Fetal antigen 1, a member of the epidermal growth factor superfamily, in neurofibromas and serum from patients with neurofibromatosis type 1

Current status and recommendations for biomarkers and biobanking in neurofibromatosis

OBJECTIVE

Clinically validated biomarkers for neurofibromatosis 1 (NF1), neurofibromatosis 2 (NF2), and schwannomatosis (SWN) have not been identified to date. The biomarker working group's goals are to (1) define biomarker needs in NF1, NF2, and SWN; (2) summarize existing data on biomarkers in NF1, NF2, and SWN; (3) outline recommendations for sample collection and biomarker development; and (4) standardize sample collection and methodology protocols where possible to promote comparison between studies by publishing standard operating procedures (SOPs).

METHODS

The biomarker group reviewed published data on biomarkers in NF1, NF2, and SWN and on biobanking efforts outside these diseases via literature search, defined the need for biomarkers in NF, and developed recommendations in a series of consensus meetings.

RESULTS

We describe existing biomarkers in NF and report consensus recommendations for SOP and a minimal clinical dataset to accompany samples derived from patients with NF1, NF2, and SWN in decentralized biobanks.

CONCLUSIONS

These recommendations are intended to provide clinicians and researchers with a common set of guidelines to collect and store biospecimens and for establishment of biobanks for NF1, NF2, and SWN.

FA1 Induces Pro-Inflammatory and Anti-Adipogenic Pathways/Markers in Human Myotubes Established from Lean, Obese, and Type 2 Diabetic Subjects but Not Insulin Resistance

AIMS

Delta like 1/fetal antigen 1 (Dlk1/FA1) is a protein secreted by hormone producing cells in adult human and mice that is known to inhibit adipogenesis. Recent studies demonstrated the role of Dlk1/FA1 in inducing insulin resistance in mice. To investigate the involvement of circulating Dlk1/FA1 in insulin resistance and type 2 diabetes in human subjects, we studied the effects of chronic FA1 on the intermediary metabolism in myotubes established from lean, obese, and type 2 diabetic (T2D) subjects.

METHODS

Myotube cultures were established from lean and obese control subjects, and obese T2D subjects and treated with soluble FA1 for 4 days supplemented with/without palmitate (PA). Lipid- and glucose metabolism were studied with labeled precursors while quantitative expression of genes was analyzed using real-time PCR.

RESULTS

Diabetic myotubes express significantly reduced insulin stimulated glucose metabolism compared to lean myotubes and a significantly decreased basal PA oxidation. Chronic FA1 exposure did not affect the intermediary metabolism in myotubes. Insulin sensitivity of glucose and lipid metabolism was not affected by chronic FA1 exposure in myotubes established from lean, obese, and T2D subjects. Instead, chronic FA1 exposure induced pro-inflammatory cytokines expression (IL-6 and CCL2) in association with reducing adipogenic markers (ADD1, AP2, CD36, and PPARg2) in myotubes. Consistent with this observation, addition of FA1 to cultured myotubes was show to significantly inhibit their differentiation into adipocyte.

CONCLUSION

Our results exclude direct effects of FA1 on glucose and lipid metabolism in cultured myotubes established from lean, obese, and T2D subjects. Therefore, the pathogenesis of FA1-induced IR might mainly be mediated via the FA1-induced stimulation of pro-inflammatory cytokines, which on turn inhibit adipogenesis in human myotubes.

