Biological activity of the beta nerve growth factor: the effects of various added proteins

Nanofibrous scaffold with incorporated protein gradient for directing neurite outgrowth

Concentration gradient of diffusible bioactive chemicals assumes many important roles in regulating cellular behavior. Among the many factors influencing functional recovery after nerve injury, such as topographical and biochemical signals, concentration gradients of neurotrophic factors provide chemotactic cues for neurite outgrowth and targeted renervation. In this study, a concentration gradient of nerve growth factor (NGF, 0-250 μg/ml) was incorporated throughout the thickness of poly(ε-caprolactone)-poly(ethylene glycol) coaxial electrospun nanofibrous scaffolds (∼700 μm thick with ∼800 nm average fiber diameter). The existence of the protein gradient upon protein release was demonstrated using a customized under-agarose-PC12 neurite outgrowth assay. When exposed to scaffolds endowed with NGF concentration gradient (NGF-CG), a significant difference in the percentage of cells bearing neurite outgrowth was observed (7.1 ± 1.9% vs. 0.8 ± 0.3% for cells exposed to high vs. low concentration surface, respectively; p < 0.05). In contrast, no significant difference was observed when cells were exposed to scaffolds that encapsulated a fixed concentration of NGF. Direct culture of PC12 cells on the substrates demonstrated the cytocompatibility and the effect of diffusible NGF gradient on neurite outgrowth. A significant difference in the percentage of cells with neurite extensions was observed when PC12 cells were seeded on NGF-CG scaffolds (21.2 ± 3.6% vs. 10.4 ± 1.3% on high vs. low concentration surface, respectively; p < 0.05). Furthermore, Z-stack confocal microscopy tracking of neurite extensions revealed the chemotatic guidance effect of NGF concentration gradient. Directed and enhanced neurite penetration into the scaffolds towards increasing NGF concentration was observed. In vitro release study indicated that the encapsulated NGF was released in a sustained manner for at least 30 days (80.4 ± 3.6% released). Taken together, this study demonstrates the feasibility of incorporating concentration gradient of diffusible bioactive chemicals in nanofibrous scaffolds via the coaxial electrospinning technique.

Role of heat shock proteins in oxygen radical-induced gastric apoptosis

BACKGROUND

The generation of reactive oxygen species (ROS) and their resultant oxidative damage is a common pathway for gastric mucosal injury. Developing strategies to protect the gastric epithelium against oxygen free radical damage is of profound pathophysiological interest. We have previously shown caspase-mediated apoptosis as a major cause of ROS-induced cell death in gastric mucosa. Because heat shock proteins (Hsps) confer protection against many cytotoxic agents, this study was undertaken to determine whether modulation of Hsps was protective against oxidative damage.

MATERIALS AND METHODS

AGS cells (human gastric mucosal cell line) received either no pretreatment, heat shock pretreatment (1 h at 42 ± 1°C), or pretreatment with an Hsp modulating drug (geldanamycin or quercetin). Cells were then exposed to hydrogen peroxide (H2O2), a representative ROS (1 mM, a physiologically relevant concentration), for 24 h. Caspase-3 activation and Poly ADP Ribose Polymerase (PARP) inactivation, as well as DNA-histone complex formation were used as measures of apoptosis. Inducible Hsps (Hsp70 and Hsp90) were detected using Western blot analysis.

RESULTS

Results showed heat shock pretreatment induced increased expression of Hsp70 without change in Hsp90. In response to H2O2 exposure alone, there was significant increase in DNA-histone complex formation as well as caspase-3 activation and PARP cleavage in gastric epithelium. Heat shock pretreatment resulted in statistically significant prevention in these measures of apoptosis. Geldanamycin increased Hsp70, but elicited cleavage of Hsp90 and subsequently resulted in an increase in H2O2-induced apoptosis. Quercetin decreased Hsp70 and resulted again in increased H2O2-induced apoptosis.

CONCLUSIONS

These findings indicate that heat shock pretreatment protects gastric mucosal cells against H2O2-induced apoptosis and that Hsp70 and Hsp90 may play key roles in this process. These results further suggest that perturbations in Hsp metabolism may induce mucosal injury in response to oxygen free radicals.

Aspirin-induced mucosal cell death in human gastric cells: role of a caspase-independent mechanism

