Conditioned medium of human mesenchymal stromal/stem cells cultured on decellularized extracellular matrix promotes murine skeletal muscle repair after acute injury

Mesenchymal stromal/stem cells (MSCs) and their secretome are known to exert beneficial effects in many pathological states. However, MSCs therapeutic properties can be reduced due to unsuitable in vitro maintenance conditions. Standard culture protocols neglect the fact that MSCs exist in vivo in the closest connection with the extracellular matrix (ECM), the complex protein network providing an instructive microenvironment. We found recently that conditioned medium from human endometrial MSCs cultured on cell-derived decellularized extracellular matrix (CM-dECM) is dramatically enriched in a number of paracrine factors such as GM-CSF, FGF-2, HGF, MMP-1, MCP-1, IL-6, IL-8, CXCL-1, -2, -5, -6 (Ushakov et al., 2024). Given that several upregulated molecules belong to myokines that are known to participate in skeletal muscle regeneration, we hypothesized that CM-dECM may promote restoration of damaged muscle tissue. Here, we found that CM-dECM injections into barium chloride-injured murine m. tibialis anterior caused myofiber hypertrophy and promoted angiogenesis. Besides, CM-dECM significantly contributed to progression of murine C2C12 myoblasts cell cycle suggesting that muscle repair in vivo may be connected with stimulation of resident myoblasts proliferation. In this study, a role for secretome of endometrial MSCs cultured on dECM in injured murine skeletal muscle regeneration was outlined first. Our findings demonstrate that culture on dECM may be considered as a novel preconditioning approach enhancing MSCs therapeutic potential.

The Decellularized Cell-Derived Extracellular Matrix Enhances the Paracrine Function of Human Mesenchymal Stromal/Stem Cells

The mesenchymal stromal/stem cells (MSCs) are known to secrete pleiotropic paracrine factors, contributing to tissue regeneration. This unique ability makes MSCs promising therapeutic tools for many diseases, including even those that were previously untreatable. Thus, the development of preconditioning approaches aimed at enhancing the paracrine function of MSCs attracts great interest. In the present work, we studied how the extracellular matrix, the essential part of the native tissue microenvironment, affects the secretory capacity of MSCs of various origins. The MSC-derived decellularized extracellular matrix (dECM), used as the cell culture substrate, triggered strong upregulation of FGF-2, MMP-1, HGF, GRO-α, GRO-β, CXCL-5, CXCL-6, IL-6, IL-8, G-CSF and MCP-1. Functional in vitro tests revealed that conditioned media derived from MSCs cultured on dECM significantly improved 3T3 fibroblast and HaCaT keratinocyte scratch wound healing, stimulated THP-1 monocyte migration and promoted capillary-like HUVEC-based tube formation compared to conditioned media from MSCs grown on plastic. In addition, we found that FAK inhibition promoted dECM-induced upregulation of paracrine factors, suggesting that this kinase participates in the MSCs' paracrine response to dECM. Together, these findings demonstrate that dECM provides cues that considerably enhance the secretory function of MSCs. Thus, dECM usage as a cell culture substrate alone or in combination with a FAK inhibitor may be viewed as a novel MSC preconditioning technique.

Long-Term Cryopreservation May Cause Genomic Instability and the Premature Senescence of Cells

Cryopreservation is an essential step for utilizing various cell types for biological research and medical purposes. At the same time, there is a lack of data on the effect of cryopreservation, especially when prolonged, on the karyotype of cells. In the present work, we analyzed the genetic stability of cells subjected to a cryopreservation procedure. The objects were immortalized Chinese hamster lung fibroblasts (CHL V-79 RJK line) and human endometrial mesenchymal stem/stromal cells (eMSCs). We showed that short-term cryopreservation in liquid nitrogen for up to 6 months did not affect the karyotype stability of CHL V-79 RJK and eMSCs. On the contrary, karyotyping of G-banded metaphase chromosomes in cells underwent 10-year cryopreservation, which revealed genomic instability in both cell lines associated with the variability of chromosome number in cells, random chromosomal rearrangements, and condensation disorder in homologs. In addition, we found out that long-term cryopreservation of eMSCs does not affect the expression of their typical surface markers and morphology, but results in a significant reduction in proliferative potential and early manifestation of cellular senescence features upon eMSCs culturing. Thus, we concluded that the long-term cryopreservation of cells of different types and biological origin can lead to irreversible changes of their karyotype and acceleration of cellular senescence.

The Dual Luminescence Lifetime pH/Oxygen Sensor: Evaluation of Applicability for Intravital Analysis of 2D- and 3D-Cultivated Human Endometrial Mesenchymal Stromal Cells

