PGF2alpha-associated vascular smooth muscle hypertrophy is ROS dependent and involves the activation of mTOR, p70S6k, and PTEN.

Prostaglandin F2alpha (PGF2alpha) increases reactive oxygen species (ROS) and induces vascular smooth muscle cell (VSMC) hypertrophy by largely unknown mechanism(s). To investigate the signaling events governing PGF2alpha-induced VSMC hypertrophy we examined the ability of the PGF2alpha analog, fluprostenol to elicit phosphorylation of Akt, the mammalian target of rapamycin (mTOR), ribosomal protein S6 kinase (p70S6k), glycogen synthase kinase-3beta (GSK-3beta), phosphatase and tensin homolog (PTEN), extracellular signal-regulated kinase 1/2 (ERK1/2) and Jun N-terminal kinase (JNK) in growth arrested A7r5 VSMC. Fluprostenol-induced hypertrophy was associated with increased ROS, mTOR translocation from the nucleus to the cytoplasm, along with Akt, mTOR, GSK-3beta, PTEN and ERK1/2 but not JNK phosphorylation. Whereas inhibition of phosphatidylinositol 3-kinase (PI3K) by LY-294002 blocked fluprostenol-induced changes in total protein content, pre-treatment with rapamycin or with the MEK1/2 inhibitor U0126 did not. Taken together, these findings suggest that fluprostenol-induced changes in A7r5 hypertrophy involve mTOR translocation and occur through PI3K-dependent mechanisms.

Age-associated changes in MAPK activation in fast- and slow-twitch skeletal muscle of the F344/NNiaHSD X Brown Norway/BiNia rat model.

We compared the tissue content, basal phosphorylation, and stretch-induced phosphorylation of the mitogen-activated protein kinase (MAPK) members; extracellular-signal-regulated kinases (ERK 1/2), p38, and c-Jun NH2-terminal kinase (JNK) in the fast-twitch extensor digitorium longus (EDL) and slow-twitch soleus of young adult (6 month), aged (30 month), and very aged (36 month) F344/NNiaHSD X Brown Norway/BiNia (F344/NXBN) rats. The expression and basal phosphorylation of the ERK 1/2, p38, and JNK MAPK proteins were regulated differently with aging in the EDL and soleus. Stretch induced significant phosphorylation of each signaling molecule in both muscle types of young adult and aged animals. In the very aged animals, stretch stimulated ERK 1/2 MAPK phosphorylation; however, EDL stretch failed to induce JNK MAPK phosphorylation, while soleus stretch was unable to induce the phosphorylation of p38 MAPK. The results suggest that skeletal muscle mechanotransduction processes are affected in very aged F344/NXBN rats and that aging alters load-induced signaling in fast- and slow-twitch muscle types differently.

Regulation of p70S6k, GSK-3beta, and calcineurin in rat striated muscle during aging.

In this study we compared the content and phosphorylation levels of several molecules believed to regulate muscle hypertrophy and fiber type changes in the extensor digitorum longus (EDL), soleus, diaphragm, and heart of adult (6 months), aged (30 months), and very aged (36 months) Fischer 344 x Brown Norway rats. With aging, the mass of the EDL and soleus decreased significantly (approximately 38% and approximately 36%, respectively), the diaphragm's mass remained unchanged while the mass of the heart increased (approximately 35%). Western blotting demonstrated that calcineurin (CnA), the 70-kDa ribosomal S6 kinase (p70(S6k)), glycogen synthase kinase-3beta (GSK-3beta), and the phosphorylated forms of GSK-3beta and p70(S6k) (p-GSK-3beta(Ser9) and p-p70(S6kThr389)) were regulated differently with aging and between muscle types. Total p70(S6k), GSK-3beta, and p-GSK-3beta(Ser9) decreased in the aged-atrophic EDL and soleus while p-p70(S6kThr389) increased. Although total p70(S6k) content diminished in the continuously active diaphragm, phosphorylation of p70(S6k )remained unchanged. Conversely, the expression of GSK-3beta and p-GSK-3beta(Ser9) increased in the diaphragm. With aging, the amount of p-p70(S6kThr389) decreased approximately 56% in the heart while p-GSK-3beta( Ser9) increased approximately 193%. Interestingly, CnA content remained unchanged in the diaphragm, increased approximately 204% in the EDL, and decreased approximately 30% and approximately 65% with aging in the soleus and heart, respectively. These results indicate remarkable differences in the regulation of molecules thought to govern protein synthesis and changes in contractile protein expression.