Transthyretin proteins regulate angiogenesis by conferring different molecular identities to endothelial cells

Protein Misfolding in Pregnancy: Current Insights, Potential Mechanisms, and Implications for the Pathogenesis of Preeclampsia

Protein misfolding disorders are a group of diseases characterized by supra-physiologic accumulation and aggregation of pathogenic proteoforms resulting from improper protein folding and/or insufficiency in clearance mechanisms. Although these processes have been historically linked to neurodegenerative disorders, such as Alzheimer's disease, evidence linking protein misfolding to other pathologies continues to emerge. Indeed, the deposition of toxic protein aggregates in the form of oligomers or large amyloid fibrils has been linked to type 2 diabetes, various types of cancer, and, in more recent years, to preeclampsia, a life-threatening pregnancy-specific disorder. While extensive physiological mechanisms are in place to maintain proteostasis, processes, such as aging, genetic factors, or environmental stress in the form of hypoxia, nutrient deprivation or xenobiotic exposures can induce failure in these systems. As such, pregnancy, a natural physical state that already places the maternal body under significant physiological stress, creates an environment with a lower threshold for aberrant aggregation. In this review, we set out to discuss current evidence of protein misfolding in pregnancy and potential mechanisms supporting a key role for this process in preeclampsia pathogenesis. Improving our understanding of this emerging pathophysiological process in preeclampsia can lead to vital discoveries that can be harnessed to create better diagnoses and treatment modalities for the disorder.

Hereditary transthyretin amyloidosis: a comprehensive review with a focus on peripheral neuropathy

Amyloidoses represent a group of diseases characterized by the pathological accumulation in the extracellular area of insoluble misfolded protein material called "amyloid". The damage to the tissue organization and the direct toxicity of the amyloidogenic substrates induce progressive dysfunctions in the organs involved. They are usually multisystem diseases involving several vital organs, such as the peripheral nerves, heart, kidneys, gastrointestinal tract, liver, skin, and eyes. Transthyretin amyloidosis (ATTR) is related to abnormalities of transthyretin (TTR), a protein that acts as a transporter of thyroxine and retinol and is produced predominantly in the liver. ATTR is classified as hereditary (ATTRv) and wild type (ATTRwt). ATTRv is a severe systemic disease of adults caused by mutations in the TTR gene and transmitted in an autosomal dominant manner with incomplete penetrance. Some pathogenic variants in TTR are preferentially associated with a neurological phenotype (progressive peripheral sensorimotor polyneuropathy); others are more frequently associated with restrictive heart failure. However, many mutations express a mixed phenotype with neurological and cardiological involvement. ATTRv is now a treatable disease. A timely and definite diagnosis is essential in view of the availability of effective therapies that have revolutionized the management of affected patients. The purpose of this review is to familiarize the clinician with the disease and with the correct diagnostic pathways in order to obtain an early diagnosis and, consequently, the possibility of an adequate treatment.

Imprinted small nucleolar RNAs: Missing link in development and disease?

The 14q32.2 (DLK1-DIO3) and 15q11-q13 (SNURF-SNRPN) imprinted gene loci harbor the largest known small nucleolar RNA clusters expressed from the respective maternal and paternal alleles. Recent studies have demonstrated significant roles for the 15q11-q13 located SNORD115-SNORD116 C/D box snoRNAs in Prader-Willi syndrome (PWS), a neurodevelopmental disorder. Even though the effect of SNORD116 deletion is apparent in the PWS phenotype, similar effects of a SNORD113-SNORD114 cluster deletion from the 14q32.2 locus in Kagami-Ogata syndrome (KOS14) and upregulation in Temple syndrome (TS14) remain to be explored. Moreover, apart from their probable involvement in neurodevelopmental disorders, snoRNAs from the SNORD113-SNORD114 cluster have been implicated in multiple biological processes, including pluripotency, development, cancers, and RNA modifications. Here we summarize the current understanding of the system to explore the possibility of a link between developmental disorders and C/D box snoRNA expression from the imprinted 14q32.2 locus. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA in Disease and Development > RNA in Development RNA Processing > Processing of Small RNAs.

Gestational Age-Dependent Regulation of Transthyretin in Mice during Pregnancy

Our prior studies have shown that protein misfolding and aggregation in the placenta are linked to the development of preeclampsia, a severe pregnancy complication. We identified transthyretin (TTR) as a key component of the aggregated protein complex. However, the regulation of native TTR in normal pregnancy remains unclear. In this study, we found that pregnant mice exhibited a remarkable and progressive decline in serum TTR levels through gestational day (gd) 12-14, followed by an increase in late pregnancy and postpartum. Meanwhile, serum albumin levels showed a modest but statistically significant increase throughout gestation. TTR protein and mRNA levels in the liver, a primary source of circulating TTR, mirrored the changes observed in serum TTR levels during gestation. Intriguingly, a similar pattern of TTR alteration was also observed in the serum of pregnant women and pregnant interleukin-10-knockout (IL-10-/-) mice with high inflammation background. In non-pregnant IL-10-/- mice, serum TTR levels were significantly lower than those in age-matched wild-type mice. Administration of IL-10 to non-pregnant IL-10-/- mice restored their serum TTR levels. Notably, dysregulation of TTR resulted in fewer implantation units, lower fetal weight, and smaller litter sizes in human TTR-overexpressing transgenic mice. Thus, TTR may play a pivotal role as a crucial regulator in normal pregnancy, and inflammation during pregnancy may contribute to the downregulation of serum TTR presence.

