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Mitoflash altered by metabolic stress in insulin-resistant skeletal muscle.

Ding Y, Fang H, Shang W, Xiao Y, Sun T, Hou N, Pan L, Sun X, Ma Q, Zhou J, Wang X, Zhang X, Cheng H - J. Mol. Med. (2015)

Bottom Line: In conjunction with in vivo imaging of skeletal muscles, we uncovered a progressive increase of mitoflash frequency along with its morphological changes.Interestingly, enhanced mitochondrial networking occurred at 12 weeks of age, and this was followed by mitochondrial fragmentation at 34 weeks.Mechanistic study revealed that the mitoflash remodeling was associated with altered expression of proteins involved in mitochondrial dynamics and quality control.

View Article: PubMed Central - PubMed

Affiliation: Institute of Molecular Medicine, Peking University, Beijing, China.

ABSTRACT

Unlabelled: Central to bioenergetics and reactive oxygen species (ROS) signaling, the mitochondrion plays pivotal roles in the pathogenesis of metabolic diseases. Recent advances have shown that mitochondrial flash ("mitoflash") visualized by the biosensor mt-cpYFP affords a frequency-coded, optical readout linked to mitochondrial ROS production and energy metabolism, at the resolution of a single mitochondrion. To investigate possible mitoflash responses to metabolic stress in insulin resistance (IR), we generated an mt-cpYFP-expressing db/db mouse model with the obesity and IR phenotypes unaltered. In conjunction with in vivo imaging of skeletal muscles, we uncovered a progressive increase of mitoflash frequency along with its morphological changes. Interestingly, enhanced mitochondrial networking occurred at 12 weeks of age, and this was followed by mitochondrial fragmentation at 34 weeks. Pioglitazone treatment normalized mitoflash frequency and morphology while restored mitochondrial respiratory function and insulin sensitivity in 12 weeks mt-cpYFP db/db mice. Mechanistic study revealed that the mitoflash remodeling was associated with altered expression of proteins involved in mitochondrial dynamics and quality control. These findings indicate that mitoflash activity may serve as an optical functional readout of the mitochondria, a robust and sensitive biomarker to gauge IR stresses and their amelioration by therapeutic interventions.

Key message: • In vivo detection of mitochondrial flashes in mt-cpYFP-expressing db/db mouse. • Mitoflash frequency increased progressively with disease development. • Mitoflash morphology revealed a biphasic change in mitochondrial networking. • Mitoflash abnormalities and mitochondrial defects are restored by pioglitazone. • Mitoflash may serve as a unique biomarker to gauge metabolic stress in insulin resistance.

No MeSH data available.


Related in: MedlinePlus

Biphasic changes of spatial properties of mitoflashes during IR progression. a–f Using an automated mitoflash detection algorithm, the proportions of punctiform, linear (length >2 μm), and lamellar (≥2 sarcomeres) mitoflashes were quantified (a, d), and mitoflash areas were measured in different groups (b, e). Note that average mitoflash size was enlarged at 12 weeks (upper panel) and diminished at 34 weeks in mt-cpYFP db/db group (lower panel). Representative images show mitoflashes of punctiform (bottom right), linear (top left and bottom left), and lamellar shapes (top right). Contours delineating mitoflash boundaries were generated automatically by the flash detection algorithm (c, f). g Hyper-connectivity of local mitochondrial networking in early IR was confirmed by the spatial spreading of photoactivated mt-PAGFP (upper images). A pair of images of the same region was taken immediately before (Pre) and 1 min after photoactivation. Note that mt-PAGFP signals co-localized with TMRM and spread beyond the region of photoactivation. h Average area of photoactivated mt-PAGFP was increased in skeletal muscle of 12-week-old db/db mice compared to that in db/m mice. Data are expressed as mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001 vs age-matched mt-cpYFP db/m or db/m mice; values were subject to Student’s t test
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Fig3: Biphasic changes of spatial properties of mitoflashes during IR progression. a–f Using an automated mitoflash detection algorithm, the proportions of punctiform, linear (length >2 μm), and lamellar (≥2 sarcomeres) mitoflashes were quantified (a, d), and mitoflash areas were measured in different groups (b, e). Note that average mitoflash size was enlarged at 12 weeks (upper panel) and diminished at 34 weeks in mt-cpYFP db/db group (lower panel). Representative images show mitoflashes of punctiform (bottom right), linear (top left and bottom left), and lamellar shapes (top right). Contours delineating mitoflash boundaries were generated automatically by the flash detection algorithm (c, f). g Hyper-connectivity of local mitochondrial networking in early IR was confirmed by the spatial spreading of photoactivated mt-PAGFP (upper images). A pair of images of the same region was taken immediately before (Pre) and 1 min after photoactivation. Note that mt-PAGFP signals co-localized with TMRM and spread beyond the region of photoactivation. h Average area of photoactivated mt-PAGFP was increased in skeletal muscle of 12-week-old db/db mice compared to that in db/m mice. Data are expressed as mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001 vs age-matched mt-cpYFP db/m or db/m mice; values were subject to Student’s t test

