The periodontal ligaments (PDLs), located between the tooth and alveolar bones, anchor the tooth and absorb the daily chewing force by mastication. In addition, the Ruffini's corpuscles in the PDLs play a pivotal role in pressure sensing to identify various food properties and to adjust occlusal force. Although recent studies have shown that branches of Ruffini's corpuscles are not formed without mechanical stimulation in the rat PDL (rPDL), there is no report to assess the regulatory mechanisms for the peripheral axonal structure by mechanically stimulated PDL cells.

We established primary PDL cell lines derived from rat molar tooth. The rPDL cells were loaded with periodic mechanical stimulation (0.5 Hz, 15% expansion). The supernatant media of the mechanically stimulated PDL cells enhanced neurite elongation, sprouting, and branching in trigeminal ganglion (TG) cells. Neurotrophic factors such as NGF and BDNF and axon guidance proteins including Wnt family are known to be involved in neurite outgrowth. The rPDL cells expressed NGF, BDNF, NT-4 and Wnt5a mRNA. The mechanical stimulation increased only Wnt5a in rPDL cells by the qPCR analysis and ELISA. Moreover, AP7677a (neutralizing anti-Ryk antibody), or strictinin (Ror1 inhibitor) suppressed the morphological changes. These findings indicate the indirect mechanisms where Wnt5a, released from the connective tissues in response to mechanical stimulation, enhances the outgrowth of the peripheral nerves.