Constitutive expression of pregnancy-associated plasma protein-A in arterial smooth muscle reduces the vascular response to injury in vivo.

Pregnancy-associated plasma protein-A (PAPP-A) functions to increase local IGF-I bioactivity. In this study, we used transgenic mice that constitutively express human PAPP-A in arterial smooth muscle to test the hypothesis that overexpression of PAPP-A enhances vascular smooth muscle cell (SMC) response to IGF-I in vivo. PAPP-A transgenic (Tg) and wild-type (WT) mice underwent unilateral carotid ligation, a model of injury-induced SMC hyperplasia and neointimal formation. In both WT and PAPP-A Tg mice, endogenous PAPP-A mRNA expression showed peak elevation 5 days after carotid ligation. However, PAPP-A Tg mice had 70-75% less neointima than WT at 5 and 10 days postligation, with a significant reduction in occlusion of the ligated artery. WT and PAPP-A Tg mice had equivalent increases in medial area and vessel remodeling postligation. There was little change in medial area and no evidence of neointima in the contralateral carotid of WT or PAPP-A Tg mice. Both WT and PAPP-A Tg carotids exhibited signs of dedifferentiation of SMC, which precedes the increase in proliferation and migration that results in neointimal formation. However, the number of proliferating cells in the media and neointima of the ligated PAPP-A Tg artery was reduced by 90% on day 5 postsurgery compared with WT. This decrease was associated with a significant decrease in an in vivo marker of IGF-I bioactivity and reduced IGF-I-stimulated receptor phosphorylation ex vivo. These data suggest differential effects of chronic (transgenic) and transient (endogenous) PAPP-A expression on neointimal formation following vascular injury that may be due in part to the differential impact on IGF-I signaling.

Myogenesis defects in a patient-derived iPSC model of hereditary GNE myopathy.

Hereditary muscle diseases are disabling disorders lacking effective treatments. UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase (GNE) myopathy (GNEM) is an autosomal recessive distal myopathy with rimmed vacuoles typically manifesting in late adolescence/early adulthood. GNE encodes the rate-limiting enzyme in sialic acid biosynthesis, which is necessary for the proper function of numerous biological processes. Outside of the causative gene, very little is known about the mechanisms contributing to the development of GNE myopathy. In the present study, we aimed to address this knowledge gap by querying the underlying mechanisms of GNE myopathy using a patient-derived induced pluripotent stem-cell (iPSC) model. Control and patient-specific iPSCs were differentiated down a skeletal muscle lineage, whereby patient-derived GNEM iPSC clones were able to recapitulate key characteristics of the human pathology and further demonstrated defects in myogenic progression. Single-cell RNA sequencing time course studies revealed clear differences between control and GNEM iPSC-derived muscle precursor cells (iMPCs), while pathway studies implicated altered stress and autophagy signaling in GNEM iMPCs. Treatment of GNEM patient-derived iMPCs with an autophagy activator improved myogenic differentiation. In summary, we report an in vitro, iPSC-based model of GNE myopathy and implicate defective myogenesis as a contributing mechanism to the etiology of GNE myopathy.

Induced Pluripotent Stem Cells From Subjects With Primary Sclerosing Cholangitis Develop a Senescence Phenotype Following Biliary Differentiation.

Primary sclerosing cholangitis (PSC) is a chronic fibroinflammatory disease of the biliary tract characterized by cellular senescence and periportal fibrogenesis. Specific disease features that are cell intrinsic and either genetically or epigenetically mediated remain unclear due in part to a lack of appropriate, patient-specific, in vitro models. Recently, our group developed systems to create induced pluripotent stem cell (iPSC)-derived cholangiocytes (iDCs) and biliary epithelial organoids (cholangioids). We use these models to investigate whether PSC cholangiocytes are intrinsically predisposed to cellular senescence. Skin fibroblasts from healthy controls and subjects with PSC were reprogrammed to pluripotency, differentiated to cholangiocytes, and subsequently grown in three-dimensional matrigel-based culture to induce formation of cholangioids. RNA sequencing (RNA-seq) on iDCs showed significant differences in gene expression patterns, including enrichment of pathways associated with cell cycle, senescence, and hepatic fibrosis, that correlate with PSC. These pathways also overlapped with RNA-seq analysis on isolated cholangiocytes from subjects with PSC. Exome sequencing on the subjects with PSC revealed genetic variants of unknown significance in the genes identified in these pathways. Three-dimensional culture revealed smaller size, lack of a central lumen, and increased cellular senescence in PSC-derived cholangioids. Congruent with this, PSC-derived iDCs showed increased secretion of the extracellular matrix molecule fibronectin as well as the inflammatory cytokines interleukin-6, and chemokine (C-C motif) ligand 2. Conditioned media (CM) from PSC-derived iDCs more potently activated hepatic stellate cells compared to control CM. Conclusion: We demonstrated efficient generation of iDCs and cholangioids from patients with PSC that show disease-specific features. PSC cholangiocytes are intrinsically predisposed to cellular senescence. These features are unmasked following biliary differentiation of pluripotent stem cells and have functional consequences in epithelial organoids.

