Fibulin-1 binds the amino-terminal head of beta-amyloid precursor protein and modulates its physiological function

A Bioinformatics-Based Study on Methylation Alterations of the FBLN1 Gene in Hippocampal Tissue of Alzheimer's Disease Model DKO and DTG Mice

Alzheimer's disease (AD) is characterized by progressive cognitive decline and late-stage neurobehavioral issues marked by amyloid-beta plaques and Tau protein tangles. This study aims to investigate Fibulin-1(FBLN1) gene expression in the hippocampal tissue of Presenilin-1/Presenilin-2 conditional double-knockout (DKO) and double-transgenic (DTG) mice, using single-cell sequencing and experimental methods to verify abnormal methylation status and correlation with AD. Genomic DNA from DKO and DTG mice was used for genotyping. Reduced Representation Bisulfite Sequencing (RRBS) identified 10 genes with abnormal methylation changes, with protein-protein interaction (PPI) analysis highlighting five core genes, including FBLN1. Single-cell sequencing, RT-PCR, and Western blotting (WB) were used to analyze FBLN1 mRNA and protein levels in the hippocampal tissues of early-stage and mid-stage AD DKO, DTG, and CBAC57 mice. RRBS identified 10 genes with abnormal methylation, with PPI highlighting five core genes. Single-cell sequencing showed significant FBLN1 expression in AD groups. RT-PCR and WB indicated elevated FBLN1 mRNA and protein levels in mid-stage AD DKO and DTG mice compared to CBAC57 mice, with no differences in early-stage AD DKO and CBAC57 mice. RRBS revealed hypomethylation of the FBLN1 gene in mid-stage AD DKO mice. Elevated FBLN1 expression in AD models suggests an age-dependent neurodegenerative mechanism independent of amyloid-beta deposition. This study enhances our understanding of AD's epigenetic mechanisms, which will aid targeted diagnosis, treatment, and prognosis.

Exosomes in the Diagnosis of Neuropsychiatric Diseases: A Review

Exosomes are 30-150 nm small extracellular vesicles (sEVs) which are highly stable and encapsulated by a phospholipid bilayer. Exosomes contain proteins, lipids, RNAs (mRNAs, microRNAs/miRNAs, long non-coding RNAs/lncRNAs), and DNA of their parent cell. In pathological conditions, the composition of exosomes is altered, making exosomes a potential source of biomarkers for disease diagnosis. Exosomes can cross the blood-brain barrier (BBB), which is an advantage for using exosomes in the diagnosis of central nervous system (CNS) diseases. Neuropsychiatric diseases belong to the CNS diseases, and many potential diagnostic markers have been identified for neuropsychiatric diseases. Here, we review the potential diagnostic markers of exosomes in neuropsychiatric diseases and discuss the potential application of exosomal biomarkers in the early and accurate diagnosis of these diseases. Additionally, we outline the limitations and future directions of exosomes in the diagnosis of neuropsychiatric diseases.

Proteomic insights into mental health status: plasma markers in young adults

Global emphasis on enhancing prevention and treatment strategies necessitates an increased understanding of the biological mechanisms of psychopathology. Plasma proteomics is a powerful tool that has been applied in the context of specific mental disorders for biomarker identification. The p-factor, also known as the "general psychopathology factor", is a concept in psychopathology suggesting that there is a common underlying factor that contributes to the development of various forms of mental disorders. It has been proposed that the p-factor can be used to understand the overall mental health status of an individual. Here, we aimed to discover plasma proteins associated with the p-factor in 775 young adults in the FinnTwin12 cohort. Using liquid chromatography-tandem mass spectrometry, 13 proteins with a significant connection with the p-factor were identified, 8 of which were linked to epidermal growth factor receptor (EGFR) signaling. This exploratory study provides new insight into biological alterations associated with mental health status in young adults.

Fibulin7 Mediated Pathological Cardiac Remodeling through EGFR Binding and EGFR-Dependent FAK/AKT Signaling Activation

Adverse remodeling after myocardial infarction (MI) result in heart failure and sudden cardiac death. Fibulin7 (FBLN7) is an adhesion protein excreted into the extracellular matrix that functions in multiple biological processes. However, whether and how FBLN7 affects post-MI cardiac remodeling remains unclear. Here, the authors identify FBLN7 as a critical profibrotic regulator of adverse cardiac remodeling. They observe significantly upregulated serum FBLN7 levels in MI patients with left ventricular remodeling compared to those without MI. Microarray dataset analysis reveal FBLN7 is upregulated in human heart samples from patients with dilated and hypertrophic cardiomyopathy compared with non-failing hearts. The authors demonstrate that FBLN7 deletion attenuated post-MI cardiac remodeling, leading to better cardiac function and reduced myocardial fibrosis, whereas overexpression of FBLN7 results in the opposite effects. Mechanistically, FBLN7 binds to the epidermal growth factor receptor (EGFR) through its EGF-like domain, together with the EGF-like calcium-binding domain, and induces EGFR autophosphorylation at tyrosine (Y) 1068 and Y1173, which activates downstream focal adhesion kinase/AKT signaling, thereby leading to fibroblast-to-myofibroblast transdifferentiation. In addition, FBLN7-EGFR mediates this signal transduction, and the fibrotic response is effectively suppressed by the inhibition of EGFR activity. Taken together, FBLN7 plays an important role in cardiac remodeling and fibrosis after MI.

Extracellular protein components of amyloid plaques and their roles in Alzheimer's disease pathology

Alzheimer's disease (AD) is pathologically defined by the presence of fibrillar amyloid β (Aβ) peptide in extracellular senile plaques and tau filaments in intracellular neurofibrillary tangles. Extensive research has focused on understanding the assembly mechanisms and neurotoxic effects of Aβ during the last decades but still we only have a brief understanding of the disease associated biological processes. This review highlights the many other constituents that, beside Aβ, are accumulated in the plaques, with the focus on extracellular proteins. All living organisms rely on a delicate network of protein functionality. Deposition of significant amounts of certain proteins in insoluble inclusions will unquestionably lead to disturbances in the network, which may contribute to AD and copathology. This paper provide a comprehensive overview of extracellular proteins that have been shown to interact with Aβ and a discussion of their potential roles in AD pathology. Methods that can expand the knowledge about how the proteins are incorporated in plaques are described. Top-down methods to analyze post-mortem tissue and bottom-up approaches with the potential to provide molecular insights on the organization of plaque-like particles are compared. Finally, a network analysis of Aβ-interacting partners with enriched functional and structural key words is presented.

