Nuclear organization during in vitro differentiation of porcine mesenchymal stem cells (MSCs) into adipocytes

Determination of adipogenesis stages of human umbilical cord-derived mesenchymal stem cells using three-dimensional label-free holotomography

Adipogenesis involves complex changes in gene expression, morphology, and cytoskeletal organization. However, the quantitative analysis of live cell images to identify their stages through morphological markers is limited. Distinct adipogenesis markers on human umbilical cord-derived mesenchymal stem cells (UC-MSCs) were identified through holotomography, a label-free live cell imaging technique. In the MSC-to-preadipocyte transition, the nucleus-to-cytoplasm ratio (0.080 vs. 0.052) and lipid droplet (LD) refractive index variation decreased (0.149 % vs. 0.061 %), whereas the LD number (20 vs. 65) increased. This event was also accompanied by the downregulation and upregulation of THY1 and Preadipocyte Factor-1 (PREF-1), respectively. In the preadipocyte to immature adipocyte shift, cell sphericity (0.20 vs. 0.43) and LD number (65 vs. 200) surged, large LDs (>10 μm3) appeared, and the major axis of the cell was reduced (143.7 μm vs. 83.12 μm). These findings indicate features of preadipocyte and immature adipocyte stages, alongside the downregulation of PREF-1 and upregulation of Peroxisome Proliferator-Activated Receptor gamma (PPARγ). In adipocyte maturation, along with PPARγ and Fatty Acid-Binding Protein 4 upregulation, cell compactness (0.15 vs. 0.29) and sphericity (0.43 vs. 0.59) increased, and larger LDs (>30 μm3) formed, marking immature and mature adipocyte stages. The study highlights the distinct adipogenic morphological biomarkers of adipogenesis stages in UC-MSCs, providing potential applications in biomedical and clinical settings, such as fostering innovative medical strategies for treating metabolic disease.

Adipose-derived mesenchymal stem cells' adipogenesis chemistry analyzed by FTIR and Raman metrics

The full understanding of molecular mechanisms of cell differentiation requires a holistic view. Here we combine label-free FTIR and Raman hyperspectral imaging with data mining to detect the molecular cell composition enabling noninvasive monitoring of cell differentiation and identifying biochemical heterogeneity. Mouse adipose-derived mesenchymal stem cells (AD-MSCs) undergoing adipogenesis were followed by Raman and FT-IR imaging, Oil Red, and immunofluorescence. A workflow of the data analysis (IRRSmetrics4stem) was designed to identify spectral predictors of adipogenesis and test machine-learning (ML) methods (hierarchical clustering, PCA, PLSR) for the control of the AD-MSCs differentiation degree. IRRSmetrics4stem provided insights into the chemism of adipogenesis. With single-cell tracking, we established IRRS metrics for lipids, proteins, and DNA variations during AD-MSCs differentiation. The over 90% predictive efficiency of the selected ML methods proved the high sensitivity of the IRRS metrics. Importantly, the IRRS metrics unequivocally recognize a switch from proliferation to differentiation. This study introduced a new bioassay identifying molecular markers indicating molecular transformations and delivering rapid and machine learning-based monitoring of adipogenesis that can be relevant to other differentiation processes. Thus, we introduce a novel, rapid, machine learning-based bioassay to identify molecular markers of adipogenesis. It can be relevant to identification of differentiation-related molecular processes in other cell types, and beyond the cell differentiation including progression of different cellular pathophysiologies reconstituted in vitro.

