INSULIN-LIKE-GROWTH-FACTOR (IGF)-I AND (IGF)-II AND IGFBP SECRETION BY OVINE SATELLITE CELL STRAINS GROWN ALONE OR IN COCULTURE WITH 3T3-L1PREADIPOCYTES

The current study was designed to examine the effects of muscle and fa t stem cell coculture on the secretion of insulinlike growth factor (I GF)-I and -II and IGF binding proteins (IGFBP) by these cells. Two she ep satellite cell strains with negligible or high potential for differ entiation (10A and O-1, respectively) were placed in coculture with 3T 3-L1 preadipocytes using a filter support to separate the two cell typ es. Media conditioned by the cells grown alone or in coculture were an alyzed for IGFs by RIA or IGFBPs by ligand blotting. The numbers of sa tellite cells and preadipocytes declined throughout the 5-d culture pe riod, although coculture slowed the 3T3-L1 decline but hastened the sa tellite cell decline. The satellite cell strains and 3T3-L1 cells secr eted small amounts of IGF-I (less than or equal to 2 ng/ml) and IGF-II (< 10 ng/ml) over the 5-d culture period. Coculture did not increase the amount of IGF-I and -II in conditioned media. The lowly differenti ating 10A cells secreted barely detectable amounts of the low molecula r weight IGFBP-3 subunit (34 kDa), IGFBP-2 (28 kDa), and IGFBP-4 (18 k Da). Coculture of 10A and 3T3-L1 cells potentiated secretion of IGFBP- 2 and -3. Strain O-1, which readily differentiates, secreted high leve ls of both IGFBP-3 subunits (34 and 39 kDa) and IGFBP-2 (28 kDa), as w ell as significant amounts of the 18 kDa IGFBP-4. Coculture did not al ter IGFBP secretion of O-1 cells, This study showed that while IGF-I a nd -II levels in media conditioned by sheep satellite cell strains are low and relatively invariant, the intensity and complexity of IGFBP p atterns increases with time in culture and with the potential for diff erentiation of the satellite cell strains. Coculture with preadipocyte s appealed to potentiate IGFBP secretion while reducing satellite cell viability.