Hepatocyte growth factor signaling regulates tooth germ development, inducing proliferation of mesenchymal cells via fission of mitochondria

Tooth morphogenesis is regulated by epithelial–mesenchymal interactions and cellular metabolism through intricate signaling pathways. Here, we identify a novel mechanism by which hepatocyte growth factor (HGF) signaling promotes mesenchymal cell proliferation during tooth germ development via the regulation of mitochondrial dynamics. Immunohistochemistry revealed spatiotemporal expression of c-Met, the HGF receptor, in both the epithelial and mesenchymal compartments of developing mouse molars. Organ culture showed recombinant HGF increased tooth germ size and mesenchymal proliferation, whereas the c-Met inhibitor PHA-665752 suppressed these effects. Mitochondrial staining and Western blotting demonstrated that HGF stimulated mitochondrial fission through increased phosphorylation of Drp1, whereas PHA-665752 or Mdivi-1, a Drp1 inhibitor, blocked this response and attenuated proliferation. The inhibition of mitochondrial fission also reduced HGF-induced tooth germ growth ex vivo. HGF activated MAPK pathways, particularly the ERK, p38, and JNK pathways, with JNK inhibition (SP600125) most effectively suppressing Drp1 phosphorylation, defining the HGF-JNK-Drp1 axis as central to this process. Epithelial proliferation was largely unaffected, underscoring a mesenchyme-specific mechanism. These findings reveal a previously unrecognized role of mitochondrial fission as a downstream effector of HGF signaling and highlight mitochondrial dynamics as a potential therapeutic target in developmental anomalies of the dentition.