Droplet Digital PCR Quantification of Selected Intracellular and Extracellular microRNAs Reveals Changes in Their Expression Pattern during Porcine In Vitro Adipogenesis

Extracellular miRNAs have attracted considerable interest because of their role in intercellular communication, as well as because of their potential use as diagnostic and prognostic biomarkers for many diseases. It has been shown that miRNAs secreted by adipose tissue can contribute to the pathophysiology of obesity. Detailed knowledge of the expression of intracellular and extracellular microRNAs in adipocytes is thus urgently required. The system of in vitro differentiation of mesenchymal stem cells (MSCs) into adipocytes offers a good model for such an analysis. The aim of this study was to quantify eight intracellular and extracellular miRNAs (miR-21a, miR-26b, miR-30a, miR-92a, miR-146a, miR-148a, miR-199, and miR-383a) during porcine in vitro adipogenesis using droplet digital PCR (ddPCR), a highly sensitive method. It was found that only some miRNAs associated with the inflammatory process (miR-21a, miR-92a) were highly expressed in differentiated adipocytes and were also secreted by cells. All miRNAs associated with adipocyte differentiation were highly abundant in both the studied cells and in the cell culture medium. Those miRNAs showed a characteristic expression profile with upregulation during differentiation.

Cell-Laden Gradient Microgel Suspensions for Spatial Control of Differentiation During Biofabrication

During tissue development, stem and progenitor cells form functional tissue with high cellular diversity and intricate micro- and macro-architecture. Current approaches have attempted to replicate this process with materials cues or through spontaneous cell self-organization. However, cell-directed and materials-directed organization are required simultaneously to achieve biomimetic structure and function. Here, it is shown how integrating live adipose derived stem cells with gradient microgel suspensions steers divergent differentiation outcomes. Microgel matrices composed of small particles are found to promote adipogenic differentiation, while larger particles fostered increased cell spreading and osteogenic differentiation. Tuning the matrix formulation demonstrates that early cell adhesion and spreading dictate differentiation outcome. Combining small and large microgels into gradients spatially directs proliferation and differentiation over time. After 21 days of culture, osteogenic conditions foster significant mineralization within the individual microgels, thereby providing cell-directed changes in composition and mechanics within the gradient porous scaffold. Freeform printing of high-density cell suspensions is performed across these gradients to demonstrate the potential for hierarchical tissue biofabrication. Interstitial porosity influences cell expansion from the print and microgel size guides spatial differentiation, thereby providing scope to fabricate tissue gradients at multiple scales through integrated and printed cell populations.

Alteration of active and repressive histone marks during adipogenic differentiation of porcine mesenchymal stem cells

A characteristic spatial distribution of the main chromatin fractions is observed in most mammalian cell nuclei, with euchromatin localized in the interior and heterochromatin at the nuclear periphery. It has been shown that interactions of heterochromatin with the nuclear lamina are necessary to establish this conventional architecture. Adipocytes are specific cells in which a reduction in lamin A/C expression is observed. We hypothesize that the loss of lamin A/C during adipogenic differentiation of mesenchymal stem cells (MSCs) may be associated with the reorganization of the main classes of chromatin in the nucleus. Thus, in this study, we examine the abundance and nuclear distribution of selected heterochromatin (H3K9me3, H3K27me3 and H4K20me3) and euchromatin (H4K8ac, H3K4me3 and H3K9ac) histone marks during in vitro adipogenesis, using the pig as a model organism. We found that not only did the expression of lamin A/C decrease in our differentiation system, but so did the expression of lamin B receptor (LBR). The level of two heterochromatin marks, H3K27me3 and H4K20me3, increased during differentiation, while no changes were observed for H3K9me3. The levels of two euchromatin histone marks, H4K8ac and H3K9ac, were significantly higher in adipocytes than in undifferentiated cells, while the level of H3K4me3 did not change significantly. The spatial distribution of all the examined histone marks altered during in vitro adipogenesis. H3K27me3 and H4K20me3 moved towards the nuclear periphery and H3K9me3 localized preferentially in the intermediate part of adipocyte nuclei. The euchromatin marks H3K9ac and H3K4me3 preferentially occupied the peripheral part of the adipocyte nuclei, while H4K8ac was more evenly distributed in the nuclei of undifferentiated and differentiated cells. Analysis of the nuclear distribution of repetitive sequences has shown their clustering and relocalization toward nuclear periphery during differentiation. Our study shows that dynamic changes in the abundance and nuclear distribution of active and repressive histone marks take place during adipocyte differentiation. Nuclear reorganization of heterochromatin histone marks may allow the maintenance of the nuclear morphology of the adipocytes, in which reduced expression of lamin A/C and LBR is observed.

