3D Scaffolds to Model the Hematopoietic Stem Cell Niche: Applications and Perspectives.

Hematopoietic stem cells (HSC) are responsible for the production of blood and immune cells during life. HSC fate decisions are dependent on signals from specialized microenvironments in the bone marrow, termed niches. The HSC niche is a tridimensional environment that comprises cellular, chemical, and physical elements. Introductorily, we will revise the current knowledge of some relevant elements of the niche. Despite the importance of the niche in HSC function, most experimental approaches to study human HSCs use bidimensional models. Probably, this contributes to the failure in translating many in vitro findings into a clinical setting. Recreating the complexity of the bone marrow microenvironment in vitro would provide a powerful tool to achieve in vitro production of HSCs for transplantation, develop more effective therapies for hematologic malignancies and provide deeper insight into the HSC niche. We previously demonstrated that an optimized decellularization method can preserve with striking detail the ECM architecture of the bone marrow niche and support HSC culture. We will discuss the potential of this decellularized scaffold as HSC niche model. Besides decellularized scaffolds, several other methods have been reported to mimic some characteristics of the HSC niche. In this review, we will examine these models and their applications, advantages, and limitations.

Growth factor stimulation improves the structure and properties of scaffold-free engineered auricular cartilage constructs.

The reconstruction of the external ear to correct congenital deformities or repair following trauma remains a significant challenge in reconstructive surgery. Previously, we have developed a novel approach to create scaffold-free, tissue engineering elastic cartilage constructs directly from a small population of donor cells. Although the developed constructs appeared to adopt the structural appearance of native auricular cartilage, the constructs displayed limited expression and poor localization of elastin. In the present study, the effect of growth factor supplementation (insulin, IGF-1, or TGF-ß1) was investigated to stimulate elastogenesis as well as to improve overall tissue formation. Using rabbit auricular chondrocytes, bioreactor-cultivated constructs supplemented with either insulin or IGF-1 displayed increased deposition of cartilaginous ECM, improved mechanical properties, and thicknesses comparable to native auricular cartilage after 4 weeks of growth. Similarly, growth factor supplementation resulted in increased expression and improved localization of elastin, primarily restricted within the cartilaginous region of the tissue construct. Additional studies were conducted to determine whether scaffold-free engineered auricular cartilage constructs could be developed in the 3D shape of the external ear. Isolated auricular chondrocytes were grown in rapid-prototyped tissue culture molds with additional insulin or IGF-1 supplementation during bioreactor cultivation. Using this approach, the developed tissue constructs were flexible and had a 3D shape in very good agreement to the culture mold (average error <400 µm). While scaffold-free, engineered auricular cartilage constructs can be created with both the appropriate tissue structure and 3D shape of the external ear, future studies will be aimed assessing potential changes in construct shape and properties after subcutaneous implantation.

Temporal changes in matrix metalloproteinases, their inhibitors, and cathepsins in mouse pubic symphysis during pregnancy and postpartum.

Remodeling and relaxation of the mouse pubic symphysis (PS) are central events in parturition. The involvement of endogenous proteins such as matrix metalloproteinases (MMPs), tissue inhibitors of matrix metalloproteinases (TIMPs), and cathepsins in these phenomena remains unclear. In this work, we used a combination of immunolocalization, protein expression/activity, and relative messenger RNA (mRNA) expression to examine the changes in selected MMPs (-2, -9, and -8), TIMPs (-1 and -2), and cathepsins (B and K) during pregnancy and postpartum in mice. Immunohistochemistry revealed the presence of all of these proteins in the cytoplasm of chondrocytes, fibrochondrocytes, and fibroblast-like cells in the interpubic tissues. Zymography showed increases in the active forms of MMP-2 and -9 primarily on days 15 to 19 of pregnancy. Western blotting showed enhanced expression of MMP-8 on days 12 to 15 of pregnancy, with no changes in cathepsins B and K. Matrix metalloproteinases 2, TIMP-1 and -2, and cathepsin B had significant relative gene expression throughout pregnancy. These findings indicate that during pregnancy and postpartum there are variations in the expression and activity of proteins that may have an important role in remodeling the pubic symphysis during these events.