Forkhead box O1 and muscle RING finger 1 protein expression in atrophic and hypertrophic denervated mouse skeletal muscle

Abstract

BackgroundForkhead box O (FoxO) transcription factors and E3 ubiquitin ligases such as Muscle RING finger 1 (MuRF1) are believed to participate in the regulation of skeletal muscle mass. The function of FoxO transcription factors is regulated by post-translational modifications such as phosphorylation and acetylation. In the present study FoxO1 protein expression, phosphorylation and acetylation as well as MuRF1 protein expression, were examined in atrophic and hypertrophic denervated skeletal muscle.MethodsProtein expression, phosphorylation and acetylation were studied semi-quantitatively using Western blots. Muscles studied were 6-days denervated mouse hind-limb muscles (anterior tibial as well as pooled gastrocnemius and soleus muscles, all atrophic), 6-days denervated mouse hemidiaphragm muscles (hypertrophic) and innervated control muscles. Total muscle homogenates were used as well as separated nuclear and cytosolic fractions of innervated and 6-days denervated anterior tibial and hemidiaphragm muscles.ResultsExpression of FoxO1 and MuRF1 proteins increased 0.3-3.7-fold in all 6-days denervated muscles studied, atrophic as well as hypertrophic. Phosphorylation of FoxO1 at S256 increased about 0.8-1-fold after denervation in pooled gastrocnemius and soleus muscles and in hemidiaphragm but not in unfractionated anterior tibial muscle. A small (0.2-fold) but statistically significant increase in FoxO1 phosphorylation was, however, observed in cytosolic fractions of denervated anterior tibial muscle. A statistically significant increase in FoxO1 acetylation (0.8-fold) was observed only in denervated anterior tibial muscle. Increases in total FoxO1 and in phosphorylated FoxO1 were only seen in cytosolic fractions of denervated atrophic anterior tibial muscle whereas in denervated hypertrophic hemidiaphragm both total FoxO1 and phosphorylated FoxO1 increased in cytosolic as well as in nuclear fractions. MuRF1 protein expression increased in cytosolic as well as in nuclear fractions of both denervated atrophic anterior tibial muscle and denervated hypertrophic hemidiaphragm muscle.ConclusionsIncreased expression of FoxO1 and MuRF1 in denervated muscles (atrophic as well as hypertrophic) suggests that these proteins participate in the tissue remodelling occurring after denervation. The effect of denervation on the level of phosphorylated and acetylated FoxO1 differed in the muscles studied and may be related to differences in fiber type composition of the muscles.

4‐Aminopyridine attenuates muscle atrophy after sciatic nerve crush injury in mice

“…The upstream FoxO transcription factors FoxO1 and FoxO3 are involved in the regulation of muscle mass and atrophy. 15,19,[48][49][50] We found that both FoxO1 and FoxO3 were significantly upregulated within 3 days of crush injury, but the significant effect of 4-AP treatment on the FoxO expression levels was evident only at day 7, and it was more pronounced on FoxO3. Although FoxO3 activation alone has been reported to be sufficient to cause significant muscle atrophy in vivo, 15,19 FoxO members are redundant in their function, and both FoxO1 and FoxO3 participate in muscle atrophy.…”

“…In line with RT‐PCR data, results of Western blot analysis in muscle homogenates confirmed the role of 4‐AP in restoring myogenin levels in affected muscle after sciatic nerve crush injury. The upstream FoxO transcription factors FoxO1 and FoxO3 are involved in the regulation of muscle mass and atrophy . We found that both FoxO1 and FoxO3 were significantly upregulated within 3 days of crush injury, but the significant effect of 4‐AP treatment on the FoxO expression levels was evident only at day 7, and it was more pronounced on FoxO3.…”

TLR2 deficiency attenuates skeletal muscle atrophy in mice

“…The expression of atrogin-1 and MuRF1 is regulated by FOXO transcription factors, especially FOXO1 and FOXO3 [27,28]. Indeed, the protein levels and activities of FOXO1 and FOXO3 are increased in the atrophic skeletal muscles of mice [29,30]. Furthermore, the overexpression of FOXO proteins was shown to increase atrogin-1 mRNA levels and induce skeletal muscle atrophy, whereas FOXO deficiency prevented skeletal muscle atrophy [27,31].…”

Quercetin glycosides prevent dexamethasone-induced muscle atrophy in mice

“…A synthetic glucocorticoid, dexamethasone (DEX), induces muscle atrophy, which involves both induction of protein degradation and suppression of general protein synthesis [ 2 ]. Recent studies show that two muscle-specific E3 ubiquitin ligases, atrogin-1/muscle atrophy F-box (atrogin-1) and muscle ring finger protein 1 (MuRF-1), the so-called atrogenes [ 3 ], play key roles in muscle atrophy caused by immobilization and denervation [ 4 , 5 ], as well as DEX treatment [ 6 ]. Furthermore, their gene expression and activities are regulated by transcription factors from the class O type forkhead (Foxo) family [ [4] , [5] , [6] , [7] ].…”