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PTEN inhibition improves muscle regeneration in mice fed a high-fat diet.

Hu Z, Wang H, Lee IH, Modi S, Wang X, Du J, Mitch WE - Diabetes (2010)

Bottom Line: We also measured PIP(3) and the enzymes regulating its level, IRS-1-associated phosphatidylinositol 3-kinase (PI3K) and PTEN.These changes were independent of impaired proliferation of muscle progenitor or satellite cells but were principally related to increased expression of PTEN, which reduced PIP(3) in muscle.In cultured muscle cells, palmitate directly stimulated PTEN expression and reduced cell growth.

View Article: PubMed Central - PubMed

Affiliation: Nephrology Division, Baylor College of Medicine, Houston, Texas, USA. zhaoyonh@bcm.edu

ABSTRACT

Objective: Mechanisms impairing wound healing in diabetes are poorly understood. To identify mechanisms, we induced insulin resistance by chronically feeding mice a high-fat diet (HFD). We also examined the regulation of phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) during muscle regeneration because augmented IGF-1 signaling can improve muscle regeneration.

Research design and methods: Muscle regeneration was induced by cardiotoxin injury, and we evaluated satellite cell activation and muscle maturation in HFD-fed mice. We also measured PIP(3) and the enzymes regulating its level, IRS-1-associated phosphatidylinositol 3-kinase (PI3K) and PTEN. Using primary cultures of muscle, we examined how fatty acids affect PTEN expression and how PTEN knockout influences muscle growth. Mice with muscle-specific PTEN knockout were used to examine how the HFD changes muscle regeneration.

Results: The HFD raised circulating fatty acids and impaired the growth of regenerating myofibers while delaying myofiber maturation and increasing collagen deposition. These changes were independent of impaired proliferation of muscle progenitor or satellite cells but were principally related to increased expression of PTEN, which reduced PIP(3) in muscle. In cultured muscle cells, palmitate directly stimulated PTEN expression and reduced cell growth. Knocking out PTEN restored cell growth. In mice, muscle-specific PTEN knockout improved the defects in muscle repair induced by HFD.

Conclusions: Insulin resistance impairs muscle regeneration by preventing myofiber maturation. The mechanism involves fatty acid-stimulated PTEN expression, which lowers muscle PIP(3). If similar pathways occur in diabetic patients, therapeutic strategies directed at improving the repair of damaged muscle could include suppression of PTEN activity.

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In HFD mice with muscle-specific PTEN deletion (MPKO), the suppression of myofiber maturation and the increase in collagen deposition were blocked. A: Hematoxylin-eosin staining revealed improved maturation of myofibers in injured tibialis anterior muscles of MPKO HFD mice (right panel) compared with results in muscles of HFD control lox/lox mice (left panel). B: MPKO improved weight gain of injured tibialis anterior muscles factored for tibia length compared with results from lox/lox HFD mice (n = 12 in each group). *P < 0.01. C: At 6 and 12 days after injury, immunostaining of the differentiation marker, desmin, increased in injured muscles of MPKO mice fed the HFD (right panel) at 6 and 12 days after injury compared with results in HFD control lox/lox mice (left panel). D: At days 12 and 21 after injury, Sirius red staining for collagen in muscles of HFD MPKO mice (right panel) revealed a significant reduction vs. results in muscles of HFD lox/lox mice (left panel). Bar graphs (lower panel) represent the fractions of injured muscle staining for collagen. n = 6. *P < 0.05. E: The ratio of p-Akt/Akt (Ser473) in muscle of lox/lox mice fed the HFD was lower than in muscle of MPKO mice (n = 6 in each group). The ratio of p-S6K1/S6K1 (Thr389) had a similar pattern (n = 6 in each group). CTX, cardiotoxin injury. (A high-quality digital representation of this figure is available in the online issue.)
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Figure 6: In HFD mice with muscle-specific PTEN deletion (MPKO), the suppression of myofiber maturation and the increase in collagen deposition were blocked. A: Hematoxylin-eosin staining revealed improved maturation of myofibers in injured tibialis anterior muscles of MPKO HFD mice (right panel) compared with results in muscles of HFD control lox/lox mice (left panel). B: MPKO improved weight gain of injured tibialis anterior muscles factored for tibia length compared with results from lox/lox HFD mice (n = 12 in each group). *P < 0.01. C: At 6 and 12 days after injury, immunostaining of the differentiation marker, desmin, increased in injured muscles of MPKO mice fed the HFD (right panel) at 6 and 12 days after injury compared with results in HFD control lox/lox mice (left panel). D: At days 12 and 21 after injury, Sirius red staining for collagen in muscles of HFD MPKO mice (right panel) revealed a significant reduction vs. results in muscles of HFD lox/lox mice (left panel). Bar graphs (lower panel) represent the fractions of injured muscle staining for collagen. n = 6. *P < 0.05. E: The ratio of p-Akt/Akt (Ser473) in muscle of lox/lox mice fed the HFD was lower than in muscle of MPKO mice (n = 6 in each group). The ratio of p-S6K1/S6K1 (Thr389) had a similar pattern (n = 6 in each group). CTX, cardiotoxin injury. (A high-quality digital representation of this figure is available in the online issue.)

