Insulin-like growth factor-I signaling is modified during chondrocyte differentiation

Abstract

Insulin-like growth factor-I (IGF-I) is a critical regulator of skeletal growth. While IGF-I has been shown to be a potent chondrocyte mitogen in vitro, its role in chondrocyte differentiation is less well characterized. We chose to study the action of IGF-I on an accepted model of chondrocyte differentiation, the ATDC5 cell line. Insulin concentrations sufficiently high to interact with the IGF-I receptor are routinely used to induce ATDC5 cells to differentiate. Therefore, we first examined the ability of IGF-I to promote chondrocyte differentiation at physiological concentrations. IGF-I could induce differentiation of these cells at concentrations below 10 nM. However, increasing IGF-I concentrations were less potent at inducing differentiation. We hypothesized that mitogenic effects of IGF-I might inhibit its differentiating effects. Indeed, the extracellular-signal-regulated kinase (ERK)-pathway inhibitor PD98059 inhibited ATDC5 cell DNA synthesis while enhancing differentiation. This suggested that the ability of IGF-I to promote both proliferation and differentiation might require that its signaling be modulated through the differentiation process. We therefore compared IGF-I-mediated ERK activation in proliferating and hypertrophic chondrocytes. IGF-I potently induced ERK activation in proliferating cells, but minimal ERK response was seen in hypertrophic cells. In contrast, IGF-I-mediated Akt activation was unchanged by differentiation, indicating intact upstream IGF-I receptor signaling. Similar findings were observed in the RCJ3·1C5·18 chondrogenic cell line and in primary chick chondrocytes. We conclude that IGF-I promotes both proliferation and differentiation of chondrocytes and that the differentiation effects of IGF-I may require uncoupling of signaling to the ERK pathway.

Signaling mechanisms leading to regulation of proliferation and differentiation of the mesenchymal chondrogenic cell line RCJ3.1C5.18 in response to IGF-I

“…5C). These data are in agreement with the findings of Phornphutkul et al (2004) who observed minimal ERK response to IGF-I in hypertrophic ATDC5 cells, but the functional role of other IGF-related signaling pathways were not studied by these investigators. Taken together, these data indicate that the MAPK/ERK1/2 pathway is being inactivated both during spontaneous and IGF-Imediated early differentiation of RCJ cells.…”

Vanadate proliferative and anti‐mineralogenic effects are mediated by MAPK and PI‐3K/Ras/Erk pathways in a fish chondrocyte cell line

“…Similar mechanisms (i.e. those related to the proliferative effect of IGF-1) have been recently reported in the mouse chondrocyte ATDC5 cell line [14] and thus, based on those results as well as our data reported in this study, we propose the existence of a mechanism involving MAPK pathway that would regulate chondrocyte proliferation and transduce vanadate effect (Fig. 5A).…”

mTOR signaling contributes to chondrocyte differentiation

“…This inhibition was seen only when bones were stimulated to grow by the inclusion of pharmacological insulin concentrations in the culture medium. We (Phornphutkul et al, 2004) and others (Pandini et al, 2002) have demonstrated that the effects of high concentration insulin are likely to be mediated by IGF-I receptors and their downstream signaling pathways. In the fetal rat metatarsal explant model, similar growth was observed in bones exposed to 10 g/ml insulin or 10 nM of IGF-I.…”