Modernizing Storage Conditions for Fresh Osteochondral Allografts by Optimizing Viability at Physiologic Temperatures and Conditions.

Objective. Osteochondral allograft (OCA) transplantation has demonstrated good long-term outcomes in treatment of cartilage defects. Viability, a key factor in clinical success, decreases with peri-implantation storage at 4°C during pathogen testing, matching logistics, and transportation. Modern, physiologic storage conditions may improve viability and enhance outcomes. Design. Osteochondral specimens from total knee arthroplasty patients (6 males, 5 females, age 56.4 ± 2.2 years) were stored in media and incubated at normoxia (21% O2) at 22°C or 37°C, and hypoxia (2% O2) at 37°C. Histology, live-dead staining, and quantitative polymerase chain reaction (qPCR) was performed 24 hours after harvest and following 7 days of incubation. Tissue architecture, cell viability, and gene expression were analyzed. Results. No significant viability or gene expression deterioration of cartilage was observed 1-week postincubation at 37°C, with or without hypoxia. Baseline viable cell density (VCD) was 94.0% ± 2.7% at day 1. At day 7, VCD was 95.1% (37°C) with normoxic storage and 92.2% (37°C) with hypoxic storage (P ≥ 0.27). Day 7 VCD (22°C) incubation was significantly lower than both the baseline and 37°C storage values (65.6%; P < 0.01). COL1A1, COL1A2, and ACAN qPCR expression was unchanged from baseline (P < 0.05) for all storage conditions at day 7, while CD163 expression, indicative of inflammatory macrophages and monocytes, was significantly lower in the 37°C groups (P < 0.01). Conclusion. Physiologic storage at 37°C demonstrates improved chondrocyte viability and metabolism, and maintained collagen expression compared with storage at 22°C. These novel findings guide development of a method to optimize short-term fresh OCA storage, which may lead to improved clinical results.

Aqueous humor rapidly stimulates myocilin secretion from human trabecular meshwork cells.

Myocilin, a protein associated with the development of glaucoma, is expressed in most eye tissues with highest expression observed in trabecular meshwork cells. In culture, primary human trabecular meshwork cells incubated in 10% fetal bovine serum have reduced myocilin expression compared to in vivo, but incubation in human aqueous humor, their normal in vivo nutrient source, restores myocilin expression to near in vivo levels. To investigate the mechanism by which human aqueous humor stimulates myocilin accumulation in conditioned media from normal human trabecular meshwork cells, three independent trabecular meshwork cell lines were cultured in Dulbecco's Modified Eagle's Medium (DMEM) containing various supplements: fetal bovine serum (10%), human serum (0.2%), porcine aqueous humor (50%), bovine serum albumin (0.1%), dexamethasone (10(-7)M), human aqueous humor (50%) or heat-inactivated human aqueous humor (50%). Conditioned media from cultured primary trabecular meshwork cells following incubation in human aqueous humor showed significant accumulation of myocilin in a time- (15 min) and dose-dependent manner (half maximal effective concentration ∼ 30%) while intracellular myocilin levels decreased. Minimal myocilin accumulation was observed in conditioned media isolated from trabecular meshwork cells cultured in DMEM containing fetal bovine or human serum, bovine serum albumin, porcine aqueous humor, dexamethasone or DMEM alone. Heat inactivation of human aqueous humor nearly eliminated human aqueous humor-stimulated myocilin secretion. Inhibitors of new protein synthesis, gene transcription, the endoplasmic reticulum/Golgi system and endocytic/exocytic secretory pathways failed to inhibit human aqueous humor-stimulated myocilin secretion. Using immunolabeling and transmission electron microscopy, myocilin was found associated with 70-90 nm vesicle-like structures within the cytoplasm of human aqueous humor treated trabecular meshwork cells. These studies suggest that myocilin secretion from trabecular meshwork cells occurs in a Golgi-independent manner following human aqueous humor treatment. Heat-labile factors in human aqueous humor are responsible for the time- and dose-dependent release of myocilin from vesicle-like structures within the cytoplasm of trabecular meshwork cells.