Mentions: After 8 months of the HFD, we found that muscle-specific knockout of PTEN improves several functions. First, blood glucose and insulin levels were lower compared with values in lox/lox mice (P < 0.01)—compatible with reduced insulin resistance as reported by Wijesekara et al. (19) (supplemental Fig. 1B). Second, the sizes of new myofibers from muscles of MPKO mice at days 6 and 12 after injury were larger compared with results from lox/lox mice (Fig. 6A; supplemental Fig. 3C and D), and the weights of tibialis anterior muscles at days 12, 21, and 28 after injury were larger (Fig. 6B). Third, MPKO was associated with greater desmin expression in regenerating muscles at 6 and 12 days postinjury (Fig. 6C). Fourth, the increase in myofiber sizes of regenerating muscles in MPKO mice was associated with higher levels of p-Akt and its downstream mediator p-S6K1 (Fig. 6E). Finally, collagen deposition was reduced in regenerating muscles of HFD MPKO mice versus values in HFD lox/lox mice (Fig. 6D).


PTEN inhibition improves muscle regeneration in mice fed a high-fat diet.

Hu Z, Wang H, Lee IH, Modi S, Wang X, Du J, Mitch WE - Diabetes (2010)

In HFD mice with muscle-specific PTEN deletion (MPKO), the suppression of myofiber maturation and the increase in collagen deposition were blocked. A: Hematoxylin-eosin staining revealed improved maturation of myofibers in injured tibialis anterior muscles of MPKO HFD mice (right panel) compared with results in muscles of HFD control lox/lox mice (left panel). B: MPKO improved weight gain of injured tibialis anterior muscles factored for tibia length compared with results from lox/lox HFD mice (n = 12 in each group). *P < 0.01. C: At 6 and 12 days after injury, immunostaining of the differentiation marker, desmin, increased in injured muscles of MPKO mice fed the HFD (right panel) at 6 and 12 days after injury compared with results in HFD control lox/lox mice (left panel). D: At days 12 and 21 after injury, Sirius red staining for collagen in muscles of HFD MPKO mice (right panel) revealed a significant reduction vs. results in muscles of HFD lox/lox mice (left panel). Bar graphs (lower panel) represent the fractions of injured muscle staining for collagen. n = 6. *P < 0.05. E: The ratio of p-Akt/Akt (Ser473) in muscle of lox/lox mice fed the HFD was lower than in muscle of MPKO mice (n = 6 in each group). The ratio of p-S6K1/S6K1 (Thr389) had a similar pattern (n = 6 in each group). CTX, cardiotoxin injury. (A high-quality digital representation of this figure is available in the online issue.)
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Figure 6: In HFD mice with muscle-specific PTEN deletion (MPKO), the suppression of myofiber maturation and the increase in collagen deposition were blocked. A: Hematoxylin-eosin staining revealed improved maturation of myofibers in injured tibialis anterior muscles of MPKO HFD mice (right panel) compared with results in muscles of HFD control lox/lox mice (left panel). B: MPKO improved weight gain of injured tibialis anterior muscles factored for tibia length compared with results from lox/lox HFD mice (n = 12 in each group). *P < 0.01. C: At 6 and 12 days after injury, immunostaining of the differentiation marker, desmin, increased in injured muscles of MPKO mice fed the HFD (right panel) at 6 and 12 days after injury compared with results in HFD control lox/lox mice (left panel). D: At days 12 and 21 after injury, Sirius red staining for collagen in muscles of HFD MPKO mice (right panel) revealed a significant reduction vs. results in muscles of HFD lox/lox mice (left panel). Bar graphs (lower panel) represent the fractions of injured muscle staining for collagen. n = 6. *P < 0.05. E: The ratio of p-Akt/Akt (Ser473) in muscle of lox/lox mice fed the HFD was lower than in muscle of MPKO mice (n = 6 in each group). The ratio of p-S6K1/S6K1 (Thr389) had a similar pattern (n = 6 in each group). CTX, cardiotoxin injury. (A high-quality digital representation of this figure is available in the online issue.)
