Unraveling the role of telomeres and telomerases in the response to neurotoxicants

Abstract

Background: Telomeres are repetitive DNA sequences that protect chromosome ends and whose length is maintained by telomerase activity [1]. While telomere dynamics are well characterized in proliferating cells, their role in post-mitotic cells such as neurons remains poorly explored [2]. Particularly, the impact of telomere attrition or telomerase dysfunction on the cellular response to neurotoxicants is largely unknown. Objective: We aimed to investigate whether telomere shortening increases the susceptibility of neuronal cells to the toxic effects of common environmental neurotoxicants (i.e., HgCl2, acetaldehyde). Methods: The effects of HgCl₂ (0-100mM) and acetaldehyde (0-10mM) on the metabolic activity (MTT reduction assay) and lysosomal integrity (Neutral Red uptake) of SH-SY5Y human neuroblastoma cells were assessed by determining IC10 and IC50 for each neurotoxicant. These assessments were performed either 24h after exposure to the neurotoxicants or following a 72h pre-treatment with 1mM XAV939, a tankyrase-1 inhibitor that limits telomerase access to telomeres, promoting telomere shortening [3]. Relative telomere length in XAV939-treated treated alone and in combination with biologically relevant, subtoxic concentrations of HgCl₂ (10 and 25 mM) or acetaldehyde (0.1 and 5 mM) was measured using quantitative real-time PCR. Results: Our findings revealed that HgCl₂ and acetaldehyde reduced the metabolic activity and lysosomal integrity of SH-SY5Y cells in a concentration-dependent manner. Also, HgCl₂ shifted the IC10 from 26 to 15 mM for metabolic activity and from 21 to 6 µM for lysosomal integrity in XAV939-treated cells, compared to cells not exposed to XAV939, suggesting that shortened telomeres may have increased the cells’ susceptibility to HgCl₂. In turn, XAV939 pretreatment did not alter the impact of acetaldehyde on those parameters. Notably, XAV939-induced telomere shortening was confirmed by qPCR analysis. Interestingly, our data showed that 100µM acetaldehyde and 10 µM HgCl₂ reduced the cells’ telomere length to 45% and 77% of control levels, respectively, at the same time point. Conclusions: Our preliminary findings suggest that telomere shortening increases SH-SY5Y cells vulnerability to the toxic effects of HgCl₂, evidencing a possible involvement of telomere-related mechanisms in the response to neurotoxicants. However, further research is required to confirm the importance of such mechanisms in neurotoxicity-related responses.