Mechanical guidance to self-organization and pattern formation of stem cells.

The self-organization of stem cells (SCs) constitutes the fundamental basis of the development of biological organs and structures. SC-driven patterns are essential for tissue engineering, yet unguided SCs tend to form chaotic patterns, impeding progress in biomedical engineering. Here, we show that simple geometric constraints can be used as an effective mechanical modulation approach that promotes the development of controlled self-organization and pattern formation of SCs. Using the applied SC guidance with geometric constraints, we experimentally uncover a remarkable deviation in cell aggregate orientation from a random direction to a specific orientation. Subsequently, we propose a dynamic mechanical framework, including cells, the extracellular matrix (ECM), and the culture environment, to characterize the specific orientation deflection of guided cell aggregates relative to initial geometric constraints, which agrees well with experimental observation. Based on this framework, we further devise various theoretical strategies to realize complex biological patterns, such as radial and concentric structures. Our study highlights the key role of mechanical factors and geometric constraints in governing SCs' self-organization. These findings yield critical insights into the regulation of SC-driven pattern formation and hold great promise for advancements in tissue engineering and bioactive material design for regenerative application.

Droplet-based proteomics reveals CD36 as a marker for progenitors in mammary basal epithelium.

Deep proteomic profiling of rare cell populations has been constrained by sample input requirements. Here, we present DROPPS (droplet-based one-pot preparation for proteomic samples), an accessible low-input platform that generates high-fidelity proteomic profiles of 100-2,500 cells. By applying DROPPS within the mammary epithelium, we elucidated the connection between mitochondrial activity and clonogenicity, identifying CD36 as a marker of progenitor capacity in the basal cell compartment. We anticipate that DROPPS will accelerate biology-driven proteomic research for a multitude of rare cell populations.

Cartilage stem/progenitor cells-derived exosomes facilitate knee cartilage repair in a subacute osteoarthritis rat model.

Cartilage defects in the knee are often associated with the progression of degenerative osteoarthritis (OA), and cartilage repair is a useful strategy for managing this disease. However, cartilage repair is challenging because of the unique environment within the tissue. Recently, stem cell-based therapies have shed new light on this issue. In this study, we prepared exosomes (EXOs) from cartilage stem/progenitor cells (CSPCs) and found that treatment with EXOs increased the viability, migration, and proliferation of cultured primary chondrocytes. In a subacute OA rat model, the application of EXOs facilitated cartilage regeneration as evidenced by histological staining. Exosomal protein analysis together with bioinformatics suggested that cyclin-dependent kinase 9 (CDK9) is a key factor for chondrocyte growth and migration. Functional studies confirmed this prediction, that is, inhibiting CDK9 reduced the beneficial effects induced by EXOs in primary chondrocytes; while overexpression of CDK9 recapitulated the EXOs-induced phenotypes. RNA-Seq data showed that a set of genes involved in cell growth and migration were up-regulated by EXOs in chondrocytes. These changes could be partially reproduced by CDK9 overexpression. Overall, our data suggest that EXOs derived from primary CSPCs hold great therapeutic potential for treating cartilage defect-associated disorders such as degenerative OA, and that CDK9 is a key factor in this process.

Identification of cells of leukemic stem cell origin with non-canonical regenerative properties.

Despite most acute myeloid leukemia (AML) patients entering remission following chemotherapy, outcomes remain poor due to surviving leukemic cells that contribute to relapse. The nature of these enduring cells is poorly understood. Here, through temporal single-cell transcriptomic characterization of AML hierarchical regeneration in response to chemotherapy, we reveal a cell population: AML regeneration enriched cells (RECs). RECs are defined by CD74/CD68 expression, and although derived from leukemic stem cells (LSCs), are devoid of stem/progenitor capacity. Based on REC in situ proximity to CD34-expressing cells identified using spatial transcriptomics on AML patient bone marrow samples, RECs demonstrate the ability to augment or reduce leukemic regeneration in vivo based on transfusion or depletion, respectively. Furthermore, RECs are prognostic for patient survival as well as predictive of treatment failure in AML cohorts. Our study reveals RECs as a previously unknown functional catalyst of LSC-driven regeneration contributing to the non-canonical framework of AML regeneration.

p53 promotes revival stem cells in the regenerating intestine after severe radiation injury.