CircINSR Regulates Fetal Bovine Muscle and Fat Development

The level of muscle development in livestock directly affects the production efficiency of livestock, and the contents of intramuscular fat (IMF) is an important factor that affects meat quality. However, the molecular mechanisms through which circular RNA (circRNA) affects muscle and IMF development remains largely unknown. In this study, we isolated myoblasts and intramuscular preadipocytes from fetal bovine skeletal muscle. Oil Red O and BODIPY staining were used to identify lipid droplets in preadipocytes, and anti-myosin heavy chain (MyHC) immunofluorescence was used to identify myotubes differentiated from myoblasts. Bioinformatics, a dual-fluorescence reporter system, RNA pull-down, and RNA-binding protein immunoprecipitation were used to determine the interactions between circINSR and the micro RNA (miR)-15/16 family. Molecular and biochemical assays were used to confirm the roles played by circINSR in myoblasts and intramuscular preadipocytes. We found that isolated myoblasts and preadipocytes were able to differentiate normally. CircINSR was found to serve as a sponge for the miR-15/16 family, which targets CCND1 and Bcl-2. CircINSR overexpression significantly promoted myoblast and preadipocyte proliferation and inhibited cell apoptosis. In addition, circINSR inhibited preadipocyte adipogenesis by alleviating the inhibition of miR-15/16 against the target genes FOXO1 and EPT1. Taken together, our study demonstrated that circINSR serves as a regulator of embryonic muscle and IMF development.

Characterization of Mesenchymal Stem Cell Differentiation within Miniaturized 3D Scaffolds through Advanced Microscopy Techniques

Three-dimensional culture systems and suitable substrates topographies demonstrated to drive stem cell fate in vitro by mechanical conditioning. For example, the Nichoid 3D scaffold remodels stem cells and shapes nuclei, thus promoting stem cell expansion and stemness maintenance. However, the mechanisms involved in force transmission and in biochemical signaling at the basis of fate determination are not yet clear. Among the available investigation systems, confocal fluorescence microscopy using fluorescent dyes enables the observation of cell function and shape at the subcellular scale in vital and fixed conditions. Contrarily, nonlinear optical microscopy techniques, which exploit multi-photon processes, allow to study cell behavior in vital and unlabeled conditions. We apply confocal fluorescence microscopy, coherent anti-Stokes Raman scattering (CARS), and second harmonic generation (SHG) microscopy to characterize the phenotypic expression of mesenchymal stem cells (MSCs) towards adipogenic and chondrogenic differentiation inside Nichoid scaffolds, in terms of nuclear morphology and specific phenotypic products, by comparing these techniques. We demonstrate that the Nichoid maintains a rounded nuclei during expansion and differentiation, promoting MSCs adipogenic differentiation while inhibiting chondrogenesis. We show that CARS and SHG techniques are suitable for specific estimation of the lipid and collagenous content, thus overcoming the limitations of using unspecific fluorescent probes.

Cell adhesion and culture medium dependent changes in the high frequency mechanical vibration induced proliferation, osteogenesis, and intracellular organization of human adipose stem cells

