Molecular forms of nerve growth factor in mouse submaxillary glands

proNGF Measurement in Cerebrospinal Fluid Samples of a Large Cohort of Living Patients With Alzheimer's Disease by a New Automated Immunoassay

The discovery of new biomarkers for Alzheimer's disease (AD) is essential for an accurate diagnosis, to conceive new strategies of treatments, and for monitoring the efficacy of potential disease-modifying therapies in clinical trials. proNGF levels in the cerebrospinal fluid (CSF) represent a promising diagnostic biomarker for AD, but its validation was hampered by the absence of a reliable immunoassay. In the literature, proNGF is currently measured in postmortem brain tissue by semiquantitative immunoblot. Here we describe the development and validation of a new method to measure proNGF in the CSF of living patients. This method, based on molecular size separation by capillary electrophoresis, is automated and shows a 40-fold increase in sensitivity with respect to the proNGF immunoblot, largely used in literature, and is robust, specific, and scalable to high-throughput. We have measured proNGF in the cerebrospinal fluid of 84 living patients with AD, 13 controls, and 15 subjective memory complaints (SMC) subjects. By comparing the proNGF levels in the three groups, we found a very significant difference between proNGF levels in AD samples compared with both controls and SMC subjects, while no significant difference was found between SMC and controls. Because of the development of this new immunoassay, we are ready to explore the potentiality of proNGF as a new biomarker for AD or subgroups thereof, as well as for other neurodegenerative diseases.

Nerve growth factor (NGF) pathway biomarkers in Down syndrome prior to and after the onset of clinical Alzheimer's disease: A paired CSF and plasma study

BACKGROUND

The discovery that nerve growth factor (NGF) metabolism is altered in Down syndrome (DS) and Alzheimer's disease (AD) brains offered a framework for the identification of novel biomarkers signalling NGF deregulation in AD pathology.

METHODS

We examined levels of NGF pathway proteins (proNGF, neuroserpin, tissue plasminogen activator [tPA], and metalloproteases [MMP]) in matched cerebrospinal fluid (CSF)/plasma samples from AD-symptomatic (DSAD) and AD-asymptomatic (aDS) individuals with DS, as well as controls (HC).

RESULTS

ProNGF and MMP-3 were elevated while tPA was decreased in plasma from individuals with DS. CSF from individuals with DS showed elevated proNGF, neuroserpin, MMP-3, and MMP-9. ProNGF and MMP-9 in CSF differentiated DSAD from aDS (area under the curve = 0.86, 0.87). NGF pathway markers associated with CSF amyloid beta and tau and differed by sex.

DISCUSSION

Brain NGF metabolism changes can be monitored in plasma and CSF, supporting relevance in AD pathology. These markers could assist staging, subtyping, or precision medicine for AD in DS.

Nerve growth factor in rheumatic diseases

OBJECTIVES

The nervous system modulates the immune response in many autoimmune syndromes by neurogenic inflammation. One of the pivotal mediators is nerve growth factor (NGF), which is known for its effects on neuronal survival and growth. There is considerable evidence that NGF acts as an important mediator of many immune responses. This article reviews the role of NGF in rheumatic diseases and strategies for potential therapeutic interventions.

METHODS

We conducted a database search using Medline and Medpilot. Eight hundred abstracts containing the keyword NGF and 1 of the following terms were reviewed: arthritis, neurogenic inflammation, rheumatoid arthritis, osteoarthritis, collagen arthritis, arteritis, psoriasis, psoriatic arthritis, Sjogren syndrome, systemic lupus erythematosus, gout, osteoporosis, lower back pain, lumbar disc herniation, nerve root compression, spondyloarthritis, spondylarthropathy, algoneurodystrophy, fibromyalgia, Kawasaki syndrome, polyarteritis nodosa, cytokine, vasculitis, pain, therapy, and antagonist. Articles were analyzed based on relevance and content. Most clinical trials and studies with human specimens were included. Studies with experimental animal models were selected if they contained relevant data.

