Aging and reprogramming: a two-way street

Hydroxyurea Facilitates Manifestation of Disease Relevant Phenotypes in Patients-Derived IPSCs-Based Modeling of Late-Onset Parkinson's Disease

Induced pluripotent stem cells (iPSCs)-derived dopaminergic neurons might be reset back to the fetal state due to reprogramming. Thus, it is a compelling challenge to reliably and efficiently induce disease phenotypes of iPSCs-derived dopaminergic neurons to model late-onset Parkinson’s disease (PD). Here, we applied a small molecule, hydroxyurea (HU), to promote the manifestation of disease relevant phenotypes in iPSCs-based modeling of PD. We established two iPS cell lines derived from two sporadic PD patients. Both patients-iPSCs-derived dopaminergic neurons did not display PD relevant phenotypes after 6 weeks culture. HU treatment remarkably induced ER stress on patients-iPSCs-derived dopaminergic neurons. Moreover, HU treatment significantly reduced neurite outgrowth, decreased the expression of p-AKT and its downstream targets (p-4EBP1 and p-ULK1), and increased the expression level of cleaved-Caspase 3 in patients-iPSCs-derived dopaminergic neurons. The findings of the present study suggest that HU administration could be a convenient and reliable approach to induce disease relevant phenotypes in PD-iPSCs-based models, facilitating to study disease mechanisms and test drug effects.

In silico clinical trials for anti-aging therapies

Therapeutic strategies targeting the hallmarks of aging can be broadly grouped into four categories, namely systemic (blood) factors, metabolic manipulation (diet regimens and dietary restriction mimetics), suppression of cellular senescence (senolytics), and cellular reprogramming, which likely have common characteristics and mechanisms of action. In evaluating the potential synergism of combining such strategies, however, we should consider the possibility of constraining trade-off phenotypes such as impairment in wound healing and immune response, tissue dysfunction and tumorigenesis. Moreover, we are rapidly learning that the benefit/risk ratio of aging-targeted interventions largely depends on intra- and inter-individual variations of susceptibility to the healthspan-, resilience-, and/or lifespan-promoting effects of the interventions. Here, we exemplify how computationally-generated proxies of the efficacy of a given lifespan/healthspan-promoting approach can predict the impact of baseline epigenetic heterogeneity on the positive outcomes of ketogenic diet and mTOR inhibition as single or combined anti-aging strategies. We therefore propose that stochastic biomathematical modeling and computational simulation platforms should be developed as in silico strategies to accelerate the performance of clinical trials targeting human aging, and to provide personalized approaches and robust biomarkers of healthy aging at the individual-to-population levels.

A systems biology approach towards understanding and treating non-neovascular age-related macular degeneration

Age-related macular degeneration (AMD) is the most common cause of blindness among the elderly in the developed world. While treatment is effective for the neovascular or “wet” form of AMD, no therapy is successful for the non-neovascular or “dry” form. Here we discuss the current knowledge on dry AMD pathobiology and propose future research directions that would expedite the development of new treatments. In our view, these should emphasize system biology approaches that integrate omic, pharmacological, and clinical data into mathematical models that can predict disease onset and progression, identify biomarkers, establish disease causing mechanisms, and monitor response to therapy.

No effective therapies exist for dry age-related macular degeneration. In this perspective, the authors propose that research should emphasize system biology approaches that integrate various ‘omics’ data into mathematical models to establish pathogenic mechanisms on which to design novel treatments, and identify biomarkers that predict disease progression and therapeutic response.

Donor-Dependent and Other Nondefined Factors Have Greater Influence on the Hepatic Phenotype Than the Starting Cell Type in Induced Pluripotent Stem Cell Derived Hepatocyte-Like Cells

Drug‐induced liver injury is the greatest cause of post‐marketing drug withdrawal; therefore, substantial resources are directed toward triaging potentially dangerous new compounds at all stages of drug development. One of the major factors preventing effective screening of new compounds is the lack of a predictive in vitro model of hepatotoxicity. Primary human hepatocytes offer a metabolically relevant model for which the molecular initiating events of hepatotoxicity can be examined; however, these cells vary greatly between donors and dedifferentiate rapidly in culture. Induced pluripotent stem cell (iPSC)‐derived hepatocyte‐like cells (HLCs) offer a reproducible, physiologically relevant and genotypically normal model cell; however, current differentiation protocols produce HLCs with a relatively immature phenotype. During the reprogramming of somatic cells, the epigenome undergoes dramatic changes; however, this “resetting” is a gradual process, resulting in an altered differentiation propensity, skewed toward the lineage of origin, particularly in early passage cultures. We, therefore, performed a comparison of human hepatocyte‐ and dermal fibroblast‐derived iPSCs, assessing the impact of epigenetic memory at all stages of HLC differentiation. These results provide the first isogenic assessment of the starting cell type in human iPSC‐derived HLCs. Despite a trend toward improvement in hepatic phenotype in albumin secretion and gene expression, few significant differences in hepatic differentiation capacity were found between hepatocyte and fibroblast‐derived iPSCs. We conclude that the donor and inter‐clonal differences have a greater influence on the hepatocyte phenotypic maturity than the starting cell type. Therefore, it is not necessary to use human hepatocytes for generating iPSC‐derived HLCs. Stem Cells Translational Medicine2017;6:1321–1331

Elixir of Life: Thwarting Aging With Regenerative Reprogramming

All living beings undergo systemic physiological decline after ontogeny, characterized as aging. Modern medicine has increased the life expectancy, yet this has created an aged society that has more predisposition to degenerative disorders. Therefore, novel interventions that aim to extend the healthspan in parallel to the life span are needed. Regeneration ability of living beings maintains their biological integrity and thus is the major leverage against aging. However, mammalian regeneration capacity is low and further declines during aging. Therefore, modalities that reinforce regeneration can antagonize aging. Recent advances in the field of regenerative medicine have shown that aging is not an irreversible process. Conversion of somatic cells to embryonic-like pluripotent cells demonstrated that the differentiated state and age of a cell is not fixed. Identification of the pluripotency-inducing factors subsequently ignited the idea that cellular features can be reprogrammed by defined factors that specify the desired outcome. The last decade consequently has witnessed a plethora of studies that modify cellular features including the hallmarks of aging in addition to cellular function and identity in a variety of cell types in vitro. Recently, some of these reprogramming strategies have been directly used in animal models in pursuit of rejuvenation and cell replacement. Here, we review these in vivo reprogramming efforts and discuss their potential use to extend the longevity by complementing or augmenting the regenerative capacity.

