Programming and Reprogramming Cellular Age in the Era of Induced Pluripotency

Advancing immunomodulatory functions in mesenchymal stem/stromal cells through targeting the GATA6-mediated pathway

BACKGROUND AIMS

The immunomodulatory capacity of mesenchymal stem/stromal cells (MSCs) is a key feature that makes them particularly valuable for regenerative medicine. However, this potential is affected by the chronological aging of the donors and the cell expansion procedures in culture. We have demonstrated that GATA binding protein 6 (GATA6) plays a pivotal role in the aging of MSCs and inhibiting GATA6 rejuvenates the characteristics of MSCs.

METHODS

In this study, we compared the immunomodulatory capabilities of young and old MSC models, using induced pluripotent stem cells-derived rejuvenated MSCs (rMSCs) and their parental MSCs (pMSCs), respectively, to identify a key mechanism involved in the differential regulation of these capabilities. Additionally, we explored the role of GATA6 in mediating the mechanism.

RESULTS

Our results demonstrated that rMSCs exhibited downregulated aging-associated regulators, including p53, p21 and GATA6, and showed enhanced suppression of T cell proliferation compared to pMSCs. Through analyzing our previous RNA-seq data and employing target gene knockdown, we determined both suppressors of cytokine signaling 3 (SOCS3) and interleukin 6 were involved in GATA6-induced regulation, collectively affecting the expression of programmed death ligand 1 (PDL1) in both pMSCs and rMSCs.

CONCLUSIONS

Our findings underline the significance of the GATA6/SOCS3/PDL1 pathway in regulating aging-associated changes in MSC immunomodulatory activity, providing valuable insights into the potential use of rMSCs in the treatment of immune diseases and regenerative medicine.

Developing enhanced immunotherapy using NKG2A knockout human pluripotent stem cell-derived NK cells

Cancer immunotherapy is gaining increasing attention. However, immune checkpoints are exploited by cancer cells to evade anti-tumor immunotherapy. Here, we knocked out NKG2A, an immune checkpoint expressed on natural killer (NK) cells, in human pluripotent stem cells (hPSCs) and differentiated these hPSCs into NK (PSC-NK) cells. We show that NKG2A knockout (KO) enhances the anti-tumor and anti-viral capabilities of PSC-NK cells. NKG2A KO endows PSC-NK cells with higher cytotoxicity against HLA-E-expressing glioblastoma (GBM) cells, leukemia cells, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-infected cells in vitro. The NKG2A KO PSC-NK cells also exerted potent anti-tumor activity in vivo, leading to substantially suppressed tumor progression and prolonged survival of tumor-bearing mice in a xenograft GBM mouse model. These findings underscore the potential of PSC-NK cells with immune checkpoint KO as a promising cell-based immunotherapy. The unlimited supply and ease of genetic engineering of hPSCs makes genetically engineered PSC-NK an attractive option for easily accessible "off-the-shelf" cancer immunotherapy.

Short Peptides Protect Fibroblast-Derived Induced Neurons from Age-Related Changes

Neurons become more vulnerable to stress factors with age, which leads to increased oxidative DNA damage, decreased activity of mitochondria and lysosomes, increased levels of p16, decreased LaminB1 proteins, and the depletion of the dendritic tree. These changes are exacerbated in vulnerable neuronal populations during the development of neurodegenerative diseases. Glu-Asp-Arg (EDR) and Lys-Glu-Asp (KED), and Ala-Glu-Asp-Gly (AEDG) peptides have previously demonstrated neuroprotective effects in various models of Alzheimer's disease. In this study, we investigated the influence of EDR, KED, and AEDG peptides on the aging of fibroblast-derived induced neurons. We used a new in vitro cellular model of human neuronal aging based on the transdifferentiation of aged dermal fibroblasts from elderly donors into induced cortical neurons. All peptides promote the arborization of the dendritic tree, increasing both the number of primary processes and the total length of dendrites. Tripeptides have no effect on the activity of mitochondria and lysosomes and the level of p16 protein in induced neurons. EDR peptide reduces oxidative DNA damage in induced neurons derived from elderly donor fibroblasts. Short peptides partially protect induced neurons from age-related changes and stimulate dendritogenesis in neurons. They can be recommended for use as neuroprotective agents.

Functional outcome of the anterior vaginal wall in a pelvic surgery injury rat model after treatment with stem cell-derived progenitors of smooth muscle cells

BACKGROUND

Stem-cell-derived therapy is a promising option for tissue regeneration. Human iPSC-derived progenitors of smooth muscle cells (pSMCs) exhibit limited proliferation and differentiation, which minimizes the risk of tumor formation while restoring smooth muscle cells (SMCs). Up to 29% of women suffer from recurrence of vaginal prolapse after prolapse surgery. Therefore, there is a need for therapies that can restore vaginal function. SMCs contribute to vaginal tone and contractility. We sought to examine whether human pSMCs can restore vaginal function in a rat model.

METHODS

Female immunocompromised RNU rats were divided into 5 groups: intact controls (n = 12), VSHAM (surgery + saline injection, n = 35), and three cell-injection groups (surgery + cell injection using pSMCs from three patients, n = 14/cell line). The surgery to induce vaginal injury was analogous to prolapse surgery. Menopause was induced by surgical ovariectomy. The vagina, urethra, bladder were harvested 10 weeks after surgery (5 weeks after cell injection). Organ bath myography was performed to evaluate the contractile function of the vagina, and smooth muscle thickness was examined by tissue immunohistochemistry. Collagen I, collagen III, and elastin mRNA and protein expressions in tissues were assessed.

RESULTS

Vaginal smooth muscle contractions induced by carbachol and KCl in the cell-injection groups were significantly greater than those in the VSHAM group. Collagen I protein expression in the vagina of the cell-injections groups was significantly higher than in the VSHAM group. Vaginal elastin protein expression was similar between the cell-injection and VSHAM groups. In the urethra, gene expression levels of collagen I, III, and elastin were all significantly greater in the cell-injection groups than in the VSHAM group. Collagen I, III, and elastin protein expression of the urethra did not show a consistent trend between cell-injection groups and the VSHAM group.

CONCLUSIONS

Human iPSC-derived pSMCs transplantation appears to be associated with improved contractile function of the surgically injured vagina in a rat model. This is accompanied by changes in extracellular protein expression the vagina and urethra. These observations support further efforts in the translation of pSMCs into a treatment for regenerating the surgically injured vagina in women who suffer recurrent prolapse after surgery.

Microglia in Health and Diseases: Integrative Hubs of the Central Nervous System (CNS)

Microglia are usually referred to as "the innate immune cells of the brain," "the resident macrophages of the central nervous system" (CNS), or "CNS parenchymal macrophages." These labels allude to their inherent immune function, related to their macrophage lineage. However, beyond their classic innate immune responses, microglia also play physiological roles crucial for proper brain development and maintenance of adult brain homeostasis. Microglia sense both external and local stimuli through a variety of surface receptors. Thus, they might serve as integrative hubs at the interface between the external environment and the CNS, able to decode, filter, and buffer cues from outside, with the aim of preserving and maintaining brain homeostasis. In this perspective, we will cast a critical look at how these multiple microglial functions are acquired and coordinated, and we will speculate on their impact on human brain physiology and pathology.