High frequency (HF) mechanical vibration appears beneficial for in vitro osteogenesis of mesenchymal stem cells (MSCs). However, the current mechanobiological understanding of the method remains insufficient. We designed high-throughput stimulators to apply horizontal or vertical high magnitude HF (HMHF; 2.5 G_peak, 100 Hz) vibration on human adipose stem cells (hASCs). We analyzed proliferation, alkaline phosphatase (ALP) activity, mineralization, and effects on the actin cytoskeleton and nuclei using immunocytochemical stainings. Proliferation was studied on a standard tissue culture plastic (sTCP) surface and on an adhesion supporting tissue culture plastic (asTCP) surface in basal (BM) and osteogenic (OM) culture medium conditions. We discovered that the improved cell adhesion was a prerequisite for vibration induced changes in the proliferation of hASCs. Similarly, the adhesion supporting surface enabled us to observe vibration initiated ALP activity and mineralization changes in OM condition. The horizontal vibration increased ALP activity, while vertical stimulation reduced ALP activity. However, mineralization was not enhanced by the HMHF vibration. We performed image-based analysis of actin and nuclei to obtain novel data of the intracellular-level responses to HF vibration in BM and OM conditions. Our quantitative results suggest that actin organizations were culture medium and stimulation direction dependent. Both stimulation directions decreased OM induced changes in nuclear size and elongation. Consequently, our findings of the nuclear deformations provide supportive evidence for the involvement of the nuclei in the mechanocoupling of HF vibration. Taken together, the results of this study enhanced the knowledge of the intracellular mechanisms of HF vibration induced osteogenesis of MSCs.

The importance of the nuclear positioning of the PPARG gene for its expression during porcine in vitro adipogenesis

Proper expression of the PPARG gene, which encodes a key transcription factor of adipogenesis, is indispensable in the formation of mature adipocytes. The positioning of a gene within the nuclear space has been implicated in gene regulation. We here report on the significance of the PPARG gene’s nuclear positioning for its activity during in vitro adipogenesis in the pig. We used an established system of differentiation of mesenchymal stem cells derived from bone marrow and adipose tissue into adipocytes. The differentiation process was carried out for 7 days, and the cells were examined using the 3D DNA/immuno-FISH and RNA/DNA-FISH approaches. PPARG transcript level was measured using real-time PCR, and PPARγ activity was detected with colorimetric assay. Changes in the nuclear location of the PPARG gene were observed when we compared undifferentiated mesenchymal stem cells with mature adipocytes. The gene moved from the nuclear periphery to the nuclear center as its transcriptional activity increased. The RNA/DNA-FISH approach shows that differences in primary transcript production correlated with the allele’s nuclear positioning. Transcriptionally active alleles preferentially occupy the central part of the nucleus, while inactive alleles are found on the nuclear periphery. We also show that transcription of PPARG begins with one allele, but that both alleles are active in later stages of differentiation. Our results provide evidence that functionally distinct alleles of the PPARG gene are positioned in different parts of the cell nucleus. This confirms the importance of nuclear architecture to the regulation of PPARG gene transcription, and thus to the fate of the adipose cell.

Combining PLGA Scaffold and MSCs for Brain Tissue Engineering: A Potential Tool for Treatment of Brain Injury

Nerve tissue engineering is an important strategy for the treatment of brain injuries. Mesenchymal stem cell (MSC) transplantation has been proven to be able to promote repair and functional recovery of brain damage, and poly (lactic-co-glycolic acid) (PLGA) has also been found to have the capability of bearing cells. In the present study, to observe the ability of PLGA scaffold in supporting the adherent growth of MSCs and neurons in vivo and vitro and to assess the effects of PLGA scaffold on proliferation and neural differentiation of MSCs, this study undertakes the following steps. First, MSCs and neurons were cultured and labeled with green fluorescent protein (GFP) or otherwise identified and the PLGA scaffold was synthesized. Next, MSCs and neurons were inoculated on PLGA scaffolds and their adhesion rates were investigated and the proliferation of MSCs was evaluated by using MTT assay. After MSCs were induced by a neural induction medium, the morphological change and neural differentiation of MSCs were detected using scanning electron microscopy (SEM) and immunocytochemistry, respectively. Finally, cell migration and adhesion in the PLGA scaffold in vivo were examined by immunohistochemistry, nuclear staining, and SEM. The experimental results demonstrated that PLGA did not interfere with the proliferation and neural differentiation of MSCs and that MSCs and neuron could grow and migrate in PLGA scaffold. These data suggest that the MSC-PLGA complex may be used as tissue engineering material for brain injuries.