ApoA-I cleaved by transthyretin has reduced ability to promote cholesterol efflux and increased amyloidogenicity

Tetrameric Transthyretin as a Protective Factor Against Alzheimer's Disease

Transthyretin (TTR) is a tetrameric protein traditionally recognized for its role in transporting thyroxine and retinol. Recent research has highlighted the potential neuroprotective functions of TTR in the setting of Alzheimer's disease (AD), which is the most common form of dementia and is caused by the deposition of amyloid beta (Aβ) and the resulting cytotoxic effects. This paper explores the mechanisms of TTR protective action, including its interaction with Aβ to prevent fibril formation and promote Aβ clearance from the brain. It also synthesizes experimental evidence suggesting that enhanced TTR stability may mitigate neurodegeneration and cognitive decline in AD. Potential therapeutic strategies such as small molecule stabilizers of TTR are discussed, highlighting their role in enhancing TTR binding to Aβ and facilitating its clearance. By consolidating current knowledge and proposing directions for future research, this review aims to underscore the significance of TTR as a neuroprotective factor in AD and the potential implications for future research.

A review of cutting-edge biomarkers for diagnosing coronary artery disease

Chronic coronary artery disease (CAD) remains a significant global healthcare burden. Current risk assessment methods have notable limitations in early detection and risk stratification. Hence, there is an urgent need for innovative biomarkers that facilitate the premature CAD diagnosis, ultimately leading to reduction in associated morbidity and mortality rates. This review comprehensively examines recent advances in emerging biomarkers for CAD detection. Our analysis delves into various aspects of these biomarkers such as their mechanisms of action, roles in the pathophysiology of the disease, and different measurement techniques employed in clinical practice. Comparative assessment of biomarker performance between CAD patients and control groups was also presented relying on their sensitivity, specificity, and area under the curve at specific cutoff points. In this regard, prominent biomarkers including Tenascin-C, IL-37, PTX3, transthyretin, soluble interleukin-6 receptor α, and miR-15a are identified as having high diagnostic potential for chronic CAD that indeed showcase promising performance metrics. These findings underscore the role of novel biomarkers in enhancing CAD risk stratification and improving patient outcomes through early intervention. However, the pursuit of an ideal and inclusive biomarker continues due to the multifaceted nature of CAD. Future randomized controlled trials are essential to bridge the gap between research findings and clinical practice in order to augment the practical application of these biomarkers in routine healthcare settings.

Synergistic Anti-Inflammatory Activity of Lipid-Free Apolipoprotein (apo) A-I and CIGB-258 in Acute-Phase Zebrafish via Stabilization of the apoA-I Structure to Enhance Anti-Glycation and Antioxidant Activities

CIGB-258, a 3 kDa peptide from heat shock protein 60, exhibits synergistic anti-inflammatory activity with apolipoprotein A-I (apoA-I) in reconstituted high-density lipoproteins (rHDLs) via stabilization of the rHDL structure. This study explored the interactions between CIGB-258 and apoA-I in the lipid-free state to assess their synergistic effects in the structural and functional enhancement of apoA-I and HDL. A co-treatment of lipid-free apoA-I and CIGB-258 inhibited the cupric ion-mediated oxidation of low-density lipoprotein (LDL) and a lowering of oxidized species in the dose-responsive manner of CIGB-258. The co-presence of CIGB-258 caused a blue shift in the wavelength of maximum fluorescence (WMF) of apoA-I with protection from proteolytic degradation. The addition of apoA-I:CIGB-258, with a molar ratio of 1:0.1, 1:0.5, and 1:1, to HDL2 and HDL3 remarkably enhanced the antioxidant ability against LDL oxidation up to two-fold higher than HDL alone. HDL-associated paraoxonase activities were elevated up to 28% by the co-addition of apoA-I and CIGB-258, which is linked to the suppression of Cu2+-mediated HDL oxidation with the slowest electromobility. Isothermal denaturation by a urea treatment showed that the co-presence of CIGB-258 attenuated the exposure of intrinsic tryptophan (Trp) and increased the mid-points of denaturation from 2.33 M for apoA-I alone to 2.57 M for an apoA-I:CIGB-258 mixture with a molar ratio of 1:0.5. The addition of CIGB-258 to apoA-I protected the carboxymethyllysine (CML)-facilitated glycation of apoA-I with the prevention of Trp exposure. A co-treatment of apoA-I and CIGB-258 synergistically safeguarded zebrafish embryos from acute death by CML-toxicity, suppressing oxidative stress and apoptosis. In adult zebrafish, the co-treatment of apoA-I+CIGB-258 exerted the highest anti-inflammatory activity with a higher recovery of swimming ability and survivability than apoA-I alone or CIGB-258 alone. A co-injection of apoA-I and CIGB-258 led to the lowest infiltration of neutrophils and interleukin (IL)-6 generation in hepatic tissue, with the lowest serum triglyceride, aspartate transaminase, and alanine transaminase levels in plasma. In conclusion, the co-presence of CIGB-258 ameliorated the beneficial functionalities of apoA-I, such as antioxidant and anti-glycation activities, by enhancing the structural stabilization and protection of apoA-I. The combination of apoA-I and CIGB-258 synergistically enforced the anti-inflammatory effect against CML toxicity in embryos and adult zebrafish.

The integration of genetically-regulated transcriptomics and electronic health records highlights a pattern of medical outcomes related to increased hepatic transthyretin expression

Transthyretin (TTR) is the precursor of the fibrils that compromise organ function in hereditary and sporadic systemic amyloidoses (ATTR). RNA-interference and anti-sense therapeutics targeting TTR hepatic transcription have been shown to reduce TTR amyloid formation. In the present study, we leveraged genetic and phenotypic information from the UK Biobank and transcriptomic profiles from the Genotype-Tissue Expression project to test the association of genetically regulated TTR gene expression with 7149 traits assessed in 420,531 individuals. We conducted a multi-tissue analysis of TTR transcription and identified an association with a operational procedure related to bone fracture (p = 5.46×10^-6). Using tissue-specific TTR expression information, we demonstrated that the association is driven by the genetic regulation of TTR hepatic expression (odds ratio [OR] = 3.46, p = 9.51×10^-5). Using the UK Biobank electronic health records (EHRs), we investigated the comorbidities affecting individuals undergoing this surgical procedure. Excluding bone fracture EHRs, we identified a pattern of health outcomes previously associated with ATTR manifestations. These included osteoarthritis (OR = 3.18, p = 9.18×10^-8), carpal tunnel syndrome (OR = 2.15, p = .002), and a history of gastrointestinal diseases (OR = 2.01, p = 8.07×10^-4). In conclusion, our study supports that TTR hepatic expression can affect health outcomes linked to physiological and pathological processes presumably related to the encoded protein.

