Simulated microgravity using a rotary cell culture system promotes chondrogenesis of human adipose-derived mesenchymal stem cells via the p38 MAPK pathway. Biochem Biophys Res Commun. 2011;414:412-418. [PMID: 21971552 DOI: 10.1016/j.bbrc.2011.09.103]

MiR-335-5p promotes chondrogenesis in mouse mesenchymal stem cells and is regulated through two positive feedback loops

Chondrogenic differentiation of mesenchymal stem cells (MSCs) is regulated by many factors and signal pathways, including transcription factors such as Sox9 and microRNAs. MiR-335-5p has been previously reported to regulate osteogenic and adipogenic differentiations of MSCs, but its role in chondrogenic differentiation of MSC remains unknown. In this study, we found that miR-335-5p and its host gene Mest are co-expressed and greatly upregulated during mouse MSCs (mMSCs) chondrogenesis. Overexpression of miR-335-5p in mMSCs increased expression of chondrogenic marker genes. Molecular mechanism explorations revealed that miR-335-5p targets Daam1 and ROCK1, a set of negative regulators of Sox9; Sox9 downregulates the expression of miR-29a and 29b, both negative regulators of Mest expression, thus forming a positive loop from miR-335-5p to Sox9 to Mest/miR-335-5p. In addition, miR-335-5p targets DKK1 during mMSC chondrogenic differentiation to increase β-catenin/TCF activity, which leads to increased level of Mest transcription. These data showed miR-335-5p positively regulates MSC chondrogenesis, and two positive feedback loops are identified for the expression of miR-335-5p and its host gene Mest during the early phase of mMSC chondrogenic differentiation.

Three-dimensional aggregates of mesenchymal stem cells: cellular mechanisms, biological properties, and applications

Mesenchymal stem cells (MSCs) are primary candidates in cell therapy and tissue engineering and are being tested in clinical trials for a wide range of diseases. Originally isolated and expanded as plastic adherent cells, MSCs have intriguing properties of in vitro self-assembly into three-dimensional (3D) aggregates reminiscent of skeletal condensation in vivo. Recent studies have shown that MSC 3D aggregation improved a range of biological properties, including multilineage potential, secretion of therapeutic factors, and resistance against ischemic condition. Hence, the formation of 3D MSC aggregates has been explored as a novel strategy to improve cell delivery, functional activation, and in vivo retention to enhance therapeutic outcomes. This article summarizes recent reports of MSC aggregate self-assembly, characterization of biological properties, and their applications in preclinical models. The cellular and molecular mechanisms underlying MSC aggregate formation and functional activation are discussed, and the areas that warrant further investigation are highlighted. These analyses are combined to provide perspectives for identifying the controlling mechanisms and refining the methods of aggregate fabrication and expansion for clinical applications.

Murine adipose tissue-derived stromal cell apoptosis and susceptibility to oxidative stress in vitro are regulated by genetic background

Adipose tissue-derived stromal cells (ADSCs) are of interest for regenerative medicine as they are isolated easily and can differentiate into multiple cell lineages. Studies of their in vitro proliferation, survival, and differentiation are common; however, genetic effects on these phenotypes remain unknown. To test if these phenotypes are genetically regulated, ADSCs were isolated from three genetically diverse inbred mouse strains- C57BL/6J (B6), BALB/cByJ (BALB), and DBA/2J (D2)- in which genetic regulation of hematopoietic stem function is well known. ADSCs from all three strains differentiated into osteogenic and chondrogenic lineages in vitro. ADSCs from BALB grew least well in vitro, probably due to apoptotic cell death after several days in culture. BALB ADSCs were also the most susceptible to the free radical inducers menadione and H₂O₂. ADSCs from the three possible F1 hybrids were employed to further define genetic regulation of ADSC phenotypes. D2, but not B6, alleles stimulated ADSC expansion in BALB cells. In contrast, B6, but not D2, alleles rescued BALB H₂O₂ resistance. We conclude that low oxidative stress resistance does not limit BALB ADSC growth in vitro, as these phenotypes are genetically regulated independently. In addition, ADSCs from these strains are an appropriate model system to investigate genetic regulation of ADSC apoptosis and stress resistance in future studies. Such investigations are essential to optimize cell expansion and differentiation and thus, potential for regenerative medicine.