Observations on the source of pregnancy-associated plasma protein A (PAPP-A)

PAPPA-mediated adipose tissue remodeling mitigates insulin resistance and protects against gestational diabetes in mice and humans

Pregnancy is a physiological state of continuous adaptation to changing maternal and fetal nutritional needs, including a reduction of maternal insulin sensitivity allowing for appropriately enhanced glucose availability to the fetus. However, excessive insulin resistance in conjunction with insufficient insulin secretion results in gestational diabetes mellitus (GDM), greatly increasing the risk for pregnancy complications and predisposing both mothers and offspring to future metabolic disease. Here, we report a signaling pathway connecting pregnancy-associated plasma protein A (PAPPA) with adipose tissue expansion in pregnancy. Adipose tissue plays a central role in the regulation of insulin sensitivity, and we show that, in both mice and humans, pregnancy caused remodeling of adipose tissue evidenced by altered adipocyte size, vascularization, and in vitro expansion capacity. PAPPA is known to be a metalloprotease secreted by human placenta that modulates insulin-like growth factor (IGF) bioavailability through prolteolysis of IGF binding proteins (IGFBPs) 2, 4, and 5. We demonstrate that recombinant PAPPA can stimulate ex vivo human adipose tissue expansion in an IGFBP-5- and IGF-1-dependent manner. Moreover, mice lacking PAPPA displayed impaired adipose tissue remodeling, pregnancy-induced insulin resistance, and hepatic steatosis, recapitulating multiple aspects of human GDM. In a cohort of 6361 pregnant women, concentrations of circulating PAPPA are inversely correlated with glycemia and odds of developing GDM. These data identify PAPPA and the IGF signaling pathway as necessary for the regulation of maternal adipose tissue physiology and systemic glucose homeostasis, with consequences for long-term metabolic risk and potential for therapeutic use.

Pulsatile secretion of pregnancy-associated plasma protein-A (PAPP-A) in non-pregnant women

No changes in PAPP-A levels could be detected when plasma samples were obtained every second day throughout the entire menstrual cycle in three healthy women. But when measured every 30 min throughout 12 consecutive hours, in four healthy women, PAPP-A followed a pulsatile pattern which may originate in the endometrium since no PAPP-A pulses were detected in a long-term hysterectomized woman, or in two men. The pulses were not related to levels of oestradiol, progesterone, FSH or LH.

In vitro release of pregnancy-associated plasma protein-A (PAPP-A) by human endometrial cells

Evidence has now accumulated to sustain the idea that pregnancy-associated plasma protein-A (PAPP-A) is not pregnancy specific: it can be localized immunohistochemically in nonpregnant human endometrium. Thus, it was of interest to see if a primary cell culture of human endometrial cells was capable of producing PAPP-A. Immunoreactive PAPP-A-like material was detected in the culture medium of glandular as well as stromal cells. The presence of PAPP-A in endometrial culture medium was specific and could not be attributed to a nonspecific protease effect on the tracer used in radioimmunoassay. The production rate of PAPP-A by stromal cells could be enhanced by the addition of medroxyprogesterone acetate (MPA). Estradiol (E2) alone or in combination with MPA did not modify the production rate of PAPP-A. The production rate of PAPP-A by glandular cells remained unchanged after treatment with MPA and/or E2. These results confirm that in nonpregnant women PAPP-A is a progesterone-dependent protein produced by the endometrium.

Serum concentration of pregnancy specific and pregnancy-associated proteins in early gestation

PAPP-A, SP1, hCG and alpha 2-PAG were determined in the serum of 17 patients at weekly intervals between 3 and 12 weeks from the last menstrual period; progesterone and 17 beta-oestradiol concentrations were also measured in the same samples. SP1 and hCG concentrations were consistently found to rise steeply from the first time the proteins were detected. PAPP-A, though detectable in early samples from 9 of the patients, started to rise sharply in all cases between 6 and 10 weeks after LMP. Alpha 2-PAG, which was detected in all serum samples, showed no consistent behaviour with advancing pregnancy. In 3 patients, alpha 2-PAG was elevated as early as 3 weeks after LMP, while in others it remained at low levels during the entire interval observed. The correlation between these proteins (except between SP1 and hCG) is therefore poor; and their synthesis or secretion seems to be independently controlled.