Glaucoma-associated myocilin: a better understanding but much more to learn.

Over a decade has passed since myocilin was identified as the first gene linked to early and late-onset primary open-angle glaucoma. During this time, considerable effort has been put forth to understand the functional role myocilin has in normal and glaucomatous eyes. Myocilin is expressed in many ocular and non-ocular tissues, is found in both intracellular and extracellular spaces, and has been linked to elevations in intraocular pressure. Mutations in the myocilin gene that have been associated with glaucoma appear to confer a gain-of-functional activity rather than loss of function. Unfortunately, what the normal function of myocilin is and how alterations in the function can confer a glaucoma phenotype have yet to be elucidated. We will review the current understanding of myocilin with special emphasis on the structural makeup of the myocilin gene and protein, its possible physiological roles internal and external to ocular cells, the regulation of intraocular pressure as evidenced through the use of perfusion culture systems and animal models, and as a causative agent in some forms of glaucoma.

Targeted disruption of the pregnancy-associated plasma protein-A gene is associated with diminished smooth muscle cell response to insulin-like growth factor-I and resistance to neointimal hyperplasia after vascular injury.

IGF-I is an important determinant of the vascular response to injury in large part through its ability to stimulate migration and proliferation of smooth muscle cells (SMCs). In this study, we used mice with targeted disruption of the pregnancy-associated plasma protein-A gene (PAPP-A-/-) and wild-type (WT) littermates to test the hypotheses that PAPP-A, a metalloproteinase that cleaves inhibitory IGF binding protein (IGFBP)-4, regulates vascular SMC responses to IGF-I in vitro and is critical for the development of vascular neointima after injury in vivo. Vascular SMCs from PAPP-A-/- mice lacked IGFBP-4 protease activity and failed to respond to treatment with IGF-I in the presence of IGFBP-4, whereas SMCs from WT mice with robust IGFBP-4 protease activity showed significant migratory and proliferative responses to IGF-I/IGFBP-4. For in vivo testing, PAPP-A-/- and WT mice underwent unilateral carotid ligation, a model of injury-induced neointimal hyperplasia. In WT mice, PAPP-A mRNA expression was markedly elevated 7 and 14 d after carotid ligation, associated with a progressive increase in neointimal hyperplasia and, in many cases, with complete occlusion of the vessel at 28 d. In contrast, PAPP-A-/- mice showed little evidence of progression resulting in a 75% reduction in neointimal area when compared with WT at 28 d. Cells staining for proliferating cell nuclear antigen were plentiful in the SMC-rich medial and neointimal areas of the injured WT vessel in stark contrast to the relatively few proliferating cells in the same areas of the PAPP-A-/- vessel. Expression of IGF-I and IGFBP-4 was similarly elevated in injured carotids from WT and PAPP-A-/- mice with no change in IGF-I receptor expression. IGFBP-5, an IGF-responsive gene, was increased 2-fold in WT but not in PAPP-A-/- carotids, suggesting reduced IGF activity in the absence of PAPP-A. Thus, PAPP-A-deficient mice are resistant to neointimal formation after injury, which may be explained in part by the ability of PAPP-A to enhance local IGF-I stimulation of vascular SMCs through proteolysis of IGFBP-4.

Stress-activated signaling pathways mediate the stimulation of pregnancy-associated plasma protein-A expression in cultured human fibroblasts.

