Untangling the role of amyloid in atherosclerosis

Concomitant amyloidosis is the primary cause of endothelial and coronary microvascular dysfunction in carpal tunnel syndrome

Study objectives

Patients with carpal tunnel syndrome (CTS) show manifestations of arterial abnormalities, including carotid intimal thickening and increased vascular stiffness. As carpal tunnel syndrome is associated with amyloidosis, we hypothesized that previously observed abnormalities can largely be related with concomitant amyloidosis rather than CTS itself.

Design

Prospective observational study.

Setting

Medeniyet University Goztepe Hospital.

Participants

61 patients with CTS (of whom 32 had biopsy-proven amyloidosis) and 36 healthy controls.

Interventions

Subjects underwent ultrasound examinations for the measurement of coronary flow velocity reserve (CFVR), flow-mediated vasodilatation (FMD) and carotid intimal-media thickness (CIMT).

Main outcome measures

Comparison of CFVR, FMD and CIMT in CTS patients with or without amyloidosis.

Results

Patients with either CTS or CTS with concomitant amyloidosis (CTS-A) had significantly lower FMD (9.7 % ± 4.0 % in CTS and 10.3 % ± 4.6 % in CTS-A groups, p < 0.05 for both) and CFVR (2.4 (2.1-2.8) in CTS and 1.8 (1.6-2.1) in CTS-A groups, p < 0.001 for both) as compared to controls, while CIMT was only increased in CTS-A group (0.70 (0.60-0.80), p < 0.001). The reduction in CFVR was solely related to an increased basal flow velocity in CTS patients while there was also a reduced hyperemic flow velocity in patients with CTS-A.

Conclusion

Most arterial phenomena in CTS patients could be attributable to concomitant amyloidosis, although endothelial dysfunction was present even in patients with CTS without amyloidosis.

Small molecules as modulators of the proteostasis machinery: Implication in cardiovascular diseases

With the escalating prevalence of cardiovascular diseases, the substantial socioeconomic burden on healthcare systems is intensifying. Accumulating empirical evidence underscores the pivotal role of the proteostasis network in regulating cardiac homeostasis and function. Disruptions in proteostasis may contribute to the loss of protein function or the acquisition of toxic functions, which are intricately linked to the development of cardiovascular ailments such as atrial fibrillation, heart failure, atherosclerosis, and cardiac aging. It is widely acknowledged that the proteostasis network encompasses molecular chaperones, autophagy, and the ubiquitin proteasome system (UPS). Consequently, the proteostasis network emerges as an appealing target for therapeutic interventions in cardiovascular diseases. Numerous small molecules, acting as modulators of the proteostasis machinery, have exhibited therapeutic efficacy in managing cardiovascular diseases. This review centers on elucidating the role of the proteostasis network in various cardiovascular diseases and explores the potential of small molecules as therapeutic agents.

Longitudinal dynamics of circulating miRNAs in a swine model of familial hypercholesterolemia during early atherosclerosis

Atherosclerosis is a complex progressive disease involving intertwined biological mechanisms. We aimed to identify miRNA expression dynamics at the early stages of atherosclerosis using a large swine model (Wisconsin Miniature Swine, WMS). A total of 18 female pigs; 9 familial hypercholesterolemic (WMS-FH) and 9 normal control swine (WMS-N) were studied. miRNA sequencing was performed on plasma cell-free RNA at 3, 6, and 9 months of age. RT-qPCR validated DE miRNAs in a new cohort of animals (n = 30) with both sexes. Gene ontology and mRNA targets for DE miRNAs were identified. In vivo multimodality imaging and histopathology were performed to document the presence of atherosclerosis at termination. 20, 19, and 9 miRNAs were significantly DE between the groups at months 3, 6, and 9, respectively. Most DE miRNAs and their target genes are involved in human atherosclerosis development. Coronary atherosclerosis was documented in 7/9 WMS-FH pigs. Control animals had no lesions. miR-138, miR-152, miR-190a, and miR-196a showed a significant diagnostic power at month 3, whereas miR-486, miR-126-3p, miR-335, and miR-423-5p were of significant diagnostic power at month 9. In conclusion, specific DE miRNAs with significant discriminatory power may be promising biomarkers for the early detection of coronary atherosclerosis.

The contribution of amyloid deposition in the aortic valve to calcification and aortic stenosis

Calcific aortic valve disease (CAVD) and stenosis have a complex pathogenesis, and no therapies are available that can halt or slow their progression. Several studies have shown the presence of apolipoprotein-related amyloid deposits in close proximity to calcified areas in diseased aortic valves. In this Perspective, we explore a possible relationship between amyloid deposits, calcification and the development of aortic valve stenosis. These amyloid deposits might contribute to the amplification of the inflammatory cycle in the aortic valve, including extracellular matrix remodelling and myofibroblast and osteoblast-like cell proliferation. Further investigation in this area is needed to characterize the amyloid deposits associated with CAVD, which could allow the use of antisense oligonucleotides and/or isotype gene therapies for the prevention and/or treatment of CAVD.

Proteostasis Response to Protein Misfolding in Controlled Hypertension

Hypertension is the most determinant risk factor for cardiovascular diseases. Early intervention and future therapies targeting hypertension mechanisms may improve the quality of life and clinical outcomes. Hypertension has a complex multifactorial aetiology and was recently associated with protein homeostasis (proteostasis). This work aimed to characterize proteostasis in easy-to-access plasma samples from 40 individuals, 20 with controlled hypertension and 20 age- and gender-matched normotensive individuals. Proteostasis was evaluated by quantifying the levels of protein aggregates through different techniques, including fluorescent probes, slot blot immunoassays and Fourier-transform infrared spectroscopy (FTIR). No significant between-group differences were observed in the absolute levels of various protein aggregates (Proteostat or Thioflavin T-stained aggregates; prefibrillar oligomers and fibrils) or total levels of proteostasis-related proteins (Ubiquitin and Clusterin). However, significant positive associations between Endothelin 1 and protein aggregation or proteostasis biomarkers (such as fibrils and ubiquitin) were only observed in the hypertension group. The same is true for the association between the proteins involved in quality control and protein aggregates. These results suggest that proteostasis mechanisms are actively engaged in hypertension as a coping mechanism to counteract its pathological effects in proteome stability, even when individuals are chronically medicated and presenting controlled blood pressure levels.