In-depth Site-specific Analysis of N-glycoproteome in Human Cerebrospinal Fluid and Glycosylation Landscape Changes in Alzheimer's Disease

As the body fluid that directly interchanges with the extracellular fluid of the central nervous system (CNS), cerebrospinal fluid (CSF) serves as a rich source for CNS-related disease biomarker discovery. Extensive proteome profiling has been conducted for CSF, but studies aimed at unraveling site-specific CSF N-glycoproteome are lacking. Initial efforts into site-specific N-glycoproteomics study in CSF yield limited coverage, hindering further experimental design of glycosylation-based disease biomarker discovery in CSF. In the present study, we have developed an N-glycoproteomic approach that combines enhanced N-glycopeptide sequential enrichment by hydrophilic interaction chromatography (HILIC) and boronic acid enrichment with electron transfer and higher-energy collision dissociation (EThcD) for large-scale intact N-glycopeptide analysis. The application of the developed approach to the analyses of human CSF samples enabled identifications of a total of 2893 intact N-glycopeptides from 511 N-glycosites and 285 N-glycoproteins. To our knowledge, this is the largest site-specific N-glycoproteome dataset reported for CSF to date. Such dataset provides molecular basis for a better understanding of the structure-function relationships of glycoproteins and their roles in CNS-related physiological and pathological processes. As accumulating evidence suggests that defects in glycosylation are involved in Alzheimer's disease (AD) pathogenesis, in the present study, a comparative in-depth N-glycoproteomic analysis was conducted for CSF samples from healthy control and AD patients, which yielded a comparable N-glycoproteome coverage but a distinct expression pattern for different categories of glycoforms, such as decreased fucosylation in AD CSF samples. Altered glycosylation patterns were detected for a number of N-glycoproteins including alpha-1-antichymotrypsin, ephrin-A3 and carnosinase CN1 etc., which serve as potentially interesting targets for further glycosylation-based AD study and may eventually lead to molecular elucidation of the role of glycosylation in AD progression.

APP Binds to the EGFR Ligands HB-EGF and EGF, Acting Synergistically with EGF to Promote ERK Signaling and Neuritogenesis

The amyloid precursor protein (APP) is a transmembrane glycoprotein central to Alzheimer's disease (AD) with functions in brain development and plasticity, including in neurogenesis and neurite outgrowth. Epidermal growth factor (EGF) and heparin-binding EGF-like growth factor (HB-EGF) are well-described neurotrophic and neuromodulator EGFR ligands, both implicated in neurological disorders, including AD. Pro-HB-EGF arose as a putative novel APP interactor in a human brain cDNA library yeast two-hybrid screen. Based on their structural and functional similarities, we first aimed to verify if APP could bind to (HB-)EGF proforms. Here, we show that APP interacts with these two EGFR ligands, and further characterized the effects of APP-EGF interaction in ERK activation and neuritogenesis. Yeast co-transformation and co-immunoprecipitation assays confirmed APP interaction with HB-EGF. Co-immunoprecipitation also revealed that APP binds to cellular pro-EGF. Overexpression of HB-EGF in HeLa cells, or exposure of SH-SY5Y cells to EGF, both resulted in increased APP protein levels. EGF and APP were observed to synergistically activate the ERK pathway, crucial for neuronal differentiation. Immunofluorescence analysis of cellular neuritogenesis in APP overexpression and EGF exposure conditions confirmed a synergistic effect in promoting the number and the mean length of neurite-like processes. Synergistic ERK activation and neuritogenic effects were completely blocked by the EGFR inhibitor PD 168393, implying APP/EGF-induced activation of EGFR as part of the mechanism. This work shows novel APP protein interactors and provides a major insight into the APP/EGF-driven mechanisms underlying neurite outgrowth and neuronal differentiation, with potential relevance for AD and for adult neuroregeneration.

Altered serum protein levels in frontotemporal dementia and amyotrophic lateral sclerosis indicate calcium and immunity dysregulation

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are neurodegenerative diseases that are considered to be on the same disease spectrum because of overlapping genetic, pathological and clinical traits. Changes in serum proteins in FTD and ALS are poorly understood, and currently no definitive biomarkers exist for diagnosing or monitoring disease progression for either disease. Here we applied quantitative discovery proteomics to analyze protein changes in FTD (N = 72) and ALS (N = 28) patient serum compared to controls (N = 22). Twenty three proteins were significantly altered in FTD compared to controls (increased-APOL1, C3, CTSH, EIF5A, MYH2, S100A8, SUSD5, WDR1; decreased-C1S, C7, CILP2, COMP, CRTAC1, EFEMP1, FBLN1, GSN, HSPG2, IGHV1, ITIH2, PROS1, SHBG, UMOD, VASN) and 14 proteins were significantly altered in ALS compared to controls (increased-APOL1, CKM, CTSH, IGHG1, IGKC, MYH2; decreased-C7, COMP, CRTAC1, EFEMP1, FBLN1, GSN, HSPG2, SHBG). There was substantial overlap in the proteins that were altered in FTD and ALS. These results were validated using western blotting. Gene ontology tools were used to assess functional pathways potentially dysregulated in the two diseases, and calcium ion binding and innate immunity pathways were altered in both diseases. When put together, these results suggest significant overlap in pathophysiological peripheral changes in FTD and ALS. This study represents the first proteomics side-by-side comparison of serum changes in FTD and ALS, providing new insights into under-recognized perturbed pathways and an avenue for biomarker development for FTD and ALS.

Proteomics Analysis of Blood Serums from Alzheimer's Disease Patients Using iTRAQ Labeling Technology

Alzheimer' disease (AD) is the most common form of dementia affecting up to 6% of the population over the age of 65. In order to discover differentially expressed proteins that might serve as potential biomarkers, the serums from AD patients and healthy controls were compared and analyzed using the proteomics approach of isobaric tagging for relative and absolute quantitation (iTRAQ). For the first time, AD biomarkers in serums are investigated in the Han Chinese population using iTRAQ labeled proteomics strategy. Twenty-two differentially expressed proteins were identified and out of which nine proteins were further validated with more sample test. Another three proteins that have been reported in the literature to be potentially associated with AD were also investigated for alteration in expression level. Functions of those proteins were mainly related to the following processes: amyloid-β (Aβ) metabolism, cholesterol transport, complement and coagulation cascades, immune response, inflammation, hemostasis, hyaluronan metabolism, and oxidative stress. These results support current views on the molecular mechanism of AD. For the first time, differential expression of zinc-alpha-2-glycoprotein (AZGP1), fibulin-1 (FBLN1), platelet basic protein (PPBP), thrombospondin-1 (THBS1), S100 calcium-binding protein A8 (S100A8), and S100 calcium-binding protein A9 (S100A9) were detected in the serums of AD patients compared with healthy controls. These proteins might play a role in AD pathophysiology and serve as potential biomarkers for AD diagnosis. Specifically, our results strengthened the crucial role of Aβ metabolism and blood coagulation in AD pathogenesis and proteins related to these two processes may be used as peripheral blood biomarkers for AD.