Pregnancy-associated plasma protein-A (PAPP-A) is an IGF binding protein protease that appears to function as a posttranslational modulator of IGF bioavailability in response to injury. A previous study indicated that the proinflammatory cytokines, TNFalpha and IL-1beta, were potent stimulators of PAPP-A expression in cultured human fibroblasts. In this study, we investigated the intracellular signaling pathways mediating cytokine-stimulated PAPP-A expression. Treatment of human fibroblasts with TNFalpha and IL-1beta (1 nm) had little or no effect on phosphatidylinositol 3-kinase and Erk1/2 activation, pathways commonly associated with proliferation. On the other hand, TNFalpha and IL-1beta induced p38, c-Jun N-terminal kinase (JNK), and nuclear factor (NF)kappaB activation, pathways more closely related to stress response. An inhibitor of p38 activation (SB203580) had no effect on TNFalpha- or IL-1beta-stimulated PAPP-A expression. The JNK inhibitor, SP600125, had no effect on IL-1beta- or TNFalpha-stimulated PAPP-A mRNA expression. However, SP600125 effectively inhibited IL-1beta-induced PAPP-A protein expression. MG-132, a proteasome inhibitor that blocked degradation of the intrinsic NFkappaB inhibitor, IkappaB, and thereby prevented NFkappaB activation, was a potent inhibitor of both TNFalpha- and IL-1beta-stimulated PAPP-A mRNA and protein expression and IGF binding protein-4 protease activity. MG-132 had no effect on JNK phosphorylation or p38 activation, and SB203580 and SP600125 had no effect on IkappaB degradation, documenting inhibitor specificity. BAY11-7082, another inhibitor of NFkappaB activation, also inhibited TNFalpha- and IL-1beta-stimulated PAPP-A expression and IGF binding protein-4 protease activity. These data indicate that NFkappaB activation is the primary mediator of cytokine-stimulated PAPP-A expression in human fibroblasts.

Closure of a Recurrent Bronchopleural Fistula Using a Matrix Seeded With Patient-Derived Mesenchymal Stem Cells.

: Management of recurrent bronchopleural fistula (BPF) after pneumonectomy remains a challenge. Although a variety of devices and techniques have been described, definitive management usually involves closure of the fistula tract through surgical intervention. Standard surgical approaches for BPF incur significant morbidity and mortality and are not reliably or uniformly successful. We describe the first-in-human application of an autologous mesenchymal stem cell (MSC)-seeded matrix graft to repair a multiply recurrent postpneumonectomy BPF. Adipose-derived MSCs were isolated from patient abdominal adipose tissue, expanded, and seeded onto bio-absorbable mesh, which was surgically implanted at the site of BPF. Clinical follow-up and postprocedural radiological and bronchoscopic imaging were performed to ensure BPF closure, and in vitro stemness characterization of patient-specific MSCs was performed. The patient remained clinically asymptomatic without evidence of recurrence on bronchoscopy at 3 months, computed tomographic imaging at 16 months, and clinical follow-up of 1.5 years. There is no evidence of malignant degeneration of MSC populations in situ, and the patient-derived MSCs were capable of differentiating into adipocytes, chondrocytes, and osteocytes using established protocols. Isolation and expansion of autologous MSCs derived from patients in a malnourished, deconditioned state is possible. Successful closure and safety data for this approach suggest the potential for an expanded study of the role of autologous MSCs in regenerative surgical applications for BPF. SIGNIFICANCE: Bronchopleural fistula is a severe complication of pulmonary resection. Current management is not reliably successful. This work describes the first-in-human application of an autologous mesenchymal stem cell (MSC)-seeded matrix graft to the repair of a large, multiply recurrent postpneumonectomy BPF. Clinical follow-up of 1.5 years without recurrence suggests initial safety and feasibility of this approach. Further assessment of MSC grafts in these difficult clinical scenarios requires expanded study.

Autosomal Recessive Bestrophinopathy Is Not Associated With the Loss of Bestrophin-1 Anion Channel Function in a Patient With a Novel BEST1 Mutation.