Estrogen inhibits Dlk1/FA1 production: a potential mechanism for estrogen effects on bone turnover

We have recently identified delta-like 1/fetal antigen 1 (Dlk1/FA1) as a novel regulator of bone mass that functions to mediate bone loss under estrogen deficiency in mice. In this report, we investigated the effects of estrogen (E) deficiency and E replacement on serum (s) levels of Dlk1/FA1 (s-Dlk1FA1) and its correlation with bone turnover markers. s-Dlk1/FA1 and bone turnover markers (serum cross-linked C-telopeptide [s-CTX] and serum osteocalcin) were measured in two cohorts: a group of pre- and postmenopausal women (n = 100) and a group of postmenopausal women, where half had received estrogen-replacement therapy (ERT, n = 166). s-Dlk1/FA1 and s-CTX were elevated in postmenopausal E-deficient women compared with premenopausal E-replete women (both p < 0.001). s-Dlk1/FA1 was correlated with s-CTX (r = 0.30, p < 0.01). ERT in postmenopausal women decreased s-Dlk1/FA1, as well as s-CTX and s-osteoclacin (all p < .0001). Changes in s-Dlk1 were significantly correlated with those observed in s-CTX (r = 0.18, p < 0.05) and s-osteocalcin (r = 0.28, p < 0.001). In conclusion, s-Dlk1/FA1 is influenced by E-deficiency and is correlated with bone turnover. Increased levels of s-Dlk1/FA1 in postmenopausal women may be a mechanism mediating the effects of estrogen deficiency on bone turnover.

Gene expression analysis identifies potential biomarkers of neurofibromatosis type 1 including adrenomedullin

PURPOSE

Plexiform neurofibromas (pNF) are Schwann cell tumors found in a third of individuals with neurofibromatosis type 1 (NF1). pNF can undergo transformation to malignant peripheral nerve sheath tumors (MPNST). There are no identified serum biomarkers of pNF tumor burden or transformation to MPNST. Serum biomarkers would be useful to verify NF1 diagnosis, monitor tumor burden, and/or detect transformation.

EXPERIMENTAL DESIGN

We used microarray gene expression analysis to define 92 genes that encode putative secreted proteins in neurofibroma Schwann cells, neurofibromas, and MPNST. We validated differential expression by quantitative reverse transcription-PCR, Western blotting, and ELISA assays in cell conditioned medium and control and NF1 patient sera.

RESULTS

Of 13 candidate genes evaluated, only adrenomedullin (ADM) was confirmed as differentially expressed and elevated in serum of NF1 patients. ADM protein concentrati on was further elevated in serum of a small sampling of NF1 patients with MPNST. MPNST cell conditioned medium, containing ADM and hepatocyte growth factor, stimulated MPNST migration and endothelial cell proliferation.

CONCLUSIONS

Thus, microarray analysis identifies potential serum biomarkers for disease, and ADM is a serum biomarker of NF1. ADM serum levels do not seem to correlate with the presence of pNFs but may be a biomarker of transformation to MPNST.

OSM-11 facilitates LIN-12 Notch signaling during Caenorhabditis elegans vulval development

Notch signaling is critical for cell fate decisions during development. Caenorhabditis elegans and vertebrate Notch ligands are more diverse than classical Drosophila Notch ligands, suggesting possible functional complexities. Here, we describe a developmental role in Notch signaling for OSM-11, which has been previously implicated in defecation and osmotic resistance in C. elegans. We find that complete loss of OSM-11 causes defects in vulval precursor cell (VPC) fate specification during vulval development consistent with decreased Notch signaling. OSM-11 is a secreted, diffusible protein that, like previously described C. elegans Delta, Serrate, and LAG-2 (DSL) ligands, can interact with the lineage defective-12 (LIN-12) Notch receptor extracellular domain. Additionally, OSM-11 and similar C. elegans proteins share a common motif with Notch ligands from other species in a sequence defined here as the Delta and OSM-11 (DOS) motif. osm-11 loss-of-function defects in vulval development are exacerbated by loss of other DOS-motif genes or by loss of the Notch ligand DSL-1, suggesting that DOS-motif and DSL proteins act together to activate Notch signaling in vivo. The mammalian DOS-motif protein Deltalike1 (DLK1) can substitute for OSM-11 in C. elegans development, suggesting that DOS-motif function is conserved across species. We hypothesize that C. elegans OSM-11 and homologous proteins act as coactivators for Notch receptors, allowing precise regulation of Notch receptor signaling in developmental programs in both vertebrates and invertebrates.