RESULTS

NGF is overexpressed in many inflammatory and degenerative rheumatic diseases. Concentrations differ to some extent and sometimes even show contradictory results. NGF is found in serum, synovial fluid, and cerebrospinal fluid, and tissue specimens. NGF concentrations can be correlated with the extent of inflammation and/or clinical activity in many conditions. In rheumatoid arthritis, NGF levels are significantly higher as compared with osteoarthritis.

CONCLUSIONS

NGF is a significant mediator and modulator of inflammation. NGF sometimes shows detrimental and sometimes regenerative activity. These findings indicate potential therapeutic interventions using either NGF antagonists or recombinant NGF.

Expression of nerve growth factor (NGF) isoforms in the rat uterus during pregnancy: accumulation of precursor proNGF

The mechanisms that promote the transient degenerative changes in the uterus innervation during pregnancy remain incompletely understood. Signaling by the nerve growth factor (NGF)-beta is important for maintaining the density of peripheral sympathetic innervation. Here, we analyzed the spatial and temporal expression of NGF isoforms in the rat uterus using RT-PCR, immunoblot analysis, and immunohistochemistry during pregnancy (d 7, 14, and 21), and postpartum (d 1, 8, and 22). Western blot analysis using antibodies to mature NGF-beta and to proNGF domain demonstrated a significant decrease in mature NGF-beta at gestational d 14 and 21 (term pregnancy) and 1 d postpartum, which paralleled a remarkable accumulation of the 26-28-, 32-, and 60-kDa proNGF forms. There were diminished ratios of mature NGF-beta to proNGF independent of uterus growth on the same gestational days. Immunohistochemistry revealed a progressive NGF-beta decline throughout pregnancy in the myometrium and a near absence at term pregnancy, which contrasted with increased NGF immunostaining in the intermyometrial connective tissue layers. More importantly, proNGF-specific antibodies identified the increased NGF immunoreactivity in the intermyometrial layers at term pregnancy as proNGF and not mature NGF-beta. Alterations in the processing of NGF and accumulation of proNGF in the intermyometrial layers, where axonal degeneration occurs, may contribute significantly to the pregnancy-related uterine denervation and to the control of myometrial activity.

ProNGF: a neurotrophic or an apoptotic molecule?

Nerve growth factor (NGF) acts on various classes of central and peripheral neurons to promote cell survival, stimulate neurite outgrowth and modulate differentiation. NGF is synthesized as a precursor, proNGF, which undergoes processing to generate mature NGF. It has been assumed, based on studies in the mouse submandibular gland, that NGF in vivo is largely mature NGF, and that mature NGF accounts for the molecule's biological activity. However, recently we have shown that proNGF is abundant in central nervous system tissues whereas mature NGF is undetectable, suggesting that proNGF may have a function distinct from its role as a precursor. A recent report that proNGF has apoptotic activity contrasts with other data demonstrating that proNGF has neurotrophic activity. This chapter will review the structure and processing of NGF and what is known about the biological activity of proNGF. Possible reasons for the discrepancies in recent reports are discussed.

Neurotrophic factors and their receptors in human sensory neuropathies

Neurotrophic factors may play key roles in pathophysiological mechanisms of human neuropathies. Nerve growth factor (NGF) is trophic to small-diameter sensory fibers and regulates nociception. This review focuses on sensory dysfunction and the potential of neurotrophic treatments. Genetic neuropathy. Mutations of the NGF high-affinity receptor tyrosine kinase A (Trk A) have been found in congenital insensitivity to pain and anhidrosis; these are likely to be partial loss-of-function mutations, as axon-reflex vasodilatation and sweating can be elicited albeit reduced, suggesting rhNGF could restore nociception in some patients. Leprous neuropathy. Decreased NGF in leprosy skin may explain cutaneous hypoalgesia even with inflammation and rhNGF may restore sensation, as spared nerve fibers show Trk A-staining. Diabetic neuropathy. NGF is depleted in early human diabetic neuropathy skin, in correlation with dysfunction of nociceptor fibers. We proposed rhNGF prophylaxis may prevent diabetic foot ulceration. Clinical trials have been disappointed, probably related to difficulty delivering adequate doses and need for multiple trophic factors. NGF and glial cell line-derived neurotrophic factor (GDNF) are both produced by basal keratinocytes and neurotrophin (NT-3) by suprabasal keratinocytes: relative mRNA expression was significantly lower in early diabetic neuropathy skin compared to controls, for NGF (P < 0.02), BDNF (P < 0.05), NT-3 (P < 0.05), GDNF (< 0.02), but not NT4/5, Trk A or p75 neurotrophin receptor (all P > 0.05). Posttranslational modifications of mature and pro-NGF may also affect bioactivity and immunoreactivity. A 53 kD band that could correspond to a prepro-NGF-like molecule was reduced in diabetic skin. Traumatic neuropathy and pain. While NGF levels are acutely reduced in injured nerve trunks, neuropathic patients with chronic skin hyperalgesia and allodynia show marked local increases of NGF levels; here anti-NGF agents may provide analgesia. Physiological combinations of NGF, NT-3 and GDNF, to mimic a 'surrogate target organ', may provide a novel 'homeostatic' approach to prevent the development and ameliorate intractable neuropathic pain (e.g., at painful amputation stumps).

