Nerve growth factor: increased angiogenesis without improved nerve regeneration

Targeting NGF but not VEGFR1 or BDNF signaling reduces endometriosis-associated pain in mice

INTRODUCTION

Endometriosis is a chronic inflammatory disease that affects ∼10 % of women. A significant fraction of patients experience limited or no efficacy with current therapies. Tissue adjacent to endometriosis lesions often exhibits increased neurite and vascular density, suggesting that disease pathology involves neurotrophic activity and angiogenesis.

OBJECTIVES

We aim to evaluate the potential for key tyrosine-kinase-receptor-coupled neurotrophic molecules to contribute to endometriosis-associated pain in mice.

METHODS

Peritoneal fluid was collected from endometriosis patients undergoing surgery and the levels of NGF and VEGFR1 regulators (VEGFA, VEGFB, PLGF, and sVEGFR1) were quantified by ELISA. VEGFR1 regulator concentrations were used to calculate VEGFR1 occupancy. We used genetic depletion, neutralizing antibodies, and pharmacological approaches to specifically block neurotrophic ligands (NGF or BDNF) or receptors (VEGFR1, TRKs) in a murine model of endometriosis-associated pain. Endometriosis-associated pain was measured using von Frey filaments, quantification of spontaneous abdominal pain-related behavior, and thermal discomfort. Disease parameters were evaluated by lesion size and prevalence. To evaluate potential toxicity, we measured the effect of entrectinib dose and schedule on body weight, liver and kidney function, and bone structure (via micro-CT).

RESULTS

We found that entrectinib (pan-Trk inhibitor) or anti-NGF treatments reduced evoked pain, spontaneous pain, and thermal discomfort. In contrast, even though calculated receptor occupancy revealed that VEGFR1 agonist levels are sufficient to support signaling, blocking VEGFR1 via antibody or tamoxifen-induced knockout did not reduce pain or lesion size in mice. Targeting BDNF-TrkB with an anti-BDNF antibody also proved ineffective. Notably, changing dosing schedule to once weekly eliminated entrectinib-induced bone-loss without decreasing efficacy against pain.

CONCLUSIONS

This suggests NGF-TrkA signaling, but not BDNF-TrkB or VEGF-VEGFR1, mediates endometriosis-associated pain. Moreover, entrectinib blocks endometriosis-associated pain and reduces lesion sizes. Our results also indicated that entrectinib-like molecules are promising candidates for endometriosis treatment.

The intriguing role of platelets as custodians of brain-derived neurotrophic factor

A State of the Art lecture titled "Platelets and neurotrophins" was presented at the International Society on Thrombosis and Haemostasis Congress in 2023. Neurotrophins, a family of neuronal growth factors known to support cognitive function, are increasingly recognized as important players in vascular health. Indeed, along with their canonical receptors, neurotrophins are expressed in peripheral tissues, particularly in the vasculature. The better-characterized neurotrophin in vascular biology is the brain-derived neurotrophic factor (BDNF). Its largest extracerebral pool resides within platelets, partly inherited from megakaryocytes and also likely internalized from circulation. Activation of platelets releases vast amounts of BDNF into their milieu and interestingly leads to platelet aggregation through binding of its receptor, the tropomyosin-related kinase B, on the platelet surface. As BDNF is readily available in plasma, a mechanism to preclude excessive platelet activation and aggregation appears critical. As such, binding of BDNF to α2-macroglobulin hinders its ability to bind its receptor and limits its platelet-activating effects to the site of vascular injury. Altogether, addition of BDNF to a forming clot facilitates not only paracrine platelet activation but also binding to fibrinogen, rendering the resulting clot more porous and plasma-permeable. Importantly, release of BDNF into circulation also appears to be protective against adverse cardiovascular and cerebrovascular outcomes, which has been reported in both animal models and epidemiologic studies. This opens an avenue for platelet-based strategies to deliver BDNF to vascular lesions and facilitate wound healing through its regenerative properties. Finally, we summarize relevant new data on this topic presented during the 2023 International Society on Thrombosis and Haemostasis Congress.

Current Knowledge and Future Therapeutic Prospects in Symptomatic Intervertebral Disc Degeneration

Intervertebral disc (IVD) degeneration is the main source of intractable lower back pain, and symptomatic IVD degeneration could be due to different degeneration mechanisms. In this article, we describe the molecular basis of symptomatic IVD degenerative disc diseases (DDDs), emphasizing the role of degeneration, inflammation, angiogenesis, and extracellular matrix (ECM) regulation during this process. In symptomatic DDD, pro-inflammatory mediators modulate catabolic reactions, resulting in changes in ECM homeostasis and, finally, neural/vascular ingrowth-related chronic intractable discogenic pain. In ECM homeostasis, anabolic protein-regulating genes show reduced expression and changes in ECM production, while matrix metalloproteinase gene expression increases and results in aggressive ECM degradation. The resultant loss of normal IVD viscoelasticity and a concomitant change in ECM composition are key mechanisms in DDDs. During inflammation, a macrophage-related cascade is represented by the secretion of high levels of pro-inflammatory cytokines, which induce inflammation. Aberrant angiogenesis is considered a key initiative pathologic step in symptomatic DDD. In reflection of angiogenesis, vascular endothelial growth factor expression is regulated by hypoxia-inducible factor-1 in the hypoxic conditions of IVDs. Furthermore, IVD cells undergoing degeneration potentially enhance neovascularization by secreting large amounts of angiogenic cytokines, which penetrate the IVD from the outer annulus fibrosus, extending deep into the outer part of the nucleus pulposus. Based on current knowledge, a multi-disciplinary approach is needed in all aspects of spinal research, starting from basic research to clinical applications, as this will provide information regarding treatments for DDDs and discogenic pain.

