Regulation of phosphatidylinositol 3‐kinase (PI3K)/Akt and nuclear factor‐kappa B signaling pathways in dystrophin‐deficient skeletal muscle in response to mechanical stretch

Abstract

Phosphatidylinositol 3-kinase (PI3K)/Akt and nuclear factor-kappa B (NF-kappaB) signaling pathways play a critical role in mediating survival signals. In this study we have investigated how loss of dystrophin (the primary cause of Duchenne muscular dystrophy) modulates the activation of PI3K/Akt and NF-kappaB signaling pathways in skeletal muscle in response to mechanical stimulation. Activation of Akt was significantly higher in diaphragm muscle from dystrophin-deficient mdx mice compared to normal mice at both prenecrotic and necrotic states. Higher activation of Akt was also observed in cultured dystrophin-deficient primary myotubes differentiated in vitro. Application of passive mechanical stretch ex vivo synergistically increased the activation of Akt in diaphragm of mdx mice. Stretch-induced activation of PDK-1 and PI3K were also higher in diaphragm of mdx mice compared to normal mice. Pretreatment of diaphragm with PI3K inhibitor LY294002 blocked the activation of Akt in normal and mdx mice. Higher activation of Akt was associated with increased phosphorylation of its downstream targets glycogen synthase kinase 3beta (GSK3beta), FKHR, and mammalian target of rapamycin (mTOR). Treatment of diaphragm muscle with LY294002 inhibited the stretch-induced activation of IkappaB (IkappaB) kinase (IKK) and NF-kappaB transcription factor in normal and mdx mice. Mechanical stretch also reduced the interaction of HDAC1 with RelA subunit of NF-kappaB in diaphragm muscle. Finally, cellular levels of Bcl-2, cIAP1, and integrin beta1 and activation of integrin linked kinase were higher in diaphragm muscle of mdx mice compared to normal mice. Taken together, our data suggest that loss of dystrophin and/or mechanical stretch results in the up-regulation of P13K/Akt and NF-kappaB signaling pathways in skeletal muscle.

Muscle inactivation of mTOR causes metabolic and dystrophin defects leading to severe myopathy

“…6 E). level, a feature that has been previously reported in both DMD and mdx muscles, irrespective of the muscle pathogenic state (Dogra et al, 2006). Consistently, immunostaining for PKB/Akt (Fig.…”

“…The myotubes were transduced by cytomegalovirus (CMV)-GFP or CMV-Cre adenovirus (Genethon) at 100 MOI on differentiation day 1 and harvested at different time points for gene expression analysis by quantitative real-time PCR or Western blotting. C2C12 myoblasts were differentiated in DME with 2% horse serum and treated at differentiation day 4 with vehicle (DMSO), up-regulation observed in dystrophin-deficient muscles (Dogra et al, 2006). Evidence for mTOR functions that do not involve the contribution of these mTORCs is supported by a recent study showing that mTOR regulates terminal oligopyrimidine mRNA translation in a raptor-and rictor-independent manner (Patursky-Polischuk et al, 2009).…”

“…Consistently with this finding, mTOR  muscles display several features reminiscent of mdx and DMD muscles. At the molecular level, these include the up-regulation of utrophin (Tinsley et al, 1998), caveolin-3 (Repetto et al, 1999, and PKB/Akt protein levels (Acharyya et al, 2005;Dogra et al, 2006;Peter and Crosbie, 2006). Finally, the functional characteristics mTOR deficiency leads to severe muscular dystrophy • Risson et al…”

PTEN Contributes to Profound PI3K/Akt Signaling Pathway Deregulation in Dystrophin-Deficient Dog Muscle

“…[17][18][19][21][22][23] Nevertheless, these studies have generally focused on one protein rather than assessing the global changes that may precipitate or exacerbate the pathology. Moreover, they have been mainly performed in the mdx mouse, a model that most likely will exhibit species specific changes that may not be reflected in the course of the human disease.…”

“…18 Also, the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway has been shown to be affected in the mdx mouse, with increased synthesis and phosphorylation of Akt. 22,23 In addition to the limited information related to the origin of signal perturbations in dystrophic muscle, almost no information is available regarding signaling pathways in clinically relevant animal models or human tissue samples. 23 It is noteworthy that the mdx mouse model of DMD is characterized by successive degeneration/regeneration processes, but does not exhibit the progressive muscle wasting and accumulation of connective tissue observed during the development of the human disease.…”