Decreased Neurotrophin TrkB Receptor Expression Reduces Lesion Size in the Apolipoprotein E–Null Mutant Mouse

Brain-Derived Neurotrophic Factor-Loaded Low-Temperature-Sensitive liposomes as a drug delivery system for repairing podocyte damage

Podocytes, cells of the glomerular filtration barrier, play a crucial role in kidney diseases and are gaining attention as potential targets for new therapies. Brain-Derived Neurotrophic Factor (BDNF) has shown promising results in repairing podocyte damage, but its efficacy via parenteral administration is limited by a short half-life. Low temperature sensitive liposomes (LTSL) are a promising tool for targeted BDNF delivery, preserving its activity after encapsulation. This study aimed to improve LTSL design for efficient BDNF encapsulation and targeted release to podocytes, while maintaining stability and biological activity, and exploiting the conjugation of targeting peptides. While cyclic RGD (cRGD) was used for targeting endothelial cells in vitro, a homing peptide (HITSLLS) was conjugated for more specific uptake by glomerular endothelial cells in vivo. BDNF-loaded LTSL successfully repaired cytoskeleton damage in podocytes and reduced albumin permeability in a glomerular co-culture model. cRGD conjugation enhanced endothelial cell targeting and uptake, highlighting an improved therapeutic effect when BDNF release was induced by thermoresponsive liposomal degradation. In vivo, targeted LTSL showed evidence of accumulation in the kidneys, and their BDNF delivery decreased proteinuria and ameliorated kidney histology. These findings highlight the potential of BDNF-LTSL formulations in restoring podocyte function and treating glomerular diseases.

A Meta-Analysis of Human Transcriptomics Data in the Context of Peritoneal Dialysis Identifies Novel Receptor-Ligand Interactions as Potential Therapeutic Targets

Peritoneal dialysis (PD) is one therapeutic option for patients with end-stage kidney disease (ESKD). Molecular profiling of samples from PD patients using different Omics technologies has led to the discovery of dysregulated molecular processes due to PD treatment in recent years. In particular, a number of transcriptomics (TX) datasets are currently available in the public domain in the context of PD. We set out to perform a meta-analysis of TX datasets to identify dysregulated receptor-ligand interactions in the context of PD-associated complications. We consolidated transcriptomics profiles from twelve untargeted genome-wide gene expression studies focusing on human cell cultures or samples from human PD patients. Gene set enrichment analysis was used to identify enriched biological processes. Receptor-ligand interactions were identified using data from CellPhoneDB. We identified 2591 unique differentially expressed genes in the twelve PD studies. Key enriched biological processes included angiogenesis, cell adhesion, extracellular matrix organization, and inflammatory response. We identified 70 receptor-ligand interaction pairs, with both interaction partners being dysregulated on the transcriptional level in one of the investigated tissues in the context of PD. Novel receptor-ligand interactions without prior annotation in the context of PD included BMPR2-GDF6, FZD4-WNT7B, ACKR2-CCL2, or the binding of EPGN and EREG to the EGFR, as well as the binding of SEMA6D to the receptors KDR and TYROBP. In summary, we have consolidated human transcriptomics datasets from twelve studies in the context of PD and identified sets of novel receptor-ligand pairs being dysregulated in the context of PD that warrant investigation in future functional studies.

Brain-Derived Neurotrophic Factor Expression and Signaling in Different Perivascular Adipose Tissue Depots of Patients With Coronary Artery Disease

Background

Brain‐derived neurotrophic factor (BDNF) is expressed in neuronal and nonneuronal cells and may affect vascular functions via its receptor, tropomyosin‐related kinase B (TrkB). In this study, we determined the expression of BDNF in different perivascular adipose tissue (PVAT) depots of patients with established coronary atherosclerosis.