Simultaneous fluorescence imaging of distinct nerve and blood vessel patterns in dual Thy1-YFP and Flt1-DsRed transgenic mice

Blood vessels and nerve tissues are critical to the development and functionality of many vital organs. However, little is currently known about their interdependency during development and after injury. In this study, dual fluorescence transgenic reporter mice were utilized to observe blood vessels and nervous tissues in organs postnatally. Thy1-YFP and Flt1-DsRed (TYFD) mice were interbred to achieve dual fluorescence in the offspring, with Thy1-YFP yellow fluorescence expressed primarily in nerves, and Flt1-DsRed fluorescence expressed selectively in blood vessels. Using this dual fluorescent mouse strain, we were able to visualize the networks of nervous and vascular tissue simultaneously in various organ systems both in the physiological state and after injury. Using ex vivo high-resolution imaging in this dual fluorescent strain, we characterized the organizational patterns of both nervous and vascular systems in a diverse set of organs and tissues. In the cornea, we also observed the dynamic patterns of nerve and blood vessel networks following epithelial debridement injury. These findings highlight the versatility of this dual fluorescent strain for characterizing the relationship between nerve and blood vessel growth and organization.

Vascularization of the Damaged Nerve under the Effect of Experimental Cell Therapy

Quantitative analysis of blood vessels in the distal segment of rat sciatic nerve after its ligation for 40 sec and subperineurial administration of mesenchymal stem cells or dissociated cells of rat embryonic spinal cord was carried our by immunohistochemical tracing of von Willebrand factor, a marker of endothelial cells of blood vessels. It was found that the number of blood vessels per unit area of the nerve trunk in 21 days after injury and administration of mesenchymal stem cells increased by more than 1.5 times in comparison with the control (damaged nerve). After administration of dissociated cells of the embryonic spinal cord, this effect was not observed. It is assumed that mesenchymal stem cells stimulate the growth of vessels of the damaged nerve via production of angiogenic factors.

Evaluation of nerve growth factor (NGF) treated mesenchymal stem cells for recovery in neurotmesis model of peripheral nerve injury

BACKGROUND

Peripheral nerve damages are a relatively common type of the nervous system injuries. Although peripheral nerves show some capacity of regeneration after injury, the extent of regeneration is not remarkable. The present study aimed to evaluate the effect of NGF treated mesenchymal stem cells on regeneration of transected sciatic nerve.

MATERIALS AND METHODS

In this experimental study, forty-two male Wistar.rats (180-200 g) were randomly divided into 6 groups (n = 7) including control, Membrane + Cell (Mem + Cell), NGF group, NGF + Cell group, NGF + Mem group and NGF + Mem + Cell group. Regeneration of sciatic nerve was evaluated using behavioral analysis, electrophysiological assessment and histological examination.

RESULTS

The rats in the NGF + Mem + Cell group showed significant decrease in sciatic functional index (SFI) and hot water paw immersion test during the 2nd to 8th weeks after surgery. (p < 0.001). At 8 weeks after surgery, electrophysiological findings showed that amplitude increased and latency decreased significantly in NGF + Mem + Cell group (p < 0.001). Measured histological parameters showed that number of nerve fibers, number of vessels and percent of vessel area also increased significantly in NGF + Mem + Cell group (p < 0.05).

CONCLUSION

The present study showed that NGF in accompany with mesenchymal stem cells improved electrophysiological and histological indices.

Preparation and Characterization of Breathable Hemostatic Hydrogel Dressings and Determination of Their Effects on Full-Thickness Defects

Hydrogel-based wound dressings provide a cooling sensation, a moist environment, and act as a barrier to microbes for wounds. In this study, a series of soft, flexible, porous non-stick hydrogel dressings were prepared through the simple repeated freeze-thawing of a poly(vinyl alcohol), human-like collagen (or and carboxymethyl chitosan) mixed solution rather than chemical cross-linking and Tween80 was added as pore-forming agent for cutaneous wound healing. Some of their physical and chemical properties were characterized. Interestingly, hydrogel PVA-HLC-T80 and PVA-HLC-CS-T80 presented excellent swelling ratios, bacterial barrier activity, moisture vapor permeability, hemostasis activity and biocompatibility. Furthermore, in vivo evaluation of the healing capacity of these two hydrogels was checked by creating a full-thickness wound defect (1.3 cm × 1.3 cm) in rabbit. Macroscopic observation and subsequent hematoxylin eosin staining (H&amp;E) staining and transmission electron microscopy (TEM) analysis at regular time intervals for 18 days revealed that the hydrogels significantly enhanced wound healing by reducing inflammation, promoting granulation tissue formation, collagen deposition and accelerating re-epithelialization. Taken together, the obtained data strongly encourage the use of these multifunctional hydrogels for skin wound dressings.

Glycoproteins functionalized natural and synthetic polymers for prospective biomedical applications: A review

Glycoproteins have multidimensional properties such as biodegradability, biocompatibility, non-toxicity, antimicrobial and adsorption properties; therefore, they have wide range of applications. They are blended with different polymers such as chitosan, carboxymethyl cellulose (CMC), polyvinyl pyrrolidone (PVP), polycaprolactone (PCL), heparin, polystyrene fluorescent nanoparticles (PS-NPs) and carboxyl pullulan (PC) to improve their properties like thermal stability, mechanical properties, resistance to pH, chemical stability and toughness. Considering the versatile charateristics of glycoprotein based polymers, this review sheds light on synthesis and characterization of blends and composites of glycoproteins, with natural and synthetic polymers and their potential applications in biomedical field such as drug delivery system, insulin delivery, antimicrobial wound dressing uses, targeting of cancer cells, development of anticancer vaccines, development of new biopolymers, glycoproteome research, food product and detection of dengue glycoproteins. All the technical scientific issues have been addressed; highlighting the recent advancement.

