Monday, September 20, 2010

Tenocyte differentiation in LSJL

LSJL upregulates tendon factors Tnmd and Scx.

Tenocytes may further differentiate into chondrocytes.  Tenocytes may be an intermediary to chondrogenic differentiation.  Why does LSJL upregulate these Tendon factors in the bone?

Mechanoactive tenogenic differentiation of human mesenchymal stem cells.

"A mesenchymal stem cell (MSC)-seeded collagen gel under static or dynamic tension [was used]. Upregulation of fibrillar collagen mRNA expression and protein production has been demonstrated in response to cyclic tensile mechanical stimulation. This study investigated the mechanisms of tenogenesis of human bone marrow-derived MSCs in a dynamic, three-dimensional (3D) tissue-engineering model by investigating the effects of cyclic stretching on matrix production and gene expression of candidate tendon and ligament markers. The 3D MSC tenogenesis culture system upregulated scleraxis, but cyclic stretching was required to maintain expression of this putative tendon marker over time. Enhanced tendinous neo-tissue development demonstrated with extracellular matrix staining was largely due to changes in matrix deposition and remodeling activity under dynamic loading conditions, as evidenced by differential regulation of matrix metalloproteinases at a transcriptional level with minimal changes in collagen mRNA levels. Regulation of Wnt gene expression with cyclic stimulation suggested a similar role for Wnt4 versus Wnt5a in tenogenesis as in cartilage development."

"Dynamic loading could promote differentiation of MSCs cultured in a collagen gel between bone anchors to create bone–ligament–bone constructs"

"An MSC–collagen gel construct was cast between bone anchors and cyclically loaded for 14 days to increase mRNA levels of collagen types I and III{both up in LSJL}, elastin{upregulated by LSJL}, and fibronectin."

"Wnt4, Wnt14, and Wnt16 have been identified in non-cartilaginous mesenchymal cells that will form tendons and ligaments."

"3D gel under tension [is the tendonogenic environment]"

"Wnt14 and ß-catenin have been shown to inhibit chondrogenesis."

"Wnt4 inhibits initiation of chondrogenesis and in chondrogenic cultures signals through the canonical Wnt pathway to accelerate terminal differentiation."

Coordinated expression of scleraxis and Sox9 genes during embryonic development of tendons and cartilage.

"Scleraxis, a basic helix-loop-helix (bHLH) type transcription factor, is expressed in mesenchymal progenitors that later form connective tissues including tendons. Sox9 is an HMG-box containing transcription factor, which is expressed at high levels in chondrocytes. The two transcription factors regulate the fate of cells interact with each other at the interface between the two tissues during divergence of their differentiation pathways. We investigated scleraxis and Sox9 mRNA expression during mouse embyogenesis focusing on the coordinated development of tendons and skeletons. In the early stage of mesenchymal tissue development at 10.5 d.p.c. scleraxis and Sox9 transcripts were expressed in the mesenchymal progenitor cells in the appendicular and axial mesenchyme. At 11.5 d.p.c., scleraxis transcripts were observed in the mesenchymal tissue surrounding skeletal primordia which express Sox9. From this stage. seleraxis expression was closely associated with, but distinct from, formation of skeletal primordia. At 13.5 d.p.c., scleraxis was expressed broadly in the interface between muscle and skeletal primordia while Sox9 expression is confined within the early skeletal primordia. Then, at 15.5 d.p.c., scleraxis transcripts were more restricted to tendons. The presence of temporal and spatial association of scleraxis expression during embryonic development of tendon precursor cells [is] in close association with that of Sox9 expression in chondrogenic cells in skeletal tissues."

"Aggrecan gene expression is enhanced by scleraxis"

Mechanical force modulates scleraxis expression in bioartificial tendons.

"cyclic stretch increased the mRNA levels of Scx, tenascin C, and Types I and III collagen in rat bone marrow-derived mesenchymal stem cells"

Fig1A shows that SCX is hardly ever upregulated in tibia but is upregulated in cartilage.  Thus the upregulation of Scx may be a sign of ectopic cartilage.

I'm not sure but I believe this is from adult mice.

"In adult tendon, Scx expression was highest in load-bearing collagen fibre bundles"

Cyclic loading at 10% of tendons increased Scx expression based on number of repetitions.  Tendons, Cartilage, and bone are composed of collagen.

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