Cells of the neuronal lineage play a major role in the generation of amyloid precursor fragments in gelsolin-related amyloidosis

Cluster-Assembled Nanoporous Super-Hydrophilic Smart Surfaces for On-Target Capturing and Processing of Biological Samples for Multi-Dimensional MALDI-MS

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) on cluster-assembled super-hydrophilic nanoporous titania films deposited on hydrophobic conductive-polymer substrates feature a unique combination of surface properties that significantly improve the possibilities of capturing and processing biological samples before and during the MALDI-MS analysis without changing the selected sample target (multi-dimensional MALDI-MS). In contrast to pure hydrophobic surfaces, such films promote a remarkable biologically active film porosity at the nanoscale due to the soft assembling of ultrafine atomic clusters. This unique combination of nanoscale porosity and super-hydrophilicity provides room for effective sample capturing, while the hydrophilic-hydrophobic discontinuity at the border of the dot-patterned film acts as a wettability-driven containment for sample/reagent droplets. In the present work, we evaluate the performance of such advanced surface engineered reactive containments for their benefit in protein sample processing and characterization. We shortly discuss the advantages resulting from the introduction of the described chips in the MALDI-MS workflow in the healthcare/clinical context and in MALDI-MS bioimaging (MALDI-MSI).

Structure, regulation and related diseases of the actin-binding protein gelsolin

Gelsolin (GSN), one of the most abundant actin-binding proteins, is involved in cell motility, shape and metabolism. As a member of the GSN superfamily, GSN is a highly structured protein in eukaryotic cells that can be regulated by calcium concentration, intracellular pH, temperature and phosphatidylinositol-4,5-bisphosphate. GSN plays an important role in cellular mechanisms as well as in different cellular interactions. Because of its participation in immunologic processes and its interaction with different cells of the immune system, GSN is a potential candidate for various therapeutic applications. In this review, we summarise the structure of GSN as well as its regulating and functional roles, focusing on distinct diseases such as Alzheimer's disease, rheumatoid arthritis and cancer. A short overview of GSN as a therapeutic target in today's medicine is also provided.

A novel transthyretin Lys70Glu (p.Lys90Glu) mutation presenting with vitreous amyloidosis and carpal tunnel syndrome

OBJECTIVE

We describe a novel TTR mutation with vitreous opacities and carpal tunnel syndrome.

MATERIALS AND METHODS

A 78 year-old woman with vitreous opacities, her daughter with dry eye syndrome, and brother with carpal tunnel syndrome were tested for a mutation in the TTR gene. The vitreous opacities were removed and stained with Congo red and immunohistochemistry against wild type TTR. Skin and gut biopsies and specimens of soft tissue were examined histopathologically. Leukocyte DNA from the proband was analysed by direct sequencing of exons 1 to 4 of the TTR gene and DNA from her daughter and brother using segregation analysis.

RESULTS

A point mutation c.268 A>C, in the TTR gene, leading to a missense mutation p.Lys90Glu was found in all subjects. The vitreous opacities were pearl string-like. Histopathology showed red to green birefringence in Congo red, typical to amyloid, and the specimens were immunoreactive with antibodies against TTR.

CONCLUSION

We present a novel autosomally inherited Lys90Glu mutation in the TTR gene. This is the first reported FAP family with this mutation in Finland.

Analysis of gelsolin expression pattern in developing chicken embryo reveals high GSN expression level in tissues of neural crest origin

Gelsolin is one of the most intensively studied actin-binding proteins. However, in the literature comprehensive studies of GSN expression during development have not been performed yet in all model organisms. In zebrafish, gelsolin is a dorsalizing factor that modulates bone morphogenetic proteins signaling pathways, whereas knockout of the gelsolin coding gene, GSN is not lethal in murine model. To study the role of gelsolin in development of higher vertebrates, it is crucial to estimate GSN expression pattern during development. Here, we examined GSN expression in the developing chicken embryo. We applied numerous methods to track GSN expression in developing embryos at mRNA and protein level. We noted a characteristic GSN expression pattern. Although GSN transcripts were present in several cell types starting from early developmental stages, a relatively high GSN expression was observed in eye, brain vesicles, midbrain, neural tube, heart tube, and splanchnic mesoderm. In older embryos, we observed a high GSN expression in the cranial ganglia and dorsal root ganglia. A detailed analysis of 10-day-old chicken embryos revealed high amounts of gelsolin especially within the head region: in the olfactory and optic systems, meninges, nerves, muscles, presumptive pituitary gland, and pericytes, but not oligodendrocytes in the brain. Obtained results suggest that GSN is expressed at high levels in some tissues of ectodermal origin including all neural crest derivatives. Additionally, we describe that silencing of GSN expression in brain vesicles leads to altered morphology of the mesencephalon. This implies gelsolin is crucial for chicken brain development.

