Natalia de Isla

Collagenous Extracellular Matrix of Cartilage Submitted to Mechanical Forces Studied by Second Harmonic Generation Microscopy

Osteoarthritis is a degenerative pathology leading to degradation of the extracellular matrix (ECM). Similar effects can be visualized when applying mechanical or biochemical constraints on cartilaginous tissue. Here, we characterized modification of the ECM appearing under mechanical compression and/or biochemical action (hypoxia environment, nitric oxide and collagenase action). In recent decades, multiphoton microscopy has proved its interest for observing living, thick and opaque biological tissues. Thus, the main components of the cartilaginous ECM can be observed without fluorescent labeling. In particular, the collagen network emits strong second harmonic generation (SHG) signal which could be collected at half of the excitation wavelength. Combining autofluorescence and SHG signal detection enables to obtain complementary structural information. Here, we proved that multiphoton microscopy represents an appropriate tool for ex vitro cartilage imaging. First, we showed that SHG signal specifically comes from collagen (collagenase digestion). Further, we verified that the use of an appropriate band‐pass filter enables to reject the autofluorescence from the ECM. Once this specificity was shown, we followed modification of the cartilage ECM submitted to mechanical or biochemical constraints (compression, enzymatic digestion). By performing textural analysis of SHG images (Haralick’s method), we showed the restructuration of the collagen network according to constraints.

Donor's age dependent proliferation decrease of human bone marrow mesenchymal stem cells is linked to diminished clonogenicity

While mesenchymal stem cells represent an interesting cell source for regenerative medicine, several points have to be investigated to improve their use in clinical, and in particular in the elderly population. This work studied the proliferation capacity of mesenchymal stem cells isolated from human bone marrow in function of donors age. Doubling time after in vitro culture, clonogenicity and phenotype were analyzed in 17 samples ranging from 3 to 85 years old (mean 47 ± 27). Results showed an increase in the doubling time for cell coming from old donor compared to cells coming from young ones. This was accompanied by a decrease in clonogenicity while no changes were observe in cell phenotype. In conclusion, this study showed an effect of donors age on the proliferation capacity of mesenchymal stem cells isolated from bone marrow that was correlated to a decrease in clonogenicity. The comprehension of molecular mechanism involved in this process could help to improve the clinical application of mesenchymal stem cells.

Research on stem cells as candidates to be differentiated into hepatocytes

Liver diseases have become one of the most important causes of morbidity and mortality in the world. Cell therapy and liver transplantation are though to be two treatment options well accepted. However, the shortage of cells sources in cytotherapy and the lack of liver donor in liver transplantation are the major obstacles for the performance of these treatment methods. It urged us to find new origins of extra-hepatic cells. A number of recent studies show that extra-hepatic mesenchymal stem cells (MSC) from different tissues can be differentiated into hepatocytes like cells (HLC). Several hepatic differentiation protocols of MSC have been published in recent years, based on cellular stimulation with exogenous cytokines/growth factors, co-culture with fetal or adult hepatocytes, 2- or 3-dimensional (2D, 3D) matrices to favor differentiation. Independently from the starting stem cells population used, some minimal criteria must be fulfilled to ensure therapeutic success: in vitro expandability, expression of hepatic like surface markers, with hepatic cell functions, and minimal or absent immunogenicity in the recipient host. In this review, we focused on stem cells originated from bone marrow, umbilical cord and adipose tissue which are widely investigated in recent years and have been proved to have liver regenerative potential, the factors used to differentiate stem cells to hepatocyte-like cells and the methods used to investigate these cells.

Active implant combining human stem cell microtissues and growth factors for bone-regenerative nanomedicine

AIMS Mesenchymal stem cells (MSCs) from adult bone marrow provide an exciting and promising stem cell population for the repair of bone in skeletal diseases. Here, we describe a new generation of collagen nanofiber implant functionalized with growth factor BMP-7 nanoreservoirs and equipped with human MSC microtissues (MTs) for regenerative nanomedicine. MATERIALS & METHODS By using a 3D nanofibrous collagen membrane and by adding MTs rather than single cells, we optimize the microenvironment for cell colonization, differentiation and growth. RESULTS & CONCLUSION Furthermore, in this study, we have shown that by combining BMP-7 with these MSC MTs in this double 3D environment, we further accelerate bone growth in vivo. The strategy described here should enhance the efficiency of therapeutic implants compared with current simplistic approaches used in the clinic today based on collagen implants soaked in bone morphogenic proteins.

Quantification of glycophorin A and glycophorin B on normal human RBCs by flow cytometry

BACKGROUND: The quantification of antigens and proteins on RBCs has been achieved by different approaches. Flow cytometry allows the results of the earliest studies to be to reappraised because it offers the possibility of measuring the immunofluorescence intensity of single cells and integrating the individual data of a large number of cells within a very short time.

Application potential of mesenchymal stem cells derived from Wharton's jelly in liver tissue engineering

The shortage of organ resource has been limiting the application of liver transplantation. Bioartificial liver construction is increasingly focused as a replacement treatment. To product a bioartificial liver, three elements must be considered: seeding cells, scaffold and bioreactor. Recent studies have shown that several methods can successfully differentiate MSC (mesenchymal stem cells) derived from Whartons jelly into hepatocyte, such as stimulating MSC by cytokines and growth factors, direct and indirect co-culture MSC with hepatocytes, or promote MSC differentiation by 3-dimensional matrix. In some cases, differentiation of MSC into hepatocytes can also be an alternative approach for whole organ transplantation in treatment of acute and chronic liver diseases. In this review, the characterization of MSC from Whartons jelly, their potential of application in liver tissue engineering on base of decellularized scaffold, their status of banking and their preclinical work performed will be discussed.

