Homage to Rita Levi-Montalcini. Molecular mechanisms of Alzheimer's disease: NGF modulation of APP processing

The therapeutic focus of the scientific community in Alzheimer's disease (AD) has been moving in the last years from attempting late rescue against cholinergic degeneration and amyloid beta plaque clearance to (i) the discovery of blood or cerebrospinal fluid markers for early diagnosis, and (ii) early therapeutic intervention with modulators of amyloid precursor protein (APP) processing. It is currently accepted idea that subtle synaptic alterations determine the first neuronal dysfunctions and cognitive deterioration, progressing overtime into neuronal degeneration in the sporadic and late onset form AD (LOAD), the most diffuse one (90% of AD cases). Synaptic loss occurs long before the appearance of a frank neuronal degeneration in LOAD. The perturbation of the nerve growth factor (NGF) signaling system in brain neurodegenerative disease like AD and Down's syndrome was for long time considered to be a pathological event, subsequent to amyloid-driven disruption of NGF retrograde transport from the cortex and hippocampus to the cell bodies of basal forebrain cholinergic neurons. Nowadays, an increasing amount of data indicate that the observed dysregulation of NGF-TrkA (tyrosine kinase A) and proNGF-p75NTR signaling systems is a good candidate for being the primus movens in the neuropathology of sporadic AD. Accordingly, an amyloid-independent strong correlation of cognitive deficits with reduction of NGF and TrkA, and accumulation of proNGF has been recently observed in mild cognitive impairment and its progression to AD. This review highlights the current knowledge about NGF and early events occurring in LOAD. The involvement of muscarinic acetylcholine receptors, cholesterol, sirtuin1, insulin-like growth factor-1, and Sunday driver protein in APP processing are also discussed. The studies reported here confirm a multitasking ability of NGF in slowing down, through both distinct and overlapping mechanisms, the amyloidogenic processing of APP in neurons of the central nervous system.Adipobiology 2013; 5: 7-18

Exploiting Focused Ultrasound to Aid Intranasal Drug Delivery for Brain Therapy

Novel effective therapeutic strategies are needed to treat brain neurodegenerative diseases and to improve the quality of life of patients affected by Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), Amyotrophic Lateral sclerosis (ALS) as well as other brain conditions. At present no effective treatment options are available; current therapeutics for neurodegenerative diseases (NDs) improve cognitive symptoms only transiently and in a minor number of patients. Further, most of the amyloid-based phase III clinical trials recently failed in AD, in spite of promising preclinical and phase I-II clinical trials, further pinpointing the need for a better knowledge of the early mechanisms of disease as well as of more effective routes of drug administration. In fact, beyond common pathological events and molecular substrates, each of these diseases preferentially affect defined subpopulations of neurons in specific neuronal circuits (selective neuronal vulnerability), leading to the typical age-related clinical profile. In this perspective, key to successful drug discovery is a robust and reproducible biological validation of potential new molecular targets together with a concomitant set up of protocols/tools for efficient and targeted brain delivery to a specific area of interest. Here we propose and discuss Focused UltraSound aided drug administration as a specific and novel technical approach to achieve optimal concentration of the drug at the target area of interest. We will focus on drug delivery to the brain through the nasal route coupled to FUS as a promising approach to achieve neuroprotection and rescue of cognitive decline in several NDs

Investigational treatments for neurodegenerative diseases caused by inheritance of gene mutations: lessons from recent clinical trials