Methods and Results

Serum, vascular tissue, and PVAT surrounding the proximal aorta (C‐PVAT) or internal mammary artery (IMA‐PVAT) was obtained from 24 patients (79% men; mean age, 71.7±9.7 years; median body mass index, 27.4±4.8 kg/m²) with coronary atherosclerosis undergoing elective coronary artery bypass surgery. BDNF protein levels were significantly higher in C‐PVAT compared with IMA‐PVAT, independent of obesity, metabolic syndrome, or systemic biomarkers of inflammation. mRNA transcripts of TrkB, the BDNF receptor, were significantly reduced in aorta compared with IMA. Vessel wall TrkB immunosignals colocalized with cells expressing smooth muscle cell markers, and confocal microscopy and flow cytometry confirmed BDNF receptor expression in human aortic smooth muscle cells. Significantly elevated levels of protein tyrosine phosphatase 1B, a negative regulator of TrkB signaling in the brain, were also observed in C‐PVAT. In vitro, inhibition of protein tyrosine phosphatase 1B blunted the effects of BDNF on smooth muscle cell proliferation, migration, differentiation, and collagen production, possibly by upregulation of low‐affinity p75 neurotrophin receptors. Expression of nerve growth factor or its receptor tropomyosin‐related kinase A did not differ between C‐PVAT and IMA‐PVAT.

Conclusions

Elevated expression of BDNF in parallel with local upregulation of negative regulators of neurotrophin signaling in perivascular fat and lower TrkB expression suggest that vascular BDNF signaling is reduced or lost in patients with coronary atherosclerosis.

BDNF Actions in the Cardiovascular System: Roles in Development, Adulthood and Response to Injury

The actions of BDNF (Brain-derived Neurotrophic Factor) in regulating neuronal development and modulating synaptic activity have been extensively studied and well established. Equally important roles for this growth factor have been uncovered in the cardiovascular system, through the examination of gene targeted animals to define critical actions in development, and to the unexpected roles of BDNF in modulating the response of the heart and vasculature to injury. Here we review the compartmentally distinct realm of cardiac myocytes, vascular smooth muscle cells, endothelial cells, and hematopoietic cells, focusing upon the actions of BDNF to modulate contractility, migration, neoangiogenesis, apoptosis and survival. These studies indicate that BDNF is an important growth factor which directs the response of the cardiovascular system to acute and chronic injury.

Endothelial tyrosine kinase receptor B prevents VE-cadherin cleavage and protects against atherosclerotic lesion development in ApoE-/- mice

Tyrosine kinase receptor B (TrkB) is a high-affinity receptor for brain-derived neurotrophic factor (BDNF). In addition to its nervous system functions, TrkB is also expressed in the aortic endothelium. However, the effects of endothelial TrkB signaling on atherosclerosis remained unknown. Immunofluorescence analysis revealed that TrkB expression is downregulated in the endothelium of atherosclerotic lesions from ApoE−/− mice compared with the atheroma-free aorta of WT mice. Endothelial TrkB knockdown led to increased lesion size, lipid deposition and inflammatory responses in the atherosclerotic lesions of the ApoE−/− mice compared with the control mice. Mechanistic studies showed that TrkB activation prevented VE-cadherin shedding by enhancing the interaction between vascular endothelial protein tyrosine phosphatase and VE-cadherin, maintaining VE-cadherin in a dephosphorylated state. Our data demonstrate that TrkB is an endothelial injury-response molecule in atherogenesis. Endothelial BDNF/TrkB signaling reduces VE-cadherin shedding and protects against atherosclerotic lesion development in ApoE−/− mice.

Tyrosine Kinase Receptor B Protects Against Coronary Artery Disease and Promotes Adult Vasculature Integrity by Regulating Ets1-Mediated VE-Cadherin Expression

Objective—

Tyrosine kinase receptor B (TrkB) is a high-affinity receptor for brain-derived neurotrophic factor. In addition to its nervous system functions, TrkB is also expressed in the cardiovascular system. However, the association of TrkB and coronary artery disease (CAD) remains unknown. We investigated the role of TrkB in the development of CAD and its mechanism.

