Characterization of differential properties of rabbit tendon stem cells and tenocytes
This study focuses on the differential properties of tendon stem cells (TSCs) and tenocytes. We show that TSCs can differentiate into adipocytes, chondrocytes, and osteocytes in vitro, and form tendon-like, cartilage-like, and bone-like tissues in vivo. In contrast, tenocytes have little such differentiation potential. Moreover, TSCs express the stem cell markers Oct-4 (left panel), SSEA-4 (middle panel), and nucleostemin (right panel), whereas tenocytes express none of these markers. Morphologically, TSCs possess smaller cell bodies and larger nuclei than ordinary tenocytes and assume cobblestone-like morphology in confluent culture whereas tenocytes are highly elongated. TSCs also proliferate more quickly than tenocytes in culture. Additionally, TSCs from patellar tendons form more numerous and larger colonies and proliferated more rapidly than TSCs from Achilles tendons.
The differentiation of TSCs in response to mechanical loading
Mechanical loading is an inherent part of tendon environment. This study focuses on determining the effect of mechanical loading on TSC differentiation. We found that the application of 4% stretching (or "clamp-to-clamp" engineering strain) to TSCs significantly increases cellular expression of collagen type I gene, but not PPAR-gamma (a marker for adipocytes), collagen type II, SOX-9 (two markers for chondrocytes), and Runx2 (marker for osteocytes). However, the application of 8% stretching to TSCs significantly increases expression of all tenocyte and non-tenocyte related genes. We postulate that excessive mechanical loading placed on tendons in vivo may cause the development of tendinopathy through loading-induced aberrant differentiation of TSCs into non-tenocytes.
Differential properties of human ACL and MCL stem cells
The aim of this study is to determine the differential properties of human ACL and MCL stem cells. We found that both hACL stem cells (hACL-SCs) and hMCL stem cells (hMCL-SCs) form colonies in culture and express the stem cell markers nucleostemin and SSEA-4. Moreover, both hACL-SCs and hMCL-SCs express CD surface markers for mesenchymal stem cells, including CD44 and CD90, but not those markers for vascular cells, CD31, CD34, CD45, and CD146. However, hACL-SCs differ from hMCL-SCs in that the size and number of hACL-SC colonies in culture are much smaller and grew more slowly than hMCL-SC colonies. Moreover, fewer hACL-SCs in cell colonies express stem cell markers STRO-1 and Oct-4 than hMCL-SCs. Finally, hACL-SCs have less multi-differentiation potential than hMCL-SCs, evidenced by differing extents of adipogenesis, chondrogenesis, and osteogenesis in the respective induction media.
The effect of platelet-rich plasma (PRP) on TSC differentiation
Platelet-rich plasma (PRP) has been widely used in orthopaedic/sports medicine for treatment of injured tendons. This study is to determine the effects of PRP, in the form of PRP-clot releasate (PRCR), on tendon stem cells (TSCs), a newly discovered cell population in tendons. We showed that PRCR treatment promotes TSC differentiation into fibroblast-like cells. In addition, PRCR treatment increases cell proliferation rates over non-treated control cells in a dose-dependent manner. Moreover, compared to control cells, PRCR treatment of TSCs markedly increases cellular expression of alpha-smooth muscle actin (alpha-SMA), collagen type I and III protein expression, and total collagen production. The findings indicate that PRCR treatment induces differentiation of TSCs into activated tenocytes.
The application of cell traction force microscopy (CTFM) to cell biology research
When a cell migrates, it generates traction forces on the underlying substrate. The cell traction force (CTF) is not only essential for cell migration; it is also used by cells to control their shape and maintain cellular homeostasis. As such, quantification of CTFs aids in better understanding of many fundamental biological processes such as morphogenesis, angiogenesis, and wound healing of tissues and organs. A new technology called cell traction force microscopy (CTFM) has been developed to determine CTFs in a quantitative fashion. The advantage of this technology is that it directly measures the "cause" (i.e. CTFs) of cell movement instead of the "effect" (i.e. cell movement itself).