TERT without the TERC?
In digging for a mechanism by which Manganese increases telomere length I have uncovered a possible explanation (different to ROCK inhibition as already discussed).
This study [1] discusses the reverse transcriptase action of telomerase, and how in telomerase the active protein consists of two main components, TERT: the catalytic part that adds TTAGGG units to the telomere, and TERC: the template part that attaches to the telomeres and allows TERT to do its work by adding the correct nucleotides.
I have discussed before how both TERT and TERC are needed, albeit with TERT being the limiting factor in human cells, and we have also engaged in (educated) speculation over the benefits of increasing the efficiency of the association of TERT and TERC.
For more information see this post: https://www.longecity.org/forum/topic/102169-alternative-methods-to-extend-telomeres/page-26#entry915527
In the current study (from 2005), they reveal that in some circumstances telomerase can forgo the requirement for the RNA template (TERC) and act directly to extend the telomere. This is termed terminal transferase activity.
Key to this is the effect of metal ions on polymerases (this will require a post in itself), and you guessed it, in the presence of sufficient manganese TERT does not need TERC to add to the telomere.
Getting into the nitty gritty of the paper, they did a series of experiments adding dGTP and dTTP to provide Gs and Ts for the telomere, using different primers and checked how many nucleotides were added in the presence or absence of Manganese (Mn 2+). Manganese decreased the efficiency of telomerase in adding repeats in the presence of both dGTP and dTTP but increased the number of base pairs added when only dGTP or dTTP was present. They explain this by the competition of two different mechanisms, i.e., Mn ions relaxing the requirement to add the correct nucleotide normally ensured by the RNA template. To test this they treated telomerase with an RNAase (to remove the RNA TERC template component of the protein) and then repeated their tests, finding that telomerase activity (i.e. nucleotide adding ability) was abolished in the absence of Mn2+ but only reduced 2-fold when Mn2+ was present. Remarkably, they also found that they could add other nucleotides (i.e. A and C) that are either not supposed to be in the telomere (the C) or shouldn't be in that position (the A), in the absence of the RNA template but when Mn2+ was present. The activity of adding these ‘improper’ nucleotides was actually enhanced in the absence of the RNA template, suggesting that TERC s acting as a quality control mechanism, as hypothesized.
As a side note, I’ve covered in the past that the speed of telomerase adding nucleotides is limited by the addition step of one of the Gs and that this can be overcome with more GTP: https://www.longecity.org/forum/topic/102169-alternative-methods-to-extend-telomeres/page-15#entry904277
It is interesting to speculate whether the presence of Mn2+ could lead to a faster rate of telomere nucleotide addition, because of the relaxation of the requirements to use the proper nucleotides. This could lead to longer telomeres even with the same concentration of telomerase, given that telomerase only has a limited time to do its work during S-phase. Further to this it is interesting to think about whether it would matter if your telomeres did not have the proper nucleotide sequence. A few extra As and Cs to my mind would not matter, as the telomere would still be doing its job of preventing the end of the strand being recognised as broken DNA. But TERT does seem to have a preference for DNA with many Gs, so you wouldn’t want to alter the telomere composition too much.
Does this paper have any practical in vivo consequences? Given the concentrations of Mn2+ used in this study, far above normal physiological levels, I am inclined to say no. But then we’ve just been discussing a paper where mothers with the highest tertile of Mn2+ concentration in their urine in the second trimester gave birth to babies with 10% longer telomeres [2]! The mechanism we have discussed in this post seems like a plausible explanation for this remarkable effect. Then again, it may be completely irrelevant. One way to find the answer might be to do full nucleotide sequencing on the blood samples they obtained in the pregnancy study and determine if the babies with longer telomeres had more variety in the nucleotide sequence of their telomeres. If they had more divergence from TTAGGG than the shorter telomere’d cohort, then this would be a slam dunk for this theory.
If and when telomere tests become more widely (and cheaply) available, it might also be worth biohackers like us seeing if the addition of a manganese supplement has any effect on the length of our leukocyte telomeres.
References
[1] Lue NF, Bosoy D, Moriarty TJ, Autexier C, Altman B, Leng S. Telomerase can act as a template- and RNA-independent terminal transferase. Proc Natl Acad Sci U S A. 2005 Jul 12;102(28):9778-83. doi: 10.1073/pnas.0502252102. Epub 2005 Jun 30. PMID: 15994230; PMCID: PMC1174988.
[2] Bi J, Wu M, Liu Y, Song L, Wang L, Liu Q, Chen K, Xiong C, Li Y, Xia W, Xu S, Zhou A, Wang Y. Association between maternal urinary manganese concentrations and newborn telomere length: Results from a birth cohort study. Ecotoxicol Environ Saf. 2021 Apr 15;213:112037. doi: 10.1016/j.ecoenv.2021.112037. Epub 2021 Feb 18. PMID: 33609998.
Edited by QuestforLife, 08 November 2023 - 11:37 AM.