Identifying the earliest-occurring clinically targetable precursors of late-onset Alzheimer's disease.

Most cases of Alzheimer's disease (AD) are late-onset dementias (LOAD). However, research on AD is predominantly of early-onset disease (EOAD). The determinants of EOAD, gene variants of APP and presenilin proteins, are not the basic precursors of LOAD. Rather, multiple other genes and associated cellular processes underlie risk for LOAD. These determinants could be modified in individuals at risk for LOAD well before signs and symptoms appear. Studying brain cells produced from patient-derived induced-pluripotent-stem-cells (iPSC), in culture, will be instrumental in developing such interventions. This paper summarises evidence accrued from iPSC culture models identifying the earliest occurring clinically targetable determinants of LOAD. Results obtained and replicated, thus far, suggest that abnormalities of bioenergetics, lipid metabolism, digestive organelle function and inflammatory activity are primary processes underlying LOAD. The application of cell culture platforms will become increasingly important in research and also on LOAD detection, assessment, and treatment in the years ahead.

Nicotinamide riboside and caffeine partially restore diminished NAD availability but not altered energy metabolism in Alzheimer's disease.

The redox co-factor nicotinamide adenine dinucleotide (NAD) declines with age, and NAD deficits are specifically associated with dysfunctional energy metabolism in late-onset Alzheimer's disease (LOAD). Nicotinamide riboside (NR), a dietary NAD precursor, has been suggested to ameliorate the aging process or neurodegeneration. We assessed whether NR with or without caffeine, which increases nicotinamide mononucleotide transferase subtype 2 (NMNAT2), an essential enzyme in NAD production, modulates bioenergetic functions in LOAD. In LOAD patients-and young or old control individuals-derived dermal fibroblasts as well as in induced pluripotent stem cell-differentiated neural progenitors and astrocytes, NR and caffeine cell type-specifically increased the NAD pool, transiently enhanced mitochondrial respiration or glycolysis and altered the expression of genes in the NAD synthesis or consumption pathways. However, continued treatment led to reversed bioenergetic effects. Importantly, NR and caffeine did not alter the characteristics of a previously documented inherent LOAD-associated bioenergetic phenotype. Thus, although NR and caffeine can partially restore diminished NAD availability, increasing NAD alone may not be sufficient to boost or restore energy metabolism in brain aging or alter aberrant energy management in LOAD. Nicotinamide riboside might still be of value in combination with other agents in preventive or therapeutic intervention strategies to address the aging process or age-associated dementia.

Reactive oxygen species-sensitive nanophotosensitizers of aminophenyl boronic acid pinacol ester conjugated chitosan-g-methoxy poly(ethylene glycol) copolymer for photodynamic treatment of cancer.

The aim of this study is to prepare reactive oxygen species (ROS)-sensitive nanophotosensitizers for targeted delivery of chlorin e6 (Ce6) and photodynamic tumor therapy. For this purpose, thiodipropionic acid (TDPA) was conjugated with phenyl boronic acid pinacol ester (PBAP) (TDPA-PBAP conjugates) and then the TDPA-PBAP conjugates were attached to the chitosan backbone of chitosan-g-methoxy poly(ethylene glycol) (ChitoPEG) copolymer (ChitoPEG-PBAP). Ce6-incorporated ChitoPEG-PBAP nanophotosensitizers have an ROS-sensitive manner in vitro. The size of ChitoPEG-PBAP nanoparticles increased or disintegrated in a responsive manner against H2O2 concentration. The Ce6 release rate from ChitoPEG-PBAP nanophotosensitizers also increased by adding H2O2. These results indicated that nanophotosensitizers have sensitivity against ROS and showed triggered Ce6 release behavior. ChitoPEG-PBAP nanophotosensitizers can be more efficiently internalized into cancer cells compared to Ce6 alone and then produce ROS in a more efficient manner. Furthermore, ChitoPEG-PBAP nanophotosensitizers suppressed the viability of cancer cells in vitro and tumor growth in vivo with higher efficacy compared to Ce6 alone. Furthermore, ChitoPEG-PBAP nanophotosensitizers were efficiently delivered to irradiated tumor tissues, indicating that ChitoPEG-PBAP nanophotosensitizers can be delivered to the tumor with ROS-sensitive manner. We suggest that a ChitoPEG-PBAP nanophotosensitizer is a promising candidate for photodynamic therapy of cancers.

