Intestinal Stem Cell Niche Insights Gathered from Both In Vivo and Novel In Vitro Models

Biomaterials to enhance stem cell transplantation

The successful transplantation of stem cells has the potential to transform regenerative medicine approaches and open promising avenues to repair, replace, and regenerate diseased, damaged, or aged tissues. However, pre-/post-transplantation issues of poor cell survival, retention, cell fate regulation, and insufficient integration with host tissues constitute significant challenges. The success of stem cell transplantation depends upon the coordinated sequence of stem cell renewal, specific lineage differentiation, assembly, and maintenance of long-term function. Advances in biomaterials can improve pre-/post-transplantation outcomes by integrating biophysiochemical cues and emulating tissue microenvironments. This review highlights leading biomaterials-based approaches for enhancing stem cell transplantation.

A Small Molecule Promoting Neural Differentiation Suppresses Cancer Stem Cells in Colorectal Cancer

Cancer stem cells (CSCs) are a tumor cell subpopulation that drives tumor progression and metastasis, leading to a poor overall survival of patients. In colorectal cancer (CRC), the hyper-activation of Wnt/β-catenin signaling by a mutation of both adenomatous polyposis coli (APC) and K-Ras increases the size of the CSC population. We previously showed that CPD0857 inactivates Wnt/β-catenin signaling by promoting the ubiquitin-dependent proteasomal degradation of β-catenin and Ras proteins, thereby decreasing proliferation and increasing the apoptosis of CRC lines. CPD0857 also decreased the growth and invasiveness of CRC cells harboring mutant K-Ras resistant to EGFR mAb therapy. Here, we show that CPD0857 treatment decreases proliferation and increases the neuronal differentiation of neural progenitor cells (NPCs). CDP0857 effectively reduced the expression of CSC markers and suppressed self-renewal capacity. CPD0857 treatment also inhibited the proliferation and expression of CSC markers in D-K-Ras MT cells carrying K-Ras, APC and PI3K mutations, indicating the inhibition of PI3K/AKT signaling. Moreover, CPD0857-treated xenograft mice showed a regression of tumor growth and decreased numbers of CSCs in tumors. We conclude that CPD0857 could serve as the basis of a drug development strategy targeting CSCs activated through Wnt/β-catenin-Ras MAPK-PI3K/AKT signaling in CRCs.

The Charming World of the Extracellular Matrix: A Dynamic and Protective Network of the Intestinal Wall

The intestinal extracellular matrix (ECM) represents a complex network of proteins that not only forms a support structure for resident cells but also interacts closely with them by modulating their phenotypes and functions. More than 300 molecules have been identified, each of them with unique biochemical properties and exclusive biological functions. ECM components not only provide a scaffold for the tissue but also afford tensile strength and limit overstretch of the organ. The ECM holds water, ensures suitable hydration of the tissue, and participates in a selective barrier to the external environment. ECM-to-cells interaction is crucial for morphogenesis and cell differentiation, proliferation, and apoptosis. The ECM is a dynamic and multifunctional structure. The ECM is constantly renewed and remodeled by coordinated action among ECM-producing cells, degrading enzymes, and their specific inhibitors. During this process, several growth factors are released in the ECM, and they, in turn, modulate the deposition of new ECM. In this review, we describe the main components and functions of intestinal ECM and we discuss their role in maintaining the structure and function of the intestinal barrier. Achieving complete knowledge of the ECM world is an important goal to understand the mechanisms leading to the onset and the progression of several intestinal diseases related to alterations in ECM remodeling.