Evidence for differential alternative splicing in blood of young boys with autism spectrum disorders

Background

Since RNA expression differences have been reported in autism spectrum disorder (ASD) for blood and brain, and differential alternative splicing (DAS) has been reported in ASD brains, we determined if there was DAS in blood mRNA of ASD subjects compared to typically developing (TD) controls, as well as in ASD subgroups related to cerebral volume.

Methods

RNA from blood was processed on whole genome exon arrays for 2-4–year-old ASD and TD boys. An ANCOVA with age and batch as covariates was used to predict DAS for ALL ASD (n=30), ASD with normal total cerebral volumes (NTCV), and ASD with large total cerebral volumes (LTCV) compared to TD controls (n=20).

Results

A total of 53 genes were predicted to have DAS for ALL ASD versus TD, 169 genes for ASD_NTCV versus TD, 1 gene for ASD_LTCV versus TD, and 27 genes for ASD_LTCV versus ASD_NTCV. These differences were significant at P <0.05 after false discovery rate corrections for multiple comparisons (FDR <5% false positives). A number of the genes predicted to have DAS in ASD are known to regulate DAS (SFPQ, SRPK1, SRSF11, SRSF2IP, FUS, LSM14A). In addition, a number of genes with predicted DAS are involved in pathways implicated in previous ASD studies, such as ROS monocyte/macrophage, Natural Killer Cell, mTOR, and NGF signaling. The only pathways significant after multiple comparison corrections (FDR <0.05) were the Nrf2-mediated reactive oxygen species (ROS) oxidative response (superoxide dismutase 2, catalase, peroxiredoxin 1, PIK3C3, DNAJC17, microsomal glutathione S-transferase 3) and superoxide radical degradation (SOD2, CAT).

Conclusions

These data support differences in alternative splicing of mRNA in blood of ASD subjects compared to TD controls that differ related to head size. The findings are preliminary, need to be replicated in independent cohorts, and predicted alternative splicing differences need to be confirmed using direct analytical methods.

Hereditary gelsolin amyloidosis

Hereditary gelsolin amyloidosis (HGA) is an autosomally dominantly inherited form of systemic amyloidosis, characterized mainly by cranial and sensory peripheral neuropathy, corneal lattice dystrophy, and cutis laxa. HGA, originally reported from Finland and now increasingly from other countries in Europe, North and South America, and Asia, may still be underdiagnosed worldwide. It is the first and so-far only known disorder caused by a gelsolin gene defect, namely a G654A or G654T mutation. Gelsolin is a principal actin-modulating protein, implicated in multiple biological processes, also in the nervous system, e.g. axonal transport, myelination, neurite outgrowth, and neuroprotection. The gelsolin gene defect causes expression of variant gelsolin, followed by systemic deposition of gelsolin amyloid (AGel) in HGA patients and even other consequences on the metabolism and function of gelsolin. In HGA, specific therapy is not yet available but correct diagnosis enables adequate symptomatic treatment which decisively improves the quality of life in these patients. A transgenic murine model of HGA expressing AGel is available, in anticipation of new treatment options targeted toward this slowly progressive but devastating amyloidosis. Present and future lessons learned from HGA may be applicable even in diagnosis and treatment of other hereditary and sporadic amyloidoses.

