Wound healing requires a coordinated interplay among cells, growth factors, and extracellular matrix proteins. Central to this process is the endogenous mesenchymal stem cell (MSC), which coordinates the repair response by recruiting other host cells and secreting growth factors and matrix proteins. MSCs are self-renewing multipotent stem cells that can differentiate into various lineages of mesenchymal origin such as bone, cartilage, tendon, and fat. In addition to multilineage differentiation capacity, MSCs regulate immune response and inflammation and possess powerful tissue protective and reparative mechanisms, making these cells attractive for treatment of different diseases. The beneficial effect of exogenous MSCs on wound healing was observed in a variety of animal models and in reported clinical cases. Specifically, they have been successfully used to treat chronic wounds and stimulate stalled healing processes. Recent studies revealed that human placental membranes are a rich source of MSCs for tissue regeneration and repair. This review provides a concise summary of current knowledge of biological properties of MSCs and describes the use of MSCs for wound healing. In particular, the scope of this review focuses on the role MSCs have in each phase of the wound-healing process. In addition, characterization of MSCs containing skin substitutes is described, demonstrating the presence of key growth factors and cytokines uniquely suited to aid in wound repair.

The optimal mesenchymal stem cell (MSC) culture conditions that would allow clinically viable tissue-engineered devices are still yet to be determined. Most MSCs are found in the bone marrow, an area that also contains numerous osteoblasts and adipocytes. Paracrine signalling may be leveraged to modulate MSC differentiation in the preparation of a tissue-engineered device. Thus, the objectives of this study were to determine the effects of adipocyte-conditioned medium (CM) on MSC differentiation to osteoblasts and to determine the effects of osteoblast CM on MSC differentiation to adipocytes. Two groups of murine MSCs were given either an osteogenic differentiation medium or an adipogenic differentiation medium. CM was taken from one group and administered to the opposite group in concentrations of 25% or 50%. Metabolic activity, total protein and alkaline phosphatase (ALP) assays were conducted on the osteogenic group at predefined time points throughout the 21 day study, while metabolic activity, triglyceride and oil red O assays were conducted on the adipogenic group at predefined time points. Adipocyte CM administered at a concentration of 50% increased the ALP production of MSCs undergoing osteogenic differentiation. Additionally, osteoblast CM increased the triglyceride production of MSCs undergoing adipogenic differentiation and enlarged the lipid vesicles that were produced by the cells. The effects of the osteoblast CM were seen at both concentrations, but were greatest at the 50% CM level.

Failure of rotator cuff repair is a well-documented problem. Successful repair is impeded by muscle atrophy, fat infiltration, devascularization, and scar tissue formation throughout the fibrocartilagenous transition zone. This case study exemplifies a technique to biologically augment rotator cuff healing. Clinically, pain and function improved. Postoperative magnetic resonance imaging evaluation confirmed construct integrity. Biological enhancement of the healing process and physiologically based alterations in rehabilitation protocols can successfully treat complicated rotator cuff tears. Prospective studies with larger sample sizes and continued follow-up are necessary to assess the definitive efficacy of this treatment modality.

Surgical treatment following breast cancer, i.e. lumpectomy and mastectomy, may not efficiently remove all cancerous cells. As such, when mesenchymal stem cells (MSCs) are incorporated into the breast reconstruction process, it is likely that those MSCs will encounter remnant cancerous cells after transplantation into the defect site. The potential interaction between breast cancer cells and MSCs remains unclear. We hypothesized that paracrine interactions might occur between cells and various proteinases, growth factors and other cytokine molecules in the local microenvironment. Conditioned media (CM) from two mouse mammary cancer cell lines (4T1 and 4T07) and one mouse mammary epithelial cell line (NMuMG) were studied in the experimental model. Post-confluent mouse MSCs (D1 cells) were differentiated with an adipogenic hormonal cocktail. Conditioned media from the three cell types did not have an inhibitory effect on D1 cell viability; however, triglyceride (TG) and Oil red O (ORO) analysis results showed that 4T1-CM significantly inhibited D1 adipocyte differentiation and reduced lipid vesicle accumulation in the differentiating D1 cells. Preliminary analysis of the conditioned media revealed that a higher presence of matrix metalloprotease-9 (MMP-9) and urokinase plasminogen activator (uPA) was present in the 4T1-CM as compared to the levels found in 4T07-CM and NMuMG-CM, which were below the detection limit. Additionally, the conditioned medium of differentiated D1 cells on day 12 had a negative effect on 4T1 and 4T07 cell viability but no effect on NMuMG cell viability. The results suggest that mouse breast cancer cells modulate mouse MSC adipogenic differentiation, the level of modulation specific to the metastatic level.