Age-Related Arteriolar Changes With Lipid and Amyloid Deposits in the Gonads of Dogs

Arteriolar lesions with lipid and/or amyloid deposits are frequently detected in canine gonads by routine histopathologic examination; however, they have never been examined in detail. In the present study, a total of 139 testes/epididymides and 200 ovaries from 72 male (4 months to 14 years old) and 105 female (7 months to 16 years old) dogs were examined for arteriolar lesions. Arteriolar lesions were detected in 21 of 72 male dogs (29%) and 54 of 105 female dogs (51%). These lesions were histologically classified into 4 types: "fibromuscular hypertrophy," characterized by thickening of the tunica intima; "focal vasculitis," characterized by mononuclear cell infiltration; "vacuolar change," consisting of lipid accumulation and infiltration of foamy cells; and "hyalinosis," characterized by irregular thickening with amyloid deposits. In the lesions of vacuolar change and hyalinosis, lipid deposition and infiltration of α-SMA-positive cells and Iba-1-positive cells were also observed. Foamy cells and amyloid deposits were immunopositive for apolipoproteins and oxidized low-density lipoprotein-related proteins. These results indicate that vacuolar change is possibly an early stage of atherosclerosis, and that amyloid may deposit as a consequence of the microenvironment associated with atherogenesis. Logistic regression analysis revealed that arteriolar lesions with lipid deposits were associated with age and interstitial cell tumors in male dogs, and with age in female dogs. Aging is likely an important risk factor of arteriolar lesions with lipid deposits of the canine gonads.

Comparison of Patterns of Coronary Artery Disease in Patients With Heart Failure by Cardiac Amyloidosis Status

BACKGROUND/PURPOSE

The aim of this study is to characterize the pattern and the severity of coronary artery lesions in cardiac amyloidosis.

METHODS

We retrospectively compared patients with heart failure who tested positive (i.e., biopsy or gene tests - HF/CA+) against those who tested negative (HF/CA-) for cardiac amyloidosis. Groups were compared demographically and angiographically for qualitative and quantitative variables to determine patterns of involvement in the major epicardial coronary vessels.

RESULTS

The study included 110 heart failure patients, of whom 55 patients (88 lesions) were in the HF/CA+ group, and 55 patients (66 lesions) were HF/CA-. Despite the advanced age of HF/CA+ patients (74.5 ± 11.0 years vs. 54.1 ± 15.0 years; p = 0.05), no severe calcification was found in the HF/CA+ group (0.0% vs. 4.5%; p = 0.018). The HF/CA+ group also had fewer ostial lesions (3.4% vs. 15.1%; p = 0.0095) and a higher, albeit not significant, Thrombolysis in Myocardial Infarction frame count (30.4 ± 12.6 vs. 26.6 ± 11 frames; p = 0.06). In the HF/CA+ group, men had a significant number of tandem lesions compared to women (14.5% vs 0.0%, p = 0.02).

CONCLUSIONS

Overall, heart failure patients with cardiac amyloidosis were older but were found to have less calcified lesions, less ostial involvement, and a reduced anterograde coronary blood flow. This is the first report examining coronary lesions in heart failure patients with cardiac amyloidosis.

Oxidation of methionine residues in human apolipoprotein A-I generates a potent pro-inflammatory molecule

Amyloid deposits of apolipoprotein A-I (apoA-I) and inflammation are common in atherosclerotic arteries. In this study, we investigated the interplay between oxidation of apoA-I methionine residues (Met(O)-ApoA-I), a known amyloidogenic modification of apoA-I, and the inflammatory response of immune cells. Soluble pre-fibrillar Met(O)-ApoA-I, but not apoA-I, induced intracellular accumulation of pro-interleukin (IL)-1β and secretion of the pro-inflammatory cytokines tumor necrosis factor α (TNFα) and IL-6 in mouse bone marrow-derived macrophages (BMDMs) and human primary monocytes. Additionally, secretion of mature IL-1β was also activated in human monocytes. The pro-inflammatory activity of Met(O)-ApoA-I was Toll-like receptor 4 (TLR4)-dependent and CD36-independent and was solely determined by oxidation of apoA-I methionine residues, in particular Met-86 and Met-148. In contrast, amyloid fibrils or reconstituted high-density lipoproteins (HDLs) generated from Met(O)-ApoA-I did not induce cytokine production in BMDMs. Although lipid-free Met(O)-ApoA-I remained functional in extracting lipids from cells and generating HDL, it gained strong pro-inflammatory properties that may aggravate local inflammation in the arteries and atherosclerosis. Our study indicates that oxidation of apoA-I methionine residues produces a potent danger-associated molecular pattern capable of stimulating pro-inflammatory cytokine secretion at levels similar to those induced by known pathogen-associated molecular patterns, such as lipopolysaccharide.

Polymorphism in disease-related apolipoprotein C-II amyloid fibrils: a structural model for rod-like fibrils

Human apolipoprotein (apo) C-II is one of several plasma apolipoproteins that form amyloid deposits in vivo and is an independent risk factor for cardiovascular disease. Lipid-free apoC-II readily self-assembles into twisted-ribbon amyloid fibrils but forms straight, rod-like amyloid fibrils in the presence of low concentrations of micellar phospholipids. Charge mutations exerted significantly different effects on rod-like fibril formation compared to their effects on twisted-ribbon fibril formation. For instance, the double mutant, K30D-D69K apoC-II, readily formed twisted-ribbon fibrils, while the rate of rod-like fibril formation in the presence of micellar phospholipid was negligible. Structural analysis of rod-like apoC-II fibrils, using hydrogen-deuterium exchange and NMR analysis showed exchange protection consistent with a core cross-β structure comprising the C-terminal 58-76 region. Molecular dynamics simulations of fibril arrangements for this region favoured a parallel cross-β structure. X-ray fibre diffraction data for aligned rod-like fibrils showed a major meridional spacing at 4.6 Å and equatorial spacings at 9.7, 23.8 and 46.6 Å. The latter two equatorial spacings are not observed for aligned twisted-ribbon fibrils and are predicted for a model involving two cross-β fibrils in an off-set antiparallel structure with four apoC-II units per rise of the β-sheet. This model is consistent with the mutational effects on rod-like apoC-II fibril formation. The lipid-dependent polymorphisms exhibited by apoC-II fibrils could determine the properties of apoC-II in renal amyloid deposits and their potential role in the development of cardiovascular disease.

Prediction of Molecular Mechanisms for LianXia NingXin Formula: A Network Pharmacology Study

Objectives: Network pharmacological methods were used to investigate the underlying molecular mechanisms of LianXia NingXin (LXNX) formula, a Chinese prescription, to treat coronary heart disease (CHD) and disease phenotypes (CHD related diseases and symptoms).

