In this study, we aimed at investigating the interactions between primary chondrocytes and mesenchymal stem/stromal cells (MSC) accounting for improved chondrogenesis in coculture systems. Expanded MSC from human bone marrow (BM-MSC) or adipose tissue (AT-MSC) were cultured in pellets alone (monoculture) or with primary human chondrocytes from articular (AC) or nasal (NC) cartilage (coculture). In order to determine the reached cell number and phenotype, selected pellets were generated by combining: (i) human BM-MSC with bovine AC, (ii) BM-MSC from HLA-A2+ with AC from HLA-A2- donors, or (iii) human green fluorescent protein transduced BM-MSC with AC. Human BM-MSC and AC were also cultured separately in transwells. Resulting tissues and/or isolated cells were assessed immunohistologically, biochemically, cytofluorimetrically, and by RT-PCR. Coculture of NC or AC (25%) with BM-MSC or AT-MSC (75%) in pellets resulted in up to 1.6-fold higher glycosaminoglycan content than what would be expected based on the relative percentages of the different cell types. This effect was not observed in the transwell model. BM-MSC decreased in number (about fivefold) over time and, if cocultured with chondrocytes, increased type II collagen and decreased type X collagen expression. Instead, AC increased in number (4.2-fold) if cocultured with BM-MSC and maintained a differentiated phenotype. Chondro-induction in MSC-chondrocyte coculture is a robust process mediated by two concomitant effects: MSC-induced chondrocyte proliferation and chondrocyte-enhanced MSC chondrogenesis. The identified interactions between progenitor and mature cell populations may lead to the efficient use of freshly harvested chondrocytes for ex vivo cartilage engineering or in situ cartilage repair.
This work examines how mechanical signals affect the barrier function and stability of engineered human microvessels in microfluidic type I collagen gels. Constructs that were exposed to chronic low flow displayed high permeabilities to bovine serum albumin and 10 kDa dextran, numerous focal leaks, low size selectivity, and short lifespan of less than one week. Higher flows promoted barrier function and increased longevity; at the highest flows, the barrier function rivaled that observed in vivo, and all vessels survived to day 14. By studying the physiology of microvessels of different geometries, we established that shear stress and transmural pressure were the dominant mechanical signals that regulated barrier function and vascular stability, respectively. In microvessels that were exposed to high flow, elevation of intracellular cyclic AMP further increased the selectivity of the barrier and strongly suppressed cell proliferation. Computational models that incorporated stress dependence successfully predicted vascular phenotype. Our results indicate that the mechanical microenvironment plays a major role in the functionality and stability of engineered human microvessels in microfluidic collagen gels.
The silk produced by silkworms are biopolymers and can be classified into two types--mulberry and nonmulberry. Mulberry silk of silkworm Bombyx mori has been extensively explored and used for century old textiles and sutures. But for the last few decades it is being extensively exploited for biomedical applications. However, the transformation of nonmulberry silk from being a textile commodity to biomaterials is relatively new. Within a very short period of time, the combination of load bearing capability and tensile strength of nonmulberry silk has been equally envisioned for bone, cartilage, adipose, and other tissue regeneration. Adding to its advantage is its diverse morphology, including macro to nano architectures with controllable degradation and biocompatibility yields novel natural material systems in vitro. Its follow on applications involve sustained release of model compounds and anticancer drugs. Its 3D cancer models provide compatible microenvironment systems for better understanding of the cancer progression mechanism and screening of anticancer compounds. Diversely designed nonmulberry matrices thus provide an array of new cutting age technologies, which is unattainable with the current synthetic materials that lack biodegradability and biocompatibility. Scientific exploration of nonmulberry silk in tissue engineering, regenerative medicine, and biotechnological applications promises advancement of sericulture industries in India and China, largest nonmulberry silk producers of the world. This review discusses the prospective biomedical applications of nonmulberry silk proteins as natural biomaterials.
Thrombospondins (TSPs) are widely known as a family of five calcium-binding matricellular proteins. While these proteins belong to the same family, they are encoded by different genes, regulate different cellular functions and are localized to specific regions of the body. TSP-5 or Cartilage Oligomeric Matrix Protein (COMP) is the only TSP that has been associated with skeletal disorders in humans, including pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED). The pentameric structure of COMP, the evidence that it interacts with multiple cellular proteins, and the recent reports of COMP acting as a 'lattice' to present growth factors to cells, inspired this review of COMP and its interacting partners. In our review, we have compiled the interactions of COMP with other proteins in the cartilage extracellular matrix and summarized their importance in maintaining the structural integrity of cartilage as well as in regulating cellular functions.
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