The Effect of Age and Nutrient Status on Growth Characteristics of Turkey Satellite Cells

Myogenic satellite cells are heterogeneous multipotential stem cells required for muscle repair, maintenance, and growth. The membrane-associated heparan sulfate proteoglycans syndecan-4 and glypican-1 differentially regulate satellite cell proliferation, differentiation, fibroblast growth factor 2 (FGF2) signal transduction, and expression of myogenic regulatory factors. The objective of Specific Aims 1 and 2 was to determine the effect of age on satellite cell proliferation and differentiation using cells isolated from the pectoralis major muscle of 1 d, 7 wk and 16 wk old turkeys. Proliferation was significantly reduced in the 16 wk satellite cells, while differentiation was decreased in the 7 wk and the 16 wk cells beginning at 48 h of differentiation. Fibroblast growth factor 2 responsiveness was highest in the 1 d and 7 wk cells during proliferation; during differentiation there was an age-dependent response to FGF2. Syndecan-4 and glypican-1 expressing satellite cell populations decreased with age. These data demonstrate that declining syndecan-4 and glypican-1 satellite cell subpopulations which may be associated with age-related changes in satellite cell proliferation, differentiation, and FGF2 responsiveness.In specific aim 3, the effect of overexpressing syndecan-4 and glypican-1 was investigated. Syndecan-4 and glypican-1 overexpression did not have a significant effect on proliferation and differentiation in 1 d, 7 wk and 16 wk satellite cells. Overexpression of syndecan-4 and glypican-1 did not affect FGF2 responsiveness during proliferation. During differentiation, overexpression of syndecan-4 and glypican-1 increased differentiation at 48 h of differentiation in 1 d, 7 wk and 16 wk cells treated with FGF2 and decreased differentiation in 16 wk cells not treated with FGF2. Expression of myogenic regulatory factors MyoD, myogenin, and MRF4 were also affected by overexpression of syndecan-4 and glypican-1. These data demonstrate that sydecan-4 and glypican-1 overexpression does not significantly impact proliferation and differentiation in 16 wk cells. Thus, syndecan-4 and glypican-1 are not responsible for the decline in proliferation, differentiation, and FGF2 responsiveness observed in 16 wk satellite cells.In addition to the role of satellite cell age on growth characteristics, nutrient status also affects satellite cell function. The objective of Specific Aim 4 was to determine the effect of nutrition on proliferation, differentiation, myogenic transcriptional regulatory factors, and syndecan-4 and glypican-1 expression in satellite cells from 1 d through 16 wk of age. A nutrient restriction similar to an in vivo feed restriction was simulated in vitro by restricting the concentration of methionine (Met). Nutrient restriction decreased proliferation at all ages. Differentiation was increased in 1 d nutrient restricted cells; while treatment of 7 wk cells with 3 mg/L Met/9.6 mg/L Cysteine (Cys) medium resulted in decreased differentiation. Reduced Met and Cys medium did not significantly affect 16 wk cells at 72 h of differentiation, though the medium with no Met and Cys resulted in significantly decreased differentiation in all ages during differentiation. Methionine and Cys restriction also had differential effects on syndecan-4, glypican-1, MyoD, myogenin and MRF4 mRNA expression. These data demonstrate that nutrient restriction differentially affects turkey satellite cells in an age specific manner.