Plasma gelsolin accumulates in macrophage nodules in brains of simian immunodeficiency virus infected rhesus macaques

Plasma gelsolin (pGSN), an isoform 1, is secreted by various types of cells in the central nervous system (CNS) and periphery, but not by the liver. pGSN circulates in blood and cerebrospinal fluid (CSF); however, its concentration in CSF is approximately twenty times lower than in plasma. It has been shown that several types of cells such as oligodendrocytes, neurons, and/or astrocytes contribute to the overall pool of pGSN in the CNS. Further, it has been postulated that pGSN plays multiple roles during microbial infection and modulates inflammatory responses; however, the exact mechanism of regulation is not known. We previously showed that levels of pGSN in CSF of individuals with advanced neurocognitive impairment due to HIV infection of the brain are decreased. Here, we show that macrophages express significant amounts of pGSN in response to HIV infection in vitro. Using immunohistochemistry of simian immunodeficiency virus infected rhesus monkey brains, we show that increased levels of pGSN are present in macrophage nodules creating locally a high level of this protein within the brain. This may not be reflected by the overall decreased level in the distinct CSF compartment.

Cerebrospinal fluid and blood biomarkers of neuroaxonal damage in multiple sclerosis

Following emerging evidence that neurodegenerative processes in multiple sclerosis (MS) are present from its early stages, an intensive scientific interest has been directed to biomarkers of neuro-axonal damage in body fluids of MS patients. Recent research has introduced new candidate biomarkers but also elucidated pathogenetic and clinical relevance of the well-known ones. This paper reviews the existing data on blood and cerebrospinal fluid biomarkers of neuroaxonal damage in MS and highlights their relation to clinical parameters, as well as their potential predictive value to estimate future disease course, disability, and treatment response. Strategies for future research in this field are suggested.

Mass spectrometric characterization of gelsolin isoforms

Gelsolin is the most widely expressed member of the actin capping and severing family of proteins. There are two isoforms of gelsolin: isoform 1, a secretory (plasma) protein that is 51 amino acids longer than isoform 2, a cytosolic protein, at the N-terminus; the first 27 amino acids is a signal sequence. Both isoforms are coded by a single gene and differ as a result of alternative initiation site/splicing. The level of gelsolin in the blood and cerebrospinal fluid (CSF) is altered in many diseases including amyloidoses and other neurodegenerative disorders. Although quantitative analysis of gelsolin has been reported, lack of suitable antibodies makes it impossible to differentiate these two isoforms by immunodetection techniques and no other technique is available. Therefore, ambiguity exists whether gelsolin present in circulation is isoform 1 or also isoform 2 released from lysed cells. We report in this communication a mass spectrometric approach to identify isoform 1 of gelsolin immunopurified from human plasma and CSF. Recombinant isoform 1 was used as reference.

Severe ataxia with neuropathy in hereditary gelsolin amyloidosis: a case report

Hereditary gelsolin amyloidosis (AGel amyloidosis) is a systemic disorder caused by a G654A or G654T gelsolin mutation, reported from Europe, North America, and Japan. Principal clinical signs are corneal lattice dystrophy, cutis laxa and cranial neuropathy, often deleterious at advanced age. Peripheral neuropathy, if present, is usually mild. We report a 78-year-old male Finnish patient who presented with ataxia and mainly sensory peripheral polyneuropathy (PNP) signs, causing severe disability and ambulation loss. Electrophysiological studies showed severe generalized chronic mainly axonal sensorimotor PNP with facial paralysis. In magnetic resonance imaging proximal lower limb and axial muscle atrophy with fatty degeneration as well as moderate spinal cord atrophy were seen. A G654A gelsolin mutation was demonstrated but no other possible causes of his disability were found. At age 79 years he became bedridden and died of pulmonary embolism. Neuropathological examination revealed marked gelsolin amyloid deposition at vascular and connective tissue sites along the entire length of the peripheral nerves extending to the spinal nerve roots, associated with severe degeneration of nerve fibers and posterior columns. Our report shows that advanced AGel amyloidosis due to degeneration of central and distal sensory nerve projections results in deleterious ataxia with fatal outcome. Severe posterior column atrophy may reflect radicular AGel deposition, although even altered gelsolin-actin interactions in neural cells possibly contribute to neurodegeneration with successive ataxia in carriers of a G654A gelsolin mutation.

Gelsolin and diseases

Gelsolin is a calcium-activated actin filament severing and capping protein found in many cell types and as a secreted form in the plasma of vertebrates. Mutant mice for gelsolin as well as clinical studies have shown that gelsolin is linked to a number of pathological conditions such as inflammation, cancer and amyloidosis. The tight regulation of gelsolin by calcium is crucial for its physiological role and constitutive activation leads to apoptosis. In the following we will give an overview on how gelsolin is regulated by calcium, and which clinical conditions have been linked to lack or misregulation of gelsolin.