: We reviewed recent major clinical trials with investigational drugs for the treatment of subjects with neurodegenerative diseases caused by inheritance of gene mutations or associated with genetic risk factors. Specifically, we discussed randomized clinical trials in subjects with Alzheimer's disease, Huntington's disease and amyotrophic lateral sclerosis bearing pathogenic gene mutations, and glucocerebrosidase-associated Parkinson's disease. Learning potential lessons to improve future therapeutic approaches is the aim of this review. Two long-term, controlled trials on three anti-β-amyloid monoclonal antibodies (solanezumab, gantenerumab and crenezumab) in subjects carrying Alzheimer's disease-linked mutated genes encoding for amyloid precursor protein or presenilin 1 or presenilin 2 failed to show cognitive or functional benefits. A major trial on tominersen, an antisense oligonucleotide designed to reduce the production of the huntingtin protein in subjects with Huntington's disease, was prematurely interrupted because the drug failed to show higher efficacy than placebo and, at highest doses, led to worsened outcomes. A 28-week trial of tofersen, an antisense oligonucleotide for superoxide dismutase 1 in patients with amyotrophic lateral sclerosis with superoxide dismutase 1 gene mutations failed to show significant beneficial effects but the 1-year open label extension of this study indicated better clinical and functional outcomes in the group with early tofersen therapy. A trial of venglustat, a potent and brain-penetrant glucosylceramide synthase inhibitor, in Parkinson's disease subjects with heterozygous glucocerebrosidase gene mutations revealed worsened clinical and cognitive performance of patients on the enzyme inhibitor compared to placebo. We concluded that clinical trials in neurodegenerative diseases with a genetic basis should test monoclonal antibodies, antisense oligonucleotides or gene editing directed against the mutated enzyme or the mutated substrate without dramatically affecting physiological wild-type variants

Neuroimmune hypothesis of atherosclerosis

Although "many roads lead to atheroma", the prevailing hypothesis at present is the Russell Ross` response-to-injury hypothesis, which states that atherosclerosis is an inflammatory disease that involves several aspects of wound healing. It is noteworthy that, emphasized by the current studies of neurotrophic factors and nerve-immune cell interactions, neuroimmune mechanisms are increasingly implicated in the pathogenesis of a number of inflammatory diseases. Here we highlight the possibility that neuroimmune mechanisms, including the participation of neurotrophic factors and immune cells, may also be involved in the process of atherogenesis.Biomedical Reviews 1999; 10: 37-44

Loss of NGF-TrkA signaling from the CNS is not sufficient to induce cognitive impairments in young adult or intermediate-aged mice

Many molecules expressed in the CNS contribute to cognitive functions either by modulating neuronal activity or by mediating neuronal trophic support and/or connectivity. An ongoing discussion is whether signaling of nerve growth factor (NGF) through its high-affinity receptor TrkA contributes to attention behavior and/or learning and memory, based on its expression in relevant regions of the CNS such as the hippocampus, cerebral cortex, amygdala and basal forebrain. Previous animal models carrying either a null allele or transgenic manipulation of Ngf or Trka have proved difficult in addressing this question. To overcome this problem, we conditionally deleted Ngf or Trka from the CNS. Our findings confirm that NGF-TrkA signaling supports survival of only a small proportion of cholinergic neurons during development; however, this signaling is not required for trophic support or connectivity of the remaining basal forebrain cholinergic neurons. Moreover, comprehensive behavioral analysis of young adult and intermediate-aged mice lacking NGF-TrkA signaling demonstrates that this signaling is dispensable for both attention behavior and various aspects of learning and memory

