Proliferation-related changes in K+ content in human mesenchymal stem cells

The outcome of tissue cryopreservation on the cellular, molecular and epigenetic characteristics of endometrial tissue and stromal cells

RESEARCH QUESTION

What impact does the cryopreservation of endometrial tissue have on cell characteristics and molecular and epigenetic profile changes in endometrial tissue and stromal cells?

DESIGN

Cellular properties, such as proliferation efficiency, surface marker expression and the differentiation potency of endometrial stromal cells (ESC) isolated from fresh (Native) and cryopreserved (Cryo) tissue were compared. Moreover, changes in the expression of genes associated with pluripotency, endometrial function and epigenetic regulation and microRNA (miRNA, miR) were assessed, as were levels of DNA methylation and histone modifications.

RESULTS

Native and Cryo cells exhibit very similar profiles including cell surface marker expression, differentiation potency and histone modifications, except for a decrease in proliferative potency and cell surface marker SUSD2 expression in Cryo cells. It was demonstrated that endometrial tissue cryopreservation led to an up-regulated expression of genes associated with pluripotency (NANOG, OCT4 [also known as POU5F1]). This confirms that despite being recovered from cryopreserved differentiated tissue, cells retained their stemness properties. In addition, alterations in DNA methyltransferase (DNMT1, DNMT3A, DNMT3B) gene regulation were observed, along with a down-regulation of hsa-miR145-5p in Cryo ESC.

CONCLUSIONS

These findings contribute to a deeper understanding of the complex effects of endometrial tissue cryopreservation, providing insights for both medical and basic research applications. Since different tissues possess unique characteristics, it is essential to select the most suitable cryopreservation method for each tissue individually. Furthermore, the study findings indicate the potential utility of slow-cooling cryopreservation for both normal and pathological endometrial tissue samples, with the purpose of isolating stromal cell cultures.

The Role of Intracellular Potassium in Cell Quiescence, Proliferation, and Death

This brief review explores the role of intracellular K+ during the transition of cells from quiescence to proliferation and the induction of apoptosis. We focus on the relationship between intracellular K+ and the growth and proliferation rates of different cells, including transformed cells in culture as well as human quiescent T cells and mesenchymal stem cells, and analyze the concomitant changes in K+ and water content in both proliferating and apoptotic cells. Evidence is discussed indicating that during the initiation of cell proliferation and apoptosis changes in the K+ content in cells occur in parallel with changes in water content and therefore do not lead to significant changes in the intracellular K+ concentration. We conclude that K+, as a dominant intracellular ion, is involved in the regulation of cell volume during the transit from quiescence, and the content of K+ and water in dividing cells is higher than in quiescent or differentiated cells, which can be considered to be a hallmark of cell proliferation and transformation.

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.

Targeting Multiple Homeostasis-Maintaining Systems by Ionophore Nigericin Is a Novel Approach for Senolysis

Within the present study we proposed a novel approach for senolysis based on the simultaneous disturbance of the several homeostasis-maintaining systems in senescent cells including intracellular ionic balance, energy production and intracellular utilization of damaged products. Of note, we could not induce senolysis by applying ouabain, amiloride, valinomycin or NH₄Cl-compounds that modify each of these systems solely. However, we found that ionophore nigericin can disturb plasma membrane potential, intracellular pH, mitochondrial membrane potential and autophagy at once. By affecting all of the tested homeostasis-maintaining systems, nigericin induced senolytic action towards stromal and epithelial senescent cells of different origins. Moreover, the senolytic effect of nigericin was independent of the senescence-inducing stimuli. We uncovered that K⁺ efflux caused by nigericin initiated pyroptosis in senescent cells. According to our data, the higher sensitivity of senescent cells compared to the control ones towards nigericin-induced death was partially mediated by the lower intracellular K⁺ content in senescent cells and by their predisposition towards pyroptosis. Finally, we proposed an interval dosing strategy to minimize the negative effects of nigericin on the control cells and to achieve maximal senolytic effect. Hence, our data suggest ionophore nigericin as a new senotherapeutic compound for testing against age-related diseases.