The oxygenation of cells and tissues and acidification of the cellular endolysosomal system are among the major factors that ensure normal functioning of an organism and are violated in various pathologies. Recording of these parameters and their changes under various conditions is an important task for both basic research and clinical applications. In the present work, we utilized internalizable dual pH/O2 lifetime sensor (Ir-HSA-FITC) based on the covalent conjugation of human serum albumin (HSA) with fluorescein isothiocyanate (FITC) as pH sensor and an orthometalated iridium complex as O2 sensor. The probe was tested for simultaneous detection of acidification level and oxygen concentration in endolysosomes of endometrial mesenchymal stem/stromal cells (enMSCs) cultivated as 2D monolayers and 3D spheroids. Using a combined FLIM/PLIM approach, we found that due to high autofluorescence of enMSCs FITC lifetime signal in control cells was insufficient to estimate pH changes. However, using flow cytometry and confocal microscopy, we managed to detect the FITC signal response to inhibition of endolysosomal acidification by Bafilomycin A1. The iridium chromophore phosphorescence was detected reliably by all methods used. It was demonstrated that the sensor, accumulated in endolysosomes for 24 h, disappeared from proliferating 2D enMSCs by 72 h, but can still be recorded in non-proliferating spheroids. PLIM showed high sensitivity and responsiveness of iridium chromophore phosphorescence to experimental hypoxia both in 2D and 3D cultures. In spheroids, the phosphorescence signal was detected at a depth of up to 60 μm using PLIM and showed a gradient in the intracellular O2 level towards their center.

Oncogene-Induced Senescence Is a Crucial Antitumor Defense Mechanism of Human Endometrial Stromal Cells

Being the major cellular component of highly dynamic tissue, endometrial stromal cells (EnSCs) are exposed to cycles of proliferation upon hormonal stimulation, which might pose risks for the accumulation of mutations and malignization. However, endometrial stromal tumors are rare and uncommon. The present study uncovered defense mechanisms that might underlie the resistance of EnSCs against oncogenic transformation. All experiments were performed in vitro using the following methods: FACS, WB, RT-PCR, IF, molecular cloning, lentiviral transduction, and CRISPR/Cas9 genome editing. We revealed that the expression of the mutant HRASG12V leads to EnSC senescence. We experimentally confirmed the inability of HRASG12V-expressing EnSCs to bypass senescence and resume proliferation, even upon estrogen stimulation. At the molecular level, the induction of oncogene-induced senescence (OIS) was accompanied by activation of the MEK/ERK, PI3K/AKT, p53/p21WAF/CIP/Rb, and p38/p16INK4a/Rb pathways; however, inhibiting either pathway did not prevent cell cycle arrest. PTEN loss was established as an additional feature of HRASG12V-induced senescence in EnSCs. Using CRISPR-Cas9-mediated PTEN knockout, we identified PTEN loss-induced senescence as a reserve molecular mechanism to prevent the transformation of HRASG12V-expressing EnSCs. The present study highlights oncogene-induced senescence as an antitumor defense mechanism of EnSCs controlled by multiple backup molecular pathways.

EGF, TGF-α and Amphiregulin Differently Regulate Endometrium-Derived Mesenchymal Stromal/Stem Cells

The prototypical receptor tyrosine kinase epidermal growth factor receptor (EGFR) is regulated by a set of its ligands, which determines the specificity of signaling and intracellular fate of the receptor. The EGFR signaling system is well characterized in immortalized cell lines such as HeLa derived from tumor tissues, but much less is known about EGFR function in untransformed multipotent stromal/stem cells (MSCs). We compared the effect of epidermal growth factor (EGF), transforming growth factor-α (TGF-α) and amphiregulin (AREG) on physiological responses in endometrial MSCs (enMSC) and HeLa cells. In addition, using Western blotting and confocal microscopy, we studied the internalization and degradation of EGFR stimulated by the three ligands in these cell lines. We demonstrated that unlike HeLa, EGF and TGF-α, but not AREG, stimulated enMSC proliferation and prevented decidual differentiation in an EGFR-dependent manner. In HeLa cells, EGF targeted EGFR for degradation, while TGF-α stimulated its recycling. Surprisingly, in enMSC, both ligands caused EGFR degradation. In both cell lines, AREG-EGFR internalization was not registered. In HeLa cells, EGFR was degraded within 2 h, restoring its level in 24 h, while in enMSC, degradation took more than 4-8 h, and the low EGFR level persisted for several days. This indicates that EGFR homeostasis in MSCs may differ significantly from that in immortalized cell lines.

Mesenchymal Stem/Stromal Cells in Three-Dimensional Cell Culture: Ion Homeostasis and Ouabain-Induced Apoptosis

This study describes the changes in ion homeostasis of human endometrial mesenchymal stem/stromal cells (eMSCs) during the formation of three-dimensional (3D) cell structures (spheroids) and investigates the conditions for apoptosis induction in 3D eMSCs. Detached from the monolayer culture, (2D) eMSCs accumulate Na⁺ and have dissipated transmembrane ion gradients, while in compact spheroids, eMSCs restore the lower Na⁺ content and the high K/Na ratio characteristic of functionally active cells. Organized as spheroids, eMSCs are non-proliferating cells with an active Na/K pump and a lower K⁺ content per g cell protein, which is typical for quiescent cells and a mean lower water content (lower hydration) in 3D eMSCs. Further, eMSCs in spheroids were used to evaluate the role of K⁺ depletion and cellular signaling context in the induction of apoptosis. In both 2D and 3D eMSCs, treatment with ouabain (1 µM) results in inhibition of pump-mediated K⁺ uptake and severe K⁺ depletion as well as disruption of the mitochondrial membrane potential. In 3D eMSCs (but not in 2D eMSCs), ouabain initiates apoptosis via the mitochondrial pathway. It is concluded that, when blocking the Na/K pump, cardiac glycosides prime mitochondria to apoptosis, and whether a cell enters the apoptotic pathway depends on the cell-specific signaling context, which includes the type of apoptotic protein expressed.