Applying hydrodynamic pressure to efficiently generate induced pluripotent stem cells via reprogramming of centenarian skin fibroblasts

Induced pluripotent stem cell (iPSC)-technology is an important platform in medicine and disease modeling. Physiological degeneration and disease onset are common occurrences in the aging population. iPSCs could offer regenerative medical options for age-related degeneration and disease in the elderly. However, reprogramming somatic cells from the elderly is inefficient when successful at all. Perhaps due to their low rates of replication in culture, traditional transduction and reprogramming approaches with centenarian fibroblasts met with little success. A simple and reproducible reprogramming process is reported here which enhances interactions of the cells with the viral vectors that leads to improved iPSC generation. The improved methods efficiently generates fully reprogrammed iPSC lines from 105-107 years old subjects in feeder-free conditions using an episomal, Sendai-Virus (SeV) reprogramming vector expressing four reprogramming factors. In conclusion, dermal fibroblasts from human subjects older than 100 years can be efficiently and reproducibly reprogrammed to fully pluripotent cells with minor modifications to the standard reprogramming procedures. Efficient generation of iPSCs from the elderly may provide a source of cells for the regeneration of tissues and organs with autologous cells as well as cellular models for the study of aging, longevity and age-related diseases.

New Insights into the Role of Epithelial⁻Mesenchymal Transition during Aging

Epithelial–mesenchymal transition (EMT) is a cellular process by which differentiated epithelial cells undergo a phenotypic conversion to a mesenchymal nature. The EMT has been increasingly recognized as an essential process for tissue fibrogenesis during disease and normal aging. Higher levels of EMT proteins in aged tissues support the involvement of EMT as a possible cause and/or consequence of the aging process. Here, we will highlight the existing understanding of EMT supporting the phenotypical alterations that occur during normal aging or pathogenesis, covering the impact of EMT deregulation in tissue homeostasis and stem cell function.

LncRNAs regulating stemness in aging

One of the most outstanding observations from next-generation sequencing approaches was that only 1.5% of our genes code for proteins. The biggest part is transcribed but give rise to different families of RNAs without coding potential. The functional relevance of these abundant transcripts remains far from elucidated. Among them are the long non-coding RNAs (lncRNAs), a relatively large and heterogeneous group of RNAs shown to be highly tissue-specific, indicating a prominent role in processes controlling cellular identity. In particular, lncRNAs have been linked to both stemness properties and detrimental pathways regulating the aging process, being novel players in the intricate network guiding tissue homeostasis. Here, we summarize the up-to-date information on the role of lncRNAs that affect stemness and hence impact upon aging, highlighting the likelihood that lncRNAs may represent an unexploited reservoir of potential therapeutic targets for reprogramming applications and aging-related diseases.

Epigenetic changes during aging and their reprogramming potential

The aging process results in significant epigenetic changes at all levels of chromatin and DNA organization. These include reduced global heterochromatin, nucleosome remodeling and loss, changes in histone marks, global DNA hypomethylation with CpG island hypermethylation, and the relocalization of chromatin modifying factors. Exactly how and why these changes occur is not fully understood, but evidence that these epigenetic changes affect longevity and may cause aging, is growing. Excitingly, new studies show that age-related epigenetic changes can be reversed with interventions such as cyclic expression of the Yamanaka reprogramming factors. This review presents a summary of epigenetic changes that occur in aging, highlights studies indicating that epigenetic changes may contribute to the aging process and outlines the current state of research into interventions to reprogram age-related epigenetic changes.

Human adult pluripotency: Facts and questions

Cellular reprogramming and induced pluripotent stem cell (IPSC) technology demonstrated the plasticity of adult cell fate, opening a new era of cellular modelling and introducing a versatile therapeutic tool for regenerative medicine. While IPSCs are already involved in clinical trials for various regenerative purposes, critical questions concerning their medium- and long-term genetic and epigenetic stability still need to be answered. Pluripotent stem cells have been described in the last decades in various mammalian and human tissues (such as bone marrow, blood and adipose tissue). We briefly describe the characteristics of human-derived adult stem cells displaying in vitro and/or in vivo pluripotency while highlighting that the common denominators of their isolation or occurrence within tissue are represented by extreme cellular stress. Spontaneous cellular reprogramming as a survival mechanism favoured by senescence and cellular scarcity could represent an adaptative mechanism. Reprogrammed cells could initiate tissue regeneration or tumour formation dependent on the microenvironment characteristics. Systems biology approaches and lineage tracing within living tissues can be used to clarify the origin of adult pluripotent stem cells and their significance for regeneration and disease.

Turning back time with emerging rejuvenation strategies

Ageing is associated with the functional decline of all tissues and a striking increase in many diseases. Although ageing has long been considered a one-way street, strategies to delay and potentially even reverse the ageing process have recently been developed. Here, we review four emerging rejuvenation strategies-systemic factors, metabolic manipulations, senescent cell ablation and cellular reprogramming-and discuss their mechanisms of action, cellular targets, potential trade-offs and application to human ageing.

Small-molecule induction of Aβ-42 peptide production in human cerebral organoids to model Alzheimer's disease associated phenotypes

Human mini-brains (MB) are cerebral organoids that recapitulate in part the complexity of the human brain in a unique three-dimensional in vitro model, yielding discrete brain regions reminiscent of the cerebral cortex. Specific proteins linked to neurodegenerative disorders are physiologically expressed in MBs, such as APP-derived amyloids (Aβ), whose physiological and pathological roles and interactions with other proteins are not well established in humans. Here, we demonstrate that neuroectodermal organoids can be used to study the Aβ accumulation implicated in Alzheimer’s disease (AD). To enhance the process of protein secretion and accumulation, we adopted a chemical strategy of induction to modulate post-translational pathways of APP using an Amyloid-β Forty-Two Inducer named Aftin-5. Secreted, soluble Aβ fragment concentrations were analyzed in MB-conditioned media. An increase in the Aβ₄₂ fragment secretion was observed as was an increased Aβ₄₂/Aβ₄₀ ratio after drug treatment, which is consistent with the pathological-like phenotypes described in vivo in transgenic animal models and in vitro in induced pluripotent stem cell-derived neural cultures obtained from AD patients. Notably in this context we observe time-dependent Aβ accumulation, which differs from protein accumulation occurring after treatment. We show that mini-brains obtained from a non-AD control cell line are responsive to chemical compound induction, producing a shift of physiological Aβ concentrations, suggesting that this model can be used to identify environmental agents that may initiate the cascade of events ultimately leading to sporadic AD. Increases in both Aβ oligomers and their target, the cellular prion protein (PrP^C), support the possibility of using MBs to further understand the pathophysiological role that underlies their interaction in a human model. Finally, the potential application of MBs for modeling age-associated phenotypes and the study of neurological disorders is confirmed.

