Involvement of notch signaling pathway in amyloid precursor protein induced glial differentiation

Amyloid Precursor Protein (APP) Regulates Gliogenesis and Neurogenesis of Human Neural Stem Cells by Several Signaling Pathways

Numerous studies have focused on the pathophysiological role of amyloid precursor protein (APP) because the proteolytic processing of APP to β-amyloid (Aβ) peptide is a central event in Alzheimer's disease (AD). However, many authors consider that alterations in the physiological functions of APP are likely to play a key role in AD. Previous studies in our laboratory revealed that APP plays an important role in the differentiation of human neural stem cells (hNSCs), favoring glial differentiation (gliogenesis) and preventing their differentiation toward a neuronal phenotype (neurogenesis). In the present study, we have evaluated the effects of APP overexpression in hNSCs at a global gene level by a transcriptomic analysis using the massive RNA sequencing (RNA-seq) technology. Specifically, we have focused on differentially expressed genes that are related to neuronal and glial differentiation processes, as well as on groups of differentially expressed genes associated with different signaling pathways, in order to find a possible interaction between them and APP. Our data indicate a differential expression in genes related to Notch, Wnt, PI3K-AKT, and JAK-STAT signaling, among others. Knowledge of APP biological functions, as well as the possible signaling pathways that could be related to this protein, are essential to advance our understanding of AD.

Heat Shock Alters the Proteomic Profile of Equine Mesenchymal Stem Cells

The aim of this research was to determine the impact of heat stress on cell differentiation in an equine mesenchymal stem cell model (EMSC) through the application of heat stress to primary EMSCs as they progressed through the cell specialization process. A proteomic analysis was performed using mass spectrometry to compare relative protein abundances among the proteomes of three cell types: progenitor EMSCs and differentiated osteoblasts and adipocytes, maintained at 37 °C and 42 °C during the process of cell differentiation. A cell-type and temperature-specific response to heat stress was observed, and many of the specific differentially expressed proteins were involved in cell-signaling pathways such as Notch and Wnt signaling, which are known to regulate cellular development. Furthermore, cytoskeletal proteins profilin, DSTN, SPECC1, and DAAM2 showed increased protein levels in osteoblasts differentiated at 42 °C as compared with 37 °C, and these cells, while they appeared to accumulate calcium, did not organize into a whorl agglomerate as is typically seen at physiological temperatures. This altered proteome composition observed suggests that heat stress could have long-term impacts on cellular development. We propose that this in vitro stem cell culture model of cell differentiation is useful for investigating molecular mechanisms that impact cell development in response to stressors.

BACE1 Overexpression Reduces SH-SY5Y Cell Viability Through a Mechanism Distinct from Amyloid-β Peptide Accumulation: Beta Prime-Mediated Competitive Depletion of sAβPPα

BACKGROUND

The Alzheimer's disease (AD)-associated amyloid-beta protein precursor (AβPP) can be cleaved by β-site AβPP cleaving enzyme 1 (BACE1) and the γ-secretase complex to yield neurotoxic amyloid-β (Aβ) peptides. However, AβPP can also be cleaved in a 'non-amyloidogenic' manner either by α-secretase to produce soluble AβPP alpha (sAβPPα) (a fragment with neuroprotective/neurogenic functions) or through alternative BACE1-mediated 'beta prime' activity yielding soluble AβPP beta prime (sAβPPβ').

OBJECTIVE

To determine whether sAβPPα depletion, as opposed to Aβ peptide accumulation, contributes to cytotoxicity in AD-relevant SH-SY5Y neuroblastoma cell models.

METHODS

AβPP proteolysis was characterized by immunoblotting in mock-, wild-type AβPP (wtAβPP)-, BACE1-, and Swedish mutant AβPP (SweAβPP)-transfected cells. AβPP beta prime cleavage was confirmed through secretase inhibitor studies and C-terminal fragment analysis. The roles of sAβPPα and sAβPPβ' in cell viability were confirmed by overexpression studies.

RESULTS

Despite producing enhanced Aβ peptide levels, wtAβPP- and SweAβPP-transfected cells did not exhibit reduced viability whereas BACE1-transfected cells did. sAβPPα generation in SH-SY5Y-BACE1 cells was virtually ablated in lieu of BACE1-mediated sAβPPβ' production. sAβPPα overexpression in SH-SY5Y-BACE1 cells restored viability whereas sAβPPβ' overexpression decreased viability further. The anti-AβPP 6E10 antibody was shown to cross-react with sAβPPβ'.

