Regulation of murine alpha 1-pregnancy-associated protein by gonadal steroids during the acute-phase response

Increased IGFBP Proteolysis, IGF-I Bioavailability, and Pappalysin Levels in Children With Prader-Willi Syndrome

CONTEXT

Prader-Willi syndrome (PWS) is associated with impaired growth hormone (GH) secretion and decreased insulin-like growth factor (IGF)-I levels. Pappalysins (PAPP-A, PAPP-A2) and stanniocalcins (STC-1, STC-2) regulate IGF binding-protein (IGFBP) cleavage and IGF bioavailability, but their implication in PWS is unknown.

OBJECTIVE

We determined serum levels of PAPP-As and STCs in association with IGF axis components in prepubertal and pubertal patients with PWS, also analyzing the effect of GH treatment.

METHODS

Forty children and adolescents with PWS and 120 sex- and age-matched controls were included. The effect of GH was evaluated at 6 months of treatment in 11 children.

RESULTS

Children with PWS had lower levels of total IGF-I, total and intact IGFBP-3, acid-labile subunit, intact IGFBP-4, and STC-1, and they had higher concentrations of free IGF-I, IGFBP-5, and PAPP-A. Patients with PWS after pubertal onset had decreased total IGF-I, total and intact IGFBP-3, and intact IGFBP-4 levels, and had increased total IGFBP-4, and STCs concentrations. GH treatment increased total IGF-I, total and intact IGFBP-3, and intact IGFBP-4, with no changes in PAPP-As, STCs, and free IGF-I levels. Standardized height correlated directly with intact IGFBP-3 and inversely with PAPP-As and the free/total IGF-I ratio.

CONCLUSION

The increase in PAPP-A could be involved in increased IGFBP proteolysis, promoting IGF-I bioavailability in children with PWS. Further studies are needed to establish the relationship between growth, GH resistance, and changes in the IGF axis during development and after GH treatment in these patients.

Pregnancy-associated alpha 2-glycoprotein (alpha 2-PAG): development of a sensitive enzyme-linked immunoassay and comparison of serum concentrations in adults and children

Using a newly-developed and very sensitive enzyme-linked immunoassay technique, we have measured circulating alpha 2-PAG concentrations in 270 adults and 181 children. In adults, levels increased with age in both sexes and were significantly higher in women in each age category studied. In contrast, there were no significant differences between the sexes in children and no changes with age between 1 and 14 years. At puberty, alpha 2-PAG concentrations increased in girls and decreased in boys. The increase in girls is consistent with the known stimulatory effects of oestrogen on alpha 2-PAG production. We discuss the possibility that androgens may have an analogous inhibitory effect in males.

Immunohistochemical localization of murine alpha 1-pregnancy-associated protein (alpha 1-PAP) in pregnant mice: relationship between serum alpha 1-PAP levels and incidence of positive cells

Using an electroimmunoassay, the murine pregnancy-associated protein alpha 1-PAP was detected in the sera of virgin MF1 but not C57BL/10 female mice. During pregnancy, alpha 1-PAP levels rose in both strains, although concentrations were higher in the latter and in both fell towards term. Using the unlabelled peroxidase anti-peroxidase (PAP) staining procedure, alpha 1-PAP was detected within mononuclear leukocytes, the majority resembling macrophages, in the small and large intestinal mucosae, Peyer's patches and hepatocytes of virgin MF1 but not C57BL/10 females. During pregnancy, alpha 1-PAP positive cells were observed in each of these sites and in the decidua and placenta of both strains. Quantitative studies revealed that the incidence of alpha 1-PAP positive cells in the gut and associated lymphoid tissues reflected the circulating levels of the protein. In the placenta, the frequency and intensity of alpha 1-PAP positive staining was also reduced towards parturition. In contrast, hepatocyte staining remained constant throughout gestation in both strains. Our observations suggest that there may be at least two types of alpha 1-PAP synthesis operative and that circulating levels of the protein in female mice are influenced by strain, pregnancy and stage of gestation. These findings are discussed in relation to the cell types involved, their contribution to serum levels and the possible role of alpha 1-PAP in fetal allograft survival.