Epigenetic Enzymes, Age, and Ancestry Regulate the Efficiency of Human iPSC Reprogramming

Epigenetic enzymes regulate higher-order chromatin architecture and cell-type specific gene expression. The ATPase BRG1 and the SWI/SNF chromatin remodeling complex are epigenetic enzymes that regulate chromatin accessibility during steady and transitional cell states. Experiments in mice show that the loss of BRG1 inhibits cellular reprogramming, while studies using human cells demonstrate that the overexpression of BRG1 enhances reprogramming. We hypothesized that the variation of SWI/SNF subunit expression in the human population would contribute to variability in the efficiency of induced pluripotent stem cells (iPSC) reprogramming. To examine the impact of an individual's sex, ancestry, and age on iPSC reprogramming, we created a novel sex and ancestry balanced cohort of 240 iPSC lines derived from human dermal fibroblasts (DF) from 80 heathy donors. We methodically assessed the reprogramming efficiency of each DF line and then quantified the individual and demographic-specific variations in SWI/SNF chromatin remodeling proteins and mRNA expression. We identified BRG1, BAF155, and BAF60a expression as strongly correlating with iPSC reprogramming efficiency. Additionally, we discovered that high efficiency iPSC reprograming is negatively correlated with donor age, positively correlated with African American descent, and uncorrelated with donor sex. These results show the variations in chromatin remodeling protein expression have a strong impact on iPSC reprogramming. Additionally, our cohort is unique in its large size, diversity, and focus on healthy donors. Consequently, this cohort can be a vital tool for researchers seeking to validate observational results from human population studies and perform detailed mechanistic studies in a controlled cell culture environment. Stem Cells 2018;36:1697-1708.

Derivation of induced pluripotent stem cells in Japanese macaque (Macaca fuscata)

Non-human primates are our closest relatives and are of special interest for ecological, evolutionary and biomedical research. The Japanese macaque (Macaca fuscata) has contributed to the progress of primatology and neurosciences over 60 years. Despite this importance, the molecular and cellular basis of the Japanese macaque remains unexplored since useful cellular tools are lacking. Here we generated induced pluripotent stem cells (iPSCs) from skin fibroblasts of the Japanese macaque with Sendai virus or plasmid vectors. The Japanese macaque iPSCs (jm-iPSCs) were established under feeder-free culture conditions, but feeder cells turned out to be essential for their maintenance. The jm-iPSCs formed human iPSC-like flat colonies which were positive for pluripotent antigens including alkaline phosphatase, SSEA4, and TRA-1-81. They also expressed endogenous OCT3/4, SOX2, L-MYC, and KLF4 and other pluripotent marker genes. The potential to differentiate into all three germ layers and neural stem cells was confirmed by embryoid body and neurosphere formation, respectively. The jm-iPSCs will provide a robust in vitro tool for investigating the underlying mechanisms of development and physiology studies with the Japanese macaque.

Clinical Trials in a Dish: A Perspective on the Coming Revolution in Drug Development

The pharmaceutical industry is facing unprecedented challenges as the cost of developing new drugs has reached unsustainable levels, fueled in large parts by a high attrition rate in clinical development. Strategies to bridge studies between preclinical testing and clinical trials are needed to reduce the knowledge gap and allow earlier decisions to be made on the continuation or discontinuation of further development of drugs. The discovery and development of human induced pluripotent stem cells (hiPSCs) have opened up new avenues that support the concept of screening for cell-based safety and toxicity at the level of a population. This approach, termed “Clinical Trials in a Dish” (CTiD), allows testing medical therapies for safety or efficacy on cells collected from a representative sample of human patients, before moving into actual clinical trials. It can be applied to the development of drugs for specific populations, and it allows predicting not only the magnitude of effects but also the incidence of patients in a population who will benefit or be harmed by these drugs. This, in turn, can lead to the selection of safer drugs to move into clinical development, resulting in a reduction in attrition. The current article offers a perspective of this new model for “humanized” preclinical drug development.

Reduction of Fibrosis and Scar Formation by Partial Reprogramming In Vivo

Transient expression of the transcription factors OCT4, SOX2, KLF4, and C-MYC (OSKM) to induce partial reprogramming while avoiding the pluripotent state and teratoma formation has recently been discussed as a strategy for regenerating damaged tissues in vivo, whereby the impact of partial reprogramming on tissue repair remains to be elucidated. Here, we activated OSKM transcription factors in cutaneous wounds of OSKM-inducible transgenic mice and found that induction of OSKM factors in excisional wounds caused a diminished fibroblast transdifferentiation to myofibroblasts and wound contraction. Gene expression analyses showed downregulation of the profibrotic marker genes transforming growth factor beta 1, Collagen I, and vascular endothelial growth factor. Consequently, histological analyses demonstrated that OSKM induction in incisional wounds resulted in reduced scar tissue formation. These data provide proof of concept that OSKM-mediated partial reprogramming in situ can diminish fibrosis and improve tissue healing with less scar formation without the risk of tumor formation. This new insight into the effects of partial reprogramming in vivo may be relevant for developing reprogramming-based regenerative therapies for tissue injury and fibrotic diseases. Stem Cells 2018;36:1216-1225.

Implications of Cellular Aging in Cardiac Reprogramming

Aging is characterized by a chronic functional decline of organ systems which leads to tissue dysfunction over time, representing a risk factor for diseases development, including cardiovascular. The aging process occurring in the cardiovascular system involves heart and vessels at molecular and cellular level, with subsequent structural modifications and functional impairment. Several modifications involved in the aging process can be ascribed to cellular senescence, a biological response that limits the proliferation of damaged cells. In physiological conditions, the mechanism of cellular senescence is involved in regulation of tissue homeostasis, remodeling, and repair. However, in some conditions senescence-driven tissue repair may fail, leading to the tissue accumulation of senescent cells which in turn may contribute to tumor promotion, aging, and age-related diseases. Cellular reprogramming processes can reverse several age-associated cell features, such as telomere length, DNA methylation, histone modifications and cell-cycle arrest. As such, induced Pluripotent Stem Cells (iPSCs) can provide models of progeroid and physiologically aged cells to gain insight into the pathogenesis of such conditions, to drive the development of new therapies for premature aging and to further explore the possibility of rejuvenating aged cells. An emerging picture is that the tissue remodeling role of cellular senescence could also be crucial for the outcomes of in vivo reprogramming processes. Experimental evidence has demonstrated that, on one hand, senescence represents a cell-autonomous barrier for a cell candidate to reprogramming, but, on the other hand, it may positively sustain the reprogramming capability of surrounding cells to generate fully proficient tissues. This review fits into this conceptual framework by highlighting the most prominent concepts that characterize aging and reprogramming and discusses how the aging tissue might provide a favorable microenvironment for in vivo cardiac reprogramming.

