EFFECTS OF AGING ON RIBOSOMAL PROTEIN-L7 MESSENGER-RNA LEVELS IN CULTURED RAT PREADIPOCYTES

Ribosomal protein L7 mRNA is a cell cycle-independent message whose le vels are lower in late passage ''senescent'' fibroblasts than early pa ssage cultures. To determine whether decreases in L7 mRNA levels also occur during aging in tissues in vivo and whether reduced L7 mRNA is c aused by terminal differentiation, we measured L7 and adipsin (a diffe rentiation-dependent serine protease) mRNA levels in undifferentiated and differentiated preadipocytes and glyceraldehyde-3-phosphate dehydr ogenase mRNA in differentiated preadipocytes cultured from perirenal f at depots of 3-, 17-, and 24-month-old male rats. L7 mRNA levels decre ased with increasing age and were not affected by differentiation. In the same cultures, adipsin mRNA levels did not increase with age but d id increase with differentiation, confirming that the preadipocytes ex posed to enriched medium had, in fact, differentiated. Glyceraldehyde- 3-phosphate dehydrogenase mRNA levels did not change with age indicati ng that the decrease in L7 mRNA was not a result of a general decrease in mRNA with age. These observations are consistent with the hypothes es that decreasing L7 mRNA levels are associated with aging and that l ate passage fibroblasts have features in common with senescence. The o bservations are not consistent with the hypothesis that senescent chan ges in cellular function are caused by terminal differentiation.