Human Mesenchymal Stem Cells on Size-Sorted Gelatin Hydrogel Microparticles Show Enhanced In Vitro Wound Healing Activities

The demand for innovative therapeutic interventions to expedite wound healing, particularly in vulnerable populations such as aging and diabetic patients, has prompted the exploration of novel strategies. Mesenchymal stem cell (MSC)-based therapy emerges as a promising avenue for treating acute and chronic wounds. However, its clinical application faces persistent challenges, notably the low survivability and limited retention time of engraftment in wound environments. Addressing this, a strategy to sustain the viability and functionality of human MSCs (hMSCs) in a graft-able format has been identified as crucial for advanced wound care. Hydrogel microparticles (HMPs) emerge as promising entities in the field of wound healing, showcasing versatile capabilities in delivering both cells and bioactive molecules/drugs. In this study, gelatin HMPs (GelMPs) were synthesized via an optimized mild processing method. GelMPs with distinct diameter sizes were sorted and characterized. The growth of hMSCs on GelMPs with various sizes was evaluated. The release of wound healing promoting factors from hMSCs cultured on different GelMPs were assessed using scratch wound assays and gene expression analysis. GelMPs with a size smaller than 100 microns supported better cell growth and cell migration compared to larger sizes (100 microns or 200 microns). While encapsulation of hMSCs in hydrogels has been a common route for delivering viable hMSCs, we hypothesized that hMSCs cultured on GelMPs are more robust than those encapsulated in hydrogels. To test this hypothesis, hMSCs were cultured on GelMPs or in the cross-linked methacrylated gelatin hydrogel (GelMA). Comparative analysis of growth and wound healing effects revealed that hMSCs cultured on GelMPs exhibited higher viability and released more wound healing activities in vitro. This observation highlights the potential of GelMPs, especially those with a size smaller than 100 microns, as a promising carrier for delivering hMSCs in wound healing applications, providing valuable insights for the optimization of advanced therapeutic strategies.

Distinct HAND2/HAND2-AS1 Expression Levels May Fine-Tune Mesenchymal and Epithelial Cell Plasticity of Human Mesenchymal Stem Cells

We previously developed several successful decellularization strategies that yielded porcine cardiac extracellular matrices (pcECMs) exhibiting tissue-specific bioactivity and bioinductive capacity when cultured with various pluripotent and multipotent stem cells. Here, we study the tissue-specific effects of the pcECM on seeded human mesenchymal stem cell (hMSC) phenotypes using reverse transcribed quantitative polymerase chain reaction (RT-qPCR) arrays for cardiovascular related gene expression. We further corroborated interesting findings at the protein level (flow cytometry and immunological stains) as well as bioinformatically using several mRNA sequencing and protein databases of normal and pathologic adult and embryonic (organogenesis stage) tissue expression. We discovered that upon the seeding of hMSCs on the pcECM, they displayed a partial mesenchymal-to-epithelial transition (MET) toward endothelial phenotypes (CD31+) and morphologies, which were preceded by an early spike (~Day 3 onward after seeding) in HAND2 expression at both the mRNA and protein levels compared to that in plate controls. The CRISPR-Cas9 knockout (KO) of HAND2 and its associated antisense long non-coding RNA (HAND2-AS1) regulatory region resulted in proliferation arrest, hypertrophy, and senescent-like morphology. Bioinformatic analyses revealed that HAND2 and HAND2-AS1 are highly correlated in expression and are expressed in many different tissue types albeit at distinct yet tightly regulated expression levels. Deviation (downregulation or upregulation) from these basal tissue expression levels is associated with a long list of pathologies. We thus suggest that HAND2 expression levels may possibly fine-tune hMSCs' plasticity through affecting senescence and mesenchymal-to-epithelial transition states, through yet unknown mechanisms. Targeting this pathway may open up a promising new therapeutic approach for a wide range of diseases, including cancer, degenerative disorders, and aging. Nevertheless, further investigation is required to validate these findings and better understand the molecular players involved, potential inducers and inhibitors of this pathway, and eventually potential therapeutic applications.