Simultaneous reprogramming and gene editing of human fibroblasts

The utility of human induced pluripotent stem cells (iPSCs) is enhanced by an ability to precisely modify a chosen locus with minimal impact on the remaining genome. However, the derivation of gene-edited iPSCs typically involves multiple steps requiring lengthy culture periods and several clonal events. Here, we describe a one-step protocol for reliable generation of clonally derived gene-edited iPSC lines from human fibroblasts in the absence of drug selection or FACS enrichment. Using enhanced episomal-based reprogramming and CRISPR/Cas9 systems, gene-edited and passage-matched unmodified iPSC lines are obtained following a single electroporation of human fibroblasts. To minimize unwanted mutations within the target locus, we use a Cas9 variant that is associated with decreased nonhomologous end-joining (NHEJ) activity. This protocol outlines in detail how this streamlined approach can be used for both monoallelic and biallelic introduction of specific base changes or transgene cassettes in a manner that is efficient, rapid (∼6-8 weeks), and cost-effective.

Recent Advances: Decoding Alzheimer's Disease With Stem Cells

Alzheimer’s disease (AD) is an irreversible neurodegenerative disorder that destroys cognitive functions. Recently, a number of high-profile clinical trials based on the amyloid cascade hypothesis have encountered disappointing results. The failure of these trials indicates the necessity for novel therapeutic strategies and disease models. In this review, we will describe how recent advances in stem cell technology have shed light on a novel treatment strategy and revolutionized the mechanistic investigation of AD pathogenesis. Current advances in promoting endogenous neurogenesis and transplanting exogenous stem cells from both bench research and clinical translation perspectives will be thoroughly summarized. In addition, reprogramming technology-based disease modeling, which has shown improved efficacy in recapitulating pathological features in human patients, will be discussed.

In Vivo Transient and Partial Cell Reprogramming to Pluripotency as a Therapeutic Tool for Neurodegenerative Diseases

In theory, human diseases in which a specific cell type degenerates, such as neurodegenerative diseases, can be therapeutically addressed by replacement of the lost cells. The classical strategy for cell replacement is exogenous cell transplantation, but now, cell replacement can also be achieved with in situ reprogramming. Indeed, many of these disorders are age-dependent, and "rejuvenating" strategies based on cell epigenetic modifications are a possible approach to counteract disease progression. In this context, transient and/or partial reprogramming of adult somatic cells towards pluripotency can be a promising tool for neuroregeneration. Temporary and controlled in vivo overexpression of Yamanaka reprogramming factors (Oct3/4, Sox2, Klf4, and c-Myc (OSKM)) has been proven feasible in different experimental settings and could be employed to facilitate in situ tissue regeneration; this regeneration can be accomplished either by producing novel stem/precursor cells, without the challenges posed by exogenous cell transplantation, or by changing the epigenetic adult cell signature to the signature of a younger cell. The risk of this procedure resides in the possible lack of perfect control of the process, carrying a potential oncogenic or unexpected cell phenotype hazard. Recent studies have suggested that these limits can be overcome by a tightly controlled cyclic regimen of short-term OSKM expression in vivo that prevents full reprogramming to the pluripotent state and avoids both tumorigenesis and the presence of unwanted undifferentiated cells. On the other hand, this strategy can enhance tissue regeneration for therapeutic purposes in aging-related neurological diseases as well. These data could open the path to further research on the therapeutic potential of in vivo reprogramming in regenerative medicine.

Silencing of the lncRNA Zeb2-NAT facilitates reprogramming of aged fibroblasts and safeguards stem cell pluripotency

Aging imposes a barrier to somatic cell reprogramming through poorly understood mechanisms. Here, we report that fibroblasts from old mice express higher levels of Zeb2, a transcription factor that activates epithelial-to-mesenchymal transition. Synthesis of Zeb2 protein is controlled by a natural antisense transcript named Zeb2-NAT. We show that transfection of adult fibroblasts with specific LNA Gapmers induces a robust downregulation of Zeb2-NAT transcripts and Zeb2 protein and enhances the reprogramming of old fibroblasts into pluripotent cells. We further demonstrate that Zeb2-NAT expression is precociously activated by differentiation stimuli in embryonic stem (ES) cells. By knocking down Zeb2-NAT, we were able to maintain ES cells challenged with commitment signals in the ground state of pluripotency. In conclusion, our study identifies a long noncoding RNA that is overlapping and antisense to the Zeb2 locus as a target for rejuvenation strategies.

The efficiency of somatic cell reprogramming is lowered by ageing. Here the authors show that the transcription factor Zeb2 and its long non-coding RNA Zeb2-NAT are expressed at high levels in older fibroblasts and their inhibition increases reprogramming efficiency.

Generating Late-Onset Human iPSC-Based Disease Models by Inducing Neuronal Age-Related Phenotypes through Telomerase Manipulation

Modeling late-onset disorders such as Parkinson's disease (PD) using iPSC technology remains a challenge, as current differentiation protocols yield cells with the properties of fetal-stage cells. Here, we tested whether it is possible to accelerate aging in vitro to trigger late-onset disease phenotypes in an iPSC model of PD. In order to manipulate a factor that is involved in natural aging as well as in premature aging syndromes, we used telomere shortening as an age-inducing tool. We show that shortened telomeres result in age-associated as well as potentially disease-associated phenotypes in human pluripotent stem cell (hPSC)-derived midbrain dopamine (mDA) neurons. Our approach provides proof of concept for the further validation of telomere shortening as an induced-aging tool for late-onset-disease modeling.

The Potential of iPSCs for the Treatment of Premature Aging Disorders

Premature aging disorders including Hutchinson-Gilford progeria syndrome (HGPS) and Werner syndrome, are a group of rare monogenic diseases leading to reduced lifespan of the patients. Importantly, these disorders mimic several features of physiological aging. Despite the interest on the study of these diseases, the underlying biological mechanisms remain unknown and no treatment is available. Recent studies on HGPS (due to mutations of the LMNA gene encoding for the nucleoskeletal proteins lamin A/C) have reported disruptions in cellular and molecular mechanisms modulating genomic stability and stem cell populations, thus giving the nuclear lamina a relevant function in nuclear organization, epigenetic regulation and in the maintenance of the stem cell pool. In this context, modeling premature aging with induced pluripotent stem cells (iPSCs) offers the possibility to study these disorders during self-renewal and differentiation into relevant cell types. iPSCs generated by cellular reprogramming from adult somatic cells allows researchers to understand pathophysiological mechanisms and enables the performance of drug screenings. Moreover, the recent development of precision genome editing offers the possibility to study the complex mechanisms underlying senescence and the possibility to correct disease phenotypes, paving the way for future therapeutic interventions.

