Fig. 3

Impact of MTALTND4 upon mitochondrial and cell physiology. A–B Dose-dependent effect on intact (ce) HeLa and HEK-293 T cells routine respiration (n = 3 and n = 4, respectively). Respirometry data were normalized for the routine respiration in the absence of the peptide. For each titration point, data are represented as fraction of their own simultaneous control (blue dotted line). C–D Mitochondrial respiration in intact (ce) HeLa and HEK-293 T cells in the presence of 10 µM MTALTND4 (n = 6–9 and n = 6, respectively). Respirometry data were expressed as flux control ratios (FCR), normalized for the routine respiration before treatment (ce_R). ce-pept_R routine respiration with MTALTND4, ce-pept_L leak respiration with MTALTND4, ce-pept_E maximal uncoupled respiration with MTALTND4. E Mitochondrial spare reserve capacity (SRC) in HeLa and HEK-293 T cells in the presence of 10 µM MTALTND4 (n = 6 and n = 6, respectively). F Mitochondrial respiration in permeabilized (pce) HEK-293 T cells in the presence of 10 µM MTALTND4 (n = 6). Respirometry data were normalized for the CI + II-sustained coupled respiration before treatment (CI + II_P). CI + II-pept_P CI + II-linked coupled respiration with MTALTND4, CI + II-pept_E CI + II-linked uncoupled respiration with MTALTND4, CIV-pept_E cytochrome c oxidase standalone capacity with MTALTND4. G Hydrogen peroxide efflux rate (pmol H₂O₂ ∙ mg proteins⁻¹ ∙ min⁻¹) in intact HEK-293 T cells in the presence of 30 µM MTALTND4 (n = 5). H Catalase activity (U ∙ mg proteins⁻¹) in intact HEK-293 T cells incubated 4 h with 30 µM MTALTND4 (n = 5). I Lactate dehydrogenase activity (U ∙ mg proteins⁻¹) in intact HEK-293 T cells incubated 4 h with 30 µM MTALTND4 (n = 5). L ATP content (nmol ATP ∙ mg proteins.⁻¹) in intact HEK-293 T cells incubated 4 h with 30 µM MTALTND4 (n = 5). M–N Proliferation (Mx cells) and viability (%) of HeLa cells measured at different time points (24, 48, and 72 h) and different MTALTND4 concentrations (0, 0.1, 10, and 30 µM) (n = 3–5). Statistical analyses: A–B one sample t test, C, D, F, G, H, I, L paired t test, E linear mixed model. Factors cell type (2 levels) and treatment (2 levels) plus interaction. M, N linear mixed model. Factor treatment (4 levels), with letters indicating statistical difference following a post hoc multi comparison test. Data shown as mean ± sem. 0.05 > p ≤ 0.09; *p ≤ 0.05; **p ≤ 0.01; ***p ≤ 0.001. A detailed summary (individual values) is reported in Additional file 1: Tables S6-S10