Ionizing radiation induces cell death in the gastrointestinal (GI) epithelium by activating p53. However, p53 also prevents animal lethality caused by radiation-induced acute GI syndrome. Through single-cell RNA-sequencing of the irradiated mouse small intestine, we find that p53 target genes are specifically enriched in regenerating epithelial cells that undergo fetal-like reversion, including revival stem cells (revSCs) that promote animal survival after severe damage of the GI tract. Accordingly, in mice with p53 deleted specifically in the GI epithelium, ionizing radiation fails to induce fetal-like revSCs. Using intestinal organoids, we show that transient p53 expression is required for the induction of revival stem cells and is controlled by an Mdm2-mediated negative feedback loop. Together, our findings reveal that p53 suppresses severe radiation-induced GI injury by promoting fetal-like reprogramming of irradiated intestinal epithelial cells.

Exploring stem cell frontiers: definitions, challenges, and perspectives for regenerative medicine.

Each year, the European Summer School on Stem Cell Biology and Regenerative Medicine (SCSS) attracts early-career researchers and actively practicing clinicians who specialise in stem cell and regenerative biology. The 16th edition of this influential course took place from 12th to 19th September 2023 on the charming Greek island of Spetses. Focusing on important concepts and recent advances in stem cells, the distinguished faculty included experts spanning the spectrum from fundamental research to clinical trials to market-approved therapies. Alongside an academically intensive programme that bridges the various contexts of stem cell research, delegates were encouraged to critically address relevant questions in stem cell biology and medicine, including broader societal implications. Here, we present a comprehensive overview and key highlights from the SCSS 2023.

TGF-ß downstream of Smad3 and MAPK signaling antagonistically regulate the viability and partial epithelial-mesenchymal transition of liver progenitor cells.

BACKGROUND: Liver progenitor cells (LPCs) are a subpopulation of cells that contribute to liver regeneration, fibrosis and liver cancer initiation under different circumstances. RESULTS: By performing adenoviral-mediated transfection, CCK-8 analyses, F-actin staining, transwell analyses, luciferase reporter analyses and Western blotting, we observed that TGF-ß promoted cytostasis and partial epithelial-mesenchymal transition (EMT) in LPCs. In addition, we confirmed that TGF-ß activated the Smad and MAPK pathways, including the Erk, JNK and p38 MAPK signaling pathways, and revealed that TGFß-Smad signaling induced growth inhibition and partial EMT, whereas TGFß-MAPK signaling had the opposite effects on LPCs. We further found that the activity of Smad and MAPK signaling downstream of TGF-ß was mutually restricted in LPCs. Mechanistically, we found that TGF-ß activated Smad signaling through serine phosphorylation of both the C-terminal and linker regions of Smad2 and 3 in LPCs. Additionally, TGFß-MAPK signaling inhibited the phosphorylation of Smad3 but not Smad2 at the C-terminus, and it reinforced the linker phosphorylation of Smad3 at T179 and S213. We then found that overexpression of mutated Smad3 at linker phosphorylation sites intensifies TGF-ß-induced cytostasis and EMT, mimicking the effects of MAPK inhibition in LPCs, whereas mutation of Smad3 at the C-terminus caused LPCs to blunt TGF-ß-induced cytostasis and partial EMT. CONCLUSION: These results suggested that TGF-ß downstream of Smad3 and MAPK signaling were mutually antagonistic in regulating the viability and partial EMT of LPCs. This antagonism may help LPCs overcome the cytostatic effect of TGF-ß under fibrotic conditions and maintain partial EMT and progenitor phenotypes.

Evidence of a pan-tissue decline in stemness during human aging.

Despite their biological importance, the role of stem cells in human aging remains to be elucidated. In this work, we applied a machine learning methodology to GTEx transcriptome data and assigned stemness scores to 17,382 healthy samples from 30 human tissues aged between 20 and 79 years. We found that ~60% of the studied tissues exhibit a significant negative correlation between the subject's age and stemness score. The only significant exception was the uterus, where we observed an increased stemness with age. Moreover, we observed that stemness is positively correlated with cell proliferation and negatively correlated with cellular senescence. Finally, we also observed a trend that hematopoietic stem cells derived from older individuals might have higher stemness scores. In conclusion, we assigned stemness scores to human samples and show evidence of a pan-tissue loss of stemness during human aging, which adds weight to the idea that stem cell deterioration may contribute to human aging.

hnRNPU is required for spermatogonial stem cell pool establishment in mice.