Precision Medicine in Parkinson's Disease Using Induced Pluripotent Stem Cells

Parkinson's disease (PD) is one of the most devastating neurological diseases; however, there is no effective cure yet. The availability of human induced pluripotent stem cells (iPSCs) provides unprecedented opportunities to understand the pathogenic mechanism and identification of new therapy for PD. Here a new model system of PD, including 2D human iPSC-derived midbrain dopaminergic (mDA) neurons, 3D iPSC-derived midbrain organoids (MOs) with cellular complexity, and more advanced microphysiological systems (MPS) with 3D organoids, is introduced. It is believed that successful integrations and applications of iPSC, organoid, and MPS technologies can bring new insight on PD's pathogenesis that will lead to more effective treatments for this debilitating disease.

Functional outcome of the anterior vaginal wall in a pelvic surgery injury rat model after treatment with stem cell-derived progenitors of smooth muscle cells

Background

Stem-cell-derived therapy is a promising option for tissue regeneration. Human iPSC-derived progenitors of smooth muscle cells (pSMCs) have limited proliferation and differentiation, which may minimize the risk of in vivo tumor formation while restoring smooth muscle cell deficiencies. Up to 30 % of women who suffer from recurrence of vaginal prolapse after prolapse surgery are faced with reoperation. Therefore, there is an unmet need for therapies that can restore vaginal tissue function. We hypothesize that human pSMCs can restore vaginal function in a vaginal-injury rat model.

Methods

Female immune-compromised RNU rats were divided into 5 groups: intact controls (n=12), VSHAM (surgery + saline injection, n=33), and cell-injection group (surgery + cell injection using three patient pSMCs lines, n=14/cell line). The surgery, similar to what is done in vaginal prolapse surgery, involved ovariectomy, urethrolysis, and vagina injury. The vagina, urethra, bladder dome and trigone were harvested 10 weeks after surgery (5 weeks after injection). Organ bath myography was performed to evaluate the contractile function of vagina, and smooth muscle thickness was examined by tissue immunohistochemistry. Collagen I, collagen III, and elastin mRNA and protein expressions in tissues were assessed.

Results

When compared to the VSHAM group, cell-injection groups showed significantly increased vaginal smooth muscle contractions induced by carbachol (groups A and C) and by KCl (group C), and significantly higher collagen I protein expression in the vagina (groups A and B). Elastin mRNA and protein expressions in the vagina did not correlate with injection group. In the urethra, mRNA expressions of collagen I, collagen III, and elastin were all significantly higher in the cell-injection groups compared to the VSHAM group. Collagen I protein expression of the urethra was also higher in the cell-injection group compared to the VSHAM group. Elastin protein expression in the urethra did not correlate with injection group.

Conclusions

Human iPSC-derived pSMCs improved contractile function of the post-surgery vagina. Additionally, pSMC injection modulated collagen I, collagen III and elastin mRNA and protein expressions in the vagina and urethra. These findings suggest that pSMCs may be a possible therapy for vaginal prolapse recurrence after surgical intervention.

Hypoxia Increases the Efficiencies of Cellular Reprogramming and Oncogenic Transformation in Human Blood Cell Subpopulations In Vitro and In Vivo

Patients with chronic hypoxia show a higher tumor incidence; however, no primary common cause has been recognized. Given the similarities between cellular reprogramming and oncogenic transformation, we directly compared these processes in human cells subjected to hypoxia. Mouse embryonic fibroblasts were employed as controls to compare transfection and reprogramming efficiency; human adipose-derived mesenchymal stem cells were employed as controls in human cells. Easily obtainable human peripheral blood mononuclear cells (PBMCs) were chosen to establish a standard protocol to compare cell reprogramming (into induced pluripotent stem cells (iPSCs)) and oncogenic focus formation efficiency. Cell reprogramming was achieved for all three cell types, generating actual pluripotent cells capable for differentiating into the three germ layers. The efficiencies of the cell reprogramming and oncogenic transformation were similar. Hypoxia slightly increased the reprogramming efficiency in all the cell types but with no statistical significance for PBMCs. Various PBMC types can respond to hypoxia differently; lymphocytes and monocytes were, therefore, reprogrammed separately, finding a significant difference between normoxia and hypoxia in monocytes in vitro. These differences were then searched for in vivo. The iPSCs and oncogenic foci were generated from healthy volunteers and patients with chronic obstructive pulmonary disease (COPD). Although higher iPSC generation efficiency in the patients with COPD was found for lymphocytes, this increase was not statistically significant for oncogenic foci. Remarkably, a higher statistically significant efficiency in COPD monocytes was demonstrated for both processes, suggesting that physiological hypoxia exerts an effect on cell reprogramming and oncogenic transformation in vivo in at least some cell types.

Human tNeurons reveal aging-linked proteostasis deficits driving Alzheimer's phenotypes

Aging is a prominent risk factor for Alzheimer's disease (AD), but the cellular mechanisms underlying neuronal phenotypes remain elusive. Both accumulation of amyloid plaques and neurofibrillary tangles in the brain1 and age-linked organelle deficits2-7 are proposed as causes of AD phenotypes but the relationship between these events is unclear. Here, we address this question using a transdifferentiated neuron (tNeuron) model directly from human dermal fibroblasts. Patient-derived tNeurons retain aging hallmarks and exhibit AD-linked deficits. Quantitative tNeuron proteomic analyses identify aging and AD-linked deficits in proteostasis and organelle homeostasis, particularly affecting endosome-lysosomal components. The proteostasis and lysosomal homeostasis deficits in aged tNeurons are exacerbated in sporadic and familial AD tNeurons, promoting constitutive lysosomal damage and defects in ESCRT-mediated repair. We find deficits in neuronal lysosomal homeostasis lead to inflammatory cytokine secretion, cell death and spontaneous development of Aß and phospho-Tau deposits. These proteotoxic inclusions co-localize with lysosomes and damage markers and resemble inclusions in brain tissue from AD patients and APP-transgenic mice. Supporting the centrality of lysosomal deficits driving AD phenotypes, lysosome-function enhancing compounds reduce AD-associated cytokine secretion and Aβ deposits. We conclude that proteostasis and organelle deficits are upstream initiating factors leading to neuronal aging and AD phenotypes.

Induced pluripotent stem cells (iPSCs): molecular mechanisms of induction and applications

The induced pluripotent stem cell (iPSC) technology has transformed in vitro research and holds great promise to advance regenerative medicine. iPSCs have the capacity for an almost unlimited expansion, are amenable to genetic engineering, and can be differentiated into most somatic cell types. iPSCs have been widely applied to model human development and diseases, perform drug screening, and develop cell therapies. In this review, we outline key developments in the iPSC field and highlight the immense versatility of the iPSC technology for in vitro modeling and therapeutic applications. We begin by discussing the pivotal discoveries that revealed the potential of a somatic cell nucleus for reprogramming and led to successful generation of iPSCs. We consider the molecular mechanisms and dynamics of somatic cell reprogramming as well as the numerous methods available to induce pluripotency. Subsequently, we discuss various iPSC-based cellular models, from mono-cultures of a single cell type to complex three-dimensional organoids, and how these models can be applied to elucidate the mechanisms of human development and diseases. We use examples of neurological disorders, coronavirus disease 2019 (COVID-19), and cancer to highlight the diversity of disease-specific phenotypes that can be modeled using iPSC-derived cells. We also consider how iPSC-derived cellular models can be used in high-throughput drug screening and drug toxicity studies. Finally, we discuss the process of developing autologous and allogeneic iPSC-based cell therapies and their potential to alleviate human diseases.