Laser microdissection and gene expression profiling in the human postmortem brain.

Laser microdissection in combination with gene expression profiling using postmortem human brain tissue provides a powerful approach to interrogating cell type-specific pathologies within neural circuits that are known to be dysfunctional in neuropsychiatric disorders. The success of these experiments critically depends on a number of factors, such as the cellular purity of the sample, the quality of the RNA, the methodologies of data normalization and computational data analysis, and how data are interpreted. Data obtained from these experiments should be validated at the protein level. Furthermore, from the perspective of disease mechanism discovery, it would be ideal to investigate whether manipulation of the expression of genes identified as differentially expressed can rescue or ameliorate the neurobiologic or behavioral phenotypes associated with the specific disease. Thus, the ultimate value of this approach rests upon the fact that the generation of novel disease-related pathophysiologic hypotheses may lead to deeper understanding of disease mechanisms and possible development of effective targeted treatments.

Fast and efficient neural conversion of human hematopoietic cells.

Neurons obtained directly from human somatic cells hold great promise for disease modeling and drug screening. Available protocols rely on overexpression of transcription factors using integrative vectors and are often slow, complex, and inefficient. We report a fast and efficient approach for generating induced neural cells (iNCs) directly from human hematopoietic cells using Sendai virus. Upon SOX2 and c-MYC expression, CD133-positive cord blood cells rapidly adopt a neuroepithelial morphology and exhibit high expansion capacity. Under defined neurogenic culture conditions, they express mature neuronal markers and fire spontaneous action potentials that can be modulated with neurotransmitters. SOX2 and c-MYC are also sufficient to convert peripheral blood mononuclear cells into iNCs. However, the conversion process is less efficient and resulting iNCs have limited expansion capacity and electrophysiological activity upon differentiation. Our study demonstrates rapid and efficient generation of iNCs from hematopoietic cells while underscoring the impact of target cells on conversion efficiency.

Selection Based on FOXA2 Expression Is Not Sufficient to Enrich for Dopamine Neurons From Human Pluripotent Stem Cells.

Human embryonic and induced pluripotent stem cells are potential cell sources for regenerative approaches in Parkinson disease. Inductive differentiation protocols can generate midbrain dopamine neurons but result in heterogeneous cell mixtures. Therefore, selection strategies are necessary to obtain uniform dopamine cell populations. Here, we developed a selection approach using lentivirus vectors to express green fluorescent protein under the promoter region of FOXA2, a transcription factor that is expressed in the floor plate domain that gives rise to dopamine neurons during embryogenesis. We first validated the specificity of the vectors in human cell lines against a promoterless construct. We then selected FOXA2-positive neural progenitors from several human pluripotent stem cell lines, which demonstrated a gene expression profile typical for the ventral domain of the midbrain and floor plate, but failed to enrich for dopamine neurons. To investigate whether this was due to the selection approach, we overexpressed FOXA2 in neural progenitors derived from human pluripotent stem cell lines. FOXA2 forced expression resulted in an increased expression of floor plate but not mature neuronal markers. Furthermore, selection of the FOXA2 overexpressing fraction also failed to enrich for dopamine neurons. Collectively, our results suggest that FOXA2 is not sufficient to induce a dopaminergic fate in this system. On the other hand, our study demonstrates that a combined approach of promoter activation and lentivirus vector technology can be used as a versatile tool for the selection of a defined cell population from a variety of human pluripotent stem cell lines.

MicroRNAs and deregulated gene expression networks in neurodegeneration.

Neurodegeneration is characterized by the progressive loss of neuronal cell types in the nervous system. Although the main cause of cell dysfunction and death in many neurodegenerative diseases is not known, there is increasing evidence that their demise is a result of a combination of genetic and environmental factors which affect key signaling pathways in cell function. This view is supported by recent observations that disease-compromised cells in late-stage neurodegeneration exhibit profound dysregulation of gene expression. MicroRNAs (miRNAs) introduce a novel concept of regulatory control over gene expression and there is increasing evidence that they play a profound role in neuronal cell identity as well as multiple aspects of disease pathogenesis. Here, we review the molecular properties of brain cells derived from patients with neurodegenerative diseases, and discuss how deregulated miRNA/mRNA expression networks could be a mechanism in neurodegeneration. In addition, we emphasize that the dysfunction of these regulatory networks might overlap between different cell systems and suggest that miRNA functions might be common between neurodegeneration and other disease entities.

