Pregnancy-associated plasma protein-A (PAPP-A), an insulin-like growth factor-binding protein (IGFBP) protease, increases insulin-like growth factor (IGF) activity through cleavage of inhibitory IGFBP-4 and the consequent release of IGF peptide for receptor activation. Mice homozygous for targeted disruption of the PAPP-A gene are born as proportional dwarfs and exhibit retarded bone ossification during fetal development. Phenotype and in vitro data support a model in which decreased IGF-II bioavailability during embryogenesis results in growth retardation and reduction in overall body size. To test the hypothesis that an increase in IGF-II during embryogenesis would overcome the growth deficiencies, PAPP-A-null mice were crossed with ΔH19 mutant mice, which have increased IGF-II expression and fetal overgrowth due to disruption of IgfII imprinting. ΔH19 mutant mice were 126% and PAPP-A-null mice were 74% the size of controls at birth. These size differences were evident at embryonic day 16.5. Importantly, double mutants were indistinguishable from controls both in terms of size and skeletal development. Body size programmed during embryo development persisted post-natally. Thus, disruption of IgfII imprinting and consequent elevation in IGF-II during fetal development was associated with rescue of the dwarf phenotype and ossification defects of PAPP-A-null mice. These data provide strong genetic evidence that PAPP-A plays an essential role in determining IGF-II bioavailability for optimal fetal growth and development.

Insulin-like growth factors (IGFs) are implicated in the development of diabetic nephropathy (DN) and are shown to increase proliferation and extracellular matrix production in mesangial cells. The IGF system is complex and is composed of ligands, receptors, six binding proteins (IGF BPs) and a novel zinc metalloproteinase – pregnancy-associated plasma protein (PAPP)-A. PAPP-A increases the local bioavailability of IGF through the cleavage of IGF BP-4. Mesangial expansion is a major component of DN, and PAPP-A is shown to be increased in the glomeruli of patients with DN. Therefore, we determined the expression of PAPP-A and components of the IGF system in normal human mesangial cells (HMCs) and their regulation by factors known to be involved in DN. Under basal conditions, HMCs expressed PAPP-A, IGF1 receptor and all six IGF BPs. Interleukin (IL)-1β was the most potent stimulus for PAPP-A expression (5-fold) followed by tumor necrosis factor (TNF)-α (2.5-fold). This PAPP-A was secreted, cell associated and proteolytically active. IL1β also increased IGF BP-1expression (3-fold) with either reduction or no effect on other IGF BPs. Generally, TNF-α treatment decreased IGF BP expression. No treatment effect on PAPP-A or IGF BPs was seen with IL6, IGFs, advanced glycation end products or prolonged hyperglycemia. In addition, stimulation of HMCs with IGF1 alone or IGF1 complexed to wild-type, but not protease-resistant, IGF BP-4 led to increased [³H]-thymidine incorporation. In conclusion, these novel findings of PAPP-A and its regulation by proinflammatory cytokines, as well as the comprehensive analysis of the IGF system regulation in HMCs, suggest a mechanism by which inflammatory states such as DN can impact IGF activity in the kidney.

Fat distribution differs between individuals, and those with visceral fat predominance develop metabolic profiles that increase the risk of adverse cardiovascular events. This is due, in part, to the proinflammatory state associated with visceral obesity as well as depot-specific adipogenesis. The IGF system is important in adipose tissue development and metabolic function. Pregnancy-associated plasma protein A (PAPPA) is a novel zinc metalloproteinase that regulates local IGF availability. The first aim of this study was to characterize PAPPA mRNA and protein expression in primary cultures of human preadipocytes isolated from omental, mesenteric, and subcutaneous depots. PAPPA expression was significantly increased in omental preadipocytes compared with mesenteric and subcutaneous preadipocytes. The second aim of this study was to investigate the factors regulating PAPPA expression, focusing on proinflammatory cytokines and resveratrol that have been shown to have negative and positive effects, respectively, on metabolism and diet-induced obesity. Treatment of cultured primary human preadipocytes with tumor necrosis factor α and interleukin 1β led to significant increases in PAPPA expression. Activated pathways mediating cytokine-induced PAPPA expression include the nuclear factor κB pathway and the MAPK family, particularly c-Jun NH₂-terminal kinase and p38 MAPK. Resveratrol, a polyphenolic compound with beneficial cardiometabolic effects, significantly downregulated PAPPA expression under basal and stimulated conditions. Effects of resveratrol on PAPPA appeared to be mediated through pathways independent of silent mating type information regulation 2 homolog 1 (SIRT1) and AMP kinase activation. Depot-specific PAPPA expression in human preadipocytes may contribute to a depot-specific function.