Detection of ER Stress in iPSC-Derived Neurons Carrying the p.N370S Mutation in the GBA1 Gene

Endoplasmic reticulum (ER) stress is involved in the pathogenesis of many human diseases, such as cancer, type 2 diabetes, kidney disease, atherosclerosis and neurodegenerative diseases, in particular Parkinson's disease (PD). Since there is currently no treatment for PD, a better understanding of the molecular mechanisms underlying its pathogenesis, including the mechanisms of the switch from adaptation in the form of unfolded protein response (UPR) to apoptosis under ER stress conditions, may help in the search for treatment methods. Genetically encoded biosensors based on fluorescent proteins are suitable tools that facilitate the study of living cells and visualization of molecular events in real time. The combination of technologies to generate patient-specific iPSC lines and genetically encoded biosensors allows the creation of cell models with new properties. Using CRISPR-Cas9-mediated homologous recombination at the AAVS1 locus of iPSC with the genetic variant p.N370S (rs76763715) in the GBA1 gene, we created a cell model designed to study the activation conditions of the IRE1-XBP1 cascade of the UPR system. The cell lines obtained have a doxycycline-dependent expression of the genetically encoded biosensor XBP1-TagRFP, possess all the properties of human pluripotent cells, and can be used to test physical conditions and chemical compounds that affect the development of ER stress, the functioning of the UPR system, and in particular, the IRE1-XBP1 cascade.

Cellular plasticity in reprogramming, rejuvenation and tumorigenesis: a pioneer TF perspective

The multistep process of in vivo reprogramming, mediated by the transcription factors (TFs) Oct4, Sox2, Klf4, and c-Myc (OSKM), holds great promise for the development of rejuvenating and regenerative strategies. However, most of the approaches developed so far are accompanied by a persistent risk of tumorigenicity. Here, we review the groundbreaking effects of in vivo reprogramming with a particular focus on rejuvenation and regeneration. We discuss how the activity of pioneer TFs generates cellular plasticity that may be critical for inducing not only reprogramming and regeneration, but also cancer initiation. Finally, we highlight how a better understanding of the uncoupled control of cellular identity, plasticity, and aging during reprogramming might pave the way to the development of rejuvenating/regenerating strategies in a nontumorigenic manner.

Cellular reprogramming as a tool to model human aging in a dish

The design of human model systems is highly relevant to unveil the underlying mechanisms of aging and to provide insights on potential interventions to extend human health and life span. In this perspective, we explore the potential of 2D or 3D culture models comprising human induced pluripotent stem cells and transdifferentiated cells obtained from aged or age-related disorder-affected donors to enhance our understanding of human aging and to catalyze the discovery of anti-aging interventions.

LRP10 and α-synuclein transmission in Lewy body diseases

Autosomal dominant variants in LRP10 have been identified in patients with Lewy body diseases (LBDs), including Parkinson's disease (PD), Parkinson's disease-dementia (PDD), and dementia with Lewy bodies (DLB). Nevertheless, there is little mechanistic insight into the role of LRP10 in disease pathogenesis. In the brains of control individuals, LRP10 is typically expressed in non-neuronal cells like astrocytes and neurovasculature, but in idiopathic and genetic cases of PD, PDD, and DLB, it is also present in α-synuclein-positive neuronal Lewy bodies. These observations raise the questions of what leads to the accumulation of LRP10 in Lewy bodies and whether a possible interaction between LRP10 and α-synuclein plays a role in disease pathogenesis. Here, we demonstrate that wild-type LRP10 is secreted via extracellular vesicles (EVs) and can be internalised via clathrin-dependent endocytosis. Additionally, we show that LRP10 secretion is highly sensitive to autophagy inhibition, which induces the formation of atypical LRP10 vesicular structures in neurons in human-induced pluripotent stem cells (iPSC)-derived brain organoids. Furthermore, we show that LRP10 overexpression leads to a strong induction of monomeric α-synuclein secretion, together with time-dependent, stress-sensitive changes in intracellular α-synuclein levels. Interestingly, patient-derived astrocytes carrying the c.1424 + 5G > A LRP10 variant secrete aberrant high-molecular-weight species of LRP10 in EV-free media fractions. Finally, we show that this truncated patient-derived LRP10 protein species (LRP10splice) binds to wild-type LRP10, reduces LRP10 wild-type levels, and antagonises the effect of LRP10 on α-synuclein levels and distribution. Together, this work provides initial evidence for a possible functional role of LRP10 in LBDs by modulating intra- and extracellular α-synuclein levels, and pathogenic mechanisms linked to the disease-associated c.1424 + 5G > A LRP10 variant, pointing towards potentially important disease mechanisms in LBDs.

Screens in aging-relevant human ALS-motor neurons identify MAP4Ks as therapeutic targets for the disease

Effective therapeutics is much needed for amyotrophic lateral sclerosis (ALS), an adult-onset neurodegenerative disease mainly affecting motor neurons. By screening chemical compounds in human patient-derived and aging-relevant motor neurons, we identify a neuroprotective compound and show that MAP4Ks may serve as therapeutic targets for treating ALS. The lead compound broadly improves survival and function of motor neurons directly converted from human ALS patients. Mechanistically, it works as an inhibitor of MAP4Ks, regulates the MAP4Ks-HDAC6-TUBA4A-RANGAP1 pathway, and normalizes subcellular distribution of RANGAP1 and TDP-43. Finally, in an ALS mouse model we show that inhibiting MAP4Ks preserves motor neurons and significantly extends animal lifespan.

Astrocytic response mediated by the CLU risk allele inhibits OPC proliferation and myelination in a human iPSC model

The C allele of rs11136000 variant in the clusterin (CLU) gene represents the third strongest known genetic risk factor for late-onset Alzheimer's disease. However, whether this single-nucleotide polymorphism (SNP) is functional and what the underlying mechanisms are remain unclear. In this study, the CLU rs11136000 SNP is identified as a functional variant by a small-scale CRISPR-Cas9 screen. Astrocytes derived from isogenic induced pluripotent stem cells (iPSCs) carrying the "C" or "T" allele of the CLU rs11136000 SNP exhibit different CLU expression levels. TAR DNA-binding protein-43 (TDP-43) preferentially binds to the "C" allele to promote CLU expression and exacerbate inflammation. The interferon response and CXCL10 expression are elevated in cytokine-treated C/C astrocytes, leading to inhibition of oligodendrocyte progenitor cell (OPC) proliferation and myelination. Accordingly, elevated CLU and CXCL10 but reduced myelin basic protein (MBP) expression are detected in human brains of C/C carriers. Our study uncovers a mechanism underlying reduced white matter integrity observed in the CLU rs11136000 risk "C" allele carriers.

Chemical screens in aging-relevant human motor neurons identify MAP4Ks as therapeutic targets for amyotrophic lateral sclerosis

Effective therapeutics is much needed for amyotrophic lateral sclerosis (ALS), an adult-onset neurodegenerative disease mainly affecting motor neurons. By screening chemical compounds in human patient-derived and aging-relevant motor neurons, we identify a neuroprotective compound and show that MAP4Ks may serve as therapeutic targets for treating ALS. The lead compound broadly improves survival and function of motor neurons directly converted from human ALS patients. Mechanistically, it works as an inhibitor of MAP4Ks, regulates the MAP4Ks-HDAC6-TUBA4A-RANGAP1 pathway, and normalizes subcellular distribution of RANGAP1 and TDP-43. Finally, in an ALS mouse model we show that inhibiting MAP4Ks preserves motor neurons and significantly extends animal lifespan.