Paracrine and Autocrine Effects of VEGF Are Enhanced in Human eMSC Spheroids

The mechanisms underlying the therapeutic potential of MSCs are the focus of intense research. We studied human MSCs isolated from desquamated endometrium (eMSCs), which, as previously shown, have high regenerative potential in various disease models. The aim was to evaluate the role of secreted VEGF in stimulating angiogenesis and maintaining eMSC viability and migration, which is important for improving the therapeutic properties of MSCs. We compared three eMSC cultures differing in the level of VEGF secretion: 3D spheroids, monolayer eMSCs, and monolayer eMSCs with VEGF knockdown. Spheroid eMSCs produced higher amounts of VEGF and had the strongest paracrine effect on HUVEC. eMSCs with VEGF knockdown did not stimulate angiogenesis. Monolayered eMSCs expressed VEGFR1, while spheroid eMSCs expressed both VEGFR1 and VEGFR2 receptors. The knockdown of VEGF caused a significant decrease in the viability and migration of eMSCs. eMSCs from 3D spheroids enhanced proliferation and migration in response to exogenous VEGF, in contrast to monolayered eMSCs. Our results suggest that the VEGF-VEGFR1 loop appears to be autocrine-involved in maintaining the viability of eMSCs, and VEGFR2 expression enhances their response to exogenous VEGF, so the angiogenic potential of eMSC can be up- or downregulated by intrinsic VEGF signals.

Single ion channel recording in 3D culture of stem cells using patch-clamp technique

Tri-dimensional (3D) cell aggregates or spheroids are considered to be closer to physiological conditions than traditional 2D cell culture. Mesenchymal stem cells (MSCs) assembling in spheroids have increased the survival of transplanted cells. The organization of stem cells in 3D culture affects cell microenvironment and their mechanical properties. The regulation of the biological processes that maintain crucial physiological reactions of MSCs is closely related to the functioning of ion channels. The pattern of expression, role and regulatory mechanisms of ion channels could be significantly different in 3D compared to 2D culture, and, thus, needed to be properly analyzed on the level of ionic currents. Electrophysiological data on the features of ion channels functioning in 3D cell culture models are currently very limited in the literature. This gap of knowledge may be associated with technical difficulties that exist when researchers try to apply the standard patch clamp method for the registration of ion channels in cells aggregated in spheroids. In this regard, our study focuses on solving emerging technical difficulties and presents an example of their successful solution. Here, we developed a specific approach and have recorded the activity of mechanosensitive stretch-activated ion channels (SACs) in endometrial MSCs (eMSCs) assembled in spheroids. Moreover, we observed functional interplay of SACs with potassium channels of big conductance (BK) in the plasma membrane of eMSC spheroids consistently to revealed earlier in routine 2D cultured cells. Additionally, we observed a significant decrease in the frequency of SACs activation in spheroids that may indicate the differences in the level of functional expression of channels in 3D culture comparing to 2D culture of eMSCs.

Store-Operated Ca2+ Entry Contributes to Piezo1-Induced Ca2+ Increase in Human Endometrial Stem Cells

Endometrial mesenchymal stem cells (eMSCs) are a specific class of stromal cells which have the capability to migrate, develop and differentiate into different types of cells such as adipocytes, osteocytes or chondrocytes. It is this unique plasticity that makes the eMSCs significant for cellular therapy and regenerative medicine. Stem cells choose their way of development by analyzing the extracellular and intracellular signals generated by a mechanical force from the microenvironment. Mechanosensitive channels are part of the cellular toolkit that feels the mechanical environment and can transduce mechanical stimuli to intracellular signaling pathways. Here, we identify previously recorded, mechanosensitive (MS), stretch-activated channels as Piezo1 proteins in the plasma membrane of eMSCs. Piezo1 activity triggered by the channel agonist Yoda1 elicits influx of Ca²⁺, a known modulator of cytoskeleton reorganization and cell motility. We found that store-operated Ca²⁺ entry (SOCE) formed by Ca²⁺-selective channel ORAI1 and Ca²⁺ sensors STIM1/STIM2 contributes to Piezo1-induced Ca²⁺ influx in eMSCs. Particularly, the Yoda1-induced increase in intracellular Ca²⁺ ([Ca²⁺]_i) is partially abolished by 2-APB, a well-known inhibitor of SOCE. Flow cytometry analysis and wound healing assay showed that long-term activation of Piezo1 or SOCE does not have a cytotoxic effect on eMSCs but suppresses their migratory capacity and the rate of cell proliferation. We propose that the Piezo1 and SOCE are both important determinants in [Ca²⁺]_i regulation, which critically affects the migratory activity of eMSCs and, therefore, could influence the regenerative potential of these cells.

Induction of Premature Cell Senescence Stimulated by High Doses of Antioxidants Is Mediated by Endoplasmic Reticulum Stress

In our previous study, we found that high doses of several substances with antioxidant capacities (Tempol, resveratrol, diphenyleneiodonium) can cause genotoxic stress and induce premature senescence in the human mesenchymal stem cells (MSCs). Here, using whole-transcriptome analysis, we revealed the signs of endoplasmic reticulum stress and unfolded protein response (UPR) in MSCs stressed with Tempol and resveratrol. In addition, we found the upregulation of genes, coding the UPR downstream target APC/C, and E3 ubiquitin ligase that regulate the stability of cell cycle proteins. We performed the molecular analysis, which further confirmed the untimely degradation of APC/C targets (cyclin A, geminin, and Emi1) in MSCs treated with antioxidants. Human fibroblasts responded to antioxidant applications similarly. We conclude that endoplasmic reticulum stress and impaired DNA synthesis regulation can be considered as potential triggers of cell damage and premature senescence stimulated by high-dose antioxidant treatments.