Nerve growth factor (NGF) in the experimental autoimmune Encephalomyelitis

ABSTRACT BREVE(in inglese) Multiple sclerosis (MS) stands out among neurological diseases by virtue of its frequency, chronicity, and tendency to attack young adults. The pathological hallmark of MS is the presenceof multiple lesions (plaques) characterized by various degrees of inflammation, demyelination, and gliosis in the central nervous system (CNS). Experimental allergic encephalomyelitis (EAE) has been extensevely studied and widely used as animal model of MS. The cerebrospinal fluid (CSF) of patients affected by MS and rodents with EAE show elevated levels of Nerve Growth Factor (NGF). This increase correlates with the course of the disease and show a maximum in corrispondence of the pick of the pathology. NGF is the best characterized member of a family of neurotrophic factors and is crucial for development of the CNS, promoting neuronal repair in a number of CNS insults. Moreover, during EAE, an upregulation of the levels of both the protein and the mRNA for NGF has been observed in the CNS tissues that produce NGF under normal conditions. There are several lines of evidence implicating a disorder of the immune system is implicated in the pathogenesis of MS. Since NGF is involved also in the functional regulation of immune cells and in the modulation of the inflammatory response, a role of NGF in EAE and MS autoimmune-inflammation can be hypothesized. Numerous immunosuppressive or immunomodulating agents have been tried even if only few have yielded positive and not long- lasting effects. Stem cells based therapy is of major interest for neurodegenerative disease’s therapy since adult CNS preserve some germinative areas also in the adulthood, in particular in the Subventricular Zone (SVZ) around the lateral ventricles. Stem cells have the potential to differentiate in a number of cell types and could be relevant in order to replace lost or damaged cells in the adult CNS. There is evidence suggesting that NGF could affect stem cells behaviour and improve stem cell repair after EAE induction. In fact, neural stem cells of the SVZ express both p75 and TrkA NGF receptors during EAE. Moreover, it has been shown that the uptake of ventricularly injected radiolabelled-NGF by SVZ cells causes migration of these cells toward the adjacent brain parenchima after EAE is induced. The major aim of my thesis was to investigate the role of neural stem cells of NGF on the SVZ during EAE. The results of my study, support the idea that NGF stimulates neural stem cells in the adulthood and prospect a potential therapeutic relevance of NGF in the autoimmune-demyelination of MS. Key Words (in inglese): Multiple Sclerosis, EAE, NGF, Inflammation, Demyelination, Stem Cells. Tissue Repair ABSTRACT BREVE(in italiano) La Sclerosi Multipla (SM) è una malattia neurologica che si distingue per la sua frequenza, cronicità e tendenza a colpire giovani adulti. La caratteristica patologica della SM è data dalla presenza di lesioni multiple (placche) nel sistema nervoso centrale (SNC) con vario grado di infiammazione, demielinizzazione e gliosi. Il più diffuso modello sperimentale per lo studio della SM è l’Encefalite Allergica Sperimentale (EAS). Il fluido cerebrospinale (FCS) di pazienti affetti da SM e di roditori con EAS presenta elevati livelli di fattore di crescita nervoso (NGF), in corrispondenza del picco massimo di manifestazione della malattia. L’NGF è il capostipite della famiglia delle neurotrofine ed è di cruciale importanza per lo sviluppo del SNC, nonché nei fenomeni di riparo tissutale a seguito di danno neuronale di varia origine e causa. Per di più nei tessuti cerebrali, dove l’NGF è prodotto in condizioni normali, si osserva un incremento sia della proteina che dell’mRNA per NGF durante l’EAS. Numerose lavori sperimentali sembrano indicare come causa della SM una disregolazione del sistema immunitario e l’NGF noto per regolare le cellule immmunitarie come pure le risposte infiammatorie. Tali osservazioni supportano l’idea che l’NGF rivesta un ruolo importante nell’infiammazione autoimmune di EAS e SM. Diversi agenti immunosoppressivi o immunomodulatori sono stati usati nella terapia clinica della SM, ma con pochi effetti positivi, peraltro limitati nel tempo. La terapia basata sull’uso di cellule staminali è di grande interesse al momento per la terapia delle mlattie neurodegenerative. Il SNC conserva alcune aree germinative contenenti cellule staminali anche nell’adulto, come ad esempio la zona subventricolare (SVZ) lungo i ventricoli laterali. Le cellule staminali hanno la potenzialità di differenziare in un gran numero di tipi cellulari diversi e si prospettano rilevanto ai fini del rimpiazzo delle cellue danneggiate o morte nel SNC. Un numero crescente di osservazioni avvalora l’ipotesi che l’NGF possa agire su tali cellule a seguito dell’induzione dell’EAS. Infatti durante l’EAE le cellule della SVZ esprimono entrambi i recettori dell’NGF, p75 e TrkA. Inoltre, se iniettato nel ventricolo, l’NGF viene captato dalle cellule della SVZ che sono recettive all’NGF e che acquisiscono così la capacità di migrare dal ventricolo verso il parenchima adiacente. L’ obiettivo della mia tesi è stato quello di studiare il ruolo dell’NGF sull’SVZ durante l’EAS. I risultati dei miei studi indicano che l’NGF è in grado di stimolare le cellule staminali cerebrali adulte e prospettano un notevole potenziale terapeutico dell’NGF nei processi autoimmunitari – demielinizzanti della SM. Key Words (in italiano): Sclerosi Multipla, EAS, NGF, Infiammazione, Demielinizzazione, Cellule Staminali, Riparo