Ca2+ binding protects against gelsolin amyloidosis

Amyloid diseases occur when native or mutant polypeptides misfold and aggregate to form deposits in the extracellular space. There are at least 20 proteins associated with amyloid diseases, including the well-known amyloid-beta peptide that is the causative agent for Alzheimer's disease (AD). This review describes familial amyloidosis of Finnish type (FAF), an amyloid disease caused by mutations in plasma gelsolin, a secreted protein that contains multiple Ca2+-binding domains. The FAF mutations result in a loss of the Ca2+-binding site in domain 2 of plasma gelsolin. The resulting decreased stability gives rise to susceptibility to the protease furin in the Golgi. Furin cleavage generates a secreted fragment that undergoes a second proteolytic event in the extracellular matrix to produce a peptide that self-assembles into amyloid plaques. Thus, Ca2+ binding in native plasma gelsolin protects against amyloid disease.

Gelsolin domain 2 Ca2+ affinity determines susceptibility to furin proteolysis and familial amyloidosis of finnish type

Mutation of aspartic acid 187 to asparagine (D187N) or tyrosine (D187Y) in domain 2 of the actin-modulating protein gelsolin causes the neurodegenerative disease familial amyloidosis of Finnish type (FAF). These mutations render plasma gelsolin susceptible to aberrant proteolysis by furin in the trans-Golgi network, the initial proteolytic event in the formation of 71 and 53 residue fragments that assemble into amyloid fibrils. Ca(2+) binding stabilizes wild-type domain 2 gelsolin against denaturation and proteolysis, but the FAF variants are unable to bind and be stabilized by Ca(2+). Though the chain of events initiating FAF has been elucidated recently, uncertainty remains about the mechanistic details that allow the FAF variants to be processed. To test the hypothesis that impaired Ca(2+) binding in the D187 variants, but not other factors specific to residue 187, increases susceptibility to aberrant proteolysis and subsequent amyloidogenesis, we designed the gelsolin variant E209Q to remove a different Ca(2+) ligand from the same Ca(2+) site that is affected in the FAF variants. Here, we show that E209Q domain 2 does not bind Ca(2+) and is not stabilized against denaturation or furin proteolysis, analogous to the behavior exhibited by the FAF variants. Transfection of full-length E209Q into COS cells results in secretion of both the full-length and furin-processed fragments, as observed with D187N and D187Y. Mutation of the furin consensus sequence in D187N and E209Q gelsolin prevents cleavage during secretion, indicating that inhibition of proprotein convertases (furin) represents a viable therapeutic approach for the treatment of FAF. Mutations that diminish domain 2 Ca(2+) binding allow furin access to an otherwise protected cleavage site, initiating the proteolytic cascade that leads to gelsolin amyloidogenesis and FAF.

The gelsolin family of actin regulatory proteins: modular structures, versatile functions

This issue of FEBS Letters includes two manuscripts describing structural studies of gelsolin, the best-characterized member of a superfamily of actin binding proteins that sever, cap, and in some cases nucleate and bundle actin filaments. The manuscripts by Narayan et al. and Irobi et al. provide snapshots of gelsolin domains activated by calcium and in complex with the actin monomer, revealing new insights into the remarkable actin regulatory activities of this versatile protein. These studies build upon nearly a quarter of a century of research on gelsolin's effects on actin dynamics and its role in normal and diseased cells. In the following minireview, we summarize the structural studies that have provided insights into gelsolin's severing and capping activities and look to the future of work on this remarkable molecule.

The calcium-signalling saga: tap water and protein crystals

Of the approximately 1,400 grams of calcium that are in the human body, less than 10 grams manage to escape being trapped in the skeleton and teeth. These few grams might be an insignificant quantity, but they are extraordinarily significant qualitatively. They circulate in the blood and extracellular spaces, and penetrate cells to regulate their most important activities.