Health relevance of the modification of low grade inflammation in ageing (inflammageing) and the role of nutrition

Ageing of the global population has become a public health concern with an important socio-economic dimension. Ageing is characterized by an increase in the concentration of inflammatory markers in the bloodstream, a phenomenon that has been termed "inflammageing". The inflammatory response is beneficial as an acute, transient reaction to harmful conditions, facilitating the defense, repair, turnover and adaptation of many tissues. However, chronic and low grade inflammation is likely to be detrimental for many tissues and for normal functions. We provide an overview of low grade inflammation (LGI) and determine the potential drivers and the effects of the "inflamed" phenotype observed in the elderly. We discuss the role of gut microbiota and immune system crosstalk and the gut-brain axis. Then, we focus on major health complications associated with LGI in the elderly, including mental health and wellbeing, metabolic abnormalities and infections. Finally, we discuss the possibility of manipulating LGI in the elderly by nutritional interventions. We provide an overview of the evidence that exists in the elderly for omega-3 fatty acid, probiotic, prebiotic, antioxidant and polyphenol interventions as a means to influence LGI. We conclude that slowing, controlling or reversing LGI is likely to be an important way to prevent, or reduce the severity of, age-related functional decline and the onset of conditions affecting health and well-being; that there is evidence to support specific dietary interventions as a strategy to control LGI; and that a continued research focus on this field is warranted.

Overcoming barriers to reprogramming and differentiation in nonhuman primate induced pluripotent stem cells

Induced pluripotent stem cells (iPS cells) generated by cellular reprogramming from nonhuman primates (NHPs) are of great significance for regenerative medicine and for comparative biology. Autologously derived stem cells would theoretically avoid any risk of rejection due to host–donor mismatch and may bypass the need for immune suppression post-transplant. In order for these possibilities to be realized, reprogramming methodologies that were initially developed mainly for human cells must be translated to NHPs. NHP studies have typically used pluripotent cells generated from young animals and thus risk overlooking complications that may arise from generating iPS cells from donors of other ages. When reprogramming is extended to a wide range of NHP species, available donors may be middle- or old-aged. Here we have pursued these questions by generating iPS cells from donors across the life span of the common marmoset (Callithrix jacchus) and then subjecting them to a directed neural differentiation protocol. The differentiation potential of different clonal cell lines was assessed using the quantitative polymerase chain reaction. The results show that cells derived from older donors often showed less neural marker induction. These deficits were rescued by a 24 h pretreatment of the cells with 0.5 % dimethyl sulfoxide. Another NHP that plays a key role in biological research is the chimpanzee (Pan troglodytes). iPS cells generated from the chimpanzee can be of great interest in comparative in vitro studies. We investigated if similar deficits in differentiation potential might arise in chimpanzee iPS cells reprogrammed using various technologies. The results show that, while some deficits were observed in iPS cell clones generated using three different technologies, there was no clear association with the vector used. These deficits in differentiation were also prevented by a 24 h pretreatment with 0.5 % dimethyl sulfoxide.

Ectopic expression of CITED2 prior to reprogramming, promotes and homogenises the conversion of somatic cells into induced pluripotent stem cells

Cited2 plays crucial roles in mouse embryonic stem cells self-renewal, the initiation of the somatic reprogramming process into induced pluripotent stem cells (iPSC) and the suppression of cell senescence. Here, we investigated the potential of CITED2 expression in combination with the Oct4, Sox2, Klf4 and c-Myc factors for reprogramming of primary mouse embryonic fibroblasts (MEF) at passage 2 and 4. The ectopic CITED2 expression in primary MEF prior to the onset of the reprogramming process, generated iPSC with less variability in the expression of endogenous pluripotency-related genes. In contrast, part of the MEF reprogrammed without ectopic expression of CITED2 at passage 4 originated partially reprogrammed iPSC or pre-iPSC. However, the overexpression of CITED2 in the pre-iPSC was insufficient to complete the reprogramming process into iPSC. These results indicated that ectopic CITED2 expression at the onset of the reprogramming process in combination with the reprogramming factors promotes a complete and homogeneous conversion of somatic cells into iPSC.

Generating CNS organoids from human induced pluripotent stem cells for modeling neurological disorders

Understanding human brain development and disease is largely hampered by the relative inaccessibility of human brain tissues. Recent advances in human induced pluripotent stem cells (hiPSCs) have led to the generation of unlimited human neural cells and thereby facilitate the investigation of human brain development and pathology. Compared with traditional 2-dimensional (2D) culture methods, culturing the hiPSC-derived neural cells in a three-dimensional (3D) free-floating manner generates human central nervous system (CNS) organoids. These 3D CNS organoids possess the unique advantage of recapitulating multi-regional or region-specific cytoarchitecture seen in the early human fetal brain development. The CNS organoids are becoming a strong complement to the animal model in studying brain development and pathology, and developing new therapies to treat neurodevelopmental diseases. Further improvements to the long-term maintenance and neural maturation of the organoids may allow them to model neurodegenerative diseases. In this review, we will summarize the current development of hiPSCs to generate CNS organoids for modeling neurological disorders and future perspective.

In Vivo Amelioration of Age-Associated Hallmarks by Partial Reprogramming

Aging is the major risk factor for many human diseases. In vitro studies have demonstrated that cellular reprogramming to pluripotency reverses cellular age, but alteration of the aging process through reprogramming has not been directly demonstrated in vivo. Here, we report that partial reprogramming by short-term cyclic expression of Oct4, Sox2, Klf4, and c-Myc (OSKM) ameliorates cellular and physiological hallmarks of aging and prolongs lifespan in a mouse model of premature aging. Similarly, expression of OSKM in vivo improves recovery from metabolic disease and muscle injury in older wild-type mice. The amelioration of age-associated phenotypes by epigenetic remodeling during cellular reprogramming highlights the role of epigenetic dysregulation as a driver of mammalian aging. Establishing in vivo platforms to modulate age-associated epigenetic marks may provide further insights into the biology of aging.

The epigenetic landscape of age-related diseases: the geroscience perspective

In this review, we summarize current knowledge regarding the epigenetics of age-related diseases, focusing on those studies that have described DNA methylation landscape in cardio-vascular diseases, musculoskeletal function and frailty. We stress the importance of adopting the conceptual framework of “geroscience”, which starts from the observation that advanced age is the major risk factor for several of these pathologies and aims at identifying the mechanistic links between aging and age-related diseases. DNA methylation undergoes a profound remodeling during aging, which includes global hypomethylation of the genome, hypermethylation at specific loci and an increase in inter-individual variation and in stochastic changes of DNA methylation values. These epigenetic modifications can be an important contributor to the development of age-related diseases, but our understanding on the complex relationship between the epigenetic signatures of aging and age-related disease is still poor. The most relevant results in this field come from the use of the so called “epigenetics clocks” in cohorts of subjects affected by age-related diseases. We report these studies in final section of this review.

