Piezos: A Novel Mechanosensitive Ion Channel Family In Odontoblast

Mechanical stimuli drive many physiological processes, including touch and painsensation,hearing, and blood pressure regulation. Mechanically-activated (MA) cationchannel activities have been recorded in many cells, but the responsible molecules havenot been identified. A novel ion channel caused rapidly-adapting MA current in a mouseneuroblastoma cell line. Expression profiling and RNAi knockdown of candidate genesidentified Piezo1(Fam38A) to be required for MA currents in these cells. Piezo1andrelated Piezo2(Fam38B) are vertebrate multipass transmembrane proteins with homologsin invertebrates, plants, and protozoa. Overexpression of mouse Piezo1or Piezo2inducedtwo kinetically-distinct MA currents. Piezos are expressed in several tissues, andknockdown of Piezo2in dorsal root ganglia neurons specifically reduced rapidly-adapting MA currents. We propose that Piezos are components of mechanically-activated cationchannels.Odontoblasts are organized as a single layer of specialized cells responsible for dentineformation and presumably for playing a role in tooth pain transmission. Each cell has anextension running into a dentinal tubule and bathing in the dentinal fluid. A dense networkof sensory unmyelinated nerve fibers surrounds the cell bodies and processes. Thus,dentinal tubules subjected to external stimuli causing dentinal fluid movements andodontoblasts/nerve complex response may represent a unique mechano-sensory systemgiving to dentine-forming cells a pivotal role in signal transduction. Mediators ofmechano-transduction identified in odontoblast include mechano-sensitive ion channelsand primary cilium. Wheather the Piezo ion channel expressed at the odontoblast and playa role in the tooth pain transmission are not concerned.To find the pinpoint of the Piezo’s experssion position and the pivotal role in the painsensation and transmission,we research according the following three steps:1. The expression of Piezo in odontoblast like cell and rat dental pulpTo identified the expression of the Piezo1and Piezo2, we used RT-PCR,Realtime-PCRand fuorescence labelling, confocal laser microscopy to check the pinpoint of the Piezo’sexperssion position and its relationship with some neuro marker,forexample NF160.Wecompare the relative expression amount of piezos in several different cell type. The resultindicate that the relative expression in OLC cells are very near which in DRG cells and itshigher than whichone in periodontal ligament cell.Research about the pinpoint of thePiezo’s experssion in rat pulp reveal that they are expressed at the odontoblast especialilyin process of OB. The odontoblast/nerves relationships are closely related by Piezo. Theyare always co-expresed with neurofilament160, the cell skeleton protein, indicated thatthe function of touch and pain transmission.2. The function of Piezos in odontoblast in vivo and in vitro.To test the actived function of Piezo in odontoblast, we use two different model in vivoand in vitro. By use Bioflux200system,we give the cell0.5dyne/cm2stress to simulate the dentinal fluid movements, we found the concentration of intracellular calcium ion canbe actived by the fluid stress and can be Inhibited by the Peptide GsMTx4,the specialblockers of Piezo1. This in vivo study reveal the possiable mechanical sensationfunction of Piezo in odontoblast.For the sake of difficulty to get the matured odontoblast, it is also difficult to measure theelectrophysiological function. We use the dentin expose model to test the Piezosexpression changing after different external stimuli. The data show us that the long timedentin exposure can rise up the Piezo expression followed the SDF1/CXCR4axis. Thisresult indicate that the Piezo ion channel may play role in external stimuli sensation andinitial phlogosis.3. The role of Piezo in differentation of dental pulp setm cell to different direction.Because the Piezo did not expression in dental pulp stem cells, we check its expression inthe tooth development, by using fuorescence labelling, we stain the E17,E19embryo andPD1,PD3,PD5,PD7mouse mandible, we did not found obviously positive cell of the piezoexpression. This result indicate the sensation of odontoblast is the terminal stage of thedental pulp stem cell differentation.We using hypoxic-ischemic brain tissue to induced the dental pulp stem cell to neuron-likedifferentiation and mineralization induction in vitro, we measure the intial stage and thelateral stage mRNA expression and the protein expression, we found that the neuron-likedifferentiation can lead the ion channel expression but mineralization induction can notraise its expression. This result can draw the conculation that the piezo ion channel is afunction of sensation in odontoblast, it only induced at the teminal stage of odontoblastdifferention, later than the secretion of dentin matrix.In one word, We propose that Piezos are components of MA cation channels. the sensoryfunction of odontoblasts highlighted by their excitable properties should be taken as aserious support to the hydrodynamic theory.