The role of transthyretin in cell biology: impact on human pathophysiology

Transthyretin (TTR) is an extracellular protein mainly produced in the liver and choroid plexus, with a well-stablished role in the transport of thyroxin and retinol throughout the body and brain. TTR is prone to aggregation, as both wild-type and mutated forms of the protein can lead to the accumulation of amyloid deposits, resulting in a disease called TTR amyloidosis. Recently, novel activities for TTR in cell biology have emerged, ranging from neuronal health preservation in both central and peripheral nervous systems, to cellular fate determination, regulation of proliferation and metabolism. Here, we review the novel literature regarding TTR new cellular effects. We pinpoint TTR as major player on brain health and nerve biology, activities that might impact on nervous systems pathologies, and assign a new link between TTR and angiogenesis and cancer. We also explore the molecular mechanisms underlying TTR activities at the cellular level, and suggest that these might go beyond its most acknowledged carrier functions and include interaction with receptors and activation of intracellular signaling pathways.

N-Terminomics Strategies for Protease Substrates Profiling

Proteases play a central role in various biochemical pathways catalyzing and regulating key biological events. Proteases catalyze an irreversible post-translational modification called proteolysis by hydrolyzing peptide bonds in proteins. Given the destructive potential of proteolysis, protease activity is tightly regulated. Dysregulation of protease activity has been reported in numerous disease conditions, including cancers, neurodegenerative diseases, inflammatory conditions, cardiovascular diseases, and viral infections. The proteolytic profile of a cell, tissue, or organ is governed by protease activation, activity, and substrate specificity. Thus, identifying protease substrates and proteolytic events under physiological conditions can provide crucial information about how the change in protease regulation can alter the cellular proteolytic landscape. In recent years, mass spectrometry-based techniques called N-terminomics have become instrumental in identifying protease substrates from complex biological mixtures. N-terminomics employs the labeling and enrichment of native and neo-N-termini peptides, generated upon proteolysis followed by mass spectrometry analysis allowing protease substrate profiling directly from biological samples. In this review, we provide a brief overview of N-terminomics techniques, focusing on their strengths, weaknesses, limitations, and providing specific examples where they were successfully employed to identify protease substrates in vivo and under physiological conditions. In addition, we explore the current trends in the protease field and the potential for future developments.

Transthyretin: From Structural Stability to Osteoarticular and Cardiovascular Diseases

Transthyretin (TTR) is a tetrameric protein transporting hormones in the plasma and brain, which has many other activities that have not been fully acknowledged. TTR is a positive indicator of nutrition status and is negatively correlated with inflammation. TTR is a neuroprotective and oxidative-stress-suppressing factor. The TTR structure is destabilized by mutations, oxidative modifications, aging, proteolysis, and metal cations, including Ca2+. Destabilized TTR molecules form amyloid deposits, resulting in senile and familial amyloidopathies. This review links structural stability of TTR with the environmental factors, particularly oxidative stress and Ca2+, and the processes involved in the pathogenesis of TTR-related diseases. The roles of TTR in biomineralization, calcification, and osteoarticular and cardiovascular diseases are broadly discussed. The association of TTR-related diseases and vascular and ligament tissue calcification with TTR levels and TTR structure is presented. It is indicated that unaggregated TTR and TTR amyloid are bound by vicious cycles, and that TTR may have an as yet undetermined role(s) at the crossroads of calcification, blood coagulation, and immune response.

Transthyretin contributes to insulin resistance and diminishes exercise-induced insulin sensitivity in obese mice by inhibiting AMPK activity in skeletal muscle

Exercise improves obesity-induced insulin resistance and metabolic disorders via mechanisms that remain unclear. Here, we show that the levels of the hepatokine transthyretin (TTR) in circulation are elevated in insulin-resistant individuals including high-fat diet (HFD)-induced obese mice, db/db mice, and patients with metabolic syndrome. Liver Ttr mRNA and circulating TTR levels were reduced in mice by treadmill training, as was the TTR levels in quadriceps femoris muscle; however, AMP-activated protein kinase (AMPK) signaling activity was enhanced. Transgenic overexpression of TTR or injection of purified TTR triggered insulin resistance in mice fed on regular chow (RC). Furthermore, TTR overexpression reduced the beneficial effects of exercise on insulin sensitivity in HFD-fed mice. TTR was internalized by muscle cells via the membrane receptor Grp78 and the internalization into the quadriceps femoris was reduced by treadmill training. The TTR/Grp78 combination in C2C12 cells was increased, whereas the AMPK activity of C2C12 cells was decreased as the TTR concentration rose. In addition, Grp78 silencing prevented the TTR internalization and reversed its inhibitory effect on AMPK activity in C2C12 cells. Our study suggests that elevated circulating TTR may contribute to insulin resistance and counteract the exercise-induced insulin sensitivity improvement; the TTR suppression might be an adaptive response to exercise through enhancing AMPK activity in skeletal muscles.NEW & NOTEWORTHY Exercise improves obesity-induced insulin resistance via mechanisms that remain unclear. The novel findings of the study are that circulating TTR (a hepatokine) level is decreased by exercise, and the elevated circulating TTR, as was the elevated transthyretin internalization mediated by Grp78, counteracts the exercise-induced insulin sensitivity by downregulating AMPK activity in skeletal muscle of obese mice. These data suggest that TTR suppression might be an adaptive response to exercise through the crosstalk between liver and muscle.

Physiological Metals Can Induce Conformational Changes in Transthyretin Structure: Neuroprotection or Misfolding Induction?

Transthyretin (TTR) is a plasma homotetrameric protein that transports thyroxine and retinol. TTR itself, under pathological conditions, dissociates into partially unfolded monomers that aggregate and form fibrils. Metal ions such as Zn2+, Cu2+, Fe2+, Mn2+ and Ca2+ play a controversial role in the TTR amyloidogenic pathway. TTR is also present in cerebrospinal fluid (CSF), where it behaves as one of the major Aβ-binding-proteins. The interaction between TTR and Aβ is stronger in the presence of high concentrations of Cu2+. Crystals of TTR, soaked in solutions of physiological metals such as Cu2+ and Fe2+, but not Mn2+, Zn2+, Fe3+, Al3+, Ni2+, revealed an unusual conformational change. Here, we investigate the effects that physiological metals have on TTR, in order to understand if metals can induce a specific and active conformation of TTR that guides its Aβ-scavenging role. The capability of certain metals to induce and accelerate its amyloidogenic process is also discussed.

The interaction of zinc with the multi-functional plasma thyroid hormone distributor protein, transthyretin: evolutionary and cross-species comparative aspects

A considerable body of evidence has been accumulated showing the interrelationship between zinc and the plasma thyroid hormone (TH) distributor protein, transthyretin (TTR). TTR is a multi-functional protein, which emerged from 5-hydroxyisourate hydrolase (HIUHase) by neo-functionalization after gene duplication during early chordate evolution. HIUHase is also a zinc-binding protein. Most biochemical and molecular biological findings have been obtained from mammalian studies. However, in the past two decades, it has become clear that fish TTR displays zinc-dependent TH binding. After a brief introduction on plasma zinc, THs and their binding proteins, this review will focus on the role of zinc in TTR functions of various vertebrates. In particular primitive fish TTR has an extremely high zinc content, with an increased number of histidine residues which are involved in TH binding. However, zinc-dependent TH binding may have been gradually lost from TTRs during higher vertebrate evolution. Although human TTR has a low zinc content, zinc plays an essential role in TTR functions other than TH binding: the stability of TTR-holo retinol binding protein 4 (holoRBP4) complex, TTR amyloidogenesis, the sequestration of amyloid β (Aβ) fibrils and cryptic proteolytic activity. The interaction of TTR with metallothioneins may be a critical step in the exertion of some of these functions. Evolutionary and physiological insights on zinc-dependent functions of TTRs are also discussed.