Large-Scale Production of Recombinant Noggin and R-Spondin1 Proteins Required for the Maintenance of Stem Cells in Intestinal Organoid Cultures

The presence of the proteins mouse R-Spondin1 (mRSpo1) and mouse Noggin (mNoggin) in a 3D-organoid culture allows for the maintenance of intestinal stem cells. Here, we describe a transient gene expression method for the production of these proteins from human embryo kidney 293 (HEK293) cells cultivated in suspension using orbitally shaken bioreactors. Plasmid DNA was delivered into cells using the cationic polymer polyethylenimine (PEI). The 7-day production cultures were performed in the presence of valproic acid (VPA), an enhancer of recombinant gene expression. Both proteins were secreted from the transfected cells. mRSpo1 was produced as a secreted Fc fusion protein (mRSpo1-Fc) and purified by protein A-based affinity chromatography. mNoggin was produced as a secreted histidine-tagged protein (mNoggin-His) and purified by immobilized metal affinity chromatography (IMAC). This transient transfection system supports a high production efficiency.

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.

Vitamin D and Wnt3A have additive and partially overlapping modulatory effects on gene expression and phenotype in human colon fibroblasts

The Wnt/β-catenin signalling pathway is essential for intestinal epithelium homeostasis, but its aberrant activation is a hallmark of colorectal cancer (CRC). Several studies indicate that the bioactive vitamin D metabolite 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) inhibits proliferation and promotes epithelial differentiation of colon carcinoma cells in part through antagonism of the Wnt/β-catenin pathway. It is now accepted that stromal fibroblasts are crucial in healthy and pathologic intestine: pericryptal myofibroblasts are constituents of the stem cell niche and cancer-associated fibroblasts (CAFs) contribute to CRC progression. However, studies on the combined action of 1,25(OH)₂D₃ and Wnt factors in colon fibroblasts are lacking. Here we show by global transcriptomic studies that 1,25(OH)₂D₃ and Wnt3A have profound, additive, partially overlapping effects on the gene expression profile of CCD-18Co human colon myofibroblasts. Moreover, 1,25(OH)₂D₃ and Wnt3A inhibit CCD-18Co cell proliferation and migration, while 1,25(OH)₂D₃ reduces, but Wnt3A increases, their capacity to contract collagen gels (a marker of fibroblast activation). These data were largely confirmed in patient-derived primary colon normal fibroblasts and CAFs, and in fibroblasts from other origins. Our results indicate that 1,25(OH)₂D₃ and Wnt3A are strong regulators of colon fibroblast biology and contribute to a better knowledge of intestinal homeostasis and stromal fibroblast action in CRC.

The atypical RhoU/Wrch1 Rho GTPase controls cell proliferation and apoptosis in the gut epithelium

BACKGROUND

The mammalian gut epithelium displays among the highest rates of self-renewal, with a turnover time of less than 5 days. Renewal involves concerted proliferation at the bottom of the crypt, migration and differentiation along the crypt-villus axis and anoïkis/shedding in the luminal epithelium. Renewal is controlled by interplay between signalling pathways, among which canonical and non-canonical Wnt signals play prominent roles. Overall 92% of colon tumours show increased canonical Wnt signalling resulting from mutations, established as major driver steps towards carcinogenesis.

RESULTS

Here, we examined the physiological role of RhoU/Wrch1 in gut homeostasis. RhoU is an atypical Rho GTPase related to Cdc42/Rac1 and identified as a transcriptional target of non-canonical Wnt signalling. We found that RHOU expression is reduced in human colorectal tumour samples. We show that RhoU is mainly expressed in the differentiated compartment of the gut epithelium. Rhou specific invalidation in the mouse gut elicits cell hyperplasia and is associated in the colon with a highly disorganized luminal epithelium. Hyperplasia affects all cell types in the small intestine and colon and has a higher impact on goblet cells. Hyperplasia is associated with a reduction of apoptosis and an increased proliferation. RhoU knockdown in human DLD-1 colon cancer cells also elicits a higher growth index and reduces cell apoptosis. Last, loss of RhoU function in the mouse gut epithelium or in DLD-1 cells increases RhoA activity and the level of phosphorylated Myosin Light Chain-2, which may functionally link RhoU activity to apoptosis.

