Fig. 1

Representative H&E stained cross-sections from the ileum of young a and old b mice. c Average number of villi per section and villi lenght. d-f Representative H&E stained ileal sections from young d and old e-f mice showing villi degeneration and crypt enlargement. g Crypts depth in old vs. young animals. h Arrowheads point to goblet-like cells containing eosinophilic secretory granules. i-l Electron micrographs of Paneth cell secretory granules from a young i and three old animals j-l. m Average number of Paneth cells per crypt. n Average number of goblet cells per villus. o-q Alcian blue stained ileal sections from a young o and two old p-q animals showing goblet cell hyperplasia and intracellular accumulation of mucin. Histology pictures were taken using a NanoZoomer 2.0 slide scanner (Hamamatsu). Measurements of villi length, villi number and crypt depth were done using NDP.view 2 software (Hamamatsu). Paneth and goblet cell counts were recorded in 40–60 well-preserved villi-crypt axes per animal. r Relative transcript levels for ileal AMPP genes, determined by qPCR using the ddCt method corrected for primer efficiencies according to Pfaffl et al. [22], (n = 16 animals/group, primer sequences and methods are described in [23]). Statistical differences (Mann–Whitney U test) and are shown by asterisks (*p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001). Scale bars are: (a, b: 500 μm); (d, e, o, p, q: 50 μm); (f, h: 25 μm); (i, j, k, l: 500 nm)