Stem Cells International

Review Article

Cellular Programming and Reprogramming: Sculpting Cell Fate for the Production of Dopamine Neurons for Cell Therapy

Table 1

Summary of the studies that have used transcription factors and other markers to obtain and enhance the production of vmDA neurons in vitro, through overexpression and selection strategies.


TF and lineage markers	Overexpression	Selection	Direct reprogramming	Comments

Pitx3	▴ mRNA levels of phenotypic markers of vmDA neurons after in vitro differentiation and the percentage of Pitx3/TH neurons after grafting [78]	▴ Enrichment for vmDA neurons [27], which restored motor function in PD models [159, 179]	iDA neurons from human and mouse fibroblasts and mouse astrocytes (in combination) iDA from Pitx3-eGFP ki mouse cells sorted for Pitx3 showed some motor improvement after transplantation in 6-OHDA mice [142, 149, 151, 180]	Specific marker for all postmitotic vmDA neurons

Nurr1	▴ mRNA levels of phenotypic markers of vmDA neurons after in vitro differentiation and the percentage of TH+ neurons after transplantation leading to behavioural recovery with no signs of teratoma [78, 146, 147, 153, 181–183]		iDA neurons from human and mouse fibroblasts and mouse astrocytes (in combination) [142, 148–151, 180]	Regulates terminal acquisition of the DA phenotype but is expressed in many cell populations. Strong context dependency.

Lmx1a/b	Lmx1a/b proteins can increase the percentage of vmDA neurons with typical electrophysiological properties [40, 111, 157, 184]		iDA neurons from human and mouse fibroblasts and mouse astrocytes (in combination) [142, 148–150, 180]	Induce specification and maintenance of vmDA neurons.

Foxa2	▴ mRNA levels of phenotypic markers and TF of vmDA neurons after in vitro differentiation. Enhanced the resistance to neurotoxins and improved motor asymmetry after transplantation [183, 184]		iDA neurons from human and mouse fibroblasts and mouse astrocytes (in combination) [142, 149, 150, 180]	Required for specification, differentiation, and survival of vmDA neurons

Otx2	▴ mRNA levels of phenotypic markers and TF of mDA neurons after in vitro differentiation in combination with FoxA2 and Lmx1a [184]	▴ Enriched the DA progenitor pool (in combination with Corin) and induced behavioural recovery after transplantation into PD models [185]	iDA neurons from mouse astrocytes (in combination) [180]	Important in midbrain regionalization, persists only in most medial vmDA (less vulnerable) populations

Ngn1/2	▾ Number of TH+ cells in combination with Nurr1 [153]	Ngn2+ progenitors isolated at E12.5 from VM led to behavioural recovery in 6-OHDA lesioned rats [179, 186]	iDA neurons from human fibroblasts and mouse astrocytes (in combination) [151, 180]	Can be substituted by other proneural genes like Mash1

Mash1 (Ascl1)	▴ In combination with Nurr1 increased the number of surviving TH+ cells after grafting and improved motor function [153]		iDA neurons from human and mouse fibroblasts and mouse astrocytes (in combination) [148, 151, 180]	Essential for direct reprogramming of fibroblast and astrocytes into iDA cells.

Engrailed			iDA neurons from human and mouse fibroblasts and mouse astrocytes (in combination) [142, 149, 150, 180]	Required for survival of mature vmDA neurons.

Sox1		▾ Sox1+ neural progenitors avoid tumor formation after transplantation but few DA neurons [125, 158, 187]	▾ Efficiency of direct reprogramming [142, 149]	Fail to produce vmDA neurons from human ESC [188].

Sox2		▾ Broadly expressed in all VM domains [179]	iDA neurons from human fibroblasts (in combination) [151]

TH		▴ TH promoter: highly enriches for DA neurons, which improved motor behavior in animal models of PD upon transplantation [127, 165, 166, 168]		Regulatory sequences are valuable for vmDA neuron enrichment mostly from primary cells.

DAT		▴ DAT promoter: highly enriches for DA neurons, which survived in vitro when cocultured with glia [189]		Restricted expression to more mature populations.

Nestin		▾ Expressed in all VM domains [179]		Allows selection of neural progenitors but dynamic expression may exclude target cells at different developmental stages.

Corin		▾ Selection from primary cells resulted in low numbers of TH neurons and no behavioral recovery of grafted animals. ▴ When combined with Otx2, the DA progenitor pool was enriched and cells induced behavioural recovery after transplantation [41, 179, 185]		Broad expression in the midline. Selection for this surface molecule is insufficient for DA enrichment.

SSEA-1 (CD15)		▴ To exclude stem cells (proliferating/undifferentiated) preventing tumor formation in grafts from mouse ES cells [127, 159, 160]		Negative selection of populations derived from mouse ES cells reduces the risk of teratoma formation.

NCAM (CD56)		▴ To isolate and/or evaluate percentage of post-mitotic neurons and prevent tumor formation in grafts [159, 171]		Positive selection of populations derived from mouse and human ES cells reduces the risk of teratoma formation.

PSA-NCAM		▴ To isolate and/or analyze percentage of progenitors or post- mitotic neurons [111, 159]		Positive selection of neural populations may result in exclusion of target neurons at different developmental stages.