Immature and neurally differentiated mouse embryonic stem cells do not express a functional Fas/Fas ligand system.

The potential of pluripotent embryonic stem (ES) cells to develop into functional cells or tissue provides an opportunity in the development of new therapies for many diseases including neurodegenerative disorders. The survival of implanted cells usually requires systemic immunosuppression, however, which severely compromises the host immune system, leading to complications in clinical transplantation. An optimal therapy would therefore be the induction of specific tolerance to the donor cells, while otherwise preserving functional immune responses. Fas ligand (FasL) is expressed in activated lymphocytes as well as cells in "immune-privileged" sites including the central nervous system. Its receptor, Fas, is expressed on various immune-reactive cell types, such as activated natural killer and T cells, monocytes, and polymorphic mononucleocytes, which can undergo apoptosis upon interaction with FasL. To render transplanted cells tolerant to host cellular immune responses, we genetically engineered mouse ES cells to express rat FasL (rFasL). The rFasL-expressing ES cells were analyzed for survival during in vitro neurodifferentiation and after transplantation to the rat brain without further immunosuppression. Although control transfected HEK-293T cells expressed functional rFasL, immature and differentiated mouse ES cells did not express the recombinant rFasL surface protein. Furthermore, there was no evidence for functional endogenous Fas and FasL expression on either ES cells or on neural cells after in vitro differentiation. Moreover, implanted rFasL-engineered ES cells did not survive in the rat brains in the absence of the immunosuppressive agent cyclosporine A. Our results indicate that immature and differentiated mouse ES cells do not express a functional Fas/FasL system. Disclosure of potential conflicts of interest is found at the end of this article.

Markers and methods for cell sorting of human embryonic stem cell-derived neural cell populations.

Neural cells differentiated in vitro from human embryonic stem cells (hESC) exhibit broad cellular heterogeneity with respect to developmental stage and lineage specification. Here, we describe standard conditions for the use and discovery of markers for analysis and cell selection of hESC undergoing neuronal differentiation. To generate better-defined cell populations, we established a working protocol for sorting heterogeneous hESC-derived neural cell populations by fluorescence-activated cell sorting (FACS). Using genetically labeled synapsin-green fluorescent protein-positive hESC-derived neurons as a proof of principle, we enriched viable differentiated neurons by FACS. Cell sorting methodology using surface markers was developed, and a comprehensive profiling of surface antigens was obtained for immature embryonic stem cell types (such as stage-specific embryonic antigen [SSEA]-3, -4, TRA-1-81, TRA-1-60), neural stem and precursor cells (such as CD133, SSEA-1 [CD15], A2B5, forebrain surface embryonic antigen-1, CD29, CD146, p75 [CD271]), and differentiated neurons (such as CD24 or neural cell adhesion molecule [NCAM; CD56]). At later stages of neural differentiation, NCAM (CD56) was used to isolate hESC-derived neurons by FACS. Such FACS-sorted hESC-derived neurons survived in vivo after transplantation into rodent brain. These results and concepts provide (a) a feasible approach for experimental cell sorting of differentiated neurons, (b) an initial survey of surface antigens present during neural differentiation of hESC, and (c) a framework for developing cell selection strategies for neural cell-based therapies.

Proteasome activator enhances survival of Huntington's disease neuronal model cells.

In patients with Huntington's disease (HD), the proteolytic activity of the ubiquitin proteasome system (UPS) is reduced in the brain and other tissues. The pathological hallmark of HD is the intraneuronal nuclear protein aggregates of mutant huntingtin. We determined how to enhance UPS function and influence catalytic protein degradation and cell survival in HD. Proteasome activators involved in either the ubiquitinated or the non-ubiquitinated proteolysis were overexpressed in HD patients' skin fibroblasts or mutant huntingtin-expressing striatal neurons. Following compromise of the UPS, overexpression of the proteasome activator subunit PA28gamma, but not subunit S5a, recovered proteasome function in the HD cells. PA28gamma also improved cell viability in mutant huntingtin-expressing striatal neurons exposed to pathological stressors, such as the excitotoxin quinolinic acid and the reversible proteasome inhibitor MG132. These results demonstrate the specific functional enhancements of the UPS that can provide neuroprotection in HD cells.

Enhanced yield of neuroepithelial precursors and midbrain-like dopaminergic neurons from human embryonic stem cells using the bone morphogenic protein antagonist noggin.

