Telomerase levels in schizophrenia: a preliminary study

Abstract

We previously demonstrated that telomere length was markedly reduced in peripheral blood lymphocytes from individuals with schizophrenia. Since reduced telomere length can be caused by decreased telomerase activity, we quantitated basal telomerase activity in peripheral blood lymphocytes derived from individuals with schizophrenia (n=53), unaffected relatives (n=31) and unrelated controls (n=59). Telomerase activity varied greatly among individuals, suggesting that this enzymatic activity is affected by various factors. We observed a nominally significant decrease in telomerase activity among individuals with schizophrenia compared to unaffected individuals (unaffected relatives and unrelated controls). Further studies are needed to investigate the role of telomerase in schizophrenia.

Figure 1. Validation of the telomerase qPCR assay

Quantitation using the qPCR-based telomerase assay was evaluated by adding varying amounts of telomere synthetic repeat (TSR) DNA or varying amounts of lymphocyte lysate to the real-time reaction. A. Typical plot depicting relationship between Ct and amount of telomere synthetic repeat (TSR) DNA. To determine if the assay detects telomere DNA in a quantitative manner, increasing amounts of synthetic telomeres (TSR in attomoles) were added to a 25 μL reaction. A linear relationship was observed between Ct and the base 10 logarithm of input telomeres (R² = 0.995, p<0.0001). B. Typical plot depicting relationship between Ct and the amount of cellular extract derived from lymphocytes. To determine if the assay detects telomerase activity in a quantitative manner, varying amounts of lymphocyte lysate were added to a 25 μL real-time reaction. The units of cellular lysate (ng) refer to the quantity of nucleic acid in the extract, which is proportional to cell number. A linear relationship was observed between Ct and the base 10 logarithm of the amount of lymphocyte lysate (R² = 0.973, p=0.0019).

Figure 2. Clozapine or haloperidol within the therapeutic range does not affect basal telomerase levels

Peripheral blood lymphocytes were isolated from three different individuals and seeded onto 6-well culture dishes. Varying quantities of clozapine, an atypical antipsychotic, or haloperidol, a typical antipsychotic, were added to the medium. After 5 days in culture, lymphocytes were harvested and telomerase levels were determined (Materials and Methods). Black-filled circles represent controls (untreated or treated with methanol, which was used to dissolve the drugs). Gray-filled circles represent values obtained with antipsychotics within the therapeutic range (0.2–1.0 μg/mL for clozapine, and 0.002 to 0.02 μg/mL for haloperidol). Open circles represent values obtained with antipsychotics outside the therapeutic range. * represents values that differ significantly from the untreated group (p≤0.05). p-values are corrected for multiple comparisons using Bonferroni’s method. Error bars=standard error of the mean.