Asymmetric cell division-dominant neutral drift model for normal intestinal stem cell homeostasis

Regulation of the Intestinal Stem Cell Pool and Proliferation in Drosophila

Understanding the regulation of somatic stem cells, both during homeostasis and in response to environmental challenges like injury, infection, chemical exposure, and nutritional changes, is critical because their dysregulation can result in tissue degeneration or tumorigenesis. The use of models such as the Drosophila and mammalian adult intestines offers valuable insights into tissue homeostasis and regeneration, advancing our knowledge of stem cell biology and cancer development. This review highlights significant findings from recent studies, unveiling the molecular mechanisms that govern self-renewal, proliferation, differentiation, and regeneration of intestinal stem cells (ISCs). These insights not only enhance our understanding of normal tissue maintenance but also provide critical perspectives on how ISC dysfunction can lead to pathological conditions such as colorectal cancer (CRC).

Gut aging: A wane from the normal to repercussion and gerotherapeutic strategies

Globally, age-related diseases represent a significant public health concern among the elderly population. In aging, healthy organs and tissues undergo structural and functional changes that put the aged adults at risk of diseases. Some of the age-related diseases include cancer, atherosclerosis, brain disorders, muscle atrophy (sarcopenia), gastrointestinal (GIT) disorders, etc. In organs, a decline in stem cell function is the starting point of many conditions and is extremely important in GIT disorder development. Many studies have established that aging affects stem cells and their surrounding supportive niche components. Although there is a significant advancement in treating intestinal aging, the rising elderly population coupled with a higher occurrence of chronic gut ailments necessitates more effective therapeutic approaches to preserve gut health. Notable therapeutic strategies such as Western medicine, traditional Chinese medicine, and other health-promotion interventions have been reported in several studies to hold promise in mitigating age-related gut disorders. This review highlights findings across various facets of gut aging with a focus on aging-associated changes of intestinal stem cells and their niche components, thus a deviation from the normal to repercussion, as well as essential therapeutic strategies to mitigate intestinal aging.

Minimizing cell number fluctuations in self-renewing tissues with a stem-cell niche

Self-renewing tissues require that a constant number of proliferating cells is maintained over time. This maintenance can be ensured at the single-cell level or the population level. Maintenance at the population level leads to fluctuations in the number of proliferating cells over time. Often, it is assumed that those fluctuations can be reduced by increasing the number of asymmetric divisions, i.e., divisions where only one of the daughter cells remains proliferative. Here, we study a model of cell proliferation that incorporates a stem-cell niche of fixed size, and explicitly model the cells inside and outside the niche. We find that in this model, fluctuations are minimized when the difference in growth rate between the niche and the rest of the tissue is maximized and all divisions are symmetric divisions, producing either two proliferating or two nonproliferating daughters. We show that this optimal state leaves visible signatures in clone size distributions and could thus be detected experimentally.

Molecular regulation mechanism of intestinal stem cells in mucosal injury and repair in ulcerative colitis

Ulcerative colitis (UC) is a chronic nonspecific inflammatory disease with complex causes. The main pathological changes were intestinal mucosal injury. Leucine-rich repeat-containing G protein coupled receptor 5 (LGR5)-labeled small intestine stem cells (ISCs) were located at the bottom of the small intestine recess and inlaid among Paneth cells. LGR5+ small ISCs are active proliferative adult stem cells, and their self-renewal, proliferation and differentiation disorders are closely related to the occurrence of intestinal inflammatory diseases. The Notch signaling pathway and Wnt/β-catenin signaling pathway are important regulators of LGR5-positive ISCs and together maintain the function of LGR5-positive ISCs. More importantly, the surviving stem cells after intestinal mucosal injury accelerate division, restore the number of stem cells, multiply and differentiate into mature intestinal epithelial cells, and repair the damaged intestinal mucosa. Therefore, in-depth study of multiple pathways and transplantation of LGR5-positive ISCs may become a new target for the treatment of UC.

Regulation and functions of cell division in the intestinal tissue

In multicellular organisms, epithelial cells are key elements of tissue organization. In developing epithelial tissues, cellular proliferation and differentiation are under the tight regulation of morphogenetic programs to ensure correct organ formation and functioning. In these processes, proliferation rates and division orientation regulate the speed, timing and direction of tissue expansion but also its proper patterning. Moreover, tissue homeostasis relies on spatio-temporal modulations of daughter cell behavior and arrangement. These aspects are particularly crucial in the intestine, which is one of the most proliferative tissues in adults, making it a very attractive adult organ system to study the role of cell division on epithelial morphogenesis and organ function. Although epithelial cell division has been the subject of intense research for many years in multiple models, it still remains in its infancy in the context of the intestinal tissue. In this review, we focus on the current knowledge on cell division and regulatory mechanisms at play in the intestinal epithelial tissue, as well as their importance in developmental biology and physiopathology.