Novel multifunctional PB and PBH hydrogels as soft filler for tissue engineering

Multifunctionalized PB and PBH hydrogels scaffolds and injectable particles with good biocompatibility and anti-biodegradation are based on pullulan and human-like collagen for skin restoration, cartilage treatment, and lacrimal drynesstherapy.

The biology of neurotrophins: cardiovascular function

This chapter addresses the role of neurotrophins in the development of the heart, blood vessels, and neural circuits that control cardiovascular function, as well as the role of neurotrophins in the mature cardiovascular system. The cardiovascular system includes the heart and vasculature whose functions are tightly controlled by the nervous system. Neurons, cardiomyocytes, endothelial cells, vascular smooth muscle cells, and pericytes are all targets for neurotrophin action during development. Neurotrophin expression continues throughout life, and several common pathologies that impact cardiovascular function involve changes in the expression or activity of neurotrophins. These include atherosclerosis, hypertension, diabetes, acute myocardial infarction, and heart failure. In many of these conditions, altered expression of neurotrophins and/or neurotrophin receptors has direct effects on vascular endothelial and smooth muscle cells in addition to effects on nerves that modulate vascular resistance and cardiac function. This chapter summarizes the effects of neurotrophins in cardiovascular physiology and pathophysiology.

Effect of Tris-acetate buffer on endotoxin removal from human-like collagen used biomaterials

Protein preparation, which has active ingredients designated for the use of biomaterials and therapeutical protein, is obtained by genetic engineering, but products of genetic engineering are often contaminated by endotoxins. Because endotoxin is a ubiquitous and potent proinflammatory agent, endotoxin removal or depletion from protein is essential for researching any biomaterials. In this study, we have used Tris-acetate (TA) buffer of neutral pH value to evaluate endotoxins absorbed on the Pierce high-capacity endotoxin removal resin. The effects of TA buffer on pH, ionic strength, incubation time as well as human-like collagen (HLC) concentration on eliminating endotoxins are investigated. In the present experiments, we design an optimal method for TA buffer to remove endotoxin from recombinant collagen and use a chromogenic tachypleus amebocyte lysate (TAL) test kit to measure the endotoxin level of HLC. The present results show that, the endotoxins of HLC is dropped to 8.3EU/ml at 25 mM TA buffer (pH7.8) with 150 mM NaCl when setting incubation time at 6h, and HLC recovery is about 96%. Under this experimental condition, it is proved to exhibit high efficiencies of both endotoxin removal and collagen recovery. The structure of treated HLC was explored by Transmission Electron Microscopy (TEM), demonstrating that the property and structure of HLC treated by TA buffer are maintained. Compared to the most widely used endotoxin removal method, Triton X-114 extraction, using TA buffer can obtain the non-toxic HLC without extra treatment for removing the toxic substances in Triton X-114. In addition, the present study aims at establishing a foundation for further work in laboratory animal science and providing a foundation for medical grade biomaterials.

Effects of self-assembled fibers on the synthesis, characteristics and biomedical applications of CCAG hydrogels

Injectable CCAG hydrogels as body filler materials were prepared by self-assembly of CCA fibers and crosslinking with β-GP.

Inflammatory mediators in intervertebral disk degeneration and discogenic pain

Although degeneration of the intervertebral disk has historically been described as a misbalance between anabolic and catabolic factors, the role of inflammatory mediators has long been neglected. However, past research clearly indicates that inflammatory mediators such as interleukin (IL)-1β, IL-6, IL-8 and tumor necrosis factor-α are expressed at higher levels in "diseased" intervertebral disks. Both disk cells as well as invading macrophages can be the source of the detected cytokines. Importantly, occurrence of inflammatory mediators in the disk can worsen the progress of degeneration by inducing the expression of matrix degrading enzymes as well as by inhibiting extracellular matrix synthesis. In addition, inflammatory mediators play a crucial role in pain development during intervertebral disk herniation (i.e., sciatica) and disk degeneration (i.e., discogenic pain). This review provides information on the most relevant inflammatory mediators during different types of disk diseases and explains how these factors can induce disk degeneration and the development of discogenic and sciatic/radiculopathic pain.

The proarrhythmic risk of cell therapy for cardiovascular diseases

Stem cell therapy is an emerging therapeutic approach for the treatment of cardiovascular diseases. Experimental studies have demonstrated that different types of stem cells, including bone marrow-derived cells, mesenchymal stem cells, skeletal myoblasts, and cardiac progenitor cells and embryonic stem cells, can improve cardiac function after myocardial injuries. Nevertheless, the potential proarrhythmic risk after stem cell transplantation remains a major concern. Several mechanisms, including the immaturity of electrical phenotypes of the transplanted cardiomyocytes, poor cell-cell coupling and cardiac nerve sprouting, may contribute to arrhythmogenic risk after stem cell transplantation. This review summarizes the potential theoretical arrhythmogenic mechanisms associated with different types of stem cells for the treatment of cardiovascular diseases. Nevertheless, current experimental and clinical data on the proarrhythmic risk for different types of stem cell transplantation are limited, and await further experimental and clinical investigation.

Mechanisms and targets of angiogenesis and nerve growth in osteoarthritis

During osteoarthritis (OA), angiogenesis is increased in the synovium, osteophytes and menisci and leads to ossification in osteophytes and the deep layers of articular cartilage. Angiogenic and antiangiogenic factors might both be upregulated in the osteoarthritic joint; however, vascular growth predominates, and the articular cartilage loses its resistance to vascularization. In addition, blood vessel growth is increased at--and disrupts--the osteochondral junction. Angiogenesis in this location is dependent on the creation of channels from subchondral bone spaces into noncalcified articular cartilage. Inflammation drives synovial angiogenesis through macrophage activation. Blood vessel and nerve growth are linked by common pathways that involve the release of proangiogenic factors, such as vascular endothelial growth factor, β-nerve growth factor and neuropeptides. Proangiogenic factors might also stimulate nerve growth, and molecules produced by vascular cells could both stimulate and guide nerve growth. As sensory nerves grow along new blood vessels in osteoarthritic joints, they eventually penetrate noncalcified articular cartilage, osteophytes and the inner regions of menisci. Angiogenesis could, therefore, contribute to structural damage and pain in OA and provide potential targets for new treatments.

