Canonical Wnt Signaling Ameliorates Aging of Intestinal Stem Cells

Wnt Signaling and Aging of the Gastrointestinal Tract

Aging is considered a risk factor for various diseases including cancers. In this aging society, there is an urgent need to clarify the molecular mechanisms involved in aging. Wnt signaling has been shown to play a crucial role in the maintenance and differentiation of tissue stem cells, and intensive studies have elucidated its pivotal role in the aging of neural and muscle stem cells. However, until recently, such studies on the gastrointestinal tract have been limited. In this review, we discuss recent advances in the study of the role of Wnt signaling in the aging of the gastrointestinal tract and aging-related carcinogenesis.

Age-Associated Loss in Renal Nestin-Positive Progenitor Cells

The decrease in the number of resident progenitor cells with age was shown for several organs. Such a loss is associated with a decline in regenerative capacity and a greater vulnerability of organs to injury. However, experiments evaluating the number of progenitor cells in the kidney during aging have not been performed until recently. Our study tried to address the change in the number of renal progenitor cells with age. Experiments were carried out on young and old transgenic nestin-green fluorescent protein (GFP) reporter mice, since nestin is suggested to be one of the markers of progenitor cells. We found that nestin⁺ cells in kidney tissue were located in the putative niches of resident renal progenitor cells. Evaluation of the amount of nestin⁺ cells in the kidneys of different ages revealed a multifold decrease in the levels of nestin⁺ cells in old mice. In vitro experiments on primary cultures of renal tubular cells showed that all cells including nestin⁺ cells from old mice had a lower proliferation rate. Moreover, the resistance to damaging factors was reduced in cells obtained from old mice. Our data indicate the loss of resident progenitor cells in kidneys and a decrease in renal cells proliferative capacity with aging.

A gut-centric view of aging: Do intestinal epithelial cells contribute to age-associated microbiota changes, inflammaging, and immunosenescence?

Intestinal epithelial cells (IECs) serve as both a physical and an antimicrobial barrier against the microbiota, as well as a conduit for signaling between the microbiota and systemic host immunity. As individuals age, the balance between these systems undergoes a myriad of changes due to age-associated changes to the microbiota, IECs themselves, immunosenescence, and inflammaging. In this review, we discuss emerging data related to age-associated loss of intestinal barrier integrity and posit that IEC dysfunction may play a central role in propagating age-associated alterations in microbiota composition and immune homeostasis.

Intestinal cellular heterogeneity and disease development revealed by single-cell technology

The intestinal epithelium is responsible for food digestion and nutrient absorption and plays a critical role in hormone secretion, microorganism defense, and immune response. These functions depend on the integral single-layered intestinal epithelium, which shows diversified cell constitution and rapid self-renewal and presents powerful regeneration plasticity after injury. Derailment of homeostasis of the intestine epithelium leads to the development of diseases, most commonly including enteritis and colorectal cancer. Therefore, it is important to understand the cellular characterization of the intestinal epithelium at the molecular level and the mechanisms underlying its homeostatic maintenance. Single-cell technologies allow us to gain molecular insights at the single-cell level. In this review, we summarize the single-cell RNA sequencing applications to understand intestinal cell characteristics, spatiotemporal evolution, and intestinal disease development.

Recombinant Porcine R-Spondin 1 Facilitates Intestinal Stem Cell Expansion along the Crypt-Villus Axis through Potentiating Wnt/β-Catenin Signaling in Homeostasis and Deoxynivalenol Injury

R-spondin 1 (RSPO1) is a ligand for the intestinal stem cell (ISC) marker Lgr5 in the crypt, which functions to amplify canonical Wnt signaling to stimulate the division of ISCs. Despite the crucial role of recombinant human RSPO1 (rhRSPO1) in homeostasis and regeneration, little is known about RSPO1 among different species. Here, we cloned the porcine RSPO1 (pRSPO1) gene and obtained rpRSPO1 protein through the expression system of the recombinant Escherichia coli Rosetta (DE3) chemical competent cells. Using the in vitro IPEC-J2 model that combines cell proliferation evaluation approaches, we identified the rpRSPO1 activity in stimulating jejunal epithelial cells. And upon deoxynivalenol challenge in mice, we found that rpRSPO1 ameliorated their growth retardation and jejunal epithelial integrity. Importantly, the ISCs in the jejunum had greater proliferation and differentiation potential that was accompanied by Wnt/β-catenin pathway activation after rpRSPO1 modulation. Subsequently, the jejunal organoids expanded from these ISCs ex vivo presented robust growth advantages. And the rpRSPO1 was able to guide Wnt/β-catenin activity to increase ISC activity. Our work systematically demonstrates that rpRSPO1 facilitates ISC expansion by potentiating Wnt/β-catenin signaling during homeostasis and responding to deoxynivalenol perturbations.

Suppressed Cellular Senescence Mediated by T-box3 in Aged Gastric Epithelial Cells may Contribute to Aging-related Carcinogenesis

Aging is a risk factor for cancers in various organs. Recent advances in the organoid culturing system have made it viable to investigate the influence of aging utilizing these mini organs. In this study, we aimed to examine the implications of aging for gastric carcinogenesis. Gastric organoids established from aged mice grew larger, proliferated vigorously, and survived longer than that from young mice. Because Wnt/β-catenin signaling was intensified in the aged organoids and because removal of Wnt-related factors diminished their proliferation, we investigated for Wnt target gene that contributed to enhanced proliferation and discovered that the aged organoids expressed the transcription factor T-box3 (Tbx3), which has been reported to suppress cellular senescence. Indeed, cellular senescence was suppressed in the aged organoids, and this resulted from enhanced G₂-M transition. As for the mechanism involved in the intensified Wnt/β-catenin signaling, we identified that Dickkopf3 (Dkk3) expression was reduced in the aged organoids due to methylation of the Dkk3 gene. Finally, the expression of TBX3 was enhanced in human atrophic gastritis and even more enhanced in human gastric cancers. In addition, its expression correlated positively with patients' age. These results indicated that the emergence of antisenescent property in aged gastric organoids due to enhanced Tbx3 expression led to accelerated cellular proliferation and organoid formation. Because the enhanced Tbx3 expression seen in aged gastric organoids was also observed in human gastric cancer tissues, this Dkk3-Wnt-Tbx3 pathway may be involved in aging-related gastric carcinogenesis.

Significance

This work provides an insight into the mechanism involved in aging-related gastric carcinogenesis through studies utilizing organoids established from young and aged murine stomachs.

NF-κB Regulation by Gut Microbiota Decides Homeostasis or Disease Outcome During Ageing

Human beings and their indigenous microbial communities have coexisted for centuries, which led to the development of co-evolutionary mechanisms of communication and cooperation. Such communication machineries are governed by sophisticated multi-step feedback loops, which typically begin with the recognition of microbes by pattern recognition receptors (PRRs), followed by a host transcriptional response leading to the release of effector molecules. Our gastrointestinal tract being the main platform for this interaction, a variety of host intestinal cells tightly regulate these loops to establish tolerance towards the microbial communities of the gut and maintain homeostasis. The transcription factor, nuclear factor kappa B (NF-κB) is an integral component of such a communication apparatus, which plays a critical role in determining the state of homeostasis or inflammation associated with dysbiosis in the host. Here we outline the crucial role of NF-κB in host response to microbial cues in the context of ageing and associated diseases.