The continuous regeneration of spermatogonial stem cells (SSCs) underpins spermatogenesis and lifelong male fertility, but the developmental origins of the SSC pool remain unclear. Here, we document that hnRNPU is essential for establishing the SSC pool. In male mice, conditional loss of hnRNPU in prospermatogonia (ProSG) arrests spermatogenesis and results in sterility. hnRNPU-deficient ProSG fails to differentiate and migrate to the basement membrane to establish SSC pool in infancy. Moreover, hnRNPU deletion leads to the accumulation of ProSG and disrupts the process of T1-ProSG to T2-ProSG transition. Single-cell transcriptional analyses reveal that germ cells are in a mitotically quiescent state and lose their unique identity upon hnRNPU depletion. We further show that hnRNPU could bind to Vrk1, Slx4, and Dazl transcripts that have been identified to suffer aberrant alternative splicing in hnRNPU-deficient testes. These observations offer important insights into SSC pool establishment and may have translational implications for male fertility.

The effect of continuous long-term illumination with visible light in different spectral ranges on mammalian cells.

One of the biggest challenges in tissue engineering and regenerative medicine is to ensure oxygen supply of cells in the (temporary) absence of vasculature. With the vision to exploit photosynthetic oxygen production by microalgae, co-cultivated in close vicinity to oxygen-consuming mammalian cells, we are searching for culture conditions that are compatible for both sides. Herein, we investigated the impact of long-term illumination on mammalian cells which is essential to enable photosynthesis by microalgae: four different cell types-primary human fibroblasts, dental pulp stem cells, and osteoblasts as well as the murine beta-cell line INS-1-were continuously exposed to warm white light, red or blue light over seven days. We observed that illumination with red light has no adverse effects on viability, metabolic activity and growth of the cells whereas exposure to white light has deleterious effects that can be attributed to its blue light portion. Quantification of intracellular glutathione did not reveal a clear correlation of this effect with an enhanced production of reactive oxygen species. Finally, our data indicate that the cytotoxic effect of short-wavelength light is predominantly a direct effect of cell illumination; photo-induced changes in the cell culture media play only a minor role.

Enhanced potent immunosuppression of intracellular adipose tissue-derived stem cell extract by priming with three-dimensional spheroid formation.

Immunomodulatory properties of mesenchymal stem cells are widely studied, supporting the use of MSCs as cell-based therapy in immunological diseases. This study aims to generate cell-free MSC extract and improves their immunomodulatory potential. Intracellular extracts were prepared from adipose-derived stem cells (ADSC) spheroid via a freeze-thawing method. The immunomodulatory capacities of ADSC spheroid extracts were investigated in vitro, including lymphocyte proliferation, T regulatory cell expansion, and macrophage assays. A comparative study was conducted with ADSC monolayer extract. The key immunomodulatory mediators presented in ADSC extract were identified. The results revealed that ADSC spheroid extract could suppress lymphocyte activation while enhancing T regulatory cell expansion. Immunomodulatory molecules such as COX-2, TSG-6, and TGF-ß1 were upregulated in ADSC priming via spheroid culture. Selective inhibition of COX-2 abrogates the effect of ADSC extract on inducing T regulatory cell expansion. Thus, ADSC spheroid extract gains high efficacy in regulating the immune responses which are associated in part by COX-2 generation. Furthermore, ADSC spheroid extract possessed a potent anti-inflammation by manipulation of TNF-α production from LPS-activated macrophage. Our current study has highlighted the opportunity of using cell-free extracts from adipose tissue-derived mesenchymal stem cells spheroid as novel immunomodulators for the treatment of immunological-associated diseases.

Adipose-derived stem cells promote glycolysis and peritoneal metastasis via TGF-ß1/SMAD3/ANGPTL4 axis in colorectal cancer.