Evidence From Human Placenta, Endoplasmic Reticulum-Stressed Trophoblasts, and Transgenic Mice Links Transthyretin Proteinopathy to Preeclampsia

BACKGROUND

We have demonstrated that protein aggregation plays a pivotal role in the pathophysiology of preeclampsia and identified several aggregated proteins in the circulation of preeclampsia patients, the most prominent of which is the serum protein TTR (transthyretin). However, the mechanisms that underlie protein aggregation remain poorly addressed.

METHODS

We examined TTR aggregates in hypoxia/reoxygenation-exposed primary human trophoblasts (PHTs) and the preeclampsia placenta using complementary approaches, including a novel protein aggregate detection assay. Mechanistic analysis was performed in hypoxia/reoxygenation-exposed PHTs and Ttr transgenic mice overexpressing transgene-encoded wild-type human TTR or Ttr^-/- mice. High-resolution ultrasound analysis was used to measure placental blood flow in pregnant mice.

RESULTS

TTR aggregation was inducible in PHTs and the TCL-1 trophoblast cell line by endoplasmic reticulum stress inducers or autophagy-lysosomal disruptors. PHTs exposed to hypoxia/reoxygenation showed increased intracellular BiP (binding immunoglobulin protein), phosphorylated IRE1α (inositol-requiring enzyme-1α), PDI (protein disulfide isomerase), and Ero-1, all markers of the unfolded protein response, and the apoptosis mediator caspase-3. Blockade of IRE1α inhibited hypoxia/reoxygenation-induced upregulation of Ero-1 in PHTs. Excessive unfolded protein response activation was observed in the early-onset preeclampsia placenta. Importantly, pregnant human TTR mice displayed aggregated TTR in the junctional zone of the placenta and severe preeclampsia-like features. High-resolution ultrasound analysis revealed low blood flow in uterine and umbilical arteries in human TTR mice compared with control mice. However, Ttr^-/- mice did not show any pregnancy-associated abnormalities.

CONCLUSIONS

These observations in the preeclampsia placenta, cultured trophoblasts, and Ttr transgenic mice indicate that TTR aggregation is an important causal contributor to preeclampsia pathophysiology.

Blood transthyretin for predicting immunoglobulin A vasculitis nephritis outcome in children

BACKGROUND

IgA vasculitis is characterized by inflammation of the blood vessels, which can result in microvascular destruction and consequently renal damage. Transthyretin is a newly discovered angiogenesis regulator in promoting microvascular regeneration. This indicates that transthyretin may act as a potential predictor of IgAV as well as IgAVN.

METHODS

This retrospective study included 125 patients newly diagnosed as IgAV with demographic and laboratory parameters. Of these, 78 patients had demonstrated internal organ damage and 47 patients with only skin and joint injury. Of 78 patients with organ impairment, 27 were diagnosed of renal involvement. Then we evaluated the relationship between NLR, total protein, albumin, globulin, transthyretin, B lymphocyte counts and the severity of IgAV.

RESULTS

For patients with internal organ or renal involvement, the level of transthyretin were lower than non-internal organ damage group (p < 0.001 for both group). Remarkably, the NLR was only higher in patients with internal organ damage group (p = 0.019). Logistic regression analysis showed that NLR and transthyretin both were risk factors for internal organ involvement (OR = 1.768, 0.973 separately), and only transthyretin is the independent risk for renal involvement (OR = 0.981, p < 0.05). The ROC analysis showed an AUC of 0.626 for NLR, 0.815 for transthyretin in predicting organ damage, 0.755 for transthyretin in patients with renal involvement (p < 0.05, to all parameters).

CONCLUSIONS

Transthyretin is a better predictor in predicting internal organ or renal involvement than NLR, and low plasma transthyretin concentration can increase the risk of renal involvement in IgAV patients.

Molecular Mechanisms of Cardiac Amyloidosis

Cardiac involvement has a profound effect on the prognosis of patients with systemic amyloidosis. Therapeutic methods for suppressing the production of causative proteins have been developed for ATTR amyloidosis and AL amyloidosis, which show cardiac involvement, and the prognosis has been improved. However, a method for removing deposited amyloid has not been established. Methods for reducing cytotoxicity caused by amyloid deposition and amyloid precursor protein to protect cardiovascular cells are also needed. In this review, we outline the molecular mechanisms and treatments of cardiac amyloidosis.

The Effect of Tafamidis on Circulating Endothelial Progenitor Cells in Patients with Transthyretin Cardiac Amyloidosis

AIMS

Endothelial microvascular dysfunction is a known mechanism of vascular pathology in cardiac amyloidosis (CA). Scientific evidence regarding the possible protective role of the amyloid transthyretin (ATTR) stabilizer, tafamidis, is lacking. Circulating endothelial progenitor cells (cEPCs) have an important role in the process of vascular repair. We aimed to examine the effect of tafamidis on cEPCs.

