Neurogenic marker abnormalities in the hippocampus in dementia with Lewy bodies

Methods to study adult hippocampal neurogenesis in humans and across the phylogeny

The hippocampus hosts the continuous addition of new neurons throughout life-a phenomenon named adult hippocampal neurogenesis (AHN). Here we revisit the occurrence of AHN in more than 110 mammalian species, including humans, and discuss the further validation of these data by single-cell RNAseq and other alternative techniques. In this regard, our recent studies have addressed the long-standing controversy in the field, namely whether cells positive for AHN markers are present in the adult human dentate gyrus (DG). Here we review how we developed a tightly controlled methodology, based on the use of high-quality brain samples (characterized by short postmortem delays and ≤24 h of fixation in freshly prepared 4% paraformaldehyde), to address human AHN. We review that the detection of AHN markers in samples fixed for 24 h required mild antigen retrieval and chemical elimination of autofluorescence. However, these steps were not necessary for samples subjected to shorter fixation periods. Moreover, the detection of labile epitopes (such as Nestin) in the human hippocampus required the use of mild detergents. The application of this strictly controlled methodology allowed reconstruction of the entire AHN process, thus revealing the presence of neural stem cells, proliferative progenitors, neuroblasts, and immature neurons at distinct stages of differentiation in the human DG. The data reviewed here demonstrate that methodology is of utmost importance when studying AHN by means of distinct techniques across the phylogenetic scale. In this regard, we summarize the major findings made by our group that emphasize that overlooking fundamental technical principles might have consequences for any given research field.

Linking COVID-19 and Parkinson's disease: Targeting the role of Vitamin-D

COVID-19 pandemic has a major effect on world health, particularly on individuals suffering from severe diseases or old aged persons. Various case studies revealed that COVID-19 might increase the progression of Parkinson's disease (PD). Coxsackievirus, dengue virus Epstein-Barr virus, hepatitis C virus, Japanese encephalitis, Western equine encephalomyelitis virus, West Nile virus, and human immunodeficiency virus have all been linked to the development of transient or permanent parkinsonism, owing to the induction of neuroinflammation/hypoxic brain injury with structural/functional damage within the basal ganglia. Coronavirus mainly infects the alveolar cells and may lead to acute respiratory distress syndrome. SARS-CoV-2 invades cells via the ACE2 receptor, which is widely expressed in the central nervous system, where the virus may precipitate or accelerate dementia. SARS-CoV-2 could enter the central nervous system directly by the olfactory/vagus nerves or through the bloodstream. Here, we talked about the importance of this viral infection in terms of the CNS as well as its implications for people with Parkinson's disease; anosmia & olfaction-related impairments in COVID-19 & PD patients. And, also discussed the role of vitamin D to sustain the progression of Parkinson's disease and the COVID-19; regular vitamin D3 consumption of 2000-5000 IU/day may reduce the risk and severity of COVID-19 in parkinsonian patients.

Evidences for Adult Hippocampal Neurogenesis in Humans

The rodent hippocampus generates new neurons throughout life. This process, named adult hippocampal neurogenesis (AHN), is a striking form of neural plasticity that occurs in the brains of numerous mammalian species. Direct evidence of adult neurogenesis in humans has remained elusive, although the occurrence of this phenomenon in the human dentate gyrus has been demonstrated in seminal studies and recent research that have applied distinct approaches to birthdate newly generated neurons and to validate markers of adult-born neurons. Our data point to the persistence of AHN until the 10th decade of human life, as well as to marked impairments in this process in patients with Alzheimer's disease. Moreover, our work demonstrates that the methods used to process and analyze postmortem human brain samples can limit the detection of various markers of AHN to the point of making them undetectable. In this Dual Perspectives article, we highlight the critical methodological aspects that should be strictly controlled in human studies and the robust evidence that supports the occurrence of AHN in humans. We also put forward reasons that may account for current discrepancies on this topic. Finally, the unresolved questions and future challenges awaiting the field are highlighted.