Intestinal stem cell aging signature reveals a reprogramming strategy to enhance regenerative potential

The impact of aging on intestinal stem cells (ISCs) has not been fully elucidated. In this study, we identified widespread epigenetic and transcriptional alterations in old ISCs. Using a reprogramming algorithm, we identified a set of key transcription factors (Egr1, Irf1, FosB) that drives molecular and functional differences between old and young states. Overall, by dissecting the molecular signature of aged ISCs, our study identified transcription factors that enhance the regenerative capacity of ISCs.

Nicotinamide mononucleotide supplementation protects the intestinal function in aging mice and D-galactose induced senescent cells

The nicotinamide adenine dinucleotide (NAD⁺) level shows a temporal decrease during the aging process, which has been deemed as an aging hallmark. Nicotinamide mononucleotide (NMN), a key NAD⁺ precursor, shows the potential to retard the age-associated functional decline in organs. In the current study, to explore whether NMN has an impact on the intestine during the aging process, the effects of NMN supplementation on the intestinal morphology, microbiota, and NAD⁺ content, as well as its anti-inflammatory, anti-oxidative and barrier functions were investigated in aging mice and D-galactose (D-gal) induced senescent IPEC-J2 cells. The results showed that 4 months of NMN administration had little impact on the colonic microbiota and NAD⁺ content in aging mice, while it significantly increased the jejunal NAD⁺ content and improved the jejunal structure including increasing the villus length and shortening the crypt. Moreover, NMN supplementation significantly up-regulated the mRNA expression of SIRT3, SIRT6, nuclear factor E2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), the catalytic subunit of glutamate-cysteine ligase (GCLC), superoxide dismutase 2 (SOD2), occludin, and claudin-1, but down-regulated the mRNA expression of tumor necrosis factor alpha (TNF-α). Specifically, in the D-gal induced senescent IPEC-J2 cells, 500 μM NMN restored the increased mRNA expression of interleukin 6 (IL6ST), IL-1A, nuclear factor (NF-κB1), and claudin-1 to normal levels to some extent. Furthermore, NMN treatment significantly affected the mRNA expression of antioxidant enzymes including NQO1, GCLC, SOD 2 and 3, and GSH-PX1, 3 and 4. In addition, 200 μM NMN enhanced the cell viability and total antioxidant capacity and lowered the reactive oxygen species level of senescent IPEC-J2 cells. Notably, NMN restored the down-regulated protein expression of occludin and claudin-1 induced by D-gal. The above data demonstrated the potential of NMN in ameliorating the structural and functional decline in the intestine during aging.

Protein disulfide isomerase PDI-6 regulates Wnt secretion to coordinate inter-tissue UPRmt activation and lifespan extension in C. elegans

Coordination of inter-tissue stress signaling is essential for organismal fitness. Neuronal mitochondrial perturbations activate the mitochondrial unfolded-protein response (UPR^mt) in the intestine via the mitokine Wnt signaling in Caenorhabditis elegans. Here, we found that the protein disulfide isomerase PDI-6 coordinates inter-tissue UPR^mt signaling via regulating the Wnt ligand EGL-20. PDI-6 is expressed in the endoplasmic reticulum (ER) and interacts with EGL-20 through disulfide bonds that are essential for EGL-20 stability and secretion. pdi-6 deficiency results in misfolded EGL-20, which leads to its degradation via ER-associated protein degradation (ERAD) machinery. Expression of PDI-6 declines drastically with aging, and animals with pdi-6 deficiency have decreased lifespan. Overexpression of PDI-6 is sufficient to maintain Wnt/EGL-20 protein levels during aging, activating the UPR^mt, and significantly extending lifespan in a Wnt- and UPR^mt-dependent manner. Our study reveals that protein disulfide isomerase facilitates Wnt secretion to coordinate the inter-tissue UPR^mt signaling and organismal aging.

Braf mutation induces rapid neoplastic transformation in the aged and aberrantly methylated intestinal epithelium

OBJECTIVE

Sessile serrated lesions (SSLs) are common across the age spectrum, but the BRAF mutant cancers arising occur predominantly in the elderly. Aberrant DNA methylation is uncommon in SSL from young patients. Here, we interrogate the role of ageing and DNA methylation in SSL initiation and progression.

DESIGN

We used an inducible model of Braf mutation to direct recombination of the oncogenic Braf V637E allele to the murine intestine. BRAF mutation was activated after periods of ageing, and tissue was assessed for histological, DNA methylation and gene expression changes thereafter. We also investigated DNA methylation alterations in human SSLs.

RESULTS

Inducing Braf mutation in aged mice was associated with a 10-fold relative risk of serrated lesions compared with young mice. There were extensive differences in age-associated DNA methylation between animals induced at 9 months versus wean, with relatively little differential Braf-specific methylation. DNA methylation at WNT pathway genes scales with age and Braf mutation accelerated age-associated DNA methylation. In human SSLs, increased epigenetic age was associated with high-risk serrated colorectal neoplasia.

CONCLUSIONS

SSLs arising in the aged intestine are at a significantly higher risk of spontaneous neoplastic progression. These findings provide support for a new conceptual model for serrated colorectal carcinogenesis, whereby risk of Braf-induced neoplastic transformation is dependent on age and may be related to age-associated molecular alterations that accumulate in the ageing intestine, including DNA methylation. This may have implications for surveillance and chemopreventive strategies targeting the epigenome.

Toward Elucidating Epigenetic and Metabolic Regulation of Stem Cell Lineage Plasticity in Skin Aging

Skin is the largest organ in human body, harboring a plethora of cell types and serving as the organismal barrier. Skin aging such as wrinkling and hair graying is graphically pronounced, and the molecular mechanisms behind these phenotypic manifestations are beginning to unfold. As in many other organs and tissues, epigenetic and metabolic deregulations have emerged as key aging drivers. Particularly in the context of the skin epithelium, the epigenome and metabolome coordinately shape lineage plasticity and orchestrate stem cell function during aging. Our review discusses recent studies that proposed molecular mechanisms that drive the degeneration of hair follicles, a major appendage of the skin. By focusing on skin while comparing it to model organisms and adult stem cells of other tissues, we summarize literature on genotoxic stress, nutritional sensing, metabolic rewiring, mitochondrial activity, and epigenetic regulations of stem cell plasticity. Finally, we speculate about the rejuvenation potential of rate-limiting upstream signals during aging and the dominant role of the tissue microenvironment in dictating aged epithelial stem cell function.

Reduced adhesion of aged intestinal stem cells contributes to an accelerated clonal drift

Analysis of clonal dynamics of intestinal stem cells supports an accelerated clonal drift upon aging, likely because of reduced adhesion of aged ISCs because of reduced canonical Wnt signaling.

Upon aging, the function of the intestinal epithelium declines with a concomitant increase in aging-related diseases. ISCs play an important role in this process. It is known that ISC clonal dynamics follow a neutral drift model. However, it is not clear whether the drift model is still valid in aged ISCs. Tracking of clonal dynamics by clonal tracing revealed that aged crypts drift into monoclonality substantially faster than young ones. However, ISC tracing experiments, in vivo and ex vivo, implied a similar clonal expansion ability of both young and aged ISCs. Single-cell RNA sequencing for 1,920 high Lgr5 ISCs from young and aged mice revealed increased heterogeneity among subgroups of aged ISCs. Genes associated with cell adhesion were down-regulated in aged ISCs. ISCs of aged mice indeed show weaker adhesion to the matrix. Simulations applying a single cell–based model of the small intestinal crypt demonstrated an accelerated clonal drift at reduced adhesion strength, implying a central role for reduced adhesion for affecting clonal dynamics upon aging.

