Simona Perga

Neuronal membrane cholesterol loss enhances amyloid peptide generation

Recent experimental and clinical retrospective studies support the view that reduction of brain cholesterol protects against Alzheimers disease (AD). However, genetic and pharmacological evidence indicates that low brain cholesterol leads to neurodegeneration. This apparent contradiction prompted us to analyze the role of neuronal cholesterol in amyloid peptide generation in experimental systems that closely resemble physiological and pathological situations. We show that, in the hippocampus of control human and transgenic mice, only a small pool of endogenous APP and its β-secretase, BACE 1, are found in the same membrane environment. Much higher levels of BACE 1–APP colocalization is found in hippocampal membranes from AD patients or in rodent hippocampal neurons with a moderate reduction of membrane cholesterol. Their increased colocalization is associated with elevated production of amyloid peptide. These results suggest that loss of neuronal membrane cholesterol contributes to excessive amyloidogenesis in AD and pave the way for the identification of the cause of cholesterol loss and for the development of specific therapeutic strategies.

The role of seladin‐1/DHCR24 in cholesterol biosynthesis, APP processing and Aβ generation in vivo

The cholesterol‐synthesizing enzyme seladin‐1, encoded by the Dhcr24 gene, is a flavin adenine dinucleotide‐dependent oxidoreductase and regulates responses to oncogenic and oxidative stimuli. It has a role in neuroprotection and is downregulated in affected neurons in Alzheimers disease (AD). Here we show that seladin‐1‐deficient mouse brains had reduced levels of cholesterol and disorganized cholesterol‐rich detergent‐resistant membrane domains (DRMs). This was associated with inefficient plasminogen binding and plasmin activation, the displacement of β‐secretase (BACE) from DRMs to APP‐containing membrane fractions, increased β‐cleavage of APP and high levels of Aβ peptides. In contrast, overexpression of seladin‐1 increased both cholesterol and the recruitment of DRM components into DRM fractions, induced plasmin activation and reduced both BACE processing of APP and Aβ formation. These results establish a role of seladin‐1 in the formation of DRMs and suggest that seladin‐1‐dependent cholesterol synthesis is involved in lowering Aβ levels. Pharmacological enhancement of seladin‐1 activity may be a novel Aβ‐lowering approach for the treatment of AD.

Cholesterol Loss Enhances TrkB Signaling in Hippocampal Neurons Aging in Vitro

Binding of the neurotrophin brain-derived neurotrophic factor (BDNF) to the TrkB receptor is a major survival mechanism during embryonic development. In the aged brain, however, BDNF levels are low, suggesting that if TrkB is to play a role in survival at this stage additional mechanisms must have developed. We here show that TrkB activity is most robust in the hippocampus of 21-d-old BDNF-knockout mice as well as in old, wild-type, and BDNF heterozygous animals. Moreover, robust TrkB activity is evident in old but not young hippocampal neurons differentiating in vitro in the absence of any exogenous neurotrophin and also in neurons from BDNF -/- embryos. Age-associated increase in TrkB activity correlated with a mild yet progressive loss of cholesterol. This, in turn, correlated with increased expression of the cholesterol catabolic enzyme cholesterol 24-hydroxylase. Direct cause-effect, cholesterol loss-high TrkB activity was demonstrated by pharmacological means and by manipulating the levels of cholesterol 24-hydroxylase. Because reduced levels of cholesterol and increased expression of choleseterol-24-hydroxylase were also observed in the hippocampus of aged mice, changes in cellular cholesterol content may be used to modulate receptor activity strength in vivo, autonomously or as a way to complement the natural decay of neurotrophin production.

Loss of Braking Signals During Inflammation A Factor Affecting the Development and Disease Course of Multiple Sclerosis

