Karaaslan Hakan, Walker Alejandro R, Gil-Bona Ana, Depalle Baptiste, Bidlack Felicitas B
bioRxiv. 2024 Jun 25:2024.05.23.595034. doi: 10.1101/2024.05.23.595034.
Tooth enamel maturation requires the removal of proteins from the mineralizing enamel matrix to allow for crystallite growth until full hardness is reached to meet the mechanical needs of mastication. While this process takes up to several years in humans before the tooth erupts, it is greatly accelerated in in the faster developing pig. As a result, pig teeth erupt with softer, protein-rich enamel that is similar to hypomineralized human enamel but continues to harden quickly after eruption.Proteins, such as albumin, that bind to enamel crystals and prevent crystal growth and enamel hardening have been suggested as cause for hypomineralized human enamel that does not naturally harden after eruption. However, albumin is abundant in pig enamel. It is unclear whether fast posteruptive enamel hardening in pigs occurs despite the high protein content or requires a facilitated protein loss to allow for crystal growth. This study asked how the protein content in porcine enamel changes after eruption in relation to saliva. Based on previous data demonstrating the high albumin content in erupted porcine enamel, we hypothesize that following pre-eruptive maturation, enamel and saliva derived enzymes facilitate protein removal from porcine enamel after eruption. We analyzed enamel and the saliva proteome at three critical timepoints: at the time of tooth eruption, 2 weeks after eruption, and enamel 6 weeks after eruption. We used only fourth deciduous premolars and saliva samples from animals sacrificed at the respective time points to determine the organic content in tooth enamel, saliva, and saliva proteins within enamel. We found a decrease in the number of proteins and their abundancy in enamel with posteruptive time, including a decrease in serum albumin within enamel. The rapid decrease in the first two weeks is in line with previously reported rapid increase in mineral density of porcine enamel after eruption. In addition to the enamel proteases KLK-4 and MMP-20, we identified serine-, cysteine-, aspartic-, and metalloproteases. Some of these were only identified in enamel, while almost half of the enzymes are in common with saliva at all timepoints. Our findings suggest that the fast posteruptive enamel maturation in the porcine model coincides with saliva exchange and influx of saliva enzymes into porous enamel.
牙釉质成熟需要从矿化的牙釉质基质中去除蛋白质，以允许微晶生长，直到达到完全硬度以满足咀嚼的机械需求。虽然这个过程在人类牙齿萌出前需要数年时间，但在发育较快的猪中会大大加速。因此，猪牙萌出时带有更软、富含蛋白质的牙釉质，这类似于矿化不足的人类牙釉质，但在萌出后仍会迅速变硬。有人认为，诸如白蛋白等与牙釉质晶体结合并阻止晶体生长和牙釉质硬化的蛋白质是矿化不足的人类牙釉质在萌出后无法自然硬化的原因。然而，白蛋白在猪牙釉质中含量丰富。目前尚不清楚，尽管蛋白质含量高，猪牙釉质在萌出后是否仍能快速硬化，还是需要促进蛋白质流失以允许晶体生长。本研究探讨了猪牙釉质中蛋白质含量在萌出后与唾液相关的变化情况。基于之前证明猪萌出后牙釉质中白蛋白含量高的数据，我们假设在萌出前成熟之后，牙釉质和唾液衍生的酶会促进猪牙釉质在萌出后蛋白质的去除。我们在三个关键时间点分析了牙釉质和唾液蛋白质组：在牙齿萌出时、萌出后2周以及萌出后6周。我们仅使用在各个时间点处死的动物的第四乳前磨牙和唾液样本，以确定牙釉质、唾液以及牙釉质内唾液蛋白质中的有机成分含量。我们发现，随着萌出后时间的推移，牙釉质中蛋白质的数量及其丰度均有所下降，包括牙釉质内血清白蛋白的减少。前两周内蛋白质数量的快速下降与之前报道猪牙釉质萌出后矿物质密度的快速增加相一致。除了牙釉质蛋白酶KLK - 4和MMP - 20外，我们还鉴定出了丝氨酸蛋白酶、半胱氨酸蛋白酶、天冬氨酸蛋白酶和金属蛋白酶。其中一些仅在牙釉质中被鉴定出来，而几乎一半的酶在所有时间点都与唾液中的酶相同。我们的研究结果表明，猪模型中牙釉质在萌出后的快速成熟与唾液交换以及唾液酶流入多孔牙釉质相吻合。
