According to WHO, oral diseases pose a health burden for many countries and affect people throughout their lifetime, causing pain, discomfort, disfigurement, and even death. Moreover, severe periodontal disease has proved to be related to many chronic and cardiovascular diseases. With almost 10% of the global population affected with periodontal disease, the problem of oral disease has been one of the top problems that pose a threat to human beings.
Our project is about tackling the problems by preventing the happening of periodontal disease. This would not only solve the problem of oral health, but it would also reduce the risk of getting other diseases related to it. Synthetic biology is the best method for us to achieve our goal inexpensively and efficiently. We believe that by developing our project, we can make the world a better place.
Not only humans, many animals, especially human rearing pets also face oral health problems, due to drastic changes in diet. Therefore, we decided to first focus on the oral health of our furry friends, dogs before we apply our solution to human beings!
There are many types of bacteria in the mouth associated with periodontal diseases. Porphyromonas gingivalis is one of the major etiological agents in periodontal diseases and has been proved to cause gingival inflammation under orthodontic appliances. Therefore one of our goals is to defeat it.
How to reach our goal
To prevent our furry friends suffered from periodontal diseases and severe systemic diseases, we drew up a developed plan. Our solution is to create a brand new dental bone, Denteeth-bone, which contains proteins and peptides that can prevent the formation of plaque and repair the damaged gingiva and tooth tissue. Additionally, to prevent the envelopment of bacteria on the teeth' surface during the teeth repairing process, we design a switch mechanism. The mechanism enables the engineered E. coli to express antibiotic peptides when the population of Porphyromonas gingivalis grows, whereas to take the dental restoration process when the population declines.
ARG is a kind of amino acid. We decided to use the direct addition of arginine to inhibit biofilm production and reduce oral odor. LL-37 is an antibiotic peptide, which can decrease the number of bacteria by promoting the autophagy process. The proteins that can repair damaged tissue are BMP2 and STATH. For more enhanced details about these proteins please see the information below.
Why do we choose antimicrobial peptide instead of Antibiotics？
First of all, antibiotics have many side effects such as flora imbalance and antibiotic resistance. Second, antimicrobial peptides have low cytotoxicity and high stability. The last reason is that antimicrobial peptides can also inhibit the hemagglutination of Porphyromonas gingivalis. Considering the information mentioned above, we finally decided to introduce one of the antimicrobial peptides, LL-37, into our project for reducing the number of bacteria.
What can LL-37 do?
To reduce the number of bacteria causing periodontal disease, we choose the antimicrobial peptide, LL-37. LL-37 can promote the autophagy process to eliminate P. gingivalis, the killer of causing periodontal disease , in cells. This way is more efficient than killing the bacteria directly.
Also, LL-37 has additional roles such as regulating the inflammatory response in wounds or infection sites, and promoting wound closure. Some study demonstrated that LL-37 have a key role in wound regeneration through vascularization. These can help the oral wound heal faster.
What can ARG do?
Based on studies , the bacteria on the teeth surface form biofilms which leads to the formation of tartar. To solve this problem, we introduce arginine into our project, which can reduce the formation of biofilms and reduce the odors as well.Because we need arginine to continuously inhibit and destroy the formation of biofilms, we decided to use the direct addition of arginine to inhibit biofilm and reduce bad oral odor.
First of all, studies said that ARG can inhibit the bacterial secretion of extracellular polymeric substances (EPS) , so the formation of biofilm will inhibit and the dissociation biofilm will be promoted.
For the odor reduction , the downstream reaction of arginine is competitive to the sulfur-containing amino acids production reaction, thus the odor production is inhibited .
What can STATH do?
Statherin is an enamel protective membrane protein that inhibits the nucleation and growth of hydroxyapatite, and also lubricates the enamel surface . It prevents the precipitation of calcium phosphate in saliva, maintaining a high calcium level in saliva available for remineralization of tooth enamel  and high phosphate levels for buffering. 
What can BMP2 do?
Connective tissue formation in the early stage of periodontal repair plays a significant role. BMP2 can induce the differentiation of mesenchymal cells , which can be a bone substitute for periodontal regeneration. Some studies have demonstrated a considerable degree of periodontal tissue regeneration in real dogs. In our project, BMP2 is responsible for repairing soft tissues in the oral cavity.
We decided to feed the dogs' engineering bacteria, DenTeeth, by a form of dental bone, DenTeeth-Bone. We designed a unique structure of our DenTeeth bone to make sure it is user-friendly and efficient to use at the same time. Furthermore, since DenTeeth-bone is a consumable product and eating too many DenTeeth-bones might negatively impact the dog's health, we construct a model using reinforcement learning to give the best feeding frequency DenTeeth-bone.
Since the efficiency optimization model relies on the detection of O.D.600 to update the parameter of weights in the policy, we plan to design a device that can measure O.D.600 easily and quickly in the future. After the device for measuring OD is created, we can combine the efficiency optimization model and device into customized products suitable for different branches of dogs. Furthermore, these detecting products can be applied to human beings in the future, which can benefit the well-being of humans.
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- Xuelian Huang , Keke Zhang et al. (2017)”Effect of arginine on the growth and biofilm formation of oral bacteria”Archives of Oral Biology 82:256-262
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