METHODS AND RESULTS

Study population included patients with ATTR-CA. cEPCs were assessed using flow cytometry by the expression of CD34⁽⁺⁾/CD133⁽⁺⁾ and vascular endothelial growth factor receptor (VEGFR)-2⁽⁺⁾ and by the formation of colony-forming units (CFUs) and production of VEGF. Tests were repeated at pre-specified time-points up to 12 months following the initiation of tafamidis. Included were 18 ATTR-CA patients at a median age of 77 (IQR 71, 85) years and male predominance (n = 15, 83%). Following the initiation of tafamidis and during 12 months of drug treatment, there was a gradual increase in the levels of CD34⁽⁺⁾/VEGFR-2⁽⁺⁾ (0.43 to 2.42% (IQR 1.53, 2.91)%, p = 0.002) and CD133⁽⁺⁾/VEGFR-2⁽⁺⁾ (0.49 to 1.64% (IQR 0.97, 2.90)%, p = 0.004). Functionally, increase in EPCs-CFUs was microscopically evident following treatment with tafamidis (from 0.5 CFUs (IQR 0.0, 1.0) to 3.0 (IQR 1.3, 3.8) p < 0.001) with a concomitant increase in EPC's viability as demonstrated by an MTT assay (from 0.12 (IQR 0.03, 0.16) to 0.30 (IQR 0.18, 0.33), p < 0.001). VEGF levels increased following treatment (from 54 (IQR 52, 72) to 107 (IQR 62, 129) pg/ml, p = 0.039).

CONCLUSIONS

Tafamidis induced the activation of the cEPCs pathway, possibly promoting endothelial repair in ATTR-CA.

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.

Neuroprotection in early stages of Alzheimer's disease is promoted by transthyretin angiogenic properties

Background

While still controversial, it has been demonstrated that vascular defects can precede the onset of other AD hallmarks features, making it an important therapeutic target. Given that the protein transthyretin (TTR) has been established as neuroprotective in AD, here we investigated the influence of TTR in the vasculature.

Methods

We evaluated the thickness of the basement membrane and the length of brain microvessels, by immunohistochemistry, in AβPPswe/PS1A246E (AD) transgenic mice and non-transgenic mice (NT) bearing one (TTR+/−) or two (TTR+/+) copies of the TTR gene. The angiogenic potential of TTR was evaluated in vitro using the tube formation assay, and in vivo using the chick chorioallantoic membrane (CAM) assay.

Results

AD transgenic mice with TTR genetic reduction, AD/TTR+/−, exhibited a thicker BM in brain microvessels and decreased vessel length than animals with normal TTR levels, AD/TTR+/+. Further in vivo investigation, using the CAM assay, revealed that TTR is a pro-angiogenic molecule, and the neovessels formed are functional. Also, TTR increased the expression of key angiogenic molecules such as proteins interleukins 6 and 8, angiopoietin 2, and vascular endothelial growth factor, by endothelial cells, in vitro, under tube formation conditions. We showed that while TTR reduction also leads to a thicker BM in NT mice, this effect is more pronounced in AD mice than in NT animals, strengthening the idea that TTR is a neuroprotective protein. We also studied the effect of TTR tetrameric stabilization on BM thickness, showing that AD mice treated with the TTR tetrameric stabilizer iododiflunisal (IDIF) displayed a significant reduction of BM thickness and increased vessel length, when compared to non-treated littermates.

Conclusion

Our in vivo results demonstrate the involvement of TTR in angiogenesis, particularly as a modulator of vascular alterations occurring in AD. Since TTR is decreased early in AD, its tetrameric stabilization can represent a therapeutic avenue for the early treatment of AD through the maintenance of the vascular structure.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00883-8.

Transthyretin Amyloidosis: Update on the Clinical Spectrum, Pathogenesis, and Disease-Modifying Therapies

ATTR amyloidosis is caused by systemic deposition of transthyretin (TTR) and comprises ATTRwt (wt for wild-type) amyloidosis, ATTRv (v for variant) amyloidosis, and acquired ATTR amyloidosis after domino liver transplantation. ATTRwt amyloidosis has classically been regarded as cardiomyopathy found in the elderly, whereas carpal tunnel syndrome has also become a major initial manifestation. The phenotypes of ATTRv amyloidosis are diverse and include neuropathy, cardiomyopathy, and oculoleptomeningeal involvement as the predominant features, depending on the mutation and age of onset. In addition to variant TTR, the deposition of wild-type TTR plays a significant role, even in patients with ATTRv amyloidosis. The formation of amyloid fibrils tends to occur in association with the basement membrane. The thickening or reduplication of the basement membrane surrounding endoneurial microvessels, which is similar to diabetic neuropathy, is observed in ATTRv amyloidosis, suggesting that common mechanisms, such as an accumulation of advanced glycation end products, may participate in the disease process. In addition to direct damage caused by amyloid fibrils, recent studies have suggested that the toxicity of nonfibrillar TTRs, such as TTR oligomers, participates in the process of tissue damage. Although liver transplantation has been performed for patients with ATTRv amyloidosis since 1990, late-onset patients were not eligible for this treatment. However, as the efficacy of orally administered tafamidis and diflunisal, which stabilize TTR tetramers, was suggested in the early 2010s, such late-onset patients have also become targets for disease-modifying therapies. Additionally, recent studies of small interfering RNA (patisiran) and antisense oligonucleotide (inotersen) therapies have demonstrated the efficacy of these gene-silencing agents. A strategy for monitoring patients that enables the choice of an appropriate treatment from comprehensive and long-term viewpoints should be established. As many patients with ATTR amyloidosis are aged and have heart failure, they are at increased risk of aggravation if they are infected by SARS-CoV2. The optimal interval of evaluation should also be considered, particularly in this COVID-19 era.