Tissutale ABSTRACT DETTAGLIATO(in inglese) The human disease multiple sclerosis (MS) is an autoimmune-based neuroinflammatory condition of the Central Nervous System (CNS), in which an attack is driven by the immune system against its own myelin. In fact, once blood brain barrier is destructed, self-reactive lymphocytes reach the brain and spinal cord initiating an inflammatory autoimmune response to myelin, the major component of oligodendrocytes (OL). OL are the axon enveloping cells of the CNS and, when damaged, the integrity and the electrical activity of naked axons are lost. Given the complexity of this multitrait disease, the immunomodulatory and anti-inflammatory drugs used in MS therapy have a limited beneficial effect and further information about autoimmune and neurodegenerative events occurring in MS is needed. NGF is an important neurotrophin, known to be involved in autoimmune response, to orchestrate the three major compartments of the body, namely, the nervous, endocrine and immune systems, and, finally, to regulate survival and differentiation of CNS glial cells and neurons under normal and pathological conditions. For all these reasons, NGF is a biological molecule relevant to MS pathology. In order to study MS, we used Experimental Allergic Encephalomyelitis (eae), the animal model resembling the human disease. We induced EAE in the Lewis rodent strain, which is more susceptible than other to develop an autoimmune response. In the first part of this study, EAE rats and eae rats with high circulating levels of anti-Nerve Growth Factor (ngf) antibodies (NGF-deprived EAE rats) were daily monitored for clinical signs of eae paralysis and relapses attacks in the chronic phase. blood, spinal cord and brain stem were used for histological examination and for neurotophin levels measurement, in particular ngf and Brain Derived Neurotrophic Factor (bdnf) evaluation, eighty-five days after eae induction (chronic stage of EAE). the results showed that low cerebral levels of NGF were found in ngf-deprived EAE rats as expected, and that Ngf deprivation caused a severe worsening of the clinical signs of the disease. these effects were not associated to changes in the amount of bdnf in the regions examined, but the spinal cord where BDNF decreased. in this study we have demonstrated that NGF levels parallel acute and chronic inflammation and that its presence in the CNS is relevant to the reduction of inflammatory cells number and to the shutdown of the CNS inflammatory response in ongoing EAE. In the second part of the study, we evaluated whether progenitor cells of the Subventricular Zone (SVZ) of the brain are affected by NGF-deprivation during chronic EAE. Neuroepithelial cells lying in the SVZ of both rodent and human have been demonstrated to be pluripotent cells forming neurospheres and differentiating both in glial and neuronal cells in vitro. These cells are known to express both p75 and TrkA NGF-receptors in Lewis rats after EAe induction and to incorporate NGF following NGF injection in the ventricle. Thus, we studied NGF effect on oligodendrocytes progenitors (OPC) proliferation and SVZ cells migration in EAE and we found that NGF-deprivation lead to an accumulation of migrating cells in the SVZ, and at the same time OPC diminish in number. Since EAE is a neuroinflammatory disorder characterized by cells damage and loss, the possibility that NGF can exert a protective/reparative in EAE, affecting progenitor survival and migration cannot be excluded. In the third part of the study, we studied spinal cord responsiveness to NGF in EAE rats both in the acute and chronic phase EAE. We found that spinal motor neurons of the IX lamina express basal levels of trkA and that TrkA strongly decreased and sometimes almost disappeared in these neurons following EAE induction. Moreover, this region was covered with more numerous astroglial cells with much stronger TrkA immunoreactivity than in controls. In the chronic EAE group it was found that TrkA immunoreactivity in motoneurons returned almost to the basal levels, suggesting the transient nature of the TrkA-immunoreactivity decline seen in acute EAE. No observable shrinkage of motoneurons was seen at the chronic stage of EAE. In the fourth part of the study, we showed that NGF affects both BrdU incorporation and neuronal commitment of progenitors cells in all the adult brain germinal zones examined also in acute EAE. In fact, NGF intracerebroventricular (icv) injected in the brain of rats with ongoing EAE, increases BrdU incorporation in SVZ, dentate gyrus, periventricular white matter and olfactory bulbs, whereas NGF deprivation had an opposite effect on BrdU incorporation in all these regions, compared to control rats. Moreover, we observed that TrkA-expressing migrating cells (NCAM/trkA double immunopositive cells) colonized the SVZ and the adjacent parenchyma. NCAM positivity was also found in some bipolar shaped cells of the adjacent white matter with a typical migratory morphology. Moreover, NGF icv administration in EAE rats stimulates the expression of early neuronal markers on proliferating precursors of the SVZ. The data obtained demonstrated that NGF and its antibody affect TrkA expression, bromodeoxyuridine (BrdU) incorporation and neuronal commitment of SVZ cells in acute EAE. Overall, the results of these studies indicate that NGF is a key factor influencing the course of EAE pathology and improving recovery response, because of the relevance of NGF in the down-regulation of inflammation-autoimmunity and in promoting the CNS reparative events in response to EAE and, probably, also to MS