CONCLUSION

sAβPPα depletion and/or sAβPPβ' accumulation, but not elevated Aβ peptide levels, represent the cytotoxic mechanism following BACE1 overexpression in SH-SY5Y cells. These data support the novel concept that competitive sAβPPα depletion by BACE1 beta prime activity might contribute to AD. The cross-reactivity of 6E10 with AβPPβ'also questions whether previous studies assessing sAβPPα as a biomarker using this antibody should be revisited.

The interplay of aryl hydrocarbon receptor/WNT/CTNNB1/Notch signaling pathways regulate amyloid beta precursor mRNA/protein expression and effected the learning and memory of mice

The amyloid beta precursor protein (APP) plays a pathophysiological role in the development of Alzheimer's disease as well as a physiological role in neuronal growth and synaptogenesis. The aryl hydrocarbon receptor (AhR)/WNT/Catenin Beta 1 (CTNNB1)/Notch signaling pathways stamp in many functions, including development and growth of neurons. However, the regulatory role of AhR-/WNT-/CTNNB1-/Notch-induced APP expression and its influence on hippocampal-dependent learning and memory deficits is not clear. Male BALB/C mice received 6-formylindolo[3,2-b]carbazole (an AhR agonist), CH223191(an AhR antagonist), DAPT (an inhibitor of Notch signaling), and XAV-939 (a WNT pathway inhibitor) at a single dose of 100 μg/kg, 1, 5 , and 5 mg/kg of body weight, respectively, via intraperitoneal injection alone or in combination. Gene expression analyses and protein assay were performed on the 7th and 29th days. To assess the hippocampal-dependent memory, all six mice also underwent contextual fear conditioning on the 28th day after treatments. Our results showed that endogenous ligand of AhR has a regulatory effect on APP gene. Also, the interaction of AhR/WNT/CTNNB1 has a positive regulatory effect, but Notch has a negative regulatory effect on the mRNA and protein expression of APP, which have a correlation with mice's learning skills and memory.

Deciphering the neuroprotective and neurogenic potential of soluble amyloid precursor protein alpha (sAPPα)

Amyloid precursor protein (APP) is a transmembrane protein expressed largely within the central nervous system. Upon cleavage, it does not produce the toxic amyloid peptide (Aβ) only, which is involved in neurodegenerative progressions but via a non-amyloidogenic pathway it is metabolized to produce a soluble fragment (sAPPα) through α-secretase. While a lot of studies are focusing on the role played by APP in the pathogenesis of Alzheimer's disease, sAPPα is reported to have numerous neuroprotective effects and it is being suggested as a candidate with possible therapeutic potential against Alzheimer's disease. However, the mechanisms through which sAPPα precisely works remain elusive. We have presented a comprehensive review of how sAPPα is regulating the neuroprotective effects in different biological models. Moreover, we have focused on the role of sAPPα during different developmental stages of the brain, neurogenic microenvironment in the brain and how this metabolite of APP is regulating the neurogenesis which is regarded as a compelling approach to ameliorate the impaired learning and memory deficits in dementia and diseases like Alzheimer's disease. sAPPα exerts beneficial physiological, biochemical and behavioral effects mitigating the detrimental effects of neurotoxic compounds. It has shown to increase the proliferation rate of numerous cell types and promised the synaptogenesis, neurite outgrowth, cell survival and cell adhesion. Taken together, we believe that further studies are warranted to investigate the exact mechanism of action so that sAPPα could be developed as a novel therapeutic target against neuronal deficits.

A systematic simulation-based meta-analytical framework for prediction of physiological biomarkers in alopecia

Background

Alopecia or hair loss is a complex polygenetic and psychologically devastating disease affecting millions of men and women globally. Since the gene annotation and environmental knowledge is limited for alopecia, a systematic analysis for the identification of candidate biomarkers is required that could provide potential therapeutic targets for hair loss therapy.

Results

We designed an interactive framework to perform a meta-analytical study based on differential expression analysis, systems biology, and functional proteomic investigations. We analyzed eight publicly available microarray datasets and found 12 potential candidate biomarkers including three extracellular proteins from the list of differentially expressed genes with a p-value < 0.05. After expression profiling and functional analysis, we studied protein–protein interactions and observed functional associations of source proteins including WIF1, SPON1, LYZ, GPRC5B, PTPRE, ZFP36L2, HBB, PHF15, LMCD1, KRT35 and VAV3 with target proteins including APCDD1, WNT1, WNT3A, SHH, ESRI, TGFB1, and APP. Pathway analysis of these molecules revealed their role in major physiological reactions including protein metabolism, signal transduction, WNT, BMP, EDA, NOTCH and SHH pathways. These pathways regulate hair growth, hair follicle differentiation, pigmentation, and morphogenesis. We studied the regulatory role of β-catenin, Nf-kappa B, cytokines and retinoic acid in the development of hair growth. Therefore, the differential expression of these significant proteins would affect the normal level and could cause aberrations in hair growth.