Peritoneal metastasis, the third most common metastasis in colorectal cancer (CRC), has a poor prognosis for the rapid progression and limited therapeutic strategy. However, the molecular characteristics and pathogenesis of CRC peritoneal metastasis are poorly understood. Here, we aimed to elucidate the action and mechanism of adipose-derived stem cells (ADSCs), a prominent component of the peritoneal microenvironment, in CRC peritoneal metastasis formation. Database analysis indicated that ADSCs infiltration was increased in CRC peritoneal metastases, and high expression levels of ADSCs marker genes predicted a poor prognosis. Then we investigated the effect of ADSCs on CRC cells in vitro and in vivo. The results revealed that CRC cells co-cultured with ADSCs exhibited stronger metastatic property and anoikis resistance, and ADSCs boosted the intraperitoneal seeding of CRC cells. Furthermore, RNA sequencing was carried out to identify the key target gene, angiopoietin like 4 (ANGPTL4), which was upregulated in CRC specimens, especially in peritoneal metastases. Mechanistically, TGF-ß1 secreted by ADSCs activated SMAD3 in CRC cells, and chromatin immunoprecipitation assay showed that SMAD3 facilitated ANGPTL4 transcription by directly binding to ANGPTL4 promoter. The ANGPTL4 upregulation was essential for ADSCs to promote glycolysis and anoikis resistance in CRC. Importantly, simultaneously targeting TGF-ß signaling and ANGPTL4 efficiently reduced intraperitoneal seeding in vivo. In conclusion, this study indicates that tumor-infiltrating ADSCs promote glycolysis and anoikis resistance in CRC cells and ultimately facilitate peritoneal metastasis via the TGF-ß1/SMAD3/ANGPTL4 axis. The dual-targeting of TGF-ß signaling and ANGPTL4 may be a feasible therapeutic strategy for CRC peritoneal metastasis.

Genetic Tools for Cell Lineage Tracing and Profiling Developmental Trajectories in the Skin.

The epidermis is the body's first line of protection against dehydration and pathogens, continually regenerating the outermost protective skin layers throughout life. During both embryonic development and wound healing, epidermal stem and progenitor cells must respond to external stimuli and insults to build, maintain, and repair the cutaneous barrier. Recent advances in CRISPR-based methods for cell lineage tracing have remarkably expanded the potential for experiments that track stem and progenitor cell proliferation and differentiation over the course of tissue and even organismal development. Additional tools for DNA-based recording of cellular signaling cues promise to deepen our understanding of the mechanisms driving normal skin morphogenesis and response to stressors as well as the dysregulation of cell proliferation and differentiation in skin diseases and cancer. In this review, we highlight cutting-edge methods for cell lineage tracing, including in organoids and model organisms, and explore how cutaneous biology researchers might leverage these techniques to elucidate the developmental programs that support the regenerative capacity and plasticity of the skin.

Mechanosensitive protein polycystin-1 promotes periosteal stem/progenitor cells osteochondral differentiation in fracture healing.

Background: Mechanical forces are indispensable for bone healing, disruption of which is recognized as a contributing cause to nonunion or delayed union. However, the underlying mechanism of mechanical regulation of fracture healing is elusive. Methods: We used the lineage-tracing mouse model, conditional knockout depletion mouse model, hindlimb unloading model and single-cell RNA sequencing to analyze the crucial roles of mechanosensitive protein polycystin-1 (PC1, Pkd1) promotes periosteal stem/progenitor cells (PSPCs) osteochondral differentiation in fracture healing. Results: Our results showed that cathepsin (Ctsk)-positive PSPCs are fracture-responsive and mechanosensitive and can differentiate into osteoblasts and chondrocytes during fracture repair. We found that polycystin-1 declines markedly in PSPCs with mechanical unloading while increasing in response to mechanical stimulus. Mice with conditional depletion of Pkd1 in Ctsk+ PSPCs show impaired osteochondrogenesis, reduced cortical bone formation, delayed fracture healing, and diminished responsiveness to mechanical unloading. Mechanistically, PC1 facilitates nuclear translocation of transcriptional coactivator TAZ via PC1 C-terminal tail cleavage, enhancing osteochondral differentiation potential of PSPCs. Pharmacological intervention of the PC1-TAZ axis and promotion of TAZ nuclear translocation using Zinc01442821 enhances fracture healing and alleviates delayed union or nonunion induced by mechanical unloading. Conclusion: Our study reveals that Ctsk+ PSPCs within the callus can sense mechanical forces through the PC1-TAZ axis, targeting which represents great therapeutic potential for delayed fracture union or nonunion.

CircPRKD3/miR-6783-3p responds to mechanical force to facilitate the osteogenesis of stretched periodontal ligament stem cells.

