Smad3 binds scleraxis and mohawk and regulates tendon matrix organization

Abstract

TGFβ plays a critical role in tendon formation and healing. While its downstream effector Smad3 has been implicated in the healing process, little is known about the role of Smad3 in normal tendon development or tenocyte gene expression. Using mice deficient in Smad3 (Smad3–/–), we show that Smad3 ablation disrupts normal tendon architecture and has a dramatic impact on normal gene and protein expression during development as well as in mature tendon. In developing and adult tendon, loss of Smad3 results in reduced protein expression of the matrix components Collagen 1 and Tenascin-C. Additionally, when compared to wild type, tendon from adult Smad3–/– mice shows a downregulation of key tendon marker genes. Finally, through in vitro work, we have established that Smad3 has the ability to physically interact with the critical transcriptional regulators Scleraxis and Mohawk. Together these results indicate a central role for Smad3 in normal tendon development and in the maintenance of mature tendon.

Three-Dimensional Culture and Transforming Growth Factor Beta3 Synergistically Promote Tenogenic Differentiation of Equine Embryo-Derived Stem Cells

“…More robust markers of tenocytes include Scleraxis (SCX), Tenomodulin (TNMD), Tenascin-C (TNC), Cartilage oligomeric matrix protein (COMP), and Thrombospondin-4 (THBS4), which are not only collectively expressed in tendons, but individually also present in other tissue types. [22][23][24][25][26] Developmental studies have also implicated genes such as Six1/2, Eph-A4, Eya1/2, Egr1/2, and Mohawk (Mkx), 25,[27][28][29][30] although it has not been established whether these genes show temporally restricted expression in tendon tissue.…”

Transcriptomic analysis of mouse limb tendon cells during development

“…However, Scx and Col1a1 gene expression and tendon matrix organisation are altered in adult tendons of Smad3 −/− mice (Berthet et al, 2013) and it was shown that SMAD3 is recruited to Scx regulatory regions in adult mouse tendons (Berthet et al, 2013), suggesting a direct role for SMAD signalling in Scx expression. Because we found a loss of Scx expression when SMAD2/3 was inhibited in mouse limb explants, we propose that in the Tgfb2 −/− ;Tgfb3 −/− and conditional Tgfbr2 mutant mice, the endogenous SMAD2/3 intracellular pathways may be activated by alternative TGF-β superfamily ligands or receptors to initiate Scx expression.…”

Tendon development and musculoskeletal assembly: emerging roles for the extracellular matrix

“…However, at other promoters it interacts with the Sin3A/ histone deacetylase (HDAC) complex to repress gene expression, including that of key myogenic factors such as MyoD (Myod1), Sox6 and the cartilage determinant Sox9 (Fig. 2B) (Anderson et al, 2009;Anderson et al, 2012;Berthet et al, 2013;Chuang et al, 2014). Thus, like Scx and Egr1/2, Mkx controls tendon maturation and ECM production and might function, in part, to maintain tenocytes by preventing them from acquiring myogenic or skeletogenic fates.…”

“…Both Scx and Mkx interact with Smad3, an essential transcriptional mediator of TGFβ signaling, to regulate tendon ECM production (Berthet et al, 2013;Hosokawa et al, 2010;Katzel et al, 2011;Oka et al, 2008;Pryce et al, 2009).…”