gms | German Medical Science

German Congress of Orthopaedics and Traumatology (DKOU 2019)

22. - 25.10.2019, Berlin

Role of WNT signaling for the undesired hypertrophy of mesenchymal stem cell chondrogenesis

Meeting Abstract

Search Medline for

  • presenting/speaker Solvig Diederichs - Universitätsklinikum Heidelberg, Forschungszentrum für Experimentelle Orthopädie, Heidelberg, Germany
  • Veronika Tonnier - Universitätsklinikum Heidelberg, Forschungszentrum für Experimentelle Orthopädie, Heidelberg, Germany
  • Wiltrud Richter - Universitätsklinikum Heidelberg, Forschungszentrum für Experimentelle Orthopädie, Heidelberg, Germany

Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2019). Berlin, 22.-25.10.2019. Düsseldorf: German Medical Science GMS Publishing House; 2019. DocAB22-382

doi: 10.3205/19dkou104, urn:nbn:de:0183-19dkou1044

Published: October 22, 2019

© 2019 Diederichs et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. See license information at



Objectives: Bone marrow-derived mesenchymal stromal cells (MSCs) may overcome the limited availability and invasive harvest of articular chondrocytes (ACs) for clinical cartilage regeneration. Yet, MSC-derived chondrocytes become hypertrophic in vitro and form bone at ectopic sites, which is undesired for cartilage regeneration. In contrast, ACs remain stable under the same conditions. The signals driving MSCs into hypertrophy are still incompletely understood.

WNT signaling controls chondrocyte hypertrophy during limb development and first studies suggested also a role for WNTs in MSC hypertrophy in vitro. Yet, specific candidate drivers in the complex WNT network and a potential crosstalk with other pro-hypertrophic pathways, i.e., BMP and hedgehog (HH) signaling, remain unknown. Uncovering this will allow improved articular cartilage neogenesis in vitro and provide novel therapeutic strategies for regeneration of cartilage tissue in damaged joints.

Methods: Expression of 71 WNT network genes was assessed via microarray at day 28 of human MSC chondrogenesis and compared with ACs to uncover WNT candidate drivers of hypertrophy. WNT molecules of interest were then followed over time via qPCR and Western blotting. WNT signaling during MSC chondrogenesis was blocked with IWP-2 and effects on hypertrophy were compared with our most potent anti-hypertrophic treatment, daily pulses of PTHrP. Specific markers of hypertrophy were assessed via qPCR. Prevention of cartilage mineralization and bone formation was determined after subcutaneous implantation into immune deficient mice via micro CT and histology.

Results and conclusion: Among 11 WNT genes with a more than 2-fold different mean expression between ACs and MSC-derived hypertrophic chondrocytes, 9 were higher expressed in the MSC group. High initial WNT5A levels and increasing WNT11 levels distinguished hypertrophic from chondral differentiation, suggesting high WNT activity as a driver of MSC hypertrophy in vitro.

Inhibition of WNT signaling by IWP-2 supported MSC chondrogenesis and reduced the pro-hypertrophic transcription factor MEF2C and multiple downstream targets including IBSP and ALP activity. Regulation of BMP4, BMP7 and their target ID1 as well as Indian hedgehog (IHH) along with its target GLI1 demonstrated that WNT activity crosstalked with BMP and HH signaling to drive MSC hypertrophy. WNT inhibition almost reached the strong anti-hypertrophic capacity of daily PTHrP pulses, yet, in vivo cartilage mineralization and ectopic bone formation were only reduced but not prevented.

In conclusion, WNT inhibition reduced hypertrophy but was alone not powerful enough to re-direct MSC chondrogenesis to articular cartilage neogenesis. The here discovered WNT-BMP-HH crosstalk suggests to use a combinatorial inhibitor approach to fully silence the pro-hypertrophic signaling network during MSC chondrogenesis.