Nerve growth factor promotes endothelial progenitor cell-mediated angiogenic responses

PURPOSE

In response to ischemia, retinal neuronal cells express nerve growth factor (NGF), which can be proangiogenic. Endothelial progenitor cells (EPCs) can participate with the resident vasculature to promote angiogenesis. We postulated that NGF may stimulate CD34⁺ EPCs to convert to an angiogenic phenotype.

METHODS

Human CD34⁺ cells and human retinal endothelial cells (HRECs) were used to examine the effect of NGF on key steps associated with neovascularization. CD34⁺ cells and HRECs were stimulated with NGF (1 to 4 pM) for 24, 48, and 72 hours. Cell migration was measured using a modified Boyden chamber assay. Expression of the receptor for the cytokine stromal derived growth factor 1 (SDF-1), CXCR-4, was assessed by flow cytometry. In vitro angiogenesis was tested using a three-dimensional (3D) extracellular matrix with HRECs/CD34⁺ cell cocultures. NGF receptor activation was assessed by western analysis.

RESULTS

NGF promoted proliferation of CD34⁺ cells but not HRECs. Pretreatment of CD34⁺ cells with NGF increased CXCR-4 expression in CD34⁺ cells, resulting in enhanced migration to SDF-1 (P < 0.0001). The enhanced tubule-forming effect of NGF in HRECs was further potentiated by coculture with NGF-pretreated CD34⁺ cells (P < 0.01). The beneficial effect of NGF was blocked (P < 0.0001) by the ERK inhibitor PD98059. In both CD34⁺ and HRECs, NGF increased phosphorylation of neurotrophic tyrosine kinase receptor type 1 (TrkA) receptor by ERK1 activation (P < 0.01).

CONCLUSIONS

Our in vitro results suggest that NGF released from ischemic nerves in vivo may contribute to the "angiogenic switch" by stimulating the angiogenic behavior of CD34⁺ cells while minimally affecting resident retinal endothelial cells.

Standardized criterion to analyze and directly compare various materials and models for peripheral nerve regeneration

Progress in understanding conditions for optimal peripheral nerve regeneration has been stunted due to lack of standardization of experimental conditions and assays. In this paper we review the large database that has been generated using the Lundborg nerve chamber model and compare various theories for their ability to explain the experimental data. Data were normalized based on systematic use of the critical axon elongation, the gap length at which the probability of axon reconnection between the stumps is just 50%. Use of this criterion has led to a rank-ordering of devices or treatments and has led, in turn, to conclusions about the conditions that facilitate regeneration. Experimental configurations that have maximized facilitation of peripheral nerve regeneration are those in which the tube wall comprised degradable polymers, including collagen and certain synthetic biodegradable polymers, and was cell-permeable rather than protein-permeable. Tube fillings that showed very high regenerative activity were suspensions of Schwann cells, a solution either of acidic or basic fibroblast growth factor, insoluble ECM substrates rather than solutions or gels, polyamide filaments oriented along the tube axis and highly porous, insoluble analogs of the ECM with specific structure and controlled degradation rate. It is suggested that the data are best explained by postulating that the quality of regeneration depends on two critical processes. The first is compression of stumps and regenerating nerve by a thick myofibroblast layer that surrounds these tissues and blocks synthesis of a nerve of large diameter (pressure cuff theory). The second is synthesis of linear columns of Schwann cells that serve as tracks for axon elongation (basement membrane microtube theory). It is concluded that experimental configurations that show high regenerative activity suppress the first process while facilitating the second.

Initial investigation of novel human-like collagen/chitosan scaffold for vascular tissue engineering

With the increasing occurrence of vascular diseases and poor long-term patency rates of current small diameter vascular grafts, it becomes urgent to pursuit biomaterial as scaffold to mimic blood vessel morphologically and mechanically. In this study, novel human-like collagen (HLC, produced by recombinant E. coli)/chitosan tubular scaffolds were fabricated by cross-linking and freeze-drying process. The scaffolds were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and tensile test, respectively. Human venous fibroblasts were expanded and seeded onto the scaffolds in the density of 1 x 10(5) cells/cm(2). After a 15-day culture under static conditions, the cell-polymer constructs were observed using SEM, confocal laser scanning microscopy (CLSM), histological examination, and biochemical assays for cell proliferation and extracellular matrix production (collagen and glycosaminoglycans). Furthermore, the scaffolds were implanted into rabbits' livers to evaluate their biocompatibility. The results indicated that HLC/chitosan tubular scaffolds (1) exhibited interconnected porous structure; (2) achieved the desirable levels of pliability (elastic up to 30% strain) and stress of 300 +/- 16 kPa; (3) were capable of enhancing cell adhesion and proliferation and ECM secretion; (4) showed superior biocompatibility. This study suggested the feasibility of HLC/chitosan composite as a promising candidate scaffold for blood vessel tissue engineering.

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.

Nerve growth factor as an angiogenic factor

Nerve growth factor (NGF), a neurotrophin that plays a crucial role in promoting neurotrophic and neurotropic effects in sympathetic neurons, has recently been identified as a novel angiogenic molecule, which exerts a variety of effects in the cardiovascular system and on endothelial cells. In fact, NGF may contribute to maintenance, survival, and function of endothelial cells by autocrine and/or paracrine mechanisms. This review summarizes the involvement of NGF in the regulation of angiogenesis in both normal and pathological conditions.