Use of Ceftriaxone in Treating Cognitive and Neuronal Deficits Associated With Dementia With Lewy Bodies

Dementia with Lewy bodies (DLB) is caused by accumulation of Lewy bodies, destruction of mitochondria, and excess of glutamate in synapses, which eventually leads to excitotoxicity, neurodegeneration, and cognitive impairments. Ceftriaxone (CEF) reduces excitotoxicity by increasing glutamate transporter 1 expression and glutamate reuptake. We investigated whether CEF can prevent cognitive decline and neurological deficits and increase neurogenesis in DLB rats. Male Wistar rats infused with viral vector containing human alpha-synuclein (α-syn) gene, SNCA, in the lateral ventricle were used as a rat model of DLB. CEF (100 mg/kg/day, i.p.) was injected in these rats for 27 days. The active avoidance test and object recognition test was performed. Finally, the brains of all the rats were immunohistochemically stained to measure α-syn, neuronal density, and newborn cells in the hippocampus and substantia nigra. The results revealed that DLB rats had learning and object recognition impairments and exhibited cell loss in the nigrostriatal dopaminergic system, and hippocampal CA1, and dentate gyrus (DG). Additionally, DLB rats had fewer newborn cells in the DG and substantia nigra pars reticulata and more α-syn immune-positive cells in the DG. Treatment with CEF improved cognitive function, reduced cell loss, and increased the number of newborn cells in the brain. To our knowledge, this is the first study showing that CEF prevents loss of neurogenesis in the brain of DLB rats. CEF may therefore has clinical potential for treating DLB.

[Neurogenesis in the adult human brain: morphological aspects]

The high prevalence of diseases leading to brain injury disability makes it extremely relevant to study the various mechanisms of neurorehabilitation, among which neurogenesis has recently received a great attention. Over the past 20 years, there has been ample evidence for neurogenesis in the adult animal brain. Despite the fact that the prenatal development of the human brain has been thoroughly studied, the number of works on the process by which new neurons form in the adult human brain is not so large. This review devoted to the investigations of neurogenesis in the adult human brain includes data on changes in neurogenesis with age in neurodegenerative diseases, strokes, epilepsy, various addictions, traumatic injuries, and natural and drug regulation. The conclusion lists the issues on which there is an agreement or conflicting views in the literature and indicates the unanswered aspects of the problem.

Importance of Proactive Treatment of Depression in Lewy Body Dementias: The Impact on Hippocampal Neurogenesis and Cognition in a Post-Mortem Study

OBJECTIVE

To examine the impact of selective serotonin reuptake inhibitors (SSRIs) and depression on neurogenesis and cognition in dementia with Lewy bodies (DLB) and Parkinson disease dementia (PDD).

METHODS

Late-stage progenitor cells were quantified in the subgranular zone (SGZ) of the hippocampal dentate gyrus of DLB/PDD patients (n = 41) and controls without dementia (n = 15) and compared between treatment groups (unmedicated, SSRIs, acetyl cholinesterase inhibitors [AChEIs], combined SSRIs and AChEIs).

RESULTS

DLB/PDD patients had more doublecortin-positive cells in the SGZ compared to controls. The doublecortin-positive cell count was higher in the SGZ of patients treated with SSRIs and correlated to higher cognitive scores.

CONCLUSION

SSRI treatment was associated with increased hippocampal neurogenesis and preservation of cognition in DLB/PDD patients.

Synucleinopathies: common features and hippocampal manifestations

Parkinson's disease (PD), dementia with Lewy Bodies (DLB), and multiple system atrophy (MSA) are three major synucleinopathies characterized by α-synuclein-containing inclusions in the brains of patients. Because the cell types and brain structures that are affected vary markedly between the disorders, the patients have different clinical manifestations in addition to some overlapping symptoms, which are the basis for differential diagnosis. Cognitive impairment and depression associated with hippocampal dysfunction are frequently observed in these disorders. While various α-synuclein-containing inclusions are found in the hippocampal formation, increasing evidence supports that small α-synuclein aggregates or oligomers may be the real culprit, causing deficits in neurotransmission and neurogenesis in the hippocampus and related brain regions, which constitute the major mechanism for the hippocampal dysfunctions and associated neuropsychiatric manifestations in synucleinopathies.

