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Endosome – mitochondria interactions are modulated by iron release from transferrin

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ABSTRACT

Using superresolution and quantitative fluorescence microscopy, Das et al. have revealed that iron-transferrin–containing endosomes directly interact with mitochondria, facilitating iron transfer in epithelial cells. Their findings further enrich the repertoire of organelle–organelle direct interactions to accomplish a functional significance.

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Tf-endosome–mitochondrial interaction does not depend on intraendosomal iron release. (A) Double-labeled fluorescence image from a representative time-lapse video of MitoTracker orange–labeled MDCK-PTR cells pulsed with AF488 lock-hTf (a); corresponding 3D rendering of AF488 lock-hTf–endosomes and mitochondria (b); the 3D-rendered image selecting kiss and run undergoing lock-hTf–endosomes (c; see Video 8); magnified ROI (d; white box in c); magnified ROI (white box in d) where the selected lock-hTf–endosome (yellow spot) is in close proximity to a mitochondrion (e). Bars: (a–d) 10.0 µm; (e) 1.0 µm. (B) Videomicrograph of the kiss and run interaction between the selected lock-hTf–endosome and mitochondrion (A e). Graph shows a definite decrease in lock-hTf–endosomal instantaneous speed (blue line) during the kiss phase (dashed boxes), defined by DT = 0 (red line). See Video 9. Video 10 shows two additional lock-hTf–endosomal kiss and run events with mitochondria displaying a similar trend of decreased endosomal instantaneous speed upon interaction. Bar, 0.5 µm. (C and D) Mean hTf-endosomal (C: 311 kiss and run events, 131 endosomes, and 6 cells) and lock-hTf–endosomal (D: 603 kiss and run events, 356 endosomes, and 10 cells) instantaneous speeds were significantly higher during run noninteractions than during their kiss phases. Error bars: 95% confidence interval; **, P < 0.001, Student’s t test.
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fig5: Tf-endosome–mitochondrial interaction does not depend on intraendosomal iron release. (A) Double-labeled fluorescence image from a representative time-lapse video of MitoTracker orange–labeled MDCK-PTR cells pulsed with AF488 lock-hTf (a); corresponding 3D rendering of AF488 lock-hTf–endosomes and mitochondria (b); the 3D-rendered image selecting kiss and run undergoing lock-hTf–endosomes (c; see Video 8); magnified ROI (d; white box in c); magnified ROI (white box in d) where the selected lock-hTf–endosome (yellow spot) is in close proximity to a mitochondrion (e). Bars: (a–d) 10.0 µm; (e) 1.0 µm. (B) Videomicrograph of the kiss and run interaction between the selected lock-hTf–endosome and mitochondrion (A e). Graph shows a definite decrease in lock-hTf–endosomal instantaneous speed (blue line) during the kiss phase (dashed boxes), defined by DT = 0 (red line). See Video 9. Video 10 shows two additional lock-hTf–endosomal kiss and run events with mitochondria displaying a similar trend of decreased endosomal instantaneous speed upon interaction. Bar, 0.5 µm. (C and D) Mean hTf-endosomal (C: 311 kiss and run events, 131 endosomes, and 6 cells) and lock-hTf–endosomal (D: 603 kiss and run events, 356 endosomes, and 10 cells) instantaneous speeds were significantly higher during run noninteractions than during their kiss phases. Error bars: 95% confidence interval; **, P < 0.001, Student’s t test.

Mentions: To investigate the prevalence of endosome–mitochondria interactions within the early endocytic pathway, we established a criterion to quantitatively measure interactions in an unbiased and semiautomated manner. Previously, quantitative analyses of cell-to-cell (Malide et al., 2012; McKee et al., 2013) or organelle–organelle interactions (Whalen et al., 2012; Bouvet et al., 2013; Wang et al., 2015) were performed using the distance transformation (DT) algorithm. DT is a representation of the digital image in terms of pixels with assigned values based on their respective distances from the boundary of a specific object. Therefore, 3D rendering of the object in question is a prerequisite for carrying out the DT operation. Here, we used the DT algorithm, built in the image analysis software Imaris, for quantitative determination of the distance of Tf-endosomes from the boundary of 3D-rendered mitochondrial surfaces, which are considered to be the anchor organelle, as they are less dynamic than endosomes. The DT criterion was evaluated for its consistency and reliability on immunofluorescent fixed cells (Fig. 2) before it was used in the analysis of time-lapse videos to study the dynamics of endosome–mitochondria interactions in live cells (see Figs. 3, 4, and 5).