Human serum levels of fetal antigen 1 (FA1/Dlk1) increase with obesity, are negatively associated with insulin sensitivity and modulate inflammation in vitro

OBJECTIVE

To investigate fetal antigen 1 (FA1) protein within the context of human obesity and its relation with insulin sensitivity.

SUBJECTS

Cross-sectional study that analyses circulating levels of FA1 in two selected human cohorts: n=127 men for the study of FA1 circulating levels in the context of obesity and insulin sensitivity (S(i)); and n=61 severely obese women before and after bariatric surgery. The response in vitro to FA1 protein on human cell lines of monocytes, preadipocytes and mature adipocytes was studied.

MEASUREMENTS

Anthropometrical parameters: body mass index, waist-to-hip ratio, waist circumference, fat-free mass and fat mass. Clinical parameters: lipid profile (high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, total cholesterol, triglycerides), glycemic profile (fasting glucose, insulin, S(i), HOMA-IR (Homeostasis Model Assessment of Insulin Resistance), cytokines (sIL-6), adipokines (adiponectin) and circulating soluble fractions of tumor necrosis factor-alpha receptors 1 and 2 (sTNFR1 and sTNFR2).

RESULTS

IN the obesity study, levels of FA1 in serum were found to increase with obesity. The S(i) index was negatively dependent on FA1 levels. In severe obesity, serum levels of FA1 decreased 1.4-fold 6 months after bariatric surgery. In vitro assays with FA1 protein on human monocytes and adipocytes cell lines modified the expression of pro-inflammatory cytokines and adipokines (tumor necrosis factor-alpha (TNFalpha), monocyte chemoattractant protein-1 (MCP-1), IL-6 (interleukin-6) and adiponectin).

CONCLUSION

FA1 serum levels were increased in obese subjects and might influence S(i). The stimulatory effect of FA1 protein on pro-inflammatory cytokines on both immune and adipose cell types could contribute to worsening the inflammatory environment observed in obesity.

Dlk1/FA1 is a novel endocrine regulator of bone and fat mass and its serum level is modulated by growth hormone

Fat and bone metabolism are two linked processes regulated by several hormonal factors. Fetal antigen 1 (FA1) is the soluble form of dlk1 (delta-like 1), which is a member of the Notch-Delta family. We previously identified FA1 as a negative regulator of bone marrow mesenchymal stem cell differentiation. Here, we studied the effects of circulating FA1 on fat and bone mass in vivo by generating mice expressing high serum levels of FA1 (FA1 mice) using the hydrodynamic-based gene transfer procedure. We found that increased serum FA1 levels led to a significant reduction in total body weight, fat mass, and bone mass in a dose-dependent manner. Reduced bone mass in FA1 mice was associated with the inhibition of mineral apposition rate and bone formation rates by 58 and 72%, respectively. Because FA1 is colocalized with GH in the pituitary gland, we explored the possible modulation of serum FA1 by GH. Serum levels of IGF-I and IGF binding proteins did not change in FA1 mice, whereas increasing serum GH in normal mice using hydrodynamic-based gene transfer procedure dramatically reduced serum FA1 levels by 60%. Conversely, serum FA1 was increased 450% in hypophysectomized mice, and this high level was reduced by 40% during GH treatment. In conclusion, our data identify the FA1 as a novel endocrine factor regulating bone mass and fat mass in vivo, and its serum levels are regulated by GH. FA1 thus provides a novel class of developmental molecules that regulate physiological functions of the postnatal organisms.

Circulating growth factor levels are associated with tumorigenesis in neurofibromatosis type 1

PURPOSE

Neurofibromatosis type 1 (NF1) is characterized by systemic development of neurofibromas. Early clinical diagnosis can be ambiguous, and genetic diagnosis can be prohibitively difficult. Dysregulation of a number of growth factors has been suggested to be a mechanism of pathogenesis. This study was performed to assess the contribution of circulating growth factors for diffuse tumorigenesis and the diagnostic value of circulating growth factor identification in serum.

