or roscovitine (GSK-3β inhibitor) and assayed for the expression of tau, P-tau, nestin (an early marker of neurogenesis), Cdk5 and GSK-3β.

Tau was not expressed in hESC, but tau expression and its phosphorylation increase upon progesterone-induced differentiation of hESC into neuroectodermal rosettes. Both Cdk5 and GSK-3β, enzymes associated with tau phosphorylation, were expressed in hESCs, EBs, and neuroectodermal rosettes. The GSK-3β inhibitor LiCl, but not the Cdk-5 inhibitor roscovitine, prevented tau phosphorylation and nestin expression and the formation of neuroectodermal precursor cells.

These preliminary results suggest that progesterone induces tau expression and its phosphorylation during the differentiation of neuroectodermal rosettes from hESC and suggest that tau and its phosphorylation is obligatory for neuronal precursor cell mitosis. The parallels between neural embryogenesis and neurodegeneration are discussed in the context of tau phosphorylation and the aberrant re-entry of neurons into the cell cycle in AD.