Blood Proteomic Profiling in Inherited (ATTRm) and Acquired (ATTRwt) Forms of Transthyretin-Associated Cardiac Amyloidosis

Transthyretin-associated forms of cardiac amyloidosis are fatal protein misfolding diseases that can be inherited (ATTRm) or acquired (ATTRwt). An accurate diagnosis of ATTR amyloidosis can be challenging as biopsy evidence, usually from the affected organ, is required. Precise biomarkers for ATTR disease identification and monitoring are undiscovered, disease-specific therapeutic options are needed, and the current understanding of ATTR molecular pathogenesis is limited. The aim of this study was to investigate and compare the serum proteomes in ATTRm and ATTRwt cardiac amyloidosis to identify differentially expressed blood proteins that were disease-specific. Using multiple-reaction monitoring mass spectrometry (MRM-MS), the concentrations of 160 proteins were analyzed in serum samples from ATTRm and ATTRwt patients, and a healthy control group. Patient and control sera were matched to age (≥60 years), gender (male), and race (Caucasian). The circulating concentrations of 123/160 proteins were significantly different in patient vs control sera; TTR and retinol-binding protein (RBP4) levels were significantly decreased (p < 0.03) in ATTRm compared to controls. In ATTRm, 14/123 proteins were identified as unique to that group and found generally to be lower than controls; moreover, the concentrations of RBP4 and 6 other proteins in this group were significantly different (p < 0.04) compared to ATTRwt. Predicted interactions among the 14 proteins unique to ATTRm were categorized as reaction and binding associations. Alternatively, 27 proteins were found to be unique to ATTRwt with associated interactions defined as activation, catalysis, and inhibition, in addition to reaction and binding. This study demonstrates significant proteomic differences between ATTR patient and control sera, and disease-associated variations in circulating levels of several proteins including TTR and RBP4. The identification of serum proteins unique to ATTRm and ATTRwt cardiac amyloidosis may have diagnostic and prognostic utility, and may provide important clues about disease mechanisms.

Restoring Soluble Amyloid Precursor Protein α Functions as a Potential Treatment for Alzheimer's Disease

Soluble amyloid precursor protein α (sAPPα), a secreted proteolytic fragment of nonamyloidogenic amyloid precursor protein (APP) processing, is known for numerous neuroprotective functions. These functions include but are not limited to proliferation, neuroprotection, synaptic plasticity, memory formation, neurogenesis, and neuritogenesis in cell culture and animal models. In addition, sAPPα influences amyloid-β (Aβ) production by direct modulation of APP β-secretase proteolysis as well as Aβ-related or unrelated tau pathology, hallmark pathologies of Alzheimer's disease (AD). Thus, the restoration of sAPPα levels and functions in the brain by increasing nonamyloidogenic APP processing and/or manipulation of its signaling could reduce AD pathology and cognitive impairment. It is likely that identification and characterization of sAPPα receptors in the brain, downstream effectors, and signaling pathways will pave the way for an attractive therapeutic target for AD prevention or intervention. © 2016 Wiley Periodicals, Inc.

Temporospatial expression of fibulin-1 after acute spinal cord injury in rats

OBJECTIVE

Fibulin-1 is a matricellular protein that plays important roles in motility inhibition in a variety of cells and blocks the proliferation of cultured neural stem cells. The biological function of fibulin-1 in the spinal cord has not been fully elucidated.

METHODS

To clarify the expressions and possible functions of fibulin-1 in spinal cord injury (SCI), we performed an acute spinal cord contusion injury model in adult rats. Our work studied the temporospatial expression patterns of fibulin-1.

RESULTS

Western blot analysis revealed that fibulin-1 levels significantly increased 5 days after spinal cord contusion. Immunohistochemistry confirmed an increased number of fibulin-1 immunopositive cells about 2 mm from the lesion site. Moreover, double immunofluorescence labeling suggested that these changes were especially prominent in neurons and microglia.

CONCLUSION

These findings suggest that fibulin-1 may be involved in neuronal apoptosis and microglial activation after SCI.

The amyloid precursor protein represses expression of acetylcholinesterase in neuronal cell lines

The toxic role of amyloid β peptides in Alzheimer's disease is well documented. Their generation is via sequential β- and γ-secretase cleavage of the membrane-bound amyloid precursor protein (APP). Other APP metabolites include the soluble ectodomains sAPPα and sAPPβ and also the amyloid precursor protein intracellular domain (AICD). In this study, we examined whether APP is involved in the regulation of acetylcholinesterase (AChE), which is a key protein of the cholinergic system and has been shown to accelerate amyloid fibril formation and increase their toxicity. Overexpression of the neuronal specific isoform, APP695, in the neuronal cell lines SN56 and SH-SY5Y substantially decreased levels of AChE mRNA, protein, and catalytic activity. Although similar decreases in mRNA levels were observed of the proline-rich anchor of AChE, PRiMA, no changes were seen in mRNA levels of the related enzyme, butyryl-cholinesterase, nor of the high-affinity choline transporter. A γ-secretase inhibitor did not affect AChE transcript levels or enzyme activity in SN56 (APP695) or SH-SY5Y (APP695) cells, showing that regulation of AChE by APP does not require the generation of AICD or amyloid β peptide. Treatment of wild-type SN56 cells with siRNA targeting APP resulted in a significant up-regulation in AChE mRNA levels. Mutagenesis studies suggest that the observed transcriptional repression of AChE is mediated by the E1 region of APP, specifically its copper-binding domain, but not the C-terminal YENTPY motif. In conclusion, AChE is regulated in two neuronal cell lines by APP in a manner independent of the generation of sAPPα, sAPPβ, and AICD.

The transcriptomic response of mixed neuron-glial cell cultures to 1,25-dihydroxyvitamin d3 includes genes limiting the progression of neurodegenerative diseases

Seasonal or chronic vitamin D deficiency and/or insufficiency is highly prevalent in the human population. Receptors for 1,25-dihydroxyvitamin D3, the hormonal metabolite of vitamin D, are found throughout the brain. To provide further information on the role of this hormone on brain function, we analyzed the transcriptomic profiles of mixed neuron-glial cell cultures in response to 1,25-dihydroxyvitamin D3. 1,25-dihydroxyvitamin D3 treatment increases the mRNA levels of 27 genes by at least 1.9 fold. Among them, 17 genes were related to neurodegenerative and psychiatric diseases, or brain morphogenesis. Notably, 10 of these genes encode proteins potentially limiting the progression of Alzheimer's disease. These data provide support for a role of 1,25-dihydroxyvitamin D3 in brain disease prevention. The possible consequences of circannual or chronic vitamin D insufficiencies on a tissue with a low regenerative potential such as the brain should be considered.

Genome-wide association study of temperament in bipolar disorder reveals significant associations with three novel Loci

BACKGROUND

The many attempts to identify genes for bipolar disorder (BD) have met with limited success, which has generally been attributed to genetic heterogeneity and small gene effects. However, it is also possible that the categorical phenotypes used in genetic studies of BD are not the most informative or biologically relevant. Although quantitative phenotypes provide an alternative to categorical phenotypes based on diagnosis, they have not been fully exploited in BD genetics due to the lack of accessible biological measures. We have explored aspects of temperament as quantitative phenotypes that might define subtypes of BD with different clinical features and courses of illness. Temperament is a heritable personality factor that establishes the baseline level of reactivity, mood, and energy of a person.