Methods: The different seed gene lists associated with the herbs of LXNX formula, the CHD co-morbid diseases and symptoms which were relieved by the LXNX formula (co-morbid diseases and symptoms) were curated manually from biomedical databases and published biomedical literatures. Module enrichment analysis was used to identify CHD-related disease modules in the protein–protein interaction (PPI) network which were also associated to the targets of LXNX formula (LXNX formula’s CHD modules). The molecular characteristics of LXNX formula’s CHD modules were investigated via functional enrichment analysis in terms of gene ontology and pathways. We performed shortest path analysis to explore the interactions between the drug targets of LXNX formula and CHD related disease phenotypes (e.g., co-morbid diseases and symptoms).

Results: We identified two significant CHD related disease modules (i.e., M146 and M203), which were targeted by the herbs of LXNX formula. Pathway and GO term functional analysis results indicated that G-protein coupled receptor signaling pathways (GPCR) of M146 and cellular protein metabolic process of M203 are important functional pathways for the respective module. This is further confirmed by the shortest path analysis between the drug targets of LXNX formula and the aforementioned disease modules. In addition, corticotropin releasing hormone (CRH) and natriuretic peptide precursor A (NPPA) are the only two LXNX formula target proteins with the low shortest path length (on average shorter than 3) to their respective CHD module and co-morbid disease and symptom gene groups.

Conclusion: G-protein coupled receptor signaling pathway and cellular protein metabolic process are the key LXNX formula’s pathways to treat CHD disease phenotypes, in which CRH and NPPA are the two key drug targets of LXNX formula. Further evidences from Chinese herb pharmacological databases indicate that Pinellia ternata (Banxia) has relatively strong adjustive functions on the two key targets.

Serum and Urine Thioflavin-T-Enhanced Fluorescence in Severe Preeclampsia

Common features of amyloid-like proteotoxic aggregates are the ability to bind Congo red (congophilia) and to induce fluorescence of thioflavin-T (ThT). Based on the prior discovery that women with preeclampsia exhibit urine congophilia, we proposed that amyloid-like protein aggregates present in urine also circulate in the bloodstream and this feature is linked to disease severity and clinical phenotype. ThT fluorescence was investigated in 217 paired serum and urine samples from women with severe features of preeclampsia (n=101; median [interquartile range] gestational age [GA], 32 [29-35] weeks), mild features of preeclampsia (n=22; GA, 36 [36-37] weeks), chronic hypertension (n=15; GA, 38 [37-39] weeks), healthy pregnant controls (n=57; GA, 39 [38-39] weeks), and nonpregnant controls (n=22). Serum and urine fluorescence attributable to advanced glycation end products was measured in the same samples with correction for autofluorescence. There were no GA-related changes in ThT fluorescence, although near-term serum ThT fluorescence increased compared with nonpregnant state. Compared with healthy pregnant controls, serum and urine ThT fluorescence was increased in severe features of preeclampsia (P<0.001 for both) but not in mild features of preeclampsia or chronic hypertension. Except for chronic hypertension, advanced glycation end products-related fluorescence of serum or urine did not differ from controls. Urine congophilia had a stronger relationship with preeclampsia severity compared with either urine or serum ThT fluorescence. However, serum ThT fluorescence was independently associated with clinical features of hemolysis, elevated liver enzyme levels, and low platelet levels syndrome (P=0.003). We demonstrate that ThT fluorescence, a marker of amyloid-like aggregates, is increased in serum of women with preeclampsia and likely because of their cytotoxicity associated with hemolysis, elevated liver enzyme levels, and low platelet levels syndrome.

Methionine oxidized apolipoprotein A-I at the crossroads of HDL biogenesis and amyloid formation

Apolipoprotein A-I (apoA-I) shares with other exchangeable apolipoproteins a high level of structural plasticity. In the lipid-free state, the apolipoprotein amphipathic α-helices interact intra- and intermolecularly, providing structural stabilization by self-association. We have reported that lipid-free apoA-I becomes amyloidogenic upon physiologically relevant (myeloperoxidase-mediated) Met oxidation. In this study, we established that Met oxidation promotes amyloidogenesis by reducing the stability of apoA-I monomers and irreversibly disrupting self-association. The oxidized apoA-I monomers also exhibited increased cellular cholesterol release capacity and stronger association with macrophages, compared to nonoxidized apoA-I. Of physiologic relevance, preformed oxidized apoA-I amyloid fibrils induced amyloid formation in nonoxidized apoA-I. This process was enhanced when self-association of nonoxidized apoA-I was disrupted by thermal treatment. Solid state NMR analysis revealed that aggregates formed by seeded nonoxidized apoA-I were structurally similar to those formed by the oxidized protein, featuring a β-structure-rich amyloid fold alongside α-helices retained from the native state. In atherosclerotic lesions, the conditions that promote apoA-I amyloid formation are readily available: myeloperoxidase, active oxygen species, low pH, and high concentration of lipid-free apoA-I. Our results suggest that even partial Met oxidation of apoA-I can nucleate amyloidogenesis, thus sequestering and inactivating otherwise antiatherogenic and HDL-forming apoA-I.-Witkowski, A., Chan, G. K. L., Boatz, J. C., Li, N. J., Inoue, A. P., Wong, J. C., van der Wel, P. C. A., Cavigiolio, G. Methionine oxidized apolipoprotein A-I at the crossroads of HDL biogenesis and amyloid formation.

Hepatocyte-like cells reveal novel role of SerpinA1 in transthyretin amyloidosis

Transthyretin (TTR)-related familial amyloid polyneuropathy (ATTR) results from aggregation and extracellular disposition of misfolded TTR variants. Growing evidence suggests the importance of hepatic chaperones for modulation of pathogenesis. We took advantage of iPSC-derived hepatocyte-like cells (HLCs) derived from ATTR patients (ATTR-HLCs) to compare chaperone gene expression to healthy individuals (H-HLCs). From the set of genes analyzed, chaperones that are predominantly located extracellularly were differently expressed. Expression of the chaperones showed a high correlation with TTR in both ATTR-HLCs and H-HLCs. In contrast, after TTR knockdown, the correlation was mainly affected in ATTR-HLCs suggesting that variant TTR expression triggers abberant chaperone expression. Serpin peptidase inhibitor clade A member 1 (SERPINA1/alpha-1 antitrypsin) was the only extracellular chaperone that was markedly upregulated after TTR knockdown in ATTR-HLCs. Co-immunoprecipitation revealed that SerpinA1 physically interacts with TTR. In vitro assays indicated that SerpinA1 can interfere with TTR aggregation. Taken together, our results suggest that extracellular chaperones play a crucial role in ATTR pathogenesis, in particular SerpinA1, which may affect amyloid formation.