Approach and Results—

We performed a case–control study in 2 independent cohort of Chinese subjects and found –69C>G polymorphisms of TrkB gene significantly associated with CAD. TrkB –69C homozygotes, which corresponded to decreased TrkB expression by luciferase reporter assay, showed increased risk for CAD. Immunofluorescence analysis revealed that TrkB was expressed in the aortic endothelium in atherosclerotic lesions in humans and ApoE –/– mice. TrkB knockdown in the aortic endothelium resulted in vascular leakage in ApoE –/– mice. Mechanistic studies showed that TrkB regulated vascular endothelial cadherin (VE-cadherin) expression through induction and activation of Ets1 transcriptional factor. Importantly, TrkB activation attenuated proatherosclerotic factors induced-endothelial hyperpermeability in human vascular endothelial cells.

Conclusions—

Our data demonstrate that TrkB protects endothelial integrity during atherogenesis by promoting Ets1-mediated VE-cadherin expression and plays a previously unknown protective role in the development of CAD.

Neurotrophins are expressed in giant cell arteritis lesions and may contribute to vascular remodeling

Introduction

Giant cell arteritis (GCA) is characterized by intimal hyperplasia leading to ischaemic manifestations that involve large vessels. Neurotrophins (NTs) and their receptors (NTRs) are protein factors for growth, differentiation and survival of neurons. They are also involved in the migration of vascular smooth muscle cells (VSMCs). Our aim was to investigate whether NTs and NTRs are involved in vascular remodelling of GCA.

Methods

We included consecutive patients who underwent a temporal artery biopsy for suspected GCA. We developed an enzymatic digestion method to obtain VSMCs from smooth muscle cells in GCA patients and controls. Neurotrophin protein and gene expression and functional assays were studied from these VSMCs. Neurotrophin expression was also analysed by immunohistochemistry in GCA patients and controls.

Results

Whereas temporal arteries of both GCA patients (n = 22) and controls (n = 21) expressed nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), tropomyosin receptor kinase B (TrkB) and sortilin, immunostaining was more intense in GCA patients, especially in the media and intima, while neurotrophin-3 (NT-3) and P75 receptor (P75^NTR) were only detected in TA from GCA patients. Expression of TrkB, a BDNF receptor, was higher in GCA patients with ischaemic complications. Serum NGF was significantly higher in GCA patients (n = 28) vs. controls (n = 48), whereas no significant difference was found for BDNF and NT-3. NGF and BDNF enhanced GCA-derived temporal artery VSMC proliferation and BDNF facilitated migration of temporal artery VSMCs in patients with GCA compared to controls.

Conclusions

Our results suggest that NTs and NTRs are involved in vascular remodelling of GCA. In GCA-derived temporal artery VSMC, NGF promoted proliferation and BDNF enhanced migration by binding to TrkB and p75^NTR receptors. Further experiments are needed on a larger number of VSMC samples to confirm these results.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-014-0487-z) contains supplementary material, which is available to authorized users.

Mutation in CYP27A1 identified in family with coronary artery disease

Coronary artery disease (CAD) is a leading cause of death worldwide. Myocardial infarction is the most severe outcome of CAD. Despite extensive efforts, the genetics of CAD is poorly understood. We aimed to identify the genetic cause of CAD in a pedigree with several affected individuals. Exome sequencing led to identification of a mutation in CYP27A1 that causes p.Arg225His in the encoded protein sterol 27-hydroxylase as the likely cause of CAD in the pedigree. The enzyme is multifunctional, and several of its functions including its functions in vitamin D metabolism and reverse cholesterol transport (RCT) are relevant to the CAD phenotype. Measurements of vitamin D levels suggested that the mutation does not affect CAD by affecting this parameter. We suggest that the mutation may cause CAD by affecting RCT. Screening of all coding regions of the CYP27A1 in 100 additional patients led to finding four variations (p.Arg14Gly, p.Arg26Lys, p.Ala27Arg, and p.Val86Met) in seven patients that may contribute to their CAD status. CYP27A1 is the known causative gene of cerebrotendinous xanthomatosis, a disorder which is sometimes accompanied by early onset atherosclerosis. This and the observation of potentially harmful variations in unrelated CAD patients provide additional evidence for the suggested causative role of the p.Arg225His mutation in CAD.