Undiscovered Roles for Transthyretin: From a Transporter Protein to a New Therapeutic Target for Alzheimer's Disease

Transthyretin (TTR), an homotetrameric protein mainly synthesized by the liver and the choroid plexus, and secreted into the blood and the cerebrospinal fluid, respectively, has been specially acknowledged for its functions as a transporter protein of thyroxine and retinol (the latter through binding to the retinol-binding protein), in these fluids. Still, this protein has managed to stay in the spotlight as it has been assigned new and varied functions. In this review, we cover knowledge on novel TTR functions and the cellular pathways involved, spanning from neuroprotection to vascular events, while emphasizing its involvement in Alzheimer’s disease (AD). We describe details of TTR as an amyloid binding protein and discuss its interaction with the amyloid Aβ peptides, and the proposed mechanisms underlying TTR neuroprotection in AD. We also present the importance of translating advances in the knowledge of the TTR neuroprotective role into drug discovery strategies focused on TTR as a new target in AD therapeutics.

A novel transthyretin/STAT4/miR-223-3p/FBXW7 signaling pathway affects neovascularization in diabetic retinopathy

MicroRNAs (miRNAs) are small RNAs without protein-coding functions that negatively regulate target genes and play important roles in physiological and pathological processes. The aim of this work was to reveal a novel miRNA/gene pathway in diabetic retinopathy (DR). A microarray was used to screen miRNAs in samples from nondiabetic controls and patients with DR, and miR-223-3p was screened as a potential candidate. Quantitative real-time PCR (qRT-PCR) revealed that the level of miR-223-3p was frequently overexpressed in DR samples and human retinal endothelial cells (hRECs) in hyperglycemia, but it was decreased in hyperglycemia after the addition of transthyretin (TTR). In addition, according to cell proliferation, tube formation, and wound healing assays, the downregulation of miR-223-3p suppressed cell migration and proliferation, whereas miR-223-3p upregulation showed the opposite effects. Furthermore, luciferase assays identified F-box and WD repeat domain-containing 7 (FBXW7) as a target mRNA of miR-223-3p. High glucose conditions facilitated the recruitment of signal transducer and activator of transcription 4 (STAT4) and promoted the transcription of miR-223-3p. In hRECs, in a hyperglycemic environment, TTR inhibited STAT4 expression, downregulated the level of miR-223-3p, and finally promoted FBXW7 expression. This study found a novel mechanism whereby TTR might affect neovascularization through a newly identified STAT4/miR-223-3p/FBXW7 cascade in DR.

Transcriptome analysis identified a novel 3-LncRNA regulatory network of transthyretin attenuating glucose induced hRECs dysfunction in diabetic retinopathy

Background

Diabetic retinopathy (DR) is the leading cause of blindness in the working age population. Transthyretin (TTR) showed a significantly decreased concentration in DR patients and exerted a visual protective effect by repressing neovascularization. This work intended to identify long non coding RNAs (lncRNAs) and explore their potential mechanism underlying the protective role of TTR.

Methods

Transcriptome of human retinal endothelial cells (hRECs) treated with low glucose (LG), high glucose (HG) or high glucose with 4 μM TTR (HG + TTR) was conducted. Differentially expressed lncRNAs, mRNAs and TTR related lncRNAs and mRNA were acquired. Functional annotation and Gene Set Enrichment Analysis were applied to analyse TTR affected pathways and processes. Weighted gene co-expression network analysis (WGCNA) was implemented to obtain hub modules and genes. LncRNA-mRNA regulatory networks were constructed based on cis, trans and competing endogenous RNAs acting mode. QRT-PCR was conducted to validate the expression of lncRNAs in aqueous humor and serum samples from 30 DR patients and 10 normal controls.

Results

RNA-sequencing of hRECs treated with low glucose (LG), high glucose (HG) or high glucose with 4 μM TTR (HG + TTR) was conducted. 146,783 protein-coding transcripts, 12,403 known lncRNA transcripts and 1184 novel non-coding transcripts were characterized. A total of 11,407 differentially expressed mRNAs (DE-mRNAs), 679 differentially expressed lncRNAs (DE-lncRNAs) in HG group versus LG group, 6206 DE-mRNAs and 194 DE-lncRNAs in HG + TTR versus HG group were obtained, respectively. 853 TTR-mRNAs and 48 TTR-lncRNAs were acquired, and functionally involved in cell cycle, apoptosis, inflammation signalling pathway, response to oxidative stress, neovascularization and autophagy. The WGCNA analysis identified a hub module of 133 genes, with the core function of oxidative stress response, angiogenesis, MAPK pathway, cell proliferation and apoptosis. After qRT-PCR validation, a 3-lncRNA regulatory network was proposed. At last, lncRNAs MSTRG.15047.3 and AC008403.3 showed significantly relative higher expression levels in both aqueous humor and serum samples, compared with normal controls, and FRMD6-AS2 was significantly down-regulated.