Effects of lipoproteins on endothelial cells and macrophages function and its possible implications on fetal adverse outcomes associated to maternal hypercholesterolemia during pregnancy

Hypercholesterolemia is one of the main risk factors associated with atherosclerosis and cardiovascular disease, the leading cause of death worldwide. During pregnancy, maternal hypercholesterolemia develops, and it can occur in a physiological (MPH) or supraphysiological (MSPH) manner, where MSPH is associated with endothelial dysfunction and early atherosclerotic lesions in the fetoplacental vasculature. In the pathogenesis of atherosclerosis, endothelial activation and endothelial dysfunction, characterized by an imbalance in the bioavailability of nitric oxide, contribute to the early stages of this disease. Macrophages conversion to foam cells, cholesterol efflux from these cells and its differentiation into a pro- or anti-inflammatory phenotype are also important processes that contribute to atherosclerosis. In adults it has been reported that native and modified HDL and LDL play an important role in endothelial and macrophage function. In this review it is proposed that fetal lipoproteins could be also relevant factors involved in the detrimental vascular effects described in MSPH. Changes in the composition and function of neonatal lipoproteins compared to adults has been reported and, although in MSPH pregnancies the fetal lipid profile does not differ from MPH, differences in the lipidomic profiles of umbilical venous blood have been reported, which could have implications in the vascular function. In this review we summarize the available information regarding the effects of lipoproteins on endothelial and macrophage function, emphasizing its possible implications on fetal adverse outcomes associated to maternal hypercholesterolemia during pregnancy.

Transthyretin Stabilization: An Emerging Strategy for the Treatment of Alzheimer's Disease?

Transthyretin (TTR), previously named prealbumin is a plasma protein secreted mainly by the liver and choroid plexus (CP) that is a carrier for thyroid hormones (THs) and retinol (vitamin A). The structure of TTR, with four monomers rich in β-chains in a globular tetrameric protein, accounts for the predisposition of the protein to aggregate in fibrils, leading to a rare and severe disease, namely transthyretin amyloidosis (ATTR). Much effort has been made and still is required to find new therapeutic compounds that can stabilize TTR ("kinetic stabilization") and prevent the amyloid genetic process. Moreover, TTR is an interesting therapeutic target for neurodegenerative diseases due to its recognized neuroprotective properties in the cognitive impairment context and interestingly in Alzheimer's disease (AD). Much evidence has been collected regarding the neuroprotective effects in AD, including through in vitro and in vivo studies as well as a wide range of clinical series. Despite this supported hypothesis of neuroprotection for TTR, the mechanisms are still not completely clear. The aim of this review is to highlight the most relevant findings on the neuroprotective role of TTR, and to summarize the recent progress on the development of TTR tetramer stabilizers.

Plasma Proteome Profiling of Coronary Artery Disease Patients: Downregulation of Transthyretin-An Important Event

Coronary artery disease (CAD) is a prevalent chronic inflammatory cardiac disorder. An early diagnosis is likely to help in the prevention and proper management of this disease. As the study of proteomics provides the potential markers for detection of a disease, in the present investigation, attempt has been made to identify disease-associated differential proteins involved in CAD pathogenesis. For this study, a total of 200 selected CAD patients were considered, who were recruited for percutaneous coronary intervention (PCI) treatment. The proteomic analysis was performed using two-dimensional gel electrophoresis (2-DE) and MALDI-TOF MS/MS. Samples were also subjected to Western blot analysis, enzyme-linked immunosorbent assay (ELISA), peripheral blood mononuclear cells isolation immunofluorescence (IF) analysis, analytical screening by fluorescence-activated cell sorting (FACS), and in silico analysis. The representative data were shown as mean ± SD of at least three experiments. A total of 19 proteins were identified. Among them, the most abundant five proteins (serotransferrin, talin-1, alpha-2HS glycoprotein, transthyretin (TTR), fibrinogen-α chain) were found to have altered level in CAD. Serotransferrin, talin-1, alpha-2HS glycoprotein, and transthyretin (TTR) were found to have lower level, whereas fibrinogen-α chain was found to have higher level in CAD plasma compared to healthy, confirmed by Western blot analysis. TTR, an important acute phase transport protein, was validated low level in 200 CAD patients who confirmed to undergo PCI treatment. Further, in silico and in vitro studies of TTR indicated a downexpression of CAD in plasma as compared to the plasma of healthy individuals. Lower level of plasma TTR was determined to be an important risk marker in the atherosclerotic-approved CAD patients. We suggest that the TTR lower level predicts disease severity and hence may serve as an important marker tool for CAD screening. However, further large-scale studies are required to determine the clinical significance of TTR.

Association between transthyretin concentrations and gestational diabetes mellitus in Chinese women

BACKGROUND

Transthyretin (TTR) is considered to be associated with insulin resistance in humans. This study aimed to investigate TTR level in gestational diabetes mellitus (GDM) and its association with glucose metabolism.

METHODS

Fifty pregnant women with GDM and 47 pregnant women with normal glucose tolerance matched for body mass index and age were enrolled in this study. Their blood samples were collected to detect TTR, retinol-binding protein 4 (RBP4), and their association with glucose and lipid metabolism.

RESULTS

Serum TTR levels in the GDM group were significantly higher than those in the control group (median, 93.44 [interquartile range, 73.81, 117.79] μg/ml vs. 80.83 [74.19, 89.38] μg/ml; P = 0.006). GDM subjects had a lower RBP4/TTR ratio than the control subjects (median, 517.57 [interquartile range, 348.38, 685.27] vs. 602.56 [460.28, 730.62]; P = 0.02). The serum TTR concentrations were positively associated with neonatal weight (r = 0.223, P = 0.028), homeostatic model assessment of insulin resistance (r = 0.246, P = 0.015), and fasting blood glucose (FBG) (r = 0.363, P < 0.001). In stepwise multivariate linear regression analysis, FBG (standardized beta = 0.27, P = 0.004) and neonatal weight (standardized beta = 0.345, P < 0.001) were independent predictors of serum TTR concentrations. Additionally, FBG (standardized beta = - 0.306, P = 0.002) and triglyceride (TG) (beta = 0.219, P = 0.025) were independently associated with RBP4/TTR ratio.

CONCLUSIONS

Serum TTR concentrations were significantly higher in women with GDM than that in women without GDM, suggesting that elevated TTR level may play a role in the pathogenesis of GDM. Meanwhile, TTR was positively and independently associated with FBG and neonatal weight, while FBG and TG were independent predictors of RBP4/TTR ratio. Moreover, serum TTR levels and RBP4/TTR ratio were considered valuable markers of insulin resistance and GDM.