Merits and challenges of iPSC-derived organoids for clinical applications

Induced pluripotent stem cells (iPSCs) have entered an unprecedented state of development since they were first generated. They have played a critical role in disease modeling, drug discovery, and cell replacement therapy, and have contributed to the evolution of disciplines such as cell biology, pathophysiology of diseases, and regenerative medicine. Organoids, the stem cell-derived 3D culture systems that mimic the structure and function of organs in vitro, have been widely used in developmental research, disease modeling, and drug screening. Recent advances in combining iPSCs with 3D organoids are facilitating further applications of iPSCs in disease research. Organoids derived from embryonic stem cells, iPSCs, and multi-tissue stem/progenitor cells can replicate the processes of developmental differentiation, homeostatic self-renewal, and regeneration due to tissue damage, offering the potential to unravel the regulatory mechanisms of development and regeneration, and elucidate the pathophysiological processes involved in disease mechanisms. Herein, we have summarized the latest research on the production scheme of organ-specific iPSC-derived organoids, the contribution of these organoids in the treatment of various organ-related diseases, in particular their contribution to COVID-19 treatment, and have discussed the unresolved challenges and shortcomings of these models.

Deriving Schwann cells from hPSCs enables disease modeling and drug discovery for diabetic peripheral neuropathy

Schwann cells (SCs) are the primary glia of the peripheral nervous system. SCs are involved in many debilitating disorders, including diabetic peripheral neuropathy (DPN). Here, we present a strategy for deriving SCs from human pluripotent stem cells (hPSCs) that enables comprehensive studies of SC development, physiology, and disease. hPSC-derived SCs recapitulate the molecular features of primary SCs and are capable of in vitro and in vivo myelination. We established a model of DPN that revealed the selective vulnerability of SCs to high glucose. We performed a high-throughput screen and found that an antidepressant drug, bupropion, counteracts glucotoxicity in SCs. Treatment of hyperglycemic mice with bupropion prevents their sensory dysfunction, SC death, and myelin damage. Further, our retrospective analysis of health records revealed that bupropion treatment is associated with a lower incidence of neuropathy among diabetic patients. These results highlight the power of this approach for identifying therapeutic candidates for DPN.

Proteostasis and lysosomal quality control deficits in Alzheimer's disease neurons

The role of proteostasis and organelle homeostasis dysfunction in human aging and Alzheimer's disease (AD) remains unclear. Analyzing proteome-wide changes in human donor fibroblasts and their corresponding transdifferentiated neurons (tNeurons), we find aging and AD synergistically impair multiple proteostasis pathways, most notably lysosomal quality control (LQC). In particular, we show that ESCRT-mediated lysosomal repair defects are associated with both sporadic and PSEN1 familial AD. Aging- and AD-linked defects are detected in fibroblasts but highly exacerbated in tNeurons, leading to enhanced neuronal vulnerability, unrepaired lysosomal damage, inflammatory factor secretion and cytotoxicity. Surprisingly, tNeurons from aged and AD donors spontaneously develop amyloid-β inclusions co-localizing with LQC markers, LAMP1/2-positive lysosomes and proteostasis factors; we observe similar inclusions in brain tissue from AD patients and APP-transgenic mice. Importantly, compounds enhancing lysosomal function broadly ameliorate these AD-associated pathologies. Our findings establish cell-autonomous LQC dysfunction in neurons as a central vulnerability in aging and AD pathogenesis.

Progress and challenges in directing the differentiation of human iPSCs into spinal motor neurons

Motor neuron (MN) diseases, including amyotrophic lateral sclerosis, progressive bulbar palsy, primary lateral sclerosis and spinal muscular atrophy, cause progressive paralysis and, in many cases, death. A better understanding of the molecular mechanisms of pathogenesis is urgently needed to identify more effective therapies. However, studying MNs has been extremely difficult because they are inaccessible in the spinal cord. Induced pluripotent stem cells (iPSCs) can generate a theoretically limitless number of MNs from a specific patient, making them powerful tools for studying MN diseases. However, to reach their potential, iPSCs need to be directed to efficiently differentiate into functional MNs. Here, we review the reported differentiation protocols for spinal MNs, including induction with small molecules, expression of lineage-specific transcription factors, 2-dimensional and 3-dimensional cultures, as well as the implementation of microfluidics devices and co-cultures with other cell types, including skeletal muscle. We will summarize the advantages and disadvantages of each strategy. In addition, we will provide insights into how to address some of the remaining challenges, including reproducibly obtaining mature and aged MNs.

A genetics-first approach to understanding autism and schizophrenia spectrum disorders: the 22q11.2 deletion syndrome

Recently, increasing numbers of rare pathogenic genetic variants have been identified that are associated with variably elevated risks of a range of neurodevelopmental outcomes, notably including Autism Spectrum Disorders (ASD), Schizophrenia Spectrum Disorders (SSD), and Intellectual Disability (ID). This review is organized along three main questions: First, how can we unify the exclusively descriptive basis of our current psychiatric diagnostic classification system with the recognition of an identifiable, highly penetrant genetic risk factor in an increasing proportion of patients with ASD or SSD? Second, what can be learned from studies of individuals with ASD or SSD who share a common genetic basis? And third, what accounts for the observed variable penetrance and pleiotropy of neuropsychiatric phenotypes in individuals with the same pathogenic variant? In this review, we focus on findings of clinical and preclinical studies of the 22q11.2 deletion syndrome (22q11DS). This particular variant is not only one of the most common among the increasing list of known rare pathogenic variants, but also one that benefits from a relatively long research history. Consequently, 22q11DS is an appealing model as it allows us to: (1) elucidate specific genotype-phenotype associations, (2) prospectively study behaviorally defined classifications, such as ASD or SSD, in the context of a known, well-characterized genetic basis, and (3) elucidate mechanisms underpinning variable penetrance and pleiotropy, phenomena with far-reaching ramifications for research and clinical practice. We discuss how findings from animal and in vitro studies relate to observations in human studies and can help elucidate factors, including genetic, environmental, and stochastic, that impact the expression of neuropsychiatric phenotypes in 22q11DS, and how this may inform mechanisms underlying neurodevelopmental expression in the general population. We conclude with research priorities for the field, which may pave the way for novel therapeutics.

Current status and future directions of clinical applications using iPS cells-focus on Japan

Regenerative medicine using iPS cell technologies has progressed remarkably in recent years. In this review, we summarize these technologies and their clinical application. First, we discuss progress in the establishment of iPS cells, including the HLA-homo iPS cell stock project in Japan and the advancement of low antigenic iPS cells using genome-editing technology. Then, we describe iPS cell-based therapies in or approaching clinical application, including those for ophthalmological, neurological, cardiac, hematological, cartilage, and metabolic diseases. Next, we introduce disease models generated from patient iPS cells and successfully used to identify therapeutic agents for intractable diseases. Clinical medicine using iPS cells has advanced safely and effectively by making full use of current scientific standards, but tests on cell safety need to be further developed and validated. The next decades will see the further spread of iPS cell technology-based regenerative medicine.

