Insulin/insulin-like growth factor-like activity in the aqueous extracts of the rotifer Brachionus plicatilis

Insulin/insulin-like growth factor (IGF)-like signaling plays important roles in the aging processes of various animals. However, little is known about this signaling in rotifers, which have been used as a model animal in aging studies. Here we report that the aqueous extracts of the rotifer Brachionus plicatilis show activity similar to that of insulin/IGFs. Rotifers were cultured under four different feeding regimens (fed, starved for about ten days, or re-fed for 30 and 120 min after starvation), and then their aqueous extracts were added to culture media of rat L6 myoblasts. Treatment with these extracts increased the phosphorylation levels of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) and two Akt substrates of approximately 48 and 60 kDa, and these phosphorylations were diminished when cells were preincubated with specific inhibitors of their upstream kinases (MAPK/ERK kinase and phosphoinositide 3-kinase, respectively). Furthermore, the extracts from fed rotifers provoked higher phosphorylation levels of MAPK/ERK and Akt substrates than the extract from starved rotifers, suggesting that the production of substance(s) with insulin/IGF-like activity is stimulated upon feeding in the rotifer.