EXPERIMENTAL DESIGN

The growth stimulation of neurofibroma-derived cells by serum from NF1 patients was tested, and serum growth factor levels in a cohort of NF1 patients (n = 39) between the ages of 7 and 70 years were analyzed.

RESULTS

Concentrations of midkine (MK) and stem cell factor, but not epidermal growth factor, were substantially increased in serum of NF1 patients when compared with healthy controls. Within the NF1 group, MK levels increased dramatically at puberty from an average of 0.79 ng/mL in patients <18 years to 1.18 ng/mL in patients >18 years old. Stem cell factor and MK concentrations above a defined threshold in serum of NF1 patients are of diagnostic benefit for 96% of patients in the cohort tested. Furthermore, serum from NF1 patients enhanced proliferation of human neurofibroma-derived primary Schwann cells and endothelial cells substantially better than normal serum.

CONCLUSIONS

Enhanced circulating growth factor levels contribute to diffuse tumorigenesis in NF1 and may provide the basis for molecular diagnosis.

Neurons in the monoaminergic nuclei of the rat and human central nervous system express FA1/dlk

The gene DLK1 encodes a member of the epidermal growth factor (EGF) superfamily, delta-like (dlk). When exposed in vivo to the action of an unknown protease, this type 1 membrane protein generates a soluble peptide referred to as Fetal antigen 1 (FA1). By acting in juxtacrine as well as paracrine/autocrine manners, both forms have been shown to be active in the differentiation/proliferation process of various cell types. In adults, FA1/dlk has been demonstrated mainly within (neuro) endocrine tissues. In this study we investigated the presence of FA1/dlk in other parts of the developing and adult rat and human CNS. Using immunocytochemistry and in situ hybridization we found that in both species FA1/dlk was expressed in neurons of the Edinger-Westphal's nucleus as well as in substantia nigra, ventral tegmental area (VTA), locus coeruleus and in certain parts of the raphe nuclei.

Does fetal antigen 1 (FA1) identify cells with regenerative, endocrine and neuroendocrine potentials? A study of FA1 in embryonic, fetal, and placental tissue and in maternal circulation

Fetal antigen 1 (FA1) is a circulating EGF multidomain glycoprotein. FA1 and its membrane-associated precursor is defined by the mRNAs referred to as delta-like (dlk), preadipocyte factor 1 (pref-1) or zona glomerulosa-specific factor (ZOG). Using a polyclonal antibody recognising both forms, the localisation of FA1/dlk was analysed in embryonic and fetal tissues between week 5 to 25 of gestation and related to germinal origin and development. FA1 was observed in endodermally derived hepatocytes, glandular cells of the pancreas anlage, and in respiratory epithelial cells. FA1 was also present in mesodermally derived cells of the renal proximal tubules, adrenal cortex, Leydig and Hilus cells of the testes and ovaries, fetal chondroblasts, and skeletal myotubes. Ectodermally derived neuro- and adenohypophysial cells, cells in the floor of the 3rd ventricle and plexus choroideus were also FA1 positive. The number of cells expressing FA1 decreased during fetal development where the expression became restricted to specific functional cells. Epidermis, gut epithelium, gall bladder, blood cells, spleen, thyroid gland, salivary glands, and smooth muscle cells were FA1 negative. Analysis of extra-embryonic tissues from normal and pathological pregnancies revealed FA1 in stromal cells surrounding the blood islands of the yolk sac as well as in placental fibroblasts where the expression was most pronounced in diploid, androgenic complete hydatidiform moles. However, as measured by ELISA, the circulating maternal FA1 levels in complete moles were not different from normal pregnancies. The results presented suggest that FA1 is a growth and/or differentiation factor extensively expressed in immature cells and down-regulated during fetal development. FA1 down-regulation was associated with a shift in the subcellular localisation indicating differential post-translational/post-transcriptional modifications during fetal development. FA1 may be a new marker of cellular subtypes with a regenerative potential and of specific cells with endocrine or neuroendocrine functions.