Neural driven angiogenesis by overexpression of nerve growth factor

Mechanisms regulating angiogenesis are crucial in adjusting tissue perfusion on metabolic demands. We demonstrate that overexpression of nerve growth factor (NGF) in brown adipose tissue (BAT) of NGF-transgenic mice elevates both mRNA and protein levels of vascular endothelial growth factor (VEGF) and VEGF-receptors. Increased vascular permeability, leukocyte-endothelial interactions (LEI), and tissue perfusion were measured using intravital microscopy. NGF-stimulation of adipocytes and endothelial cells elevates mRNA expression of VEGF and its receptors, an effect blocked by NGF neutralizing antibodies. These data suggest an activation of angiogenesis as a result of both: stimulation of adipozytes and direct mitogenic effects on endothelial cells. The increased nerve density associated with vessels strengthened our hypothesis that tissue perfusion is regulated by neural control of vessels and that the interaction between the NGF and VEGF systems is the critical driver for the activated angiogenic process. The interaction of VEGF- and NGF-systems gives new insights into neural control of organ vascularization and perfusion.

Ultrastructural analysis of guided nerve regeneration using progesterone- and pregnenolone-loaded chitosan prostheses

Recently, numerous guide chambers for the treatment of injured nerves made up of different biomaterials have been designed, capable of hosting living cells or carrying neurotrophic or neuroactive substances to be directly released to the injured tissue. In this study, chitosan prostheses containing neurosteroids (progesterone and pregnenolone) were used for bridging a 10-mm gap in the rabbit facial nerve. Gas chromatography was used to quantify neurosteroid content in the prostheses prior to and after subcutaneous implantation at different periods of up to 60 days. The regeneration of the nerve fibers were evaluated at 15 and 45 days after axotomy by means of ultrastructural morphometric analysis. Different nerve fibers regenerative patterns were seen depending the groups studied and the analyzed stages. At 15 days after axotomy, the newly regenerating tissue revealed Schwann cells holding nonmyelinated nerve fiber bundles in an incipient and organized regenerative pattern. At 45 days, the regenerating tissue showed myelinated nerve fibers of different sizes, shapes, and myelin sheath thickness. Although the regeneration of the nerve fibers under neurosteroid treatment showed statistically significant differences in comparison with vehicle regenerated tissue, progesterone-loaded chitosan prostheses produced the best guided nerve regeneration response. These findings indicate that chitosan prostheses allowed regeneration of nerve fibers in their lumen, and when containing neurosteroids produced a faster guided nerve regeneration acting as a long-lasting release delivery vehicle.

Chitin-based tubes for tissue engineering in the nervous system

The purpose of this study was to investigate chitin and chitosan as potential materials for biodegradable nerve guides. Transparent chitin hydrogel tubes were synthesized, for the first time, from chitosan solutions using acylation chemistry and mold casting techniques. Alkaline hydrolysis of chitin tubes resulted in chitosan tubes, with the extent of hydrolysis controlling the resulting amine content. This, in turn, impacted compressive strength and cell adhesion. Chitosan tubes were mechanically stronger than their chitin origins, as measured by the transverse compressive test, where tubes having degrees of acetylation of 1%, 3%, 18% (i.e. chitosan) and 94% (i.e. chitin) supported loads at a 30% displacement of 40.6 +/- 4.3, 25.3 +/- 4.5, 10.6 +/- 0.8, and 8.7 +/- 0.4 g, respectively. However, the chitin processing methodology could be optimized for compressive strength, by either incorporating reinforcing coils in the tube wall, or air-drying the hydrogel tubes. Chitin and chitosan supported adhesion and differentiation of primary chick dorsal root ganglion neurons in vitro. Chitosan films showed significantly enhanced neurite outgrowth relative to chitin films, reflecting the dependence of nerve cell affinity on the amine content in the polysaccharide: neurites extended 1794.7 +/- 392.0 microm/mm(2) on chitosan films vs. 140.5 +/- 41.6 microm/mm(2) on chitin films after 2 days of culture. This implies that cell adhesion and neurite extension can be adjusted by amine content, which is important for tissue engineering in the nervous system. The methods for easy processing and modification of chitin and chitosan described herein, allow the mechanical properties and cyto-compatibility to be controlled and provide a means for a broader investigation into their use in biomedical applications.

Stress alters vascular?endothelial growth factor expression in rat arteries: Role of nerve growth factor

The aim of this study was to investigate the role of stress and nerve growth factor (NGF) on the expression of vascular-endothelial growth factor (VEGF) and NGF high-affinity receptor (tyrosine kinase A, TrKA) in the ascending and abdominal aorta.Adult male rats were exposed to immobilization stress for one hour or injected with purified murine NGF. Four hours after treatments, rats were sacrificed and VEGF, NGF and TrkA expression in ascending and abdominal aorta evaluated. The effects of anti-NGF treatment on arterial VEGF expression and on stress-induced arterial cell proliferation were also studied in control and stressed rats.The data indicated that both stress and NGF injection induced a rapid increase of arterial VEGF associated with an elevated level of NGF and TrkA in arterial tissues. Blocking NGF action by neutralizing NGF-antibodies, results in down-regulation of stress-induced VEGF expression by arteries and in the blockade of stress-induced proliferation of cells from the arterial wall.Overall our data demonstrated that NGF is involved in the regulation of VEGF and in cardiac vessels response after emotional stress.