Neuropeptide Treatment with Cerebrolysin Enhances the Survival of Grafted Neural Stem Cell in an α-Synuclein Transgenic Model of Parkinson's Disease

Neuronal stem cell (NSC) grafts have been investigated as a potential neuro-restorative therapy in Parkinson’s disease (PD) but their use is compromised by the death of grafted cells. We investigated the use of Cerebrolysin (CBL), a neurotrophic peptide mixture, as an adjunct to NSC therapy in the α-synuclein (α-syn) transgenic (tg) model of PD. In vehicle-treated α-syn tg mice, there was decreased survival of NSCs. In contrast, CBL treatment enhanced the survival of NSCs in α-syn tg groups and ameliorated behavioral deficits. The grafted NSCs showed lower levels of terminal deoxynucleotidyl transferase dUTP nick end labeling positive cells in the CBL-treated mice when compared with vehicle-treated α-syn tg mice. No evidence of tumor growth was detected. Levels of α-syn were similar in the vehicle in CBL-treated tg mice. In conclusion, CBL treatment might be a potential adjuvant for therapeutic NSC grafting in PD.

Alterations of neuronal precursor cells in stages of human adult neurogenesis in heroin addicts

BACKGROUND

Adult neurogenesis has been shown to occur throughout life and different brain pathologies were demonstrated to be associated with altered neurogenesis. Here, an impact of heroin addiction on neurogenesis in humans is hypothesised.

METHODS

Post mortem hippocampal specimens of drug addicts with known heroin abuse and a group of non-addictive control subjects were analysed, using antibodies indicating different stages of neurogenesis. The subgranular zone of the dentate gyrus was examined qualitatively and quantitatively.

RESULTS

The data indicate (i) a decreased number of neural precursor cells, (ii) accompanied by low rates of proliferation and (iii) a marked loss of dendritic trees in targeting cells in heroin fatalities. (iv) The age-dependent increase of differentiating cells in the healthy controls was not observed in the addicts. Additionally, double immunofluorescence labelling indicated the precursor nature of Musashi-1 positive cells in the human subgranular zone of the dentate gyrus.

CONCLUSIONS

Present data firstly demonstrate the influence of drug addiction with known heroin abuse on different developmental stages of progenitors in the dentate gyrus. The patterns of antibody staining suggest a distinct inhibition of neurogenesis at the stage of neural precursor cells and revealed morphological changes in targeting cells in cases of heroin addicts as compared to healthy controls. These alterations could be considerable for memory and cognitive deficits as well as addictive behaviour in chronic drug abusers and may give rise to specific pro-neurogenic therapies.

Severely impaired hippocampal neurogenesis associates with an early serotonergic deficit in a BAC α-synuclein transgenic rat model of Parkinson's disease

Parkinson's disease (PD) is a multisystem disorder, involving several monoaminergic neurotransmitter systems resulting in a broad range of motor and non-motor symptoms. Pathological hallmarks of PD are the loss of dopaminergic neurons and the accumulation of alpha-synuclein, however also being present in the serotonergic raphe nuclei early in the disease course. The dysfunction of the serotonergic system projecting to the hippocampus may contribute to early non-motor symptoms such as anxiety and depression. The adult hippocampal dentate gyrus (DG), a unique niche of the forebrain continuously generating new neurons, may particularly present enhanced susceptibility towards accumulating alpha-synuclein levels. The underlying molecular mechanisms in the context of neuronal maturation and survival of new-born neurons are yet not well understood. To characterize the effects of overexpression of human full-length alpha-synuclein on hippocampal cellular and synaptic plasticity, we used a recently generated BAC alpha-synuclein transgenic rat model showing important features of PD such as widespread and progressive alpha-synuclein aggregation pathology, dopamine loss and age-dependent motor decline. At the age of four months, thus prior to the occurrence of the motor phenotype, we observed a profoundly impaired dendritogenesis of neuroblasts in the hippocampal DG resulting in severely reduced survival of adult new-born neurons. Diminished neurogenesis concurred with a serotonergic deficit in the hippocampus as defined by reduced levels of serotonin (5-HT) 1B receptor, decreased 5-HT neurotransmitter levels, and a loss of serotonergic nerve terminals innervating the DG/CA3 subfield, while the number of serotonergic neurons in the raphe nuclei remained unchanged. Moreover, alpha-synuclein overexpression reduced proteins involved in vesicle release, in particular synapsin-1 and Rab3 interacting molecule (RIM3), in conjunction with an altered ultrastructural architecture of hippocampal synapses. Importantly, BAC alpha-synuclein rats showed an early anxiety-like phenotype consisting of reduced exploratory behavior and feeding. Taken together, these findings imply that accumulating alpha-synuclein severely affects hippocampal neurogenesis paralleled by impaired 5-HT neurotransmission prior to the onset of aggregation pathology and overt motor deficits in this transgenic rat model of PD.