Fecal microbiota transfer between young and aged mice reverses hallmarks of the aging gut, eye, and brain

BACKGROUND

Altered intestinal microbiota composition in later life is associated with inflammaging, declining tissue function, and increased susceptibility to age-associated chronic diseases, including neurodegenerative dementias. Here, we tested the hypothesis that manipulating the intestinal microbiota influences the development of major comorbidities associated with aging and, in particular, inflammation affecting the brain and retina.

METHODS

Using fecal microbiota transplantation, we exchanged the intestinal microbiota of young (3 months), old (18 months), and aged (24 months) mice. Whole metagenomic shotgun sequencing and metabolomics were used to develop a custom analysis workflow, to analyze the changes in gut microbiota composition and metabolic potential. Effects of age and microbiota transfer on the gut barrier, retina, and brain were assessed using protein assays, immunohistology, and behavioral testing.

RESULTS

We show that microbiota composition profiles and key species enriched in young or aged mice are successfully transferred by FMT between young and aged mice and that FMT modulates resulting metabolic pathway profiles. The transfer of aged donor microbiota into young mice accelerates age-associated central nervous system (CNS) inflammation, retinal inflammation, and cytokine signaling and promotes loss of key functional protein in the eye, effects which are coincident with increased intestinal barrier permeability. Conversely, these detrimental effects can be reversed by the transfer of young donor microbiota.

CONCLUSIONS

These findings demonstrate that the aging gut microbiota drives detrimental changes in the gut-brain and gut-retina axes suggesting that microbial modulation may be of therapeutic benefit in preventing inflammation-related tissue decline in later life. Video abstract.

Aging of intestinal stem cells

The intestine is one of the organs that relies on stem cell function for maintaining tissue homeostasis. Recent findings on intestinal aging show that intestinal architecture, such as villus length, crypt size, and cell composition changes in the aged crypts. The correspondent decline in the regenerative capacity of the intestine is mainly due to a decline in intestinal stem cell function upon aging, as the underlying mechanisms of aging intestinal stem cells are beginning to unravel. This review summarizes our current knowledge on stem cell-intrinsic mechanisms of aging of intestinal stem cells and their connection to extrinsic factors, such as niche cells and microbiota and will introduce recent approaches to attenuate or even revert the aging of intestinal stem cells.

Intestinal Epithelial NAD+ Biosynthesis Regulates GLP-1 Production and Postprandial Glucose Metabolism in Mice

Obesity is associated with perturbations in incretin production and whole-body glucose metabolism, but the precise underlying mechanism remains unclear. Here, we tested the hypothesis that nicotinamide phosphoribosyltransferase (NAMPT), which mediates the biosynthesis of nicotinamide adenine dinucleotide (NAD+), a key regulator of cellular energy metabolism, plays a critical role in obesity-associated intestinal pathophysiology and systemic metabolic complications. To this end, we generated a novel mouse model, namely intestinal epithelial cell-specific Nampt knockout (INKO) mice. INKO mice displayed diminished glucagon-like peptide-1 (GLP-1) production, at least partly contributing to reduced early-phase insulin secretion and postprandial hyperglycemia. Mechanistically, loss of NAMPT attenuated the Wnt signaling pathway, resulting in insufficient GLP-1 production. We also found that diet-induced obese mice had compromised intestinal NAMPT-mediated NAD+ biosynthesis and Wnt signaling pathway, associated with impaired GLP-1 production and whole-body glucose metabolism, resembling the INKO mice. Finally, administration of a key NAD+ intermediate, nicotinamide mononucleotide (NMN), restored intestinal NAD+ levels and obesity-associated metabolic derangements, manifested by a decrease in ileal Proglucagon expression and GLP-1 production as well as postprandial hyperglycemia in INKO and diet-induced obese mice. Collectively, our study provides mechanistic and therapeutic insights into intestinal NAD+ biology related to obesity-associated dysregulation of GLP-1 production and postprandial hyperglycemia.

Different responses to DNA damage determine ageing differences between organs

Organs age differently, causing wide heterogeneity in multimorbidity, but underlying mechanisms are largely elusive. To investigate the basis of organ-specific ageing, we utilized progeroid repair-deficient Ercc1^{Δ /-} mouse mutants and systematically compared at the tissue, stem cell and organoid level two organs representing ageing extremes. Ercc1^{Δ /-} intestine shows hardly any accelerated ageing. Nevertheless, we found apoptosis and reduced numbers of intestinal stem cells (ISCs), but cell loss appears compensated by over-proliferation. ISCs retain their organoid-forming capacity, but organoids perform poorly in culture, compared with WT. Conversely, liver ages dramatically, even causing early death in Ercc1-KO mice. Apoptosis, p21, polyploidization and proliferation of various (stem) cells were prominently elevated in Ercc1^{Δ /-} liver and stem cell populations were either largely unaffected (Sox9+), or expanding (Lgr5+), but were functionally exhausted in organoid formation and development in vitro. Paradoxically, while intestine displays less ageing, repair in WT ISCs appears inferior to liver as shown by enhanced sensitivity to various DNA-damaging agents, and lower lesion removal. Our findings reveal organ-specific anti-ageing strategies. Intestine, with short lifespan limiting time for damage accumulation and repair, favours apoptosis of damaged cells relying on ISC plasticity. Liver with low renewal rates depends more on repair pathways specifically protecting the transcribed compartment of the genome to promote sustained functionality and cell preservation. As shown before, the hematopoietic system with intermediate self-renewal mainly invokes replication-linked mechanisms, apoptosis and senescence. Hence, organs employ different genome maintenance strategies, explaining heterogeneity in organ ageing and the segmental nature of DNA-repair-deficient progerias.

Integrity of the Intestinal Barrier: The Involvement of Epithelial Cells and Microbiota-A Mutual Relationship

Simple Summary

The gastrointestinal tract is a complex organization of various types of epithelial cells forming a single layer of the mucosal barrier, the host mucosal immune system, and microorganisms termed as gut microbiota inhabiting this area. The mucosal barrier, including physical and chemical factors, spatially segregates gut microbiota and the host immune system preventing the development of immune response directed towards non-pathogenic commensals and dietary antigens. However, for the maintenance of the integrity of the mucosal surfaces, cross-talk between epithelial cells and microbiota is required. The microbiome and the intestinal epithelium developed a complex dependence necessary for sustaining intestinal homeostasis. In this review, we highlight the role of specific epithelial cell subtypes and their role in barrier arrangement, the mechanisms employed by them to control intestinal microbiota as well as the mechanisms utilized by the microbiome to regulate intestinal epithelial function. This review will provide information regarding the development of inflammatory disorders dependent on the loss of intestinal barrier function and composition of the intestinal microbiota.