Cell milieu significantly affects the fate of AApoAI amyloidogenic variants: predestination or serendipity?

BACKGROUND

Specific apolipoprotein A-I variants are associated to severe hereditary amyloidoses. The organ distribution of AApoAI amyloidosis seems to depend on the position of the mutation, since mutations in residues from 1 to 75 are mainly associated to hepatic and renal amyloidosis, while mutations in residues from 173 to 178 are mostly responsible for cardiac, laryngeal, and cutaneous amyloidosis. Molecular bases of this tissue specificity are still poorly understood, but it is increasingly emerging that protein destabilization induced by amyloidogenic mutations is neither necessary nor sufficient for amyloidosis development.

METHODS

By using a multidisciplinary approach, including circular dichroism, dynamic light scattering, spectrofluorometric and atomic force microscopy analyses, the effect of target cells on the conformation and fibrillogenic pathway of the two AApoAI amyloidogenic variants AApoAI^L75P and AApoAI^L174S has been monitored.

RESULTS

Our data show that specific cell milieus selectively affect conformation, aggregation propensity and fibrillogenesis of the two AApoAI amyloidogenic variants.

CONCLUSIONS

An intriguing picture emerged indicating that defined cell contexts selectively induce fibrillogenesis of specific AApoAI variants.

GENERAL SIGNIFICANCE

An innovative methodological approach, based on the use of whole intact cells to monitor the effects of cell context on AApoAI variants fibrillogenic pathway, has been set up.

Protein aggregation, cardiovascular diseases, and exercise training: Where do we stand?

Cells ensure their protein quality control through the proteostasis network. Aging and age-related diseases, such as neurodegenerative and cardiovascular diseases, have been associated to the reduction of proteostasis network efficiency and, consequently, to the accumulation of protein misfolded aggregates. The decline in protein homeostasis has been associated with the development and progression of atherosclerotic cardiovascular disease, cardiac hypertrophy, cardiomyopathies, and heart failure. Exercise training is a key component of the management of patients with cardiovascular disease, consistently improving quality of life and prognosis. In this review, we give an overview on age-related protein aggregation, the role of the increase of misfolded protein aggregates on cardiovascular pathophysiology, and describe the beneficial or deleterious effects of the proteostasis network on the development of cardiovascular disease. We subsequently discuss how exercise training, a key lifestyle intervention in those with cardiovascular disease, could restore proteostasis and improve disease status.

Quantitative proteomic study of the plasma reveals acute phase response and LXR/RXR and FXR/RXR activation in the chronic unpredictable mild stress mouse model of depression

Major depressive disorder is a severe neuropsychiatric disease that negatively impacts the quality of life of a large portion of the population. However, the molecular mechanisms underlying depression are still unclear. The pathogenesis of depression involves several brain regions. However, most previous studies have focused only on one specific brain region. Plasma and brain tissues exchange numerous components through the blood-brain barrier. Therefore, in the present study, plasma samples from control (CON) mice and mice subjected to chronic unpredictable mild stress (CUMS) were used to investigate the molecular pathogenesis of depression, and the association between the peripheral circulation and the central nervous system. A total of 47 significant differentially expressed proteins were identified between the CUMS and CON group by an isobaric tag for relative and absolute quantitation (iTRAQ) coupled with tandem mass spectrometry approach. These 47 differentially expressed proteins were analyzed with ingenuity pathway analysis (IPA) software. This revealed that the acute phase response, LXR/RXR and FXR/RXR activation, the complement system and the intrinsic prothrombin activation pathway were significantly changed. Four of the significant differentially expressed proteins (lipopolysaccharide binding protein, fibrinogen β chain, α-1 antitrypsin, and complement factor H) were validated by western blotting. the present findings provide a novel insight into the molecular pathogenesis of depression.

Unraveling the aggregation propensity of human insulin C-peptide

Over the last 20 years, proinsulin C-peptide emerged as an important player in various biological events. Much time and effort has been spent in exploring all functional features of C-peptide and recording its implications in Diabetes mellitus. Only a few studies, though, have addressed C-peptide oligomerization and link this procedure with Diabetes. The aim of our work was to examine the aggregation propensity of C-peptide, utilizing Transmission Electron Microscopy, Congo Red staining, ATR-FTIR, and X-ray fiber diffraction at a 10 mg ml^-1 concentration. Our experimental work clearly shows that C-peptide self-assembles into amyloid-like fibrils and therefore, the aggregation propensity of C-peptide is a characteristic novel feature that should be related to physiological and also pathological conditions. © 2016 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 108: 1-8, 2017.

Understanding the progression of atherosclerosis through gene profiling and co-expression network analysis in Apob(tm2Sgy)Ldlr(tm1Her) double knockout mice

The objective of the study was to gain molecular insights into the progression of atherosclerosis in Apob(tm2Sgy)Ldlr(tm1Her) mice, using transcriptome profiles. Weighted gene co network analysis (WGCNA) and time course analysis using limma were used to study disease progression from 0 to 20weeks. Five co-expression modules were identified by WGCNA using the expression values of 2153 genes. Genes associated with autophagy, endoplasmic reticulum stress, inflammation and lipid metabolism were differentially expressed at early stages of atherosclerosis. Time course analysis highlighted activation of inflammatory gene signaling at 4weeks, cell proliferation and calcification at 8weeks, amyloid like structures and oxidative stress at 14weeks and enhanced production of inflammatory cytokines at 20weeks. Our results suggest that maximum gene perturbations occur during early atherosclerosis which could be the danger signals associated with subclinical disease. Understanding these genes and associated pathways can help in improvement of diagnostic and therapeutic targets for atherosclerosis.

Structural Stability and Local Dynamics in Disease-Causing Mutants of Human Apolipoprotein A-I: What Makes the Protein Amyloidogenic?