Molecular forms of NGF in human and rat neuropathic tissues: decreased NGF precursor-like immunoreactivity in human diabetic skin

Precursors of NGF have been shown to be the predominant forms of this neurotrophin in human brain and peripheral tissues, and proNGF has been shown recently to preferentially bind p75NTR with high affinity. In our studies of human and rat skin and nerve extracts, a 53 kDa band was detected by Western blot using antibodies against rhNGF or prepro-NGF (-91 to -60), that could correspond to a previously described modified prepro-NGF-like molecule. The relative optical intensity of the 53-kDa bands was markedly reduced in skin extracts from patients with subclinical diabetic neuropathy (diabetic: 1.5, 1.0-8.0, n = 6; controls: 52.0, 23.0-85.0, n = 6, p = 0.0022) but was increased in extracts of inflamed colon from patients with Crohn's disease (inflamed: median 12.0, range 0.1-12.0, n = 11: controls: 0.1, 0.1-3.0, n = 8, p = 0.0055). Antibodies to both rhNGF and prepro-NGF immunostained basal keratinocytes in tissue sections of normal human and rat skin showed accumulation of immunoreactivity in nerve fibers distal to sciatic nerve ligation in rats. Prepro-NGF antibody immunostained rat large/medium sensory neurons, whereas only small sensory neurons were stained with antibodies to mature rhNGF, suggesting that prepro-NGF may be preferentially taken up and transported by p75NTR. The different molecular forms derived from prepro-NGF are likely to be of importance in sensory mechanisms, and deserve further investigation.

The precursor pro-nerve growth factor is the predominant form of nerve growth factor in brain and is increased in Alzheimer's disease

Nerve growth factor (NGF) is important for regulation, differentiation, and survival of peripheral and central nervous system neurons, including basal forebrain cholinergic neurons (BFCN) which degenerate in Alzheimer's disease (AD). Mature NGF protein is processed from a larger precursor, proNGF. We demonstrate that proNGF is the predominant form of NGF in mouse, rat, and human brain tissue, whereas little or no mature NGF is detected. Previous reports showed NGF protein, measured by ELISA, is increased in AD BFCN target regions such as hippocampus and cortex. Using Western blotting, we demonstrate a twofold increase in proNGF in AD parietal cortex compared to controls, indicating that it is this precursor form, proNGF, that accumulates in AD. This increase may reflect either a role for biologically active proNGF or posttranslational disturbances in NGF biosynthesis that decrease the processing of proNGF to mature NGF in AD.

Cultivation of epithelia from the secretory coil of the ovine apocrine gland: evidence of secretory cell function and ductal morphogenesis in vitro