Preoperative prealbumin levels on admission as an independent predictive factor in patients with gastric cancer

BACKGROUND

To explore the role of preoperative prealbumin levels in predicting the prognosis of patients with gastric cancer.

METHODS

A total of 989 gastric cancer patients in the Affiliated Tumour Hospital of Harbin Medical University who underwent gastrectomy were included in this retrospective study. The preoperative prealbumin level, clinicopathological data, and follow-up data were recorded. According to the maximum chi-square survival correlation value, the survival of patients with low preoperative prealbumin (<140 mg/L) and high preoperative prealbumin (≥140 mg/L) were compared using the log-rank test and the Cox proportional hazard regression model.

RESULTS

Based on the best cut-off value of 140 mg/L, we divided the patients into the lower prealbumin group (<140 mg/L) and the higher prealbumin group (≥140 mg/L). Compared with the higher prealbumin group, the lower prealbumin group were older and had larger tumor volumes, lower hemoglobin (Hb) levels, and more upper gastric cancer tumors. The univariate analysis showed that prealbumin and other clinicopathological factors, including age, hemoglobin, tumor size, macroscopic type, cell differentiation, liver metastasis, operation type, N stage, and T stage, were significant prognostic factors. The multivariable analysis showed that age, prealbumin, macroscopic type, location, T stage, and N stage were independent prognostic factors.

CONCLUSIONS

The preoperative prealbumin level was an independent prognostic factor for patients with gastric cancer. The preoperative prealbumin level can be used to predict the prognosis of patients with gastric cancer and guide clinical practice.

The catalytic kinetics of chicken transthyretin towards human Aβ1-42

The novel property of transthyretin (TTR) as a protease has been proposed to be significant. However, the study of TTR proteolysis properties has not been completely elucidated. Herein, we first report the catalytic activity of chicken TTR from plasma determined by using fluorescently labeled amyloid beta 1-42 peptide (Aβ_1-42), and compared it with human TTR (human TTR) from plasma and recombinant Crocodylus porosus TTR. The enzyme kinetic study revealed that the affinity for Aβ_1-42 of chicken TTR and C. porosus TTR (K_M values were 12.72 ± 0.27 μM and 16.21 ± 0.02 μM, respectively) were significantly lower than human TTR (K_M was 43.05 ± 0.39 μM). In addition, the catalytic efficiency of chicken TTR (K_cat/K_M was 310,386.87 ± 13,627.12 M^-1 s^-1) was 4.3 and 5.5 folds higher than those of C. porosus TTR and human TTR (K_cat/K_M were 72,893.80 ± 355.74 M^-1 s^-1 and 56,519.12 ± 5009.50 M^-1 s^-1, respectively), respectively. These results does not only indicated the relationship between structure and the proteolytic activity of TTR, but also suggested a potential development of TTR as a therapeutic anti-Aβ agent.

Elevated Expression of A-Raf and FA2H in Hepatocellular Carcinoma is Associated with Lipid Metabolism Dysregulation and Cancer Progression

BACKGROUND

Identification of events leading to hepatocellular carcinoma (HCC) progression is essential for understanding its pathophysiology. The aims of this study are to identify and characterize differentially expressed proteins in serum of HCC-bearing rats and the corresponding controls during cancer initiation, progression and tumorigenesis.

METHODS

Chemical carcinogens, N-Nitrosodiethylamine and 2-aminoacetylfluorine are administered to induce HCC to male Wistar rats. The 2D-Electrophoresis and PD-Quest analyses are performed to identify several differentially expressed proteins in serum of HCC-bearing animals. These proteins are further characterized by MALDI-TOF-MS/MS analyses. Using pathwaylinker a HCC-specific network is analyzed among the MALDITOF- MS/MS characterized proteins and their interactors.

RESULTS

Carcinogen administration caused inflammation leading to liver injury and HCC development. Liver inflammation was confirmed by increase in the levels of TNF-α and IL-6 in carcinogen treated rats. We report significant increase in expression of two differentially expressed proteins, namely, A-Raf and Fatty Acid 2- Hydroxylase (FA2H), at early stage of HCC initiation, during its progression and at tumor stage. Real-time PCR analysis of mRNA for these proteins confirmed up-regulation of their transcripts. Further, we validated our experimental data with sera of clinically confirmed liver cancer patients.

CONCLUSION

The study suggests that FA2H and A-Raf play a major role in the progression of HCC.

The Extracellular Protein, Transthyretin Is an Oxidative Stress Biomarker

The extracellular protein, transthyretin is responsible for the transport of thyroxin and retinol binding protein complex to the various parts of the body. In addition to this transport function, transthyretin has also been involved in cardiovascular malfunctions, polyneuropathy, psychological disorders, obesity and diabetes, etc. Recent developments have evidenced that transthyretin has been associated with many other biological functions that are directly or indirectly associated with the oxidative stress, the common hallmark for many human diseases. In this review, we have attempted to address that transthyretin is associated with oxidative stress and could be an important biomarker. Potential future perspectives have also been discussed.

The hypolipidemic effects of Tamarindus indica fruit pulp extract in normal and diet-induced hypercholesterolemic hamsters are associated with altered levels of serum proteins

The hypolipidemic effects of Tamarindus indica fruit pulp extract (Ti-FPE) have been earlier reported but the underlying molecular mechanisms are still uncertain. In this study, hamsters fed with Ti-FPE, both in the absence and presence of high-cholesterol diet, were shown to have significantly reduced levels of serum triglyceride, LDL-C and total cholesterol. The Ti-FPE-fed non-hypercholesterolemic hamsters also showed significant enhanced levels of serum apolipoprotein A1, antithrombin III, transferrin and vitamin D binding protein. In diet-induced hypercholesterolemic hamsters, apolipoprotein A1, antithrombin III and transferrin, which were relatively low in levels, became significantly enhanced when the hamsters were fed with Ti-FPE. These Ti-FPE-fed hypercholesterolemic hamsters also showed significant higher levels of serum vitamin D binding protein. When the different treated groups of hamsters were analyzed for the levels of the four serum proteins by ELISA, similar altered abundance were detected. Ingenuity Pathway Analysis of the Ti-FPE modulated serum proteins singled out "Lipid metabolism, molecular transport, small molecule biochemistry" as the top network. Our results suggest that the hypolipidemic effects of Ti-FPE are associated with alterations of serum proteins that are known to be cardioprotective and involved in the metabolism of lipids. The MS data have been deposited to the ProteomeXchange Consortium with the dataset identifier PXD010232.

