Journal: Frontiers in Physiology
Article Title: Loss-of-function mitochondrial DNA polymerase gamma variants cause vascular smooth muscle cells to secrete a diffusible mitogenic factor
doi: 10.3389/fphys.2024.1488248
Figure Lengend Snippet: Loss-of-function POLG variants minimally affect mitochondrial membrane potential, ROS production, and cellular respiration in A7r5 cells. (A) Example image of A7r5 cells transfected with pPOLG:P2AT2A:EGFP3xNLS labeled with Hoechst 33342 and TMRM (25 nM) and treated with oligomycin (10 µM). The green circle overlays highlight transfected cells, and the white box is zoomed in on the far right. Orange asterisks highlight cells with minimal TMRM staining. Scale bars: 50 µm for composite images and 10 µm for zoomed images. (B) Average TMRM intensity for all 13,210 cells in one of two experimental replicates. ** p < 0.005 for Tukey’s honest significant different test. (C, D) TMRM values in the control-treated well, where each cell was normalized as its TMRM intensity less the mean FCCP value and divided by the difference between the mean of oligomycin- and FCCP-treated wells. Data are compiled from four fields of view in each quadruplicate well in each of two independent experiments. (E) Example distribution of nuclear GFP mean intensity and triple Gaussian fit. Cells with mean intensity higher than mean + (3 x SD) of first Gaussian peak are defined as transfected. Summary statistics of the transfection efficiency are shown below. (F) Representative images of MitoSOX (5 µM) in cultured transfected with WT pPOLG:P2AT2A:EGFP3xNLS treated with antimycin A (1 µM). Green circle overlays represent transfected cells, and the white box is zoomed in on the far right. Scale bars: 50 µm for composite images and 10 µm for zoomed images. (G) MitoSOX intensity was measured using nuclear regions of interest and normalized to the means of control-treated, WT-transfected cells on each of two independent experiments, imaging four fields of view in each quadruplicate well. AA indicates wells treated with antimycin A (1 µM) to stimulate ROS production. ** p < 0.005 for two-sample t -test. (H) Data in (G) are re-plotted by simplified cell ploidy. ** indicates p < 0.005 for Dunnett’s post hoc tests versus 2N. (I) A7r5 oxygen consumption rates per cell in Seahorse XFe Mito Stress Test. Lines show mean plus standard error bands for two independent experiments with 6–8 technical replicates each. Oligomycin (1 µM), FCCP (1 µM), rotenone, and antimycin A (1 µM) were added, as indicated with the arrows. (J) Oxygen consumption rate normalized to POLG separately for GM and DM conditions. One outlier ( > 3) in the GM for non-mitochondrial OCR for NLSGFP (4.283) and one well corresponding to five points in N1098I DM were removed for clarity but not removed from statistical analysis. For each experimental paradigm (TMRM, MitoSOX, and Seahorse), data show the results of two independent experiments, with technical quadruplicate wells for TMRM and MitoSOX and eight technical replicates per Seahorse plate.
Article Snippet: To create POLG-expression constructs with self-cleaving nuclear-targeted EGPF, we cloned the POLG (or variants) coding sequences and a P2AT2A (Addgene 87829) sequence 5′ of the EGFP3xNLS on pEGFP-C1 EGFP-3XNLS (Addgene 58468) by Gibson assembly.
Techniques: Membrane, Transfection, Labeling, Staining, Control, Cell Culture, Imaging