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A novel cellular defect in diabetes: membrane repair failure.

Howard AC, McNeil AK, Xiong F, Xiong WC, McNeil PL - Diabetes (2011)

Bottom Line: Skeletal muscle myopathy is a common diabetes complication.Downhill running also resulted in a higher level of repair failure in diabetic mice.However, a repair defect could be induced, in the absence of high glucose, by enhancing AGE binding to RAGE, or simply by increasing cell exposure to AGE.

View Article: PubMed Central - PubMed

Affiliation: Institute of Molecular Medicine and Genetics, Georgia Health Sciences University, Augusta, Georgia, USA.

ABSTRACT

Objective: Skeletal muscle myopathy is a common diabetes complication. One possible cause of myopathy is myocyte failure to repair contraction-generated plasma membrane injuries. Here, we test the hypothesis that diabetes induces a repair defect in skeletal muscle myocytes.

Research design and methods: Myocytes in intact muscle from type 1 (INS2(Akita+/-)) and type 2 (db/db) diabetic mice were injured with a laser and dye uptake imaged confocally to test repair efficiency. Membrane repair defects were also assessed in diabetic mice after downhill running, which induces myocyte plasma membrane disruption injuries in vivo. A cell culture model was used to investigate the role of advanced glycation end products (AGEs) and the receptor for AGE (RAGE) in development of this repair defect.

Results: Diabetic myocytes displayed significantly more dye influx after laser injury than controls, indicating a repair deficiency. Downhill running also resulted in a higher level of repair failure in diabetic mice. This repair defect was mimicked in cultured cells by prolonged exposure to high glucose. Inhibition of the formation of AGE eliminated this glucose-induced repair defect. However, a repair defect could be induced, in the absence of high glucose, by enhancing AGE binding to RAGE, or simply by increasing cell exposure to AGE.

Conclusions: Because one consequence of repair failure is rapid cell death (via necrosis), our demonstration that repair fails in diabetes suggests a new mechanism by which myopathy develops in diabetes.

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Exercised-induced myocyte disruptions are not repaired in diabetic mice. A: Paired transmission and fluorescence micrographs showing EBD-labeled myofibers (arrows) in the gastrocnemius muscle from diabetic (INS2) and control (Ctl) (B6) mice that run downhill for 60 min and then are injected with the EBD tracer. Myocytes that were injured by running and failed to repair are labeled. B: The number of EBD myofibers counted from such micrographs in the gastrocnemius and quadriceps muscles of diabetic INS2 and control B6 mice. Data are presented as the mean ± SEM. *P < 0.05; n = 5 mice for the “Run” groups and 4 mice for the “Not Run” groups. Scale bar, 100 μm and 20× magnification. (A high-quality digital representation of this figure is available in the online issue.)
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Figure 2: Exercised-induced myocyte disruptions are not repaired in diabetic mice. A: Paired transmission and fluorescence micrographs showing EBD-labeled myofibers (arrows) in the gastrocnemius muscle from diabetic (INS2) and control (Ctl) (B6) mice that run downhill for 60 min and then are injected with the EBD tracer. Myocytes that were injured by running and failed to repair are labeled. B: The number of EBD myofibers counted from such micrographs in the gastrocnemius and quadriceps muscles of diabetic INS2 and control B6 mice. Data are presented as the mean ± SEM. *P < 0.05; n = 5 mice for the “Run” groups and 4 mice for the “Not Run” groups. Scale bar, 100 μm and 20× magnification. (A high-quality digital representation of this figure is available in the online issue.)

Mentions: Plasma membrane disruptions are induced in vivo in muscle undergoing eccentric contractions, such as those produced by downhill running (11). To determine if membrane repair fails at a greater rate in diabetic mice during eccentric contraction-induced injury, we monitored myocyte permeability to EBD. EBD is a fluorescent dye that enters only into cells lacking an intact plasma membrane barrier and is effective at identifying injured muscle fibers without the presence of a counter-stain (16,20). We injected this dye into mice after running, so that myofibers that suffered a disruption and failed to repair would be labeled. The morphology of the EBD-positive fibers is illustrated in Fig. 2A (white arrows). As expected, in both normal and diabetic mice, running induced an increase in the number of EBD-positive fibers. However, running induced a significantly higher number of EBD-positive fibers in the diabetic mice (Fig. 2B, INS2 vs. control).


A novel cellular defect in diabetes: membrane repair failure.