Lactate receptor HCAR1 regulates cell growth, metastasis and maintenance of cancer‑specific energy metabolism in breast cancer cells

Under aerobic conditions, the preferential use of anaerobic glycolysis by tumour cells leads to a high level of lactate accumulation in tumour microenvironment. Lactate acts not only as a cellular energy source but also as a signalling molecule that regulates cancer cell growth, metastasis and metabolism. It has been reported that a G‑protein‑coupled receptor for lactate named hydroxycarboxylic acid receptor 1 (HCAR1) is highly expressed in numerous types of cancer, but the detailed mechanism remains unclear. In the present study, it was reported that HCAR1 is highly expressed in breast cancer cells. Genetic deletion of HCAR1 in MCF7 cells leads to reduced cell proliferation and migration. Moreover, it was observed that knockout (KO) of HCAR1 attenuated the expression and activity of phosphofructokinase and hexokinase, key rate‑limiting enzymes in glycolysis. Using an extracellular flux analyzer, it was showed that KO of HCAR1 promoted a metabolic shift towards a decreased glycolysis state, as evidenced by a decreased extracellular acidification rate and increased oxygen consumption rate in MCF7 cells. Taken together, our results suggested that lactate acts through HCAR1 as a metabolic regulator in breast cancer cells that may be therapeutically exploited.

Monovalent ions and stress-induced senescence in human mesenchymal endometrial stem/stromal cells

Monovalent ions are involved in growth, proliferation, differentiation of cells as well as in their death. This work concerns the ion homeostasis during senescence induction in human mesenchymal endometrium stem/stromal cells (hMESCs): hMESCs subjected to oxidative stress (sublethal pulse of H₂O₂) enter the premature senescence accompanied by persistent DNA damage, irreversible cell cycle arrest, increased expression of the cell cycle inhibitors (p53, p21) cell hypertrophy, enhanced β-galactosidase activity. Using flame photometry to estimate K⁺, Na⁺ content and Rb⁺ (K⁺) fluxes we found that during the senescence development in stress-induced hMESCs, Na⁺/K⁺pump-mediated K⁺ fluxes are enhanced due to the increased Na⁺ content in senescent cells, while ouabain-resistant K⁺ fluxes remain unchanged. Senescence progression is accompanied by a peculiar decrease in the K⁺ content in cells from 800-900 to 500-600 µmol/g. Since cardiac glycosides are offered as selective agents for eliminating senescent cells, we investigated the effect of ouabain on ion homeostasis and viability of hMESCs and found that in both proliferating and senescent hMESCs, ouabain (1 nM-1 µM) inhibited pump-mediated K⁺ transport (ID₅₀ 5 × 10^-8 M), decreased cell K⁺/Na⁺ ratio to 0.1-0.2, however did not induce apoptosis. Comparison of the effect of ouabain on hMESCs with the literature data on the selective cytotoxic effect of cardiac glycosides on senescent or cancer cells suggests the ion pump blockade and intracellular K⁺ depletion should be synergized with target apoptotic signal to induce the cell death.

Ion channels in stem cells and their roles in stem cell biology and vascular diseases

Stem cell therapy may be a promising option for the treatment of vascular diseases. In recent years, significant progress has been made in stem cell research, especially in the mechanism of stem cell activation, homing and differentiation in vascular repair and reconstruction. Current research on stem cells focuses on protein expression and transcriptional networks. Ion channels are considered to be the basis for the generation of bioelectrical signals, which control the proliferation, differentiation and migration of various cell types. Although heterogeneity of multiple ion channels has been found in different types of stem cells, it is unclear whether the heterogeneous expression of ion channels is related to different cell subpopulations and/or different stages of the cell cycle. There is still a long way to go in clinical treatment by using the regulation of stem cell ion channels. In this review, we reviewed the main ion channels found on stem cells, their expression and function in stem cell proliferation, differentiation and migration, and the research status of stem cells' involvement in vascular diseases.

Efficient Citrus (Citrus unshiu) Byproduct Extract-Based Approach for Lactobacillus sakei WiKim31 Shelf-Life Extension

Lactic acid bacteria produce various bioactive compounds widely used in human healthcare. However, studies on cryoprotective agents for the efficient storage of lactic acid bacteria after freeze-drying are still lacking. Here, we report the shelf-life extension effects of a highly efficient and eco-friendly cryoprotective agent and a cold adaptation method on Lactobacillus sakei WiKim31. Cold adaptation of L. sakei WiKim31 increased exopolysaccharide expression in response to abiotic stress. As a possible cryoprotective agent, the citrus byproduct (CP) contains a variety of sugars, amino acids, and cations, exhibiting high antioxidant activity. L. sakei WiKim31 powders formulated with CP or a mixture of soy powder (SP) and CP exhibited high cell viability at 58.3 and 76.3%, respectively, after 56 days of storage. These results indicate that CP can be efficiently used as a novel cryoprotective agent either alone or in combination with SP to improve the storage conditions of L. sakei WiKim31 and preserve it longer.