Establishment and characterization of human pluripotent stem cells-derived brain organoids to model cerebellar diseases

The establishment of robust human brain organoids to model cerebellar diseases is essential to study new therapeutic strategies for cerebellum-associated disorders. Machado-Joseph disease (MJD) is a cerebellar hereditary neurodegenerative disease, without therapeutic options able to prevent the disease progression. In the present work, control and MJD induced-pluripotent stem cells were used to establish human brain organoids. These organoids were characterized regarding brain development, cell type composition, and MJD-associated neuropathology markers, to evaluate their value for cerebellar diseases modeling. Our data indicate that the organoids recapitulated, to some extent, aspects of brain development, such as astroglia emerging after neurons and the presence of ventricular-like zones surrounded by glia and neurons that are found only in primate brains. Moreover, the brain organoids presented markers of neural progenitors proliferation, neuronal differentiation, inhibitory and excitatory synapses, and firing neurons. The established brain organoids also exhibited markers of cerebellar neurons progenitors and mature cerebellar neurons. Finally, MJD brain organoids showed higher ventricular-like zone numbers, an indication of lower maturation, and an increased number of ataxin-3-positive aggregates, compared with control organoids. Altogether, our data indicate that the established organoids recapitulate important characteristics of human brain development and exhibit cerebellar features, constituting a resourceful tool for testing therapeutic approaches for cerebellar diseases.

Enhancing iPSC-CM Maturation Using a Matrigel-Coated Micropatterned PDMS Substrate

Cardiac myocytes isolated from adult heart tissue have a rod-like shape with highly organized intracellular structures. Cardiomyocytes derived from human pluripotent stem cells (iPSC-CMs), on the other hand, exhibit disorganized structure and contractile mechanics, reflecting their pronounced immaturity. These characteristics hamper research using iPSC-CMs. The protocol described here enhances iPSC-CM maturity and function by controlling the cellular shape and environment of the cultured cells. Microstructured silicone membranes function as a cell culture substrate that promotes cellular alignment. iPSC-CMs cultured on micropatterned membranes display an in-vivo-like rod-shaped morphology. This physiological cellular morphology along with the soft biocompatible silicone substrate, which has similar stiffness to the native cardiac matrix, promotes maturation of contractile function, calcium handling, and electrophysiology. Incorporating this technique for enhanced iPSC-CM maturation will help bridge the gap between animal models and clinical care, and ultimately improve personalized medicine for cardiovascular diseases. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Cardiomyocyte differentiation of iPSCs Basic Protocol 2: Purification of differentiated iPSC-CMs using MACS negative selection Basic Protocol 3: Micropatterning on PDMS.

Generation and Application of Directly Reprogrammed Endothelial Cells

Cell-based therapy has emerged as a promising option for treating advanced ischemic cardiovascular disease by inducing vascular regeneration. However, clinical trials with adult cells turned out disappointing in general. As a newer approach, direct reprogramming has emerged to efficiently generate endothelial cells (ECs), which can promote neovascularization and vascular regeneration. This review provides recent updates on the direct endothelial reprogramming. In general, directly reprogrammed ECs can be generated by two approaches: one by transitioning through a plastic intermediate state and the other in a one-step transition without any intermediate states toward pluripotency. Moreover, the methods to deliver reprogramming factors and chemicals for the fate conversion are highlighted. Next, the therapeutic effects of the directly reprogrammed ECs on animal models are reviewed in detail. Other applications using directly reprogrammed ECs, such as tissue engineering and disease modeling, are also discussed. Lastly, the remaining questions and foremost challenges are addressed.

Human Brain Organoid: A Versatile Tool for Modeling Neurodegeneration Diseases and for Drug Screening

Clinical trials serve as the fundamental prerequisite for clinical therapy of human disease, which is primarily based on biomedical studies in animal models. Undoubtedly, animal models have made a significant contribution to gaining insight into the developmental and pathophysiological understanding of human diseases. However, none of the existing animal models could efficiently simulate the development of human organs and systems due to a lack of spatial information; the discrepancy in genetic, anatomic, and physiological basis between animals and humans limits detailed investigation. Therefore, the translational efficiency of the research outcomes in clinical applications was significantly weakened, especially for some complex, chronic, and intractable diseases. For example, the clinical trials for human fragile X syndrome (FXS) solely based on animal models have failed such as mGluR5 antagonists. To mimic the development of human organs more faithfully and efficiently translate in vitro biomedical studies to clinical trials, extensive attention to organoids derived from stem cells contributes to a deeper understanding of this research. The organoids are a miniaturized version of an organ generated in vitro, partially recapitulating key features of human organ development. As such, the organoids open a novel avenue for in vitro models of human disease, advantageous over the existing animal models. The invention of organoids has brought an innovative breakthrough in regeneration medicine. The organoid-derived human tissues or organs could potentially function as invaluable platforms for biomedical studies, pathological investigation of human diseases, and drug screening. Importantly, the study of regeneration medicine and the development of therapeutic strategies for human diseases could be conducted in a dish, facilitating in vitro analysis and experimentation. Thus far, the pilot breakthrough has been made in the generation of numerous types of organoids representing different human organs. Most of these human organoids have been employed for in vitro biomedical study and drug screening. However, the efficiency and quality of the organoids in recapitulating the development of human organs have been hindered by engineering and conceptual challenges. The efficiency and quality of the organoids are essential for downstream applications. In this article, we highlight the application in the modeling of human neurodegenerative diseases (NDDs) such as FXS, Alzheimer's disease (AD), Parkinson's disease (PD), and autistic spectrum disorders (ASD), and organoid-based drug screening. Additionally, challenges and weaknesses especially for limits of the brain organoid models in modeling late onset NDDs such as AD and PD., and future perspectives regarding human brain organoids are addressed.

Human-Induced Pluripotent Stem Cell Technology: Toward the Future of Personalized Psychiatry

The polygenic and multifactorial nature of many psychiatric disorders has hampered implementation of the personalized medicine approach in clinical practice. However, induced pluripotent stem cell (iPSC) technology has emerged as an innovative tool for patient-specific disease modeling to expand the pathophysiology knowledge and treatment perspectives in the last decade. Current technologies enable adult human somatic cell reprogramming into iPSCs to generate neural cells and direct neural cell conversion to model organisms that exhibit phenotypes close to human diseases, thereby effectively representing relevant aspects of neuropsychiatric disorders. In this regard, iPSCs reflect patient pathophysiology and pharmacological responsiveness, particularly when cultured under conditions that emulate spatial tissue organization in brain organoids. Recently, the application of iPSCs has been frequently associated with gene editing that targets the disease-causing gene to deepen the illness pathophysiology and to conduct drug screening. Moreover, gene editing has provided a unique opportunity to repair the putative causative genetic lesions in patient-derived cells. Here, we review the use of iPSC technology to model and potentially treat neuropsychiatric disorders by illustrating the key studies on a series of mental disorders, including schizophrenia, major depressive disorder, bipolar disorder, and autism spectrum disorder. Future perspectives will involve the development of organ-on-a-chip platforms that control the microenvironmental conditions so as to reflect individual pathophysiological by adjusting physiochemical parameters according to personal health data. This strategy could open new ways by which to build a disease model that considers individual variability and tailors personalized treatments.

Methods for culturing adult CNS neurons reveal a CNS conditioning effect

Neuronal cultures provide a basis for reductionist insights that rely on molecular and pharmacological manipulation. However, the inability to culture mature adult CNS neurons limits our understanding of adult neuronal physiology. Here, we report methods for culturing adult central nervous system neurons in large numbers and across multiple brain regions for extended time periods. Primary adult neuronal cultures develop polarity; they establish segregated dendritic and axonal compartments, maintain resting membrane potentials, exhibit spontaneous and evoked electrical activity, and form neural networks. Cultured adult neurons isolated from different brain regions such as the hippocampus, cortex, brainstem, and cerebellum exhibit distinct cell morphologies, growth patterns, and spontaneous firing characteristics reflective of their regions of origin. Using adult motor cortex cultures, we identify a CNS "conditioning" effect after spinal cord injury. The ability to culture adult neurons offers a valuable tool for studying basic and therapeutic science of the brain.