Abstract

The gastrointestinal tract, which is constantly exposed to a multitude of stimuli, is considered responsible for maintaining the homeostasis of the host. It is inhabited by billions of microorganisms, the gut microbiota, which form a mutualistic relationship with the host. Although the microbiota is generally recognized as beneficial, at the same time, together with pathogens, they are a permanent threat to the host. Various populations of epithelial cells provide the first line of chemical and physical defense against external factors acting as the interface between luminal microorganisms and immunocompetent cells in lamina propria. In this review, we focus on some essential, innate mechanisms protecting mucosal integrity, thus responsible for maintaining intestine homeostasis. The characteristics of decisive cell populations involved in maintaining the barrier arrangement, based on mucus secretion, formation of intercellular junctions as well as production of antimicrobial peptides, responsible for shaping the gut microbiota, are presented. We emphasize the importance of cross-talk between gut microbiota and epithelial cells as a factor vital for the maintenance of the homeostasis of the GI tract. Finally, we discuss how the imbalance of these regulations leads to the compromised barrier integrity and dysbiosis considered to contribute to inflammatory disorders and metabolic diseases.

OUP accepted manuscript

Stem cell therapies, including stem cell transplantation and rejuvenation of stem cells in situ, are promising avenues for tackling a broad range of diseases. Stem cells can both self-renew and differentiate into other cell types, and play a significant role in the regulation of tissue homeostasis and regeneration after cell degeneration or injury. However, stem cell exhaustion or dysfunction increases with age and impedes the normal function of multiple tissues and systems. Thus, stem cell therapies could provide a solution to aging and age-associated diseases. Here, we discuss recent advances in understanding the mechanisms that regulate stem cell regeneration. We also summarize potential strategies for rejuvenating stem cells that leverage intrinsic and extrinsic factors. These approaches may pave the way toward therapeutic interventions aiming at extending both health and life span.

Aging-Related Impairments to M Cells in Peyer's Patches Coincide With Disturbances to Paneth Cells

The decline in mucosal immunity during aging increases susceptibility, morbidity and mortality to infections acquired via the gastrointestinal and respiratory tracts in the elderly. We previously showed that this immunosenescence includes a reduction in the functional maturation of M cells in the follicle-associated epithelia (FAE) covering the Peyer’s patches, diminishing the ability to sample of antigens and pathogens from the gut lumen. Here, co-expression analysis of mRNA-seq data sets revealed a general down-regulation of most FAE- and M cell-related genes in Peyer’s patches from aged mice, including key transcription factors known to be essential for M cell differentiation. Conversely, expression of ACE2, the cellular receptor for SARS-Cov-2 virus, was increased in the aged FAE. This raises the possibility that the susceptibility of aged Peyer’s patches to infection with the SARS-Cov-2 virus is increased. Expression of key Paneth cell-related genes was also reduced in the ileum of aged mice, consistent with the adverse effects of aging on their function. However, the increased expression of these genes in the villous epithelium of aged mice suggested a disturbed distribution of Paneth cells in the aged intestine. Aging effects on Paneth cells negatively impact on the regenerative ability of the gut epithelium and could indirectly impede M cell differentiation. Thus, restoring Paneth cell function may represent a novel means to improve M cell differentiation in the aging intestine and increase mucosal vaccination efficacy in the elderly.

Impact of the Age of Cecal Material Transfer Donors on Alzheimer’s Disease Pathology in 5xFAD Mice

Alzheimer’s disease is a progressive neurodegenerative disorder affecting around 30 million patients worldwide. The predominant sporadic variant remains enigmatic as the underlying cause has still not been identified. Since efficient therapeutic treatments are still lacking, the microbiome and its manipulation have been considered as a new, innovative approach. 5xFAD Alzheimer’s disease model mice were subjected to one-time fecal material transfer after antibiotics-treatment using two types of inoculation: material derived from the caecum of age-matched (young) wild type mice or from middle aged, 1 year old (old) wild type mice. Mice were profiled after transfer for physiological parameters, microbiome, behavioral tasks, and amyloid deposition. A single time transfer of cecal material from the older donor group established an aged phenotype in the recipient animals as indicated by elevated cultivatable fecal Enterobacteriaceae and Lactobacillaceae representative bacteria, a decreased Firmicutes amount as assessed by qPCR, and by increased levels of serum LPS binding protein. While behavioral deficits were not accelerated, single brain regions (prefrontal cortex and dentate gyrus) showed higher plaque load after transfer of material from older animals. We could demonstrate that the age of the donor of cecal material might affect early pathological hallmarks of Alzheimer’s disease. This could be relevant when considering new microbiome-based therapies for this devastating disorder.

The Aged Intestine: Performance and Rejuvenation

Owing to the growing elderly population, age-related problems are gaining increasing attention from the scientific community. With senescence, the intestine undergoes a spectrum of changes and infirmities that are likely the causes of overall aging. Therefore, identification of the aged intestine and the search for novel strategies to rescue it, are required. Although progress has been made in research on some components of the aged intestine, such as intestinal stem cells, the comprehensive understanding of intestinal aging is still limited, and this restricts the in-depth search for efficient strategies. In this concise review, we discuss several aspects of intestinal aging. More emphasis is placed on the appraisal of current and potential strategies to alleviate intestinal aging, as well as future targets to rejuvenate the aged intestine.

Organoids: An Emerging Tool to Study Aging Signature across Human Tissues. Modeling Aging with Patient-Derived Organoids

The biology of aging is focused on the identification of novel pathways that regulate the underlying processes of aging to develop interventions aimed at delaying the onset and progression of chronic diseases to extend lifespan. However, the research on the aging field has been conducted mainly in animal models, yeast, Caenorhabditis elegans, and cell cultures. Thus, it is unclear to what extent this knowledge is transferable to humans since they might not reflect the complexity of aging in people. An organoid culture is an in vitro 3D cell-culture technology that reproduces the physiological and cellular composition of the tissues and/or organs. This technology is being used in the cancer field to predict the response of a patient-derived tumor to a certain drug or treatment serving as patient stratification and drug-guidance approaches. Modeling aging with patient-derived organoids has a tremendous potential as a preclinical model tool to discover new biomarkers of aging, to predict adverse outcomes during aging, and to design personalized approaches for the prevention and treatment of aging-related diseases and geriatric syndromes. This could represent a novel approach to study chronological and/or biological aging, paving the way to personalized interventions targeting the biology of aging.

