Analysing aged neural stem cells and the impact of different apolipoprotein E genotypes

Introduction:

Stem cell ageing results in loss of organ function and onset of age-related diseases, like Alzheimer's disease (AD). AD is the most common form of dementia. The disease is characterized by complex molecular genetics, cognitive impairment, progressive neurodegeneration, and brain atrophy. Different therapeutic approaches are being developed to counteract the loss of affected neurons. Another therapeutic approach aims the modulation of stem cell plasticity of existing neuronal progenitors for increasing their dividing capacity and regeneration of neuronal tissue. The apolipoprotein E (APOE4) isoform has been discovered showing genome-wide significant association with the sporadic, late-onset form of AD (LOAD). Further, APOE is necessary for maintenance of adult neural stem cells (NSCs) in the adult brain. The underlying mechanisms for stem cell aging and age-related diseases are poorly understood. Therefore, the aim of the study was the characterization of aging markers including APOE in human NSC from young and old individuals, to establish a useful in vitro model for analyzing aging-dependent alterations.

Methods:

Induced pluripotent stem (iPS) cell lines were generated from blood of young, middle age, and old donors. Further, iPS cells were obtained from LOAD patients carrying APOE4. We generated NSCs and analysed them by transcript and protein expression analysis. Telomere length was investigated in blood, iPS cells and NSCs using a qPCR-based method. We induced the expression of APOE2 and APOE3 using expression plasmids to recover APOE expression in NSCs from APOE4 carriers.

Results:

The successful differentiation of NSCs from iPS cells was shown by the expression of crucial marker genes including PAX6 and SOX2. We also analyzed the gene expression of aging marker genes according to the literature and found that aging markers were differently expressed in NSCs from differently aged donors including PTEN, FGF2, and HEYL. There are also aging markers that showed an APOE4-dependent expression pattern like CDKN2A and ADORA1. Telomere length was analyzed as an aging marker and revealed an elongation of telomeres in iPS cells in comparison to the corresponding donor blood. Shortening of telomere length was shown after differentiation of iPS cells into NSCs.

Conclusion:

We successfully established a stem cell model, which can be used to understand common and rare molecular and cellular mechanism of aging. We demonstrated that telomere length and the expression of certain markers represent powerful aging markers in NSCs.