FoxO3 Controls Autophagy in Skeletal Muscle In Vivo

Abstract

Autophagy allows cell survival during starvation through the bulk degradation of proteins and organelles by lysosomal enzymes. However, the mechanisms responsible for the induction and regulation of the autophagy program are poorly understood. Here we show that the FoxO3 transcription factor, which plays a critical role in muscle atrophy, is necessary and sufficient for the induction of autophagy in skeletal muscle in vivo. Akt/PKB activation blocks FoxO3 activation and autophagy, and this effect is not prevented by rapamycin. FoxO3 controls the transcription of autophagy-related genes, including LC3 and Bnip3, and Bnip3 appears to mediate the effect of FoxO3 on autophagy. This effect is not prevented by proteasome inhibitors. Thus, FoxO3 controls the two major systems of protein breakdown in skeletal muscle, the ubiquitin-proteasomal and autophagic/lysosomal pathways, independently. These findings point to FoxO3 and Bnip3 as potential therapeutic targets in muscle wasting disorders and other degenerative and neoplastic diseases in which autophagy is involved.

Loss of the novel Vcp (valosin containing protein) interactor Washc4 interferes with autophagy-mediated proteostasis in striated muscle and leads to myopathy in vivo

“…In vivo transfection was performed by intramuscular injection of expression plasmids (WASHC4-eGFP and VCP-mCherry) in flexor digitorum brevis (FDB) muscle followed by electroporation as described [45]. Flexor digitorum brevis muscle muscles were digested in type I collagenase (Worthington Biochemical Corp., LS004194) at 37°C for 1 h, dissociated into single fibers, plated on glass coverslips coated with laminin (Sigma-Aldrich, L2020) and cultured as described [46]. …”

Long live FOXO: unraveling the role of FOXO proteins in aging and longevity

“…As previously mentioned, decreased autophagy has been related to premature aging and age‐related associated disorders (Hara et al ., 2006; Komatsu et al ., 2006; Jung et al ., 2008; Pickford et al ., 2008; Masiero et al ., 2009; Lee et al ., 2010a, 2010b). Foxo factors have been shown to regulate autophagy in mouse muscle, particularly Foxo3, which induces the expression of several autophagy genes and increases autophagosome formation (Mammucari et al ., 2007; Zhao et al ., 2007; Webb & Brunet, 2014). Foxo1 and Foxo3 overexpression also promotes mitophagy (degradation of mitochondria by the autophagy–lysosomal pathway) by upregulating the expression of the mouse mitochondrial E3 ubiquitin protein ligase 1 (Lokireddy et al ., 2012).…”

Evidence that a mitochondrial death spiral underlies antagonistic pleiotropy

“…These effects of Tor and Foxo on autophagy components are physiologically significant. Tor activation decreases autophagy (Kim et al ., 2011), whereas loss of Foxo decreases autophagy in muscle and other tissues (Mammucari et al ., 2007). …”

“…Unfortunately, phosphorylation status of autophagy components is difficult to evaluate due to lack of phospho‐specific antibodies. In addition, Tor activity is less effective in regulating autophagy when Foxo activity is low (Mammucari et al ., 2007), most likely because of the low expression of autophagy proteins.…”