Changes in insulin and IGF-I receptor expression during differentiation of human preadipocytes

Abstract

Mature adipocytes originate from fibroblast-like precursor cells, preadipocytes, which differentiate to obtain the characteristics of adipocytes. Our aim was to investigate how differentiation of human preadipocytes affects the distribution of insulin receptors (IR) and IGF-I receptors (IGF-IR) and other cell characteristics. Preadipocytes were differentiated using indomethacine, dexamethasone, isobutyl-methylxantine (IBMX) and high concentration of insulin. Gene expression was quantified by real-time RT-PCR in preadipocytes (PA), differentiated preadipocytes (dPA) and mature adipocytes (mAD). The amount of expressed receptor protein was analyzed using receptor specific ELISAs and Western blot. We also studied DNA synthesis with radiolabeled thymidine incorporation and glucose accumulation with radiolabeled glucose. Differentiation of PA increased gene expression of IR but not IGF-IR. GLUT4, growth hormone receptor (GHR) and adiponectin appeared or increased. In PA and dPA only IR-A was expressed whereas also IR-B was detected in mAD. By Western blot and ELISA, IR and IGF-IR were detected in PA, dPA and mAD. During differentiation the ratio of IR to IGF-IR increased severalfold. In PA both the IR and the IGF-IR was phosphorylated by their own ligand at 1 nM and in dPA the activation of both receptors was stimulated by IGF-I, but not insulin, at 1 nM. Accumulation of glucose in PA was increased by insulin at 10 nM and by IGF-I at 1 nM and 10 nM. DNA synthesis was increased by insulin and IGF-I at 10 nM.In conclusion, both IR and IGF-IR are present in human preadipocytes and adipocytes.Differentiation is characterized by an increased IR/IGF-IR ratio.

Insulin and Insulin-like Growth Factor-1 Receptors Act as Ligand-specific Amplitude Modulators of a Common Pathway Regulating Gene Transcription

“…Indeed, in IRKO cells, the IGF-1 response on gene expression was only moderately decreased due to the low number of IR in brown preadipocytes. In adipocytes, however, the IR/IGF1R ratio is changed as IR expression increases with adipocyte differentiation (21,25) (Fig. 5).…”

Insulin‐like growth factor 1 has multisystem effects on foetal and preterm infant development

“…In vitro human pre‐adipocytes contain half as much insulin receptor as IGF‐1 receptor protein, while in mature adipocytes, 10 times more insulin receptor than IGF‐1 receptor protein is found. Thus, adipocyte differentiation is characterised by an increased insulin receptor/IGF‐1 receptor ratio, which indicates that insulin sensitivity increases with increasing gestational age 54. In keeping with this, foetal tissues are thought to be less responsive to insulin until 28–30 weeks of gestation 55.…”

Adipocyte expression of the glucose-dependent insulinotropic polypeptide receptor involves gene regulation by PPARγ and histone acetylation

“…of preadipocyte differentiation ( 37,38 ), but recent studies have emphasized the critical contribution made by insulin (39)(40)(41). Both IGF-I and insulin receptor are expressed early in the differentiation of human preadipocytes ( 42 ). Insulin receptor knockout mice display underdeveloped adipose tissue ( 41 ), and mouse embryonic fi broblasts derived from these mutants fail to differentiate into adipocytes ( 40 ).…”