METHODS

We have performed a genome-wide association study with genotype data from the Bipolar Genome Study and 1263 bipolar subjects that had completed the Temperament Evaluation of Memphis, Pisa, Paris, and San Diego Autoquestionnaire (TEMPS-A). The TEMPS-A is designed to assess lifelong, milder aspects of bipolar symptomatology and defines five temperaments: hyperthymic, dysthymic, cyclothymic, irritable, and anxious.

RESULTS

The irritable temperament produced the most significant result with a genome-wide significant p value of 1.7 × 10(-8) on chromosome 1. The hyperthymic temperament produced additional genome-wide significant p values of 4.1 × 10(-8) and 2.1 × 10(-8) on chromosomes 12 and 22, respectively.

CONCLUSIONS

These results suggest that aspects of temperament might define subtypes of BD that are more clinically and genetically homogenous, which might aid in the identification of predisposing genetic variants.

Identification of a novel amyloid precursor protein processing pathway that generates secreted N-terminal fragments

Alzheimer's disease (AD) is a neurodegenerative disorder of the central nervous system. The proteolytic processing of the amyloid precursor protein (APP) into the β-amyloid (Aβ) peptide is a central event in AD. While the pathway that generates Aβ is well described, many questions remain concerning general APP metabolism and its metabolites. It is becoming clear that the amino-terminal region of APP can be processed to release small N-terminal fragments (NTFs). The purpose of this study was to investigate the occurrence and generation of APP NTFs in vivo and in cell culture (SH-SY5Y) in order to delineate the cellular pathways implicated in their generation. We were able to detect 17- to 28-kDa APP NTFs in human and mouse brain tissue that are distinct from N-APP fragments previously reported. We show that the 17- to 28-kDa APP NTFs were highly expressed in mice from the age of 2 wk to adulthood. SH-SY5Y studies indicate the generation of APP NTFs involves a novel APP processing pathway, regulated by protein kinase C, but independent of α-secretase or β-secretase 1 (BACE) activity. These results identify a novel, developmentally regulated APP processing pathway that may play an important role in the physiological function of APP.

Tol2 gene trap integrations in the zebrafish amyloid precursor protein genes appa and aplp2 reveal accumulation of secreted APP at the embryonic veins

BACKGROUND

The single spanning transmembrane amyloid precursor protein (APP) and its proteolytic product, amyloid-beta (Ab) peptide, have been intensely studied due to their role in the pathogenesis of Alzheimer's disease. However, the biological role of the secreted ectodomain of APP, which is also generated by proteolytic cleavage, is less well understood. Here, we report Tol2 red fluorescent protein (RFP) transposon gene trap integrations in the zebrafish amyloid precursor protein a (appa) and amyloid precursor-like protein 2 (aplp2) genes. The transposon integrations are predicted to disrupt the appa and aplp2 genes to primarily produce secreted ectodomains of the corresponding proteins that are fused to RFP.

RESULTS

Our results indicate the Appa-RFP and Aplp2 fusion proteins are likely secreted from the central nervous system and accumulate in the embryonic veins independent of blood flow.

CONCLUSIONS

The zebrafish appa and aplp2 transposon insertion alleles will be useful for investigating the biological role of the secreted form of APP.

Metalloprotease meprin beta generates nontoxic N-terminal amyloid precursor protein fragments in vivo

Identification of physiologically relevant substrates is still the most challenging part in protease research for understanding the biological activity of these enzymes. The zinc-dependent metalloprotease meprin β is known to be expressed in many tissues with functions in health and disease. Here, we demonstrate unique interactions between meprin β and the amyloid precursor protein (APP). Although APP is intensively studied as a ubiquitously expressed cell surface protein, which is involved in Alzheimer disease, its precise physiological role and relevance remain elusive. Based on a novel proteomics technique termed terminal amine isotopic labeling of substrates (TAILS), APP was identified as a substrate for meprin β. Processing of APP by meprin β was subsequently validated using in vitro and in vivo approaches. N-terminal APP fragments of about 11 and 20 kDa were found in human and mouse brain lysates but not in meprin β(-/-) mouse brain lysates. Although these APP fragments were in the range of those responsible for caspase-induced neurodegeneration, we did not detect cytotoxicity to primary neurons treated by these fragments. Our data demonstrate that meprin β is a physiologically relevant enzyme in APP processing.

Structural basis for matrix metalloproteinase-2 (MMP-2)-selective inhibitory action of β-amyloid precursor protein-derived inhibitor

Unlike other synthetic or physiological inhibitors for matrix metalloproteinases (MMPs), the β-amyloid precursor protein-derived inhibitory peptide (APP-IP) having an ISYGNDALMP sequence has a high selectivity toward MMP-2. Our previous study identified amino acid residues of MMP-2 essential for its selective inhibition by APP-IP and demonstrated that the N to C direction of the decapeptide inhibitor relative to the substrate-binding cleft of MMP-2 is opposite that of substrate. However, detailed interactions between the two molecules remained to be clarified. Here, we determined the crystal structure of the catalytic domain of MMP-2 in complex with APP-IP. We found that APP-IP in the complex is indeed embedded into the substrate-binding cleft of the catalytic domain in the N to C direction opposite that of substrate. With the crystal structure, it was first clarified that the aromatic side chain of Tyr(3) of the inhibitor is accommodated into the S1' pocket of the protease, and the carboxylate group of Asp(6) of APP-IP coordinates bidentately to the catalytic zinc of the enzyme. The Ala(7) to Pro(10) and Tyr(3) to Ile(1) strands of the inhibitor extend into the nonprime and the prime sides of the cleft, respectively. Therefore, the decapeptide inhibitor has long range contact with the substrate-binding cleft of the protease. This mode of interaction is probably essential for the high MMP-2 selectivity of the inhibitor because MMPs share a common architecture in the vicinity of the catalytic center, but whole structures of their substrate-binding clefts have sufficient variety for the inhibitor to distinguish MMP-2 from other MMPs.

A proteomic approach for the diagnosis of bacterial meningitis

Background

The discrimination of bacterial meningitis (BM) versus viral meningitis (VM) shapes up as a problem, when laboratory data are not equivocal, in particular, when Gram stain is negative.

Methodology/Principal Findings

With the aim to determine reliable marker for bacterial or viral meningitis, we subjected cerebrospinal fluid (CSF) to a quantitative proteomic screening. By using a recently established 2D-DIGE protocol which was adapted to the individual CSF flow, we compared a small set of patients with proven BM and VM. Thereby, we identified six potential biomarkers out of which Prostaglandin-H2 D-isomerase was already described in BM, showing proof of concept. In the subsequent validation phase on a more comprehensive collective of 80 patients, we could validate that in BM high levels of glial fibrillary acidic protein (GFAP) and low levels of soluble amyloid precursor protein alpha/beta (sAPPα/β) are present as possible binding partner of Fibulin-1.