Conclusions

TTR regulated mRNAs and biological processes including oxidative stress, inflammation signalling and autophagy. A 3-lncRNA regulatory network was characterized underlying TTR repressing neovascularization, and showed potential diagnostic performance in DR.

Hereditary transthyretin amyloidosis: a model of medical progress for a fatal disease

Hereditary amyloidogenic transthyretin (ATTRv) amyloidosis with polyneuropathy (also known as familial amyloid polyneuropathy) is a condition with adult onset caused by mutation of transthyretin (TTR) and characterized by extracellular deposition of amyloid and destruction of the somatic and autonomic PNS, leading to loss of autonomy and death. This disease represents a model of the scientific and medical progress of the past 30 years. ATTRv amyloidosis is a worldwide disease with broad genetic and phenotypic heterogeneity that presents a diagnostic challenge for neurologists. The pathophysiology of the neuropathy is increasingly understood and includes instability and proteolysis of mutant TTR leading to deposition of amyloid with variable lengths of fibrils, microangiopathy and involvement of Schwann cells. Wild-type TTR is amyloidogenic in older individuals. The main symptoms are neuropathic, but the disease is systemic; neurologists should be aware of cardiac, eye and kidney involvement that justify a multidisciplinary approach to management. Infiltrative cardiomyopathy is usually latent but present in half of patients. Disease-modifying therapeutics that have been developed include liver transplantation and TTR stabilizers, both of which can slow progression of the disease and increase survival in the early stages. Most recently, gene-silencing drugs have been used to control disease in the more advanced stages and produce some degree of improvement.

Uncovering the Neuroprotective Mechanisms of Curcumin on Transthyretin Amyloidosis

Transthyretin (TTR) amyloidoses (ATTR amyloidosis) are diseases associated with transthyretin (TTR) misfolding, aggregation and extracellular deposition in tissues as amyloid. Clinical manifestations of the disease are variable and include mainly polyneuropathy and/or cardiomyopathy. The reasons why TTR forms aggregates and amyloid are related with amino acid substitutions in the protein due to mutations, or with environmental alterations associated with aging, that make the protein more unstable and prone to aggregation. According to this model, several therapeutic approaches have been proposed for the diseases that range from stabilization of TTR, using chemical chaperones, to clearance of the aggregated protein deposited in tissues in the form of oligomers or small aggregates, by the action of disruptors or by activation of the immune system. Interestingly, different studies revealed that curcumin presents anti-amyloid properties, targeting multiple steps in the ATTR amyloidogenic cascade. The effects of curcumin on ATTR amyloidosis will be reviewed and discussed in the current work in order to contribute to knowledge of the molecular mechanisms involved in TTR amyloidosis and propose more efficient drugs for therapy.

Ultrastructure in Transthyretin Amyloidosis: From Pathophysiology to Therapeutic Insights

Transthyretin (TTR) amyloidosis is caused by systemic deposition of wild-type or variant amyloidogenic TTR (ATTRwt and ATTRv, respectively). ATTRwt amyloidosis has traditionally been termed senile systemic amyloidosis, while ATTRv amyloidosis has been called familial amyloid polyneuropathy. Although ATTRwt amyloidosis has classically been regarded as one of the causes of cardiomyopathy occurring in the elderly population, recent developments in diagnostic techniques have significantly expanded the concept of this disease. For example, this disease is now considered an important cause of carpal tunnel syndrome in the elderly population. The phenotypes of ATTRv amyloidosis also vary depending on the mutation and age of onset. Peripheral neuropathy usually predominates in patients from the conventional endemic foci, while cardiomyopathy or oculoleptomeningeal involvement may also become major problems in other patients. Electron microscopic studies indicate that the direct impact of amyloid fibrils on surrounding tissues leads to organ damage, whereas accumulating evidence suggests that nonfibrillar TTR, such as oligomeric TTR, is toxic, inducing neurodegeneration. Microangiopathy has been suggested to act as an initial lesion, increasing the leakage of circulating TTR. Regarding treatments, the efficacy of liver transplantation has been established for ATTRv amyloidosis patients, particularly patients with early-onset amyloidosis. Recent phase III clinical trials have shown the efficacy of TTR stabilizers, such as tafamidis and diflunisal, for both ATTRwt and ATTRv amyloidosis patients. In addition, a short interfering RNA (siRNA), patisiran, and an antisense oligonucleotide (ASO), inotersen, have been shown to be effective for ATTRv amyloidosis patients. Given their ability to significantly reduce the production of both wild-type and variant TTR in the liver, these gene-silencing drugs seem to be the optimal therapeutic option for ATTR amyloidosis. Hence, the long-term efficacy and tolerability of novel therapies, particularly siRNA and ASO, must be determined to establish an appropriate treatment program.