Three-Dimensional Scaffolds for Bone Tissue Engineering

Immobilization using external or internal splints is a standard and effective procedure to treat minor skeletal fractures. In the case of major skeletal defects caused by extreme trauma, infectious diseases or tumors, the surgical implantation of a bone graft from external sources is required for a complete cure. Practical disadvantages, such as the risk of immune rejection and infection at the implant site, are high in xenografts and allografts. Currently, an autograft from the iliac crest of a patient is considered the "gold standard" method for treating large-scale skeletal defects. However, this method is not an ideal solution due to its limited availability and significant reports of morbidity in the harvest site (30%) as well as the implanted site (5-35%). Tissue-engineered bone grafts aim to create a mechanically strong, biologically viable and degradable bone graft by combining a three-dimensional porous scaffold with osteoblast or progenitor cells. The materials used for such tissue-engineered bone grafts can be broadly divided into ceramic materials (calcium phosphates) and biocompatible/bioactive synthetic polymers. This review summarizes the types of materials used to make scaffolds for cryo-preservable tissue-engineered bone grafts as well as the distinct methods adopted to create the scaffolds, including traditional scaffold fabrication methods (solvent-casting, gas-foaming, electrospinning, thermally induced phase separation) and more recent fabrication methods (fused deposition molding, stereolithography, selective laser sintering, Inkjet 3D printing, laser-assisted bioprinting and 3D bioprinting). This is followed by a short summation of the current osteochondrogenic models along with the required scaffold mechanical properties for in vivo applications. We then present a few results of the effects of freezing and thawing on the structural and mechanical integrity of PLLA scaffolds prepared by the thermally induced phase separation method and conclude this review article by summarizing the current regulatory requirements for tissue-engineered products.

Reducing oxidative protein folding alleviates senescence by minimizing ER-to-nucleus H2 O2 release

Oxidative protein folding occurs in the endoplasmic reticulum (ER) to generate disulfide bonds, and the by-product is hydrogen peroxide (H₂ O₂ ). However, the relationship between oxidative protein folding and senescence remains uncharacterized. Here, we find that the protein disulfide isomerase (PDI), a key oxidoreductase that catalyzes oxidative protein folding, accumulated in aged human mesenchymal stem cells (hMSCs) and deletion of PDI alleviated hMSCs senescence. Mechanistically, knocking out PDI slows the rate of oxidative protein folding and decreases the leakage of ER-derived H₂ O₂ into the nucleus, thereby decreasing the expression of SERPINE1, which was identified as a key driver of cell senescence. Furthermore, we show that depletion of PDI alleviated senescence in various cell models of aging. Our findings reveal a previously unrecognized role of oxidative protein folding in promoting cell aging, providing a potential target for aging and aging-related disease intervention.

Candidate genes responsible for lipid droplets formation during adipogenesis simultaneously affect osteoblastogenesis

INTRODUCTION

With cellular lipid storage varying, the balance between lipid intake and lipid degradation was a must to keep healthy and determined the level of lipid droplets. Although lipid droplets accumulation had been well demonstrated in adipocytes, gene expression profiling and gene function during adipogenesis and osteoblastogenesis remain unknown.

MATERIAL AND METHODS

Here, this work profiled gene transcriptional landscapes of lipid droplets formation during adipogenesis from human mesenchymal stem cells (hMSCs) using RNA-Seq technique. By using RNA interference (RNAi) we investigated the function of candidate genes during adipogenesis and osteoblastogenesis using Oil Red/Alizarin Red/alkaline phosphatase (ALPL) staining and qRT-PCR (quantitative real-time PCR).

RESULTS

Eleven differentially up-regulated genes associated with lipid droplets formation were identified at 3, 5, 7, 14, 21, and 28 days during adipogenesis. Unexpectedly, APOB per se inhibiting adipogenesis weakened osteoblastogenesis and METTL7A facilitating adipogenesis negligibly inhibited osteoblastogenesis according to the phenotypic characterization of adipocytes and osteoblasts and transcriptional condition of biomarkers through lentivirus transfection assays.

CONCLUSIONS

The establishment of the gene transcriptional profiling of lipid droplets formation would provide the molecular switches of hMSCs cell fate determination and the study targets for fat metabolic diseases.