The secretory coil of the ovine apocrine gland is composed predominantly of two cell types, secretory cells lining the lumen and myoepithelial cells adjacent to the basement membrane. The glands synthesize a number of hormones and growth factors, but analysis of the functions of these molecules may be hampered by the mixing of apocrine and sebaceous secretions in the pilary canal. The purpose of this study was to isolate the glands and devise simple culture procedures to facilitate investigations of secretory cell function. The most successful approach involved microdissection of the secretory coils individually from skin biopsies and culture in Dulbecco's modified Eagle's medium. After 1-2 wk in medium, cell outgrowths were seen from explants. These consisted predominantly of populations of epithelial cells, many containing granules. Smaller granules were usually concentrated around the cell nuclei and accumulated lipophilic dyes. Large granules were unreactive. Western analysis showed that cells in culture synthesized nerve growth factor-like peptides, a feature consistent with one of the functions of the gland in vivo. When isolated secretor, coils were explanted to culture dishes coated with matrigel, highly compact, multilayered masses of cells grew out. Subsequently, tubular structures formed. The observations suggest that some differentiated functions of gland cells were retained in vitro and that the procedures described provide a system for the study, of apocrine secretions in isolation from those of other skin glands.

Interactions between epidermal growth factor and the Tabby mutation in skin

Mutations of the X-linked genes Tabby (Ta) in mice and EDA in humans result in developmental and functional abnormalities, primarily in the skin and hair follicles. Although both genes are believed to encode membrane-associated proteins, it has been suggested that, in the mouse, the mutation is linked to a deficiency of epidermal growth factor (EGF). This study investigated relationships between the skin abnormalities of Ta mice and the EGF signal pathway. The distribution of endogenous EGF in tissues of Ta/Y and +/Y animals was examined and, because of its reported morphogenetic actions and ability to overcome receptor signalling defects in vivo, the effects of exogenous EGF on the hair follicle population were determined. EGF levels were similar in a number of tissues of Ta/Y and +/Y mice, but amounts in Ta/Y submaxillary glands were reduced, probably due to a smaller gland size. Exogenous EGF inhibited hair follicle development and decreased follicle density in both genotypes. It was concluded from comparisons of the distributions of EGF and its effects in skin with those in mice bearing mutations in the EGF signal pathway that the normal phenotype results from interactions between EGF and the Ta peptide in skin.

Skin2--an in vitro human skin model: the correlation between in vivo and in vitro testing of surfactants

The availability of an in vitro test system to replace animal testing of potential irritants is becoming more and more urgent especially in Europe as a consequence of the European Community Cosmetics Directive. To evaluate the ability of Advanced Tissue Sciences' (ATS) ZK1301 skin model to predict the skin irritation potential of surfactants, we performed a pilot validation study utilizing four different laboratories. The in vitro protocol was designed as a quantitative pre-screen for the clinical patch studies. Sixteen substances, representing various surfactant categories and ranges of irritation potential, were tested. The 3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay was used to quantitate viability in vitro. We documented the viability of tissues exposed to unknown substances for specific periods. The in vitro results were calculated as percent distilled water controls (DWC). The time required to reduce the viability of each tissue to 50% of the distilled water controls (T50) was compared to mean erythema and edema scores from the clinical studies by Pearson's correlation. The individual laboratories demonstrated coefficients of 0.72. The results indicated that the 30 min percent untreated control values best predicted the 24 h clinical patch scores. No statistically significant interlab variability was found. Only one false negative was seen when non/mild and moderate/severe irritant categories were assigned according to the in vitro scores. These results demonstrate that the skin2 in vitro test system may serve as a good screening method prior to clinical patch studies.

Commercial mouse and human nerve growth factors contain nerve growth factor prohormone isoforms

Highly sensitive chemiluminescence immunoblot analysis was utilized to examine the purity of mouse 2.5S-, beta- and 7S nerve growth factors as well as that of recombinant human beta-nerve growth factor obtained from commercial vendors. Three polyclonal antisera and two monoclonal antibodies to 13 kDa nerve growth factor (2.5S NGF and beta-NGF) were employed for assessing the purity of each preparation. In addition, polyclonal antisera against two prepro-NGF specific domains were used for immunoblotting analysis to ascertain the identity of high molecular weight nerve growth factor immunoreactive proteins as prohormones. Both the mouse and human NGF preparations contained 53 and 60 kDa immunoreactive proteins. Of these, the mouse 60 kDa and the human 53 kDa proteins strongly immunoreacted with both prepro-nerve growth factor specific domain antibodies suggesting that they are two NGF prohormone isoforms. In addition, both the mouse and human nerve growth factor preparations contained proteins that were immunoreactive to polyclonal antisera and monoclonal antibodies to mouse 2.5S and/or beta-NGF. High molecular weight aggregates of prohormones were also observed in mouse and human nerve growth factor samples. In summary, none of the ten NGF samples examined were pure as stated. Our study cautions investigators in the field to be aware of the presence of nerve growth factor prohormones and other proteins in various mouse and human nerve growth factors sold commercially.