Mechanisms of action of Coxiella burnetii effectors inferred from host-pathogen protein interactions

Coxiella burnetii is an obligate Gram-negative intracellular pathogen and the etiological agent of Q fever. Successful infection requires a functional Type IV secretion system, which translocates more than 100 effector proteins into the host cytosol to establish the infection, restructure the intracellular host environment, and create a parasitophorous vacuole where the replicating bacteria reside. We used yeast two-hybrid (Y2H) screening of 33 selected C. burnetii effectors against whole genome human and murine proteome libraries to generate a map of potential host-pathogen protein-protein interactions (PPIs). We detected 273 unique interactions between 20 pathogen and 247 human proteins, and 157 between 17 pathogen and 137 murine proteins. We used orthology to combine the data and create a single host-pathogen interaction network containing 415 unique interactions between 25 C. burnetii and 363 human proteins. We further performed complementary pairwise Y2H testing of 43 out of 91 C. burnetii-human interactions involving five pathogen proteins. We used the combined data to 1) perform enrichment analyses of target host cellular processes and pathways, 2) examine effectors with known infection phenotypes, and 3) infer potential mechanisms of action for four effectors with uncharacterized functions. The host-pathogen interaction profiles supported known Coxiella phenotypes, such as adapting cell morphology through cytoskeletal re-arrangements, protein processing and trafficking, organelle generation, cholesterol processing, innate immune modulation, and interactions with the ubiquitin and proteasome pathways. The generated dataset of PPIs-the largest collection of unbiased Coxiella host-pathogen interactions to date-represents a rich source of information with respect to secreted pathogen effector proteins and their interactions with human host proteins.

Hemostatic properties and protein expression profile of therapeutic apheresis plasma treated with amotosalen and ultraviolet A for pathogen inactivation

BACKGROUND

The INTERCEPT Blood System (IBS) using amotosalen-HCl and ultraviolet (UV)A inactivates a large spectrum of microbial pathogens and white blood cells in therapeutic plasma. Our aim was to evaluate to what extent IBS modifies the capacity of plasma to generate thrombin and induces qualitative or quantitative modifications of plasma proteins.

STUDY DESIGN AND METHODS

Plasma units from four donors were collected by apheresis. Samples were taken before (control [CTRL]) and after IBS treatment and stored at -80°C until use. The activities of plasma coagulation factors and inhibitors and the thrombin generation potential were determined using assays measuring clotting times and the calibrated automated thrombogram (CAT), respectively. The proteomic profile of plasma proteins was examined using a two-dimensional differential in-gel electrophoresis (2D-DIGE) method.

RESULTS

Nearly all of the procoagulant and antithrombotic factors tested retained at least 78% of their initial pre-IBS activity. Only FVII and FVIII displayed a lower level of conservation (67%), which nevertheless remained within the reference range for conventional plasma coagulation factors. The thrombin generation profile of plasma was conserved after IBS treatment. Among the 1331 protein spots revealed by 2D-DIGE analysis, only four were differentially expressed in IBS plasma compared to CTRL plasma and two were identified by mass spectrometric analysis as transthyretin and apolipoprotein A1.

CONCLUSION

The IBS technique for plasma moderately decreases the activities of plasma coagulation factors and antithrombotic proteins, with no impact on the thrombin generation potential of plasma and very limited modifications of the proteomic profile.

Network-Based Analysis on Orthogonal Separation of Human Plasma Uncovers Distinct High Density Lipoprotein Complexes

High density lipoprotein (HDL) particles are blood-borne complexes whose plasma levels have been associated with protection from cardiovascular disease (CVD). Recent studies have demonstrated the existence of distinct HDL subspecies; however, these have been difficult to isolate and characterize biochemically. Here, we present the first report that employs a network-based approach to systematically infer HDL subspecies. Healthy human plasma was separated into 58 fractions using our previously published three orthogonal chromatography techniques. Similar local migration patterns among HDL proteins were captured with a novel similarity score, and individual comigration networks were constructed for each fraction. By employing a graph mining algorithm, we identified 183 overlapped cliques, among which 38 were further selected as candidate HDL subparticles. Each of these 38 subparticles had at least two literature supports. In addition, GO function enrichment analysis showed that they were enriched with fundamental biological and CVD protective functions. Furthermore, gene knockout experiments in mouse model supported the validity of these subparticles related to three apolipoproteins. Finally, analysis of an apoA-I deficient human patient's plasma provided additional support for apoA-I related complexes. Further biochemical characterization of these putative subspecies may facilitate the mechanistic research of CVD and guide targeted therapeutics aimed at its mitigation.

Differential regulation of urine proteins in urothelial neoplasm

Urothelial neoplasm of the urinary bladder has a high rate of multifocality and recurrence. To understand this we first need to understand the changes in the molecular level that distinguishes a normal individual from a patient and also a low grade neoplasm from a high grade. In this work we aim to study the urine proteome of Indian patients with urothelial neoplasm categorised on the basis of their p53 immunohistochemistry. The urine samples of pre-operative patients were subjected to two dimensional gel electrophoresis followed by densitometric analysis and spot identification using MALDI mass spectrometry. Our study shows that few proteins such as albumin, alpha 1 antitrypsin, apolipoprotein A1, transferrin, transthyretin, haptoglobin and haemoglobin β chain were upregulated and inter alpha trypsin inhibitor heavy chain was downregulated in the disease samples. Further we have reported that some of these proteins show an association with disease severity. The present study marks the first step in the identification of new diagnostic markers as well as therapeutic targets.

BIOLOGICAL SIGNIFICANCE

Bladder carcinoma is the ninth most common cancer worldwide. It has gained attention within both clinicians and cancer biologists because of its recurrence and mortality rate. Identifying the prognostic factors of progression is a challenge, so that high risk patients who may be a candidate for a radical cystectomy may be identified. In this study we have attempted to study the changes observed in the urinary protein levels of urothelial neoplasm patients. The samples were graded based on p53 immunohistochemistry staining. We have reported eight (8) proteins, mostly highly abundant; those have exhibited differential regulation in case of diseased samples. This study is first of its kind that associates the changes in the urinary protein levels to that of the severity of the disease. We believe that the findings can be used as a stepping stone in the development of a noninvasive prognostic tool for the disease. This article is part of a Special Issue entitled: Proteomics in India.

Transthyretin Antisense Oligonucleotides Lower Circulating RBP4 Levels and Improve Insulin Sensitivity in Obese Mice

Circulating transthyretin (TTR) is a critical determinant of plasma retinol-binding protein 4 (RBP4) levels. Elevated RBP4 levels cause insulin resistance, and the lowering of RBP4 levels improves glucose homeostasis. Since lowering TTR levels increases renal clearance of RBP4, we determined whether decreasing TTR levels with antisense oligonucleotides (ASOs) improves glucose metabolism and insulin sensitivity in obesity. TTR-ASO treatment of mice with genetic or diet-induced obesity resulted in an 80-95% decrease in circulating levels of TTR and RBP4. Treatment with TTR-ASOs, but not control ASOs, decreased insulin levels by 30-60% and improved insulin sensitivity in ob/ob mice and high-fat diet-fed mice as early as after 2 weeks of treatment. The reduced insulin levels were sustained for up to 9 weeks of treatment and were associated with reduced adipose tissue inflammation. Body weight was not changed. TTR-ASO treatment decreased LDL cholesterol in high-fat diet-fed mice. The glucose infusion rate during a hyperinsulinemic-euglycemic clamp was increased by 50% in high-fat diet-fed mice treated with TTR-ASOs, demonstrating improved insulin sensitivity. This was also demonstrated by 20% greater inhibition of hepatic glucose production, a 45-60% increase of glucose uptake into skeletal and cardiac muscle, and a twofold increase in insulin signaling in muscle. These data show that decreasing circulating TTR levels or altering TTR-RBP4 binding could be a potential therapeutic approach for the treatment of type 2 diabetes.

