Neural EGFL-Like 1 Regulates Cartilage Maturation through Runt-Related Transcription Factor 3-Mediated Indian Hedgehog Signaling

Am J Pathol. 2018 Feb;188(2):392-403. doi: 10.1016/j.ajpath.2017.09.020. Epub 2017 Nov 11.


The pro-chondrogenic function of runt-related transcription factor 2 (Runx2) was previously considered to be dependent on direct binding with the promoter of Indian hedgehog (Ihh)-the major regulator of chondrocyte differentiation, proliferation, and maturation. The authors' previous studies identified neural EGFL like 1 (Nell-1) as a Runx2-responsive growth factor for chondrogenic differentiation and maturation. In this study, it was further revealed that the pro-chondrogenic activities of Nell-1 also rely on Ihh signaling, by showing: i) Nell-1 significantly elevated Ihh signal transduction; ii) Nell-1 deficiency markedly reduced Ihh activation in chondrocytes; and iii) Nell-1-stimulated chondrogenesis was significantly reduced by the specific hedgehog inhibitor cyclopamine. Importantly, the authors demonstrated that Nell-1-responsive Ihh signaling and chondrogenic differentiation extended to Runx2-/- models in vitro and in vivo. In Runx2-/- chondrocytes, Nell-1 stimulated the expression and signal transduction of Runx3, another transcription factor required for complete chondrogenic differentiation and maturation. Furthermore, knocking down Runx3 in Runx2-/- chondrocytes abolished Nell-1's stimulation of Ihh-associated molecule expression, which validates Runx3 as a major mediator of Nell-1-stimulated Ihh activation. For the first time, the Runx2→Nell-1→Runx3→Ihh signaling cascade during chondrogenic differentiation and maturation has been identified as an alternative, but critical, pathway for Runx2 to function as a pro-chondrogenic molecule via Nell-1.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Calcium-Binding Proteins / physiology*
  • Cartilage / cytology
  • Cartilage / physiology
  • Cell Differentiation / physiology
  • Cells, Cultured
  • Chondrocytes / cytology
  • Chondrocytes / physiology*
  • Chondrogenesis / physiology
  • Core Binding Factor Alpha 1 Subunit / deficiency
  • Core Binding Factor Alpha 1 Subunit / physiology*
  • Core Binding Factor Alpha 3 Subunit / physiology
  • Glycoproteins / physiology*
  • Hedgehog Proteins / physiology*
  • Mice, Knockout
  • Signal Transduction / physiology


  • Calcium-Binding Proteins
  • Core Binding Factor Alpha 1 Subunit
  • Core Binding Factor Alpha 3 Subunit
  • Glycoproteins
  • Hedgehog Proteins
  • Nell1 protein, mouse
  • Runx2 protein, mouse
  • Runx3 protein, mouse
  • ihh protein, mouse