Conclusions/Significance

We conclude that our CSF flow-adapted 2D-DIGE protocol is valid especially in comparing samples with high differences in total protein and suppose that GFAP and sAPPα/β have a high potential as additional diagnostic markers for differentiation of BM from VM. In the clinical setting, this might lead to an improved early diagnosis and to an individual therapy.

Proteomic analysis of Alzheimer's disease cerebrospinal fluid from neuropathologically diagnosed subjects

A crucial need exists for reliable Alzheimer's disease (AD) diagnostic and prognostic tests. Given its intimate communication with the brain, the cerebrospinal fluid (CSF) has been surveyed intensively for reliable AD biomarkers. The heterogeneity of AD pathology and the unavoidable difficulties associated with the clinical diagnosis and differentiation of this dementia from other pathologies have confounded biomarker studies in antemortem CSF samples. Using postmortem ventricular CSF (V-CSF) pools, two-dimensional difference gel electrophoresis (2D DIGE) analyses revealed a set of proteins that showed significant differences between neuropathologically-diagnosed AD and elderly non-demented controls (NDC), as well as subjects with non-AD dementias. The 2D DIGE system identified a set of 21 different protein biomarkers. This panel of proteins probably reflects fundamental pathological changes that are divergent from both normal aging and non-AD dementias.

Shotgun proteomics implicates extracellular matrix proteins and protease systems in neuronal development induced by astrocyte cholinergic stimulation

Astrocytes play an important role in neuronal development through the release of soluble factors that affect neuronal maturation. Shotgun proteomics followed by gene ontology analysis was used in this study to identify proteins present in the conditioned medium of primary rat astrocytes. One hundred and thirty three secreted proteins were identified, the majority of which were never before reported to be produced by astrocytes. Extracellular proteins were classified based on their biological and molecular functions; most of the identified proteins were involved in neuronal development. Semi-quantitative proteomic analysis was carried out to identify changes in the levels of proteins released by astrocytes after stimulation with the cholinergic agonist carbachol, as we have previously reported that carbachol-treated astrocytes elicit neuritogenesis in hippocampal neurons through the release of soluble factors. Carbachol up-regulated secretion of 15 proteins and down-regulated the release of 17 proteins. Changes in the levels of four proteins involved in neuronal differentiation (thrombospondin-1, fibronectin, plasminogen activator inhibitor-1, and plasminogen activator urokinase) were verified by western blot or ELISA. In conclusion, this study identified a large number of proteins involved in neuronal development in the astrocyte secretome and implicated extracellular matrix proteins and protease systems in neuronal development induced by astrocyte cholinergic stimulation.

Interaction of amyloid precursor protein with contactins and NgCAM in the retinotectal system

The amyloid precursor protein (APP) plays a central role in Alzheimer's disease, but its actions in normal development are not well understood. Here, a tagged APP ectodomain was used to identify extracellular binding partners in developing chick brain. Prominent binding sites were seen in the olfactory bulb and on retinal axons growing into the optic tectum. Co-precipitation from these tissues and tandem mass spectrometry led to the identification of two associated proteins: contactin 4 and NgCAM. In vitro binding studies revealed direct interactions among multiple members of the APP and contactin protein families. Levels of the APP processing fragment, CTFalpha, were modulated by both contactin 4 and NgCAM. In the developing retinotectal system, APP, contactin 4 and NgCAM are expressed in the retina and tectum in suitable locations to interact. Functional assays revealed regulatory effects of both APP and contactin 4 on NgCAM-dependent growth of cultured retinal axons, demonstrating specific functional interactions among these proteins. These studies identify novel binding and functional interactions among proteins of the APP, contactin and L1CAM families, with general implications for mechanisms of APP action in neural development and disease.

Expression of extracellular matrix proteins fibulin-1 and fibulin-2 by human corneal fibroblasts

PURPOSE

The fibulins are a family of extracellular matrix (ECM) molecules that regulate the organ shape along with other growth factors and stromal cells. We report here the in vitro expression of ECM proteins fibulin-1 and fibulin-2 by human corneal fibroblasts. The ability of fibulin-1 to modulate cell motility was investigated.

METHODS

Fibulin-1 and fibulin-2 mRNA and proteins expression were analyzed in primary and immortalized human corneal fibroblasts (CHN) respectively by gene array, RT-PCR, and immunocytochemistry. The motility and adhesion of the cells transfected with fibulin-1 siRNA were analyzed on tissue culture polystyrene coated with Matrigel or ECM secreted by those fibroblasts.

RESULTS

(1) The microarray analysis shows the expression of fibulin-1, fibulin-2, and their binding partners (i.e., fibronectin, nidogen-1, aggrecan, fibrilin-1, endostatin, and laminin alpha-2 chain). Interestingly, a matrix metalloprotease, ADAMTS-1, for which fibulin-1 acts as a cofactor, was also detected in CHN. (2) The synthesis by CHN of fibulin-1 and 2 mRNA and proteins was confirmed respectively by RT-PCR and immunocytochemistry. (3) Transfection of CHN by fibulin-1 siRNA has no effect on cell adhesion but increases cell migration compared with that of the control cells. This observation suggests an important role of fibulin-1 on cell motility.

CONCLUSIONS

The expression of fibulins and that of their binding partners by human corneal fibroblasts indicate the important role of these proteins in the organization of supramolecular ECM structures of cornea. The variation of their expression and the structural changes of fibulins remain to be determined in corneal pathology.

Structure and functions of the human amyloid precursor protein: the whole is more than the sum of its parts

The amyloid precursor protein (APP) is a transmembrane protein that plays major roles in the regulation of several important cellular functions, especially in the nervous system, where it is involved in synaptogenesis and synaptic plasticity. The secreted extracellular domain of APP, sAPPalpha, acts as a growth factor for many types of cells and promotes neuritogenesis in post-mitotic neurons. Alternative proteolytic processing of APP releases potentially neurotoxic species, including the amyloid-beta (Abeta) peptide that is centrally implicated in the pathogenesis of Alzheimer's disease (AD). Reinforcing this biochemical link to neuronal dysfunction and neurodegeneration, APP is also genetically linked to AD. In this review, we discuss the biological functions of APP in the context of tissue morphogenesis and restructuring, where APP appears to play significant roles both as a contact receptor and as a diffusible factor. Structural investigation of APP, which is necessary for a deeper understanding of its roles at a molecular level, has also been advancing rapidly. We summarize recent progress in the determination of the structure of isolated APP fragments and of the conformations of full-length sAPPalpha, in both monomeric and dimeric states. The potential role of APP dimerization for the regulation of its biological functions is also discussed.

