Mitogenic activity of high molecular weight forms of insulin-like growth factor-II in amniotic fluid

Abstract

Amniotic fluid (AF) collected from ewes and goats at mid gestation displayed mitogenic activity in mouse fibroblasts. Upon fractionation of this material by size exclusion chromatography, the mitogenic activity was resolved into two peaks, whose activity was inhibited by an anti-IGF type 1 receptor blocking antibody. One of the peaks contained IGF-I and IGF-II (mature form), whereas the other contained high M r precursor forms of IGF-II. The presence in this latter fraction of IGF-binding proteins (IGFBP) suggests that the AF IGFBPs do not efficiently inhibit the mitogenic activity of the high M r forms of IGF-II. In agreement with this conclusion, exogenous IGFBP-1 failed to affect this activity. Analysis of IGF-II in sheep AF showed that the AF concentrations of both forms of IGF-II increased dramatically from mid pregnancy until 106-120 days of gestation, and fell thereafter. The amniotic IGFBPs followed a similar evolution. High M r forms of IGF-II were also found in human AF, with a pattern of electrophoretic migration different from that of sheep. We suggest that the precursor forms of IGF-II may play an important role in foetal development.

Human amniotic fluid stimulates the proliferation of human fetal and adult skin fibroblasts: The roles of bFGF and PDGF and of the ERK and Akt signaling pathways

“…However, after gel filtration on Sephadex G‐10 columns, the void volume seems to possess stimulatory activity, in contrast to the total volume that inhibits cell proliferation. Similar results were obtained with AF from ewes and goats 22 . In addition, the authors have shown that the mitogenic activity in some fractions after gel filtration is potently inhibited by an antibody against IGF type 1 receptor.…”

“…It is known from the literature that AF contains a large number of growth factors, such as bFGF, PDGF, TGF‐β, IGF‐I, and EGF 22–25 . Having already shown that the mitogenicity of AF is due to (more than one) growth factors we proceeded to identify these factors.…”

“…[17][18][19] Nevertheless, AF has been used on burned and ulcerated surfaces, 20,21 although the mechanisms of its action and especially the role of the growth factors included in it are still under investigation. A wide variety of cytokines and growth factors have been identified in AF, among them molecules known to affect fibroblast proliferation, such as platelet-derived growth factor-BB (PDGF-BB), basic fibroblast growth factor (bFGF), insulin-like growth factors (IGFs), epidermal growth factor (EGF), and TGF-b, [22][23][24][25] most of them in relatively low levels compared with their levels in serum or to the concentrations typically used in experiments in vitro.…”

Impaired mesenchymal stem cell differentiation and osteoclastogenesis in mice deficient for Igf2-P2 transcripts

“…In mammals, high molecular weight forms of IGF2 correspond to precursor forms. They are known to be potent mitogens and better activators of the IGF type I receptor than is the fully processed form of IGF2 (Valenzano et al, 1998;Blahovec et al, 2001). To standardize the results, the same amounts of total proteins were used for all samples and the western membranes were stained with Ponceau Red.…”

Animal insulin-like growth factor binding proteins and their biological functions

“…Their properties are the same or very similar to those of human IGFBP-1 andIGFBP-3 (Bla-hovec et al, 1999, 2001a). The recent studies have however shown that these mitogenically active proteins are probably high molecular precursor forms of IGF-II (Blahovec et al, 2001b).…”