Pegylation of high-density lipoprotein decreases plasma clearance and enhances antiatherogenic activity

RATIONALE

Infusions of apolipoprotein AI (apoAI), mimetic peptides, or high-density lipoprotein (HDL) remain a promising approach for the treatment of atherosclerotic coronary disease. However, rapid clearance leads to a requirement for repeated administration of large amounts of material and limits effective plasma concentrations.

OBJECTIVE

Because pegylation of purified proteins is commonly used as a method to increase their half-life in the circulation, we determined whether pegylation of apoAI or HDL would increase its plasma half-life and in turn its antiatherogenic potential.

METHODS AND RESULTS

Initial pegylation attempts using lipid-poor apoAI showed a marked tendency to form multi-pegylated (PEG) species with reduced ability to promote cholesterol efflux from macrophage foam cells. However, pegylation of human holo-HDL or reconstituted phospholipid/apoAI particles (rHDL) led to selective N-terminal monopegylation of apoAI with full preservation of cholesterol efflux activity. The plasma clearance of PEG-rHDL was estimated after injection into hypercholesterolemic Apoe-/- mice; the half-life of pegylated PEG-apoAI after injection of PEG-rHDL was increased ≈7-fold compared with apoAI in nonpegylated rHDL. In comparison with nonpegylated rHDL, infusion of PEG-rHDL (40 mg/kg) into hypercholesterolemic Apoe-/- mice led to more pronounced suppression of bone marrow myeloid progenitor cell proliferation and monocytosis, as well as reduced atherosclerosis and a stable plaque phenotype.

CONCLUSIONS

We describe a novel method for effective monopegylation of apoAI in HDL particles, in which lipid binding seems to protect against pegylation of key functional residues. Pegylation of apoAI in rHDL markedly increases its plasma half-life and enhances antiatherogenic properties in vivo.

Studies on the peptidase activity of transthyretin (TTR)

Transthyretin (TTR) is a plasma protein transporter of thyroxine (T(4)) and retinol and also has peptidase activity. In order to characterize TTR peptidase activity we used fluorescence resonance energy transfer (FRET) peptides derived from Abz-KLRSSK-Q-EDDnp and from two portion-mixing libraries as substrates. Most of the susceptible FRET peptides were cleaved at more than one peptide bond, without particular substrate specificity. The more relevant observation was that the peptides containing E or D were cleaved at only one peptide bond and TTR was competitively inhibited by glutathione analog peptide γ-E-A-G-OH that contains two free carboxyl groups. The dependence on ionic interactions of TTR hydrolytic activity was confirmed by the large inhibitory effects of salt and ionic surfactants. TTR was not inhibited by any usual peptidase inhibitors, except by ortho-phenanthroline and EDTA. The mechanism of TTR catalysis was explored by the pH-profile of TTR hydrolytic activity in different temperatures and by proton inventory. The obtained pK and heat of ionization values suggest that a carboxylate and an ammonium group, possibly from a lysine side chain are involved. These results support the recently proposed inducible metalloprotease mechanism for TTR based on its 3D structure in presence of Zn(2+) and a series of point mutations [Liz et al., Biochem. J 443 (2012) 769-778].

Tamarindus indica extract alters release of alpha enolase, apolipoprotein A-I, transthyretin and Rab GDP dissociation inhibitor beta from HepG2 cells

BACKGROUND

The plasma cholesterol and triacylglycerol lowering effects of Tamarindus indica extract have been previously described. We have also shown that the methanol extract of T. indica fruit pulp altered the expression of lipid-associated genes including ABCG5 and APOAI in HepG2 cells. In the present study, effects of the same extract on the release of proteins from the cells were investigated using the proteomics approach.

METHODOLOGY/PRINCIPAL FINDINGS

When culture media of HepG2 cells grown in the absence and presence of the methanol extract of T. indica fruit pulp were subjected to 2-dimensional gel electrophoresis, the expression of seven proteins was found to be significantly different (p<0.03125). Five of the spots were subsequently identified as alpha enolase (ENO1), transthyretin (TTR), apolipoprotein A-I (ApoA-I; two isoforms), and rab GDP dissociation inhibitor beta (GDI-2). A functional network of lipid metabolism, molecular transport and small molecule biochemistry that interconnects the three latter proteins with the interactomes was identified using the Ingenuity Pathways Analysis software.

CONCLUSION/SIGNIFICANCE

The methanol extract of T. indica fruit pulp altered the release of ENO1, ApoA-I, TTR and GDI-2 from HepG2 cells. Our results provide support on the effect of T. indica extract on cellular lipid metabolism, particularly that of cholesterol.

Transthyretin is a metallopeptidase with an inducible active site

TTR (transthyretin) was found recently to possess proteolytic competency besides its well-known transport capabilities. It was described as a cryptic serine peptidase cleaving multiple natural substrates (including β-amyloid and apolipoprotein A-I) involved in diseases such as Alzheimer's disease and atherosclerosis. In the present study, we aimed to elucidate the catalytic machinery of TTR. All attempts to identify a catalytic serine residue were unsuccessful. However, metal chelators abolished TTR activity. Proteolytic inhibition by EDTA or 1,10-phenanthroline could be reversed with Zn2+ and Mn2+. These observations, supported by analysis of three-dimensional structures of TTR complexed with Zn2+, led to the hypothesis that TTR is a metallopeptidase. Site-directed mutagenesis of selected amino acids unambiguously confirmed this hypothesis. The TTR active site is inducible and constituted via a protein rearrangement resulting in ~7% of proteolytically active TTR at pH 7.4. The side chain of His88 is shifted near His90 and Glu92 establishing a Zn2+-chelating pattern HXHXE not found previously in any metallopeptidase and only conserved in TTR of humans and some other primates. Point mutations of these three residues yielded proteins devoid of proteolytic activity. Glu72 was identified as the general base involved in activation of the catalytic water. Our results unveil TTR as a metallopeptidase and define its catalytic machinery.

Transthyretin: roles in the nervous system beyond thyroxine and retinol transport

Transthyretin (TTR) is a plasma- and cerebrospinal fluid-circulating protein. Besides the primordially attributed systemic role as a transporter molecule of thyroxine (T₄) and retinol (through the binding to retinol-binding protein [RBP]), TTR has been recognized as a protein with important functions in several aspects of the nervous system physiology. TTR has been shown to play an important role in behavior, cognition, amidated neuropeptide processing and nerve regeneration. Furthermore, it has been proposed that TTR is neuroprotective in Alzheimer's disease and cerebral ischemia. Mutations in TTR are a well-known cause of familial amyloidotic polyneuropathy, an autosomal dominant neurodegenerative disorder characterized by systemic deposition of TTR amyloid fibrils, particularly in the peripheral nervous system. The purpose of this review is to highlight the roles of TTR in the nervous system, beyond its systemic role as a transporter molecule of T₄ and RBP-retinol.

