(a) TL was determined by Q-FISH analysis on heart tissue sections after MI in the left ventricular infarct remote area in mice transduced with AAV9-Tert and AAV9-empty. Four animals (hearts) per group were analysed (n = 4). TL is represented as mean telomere fluorescence per nucleus in arbitrary units of fluorescence (a.u.). The black line indicates mean TL. Statistical analysis: two-sided Student’s t-test, P-values are depicted. Scale bar, 25 μm. (b) Fractions of nuclei per mouse (from A), which fall below the 20th percentile of the control (AAV9-empty) TL are represented as the percentage of cells with short telomeres. Statistical analysis: two-sided Student’s t-test, P-values are shown. (c) Representative images of heart sections subjected to telomere Q-FISH analysis. Nuclei are stained with DAPI and telomeres with a specific CY3-labelled probe. Nuclei stained with DAPI (blue) and telomeres with CY3-labelled probe (red). Scale bars, 20 μm (left image); 2 μm (zoom in). (d) TL (in kb) measured in peripheral blood leukocytes by using HT-Q-FISH technology. Each spot represents the mean TL of one individual mouse (from left to right n = 6, 3, 13, 20). Mean TL among all mice per group is indicated by the black horizontal lines. Statistical analysis: two-sided Student’s t-test, P-values are shown.