Abundant proteins in platelet-rich fibrin and their potential contribution to wound healing: An explorative proteomics study and review of the literature

Background/purpose

It is well-known that diverse types of blood proteins contribute to healing process via different mechanisms. Presence and potential involvements of blood-derived abundant proteins in the platelet-rich fibrin (PRF) to its regenerative capacity have not been sufficiently emphasized in the literature. The aim of this paper was to analyze the abundant proteome content of PRF and summarize previously reported effects of identified proteins on wound healing via a literature review.

Materials and methods

The PRF samples obtained from non-smoking, systemically healthy volunteers were subjected to 2D gel electrophoresis after extracting the proteins from fibrin matrices. All matching spots were excised from the gels and identified by MALDI TOF/TOF MS/MS analysis. A literature review was conducted to reveal possible contributions of identified proteins to wound healing.

Results

Totally, thirty-five blood proteins were commonly identified among all studied samples. These proteins included serine protease inhibitors, such as alpha-1-antitrypsin, alpha-1-antichymotrypsin, alpha-1-acid glycoprotein, inter-alpha-trypsin-inhibitor, protease C1 inhibitor, and complement proteins. In addition, abundant presence of immunoglobulin G was observed. The abundance of albumin, haptoglobin, ceruloplasmin vitronectin, fetuin-A, ficolin-3 and transthyretin was also detected.

Conclusion

The results of this study indicated that PRF abundantly contains blood-origin actors which were previously reported for their direct contribution to wound healing. Further studies exploring the protein content of PRF are needed to reveal its undisclosed potential roles in the healing process.

Pax6 regulation of Sox9 in the mouse retinal pigmented epithelium controls its timely differentiation and choroid vasculature development

The synchronized differentiation of neuronal and vascular tissues is crucial for normal organ development and function, although there is limited information about the mechanisms regulating the coordinated development of these tissues. The choroid vasculature of the eye serves as the main blood supply to the metabolically active photoreceptors, and develops together with the retinal pigmented epithelium (RPE). Here, we describe a novel regulatory relationship between the RPE transcription factors Pax6 and Sox9 that controls the timing of RPE differentiation and the adjacent choroid maturation. We used a novel machine learning algorithm tool to analyze high resolution imaging of the choroid in Pax6 and Sox9 conditional mutant mice. Additional unbiased transcriptomic analyses in mutant mice and RPE cells generated from human embryonic stem cells, as well as chromatin immunoprecipitation and high-throughput analyses, revealed secreted factors that are regulated by Pax6 and Sox9. These factors might be involved in choroid development and in the pathogenesis of the common blinding disease: age-related macular degeneration (AMD).

Negative effects of transthyretin in high myopic vitreous on diabetic retinopathy

AIM

To analyze the relationship between vitreous transthyretin (TTR) levels, high myopia and diabetic retinopathy (DR).

METHODS

We selected 6722 individuals from the southern Jiangsu Province for diabetes and ophthalmic examinations. The TTR concentration in the vitreous of 50 patients with high myopia and diabetes, 50 patients with only DR, and 20 healthy controls were determined by ELISA. Key factors in Tie2 pathway in DR development including vascular endothecial growth factor (VEGF), Tie2, Angpt1, Angpt2, vascular endothelial growth factor receptor (VEGFR) 1 and VEGFR2 were also detected by ELISA.

RESULTS

The prevalence of DR in patients with diabetes and myopia [<6.00 diopter (D)], diabetes and high myopia (>6.00 D), and diabetes without myopia were 11.1%, 2.5%, and 60.0%, respectively. The vitreous TTR concentration of patients with diabetes and high myopia was approximately 6.5- and 4.2-times higher than those of patients with DR and healthy controls, respectively (P<0.05). Following the vitreous TTR concentration, the levels of VEGF, Tie2, Angpt1, Angpt2, VEGFR1 and VEGFR2 in vitreous of diabetes and high myopia patients, DR patients and healthy controls were detected as dramatically fluctuated.

CONCLUSION

The results suggest that TTR can affect the vitreous contents of key factors in Tie2 pathway for neovascularization, and there should be a protective association between abundant TTR levels in the vitreous of highly myopic patients and a decreased risk of DR.

Is Vascular Amyloidosis Intertwined with Arterial Aging, Hypertension and Atherosclerosis?

Vascular amyloidosis (VA) is a component of aging, but both VA and aging move forward together. Although, not all age-related molecules are involved with VA, some molecules are involved in a crosstalk between both of them. However, the cellular mechanism by which, vascular cells are phenotypically shifted to arterial remodeling, is not only involved in aging but also linked to VA. Additionally, patients with hypertension and atherosclerosis are susceptible to VA, while amyloidosis alone may provide fertile soil for the initiation and progression of subsequent hypertension and atherosclerosis. It is known that hypertension, atherosclerosis and amyloidosis can be viewed as accelerated aging. This review summarizes the available experimental and clinical evidence to help the reader to understand the advance and underlying mechanisms for VA involvement in and interaction with aging. Taken together, it is clear that VA, hypertension and atherosclerosis are closely intertwined with arterial aging as equal partners.