Multifactorial causation of early onset colorectal cancer

The multiple-hit hypothesis of cancer, including colorectal cancer (CRC), states that neoplastic development requires a sequence of mutations and epigenetic changes in driver genes. We have previously proposed that obesity increases CRC risk by supporting neoplastic development through adipokine-induced signaling, and this proliferative signaling substitutes for specific driver gene mutations. In support of this hypothesis, analyses of The Cancer Genome Atlas (TCGA) mutation data have revealed that obese patients with microsatellite stable CRC exhibit fewer driver gene mutations than CRC patients with normal body mass index. The lower number of driver gene mutations required for cancer development may shorten the neoplastic process and lead to an early onset of CRC. Therefore, obesity could be one factor explaining the rise of CRC incidence among younger individuals (< 50 years of age); furthermore, early onset CRC has been associated with the increasing incidence of metabolic syndrome and obesity in this age group. However, CRC incidence among older individuals (> 50 years of age) is stable or declining, despite the high rates of metabolic syndrome and obesity in this age group. In search for explanations of this phenomenon, we discuss several factors that may contribute to the divergent CRC incidence trends in populations under, and above, the age of 50, despite the rising levels of metabolic syndrome and obesity across all ages. First, older individuals with metabolic dysregulation are more frequently on maintenance medications, such as aspirin, β-blockers, lipid-lowering drugs, ACE inhibitors, metformin, etc., compared to younger individuals. Such treatments may suppress specific adipokine-induced proliferative signaling pathways, and therefore counteract and slow down neoplastic development in medicated overweight/obese individuals. Second, in the past decades, the incidence of infectious diseases accompanied by febrile episodes has been decreasing and the use of antipyretics increasing. Compared to normal cells, neoplastic cells are more sensitive to high body temperature; therefore, the decreased number of febrile episodes in childhood and adolescence may contribute to increased cancer incidence before the age of 50. Third, obesity at younger age may expand the stem cell compartment. An increased number of intestinal stem cells and stem cell divisions translates into a higher probability of sporadic mutations in the stem cells, and therefore, a greater chance of neoplasia. In conclusion, we hypothesize that early onset CRC has multifactorial causation and the proposed associations could be examined through analyses of existing data.

Dietary fructose improves intestinal cell survival and nutrient absorption

Fructose consumption is linked to the rising incidence of obesity and cancer, which are two of the leading causes of morbidity and mortality globally1,2. Dietary fructose metabolism begins at the epithelium of the small intestine, where fructose is transported by glucose transporter type 5 (GLUT5; encoded by SLC2A5) and phosphorylated by ketohexokinase to form fructose 1-phosphate, which accumulates to high levels in the cell3,4. Although this pathway has been implicated in obesity and tumour promotion, the exact mechanism that drives these pathologies in the intestine remains unclear. Here we show that dietary fructose improves the survival of intestinal cells and increases intestinal villus length in several mouse models. The increase in villus length expands the surface area of the gut and increases nutrient absorption and adiposity in mice that are fed a high-fat diet. In hypoxic intestinal cells, fructose 1-phosphate inhibits the M2 isoform of pyruvate kinase to promote cell survival5-7. Genetic ablation of ketohexokinase or stimulation of pyruvate kinase prevents villus elongation and abolishes the nutrient absorption and tumour growth that are induced by feeding mice with high-fructose corn syrup. The ability of fructose to promote cell survival through an allosteric metabolite thus provides additional insights into the excess adiposity generated by a Western diet, and a compelling explanation for the promotion of tumour growth by high-fructose corn syrup.

The Emerging Mechanisms of Wnt Secretion and Signaling in Development

Wnts are highly-conserved lipid-modified secreted proteins that activate multiple signaling pathways. These pathways regulate crucial processes during various stages of development and maintain tissue homeostasis in adults. One of the most fascinating aspects of Wnt protein is that despite being hydrophobic, they are known to travel several cell distances in the extracellular space. Research on Wnts in the past four decades has identified several factors and uncovered mechanisms regulating their expression, secretion, and mode of extracellular travel. More recently, analyses on the importance of Wnt protein gradients in the growth and patterning of developing tissues have recognized the complex interplay of signaling mechanisms that help in maintaining tissue homeostasis. This review aims to present an overview of the evidence for the various modes of Wnt protein secretion and signaling and discuss mechanisms providing precision and robustness to the developing tissues.

Balancing DNA repair to prevent ageing and cancer

DNA damage is a constant stressor to the cell. Persistent damage to the DNA over time results in an increased risk of mutation and an accumulation of mutations with age. Loss of efficient DNA damage repair can lead to accelerated ageing phenotypes or an increased cancer risk, and the trade-off between cancer susceptibility and longevity is often driven by the cell's response to DNA damage. High levels of mutations in DNA repair mutants often leads to excessive cell death and stem cell exhaustion which may promote premature ageing. Stem cells themselves have distinct characteristics that enable them to retain low mutation rates. However, when mutations do arise, stem cell clonal expansion can also contribute to age-related tissue dysfunction as well as heightened cancer risk. In this review, we will highlight increasing DNA damage and mutation accumulation as hallmarks common to both ageing and cancer. We will propose that anti-ageing interventions might be cancer preventative and discuss the mechanisms through which they may act.

The bright side of fibroblasts: molecular signature and regenerative cues in major organs

Fibrosis is a pathologic process characterized by the replacement of parenchymal tissue by large amounts of extracellular matrix, which may lead to organ dysfunction and even death. Fibroblasts are classically associated to fibrosis and tissue repair, and seldom to regeneration. However, accumulating evidence supports a pro-regenerative role of fibroblasts in different organs. While some organs rely on fibroblasts for maintaining stem cell niches, others depend on fibroblast activity, particularly on secreted molecules that promote cell adhesion, migration, and proliferation, to guide the regenerative process. Herein we provide an up-to-date overview of fibroblast-derived regenerative signaling across different organs and discuss how this capacity may become compromised with aging. We further introduce a new paradigm for regenerative therapies based on reverting adult fibroblasts to a fetal/neonatal-like phenotype.

Epigenetic Drifts during Long-Term Intestinal Organoid Culture

Organoids retain the morphological and molecular patterns of their tissue of origin, are self-organizing, relatively simple to handle and accessible to genetic engineering. Thus, they represent an optimal tool for studying the mechanisms of tissue maintenance and aging. Long-term expansion under standard growth conditions, however, is accompanied by changes in the growth pattern and kinetics. As a potential explanation of these alterations, epigenetic drifts in organoid culture have been suggested. Here, we studied histone tri-methylation at lysine 4 (H3K4me3) and 27 (H3K27me3) and transcriptome profiles of intestinal organoids derived from mismatch repair (MMR)-deficient and control mice and cultured for 3 and 20 weeks and compared them with data on their tissue of origin. We found that, besides the expected changes in short-term culture, the organoids showed profound changes in their epigenomes also during the long-term culture. The most prominent were epigenetic gene activation by H3K4me3 recruitment to previously unmodified genes and by H3K27me3 loss from originally bivalent genes. We showed that a long-term culture is linked to broad transcriptional changes that indicate an ongoing maturation and metabolic adaptation process. This process was disturbed in MMR-deficient mice, resulting in endoplasmic reticulum (ER) stress and Wnt activation. Our results can be explained in terms of a mathematical model assuming that epigenetic changes during a long-term culture involve DNA demethylation that ceases if the metabolic adaptation is disturbed.

Secretory Sorcery: Paneth Cell Control of Intestinal Repair and Homeostasis

Paneth cells are professional secretory cells that classically play a role in the innate immune system by secreting antimicrobial factors into the lumen to control enteric bacteria. In this role, Paneth cells are able to sense cues from luminal bacteria and respond by changing production of these factors to protect the epithelial barrier. Paneth cells rely on autophagy to regulate their secretory capability and capacity. Disruption of this pathway through mutation of genes, such as Atg16L1, results in decreased Paneth cell function, dysregulated enteric microbiota, decreased barrier integrity, and increased risk of diseases such as Crohn's disease in humans. Upon differentiation Paneth cells migrate downward and intercalate among active intestinal stem cells at the base of small intestinal crypts. This localization puts them in a unique position to interact with active intestinal stem cells, and recent work shows that Paneth cells play a critical role in influencing the intestinal stem cell niche. This review discusses the numerous ways Paneth cells can influence intestinal stem cells and their niche. We also highlight the ways in which Paneth cells can alter cells and other organ systems.

