Dysregulation of brain olfactory and taste receptors in AD, PSP and CJD, and AD-related model

Taste identification used as a potential discriminative test among depression and Alzheimer׳s disease in elderly: A pilot study

Major Depression and Alzheimer׳s disease (AD) are two diseases in the elderly characterized by an overlap of early symptoms including memory and emotional disorders. The identification of specific markers would facilitate their diagnosis. The aim of this study was to identify such markers by investigating gustatory function in depressed and AD patients. We included 20 patients with unipolar major depressive episodes (MDE), 20 patients with mild to moderate AD and 24 healthy individuals. We investigated the cognitive profile (depression, global cognitive efficiency and social/physical anhedonia) and gustatory function (ability to identify four basic tastes and to judge their intensity and hedonic value) in all participants. We found that AD patients performed worse than healthy participants in the taste identification test (for the analysis of all tastants together); however, this was not the case for depressed patients. We found no significant differences among the three groups in their ability to evaluate the intensity and hedonic value of the four tastes. Overall, our findings suggest that a taste identification test may be useful to distinguish AD and healthy controls but further investigation is required to conclude whether such a test can differentiate AD and depressed patients.

Decrease in olfactory and taste receptor expression in the dorsolateral prefrontal cortex in chronic schizophrenia

We have recently identified up- or down-regulation of the olfactory (OR) and taste (TASR) chemoreceptors in the human cortex in several neurodegenerative diseases, raising the possibility of a general deregulation of these genes in neuropsychiatric disorders. In this study, we explore the possible deregulation of OR and TASR gene expression in the dorsolateral prefrontal cortex in schizophrenia. We used quantitative polymerase chain reaction on extracts from postmortem dorsolateral prefrontal cortex of subjects with chronic schizophrenia (n = 15) compared to control individuals (n = 14). Negative symptoms were evaluated premortem by the Positive and Negative Syndrome and the Clinical Global Impression Schizophrenia Scales. We report that ORs and TASRs are deregulated in the dorsolateral prefrontal cortex in schizophrenia. Seven out of eleven ORs and four out of six TASRs were down-regulated in schizophrenia, the most prominent changes of which were found in genes from the 11p15.4 locus. The expression did not associate with negative symptom clinical scores or the duration of the illness. However, most ORs and all TASRs inversely associated with the daily chlorpromazine dose. This study identifies for the first time a decrease in brain ORs and TASRs in schizophrenia, a neuropsychiatric disease not linked to abnormal protein aggregates, suggesting that the deregulation of these receptors is associated with altered cognition of these disorders. In addition, the influence of antipsychotics on the expression of ORs and TASRs in schizophrenia suggests that these receptors could be involved in the mechanism of action or side effects of antipsychotics.

Mesencephalic dopaminergic neurons express a repertoire of olfactory receptors and respond to odorant-like molecules

Background

The mesencephalic dopaminergic (mDA) cell system is composed of two major groups of projecting cells in the Substantia Nigra (SN) (A9 neurons) and the Ventral Tegmental Area (VTA) (A10 cells). Selective degeneration of A9 neurons occurs in Parkinson’s disease (PD) while abnormal function of A10 cells has been linked to schizophrenia, attention deficit and addiction. The molecular basis that underlies selective vulnerability of A9 and A10 neurons is presently unknown.

Results

By taking advantage of transgenic labeling, laser capture microdissection coupled to nano Cap-Analysis of Gene Expression (nanoCAGE) technology on isolated A9 and A10 cells, we found that a subset of Olfactory Receptors (OR)s is expressed in mDA neurons. Gene expression analysis was integrated with the FANTOM5 Helicos CAGE sequencing datasets, showing the presence of these ORs in selected tissues and brain areas outside of the olfactory epithelium. OR expression in the mesencephalon was validated by RT-PCR and in situ hybridization. By screening 16 potential ligands on 5 mDA ORs recombinantly expressed in an heterologous in vitro system, we identified carvone enantiomers as agonists at Olfr287 and able to evoke an intracellular Ca²⁺ increase in solitary mDA neurons. ORs were found expressed in human SN and down-regulated in PD post mortem brains.

Conclusions

Our study indicates that mDA neurons express ORs and respond to odor-like molecules providing new opportunities for pharmacological intervention in disease.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-729) contains supplementary material, which is available to authorized users.

Computational genetics analysis of grey matter density in Alzheimer's disease

Background

Alzheimer’s disease is the most common form of progressive dementia and there is currently no known cure. The cause of onset is not fully understood but genetic factors are expected to play a significant role. We present here a bioinformatics approach to the genetic analysis of grey matter density as an endophenotype for late onset Alzheimer’s disease. Our approach combines machine learning analysis of gene-gene interactions with large-scale functional genomics data for assessing biological relationships.

Results

We found a statistically significant synergistic interaction among two SNPs located in the intergenic region of an olfactory gene cluster. This model did not replicate in an independent dataset. However, genes in this region have high-confidence biological relationships and are consistent with previous findings implicating sensory processes in Alzheimer’s disease.

