DES(1-3) IGF-I POTENTLY ENHANCES DIFFERENTIATED CELL-GROWTH IN OLFACTORY-BULB ORGAN-CULTURE

We recently provided evidence that newborn rat olfactory bulb (OB) cou ld be maintained in serum-free organ culture with combinations of insu lin-like growth factor-I (IGF-I) and basic fibroblast growth factor (b FGF), both of which are locally synthesized. Des (1-3), or truncated, IGF-I is a potent analog of IGF I isolated from rat and human brain. W e proposed in this study to examine the effects of des (1-3) IGF-I on cell function, morphology and on neuronal and glial cell differentiati on in our cultured OB model, using cell-specific immunostains for neur ons (150 kDa neurofilament) and glial cells (glial fibrillary associat ed protein- GFAP). OB were cultured in Iscove's serum free medium cont aining IGF-I or des (1-3) IGF-I both alone or in combination with bFGF . Dose dependent responses of C-14 amino acid uptake showed des (1-3) IGF-I to be 3-5 fold more potent than IGF-I with a half maximal respon se at about 20 ng/ml in comparison to 100 ng/ml of IGF-I. The maximum response to IGF-I +/- bFGF was seen at 150 ng/ml; a ten-fold higher do se of insulin +/- bFGF was required to achieve the same response. Whil e morphology was close to fresh 6 day OB following culture with IGF-I( 150 ng/ml) and bFGF (25 ng/ml), the substitution of des (1-3) IGF-I at 50 ng/ml markedly improved morphology. Neurons were identified follow ing culture in IGF-I or bFGF alone, but showed greater organisation in the mitral layer following combined IGF-I/bFGF culture. However, in c ontrast to IGF-I (150 ng/ml), des (1-3) IGF-I (50 ng/ml) supported mar ked neuronal expression. Furthermore, when des (1-3) IGF-I (50 ng/ml) was substituted for IGF-I, in combination with bFGF, the pattern of en hanced neuronal expression in the mitral layer was very close to that seen in the fresh 6 day bulb, with dendrites projecting to the glomeru lar layer. In OBs treated with no growth factors, or either IGF-I, des (1-3) IGF-I or bFGF alone, glial expression was widespread and poorly organised, suggesting an injury response. In contrast, following trea tment with combinations of bFGF with IGF-I or des (1-3) IGF-I, a more ordered, though enhanced glial response was seen in glomerular and gra nule cell layers. This study using an OB organ culture system suggests that des (1-3) IGF-I, which may be derived from brain, is a potent su pporter of viability and differentiated cell growth and organisation i n the newborn rat olfactory bulb.