It is currently not known whether dopamine (DA) neurons derived from human embryonic stem cells (hESCs) can survive in vivo and alleviate symptoms in models of Parkinson disease (PD). Here, we report the use of Noggin (a bone morphogenic protein antagonist) to induce neuroectodermal cell development and increase the yield of DA neurons from hESCs. A combination of stromal-derived inducing activity and Noggin markedly enhanced the generation of neuroepithelial progenitors that could give rise to DA neurons. In addition, Noggin diminished the occurrence of a fibroblast-like Nestin-positive precursor population that differentiated into myocytes. After transplantation of differentiated hESCs to a rodent model of PD, some grafts contained human midbrain-like DA neurons. This protocol demonstrates hESC derivation and survival of human DA neurons appropriate for cell therapy in PD.

Tailoring human embryonic stem cells for neurodegenerative disease therapy.

Embryonic stem (ES) cells are expected to become a cell source and biological delivery system for use in a variety of neurodegenerative diseases, and will likely play a role in the development of novel cell-based therapies for these indications. These applications require the in vitro differentiation of ES cells into stable, safe and functional neural cell populations. Initial experiments with mouse ES cells are now in the process of being translated and developed into studies on human (h)ES cells. Despite their potential, several hurdles must be overcome to render hES cells a reliable and efficient system to produce cell types for therapeutic application and as a model system for therapy development. This review discusses the current state of research into hES cells, with an emphasis on neurodegenerative diseases.

Implementations of translational medicine.

New developments in science are rapidly influencing and shaping basic and clinical research and medicine. This has led to the emergence of multiple opportunities and challenges on many levels in the bio-medical and other associated fields. To face these opportunities and challenges, new concepts and strategies are needed. These can be provided by translational research/medicine as an integrative concept based on a multidirectional understanding of research and medicine embedded in a socio-economical environment. Although the implementation of translational research/medicine faces many obstacles, some of its goals have already been part of new programs in local institutions and in medical or scientific societies. These implementations are important in creating a unified national and international system of translational research/medicine.

Cell type-specific gene expression of midbrain dopaminergic neurons reveals molecules involved in their vulnerability and protection.

Molecular differences between dopamine (DA) neurons may explain why the mesostriatal DA neurons in the A9 region preferentially degenerate in Parkinson's disease (PD) and toxic models, whereas the adjacent A10 region mesolimbic and mesocortical DA neurons are relatively spared. To characterize innate physiological differences between A9 and A10 DA neurons, we determined gene expression profiles in these neurons in the adult mouse by laser capture microdissection, microarray analysis and real-time PCR. We found 42 genes relatively elevated in A9 DA neurons, whereas 61 genes were elevated in A10 DA neurons [> 2-fold; false discovery rate (FDR) < 1%]. Genes of interest for further functional analysis were selected by criteria of (i) fold differences in gene expression, (ii) real-time PCR validation and (iii) potential roles in neurotoxic or protective biochemical pathways. Three A9-elevated molecules [G-protein coupled inwardly rectifying K channel 2 (GIRK2), adenine nucleotide translocator 2 (ANT-2) and the growth factor IGF-1] and three A10-elevated peptides (GRP, CGRP and PACAP) were further examined in both alpha-synuclein overexpressing PC12 (PC12-alphaSyn) cells and rat primary ventral mesencephalic (VM) cultures exposed to MPP+ neurotoxicity. GIRK2-positive DA neurons were more vulnerable to MPP+ toxicity and overexpression of GIRK2 increased the vulnerability of PC12-alphaSyn cells to the toxin. Blocking of ANT decreased vulnerability to MPP+ in both cell culture systems. Exposing cells to IGF-1, GRP and PACAP decreased vulnerability of both cell types to MPP+, whereas CGRP protected PC12-alphaSyn cells but not primary VM DA neurons. These results indicate that certain differentially expressed molecules in A9 and A10 DA neurons may play key roles in their relative vulnerability to toxins and PD.

Context-dependent neuronal differentiation and germ layer induction of Smad4-/- and Cripto-/- embryonic stem cells.

