Fig 1.
A and B. IGF-1 (1A) and IGF-1 receptor (1B) mRNA levels in Low (0.28) and High AA (9 mM) refed L6 skeletal muscle cells. IGF-1 mRNA levels increased significantly (p< 0.05), while IGF-1 receptor mRNA levels showed a decreased trend (p<0.1). Confluent, non-proliferating L6 cells were subjected to starvation in very low amino acid media for 24 hours (0.14 mM) and then cultured in presence of either Low AA (0.28 mM) or High AA (9 mM) concentrations for 18 hours, followed by RNA extraction at the end of 18hrs incubation. mRNA levels were quantified by real time PCR as described in methods. Mean±SE. a p<0.05 n = 15/group.
Table 1.
IGF-1, IGF-1receptor mRNA, and L-[U-14C]-phenylalanine incorporation into proteins, in confluent non-proliferating L6 skeletal muscle cells.
Cells were amino acid refed at High AA concentrations (9 mM) with or without presence of inhibitors of molecules in the IGF-1receptor signaling pathway (mean±SE, n = 4-5/group).
Fig 2.
A-C. 2A. Refeed L6 skeletal muscle cells in media with High AA concentration (9 mM) showed increased phenylalanine incorporation rates by 35% in siRNA control cells; but only 14% in IGF-1 knockdown cells compared to Low AA refed cells. 2B. siRNA knock-down of IGF-1 reduced cell growth. Cell numbers were similar in Low AA and High AA provided cells but decreased in High AA-IGF-1 siRNA treated cells. 2C. Differences in L-[U-14C]- phenylalanine incorporation rates between control and siRNA, IGF-1 knockdown cells did not remain accounting for cell numbers. The two High AA treated groups showed significantly increased phenylalanine incorporation compared to Low AA treated cells regardless of IGF-1 levels. Mean±SE. a p< 0.001 vs Low AA siRNA control cells. b p< 0.01 vs High AA siRNA control cells. AU. Arbitrary unit. Fold change from untreated control cells.