Reprogramming neurons for regeneration: The fountain of youth

Neurons in the central nervous system (CNS) are terminally differentiated cells that gradually lose their ability to support regeneration during maturation due to changes in transcriptomic and chromatin landscape. Similar transcriptomic changes also occur during development when stem cells differentiate into different types of somatic cells. Importantly, differentiated cells can be reprogrammed back to induced pluripotent stems cells (iPSCs) via global epigenetic remodeling by combined overexpression of pluripotent reprogramming factors, including Oct4, Sox2, Klf4, c-Myc, Nanog, and/or Lin28. Moreover, recent findings showed that many proneural transcription factors were able to convert non-neural somatic cells into neurons bypassing the pluripotent stage via direct reprogramming. Interestingly, many of these factors have recently been identified as key regulators of CNS neural regeneration. Recent studies indicated that these factors could rejuvenate mature CNS neurons back to a younger state through cellular state reprogramming, thus favoring regeneration. Here we will review some recent findings regarding the roles of genetic cellular state reprogramming in regulation of neural regeneration and explore the potential underlying molecular mechanisms. Moreover, by using newly emerging techniques, such as multiomics sequencing with big data analysis and Crispr-based gene editing, we will discuss future research directions focusing on better revealing cellular state reprogramming-induced remodeling of chromatin landscape and potential translational application.

Mapping cis-regulatory elements in human neurons links psychiatric disease heritability and activity-regulated transcriptional programs

Genome-wide association studies (GWASs) have identified hundreds of loci associated with psychiatric diseases, yet there is a lack of understanding of disease pathophysiology. Common risk variants can shed light on the underlying molecular mechanisms; however, identifying causal variants remains challenging. We map cis-regulatory elements in human neurons derived from pluripotent stem cells. This system allows us to determine enhancers that activate the transcription of neuronal activity-regulated gene programs, which are thought to be critical for synaptic plasticity and are not possible to identify from postmortem tissues. Using the activity-by-contact model, we create variant-to-gene maps to interpret the function of GWAS variants. Our work nominates a subset of variants to elucidate the molecular mechanisms involving GWAS-significant loci. It also highlights that in vitro human cellular models are a powerful platform for identifying and mechanistic studies of human trait-associated genetic variants in cell states that are inaccessible from other types of human samples.

Human stem cell models of neurodegeneration: From basic science of amyotrophic lateral sclerosis to clinical translation

Neurodegenerative diseases are characterized by progressive cell loss leading to disruption of the structure and function of the central nervous system. Amyotrophic lateral sclerosis (ALS) was among the first of these disorders modeled in patient-specific iPSCs, and recent findings have translated into some of the earliest iPSC-inspired clinical trials. Focusing on ALS as an example, we evaluate the status of modeling neurodegenerative diseases using iPSCs, including methods for deriving and using disease-relevant neuronal and glial lineages. We further highlight the remaining challenges in exploiting the full potential of iPSC technology for understanding and potentially treating neurodegenerative diseases such as ALS.

Detection of Soluble and Insoluble Protein Species in Patient-Derived iPSCs

Protein aggregation is one of the hallmarks of many neurodegenerative diseases. While protein aggregation is a heavily studied aspect of neurodegenerative disease, methods of detection vary from one model system to another. Induced pluripotent stem cells (iPSCs) present an opportunity to model disease using patient-specific cells. However, iPSC-derived neurons are fetal-like in maturity, making it a challenge to detect key features such as protein aggregation that are often exacerbated with age. Nevertheless, we have previously found abnormal soluble and insoluble protein burden in motor neurons generated from amyotrophic lateral sclerosis (ALS) iPSCs, though protein aggregation has not been readily detected in iPSC-derived neurons from other neurodegenerative diseases. Therefore, here we present an ultracentrifugation method that detects insoluble protein species in various models of neurodegenerative disease, including Huntington's disease, Alzheimer's disease, and ALS. This method is able to detect soluble, insoluble, and SDS-resistant species in iPSC-derived neurons and is designed to be flexible for optimal detection of various aggregation-prone proteins.

Directly Reprogrammed Human Neurons to Understand Age-Related Energy Metabolism Impairment and Mitochondrial Dysfunction in Healthy Aging and Neurodegeneration

Brain aging is characterized by several molecular and cellular changes grouped as the hallmarks or pillars of aging, including organelle dysfunction, metabolic and nutrition-sensor changes, stem cell attrition, and macromolecular damages. Separately and collectively, these features degrade the most critical neuronal function: transmission of information in the brain. It is widely accepted that aging is the leading risk factor contributing to the onset of the most prevalent pathological conditions that affect brain functions, such as Alzheimer's, Parkinson's, and Huntington's disease. One of the limitations in understanding the molecular mechanisms involved in those diseases is the lack of an appropriate cellular model that recapitulates the “aged” context in human neurons. The advent of the cellular reprogramming of somatic cells, i.e., dermal fibroblasts, to obtain directly induced neurons (iNs) and induced pluripotent stem cell- (iPSC-) derived neurons is technical sound advances that could open the avenues to understand better the contribution of aging toward neurodegeneration. In this review, we will summarize the commonalities and singularities of these two approaches for the study of brain aging, with an emphasis on the role of mitochondrial dysfunction and redox biology. We will address the evidence showing that iNs retain age-related features in contrast to iPSC-derived neurons that lose the aging signatures during the reprogramming to pluripotency, rendering iNs a powerful strategy to deepen our knowledge of the processes driving normal cellular function decline and neurodegeneration in a human adult model. We will finally discuss the potential utilization of these novel technologies to understand the differential contribution of genetic and epigenetic factors toward neuronal aging, to identify and develop new drugs and therapeutic strategies.

Human iPSC-Derived Neurons as A Platform for Deciphering the Mechanisms behind Brain Aging

With an increased life expectancy among humans, aging has recently emerged as a major focus in biomedical research. The lack of in vitro aging models-especially for neurological disorders, where access to human brain tissues is limited-has hampered the progress in studies on human brain aging and various age-associated neurodegenerative diseases at the cellular and molecular level. In this review, we provide an overview of age-related changes in the transcriptome, in signaling pathways, and in relation to epigenetic factors that occur in senescent neurons. Moreover, we explore the current cell models used to study neuronal aging in vitro, including immortalized cell lines, primary neuronal culture, neurons directly converted from fibroblasts (Fib-iNs), and iPSC-derived neurons (iPSC-iNs); we also discuss the advantages and limitations of these models. In addition, the key phenotypes associated with cellular senescence that have been observed by these models are compared. Finally, we focus on the potential of combining human iPSC-iNs with genome editing technology in order to further our understanding of brain aging and neurodegenerative diseases, and discuss the future directions and challenges in the field.

Sirt1 promotes tissue regeneration in zebrafish through regulating the mitochondrial unfolded protein response

The mitochondrial unfolded protein response (UPRmt) is an organellar stress signaling pathway that functions to detect and restore disruption of mitochondrial proteostasis. The UPRmt is involved in a wide range of physiological and disease conditions, including aging, stem cell maintenance, innate immunity, neurodegeneration, and cancer. Here we report that the UPRmt is integral to zebrafish fin regeneration. Taking advantage of a novel zebrafish UPRmt reporter, we observed that UPRmt activation occurs in regenerating fin tissue shortly after injury. Through chemical and genetic approaches, we discovered that the Sirt1-UPRmt pathway, best known for its role in promoting lifespan extension, is crucial for fin regeneration. The metabolism of NAD+ is an important contributor to Sirt1 activity in this context. We propose that Sirt1 activation induces mitochondrial biogenesis in injured fin tissue, which leads to UPRmt activation and promotes tissue regeneration.

