CXCL12-CXCR4 Interplay Facilitates Palatal Osteogenesis in Mice

Abstract

Cranial neural crest cells (CNCCs), identified by expression of transcription factor Sox9, migrate to the first branchial arch and undergo proliferation and differentiation to form the cartilage and bone structures of the orofacial region, including the palatal bone. Sox9 promotes osteogenic differentiation and stimulates CXCL12-CXCR4 chemokinereceptor signaling, which elevates alkaline phosphatase (ALP)-activity in osteoblasts to initiate bone mineralization. Disintegration of the midline epithelial seam (MES) is crucial for palatal fusion. Since we earlier demonstrated chemokine-receptor mediated signaling by the MES, we hypothesized that chemokine CXCL12 is expressed by the disintegrating MES to promote the formation of an osteogenic center by CXCR4-positive osteoblasts. Disturbed migration of CNCCs by excess oxidative and inflammatory stress is associated with increased risk of cleft lip and palate (CLP). The cytoprotective heme oxygenase (HO) enzymes are powerful guardians harnessing injurious oxidative and inflammatory stressors and enhances osteogenic ALP-activity. By contrast, abrogation of HO-1 or HO-2 expression promotes pregnancy pathologies. We postulate that Sox9, CXCR4, and HO-1 are expressed in the ALP-activity positive osteogenic regions within the CNCCs-derived palatal mesenchyme. To investigate these hypotheses, we studied expression of Sox9, CXCL12, CXCR4, and HO-1 in relation to palatal osteogenesis between E15 and E16 using (immuno)histochemical staining of coronal palatal sections in wild-type (wt) mice. In addition, the effects of abrogated HO-2 expression in HO-2 KO mice and inhibited HO-1 and HO-2 activity by administrating HO-enzyme activity inhibitor SnMP at E11 in wt mice were investigated at E15 or E16 following palatal fusion. Overexpression of Sox9, CXCL12, CXCR4, and HO-1 was detected in the ALP-activity positive osteogenic regions within the palatal mesenchyme. Overexpression of Sox9 and CXCL12 by the disintegrating MES was detected. Neither palatal fusion nor MES disintegration seemed affected by either HO-2 abrogation or inhibition of HO-activity. Sox9 progenitors seem important to maintain the CXCR4-positive osteoblast pool to drive osteogenesis. Sox9 expression may facilitate MES disintegration and palatal fusion by promoting epithelial-to-mesenchymal transformation (EMT). CXCL12 expression by

Single-cell RNA-sequencing analysis reveals the molecular mechanism of subchondral bone cell heterogeneity in the development of osteoarthritis

“…There is little difference between chemokine interaction pairs in OBs, and they all express CXCR4 to promote OB proliferation and differentiation; however, only MinOBs do not secrete CXCL12. 27 At the end of osteogenic differentiation, CXCL12 is downregulated. 28 We found that the overall expression of the ephrin receptor and NOTCH family members decreased gradually from EnOBs to StOBs to MinOBs.…”

“…There is little difference between chemokine interaction pairs in OBs, and they all express CXCR4 to promote OB proliferation and differentiation; however, only MinOBs do not secrete CXCL12 27. At the end of osteogenic differentiation, CXCL12 is downregulated 28.…”

Single-cell RNA-sequencing analysis reveals the molecular mechanism of subchondral bone cell heterogeneity in the development of osteoarthritis

“…There is little difference between chemokine interaction pairs in OBs, and they all express CXCR4 to promote OB proliferation and differentiation, however, only MinOBs do not secrete CXCL12. 24 At the end of osteogenic differentiation, CXCL12 is downregulated. 25 We found that the overall expression of the ephrin receptor and NOTCH family members decreased gradually from EnOBs to StOBs to MinOBs.…”

The CXCR4/SDF-1 Axis in the Development of Facial Expression and Non-somitic Neck Muscles

“…Although the first known activity of CXCR4 was the regulation of HIV- infection and cancer metastasis ( Bleul et al, 1997 ; Helbig et al, 2003 ; Doi et al, 2018 ; Shanmugam et al, 2018 ; Bianchi and Mezzapelle, 2020 ), CXCR4 is also an abundantly expressed chemokine receptor throughout embryogenesis ( Yusuf et al, 2005 ; Yusuf et al, 2006 ). The functions of the CXCR4/SDF-1 axis during embryogenesis include heart ventricular septum formation, gut vascular morphogenesis, sympathetic precursor cell migration, dentate granule cell migration, B lymphocyte migration, sensory neuron clustering, limb neuromuscular development and palatal osteogenesis ( Bagri et al, 2002 ; Odemis et al, 2005 ; Kasemeier-Kulesa et al, 2010 ; Escot et al, 2013 ; Mahadevan et al, 2014 ; Terheyden-Keighley et al, 2018 ; Laparidou et al, 2020 ; Verheijen et al, 2020 ; Yahya et al, 2020a ).…”