Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Bonyadirad, E.
Expression, Regulation and Function of ST2/IL1RL1 in
Growth Plate Chondrocyte
Doktoratsstudium der Medizinischen Wissenschaft; Humanmedizin; [ Dissertation ] Graz Medical University; 2018. pp.
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- Autor*innen der Med Uni Graz:
- Betreuer*innen:
- Schäfer Ute
- Weinberg Annelie-Martina
- Altmetrics:
- Abstract:
- Bone tissue is a well-known site of expression of ST2 (IL1RL1). However, knowledge about expression, regulation, and function of ST2 in chondrocytes is limited. Immunohistochemical analysis indicated prominent ST2 expression in hypertrophic chondrocytes of murine growth plates in both femur and tibia whilst this expression was low or absent in resting and proliferative zones. This result was verified by significant up-regulation of both surface receptor (ST2L) and soluble (sST2) isoforms during hypertrophic differentiation of ATDC5 cells concomitant with the expression of hypertrophic markers Collagen 10 (Col X), Runt-related transcription factor 2 (Runx2) and matrix metalloprotease 13 (MMP- 13). Key transcription factor Runx2 promotes hypertrophic differentiation of chondrocytes through induction of markers like Col X and MMP-13. Gain and loss of Runx2 function using stable cDNA transfection and siRNA knockdown revealed ST2 to be a novel Runx2 target in chondrocytes. Runx2 mediated up-regulation of ST2 was further corroborated in primary human growth plate chondrocytes (PHCs). The ST2 isoforms arise from proximal and distal promoters in a cell-type specific manner. We demonstrate the dominant promoter driving expression of ST2 isoforms in ATDC5 and PHCs to be the proximal promoter even though distal promoter is also capable of sST2 expression in ATDC5 chondrocytes. Consistent with pronounced ST2 expression in hypertrophic chondrocytes, we observed a perceptible hypertrophic size reduction alongside significantly diminished expression of Col X and osteocalcin (OSC) in growth plates of femur and tibia from ST2 knockout mice in comparison with wild type (WT) control. These observations were substantiated by the effect of siRNA-mediated ST2 knockdown in ATDC5 cells. The ST2 silencing was associated with a slight decrease of Col X, significant suppression of OSC and vascular endothelial growth factor A (VEGFA) and enhanced expression of proliferative stage markers Collagen II (Col II) and Sox9 in ATDC5 cells. Thus, our investigation suggests that ST2 is a new regulator of early and late chondrocyte differentiation in ATDC5 chondrocytes. Furthermore, Runx2 mediated modulation of Runx3 another member of runtrelated transcription factor family was documented in ATDC5 and PHCs. The impact of Runx3 knockdown on differentiation markers in ATDC5 was similar to 13 that observed by ST2 silencing indicating that ST2 and Runx3 appose proliferating and act towards promotion of hypertrophic differentiation. Eventually, the suppressive influence of ST2 and Runx3 knockdown on the Runx2 mediated upregulation of hypertrophic markers Col X, OSC, VEGFA and MMP-13 propose a cooperative regulation of chondrocyte hypertrophy through Runx2 associated activation of downstream targets ST2 and Runx3 in ATDC5 chondrocytes. Taken together, this study points for the 1st time to the expression, regulation, and function of ST2 in chondrocyte, in particular, post-natal growth plate chondrocyte where bone growth is controlled by a complex molecular and biochemical mechanisms which are not fully known. Our investigation provides an important new insight into the role of ST2 in growth plate chondrocyte function, thereby allowing further comprehension of the highly orchestrated process of longitudinal bone growth.