Conclusion

Our integrative approach helps to prioritize the biomarkers that ultimately lessen the economic burden of experimental studies. It will also be valuable to discover mutants in genomic data in order to increase the identification of new biomarkers for similar problems.

Electronic supplementary material

The online version of this article (10.1186/s40709-019-0094-x) contains supplementary material, which is available to authorized users.

miR-9 stimulation enhances the differentiation of neural stem cells with zoanthamine by regulating Notch signaling

The protective effect of zoanthamine on Alzheimer's disease by enhancing differentiation of neural stem cells (NSCs) was evaluated. NSCs were isolated from C57BL/6 mice and assessed by cell viability and apoptosis assays. The cells were separated into five different groups: green fluorescent protein (GFP; transfected with GFP), amyloid precursor protein (APP; transfected with APP), APP + zoanthamine, APP + miR-9 inhibitor, and APP + miR-9 inhibitor + zoanthamine. The effects of zoanthamine on the differentiation of NSCs was determined. Moreover, the effects of zoanthamine on the expression of miR-9 and Notch signalling pathway members was assessed by western blot analysis and reverse-transcription polymerase chain reaction. There was a significant increase in cell viability and a decrease in apoptosis of NSCs in the APP + zoanthamine group compared with the APP group. Treatment with zoanthamine attenuated miR-9 expression and neuronal cell differentiation in APP-treated NSCs. Moreover, in the APP + miR-9 inhibitor group, neuronal cell differentiation and miR-9 expression were significantly reduced, and treatment with zoanthamine reduced the number of differentiated cells and miR-9 expression compared with the APP + miR-9 inhibitor group. There was a significant reduction in the expression of Hes1 and NICD proteins in the APP + zoanthamine group relative to the APP group. In addition, the levels of Hes1 and NICD were enhanced by inhibition of miR-9 but zoanthamine prevented these increases. In conclusion, these results suggest that treatment with zoanthamine enhances the differentiation of NSCs by regulating Notch signalling via elevated miR-9 expression.

Physiological effects of amyloid precursor protein and its derivatives on neural stem cell biology and signaling pathways involved

The pathological implication of amyloid precursor protein (APP) in Alzheimer's disease has been widely documented due to its involvement in the generation of amyloid-β peptide. However, the physiological functions of APP are still poorly understood. APP is considered a multimodal protein due to its role in a wide variety of processes, both in the embryo and in the adult brain. Specifically, APP seems to play a key role in the proliferation, differentiation and maturation of neural stem cells. In addition, APP can be processed through two canonical processing pathways, generating different functionally active fragments: soluble APP-α, soluble APP-β, amyloid-β peptide and the APP intracellular C-terminal domain. These fragments also appear to modulate various functions in neural stem cells, including the processes of proliferation, neurogenesis, gliogenesis or cell death. However, the molecular mechanisms involved in these effects are still unclear. In this review, we summarize the physiological functions of APP and its main proteolytic derivatives in neural stem cells, as well as the possible signaling pathways that could be implicated in these effects. The knowledge of these functions and signaling pathways involved in the onset or during the development of Alzheimer's disease is essential to advance the understanding of the pathogenesis of Alzheimer's disease, and in the search for potential therapeutic targets.

Osthole Stimulated Neural Stem Cells Differentiation into Neurons in an Alzheimer's Disease Cell Model via Upregulation of MicroRNA-9 and Rescued the Functional Impairment of Hippocampal Neurons in APP/PS1 Transgenic Mice