Solution Conformation and Heparin-induced Dimerization of the Full-length Extracellular Domain of the Human Amyloid Precursor Protein

Proteolytic cleavage of the amyloid precursor protein (APP) by beta and gamma-secretases gives rise to the beta-amyloid peptide, considered to be a causal factor in Alzheimer's disease. Conversely, the soluble extracellular domain of APP (sAPPalpha), released upon its cleavage by alpha-secretase, plays a number of important physiological functions. Several APP fragments have been structurally characterized at atomic resolution, but the structures of intact APP and of full-length sAPPalpha have not been determined. Here, ab initio reconstruction of molecular models from high-resolution solution X-ray scattering (SAXS) data for the two main isoforms of sAPPalpha (sAPPalpha(695) and sAPPalpha(770)) provided models of sufficiently high resolution to identify distinct structural domains of APP. The fragments for which structures are known at atomic resolution were fitted within the solution models of full-length sAPPalpha, allowing localization of important functional sites (i.e. glycosylation, protease inhibitory and heparin-binding sites). Furthermore, combined results from SAXS, analytical ultracentrifugation (AUC) and size-exclusion chromatography (SEC) analysis indicate that both sAPPalpha isoforms are monomeric in solution. On the other hand, SEC, bis-ANS fluorescence, AUC and SAXS measurements showed that sAPPalpha forms a 2:1 complex with heparin. A conformational model for the sAPPalpha:heparin complex was also derived from the SAXS data. Possible implications of such complex formation for the physiological dimerization of APP and biological signaling are discussed in terms of the structural models proposed.

The amyloid precursor protein and postnatal neurogenesis/neuroregeneration

The amyloid precursor protein (APP) is the source of amyloid-beta (Abeta) peptide, produced via its sequential cleavage beta- and gamma-secretases. Various biophysical forms of Abeta (and the mutations of APP which results in their elevated levels) have been implicated in the etiology and early onset of Alzheimer's disease. APP's evolutionary conservation and the existence of APP-like isoforms (APLP1 and APLP2) which lack the Abeta sequence, however, suggest that these might have important physiological functions that are unrelated to Abeta production. Soluble N-terminal fragments of APP have been known to be neuroprotective, and the interaction of its cytoplasmic C-terminus with a myriad of proteins associates it with diverse processes such as axonal transport and transcriptional regulation. The notion for an essential postnatal function of APP has been demonstrated genetically, as mice deficient in both APP and APLP2 or all three APP isoforms exhibit early postnatal lethality and neuroanatomical abnormalities. Recent findings have also brought to light two possible functions of the APP family in the brain-regulation of neural progenitor cell proliferation and axonal outgrowth after injury. Interestingly, these two apparently related neurogenic/neuroregenerative functions of APP involve two separate domains of the molecule.

A Two Decade Contribution of Molecular Cell Biology to the Centennial of Alzheimer's Disease: Are We Progressing Toward Therapy?

Alzheimer's disease (AD), described for the first time 100 years ago, is a neurodegenerative disease characterized by two neuropathological hallmarks: neurofibrillary tangles containing hyperphosphorylated tau and senile plaques. These lesions are likely initiated by an imbalance between production and clearance of amyloid beta, leading to increased oligomerization of these peptides, formation of amyloid plaques in the brain of the patient, and final dementia. Amyloid beta is generated from amyloid precursor protein (APP) by subsequent beta- and gamma-secretase cleavage, the latter being a multiprotein complex consisting of presenilin-1 or -2, nicastrin, APH-1, and PEN-2. Alternatively, APP can be cleaved by alpha- and gamma-secretase, precluding the production of Abeta. In this review, we discuss the major breakthroughs during the past two decades of molecular cell biology and the current genetic and cell biological state of the art on APP proteolysis, including structure-function relationships and subcellular localization. Finally, potential directions for cell biological research toward the development of AD therapies are briefly discussed.

The amyloid-beta precursor protein: integrating structure with biological function

Proteolytic processing of the amyloid-beta precursor protein (APP) generates the Abeta amyloid peptide of Alzheimer's disease. The biological function of APP itself remains, however, unclear. In the current review, we study in detail the different subdomains of APP and try to assign functional significance to particular structures identified in the protein.

Extracellular matrix alterations in brains lacking four of its components

The organization of the brain extracellular matrix appears to be based on aggregates of hyaluronan and proteoglycans, connected by oligomeric glycoproteins. Mild phenotypical consequences were reported from several mouse strains lacking components of this matrix such as neurocan, brevican, tenascin-R, and tenascin-C. To further challenge the flexibility of the extracellular matrix network of the brain, mice lacking all four brain extracellular matrix molecules were generated, which were found to be viable and fertile. Analysis of the brains of 1-month-old quadruple KO mice revealed increased protein levels of fibulin-1 and fibulin-2. Histochemical analysis showed an unusual parenchymal deposition of these fibulins. The quadruple KO mice also displayed obvious changes in the pattern of deposition of hyaluronan. Further, an almost quadruple knockout like extracellular environment was noticed in the brains of triple knockout mice lacking both tenascins and brevican, since these brains had strongly reduced levels of neurocan.

Transcriptional and posttranscriptional regulation of fibulin-1 by estrogens leads to differential induction of messenger ribonucleic acid variants in ovarian and breast cancer cells

Fibulin-1 is an extracellular matrix protein overexpressed in epithelial ovarian and breast cancers. In estrogen receptor (ER)-positive ovarian and breast cancer cell lines, fibulin-1 mRNA levels are markedly increased by estrogens. Transfection experiments using fibulin-1 promoter constructs indicate that 17beta-estradiol (E2) increases fibulin-1 gene transcription and that ERalpha is more potent than ERbeta to mediate E2 regulation of the transfected fibulin-1 promoter. Using SL2 cells devoid of specificity protein 1 (Sp1) and site-directed mutagenesis of GC boxes, we evidenced that the E2 regulation occurs through a proximal specificity protein 1 binding site. In addition, we show that fibulin-1C and -1D mRNAs, the two major fibulin-1 splicing variants, are differentially induced by E2. The induction of both mRNAs variants is direct and independent of a newly synthesized protein intermediate. Interestingly, actinomycin D chase experiments demonstrate that E2 treatment selectively shortens the fibulin-1D mRNA half-life. This indicates that estrogens affect differentially the stability of fibulin-1 variants and may explain the lower accumulation of fibulin-1D mRNA on E2 treatment. In conclusion, our data show that estrogens, via ERalpha, are key regulators of fibulin-1 expression at both the transcriptional and posttranscriptional levels. The preferential induction of the fibulin-1C variant, which is overexpressed in ovarian and breast cancer, might play an important role in estrogen-promoted carcinogenesis.