Effects of IGFBP3 knockdown on human endometrial mesenchymal stromal cells stress-induced senescence

Insulin-like growth factor binding protein 3 (IGFBP3) is known for its pleiotropic ability to regulate various cellular processes such as proliferation, apoptosis, differentiation etc. It has recently been shown that IGFBP3 is part of the secretome of senescent human endometrial mesenchymal stromal cells (MESCs) (Griukova et al., 2019) that takes part in paracrine propagation of senescence-like phenotype in MESCs (Vassilieva et al., 2020); however, mechanisms of pro-senescent IGFBP3 action in MESCs remain still unexplored. This study is aimed at elucidating the role of IGFBP3 upregulation in senescent MESCs. IGFBP3 knockdown in MESCs committed to H₂O₂-induced senescence led to partial abrogation of p21/Rb axis, to elevated ERK phosphorylation and to increase in SA-β-gal activity. Additionally, MESCs derived from various donors were found to demonstrate different IGFBP3 regulation during stress-induced senescence. Obtained results suggest ambiguous role of IGFBP3 in stress-induced senescence of MESCs.

Outcomes of Deferoxamine Action on H2O2-Induced Growth Inhibition and Senescence Progression of Human Endometrial Stem Cells

Mesenchymal stem cells (MSCs) are broadly applied in regenerative therapy to replace cells that are lost or impaired during disease. The low survival rate of MSCs after transplantation is one of the major limitations heavily influencing the success of the therapy. Unfavorable microenvironments with inflammation and oxidative stress in the damaged regions contribute to MSCs loss. Most of the strategies developed to overcome this obstacle are aimed to prevent stress-induced apoptosis, with little attention paid to senescence-another common stress reaction of MSCs. Here, we proposed the strategy to prevent oxidative stress-induced senescence of human endometrial stem cells (hMESCs) based on deferoxamine (DFO) application. DFO prevented DNA damage and stress-induced senescence of hMESCs, as evidenced by reduced levels of reactive oxygen species, lipofuscin, cyclin D1, decreased SA-β-Gal activity, and improved mitochondrial function. Additionally, DFO caused accumulation of HIF-1α, which may contribute to the survival of H2O2-treated cells. Importantly, cells that escaped senescence due to DFO preconditioning preserved all the properties of the initial hMESCs. Therefore, once protecting cells from oxidative damage, DFO did not alter further hMESCs functioning. The data obtained may become the important prerequisite for development of a new strategy in regenerative therapy based on MSCs preconditioning using DFO.

Generation of Therapeutically Potent Spheroids from Human Endometrial Mesenchymal Stem/Stromal Cells

Endometrial mesenchymal stem/stromal cells (eMSCs) hold great promise in bioengineering and regenerative medicine due to their high expansion potential, unique immunosuppressive properties and multilineage differentiation capacity. Usually, eMSCs are maintained and applied as a monolayer culture. Recently, using animal models with endometrial and skin defects, we showed that formation of multicellular aggregates known as spheroids from eMSCs enhances their tissue repair capabilities. In this work, we refined a method of spheroid formation, which makes it possible to obtain well-formed aggregates with a narrow size distribution both at early eMSC passages and after prolonged cultivation. The use of serum-free media allows this method to be used for the production of spheroids for clinical purposes. Wound healing experiments on animals confirmed the high therapeutic potency of the produced eMSC spheroids in comparison to the monolayer eMSC culture.

"All-In-One" Genetic Tool Assessing Endometrial Receptivity for Personalized Screening of Female Sex Steroid Hormones

Endometrium is the uterine lining that undergoes hundreds of cycles of proliferation, differentiation, and desquamation throughout a woman's reproductive life. Recently, much attention is paid to the appropriate endometrial functioning, as decreased endometrial receptivity is stated to be one of the concerns heavily influencing successes of embryo implantation rates and the efficacy of in vitro fertilization (IVF) treatment. In order to acquire and maintain the desired endometrial receptivity during IVF cycles, luteal phase support by various progestagens or other hormonal combinations is generally recommended. However, today, the selection of the specific hormonal therapy during IVF seems to be empirical, mainly due to a lack of appropriate tools for personalized approach. Here, we designed the genetic tool for patient-specific optimization of hormonal supplementation schemes required for the maintenance of endometrial receptivity during luteal phase. We optimized and characterized in vitro endometrial stromal cell (ESC) decidualization model as the adequate physiological reflection of endometrial sensitivity to steroid hormones. Based on the whole transcriptome RNA sequencing and the corresponding bioinformatics, we proposed that activation of the decidual prolactin (PRL) promoter containing ancient transposons MER20 and MER39 may reflect functioning of the core decidual regulatory network. Furthermore, we cloned the sequence of decidual PRL promoter containing MER20 and part of MER39 into the expression vector to estimate the effectiveness of ESC decidual response and verified sensitivity of the designed system. We additionally confirmed specificity of the generated tool using human diploid fibroblasts and adipose-derived human mesenchymal stem cells. Finally, we demonstrated the possibility to apply our tool for personalized hormone screening by comparing the effects of natural progesterone and three synthetic analogs (medroxyprogesterone 17-acetate, 17α-hydroxyprogesterone caproate, dydrogesterone) on decidualization of six ESC lines obtained from patients planning to undergo the IVF procedure. To sum up, we developed the "all-in-one" genetic tool based on the MER20/MER39 expression cassette that provides the ability to predict the most appropriate hormonal cocktail for endometrial receptivity maintenance specifically and safely for the patient, and thus to define the personal treatment strategy prior to the IVF procedure.

