Telomere length and human hippocampal neurogenesis

Abstract

Short telomere length is a risk factor for age-related disease, but it is also associated with reduced hippocampal volumes, age-related cognitive decline and psychiatric disorder risk. The current study explored whether telomere shortening might have an influence on cognitive function and psychiatric disorder pathophysiology, via its hypothesised effects on adult hippocampal neurogenesis. We modelled telomere shortening in human hippocampal progenitor cells in vitro using a serial passaging protocol that mimics the end-replication problem. Serially passaged progenitors demonstrated shorter telomeres (P ≤ 0.05), and reduced rates of cell proliferation (P ≤ 0.001), with no changes in the ability of cells to differentiate into neurons or glia. RNA-sequencing and gene-set enrichment analyses revealed an effect of cell ageing on gene networks related to neurogenesis, telomere maintenance, cell senescence and cytokine production. Downregulated transcripts in our model showed a significant overlap with genes regulating cognitive function (P ≤ 1 × 10^-5), and risk for schizophrenia (P ≤ 1 × 10^-10) and bipolar disorder (P ≤ 0.005). Collectively, our results suggest that telomere shortening could represent a mechanism that moderates the proliferative capacity of human hippocampal progenitors, which may subsequently impact on human cognitive function and psychiatric disorder pathophysiology.

Fig. 1. Protocol summary.

A summary of our in vitro protocol, which considered telomere length, mRNA expression, cell markers of proliferation, and cell markers of differentiation, in association with cell passaging.

Fig. 2. Telomeres are shorter in serially passaged hippocampal progenitor cells.

This bar chart shows the relative telomere length in cells at baseline (P21) and serially passaged cells (P29). There is a significant reduction in telomere length in serially passaged cells relative to cells at baseline. Group differences were detected using an independent samples t-test. Significant differences were considered when P ≤ 0.05, indicated by *.

Fig. 3. Proliferation rates are lower in serially passaged hippocampal progenitor cells.

Bar charts (top) show the percentage of BrdU (a) and Ki67 (b) -positive cells relative to the percentage of DAPI stained nuclei (y-axis), in cells at baseline and serially passaged cells (x-axis). Each datapoint represents one biological replicate (N = 4). * represents an uncorrected P ≤ 0.05, and *** represents an uncorrected P ≤ 0.001. Each of the images (below) are representative of a field of immuno-stained cells, taken using a ×10 objective with the CellInsight High Content Screening Platform. Each composite image includes the nuclear marker DAPI in blue. Scale bar = 100  μm.

Fig. 4. There are no differences in the rates of cell differentiation in serially passaged cells.

The bar charts (right) show the percentage of MAP-2 (a), CC3 (b), S100β (c) and DCX (d) -positive cells relative to the percentage of DAPI stained nuclei (y-axis), in cells at baseline and serially passaged cells (x-axis). Each datapoint represents one biological replicate (N = 4). * represents an uncorrected P ≤ 0.05. Each of the images (left) are representative of a field of immuno-stained cells, taken using a ×10 objective with the CellInsight High Content Screening Platform. Each composite image includes the nuclear marker DAPI in blue. Scale bar = 100 μm.

Fig. 5. Differentially expressed genes in serially passaged cells relative to cells at baseline, and gene sets implicated in cell ageing.

a A volcano plot summarising the RNA-sequencing results, where log2(Fold change) is shown on the x-axis, and the strength of the association given by −Log₁₀(P), is shown on the y-axis. b Examples of gene sets which significantly overlap with the upregulated genes in our cell model. All gene sets represent those which surpassed a false discovery rate correction, P_FDR < 0.05, in our enrichment analysis, as marked by the dashed line. c Examples of gene sets which significantly overlap with the downregulated genes in our cell model. d A bar plot showing the genetic overlap between various traits as assayed by GWAS (y-axis) and genes either upregulated or downregulated in association with cell ageing. The strength of the association is shown on the y-axis (−log(p)). The dashed line represents the threshold of significance (corrected for the number of tests).