Endosome – mitochondria interactions are modulated by iron release from transferrin
Tf-endosome–mitochondrial interaction does not depend on intraendosomal iron release. (A) Double-labeled fluorescence image from a representative time-lapse video of MitoTracker orange–labeled MDCK-PTR cells pulsed with AF488 lock-hTf (a); corresponding 3D rendering of AF488 lock-hTf–endosomes and mitochondria (b); the 3D-rendered image selecting kiss and run undergoing lock-hTf–endosomes (c; see Video 8); magnified ROI (d; white box in c); magnified ROI (white box in d) where the selected lock-hTf–endosome (yellow spot) is in close proximity to a mitochondrion (e). Bars: (a–d) 10.0 µm; (e) 1.0 µm. (B) Videomicrograph of the kiss and run interaction between the selected lock-hTf–endosome and mitochondrion (A e). Graph shows a definite decrease in lock-hTf–endosomal instantaneous speed (blue line) during the kiss phase (dashed boxes), defined by DT = 0 (red line). See Video 9. Video 10 shows two additional lock-hTf–endosomal kiss and run events with mitochondria displaying a similar trend of decreased endosomal instantaneous speed upon interaction. Bar, 0.5 µm. (C and D) Mean hTf-endosomal (C: 311 kiss and run events, 131 endosomes, and 6 cells) and lock-hTf–endosomal (D: 603 kiss and run events, 356 endosomes, and 10 cells) instantaneous speeds were significantly higher during run noninteractions than during their kiss phases. Error bars: 95% confidence interval; **, P < 0.001, Student’s t test.
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fig5: Tf-endosome–mitochondrial interaction does not depend on intraendosomal iron release. (A) Double-labeled fluorescence image from a representative time-lapse video of MitoTracker orange–labeled MDCK-PTR cells pulsed with AF488 lock-hTf (a); corresponding 3D rendering of AF488 lock-hTf–endosomes and mitochondria (b); the 3D-rendered image selecting kiss and run undergoing lock-hTf–endosomes (c; see Video 8); magnified ROI (d; white box in c); magnified ROI (white box in d) where the selected lock-hTf–endosome (yellow spot) is in close proximity to a mitochondrion (e). Bars: (a–d) 10.0 µm; (e) 1.0 µm. (B) Videomicrograph of the kiss and run interaction between the selected lock-hTf–endosome and mitochondrion (A e). Graph shows a definite decrease in lock-hTf–endosomal instantaneous speed (blue line) during the kiss phase (dashed boxes), defined by DT = 0 (red line). See Video 9. Video 10 shows two additional lock-hTf–endosomal kiss and run events with mitochondria displaying a similar trend of decreased endosomal instantaneous speed upon interaction. Bar, 0.5 µm. (C and D) Mean hTf-endosomal (C: 311 kiss and run events, 131 endosomes, and 6 cells) and lock-hTf–endosomal (D: 603 kiss and run events, 356 endosomes, and 10 cells) instantaneous speeds were significantly higher during run noninteractions than during their kiss phases. Error bars: 95% confidence interval; **, P < 0.001, Student’s t test.
Mentions: To investigate the prevalence of endosome–mitochondria interactions within the early endocytic pathway, we established a criterion to quantitatively measure interactions in an unbiased and semiautomated manner. Previously, quantitative analyses of cell-to-cell (Malide et al., 2012; McKee et al., 2013) or organelle–organelle interactions (Whalen et al., 2012; Bouvet et al., 2013; Wang et al., 2015) were performed using the distance transformation (DT) algorithm. DT is a representation of the digital image in terms of pixels with assigned values based on their respective distances from the boundary of a specific object. Therefore, 3D rendering of the object in question is a prerequisite for carrying out the DT operation. Here, we used the DT algorithm, built in the image analysis software Imaris, for quantitative determination of the distance of Tf-endosomes from the boundary of 3D-rendered mitochondrial surfaces, which are considered to be the anchor organelle, as they are less dynamic than endosomes. The DT criterion was evaluated for its consistency and reliability on immunofluorescent fixed cells (Fig. 2) before it was used in the analysis of time-lapse videos to study the dynamics of endosome–mitochondria interactions in live cells (see Figs. 3, 4, and 5).

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Using superresolution and quantitative fluorescence microscopy, Das et al. have revealed that iron-transferrin&ndash;containing endosomes directly interact with mitochondria, facilitating iron transfer in epithelial cells. Their findings further enrich the repertoire of organelle&ndash;organelle direct interactions to accomplish a functional significance.

No MeSH data available.


Related in: MedlinePlus