Mentions: Using an automated mitoflash detection algorithm [28], we classified mitoflashes into three categories—punctiform, linear, and lamellar—and measured the area. At 12 weeks, more lamellar mitoflashes were detected in mt-cpYFP db/db, and the histogram of the mitoflash area was shifted rightward, with network mitoflash events (>10 μm2) twice as frequent as in the mt-cpYFP db/m group (Fig. 3a, b). The average area of a mitoflash increased from 4.08 μm2 (n = 90 events from 4 mice, 6–20 skeletal muscle cells/mouse, average observation area = 3823.1 ± 167.9 μm2/cell) in mt-cpYFP db/m mice to 7.60 μm2 in mt-cpYFP db/db mice (n = 622 events from 7 mice, 7–25 skeletal muscle cells/mouse, average observation area = 3848.9 ± 134.1 μm2/cell, p < 0.05 vs control) (Fig. 3c). This finding showed enhanced local mitoflash networking is a prominent feature of the mitochondrial response in skeletal muscles in the relatively early phase of IR.Fig. 3


Mitoflash altered by metabolic stress in insulin-resistant skeletal muscle.

Ding Y, Fang H, Shang W, Xiao Y, Sun T, Hou N, Pan L, Sun X, Ma Q, Zhou J, Wang X, Zhang X, Cheng H - J. Mol. Med. (2015)