CONCLUSION

RhoU is mostly expressed in the differentiated compartment of the gut. It plays a role in homeostasis as its specific invalidation elicits hyperplasia of all cell types. This mainly results from a reduction of apoptosis, through actomyosin-dependent mechanisms.

SIGNIFICANCE

RhoU negatively controls cell growth in the intestinal epithelium. Since its expression is sensitive to non-canonical Wnt signals and is reduced in colorectal tumours, downregulating RhoU may thus have an instrumental role in tumour progression.

Three-Dimensional Organoids in Cancer Research: The Search for the Holy Grail of Preclinical Cancer Modeling

Most solid tumors become therapy resistant and will relapse, with no durable treatment option available. One major impediment to our understanding of cancer biology and finding innovative approaches to cancer treatment stems from the lack of better preclinical tumor models that address and explain tumor heterogeneity and person-to-person differences in therapeutic and toxic responses. Past cancer research has been driven by inadequate in vitro assays utilizing two-dimensional monolayers of cancer cells and animal models. Additionally, animal models do not truly mimic the original human tumor, are time consuming, and usually costly. New preclinical models are needed for innovation in cancer translational research. Hence, it is time to welcome the three-dimensional (3D) organoids: self-organizing cells grown in 3D culture systems mimicking the parent tissues from which the primary cells originate. The 3D organoids offer deeper insights into the crucial cellular processes in tissue and organ formation and pathological processes. Generation of near-perfect physiological microenvironments allow 3D organoids to couple with gene editing tools, such as the clustered regularly interspersed short palindromic repeat (CRISPR)/CRISPR-associated 9 and the transcription activator-like effector nucleases to model human diseases, offering distinct advantages over current models. We explain in this expert review that through recapitulating patients' normal and tumor tissues, organoid technology can markedly advance personalized medicine and help reveal once hidden aspects of cancers. The use of defined tissue- or organ-specific matrices, among other factors, will likely allow organoid technology to realize its potential in innovating many fields of life sciences.

Overview of the oncogenic signaling pathways in colorectal cancer: Mechanistic insights

Colorectal cancer is a multifaceted disease which is therapeutically challenging. Based on insights gleaned from almost a quarter century of research, it is obvious that deregulation of spatio-temporally controlled signaling pathways play instrumental role in development and progression of colorectal cancer. High-throughput technologies have helped to develop a sharper and broader understanding of the wide ranging signal transduction cascades which also contribute to development of drug resistance, loss of apoptosis and, ultimately, of metastasis. In this review, we have set the spotlight on role of JAK/STAT, TGF/SMAD, Notch, WNT/β-Catenin, SHH/GLI and p53 pathways in the development and progression of colorectal cancer. We have also highlighted recent reports on TRAIL-mediated pathways and molecularly distinct voltage-gated sodium channels in colorectal cancer.

Milk phospholipids ameliorate mouse colitis associated with colonic goblet cell depletion via the Notch pathway

Milk phospholipids attenuated the severity of DSS-induced mouse colitis and prevented the depletion of colonic goblet cells through balancing the over-activated Notch pathway mediated by colonic myofibroblasts.

Intestinal organoids for modelling intestinal development and disease

Gastrointestinal diseases are becoming increasingly prevalent in developed countries. Immortalized cells and animal models have delivered important but limited insight into the mechanisms that initiate and propagate these diseases. Human-specific models of intestinal development and disease are desperately needed that can recapitulate structure and function of the gut in vitro Advances in pluripotent stem cells and primary tissue culture techniques have made it possible to culture intestinal epithelial cells in three dimensions that self-assemble to form 'intestinal organoids'. These organoids allow for new, human-specific models that can be used to gain insight into gastrointestinal disease and potentially deliver new therapies to treat them. Here we review current in vitro models of intestinal development and disease, considering where improvements could be made and potential future applications in the fields of developmental modelling, drug/toxicity testing and therapeutic uses.This article is part of the theme issue 'Designer human tissue: coming to a lab near you'.