Mol Neurobiol. 2019 Feb;56(2):1248-1261. doi: 10.1007/s12035-018-1167-9.

Neuronal and Glial Differentiation of Human Neural Stem Cells Is Regulated by Amyloid Precursor Protein (APP) Levels.

Raquel Coronel1, María Lachgar1, Adela Bernabeu-Zornoza1, Charlotte Palmer1, Marta Domínguez-Alvaro1, Ana Revilla1, Inmaculada Ocaña1, Andrés Fernández2, Alberto Martínez-Serrano3, Eva Cano2, Isabel Liste1*.

1 Unidad de Regeneración Neural, Unidad Funcional de Investigación de Enfermedades Crónicas, Instituto de Salud Carlos III (ISCIII), Majadahonda, 28220, Madrid, Spain.

2 Unidad de Neuroinflamación, Unidad Funcional de Investigación de Enfermedades Crónicas, Instituto de Salud Carlos III (ISCIII), Majadahonda, Madrid, Spain.

3 Centro de Biología Molecular “Severo Ochoa” (CBMSO), Universidad Autónoma de Madrid-Consejo Superior de Investigaciones Científicas (UAM-CSIC), Campus UAM Cantoblanco, Madrid, Spain.

* Correspondence to: Isabel Liste Ph.D.; Tel: +34 918223292; Fax: +34 918223269; E-mail: iliste@isciii.es

 

Abstract

Amyloid precursor protein (APP) is implicated in neural development as well as in the pathology of Alzheimer’s disease (AD); however, its biological function still remains unclear. It has been reported that APP stimulates the proliferation and neuronal differentiation of neural stem cells (NSCs), while other studies suggest an important effect enhancing gliogenesis in NSCs. As expected, APP protein/mRNA is detected in hNS1 cells, a model cell line of human NSCs, both under proliferation and throughout the differentiation period. To investigate the potential function that APP plays in cell fate specification and differentiation of hNS1 cells, we transiently increased human APP levels in these cells and analyzed its cell intrinsic effects. Our data indicate that increased levels of APP induce early cell cycle exit and instructively direct hNS1 cell fate towards a glial phenotype, while decreasing neuronal differentiation. Since elevated APP levels also enhanced APP intracellular domain (AICD)-immunoreactivity, these effects could be, in part, mediated by the APP/AICD system. The AICD domain can play a potential role in signal transduction by its molecular interaction with different target genes such as GSK3B, whose expression was also increased in APP-overexpressing cells that, in turn, may contribute to promoting gliogenesis and inhibiting neurogenesis in NSCs. These data suggest an important action of APP in modulating hNSCs differentiation (probably in an AICD-GSK-3β-dependent manner) and may thus be important for the future development of stem cell therapy strategies for the diseased mammalian brain.

https://doi.org/10.1007/s12035-018-1167-9

 

Supplement

The pathological involvement of amyloid precursor protein (APP) in Alzheimer’s disease (AD), as well as in other neurological conditions such as Down syndrome (DS) or brain injury, has been widely documented; mainly due to its involvement in the generation of the amyloid-β (Aβ) peptide [1,2]. AD is the most common neurodegenerative disease and the most frequent form of dementia in the elderly population. It is characterized by the progressive loss of neurons and, currently, there is no effective cure for this disorder [3].

Aβ peptide is a derivative of APP and, its aggregation and accumulation in the brain, causes the so-called amyloid plaques. The formation of these plaques in the brain is one of the main characteristics of AD [4], although they can also appear in people with DS who manifest an early onset AD. The main theory that defends this fact is that the APP gene is encoded on chromosome 21, being the trisomy of the 21 chromosome responsible of DS [5].

Given that APP seems to contribute to the development and progression of AD, several studies have focused on determining its pathological function. However, the physiological function of APP is not well known yet, and there is no clear consensus on it.

APP is a glycoprotein expressed ubiquitously in a wide variety of tissues, being especially abundant in the brain. The APP expression is detected at early stages of nervous system development, which suggests an important role of this protein in neural growth and maturation; specifically, in the proliferation, differentiation and maturation of neural stem cells (NSCs) [6]. In addition, in the adult brain, APP could also regulate important functions such as the proliferation of neural progenitor cells (NPCs), as well as axonal outgrowth after injury [7].

Regarding the biological functions of APP, there are evidences that seem to indicate that this protein acts in the processes of synaptogenesis and neurite outgrowth, neurogenesis, gliogenesis and neuronal migration [1,8,9].

Briefly, neurogenesis is the cellular process by which new neurons are generated from NSCs/NPCs. On the other hand, gliogenesis is the cellular process by which new glial cells are generated from NSCs/NPCs. Both events occur mainly during embryonic development and remain, although to a lesser extent, in the adult brain [10]. It should be noted that, both in patients with AD and in people with DS, the processes of neurogenesis and gliogenesis are altered, with a marked decrease in neurons, both new and mature, as well as an increase in glial cells and microglia in the brains [11,12].

Stem cells are characterized by their capacity for self-renewal (production of more stem cells) and differentiation (the process by which cells acquire a specific form and function, more specialized, towards a defined lineage). NSCs are multipotent stem cells with the capacity for self-renewal and differentiation towards neural lineage, that is, towards cell types of the central nervous system, including neurons and glial cells. These cells can be obtained from fetal, neonatal and adult brain tissue, as well as the differentiation of pluripotent stem cells (cells in a more undifferentiated stage than multipotent stem cells) [13]. Human NSCs have become a good model for the study of several cellular processes, including neurogenesis and gliogenesis, as well as the physiological and pathological molecular mechanisms associated with neurodegeneration.

In our recent publication, we aimed to identify the cellular effects of APP in the differentiation of human NSCs [14]. For this, we used the hNS1 cell line, a model of human NSCs obtained from the human fetal forebrain. Our results shown that a transient increase in the expression of APP favored the differentiation of these human NSCs towards glial cells (gliogenesis), simultaneously that it prevented the differentiation of these cells towards neurons (neurogenesis). These effects that APP exerts in the biology and differentiation of human NSCs could be mediated, at least in part, by the APP/AICD/GSK-3β system, where AICD is another derivative of APP that acts as a transcriptional regulator, in this case of the GSK3B gene [15,16]. In this context, our results indicated that the transient increase in APP expression was also accompanied by an increase in the expression of AICD and GSK-3β, and several studies and evidence indicate the importance of GSK-3β in the proliferation and differentiation of NSCs [17].

In conclusion, our results show that APP appears to be involved in the control of the generation of new neurons and glial cells, through the APP/AICD/GSK-3β system, in human NSCs. This finding could have implications in the context of the biological and physiological role of APP, as well as in researches related to AD and DS. A better knowledge of the role of APP and the mechanisms involved in neurodevelopment could help to clarify and understand the cellular processes that develop in neurodegenerative diseases, being essential to deepen in this field for the development and design of regenerative therapies.

 

 

Figure 1. Schematic illustration of the different sources of human NSCs, the cellular effects of APP in the differentiation of human NSCs, and possible molecular mechanisms involved in these effects. The transient increase of the APP expression appears to favor the differentiation of human NSCs towards glial cells (gliogenesis), while it prevents the differentiation of these cells towards neurons (neurogenesis). These effects that APP exerts in the biology and differentiation of human NSCs could be mediated, at least in part, by the APP/AICD/GSK-3β system.

 

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