Abstract
The fast-ageing killifish has gained increasing attention as a promising gerontology model to study age-related processes and neurodegeneration. Interestingly, it is the first vertebrate model organism that shows physiological neuron loss at old age in its central nervous system (CNS), including its brain and retina. However, the fact that the killifish brain and retina are ever-growing tissues complicates studying neurodegenerative events in aged fish. Indeed, recent studies showed that the method of tissue sampling, either using sections or whole-organs, has a large effect on the observed cell densities in the fast-expanding CNS. Here, we elaborated on how these two sampling methods affect neuronal counts in the senescent retina and how this tissue grows upon ageing. Analysis of the different retinal layers in cryosections revealed age-dependent reduction in cellular density but evaluation of whole-mount retinas did not detect any neuron loss, as a result of an extremely fast retinal expansion with age. Using BrdU pulse-chase experiments, we showed that the young adult killifish retina mainly grows by cell addition. However, with increasing age, the neurogenic potency of the retina declines while the tissue keeps on growing. Further histological analyses revealed tissue stretching, including cell size increase, as the main driver of retinal growth at old age. Indeed, both cell size and inter-neuronal distance augment with ageing, thereby decreasing neuronal density. All in all, our findings urge the ‘ageing science’ community to consider cell quantification bias and employ tissue-wide counting methods to reliably quantify neuronal numbers in this unique gerontology model.
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Acknowledgements
The authors would like to thank Simon Buys, Arnold Van Den Eynde and Rony Van Aerschot for the daily fish maintenance and environmental control; Stephanie Mentens, Marijke Christiaens and Nele Michiels for their technical support. S.B. and Lu.M hold a personal Research Foundation Flanders (FWO, Belgium) fellowship (1165020N and 1S42720N, respectively). Killifish housing and breeding is financially supported by a small equipment Grant KA-16-00745 (KU Leuven) while experiments are supported by a FWO research grant (G092222N).
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Conceptualization: SB, LuM and LM; Methodology: SB, LuM, P-JS; Writing—original draft preparation: SB; Writing—review and editing: SB, LuM, P-JS, LM; Funding acquisitions: Research Foundation Flanders, KU Leuven; Visualization: SB, LuM; and Supervision: LM.
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Bergmans, S., Serneels, PJ., Masin, L. et al. Tissue stretching is a confounding factor for the evaluation of neurodegeneration in the fast-ageing killifish. Biogerontology 24, 403–419 (2023). https://doi.org/10.1007/s10522-023-10026-1
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DOI: https://doi.org/10.1007/s10522-023-10026-1