Howard AC, McNeil AK, Xiong F, Xiong WC, McNeil PL - Diabetes (2011)

Exercised-induced myocyte disruptions are not repaired in diabetic mice. A: Paired transmission and fluorescence micrographs showing EBD-labeled myofibers (arrows) in the gastrocnemius muscle from diabetic (INS2) and control (Ctl) (B6) mice that run downhill for 60 min and then are injected with the EBD tracer. Myocytes that were injured by running and failed to repair are labeled. B: The number of EBD myofibers counted from such micrographs in the gastrocnemius and quadriceps muscles of diabetic INS2 and control B6 mice. Data are presented as the mean ± SEM. *P < 0.05; n = 5 mice for the “Run” groups and 4 mice for the “Not Run” groups. Scale bar, 100 μm and 20× magnification. (A high-quality digital representation of this figure is available in the online issue.)
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Related In: Results  -  Collection

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Figure 2: Exercised-induced myocyte disruptions are not repaired in diabetic mice. A: Paired transmission and fluorescence micrographs showing EBD-labeled myofibers (arrows) in the gastrocnemius muscle from diabetic (INS2) and control (Ctl) (B6) mice that run downhill for 60 min and then are injected with the EBD tracer. Myocytes that were injured by running and failed to repair are labeled. B: The number of EBD myofibers counted from such micrographs in the gastrocnemius and quadriceps muscles of diabetic INS2 and control B6 mice. Data are presented as the mean ± SEM. *P < 0.05; n = 5 mice for the “Run” groups and 4 mice for the “Not Run” groups. Scale bar, 100 μm and 20× magnification. (A high-quality digital representation of this figure is available in the online issue.)
Mentions: Plasma membrane disruptions are induced in vivo in muscle undergoing eccentric contractions, such as those produced by downhill running (11). To determine if membrane repair fails at a greater rate in diabetic mice during eccentric contraction-induced injury, we monitored myocyte permeability to EBD. EBD is a fluorescent dye that enters only into cells lacking an intact plasma membrane barrier and is effective at identifying injured muscle fibers without the presence of a counter-stain (16,20). We injected this dye into mice after running, so that myofibers that suffered a disruption and failed to repair would be labeled. The morphology of the EBD-positive fibers is illustrated in Fig. 2A (white arrows). As expected, in both normal and diabetic mice, running induced an increase in the number of EBD-positive fibers. However, running induced a significantly higher number of EBD-positive fibers in the diabetic mice (Fig. 2B, INS2 vs. control).

Bottom Line: Skeletal muscle myopathy is a common diabetes complication.Downhill running also resulted in a higher level of repair failure in diabetic mice.However, a repair defect could be induced, in the absence of high glucose, by enhancing AGE binding to RAGE, or simply by increasing cell exposure to AGE.

View Article: PubMed Central - PubMed

Affiliation: Institute of Molecular Medicine and Genetics, Georgia Health Sciences University, Augusta, Georgia, USA.

ABSTRACT

Objective: Skeletal muscle myopathy is a common diabetes complication. One possible cause of myopathy is myocyte failure to repair contraction-generated plasma membrane injuries. Here, we test the hypothesis that diabetes induces a repair defect in skeletal muscle myocytes.

Research design and methods: Myocytes in intact muscle from type 1 (INS2(Akita+/-)) and type 2 (db/db) diabetic mice were injured with a laser and dye uptake imaged confocally to test repair efficiency. Membrane repair defects were also assessed in diabetic mice after downhill running, which induces myocyte plasma membrane disruption injuries in vivo. A cell culture model was used to investigate the role of advanced glycation end products (AGEs) and the receptor for AGE (RAGE) in development of this repair defect.

Results: Diabetic myocytes displayed significantly more dye influx after laser injury than controls, indicating a repair deficiency. Downhill running also resulted in a higher level of repair failure in diabetic mice. This repair defect was mimicked in cultured cells by prolonged exposure to high glucose. Inhibition of the formation of AGE eliminated this glucose-induced repair defect. However, a repair defect could be induced, in the absence of high glucose, by enhancing AGE binding to RAGE, or simply by increasing cell exposure to AGE.

Conclusions: Because one consequence of repair failure is rapid cell death (via necrosis), our demonstration that repair fails in diabetes suggests a new mechanism by which myopathy develops in diabetes.

Show MeSH
Related in: MedlinePlus