Use of proteomics to demonstrate a hierarchical oxidative stress response to diesel exhaust particle chemicals in a macrophage cell line

Epidemiological studies demonstrate an association between short term exposure to ambient particulate matter (PM) and cardiorespiratory morbidity and mortality. Although the biological mechanisms of these adverse effects are unknown, emerging data suggest a key role for oxidative stress. Ambient PM and diesel exhaust particles (DEP) contain redox cycling organic chemicals that induce pro-oxidative and pro-inflammatory effects in the lung. These responses are suppressed by N-acetylcysteine (NAC), which directly complexes to electrophilic DEP chemicals and exert additional antioxidant effects at the cellular level. A proteomics approach was used to study DEP-induced responses in the macrophage cell line, RAW 264.7. We demonstrate that in the dose range 10-100 microg/ml, organic DEP extracts induce a progressive decline in the cellular GSH/GSSG ratio, in parallel with a linear increase in newly expressed proteins on the two-dimensional gel. Using matrix-assisted laser desorption ionization time-of-flight mass spectrometry and electrospray ionization-liquid chromatography/mass spectrometry/mass spectrometry analysis, 32 newly induced/NAC-suppressed proteins were identified. These include antioxidant enzymes (e.g. heme oxygenase-1 and catalase), pro-inflammatory components (e.g. p38MAPK and Rel A), and products of intermediary metabolism that are regulated by oxidative stress. Heme oxygenase-1 was induced at low extract dose and with minimal decline in the GSH/GSSG ratio, whereas MAP kinase activation required a higher chemical dose and incremental levels of oxidative stress. Moreover, at extract doses >50 microg/ml, there is a steep decline in cellular viability. These data suggest that DEP induce a hierarchical oxidative stress response in which some of these proteins may serve as markers for oxidative stress during PM exposures.

Novel processing of beta-amyloid precursor protein catalyzed by membrane type 1 matrix metalloproteinase releases a fragment lacking the inhibitor domain against gelatinase A

In various mammalian cell lines, beta-amyloid precursor protein (APP) is proteolytically processed to release its NH(2)-terminal extracellular domain as a soluble APP (sAPP) that contains the inhibitor domain against gelatinase A. To investigate roles of sAPP in the regulation of gelatinase A activity, we examined the correlation between the activation of progelatinase A and processing of APP. We found that stimulation of HT1080 fibrosarcoma cells with concanavalin A led to an activation of endogenous progelatinase A and to a novel processing of APP, which releases a COOH-terminally truncated form of sAPP (sAPPtrc) into the culture medium. Reverse zymographic analysis showed that sAPPtrc lacked an inhibitory activity against gelatinase A. Analyses of production of sAPPtrc in the presence of various metalloproteinase inhibitors showed that membrane type 1 matrix metalloproteinase (MT1-MMP), an activator of progelatinase A, is most likely responsible for the production of sAPPtrc. When the concanavalin A-stimulated HT1080 cells were cultured in the condition that inhibited MT1-MMP activity, sAPP and APP were associated with the extracellular matrix deposited by the cells, whereas these gelatinase A inhibitors in the matrix were displaced by sAPPtrc after exertion of MT1-MMP activity. Taken together, these data support a model in which MT1-MMP-catalyzed release of sAPPtrc leads to reduction of the extracellular matrix-associated gelatinase A inhibitor, sAPP, thus making it feasible for gelatinase A to exert proteolytic activity only near its activator, MT1-MMP.

Expression of Bcl-2 on leukocytes in prostatic fluid from patients with acute and chronic prostatitis

In our continuing investigation to clarify the significance of leukocytosis and its prolongation in prostatic fluid (PF) from prostatitis patients, we investigated whether expression of the antiapoptotic gene Bcl-2 on leukocytes in prostatic fluid has any relation with prolonged leukocytosis in prostatitis. The subjects were eight patients with acute bacterial prostatitis (ABP) and eight with nonbacterial prostatitis (NBP) with a history of more than 2 years. Twelve micrograms of protein obtained from leukocytes in PF were subjected to Western blot analysis. Bcl-2 was expressed in seven of eight (87.5%) and six of eight (75.0%) patients with NBP and ABP, respectively. Quantitative density analysis of the Bcl-2 band did not show any statistically significant differences between patients with NBP and those with ABP. These results suggest that the expression of antiapoptotic Bcl-2 on leukocytes in PF is not a cause of leukocyte longevity in long-term prostatitis.

Fibulins: a versatile family of extracellular matrix proteins

Fibulins are a newly recognized family of extracellular matrix proteins. The five known members of the family share an elongated structure and many calcium-binding sites, owing to the presence of tandem arrays of epidermal growth factor-like domains. They have overlapping binding sites for several basement-membrane proteins, tropoelastin, fibrillin, fibronectin and proteoglycans, and they participate in diverse supramolecular structures. New insights into their biological roles are now emerging from studies of transgenic mice and of some inherited human diseases.

Identification of a region of beta-amyloid precursor protein essential for its gelatinase A inhibitory activity

Because beta-amyloid precursor protein (APP) has the abilities both to interact with extracellular matrix and to inhibit gelatinase A activity, this molecule is assumed to play a regulatory role in the gelatinase A-catalyzed degradation of extracellular matrix. To determine a region of APP essential for the inhibitory activity, we prepared various derivatives of APP. Functional analyses of proteolytic fragments of soluble APP (sAPP) and glutathione S-transferase fusion proteins, which contain various COOH-terminal parts of sAPP, showed that a site containing residues 579-601 of APP(770) is essential for the inhibitory activity. Moreover, a synthetic decapeptide containing the ISYGNDALMP sequence corresponding to residues 586-595 of APP(770) had a gelatinase A inhibitory activity slightly higher than that of sAPP. Studies of deletion of the NH(2)- and COOH-terminal residues and alanine replacement of internal residues of the decapeptide further revealed that Tyr(588), Asp(591), and Leu(593) of APP mainly stabilize the interaction between gelatinase A and the inhibitor. We also found that the residues of Ile(586), Met(594), and Pro(595) modestly contribute to the inhibitory activity. The APP-derived decapeptide efficiently inhibited the activity of gelatinase A (IC(50) = 30 nm), whereas its inhibitory activity toward membrane type 1 matrix metalloproteinase was much weaker (IC(50) = 2 microm). The decapeptide had poor inhibitory activity toward gelatinase B, matrilysin, and stromelysin (IC(50) > 10 microm). The APP-derived inhibitor formed a complex with active gelatinase A but not with progelatinase A, and the complex formation was prevented completely by a hydroxamate-based synthetic inhibitor. Therefore, the decapeptide region of APP is likely an active site-directed inhibitor that has high selectivity toward gelatinase A.