Aspirin and other nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used for the treatment of pain and inflammation. Their use may result in gastroduodenal side effects, such as gastric irritation and ulcer formation. Although various strategies have been employed to minimize these adverse effects induced by NSAIDs, effective therapeutic targeting of this problem has been prevented by an incomplete understanding of the mechanisms underlying their pathogenesis. This study was undertaken to determine the role that non-caspase-mediated apoptosis plays in inducing cellular injury and death in gastric mucosa exposed to aspirin. We proposed that the responsible mechanism was through mitochondrial failure, increased mitochondrial membrane permeability, and translocation of the intramitochondrial protein apoptosis-inducing factor (AIF). Human gastric adenocarcinoma mucosal cells (AGS cells) received no pretreatment or were preincubated with caspase inhibitors for 30 min. Cells were then treated with 40 mM aspirin for 2-4 h. Apoptosis was assessed by measuring the DNA-histone complex formation. Cell viability was determined by an acridine orange-ethidium bromide (EtBr) assay. The activation of AIF was evaluated by both Western blotting of the cytosol and mitochondrial extracts as well as by visualization and staining using fluorescence microscopy. Results showed that caspase inhibitor preincubation decreased DNA-histone complex formation when compared to aspirin treatment alone. Based on light microscope visualization, however, we determined that caspase inhibitor preincubation was unable to prevent AGS cell damage and death. These findings were confirmed by the acridine orange-EtBr test, which showed decreased cell viability with caspase inhibitor preincubation and aspirin treatment. We then tested whether non-caspase-mediated cell death occurred through an AIF mitochondrial pathway using Western blotting and fluorescence microscopy to determine AIF activation. The results showed that untreated cells had AIF localized to the mitochondria and cytosol. With 40 mM ASA at 4 h, translocation of AIF from the mitochondria to the nucleus occurred, showing activation. Caspase inhibition with z-VAD was unable to prevent AIF localization to the nucleus and subsequently unable to prevent cell death. Our results indicate that ASA in the presence of caspase inhibitors causes gastric mucosal cell death through a caspase-independent pathway suggestive of apoptosis-like programmed cell death. Effective therapeutic targeting of aspirin-induced apoptosis likely requires inhibition of both mitochondrial and caspase-mediated pathways.

Oxygen radical induced gastric mucosal cell death: apoptosis or necrosis?

Reactive oxygen species (ROS) and resultant oxidative damage is a common pathway for gastric mucosal injury. This study was undertaken to determine whether apoptosis or necrosis was responsible for hydrogen peroxide (a representative ROS)-induced gastric mucosal death and whether caspase cascade blockade could prevent this process. AGS cells (human gastric adenocarcinoma cells) were exposed to hydrogen peroxide (H(2)O(2)), 0.5-2 mM, from 6 to 24 h. Lactic dehydrogenase (LDH) measured necrosis, whereas Caspase-3 and PARP activation and DNA-histone complex formation measured apoptosis. In addition, AGS cells received no pretreatment or preincubation for 1 h with 50-100 microM z-VAD, a pan-caspase inhibitor, and were then treated with 1-2 mM H(2)O(2). With high concentrations of H(2)O(2), cell death was predominantly necrotic, whereas lower concentrations evoked time and concentration dependent apoptosis. Furthermore, z-VAD pretreatment prevented oxidant induced apoptosis and necrosis. Since caspase cascade blockade prevents both processes, our results support the hypothesis that H(2)O(2) induced cell death is predominantly a caspase-mediated apoptosis.

Nerve guidance channels as drug delivery vehicles

Nerve guidance channels (NGCs) have been shown to facilitate regeneration after transection injury to the peripheral nerve or spinal cord. Various therapeutic molecules, including neurotrophic factors, have improved regeneration and functional recovery after injury when combined with NGCs; however, their impact has not been maximized partly due to the lack of an appropriate drug delivery system. To address this limitation, nerve growth factor (NGF) was incorporated into NGCs of poly(2-hydroxyethyl methacrylate-co-methyl methacrylate), P(HEMA-co-MMA). The NGCs were synthesized by a liquid-liquid centrifugal casting process and three different methods of protein incorporation were compared in terms of protein distribution and NGF release profile: (1) NGF was encapsulated (with BSA) in biodegradable poly(d,l-lactide-co-glycolide) 85/15 microspheres, which were combined with a PHEMA polymerization formulation and coated on the inside of pre-formed NGCs by a second liquid-liquid centrifugal casting technique; (2) pre-formed NGCs were imbibed with a solution of NGF/BSA and (3) NGF/BSA alone was combined with a PHEMA formulation and coated on the inside of pre-formed NGCs by a second liquid-liquid centrifugal casting technique. Using a fluorescently labelled model protein, the distribution of proteins in NGCs prepared with a coating of either protein-loaded microspheres or protein alone was found to be confined to the inner PHEMA layer. Sustained release of NGF was achieved from NGCs with either NGF-loaded microspheres or NGF alone incorporated into the inner layer, but not from channels imbibed with NGF. By day 28, NGCs with microspheres released a total of 220 pg NGF/cm of channel whereas those NGCs imbibed with NGF released 1040 pg/cm and those NGCs with NGF incorporated directly in a PHEMA layer released 8624 pg/cm. The release of NGF from NGCs with microspheres was limited by a slow-degrading microsphere formulation and by the maximum amount of microspheres that could be incorporated into the NGCs structure. Notwithstanding, the liquid-liquid centrifugal casting process is promising for localized and controlled release of multiple factors that are key to tissue regeneration.

