Regulation of contraction-stimulated system A amino acid uptake in skeletal muscle: role of vicinal sulfhydryls

Acute mechanical overload increases IGF-I and MMP-9 mRNA in 3D tissue-engineered skeletal muscle

Skeletal muscle (SkM) is a tissue that responds to mechanical load following both physiological (exercise) or pathophysiological (bed rest) conditions. The heterogeneity of human samples and the experimental and ethical limitations of animal studies provide a rationale for the study of SkM plasticity in vitro. Many current in vitro approaches of mechanical loading of SkM disregard the three-dimensional (3D) structure in vivo. Tissue engineered 3D SkM, that displays highly aligned and differentiated myotubes, was used to investigate mechano-regulated gene transcription of genes implicated in hypertrophy/atrophy. Static loading (STL) and ramp loading (RPL) at 10 % strain for 60 min were used as mechano-stimulation with constructs sampled immediately for RNA extraction. STL increased IGF-I mRNA compared to both RPL and CON (control, p = 0.003 and 0.011 respectively) whilst MMP-9 mRNA increased in STL and RPL compared to CON (both p < 0.05). IGFBP-2 mRNA was differentially regulated in RPL and STL compared to CON (p = 0.057), whilst a reduction in IGFBP-5 mRNA was found for STL and RPL compared to CON (both p < 0.05). There was no effect in the expression of putative atrophic genes, myostatin, MuRF-1 and MAFBx (all p > 0.05). These data demonstrate a transcriptional signature associated with SkM hypertrophy within a tissue-engineered model that more greatly recapitulates the in vivo SkM structure compared previously published studies.

Effect of PAO (phenylarsine oxide) on the inhibitory effect of insulin and IGF-1 on insulin release from INS-1 cells

Phenylarsine oxide (PAO) which complexes vicinal thiol groups is a valuable pharmacological tool to investigate the interaction of peptides such as insulin with their receptors and the signal transduction from the receptor to the cell interior. This tool was now used to elucidate the inhibitory effects of insulin and IGF-1 on insulin secretion via their receptors. Insulin and IGF-1 inhibited insulin release from INS-1 cells, an insulin secreting cell line. PAO was able to reverse this inhibitory effect of both hormones. Dimercaptopropanol (DMP), which is well known to antagonize PAO effects, inhibited the abolishment of PAO effect on the inhibitory effect of insulin and IGF-1 regarding insulin release. Membrane bound GLUT2 in INS-1 cells was increased by either insulin and IGF-1 which is counteracted by PAO. Thus the inhibitory effect of insulin and IGF-1 on insulin release is operative and can be disturbed by a thiol interacting compound such as PAO. This may happen at the receptor level or at the sub-receptor level.