BACKGROUND In a recent genome-wide transcriptional analysis, we identified a gene signature for multiple sclerosis (MS), which reverted back to normal during pregnancy. Reversion was particularly evident for 7 genes: SOCS2, TNFAIP3, NR4A2, CXCR4, POLR2J, FAM49B, and STAG3L1, most of which encode negative regulators of inflammation. OBJECTIVES To corroborate dysregulation of genes, to evaluate the prognostic value of genes, and to study modulation of genes during different treatments. DESIGN Comparison study. SETTING Italian referral center for MS. PATIENTS Quantitative polymerase chain reaction measurements were performed for 274 patients with MS and 60 healthy controls. Of the 274 patients with MS, 113 were treatment-naive patients in the initial stages of their disorder who were followed up in real-world clinical settings and categorized on the basis of disease course. The remaining 161 patients with MS received disease-modifying therapies (55 patients were treated with interferon beta, 52 with glatiramer acetate, and 54 with natalizumab) for a mean (SD) of 12 (2) months. MAIN OUTCOME MEASURES Gene expression levels, relapse rate, and change in Expanded Disability Status Scale. RESULTS We found a dysregulated gene pathway (P ≤ .006), with a downregulation of genes encoding negative regulators. The SOCS2, NR4A2, and TNFAIP3 genes were inversely correlated with both relapse rate (P ≤ .002) and change in Expanded Disability Status Scale (P ≤ .005). SOCS2 was modulated by both interferon beta and glatiramer acetate, TNFAIP3 was modulated by glatiramer acetate, and NR4A2 was not altered at all. No changes were induced by natalizumab. CONCLUSIONS We demonstrate that there is a new molecular pathogenic mechanism that underlies the initiation and progression of MS. Defects in negative-feedback loops of inflammation lead to an overactivation of the immune system so as to predispose the brain to inflammation-sensitive MS.

Cyp46-mediated cholesterol loss promotes survival in stressed hippocampal neurons

Aged neurons constitute an outstanding example of survival robustness, outliving the accumulation of reactive oxygen species (ROS) derived from various physiological activities. Since during aging hippocampal neurons experience a progressive loss of membrane cholesterol and, by virtue of this, a gradual and sustained increase in the activity of the survival receptor tyrosine kinase TrkB, we have tested in this study if cholesterol loss is functionally associated to survival robustness during aging. We show that old neurons that did not undergo the cholesterol drop, upon knockdown of the cholesterol hydroxylating enzyme Cyp46, presented low TrkB activity and increased apoptotic levels. In further agreement, inducing cholesterol loss in young neurons led to the early appearance of TrkB activity. In vivo, Cyp46 knockdown led to the appearance of damaged hippocampal neurons in old mice exposed to exogenous stressful stimuli. Cholesterol loss seems therefore to contribute to neuronal survival in conditions of prominent stress, either acute or chronic. The relevance of this pathway in health and disease is discussed.

Acute-phase proteins investigation based on lectins affinity capture prior to 2-DE separation: Application to serum from multiple sclerosis patients

Plasma acute‐phase proteins (APPs) glyco‐isoforms are important biomarkers of inflammatory processes such as those occurring in multiple sclerosis (MS). Specific analysis of these proteins is often hampered by sample biochemical complexity. The aim of our study was to set up a method to accurately visualize, identify and quantify APPs glyco‐isoforms in human serum. An enrichment strategy based on affinity chromatography using the carbohydrate‐binding proteins concanavalin A (ConA) and erythrina cristagalli lectin (ECL) was applied to pooled serum samples from 15 patients and 9 healthy individuals. Image analysis of 2‐DE detected 30 spots with a fold change higher than 1.5. A total of 14 were statistically significant (p value<0.05): 7 up‐regulated and 7 down‐regulated in MS samples. ESI LC‐Nanospray IT mass spectrometry analysis confirmed that all of them were APPs isoforms supporting the idea that the accurate analysis of differential glycosylation profiles in these biomarkers is instrumental to distinguish between MS patients and healthy subjects. Additionally, overlaps in ConA/ECL maps protein patterns suggest how the used lectins are able to bind sugars harbored by the same oligosaccharide structure. Among identified proteins, the presence of complex and/or hybrid type N‐linked sugar structures is well known. Performing galectin‐3 binding and Western blotting, we were able to demonstrate a correlation between hybrid type glyco‐isoforms of β‐haptoglobin and MS. In conclusion, although the patho‐physiological role of the identified species still remains unclear and further validations are needed, these findings may have a relevant impact on disease‐specific marker identification approaches.