Update of the NGF saga

Nerve growth factor (NGF), initially characterized for its survival and differentiating actions on embryonic sensory and sympathetic neurons, is now known to display a greatly extended spectrum of biological functions. NGF exerts a profound modulatory role on sensory nociceptive nerve physiology during adulthood which appears to correlate with hyperalgesic phenomena occurring in tissue inflammation. Other newly detected NGF-responsive cells belong to the hematopoietic-immune and neuroendocrine systems. In particular, mast cells and NGF both appear to be involved in neuroimmune interactions and tissue inflammation, with NGF acting as a general "alert" molecule capable of recruiting and priming both local tissue and systemic defense processes following stressful events. NGF can thus be viewed as a multifactorial mediator modulating neuroimmune-endocrine functions of vital importance to the regulation of homeostatic interactions, with potential involvement in pathological processes deriving from dysregulation of either local or systemic homeostatic balances.

Comparison between epidermal growth factor, transforming growth factor-alpha and EGF receptor levels in regions of adult rat brain

Examination of adult rat brain regions by specific radioimmunoassays revealed a widespread distribution of transforming growth factor-alpha (TGF-alpha), but not epidermal growth factor (EGF), the peptide that had previously been reported to be present in rodent brain. Polyadenylated RNA samples from the different regions of rat brain were analyzed by Northern blot to identify mRNA species encoding precursor proteins for EGF (preproEGF), TGF-alpha (preproTGF-alpha), and the EGF/TGF-alpha receptor. The results indicate that TGF-alpha is the most abundant ligand for the EGF/TGF-alpha receptor in most parts of the brain analyzed. Message for preproEGF was only detectable after prolonged autoradiographic exposure; levels of preproEGF mRNA were between two and three orders of magnitude lower in brain than those expressed in control tissue (kidney), and one to two orders of magnitude lower than preproTGF-alpha mRNA levels in all brain regions. These results were confirmed by analysis of mRNA by RT/PCR, and support the hypothesis that expression of preproEGF mRNA in the brain is limited to smaller discrete areas, whereas preproTGF-alpha gene expression is almost ubiquitous.

Identification of pro-epidermal growth factor and high molecular weight epidermal growth factors in adult mouse urine

By use of immunoblot analysis, we demonstrate the presence of a pro-Epidermal growth factor (EGF) with an approximate molecular weight of 165 kDa in adult mouse urine. In addition, urine contains four high molecular weight EGFs with approximate molecular weights of 116, 97, 66 and 56 kDa. The 165 kDa pro-EGF as well as the 66 and 56 kDa EGFs also are detectable in mouse kidney extract. Neither urine nor kidney contain the mature EGF of 6 kDa. The 165 kDa pro-EGF is the major product synthesized in renal tissue and secreted in urine. The finding of high molecular weight EGFs in urine suggests that part of pro-EGF secreted into urine undergoes partial proteolysis distal to its site of synthesis.

Biological actions of 53 kDa nerve growth factor as studied by a blot and culture technique

A blot and culture technique has been utilized to examine the biological actions of 53,000 Dalton (53 kDa) nerve growth factor (NGF) present in the submaxillary gland (SMG) of adult male and female mice. SMG-proteins were first resolved by sodium dodecylsulfate (SDS) polyacrylamide gel electrophoresis (PAGE) under reducing conditions and then transferred to a nitrocellulose (NTC) sheet by electroblotting. Specific areas corresponding to 53 kDa NGF were cut and cultured with the rat pheochromocytoma cell line, PC-12. NTC strips bearing the 53 kDa NGF band stimulated cell flattening and neurite formation in serum containing growth medium and augmented cell survival in serum-free growth medium. Similar results were obtained with NTC strips bearing the 13 kDa NGF band. The results suggest that 53 kDa NGF, like 13 kDa NGF, exerts both tropic and trophic actions on its target neurons.