BACKGROUND: The mechanotransduction mechanisms by which cells regulate tissue remodeling are not fully deciphered. Circular RNAs (circRNAs) are crucial to various physiological processes, including cell cycle, differentiation, and polarization. However, the effects of mechanical force on circRNAs and the role of circRNAs in the mechanobiology of differentiation and remodeling in stretched periodontal ligament stem cells (PDLSCs) remain unclear. This article aims to explore the osteogenic function of mechanically sensitive circular RNA protein kinase D3 (circPRKD3) and elucidate its underlying mechanotransduction mechanism. MATERIALS AND METHODS: PDLSCs were elongated with 8% stretch at 0.5 Hz for 24 h using the Flexcell® FX-6000™ Tension System. CircPRKD3 was knockdown or overexpressed with lentiviral constructs or plasmids. The downstream molecules of circPRKD3 were predicted by bioinformatics analysis. The osteogenic effect of related molecules was evaluated by quantitative real-time PCR (qRT-PCR) and western blot. RESULTS: Mechanical force enhanced the osteogenesis of PDLSCs and increased the expression of circPRKD3. Knockdown of circPRKD3 hindered PDLSCs from osteogenesis under mechanical force, while overexpression of circPRKD3 promoted the early osteogenesis process of PDLSCs. With bioinformatics analysis and multiple software predictions, we identified hsa-miR-6783-3p could act as the sponge of circPRKD3 to indirectly regulate osteogenic differentiation of mechanically stimulated PDLSCs. CONCLUSIONS: Our results first suggested that both circPRKD3 and hsa-miR-6783-3p could enhance osteogenesis of stretched PDLSCs. Furthermore, hsa-miR-6783-3p could sponge circPRKD3 to indirectly regulate RUNX2 during the periodontal tissue remodeling process in orthodontic treatment.

The extracts of osteoblast developed from adipose-derived stem cell and its role in osteogenesis.

Cell-based therapy has become an achievable choice in regenerative medicines, particularly for musculoskeletal disorders. Adipose-derived stem cells (ASCs) are an outstanding resource because of their ability and functions. Nevertheless, the use of cells for treatment comes with difficulties in operation and safety. The immunological barrier is also a major limitation of cell therapy, which can lead to unexpected results. Cell-derived products, such as cell extracts, have gained a lot of attention to overcome these limitations. The goal of this study was to optimize the production of ASC-osteoblast extracts as well as their involvement in osteogenesis. The extracts were prepared using a freeze-thaw method with varying temperatures and durations. Overall, osteogenic-associated proteins and osteoinductive potential of the extracts prepared from the osteogenic-induced ASCs were assessed. Our results demonstrated that the freeze-thaw approach is practicable for cell extracts production, with minor differences in temperature and duration having no effect on protein concentration. The ASC-osteoblast extracts contain a significant level of essential specialized proteins that promote osteogenicity. Hence, the freeze-thaw method is applicable for extract preparation and ASC-osteoblast extracts may be beneficial as an optional facilitating biologics in bone anabolic treatment and bone regeneration.

DPSCs regulate epithelial-T cell interactions in oral submucous fibrosis.

BACKGROUND: Oral submucous fibrosis (OSF) is a precancerous lesion characterized by fibrous tissue deposition, the incidence of which correlates positively with the frequency of betel nut chewing. Prolonged betel nut chewing can damage the integrity of the oral mucosal epithelium, leading to chronic inflammation and local immunological derangement. However, currently, the underlying cellular events driving fibrogenesis and dysfunction are incompletely understood, such that OSF has few treatment options with limited therapeutic effectiveness. Dental pulp stem cells (DPSCs) have been recognized for their anti-inflammatory and anti-fibrosis capabilities, making them promising candidates to treat a range of immune, inflammatory, and fibrotic diseases. However, the application of DPSCs in OSF is inconclusive. Therefore, this study aimed to explore the pathogenic mechanism of OSF and, based on this, to explore new treatment options. METHODS: A human cell atlas of oral mucosal tissues was compiled using single-cell RNA sequencing to delve into the underlying mechanisms. Epithelial cells were reclustered to observe the heterogeneity of OSF epithelial cells and their communication with immune cells. The results were validated in vitro, in clinicopathological sections, and in animal models. In vivo, the therapeutic effect and mechanism of DPSCs were characterized by histological staining, immunohistochemical staining, scanning electron microscopy, and atomic force microscopy. RESULTS: A unique epithelial cell population, Epi1.2, with proinflammatory and profibrotic functions, was predominantly found in OSF. Epi1.2 cells also induced the fibrotic process in fibroblasts by interacting with T cells through receptor-ligand crosstalk between macrophage migration inhibitory factor (MIF)-CD74 and C-X-C motif chemokine receptor 4 (CXCR4). Furthermore, we developed OSF animal models and simulated the clinical local injection process in the rat buccal mucosa using DPSCs to assess their therapeutic impact and mechanism. In the OSF rat model, DPSCs demonstrated superior therapeutic effects compared with the positive control (glucocorticoids), including reducing collagen deposition and promoting blood vessel regeneration. DPSCs mediated immune homeostasis primarily by regulating the numbers of KRT19 + MIF + epithelial cells and via epithelial-stromal crosstalk. CONCLUSIONS: Given the current ambiguity surrounding the cause of OSF and the limited treatment options available, our study reveals that epithelial cells and their crosstalk with T cells play an important role in the mechanism of OSF and suggests the therapeutic promise of DPSCs.