Adenosine triphosphate induces activation of caspase-3 in apoptosis of human granulosa-luteal cells

Adenosine triphosphate (ATP) has been shown to induce programmed cell death in various systems. However, little is known about the effect of ATP on human granulosa-luteal cells (hGLCs). The present study was designed to examine the effect of ATP on the activation of the caspase signaling pathway and its role in inducing programmed cell death. Human GLCs were collected from patients undergoing in vitro fertilization programs, and then were cultured in FBS-supplemented DMEM for 3 days prior to our studies. To examine the dose-response relationship, hGLCs were treated with increasing concentrations of ATP (10 microM, 100 microM, 1 mM or 10 mM) for 24 hours. For time-course experiments, hGLCs were treated with 10 mM ATP for 6, 12, or 24 hours. Western blot analysis was performed using antibodies against the pro- and active forms of caspase-3, -9, or PARP. To quantify the induction of apoptosis, DNA fragmentation was measured using the cell death detection enzyme-linked immunosorbent assay. To examine the effect of human chorionic gonadotropin (hCG) in protecting cells from apoptosis, hGLCs were treated with 10 IU hCG in the presence of 10 mM ATP for 12 hours. It was demonstrated that ATP was capable of inducing DNA fragmentation in a dose- and time-dependent manner. Furthermore, Western blot analysis, which detected the pro- and active forms of caspase-3, or PARP, demonstrated that ATP activated the caspase-signaling pathway, leading to the proteolytic conversion of pro-caspase-3 to active caspase-3, and the subsequent cleavage of the caspase substrate PARP. Based on our observation, caspase-9 was not triggered by ATP. Interestingly, hCG attenuated the effect of ATP in activating the caspase signaling pathway. To our knowledge, this is the first demonstration of the ATP-induced activation of the caspase signaling pathway in the human ovary. These results support the notion that the caspase-signaling pathway is involved in mediating ATP actions in the human ovary.

Nitric oxide induces caspase-dependent apoptosis and necrosis in neonatal rat cardiomyocytes

Excessive nitric oxide (NO) production has been implicated in the pathophysiology of cardiomyocyte (CMC) apoptosis and necrosis induced by ischemia/reperfusion, inflammation and NO-donating chemicals. Although caspases are known to be involved in apoptosis, the present study examined whether caspases also play a role in NO-induced CMC necrosis. Neonatal rat CMCs were labeled with Annexin-V and propidium iodide, and apoptosis and necrosis were analyzed by confocal images and fluorescence activated cell sorter analysis. CMC apoptosis and necrosis were also evaluated by determining DNA fragmentation in the cell and the supernatant fractions. Treatment of CMCs with the NO donor, diethylenetriamine NO (DETA/NO) or S-nitroso-N-acetyl-penicillamine (SNAP) at concentrations of 10 and 100 microM for 24h induced predominantly apoptosis over necrosis, but a higher concentration (1mM) of DETA/NO or SNAP provoked both apoptosis and necrosis. The lower doses of DETA/NO-induced apoptosis was associated with a gradual increase in caspase-3 activity over 24h without appreciable activation of poly ADP-ribose polymerase (PARP), while the higher dose of DETA/NO induced a marked increase in caspase-3 activity and CMC apoptosis until 2h after the treatment, and increased necrotic CMCs thereafter associated with robust activation of PARP. The caspase inhibitor Z-DEVD-FMK but not the poly ADP-ribose polymerase (PARP) inhibitor 3-aminobenzamide (3-AB) abolished caspase-3 activation and CMC apoptosis induced by 100 microM DETA/NO. However, both Z-DEVD-FMK and 3-AB abolished PARP activation and CMC necrosis induced by 1mM DETA/NO. The amount of nicotinamide adenine dinucleotide (NAD) and adenine nucleotides in CMCs was not significantly affected by treatment with 10 and 100 microM DETA/NO, but was significantly reduced by treatment with 1mM DETA/NO without a decline of adenylate energy charge. The depletion of NAD and adenine nucleotides was abrogated by Z-DEVD-FMK and 3-AB. These results suggest that caspase activation play a crucial role in CMC apoptosis induced by lower concentrations of NO as well as in CMC necrosis induced by a higher concentration of and a longer exposure to NO. NO-induced CMC necrosis is likely mediated by PARP activation which occurs as a consequence of caspase activation.

Disruption of cell cycle kinetics and cyclin-dependent kinase system by ethanol in cultured cerebellar granule progenitors

An in vitro model of neuronal precursors, primary culture of cerebellar granule progenitors (CGPs), was used to investigate the mechanisms underlying ethanol-induced cell cycle damage. The CGP cultures were generated from 3-day-old rats. Ethanol significantly inhibited the proliferation of the CGPs in culture. Analysis of cell cycle kinetics by a cumulative 5-bromo-2'-deoxyuridine (BrdU) labeling technique demonstrated that ethanol exposure increased the duration of the cell cycle and decreased the growth fraction (the cycling population). The duration of the S-phase and total cell cycle was significantly prolonged by ethanol exposure by 220% and 135%, respectively, while the growth fraction was decreased from 44% in the control groups to 22% in the ethanol-exposed cultures. Cyclin-dependent kinase 2 (Cdk2) is a key protein that regulates both the passage from G1 into S, and the S phase progression. The results from in vitro phosphorylation assay and Western blot demonstrated that ethanol dramatically down-regulated both the activity and the expression of Cdk2. In addition, ethanol significantly decreased the expression of Cyclin A and Cyclin D(2). Further studies using in situ TUNEL assay and DNA fragmentation ELISA showed that ethanol caused a delayed apoptosis, i.e. the ethanol-induced apoptosis was evident only after chronic exposure. On the other hand, ethanol did not affect the necrotic index. In conclusion, ethanol decreases the cycling pool of CGPs by inducing cell cycle delay and promoting apoptosis. Ethanol-mediated disturbance of the cyclin-dependent kinase system may be an important mechanism to account for cell cycle arrest in neuronal precursor cells.