Hydrolysis products generated by lipoprotein lipase and endothelial lipase differentially impact THP-1 macrophage cell signalling pathways

Macrophages express lipoprotein lipase (LPL) and endothelial lipase (EL) within atherosclerotic plaques; however, little is known about how lipoprotein hydrolysis products generated by these lipases might affect macrophage cell signalling pathways. We hypothesized that hydrolysis products affect macrophage cell signalling pathways associated with atherosclerosis. To test our hypothesis, we incubated differentiated THP-1 macrophages with products from total lipoprotein hydrolysis by recombinant LPL or EL. Using antibody arrays, we found that the phosphorylation of six receptor tyrosine kinases and three signalling nodes--most associated with atherosclerotic processes--was increased by LPL derived hydrolysis products. EL derived hydrolysis products only increased the phosphorylation of tropomyosin-related kinase A, which is also implicated in playing a role in atherosclerosis. Using electrospray ionization-mass spectrometry, we identified the species of triacylglycerols and phosphatidylcholines that were hydrolyzed by LPL and EL, and we identified the fatty acids liberated by gas chromatography-mass spectrometry. To determine if the total liberated fatty acids influenced signalling pathways, we incubated differentiated THP-1 macrophages with a mixture of the fatty acids that matched the concentrations of liberated fatty acids from total lipoproteins by LPL, and we subjected cell lysates to antibody array analyses. The analyses showed that only the phosphorylation of Akt was significantly increased in response to fatty acid treatment. Overall, our study shows that macrophages display potentially pro-atherogenic signalling responses following acute treatments with LPL and EL lipoprotein hydrolysis products.

The annexin A2/S100A10 system in health and disease: emerging paradigms

Since its discovery as a src kinase substrate more than three decades ago, appreciation for the physiologic functions of annexin A2 and its associated proteins has increased dramatically. With its binding partner S100A10 (p11), A2 forms a cell surface complex that regulates generation of the primary fibrinolytic protease, plasmin, and is dynamically regulated in settings of hemostasis and thrombosis. In addition, the complex is transcriptionally upregulated in hypoxia and promotes pathologic neoangiogenesis in the tissues such as the retina. Dysregulation of both A2 and p11 has been reported in examples of rodent and human cancer. Intracellularly, A2 plays a critical role in endosomal repair in postarthroplastic osteolysis, and intracellular p11 regulates serotonin receptor activity in psychiatric mood disorders. In human studies, the A2 system contributes to the coagulopathy of acute promyelocytic leukemia, and is a target of high-titer autoantibodies in patients with antiphospholipid syndrome, cerebral thrombosis, and possibly preeclampsia. Polymorphisms in the human ANXA2 gene have been associated with stroke and avascular osteonecrosis of bone, two severe complications of sickle cell disease. Together, these new findings suggest that manipulation of the annexin A2/S100A10 system may offer promising new avenues for treatment of a spectrum of human disorders.

Effect of Tie-2 conditional deletion of BDNF on atherosclerosis in the ApoE null mutant mouse

The reduced expression (haplodeficiency) of the main brain derived neurotrophic factor receptor, namely TrkB is associated with reduced atherosclerosis, smooth muscle cells accumulation and collagen content in the lesion. These data support the concept that brain derived neurotrophic factor of vascular origin may contribute to atherosclerosis. However, to date, no experimental approach was possible to investigate this issue due to the lethality of brain derived neurotrophic factor null mice. To overcome these limitations, we generated a mouse model with a conditional deletion of brain derived neurotrophic factor in endothelial cells (Tie-2 Cre recombinase) on an atherosclerotic prone background (apolipoprotein E knock out) and investigated the effect of conditional brain derived neurotrophic factor deficiency on atherosclerosis. Despite brain derived neurotrophic factor reduction in the vascular wall, mice with conditional deletion of brain derived neurotrophic factor did not develop larger atherosclerotic lesion compared to controls. Smooth muscle cell content as well as the distribution of total and fibrillar collagen was similar in the atherosclerotic lesions from mice with brain derived neurotrophic factor conditional deficiency compared to controls. Finally an extended gene expression analysis failed to identify pro-atherogenic gene expression patterns among the animal with brain derived neurotrophic factor deficiency. In spite of the reduced brain derived neurotrophic factor expression, similar atherosclerosis development was observed in the brain derived neurotrophic factor conditional deficient mouse compared to controls. These pieces of evidence indicate that endothelial derived-brain derived neurotrophic factor is not a pro-atherogenic factor and would rather suggest to investigate the role of other TrkB activators on atherosclerosis.