PURPOSE: Mutations in BEST1, encoding bestrophin-1 (Best1), cause autosomal recessive bestrophinopathy (ARB). Encoding bestrophin-1 is a pentameric anion channel localized to the basolateral plasma membrane of the RPE. Here, we characterize the effects of the mutations R141H (CGC > CAC) and I366fsX18 (c.1098_1100+7del), identified in a patient in our practice, on Best1 trafficking, oligomerization, and channel activity. METHODS: Currents of Cl- were assessed in transfected HEK293 cells using whole-cell patch clamp. Best1 localization was assessed by confocal microscopy in differentiated, human-induced pluripotent stem cell-derived RPE (iPSC-RPE) cells following expression of mutants via adenovirus-mediated gene transfer. Oligomerization was evaluated by coimmunoprecipitation in iPSC-RPE and MDCK cells. RESULTS: Compared to Best1, Best1 I366fsX18 currents were increased while Best1 R141H Cl- currents were diminished. Coexpression of Best1 R141H with Best1 or Best1 I366fsX18 resulted in rescued channel activity. Overexpressed Best1, Best1 R141H, and Best1 I366fsX18 were all properly localized in iPSC-RPE cells; Best1 R141H and Best1 I366fsX18 coimmunoprecipitated with endogenous Best1 in iPSC-RPE cells and with each other in MDCK cells. CONCLUSIONS: The first 366 amino acids of Best1 are sufficient to mediate channel activity and homo-oligomerization. The combination of Best1 and Best1 R141H does not cause disease, while Best1 R141H together with Best1 I366fsX18 causes ARB. Since both combinations generate comparable Cl- currents, this indicates that ARB in this patient is not caused by a loss of channel activity. Moreover, Best1 I366fsX18 differs from Best1 in that it lacks most of the cytosolic C-terminal domain, suggesting that the loss of this region contributes significantly to the pathogenesis of ARB in this patient.

Molecular regulation of the IGF-binding protein-4 protease system in human fibroblasts: identification of a novel inducible inhibitor.

The IGF-binding protein-4 (IGFBP-4) protease system is an important regulator of local IGF bioavailability and cell growth. Recently, the IGF-dependent IGFBP-4 protease secreted by cultured human fibroblasts was identified as pregnancy-associated plasma protein A (PAPP-A). In pregnancy serum, PAPP-A circulates as a disulfide-bound complex with the precursor form of major basic protein (pro-MBP), and in this complex PAPP-A's proteolytic activity is not evident. In this study we analyzed the IGFBP-4 protease system in normal human fibroblasts to determine regulation outside of pregnancy. Treatment with the phorbol ester tumor promoter, beta-phorbol 12,13-didecanoate (beta-PDD), resulted in time-dependent inhibition of the IGF-dependent IGFBP-4 protease activity in cell-conditioned medium, which was evident at 6 h and complete by 24 h. PAPP-A mRNA was constitutively expressed in control cells, and levels were decreased only after 24 h of beta-PDD treatment. Secretion of PAPP-A protein into conditioned medium did not change with beta-PDD treatment. On the other hand, pro-MBP mRNA was undetectable in control human fibroblasts, and treatment with beta-PDD induced pro-MBP mRNA and protein expression within 6 h. beta-PDD-induced pro-MBP mRNA expression and protease inhibition were blocked with an inhibitor of RNA synthesis, actinomycin D. Actinomycin D had no effect on PAPP-A mRNA levels in the absence or presence of beta-PDD. Similarly, transformation of human fibroblasts with simian virus 40 large T antigen resulted in the synthesis of pro-MBP mRNA and protein and inhibition of IGFBP-4 protease activity. Coculture of fibroblasts with cells transfected with pro-MBP cDNA resulted in inhibition of IGFBP-4 proteolytic activity without having any effect on PAPP-A synthesis. In summary, phorbol ester tumor promoters and simian virus 40 transformation regulate IGFBP-4 proteolysis in human fibroblasts through induction of a novel inhibitor of PAPP-A, pro-MBP. These findings expand our understanding of the IGFBP-4 protease system and suggest an additional level of local cell growth control.

Pregnancy-associated plasma protein a gene expression as a target of inflammatory cytokines.

Pregnancy-associated plasma protein A (PAPP-A) cleaves IGF-binding protein-4 (IGFBP-4) and appears to enhance local IGF bioavailability in response to injury. In this study we determined the effects of growth factors and cytokines involved in the healing process on PAPP-A expression in human dermal fibroblasts. There was no effect of platelet-derived growth factor, epidermal growth factor, or basic fibroblast growth factor on PAPP-A mRNA expression in these cells. However, treatment with the proinflammatory cytokines, TNFalpha and IL-1 beta, resulted in time- and dose-dependent increases in PAPP-A mRNA and protein expression (3- to 4-fold maximal effects), which were prevented by actinomycin D. On the other hand, interferon-gamma (IFN gamma) treatment markedly inhibited PAPP-A expression. IGFBP-4 proteolytic activity was increased 4-fold in medium from TNFalpha- and IL-1 beta-treated (1 nm) cells and decreased 40% in medium from IFN gamma-treated (1 nm) cells. IGF-I-stimulated [(3)H]thymidine incorporation was significantly enhanced by pretreatment with 1 nm TNFalpha, and this enhancement was blocked in the presence of protease-resistant IGFBP-4. In conclusion, PAPP-A expression is regulated by inflammatory cytokines in adult human fibroblasts, with functional consequences on IGFBP-4 protease activity and IGF-I bioavailability. These data provide a mechanism for the regulation of PAPP-A in response to injury and further implicate PAPP-A in the wound-healing processes.

