[125I]EGF binding in basal ganglia of patients with Parkinson's disease and progressive supranuclear palsy and in MPTP-treated monkeys

Association between epidermal growth factor receptor gene polymorphisms and susceptibility to Parkinson's disease

OBJECTIVE

The progressive loss of dopaminergic neurons in the mesencephalic substantia nigra is recognized as an important pathological feature of Parkinson's disease (PD). Several research studies have suggested that the EGFR signaling pathway may play a significant role in the survival and functional development of dopaminergic neurons. Therefore, genetic variations in these pathways may be related with PD susceptibility. The aim of our study was to explore the association between selected single nucleotide polymorphisms (SNPs) of the epidermal growth factor receptor (EGFR) gene, including rs730437, rs3752651 and rs11506105, and susceptibility to Parkinson's disease in a Han Chinese population.

METHODS

A total of 870 Han Chinese subjects, including 435 PD patients and 435 healthy controls, were enrolled in this case-control study. Peripheral blood was obtained from all subjects for DNA extraction, and selected SNPs (rs730437, rs3752651, rs11506105) of the EGFR gene were genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Differences in the frequencies of genotype and allele gene polymorphisms between patients with PD and healthy controls were analyzed using the Chi-square test. Logistic regression analysis was applied for calculating the odds ratios (ORs) and 95 % confidence intervals (CIs) to evaluate potential associations.

RESULTS

We observed statistically significant differences in rs730437 in the additive models (AC vs. AA: P = 0.047), dominant models (CC + AC vs. AA: P = 0.024) and alleles (C vs. A: P = 0.018). Further subgroup analyses indicated that the C allele of rs730437 showed lower prevalence in the EOPD, compared with matched controls (P = 0.005). The frequency of the GG genotype and G allele for rs11506105 was lower in PD subjects than in healthy controls in the entire study population (P = 0.028, P = 0.034, respectively) and female group (P = 0.024, P = 0.007, respectively). No significant association was found between rs3752651 polymorphism and PD susceptibility in either the whole or subgroup analyses. The analysis of gene haplotypes revealed that the AAT haplotype was related with PD susceptibility.

CONCLUSION

The rs730437 and rs11506105 polymorphisms, but not the rs3752651 polymorphism, of the EGFR gene may be related with susceptibility to PD in a Han Chinese population. An investigation using a larger sample size is warranted to further analyze potential associations between the EGFR gene and PD.

Decoding Common Features of Neurodegenerative Disorders: From Differentially Expressed Genes to Pathways

BACKGROUND

Neurodegeneration is a progressive/irreversible loss of neurons, building blocks of our nervous system. Their degeneration gradually collapses the entire structural and functional system manifesting in myriads of clinical disorders categorized as Neurodegenerative Disorders (NDs) such as Alzheimer's Disease, (AD), Parkinson's Disease (PD), Frontotemporal Dementia (FTD) and Amyotrophic Lateral Sclerosis (ALS). NDs are characterized by a puzzling interplay of molecular and cellular defects affecting subset of neuronal populations in specific affected brain areas.

OBJECTIVE

In present study, comparative in silico analysis was performed by utilizing gene expression datasets of AD, PD, FTD and ALS to identify potential common features to gain insights into complex molecular pathophysiology of the selected NDs.

METHODS

Gene expression data of four disorders were subjected to the identification of Differential Gene Expression (DEG) and their mapping on biological processes, KEGG pathways and molecular functions. Detailed comparative analysis was performed to highlight the common grounds of these dis-orders at various stages.

RESULTS

Astoundingly, 106 DEGs were found to be common across all disorders. Alongwith in total 100 GO terms and 7 KEGG pathways were found to be significantly enriched across all disorders. EGFR, CDC42 and CREBBP have been identified as the significantly interacting nodes in gene-gene in-teraction and in Protein-Protein Interaction (PPI) network as well. Furthermore, interaction of common DEGs targets with miRNA's has been scrutinized.

CONCLUSION

The complex molecular underpinnings of these disorders are currently elusive. Despite heterogeneous clinical and pathological expressions, common features have been recognized in many NDs which provide evidence of their convergence.

Central role of the EGF receptor in neurometabolic aging

A strong connection between neuronal and metabolic health has been revealed in recent years. It appears that both normal and pathophysiological aging, as well as neurodegenerative disorders, are all profoundly influenced by this "neurometabolic" interface, that is, communication between the brain and metabolic organs. An important aspect of this "neurometabolic" axis that needs to be investigated involves an elucidation of molecular factors that knit these two functional signaling domains, neuronal and metabolic, together. This paper attempts to identify and discuss a potential keystone signaling factor in this "neurometabolic" axis, that is, the epidermal growth factor receptor (EGFR). The EGFR has been previously demonstrated to act as a signaling nexus for many ligand signaling modalities and cellular stressors, for example, radiation and oxidative radicals, linked to aging and degeneration. The EGFR is expressed in a wide variety of cells/tissues that pertain to the coordinated regulation of neurometabolic activity. EGFR signaling has been highlighted directly or indirectly in a spectrum of neurometabolic conditions, for example, metabolic syndrome, diabetes, Alzheimer's disease, cancer, and cardiorespiratory function. Understanding the positioning of the EGFR within the neurometabolic domain will enhance our appreciation of the ability of this receptor system to underpin highly complex physiological paradigms such as aging and neurodegeneration.