Impairment of the nerve growth factor pathway driving amyloid accumulation in cholinergic neurons: the incipit of the Alzheimer′s disease story?

The current idea behind brain pathology is that disease is initiated by mild disturbances of common physiological processes. Overtime, the disruption of the neuronal homeostasis will determine irreversible degeneration and neuronal apoptosis. This could be also true in the case of nerve growth factor (NGF) alterations in sporadic Alzheimer′s disease (AD), an age-related pathology characterized by cholinergic loss, amyloid plaques and neurofibrillary tangles. In fact, the pathway activated by NGF, a key neurotrophin for the metabolism of basal forebrain cholinergic neurons (BFCN), is one of the first homeostatic systems affected in prodromal AD. NGF signaling dysfunctions have been thought for decades to occur in AD late stages, as a mere consequence of amyloid-driven disruption of the retrograde axonal transport of neurotrophins to BFCN. Nowadays, a wealth of knowledge is potentially opening a new scenario: NGF signaling impairment occurs at the onset of AD and correlates better than amyloid load with cognitive decline. The recent acceleration in the characterization of anatomical, functional and molecular profiles of early AD is aimed at maximizing the efficacy of existing treatments and setting novel therapies. Accordingly, the elucidation of the molecular events underlying APP metabolism regulation by the NGF pathway in the septo-hippocampal system is crucial for the identification of new target molecules to slow and eventually halt mild cognitive impairment (MCI) and its progression toward AD

FMRP-Driven Neuropathology in Autistic Spectrum Disorder and Alzheimer’s disease: A Losing Game

International audienceFragile X mental retardation protein (FMRP) is an RNA binding protein (RBP) whose absence is essentially associated to Fragile X Syndrome (FXS). As an RNA Binding Protein (RBP), FMRP is able to bind and recognize different RNA structures and the control of specific mRNAs is important for neuronal synaptic plasticity. Perturbations of this pathway have been associated with the autistic spectrum. One of the FMRP partners is the APP mRNA, the main protagonist of Alzheimer’s disease (AD), thereby regulating its protein level and metabolism. Therefore FMRP is associated to two neurodevelopmental and age-related degenerative conditions, respectively FXS and AD. Although these pathologies are characterized by different features, they have been reported to share a number of common molecular and cellular players. The aim of this review is to describe the double-edged sword of FMRP in autism and AD, possibly allowing the elucidation of key shared underlying mechanisms and neuronal circuits. As an RBP, FMRP is able to regulate APP expression promoting the production of amyloid β fragments. Indeed, FXS patients show an increase of amyloid β load, typical of other neurological disorders, such as AD, Down syndrome, Parkinson’s Disease, etc. Beyond APP dysmetabolism, the two neurodegenerative conditions share molecular targets, brain circuits and related cognitive deficits. In this review, we will point out the potential common neuropathological pattern which needs to be addressed and we will hopefully contribute to clarifying the complex phenotype of these two neurorological disorders, in order to pave the way for a novel, common disease-modifying therapy

Pharmacological targeting of microglia dynamics in Alzheimer's disease: Preclinical and clinical evidence

Numerous clinical trials of anti-amyloid agents for Alzheimer's disease (AD) were so far unsuccessful thereby challenging the validity of the amyloid hypothesis. This lack of progress has encouraged researchers to investigate alternative mechanisms in non-neuronal cells, among which microglia represent nowadays an attractive target. Microglia play a key role in the developing brain and contribute to synaptic remodeling in the mature brain. On the other hand, the intimate relationship between microglia and synapses led to the so-called synaptic stripping hypothesis, a process in which microglia selectively remove synapses from injured neurons. Synaptic stripping, along with the induction of a microglia-mediated chronic neuroinflammatory environment, promote the progressive synaptic degeneration in AD. Therefore, targeting microglia may pave the way for a new disease modifying approach. This review provides an overview of the pathophysiological roles of the microglia cells in AD and describes putative targets for pharmacological intervention. It also provides evidence for microglia-targeted strategies in preclinical AD studies and in early clinical trials