Stage-specific changes in neurogenic and glial markers in Alzheimer's disease

BACKGROUND

Reports of altered endogenous neurogenesis in people with Alzheimer's disease (AD) and transgenic AD models have suggested that endogenous neurogenesis may be an important treatment target, but there is considerable discrepancy among studies. We examined endogenous neurogenesis and glia changes across the range of pathologic severity of AD in people with and without dementia to address this key question.

METHODS

Endogenous neurogenesis and glia in the subventricular zone and dentate gyrus neurogenic niches were evaluated using single and double immunohistochemistry and a validated antibody selection for stage-specific and type-specific markers in autopsy tissue from a representative cohort of 28 participants in the Medical Research Council Cognitive Function and Ageing Study. Immunopositive cells were measured blinded to diagnosis using bright-field and fluorescent microscopy.

RESULTS

The number of newly generated neurons significantly declined only in the dentate gyrus of patients with severe tau pathology. No other changes in other neurogenic markers were observed in either of the neurogenic niches. Alterations in astrocytes and microglia were also observed in the dentate gyrus across the different stages of tau pathology. No change in any of the markers was observed in individuals who died with dementia compared with individuals who did not die with dementia.

CONCLUSIONS

Alterations in endogenous neurogenesis appeared to be confined to a reduction in the generation of new neurons in the dentate gyrus of patients with AD and severe neurofibrillary tangle pathology and were accompanied by changes in the glia load. These data suggest that intervention enhancing endogenous neurogenesis may be a potential therapeutic target in AD.

Proliferation in the Alzheimer hippocampus is due to microglia, not astroglia, and occurs at sites of amyloid deposition

Microglia and astrocytes contribute to Alzheimer's disease (AD) etiology and may mediate early neuroinflammatory responses. Despite their possible role in disease progression and despite the fact that they can respond to amyloid deposition in model systems, little is known about whether astro- or microglia can undergo proliferation in AD and whether this is related to the clinical symptoms or to local neuropathological changes. Previously, proliferation was found to be increased in glia-rich regions of the presenile hippocampus. Since their phenotype was unknown, we here used two novel triple-immunohistochemical protocols to study proliferation in astro- or microglia in relation to amyloid pathology. We selected different age-matched cohorts to study whether proliferative changes relate to clinical severity or to neuropathological changes. Proliferating cells were found across the hippocampus but never in mature neurons or astrocytes. Almost all proliferating cells were colabeled with Iba1+, indicating that particularly microglia contribute to proliferation in AD. Proliferating Iba1+ cells was specifically seen within the borders of amyloid plaques, indicative of an active involvement in, or response to, plaque accumulation. Thus, consistent with animal studies, proliferation in the AD hippocampus is due to microglia, occurs in close proximity of plaque pathology, and may contribute to the neuroinflammation common in AD.

