A subset of gut leukocytes has telomerase-dependent “hyper-long” telomeres and require telomerase for function in zebrafish

ABSTRACT Telomerase, the enzyme capable of elongating telomeres, is usually restricted in human somatic cells, which contributes to progressive telomere(definition) shortening with cell-division and ageing. Using the zebrafish model, we show that subsets gut immune cells have telomerase-dependent “hyper-long” telomeres, which we identified as being predominantly macrophages and dendritics ( mpeg1 . 1 + and cd45 + mhcII + ). Notably, mpeg + macrophages have much longer telomeres in the gut than in their haematopoietic tissue of origin, suggesting that there is a gut-specific modulation of telomerase in these cells. Moreover, we show that a subset of gut mpeg + cells express telomerase ( tert ) in young WT zebrafish, but that the relative proportion of these cells decreases with ageing. Importantly, this is accompanied by telomere shortening and DNA damage responses with ageing and a telomerase-dependent decrease in expression of autophagy(definition) and immune activation markers. Finally, these telomerase-dependent molecular alterations are accompanied by impaired phagocytosis of E . coli and increased gut permeability in vivo . Together, our data show that limiting levels of telomerase lead to changes in gut immunity and gut permeability, which, together, are likely contributors to local and systemic tissue degeneration and increased susceptibility to infection with ageing. GRAPHICAL ABSTRACT Our data show that limiting levels of telomerase contribute to alterations in gut immunity, namely increased apoptosis, decreased autophagy and immune activation of mpeg + macrophages in the gut. This is accompanied by a decreased ability to clear pathogens and increased gut permeability. Together, these are likely contributors to local and systemic tissue degeneration and susceptibility to infection with ageing.