Downregulation of SUV39H1 and CITED2 Exerts Additive Effect on Promoting Adipogenic Commitment of Human Mesenchymal Stem Cells

Human adipogenesis is the process through which uncommitted human mesenchymal stem cells (hMSCs) differentiate into adipocytes. Through a siRNA-based high-throughput screen that identifies adipogenic regulators whose expression knockdown leads to enhanced adipogenic differentiation of hMSCs, two new regulators, SUV39H1, a histone methyltransferase that catalyzes H3K9Me3, and CITED2, a CBP/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 were uncovered. Both SUV39H1 and CITED2 are normally downregulated during adipogenic differentiation of hMSCs. Further expression knockdown induced by siSUV39H1 or siCITED2 at the adipogenic initiation stage significantly enhanced adipogenic differentiation of hMSCs as compared with siControl treatment, with siSUV39H1 acting by both accelerating fat accumulation in individual adipocytes and increasing the total number of committed adipocytes, whereas siCITED2 acting predominantly by increasing the total number of committed adipocytes. In addition, both siSUV39H1 and siCITED2 were able to redirect hMSCs to undergo adipogenic differentiation in the presence of osteogenic inducing media, which normally only induces osteogenic differentiation of hMSCs in the absence of siSUV39H1 or siCITED2. Interestingly, simultaneous knockdown of both SUV39H1 and CITED2 resulted in even greater levels of adipogenic differentiation of hMSCs and expression of CEBPα and PPARγ, two master regulators of adipogenesis, as compared with those elicited by single gene knockdown. Furthermore, the effects of co-knockdown were equivalent to the additive effect of individual gene knockdown. Taken together, this study demonstrates that SUV39H1 and CITED2 are both negative regulators of human adipogenesis, and downregulation of both genes exerts an additive effect on promoting adipogenic differentiation of hMSCs through augmented commitment.

Thermoresponsive Poly(vinyl methyl ether) (PVME) Retained by 3-Aminopropyltriethoxysilane (APTES) Network

Thermoresponsive polymers (TRP)s have been widely used for various applications from controlling membrane fouling in separation to cell/cell sheet harvesting in regenerative medicine. While poly(N-isopropylacrylamide) (pNIPAAm) is the most commonly used TRP, less expensive and easily processed poly(vinyl methyl ether) (PVME) also shows a hydrophilic to hydrophobic transition at 32-35 °C, near physiological conditions. In this study, we investigated the processing conditions for retaining a stable layer of PVME thin film on silica surfaces via entrapment in a 3-aminopropyltriethoxysilane (APTES) network. In addition, the thermoresponsive behaviors (TRB) of the retained PVME films were evaluated. Blend thin films of PVME/APTES with 90:10 and 50:50 mass ratios were spin-coated from their solutions in ethanol under ambient conditions and then annealed in a vacuum oven at 40, 60, 80, or 120 °C for 1, 2, or 3 days. The annealed films were then thoroughly rinsed with room temperature water and then soaked in water for 3 days. Our results showed that annealing at a temperature of ≥40 °C was necessary for retaining a PVME film on the surface. The higher annealing temperature led to greater film retention, probably due to the formation of a tighter APTES network. Regardless of processing conditions, all retained PVME films showed TRB, determined by water contact angles below and above the transition temperature of PVME. Additionally, particle attachment and protein adsorption on retained PVME films showed lower attachment or adsorption at room temperature as compared to that at 37 °C, and a greater difference was observed for the 90:10 blend where more PVME was consisted. Furthermore, human mesenchymal stem cells attached and proliferated on the retained PVME surfaces at 37 °C and rapidly detached at room temperature. These results illustrated the potential applications of PVME surfaces as thermoresponsive supports for low-fouling applications and noninvasive cell harvesting.

Mechanical Cues Regulating Proangiogenic Potential of Human Mesenchymal Stem Cells through YAP-Mediated Mechanosensing

Stem cells secrete trophic factors that induce angiogenesis. These soluble factors are promising candidates for stem cell-based therapies, especially for cardiovascular diseases. Mechanical stimuli and biophysical factors presented in the stem cell microenvironment play important roles in guiding their behaviors. However, the complex interplay and precise role of these cues in directing pro-angiogenic signaling remain unclear. Here, a platform is designed using gelatin methacryloyl hydrogels with tunable rigidity and a dynamic mechanical compression bioreactor to evaluate the influence of matrix rigidity and mechanical stimuli on the secretion of pro-angiogenic factors from human mesenchymal stem cells (hMSCs). Cells cultured in matrices mimicking mechanical elasticity of bone tissues in vivo show elevated secretion of vascular endothelial growth factor (VEGF), one of representative signaling proteins promoting angiogenesis, as well as increased vascularization of human umbilical vein endothelial cells (HUVECs) with a supplement of conditioned media from hMSCs cultured across different conditions. When hMSCs are cultured in matrices stimulated with a range of cyclic compressions, increased VEGF secretion is observed with increasing mechanical strains, which is also in line with the enhanced tubulogenesis of HUVECs. Moreover, it is demonstrated that matrix stiffness and cyclic compression modulate secretion of pro-angiogenic molecules from hMSCs through yes-associated protein activity.

