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GPC4 Downregulation in iPSCs Promotes Differentiation into Dopaminergic Neurons that Rescue Parkinson's Disease Symptom

Review of "Enhanced differentiation of human induced pluripotent stem cells toward the midbrain dopaminergic neuron lineage through GLYPICAN‐4 downregulation" from STEM CELLS Translational Medicine by Stuart P. Atkinson

A recent STEM CELLS Translational Medicine article from researchers led by Rosanna Dono (Aix Marseille University, Marseille, France) [1] explored an alternative approach to the enhanced differentiation of human induced PSCs (iPSCs) into ventral midbrain dopaminergic (VMDA) neurons, which may form part of cell transplant therapies for Parkinson's disease [2]. Specifically, the authors focused on the cell membrane protein GLYPICAN‐4 (GPC4), a cell surface heparan sulfate proteoglycan that forms part of a family that regulate developmental processes by fine‐tuning cellular responses to extracellular proteins [3-5] and modulate the activity of those morphogens involved in ventral midbrain fate during development. Further evidence derives from previous research from the Dono lab (including a  STEM CELLS study), which suggested that Gpc4 downregulation in mouse embryonic stem cells (ESCs) promoted differentiation into functional dopaminergic neurons that improved motor recovery upon brain transplantation in a rat model of Parkinson's disease [6, 7].

Corti et al. first established that the stable downregulation of GPC4 expression in human iPSCs (GPC4sh-iPSCs) via short-hairpin RNA failed to negatively impact pluripotency and self-renewal; however, loss of GPC4 expression did impair the tumorigenic potential of iPSCs following in vivo transplantation in nude mice. The subsequent differentiation of GPC4sh-iPSCs via a previously described floor‐plate based differentiation strategy [8], which employs dual SMAD inhibition to generate neuroepithelial cells and the progressive activation of SHH, WNT, and FGF8 signaling pathways to induce VMDA progenitor identity, suggested that GPC4 loss prompted a higher propensity for the generation of VMDA progenitors without changes in proliferation or survival when compared to control iPSCs. Encouragingly, VMDA progenitors derived from GPC4sh-iPSCs also acquired a mature phenotype and a specific VMDA neuron identity upon exposure to neuronal differentiation signals.

The authors also assessed the ongoing VMDA differentiation of GPC4sh-iPSCs following transplantation into the denervated striatum of a Parkinson's disease rat model. Fascinatingly, the transplantation of GPC4sh-iPSCs after the early stage of in vitro VMDA differentiation fostered the eventual generation of VMDA progenitors in a significantly more efficient manner than control iPSCs, suggesting that the downregulation of GPC4 may represent an exciting strategy to generate iPSC-derived VMDA neurons in vivo.

The authors describe GPC4 downregulation as a safe and efficient means to enhance the generation of therapeutically relevant neural cells and anticipate that this strategy may lead to the establishment of human iPSCs lines suitable for translational applications.

For more on how the modulation of cell surface heparan sulfate proteoglycan expression may bring human iPSC-derived cell therapies closer to the clinical application in Parkinson's disease patients, stay tuned to the Stem Cells Portal!


References

  1. Corti S, Bonjean R, Legier T, et al., Enhanced differentiation of human induced pluripotent stem cells toward the midbrain dopaminergic neuron lineage through GLYPICAN-4 downregulation. STEM CELLS Translational Medicine 2021;10:725-742.
  2. Kalia LV and Lang AE, Parkinson's disease. The Lancet 2015;386:896-912.
  3. Yu C, Griffiths LR, and Haupt LM, Exploiting Heparan Sulfate Proteoglycans in Human Neurogenesis—Controlling Lineage Specification and Fate. Frontiers in Integrative Neuroscience 2017;11:28.
  4. Filmus J, Capurro M, and Rast J, Glypicans. Genome Biology 2008;9:224.
  5. Fico A, Maina F, and Dono R, Fine-tuning of cell signaling by glypicans. Cellular and Molecular Life Sciences 2011;68:923-929.
  6. Fico A, De Chevigny A, Egea J, et al., Modulating Glypican4 Suppresses Tumorigenicity of Embryonic Stem Cells While Preserving Self-Renewal and Pluripotency. STEM CELLS 2012;30:1863-1874.
  7. Fico A, de Chevigny A, Melon C, et al., Reducing Glypican-4 in ES Cells Improves Recovery in a Rat Model of Parkinson´s Disease by Increasing the Production of Dopaminergic Neurons and Decreasing Teratoma Formation. The Journal of Neuroscience 2014;34:8318.
  8. Nolbrant S, Heuer A, Parmar M, et al., Generation of high-purity human ventral midbrain dopaminergic progenitors for in vitro maturation and intracerebral transplantation. Nature Protocols 2017;12:1962-1979.