Proteomic profile of human aortic stenosis: insights into the degenerative process

Degenerative aortic stenosis is the most common worldwide cause of valve replacement. While it shares certain risk factors with coronary artery disease, it is not delayed or reversed by reducing exposure to risk factors (e.g., therapies that lower lipids). Therefore, it is necessary to better understand its pathophysiology for preventive measures to be taken. In this work, aortic valve samples were collected from 20 patients that underwent aortic valve replacement (55% males, mean age of 74 years) and 20 normal control valves were obtained from necropsies (40% males, mean age of 69 years). The proteome of the samples was analyzed by quantitative differential electrophoresis (2D-DIGE) and mass spectrometry, and 35 protein species were clearly increased in aortic valves, including apolipoprotein AI, alpha-1-antitrypsin, serum albumin, lumican, alfa-1-glycoprotein, vimentin, superoxide dismutase Cu-Zn, serum amyloid P-component, glutathione S-transferase-P, fatty acid-binding protein, transthyretin, and fibrinogen gamma. By contrast, 8 protein species were decreased (transgelin, haptoglobin, glutathione peroxidase 3, HSP27, and calreticulin). All of the proteins identified play a significant role in cardiovascular processes, such as fibrosis, homeostasis, and coagulation. The significant changes observed in the abundance of key cardiovascular proteins strongly suggest that they can be involved in the pathogenesis of degenerative aortic stenosis. Further studies are warranted to better understand this process before we can attempt to modulate it.

The fibrillogenic L178H variant of apolipoprotein A-I forms helical fibrils

A number of amyloidogenic variants of apoA-I have been discovered but most have not been analyzed. Previously, we showed that the G26R mutation of apoA-I leads to increased β-strand structure, increased N-terminal protease susceptibility, and increased fibril formation after several days of incubation. In vivo, this and other variants mutated in the N-terminal domain (residues 26 to ∼90) lead to renal and hepatic accumulation. In contrast, several mutations identified within residues 170 to 178 lead to cardiac, laryngeal, and cutaneous protein deposition. Here, we describe the structural changes in the fibrillogenic variant L178H. Like G26R, the initial structure of the protein exhibits altered tertiary conformation relative to wild-type protein along with decreased stability and an altered lipid binding profile. However, in contrast to G26R, L178H undergoes an increase in helical structure upon incubation at 37°C with a half time (t_1/2) of about 12 days. Upon prolonged incubation, the L178H mutant forms fibrils of a diameter of 10 nm that ranges in length from 30 to 120 nm. These results show that apoA-I, known for its dynamic properties, has the ability to form multiple fibrillar conformations, which may play a role in the tissue-specific deposition of the individual variants.

Transthyretin and the brain re-visited: is neuronal synthesis of transthyretin protective in Alzheimer's disease?

Since the mid-1990's a trickle of publications from scattered independent laboratories have presented data suggesting that the systemic amyloid precursor transthyretin (TTR) could interact with the amyloidogenic β-amyloid (Aβ) peptide of Alzheimer's disease (AD). The notion that one amyloid precursor could actually inhibit amyloid fibril formation by another seemed quite far-fetched. Further it seemed clear that within the CNS, TTR was only produced in choroid plexus epithelial cells, not in neurons. The most enthusiastic of the authors proclaimed that TTR sequestered Aβ in vivo resulting in a lowered TTR level in the cerebrospinal fluid (CSF) of AD patients and that the relationship was salutary. More circumspect investigators merely showed in vitro interaction between the two molecules. A single in vivo study in Caenorhabditis elegans suggested that wild type human TTR could suppress the abnormalities seen when Aβ was expressed in the muscle cells of the worm. Subsequent studies in human Aβ transgenic mice, including those from our laboratory, also suggested that the interaction reduced the Aβ deposition phenotype. We have reviewed the literature analyzing the relationship including recent data examining potential mechanisms that could explain the effect. We have proposed a model which is consistent with most of the published data and current notions of AD pathogenesis and can serve as a hypothesis which can be tested.

Extracellular modifications of HDL in vivo and the emerging concept of proteolytic inactivation of preβ-HDL

PURPOSE OF REVIEW

Both quantity and quality of the circulating HDL particle matter for the optimal antiatherogenic potential of HDL. This review summarizes various mechanisms capable of inducing extracellular modifications of HDL and reducing the function of HDL subclasses as cholesterol acceptors. Special emphasis is laid on the proteolytic inactivation of lipid-poor preβ-migrating HDL (preβ-HDL).

RECENT FINDINGS

HDL particles can undergo functional inactivation in vivo. During atherogenesis, different cell types in the arterial intima release enzymes into the intimal fluid, potentially capable of causing structural and chemical modifications of the various components present in the lipid core or in the polar surface of the HDL particles. Enzymatic oxidation, lipolysis and proteolysis, and nonenzymatic glycosylation are among the HDL modifications that adversely affect HDL functionality. Proteolysis of preβ-HDL by various proteases present in the arterial intima has emerged as a potential mechanism that impairs the efficiency of HDL to promote cholesterol efflux from macrophage foam cells, the mast cell-derived neutral protease chymase being a prime example of such impairment. A paradigm of proteolytic inactivation of preβ-HDL in vivo is emerging.

SUMMARY

Several extracellular enzymes present in the arterial intima may compromise various cardioprotective functions of HDL. Observations on proteolysis of specific lipid-poor HDL subpopulations in vivo constitute the basis for future studies evaluating the actual impact of proteolytic microenvironments on the initiation and progression of atherosclerotic lesions.

Human apolipoprotein A-I-derived amyloid: its association with atherosclerosis

Amyloidoses constitute a group of diseases in which soluble proteins aggregate and deposit extracellularly in tissues. Nonhereditary apolipoprotein A-I (apoA-I) amyloid is characterized by deposits of nonvariant protein in atherosclerotic arteries. Despite being common, little is known about the pathogenesis and significance of apoA-I deposition. In this work we investigated by fluorescence and biochemical approaches the impact of a cellular microenvironment associated with chronic inflammation on the folding and pro-amyloidogenic processing of apoA-I. Results showed that mildly acidic pH promotes misfolding, aggregation, and increased binding of apoA-I to extracellular matrix elements, thus favoring protein deposition as amyloid like-complexes. In addition, activated neutrophils and oxidative/proteolytic cleavage of the protein give rise to pro amyloidogenic products. We conclude that, even though apoA-I is not inherently amyloidogenic, it may produce non hereditary amyloidosis as a consequence of the pro-inflammatory microenvironment associated to atherogenesis.

Modified apolipoprotein (apo) A-I by artificial sweetener causes severe premature cellular senescence and atherosclerosis with impairment of functional and structural properties of apoA-I in lipid-free and lipid-bound state

Long-term consumption of artificial sweeteners (AS) has been the recent focus of safety concerns. However, the potential risk of the AS in cardiovascular disease and lipoprotein metabolism has not been investigated sufficiently. We compared the influence of AS (aspartame, acesulfame K, and saccharin) and fructose in terms of functional and structural correlations of apolipoprotein (apo) A-I and high-density lipoproteins (HDL), which have atheroprotective effects. Long-term treatment of apoA-I with the sweetener at physiological concentration (3 mM for 168 h) resulted in loss of antioxidant and phospholipid binding activities with modification of secondary structure. The AS treated apoA-I exhibited proteolytic cleavage to produce 26 kDa-fragment. They showed pro-atherogenic properties in acetylated LDL phagocytosis of macrophages. Each sweetener alone or sweetener-treated apoA-I caused accelerated senescence in human dermal fibroblasts. These results suggest that long-term consumption of AS might accelerate atherosclerosis and senescence via impairment of function and structure of apoA-I and HDL.