An approach to preparing decellularized whole liver organ scaffold in rat

OBJECTIVES In present study, we plan to produce a decellularization protocol from rat liver to generate a three-dimensional whole organ scaffold. METHODS A combination of 1% SDS and 1% tritonX-100 were used orderly to decellularize rat livers. After about 6 h of interactive antegrade/retrograde perfusion, a decellularized whole translucent liver scaffold with integrated blood vessel networks was generated. The decellularized livers are charactered by light microscopy, scanning electron microscopy, and biochemical analysis (DNA quantification) for preservation of the three-dimension of extracellular matrix architecture. RESULTS The decellularization protocol was verified by observation of the whole translucent liver organ with intact vascular trees under macroscopy, in conjunction with the hematoxylin-eosin staining that showed no cells or nuclear material remained. Additionally, the Massons stain indicted that the extracellular proteins were well kept and scanning electron microscopy (SEM) revealed a preserved decellularized matrix architecture. Compared to normal livers, DNA in the decellularized livers was quantified less than 10% at the same mass. CONCLUSIONS The current method of decellularization protocol was feasible, simple and quick, and was verified by an absence of residual cells. The decellularized extracellular matrix had preserved integrate vascular network and a three-dimensional architecture.

Research progress in liver tissue engineering

Liver transplantation is the definitive treatment for patients with end-stage liver diseases (ESLD). However, it is hampered by shortage of liver donor. Liver tissue engineering, aiming at fabricating new livers in vitro, provides a potential resolution for donor shortage. Three elements need to be considered in liver tissue engineering: seeding cell resources, scaffolds and bioreactors. Studies have shown potential cell sources as hepatocytes, hepatic cell line, mesenchymal stem cells and others. They need scaffolds with perfect biocompatiblity, suitable micro-structure and appropriate degradation rate, which are essential charateristics for cell attachment, proliferation and secretion in forming extracellular matrix. The most promising scaffolds in research include decellularized whole liver, collagens and biocompatible plastic. The development and function of cells in scaffold need a microenvironment which can provide them with oxygen, nutrition, growth factors, et al. Bioreactor is expected to fulfill these requirements by mimicking the living condition in vivo. Although there is great progress in these three domains, a large gap stays still between their researches and applications. Herein, we summarized the recent development in these three major fields which are indispensable in liver tissue engineering.

Mechanical stimulations on human bone marrow mesenchymal stem cells enhance cells differentiation in a three-dimensional layered scaffold

Scaffolds laden with stem cells are a promising approach for articular cartilage repair. Investigations have shown that implantation of artificial matrices, growth factors or chondrocytes can stimulate cartilage formation, but no existing strategies apply mechanical stimulation on stratified scaffolds to mimic the cartilage environment. The purpose of this study was to adapt a spraying method for stratified cartilage engineering and to stimulate the biosubstitute. Human mesenchymal stem cells from bone marrow were seeded in an alginate (Alg)/hyaluronic acid (HA) or Alg/hydroxyapatite (Hap) gel to direct cartilage and hypertrophic cartilage/subchondral bone differentiation, respectively, in different layers within a single scaffold. Homogeneous or composite stratified scaffolds were cultured for 28 days and cell viability and differentiation were assessed. The heterogeneous scaffold was stimulated daily. The mechanical behaviour of the stratified scaffolds were investigated by plane–strain compression tests. Results showed that the spraying process did not affect cell viability. Moreover, cell differentiation driven by the microenvironment was increased with loading: in the layer with Alg/HA, a specific extracellular matrix of cartilage, composed of glycosaminoglycans and type II collagen was observed, and in the Alg/Hap layer more collagen X was detected. Hap seemed to drive cells to a hypertrophic chondrocytic phenotype and increased mechanical resistance of the scaffold. In conclusion, mechanical stimulations will allow for the production of a stratified biosubstitute, laden with human mesenchymal stem cells from bone marrow, which is capable in vivo to mimic all depths of chondral defects, thanks to an efficient combination of stem cells, biomaterial compositions and mechanical loading.

Interest of multimodal imaging in tissue engineering

One of the major limitations when imaging biological tissues results in their thickness and opacity. To overcome these limitations and to visualize some structures of interest and to precise the relationship between the structure and the biological function [6], new imaging methods have been developed. Confocal Laser Scanning Microscopy (CLSM) is the reference technique for biological imaging. But CLSM induces some problems of photo toxicity for tissue which are observed in hard conditions. To overcome this gap, linear optical microscopy also called multiphoton microscopy continues to prove its useful for imaging live tissues in particular with reduced toxicity [9,10]. Multiphoton imaging is noninvasive, by keeping the cells alive and enables to be close to physiological conditions and allows a deeper penetration into samples [3,11] than more usual UV-visible techniques [7]. MP-excitation needs a quasi simultaneous absorption of two (or 3) photons, that means a spatio-temporal confinement of photons. A way to satisfy it and to bring a molecule into its excited state consists in using short impulsions at very high frequency. To come back to its fundamental state, many desexcitation ways among which fluorescence emission are possible. The emitted signal is specific to a molecule and its physicochemical environment and can be resolved as well spatially as temporally or spectrally. Some new tools have been developed to obtain complementary information. FLIM (Fluorescence Lifetime Imaging Microscopy) provides a discrimination of molecules on their different lifetimes (contrast image) whereas their emission spectra overlap. Importantly, the lifetime value measured for by FLIM is a property of individual fluorescent molecules and is therefore largely independent of fluorophore concentration and photobleaching [5]. In addition, the emission of specific fluorophores can be contrasted against a strong auto-fluorescence background as encountered in many biological tissues.