Neuromuscular pathology in hereditary gelsolin amyloidosis

Hereditary gelsolin amyloidosis (AGel amyloidosis) is a systemic disorder reported worldwide in kindreds with a G654A or G654T gelsolin gene mutation. The clinically characteristic peripheral nerve involvement has been poorly characterized morphologically, and its pathogenesis remains unknown. We studied peripheral nerve and skeletal muscle biopsy or autopsy specimens of 35 patients with a G654A gelsolin gene mutation. Histological, immunohistochemical, and electron microscopic studies showed consistent deposition of gelsolin amyloid (AGel), particularly in the vascular walls and perineurial sheaths. Nerve roots were more severely affected than distal nerves. The amyloid deposits also displayed variable immunoreactivity for apolipoprotein E, amyloid P component, cystatin C, and alpha-smooth muscle actin. Sural nerve morphometry showed preferential age-related large myelinated nerve fiber loss and reduction of myelin sheath cross-sectional area. There was evidence of denervation atrophy and fiber type grouping in skeletal muscle. Our study shows that marked proximal nerve involvement with AGel angiopathy is an essential feature of AGel amyloidosis. The preferential large fiber loss, not generally seen in amyloid neuropathy, may be caused by ischemia due to AGel angiopathy. Deficient actin modulation by variant gelsolin in neurons and Schwann cells, however, may alter axonal transport and myelination and contribute to AGel polyneuropathy.

Furin initiates gelsolin familial amyloidosis in the Golgi through a defect in Ca(2+) stabilization

Hereditary familial amyloidosis of Finnish type (FAF) leading to amyloid in the peripheral and central nervous systems stems from deposition of a 71 residue fragment generated from the D187N/Y variants of plasma gelsolin by two sequential endoproteolytic events. We identify the protease accomplishing the first cleavage as furin, a proprotein convertase. Endoproteolysis of plasma gelsolin occurs in the trans-Golgi network due to the inability of the FAF variants to bind and be stabilized by Ca(2+). Secretion and processing of the FAF variants by furin can be uncoupled by blocking the convergence of the exocytic pathway transporting plasma gelsolin and the endocytic recycling of furin. We propose that coincidence of membrane trafficking pathways contributes to the development of proteolysis-initiated amyloid disease.

Genetics of the corneal dystrophies: what we have learned in the past twenty-five years

PURPOSE

To indicate important changes in our understanding of the corneal dystrophies.

METHODS

A review of the literature of the last quarter of a century.

RESULTS

The earliest clinical classifications of the corneal dystrophies were based on the application of clinical, biological, histochemical, and ultrastructural methods. Since then, the first great impetus to our understanding has come from the application of techniques to map disorders to specific chromosome loci, using polymorphic markers. More recently, using candidate gene and related approaches, it has been possible to identify genes causing several of the corneal dystrophies and the mutations responsible for their phenotypic variation. A notable success has been to show that several important "stromal" dystrophies result from mutations in the gene beta ig-h3, which encodes for the protein keratoepithelin (beta ig-h3).

CONCLUSIONS

For the corneal dystrophies, as with other inherited disorders, there is room for two sorts of classification system, one based mainly on clinical presentation and the other on an up-to-date understanding of the genetic mechanisms. They are not mutually exclusive. Some developmental corneal disorders are also discussed.

Equilibria and kinetics of folding of gelsolin domain 2 and mutants involved in familial amyloidosis-Finnish type

Mutations D187N and D187Y in domain 2 of the actin-regulating protein gelsolin cause familial amyloidosis-Finnish type (FAF). We have constructed and expressed a recombinant version of gelsolin domain 2 that is sufficiently stable for kinetic and equilibrium measurements. The wild-type domain and the two amyloidogenic mutants fold via simple two-state kinetics without the accumulation of an intermediate. Unfolding kinetics exhibits significant curvature with increasing urea concentration, indicating that the transition state for unfolding becomes more native-like under increasingly denaturing conditions in accordance with the Hammond postulate. Mutations D187N and D187Y destabilize gelsolin domain 2 by 1.22 and 2.16 kcal. mol(-1) (1 kcal = 4.18 kJ) respectively. The mutations do not prevent disulfide bond formation despite their direct contiguity with a cysteine residue involved in disulfide linkage. The destabilization conferred on gelsolin domain 2 by the FAF mutations is sufficient to predict that an appreciable fraction is unfolded and, therefore, extremely susceptible to proteolysis at body temperature.