Influence of donor age on induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) are being pursued as a source of cells for autologous therapies, many of which will be aimed at aged patients. To explore the impact of age on iPSC quality, we produced iPSCs from blood cells of 16 donors aged 21-100. We find that iPSCs from older donors retain an epigenetic signature of age, which can be reduced through passaging. Clonal expansion via reprogramming also enables the discovery of somatic mutations present in individual donor cells, which are missed by bulk sequencing methods. We show that exomic mutations in iPSCs increase linearly with age, and all iPSC lines analyzed carry at least one gene-disrupting mutation, several of which have been associated with cancer or dysfunction. Unexpectedly, elderly donors (>90 yrs) harbor fewer mutations than predicted, likely due to a contracted blood progenitor pool. These studies establish that donor age is associated with an increased risk of abnormalities in iPSCs and will inform clinical development of reprogramming technology.

Human-Induced Pluripotent Stem Cell-Derived Mesenchymal Stem Cells as an Individual-Specific and Renewable Source of Adult Stem Cells

This chapter deals with the employment of human-induced pluripotent stem cells (hiPSCs) as a candidate to differentiate into mesenchymal stem cells (MSCs). This would enable to help establish a regular source of human MSCs with the aim of avoiding the problems associated with procuring the MSCs either from different healthy individuals or patients, limited extraction potentials, batch-to-batch variations or from diverse sources such as bone marrow or adipose tissue. The procedures described herein allow for a guided and ensured approach for the regular maintenance of hiPSCs and their subsequent differentiation into MSCs using the prescribed medium. Subsequently, an easy protocol for the successive isolation and purification of the hiPSC-differentiated MSCs is outlined, which is carried out through passaging and can be further sorted through flow cytometry. Further, the maintenance and expansion of the resultant hiPSC-differentiated MSCs using appropriate characterization techniques, i.e., Reverse-transcription PCR and immunostaining is also elaborated. The course of action has been deliberated keeping in mind the awareness and the requisites available to even beginner researchers who mostly have access to regular consumables and medium components found in the general laboratory.

Are reprogrammed cells a useful tool for studying dopamine dysfunction in psychotic disorders? A review of the current evidence

Since 2006, reprogrammed cells have increasingly been used as a biomedical research technique in addition to neuro-psychiatric methods. These rapidly evolving techniques allow for the generation of neuronal sub-populations, and have sparked interest not only in monogenetic neuro-psychiatric diseases, but also in poly-genetic and poly-aetiological disorders such as schizophrenia (SCZ) and bipolar disorder (BPD). This review provides a summary of 19 publications on reprogrammed adult somatic cells derived from patients with SCZ, and five publications using this technique in patients with BPD. As both disorders are complex and heterogeneous, there is a plurality of hypotheses to be tested in vitro. In SCZ, data on alterations of dopaminergic transmission in vitro are sparse, despite the great explanatory power of the so-called DA hypothesis of SCZ. Some findings correspond to perturbations of cell energy metabolism, and observations in reprogrammed cells suggest neuro-developmental alterations. Some studies also report on the efficacy of medicinal compounds to revert alterations observed in cellular models. However, due to the paucity of replication studies, no comprehensive conclusions can be drawn from studies using reprogrammed cells at the present time. In the future, findings from cell culture methods need to be integrated with clinical, epidemiological, pharmacological and imaging data in order to generate a more comprehensive picture of SCZ and BPD.

miR-302 Attenuates Amyloid-β-Induced Neurotoxicity through Activation of Akt Signaling

Deficiency of insulin signaling has been linked to diabetes and ageing-related neurodegenerative diseases such as Alzheimer's disease (AD). In this regard, brains exhibit defective insulin receptor substrate-1 (IRS-1) and hence result in alteration of insulin signaling in progression of AD, the most common cause of dementia. Consequently, dysregulation of insulin signaling plays an important role in amyloid-β (Aβ)-induced neurotoxicity. As the derivation of induced pluripotent stem cells (iPSC) involves cell reprogramming, it may provide a means for regaining the control of ageing-associated dysfunction and neurodegeneration via affecting insulin-related signaling. To this, we found that an embryonic stem cell (ESC)-specific microRNA, miR-302, silences phosphatase and tensin homolog (PTEN) to activate Akt signaling, which subsequently stimulates nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) elevation and hence inhibits Aβ-induced neurotoxicity. miR-302 is predominantly expressed in iPSCs and is known to regulate several important biological processes of anti-oxidative stress, anti-apoptosis, and anti-aging through activating Akt signaling. In addition, we also found that miR-302-mediated Akt signaling further stimulates Nanog expression to suppress Aβ-induced p-Ser307 IRS-1 expression and thus enhances tyrosine phosphorylation and p-Ser 473-Akt/p-Ser 9-GSK3β formation. Furthermore, our in vivo studies revealed that the mRNA expression levels of both Nanog and miR-302-encoding LARP7 genes were significantly reduced in AD patients' blood cells, providing a novel diagnosis marker for AD. Taken together, our findings demonstrated that miR-302 is able to inhibit Aβ-induced cytotoxicity via activating Akt signaling to upregulate Nrf2 and Nanog expressions, leading to a marked restoration of insulin signaling in AD neurons.

Self-Organizing 3D Human Neural Tissue Derived from Induced Pluripotent Stem Cells Recapitulate Alzheimer's Disease Phenotypes

The dismal success rate of clinical trials for Alzheimer's disease (AD) motivates us to develop model systems of AD pathology that have higher predictive validity. The advent of induced pluripotent stem cells (iPSCs) allows us to model pathology and study disease mechanisms directly in human neural cells from healthy individual as well as AD patients. However, two-dimensional culture systems do not recapitulate the complexity of neural tissue, and phenotypes such as extracellular protein aggregation are difficult to observe. We report brain organoids that use pluripotent stem cells derived from AD patients and recapitulate AD-like pathologies such as amyloid aggregation, hyperphosphorylated tau protein, and endosome abnormalities. These pathologies are observed in an age-dependent manner in organoids derived from multiple familial AD (fAD) patients harboring amyloid precursor protein (APP) duplication or presenilin1 (PSEN1) mutation, compared to controls. The incidence of AD pathology was consistent amongst several fAD lines, which carried different mutations. Although these are complex assemblies of neural tissue, they are also highly amenable to experimental manipulation. We find that treatment of patient-derived organoids with β- and γ-secretase inhibitors significantly reduces amyloid and tau pathology. Moreover, these results show the potential of this model system to greatly increase the translatability of pre-clinical drug discovery in AD.

