FoxA Family Members Are Crucial Regulators of the Hypertrophic Chondrocyte Differentiation Program

Abstract

During endochondral ossification small immature chondrocytes enlarge to form hypertrophic chondrocytes, which express collagen X. In this work, we demonstrate that FoxA factors are induced during chondrogenesis, bind to conserved binding sites in the collagen X enhancer, and can promote the expression of a collagen X-luciferase reporter in both chondrocytes and fibroblasts. In addition, we demonstrate by both gain and loss of function analyses that FoxA factors play a crucial role driving the expression of both endogenous collagen X and other hypertrophic chondrocyte-specific genes. Mice engineered to lack expression of both FoxA2 and FoxA3 in their chondrocytes display defects in chondrocyte hypertrophy, alkaline phosphatase expression, and mineralization in their sternebrae and in addition exhibit postnatal dwarfism that is coupled to significantly decreased expression of both collagen X and MMP13 in their growth plates. Together, our findings indicate that FoxA family members are crucial regulators of the hypertrophic chondrocyte differentiation program.

Indian Hedgehog Signaling Regulates Transcription and Expression of Collagen Type X via Runx2/Smads Interactions

“…This is consistent with our finding because Runx2 is a known downstream target for BMP signaling (28). Also, Smads and Runx2 have been reported to interact in the transcription of collagen type X (18,29,30). Interestingly, we identified three conventional Smad-binding sites in the 250-bp basic COL10A1 promoter (Fig.…”

“…3, A and C). In addition to Runx2/3, previous studies have shown that chondrocyte hypertrophy is also regulated by Mef2c/d and Foxa2/3 (16,18,23). However, our data show that Ihh did not induce Mef2c, Foxa2, or Foxa3 mRNA expression (Fig.…”

“…Previous studies have suggested that Runx2/3, Smads, Mef2c transcription factor, and FoxA family members act as enhancers for Col10␣1 expression and subsequent induction of hypertrophic differentiation (15,16,18,23,29,30). The COL10A1 distal enhancer region is highly conserved among mammals, including humans, cows, and mice (19).…”

“…In addition to Runx2, Col10␣1 expression is also acti-vated by myocyte enhancer factor-2c (Mef2c) through several conserved sequences in the promoter resembling MEF2-binding sites, which are antagonized by a co-repressor histone deacetylase 4 (Hdac4) (16,17). Recent investigation using the chick Col Xb2 enhancer identified FoxA factors as additional regulators of hypertrophic chondrocyte (18). Interestingly, we have previously found that Ihh overexpression by adenoviruses in chondrocytes induced Col10␣1 expression in vitro.…”

Development of the Endochondral Skeleton

“…SOX9 has been proposed to both prevent cells from prematurely entering the prehypertrophic stage and to promote the subsequent hypertrophy (Dy et al 2012). The transcription factors FoxA2 and FoxA3 are necessary for chondrocyte hypertrophy (Ionescu et al 2012). SHOX2, a homeodomain-containing transcription factor, is necessary for RUNX2/RUNX3 expression and hypertrophy within the stylopod (see Box 1) (Cobb et al 2006;Yu et al 2007).…”