ApoA-I, the major protein of plasma high-density lipoprotein, removes cellular cholesterol and protects against atherosclerosis. ApoA-I mutations can cause familial amyloidosis, a life-threatening disease wherein N-terminal protein fragments form fibrils in vital organs. To unveil the protein misfolding mechanism and to understand why some mutations cause amyloidosis while others do not, we analyzed the structure, stability, and lipid-binding properties of naturally occurring mutants of full-length human apoA-I causing either amyloidosis (G26R, W50R, F71Y, and L170P) or aberrant lipid metabolism (L159R). Global and local protein conformation and dynamics in solution were assessed by circular dichroism, fluorescence, and hydrogen-deuterium exchange mass spectrometry. All mutants showed increased deuteration in residues 14-22, supporting our hypothesis that decreased protection of this major amyloid "hot spot" can trigger protein misfolding. In addition, L159R showed local helical unfolding near the mutation site, consistent with cleavage of this mutant in plasma to generate the labile 1-159 fragment. Together, the results suggest that reduced protection of the major amyloid "hot spot", combined with the structural integrity of the native helix bundle conformation, shifts the balance from protein clearance to β-aggregation. A delicate balance between the overall structural integrity of a globular protein and the local destabilization of its amyloidogenic segments may be a fundamental determinant of this and other amyloid diseases. Furthermore, mutation-induced conformational changes observed in the helix bundle, which comprises the N-terminal 75% of apoA-I, and its flexible C-terminal tail suggest the propagation of structural perturbations to distant sites via an unexpected template-induced ensemble-based mechanism, challenging the classical structure-based view.

Transthyretin Amyloidosis: Chaperone Concentration Changes and Increased Proteolysis in the Pathway to Disease

Transthyretin amyloidosis is a conformational pathology characterized by the extracellular formation of amyloid deposits and the progressive impairment of the peripheral nervous system. Point mutations in this tetrameric plasma protein decrease its stability and are linked to disease onset and progression. Since non-mutated transthyretin also forms amyloid in systemic senile amyloidosis and some mutation bearers are asymptomatic throughout their lives, non-genetic factors must also be involved in transthyretin amyloidosis. We discovered, using a differential proteomics approach, that extracellular chaperones such as fibrinogen, clusterin, haptoglobin, alpha-1-anti-trypsin and 2-macroglobulin are overrepresented in transthyretin amyloidosis. Our data shows that a complex network of extracellular chaperones are over represented in human plasma and we speculate that they act synergistically to cope with amyloid prone proteins. Proteostasis may thus be as important as point mutations in transthyretin amyloidosis.

The potential of chitosan and its derivatives in prevention and treatment of age-related diseases

Age-related, diet-related and protein conformational diseases, such as atherosclerosis, diabetes mellitus, cancer, hypercholesterolemia, cardiovascular and neurodegenerative diseases are common in the elderly population. The potential of chitosan, chitooligosaccharides and their derivatives in prevention and treatment of age-related dysfunctions is reviewed and discussed in this paper. The influence of oxidative stress, low density lipoprotein oxidation, increase of tissue stiffness, protein conformational changes, aging-associated chronic inflammation and their pathobiological significance have been considered. The chitosan-based functional food also has been reviewed.

Amyloid-Forming Properties of Human Apolipoproteins: Sequence Analyses and Structural Insights

Apolipoproteins are protein constituents of lipoproteins that transport cholesterol and fat in circulation and are central to cardiovascular health and disease. Soluble apolipoproteins can transiently dissociate from the lipoprotein surface in a labile free form that can misfold, potentially leading to amyloid disease. Misfolding of apoA-I, apoA-II, and serum amyloid A (SAA) causes systemic amyloidoses, apoE4 is a critical risk factor in Alzheimer's disease, and apolipoprotein misfolding is also implicated in cardiovascular disease. To explain why apolipoproteins are over-represented in amyloidoses, it was proposed that the amphipathic α-helices, which form the lipid surface-binding motif in this protein family, have high amyloid-forming propensity. Here, we use 12 sequence-based bioinformatics approaches to assess amyloid-forming potential of human apolipoproteins and to identify segments that are likely to initiate β-aggregation. Mapping such segments on the available atomic structures of apolipoproteins helps explain why some of them readily form amyloid while others do not. Our analysis shows that nearly all amyloidogenic segments: (i) are largely hydrophobic, (ii) are located in the lipid-binding amphipathic α-helices in the native structures of soluble apolipoproteins, (iii) are predicted in both native α-helices and β-sheets in the insoluble apoB, and (iv) are predicted to form parallel in-register β-sheet in amyloid. Most of these predictions have been verified experimentally for apoC-II, apoA-I, apoA-II and SAA. Surprisingly, the rank order of the amino acid sequence propensity to form amyloid (apoB>apoA-II>apoC-II≥apoA-I, apoC-III, SAA, apoC-I>apoA-IV, apoA-V, apoE) does not correlate with the proteins' involvement in amyloidosis. Rather, it correlates directly with the strength of the protein-lipid association, which increases with increasing protein hydrophobicity. Therefore, the lipid surface-binding function and the amyloid-forming propensity are both rooted in apolipoproteins' hydrophobicity, suggesting that functional constraints make it difficult to completely eliminate pathogenic apolipoprotein misfolding. We propose that apolipoproteins have evolved protective mechanisms against misfolding, such as the sequestration of the amyloidogenic segments via the native protein-lipid and protein-protein interactions involving amphipathic α-helices and, in case of apoB, β-sheets.

Targeting the ubiquitin-proteasome system in atherosclerosis: status quo, challenges, and perspectives

SIGNIFICANCE

Atherosclerosis is a vascular disease of worldwide significance with fatal complications such as myocardial infarction, stroke, and peripheral artery disease. Atherosclerosis is recognized as a chronic inflammatory disease leading to arterial plaque formation and vessel narrowing in different vascular beds. Besides the strong inflammatory nature of atherosclerosis, it is also characterized by proliferation, apoptosis, and enhanced oxidative stress. The ubiquitin-proteasome system (UPS) is the major intracellular degradation system in eukaryotic cells. Besides its essential role in the degradation of dysfunctional and oxidatively damaged proteins, it is involved in many processes that influence disease progression in atherosclerosis. Hence, it is logical to ask whether targeting the proteasome is a reasonable and feasible option for the treatment of atherosclerosis.

RECENT ADVANCES

Several lines of evidence suggest stage-specific dysfunction of the UPS in atherogenesis. Regulation of key processes by the proteasome in atherosclerosis, as well as the modulation of these processes by proteasome inhibitors in vascular cells, is outlined in this review. The treatment of atherosclerotic animal models with proteasome inhibitors yielded partly opposing results, the potentially underlying reasons of which are discussed here.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Targeting UPS function in atherosclerosis is a promising but challenging option. Limitations of current proteasome inhibitors, dose dependency, and the cell specificity of effects, as well as the potential of future therapeutics are discussed. A stage-specific in-depth exploration of UPS function in atherosclerosis in the future will help identify targets and windows for beneficial intervention.