Detection of chymase-digested C-terminally truncated apolipoprotein A-I in normal human serum

In atherosclerotic artery walls, mast cells, an inflammatory cell, are activated and secrete some proteases including chymase. Chymase, a chymotrypsin-like protease, cleaves the C-terminus of apolipoprotein A-I (apoA-I) at Phe225. This cleavage reduces the ability of apoA-I to promote the efflux of cellular cholesterol. The aim of this study is to detect C-terminally truncated apoA-I in normal human serum. For this purpose, we generated a monoclonal antibody that specifically recognizes C-terminally truncated apoA-I by immunizing mice with a peptide that corresponds to human apoA-I amino acid residues 216-225. The monoclonal antibody, termed 16-4 mAb, selectively reacted with recombinant C-terminally truncated apoA-I, but not recombinant full-length apoA-I. A two-dimensional electrophoresis analysis also indicated that only two out of six spots that contained apoA-I fragments and had a molecular mass of 26 kDa after chymase digestion reacted with the 16-4 mAb. We detected an extremely small amount of C-terminally truncated apoA-I in normal human serum by concentrating the serum through affinity chromatography using a 16-4 mAb-conjugated resin, and then performing Western blot analysis. The 16-4 mAb could be useful to examine whether C-terminally truncated apoA-I is associated with the progression of atherosclerosis.

Association of TTR polymorphisms with hippocampal atrophy in Alzheimer disease families

In vitro and animal model studies suggest that transthyretin (TTR) inhibits the production of the amyloid β protein, a major contributor to Alzheimer disease (AD) pathogenesis. We evaluated the association of 16 TTR single nucleotide polymorphisms (SNPs) with AD risk in 158 African American and 469 Caucasian discordant sibships from the MIRAGE Study. There was no evidence for association of TTR with AD in either population sample. To examine the possibility that TTR SNPs affect specific components of the AD process, we tested association of these SNPs with four measures of neurodegeneration and cerebrovascular disease defined by magnetic resonance imaging (MRI) in a subset of 48 African American and 265 Caucasian sibships. Five of seven common SNPs and several haplotypes were significantly associated with hippocampal atrophy in the Caucasian sample. Two of these SNPs also showed marginal evidence for association in the African American sample. Results for the other MRI traits were unremarkable. This study highlights the potential value of neuroimaging endophenotypes as a tool for finding genes influencing AD pathogenesis.

Urinary proteomics based on capillary electrophoresis-coupled mass spectrometry in kidney disease: discovery and validation of biomarkers, and clinical application

Use of capillary electrophoresis coupled to mass spectrometry (CE-MS) technology in proteome analysis has increased, with a focus on the identification of biomarker peptides in clinical proteomics. Among the reported applications, the main focus is on the urinary biomarkers for kidney disease. In this review, we discuss the principal, theoretical, and practical obstacles that are encountered when using CE-MS for the analysis of body fluids for biomarker discovery. We present several examples of a successful application of CE-MS for biomarker discovery in kidney disease, implications for disease diagnosis, prognosis, and therapy evaluation, and will also discuss current challenges and possible future improvements.

Aboard transthyretin: From transport to cleavage

Transthyretin (TTR) is a plasma and cerebrospinal fluid protein mainly recognized as the transporter of thyroxine (T(4)) and retinol. Mutated TTR leads to familial amyloid polyneuropathy, a neurodegenerative disorder characterized by TTR amyloid deposition particularly in peripheral nerves. Beside its transport activities, TTR is a cryptic protease and participates in the biology of the nervous system. Several studies have been directed at finding new ligands of TTR to further explore the biology of the protein. From the identified ligands, some were in fact TTR protease substrates. In this review, we will discuss the existent information concerning TTR ligands/substrates.

Sampling the N-terminal proteome of human blood

The proteomes of blood plasma and serum represent a potential gold mine of biological and diagnostic information, but challenges such as dynamic range of protein concentration have hampered efforts to unlock this resource. Here we present a method to label and isolate N-terminal peptides from human plasma and serum. This process dramatically reduces the complexity of the sample by eliminating internal peptides. We identify 772 unique N-terminal peptides in 222 proteins, ranging over six orders of magnitude in abundance. This approach is highly suited for studying natural proteolysis in plasma and serum. We find internal cleavages in plasma proteins created by endo- and exopeptidases, providing information about the activities of proteolytic enzymes in blood, which may be correlated with disease states. We also find signatures of signal peptide cleavage, coagulation and complement activation, and other known proteolytic processes, in addition to a large number of cleavages that have not been reported previously, including over 200 cleavages of blood proteins by aminopeptidases. Finally, we can identify substrates from specific proteases by exogenous addition of the protease combined with N-terminal isolation and quantitative mass spectrometry. In this way we identified proteins cleaved in human plasma by membrane-type serine protease 1, an enzyme linked to cancer progression. These studies demonstrate the utility of direct N-terminal labeling by subtiligase to identify and characterize endogenous and exogenous proteolysis in human plasma and serum.

Transthyretin in peripheral nerve regeneration

Transthyretin (TTR) is the protein transporter of thyroxine and retinol. Several TTR mutations are associated with familial amyloid polyneuropathy, a neurodegenerative disorder characterized by extracellular deposition of TTR aggregates and fibrils in the peripheral nervous system. Several reports suggest new TTR functions in the nervous system particularly in nerve regeneration and in neuroprotection in Alzheimer’s disease. The fact that TTR increases axonal growth during peripheral nervous system, regeneration and allows an appropriate retrograde transport may represent the missing link explaining the preferential deposition of mutated TTR in the peripheral nervous system of familial amyloid polyneuropathy patients. This paper discusses the details explaining the role of TTR during nerve regeneration.

Evolutionary changes to transthyretin: structure-function relationships

Transthyretin is one of the three major thyroid hormone-binding proteins in plasma and/or cerebrospinal fluid of vertebrates. It transports retinol via binding to retinol-binding protein, and exists mainly as a homotetrameric protein of approximately 55 kDa in plasma. The first 3D structure of transthyretin was an X-ray crystal structure from human transthyretin. Elucidation of the structure-function relationship of transthyretin has been of significant interest since its highly conserved structure was shown to be associated with several aspects of metabolism and with human diseases such as amyloidosis. Transthyretin null mice do not have an overt phenotype, probably because transthyretin is part of a network with other thyroid hormone distributor proteins. Systematic study of the evolutionary changes of transthyretin structure is an effective way to elucidate its function. This review summarizes current knowledge about the evolution of structural and functional characteristics of vertebrate transthyretins. The molecular mechanism of evolutionary change and the resultant effects on the function of transthyretin are discussed.