A high cholesterol diet given to apolipoprotein E-knockout mice has a differential effect on the various neurotrophin systems in the hippocampus

Apolipoprotein E (apoE) is one of the major transporters of cholesterol in the body and is essential for maintaining various neural functions in the brain. Given that hypercholesterolemia is a risk factor in Alzheimer's disease (AD), it has been suggested that altered cholesterol metabolism may be involved in the development of the pathogenesis, including neural degeneration, commonly observed in AD patients. Neurotrophic factors and their receptors, which are known to regulate various neural functions, are also known to be altered in various neurodegenerative diseases. We therefore hypothesized that cholesterol metabolism may itself influence the neurotrophin system within the brain. We decided to investigate this possibility by modulating the amount of dietary cholesterol given to apoE-knockout (apoE-KO) and wild-type (WT) mice, and examining the mRNA expression of various neurotrophin ligands and receptors in their hippocampal formations. Groups of eight-week-old apoE-KO and WT mice were fed a diet containing either "high" (HCD) or "normal" (ND) levels of cholesterol for a period of 12 weeks. We found that high dietary cholesterol intake elevated BDNF mRNA expression in both apoE-KO and WT mice and TrkB mRNA expression in apoE-KO animals. On the other hand, NGF and TrkA mRNA levels remained unchanged irrespective of both diet and mouse type. These findings indicate that altered cholesterol metabolism induced by HCD ingestion combined with apoE deficiency can elicit a differential response in the various neurotrophin ligand/receptor systems in the mouse hippocampus. Whether such changes can lead to neural degeneration, and the mechanisms that may be involved in this, awaits further research.

Vascular BDNF expression and oxidative stress during aging and the development of chronic hypertension

Brain-derived neurotrophic factor (BDNF) and TrK receptors play an important role in vascular development and response to injury. In this study, we investigated the participation of the BDNF/TrK pathway and oxidative stress during the development of hypertension in spontaneously hypertensive rats (SHR). In SHR and normotensive rats (WKY) at 6 and 13 weeks of age, we studied (i) plasma antioxidant capacity, (ii) production of superoxide and NAD(P)H oxidase activity in aorta (iii) plasma BDNF and vascular expression of BDNF, TrKB, NAD(P)H oxidase subunits, AT1 receptor, and MCP-1. In 6- and 13-week-old SHR aorta, superoxide level was twice than in WKY aorta. At 13 weeks, when blood pressure in SHR was 60 mmHg higher in SHR than in WKY, an enhancement of NAD(P)H oxidase activity in SHR was associated with an increase in p47phox, AT1, and BDNF expression in vessels. MCP-1 expression increased with blood pressure. Our study demonstrated that in SHR rats, an increase in levels of vascular oxidative stress and in aortic BDNF and TrKB expression occurs prior to the rise in blood pressure, while a reinforcement of vascular and circulating oxidative stress markers is brought about later by hypertension.

Serum brain-derived neurotrophic factor and platelet activation evaluated by soluble P-selectin and soluble CD-40-ligand in patients with acute myocardial infarction

Little is known about the role of neurotrophins (NT) under adult vascular homeostasis in normal and pathological conditions. The NT family, including nerve growth factor and brain-derived neurotrophic factor (BDNF) are expressed in atherosclerotic vessels. Previous studies demonstrated that plasma BDNF levels were increased in the coronary circulation in patients with unstable angina. However, the role of BDNF during the onset and evolution of unstable angina remains to be elucidated. The objective of this study was to evaluate the relationship between BDNF, functional parameters and biological markers associated with inflammatory processes and platelet activation. BDNF serum levels were assessed in patients with acute myocardial infarction (MI) (n = 20) or stable angina pectoris (SAP) (n = 20) who underwent coronary angiography. Serum levels of IL-6, MCP1, sVCAM, soluble CD-40-ligand (sCD40L) and soluble P-selectin (sP-selectin) were measured simultaneously by flux cytometry. Median BDNF levels were higher in the MI than in the SAP group (1730 vs. 877 pg/mL, respectively; P = 0.025). In MI patients, we observed a significant correlation between BDNF and sP-selectin (r = 0.58, P = 0.023), although we found a non-significant trend between BDNF and sCD40L (r = +0.35, P = 0.144). By contrast, no such correlation was observed in SAP patients (r = -0.22, P = 0.425). No difference was observed between the two groups regarding baseline demographics, risk factors, biological data and angiographic findings. The study suggests that BDNF serum levels in MI patients could be related to platelet activation and the inflammatory response. Further studies are needed to investigate the role of NT in the setting of acute MI.