Alzheimer's disease (AD) is the most serious neurodegenerative disease worldwide and is characterized by progressive cognitive impairment and multiple neurological changes, including neuronal loss in the brain. However, there are no available drugs to delay or cure this disease. Consequently, neuronal replacement therapy may be a strategy to treat AD. Osthole (Ost), a natural coumarin derivative, crosses the blood-brain barrier and exerts strong neuroprotective effects against AD in vitro and in vivo. Recently, microRNAs (miRNAs) have demonstrated a crucial role in pathological processes of AD, implying that targeting miRNAs could be a therapeutic approach to AD. In the present study, we investigated whether Ost could enhance cell viability and prevent cell death in amyloid precursor protein (APP)-expressing neural stem cells (NSCs) as well as promote APP-expressing NSCs differentiation into more neurons by upregulating microRNA (miR)-9 and inhibiting the Notch signaling pathway in vitro. In addition, Ost treatment in APP/PS1 double transgenic (Tg) mice markedly restored cognitive functions, reduced Aβ plague production and rescued functional impairment of hippocampal neurons. The results of the present study provides evidence of the neurogenesis effects and neurobiological mechanisms of Ost against AD, suggesting that Ost is a promising drug for treatment of AD or other neurodegenerative diseases.

GFAP expression and social deficits in transgenic mice overexpressing human sAPPα

Autistic individuals display impaired social interactions and language, and restricted, stereotyped behaviors. Elevated levels of secreted amyloid precursor protein-alpha (sAPPα), the product of α-secretase cleavage of APP, are found in the plasma of some individuals with autism. The sAPPα protein is neurotrophic and neuroprotective and recently showed a correlation to glial differentiation in human neural stem cells (NSCs) via the IL-6 pathway. Considering evidence of gliosis in postmortem autistic brains, we hypothesized that subsets of patients with autism would exhibit elevations in CNS sAPPα and mice generated to mimic this observation would display markers suggestive of gliosis and autism-like behavior. Elevations in sAPPα levels were observed in brains of autistic patients compared to controls. Transgenic mice engineered to overexpress human sAPPα (TgsAPPα mice) displayed hypoactivity, impaired sociability, increased brain glial fibrillary acidic protein (GFAP) expression, and altered Notch1 and IL-6 levels. NSCs isolated from TgsAPPα mice, and those derived from wild-type mice treated with sAPPα, displayed suppressed β-tubulin III and elevated GFAP expression. These results suggest that elevations in brain sAPPα levels are observed in subsets of individuals with autism and TgsAPPα mice display signs suggestive of gliosis and behavioral impairment.

The amyloid precursor protein (APP) triplicated gene impairs neuronal precursor differentiation and neurite development through two different domains in the Ts65Dn mouse model for Down syndrome

Intellectual disability in Down syndrome (DS) appears to be related to severe proliferation impairment during brain development. Recent evidence shows that it is not only cellular proliferation that is heavily compromised in DS, but also cell fate specification and dendritic maturation. The amyloid precursor protein (APP), a gene that is triplicated in DS, plays a key role in normal brain development by influencing neural precursor cell proliferation, cell fate specification, and neuronal maturation. APP influences these processes via two separate domains, the APP intracellular domain (AICD) and the soluble secreted APP. We recently found that the proliferation impairment of neuronal precursors (NPCs) from the Ts65Dn mouse model for DS was caused by derangement of the Shh pathway due to overexpression of patched1(Ptch1), its inhibitory regulator. Ptch1 overexpression was related to increased levels within the APP/AICD system. The overall goal of this study was to determine whether APP contributes to neurogenesis impairment in DS by influencing in addition to proliferation, cell fate specification, and neurite development. We found that normalization of APP expression restored the reduced neuronogenesis, the increased astrogliogenesis, and the reduced neurite length of trisomic NPCs, indicating that APP overexpression underpins all aspects of neurogenesis impairment. Moreover, we found that two different domains of APP impair neuronal differentiation and maturation in trisomic NPCs. The APP/AICD system regulates neuronogenesis and neurite length through the Shh pathway, whereas the APP/secreted AP system promotes astrogliogenesis through an IL-6-associated signaling cascade. These results provide novel insight into the mechanisms underlying brain development alterations in DS.

β-secretase cleavage of the fly amyloid precursor protein is required for glial survival

β-secretase (or BACE1) is the key enzyme in the production of β-amyloid (Aβ), which accumulates in the senile plaques characteristic for Alzheimer's disease. Consequently, the lack of BACE1 prevents β-processing of the amyloid precursor protein and Aβ production, which made it a promising target for drug development. However, the loss of BACE1 is also detrimental, leading to myelination defects and altered neuronal activity, functions that have been associated with the cleavage of Neuregulin and a voltage-gated sodium channel subunit. Here we show that the Drosophila ortholog of BACE, dBACE, is required for glial survival. Cell-specific knockdown experiments reveal that this is a non-cell autonomous function, as a knockdown of dBACE in photoreceptor neurons leads to progressive degeneration of glia in their target zone, the lamina. Interestingly, this phenotype is suppressed by the loss of the fly amyloid precursor protein (APPL), whereas a secretion-deficient form of APPL enhances the degeneration. This shows that full-length APPL in neurons promotes the death of neighboring glial cells and that β-processing of APPL is needed to prevent glial death. These results therefore not only demonstrate a novel function for an APP protein in glia, but they also show this function specifically requires regulation by β-cleavage.