Regulation of pregnancy-associated plasma protein-A expression in cultured human osteoblasts.

Pregnancy-associated plasma protein-A (PAPP-A) is a metalloproteinase secreted by cultured human osteoblasts that has been implicated in the regulation of local insulin-like growth factor (IGF) bioavailability during bone growth and remodeling. However, very little is known about the regulation of PAPP-A expression in bone. In this study, we determined the effect of systemic and local osteoregulatory factors on PAPP-A mRNA and protein expression in normal human osteoblasts (hOB cells). Treatment of hOB cells with particular peptide growth factors (basic fibroblast growth factor, epidermal growth factor), steroid hormones (dexamethasone, 1,25-dihydroxyvitamin D(3)), and cytokines [interleukin-6 (IL-6), IL-13, oncostatin M] with known involvement in bone cell physiology had no significant effect on PAPP-A expression. Agents that increase intracellular cyclic AMP (forskolin, prostaglandin E(2)) increased PAPP-A mRNA and protein expression approximately 3-fold. Tumor necrosis factor alpha (TNFalpha), IL-1beta, and IL-4 also increased PAPP-A expression 3- to 4-fold. Transforming growth factor beta (TGFbeta) was previously shown to stimulate PAPP-A expression in hOB cells. The effects of TGFbeta, TNFalpha, and IL-1beta were additive, whereas the effects of TGFbeta and IL-4 were synergistic. In summary, TNFalpha, IL-1beta, and IL-4 were identified as potent stimulators of PAPP-A expression in primary cultures of human osteoblasts. These findings suggest a mechanism whereby cytokines present in bone and bone marrow could augment IGF bioavailability during skeletal growth and remodeling.

Indirect targeting of IGF receptor signaling in vivo by substrate-selective inhibition of PAPP-A proteolytic activity.

The insulin-like growth factor (IGF) signaling pathway is involved in certain human cancers, and the feasibility of directly targeting the IGF receptor has been actively investigated. However, recent evidence from clinical trials suggests that this approach can be problematic. We have developed an alternative strategy to indirectly inhibit the IGF signaling by targeting the metalloproteinase, pregnancy-associated plasma protein-A (PAPP-A). PAPP-A associated with the cell surface cleaves IGF binding protein-4 (IGFBP-4), when IGF is bound to IGFBP-4, and thereby increases IGF bioavailability for receptor activation in an autocrine/paracrine manner. We hypothesized that inhibition of PAPP-A would suppress excessive local IGF signaling in tissues where this is caused by increased PAPP-A proteolytic activity. To test this hypothesis, we developed an inhibitory monoclonal antibody, mAb 1/41, which targets a unique substrate-binding exosite of PAPP-A. This inhibitor selectively and specifically inhibits proteolytic cleavage of IGFBP-4 with an inhibitory constant (Ki) of 135 pM. In addition, it inhibited intracellular signaling of the IGF receptor (AKT phosphorylation) in monolayers of A549 cells, an IGF-responsive lung cancer-derived cell line found to express high levels of PAPP-A. We further showed that mAb 1/41 is effective towards PAPP-A bound to cell surfaces, and that it is capable of inhibiting PAPP-A activity in vivo. Using a murine xenograft model of A549 cells, we demonstrated that mAb 1/41 administered intraperitoneally significantly inhibited tumor growth. Analysis of xenograft tumor tissue recovered from treated mice showed penetration of mAb 1/41, reduced IGFBP-4 proteolysis, and reduced AKT phosphorylation. Our study provides proof of concept that IGF signaling can be selectively reduced by targeting a regulatory proteinase that functions extracellularly, upstream of the IGF receptor. PAPP-A targeting thus represents an alternative therapeutic strategy for inhibiting IGF receptor signaling.