Amyloidogenic mutations in human apolipoprotein A-I are not necessarily destabilizing - a common mechanism of apolipoprotein A-I misfolding in familial amyloidosis and atherosclerosis

High-density lipoproteins and their major protein, apolipoprotein A-I (apoA-I), remove excess cellular cholesterol and protect against atherosclerosis. However, in acquired amyloidosis, nonvariant full-length apoA-I deposits as fibrils in atherosclerotic plaques; in familial amyloidosis, N-terminal fragments of variant apoA-I deposit in vital organs, damaging them. Recently, we used the crystal structure of Δ(185-243)apoA-I to show that amyloidogenic mutations destabilize apoA-I and increase solvent exposure of the extended strand 44-55 that initiates β-aggregation. In the present study, we test this hypothesis by exploring naturally occurring human amyloidogenic mutations, W50R and G26R, within or close to this strand. The mutations caused small changes in the protein's α-helical content, stability, proteolytic pattern and protein-lipid interactions. These changes alone were unlikely to account for amyloidosis, suggesting the importance of other factors. Sequence analysis predicted several amyloid-prone segments that can initiate apoA-I misfolding. Aggregation studies using N-terminal fragments verified this prediction experimentally. Three predicted N-terminal amyloid-prone segments, mapped on the crystal structure, formed an α-helical cluster. Structural analysis indicates that amyloidogenic mutations or Met86 oxidation perturb native packing in this cluster. Taken together, the results suggest that structural perturbations in the amyloid-prone segments trigger α-helix to β-sheet conversion in the N-terminal ~ 75 residues forming the amyloid core. Polypeptide outside this core can be proteolysed to form 9-11 kDa N-terminal fragments found in familial amyloidosis. Our results imply that apoA-I misfolding in familial and acquired amyloidosis follows a similar mechanism that does not require significant structural destabilization or proteolysis. This novel mechanism suggests potential therapeutic interventions for apoA-I amyloidosis.

Tanshinone IIA promotes non-amyloidogenic processing of amyloid precursor protein in platelets via estrogen receptor signaling to phosphatidylinositol 3-kinase/Akt

Amyloid β peptide (Aβ) is a proteolytic product of amyloid precursor protein (APP). Recent findings suggested that platelet-derived Aβ is closely associated with the pathogenesis of atherosclerosis (AS). Tanshinone IIA (Tan IIA), a pharmacologically active component of the Chinese herb Salvia miltiorrhiza Bunge, has long been used to treat AS and was also identified as a phytoestrogen. However, it has not been elucidated whether Tan IIA intervenes with platelet APP processing and whether such an intervention is associated with its estrogenic activity. Using human platelets, this study demonstrated that Tan IIA promoted the non-amyloidogenic cleavage of APP via estrogenic activity. The phosphatidylinositol 3-kinase/Akt pathway may be involved in this effect of Tan IIA on platelet APP metabolism as a downstream effector of estrogen receptor signaling. This study aimed to extend the existing data and provide new insights into the mechanism underlying the vasoprotective effect of Tan IIA.

Amyloid-β increases metallo- and cysteine protease activities in human macrophages

BACKGROUND/AIMS

Amyloid-β (Aβ) plays a crucial role in the onset and progression of atherosclerosis. Macrophages are a source of matrix metalloproteinases (MMPs), cysteine proteases and transforming growth factor (TGF)-β1 in the vascular wall. The aims of this study were to analyze the capacity of Aβ peptide (1-40) (Aβ40), Aβ peptide (1-42) (Aβ42) and fibrillar Aβ42 (fAβ42) to modulate the expression and activity of MMP-9, MMP-2 and tissue inhibitor of MMP-1 (TIMP-1) in human monocyte-derived macrophages (HMDM). Additionally, we analyzed whether Aβ internalization alters the secretion of cathepsin S (CatS) and TGF-β1 by macrophages.

METHODS

HMDM were exposed to native and fibrillar Aβ. MMPs and TIMP-1 expression was analyzed by real-time PCR, and MMP abundance by zymography. Protein levels of precursor and active forms of CatS were analyzed by Western blot and TGF-β1 levels by ELISA.

RESULTS

Aβ40, Aβ42 and especially fAβ42 strongly induced MMP-9/MMP-2 levels. Moreover, we showed enhanced active CatS and reduced TGF-β1 protein levels in the secretome of Aβ42 and fAβ42-exposed macrophages.

CONCLUSIONS

Aβ can regulate the proinflammatory state of human macrophages by inducing metallo- and cysteine protease levels and by reducing TGF-β1 secretion. These effects may be crucial in atherosclerosis progression.

Insulin-degrading enzyme deficiency in bone marrow cells increases atherosclerosis in LDL receptor-deficient mice

BACKGROUND

Insulin-degrading enzyme (IDE), a protease implicated in several chronic diseases, associates with the cytoplasmic domain of the macrophage Type A scavenger receptor (SR-A). Our goal was to investigate the effect of IDE deficiency (Ide(-/-)) on diet-induced atherosclerosis in low density lipoprotein-deficient (Ldlr(-/-)) mice and on SR-A function.

METHODS

Irradiated Ldlr(-/-) or Ide(-/-)Ldlr(-/-) mice were reconstituted with wild-type or Ide(-/-) bone marrow and, 6 weeks later, were placed on a high-fat diet for 8 weeks.

RESULTS

After 8 weeks on a high-fat diet, male Ldlr(-/-) recipients of Ide(-/-) bone marrow had more atherosclerosis, higher serum cholesterol and increased lesion-associated β-amyloid, an IDE substrate, and receptor for advanced glycation end products (RAGE), a proinflammatory receptor for β-amyloid, compared to male Ldlr(-/-) recipients of wild-type bone marrow. IDE deficiency in male Ldlr(-/-) recipient mice did not affect atherosclerosis or cholesterol levels and moderated the effects of IDE deficiency of bone marrow-derived cells. No differences were seen between Ldlr(-/-) and Ide(-/-)Ldlr(-/-) female mice reconstituted with Ide(-/-) or wild-type bone marrow. IDE deficiency in macrophages did not alter SR-A levels, cell surface SR-A, or foam cell formation.

CONCLUSION

IDE deficiency in bone marrow-derived cells results in larger atherosclerotic lesions, increased lesion-associated Aβ and RAGE, and higher serum cholesterol in male, Ldlr(-/-) mice.