Adenosine-5'-triphosphate suppresses proliferation and migration capacity of human endometrial stem cells

Extracellular ATP through the activation of the P2X and P2Y purinergic receptors affects the migration, proliferation and differentiation of many types of cells, including stem cells. High plasticity, low immunogenicity and immunomodulation ability of mesenchymal stem cells derived from human endometrium (eMSCs) allow them to be considered a prominent tool for regenerative medicine. Here, we examined the role of ATP in the proliferation and migration of human eMSCs. Using a wound healing assay, we showed that ATP-induced activation of purinergic receptors suppressed the migration ability of eMSCs. We found the expression of one of the ATP receptors, the P2X₇ receptor in eMSCs. In spite of this, cell activation with specific P2X₇ receptor agonist, BzATP did not significantly affect the cell migration. The allosteric P2X₇ receptor inhibitor, AZ10606120 also did not prevent ATP-induced inhibition of cell migration, confirming that inhibition occurs without P2X₇ receptor involvement. Flow cytometry analysis showed that high concentrations of ATP did not have a cytotoxic effect on eMSCs. At the same time, ATP induced the cell cycle arrest, suppressed the proliferative and migration capacity of eMSCs and therefore could affect the regenerative potential of these cells.

Paracrine senescence of human endometrial mesenchymal stem cells: a role for the insulin-like growth factor binding protein 3

Stress-induced premature cell senescence is well recognized to be accompanied by emerging the senescence-associated secretory phenotype (SASP). Secreted SASP factors can promote the senescence of normal neighboring cells through autocrine/paracrine pathways and regulate the senescence response, as well. Regarding human endometrium-derived mesenchymal stem cells (MESCs), the SASP regulation mechanisms as well as paracrine activity of senescent cells have not been studied yet. Here, we examined the role of insulin-like growth factor binding protein 3 (IGFBP3) in the paracrine senescence induction in young MESCs. The H₂O₂-induced premature senescence of MESCs led to increased IGFBP3 in conditioned media (CM). The inhibitory analysis of both MAPK and PI3K signaling pathways showed that IGFBP3 releasing from senescent cells is mainly regulated by PI3K/Akt pathway activity. IGFBP3 appears to be an important senescence-mediating factor as its immunodepletion from the senescent CM weakened the pro-senescent effect of CM on young MESCs and promoted their growth. In contrast, young MESCs acquired the senescence phenotype in response to simultaneous addition of recombinant IGFBP3 (rIGFBP3). The mechanism of extracellular IGFBP3 internalization was also revealed. The present study is the first to demonstrate a significant role of extracellular IGFBP3 in paracrine senescence induction of young MESCs.

Molecular basis of senescence transmitting in the population of human endometrial stromal cells

Hormone-regulated proliferation and differentiation of endometrial stromal cells (ESCs) determine overall endometrial plasticity and receptivity to embryos. Previously we revealed that ESCs may undergo premature senescence, accompanied by proliferation loss and various intracellular alterations. Here we focused on whether and how senescence may be transmitted within the ESCs population. We revealed that senescent ESCs may induce paracrine senescence in young counterparts via cell contacts, secreted factors and extracellular vesicles. According to secretome-wide profiling we identified plasminogen activator inhibitor -1 (PAI-1) to be the most prominent protein secreted by senescent ESCs (data are available via ProteomeXchange with identifier PXD015742). By applying CRISPR/Cas9 techniques we disclosed that PAI-1 secreted by senescent ESCs may serve as the master-regulator of paracrine senescence progression within the ESCs population. Unraveled molecular basis of senescence transduction in the ESCs population may be further considered in terms of altered endometrial plasticity and sensitivity to invading embryo, thus contributing to the female infertility curing.

Cell Cycle-Dependent Expression of Bk Channels in Human Mesenchymal Endometrial Stem Cells

The study of ion channels in stem cells provides important information about their role in stem cell fate. Previously we have identified the activity of calcium-activated potassium channels of big conductance (BK channels) in human endometrium-derived mesenchymal stem cells (eMSCs). BK channels could have significant impact into signaling processes by modulating membrane potential. The membrane potential and ionic permeability dynamically changes during cycle transitions. Here, we aimed at verification of the role of BK channels as potassium transporting pathway regulating cell cycle passageway of eMSCs. The functional expression of native BK channels was confirmed by patch-clamp and immunocytochemistry. In non-synchronized cells immunofluorescent analysis revealed BK-positive and BK-negative stained eMSCs. Using cell synchronization, we found that the presence of BK channels in plasma membrane was cell cycle-dependent and significantly decreased in G2M phase. However, the study of cell cycle progression in presence of selective BK channel inhibitors showed no effect of pore blockers on cycle transitions. Thus, BK channel-mediated K+ transport is not critical for the fundamental mechanism of passageway through cell cycle of eMSCs. At the same time, the dynamics of the presence of BK channels on plasma membrane of eMSCs can be a novel indicator of cellular proliferation.