Lower human defensin 5 in elderly people compared to middle-aged is associated with differences in the intestinal microbiota composition: the DOSANCO Health Study

Recently, aging is considered a risk factor for various diseases. Although changes in the intestinal microbiota along with aging are thought to associate with the increased disease risk, mechanisms that cause age-related transition of the intestinal microbiota remain unknown. This study aims to clarify relationships between the amount of human defensin 5 (HD5), a Paneth cell α-defensin, which is known to regulate the intestinal microbiota, and age-related differences of the intestinal microbiota composition. Fecal samples from 196 healthy Japanese (35 to 81 years old) were collected and measured HD5 concentration. HD5 concentration in the elderly group (age > 70 years old) was significantly lower than the middle-aged group (age ≤ 70 years old). Furthermore, individual age was negatively correlated with HD5 concentration (r =  - 0.307, p < 0.001). In β-diversity, the intestinal microbiota of the elderly showed a significantly different composition compared to the middle-aged. At the genus level, relative abundance of Collinsella, Alistipes, Peptococcaceae; unassigned, Lactobacillus, Lactococcus, Weissella, Christensenellaceae R-7 group, Megasphaera, and [Eubacterium] eligens group was significantly higher, and Lachnospiraceae; unassigned, Blautia, Anaerostipes, Fusicatenibacter, Dorea, and Faecalibacterium was significantly lower in the elderly compared to the middle-aged. In addition, HD5 concentration was negatively correlated with Alistipes, Peptococcaceae; unassigned, and Christensenellaceae R-7 group and positively correlated with Lachnospiraceae; unassigned and Dorea. These results provide novel insights into the immunosenescence of enteric innate immunity, indicating low HD5 is suggested to contribute to the age-related differences in the intestinal microbiota and may relate to increased risk of diseases in elderly people.

Metabolic Regulation of Stem Cells in Aging

PURPOSE OF REVIEW

From invertebrates to vertebrates, the ability to sense nutrient availability is critical for survival. Complex organisms have evolved numerous signaling pathways to sense nutrients and dietary fluctuations, which influence many cellular processes. Although both overabundance and extreme depletion of nutrients can lead to deleterious effects, dietary restriction without malnutrition can increase lifespan and promote overall health in many model organisms. In this review, we focus on age-dependent changes in stem cell metabolism and dietary interventions used to modulate stem cell function in aging.

RECENT FINDINGS

Over the last half-century, seminal studies have illustrated that dietary restriction confers beneficial effects on longevity in many model organisms. Many researchers have now turned to dissecting the molecular mechanisms by which these diets affect aging at the cellular level. One subpopulation of cells of particular interest are adult stem cells, the most regenerative cells of the body. It is generally accepted that the regenerative capacity of stem cells declines with age, and while the metabolic requirements of each vary across tissues, the ability of dietary interventions to influence stem cell function is striking.

SUMMARY

In this review, we will focus primarily on how metabolism plays a role in adult stem cell homeostasis with respect to aging, with particular emphasis on intestinal stem cells while also touching on hematopoietic, skeletal muscle, and neural stem cells. We will also discuss key metabolic signaling pathways influenced by both dietary restriction and the aging process, and will examine their role in improving tissue homeostasis and lifespan. Understanding the mechanisms behind the metabolic needs of stem cells will help bridge the divide between a basic science interpretation of stem cell function and a whole-organism view of nutrition, thereby providing insight into potential dietary or therapeutic interventions.

Colon Crypts of Subjects With Familial Adenomatous Polyposis Show an Increased Number of LGR5+ Ectopic Stem Cells

INTRODUCTION

Familial adenomatous polyposis (FAP) is a hereditary colorectal cancer (CRC) syndrome characterized by accelerated adenoma development due to inherited (or de novo) mutations in the APC regulator of WNT signaling pathway (APC) gene. The mechanism underlying this accelerated polyp development in subjects with FAP has not been defined. Given that LGR5+ stem cells drive crypt cell proliferation, we hypothesized that FAP crypts would demonstrate aberrant leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5) staining patterns.

METHODS

Biopsies were taken from 11 healthy subjects, 7 subjects with Lynch syndrome, 4 subjects with FAP, and 1 subject with MUTYH-associated polyposis syndrome during routine screening or surveillance colonoscopy. Crypt staining was evaluated by immunohistochemistry of paraffin-embedded tissue sections. Stem cell numbers were estimated by immunofluorescence staining of isolated crypts using antibodies against LGR5 and other proteins.

RESULTS

Subjects with FAP exhibited a greater number of LGR5+ stem cells in their crypts than healthy subjects and subjects with Lynch syndrome and MUTYH-associated polyposis syndrome. Most crypts of subjects with FAP harbored LGR5+ cells located above the lower third of the crypts.

DISCUSSION

These findings support a model in which inactivation of one copy of APC leads to increased numbers of LGR5+ stem cells, many of which are ectopic, in colon crypts of subjects with FAP. Overabundant and ectopic LGR5+ stem cells could lead to an expanded proliferative zone of dividing cells more likely to develop mutations that would contribute to the accelerated adenoma development observed in FAP.

Suppression of elevated Cdc42 activity promotes the regenerative potential of aged intestinal stem cells

Homeostasis in the intestinal epithelium is maintained by Lgr5-positive intestinal stem cells (ISCs) located at the base of the crypt. The function of ISCs is reduced upon aging which leads to a decline of regeneration of the intestinal epithelium. We report that aged intestinal crypts present with an elevated activity of the small RhoGTPase Cdc42. Elevation of Cdc42 activity in young animals by genetic means causes premature ISC aging, whereas pharmacological suppression of elevated Cdc42 activity restores organoid formation potential in vitro. Consistent with a critical role of elevated Cdc42 activity in aged ISCs for a reduced regenerative capacity of aged ISCs, suppression of Cdc42 activity in vivo improves crypt regeneration in aged mice. Thus, pharmacological reduction of Cdc42 activity can improve the regeneration of aged intestinal epithelium.

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Intestinal stem cells show high RhoGTPase Cdc42 activity compared to Paneth cells

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Cdc42 activity is further increased in aged intestinal stem cells (ISCs)

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Attenuation of Cdc42 activity ex vivo or in vivo improves the function of aged ISCs

Age-related changes in polycomb gene regulation disrupt lineage fidelity in intestinal stem cells

Tissue homeostasis requires long-term lineage fidelity of somatic stem cells. Whether and how age-related changes in somatic stem cells impact the faithful execution of lineage decisions remains largely unknown. Here, we address this question using genome-wide chromatin accessibility and transcriptome analysis as well as single-cell RNA-seq to explore stem-cell-intrinsic changes in the aging Drosophila intestine. These studies indicate that in stem cells of old flies, promoters of Polycomb (Pc) target genes become differentially accessible, resulting in the increased expression of enteroendocrine (EE) cell specification genes. Consistently, we find age-related changes in the composition of the EE progenitor cell population in aging intestines, as well as a significant increase in the proportion of EE-specified intestinal stem cells (ISCs) and progenitors in aging flies. We further confirm that Pc-mediated chromatin regulation is a critical determinant of EE cell specification in the Drosophila intestine. Pc is required to maintain expression of stem cell genes while ensuring repression of differentiation and specification genes. Our results identify Pc group proteins as central regulators of lineage identity in the intestinal epithelium and highlight the impact of age-related decline in chromatin regulation on tissue homeostasis.