A review of the role of apolipoprotein C-II in lipoprotein metabolism and cardiovascular disease

The focus of this review is on the role of apolipoprotein C-II (apoC-II) in lipoprotein metabolism and the potential effects on the risk of cardiovascular disease (CVD). We searched PubMed/Scopus for articles regarding apoC-II and its role in lipoprotein metabolism and the risk of CVD. Apolipoprotein C-II is a constituent of chylomicrons, very low-density lipoprotein, low-density lipoprotein, and high-density lipoprotein (HDL). Apolipoprotein C-II contains 3 amphipathic α-helices. The lipid-binding domain of apoC-II is located in the N-terminal, whereas the C-terminal helix of apoC-II is responsible for the interaction with lipoprotein lipase (LPL). At intermediate concentrations (approximately 4 mg/dL) and in normolipidemic subjects, apoC-II activates LPL. In contrast, both an excess and a deficiency of apoC-II are associated with reduced LPL activity and hypertriglyceridemia. Furthermore, excess apoC-II has been associated with increased triglyceride-rich particles and alterations in HDL particle distribution, factors that may increase the risk of CVD. However, there is not enough current evidence to clarify whether increased apoC-II causes hypertriglyceridemia or is an epiphenomenon reflecting hypertriglyceridemia. A number of pharmaceutical interventions, including statins, fibrates, ezetimibe, nicotinic acid, and orlistat, have been shown to reduce the increased apoC-II concentrations. An excess of apoC-II is associated with increased triglyceride-rich particles and alterations in HDL particle distribution. However, prospective trials are needed to assess if apoC-II is a CVD marker or a risk factor in high-risk patients.

Shear flow induced changes in apolipoprotein C-II conformation and amyloid fibril formation

The misfolding and self-assembly of proteins into amyloid fibrils that occur in several debilitating diseases are affected by a variety of environmental factors, including mechanical factors associated with shear flow. We examined the effects of shear flow on amyloid fibril formation by human apolipoprotein C-II (apoC-II). Shear fields (150, 300, and 500 s(-1)) accelerated the rate of apoC-II fibril formation (1 mg/mL) approximately 5-10-fold. Fibrils produced at shear rates of 150 and 300 s(-1) were similar to the twisted ribbon fibrils formed in the absence of shear, while at 500 s(-1), tangled ropelike structures were observed. The mechanism of the shear-induced acceleration of amyloid fibril formation was investigated at low apoC-II concentrations (50 μg/mL) where fibril formation does not occur. Circular dichroism and tryptophan fluorescence indicated that shear induced an irreversible change in apoC-II secondary structure. Fluorescence resonance energy transfer experiments using the single tryptophan residue in apoC-II as the donor and covalently attached acceptors showed that shear flow increased the distance between the donor and acceptor molecules. Shear-induced higher-order oligomeric species were identified by sedimentation velocity experiments using fluorescence detection, while fibril seeding experiments showed that species formed during shear flow are on the fibril formation pathway. These studies suggest that physiological shear flow conditions and conditions experienced during protein manufacturing can exert significant effects on protein conformation, leading to protein misfolding, aggregation, and amyloid fibril formation.

Apolipoproteins and amyloid fibril formation in atherosclerosis

Amyloid fibrils arise from the aggregation of misfolded proteins into highly-ordered structures. The accumulation of these fibrils along with some non-fibrillar constituents within amyloid plaques is associated with the pathogenesis of several human degenerative diseases. A number of plasma apolipoproteins, including apolipoprotein (apo) A-I, apoA-II, apoC-II and apoE are implicated in amyloid formation or influence amyloid formation by other proteins. We review present knowledge of amyloid formation by apolipoproteins in disease, with particular focus on atherosclerosis. Further insights into the molecular mechanisms underlying their amyloidogenic propensity are obtained from in vitro studies which describe factors affecting apolipoprotein amyloid fibril formation and interactions. Additionally, we outline the evidence that amyloid fibril formation by apolipoproteins might play a role in the development and progression of atherosclerosis, and highlight possible molecular mechanisms that could contribute to the pathogenesis of this disease.

Synthesis of peptide sequences derived from fibril-forming proteins

The pathogenesis of a large number of diseases, including Alzheimer's Disease, Parkinson's Disease, and Creutzfeldt-Jakob Disease (CJD), is associated with protein aggregation and the formation of amyloid, fibrillar deposits. Peptide fragments of amyloid-forming proteins have been found to form fibrils in their own right and have become important tools for unlocking the mechanism of amyloid fibril formation and the pathogenesis of amyloid diseases. The synthesis and purification of peptide sequences derived from amyloid fibril-forming proteins can be extremely challenging. The synthesis may not proceed well, generating a very low quality crude product which can be difficult to purify. Even clean crude peptides can be difficult to purify, as they are often insoluble or form fibrils rapidly in solution. This chapter presents methods to recognise and to overcome the difficulties associated with the synthesis, and purification of fibril-forming peptides, illustrating the points with three synthetic examples.

Effect of low-density lipoprotein apheresis on plasma levels of apolipoprotein e4

Apolipoprotein E4 (apoE4) is a positively charged proinflammatory apolipoprotein bound to high-density lipoprotein (HDL) cholesterol and remnant lipoproteins. ApoE4 is associated with an increased risk of cardiovascular and cerebrovascular disease. Low-density lipoprotein (LDL) apheresis, a therapy for patients with familial hypercholesterolemia, removes apolipoprotein B and other positively charged plasma proteins but negatively charged proteins such as HDL cholesterol are generally spared. Despite their negative charge, LDL apheresis still removes 10% to 15% of HDL cholesterol, in particular, inflammatory HDL cholesterol. Patients with familial hypercholesterolemia have increased plasma levels of apoE4 and apoE4-bound HDL cholesterol. We tested the hypothesis that LDL apheresis would reduce the plasma levels of apoE4. We analyzed the plasma apoE4 levels using enzyme-linked immunosorbent assay immediately before and after LDL apheresis in 10 patients with familial hypercholesterolemia who had tested positive for the apoE4 isoform. After one treatment, the mean plasma apoE4 levels had been reduced by 39%, LDL cholesterol by 75%, triglycerides by 38%, and HDL cholesterol by 18%. The change in HDL cholesterol was significantly related to the apoE4 baseline values (r = -0.83, p = 0.001) and apoE4 levels after apheresis (r = 0.816, p = 0.004). In conclusion, LDL apheresis acutely reduced the plasma levels of apoE4. The mechanism of apoE4 reduction by LDL apheresis might be related to the selective reduction of a particular HDL cholesterol.