Clinically relevant preservation conditions for mesenchymal stem/stromal cells derived from perinatal and adult tissue sources

The interplay between mesenchymal stem/stromal cells (MSCs) and preservation conditions is critical to maintain the viability and functionality of these cells before administration. We observed that Ringer lactate (RL) maintained high viability of bone marrow–derived MSCs for up to 72 h at room temperature (18°C–22°C), whereas adipose‐derived and umbilical cord‐derived MSCs showed the highest viability for 72 h at a cold temperature (4°C–8°C). These cells maintained their adherence ability with an improved recovery rate and metabolic profiles (glycolysis and mitochondrial respiration) similar to those of freshly harvested cells. Growth factor and cytokine analyses revealed that the preserved cells released substantial amounts of leukaemia inhibitory factors (LIFs), hepatocyte growth factor (HGF) and vascular endothelial growth factor‐A (VEGF‐A), as well as multiple cytokines (eg IL‐4, IL‐6, IL‐8, MPC‐1 and TNF‐α). Our data provide the simplest clinically relevant preservation conditions that maintain the viability, stemness and functionality of MSCs from perinatal and adult tissue sources.

EMF frequency dependent differentiation of rat bone marrow mesenchymal stem cells to astrocyte cells

The numerous factors regulate the bone marrow mesenchymal stem cell (BMMSC) self-renewal and differentiation response. We aimed to analyze the influence of electromagnetic field (EMF) as an external inducing factor on rat BMMSC differentiation and proliferation to neuron and astrocyte cells. BMMSCs extracted from the rats femurs and tibias and incubated in a cell-cultured CO₂ incubator. After the third passages, the plates selected randomly and then divided into seven groups (Sham exposed, three groups of square, and three groups of sinusoidal waveform EMF (25, 50, and 75 Hz, 400 μT, 1 h/day). The BMMSCs exposed to EMF at the middle of a Helmholtz coil for 7 days. The viable cell counting and proliferation performed by the MTT test and BMMSC differentiation into the neuron and the astrocyte cell was studied by immunocytochemistry staining. The results confirmed BMMSC viability and proliferation rate reduction in sinusoidal 25 Hz, square 50 Hz and sinusoidal 75 Hz EMF groups compare to sham. The maximum BMMSC differentiation to neuron was considered in sinusoidal 50 Hz and 75 Hz EMF groups. The increase of BMMSC differentiation to astrocyte cell was frequency dependent and the most differentiation was shown in square 75 Hz, and sinusoidal 75 Hz EMF groups. In conclusion, the results suggest that both square and sinusoidal EMF could affect BMMSC development and differentiation to neuron and astrocyte cells. Further studies for the consequence of EMF with wider flux density and frequency on BMMSC are recommended.

Role of Aquaporins in the Physiological Functions of Mesenchymal Stem Cells

Aquaporins (AQPs) are a family of membrane water channel proteins that control osmotically-driven water transport across cell membranes. Recent studies have focused on the assessment of fluid flux regulation in relation to the biological processes that maintain mesenchymal stem cell (MSC) physiology. In particular, AQPs seem to regulate MSC proliferation through rapid regulation of the cell volume. Furthermore, several reports have shown that AQPs play a crucial role in modulating MSC attachment to the extracellular matrix, their spread, and migration. Shedding light on how AQPs are able to regulate MSC physiological functions can increase our knowledge of their biological behaviours and improve their application in regenerative and reparative medicine.

Intracellular K+ and water content in human blood lymphocytes during transition from quiescence to proliferation

Many evidence shows that K⁺ ions are required for cell proliferation, however, changes in intracellular K⁺ concentration during transition of cells from quiescence to cycling are insufficiently studied. Here, we show using flame emission assay that a long-term increase in cell K⁺ content per g cell protein is a mandatory factor for transition of quiescent human peripheral blood lymphocytes (PBL) to proliferation induced by phytohemagglutinin, phorbol ester with ionomycin, and anti-CD3 antibodies with interleukin-2 (IL-2). The long-term increase in K⁺ content is associated with IL-2-dependent stage of PBL activation and accompanies the growth of small lymphocytes and their transformation into blasts. Inhibition of PBL proliferation with drugs specific for different steps of G0/G1/S transit prevented both blast-transformation and an increase in K⁺ content per cell protein. Determination of the water content in cells by measuring the density of cells in the Percoll gradient showed that, unlike the K⁺ content, the concentration of K⁺ in cell water remains unchanged, since water and K⁺ change in parallel. Correlation of proliferation with high cell K⁺ and water content has been confirmed by the data obtained in comparative study of PBL and permanently cycling Jurkat cells. Our data suggest that K⁺ is important for successful proliferation as the main intracellular ion that participates in regulation of cell water content during cell transition from quiescence to proliferation. We concluded that high K⁺ content in cells and the associated high water content is a characteristic feature of proliferating cells.