Purification and characterization of murine beta-nerve growth factor

Beta-nerve growth factor (beta-NGF) is a trophic factor in the nervous system. We aimed to isolate and characterize this protein in view of its potential therapeutic use in neurodegenerative diseases. For purification a two-step ion-exchange procedure was followed. The characterization was performed using separation and immunological techniques, as well as a biological assay. These studies showed that the obtained protein consisted of a mixture of beta-NGF molecules, intact at their NH2-terminal extreme, and molecules which have lost the NH2-terminal octapeptide and exhibit modifications increasing its hydrophobicity. All these molecular species were recognized immunologically and showed biological activity.

Caspase inhibitors are functionally neuroprotective against oxygen glucose deprivation induced CA1 death in rat organotypic hippocampal slices

We have explored the neuroprotective efficacy of the cell penetrant caspase inhibitor, Ac-YVAD-cmk, in a hippocampal slice model of neuronal cell death induced by oxygen and glucose deprivation. Organotypic hippocampal slice cultures were prepared from 8 to 10-day-old rats and maintained for 10 to 12 days in vitro. Pre-treatment with Ac-YVAD-cmk prior to 45 min oxygen and glucose deprivation was neuroprotective as measured by propidium iodide uptake, with an EC(50) between 1 and 10 micromol/l. Ac-YVAD-cmk was also able to preserve synaptic function in the organotypic hippocampal slice cultures 24 h after oxygen and glucose deprivation. Ac-YVAD-cmk prevented the increase in histone-associated DNA fragmentation induced by oxygen and glucose deprivation. Interleukin-1beta did not reverse the protective effect of Ac-YVAD-cmk, and interleukin-1 receptor antagonist alone was not protective. These results show that caspase inhibitors are neuroprotective in a hippocampal slice culture system, using structural, biochemical and electrophysiological endpoints, and that this effect is not a result of inhibition of interleukin-1beta production.

NGF release from poly(D,L-lactide-co-glycolide) microspheres. Effect of some formulation parameters on encapsulated NGF stability

Poly(d,l-lactide-co-glycolide) (PLGA 37.5/25 and 25/50) biodegradable microparticles, which allow the locally delivery of a precise amount of a drug by stereotactic injection in the brain, were prepared by a W/O/W emulsion solvent evaporation/extraction method which had been previously optimized. The aim of this work was to study the influence of two formulation parameters (the presence of NaCl in the dispersing phase and the type of PLGA) on the NGF release profiles and NGF stability during microencapsulation. A honey-comb-like structure characterized the internal morphology of the microspheres. The initial burst was attributed to the rapid penetration of the release medium inside the matrix through a network of pores and to the desorption of weakly adsorbed protein from the surface of the internal cavities. The non-release fraction of the encapsulated protein observed after twelve weeks of incubation was accounted for firstly by the adsorption of the released protein on the degrading microparticles and secondly by the entanglement of the encapsulated protein in the polymer chains. The use of sodium chloride in the dispersing phase of the double emulsion markedly reduced the burst effect by making the microparticle morphology more compact. Unfortunately, it induced in parallel a pronounced NGF denaturation. Finally, it appeared that microparticles made from a hydrophilic uncapped PLGA 37.5/25 in the absence of salt, allowed the release of intact NGF at least during the first 24 h as determined by both ELISA and a PC12 cell-based bioassay.

Molecular mechanisms regulating NGF-mediated enhancement of cholinergic neuronal phenotype: c-fos trans-activation of the choline acetyltransferase gene

Nerve growth factor (NGF) enhances expression of the cholinergic phenotype observed as increased choline acetyltransferase (ChAT) activity, immunoreactivity, and mRNA. In the present study, treatment of cultured rat embryonic basal forebrain neurons with anti-c-fos, prior to administering NGF, blocked NGF-mediated increases in ChAT activity by 67%; basal ChAT activity was not affected by the antisense oligonucleotide treatment. Reverse transcription-polymerase chain reaction (RT-PCR) revealed that anti-c-fos treatment resulted in not only blockade but enhancement of steady-state ChAT mRNA at different time points. These data suggest that c-fos is an important component in NGF-mediated changes in the cholinergic phenotype and support the hypothesis that c-fos plays a role in the regulation of transcription of the ChAT gene. Elucidation of mechanisms underlying this regulation may aid drug development in neurodegenerative disease.