Selection of biomaterials for peripheral nerve regeneration using data from the nerve chamber model

Peripheral nerve regeneration has been studied in a variety of animal models. Of these, the nerve chamber model has clearly dominated. It has been used to generate a large base of data that, however, cannot be analyzed usefully due to lack of standardization of experimental conditions and assays. Lack of standardization of critical experimental parameters of the model has, however, greatly limited the opportunity to compare directly data from independent investigators; as a result, progress in understanding conditions for optimal nerve regeneration has been stunted. In this article, we provide an overview of the major experimental parameters that must be controlled in order to generate data from independent investigators that can be compared directly (normalized data). Such parameters include the gap length, animal species, and the identity of assays used to evaluate the product of the regenerative process. Use of the recently introduced concept of critical axon elongation, the gap length at which the probability of axonal outgrowth (reinnervation) across the gap is 50%, leads to generation of a normalized database that includes data from several independent investigators. Conclusions are drawn about the relative efficacy of the various biomaterials and devices employed. Nerve chamber configurations that had the highest regenerative activity were those in which the tube wall comprised collagen and certain synthetic biodegradable polymers rather than silicone, and was cell-permeable rather than protein-permeable. In addition, the following tube fillings showed very high regenerative activity: suspensions of Schwann cells; a solution either of acidic or basic fibroblast growth factor; insoluble ECM substrates rather than solutions or gels; polyamide filaments oriented along the tube axis; highly porous, insoluble analogs of the ECM with specific structure and controlled degradation rate.

Reverse Effects of Tetraarsenic Oxide on the Angiogenesis Induced by Nerve Growth Factor in the Rat Cornea

To compare the antiangiogenic effects of tetraarsenic oxide (As4O6) with those of diarsenic oxide (As2O3) in the rat cornea, rat cornea micropocket assay was conducted to induce angiogenesis by implantation of the pellet contained 1.0 ng of nerve growth factor (NGF). Ten of thirty eyes of Sprague-Dawley rats were randomly assigned to one of three groups, namely, control group (no medication), As2O3 group (50 mg/kg As2O3, PO, s.i.d.), and As4O6 group (50 mg/kg As4O6, PO, s.i.d.). After implantation, the number of new vessels, vessel length and clock hour of neovascularization were examined under the microscope from day 3 to day 7. The area of neovascularization was calculated using a mathematical formula. Although new vessels in control and As2O3 groups were first noticed at day 3, whereas those of As4O6 group were first observed on day 5. The number, length, clock hour of neovascularization and areas of the vessels in As4O6 group showed more significant inhibition than those of control and As2O3 groups from day 5 (P<0.05). However, there were no differences in all parameters between control group and As2O3 group during the entire study period. These results showed that As4O6 had antiangiogenic effects on the new vessels induced by NGF in the rat cornea.

Mesenchymal stem cell injection induces cardiac nerve sprouting and increased tenascin expression in a Swine model of myocardial infarction

Stem Cell Induces Cardiac Nerve Sprouting.

INTRODUCTION

Mesenchymal stem cell (MSC) transplantation is a promising technique to improve cardiac function. Whether MSC can increase cardiac nerve density and contribute to the improved cardiac function is unclear.

METHODS AND RESULTS

Anterior wall myocardial infarction was created in 16 swine. One month later, 6 swine were given MSC and fresh bone marrow (BM) into infarcted myocardium (MSC group). Four swine were given fresh BM only (BM group), and 6 swine were given culture media (MI-only group). The swine were sacrificed 95.8 +/- 3.5 days after MI. Six normal swine were used as control. Immunocytochemical staining was performed using antibodies against growth-associated protein 43 (GAP43), tyrosine hydroxylase (TH), and three subtypes of tenascin (R, C, and X). Five fields per slide were counted for nerve density. The results show the following. (1). There were more GAP43-positive nerves in the MSC group than in the BM, MI-only, or Control group (P < 0.0001). TH staining showed higher nerve densities in the MSC group than in the MI-only (P < 0.01) or Control group (P < 0.0001) in the atria. (2). There were more sympathetic (TH-positive) nerves in myocardium distant from infarct than in the peri-infarct area (P < 0.05). (3). Optical intensity and color analyses showed significantly higher tenascin R and tenascin C expression in the MSC and BM groups than in the MI-only or Control group (P < 0.01).

CONCLUSION

MSC injected with BM into swine infarct results in overexpression of cardiac tenascin, increased the magnitude of cardiac nerve sprouting in both atria and ventricles, and increased the magnitude of atrial sympathetic hyperinnervation 2 months after injection.

Deletion of neuropeptide Y (NPY) 2 receptor in mice results in blockage of NPY-induced angiogenesis and delayed wound healing

Neuropeptide Y (NPY), a 36-aa peptide, is widely distributed in the brain and peripheral tissues. Whereas physiological roles of NPY as a hormoneneurotransmitter have been well studied, little is known about its other peripheral functions. Here, we report that NPY acts as a potent angiogenic factor in vivo using the mouse corneal micropocket and the chick chorioallantoic membrane (CAM) assays. Unlike vascular endothelial growth factor (VEGF), microvessels induced by NPY had distinct vascular tree-like structures showing vasodilation. This angiogenic pattern was similar to that induced by fibroblast growth factor-2, and the angiogenic response was dose-dependent. In the developing chick embryo, NPY stimulated vascular sprouting from preexisting blood vessels. When [Leu(31)Pro(34)]NPY, a NPY-based analogue lacking high affinity for the NPY Y(2) receptor but capable of stimulating both Y(1) and Y(5) receptors, was used in the corneal model, no angiogenic response could be detected. In addition, NPY failed to induce angiogenesis in Y(2) receptor-null mice, suggesting that this NPY receptor subtype was mediating the angiogenic signal. In support of this finding, the Y(2) receptor, but not Y(1), Y(4), or Y(5) receptors, was found to be widely expressed in newly formed blood vessels. Further, a delay of skin wound healing with reduced neovascularization was found in Y(2) receptor-null mice. These data demonstrate that NPY may play an important role in the regulation of angiogenesis and angiogenesis-dependent tissue repair.