Anti-Aging Strategies Based on Cellular Reprogramming

Aging can be defined as the progressive decline in the ability of a cell or organism to resist stress and disease. Recent advances in cellular reprogramming technologies have enabled detailed analyses of the aging process, often involving cell types derived from aged individuals, or patients with premature aging syndromes. In this review we discuss how cellular reprogramming allows the recapitulation of aging in a dish, describing novel experimental approaches to investigate the aging process. Finally, we explore the role of epigenetic dysregulation as a driver of aging, discussing how epigenetic reprogramming may be harnessed to ameliorate aging hallmarks, both in vitro and in vivo. A better understanding of the reprogramming process may indeed assist the development of novel therapeutic strategies to extend a healthy lifespan.

iPSCs: On the Road to Reprogramming Aging

Aging is characterized by irreversible loss of physiological integrity, often accompanied by an organism's loss of function and increased vulnerability to death. Defects in the mechanisms preserving cellular homeostasis over time may give rise to accelerated aging. Somatic cell reprogramming of aged cells can be associated with rejuvenation, erasing certain age-associated features, and illustrating the reversibility potential of aging. Here, we focus on recent advances in the generation of human induced pluripotent stem cells from progeroid syndromes and late-onset diseases such as Alzheimer's or Parkinson's. These cellular models have contributed to a better understanding of such pathologies, as well as to the development of novel therapeutic approaches. We also discuss different strategies to identify and target age-associated reprogramming barriers to facilitate the treatment of age-related disorders.

Bioinformatic and Genomic Analyses of Cellular Reprogramming and Direct Lineage Conversion

Cellular reprogramming, whereby cell fate can be changed by the expression of a few defined factors, is a remarkable process that harnesses the innate ability of a cell's own genome to rework its expressional networks and function. Since cell lineages are defined by global regulation of gene expression, transcriptional regulators, and coupled to the epigenetic markings of the chromatin, changing the cell fate necessitates broad changes to these central cellular features. To properly characterize these changes, and the mechanisms that drive them, computational and genomic approaches are perfectly suited to provide a holistic picture of the reprogramming mechanisms. In particular, the use of bioinformatic analysis has been a major driver in the study of cellular reprogramming, both as it relates to induced pluripotency or direct lineage conversion. This review will summarize many of the bioinformatic studies that have advanced our knowledge of reprogramming and address future directions for these investigations.

Modeling Alzheimer's disease with human induced pluripotent stem (iPS) cells

In the last decade, induced pluripotent stem (iPS) cells have revolutionized the utility of human in vitro models of neurological disease. The iPS-derived and differentiated cells allow researchers to study the impact of a distinct cell type in health and disease as well as performing therapeutic drug screens on a human genetic background. In particular, clinical trials for Alzheimer's disease (AD) have been failing. Two of the potential reasons are first, the species gap involved in proceeding from initial discoveries in rodent models to human studies, and second, an unsatisfying patient stratification, meaning subgrouping patients based on the disease severity due to the lack of phenotypic and genetic markers. iPS cells overcome this obstacles and will improve our understanding of disease subtypes in AD. They allow researchers conducting in depth characterization of neural cells from both familial and sporadic AD patients as well as preclinical screens on human cells. In this review, we briefly outline the status quo of iPS cell research in neurological diseases along with the general advantages and pitfalls of these models. We summarize how genome-editing techniques such as CRISPR/Cas9 will allow researchers to reduce the problem of genomic variability inherent to human studies, followed by recent iPS cell studies relevant to AD. We then focus on current techniques for the differentiation of iPS cells into neural cell types that are relevant to AD research. Finally, we discuss how the generation of three-dimensional cell culture systems will be important for understanding AD phenotypes in a complex cellular milieu, and how both two- and three-dimensional iPS cell models can provide platforms for drug discovery and translational studies into the treatment of AD.

iPSCs-based anti-aging therapies: Recent discoveries and future challenges

The main biological hallmarks of the aging process include stem cell exhaustion and cellular senescence. Consequently, research efforts to treat age-related diseases as well as anti-aging therapies in general have recently focused on potential 'reprogramming' regenerative therapies. These new approaches are based on induced pluripotent stem cells (iPSCs), including potential in vivo reprogramming for tissue repair. Another possibility is targeting pathways of cellular senescence, e.g., through modulation of p16INK4a signaling and especially inhibition of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Here, we reviewed and discussed these recent developments together with their possible usefulness for future treatments against sarcopenia, a major age-related condition.

The Emergence of Geroscience as an Interdisciplinary Approach to the Enhancement of Health Span and Life Span

Research on the biology of aging has accelerated rapidly in the last two decades. It is now at the point where translation of the findings into useful approaches to improve the health of the elderly population seems possible. In trying to fill that gap, a new field termed geroscience will be articulated here that attempts to identify the biological underpinnings for the age-dependency of most chronic diseases. Herein, I will review the major conceptual issues leading to the formulation of geroscience as a field, as well as give examples of current areas of inquiry in which basic aging biology research could lead to therapeutic approaches to address age-related chronic diseases, not one at a time, but most of them in unison.

Chromatin-wide and transcriptome profiling integration uncovers p38α MAPK as a global regulator of skeletal muscle differentiation

Background

Extracellular stimuli induce gene expression responses through intracellular signaling mediators. The p38 signaling pathway is a paradigm of the mitogen-activated protein kinase (MAPK) family that, although originally identified as stress-response mediator, contributes to establishing stem cell differentiation fates. p38α is central for induction of the differentiation fate of the skeletal muscle stem cells (satellite cells) through not fully characterized mechanisms.

Methods

To investigate the global gene transcription program regulated by p38α during satellite cell differentiation (myogenesis), and to specifically address whether this regulation occurs through direct action of p38α on gene promoters, we performed a combination of microarray gene expression and genome-wide binding analyses. For experimental robustness, two myogenic cellular systems with genetic and chemical loss of p38α function were used: (1) satellite cells derived from mice with muscle-specific deletion of p38α, and (2) the C2C12 murine myoblast cell line cultured in the absence or presence of the p38α/β inhibitor SB203580. Analyses were performed at cell proliferation and early differentiation stages.

Results

We show that p38α binds to a large set of active promoters during the transition of myoblasts from proliferation to differentiation stages. p38α-bound promoters are enriched with binding motifs for several transcription factors, with Sp1, Tcf3/E47, Lef1, FoxO4, MyoD, and NFATc standing out in all experimental conditions. p38α association with chromatin correlates very well with high levels of transcription, in agreement with its classical function as an activator of myogenic differentiation. Interestingly, p38α also associates with genes repressed at the onset of differentiation, thus highlighting the relevance of p38-dependent chromatin regulation for transcriptional activation and repression during myogenesis.

Conclusions

These results uncover p38α association and function on chromatin at novel classes of target genes during skeletal muscle cell differentiation. This is consistent with this MAPK isoform being a transcriptional regulator.

Electronic supplementary material

The online version of this article (doi:10.1186/s13395-016-0074-x) contains supplementary material, which is available to authorized users.

