IGF and IGF-binding protein expression in the growth plate of normal, dexamethasone-treated and human IGF-II transgenic mice

Abstract

Glucocorticoid (GC) treatment in childhood can lead to suppression of longitudinal growth as a side effect. The actions of GCs are thought to be mediated in part by impaired action of the insulin-like growth factors (IGF-I and IGF-II) and their binding proteins (IGFBP-1 to -6). We have studied the effects of GCs on IGF and IGFBP expression at the local level of the growth plate, using non-radioactive in situ hybridization.We treated 3-week-old normal mice for 4 weeks with dexamethasone (DXM). We also treated human IGF-II (hIGF-II) transgenic mice in order to investigate whether IGF-II could protect against the growth retarding effect of this GC. DXM treatment resulted in general growth retardation in both mice strains, however, only in normal mice was tibial length decreased. In both normal and hIGF-II trangenic mice, the total width of the growth plate was not affected, whereas the width of the proliferative zone decreased as a result of the DXM treatment. Additionally, only in normal mice, the width of the hypertrophic zone thickened.Only expression of IGF-I, IGF-II and IGFBP-2 could be detected in the growth plates of 7-week-old normal mice. IGFBP-1, -3, -4, -5 and -6 mRNAs were not detected. DXM treatment of normal mice induced a significant 2·4-fold increase in the number of cells expressing IGF-I mRNA, whereas IGF-II and IGFBP-2 mRNA levels were not affected.In hIGF-II transgenic mice, IGF-I mRNA levels were significantly increased, while endogenous IGF-II and IGFBP-2 mRNAs were unaffected, compared to normal animals. DXM treatment of the hIGF-II transgenic mice induced a further increase of IGF-I mRNA expression, to a similar extent as in DXM-treated normal mice.The increase of IGF-I due to DXM treatment in normal mice might be a reaction in order to minimize the GC-induced growth retardation. Another possibility could be that the increase of IGF-I would contribute to the GC-induced growth retardation by accelerating the differentiation of chondrocytes, resulting in accelerated ossification. In the growth plates of hIGF-II transgenic mice, the higher basal level of IGF-I, might be responsible for the observed partial protection against the adverse effects of GCs on bone.

Dexamethasone-induced expression of the glucocorticoid response gene lipocalin 2 in chondrocytes

“…In addition, both Silvestrini et al (59) and Smink et al (60) reported that GC reduced growth cartilage width by inhibiting chondrocyte proliferation and increasing the apoptosis of terminal hypertrophic chondrocytes. Studies by our group and others have also shown that GCs impair chondrocyte proliferation and increase apoptosis (33,35,50,53,55,61). However, the mechanisms by which GCs exert control over chondrocyte dynamics are presently unclear.…”

Disruption of insulin-like growth factor-I expression in type IIαI collagen-expressing cells reduces bone length and width in mice

“…Furthermore, it is also not known whether IGF-I produced by different cell types within the bone (i.e., osteoblast, chondroblast, osteoclast, or marrow cells) exerts differential effects on longitudinal growth, bone width, and mineral deposition. In this regard, IGF-I produced by chondrocytes has been proposed to play a significant role in the regulation of longitudinal bone growth (33,47). This prediction is based on the findings that 1) chondrocytes both produce and respond to IGF-I (34,40), and 2) the rate of longitudinal growth is dependent on the rate of chondrocyte proliferation, as well as hypertrophic differentiation, which is accompanied by cell enlargement, which is disturbed in the IGF-I KO mice (49,50,53).…”

Overexpression of human IGF-II mRNA in the brain of transgenic mice modulates IGFBP-2 gene expression in the medulla oblongata

“…In a previous study, we found upregulation of IGF-I expression in the growth plate of hIGF-II-transgenic mice in comparison with normal mice (Smink et al 2002). In addition, IGFBP-2 and -5 were increased in the spleen and thymus of these mice, whereas IGFBP-3 was increased exclusively in the spleen (Smink et al 1999).…”

“…The SV40 fragment detects only the mRNAs of the transgene as verified by Northern blot analysis (van Buul-Offers et al 1995). The use of both probes makes it possible to discriminate between endogenous and transgene IGF-II mRNAs (Smink et al 1999(Smink et al , 2002. Probes were checked for cross-hybridization, using in situ hybridization on different types of mouse tissues (spleen, thymus and whole embryos) for the IGFBP probes (Smink et al 1999, van Kleffens et al 2001; and on spleen and growth plate cartilage for the IGF probes (Smink et al 2002).…”