Mice born with the deletion of the gene for pregnancy-associated plasma protein-A (PAPP-A), a model of reduced local IGF activity, live ∼30% longer than their wild-type (WT) littermates. In this study, we investigated metabolic consequences of PAPP-A gene deletion and possible relationship to lifespan extension. Specifically, we determined whether 18-month-old PAPP-A knockout (KO) mice when compared with their WT littermates have reduced energy expenditure and/or altered glucose–insulin sensitivity. Food intake, and total energy expenditure and resting energy expenditure as measured by calorimetry were not different between PAPP-A KO and WT mice when subjected to the analysis of covariance with body weight as the covariate. However, there was an increase in spontaneous physical activity in PAPP-A KO mice. Both WT and PAPP-A KO mice exhibited mild insulin resistance with age, as assessed by fasting glucose/insulin ratios. Oral glucose tolerance and insulin sensitivity were not significantly different between the two groups of mice, although there appeared to be a decrease in the average size of the pancreatic islets in PAPP-A KO mice. Thus, neither reduced ‘rate of living’ nor altered glucose–insulin homeostasis can be considered key determinants of the enhanced longevity of PAPP-A KO mice. These findings are discussed in the context of those from other long-lived mouse models.

We investigated pregnancy-associated plasma protein-A (PAPP-A) in diabetic nephropathy. Normal human kidney showed specific staining for PAPP-A in glomeruli, and this staining was markedly increased in diabetic kidney. To assess the possible contribution of PAPP-A in the development of diabetic nephropathy, we induced diabetes with streptozotocin in 14-month-old WT and Papp-A knockout (KO) mice. Renal histopathology was evaluated after 4 months of stable hyperglycemia. Kidneys from diabetic WT mice showed multiple abnormalities including thickening of Bowman's capsule (100% of mice), increased glomerular size (80% of mice), tubule dilation (80% of mice), and mononuclear cell infiltration (90% of mice). Kidneys of age-matched non-diabetic WT mice had similar evidence of tubule dilation and mononuclear cell infiltration to those of diabetic WT mice, indicating that these changes were predominantly age-related. However, thickened Bowman's capsule and increased glomerular size appeared specific for the experimental diabetes. Kidneys from diabetic Papp-A KO mice had significantly reduced or no evidence of changes in Bowman's capsule thickening and glomerular size. There was also a shift to larger mesangial area and increased macrophage staining in diabetic WT mice compared with Papp-A KO mice. In summary, elevated PAPP-A expression in glomeruli is associated with diabetic nephropathy in humans and absence of PAPP-A is associated with resistance to the development of indicators of diabetic nephropathy in mice. These data suggest PAPP-A as a potential therapeutic target for diabetic nephropathy.

Pregnancy-associated plasma protein A (PAPP-A), a metalloproteinase that regulates IGF bioavailability in vitro through cleavage of inhibitory IGF-binding protein-4 (IGFBP-4), has been implicated in skeletal development and injury repair responses. However, direct in vivo data are lacking. In this study, we used PAPP-A knock-out (KO) mice to determine the role of PAPP-A in fracture repair. Stabilized mid-shaft fractures were produced in femurs of 3-month-old mice. At 14 days post-fracture, complete bony bridging of the fracture callus was seen radiographically in wild-type but not in PAPP-A KO mice. Histological examination 5 to 28 days post-fracture showed reductions in the amount of intramembranous bone formation, cartilage production, endochondral ossification and remodeling in PAPP-A KO compared with wild-type mice. However, fracture healing appeared similar in both groups at 42 days post-fracture when analyzed by histology. A similar degree of healing strength in wild-type and PAPP-A KO femurs was demonstrated by mechanical testing at 28 and 42 days post-fracture. Untreated cultures of day 5 fracture calluses from wild-type mice showed robust IGFBP-4 protease activity and IGF receptor phosphorylation, whereas fracture calluses from PAPP-A KO mice had no IGFBP-4 protease activity and reduced IGF receptor phosphorylation. These data demonstrate a marked delay in fracture healing in PAPP-A KO compared with wild-type mice, and suggest that PAPP-A is necessary in the early phases of the process for expeditious fracture repair. The ability of PAPP-A to enhance local IGF action may be an important mechanism for optimizing the fracture repair response.