Allosteric inhibition of a stem cell RNA-binding protein by an intermediary metabolite

Gene expression and metabolism are coupled at numerous levels. Cells must sense and respond to nutrients in their environment, and specialized cells must synthesize metabolic products required for their function. Pluripotent stem cells have the ability to differentiate into a wide variety of specialized cells. How metabolic state contributes to stem cell differentiation is not understood. In this study, we show that RNA-binding by the stem cell translation regulator Musashi-1 (MSI1) is allosterically inhibited by 18-22 carbon ω-9 monounsaturated fatty acids. The fatty acid binds to the N-terminal RNA Recognition Motif (RRM) and induces a conformational change that prevents RNA association. Musashi proteins are critical for development of the brain, blood, and epithelium. We identify stearoyl-CoA desaturase-1 as a MSI1 target, revealing a feedback loop between ω-9 fatty acid biosynthesis and MSI1 activity. We propose that other RRM proteins could act as metabolite sensors to couple gene expression changes to physiological state.

Role of α-synuclein in adult neurogenesis and neuronal maturation in the dentate gyrus

α-Synuclein has been reported to be important in modulating brain plasticity and to be a key protein in neurodegenerative diseases, including Lewy body dementia (LBD). We investigated how α-synuclein levels modulate adult neurogenesis and the development of dendritic arborization and spines in the dentate gyrus, in which new neurons are constantly added. In the human hippocampus, levels of endogenous α-synuclein were increased in LBD, and the numbers of SOX2-positive cells were decreased. We investigated whether newly generated neurons were modulated by endogenous α-synuclein, and we found increased adult neurogenesis in α/β-synuclein knock-out mice. In contrast, overexpression of human wild-type α-synuclein (WTS) decreased the survival and dendritic development of newborn neurons. Endogenous α-synuclein expression levels increased the negative impact of WTS on dendrite development, suggesting a toxic effect of increasing amounts of α-synuclein. To attempt a rescue of the dendritic phenotype, we administered rolipram to activate the cAMP response element-binding protein pathway, which led to a partial rescue of neurite development. The current work provides novel insights into the role of α-synuclein in adult hippocampal neurogenesis.

Neurogenic abnormalities in Alzheimer's disease differ between stages of neurogenesis and are partly related to cholinergic pathology

Neurogenesis occurs in the subventricular zone and the sub-granular layer of the hippocampus and is thought to take place in 5 stages, including proliferation, differentiation, migration, targeting, and integration phases, respectively. In Alzheimer's disease (AD) both increased and decreased neurogenesis has been reported and cholinergic activity is assumed to be involved in neurogenesis. The aim of this study was to systematically assess different phases of neurogenesis and their relation to AD and cholinergic pathology. We investigated post-mortem brain tissue from 20 AD patients and 21 non-demented controls that was neuropathologically characterized according to standardized criteria. Hippocampal sections were stained with antibodies against neurogenic markers Musashi-1, nestin, PSA-NCAM, doublecortin, and β-III-tubulin as well as ChAT (choline-acetyltransferase). Using image analysis immunoreactivity was assessed in the subventricular zone, the sub-granular layer, and the granule cell layer by determining the integrated optical density. In the sub-granular layer and the granule cell layer Musashi-1 and ChAT immunoreactivities were significantly lower in AD and decreased with increasing Braak stages. Conversely, immunorreactivities of both nestin and PSA-NCAM were significantly higher in AD and increased with increasing Braak stages while no changes were seen for doublecortin and β-III-tubulin, except for significantly higher doublecortin levels in the granule cell layer of AD cases. Of note, Musashi-1 immunoreactivity significantly correlated with ChAT immuonoreactivity across different Braak stages. In the subventricular zone only nestin immunoreactivity was significantly higher in AD and significantly increased with increasing Braak stages, while no significant differences were seen for all other markers. Our finding of a reduction of ChAT and Musashi-1 levels in AD is compatible with the assumption that cholinergic pathology per se has a detrimental influence on neurogenesis. We conclude that neurogenic abnormalities in AD differ between phases and areas of neurogenesis and stages of AD; while hippocampal stem cells (Musashi-1) decrease, proliferation (nestin) increases and differentiation/migration phase as well as axonal/dendritic targeting (doublecortin and β-III-tubulin) remains virtually unchanged. This suggests an attenuation of stem cells together with compensatory increased proliferation that, however, does not result in an increased number of migratory neuroblasts and differentiated neurons in AD.