Vitamin D Binding Protein Isoforms and Apolipoprotein E in Cerebrospinal Fluid as Prognostic Biomarkers of Multiple Sclerosis

Background Multiple sclerosis (MS) is a multifactorial autoimmune disease of the central nervous system with a heterogeneous and unpredictable course. To date there are no prognostic biomarkers even if they would be extremely useful for early patient intervention with personalized therapies. In this context, the analysis of inter-individual differences in cerebrospinal fluid (CSF) proteome may lead to the discovery of biological markers that are able to distinguish the various clinical forms at diagnosis. Methods To this aim, a two dimensional electrophoresis (2-DE) study was carried out on individual CSF samples from 24 untreated women who underwent lumbar puncture (LP) for suspected MS. The patients were clinically monitored for 5 years and then classified according to the degree of disease aggressiveness and the disease-modifying therapies prescribed during follow up. Results The hierarchical cluster analysis of 2-DE dataset revealed three protein spots which were identified by means of mass spectrometry as Apolipoprotein E (ApoE) and two isoforms of vitamin D binding protein (DBP). These three protein spots enabled us to subdivide the patients into subgroups correlated with clinical classification (MS aggressive forms identification: 80%). In particular, we observed an opposite trend of values for the two protein spots corresponding to different DBP isoforms suggesting a role of a post-translational modification rather than the total protein content in patient categorization. Conclusions These findings proved to be very interesting and innovative and may be developed as new candidate prognostic biomarkers of MS aggressiveness, if confirmed.

Altered NR4A Subfamily Gene Expression Level in Peripheral Blood of Parkinson’s and Alzheimer’s Disease Patients

Parkinson’s disease (PD) is a neurodegenerative pathology characterized by the degeneration of midbrain dopamine neurons, whose development and maintenance in brain is related to the transcription factor NR4A2 (also called Nurr1). Notably, NR4A2 is a neuroprotective agent with anti-inflammatory role in microglia and astrocytes. Furthermore, mutations in NR4A2 gene are associated to the familial form of PD, and its gene expression level is down-regulated in blood obtained from PD patients. NR4A2 belongs to the NR4A subfamily consisting of three members: NR4A1, NR4A2, and NR4A3. The NR4A subfamily shares high degree of homology in their molecular structure and cooperates in a spectrum of functions ranging from central nervous system to immune control during physiological and pathological conditions. Considering the close functional link between the member of NR4A subfamily, we performed a gene expression analysis of NR4A1, NR4A2, and NR4A3 in peripheral blood obtained from PD patients and healthy controls (HC). Then, in order to evaluate possible involvement of the NR4A subfamily in other neurodegenerative processes, we carried out the same analysis on blood obtained from Alzheimer’s disease (AD) patients. A correlation between clinical features and gene expression was also evaluated. We found a marked down-regulated gene expression of the NR4A subfamily obtained from PD patients, but only a NR4A1 decrease in AD patients compared to HC. This study reports that the entire NR4A subfamily and not only NR4A2 could be systemically involved in PD suggesting that the study of these factors could be a promising approach to develop PD therapy.

Monocytes and CD4+ T cells contribution to the under-expression of NR4A2 and TNFAIP3 genes in patients with multiple sclerosis.

We recently found a gene signature for multiple sclerosis (MS) that reverted to normal during pregnancy in MS patients and included NR4A2 and TNFAIP3, key molecules in anti-inflammatory processes. Here we focus on the expression levels of these two genes in monocytes and CD4+ T cells from healthy controls and treatment-naïve RRMS patients. Our findings show that monocytes play a key role in the dysregulated anti-inflammatory response, being the expression of both genes down-regulated in these cells in RRMS patients with respect to healthy individuals. CD4+ T cells seem to have only a marginal part, because we can observe only a slight down-regulation in NR4A2.

Effects of Isoxazolo-Pyridinone 7e, a Potent Activator of the Nurr1 Signaling Pathway, on Experimental Autoimmune Encephalomyelitis in Mice

Multiple sclerosis (MS) is an autoimmune chronic disease of the central nervous system (CNS) characterized by immune-mediated inflammation, demyelination and subsequent axonal damage. Gene expression profiling showed that Nurr1, an orphan nuclear receptor, is down-regulated in peripheral blood mononuclear cells of MS patients. Nurr1 exerts an anti-inflammatory role repressing the activity of the pro-inflammatory transcription factor NF-kB. Here, we report that the preventive treatment with isoxazolo-pyridinone 7e, an activator of Nurr1 signaling pathway, reduces the incidence and the severity of a MS murine model, i.e. experimental autoimmune encephalomyelitis (EAE). The compound is able to attenuate inflammation and neurodegeneration in spinal cords of EAE mice by an NF-kB pathway-dependent process.