Glycosylation and sialylation of macrophage-derived human apolipoprotein E analyzed by SDS-PAGE and mass spectrometry: evidence for a novel site of glycosylation on Ser290

Apolipoprotein E (apoE) is a 34-kDa glycoprotein secreted from various cells including hepatocytes and macrophages and plays an important role in remnant lipoprotein clearance, immune responses, Alzheimer disease, and atherosclerosis. Cellular apoE and plasma apoE exist as multiple glycosylated and sialylated glycoforms with plasma apoE being less glycosylated/sialylated than cell-derived apoE. Some of the glycan structures on plasma apoE are characterized; however, the more complicated structures on plasma and cellular/secreted apoE remain unidentified. We investigated glycosylation and sialylation of cellular and secreted apoE from primary human macrophages by one- and two-dimensional gel electrophoresis and mass spectrometry. Our results identify eight different glycoforms with (HexNAc)(2)-Hex(2)-(NeuAc)(2) being the most complex glycan detected on Thr(194) in both cellular and secreted apoE. Four additional glycans were identified on apoE(283-299), and using beta-elimination/alkylation by methylamine in vitro, we identified Ser(290) as a novel site of glycan attachment. Comparison of plasma and cellular/secreted apoE from the same donor confirmed that cell-derived apoE is more extensively sialylated than plasma apoE. Given the importance of the C terminus of apoE in regulating apoE solubility, stability, and lipid binding, these results may have important implications for our understanding of apoE biochemistry.

Genome-wide analysis of YY2 versus YY1 target genes

Yin Yang 1 (YY1) is a critical transcription factor controlling cell proliferation, development and DNA damage responses. Retrotranspositions have independently generated additional YY family members in multiple species. Although Drosophila YY1 [pleiohomeotic (Pho)] and its homolog [pleiohomeotic-like (Phol)] redundantly control homeotic gene expression, the regulatory contributions of YY1-homologs have not yet been examined in other species. Indeed, targets for the mammalian YY1 homolog YY2 are completely unknown. Using gene set enrichment analysis, we found that lentiviral constructs containing short hairpin loop inhibitory RNAs for human YY1 (shYY1) and its homolog YY2 (shYY2) caused significant changes in both shared and distinguishable gene sets in human cells. Ribosomal protein genes were the most significant gene set upregulated by both shYY1 and shYY2, although combined shYY1/2 knock downs were not additive. In contrast, shYY2 reversed the anti-proliferative effects of shYY1, and shYY2 particularly altered UV damage response, platelet-specific and mitochondrial function genes. We found that decreases in YY1 or YY2 caused inverse changes in UV sensitivity, and that their combined loss reversed their respective individual effects. Our studies show that human YY2 is not redundant to YY1, and YY2 is a significant regulator of genes previously identified as uniquely responding to YY1.

Methionine oxidation induces amyloid fibril formation by full-length apolipoprotein A-I

Apolipoprotein A-I (apoA-I) is the major protein component of HDL, where it plays an important role in cholesterol transport. The deposition of apoA-I derived amyloid is associated with various hereditary systemic amyloidoses and atherosclerosis; however, very little is known about the mechanism of apoA-I amyloid formation. Methionine residues in apoA-I are oxidized via several mechanisms in vivo to form methionine sulfoxide (MetO), and significant levels of methionine oxidized apoA-I (MetO-apoA-I) are present in normal human serum. We investigated the effect of methionine oxidation on the structure, stability, and aggregation of full-length, lipid-free apoA-I. Circular dichrosim spectroscopy showed that oxidation of all three methionine residues in apoA-I caused partial unfolding of the protein and decreased its thermal stability, reducing the melting temperature (T(m)) from 58.7 degrees C for native apoA-I to 48.2 degrees C for MetO-apoA-I. Analytical ultracentrifugation revealed that methionine oxidation inhibited the native self association of apoA-I to form dimers and tetramers. Incubation of MetO-apoA-I for extended periods resulted in aggregation of the protein, and these aggregates bound Thioflavin T and Congo Red. Inspection of the aggregates by electron microscopy revealed fibrillar structures with a ribbon-like morphology, widths of approximately 11 nm, and lengths of up to several microns. X-ray fibre diffraction studies of the fibrils revealed a diffraction pattern with orthogonal peaks at spacings of 4.64 A and 9.92 A, indicating a cross-beta amyloid structure. This systematic study of fibril formation by full-length apoA-I represents the first demonstration that methionine oxidation can induce amyloid fibril formation.

Misfolded proteins activate factor XII in humans, leading to kallikrein formation without initiating coagulation

When blood is exposed to negatively charged surface materials such as glass, an enzymatic cascade known as the contact system becomes activated. This cascade is initiated by autoactivation of Factor XII and leads to both coagulation (via Factor XI) and an inflammatory response (via the kallikrein-kinin system). However, while Factor XII is important for coagulation in vitro, it is not important for physiological hemostasis, so the physiological role of the contact system remains elusive. Using patient blood samples and isolated proteins, we identified a novel class of Factor XII activators. Factor XII was activated by misfolded protein aggregates that formed by denaturation or by surface adsorption, which specifically led to the activation of the kallikrein-kinin system without inducing coagulation. Consistent with this, we found that Factor XII, but not Factor XI, was activated and kallikrein was formed in blood from patients with systemic amyloidosis, a disease marked by the accumulation and deposition of misfolded plasma proteins. These results show that the kallikrein-kinin system can be activated by Factor XII, in a process separate from the coagulation cascade, and point to a protective role for Factor XII following activation by misfolded protein aggregates.

An altered pattern of circulating apolipoprotein E3 isoforms is implicated in preeclampsia

Preeclampsia is a common pregnancy complication that is an important cause of preterm birth and fetal growth restriction. Because there is no diagnostic test yet available for preeclampsia, we used a proteomic approach to identify novel serum/plasma biomarkers for this condition. We conducted case control studies comparing nulliparous women who developed preeclampsia at 36-38 weeks of gestation with healthy nulliparous women matched by gestational age at sampling. Serum/plasma was depleted of six abundant proteins and analyzed by two-dimensional gel electrophoresis (n = 12 per group) and difference gel electrophoresis (n = 12 per group). Differences in abundance of protein spots were detected by univariate and multivariate statistical analyses. Proteins were identified by mass spectrometry and expression of selected proteins was validated by immunoblotting. Proteins whose concentrations were selectively associated with preeclampsia included apolipoprotein E (apoE), apoC-II, complement factor C3c, fibrinogen, transthyretin, and complement factor H-related protein 2. An increase in a deglycosylated isoform of apoE3 and concomitantly decreased amounts of one apoE3 glycoisoform were identified in preeclamptic plasma and confirmed by immunoblotting. Altered production of these preeclampsia-related apoE3 isoforms might impair reverse cholesterol transport, contributing to arterial damage. These findings point to a novel mechanistic link between preeclampsia and subsequent cardiovascular disease.