Identification of genes with differential regulation in primate endometrium during the proliferative and secretory phases of the cycle

To study gene expression in the endometrium at different stages of the menstrual cycle, differential mRNA display and reverse Northern analysis were performed on uterine tissues from cynomolgus monkeys. Eutopic endometrial RNA was prepared from uteri of animals that were either ovariectomized and supplemented with hormones, or were not ovariectomized but were subjected to surgically induced endometriosis. A number of genes were identified whose levels fluctuated between the proliferative and secretory phases of the cycle. Expression of four genes thus identified was further examined by in situ hybridization to normal human endometrial biopsies. Iodothyronine deiodinase was uniformly expressed at all stages of the human cycle that were studied: proliferative, secretory, and menstrual. Fibulin 1, osteopontin, and cathepsin H exhibited complex temporal and spatial regulation. Fibulin 1 was expressed in glandular epithelia during the menstrual phase, but expression switched to the stroma during the secretory phase. During the menstrual phase, osteopontin was expressed at high levels in glandular epithelia and in isolated stromal cells that may be of immune origin. Secretory phase expression of osteopontin was confined to a sub-population of epithelial cells. Cathepsin H was expressed in proliferative and menstrual phase endometrium, but expression disappeared in the secretory phase. Messenger RNA for fibulin 1, osteopontin, and iodothyronine deiodinase was detected in an endometriosis sample. Our data support functional roles for fibulin 1, osteopontin, cathepsin H and thyroid hormone in endometrium.

Potential use of stem cells in neuroreplacement therapies for neurodegenerative diseases

The use of stem cells for neuroreplacement therapy is no longer science fiction--it is science fact. We have succeeded in the development of neural and mesenchymal stem cell transplantation to produce neural cells in the brain. We have also seen improvement in cognitive function following stem cell transplantation in a memory-impaired aged animal model. These results promise a bright future for stem cell therapies in neurodegenerative diseases. Before we begin to think about clinical applications beyond the present preclinical studies, we have to consider the pathophysiological environment of individual diseases and weigh the factors that affect stem cell biology. Here, I not only review potential therapeutic applications of stem cell strategies in neurodegenerative diseases, but also discuss stem cell biology regarding factors that are altered under disease conditions.

Solution studies and structural model of the extracellular domain of the human amyloid precursor protein

The amyloid precursor protein (APP) is the precursor of the beta-amyloid peptide (Abeta), which is centrally related to the genesis of Alzheimer's disease (AD). In addition, APP has been suggested to mediate and/or participate in events that lead to neuronal degeneration in AD. Despite the fact that various aspects of the cell biology of APP have been investigated, little information on the structure of this protein is available. In this work, the solution structure of the soluble extracellular domain of APP (sAPP, composing 89% of the amino acid residues of the whole protein) has been investigated through a combination of size-exclusion chromatography, circular dichroism, and synchrotron radiation small-angle x-ray scattering (SAXS) studies. sAPP is monomeric in solution (65 kDa obtained from SAXS measurements) and exhibits an anisometric molecular shape, with a Stokes radius of 39 or 51 A calculated from SAXS or chromatographic data, respectively. The radius of gyration and the maximum molecular length obtained by SAXS were 38 A and 130 A, respectively. Analysis of SAXS data further allowed building a structural model for sAPP in solution. Circular dichroism data and secondary structure predictions based on the amino acid sequence of APP suggested that a significant fraction of APP (30% of the amino acid residues) is not involved in standard secondary structure elements, which may explain the elongated shape of the molecule recovered in our structural model. Possible implications of the structure of APP in ligand binding and molecular recognition events involved in the biological functions of this protein are discussed.

The secretory beta-amyloid precursor protein is a motogen for human epidermal keratinocytes

Cell migration is known to be triggered by constituents of the extracellular matrix such as fibronectin and by soluble mediators commonly summarized as motogens. Many growth factors such as the epidermal growth factor (EGF) have been shown to act as motogens. Recently, the secretory N-terminal portion of the beta-amyloid precursor protein (sAPP) has been identified as a keratinocyte growth factor. Hence, in this study we analysed whether sAPP stimulates also keratinocyte migration employing the stroboscopic cell motility assay. The migration velocity as well as the frequency of lamellipodia protrusion and ruffle formation were increased about two-fold thus corresponding to the effect of EGF. Using a newly developed beta1-integrin migration track assay we observed that sAPP increased the proportion of migrating keratinocytes and their directional persistence. sAPP appeared to operate synergistically with fibronectin with respect to its motogenic effect. Using a modified Boyden chamber assay we showed that sAPP besides its chemokinetic effect functions as a chemoattractant. Like EGF, sAPP exerted its motogenic effect through the activation of Rac kinase but the receptor for sAPP appears to be distinct. The results suggest that sAPP operates as a motogen in the human epidermis, where it may participate in the regulation of reepithelialization during wound healing.

Structural and functional characterization of the human and mouse fibulin-1 gene promoters: role of Sp1 and Sp3

Fibulin-1 is a multifunctional extracellular protein involved in diverse biological processes including cardiovascular development, haemostasis and cancer. To investigate the transcriptional regulation of the gene encoding fibulin-1 we cloned and analysed about 4.0 kb of the 5'-flanking regions of both the human and mouse fibulin-1 genes. The human and mouse fibulin-1 promoters share little sequence similarity except for a short region of approx. 150-170 bp immediately upstream of the translation start site. The conserved region contains a TATA-like sequence (ATAATT) and multiple consensus binding sites for Sp1 and activator protein 2 (AP-2). That the short conserved region in each gene confers basal promoter activity is demonstrated by transient transfections of promoter deletion constructs for both the human and mouse genes into cells that express fibulin-1 constitutively. Co-transfections of promoter constructs with expression plasmids for Sp1, Sp3 and Sp4 into Drosophila SL2 cells indicate that Sp1 and Sp3 are essential for transcriptional activation and that these two factors act synergistically. Electrophoretic mobility-shift assays show that Sp1 and Sp3, but not AP-2, bind to the basal promoter of the human fibulin-1 gene. The results demonstrate the functional importance of Sp1 and Sp3 in regulating the expression of the fibulin-1 gene.

The fibulin-1 gene (FBLN1) is disrupted in a t(12;22) associated with a complex type of synpolydactyly

Molecular analysis of the reciprocal chromosomal translocation t(12;22)(p11.2;q13.3) cosegregating with a complex type of synpolydactyly showed involvement of an alternatively spliced exon of the fibulin-1 gene (FBLN1 located in 22q13.3) and the C12orf2 (HoJ-1) gene on the short arm of chromosome 12. Investigation of the possible functional involvement of the fibulin-1 protein (FBLN1) in the observed phenotype showed that FBLN1 is expressed in the extracellular matrix (ECM) in association with the digits in the developing limb. Furthermore, fibroblasts derived from patients with the complex type of synpolydactyly displayed alterations in the level of FBLN1-D splice variant incorporated into the ECM and secreted into the conditioned culture medium. By contrast, the expression of the FBLN1-C splice variant was not perturbed in the patient fibroblasts. Based on these findings, we propose that the t(12;22) results in haploinsufficiency of the FBLN1-D variant, which could lead to the observed limb malformations.