All in the Family: How the APPs Regulate Neurogenesis

Recent intriguing evidence suggests that metabolites of amyloid precursor protein (APP), mutated in familial forms of Alzheimer’s disease (AD), play critical roles in developmental and postnatal neurogenesis. Of note is soluble APPα (sAPPα) that regulates neural progenitor cell proliferation. The APP family encompasses a group of ubiquitously expressed and evolutionarily conserved, type I transmembrane glycoproteins, whose functions have yet to be fully elucidated. APP can undergo proteolytic cleavage by mutually exclusive pathways. The subtle structural differences between metabolites generated in the different pathways, as well as their equilibrium, may be crucial for neuronal function. The implications of this new body of evidence are significant. Miscleavage of APP would readily impact developmental and postnatal neurogenesis, which might contribute to cognitive deficits characterizing Alzheimer’s disease. This review will discuss the implications of the role of the APP family in neurogenesis for neuronal development, cognitive function, and brain disorders that compromise learning and memory, such as AD.

Amyloid precursor proteins, neural differentiation of pluripotent stem cells and its relevance to Alzheimer's disease

Alzheimer's disease (AD) is a leading cause of age-related dementia that is characterized by an extensive loss of neurons and synaptic transmission. The pathological hallmarks of AD are neurofibrillary tangles and deposition of β-amyloid (Aβ) plaques. Previous research has investigated how Aβ fragments disrupt synaptic mechanisms in the vulnerable regions of the brain. There is a tremendous potential for stem cell technology to extend upon this research, not only in terms of developing therapeutic applications, but also in modeling AD. Indeed, the advent of induced pluripotent stem cell technology has opened up exciting new avenues for generating patient and disease-specific cell lines from somatic cells that may be used to model AD. Amyloid precursor protein (APP) is a key protein in neuronal development and this article reviews the role of APP in AD. Stem cell technology offers the opportunity to make use of APP in the directed differentiation of induced pluripotent stem cells into functional neurons, a process that may help generate a model of AD and thereby facilitate an understanding of the mechanisms underlying this disease.

Secreted amyloid precursor proteins promote proliferation and glial differentiation of adult hippocampal neural progenitor cells

Amyloid precursor protein (APP) is an integral membrane glycoprotein present at high levels in nerve cells. Two soluble secreted forms, sAPPα and sAPPβ, are processed from APP by two mutually exclusive proteolytic pathways. sAPPα shows a range of neuroprotective and growth factor properties, including reduction of neuronal injury and improvement in memory performance, in contrast to the generally less potent sAPPβ. In addition, sAPPα has been shown to increase the proliferation of both embryonic neural stem cells and neural progenitor cells (NPCs) derived from the subventricular zone (SVZ) of the adult brain. However, an effect of sAPPα (or sAPPβ) on adult hippocampal progenitor cell proliferation and differentiation has not previously been observed. In this study, we examined the effect of both the α- and β-cleaved ectodomains of sAPP on adult NPCs isolated from the subgranular zone (SGZ) of the rat hippocampus in the presence or absence of depolarizing conditions. Assays were performed to examine the effect of sAPPα and sAPPβ on SGZ-derived adult NPC proliferation in parallel with SVZ-derived cells and on differentiation with SGZ-derived cells. We observed both sAPPα and sAPPβ increased the proliferation of SGZ-derived NPCs in vitro. Further, treatment of SGZ-derived NPCs with either sAPPα or sAPPβ increased the number of cells expressing the astrocytic marker GFAP and promoted cell survival. The effect on differential fate was observed in both the presence and absence of depolarizing conditions. Thus, both sAPPα and sAPPβ exert a complex range of effects on SGZ-derived adult NPCs, including increasing NPC proliferation, maintaining cell viability, yet promoting glial over neuronal differentiation. These findings provide the first direct support for the secreted forms of APP regulating SGZ-derived NPCs, and raise the possibility some or all of the effects may have therapeutic benefit in models of neurological disease.