Biphasic changes of spatial properties of mitoflashes during IR progression. a–f Using an automated mitoflash detection algorithm, the proportions of punctiform, linear (length >2 μm), and lamellar (≥2 sarcomeres) mitoflashes were quantified (a, d), and mitoflash areas were measured in different groups (b, e). Note that average mitoflash size was enlarged at 12 weeks (upper panel) and diminished at 34 weeks in mt-cpYFP db/db group (lower panel). Representative images show mitoflashes of punctiform (bottom right), linear (top left and bottom left), and lamellar shapes (top right). Contours delineating mitoflash boundaries were generated automatically by the flash detection algorithm (c, f). g Hyper-connectivity of local mitochondrial networking in early IR was confirmed by the spatial spreading of photoactivated mt-PAGFP (upper images). A pair of images of the same region was taken immediately before (Pre) and 1 min after photoactivation. Note that mt-PAGFP signals co-localized with TMRM and spread beyond the region of photoactivation. h Average area of photoactivated mt-PAGFP was increased in skeletal muscle of 12-week-old db/db mice compared to that in db/m mice. Data are expressed as mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001 vs age-matched mt-cpYFP db/m or db/m mice; values were subject to Student’s t test
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Fig3: Biphasic changes of spatial properties of mitoflashes during IR progression. a–f Using an automated mitoflash detection algorithm, the proportions of punctiform, linear (length >2 μm), and lamellar (≥2 sarcomeres) mitoflashes were quantified (a, d), and mitoflash areas were measured in different groups (b, e). Note that average mitoflash size was enlarged at 12 weeks (upper panel) and diminished at 34 weeks in mt-cpYFP db/db group (lower panel). Representative images show mitoflashes of punctiform (bottom right), linear (top left and bottom left), and lamellar shapes (top right). Contours delineating mitoflash boundaries were generated automatically by the flash detection algorithm (c, f). g Hyper-connectivity of local mitochondrial networking in early IR was confirmed by the spatial spreading of photoactivated mt-PAGFP (upper images). A pair of images of the same region was taken immediately before (Pre) and 1 min after photoactivation. Note that mt-PAGFP signals co-localized with TMRM and spread beyond the region of photoactivation. h Average area of photoactivated mt-PAGFP was increased in skeletal muscle of 12-week-old db/db mice compared to that in db/m mice. Data are expressed as mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001 vs age-matched mt-cpYFP db/m or db/m mice; values were subject to Student’s t test
Mentions: Using an automated mitoflash detection algorithm [28], we classified mitoflashes into three categories—punctiform, linear, and lamellar—and measured the area. At 12 weeks, more lamellar mitoflashes were detected in mt-cpYFP db/db, and the histogram of the mitoflash area was shifted rightward, with network mitoflash events (>10 μm2) twice as frequent as in the mt-cpYFP db/m group (Fig. 3a, b). The average area of a mitoflash increased from 4.08 μm2 (n = 90 events from 4 mice, 6–20 skeletal muscle cells/mouse, average observation area = 3823.1 ± 167.9 μm2/cell) in mt-cpYFP db/m mice to 7.60 μm2 in mt-cpYFP db/db mice (n = 622 events from 7 mice, 7–25 skeletal muscle cells/mouse, average observation area = 3848.9 ± 134.1 μm2/cell, p < 0.05 vs control) (Fig. 3c). This finding showed enhanced local mitoflash networking is a prominent feature of the mitochondrial response in skeletal muscles in the relatively early phase of IR.Fig. 3

Bottom Line: In conjunction with in vivo imaging of skeletal muscles, we uncovered a progressive increase of mitoflash frequency along with its morphological changes.Interestingly, enhanced mitochondrial networking occurred at 12 weeks of age, and this was followed by mitochondrial fragmentation at 34 weeks.Mechanistic study revealed that the mitoflash remodeling was associated with altered expression of proteins involved in mitochondrial dynamics and quality control.

View Article: PubMed Central - PubMed

Affiliation: Institute of Molecular Medicine, Peking University, Beijing, China.

ABSTRACT

Unlabelled: Central to bioenergetics and reactive oxygen species (ROS) signaling, the mitochondrion plays pivotal roles in the pathogenesis of metabolic diseases. Recent advances have shown that mitochondrial flash ("mitoflash") visualized by the biosensor mt-cpYFP affords a frequency-coded, optical readout linked to mitochondrial ROS production and energy metabolism, at the resolution of a single mitochondrion. To investigate possible mitoflash responses to metabolic stress in insulin resistance (IR), we generated an mt-cpYFP-expressing db/db mouse model with the obesity and IR phenotypes unaltered. In conjunction with in vivo imaging of skeletal muscles, we uncovered a progressive increase of mitoflash frequency along with its morphological changes. Interestingly, enhanced mitochondrial networking occurred at 12 weeks of age, and this was followed by mitochondrial fragmentation at 34 weeks. Pioglitazone treatment normalized mitoflash frequency and morphology while restored mitochondrial respiratory function and insulin sensitivity in 12 weeks mt-cpYFP db/db mice. Mechanistic study revealed that the mitoflash remodeling was associated with altered expression of proteins involved in mitochondrial dynamics and quality control. These findings indicate that mitoflash activity may serve as an optical functional readout of the mitochondria, a robust and sensitive biomarker to gauge IR stresses and their amelioration by therapeutic interventions.

Key message: • In vivo detection of mitochondrial flashes in mt-cpYFP-expressing db/db mouse. • Mitoflash frequency increased progressively with disease development. • Mitoflash morphology revealed a biphasic change in mitochondrial networking. • Mitoflash abnormalities and mitochondrial defects are restored by pioglitazone. • Mitoflash may serve as a unique biomarker to gauge metabolic stress in insulin resistance.

No MeSH data available.


Related in: MedlinePlus