Conclusions

Previous genetic studies of Alzheimer’s disease have revealed only a small portion of the overall variability due to DNA sequence differences. Some of this missing heritability is likely due to complex gene-gene and gene-environment interactions. We have introduced here a novel bioinformatics analysis pipeline that embraces the complexity of the genetic architecture of Alzheimer’s disease while at the same time harnessing the power of functional genomics. These findings represent novel hypotheses about the genetic basis of this complex disease and provide open-access methods that others can use in their own studies.

Subtype and regional-specific neuroinflammation in sporadic creutzfeldt-jakob disease

The present study identifies deregulated cytokines and mediators of the immune response in the frontal cortex and cerebellum of sporadic Creutzfeldt-Jakob disease (sCJD) MM1 and VV2 subtypes compared to age-matched controls. Deregulated genes include pro- and anti-inflammatory cytokines, toll-like receptors, colony stimulating factors, cathepsins, members of the complement system, and members of the integrin and CTL/CTLD family with particular regional and sCJD subtype patterns. Analysis of cytokines and mediators at protein level shows expression of selected molecules and receptors in neurons, in astrocytes, and/or in microglia, thus suggesting interactions between neurons and glial cells, mainly microglia, in the neuroinflammatory response in sCJD. Similar inflammatory responses have been shown in the tg340 sCJD MM1 mice, revealing a progressive deregulation of inflammatory mediators with disease progression. Yet, inflammatory molecules involved are subjected to species differences in humans and mice. Moreover, inflammatory-related cell signaling pathways NFκB/IKK and JAK/STAT are activated in sCJD and sCJD MM1 mice. Together, the present observations show a self-sustained complex inflammatory and inflammatory-related responses occurring already at early clinical stages in animal model and dramatically progressing at advanced stages of sCJD. Considering this scenario, measures tailored to modulate (activate or inhibit) specific molecules could be therapeutic options in CJD.

Olfactory bulb involvement in neurodegenerative diseases

Olfactory dysfunction is a common and early symptom of many neurodegenerative diseases, particularly of Parkinson's disease and other synucleinopathies, Alzheimer's disease (AD), and mild cognitive impairment heralding its progression to dementia. The neuropathologic changes of olfactory dysfunction in neurodegenerative diseases may involve the olfactory epithelium, olfactory bulb/tract, primary olfactory cortices, and their secondary targets. Olfactory dysfunction is related to deposition of pathological proteins, α-synuclein, hyperphosphorylated tau protein, and neurofilament protein in these areas, featured by neurofibrillary tangles, Lewy bodies and neurites inducing a complex cascade of molecular processes including oxidative damage, neuroinflammation, and cytosolic disruption of cellular processes leading to cell death. Damage to cholinergic, serotonergic, and noradrenergic systems is likely involved, since such damage is most marked in those diseases with severe anosmia. Recent studies of olfactory dysfunction have focused its potential as an early biomarker for the diagnosis of neurodegenerative disorders and their disease progression. Here, we summarize the current knowledge on neuropathological and pathophysiological changes of the olfactory system in the most frequent neurodegenerative diseases, in particular AD and synucleinopathies. We also present neuropathological findings in the olfactory bulb and tract in a large autopsy cohort (n = 536, 57.8 % female, mean age 81.3 years). The severity of olfactory bulb HPτ, Aβ, and αSyn pathology correlated and increased significantly (P < 0.001) with increasing neuritic Braak stages, Thal Aβ phases, and cerebral Lewy body pathology, respectively. Hence, further studies are warranted to investigate the potential role of olfactory biopsies (possibly restricted to the olfactory epithelium) in the diagnostic process of neurodegenerative diseases in particular in clinical drug trials to identify subjects showing early, preclinical stages of neurodegeneration and to stratify clinically impaired cohorts according to the underlying cerebral neuropathology.

NanoCAGE analysis of the mouse olfactory epithelium identifies the expression of vomeronasal receptors and of proximal LINE elements

By coupling laser capture microdissection to nanoCAGE technology and next-generation sequencing we have identified the genome-wide collection of active promoters in the mouse Main Olfactory Epithelium (MOE). Transcription start sites (TSSs) for the large majority of Olfactory Receptors (ORs) have been previously mapped increasing our understanding of their promoter architecture. Here we show that in our nanoCAGE libraries of the mouse MOE we detect a large number of tags mapped in loci hosting Type-1 and Type-2 Vomeronasal Receptors genes (V1Rs and V2Rs). These loci also show a massive expression of Long Interspersed Nuclear Elements (LINEs). We have validated the expression of selected receptors detected by nanoCAGE with in situ hybridization, RT-PCR and qRT-PCR. This work extends the repertory of receptors capable of sensing chemical signals in the MOE, suggesting intriguing interplays between MOE and VNO for pheromone processing and positioning transcribed LINEs as candidate regulatory RNAs for VRs expression.