Nerve growth factor promotes angiogenesis and arteriogenesis in ischemic hindlimbs

BACKGROUND

The neurotrophin nerve growth factor (NGF) regulates neuron survival and differentiation. Implication in neovascularization is supported by statement of NGF and its high-affinity receptor at vascular level and by NGF property of stimulating vascular endothelial cell proliferation. The present study investigated the involvement of endogenous NGF in spontaneous reparative response to ischemia. Mechanisms and therapeutic potential of NGF-induced neovascularization were examined.

METHODS AND RESULTS

Unilateral limb ischemia was produced in CD1 mice by femoral artery resection. By ELISA and immunohistochemistry, we documented that statement of NGF and its high-affinity receptor is upregulated in ischemic muscles. The functional relevance of this phenomenon was assessed by means of NGF-neutralizing antibody. Chronic NGF blockade abrogated the spontaneous capillarization response to ischemia and augmented myocyte apoptosis. Then we tested whether NGF administration may exert curative effects. Repeated NGF injection into ischemic adductors increased capillary and arteriole density, reduced endothelial cell and myofiber apoptosis, and accelerated perfusion recovery, without altering systemic hemodynamics. In normoperfused muscles, NFG-induced capillarization was blocked by vascular endothelial growth factor-neutralizing antibodies, dominant-negative Akt, or NO synthase inhibition.

CONCLUSIONS

These results indicate that NGF plays a functional role in reparative neovascularization. Furthermore, supplementation of the growth factor promotes angiogenesis through a vascular endothelial growth factor-Akt-NO-mediated mechanism. In the setting of ischemia, potentiation of NGF pathway stimulates angiogenesis and arteriogenesis, thereby accelerating hemodynamic recovery. NGF might be envisaged as a utilitarian target for the treatment of ischemic vascular disease.

The origins of intracrine hormone action

A growing number of peptide hormones and growth factors have been shown to operate in the intracellular space after either internalization or retention in their cells of synthesis. These factors, called intracrines, in many cases are expressed as multiple isoforms, traffic to nucleus or nucleolus, and regulate gene transcription. Some intracrines are angiogenic. It is here argued that intracrine action is the modern analogue of a biologically ancient mechanism for regulating message translation and ribosome synthesis. The implications of this view for research and therapeutics are discussed.

Nerve growth factor displays stimulatory effects on human skin and lung fibroblasts, demonstrating a direct role for this factor in tissue repair

Nerve growth factor (NGF) is a polypeptide which, in addition to its effect on nerve cells, is believed to play a role in inflammatory responses and in tissue repair. Because fibroblasts represent the main target and effector cells in these processes, to investigate whether NGF is involved in lung and skin tissue repair, we studied the effect of NGF on fibroblast migration, proliferation, collagen metabolism, modulation into myofibroblasts, and contraction of collagen gel. Both skin and lung fibroblasts were found to produce NGF and to express tyrosine kinase receptor (trkA) under basal conditions, whereas the low-affinity p75 receptor was expressed only after prolonged NGF exposure. NGF significantly induced skin and lung fibroblast migration in an in vitro model of wounded fibroblast and skin migration in Boyden chambers. Nevertheless NGF did not influence either skin or lung fibroblast proliferation, collagen production, or metalloproteinase production or activation. In contrast, culture of both lung and skin fibroblasts with NGF modulated their phenotype into myofibroblasts. Moreover, addition of NGF to both fibroblast types embedded in collagen gel increased their contraction. Fibrotic human lung or skin tissues displayed immunoreactivity for NGF, trkA, and p75. These data show a direct pro-fibrogenic effect of NGF on skin and lung fibroblasts and therefore indicate a role for NGF in tissue repair and fibrosis.

Nerve growth factor control of neuronal expression of angiogenetic and vasoactive factors

In postnatal tissues, angiogenesis occurs in nontumoral conditions on appropriate stimuli. In the nervous tissue, hypoxia, neural graft, increased neural function, and synaptic activity are associated with neoangiogenesis. We have investigated the occurrence of neoangiogenesis in the superior cervical ganglia (scg) of newborn rats treated for 8--21 days with 6-hydroxy-dopamine (6-OHDA), nerve growth factor (NGF), or 6-OHDA + NGF. The two latter treatments induced a significant increase in scg size. However, the increase after combined treatment far exceeded that of NGF alone. Similarly, histological and histochemical analysis revealed neuronal hypertrophy and endothelial cell hyperplasia associated with stromal hypertrophy (as described by laminin immunostaining) and increased vascular bed (as revealed by platelet/endothelial cell adhesion molecule-1 immunostaining) in 6-OHDA + NGF-treated pups. NGF, either alone or associated with 6-OHDA, also induced a significant up-regulation of NADPH diaphorase, neuronal nitric oxide synthase, and vascular endothelial growth factor expression in scg neurons. The present investigation suggests that the increase of scg size induced by NGF and 6-OHDA + NGF is associated with neoangiogenesis, and that the induction of vasoactive and angiogenic factors in neurons represents a further and previously undisclosed effect of NGF.

The effect of endothelial cell growth factor on peripheral nerve regeneration

Neural regeneration after grafting can be unpredictable. In an effort to enhance the return of function after cable grafting, we studied the effects of an angiogenic factor, endothelial cell growth factor (ECGF), on regenerating nerves. Cable grafts on the sciatic nerve were established in 18 rats and treated with ECGF or a control saline solution. At 5 weeks, nerve conduction studies were performed, and the animals were killed for histologic measurements of graft vascularity and axon counts. A significant increase in vascularity was noted in the treated group versus the control group; neither the axon counts nor the nerve conduction velocities differed significantly between the two groups, although the treated group appeared to show improved neural conduction compared with the control group.