Activation of transforming growth factor-beta (TGF-beta) receptors typically elicits mesodermal development, whereas inhibition of this pathway induces neural fates. In vitro differentiated mouse embryonic stem (ES) cells with deletion of the TGF-beta pathway-related factors Smad4 or Cripto exhibited increased numbers of neurons. Cripto-/- ES cells developed into neuroecto-/epidermal cell types, while Smad4-/- cells also displayed mesodermal differentiation. ES cell differentiation into catecholaminergic neurons showed that these ES cells retained their ability to develop into dopaminergic and serotonergic neurons with typical expression patterns of midbrain and hindbrain genes. In vivo, transplanted ES cells to the mouse striatum became small neuronal grafts, or large grafts with cell types from all germ layers independent of their ES cell genotype. This demonstrates that Smad4-/- and Cripto-/- ES cells favor a neural fate in vitro, but also express the mesodermal phenotype, implying that deletion of either Smad4 or Cripto is not sufficient to block nonneuronal tissue formation.

Stem cells may reshape the prospect of Parkinson's disease therapy.

The concept of cell replacement to compensate for cell loss and restore functionality has entered several disease entities including neurodegenerative disorders. Recent clinical studies have shown that transplantation of fetal dopaminergic (DA) cells into the brain of Parkinson's disease (PD) patients can reduce disease-associated motor deficits. However, the use of fetal tissue is associated with practical and ethical problems including low efficiency, variability in the clinical outcome and controversy regarding the use of fetuses as donor. An alternative cell resource could be embryonic stem (ES) cells, which can be cultivated in unlimited amounts and which have the potential to differentiate into mature DA cells. Several differentiation protocols have been developed, and some progress has been made in understanding the mechanisms underlying DA specification in ES cell development, but the "holy grail" in this paradigm, which is the production of sufficient amounts of the "right" therapeutic DA cell, has not yet been accomplished. To achieve this goal, several criteria on the transplanted DA cells need to be fulfilled, mainly addressing cell survival, accurate integration in the brain circuitry, normal function, no tumor formation, and no immunogenicity. Here, we summarize the current state of ES cell-derived DA neurogenesis and discuss the aspects involved in generating an optimal cell source for cell replacement in PD.

Generalized brain and skin proteasome inhibition in Huntington's disease.

Mutated intracellular huntingtin is widely expressed in tissues of Huntington's disease (HD) patients. Intraneuronal nuclear protein aggregates of mutant huntingtin are present in HD brains, suggesting a dysfunction of the ubiquitin proteasome system (UPS). Because many cells and tissues can cope with the abnormal gene effects while others dysfunction and die, we determined gene-induced effects and considered the hypothesis that the gene causes multiple intracellular problems, but severe pathology is seen only in selected brain regions. In this study, we found inhibition of UPS function in both early (0-1, with no or little neuronal loss) and late (3-4, with more severe neuronal loss) stage HD patients' cerebellum, cortex, substantia nigra and caudate-putamen brain regions. Late HD stage increases in ubiquitin levels were unique to caudate-putamen. HD patients' skin fibroblasts also had UPS inhibition similar to brain despite increases in proteasome beta-subunit expression. Gene delivery and expression of proteasome activator PA28 increased UPS function in normal but not HD fibroblasts. These generalized UPS problems are associated with severe neuronal pathology only when coupled with decreases in brain-derived neurotrophic factor levels, mitochondrial complex II/III activity, and increases of ubiquitin levels particularly as seen in the caudate-putamen of HD patients.

Temporally induced Nurr1 can induce a non-neuronal dopaminergic cell type in embryonic stem cell differentiation.

The nuclear transcription factor Nurr1 is involved in the development and maintenance of the midbrain dopaminergic (DA) neuronal phenotype. We analysed the cellular and biological effects of Nurr1 during embryonic stem (ES) cell differentiation using the ROSA26-engineered Tet-inducible ES cell line J1-rtTA that does not express transgenes in mature neurons. Induction of Nurr1 at nestin-positive precursor and later stages of ES cell differentiation produced a non-neuronal DA cell type including functional DA transporters. In these cells, we found a clear correlation between Nurr1 and TH gene expression and specific midbrain DA cellular markers such as AADC, AHD2 and calbindin. Nurr1 did not alter gene expression of non-DA neuronal phenotypes and did not influence other midbrain developmental transcription factors, such as Otx1, Otx2, En-1, GBX2, Pitx3 and lmx1b. In addition, Nurr1 expression was required for maintenance of the DA phenotype and mediated up-regulation of the tyrosine kinase Ret and associated trophic factor GDNF-family receptors alpha 1, 2, and 4. This demonstrates that Nurr1 is sufficient to induce and maintain a midbrain-like DA biochemical and functional cellular phenotype independent of neurogenesis.