Transthyretin represses neovascularization in diabetic retinopathy

PURPOSE

The apoptosis of human umbilical vein endothelial cells has been reportedly induced by the protein transthyretin (TTR). In human ocular tissue, TTR is generally considered to be secreted mainly by retinal pigment epithelial cells (hRPECs); however, whether TTR affects the development of neovascularization in diabetic retinopathy (DR) remains unclear.

METHODS

Natural and simulated DR media were used to culture human retinal microvascular endothelial cells (hRECs). Hyperglycemia was simulated by increasing the glucose concentration from 5.5 mM up to 25 mM, while hypoxia was induced with 200 µM CoCl₂. To understand the effects of TTR on hRECs, cell proliferation was investigated under natural and DR conditions. Overexpression of TTR, an in vitro wound-healing assay, and a tube formation assay were employed to study the repression of TTR on hRECs. Real-time fluorescence quantitative PCR (qRT-PCR) was used to study the mRNA levels of DR-related genes, such as Tie2, VEGFR1, VEGFR2, Angpt1, and Angpt2.

RESULTS

The proliferation of hRECs was significantly decreased in the simulated hyperglycemic and hypoxic DR environments. The cells were further repressed by added exogenous or endogenous TTR only under hyperglycemic conditions. The in vitro migration and tube formation processes of the hRECs were inhibited with TTR; furthermore, in the hyperglycemia and hyperglycemia/hypoxia environments, the levels of Tie2 and Angpt1 mRNA were enhanced with exogenous TTR, while those of VEGFR1, VEGFR2, and Angpt1 were repressed.

CONCLUSIONS

In hyperglycemia, the proliferation, migration, and neovascularization of hRECs were significantly inhibited by TTR. The key genes for DR neovascularization, including Tie2, VEGFR1, VEGFR2, Angpt1, and Angpt2, were regulated by TTR. Under DR conditions, TTR significantly represses neovascularization by inhibiting the proliferation, migration and tube formation of hRECs.

Peripheral Blood Cell Gene Expression Diagnostic for Identifying Symptomatic Transthyretin Amyloidosis Patients: Male and Female Specific Signatures

Background: Early diagnosis of familial transthyretin (TTR) amyloid diseases remains challenging because of variable disease penetrance. Currently, patients must have an amyloid positive tissue biopsy to be eligible for disease-modifying therapies. Endomyocardial biopsies are typically amyloid positive when cardiomyopathy is suspected, but this disease manifestation is generally diagnosed late. Early diagnosis is often difficult because patients exhibit apparent symptoms of polyneuropathy, but have a negative amyloid biopsy. Thus, there is a pressing need for an additional early diagnostic strategy for TTR-aggregation-associated polyneuropathy and cardiomyopathy.

Methods and Findings: Global peripheral blood cell mRNA expression profiles from 263 tafamidis-treated and untreated V30M Familiar Amyloid Neuropathy patients, asymptomatic V30M carriers, and healthy, age- and sex-matched controls without TTR mutations were used to differentiate symptomatic from asymptomatic patients. We demonstrate that blood cell gene expression patterns reveal sex-independent, as well as male- and female-specific inflammatory signatures in symptomatic FAP patients, but not in asymptomatic carriers. These signatures differentiated symptomatic patients from asymptomatic V30M carriers with >80% accuracy. There was a global downregulation of the eIF2 pathway and its associated genes in all symptomatic FAP patients. We also demonstrated that the molecular scores based on these signatures significantly trended toward normalized values in an independent cohort of 46 FAP patients after only 3 months of tafamidis treatment.

Conclusions: This study identifies novel molecular signatures that differentiate symptomatic FAP patients from asymptomatic V30M carriers as well as affected males and females. We envision using this approach, initially in parallel with amyloid biopsies, to identify individuals who are asymptomatic gene carriers that may convert to FAP patients. Upon further validation, peripheral blood cell mRNA expression profiling could become an independent early diagnostic. This quantitative gene expression signature for symptomatic FAP could also become a biomarker to demonstrate significant disease-modifying effects of drugs and drug candidates. For example, when new disease modifiers are being evaluated in a FAP clinical trial, such surrogate biomarkers have the potential to provide an objective, quantitative and mechanistic molecular diagnostic of disease response to therapy.

Repression of retinal microvascular endothelial cells by transthyretin under simulated diabetic retinopathy conditions

AIM

To investigate biological effects of transthyretin (TTR) on the development of neovascularization under simulated diabetic retinopathy (DR) condition associated with high glucose and hypoxia.

METHODS

Human retinal microvascular endothelial cells (hRECs) were cultured in normal and simulated DR environments with high glucose and hypoxia. The normal serum glucose concentration is approximately 5.5 mmol/L; thus, hyperglycemia was simulated with 25 mmol/L glucose, while hypoxia was induced using 200 µmol/L CoCl2. The influence of TTR on hRECs and human retinal pigment epithelial cells (hRPECs) was determined by incubating the cells with 4 µmol/L TTR in normal and abnormal media. A co-culture system was then employed to evaluate the effects of hRPECs on hRECs.

RESULTS

Decreased hRECs and hRPECs were observed under abnormal conditions, including high-glucose and hypoxic media. In addition, hRECs were significantly inhibited by 4 µmol/L exogenous TTR during hyperglycemic culture. During co-culture, hRPECs inhibited hRECs in both the normal and abnormal environments.

