Journal: The Journal of Biological Chemistry
Article Title: HuR-driven reversible mitochondrial shuttling buffers cytosolic miRNA levels in hepatic cells
doi: 10.1016/j.jbc.2026.111255
Figure Lengend Snippet: The starvation-induced enrichment of mito-miRs in hepatic cell mitochondria. A , fold change in cellular miRNA content after 16 h of amino acid starvation of Huh7 cells. Relative levels of various miRNAs were quantified using qRT–PCR. Data were normalized to U6 snRNA (n = 3). B , miRNA-specific Ct values are plotted to show the changes in their relative abundance in purified mitochondria after amino acid starvation of Huh7 cells. The analysis indicates a significant decrease in Ct values for miRNAs let-7b, let-7g, and miR-181a in starved cell mitochondria, reflecting their enrichment in the mitochondrial fraction on starvation. A bar diagram displays the fold enrichment of let-7b and let-7g mito-miRs in purified mitochondria compared with let-7a (n = 3). C , Western blot analysis done with fed and starved Huh7 extracts exhibited increased levels of expression of the stress marker protein phosphorylated–eukaryotic initiation factor 2 alpha and cleaved PARP, accompanied by decreased 4EBP1 (eukaryotic initiation factor 4E–binding protein 1) phosphorylation. β-actin served as the loading control for all samples. Relative levels, quantified from band intensity, are plotted at the bottom of Western blot panels against the beta-actin normalized value of Fed Huh7 cells as a unit. D , cellular miRNA levels change in the liver of mice under a normal diet (fed) and after 12h of starvation, as estimated by qRT–PCR and normalization against U6 snRNA levels (n = 3). E , the fold changes of let-7b and let-7g in the isolated pure mitochondrial fraction obtained from the liver of mice having a normal diet (fed) or starved for 12 h. Levels of each miRNA in the fed condition are considered as units (n = 3). F and G , the relative enrichment of mito-miRs with the outer membrane and intermembrane space (OM + IMS) ( F ) and inner membrane and mitochondrial matrix (IM + matrix) ( G ) of mitochondria isolated from control (fed) and 16 h amino acid–starved Huh7 cells (starved). Ct values are plotted (n = 6). H , fold change in mitochondrial miR-122 and let-7g levels in control and methionine/choline-deficient (MCD) diet–exposed animal’s liver mitochondria (n = 4). I , Western blot analysis ( left panel ) and relative quantification ( right panel ) of different proteins present in the mitochondrial fractions isolated from the control and MCD diet–exposed animal liver (n = 3). J , effect of thapsigargin (TG) on the expression of stress-responsive proteins in Huh7 cells determined by Western blot analysis. β-actin was used as a loading control. K – L , effect of TG treatment (2.5 micromolar;16 h) on cellular ( K ) and mitochondrial ( L ) miRNA content. Relative levels of miRNAs were measured and plotted. For cellular and mitochondrial samples, U6 and let-7a levels were used for normalization. Relative change in let-7a in mitochondrial fraction was determined from Ct values and plotted in L . Values at the control set were used as a unit (n = 3). M , cellular miR-122 levels increased, whereas its mitochondrial levels remained unchanged when cells were treated (10 micromolar, 24 h) with a pharmacological blocker of extracellular vesicle production, GW4869, a powerful, selective, noncompetitive inhibitor of neutral sphingomyelinase (N-SMase), an enzyme crucial for generating ceramide, which drives the formation and release of exosomes (extracellular vesicles) from cells . Normalization was done with U6 snRNA and let-7a for cellular and mitochondrial miR-122, respectively (n = 3). Statistically analyzed data are indicated as mean ± SD of three experiments, with statistical significance marked as ns (nonsignificant), ∗ p < 0.05, ∗∗ p < 0.01, ∗∗∗ p < 0.001, and ∗∗∗∗ p < 0.0001, calculated using two-tailed Student’s t test. PARP, poly(ADP-ribose) polymerase; qRT–PCR, quantitative RT–PCR.
Article Snippet: They were randomly assigned to two groups and fed either a standard chow or an MCD diet (MP Biomedicals; catalog no.: 0296043910) for 4 weeks.
Techniques: Quantitative RT-PCR, Purification, Western Blot, Expressing, Marker, Binding Assay, Phospho-proteomics, Control, Isolation, Membrane, Quantitative Proteomics, Two Tailed Test