Exploring Anti-Fibrotic Effects of Adipose-Derived Stem Cells: Transcriptome Analysis upon Fibrotic, Inflammatory, and Hypoxic Conditioning.

Autologous fat transfers show promise in treating fibrotic skin diseases, reversing scarring and stiffness, and improving quality of life. Adipose-derived stem cells (ADSCs) within these grafts are believed to be crucial for this effect, particularly their secreted factors, though the specific mechanisms remain unclear. This study investigates transcriptomic changes in ADSCs after in vitro fibrotic, inflammatory, and hypoxic conditioning. High-throughput gene expression assays were conducted on ADSCs exposed to IL1-ß, TGF-ß1, and hypoxia and in media with fetal bovine serum (FBS). Flow cytometry characterized the ADSCs. RNA-Seq analysis revealed distinct gene expression patterns between the conditions. FBS upregulated pathways were related to the cell cycle, replication, wound healing, and ossification. IL1-ß induced immunomodulatory pathways, including granulocyte chemotaxis and cytokine production. TGF-ß1 treatment upregulated wound healing and muscle tissue development pathways. Hypoxia led to the downregulation of mitochondria and cellular activity.

Single dose human perinatal stem cells accelerate healing of cold-induced rat burn wound.

Temporal phases of wound healing and their corresponding healing factors are essential in wound regeneration. Mesenchymal stem cells (MSCs) accelerate wound healing via their paracrine secretions by enhancing cell migration, angiogenesis, and reducing inflammation. This study evaluated the local therapeutic effect of human umbilical cord MSCs (hUCMSCs) in the healing of cold-induced burn wounds. An in vitro wound (scratch) was developed in rat skin fibroblasts. The culture was maintained in the conditioned medium (CM) which was prepared by inducing an artificial wound in hUCMSCs in a separate experiment. Treated fibroblasts were analyzed for the gene expression profile of healing mediators involved in wound closure. Findings revealed enhanced cell migration and increased levels of healing mediators in the treated fibroblasts relative to the untreated group. Cold-induced burn wounds were developed in Wistar rats, followed by a single injection of hUCMSCs. Wound healing pattern was examined based on the healing phases: hemostasis/inflammation (Days 1, 3), cell proliferation (Day 7), and remodeling (Day 14). Findings exhibited enhanced wound closure in the treated wound. Gene expression, histological, and immunohistochemical analyses further confirmed enhanced wound regeneration after hUCMSC transplantation. Temporal gene expression profile revealed that the level of corresponding cytokines was substantially increased in the treated wound as compared with the control, indicating improvement in the processes of angiogenesis and remodeling, and a substantial reduction in inflammation. Histology revealed significant collagen formation along with regenerated skin layers and appendages, whereas immunohistochemistry exhibited increased neovascularization during remodeling. Leukocyte infiltration was also suppressed in the treated group. Overall findings demonstrate that a single dose of hUCMSCs enhances wound healing in vivo, and their secreted growth factors accelerate cell migration in vitro.

Organ Frame Elements or Free Intercellular Gel-Like Matrix as Necessary Conditions for Building Organ Structures during Regeneration.

Over the past decades, an unimaginably large number of attempts have been made to restore the structure of mammalian organs after injury by introducing stem cells into them. However, this procedure does not lead to full recovery. At the same time, it is known that complete regeneration (restitution without fibrosis) is possible in organs with proliferating parenchymal cells. An analysis of such models allows to conclude that the most important condition for the repair of histological structures of an organ (in the presence of stem cells) is preservation of the collagen frame structures in it, which serve as "guide rails" for proliferating and differentiating cells. An alternative condition for complete reconstruction of organ structures is the presence of a free "morphogenetic space" containing a gel-like matrix of the embryonic-type connective tissue, which exists during embryonal development of organs in mammals or during complete regeneration in amphibians. Approaches aimed at preserving frame structures or creating a "morphogenetic space" could radically improve the results of organ regeneration using both local and exogenous stem cells.