"Empowering" Cardiac Cells via Stem Cell Derived Mitochondrial Transplantation- Does Age Matter?

With cardiovascular diseases affecting millions of patients, new treatment strategies are urgently needed. The use of stem cell based approaches has been investigated during the last decades and promising effects have been achieved. However, the beneficial effect of stem cells has been found to being partly due to paracrine functions by alterations of their microenvironment and so an interesting field of research, the “stem- less” approaches has emerged over the last years using or altering the microenvironment, for example, via deletion of senescent cells, application of micro RNAs or by modifying the cellular energy metabolism via targeting mitochondria. Using autologous muscle-derived mitochondria for transplantations into the affected tissues has resulted in promising reports of improvements of cardiac functions in vitro and in vivo. However, since the targeted treatment group represents mainly elderly or otherwise sick patients, it is unclear whether and to what extent autologous mitochondria would exert their beneficial effects in these cases. Stem cells might represent better sources for mitochondria and could enhance the effect of mitochondrial transplantations. Therefore in this review we aim to provide an overview on aging effects of stem cells and mitochondria which might be important for mitochondrial transplantation and to give an overview on the current state in this field together with considerations worthwhile for further investigations.

Hallmarks of aging and immunosenescence: Connecting the dots

Aging is a natural physiological process that features various and variable challenges, associated with loss of homeostasis within the organism, often leading to negative consequences for health. Cellular senescence occurs when cells exhaust the capacity to renew themselves and their tissue environment as the cell cycle comes to a halt. This process is influenced by genetics, metabolism and extrinsic factors. Immunosenescence, the aging of the immune system, is a result of the aging process, but can also in turn act as a secondary inducer of senescence within other tissues. This review aims to summarize the current state of knowledge regarding hallmarks of aging in relation to immunosenescence, with a focus on aging-related imbalances in the medullary environment, as well as the components of the innate and adaptive immune responses. Aging within the immune system alters its functionality, and has consequences for the person's ability to fight infections, as well as for susceptibility to chronic diseases such as cancer and cardiovascular disease. The senescence-associated secretory phenotype is described, as well as the involvement of this phenomenon in the paracrine induction of senescence in otherwise healthy cells. Inflammaging is discussed in detail, along with the comorbidities associated with this process. A knowledge of these processes is required in order to consider possible targets for the application of senotherapeutic agents - interventions with the potential to modulate the senescence process, thus prolonging the healthy lifespan of the immune system and minimizing the secondary effects of immunosenescence.

The rationale for selenium supplementation in inflammatory bowel disease: A mechanism-based point of view

Management of inflammatory bowel disease (IBD) has always been a challenge for physicians. Current treatment protocols may cause numerous adverse effects. Selenium is known for its putative antiinflammatory properties. Selenium is needed for the biosynthesis of enzymatically active selenoproteins, which contribute to antioxidative defense, and effective function of immune systems. Several studies have shown that patients with IBD have a lower selenium level compared to healthy subjects. Hence, experimental studies mimicking ulcerative colitis and Crohn's disease investigated the effect of selenium supplementation on IBD. Previous studies indicated the following: 1) Selenoproteins can curb the inflammatory response and attenuate oxidative stress. This antiinflammatory property caused remission in animal models of colitis. 2) Selenium supports protective gut microbiota, which indirectly improves management of IBD. 3) Selenium may block some of the predominant tumorigenesis pathways proposed in colitis-associated colorectal cancer. 4) Selenium supplementation showed promising results in preliminary clinical studies, particularly in patients with selenium deficiency. While selenium supplementation seems to be beneficial for IBD, clinical studies have remained too preliminary in this regard. Randomized clinical trials are needed to measure the short-term and long-term effects of selenium on both active and quiescent IBD, particularly in patients with IBD who have documented selenium deficiency.

Signaling Network Centered on mTORC1 Dominates Mammalian Intestinal Stem Cell Ageing

The intestine integrates the function of digestion, absorption, and barrier, which is easily damaged by the external factors upon ageing. The intestinal stem cells (ISCs) exist at the intestinal crypt base and play an indispensable role in intestinal homeostasis and regeneration. The intestine ageing contributes to malabsorption and other associated illnesses, which were considered to be related to ISCs. Here, we summarize the current research progress of mammalian ISCs ageing and pay more attention to the central regulatory role of the mTORC1 signaling pathway in regulating mammalian ISCs ageing, and its related AMPK, FOXO, Wnt signaling pathways. Furthermore, we also discuss the interventions aimed at mTORC1 and its associated signaling pathways, which may provide potential strategies for rejuvenating aged ISCs and the therapy of age-related intestinal diseases. Graphical abstract Many signaling pathways are altered in the ageing ISCs, thereby inducing the decrease of ISC self-renewal, differentiation, and regeneration, an increasing of oxidative stress may contribute to damage to the ISCs. Interventions such as calorie restriction, fasting and so on can effectively alleviate these adverse effects.

Wound Induced Hair Neogenesis - A Novel Paradigm for Studying Regeneration and Aging

Hair follicles are the signature dermal appendage of mammals. They can be thought of as mini-organs with defined polarity, distinct constituent cell types, dedicated neurovascular supply, and specific stem cell compartments. Strikingly, some mammals show a capacity for adult hair follicle regeneration in a phenomenon known as wound-induced hair neogenesis (WIHN). In WIHN functional hair follicles reemerge during healing of large cutaneous wounds, and they can be counted to provide an index of regeneration. While age-related decline in hair follicle number and cycling are widely appreciated in normal physiology, it is less clear whether hair follicle regeneration also diminishes with age. WIHN provides an extraordinary quantitative system to address questions of mammalian regeneration and aging. Here we review cellular and molecular underpinnings of WIHN, explore known age-related changes to these elements, and present unanswered questions for future exploration.

Age-related changes in intestinal immunity and the microbiome

The gastrointestinal (GI) tract is a vitally important site for the adsorption of nutrients as well as the education of immune cells. Homeostasis of the gut is maintained by the interplay of the intestinal epithelium, immune cells, luminal Ags, and the intestinal microbiota. The well-being of the gut is intrinsically linked to the overall health of the host, and perturbations to this homeostasis can have severe impacts on local and systemic health. One factor that causes disruptions in gut homeostasis is age, and recent research has elucidated how critical systems within the gut are altered during the aging process. Intestinal stem cell proliferation, epithelial barrier function, the gut microbiota, and the composition of innate and adaptive immune responses are all altered in advanced age. The aging population continues to expand worldwide, a phenomenon referred to as the "Silver Tsunami," and every effort must be made to understand how best to prevent and treat age-related maladies. Here, recent research about changes observed in the intestinal epithelium, the intestinal immune system, the microbiota, and how the aging gut interacts with and influences other organs such as the liver, lung, and brain are reviewed. Better understanding of these age-related changes and their impact on multi-organ interactions will aid the development of therapies to increase the quality of life for all aged individuals.