Mother cells control daughter cell proliferation in intestinal organoids to minimize proliferation fluctuations

During renewal of the intestine, cells are continuously generated by proliferation. Proliferation and differentiation must be tightly balanced, as any bias toward proliferation results in uncontrolled exponential growth. Yet, the inherently stochastic nature of cells raises the question how such fluctuations are limited. We used time-lapse microscopy to track all cells in crypts of growing mouse intestinal organoids for multiple generations, allowing full reconstruction of the underlying lineage dynamics in space and time. Proliferative behavior was highly symmetric between sister cells, with both sisters either jointly ceasing or continuing proliferation. Simulations revealed that such symmetric proliferative behavior minimizes cell number fluctuations, explaining our observation that proliferating cell number remained constant even as crypts increased in size considerably. Proliferative symmetry did not reflect positional symmetry but rather lineage control through the mother cell. Our results indicate a concrete mechanism to balance proliferation and differentiation with minimal fluctuations that may be broadly relevant for other tissues.

Intestinal plasticity and metabolism as regulators of organismal energy homeostasis

The small intestine displays marked anatomical and functional plasticity that includes adaptive alterations in adult gut morphology, enteroendocrine cell profile and their hormone secretion, as well as nutrient utilization and storage. In this Perspective, we examine how shifts in dietary and environmental conditions bring about changes in gut size, and describe how the intestine adapts to changes in internal state, bowel resection and gastric bypass surgery. We highlight the critical importance of these intestinal remodelling processes in maintaining energy balance of the organism, and in protecting the metabolism of other organs. The intestinal resizing is supported by changes in the microbiota composition, and by activation of carbohydrate and fatty acid metabolism, which govern the intestinal stem cell proliferation, intestinal cell fate, as well as survivability of differentiated epithelial cells. The discovery that intestinal remodelling is part of the normal physiological adaptation to various triggers, and the potential for harnessing the reversible gut plasticity, in our view, holds extraordinary promise for developing therapeutic approaches against metabolic and inflammatory diseases.

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.

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.

Chewing the Fat with Microbes: Lipid Crosstalk in the Gut

It is becoming increasingly important for any project aimed at understanding the effects of diet on human health, to also consider the combined effect of the trillions of microbes within the gut which modify and are modified by dietary nutrients. A healthy microbiome is diverse and contributes to host health, partly via the production and subsequent host absorption of secondary metabolites. Many of the beneficial bacteria in the gut rely on specific nutrients, such as dietary fiber, to survive and thrive. In the absence of those nutrients, the relative proportion of good commensal bacteria dwindles while communities of opportunistic, and potentially pathogenic, bacteria expand. Therefore, it is unsurprising that both diet and the gut microbiome have been associated with numerous human diseases. Inflammatory bowel diseases and colorectal cancer are associated with the presence of certain pathogenic bacteria and risk increases with consumption of a Western diet, which is typically high in fat, protein, and refined carbohydrates, but low in plant-based fibers. Indeed, despite increased screening and better care, colorectal cancer is still the 2nd leading cause of cancer death in the US and is the 3rd most diagnosed cancer among US men and women. Rates are rising worldwide as diets are becoming more westernized, alongside rising rates of metabolic diseases like obesity and diabetes. Understanding how a modern diet influences the microbiota and how subsequent microbial alterations effect human health will become essential in guiding personalized nutrition and healthcare in the future. Herein, we will summarize some of the latest advances in understanding of the three-way interaction between the human host, the gut microbiome, and the specific class of dietary nutrients, lipids.

Intestinal organoids in coculture: redefining the boundaries of gut mucosa ex vivo modeling

All-time preservation of an intact mucosal barrier is crucial to ensuring intestinal homeostasis and, hence, the organism's overall health maintenance. This complex process relies on an equilibrated signaling system between the intestinal epithelium and numerous cell populations inhabiting the gut mucosa. Any perturbations of this delicate cross talk, particularly regarding the immune cell compartment and microbiota, may sustainably debilitate the intestinal barrier function. As a final joint event, a critical rise in epithelial permeability facilitates the exposure of submucosal immunity to microbial antigens, resulting in uncontrolled inflammation, collateral tissue destruction, and dysbiosis. Organoid-derived intestinal coculture models have established themselves as convenient tools to reenact such pathophysiological events, explore interactions between selected cell populations, and assess their roles with a central focus on intestinal barrier recovery and stabilization.

Cellular origins and lineage relationships of the intestinal epithelium

Knowledge of the development and hierarchical organization of tissues is key to understanding how they are perturbed in injury and disease, as well as how they may be therapeutically manipulated to restore homeostasis. The rapidly regenerating intestinal epithelium harbors diverse cell types and their lineage relationships have been studied using numerous approaches, from classical label-retaining and genetic lineage tracing methods to novel transcriptome-based annotations. Here, we describe the developmental trajectories that dictate differentiation and lineage specification in the intestinal epithelium. We focus on the most recent single-cell RNA-sequencing (scRNA-seq)-based strategies for understanding intestinal epithelial cell lineage relationships, underscoring how they have refined our view of the development of this tissue and highlighting their advantages and limitations. We emphasize how these technologies have been applied to understand the dynamics of intestinal epithelial cells in homeostatic and injury-induced regeneration models.