Morphological and biochemical characterization and analysis of apoptosis

Apoptosis is a form of programmed cell death serving physiologic and homeostatic functions. However, recent evidence implicating apoptosis in the etiology and pathophysiology of known human diseases, such as heart diseases, cancer, AIDS, and neurodegenerative and autoimmune diseases are continually surfacing. This has spawned the need for identifying which methods are the most effective and well accepted to decipher its presence in a variety of research settings. We have therefore detailed the morphology and biochemical features of apoptotic cell death, with an emphasis on discriminating it from necrosis. In addition, we describe specific and selective techniques which are optimal to target hallmark apoptotic features, such as microscopy, Annexin V labeling, in situ nick-end labeling (TUNEL), and DNA fragmentation analysis by gel electrophoresis and ELISA for oligonucleosome-sized DNA. The advantages and disadvantages of each technique are discussed, as well as their experimental importance relative to one another. The methods have been described in a stepwise fashion, and can readily be applied in the majority of cell systems. Whether working on the tissue or single cell level, these methods are highly effective in qualifying and quantifying apoptosis. The application of these methods in conjunction with molecular techniques can further delineate the underlying mechanisms of apoptosis.

Serotonin-activated alpha 2-macroglobulin inhibits neurite outgrowth and survival of embryonic sensory and cerebral cortical neurons

Methylamine-modified alpha-2-macroglobulin (MA-alpha 2M) has been recently shown to inhibit the biological activity of beta-nerve growth factor (NGF) in promoting neurite outgrowth by embryonic dorsal root ganglia in culture (Koo PH, Liebl DJ, J Neurosci Res 31:678-692, 1992). The objectives of this study are to determine whether alpha 2M can also be modified by larger aromatic biogenic amines such as 5-hydroxytryptamine (5HT; serotonin), the nature of interaction between NGF and 5HT-modified alpha-2-M (5HT-alpha 2M), and the effect of 5HT-alpha 2M on the neurite extension and the growth of embryonic sensory and cholinergic neurons in 2 disparate animal species (chicken and rats). This study demonstrates that each mole of alpha 2M can combine with 15.2 +/- 1.8 moles of 5HT, in which up to 4.5 +/- 0.4 moles may be covalently bonded. As determined by gel filtration and polyacrylamide gel electrophoresis studies, both 5HT-alpha 2M and normal alpha 2M combine noncovalently with NGF, but 5HT-alpha 2M by comparison can combine with NGF somewhat more effectively. In contrast to normal alpha 2M, 5HT-alpha 2M at concentrations greater than about 0.17 microM exerts a dose-dependent inhibition on the NGF-stimulated neurite outgrowth by embryonic dorsal root ganglia and dissociated cells in culture, and the inhibitory effect can be overcome by higher NGF concentrations. Both 5HT-alpha 2M and MA-alpha 2M at 1.0 microM inhibit neurite extension by embryonic rat cerebral cortical cells and seriously damage these cells in culture. Such neurite-inhibitory activity, however, can only be partially blocked by extraneously added NGF alone. Normal alpha 2M (at 1.0 microM) and 5HT (at 188 microM), on the other hand, under the identical conditions produce very little or no effect on the normal cellular and axonal growth of these cells. We conclude that alpha 2M can potentially interact with nucleophilic monoamines, including neurotransmitters, to form inhibitory complexes which may inhibit/regulate NGF-promoted neurite outgrowth and neuronal survival. In addition, higher concentrations of such complexes can seriously damage certain CNS neurons which do not depend solely on NGF for survival.

Cholinergic marker deficits induced by lesions of the nucleus basalis of Meynert are attenuated by nerve growth factor in young, but not in aged, F344 rats

To investigate the efficacy of nerve growth factor (NGF) in promoting recovery from cholinergic damage, young (3-4 month old) and aged (22-23 month old) Fischer 344 rats received NMDA-induced unilateral lesions of the nucleus basalis of Meynert and subcutaneous osmotic pumps (2-week duration) connected to permanently implanted cannulas directed at the lateral ventricle ipsilateral to the lesion. Pumps were filled with either artificial CSF/rat serum albumin (the vehicle) or 5.0 micrograms of angiotensin-free, beta-NGF. Fourteen days after surgery, all subjects were sacrificed and their brains regionally dissected (frontal and occipital cortices, striatum, and dorsal and ventral hippocampi) and assayed for choline acetyltransferase (CAT) and acetylcholinesterase (AChE). Results indicated that the lesion decreased CAT and AChE levels within the frontal cortex of both young (29.8% and 39.4% depletion, respectively) and aged (30.5% and 34.8% depletion, respectively) animals. Only in young animals did NGF reduce these lesion-induced CAT (by 34.2%) and AChE deficits (by 65.5%). In fact, NGF exacerbated frontal cortical CAT depletions in aged animals in that percent depletion was 11.3% more following treatment (30.5% vs. 41.8% depletion in Aged/CSF and Aged/NGF groups, respectively). Lower CAT and AChE levels were found in the striatum of aged animals, an effect not reversed by NGF treatment. In contrast, NGF in young animals enhanced striatal CAT activity on the non-lesioned side by 22.2%.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of nerve growth factor-stimulated neurite outgrowth by methylamine-modified alpha 2-macroglobulin