High doses of synthetic antioxidants induce premature senescence in cultivated mesenchymal stem cells

Stress-induced premature senescence program is known to be activated in cells by various genotoxic stressors, and oxidative stress is considered to be the main of those. To this end, many studies discover antioxidants as protective anti-aging agents. In the current study, we examined the effects of different antioxidants (Tempol, resveratrol, NAC, DPI) on the mesenchymal stem cells maintained in normal physiological conditions. We used high, but non-cytotoxic antioxidant doses which are widely used in laboratory practice to protect cells from oxidative damage. We show that these substances induce reversible block of cell proliferation and do not cause any genotoxic effects when applied to the quiescent cells. However, the same doses of the same substances, when applied to the proliferating cells, can induce irreversible cell cycle arrest, DNA strand breaks accumulation and DNA damage response activation. As a consequence, antioxidant-induced DNA damage results in the stress-induced premature senescence program activation. We conclude that high doses of antioxidants, when applied to the proliferating cells that maintain physiological levels of reactive oxygen species, can cause DNA damage and induce premature senescence which suggests to re-estimate believed unconditional anti-aging antioxidant properties.

P38 MAPK inhibition prevents polybrene-induced senescence of human mesenchymal stem cells during viral transduction

The unique capacity of mesenchymal stem cells (MSCs) to migrate to the sites of damage, following intravenous transplantation, along with their proliferation and differentiation abilities make them promising candidates for MSC-based gene therapy. This therapeutic approach requires high efficacy delivery of stable transgenes to ensure their adequate expression in MSCs. One of the methods to deliver transgenes is via the viral transduction of MSCs. However, due to low transduction efficiency of MSCs, various polications are used to promote the association of viral particles with membranes of target cells. Among these polications polybrene is the most widely used one. Unfortunately, viral infection in presence of polybrene was shown to negatively affect proliferation rate of stem cells. The molecular mechanism underlying this effect is not yet uncovered. Therefore, the present study aimed to elucidate the mechanism of this phenomenon as well as to develop an effective approach to overcome the negative impact of polybrene on the properties of human endometrium-derived mesenchymal stem cells (hMESCs) during lentiviral infection. We found that the negative effect on proliferation observed during the viral infection in presence of polybrene is mediated by the polycation itself. Furthermore, we revealed that the treatment with polybrene alone led to the p38 MAPK-dependent premature senescence of hMESCs. These findings allowed us to develop an effective strategy to attenuate the negative polybrene impact on the hMESCs properties during lentiviral infection by inhibiting the activity of p38 MAPK. Importantly, the proposed approach did not attenuate the transduction efficiency of hMESCs, yet prevented polybrene-induced senescence and thereby restored the proliferation of the infected cells. These results provide the plausible means to reduce side effects of polybrene during the viral infection of primary cells, particularly MSCs.

Quiescent Human Mesenchymal Stem Cells Are More Resistant to Heat Stress than Cycling Cells

Quiescence is the prevailing state of many cell types under homeostatic conditions. Yet, surprisingly, little is known about how quiescent cells respond to environmental challenges. The aim of the present study is to compare stress responses of cycling and quiescent mesenchymal stem cells (MSC). Human endometrial mesenchymal cells (eMSС) were employed as adult stem cells. eMSC quiescence was modeled by serum starvation. Sublethal heat shock (HS) was used as a stress factor. Both quiescent and cycling cells were heated at 45°C for 30 min and then returned to standard culture conditions for their recovery. HS response was monitored by DNA damage response, stress-induced premature senescence (SIPS), cell proliferation activity, and oxidative metabolism. It has been found that quiescent cells repair DNA more rapidly, resume proliferation, and undergo SIPS less than proliferating cells. HS-enforced ROS production in heated cycling cells was accompanied with increased expression of genes regulating redox-active proteins. Quiescent cells exposed to HS did not intensify the ROS production, and genes involved in antioxidant defense were mostly silent. Altogether, the results have shown that quiescent cells are more resistant to heat stress than cycling cells. Next-generation sequencing (NGS) demonstrates that HS-survived cells retain differentiation capacity and do not exhibit signs of spontaneous transformation.

Cytogenetic and Transcriptomic Analysis of Human Endometrial MSC Retaining Proliferative Activity after Sublethal Heat Shock

Temperature is an important exogenous factor capable of leading to irreversible processes in the vital activity of cells. However, the long-term effects of heat shock (HS) on mesenchymal stromal cells (MSC) remain unstudied. We investigated the karyotype and DNA repair drivers and pathways in the human endometrium MSC (eMSC) survived progeny at passage 6 after sublethal heat stress (sublethal heat stress survived progeny (SHS-SP)). G-banding revealed an outbreak of random karyotype instability caused by chromosome breakages and aneuploidy. Molecular karyotyping confirmed the random nature of this instability. Transcriptome analysis found homologous recombination (HR) deficiency that most likely originated from the low thermostability of the AT-rich HR driving genes. SHS-SP protection from transformation is provided presumably by low oncogene expression maintained by tight co-regulation between thermosensitive HR drivers BRCA, ATM, ATR, and RAD51 (decreasing expression after SHS), and oncogenes mTOR, MDM2, KRAS, and EGFR. The cancer-related transcriptomic features previously identified in hTERT transformed MSC in culture were not found in SHS-SP, suggesting no traits of malignancy in them. The entrance of SHS-SP into replicative senescence after 25 passages confirms their mortality and absence of transformation features. Overall, our data indicate that SHS may trigger non-tumorigenic karyotypic instability due to HR deficiency and decrease of oncogene expression in progeny of SHS-survived MSC. These data can be helpful for the development of new therapeutic approaches in personalized medicine.