Application of ECIS to Assess FCCP-Induced Changes of MSC Micromotion and Wound Healing Migration

Electric cell-substrate impedance sensing (ECIS) is an emerging technique for sensitively monitoring morphological changes of adherent cells in tissue culture. In this study, human mesenchymal stem cells (hMSCs) were exposed to different concentrations of carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) for 20 h and their subsequent concentration-dependent responses in micromotion and wound healing migration were measured by ECIS. FCCP disrupts ATP synthesis and results in a decrease in cell migration rates. To detect the change of cell micromotion in response to FCCP challenge, time-series resistances of cell-covered electrodes were monitored and the values of variance were calculated to verify the difference. While Seahorse XF-24 extracellular flux analyzer can detect the effect of FCCP at 3 μM concentration, the variance calculation of the time-series resistances measured at 4 kHz can detect the effect of FCCP at concentrations as low as 1 μM. For wound healing migration, the recovery resistance curves were fitted by sigmoid curve and the hill slope showed a concentration-dependent decline from 0.3 μM to 3 μM, indicating a decrease in cell migration rate. Moreover, dose dependent incline of the inflection points from 0.3 μM to 3 μM FCCP implied the increase of the half time for wound recovery migration. Together, our results demonstrate that partial uncoupling of mitochondrial oxidative phosphorylation reduces micromotion and wound healing migration of hMSCs. The ECIS method used in this study offers a simple and sensitive approach to investigate stem cell migration and its regulation by mitochondrial dynamics.

Sustained and Prolonged Delivery of Protein Therapeutics from Two-Dimensional Nanosilicates

We present a nanoengineered system for sustained and prolonged delivery of protein therapeutics, which has the potential to impact current orthopedic regeneration strategies. Specifically, we introduce two-dimensional nanosilicates with a high surface area and charged characteristics for delivery of active proteins for more than 30 days. The nanosilicates show high binding efficacy without altering the protein conformation and bioactivity. The released proteins are able to maintain high activity as demonstrated by enhanced differentiation of human mesenchymal stem cells at 10-fold lower concentration compared to the exogenous control. Utilizing the nanosilicates as a delivery vehicle could minimize the negative side effects observed because of the use of supraphysiological dosages of protein therapeutics for orthopedic regeneration strategies.

Ectopic microRNAs used to preserve human mesenchymal stem cell potency and epigenetics

Human mesenchymal stem cells (hMSCs) have remarkable potential for use in regenerative medicine. However, one of the great challenges is preserving their potency for long time. This study investigated the effect of miRNA ectopic expression on their proliferation and also on the expression level of Parp1 as an epigenetic switch preserving pluripotency in hMSCs. A cationic liposome was prepared as an efficient carrier for miRNA delivery. The miRNA loading efficiency and physical stability of vesicles were measured, and their scanning electron microscopic shapes determined. hMSCs were transfected with miR-302a and miR-34a followed by assessment of their proliferation potency with MTT assay and measurement of the expression of Parp1 by quantitative polymerase chain reaction (QPCR). Cell transfection with miR-302a and miR-34a efficiently and differentially affects the proliferation potency of hMSCs and the expression level of Parp1 as the key epigenetic factor involved in pluripotency. While miR-302a increases Parp1 expression, miR-34a suppresses it significantly, showing differential effects. Our results demonstrated that miRNA-based treatments represent efficient therapeutic systems and hold a great promise for future use in regenerative medicine through modification of hMSC pluripotency and epigenome.

The Role of Cellular Proliferation in Adipogenic Differentiation of Human Adipose Tissue-Derived Mesenchymal Stem Cells

Mitotic clonal expansion has been suggested as a prerequisite for adipogenesis in murine preadipocytes, but the precise role of cell proliferation during human adipogenesis is unclear. Using adipose tissue-derived human mesenchymal stem cells as an in vitro cell model for adipogenic study, a group of cell cycle regulators, including Cdk1 and CCND1, were found to be downregulated as early as 24 h after adipogenic initiation and consistently, cell proliferation activity was restricted to the first 48 h of adipogenic induction. Cell proliferation was either further inhibited using siRNAs targeting cell cycle genes or enhanced by supplementing exogenous growth factor, basic fibroblast growth factor (bFGF), at specific time intervals during adipogenesis. Expression knockdown of Cdk1 at the initiation of adipogenic induction resulted in significantly increased adipocytes, even though total number of cells was significantly reduced compared to siControl-treated cells. bFGF stimulated proliferation throughout adipogenic differentiation, but exerted differential effect on adipogenic outcome at different phases, promoting adipogenesis during mitotic phase (first 48 h), but significantly inhibiting adipogenesis during adipogenic commitment phase (days 3-6). Our results demonstrate that cellular proliferation is counteractive to adipogenic commitment in human adipogenesis. However, cellular proliferation stimulation can be beneficial for adipogenesis during the mitotic phase by increasing the population of cells capable of committing to adipocytes before adipogenic commitment.

