Generation of induced neurons via direct conversion in vivo

Abstract

Cellular reprogramming is a new and rapidly emerging field in which somatic cells can be turned into pluripotent stem cells or other somatic cell types simply by the expression of specific combinations of genes. By viral expression of neural fate determinants, it is possible to directly reprogram mouse and human fibroblasts into functional neurons, also known as induced neurons. The resulting cells are nonproliferating and present an alternative to induced pluripotent stem cells for obtaining patient-and disease-specific neurons to be used for disease modeling and for development of cell therapy. In addition, because the cells do not pass a stem cell intermediate, direct neural conversion has the potential to be performed in vivo. In this study, we show that transplanted human fibroblasts and human astrocytes, which are engineered to express inducible forms of neural reprogramming genes, convert into neurons when reprogramming genes are activated after transplantation. Using a transgenic mouse model to specifically direct expression of reprogramming genes to parenchymal astrocytes residing in the striatum, we also show that endogenous mouse astrocytes can be directly converted into neural nuclei (NeuN)-expressing neurons in situ. Taken together, our data provide proof of principle that direct neural conversion can take place in the adult rodent brain when using transplanted human cells or endogenous mouse cells as a starting cell for neural conversion.T he ability to reprogram somatic cells to pluripotent stem cells or other somatic cell types by expressing key combinations of genes has opened up new possibilities for disease modeling and cell therapy (1, 2). Using this technique, it is possible to directly reprogram mouse and human fibroblasts into functional neurons, also known as induced neurons (iNs), using viral delivery of the three neural conversion factors achaete-scute complex-like 1 (Ascl1), brain-2 (Brn2a), and myelin transcription factor-like 1 (Myt1l) (ABM) (3, 4). A growing number of studies now show that by altering the combination of genes used for reprogramming, different subtypes of neurons are obtained (3,5,6). Importantly, the resulting cells are nonproliferating, which makes them an interesting alternative to induced pluripotent stem cells as a source of patient-specific neurons for cell replacement therapy, once efficient grafting strategies for these cells are developed.The adult brain has a very limited inherent capacity for repair, and new neurons are only formed in two discrete regions: the subventricular zone of the lateral ventricles, which generates neurons migrating to the olfactory bulb, and the hippocampus (7,8). Experimental studies have shown that these endogenous progenitors can also be recruited to generate new neurons in other regions as well in response to injury (9-11). However, the number of new neurons is very low, their migration is hard to control, and the therapeutic implications are unclear. Several cell types residing outside the neurogenic niche, such as parenchymal...

Direct reprogramming of human fibroblasts into sweat gland-like cells

“…8 Torper's study showed that human fibroblasts and astrocytes could be transplanted and converted into neurons when specific genes were activated. 27 In addition, Torper also found that mouse astrocytes could be directly reprogrammed into neurons with nuclear expression in vivo.…”

Vers une régénération induite du système nerveux

“…[36,37]. Il est donc tout à fait envisageable que les cellules reprogrammées aient eu pour origine des astrocytes réactionnels plutôt que quiescents.…”

“…Ascl1 [39] Sox2 ± VPA [41] Fezf2 [42,43] Neurog2 + FGF2/EGF [40] Neurog2 + FGF2/EGF [40] Sox2 + BDNF/VPA [37] Ascl1, Brn2, Mytl1 [36] NeuroD1 [33] NeuroD1 [33] Gliose réactionnelle [43]. Nous montrons que Fezf2 suffit à reprogrammer les neurones calleux postmitotiques en neurones corticofugaux, exprimant en combinaison les marqueurs spécifiques des couches corticales V et VI, et capables de projeter leurs axones vers des cibles sous-corticales (thalamus) et sous-cérébrales (moelle épinière), typiques des neurones des couches VI et V du cortex, au détriment des connexions corticales (via le corpus calleux) normalement établies par les neurones ciblés [43] (Figure 1C).…”

Epigenetic setting and reprogramming for neural cell fate determination and differentiation

“…Transdifferentiation is the conversion of a differentiated cell to alternative lineage(s), such as conversion from fibroblasts to neurons [94][95][96][97]. Regarding glial cells, we have previously shown that activation of the JAK/STAT signalling pathway can induce transdifferentiation from oligodendrocytes into astrocytes [98].…”