A composite that utilizes the osteoinductivity of demineralized bone matrix (DBM) and the attractive characteristics of polylactide (PL) may be useful as a tissue-engineered bone substitute. The objective of this study was to investigate the potential of a composite system consisting of DBM fragments and PL beads to support the attachment and proliferation of multipotent mouse marrow stromal cells and to provide a structure for the cells' differentiation into the osteoblast lineage. Furthermore, the overarching goal was to provide a preliminary assessment of the DBM/PL cultures in order to facilitate the development of injectable composite DBM/PL systems in the long term. Demineralized bone matrix fragments were produced from bovine femurs and polylactide beads were produced by a single emulsion process. Differential scanning calorimetry and gel-permeation chromatography were used to characterize the PL samples. Multipotent mouse marrow stromal cells were cultured on several different substrate mixtures including 100% DBM, 70% DBM:30% PL, 50% DBM:50% PL and 100% PL. Cells were analyzed using a LIVE/DEAD(®) Viability/Cytotoxicity kit as well as scanning electron microscopy. Lactic acid and glucose levels were measured throughout the study. Osteogenic differentiation of the MSCs was assessed with an alkaline phosphatase activity (ALP) assay and RT-PCR for expression of bone sialoprotein, osteocalcin and runt-related transcription factor 2. All cell types attached more readily to DBM fragments than PL beads resulting in more lactic acid production in the samples containing mostly DBM. The ALP activity and gene expression results indicate that the optimal mixture for the D1 line of multipotent mouse marrow stromal cells differentiation into osteoblasts is 100% PL. However, it is likely that the decreased pH in the DBM containing samples resulted in an environment that was not very conducive for osteogenic differentiation.

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The biochemical factors that regulate cell proliferation and differentiation can provide a means of optimizing culture conditions to develop a tissue-engineered osteochondral construct. Thus, the objectives of this study were to determine the effects of chondrocyte conditioned medium (CM) on the osteogenic differentiation of mesenchymal stem cells (MSCs) cultured on poly(L-lactide-co-epsilon-caprolactone)/hydroxyapatite (PLA/PCL/HAP) scaffolds and to determine the effect of osteoblast CM on the chondrogenic differentiation of MSCs cultured in alginate. In addition, the biomaterial's effect on MSC differentiation was also investigated. MSCs were grown in two groups: (1) on porous PLA/PCL/HAP scaffolds in osteogenic differentiation medium or (2) encapsulated in alginate in chondrogenic differentiation medium. CM was taken from one group and administered to the 'opposite' group in volumetric concentrations of 25% or 50% at each medium change. The osteogenic group samples that were administered chondrocyte CM showed higher alkaline phosphatase activity than the controls that were not administered CM. Additionally, the cells that were given chondrocyte CM had higher osteocalcin and sialoprotein expression than the controls. Samples in the chondrogenic group that were administered osteoblast CM at a volumetric concentration of 50% produced more sGAG than the controls. The aggrecan and Sox9 expression was significantly higher in the samples given 50% CM as compared to the controls. The study also showed that culturing cells in alginate, without differentiation medium, can produce similar levels of differentiation as cells that were administered differentiation medium.

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