Multiple anti-apoptotic pathways stimulated by EGF in cytotrophoblasts

Epidermal growth factor (EGF) reduces apoptosis in primary cytotrophoblast (CT) in culture through two separate pathways: the extracellular signal related kinase (ERK) 1/2 and phosphatidyl inositol 3-kinase (PI-3 kinase) paths. Whether other pathways are involved in survival signalling is unknown. We here show that the c-Jun NH2 terminal kinase (JNK) and the mitogen activated kinase (MAPK) p38 are also activated by EGF as seen by increases in JNK and p38 phosphorylation. However, inhibition of JNK phosphorylation with the specific inhibitor SP600125 increases apoptosis in a manner refractory to the addition of EGF but inhibition of p38 phosphorylation with its specific inhibitor SB 203580 does not increase apoptosis. EGF also activates sphingosine kinase-1 (SPHK-1), which converts sphingosine to sphingosine-1-phosphate, and its inhibition with dimethyl sphingosine (DMS) increased trophoblast death. Inhibition of SPHK-1 also did not affect EGF stimulated phosphorylation of PI-3 kinase, Akt, ERK1/2 or p38 but inhibition of PI-3 kinase with a specific inhibitor LY294002 partly (40%) inhibited the EGF-stimulated increase in SPHK-1 activity. We conclude that, in addition to the PI-3 kinase and ERK1/2 pathways, EGF acts through its receptor to stimulate JNK, p38 and SPHK-1 pathways, but that the JNK and SPHK-1, and not the p38, pathways are involved in suppressing apoptosis. This information provides evidence that EGF stimulates survival along multiple pathways that differ in trophoblast and other cell types.

Activation of epidermal growth factor receptor signals induction of nitric oxide synthase-2 in human optic nerve head astrocytes in glaucomatous optic neuropathy

Glaucoma is an optic neuropathy that is associated with elevated intraocular pressure in most patients. We have previously demonstrated that the mechanism by which pressure damages optic nerve axons involves excessive nitric oxide generated by inducible nitric oxide synthase (NOS-2). We have now found that activation of the epidermal growth factor receptor (EGFR) induces NOS-2 in astrocytes of the human optic nerve head (ONH) in vitro and EGFR is significantly upregulated and tyrosine phosphorylated in reactive astrocytes in human glaucomatous ONHs in vivo. Furthermore, in response to elevated hydrostatic pressure, EGFR rapidly becomes phosphorylated in the nucleus. This pressure-dependent activation of EGFR is necessary for NOS-2 induction. Our results suggest that activation and nuclear localization of EGFR may be needed for induction of NOS-2 in response to elevated intraocular pressure in glaucomatous optic neuropathy. Identification of this key signaling pathway provides new therapeutic approaches to pharmacological neuroprotection for glaucoma.

Expression of Trk isoforms in brain regions and in the striatum of patients with Alzheimer's disease

The TrkAII tyrosine kinase receptor differs from the TrkAI isoform by an insertion of six amino acids in the extracellular domain. We used RT-PCR to determine their respective distribution in rat and human brain. Only trkAII transcripts were detected in 12 rat brain regions, while both trkAI and trkAII transcripts were detected in the cerebellum and pituitary gland. In human, both trkAI and trkAII transcripts were detected in the frontal, temporal, and occipital cortex and thalamus, while only trkAI transcripts were detected in the hippocampus and cerebellum. In the caudate and putamen, trkAII transcripts were exclusively detected. Thereafter, we studied the expression of TrkA isoforms in the striatum of five patients with Alzheimer's disease (AD), four patients with non-AD dementia, seven patients with Parkinson's disease, and six paired nondemented elderly control individuals. In controls and non-AD patients, a constant expression of trkAII transcripts was detected within all striatum parts. In AD patients, a heterogeneous decrease in trkAII expression was observed in the caudate, putamen, and ventral striatum, resulting either in a drop of trkAII transcript levels or in a weak coamplification of trkAII and trkAI transcripts. The alteration of TrkAII gene expression paralleled those of choline acetyltransferase. Together with previous data, this suggests that the alteration of trk gene expression could contribute to a decrease in NGF binding sites and its protective effects on cholinergic neurons of AD patients.

Recent advances in atypical parkinsonian disorders

Recent advances in epidemiologic, diagnostic, pathologic, and management aspects of atypical parkinsonian disorders are reviewed and placed in perspective. The implications of considering progressive supranuclear palsy and corticobasal degeneration as tauopathies, and multiple system atrophy and dementia with Lewy bodies as alpha-synucleopathies are discussed.