Role of Phosphoinositide 3-OH Kinase p110β in Skeletal Myogenesis

Abstract

Phosphoinositide 3-OH kinase (PI3K) regulates a number of developmental and physiologic processes in skeletal muscle; however, the contributions of individual PI3K p110 catalytic subunits to these processes are not well-defined. To address this question, we investigated the role of the 110-kDa PI3K catalytic subunit ␤ (p110␤) in myogenesis and metabolism. In C2C12 cells, pharmacological inhibition of p110␤ delayed differentiation. We next generated mice with conditional deletion of p110␤ in skeletal muscle (p110␤ muscle knockout [p110␤-mKO] mice). While young p110␤-mKO mice possessed a lower quadriceps mass and exhibited less strength than control littermates, no differences in muscle mass or strength were observed between genotypes in old mice. However, old p110␤-mKO mice were less glucose tolerant than old control mice. Overexpression of p110␤ accelerated differentiation in C2C12 cells and primary human myoblasts through an Akt-dependent mechanism, while expression of kinase-inactive p110␤ had the opposite effect. p110␤ overexpression was unable to promote myoblast differentiation under conditions of p110␣ inhibition, but expression of p110␣ was able to promote differentiation under conditions of p110␤ inhibition. These findings reveal a role for p110␤ during myogenesis and demonstrate that long-term reduction of skeletal muscle p110␤ impairs whole-body glucose tolerance without affecting skeletal muscle size or strength in old mice.

Transcriptional and Chromatin Dynamics of Muscle Regeneration after Severe Trauma

“…One component of the IGF pathway, the PI3K component, is essential for skeletal muscle regeneration and is composed of three primary classes (classes I, II, III) that are structurally and functionally distinct. The three class IA PI3K p110 catalytic subunits (α, β, and δ) are expressed in skeletal muscle (Matheny and Adamo, 2010) and of these subunits, p110α and p110β have been shown to positively influence myoblast proliferation and differentiation (Matheny et al., 2012, Matheny et al., 2015). In the early and middle periods following injury, we observed differential enhancer binding and increases in expression of PI3K catalytic subunits p110α ( Pik3ca ), p110β ( Pik3cb ), and p110δ ( Pik3cd ) as well as the PI3K p85α ( Pik3r1 ) regulatory subunit for the injured muscle compared with the contralateral control (Figure 6A).…”

p110α of PI3K is necessary and sufficient for quiescence exit in adult muscle satellite cells

“…Here, we demonstrated that p110α of PI3K and the PI3K‐mediated signaling pathway exert such functions in MuSCs. Unlike MuSC‐specific deletion of p110α using Pax7‐Cre, which resulted in embryonic lethality (Fig EV2A), that of p110β of PI3K (with a Myf5 ‐Cre line) had no obvious deleterious effects on mouse development and survival, as well as muscle mass and strength in vivo (Matheny et al , ). This is likely due to the fact that p110α is the predominant form of PI3K expressed in QSCs, while p110β is barely detectable in QSCs based on the RNA‐seq data from us and others (Liu et al , ; Ryall et al , ).…”

AKT 2 is the predominant AKT isoform expressed in human skeletal muscle

“…Generation of bacmid DNA, SF9 insect cell‐mediated virus production, and viral transductions of human myoblasts were performed as described (Matheny et al. ).…”

“…Real time PCR was performed as previously described (Matheny et al. ), normalizing to HPRT1 gene expression. Primers/probes for real‐time PCR were purchased from Life Technologies: AKT1 (Hs00920503_m1), AKT2 (Hs01086102_m1), AKT3 (Hs00987350_m1), HPRT1 (Hs02800695_m1).…”

“…Extraction of protein from muscle samples was performed as described (Matheny et al. ), and protein concentrations were determined by the method of Bradford (Bradford ). Immunoprecipitations and western immunoblotting were performed exactly as described previously (Matheny et al.…”