H-type blood vessels participate in alveolar bone remodeling during murine tooth extraction healing

Objectives: We aimed to investigate whether skeletal-specific H-type blood vessels exist in alveolar bone and how they function in alveolar bone remodeling.

Materials and methods: H-type vessels with high expression of CD31 and Endomucin (CD31^hi Emcn^hi ) were immunostained in alveolar bone. Abundance and age-related changes in CD31^hi Emcn^hi endothelial cells (H-ECs) were detected by flow cytometry. Osteoprogenitors association with H-type vessels and bone mass were detected in tooth extraction model of alveolar bone remodeling by immunohistofluorescence and micro-CT, respectively. Transcription and expression of H-EC feature genes during in vitro Notch inhibition were measured by RT-qPCR and immunocytofluorescence.

Results: We verified that H-type vessels existed in alveolar bone, the abundance of which was highest at infancy age, then decreased but maintained a constant level during aging. In tooth extraction model, H-ECs significantly increased with concomitant perivascular accumulation of Runx2⁺ osteoprogenitors and gradually augmentation of bone mass. Notch inhibition of in vitro cultured H-ECs resulted in decreased expression levels of Emcn and hes1, but not Pecam1 or Kdr genes, with decreased expression levels of H-EC numbers, accordingly.

Conclusions: The present study suggests that H-type vessels promote osteogenesis during alveolar bone remodeling. Notch signaling pathway regulates expression of Emcn and possibly determines fate and functions of alveolar H-ECs.