alpha 2-Macroglobulin (alpha 2M) is a rather ubiquitous protein in extracellular spaces of mammals. It is an inhibitor of endopeptidases, can be modified by aliphatic amines, and combines with a number of hormones/cytokines such as beta-nerve growth factor (NGF) [Koo PH, Stach RW (1989): J Neurosci Res 22:247]. The objective of this study is to compare the NGF-binding properties of methylamine-modified human alpha 2M (MA-alpha 2M) versus normal alpha 2M and their effects on the biological activity of NGF and neurite extension by embryonic chicken dorsal root ganglia. As determined by gel filtration, polyacrylamide gel electrophoresis, and equilibrium binding studies, these two forms of alpha 2M are similar in their binding affinities, with MA-alpha 2M binding about twice as much NGF as normal alpha 2M. Both normal alpha 2M and MA-alpha 2M combine noncovalently with NGF, and prior modification of alpha 2M is unnecessary for the binding to occur. In contrast to normal alpha 2M, MA-alpha 2M potently inhibits the biological activity of NGF and exerts a dose-dependent inhibition on the NGF-stimulated neurite outgrowth by embryonic chicken dorsal root ganglia in culture. The inhibitory effect of MA-alpha 2M can be overcome by higher NGF concentrations, but is irreversible at lower NGF concentrations. Trypsin-modified alpha 2M combines covalently and noncovalently with more NGF than normal alpha 2M but has very little neurite inhibitory activity. The mechanism of inhibition by MA-alpha 2M is discussed.

Interaction of nerve growth factor with murine alpha-macroglobulin

The murine nerve growth factor, when injected i.v. or, combined in vitro with plasma, was found largely associated with the mouse alpha-macroglobulin (a homologue of human alpha 2-macroglobulin). The nerve growth factor-alpha-macroglobulin complex produced is sufficiently stable to resist separation by gel filtration in 1.0 M sodium chloride, polyacrylamide gel electrophoresis, and immunoprecipitation by antibodies against alpha-macroglobulin. As determined by equilibrium binding studies and computer generated Scatchard analysis, alpha-macroglobulin apparently possesses two types of binding sites with the apparent dissociation constants of 1.2 x 10(-6) and 2.9 x 10(-9) M, respectively, saturable by 3.7 and 0.03 moles of nerve growth factor. Hence, about one mole of nerve growth factor is bound to each of the four subunits of alpha-macroglobulin. Nerve growth factor can be readily dissociated from alpha-macroglobulin in sodium dodecyl sulfate gel electrophoresis in the absence of a reductant. Procedures that affect the proteinase-binding or methylamine- activities of alpha-macroglobulin do not affect the binding of nerve growth factor, and the binding is unaffected by the presence of zinc ions or EDTA. Hence, nerve growth factor is noncovalently associated with alpha-macroglobulin at a site separate from that of the proteinase-, methylamine-, and zinc-binding sites of alpha-macroglobulin. Mouse alpha-macroglobulin can protect the nerve growth factor from inactivation by trypsin. Even in the presence of trypsin, alpha-macroglobulin-nerve growth factor complexes still can stimulate the neurite outgrowth by dorsal root ganglia of 9-day-old chicken embryos. Since alpha-macroglobulin can specifically and noncovalently carry nerve growth factor, one important role of this alpha-macroglobulin in the circulation and extracellular spaces may be to protect the nerve growth factor from proteinase inactivation.

Macrophage colony-stimulating factor in nerve growth factor preparations

Following a report that nerve growth factor preparations have granulocyte-colony-stimulating activity, we investigated the presence of colony-stimulating factors in 7s mouse submaxillary nerve growth factor and its subunits. Macrophage colonies were formed in mouse bone marrow cultures after exposure to preparations of 7s nerve growth factor, the gamma subunit, and, to a small extent, the alpha subunit; the beta subunit, which is responsible for the nerve growth function, did not stimulate colony growth. Furthermore, the esteropeptidase activity of the gamma subunit was not detected in preparations of macrophage colony-stimulating factor purified from the giant cell tumor (GCT) cell line. Immunoprecipitation of radiolabeled gamma subunit with a polyclonal antibody to L-cell macrophage colony-stimulating factor showed a protein band that could represent the gamma subunit of nerve growth factor. Separation of the macrophage activity from the esteropeptidase activity of the gamma subunit was accomplished on the basis of molecular size. Thus, macrophage colony-stimulating factor was a contaminant of nerve growth factor produced by the mouse submaxillary gland and copurified with the gamma subunit.