The Parkinson's-disease-associated mutation LRRK2-G2019S alters dopaminergic differentiation dynamics via NR2F1

Increasing evidence suggests that neurodevelopmental alterations might contribute to increase the susceptibility to develop neurodegenerative diseases. We investigate the occurrence of developmental abnormalities in dopaminergic neurons in a model of Parkinson's disease (PD). We monitor the differentiation of human patient-specific neuroepithelial stem cells (NESCs) into dopaminergic neurons. Using high-throughput image analyses and single-cell RNA sequencing, we observe that the PD-associated LRRK2-G2019S mutation alters the initial phase of neuronal differentiation by accelerating cell-cycle exit with a concomitant increase in cell death. We identify the NESC-specific core regulatory circuit and a molecular mechanism underlying the observed phenotypes. The expression of NR2F1, a key transcription factor involved in neurogenesis, decreases in LRRK2-G2019S NESCs, neurons, and midbrain organoids compared to controls. We also observe accelerated dopaminergic differentiation in vivo in NR2F1-deficient mouse embryos. This suggests a pathogenic mechanism involving the LRRK2-G2019S mutation, where the dynamics of dopaminergic differentiation are modified via NR2F1.

Induced Pluripotent Stem Cells in Psychiatry: An Overview and Critical Perspective

A key challenge in psychiatry research is the development of high-fidelity model systems that can be experimentally manipulated to explore and test pathophysiological mechanisms of illness. In this respect, the emerging capacity to derive neural cells and circuits from human induced pluripotent stem cells (iPSCs) has generated significant excitement. This review aims to provide a critical appraisal of the potential for iPSCs in illuminating pathophysiological mechanisms in the context of other available technical approaches. We discuss the selection of iPSC phenotypes relevant to psychiatry, the information that researchers can draw on to help guide these decisions, and how researchers choose between the use of 2-dimensional cultures and the use of more complex 3-dimensional model systems. We discuss the strengths and limitations of current models and the challenges and opportunities that they present. Finally, we discuss the potential of iPSC-based model systems for clarifying the mechanisms underlying genetic risk for psychiatry and the steps that will be needed to ensure that robust and reliable conclusions can be drawn. We argue that while iPSC-based models are ideally placed to study fundamental processes occurring within and between neural cells, they are often less well suited for case-control studies, given issues relating to statistical power and the challenges in identifying which cellular phenotypes are meaningful at the level of the whole individual. Our aim is to highlight the importance of considering the hypotheses of a given study to guide decisions about which, if any, iPSC-based system is most appropriate to address it.

Modeling Sporadic Alzheimer's Disease in Human Brain Organoids under Serum Exposure

Alzheimer's disease (AD) is a progressive neurodegenerative disease with no cure. Huge efforts have been made to develop anti-AD drugs in the past decades. However, all drug development programs for disease-modifying therapies have failed. Possible reasons for the high failure rate include incomplete understanding of complex pathophysiology of AD, especially sporadic AD (sAD), and species difference between humans and animal models used in preclinical studies. In this study, sAD is modeled using human induced pluripotent stem cell (hiPSC)-derived 3D brain organoids. Because the blood-brain barrier (BBB) leakage is a well-known risk factor for AD, brain organoids are exposed to human serum to mimic the serum exposure consequence of BBB breakdown in AD patient brains. The serum-exposed brain organoids are able to recapitulate AD-like pathologies, including increased amyloid beta (Aβ) aggregates and phosphorylated microtubule-associated tau protein (p-Tau) level, synaptic loss, and impaired neural network. Serum exposure increases Aβ and p-Tau levels through inducing beta-secretase 1 (BACE) and glycogen synthase kinase-3 alpha / beta (GSK3α/β) levels, respectively. In addition, single-cell transcriptomic analysis of brain organoids reveals that serum exposure reduced synaptic function in both neurons and astrocytes and induced immune response in astrocytes. The human brain organoid-based sAD model established in this study can provide a powerful platform for both mechanistic study and therapeutic development in the future.

The Cutting Edge of Disease Modeling: Synergy of Induced Pluripotent Stem Cell Technology and Genetically Encoded Biosensors

The development of cell models of human diseases based on induced pluripotent stem cells (iPSCs) and a cell therapy approach based on differentiated iPSC derivatives has provided a powerful stimulus in modern biomedical research development. Moreover, it led to the creation of personalized regenerative medicine. Due to this, in the last decade, the pathological mechanisms of many monogenic diseases at the cell level have been revealed, and clinical trials of various cell products derived from iPSCs have begun. However, it is necessary to reach a qualitatively new level of research with cell models of diseases based on iPSCs for more efficient searching and testing of drugs. Biosensor technology has a great application prospect together with iPSCs. Biosensors enable researchers to monitor ions, molecules, enzyme activities, and channel conformation in live cells and use them in live imaging and drug screening. These probes facilitate the measurement of steady-state concentrations or activity levels and the observation and quantification of in vivo flux and kinetics. Real-time monitoring of drug action in a specific cellular compartment, organ, or tissue type; the ability to screen at the single-cell resolution; and the elimination of the false-positive results caused by low drug bioavailability that is not detected by in vitro testing methods are a few of the benefits of using biosensors in drug screening. Here, we discuss the possibilities of using biosensor technology in combination with cell models based on human iPSCs and gene editing systems. Furthermore, we focus on the current achievements and problems of using these methods.

Studying SARS-CoV-2 infectivity and therapeutic responses with complex organoids

Clinical management of patients with severe complications of COVID-19 has been hindered by a lack of effective drugs and a failure to capture the extensive heterogeneity of the disease with conventional methods. Here we review the emerging roles of complex organoids in the study of SARS-CoV-2 infection, modelling of COVID-19 disease pathology and in drug, antibody and vaccine development. We discuss opportunities for COVID-19 research and remaining challenges in the application of organoids.

Phenotyping Neurodegeneration in Human iPSCs

Induced pluripotent stem cell (iPSC) technology holds promise for modeling neurodegenerative diseases. Traditional approaches for disease modeling using animal and cellular models require knowledge of disease mutations. However, many patients with neurodegenerative diseases do not have a known genetic cause. iPSCs offer a way to generate patient-specific models and study pathways of dysfunction in an in vitro setting in order to understand the causes and subtypes of neurodegeneration. Furthermore, iPSC-based models can be used to search for candidate therapeutics using high-throughput screening. Here we review how iPSC-based models are currently being used to further our understanding of neurodegenerative diseases, as well as discuss their challenges and future directions.

Making Sense of Patient-Derived iPSCs, Transdifferentiated Neurons, Olfactory Neuronal Cells, and Cerebral Organoids as Models for Psychiatric Disorders

The improvement of experimental models for disorders requires a constant approximation towards the dysregulated tissue. In psychiatry, where an impairment of neuronal structure and function is assumed to play a major role in disease mechanisms and symptom development, this approximation is an ongoing process implicating various fields. These include genetic, animal, and post-mortem studies. To test hypotheses generated through these studies, in vitro models using non-neuronal cells such as fibroblasts and lymphocytes have been developed. For brain network disorders, cells with neuronal signatures would, however, represent a more adequate tissue. Considering the limited accessibility of brain tissue, research has thus turned towards neurons generated from induced pluripotent stem cells as well as directly induced neurons, cerebral organoids, and olfactory neuroepithelium. Regarding the increasing importance and amount of research using these neuronal cells, this review aims to provide an overview of all these models to make sense of the current literature. The development of each model system and its use as a model for the various psychiatric disorder categories will be laid out. Also, advantages and limitations of each model will be discussed, including a reflection on implications and future perspectives.