CONCLUSION

hREC growth is inhibited by exogenous TTR under simulated DR environments with high-glucose and hypoxic, particularly in the medium containing 25 mmol/L glucose. hRPECs, which manufacture TTR in the eye, also represses hRECs in the same environment. TTR is predicted to inhibit the proliferation of hRECs and neovascularization.

Understanding Pre-Eclampsia Using Alzheimer's Etiology: An Intriguing Viewpoint

Characterized by hypertension and proteinuria after the 20th week of gestation, pre-eclampsia (PE) is a major cause of maternal, fetal, and neonatal morbidity and mortality. Despite being recognized for centuries, PE still lacks a reliable, early means of diagnosis or prediction, and a safe and effective therapy. We have recently reported that the event of toxic protein misfolding and aggregation is a critical etiological manifestation in PE. Using comparative proteomic analysis of gestational age-matched sera from PE and normal pregnancy, we identified several proteins that appeared to be dysregulated in PE. Our efforts so far have focused on transthyretin (TTR), a transporter of thyroxine and retinol, and amyloid precursor protein whose aggregates were detected in the PE placenta. Based on these results and detection of TTR aggregates in sera from PE patients, we proposed that PE could be a disease of protein misfolding and aggregation. Protein misfolding and aggregation have long been linked with many neurodegenerative diseases such as Alzheimer's disease. However, linkage of protein misfolding and aggregation with the PE pathogenesis is a new and novel concept. This review aims to understand the roles of aggregated proteins in PE using the cues from the Alzheimer's etiology.

Liver transplantation in transthyretin amyloidosis: issues and challenges

Hereditary transthyretin amyloidosis (ATTR) is a rare worldwide autosomal dominant disease caused by the systemic deposition of an amyloidogenic variant of transthyretin (TTR), which is usually derived from a single amino acid substitution in the TTR gene. More than 100 mutations have been described, with V30M being the most prevalent. Each variant has a different involvement, although peripheral neuropathy and cardiomyopathy are the most common. Orthotopic liver transplantation (OLT) was implemented as the inaugural disease-modifying therapy because the liver produces the circulating unstable TTR. In this review, we focus on the results and long-term outcomes of OLT for ATTR after more than 2063 procedures and 23 years of experience. After successful OLT, neuropathy and organ impairment are not usually reversed, and in some cases, the disease progresses. The overall 5-year survival rate is approximately 100% for V30M patients and 59% for non-ATTR V30M patients. Cardiac-related death and septicemia are the main causes of mortality. Lower survival is related to malnutrition, a longer duration of disease, cardiomyopathy, and a later onset (particularly for males). Deposits, which are composed of a mixture of truncated and full-length TTR (type A) fibrils, have been associated with posttransplant myocardial dysfunction. A higher incidence of early hepatic artery thrombosis of the graft has also been documented for these patients. Liver-kidney/heart transplantation is an alternative for patients with advanced renal disease or heart failure. The sequential procedure, in which ATTR livers are reused in patients with liver disease, reveals that neuropathy in the recipient may appear as soon as 6 years after OLT, and ATTR deposits may appear even earlier. Long-term results of trials with amyloid protein stabilizers or disrupters, silencing RNA, and antisense oligonucleotides will highlight the value and limitations of liver transplantation.

Oligomeric TTR V30M aggregates compromise cell viability, erythropoietin gene expression and promoter activity in the human hepatoma cell line Hep3B

Familial amyloidotic polyneuropathy, ATTRV30M (p. TTRV50M) amyloidosis, is a neurodegenerative disease characterized by systemic extracellular amyloid deposition of a mutant transthyretin, TTR V30M. Anemia, with low erythropoietin (EPO) levels and spared kidney function, affects about 25% of symptomatic patients, suggesting a blockage of EPO-producing cells. Early non-fibrillar TTR aggregates are highly cytotoxic, inducing oxidative stress, the expression of apoptosis-related molecules and secretion of pro-inflammatory cytokines, factors capable of inhibiting EPO production. Low EPO levels in these patients are not related to renal amyloid deposition or the presence of circulating TTR V30M. However, the role of early non-fibrillar TTR aggregates remains unexplored. We used the EPO producing Hep3B human hepatoma cell line to study the effect of TTR oligomeric aggregates on EPO expression. Hep3B cells were incubated with soluble and oligomeric TTR V30M, and cell proliferation as well as caspase 3/7 activation was evaluated. Relative quantification of EPO mRNA transcripts was performed by real-time PCR. Significant reductions in cell viability (13 ± 7.3%) and activation of caspases 3/7 were seen after 24 h in the presence of oligomeric TTR V30M. Also, EPO expression was significantly reduced (50 ± 2.8%), in normoxic conditions. A reporter assay was constructed with a PCR fragment of the EPO promoter linked to the luciferase gene to evaluate the role of transcription factors targeting the promoter. A significant reduction of EPO promoter activity (53 ± 6.5%) was observed in transfected cells exposed to TTR oligomers. Our results show that oligomeric TTR V30M reduces EPO expression, at least in part through inhibition of promoter activity.