Disulfide bond formation between nerve growth factor and the nerve growth factor receptor from embryonic sensory neurons

Recent studies with sympathetic neurons using radiolabeled nerve growth factor have indicated that a high-molecular-weight covalent complex is formed. This complex is between the nerve growth factor and the high-affinity (type I) receptor and occurs through the formation of a disulfide bond. Studies presented in the present article demonstrate a similar complex is formed on chicken embryonic sensory neurons. The formation of this complex is inhibited by the addition of unlabeled nerve growth factor, metabolic energy inhibitors (dinitrophenol and NaF), and of sulfhydryl reagents. On the other hand, formation of this complex is not inhibited by temperature, or by the addition of insulin or epidermal growth factor. The receptor involved in the covalent complex formation is the high-affinity (type I) receptor. The molecular weight of this complex is approximately 232,000 daltons. Evidence indicates that this covalent complex may be required for the biological activity of the nerve growth factor.

Phenylmethylsulfonyl fluoride (PMSF) inhibits nerve growth factor binding to the high affinity (type I) nerve growth factor receptor

Dorsal root ganglia were extirpated from 9-day old embryonic chickens and solubilized in phosphate buffered saline containing 0.5% Noniodet P 40 detergent. When nerve growth factor binding studies are performed on these samples, the expected curvilinear Rosenthal (Scatchard) plot is obtained. However, when the solubilized cell sample is made 1-2 mM in phenylmethylsulfonyl fluoride and nerve growth factor binding is determined, a linear Rosenthal (Scatchard) plot is obtained. The equilibrium dissociation constant obtained from the slope of the line is 1.9 X 10(-9) M, identical to the equilibrium dissociation constant of the low affinity receptor. A similar phenomenon is observed when rat pheochromocytoma cells are solubilized in the non-ionic detergent and nerve growth factor binding is determined. No high affinity binding can be detected for either cell type when detergent solubilized cells are incubated with phenylmethylsulfonyl fluoride.

Covalent attachment of 125I-beta nerve growth factor to its receptors on sympathetic neurons

When 125I-beta nerve growth factor binds to sympathetic and sensory neurons, some labeled ligand is sequestered (becomes inaccessible to the external milieu) in a time- and energy-dependent manner. It would appear that the higher affinity receptor (type I) participates in this process to a greater extent than does the lower affinity receptor (type II) [ Olender and Stach , 1980; Olender et al., 1981]. A small portion of the sequestered 125I-beta nerve growth factor is found as part of a high molecular weight complex. When cells, which have been incubated with 125I-beta nerve growth factor, are solubilized with Triton X-100 and subjected to sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis, a complex with an apparent molecular weight of approximately 240,000 is obtained. The formation of the covalent complex can be prevented by the prior addition of excess unlabeled beta nerve growth factor or sodium fluoride and dinitrophenol. The covalent 125I-beta nerve growth factor-receptor complex is dissociated in 50 mM dithiothreitol indicating that disulfide linkages are involved. At concentrations of beta nerve growth factor (3.8 X 10(-11) -3.8 X 10(-10) M) where maximal fiber outgrowth occurs in vitro, approximately 50-266 attomoles (0.3-1.6% of the type I receptors) of the covalent complex are formed per 10(7) nerve cells. These data suggest that a small portion of the 125I-beta nerve growth sequestered by sympathetic neurons becomes covalently attached to its receptor subsequent to its sequestration in a manner which appears to involve type I receptors.

Binding constants of isolated NGF-receptors from different species

It is known that NGF-responsive cells bind NGF at cell surface receptors in a specific and saturable fashion and there are two separate kinds of receptor-ligand binding interactions as judged by Rosenthal analyses. Following isolation of nerve growth factor receptors from embryonic chicken sensory ganglia, rat pheochromocytoma cells and human neuroblastoma cells, equilibrium binding studies were carried out and two different equilibrium binding constants similar to that described for whole cells were determined. This evidence is consistent with the hypothesis that there are two different receptors for NGF which have been conserved.

Serum-free culture of chicken embryonic sensory ganglia in a balanced salt solution with nerve growth factor for periods up to two weeks

Culture of embryonic chicken dorsal root ganglia for periods exceeding a week generally require serum supplementation and a trophic factor such as nerve growth factor. In this communication we describe the culture of chicken E-9 dorsal root ganglia for periods up to 2 weeks in a system that is composed only of a simple basic salts solution and 10 ng/ml (3.8 X 10(-10)M) beta nerve growth factor. Commercially available tissue culture dishes are used which have a hydrophilic, gas-diffusable membrane on the bottom to which the ganglia directly attach, eliminating the need for added substratum. Sparse fiber outgrowth appears after 24 hours and growth of the fibers continues for 120 hours of incubation. At this time, the fibers are extremely dense and reach approximately 3.5-4.0 diameters from the body of the ganglion. Continued survival of these fibers appears to depend on the concentration of nonneuronal cells present in the dish. No fiber outgrowth occurs at any time in the absence of beta nerve growth factor. The simplicity and purity of this culture system makes it an attractive tool in the study of primary cell-cell interactions, the production of trophic factors by nonneuronal cells, and biochemical and physiological analyses of growing neurons.