Rspo3 regulates the abnormal differentiation of small intestinal epithelial cells in diabetic state

Background

The complications caused by diabetes mellitus (DM) are the focus of clinical treatment. However, little is known about diabetic enteropathy (DE) and its potential underlying mechanism.

Methods

Intestinal epithelial cells (IECs) and intestinal epithelial stem cells (IESCs) were harvested from BKS.Cg-Dock7^m+/+Lepr^db/JNju (DM) mice, and the expression of R-Spondin 3 (Rspo3) was detected by RT-qPCR, Western blotting, immunohistochemistry, and immunofluorescence. The role of Rspo3 in the abnormal differentiation of IECs during DM was confirmed by knockdown experiments. Through miRNA expression profiling, bioinformatics analysis, and RT-qPCR, we further analyzed the differentiation-related miRNAs in the IECs from mice with DM.

Results

Abnormal differentiation of IECs was observed in the mice with DM. The expression of Rspo3 was upregulated in the IECs from the mice with DM. This phenomenon was associated with Rspo3 overexpression. Additionally, Rspo3 is a major determinant of Lgr5+ stem cell identity in the diabetic state. Microarray analysis, bioinformatics analysis, and luciferase reporter assays revealed that microRNA (miR)-380-5p directly targeted Rspo3. Moreover, miR-380-5p upregulation was observed to attenuate the abnormal differentiation of IECs by regulating Rspo3 expression.

Conclusions

Together, our results provide definitive evidence of the essential role of Rspo3 in the differentiation of IECs in DM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02385-8.

Cytoskeletal Control and Wnt Signaling-APC's Dual Contributions in Stem Cell Division and Colorectal Cancer

Intestinal epithelium architecture is sustained by stem cell division. In principle, stem cells can divide symmetrically to generate two identical copies of themselves or asymmetrically to sustain tissue renewal in a balanced manner. The choice between the two helps preserve stem cell and progeny pools and is crucial for tissue homeostasis. Control of spindle orientation is a prime contributor to the specification of symmetric versus asymmetric cell division. Competition for space within the niche may be another factor limiting the stem cell pool. An integrative view of the multiple links between intracellular and extracellular signals and molecular determinants at play remains a challenge. One outstanding question is the precise molecular roles of the tumour suppressor Adenomatous polyposis coli (APC) for sustaining gut homeostasis through its respective functions as a cytoskeletal hub and a down regulator in Wnt signalling. Here, we review our current understanding of APC inherent activities and partners in order to explore novel avenues by which APC may act as a gatekeeper in colorectal cancer and as a therapeutic target.

Role of an active reserve stem cell subset of enteroendocrine cells in intestinal stem cell dynamics and the genesis of small intestinal neuroendocrine tumors

Small intestinal neuroendocrine tumors (SI-NET) are serotonin-secreting well-differentiated neuroendocrine tumors of putative enterochromaffin (EC) cell origin. Recent studies recognize a subset of EC cells that is label-retaining at the +4 position in the crypt and functions as a reserve intestinal stem cell. Importantly, this +4 reserve EC cell subset not only contributes to regeneration of the intestinal epithelium during injury and inflammation but also to basal crypt homeostasis at a constant rate. The latter function suggests that the +4 EC cell subset serves as an active reserve stem cell via a constant rate of dedifferentiation. Characterization of early tumor formation of SI-NET, observed as crypt-based EC cell clusters in many cases of familial SI-NETs, suggests that the +4 active reserve EC cell subset is the cell of origin. This newly discovered active reserve stem cell property of EC cells can account for unique biological mechanisms and processes associated with the genesis and development of SI-NETs. The recognition of this property of the +4 active reserve EC cell subset may provide novel opportunities to explore NETs in the gastrointestinal tract and other organs.

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 Hippo Pathway Effector YAP1 Regulates Intestinal Epithelial Cell Differentiation

The human intestine is covered by epithelium, which is continuously replaced by new cells provided by stem cells located at the bottom of the glands. The maintenance of intestinal stem cells is supported by a niche which is composed of several signaling proteins including the Hippo pathway effectors YAP1/TAZ. The role of YAP1/TAZ in cell proliferation and regeneration is well documented but their involvement on the differentiation of intestinal epithelial cells is unclear. In the present study, the role of YAP1/TAZ on the differentiation of intestinal epithelial cells was investigated using the HT29 cell line, the only multipotent intestinal cell line available, with a combination of knockdown approaches. The expression of intestinal differentiation cell markers was tested by qPCR, Western blot, indirect immunofluorescence and electron microscopy analyses. The results show that TAZ is not expressed while the abolition of YAP1 expression led to a sharp increase in goblet and absorptive cell differentiation and reduction of some stem cell markers. Further studies using double knockdown experiments revealed that most of these effects resulting from YAP1 abolition are mediated by CDX2, a key intestinal cell transcription factor. In conclusion, our results indicate that YAP1/TAZ negatively regulate the differentiation of intestinal epithelial cells through the inhibition of CDX2 expression.