Human mesenchymal stem cells in spheroids improve fertility in model animals with damaged endometrium

BACKGROUND

Asherman's syndrome (AS) is one of the gynecological disorders caused by the destruction of the endometrium. For some cases of AS available surgical methods and hormonal therapy are ineffective. Stem cell transplantation may offer a potential alternative for AS cure.

METHODS

Human endometrial mesenchymal stem cells (eMSC) organized in spheroids were transplanted in rats with damaged endometrium modeled on AS. Treatment response was defined as pregnancy outcome and litter size.

RESULTS

Application of eMSC in spheroids significantly improved the rat fertility with the AS model. eMSC organized in spheroids retain all properties of eMSC in monolayer: growth characteristics, expression of CD markers, and differentiation potential. Synthesis of angiogenic and anti-inflammatory factors drastically increased in eMSC assembled into spheroids.

CONCLUSIONS

Human endometrial mesenchymal stem cells (eMSC) can be successfully applied for Asherman's syndrome (AS) treatment in the rat model. eMSC organized in spheroids were more therapeutically effective than the cells in monolayer. After transplantation of eMSC in spheroids the pregnancy outcome and litter size in rats with AS was higher than in rats that received autologous rat bone marrow cells. It suggests the therapeutic plausibility of heterologous eMSC in case of failure to use autologous cells.

Senescence-messaging secretome factors trigger premature senescence in human endometrium-derived stem cells

Accumulating evidence suggests that the senescence-messaging secretome (SMS) factors released by senescent cells play a key role in cellular senescence and physiological aging. Phenomenon of the senescence induction in human endometrium-derived mesenchymal stem cells (MESCs) in response to SMS factors has not yet been described. In present study, we examine a hypothesis whether the conditioned medium from senescent cells (CM-old) may promote premature senescence of young MESCs. In this case, we assume that SMS factors, containing in CM-old are capable to trigger senescence mechanism in a paracrine manner. A long-term cultivation MESCs in the presence of CM-old caused deceleration of cell proliferation along with emerging senescence phenotype, including increase in both the cell size and SA-β-Gal activity. The phosphorylation of p53 and MAPKAPK-2, a direct target of p38MAPK, as well as the expression of p21Cip1 and p16Ink4a were increased in CM-old treated cells with senescence developing whereas the Rb phosphorylation was diminished. The senescence progression was accompanied by both enhanced ROS generation and persistent activation of DNA damage response, comprising protein kinase ATM, histone H2A.X, and adapter protein 53BP1. Thus, we suggest that a senescence inducing signal is transmitted through p16/MAPKAPK-2/Rb and DDR-mediated p53/p21/Rb signaling pathways. This study is the first to demonstrate that the SMS factors secreted in conditioned medium of senescent MESCs trigger a paracrine mechanism of premature senescence in young cells.

Proteomic analysis of affinity-purified extracellular proteasomes reveals exclusively 20S complexes

Proteasome-mediated proteolysis is important for many basic cellular processes. In addition to their functions in the cell, proteasomes have been found in physiological fluids of both healthy and diseased humans including cancer patients. Higher levels of these proteasomes are associated with higher cancer burden and stage. The etiology and functions of these proteasomes, referred to as circulating, plasmatic, or extracellular proteasomes (ex-PSs), are unclear. Here we show that human cancer cell lines, as well as human endometrium-derived mesenchymal stem cells (hMESCs), release proteasome complexes into culture medium (CM). To define ex-PS composition, we have affinity purified them from CM conditioned by human leukemia cell line K562. Using matrix-assisted laser desorption/ionization (MALDI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry (MS), we have identified core 20S proteasome subunits and a set of 15 proteasome-interacting proteins (PIPs), all previously described as exosome cargo proteins. Three of them, PPIase A, aldolase A, and transferrin, have never been reported as PIPs. The study provides compelling arguments that ex-PSs do not contain 19S or PA200 regulatory particles and are represented exclusively by the 20S complex.