Sequestration requirements for the degradation of 125I-labeled beta nerve growth factor bound to embryonic sensory neurons

Nerve growth factor interacts with responsive cells by binding to cell surface membrane receptors. There are two different receptors on both embryonic sensory and sympathetic neurons, a high-affinity (type I) receptor and a lower-affinity (type II) receptor. Sequestration, which we have defined as bound nerve growth factor that becomes inaccessible to the external milieu with time, occurs through the type I receptor on both sensory and sympathetic neurons. We describe here a process subsequent to sequestration involving internalization and degradation of bound nerve growth factor and showing that bound nerve growth factor is not degraded under the following conditions: (1) low temperature, ie 4 degrees C; (2) when a large excess of unlabeled nerve growth factor is added concomitantly with the labeled nerve growth factor and the temperature is raised from 4 degrees C to 37 degrees C; (3) when metabolic inhibitors sodium fluoride and dinitrophenol are added concomitantly with the labeled nerve growth factor and the temperature is raised from 4 degrees to 37 degrees C. On the other hand, conditions that allow bound nerve growth factor to be degraded are the following: (1) incubation of the sensory nerve cells at low temperature (ie, 4 degrees C) only in the presence of labeled nerve growth factor, then raising the temperature to 37 degrees C; (2) when sodium fluoride and dinitrophenol are added when the temperature is raised to 37 degrees C; (3) when excess unlabeled nerve growth factor is added when the temperature is raised to 37 degrees C. These studies are consistent with the idea that nerve growth factor has to bind to the cells in order to be degraded; however, binding is not sufficient for degradation to occur. Second, the bound nerve growth factor must be sequestered in order to be degraded. Third, the process of internalization of the bound nerve growth factor, unlike sequestration, is not an energy-dependent process. Thus, it seems reasonable to suggest the following steps for the interaction of nerve growth factor with responsive cells: binding to a cell surface membrane receptor, followed by sequestration of the bound nerve growth factor, and finally, internalization of the sequestered nerve growth factor.

Decrease in the number of lower affinity (type II) nerve growth factor receptors on embryonic sensory neurons does not affect fiber outgrowth

Nerve growth factor binds to two different specific receptors on responsive cells. The relationship of these two receptors is not fully understood at this time. We have studied the binding of labeled NGF to a different strain of white leghorn chicken embryo dorsal root ganglionic cells. The equilibrium dissociation constants for the two sites (KdI = 4.1 +/- 1.8 x 10(-11) M, KdII = 1.0 +/- 0.8 x 10(-9) M) are identical to those obtained previously. Also, the number of type I sites per cell (3.8 +/- 1.3 x 10(3)) is the same as that previously determined. However, the number of type II sites per cell (1.9 +/- 1.3 x 10(4)) is significantly different than that previously determined. This 2.5-fold decrease in the number of type II sites does not affect the concentration of NGF needed to obtain maximal fiber outgrowth from explanted sensory ganglia. The rate of association (1.2 +/- 0.2 x 10(7) M-1 sec-1 at 22 degrees C) of labeled NGF with receptors on sensory neurons from this different strain of chickens is identical to that previously obtained. The rate of association of NGF with its receptors on sensory neurons was also determined at 4 degrees C. This rate constant (2.1 +/- 1.1 x 10(6) M-1 sec-1) along with the rate constants obtained at 22 degrees and 37 degrees C were used to determine an activation energy for the binding of NGF to its receptors. The activation energy obtained (16.2 kcal/mole) suggests that binding is not a diffusion-controlled process.

Sequestration of 125I-labeled beta nerve growth factor by embryonic sensory neurons

Nerve growth factor (NGF) binds to two specific receptors on sensory nerve cells. These two receptors are characterized by different equilibrium dissociation constants. The higher affinity (type I) receptors have an equilibrium dissociation constant of 3.3 X 10(-11) M. The lower affinity (type II) receptors have an equilibrium dissociation constant of 1.7 X 10(-9) M. These two receptors are not a result of negative cooperativity, but apparently are different receptors. At 22 degrees C the rate of association is 1 X 10(7) M-1 S-1 and the rates of dissociation are 6.5 X 10(-4) S-1 (type I) and 3.2 X 10(-2) S-1 (type II). After binding, a time-dependent process occurs that makes that NGF inaccessible to the external milieu (sequestered). The sequestration process is energy-dependent, but apparently temperature-independent. The data suggest that only the type I receptors are involved in the sequestration process. This process is similar to that observed on sympathetic neurons and may be the first step in the internalization of NGF by responsive cells.

Interaction of [125I] beta nerve growth factor with acidic proteins

We have demonstrated that the beta nerve growth factor will interact with various acidic proteins apparently nonspecifically. When 125I-labeled beta nerve growth factor at a concentration of 3.8 X 10(-10) M is incubated with an acidic protein at 2 mg/ml (4.5 X 10(-6)-4.4 X 10(-5) M), a complex is formed. This complex changes the isoelectric point of the 125I-labeled beta nerve growth factor sufficiently so that the 125I-labeled beta nerve growth factor migrates anomalously in polyacrylamide gel electrophoresis. The interaction between beta nerve growth factor and bovine serum albumin, which appears to be complex, may be the cause of the previously reported activation of the beta nerve growth factor when bovine serum albumin is present in a typical bioassay.