Blunted Akt/FOXO signalling and activation of genes controlling atrophy and fuel use in statin myopathy.
J Physiol. 2009 Jan 15 ;587(Pt 1):219-30. Epub 2008 Nov 10. PMID: 19001041
Joanne E Mallinson
Statins are used clinically for cholesterol reduction, but statin therapy is associated with myopathic changes through a poorly defined mechanism. We used an in vivo model of statin myopathy to determine whether statins up-regulate genes associated with proteasomal- and lysosomal-mediated proteolysis and whether PDK gene expression is simultaneously up-regulated leading to the impairment of muscle carbohydrate oxidation. Animals were dosed daily with 80 mg kg(-1) day(-1) simvastatin for 4 (n = 6) and 12 days (n = 5), 88 mg kg(-1) day(-1) simvastatin for 12 days (n = 4), or vehicle (0.5% w/v hydroxypropyl-methylcellulose and 0.1% w/v polysorbate 80; Control, n = 6) for 12 days by oral gavage. We found, in biceps femoris muscle, decreased Akt(Ser473), FOXO1(Ser253) and FOXO3a(Ser253) phosphorylation in the cytosol (P<0.05, P<0.05, P<0.001, respectively) and decreased phosphorylation of FOXO1 in the nucleus after 12 days simvastatin when compared to Control (P<0.05). This was paralleled by a marked increase in the transcription of downstream targets of FOXO, i.e. MAFbx (P<0.001), MuRF-1 (P<0.001), cathepsin-L (P<0.05), PDK2 (P<0.05) and PDK4 (P<0.05). These changes were accompanied by increased PPARalpha (P<0.05), TNFalpha (P<0.01), IL6 (P<0.01), Mt1A (P<0.01) mRNA and increased muscle glycogen (P<0.05) compared to Control. RhoA activity decreased after 4 days simvastatin (P<0.05); however, activity was no different from Control after 12 days. Simvastatin down-regulated PI3k/Akt signalling, independently of RhoA, and up-regulated FOXO transcription factors and downstream gene targets known to be implicated in proteasomal- and lysosomal-mediated muscle proteolysis, carbohydrate oxidation, oxidative stress and inflammation in an in vivo model of statin-induced myopathy. These changes occurred in the main before evidence of extensive myopathy or a decline in the muscle protein to DNA ratio.