Calcium alterations signal either to senescence or to autophagy induction in stem cells upon oxidative stress

Intracellular calcium ([Ca2+]i) has been reported to play an important role in autophagy, apoptosis and necrosis, however, a little is known about its impact in senescence. Here we investigated [Ca2+]i contribution to oxidative stress-induced senescence of human endometrium-derived stem cells (hMESCs). In hMESCs sublethal H2O2-treatment resulted in a rapid calcium release from intracellular stores mediated by the activation of PLC/IP3/IP3R pathway. Notably, further senescence development was accompanied by persistently elevated [Ca2+]i levels. In H2O2-treated hMESCs, [Ca2+]i chelation by BAPTA-AM (BAPTA) was sufficient to prevent the expansion of the senescence phenotype, to decrease endogenous reactive oxygen species levels, to avoid G0/G1 cell cycle arrest, and finally to retain proliferation. Particularly, loading with BAPTA attenuated phosphorylation of the main DNA damage response members, including ATM, 53BP1 and H2A.X and reduced activation of the p53/p21/Rb pathway in H2O2-stimulated cells. Next, we revealed that BAPTA induced an early onset of AMPK-dependent autophagy in H2O2-treated cells as confirmed by both the phosphorylation status of AMPK/mTORC1 pathway and the dynamics of the LC3 lipidization. Summarizing the obtained data we can assume that calcium chelation is able to trigger short-term autophagy and to prevent the premature senescence of hMESCs under oxidative stress.

Local calcium signalling is mediated by mechanosensitive ion channels in mesenchymal stem cells

Mechanical forces are implicated in key physiological processes in stem cells, including proliferation, differentiation and lineage switching. To date, there is an evident lack of understanding of how external mechanical cues are coupled with calcium signalling in stem cells. Mechanical reactions are of particular interest in adult mesenchymal stem cells because of their promising potential for use in tissue remodelling and clinical therapy. Here, single channel patch-clamp technique was employed to search for cation channels involved in mechanosensitivity in mesenchymal endometrial-derived stem cells (hMESCs). Functional expression of native mechanosensitive stretch-activated channels (SACs) and calcium-sensitive potassium channels of different conductances in hMESCs was shown. Single current analysis of stretch-induced channel activity revealed functional coupling of SACs and BK channels in plasma membrane. The combination of cell-attached and inside-out experiments have indicated that highly localized Ca²⁺ entry via SACs triggers BK channel activity. At the same time, SK channels are not coupled with SACs despite of high calcium sensitivity as compared to BK. Our data demonstrate novel mechanism controlling BK channel activity in native cells. We conclude that SACs and BK channels are clusterized in functional mechanosensitive domains in the plasma membrane of hMESCs. Co-clustering of ion channels may significantly contribute to mechano-dependent calcium signalling in stem cells.

Digital holographic microscopy in label-free analysis of cultured cells' response to photodynamic treatment

A methodology providing noninvasive monitoring and evaluation of the effect of photodynamic treatment on live cells in vitro is presented. Variations in morphological characteristics of cells in the course and after treatment are recorded by means of digital holographic microscopy. High-precision measurements of phase shift gained by probe radiation in HeLa and human endometrial mesenchymal stem cell cultures demonstrate for the first time changes of their volume occurred in response to treatment.

Tetraploidization or autophagy: The ultimate fate of senescent human endometrial stem cells under ATM or p53 inhibition

Previously we demonstrated that endometrium-derived human mesenchymal stem cells (hMESCs) via activation of the ATM/p53/p21/Rb pathway enter the premature senescence in response to oxidative stress. Down regulation effects of the key components of this signaling pathway, particularly ATM and p53, on a fate of stressed hMESCs have not yet been investigated. In the present study by using the specific inhibitors Ku55933 and Pifithrin-α, we confirmed implication of both ATM and p53 in H(2)O(2)-induced senescence of hMESCs. ATM or p53 down regulation was shown to modulate differently the cellular fate of H(2)O(2)-treated hMESCs. ATM inhibition allowed H(2)O(2)-stimulated hMESCs to escape the permanent cell cycle arrest due to loss of the functional ATM/p53/p21/Rb pathway, and induced bypass of mitosis and re-entry into S phase, resulting in tetraploid cells. On the contrary, suppression of the p53 transcriptional activity caused a pronounced cell death of H(2)O(2)-treated hMESCs via autophagy induction. The obtained data clearly demonstrate that down regulation of ATM or p53 shifts senescence of human endometrial stem cells toward tetraploidization or autophagy.

Interaction between ROS dependent DNA damage, mitochondria and p38 MAPK underlies senescence of human adult stem cells

Human endometrium-derived mesenchymal stem cells (hMESCs) enter the premature senescence under sublethal oxidative stress, however underlying mechanism remains unknown. Here, we showed that exogenous H2O2 induces a rapid phosphorylation and co-localization of ATM, H2A.X, 53BP1 leading to DNA damage response (DDR) activation. DDR was accompanied with nuclear translocation of p-p53 followed by up-regulation of p21Waf1 and the permanent hypophosphorylation of pRb. Additionally, the increased p38MAPK/MAPKAPK-2 activation persisted in H2O2-treated cells. We suggest that both p53/p21/pRb and p38MAPK/MAPKAPK-2 pathways are responsible for establishing an irreversible cell cycle arrest that is typical of senescence. The process of further stabilization of senescence required prolonged DDR signaling activation that was provided by the permanent ROS production which in turn was regulated by both p38MAPK and the increased functional mitochondria. To reverse senescence, the pharmacological inhibition of p38MAPK was performed. Cell treatment with SB203580 was sufficient to recover partially senescence phenotype, to block the ROS elevation, to decrease the mitochondrial function, and finally to rescue proliferation. Thus, suppression of the p38MAPK pathway resulted in a partial prevention of H2O2-induced senescence of hMESCs. The current study is the first to reveal the molecular mechanism of the premature senescence of hMESCs in response to oxidative stress.