Functional consequences of amyloidosis mutation for gelsolin polypeptide -- analysis of gelsolin-actin interaction and gelsolin processing in gelsolin knock-out fibroblasts

Gelsolin, an actin-modulating protein, derived from a single gene exists in intracellular and secreted forms. A point mutation at position 187 of both forms of gelsolin causes familial amyloidosis of the Finnish type (FAF). Here, we expressed both isoforms of the wild-type and FAF mutant gelsolin in mouse embryonic gelsolin-null fibroblasts. We demonstrate that the FAF mutation does not interfere with the normal actin-modulating function of intracellular gelsolin, and that aberrant processing of secreted FAF gelsolin to FAF amyloid precursor takes place in the gelsolin-negative background. These results suggest that, in patients with FAF, symptoms are caused by the accumulation in their tissues of amyloid derived from plasma gelsolin and are not due to functional differences in cytoplasmic gelsolin.

The amyloidogenicity of gelsolin is controlled by proteolysis and pH

BACKGROUND

Normally, gelsolin functions in plasma as part of the actin-scavenging system to assemble and disassemble actin filaments. The Asp 187-->Asn (D187N) Asp 187-->Tyr (D187Y) gelsolin mutations facilitate two proteolytic cuts in the parent protein generating a 71-residue fragment that forms amyloid fibrils in humans, putatively causing Finnish type familial amyloidosis (FAF). We investigated the role of the D187N mutation in amyloidogenicity using biophysical studies in vitro.

RESULTS

Both the recombinant wild-type and D187N FAF-associated gelsolin fragments adopt an ensemble of largely unfolded structures that do not self-associate into amyloid at pH 7. 5. Incubation of either fragment at low pHs (6.0-4.0) leads to the formation of well-defined fibrils within 72 hours, however.

CONCLUSIONS

The D187N mutation has been suggested to destabilize the structure of the gelsolin parent protein (specifically domain 2), facilitating two proteolytic cleavage events. Our studies demonstrate that generating the largely unstructured peptide is not sufficient alone for amyloid formation in vitro (on a time scale of months). A drop in pH or an analogous environmental change appears necessary to convert the unstructured fragment into amyloid fibrils, probably through an associative mechanism. The wild-type gelsolin fragment will make amyloid fibrils from pH 6 to 4 in vitro, but neither the wild-type fragment nor fibrils have been observed in vivo. It is possible that domain 2 of wild-type gelsolin is stable in the context of the whole protein and not susceptible to the proteolytic degradation that affords the 71-residue FAF-associated peptide.

Gelsolin-related spinal and cerebral amyloid angiopathy

Gelsolin-related amyloidosis (familial amyloidosis, Finnish type) is a rare disorder, reported worldwide in kindreds carrying a G654A or G654T gelsolin gene mutation. Facial palsy, mild peripheral neuropathy, and corneal lattice dystrophy are characteristic, but atrophic bulbar palsy, ataxia of gait, and minor cognitive impairment may occur. In histological and immunohistochemical studies of the central nervous system in 4 patients with a G654A gelsolin mutation, we found widespread spinal, cerebral, and meningeal amyloid angiopathy, with deposition of gelsolin-related amyloid (AGel). Marked extravascular deposits occurred in the dura, spinal nerve roots, and sensory ganglia. The amyloid deposits were also variably immunoreactive for apolipoprotein E (ApoE), alpha1-antichymotrypsin (alpha1-ACT), and cystatin C (Cys C). Cerebral perivascular fibrinogen immunoreactivity was occasionally noted. The patients showed posterior column degeneration and diffuse loss of myelin in the centrum semiovale with perivascular accentuation. Postmortem magnetic resonance imaging, performed on 1 patient, showed white matter lesions, colocalizing with the histological abnormalities. Our study shows that deposition of AGel in the spinal and cerebral blood vessel walls, meninges, as well as spinal nerve roots and sensory ganglia is an essential feature of this form of systemic amyloidosis and may contribute to the central nervous system symptoms.

Functions of gelsolin: motility, signaling, apoptosis, cancer

Several new members of the gelsolin family have been discovered in the past year. Determination of the structure of gelsolin and identification of lysophosphatidic acid as a negative regulator provide novel functional insights. Gelsolin is an obligate downstream effector of Rac for motility in dermal fibroblasts, regulates phosphoinositide signaling pathways and ion channel function in vivo, and acts as both a regulator and effector of apoptosis.