Cardiovascular actions of neurotrophins

Neurotrophins were christened in consideration of their actions on the nervous system and, for a long time, they were the exclusive interest of neuroscientists. However, more recently, this family of proteins has been shown to possess essential cardiovascular functions. During cardiovascular development, neurotrophins and their receptors are essential factors in the formation of the heart and critical regulator of vascular development. Postnatally, neurotrophins control the survival of endothelial cells, vascular smooth muscle cells, and cardiomyocytes and regulate angiogenesis and vasculogenesis, by autocrine and paracrine mechanisms. Recent studies suggest the capacity of neurotrophins, via their tropomyosin-kinase receptors, to promote therapeutic neovascularization in animal models of hindlimb ischemia. Conversely, the neurotrophin low-affinity p75(NTR) receptor induces apoptosis of endothelial cells and vascular smooth muscle cells and impairs angiogenesis. Finally, nerve growth factor looks particularly promising in treating microvascular complications of diabetes or reducing cardiomyocyte apoptosis in the infarcted heart. These seminal discoveries have fuelled basic and translational research and thus opened a new field of investigation in cardiovascular medicine and therapeutics. Here, we review recent progress on the molecular signaling and roles played by neurotrophins in cardiovascular development, function, and pathology, and we discuss therapeutic potential of strategies based on neurotrophin manipulation.

A novel cardiac hypertrophic factor, neurotrophin-3, is paradoxically downregulated in cardiac hypertrophy

The neurotrophin family plays pivotal roles in the development of the nervous system. Recently, the role of the neurotrophin in non-neural tissue has been extensively investigated. Among them, neurotrophin-3 and its receptor TrkC are critical for embryonic heart development, though little is known about neurotrophin-3/TrkC function in adult heart. Moreover, the expressions of other neurotrophin and Trk families in the cardiovascular system have not been fully determined. In adult and neonatal rats, only TrkC mRNA was expressed more abundantly in heart than aorta among the neurotrophin receptors, while all neurotrophins were equally expressed in the cardiovascular system. Immunohistochemistry confirmed the protein expressions of neurotrophin-3/TrkC in rat ventricles. In primary-cultured rat cardiomyocytes, neurotrophin-3 strongly activated p38 mitogen-activated protein kinase, extracellular signal-regulated kinase 1/2, and Jun N-terminal kinase pathways in Western blot analysis. In Northern blot analysis, neurotrophin-3 strongly increased mRNA expressions of cardiac hypertrophic markers (skeletal alpha-actin and atrial natriuretic peptide) in cardiomocytes. [(3)H]-phenylalanine uptake into cardiomyocytes, myofilament reorganization, and cardiomyocyte size were also augmented with neurotrophin-3 stimulation, indicating that neurotrophin-3 is a novel cardiac hypertrophic factor. Unexpectedly, neurotrophin-3 was downregulated in cardiac hypertrophy induced by pressure overload (in vivo), and in cardiomyocyte hypertrophy evoked by endothelin-1 stimulation (in vitro). Interestingly, the cell size and BNP mRNA expression level (markers of hypertrophy) were greater in cardiomyocytes treated with both neurotrophin-3 and endothelin-1 than in those stimulated with endothelin-1 alone. These findings demonstrate that neurotrophin-3 is a unique hypertrophic factor, which is paradoxically downregulated in cardiac hypertrophy and might counteract hypertrophic change.