Effects of mutated pregnancy-associated plasma protein-a on atherosclerotic lesion development in mice.

Pregnancy-associated plasma protein-A (PAPP-A) is a large multidomain metalloprotease involved in cleavage of IGF binding protein (IGFBP)-4 and -5 thereby causing release of bioactive IGF. Individual domains of PAPP-A have been characterized in vitro, including the metzincin proteolytic domain important for IGFBP proteolytic activity, short consensus repeats critical for cell surface association, and Lin-12/Notch repeat module demonstrated to determine IGFBP substrate specificity. To test the hypothesis that specific cleavage of IGFBP-4 by PAPP-A in close proximity to the cell surface is required for development of lesions in a murine model of atherosclerosis, the following PAPP-A transgenic (Tg) mice were generated: Tg(E483A), which lacks all PAPP-A proteolytic activity; Tg(D1499A), which selectively lacks proteolytic activity against IGFBP-4; and Tg(K1296A/K1316A), in which cell surface binding is compromised. Following cross-breeding with apolipoprotein E (ApoE) knockout (KO) mice, ApoE KO/Tg mice were fed a high-fat diet to promote aortic lesion development. Lesion area was increased 2-fold in aortas from ApoE KO/Tg wild-type compared with ApoE KO mice (P < 0.001). However, there was no significant increase in the lesion area in any of the ApoE KO/Tg mutant mice. We conclude that PAPP-A proteolytic activity is required for the lesion-promoting effect of PAPP-A and that its specificity must be directed against IGFBP-4. Furthermore, our data demonstrate that cleavage of IGFBP-4 at a distance from the cell surface, and hence from the IGF receptor, is not effective in promoting the development of the atherosclerotic lesions. Thus, PAPP-A exerts its effect while bound to the cell surface in vivo.

Mice deficient in PAPP-A show resistance to the development of diabetic nephropathy.

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.

ATP-sensitive potassium (KATP) channel activation decreases intraocular pressure in the anterior chamber of the eye.

PURPOSE. ATP-sensitive potassium channel (K(ATP)) openers target key cellular events, many of which have been implicated in glaucoma. The authors sought to determine whether K(ATP) channel openers influence outflow facility in human anterior segment culture and intraocular pressure (IOP) in vivo. METHODS. Anterior segments from human eyes were placed in perfusion organ culture and treated with the K(ATP) channel openers diazoxide, nicorandil, and P1075 or the K(ATP) channel closer glyburide (glibenclamide). The presence, functionality, and specificity of K(ATP) channels were determined by RT-PCR, immunohistochemistry, and inside-out patch clamp in human trabecular meshwork (TM) tissue or primary cultures of normal human trabecular meshwork (NTM) cells. The effect of diazoxide on IOP in anesthetized Brown Norway rats was measured with a rebound tonometer. RESULTS. K(ATP) channel openers increased outflow facility in human anterior segments (0.14 ± 0.02 to 0.26 ± 0.09 µL/min/mm Hg; P < 0.001) compared with fellow control eyes (0.22 ± 0.11 to 0.21 ± 0.11 µL/min/mm Hg; P > 0.5). The effect was reversible, with outflow facility returning to baseline after drug removal. The addition of glyburide inhibited diazoxide from increasing outflow facility. Electrophysiology confirmed the presence and specificity of functional K(ATP) channels. K(ATP) channel subunits K(ir)6.1, K(ir)6.2, SUR2A, and SUR2B were expressed in TM and NTM cells. In vivo, diazoxide significantly lowered IOP in Brown Norway rats. CONCLUSIONS. Functional K(ATP) channels are present in the trabecular meshwork. When activated by K(ATP) channel openers, these channels increase outflow facility through the trabecular outflow pathway in human anterior segment organ culture and decrease IOP in Brown Norway rat eyes.

Transforming growth factor-beta1 modulates insulin-like growth factor binding protein-4 expression and proteolysis in cultured periosteal explants.