When rejuvenation is a problem: challenges of modeling late-onset neurodegenerative disease

In contrast to the successful modeling of early-onset disorders using patient-specific cells, modeling of late-onset neurodegenerative diseases such as Parkinson's disease remains a challenge. This might be related to the often ignored fact that current induced pluripotent stem cell (iPSC) differentiation protocols yield cells that typically show the behavior of fetal stage cells. Acknowledging aging as a contributing factor in late-onset neurodegenerative disorders represents an important step on the road towards faithfully recreating these diseases in vitro. Here, we summarize progress in the field and review the strategies and challenges for triggering late-onset disease phenotypes.

Pluripotent stem cell-based disease modeling: current hurdles and future promise

Human induced pluripotent stem cells (hiPSCs) can yield unlimited numbers of patient-specific cells of any type and may be an important tool in efforts to overcome current shortcomings in biomedical research. In vitro disease models based on the use of hiPSCs have been proposed for various applications. Those include drug discovery and validation, efficacy, safety and toxicity assays, the elucidation of previously unknown disease mechanisms, the enhancement of animal based assays, the promise of conducting clinical trials in the dish and the identification of cell types and stages suitable for cell replacement therapies. Here, we provide an overview of the current state of hiPSC-based disease modeling and discuss recent progress and remaining challenges on the road to realizing the full potential of this novel technology.

Back and forth in time: Directing age in iPSC-derived lineages

The advent of induced pluripotent stem cells (iPSC) has transformed the classic approach of studying human disease, providing in vitro access to disease-relevant cells from patients for the study of disease pathogenesis and for drug screening. However, in spite of the broad repertoire of iPSC-based disease models developed in recent years, increasing evidence suggests that this technology might not be fully suitable for the study of conditions of old age, such as neurodegeneration. The difficulty in recapitulating late-stage features of disease in cells of pluripotent origin is believed to be a discrepancy between the fetal-like nature of iPSC-progeny and the advanced age of onset of neurodegenerative syndromes. In parallel to the issue of functional immaturity known to affect derivatives of pluripotent cells, latest findings suggest that reprogramming also subjects cells to a process of "rejuvenation", giving rise to cells that are too "young" to manifest phenotypes of age-related diseases. Thus, following the significant progress in manipulating cellular fate, the stem cell field will now have to face the new challenge of controlling cellular age, in order to fully harness the potential of iPSC-technology to advance the research and cure of diseases of the aging brain. This article is part of a Special Issue entitled SI: Exploiting human neurons.

Proceedings: consideration of genetics in the design of induced pluripotent stem cell-based models of complex disease

The goal of exploiting induced pluripotent stem cell (iPSC) technology for the discovery of new mechanisms and treatments of disease is being pursued by many laboratories, and analyses of rare monogenic diseases have already provided ample evidence that this approach has merit. Considering the enormous medical burden imposed by common chronic diseases, successful implementation of iPSC-based models has the potential for major impact on these diseases as well. Since common diseases represent complex traits with varying genetic and environmental contributions to disease manifestation, the use of iPSC technology poses unique challenges. In this perspective, we will consider how the genetics of complex disease and mechanisms underlying phenotypic variation affect experimental design.

Epigenetic regulation of ageing: linking environmental inputs to genomic stability

Ageing is affected by both genetic and non-genetic factors. Here, we review the chromatin-based epigenetic changes that occur during ageing, the role of chromatin modifiers in modulating lifespan and the importance of epigenetic signatures as biomarkers of ageing. We also discuss how epigenome remodelling by environmental stimuli affects several aspects of transcription and genomic stability, with important consequences for longevity, and outline epigenetic differences between the 'mortal soma' and the 'immortal germ line'. Finally, we discuss the inheritance of characteristics of ageing and potential chromatin-based strategies to delay or reverse hallmarks of ageing or age-related diseases.

NF-κB activation impairs somatic cell reprogramming in ageing

Ageing constitutes a critical impediment to somatic cell reprogramming. We have explored the regulatory mechanisms that constitute age-associated barriers, through derivation of induced pluripotent stem cells (iPSCs) from individuals with premature or physiological ageing. We demonstrate that NF-κB activation blocks the generation of iPSCs in ageing. We also show that NF-κB repression occurs during cell reprogramming towards a pluripotent state. Conversely, ageing-associated NF-κB hyperactivation impairs the generation of iPSCs by eliciting the reprogramming repressor DOT1L, which reinforces senescence signals and downregulates pluripotency genes. Genetic and pharmacological NF-κB inhibitory strategies significantly increase the reprogramming efficiency of fibroblasts from Néstor-Guillermo progeria syndrome and Hutchinson-Gilford progeria syndrome patients, as well as from normal aged donors. Finally, we demonstrate that DOT1L inhibition in vivo extends lifespan and ameliorates the accelerated ageing phenotype of progeroid mice, supporting the interest of studying age-associated molecular impairments to identify targets of rejuvenation strategies.

Muscle stem cell aging: regulation and rejuvenation

Aging is characterized by a progressive decline of physiological integrity leading to the loss of tissue function and vulnerability to disease, but its causes remain poorly understood. Skeletal muscle has an outstanding regenerative capacity that relies on its resident stem cells (satellite cells). This capacity declines with aging, and recent discoveries have redefined our view of why this occurs. Here, we discuss how an interconnection of extrinsic changes in the systemic and local environment and cell-intrinsic mechanisms might provoke failure of normal muscle stem cell functions with aging. We focus particularly on the emergent biology of rejuvenation of old satellite cells, including cells of geriatric age, by restoring traits of youthfulness, with the final goal of improving human health during aging.

Use of human pluripotent stem cells to study and treat retinopathies

Human cell types affected by retinal diseases (such as age-related macular degeneration or retinitis pimentosa) are limited in cell number and of reduced accessibility. As a consequence, their isolation for in vitro studies of disease mechanisms or for drug screening efforts is fastidious. Human pluripotent stem cells (hPSCs), either of embryonic origin or through reprogramming of adult somatic cells, represent a new promising way to generate models of human retinopathies, explore the physiopathological mechanisms and develop novel therapeutic strategies. Disease-specific human embryonic stem cells were the first source of material to be used to study certain disease states. The recent demonstration that human somatic cells, such as fibroblasts or blood cells, can be genetically converted to induce pluripotent stem cells together with the continuous improvement of methods to differentiate these cells into disease-affected cellular subtypes opens new perspectives to model and understand a large number of human pathologies, including retinopathies. This review focuses on the added value of hPSCs for the disease modeling of human retinopathies and the study of their molecular pathological mechanisms. We also discuss the recent use of these cells for establishing the validation studies for therapeutic intervention and for the screening of large compound libraries to identify candidate drugs.