Cell Reprogramming to Model Huntington's Disease: A Comprehensive Review

Huntington’s disease (HD) is a neurodegenerative disorder characterized by the progressive decline of motor, cognitive, and psychiatric functions. HD results from an autosomal dominant mutation that causes a trinucleotide CAG repeat expansion and the production of mutant Huntingtin protein (mHTT). This results in the initial selective and progressive loss of medium spiny neurons (MSNs) in the striatum before progressing to involve the whole brain. There are currently no effective treatments to prevent or delay the progression of HD as knowledge into the mechanisms driving the selective degeneration of MSNs has been hindered by a lack of access to live neurons from individuals with HD. The invention of cell reprogramming provides a revolutionary technique for the study, and potential treatment, of neurological conditions. Cell reprogramming technologies allow for the generation of live disease-affected neurons from patients with neurological conditions, becoming a primary technique for modelling these conditions in vitro. The ability to generate HD-affected neurons has widespread applications for investigating the pathogenesis of HD, the identification of new therapeutic targets, and for high-throughput drug screening. Cell reprogramming also offers a potential autologous source of cells for HD cell replacement therapy. This review provides a comprehensive analysis of the use of cell reprogramming to model HD and a discussion on recent advancements in cell reprogramming technologies that will benefit the HD field.

Photoperiod-induced alterations in biomarkers of oxidative stress and biochemical pathways in rats of different ages: Focus on individual physiological reactivity

Effects of photoperiodicity caused by both the age and individual physiological reactivity estimated by resistance to hypobaric hypoxia on the levels of lipid peroxidation, protein oxidation (aldehydic and ketonic derivatives), total antioxidant capacity, activities of antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase), and biochemical parameters of aerobic and anaerobic pathways in hepatic tissue depending on the blood melatonin level were studied. The study was carried out on 96 6- and 21-month-old male rats divided into hypoxia resistance groups (LR, low resistance, HR, high resistance). The analyses were conducted at four photoperiods: winter (January), spring (March), summer (July), and autumn (October). Our results indicate a significant effect of melatonin, i.e. over 80%, revealed by the complete statistical model of the studied biomarkers of oxidative stress and oxygen-dependent parameters of metabolism. The effects of melatonin vary with age and between photoperiods, which in turn was determined by individual physiological reactivity. In terms of the photoperiods, the melatonin content in the group of the adult animals with low resistance to hypoxia decreased from winter to summer. In a group of old animals in comparison with adults, the melatonin content in all the studied photoperiods was much lower as well, regardless of their hypoxia resistance. In the group of old animals with low resistance to hypoxia, the melatonin content decreased throughout the photoperiods as follows: winter, autumn, summer, and spring. As can be concluded, spring is a critical period for old animals, particularly those with low hypoxia resistance. The important role of melatonin in these processes was also confirmed by our correlation analysis between oxidative stress biomarkers, energy-related metabolites, and antioxidant enzymes in the hepatic tissue of rats of different ages, with different resistance to hypoxia, and in different photoperiods. The melatonin concentration in the blood of highly resistant rats was higher than in those with low resistance to hypoxia. Melatonin determines the individual constitutional level of resistance to hypoxia and is responsible for individual enzymatic antioxidative responses, depending on the four photoperiods. Our studies have shown that melatonin levels are related to the redox characteristics of antioxidant defenses against lipid peroxidation and oxidative modification of proteins in old rats with low resistance to hypoxia, compared to a group of highly resistant adults. Finally, the melatonin-related mechanisms of antioxidative protection depend on metabolic processes in hepatic tissue and exhibit photoperiodical variability in adult and old rats.

Rejuvenated Stem/Progenitor Cells for Cartilage Repair Using the Pluripotent Stem Cell Technology

It is widely accepted that chondral defects in articular cartilage of adult joints are never repaired spontaneously, which is considered to be one of the major causes of age-related degenerative joint disorders, such as osteoarthritis. Since mobilization of subchondral bone (marrow) cells and addition of chondrocytes or mesenchymal stromal cells into full-thickness defects show some degrees of repair, the lack of self-repair activity in adult articular cartilage can be attributed to lack of reparative cells in adult joints. In contrast, during a fetal or embryonic stage, joint articular cartilage has a scar-less repair activity, suggesting that embryonic joints may contain cells responsible for such activity, which can be chondrocytes, chondroprogenitors, or other cell types such as skeletal stem cells. In this respect, the tendency of pluripotent stem cells (PSCs) to give rise to cells of embryonic characteristics will provide opportunity, especially for humans, to obtain cells carrying similar cartilage self-repair activity. Making use of PSC-derived cells for cartilage repair is still in a basic or preclinical research phase. This review will provide brief overviews on how human PSCs have been used for cartilage repair studies.

Implications of genetic variation in the complement system in age-related macular degeneration

Age-related macular degeneration (AMD) is the main cause of vision loss among the elderly in the Western world. While AMD is a multifactorial disease, the complement system was identified as one of the main pathways contributing to disease risk. The strong link between the complement system and AMD was demonstrated by genetic associations, and by elevated complement activation in local eye tissue and in the systemic circulation of AMD patients. Several complement inhibitors have been and are being explored in clinical trials, but thus far with limited success, leaving the majority of AMD patients without treatment options to date. This indicates that there is still a gap of knowledge regarding the functional implications of the complement system in AMD pathogenesis and how to bring these towards clinical translation. Many different experimental set-ups and disease models have been used to study complement activation in vivo and in vitro, and recently emerging patient-derived induced pluripotent stem cells and genome-editing techniques open new opportunities to study AMD disease mechanisms and test new therapeutic strategies in the future. In this review we provide an extensive overview of methods employed to understand the molecular processes of complement activation in AMD pathogenesis. We discuss the findings, advantages and challenges of each approach and conclude with an outlook on how recent, exciting developments can fill in current knowledge gaps and can aid in the development of effective complement-targeting therapeutic strategies in AMD.

ApoE-Isoform-Dependent SARS-CoV-2 Neurotropism and Cellular Response

ApoE4, a strong genetic risk factor for Alzheimer disease, has been associated with increased risk for severe COVID-19. However, it is unclear whether ApoE4 alters COVID-19 susceptibility or severity, and the role of direct viral infection in brain cells remains obscure. We tested the neurotropism of SARS-CoV2 in human-induced pluripotent stem cell (hiPSC) models and observed low-grade infection of neurons and astrocytes that is boosted in neuron-astrocyte co-cultures and organoids. We then generated isogenic ApoE3/3 and ApoE4/4 hiPSCs and found an increased rate of SARS-CoV-2 infection in ApoE4/4 neurons and astrocytes. ApoE4 astrocytes exhibited enlarged size and elevated nuclear fragmentation upon SARS-CoV-2 infection. Finally, we show that remdesivir treatment inhibits SARS-CoV2 infection of hiPSC neurons and astrocytes. These findings suggest that ApoE4 may play a causal role in COVID-19 severity. Understanding how risk factors impact COVID-19 susceptibility and severity will help us understand the potential long-term effects in different patient populations.