OBJECTIVE: Periosteum is involved in bone growth and fracture healing and has been used as a cell source and tissue graft for tissue engineering and orthopedic reconstruction including joint resurfacing. Periosteum can be induced by transforming growth factor beta (TGF-beta) or insulin-like growth factor-I (IGF-I) alone or in combination to form cartilage. However, little is known about the interaction between IGF and TGF-beta signaling during periosteal chondrogenesis. The purpose of this study was to determine the effect of TGF-beta1 on IGF binding protein-4 (IGFBP-4) and the IGFBP-4 protease pregnancy-associated plasma protein-A (PAPP-A) expression in cultured periosteal explants. DESIGN: Periosteal explants from rabbits were cultured with or without TGF-beta1. IGFBP-4 and PAPP-A mRNA levels were determined by real-time quantitative PCR. Conditioned medium was analyzed for IGFBP-4 and PAPP-A protein levels and IGFBP-4 protease activity. RESULTS: TGF-beta1-treated explants contained lower IGFBP-4 mRNA levels throughout the culture period with a maximum reduction of 70% on day 5 of culture. Lower levels of IGFBP-4 protein were also detected in the conditioned medium from TGF-beta1-treated explants. PAPP-A mRNA levels were increased 1.6-fold, PAPP-A protein levels were increased threefold, and IGFBP-4 protease activity was increased 8.5-fold between 7 and 10days of culture (the onset of cartilage formation in this model) in conditioned medium from TGF-beta1-treated explants. CONCLUSIONS: This study demonstrates that TGF-beta1 modulates the expression of IGFBP-4 and PAPP-A in cultured periosteal explants.

Pregnancy associated plasma protein-A and risk stratification of patients presenting with chest pain in the emergency department.

BACKGROUND: The aim of this study was to evaluate the clinical utility of serum pregnancy associated plasma protein-A (PAPP-A) levels in assisting triage of an intermediate to high-risk patient presenting with chest pain in the Emergency Department and no definite evidence of an acute coronary syndrome. METHODS: Serum levels of PAPP-A were measured in 59 patients presenting with chest pain to the Emergency Department. The patients were independently grouped according to the presence of acute coronary syndromes or the absence thereof. RESULTS: In a multivariate model that corrected for age, sex, type of chest pain, number of risk factors, history of coronary artery disease, troponin levels, and non-specific ECG changes, PAPP-A levels were still predictive of a final diagnosis of acute coronary syndrome in patients presenting with chest pain to the Emergency Department (Odds Ratio, 2.093; 95th confidence intervals, 1.037-4.224; p=0.039). CONCLUSIONS: Elevated serum PAPP-A levels were predictive of a diagnosis of acute coronary syndrome in intermediate- to high-risk patients presenting to the Emergency Department with chest pain and no definite evidence of an acute coronary syndrome. Thus, serum PAPP-A may be valuable as an adjunct, minimally invasive marker to improve risk stratification in chest pain patients.

Cytokine stimulation of pregnancy-associated plasma protein A expression in human coronary artery smooth muscle cells: inhibition by resveratrol.

Through specific cleavage of proteins that bind and inhibit insulin-like growth factor-I (IGF-I), pregnancy-associated plasma protein-A (PAPP-A) enhances local IGF-I availability, and, consequently, receptor activation. PAPP-A expression is increased in experimental models of vascular injury and in human atherosclerotic plaque; however, little is known about the regulation of PAPP-A gene expression in vascular cells. In this study, we tested the hypothesis that proinflammatory cytokines involved in the vascular injury response stimulate PAPP-A gene expression in human coronary artery smooth muscle cells (hCASMC) in culture. Tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta stimulated PAPP-A gene expression in a time- and dose-dependent manner. The effect of these cytokines appears to be at the level of transcription because actinomycin D completely prevented the induction of PAPP-A gene expression. Accumulation of PAPP-A in cell-conditioned medium paralleled mRNA synthesis, as did proteolytic activity against IGF binding protein-4 (IGFBP-4). Interestingly, pretreatment of hCASMC with resveratrol, a polyphenol found in the skin of grapes and in red wine purported to underlie the "French paradox," inhibited TNF-alpha- and IL-1beta-induced PAPP-A expression and, hence, its IGFBP-4 proteolytic activity. Resveratrol had no effect on basal PAPP-A expression and protease activity. Our finding that PAPP-A gene expression in hCASMC is stimulated by TNF-alpha and IL-1beta suggests a mechanism for the regulation of PAPP-A in response to vascular injury that may contribute to the enhanced IGF-I bioactivity in intimal hyperplasia and atherosclerotic plaque development. Our results also suggest that PAPP-A may be a target of the cardiovascular system-protective effects of resveratrol.