Senescence-accelerated mouse prone 8 mice exhibit specific morphological changes in the small intestine during senescence and after pectin supplemented diet

Impairment of gastrointestinal function and reduction of nutrient absorption associated with aging contribute to increased risk of malnutrition in the elderly population, resulting in physical weakness and vulnerability to disease. The present study was performed to examine the relationships between aging-associated morphological changes of the small intestine and nutrient malabsorption using senescence-accelerated mouse prone 8 (SAMP8) mice. Comparison of the morphology of the small intestine of young (22-week-old) and senescent (43-week-old) SAMP8 mice showed no significant changes in villus length, while the mRNA expression levels of secretory cell marker genes were significantly reduced in senescent mice. In addition, crypts recovered from the small intestine of senescent mice showed a good capacity to form intestinal organoids ex vivo, suggesting that the regenerative capacity of intestinal stem cells (ISCs) was unaffected by accelerated senescence. These results indicated that changes induced by accelerated senescence in the small intestine of SAMP8 mice are different from changes reported previously in normal aging mouse models. Biochemical analyses of serum before and during senescence also indicated that senescent SAMP8 mice are not in a malabsorption state. Furthermore, a diet supplemented with persimmon pectin had a mild effect on the small intestine of senescent SAMP8 mice. Intestinal villus length was slightly increased in the medial part of the small intestine of pectin-fed mice. In contrast, intestinal crypt formation capacity was enhanced by the pectin diet. Organoid culture derived from the small intestine of mice fed pectin exhibited a greater number of lobes per organoid compared with those from mice fed a control diet, and Lyz1 and Olfm4 mRNA levels were significantly increased. In conclusion, accelerated senescence induced exclusive changes in the small intestine, which were not related to nutrient malabsorption. Therefore, the SAMP8 strain may not be a suitable model to evaluate the effects of aging on intestinal homeostasis and nutrient absorption impairment.

High Canonical Wnt/β-Catenin Activity Sensitizes Murine Hematopoietic Stem and Progenitor Cells to DNA Damage

Aging is characterized by the accumulation of DNA damage and a decrease in stem cell functionality, yet molecular mechanisms that limit the maintenance of stem cells in response to DNA damage remain to be delineated. Here we show in mouse models that DNA damage leads to a transient over-activation of Wnt signaling in hematopoietic stem cells (HSCs), and that high activity of canonical Wnt/β-catenin signaling sensitizes HSCs to DNA damage induced by X-irradiation which results in preferential maintenance of HSCs with low levels of Wnt signaling. The study shows that genetic or chemical activation of canonical Wnt signaling enhances radiosensitivity of HSCs while inhibition of Wnt signaling decreases it. Together, these results indicate that levels of Wnt signaling activity mediate heterogeneity in the sensitivity of HSCs to DNA damage induced depletion. These findings could be relevant for molecular alterations and selection of stem cells in the context of DNA damage accumulation during aging and cancer formation.

IRF2 maintains the stemness of colonic stem cells by limiting physiological stress from interferon

The physiological stresses that diminish tissue stem-cell characteristics remain largely unknown. We previously reported that type I interferon (IFN), which is essential for host antiviral responses, is a physiological stressor for hematopoietic stem cells (HSCs) and small intestinal stem cells (ISCs) and that interferon regulatory factor-2 (IRF2), which attenuates IFN signaling, maintains their stemness. Here, using a dextran sodium sulfate (DSS)-induced colitis model, we explore the role of IRF2 in maintaining colonic epithelial stem cells (CoSCs). In mice with a conditional Irf2 deletion in the intestinal epithelium (hereafter Irf2ΔIEC mice), both the number and the organoid-forming potential of CoSCs were markedly reduced. Consistent with this finding, the ability of Irf2ΔIEC mice to regenerate colon epithelium after inducing colitis was severely impaired, independently of microbial dysbiosis. Mechanistically, CoSCs differentiated prematurely into transit-amplifying (TA) cells in Irf2ΔIEC mice, which might explain their low CoSC counts. A similar phenotype was induced in wild-type mice by repeated injections of low doses of poly(I:C), which induces type I IFN. Collectively, we demonstrated that chronic IFN signaling physiologically stresses CoSCs. This study provides new insight into the development of colitis and molecular mechanisms that maintain functional CoSCs throughout life.

Improvement of intestinal stem cells and barrier function via energy restriction in middle-aged C57BL/6 mice

This study aimed to reveal the impact of energy restriction on the intestine via structural and molecular changes in terms of intestinal stem cell (ISC) function, ISC niche, intestinal epithelial barrier function, and intestinal immune function. Female C57BL/6J mice, aged 12 months, fed a commercial chow were used in this study. The ISC function, ISC niche, intestinal epithelial barrier function, and intestinal immune function were assessed. Energy restriction reversed aging-induced intestinal shortening and made the crypts shallower. The intestinal epithelial cells isolated from the intestine showed a significant increase in the expression levels of stem cell-associated genes in small intestinal epithelial cells as detected by flow cytometry. Despite the increase in the number of stem cells and the expression levels of markers, no increase or decrease was found in the enteroid complexity of the small intestine and colonic enteroid formation in vitro. The colonic mucous layer was measured in mice of the energy restricted (ER)-treated group to investigate the epithelial barrier function in the colon. The results revealed that the barrier was more complete. The fluorescence intensity of tight junction markers claudin-2 and zonula occludens-1 increased and the mRNA expression profiles of monocyte chemotactic protein 1 and interleukin-6 decreased in the colon of mice in the ER-treated group. The beneficial effects of ER on the colon in terms of the integrity of the mucosal barrier and alleviation of inflammation were confirmed, thus highlighting the importance of modulating the intestinal function in developing effective antiaging dietary interventions.

Tissue Adaptation to Environmental Cues by Symmetric and Asymmetric Division Modes of Intestinal Stem Cells

Tissues must adapt to the different external stimuli so that organisms can survive in their environments. The intestine is a vital organ involved in food processing and absorption, as well as in innate immune response. Its adaptation to environmental cues such as diet and biotic/abiotic stress involves regulation of the proliferative rate and a switch of division mode (asymmetric versus symmetric) of intestinal stem cells (ISC). In this review, we outline the current comprehension of the physiological and molecular mechanisms implicated in stem cell division modes in the adult Drosophila midgut. We present the signaling pathways and polarity cues that control the mitotic spindle orientation, which is the terminal determinant ensuring execution of the division mode. We review these events during gut homeostasis, as well as during its response to nutrient availability, bacterial infection, chemical damage, and aging. JNK signaling acts as a central player, being involved in each of these conditions as a direct regulator of spindle orientation. The studies of the mechanisms regulating ISC divisions allow a better understanding of how adult stem cells integrate different signals to control tissue plasticity, and of how various diseases, notably cancers, arise from their alterations.

The eroding chromatin landscape of aging stem cells

Adult stem cells undergo both replicative and chronological aging in their niches, with catastrophic declines in regenerative potential with age. Due to repeated environmental insults during aging, the chromatin landscape of stem cells erodes, with changes in both DNA and histone modifications, accumulation of damage, and altered transcriptional response. A body of work has shown that altered chromatin is a driver of cell fate changes and a regulator of self-renewal in stem cells and therefore a prime target for juvenescence therapeutics. This review focuses on chromatin changes in stem cell aging and provides a composite view of both common and unique epigenetic themes apparent from the studies of multiple stem cell types.