The cellular and molecular basis of peripheral nerve regeneration

Functional recovery from peripheral nerve injury and repair depends on a multitude of factors, both intrinsic and extrinsic to neurons. Neuronal survival after axotomy is a prerequisite for regeneration and is facilitated by an array of trophic factors from multiple sources, including neurotrophins, neuropoietic cytokines, insulin-like growth factors (IGFs), and glial-cell-line-derived neurotrophic factors (GDNFs). Axotomized neurons must switch from a transmitting mode to a growth mode and express growth-associated proteins, such as GAP-43, tubulin, and actin, as well as an array of novel neuropeptides and cytokines, all of which have the potential to promote axonal regeneration. Axonal sprouts must reach the distal nerve stump at a time when its growth support is optimal. Schwann cells in the distal stump undergo proliferation and phenotypical changes to prepare the local environment to be favorable for axonal regeneration. Schwann cells play an indispensable role in promoting regeneration by increasing their synthesis of surface cell adhesion molecules (CAMs), such as N-CAM, Ng-CAM/L1, N-cadherin, and L2/HNK-1, by elaborating basement membrane that contains many extracellular matrix proteins, such as laminin, fibronectin, and tenascin, and by producing many neurotrophic factors and their receptors. However, the growth support provided by the distal nerve stump and the capacity of the axotomized neurons to regenerate axons may not be sustained indefinitely. Axonal regenerations may be facilitated by new strategies that enhance the growth potential of neurons and optimize the growth support of the distal nerve stump in combination with prompt nerve repair.

Brain-derived neurotrophic factor and peripheral nerve regeneration: a functional evaluation

The potential benefit of brain-derived neurotrophic factor (BDNF) on motor-nerve regeneration after transection injury in 24 adult rats was evaluated after entubulation repair. Gait analysis for ankle angle and tension transduction device (TTD) strain-gauge measurements yielded functional evaluation of regeneration. The BDNF (15 mg/mL) or phosphate buffered saline (control) was injected into the silicone elastomer (Silastic) channel. Gait analysis performed 0, 2, 4, 6, 10, and 12 weeks after injury demonstrated a significant difference between uninjured and injured legs of 23 and 43 degrees, respectively (P<.001, analysis of variance). The TTD evaluation 13 weeks after injury demonstrated a significant decrease in force development of injured compared to uninjured legs, 148 and 58 g, respectively (P<.001). No functional benefits were demonstrated between BDNF-treated versus control-treated animals in either model for a single exposure to BDNF.

Hyperbaric Oxygen Treatment after rat Peroneal Nerve Transection and Entubulation

Rat peroneal nerves were transected and entubulated with a Silastic channel. The experimental group was treated with hyperbaric oxygen to evaluate changes in acute edema, functional recovery, and histology. Hyperbaric oxygen was administered with 100% O2 at 2.5 atmospheres absolute for 90 minutes twice a day for 1 week and then four times a day for 1 week. Acute edema changes based on nerve water weight and transfascicular area measurements were greater in injured than in uninjured nerves but demonstrated no differences between hyperbaric oxygen–treated and –untreated groups 2, 8, and 16 days after surgery. Functional evaluation with gait analysis demonstrated significant changes between injured and uninjured groups 1,3,7, and 13 weeks after injury but no differences between hyperbaric oxygen-treated and –untreated groups. Thirteen weeks after the initial injury, elicited muscle force measurements demonstrated no significant improvement from hyperbaric oxygen treatment of injured nerves. Histologic evaluation of nerve area, myelinated axon number, myelinated axon area, myelin thickness, and blood vessel number and area revealed no significant differences between hyperbaric oxygen–treated and –untreated groups. Hyperbaric oxygen was not associated with improvement of nerve regeneration with any of the outcome variables in this model.

Regeneration of guinea pig facial nerve: the effect of hypergravity

Exposure to moderate hypergravity improves the regenerative capacity of sectioned guinea-pig facial nerve. The improvement in regeneration is tri-directional as follows: a) an average 1.7 fold increase in rate of regeneration in guinea pigs subjected to hypergravity; b) a 25% enhancement of facial muscle activity following the exposure to hypergravity; and c) improvement in the quality of regeneration from an esthetic standpoint. A good correlation was recorded between the histological structure of the severed nerve at the end of the regeneration and the clinical results.

Tension transduction device for functional evaluation of the rat peroneal nerve

Current techniques for evaluating animal model nerve regeneration lack accurate, sensitive and reproducible methods to determine neuromuscular function. We have developed a tension transduction apparatus which measures the magnitude of ankle dorsiflexion produced by normal rats during bipolar stimulation of the surgically exposed peroneal nerve. Three groups of animals were used to evaluate the consistency and overall reliability of this apparatus. Within the first group of 4 animals, we determined variability in a single testing period of 8 successive stimulations. The mean normalized standard deviation of dorsiflexion tension produced was 2.9% of the mean. In the second group, comparison of right and left dorsiflexion tension in 8 animals showed a difference of less than 2% (right: 134.2 g; left: 131.6 g), demonstrating that one lower limb can be used as a control for the contralateral limb. In the third group, 12 animals were tested on two separate occasions, 2 months apart, tension production increased 10% (from 122 to 134 g) and corresponded with an average weight increase, per animal, of 100 g (30%) during the 2-month rest period. Despite the increase in weight and strength, the initial procedure had a negative effect upon the maximum tension produced compared to a previously unoperated leg (prior operation: 134 g; no prior operation: 144 g). The reproducibility of data obtainable with this new device allows for its incorporation in future studies, as well as the correlation of such functional data with other current methods of studying nerve regeneration.