Human mesenchymal stem cell homing induced by SKOV3 cells

Human mesenchymal stem cell (hMSC) homing is the migration of endogenous and exogenous hMSCS to the target organs and the subsequent colonization under the action chemotaxic factors. This is an important process involved in the repair of damaged tissues. However, we know little about the mechanism of hMSC homing. Stromal cell derived factor-1 (SDF-1) is a cytokine secreted by stromal cells. Its only receptor CXCR4 is widely expressed in blood cells, immune cells and cells in the central nervous system. SDF-1/CXCR4 signaling pathway plays an important role in hMSC homing and tissue repair. Human cbll1 gene encodes E3 ubiquitin-protein ligase Hakai (also known as CBLL1) consisting of RING-finger domain that is involved in ubiquitination, endocytosis and degradation of epithelial cadherin (E-cadherin) as well as in the regulation of cell proliferation. We successfully constructed LV3-CXCR4 siRNA lentiviral vector, LV3-CBLL1 RNAi lentiviral vector and the corresponding cell systems which were used to induce hMSC homing in the presence of SKOV3 cells. Thus the mechanism of hMSC homing was studied.

Activation of autophagy by FOXO3 regulates redox homeostasis during osteogenic differentiation

Bone remodeling is a continuous physiological process that requires constant generation of new osteoblasts from mesenchymal stem cells (MSCs). Differentiation of MSCs to osteoblast requires a metabolic switch from glycolysis to increased mitochondrial respiration to ensure the sufficient energy supply to complete this process. As a consequence of this increased mitochondrial metabolism, the levels of endogenous reactive oxygen species (ROS) rise. In the current study we analyzed the role of forkhead box O3 (FOXO3) in the control of ROS levels in human MSCs (hMSCs) during osteogenic differentiation. Treatment of hMSCs with H₂O₂ induced FOXO3 phosphorylation at Ser294 and nuclear translocation. This ROS-mediated activation of FOXO3 was dependent on mitogen-activated protein kinase 8 (MAPK8/JNK) activity. Upon FOXO3 downregulation, osteoblastic differentiation was impaired and hMSCs lost their ability to control elevated ROS levels. Our results also demonstrate that in response to elevated ROS levels, FOXO3 induces autophagy in hMSCs. In line with this, impairment of autophagy by autophagy-related 7 (ATG7) knockdown resulted in a reduced capacity of hMSCs to regulate elevated ROS levels, together with a reduced osteoblast differentiation. Taken together our findings are consistent with a model where in hMSCs, FOXO3 is required to induce autophagy and thereby reduce elevated ROS levels resulting from the increased mitochondrial respiration during osteoblast differentiation. These new molecular insights provide an important contribution to our better understanding of bone physiology.

Secreted Frizzled-Related Protein Promotes Bone Regeneration by Human Bone Marrow-Derived Mesenchymal Stem Cells

Secreted frizzled-related protein (sFRP)-3 is a negative regulator of Wnt signaling in human mesenchymal stem cells (hMSCs). The present study investigated the effects sFRP-3 on osteogenic differentiation by assessing osteogenic gene expression in hMSCs in vitro and by examining bone regeneration in a rat bone defect model. sFRP-3 treatment induced osteogenic differentiation in hMSCs as determined by alkaline phosphatase, collagen type I, osteocalcin, and Runt-related transcription factor 2 gene expression. hMSCs with or without sFRP-3 were implanted into a rat calvarial bone defect; a radiographic analysis by micro-computed tomography and histological analysis 4 and 8 weeks after implantation showed greater bone regeneration in the sFRP(+) than in the sFRP(−) group. These results suggest that modulation of Wnt signaling contributes to osteogenic differentiation in hMSCs. Specifically, sFRP-3 induces osteoblastic differentiation of cultured MSCs and bone regeneration in a calvarial bone defect, suggesting that it can be a useful agent for the treatment of bone defects.