Early Growth Response Genes Increases Rapidly After Mechanical Overloading and Unloading in Tendon Constructs

Abstract

Tendon cells exist in a dense extracellular matrix and mechanical loading is important for the strength development of this matrix. We therefore use a three‐dimensional (3D) culture system for tendon formation in vitro. The objectives of this study were to elucidate the temporal expression of tendon‐related genes during the formation of artificial tendons in vitro and to investigate if early growth response‐1 (EGR1), EGR2, FOS, and cyclooxygenase‐1 and ‐2 (PTGS1 and PTGS2) are sensitive to mechanical loading. First, we studied messenger RNA (mRNA) levels of several tendon‐related genes during formation of tendon constructs. Second, we studied the mRNA levels of, for example, EGR1 and EGR2 after different degrees of loading; dynamic physiologic‐range loading (2.5% strain), dynamic overloading (approximately 10% strain), or tension release. The gene expression for tendon‐related genes (i.e., EGR2, MKX, TNMD, COL3A1) increased with time after seeding into this 3D model. EGR1, EGR2, FOS, PTGS1, and PTGS2 did not respond to physiologic‐range loading. But overloading (and tension release) lead to elevated levels of EGR1 and EGR2 (p ≤ 0.006). FOS and PTGS2 were increased after overloading (both p < 0.007) but not after tension release (p = 0.06 and 0.08). In conclusion, the expression of tendon‐related genes increases during the formation of artificial tendons in vitro, including EGR2. Furthermore, the gene expression of EGR1 and EGR2 in human tendon cells appear to be sensitive to overloading and unloading but did not respond to the single episode of physiologic‐range loading. These findings could be helpful for the understanding of tendon tensional homeostasis. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:173–181, 2020

EGR1 Transcription Factor is a Multifaceted Regulator of Matrix Production in Tendons and Other Connective Tissues

“…Consistent with this mechanosensor function, Egr1 is activated by mechanical loading in 3D-engineered tendons made of human tendon cells [113] and equine tenocytes derived from induced-pluripotent stem cells [114]. Moreover, EGR1 regulates tendon gene expression downstream of mechanical signals in 3D-engineered tendons made of mouse mesenchymal cells [85,113]. Forced-EGR1 expression prevents the downregulation of the tendon genes, Scx, Tnmd, Col1a1, Col1a2, and Tgfb2 in 3D-engineered tendons after tension release [85].…”

“…Since EGR1 has been shown to directly activate Tgfb2 transcription in mouse developping limbs [73], EGR1 is one possible mechanosensor protein downstream of mechanical forces and upstream of TGFβ signalling in developing limbs. Consistent with this mechanosensor function, Egr1 is activated by mechanical loading in 3D-engineered tendons made of human tendon cells [113] and equine tenocytes derived from induced-pluripotent stem cells [114]. Moreover, EGR1 regulates tendon gene expression downstream of mechanical signals in 3D-engineered tendons made of mouse mesenchymal cells [85,113].…”

Comparison of Tendon Development Versus Tendon Healing and Regeneration

“…There is increasing evidence that Egr1 is also mechanically-sensitive. Egr1 is activated when mechanical stimulation is applied to 3D-engineered tendons induced in mouse, equine, and human tendons ( Yang et al, 2019 ; Herchenhan et al, 2020 ).…”

Glucocorticoid counteracts cellular mechanoresponses by LINC01569-dependent glucocorticoid receptor–mediated mRNA decay

“…Given that cellular responses to mechanical stretch are dependent on mechanotransduction, which transforms physical cues into gene expression and signaling pathways, we paid more attention to candidate genes involved in mechanotransduction. Therefore, we selected three differentially expressed mechanosensor genes and further investigated, including EGR1 (25,26), CITED2 (27), and BMP7 (28,29), all of which act as mechanosensitive molecular switches and regulate transcription downstream of mechanical signals. qRT-PCR and Western blot assays verified that EGR1, CITED2, and BMP7 were significantly down-regulated by TA in stretched HSFBs (Fig.…”