Mentions: After 8 months of the HFD, we found that muscle-specific knockout of PTEN improves several functions. First, blood glucose and insulin levels were lower compared with values in lox/lox mice (P < 0.01)—compatible with reduced insulin resistance as reported by Wijesekara et al. (19) (supplemental Fig. 1B). Second, the sizes of new myofibers from muscles of MPKO mice at days 6 and 12 after injury were larger compared with results from lox/lox mice (Fig. 6A; supplemental Fig. 3C and D), and the weights of tibialis anterior muscles at days 12, 21, and 28 after injury were larger (Fig. 6B). Third, MPKO was associated with greater desmin expression in regenerating muscles at 6 and 12 days postinjury (Fig. 6C). Fourth, the increase in myofiber sizes of regenerating muscles in MPKO mice was associated with higher levels of p-Akt and its downstream mediator p-S6K1 (Fig. 6E). Finally, collagen deposition was reduced in regenerating muscles of HFD MPKO mice versus values in HFD lox/lox mice (Fig. 6D).

Bottom Line: We also measured PIP(3) and the enzymes regulating its level, IRS-1-associated phosphatidylinositol 3-kinase (PI3K) and PTEN.These changes were independent of impaired proliferation of muscle progenitor or satellite cells but were principally related to increased expression of PTEN, which reduced PIP(3) in muscle.In cultured muscle cells, palmitate directly stimulated PTEN expression and reduced cell growth.

View Article: PubMed Central - PubMed

Affiliation: Nephrology Division, Baylor College of Medicine, Houston, Texas, USA. zhaoyonh@bcm.edu

ABSTRACT

Objective: Mechanisms impairing wound healing in diabetes are poorly understood. To identify mechanisms, we induced insulin resistance by chronically feeding mice a high-fat diet (HFD). We also examined the regulation of phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) during muscle regeneration because augmented IGF-1 signaling can improve muscle regeneration.

Research design and methods: Muscle regeneration was induced by cardiotoxin injury, and we evaluated satellite cell activation and muscle maturation in HFD-fed mice. We also measured PIP(3) and the enzymes regulating its level, IRS-1-associated phosphatidylinositol 3-kinase (PI3K) and PTEN. Using primary cultures of muscle, we examined how fatty acids affect PTEN expression and how PTEN knockout influences muscle growth. Mice with muscle-specific PTEN knockout were used to examine how the HFD changes muscle regeneration.

Results: The HFD raised circulating fatty acids and impaired the growth of regenerating myofibers while delaying myofiber maturation and increasing collagen deposition. These changes were independent of impaired proliferation of muscle progenitor or satellite cells but were principally related to increased expression of PTEN, which reduced PIP(3) in muscle. In cultured muscle cells, palmitate directly stimulated PTEN expression and reduced cell growth. Knocking out PTEN restored cell growth. In mice, muscle-specific PTEN knockout improved the defects in muscle repair induced by HFD.

Conclusions: Insulin resistance impairs muscle regeneration by preventing myofiber maturation. The mechanism involves fatty acid-stimulated PTEN expression, which lowers muscle PIP(3). If similar pathways occur in diabetic patients, therapeutic strategies directed at improving the repair of damaged muscle could include suppression of PTEN activity.

Show MeSH
Related in: MedlinePlus