- Policy & Practices
Recently, at the University of California, San Diego, a bacteria was designed which could make and release proteins.1 The bacteria has a gene for a protein of choice, and a gene that induces lysis of the bacteria. Under influence of the small molecule N-Acyl homoserine lactone (AHL), expression of these two genes can be induced. When bacterial colonies get to a concentration which is high enough, the lysis gene will be activated and lyse the bacterial membrane. This causes the proteins of interest to be released. The application which the authors created is the introduction of cancer drugs inside the human body.
An important aspect of this transporter bacteria is that they can release the proteins on time. Currently this mechanism is included by activating protein expression with the small molecule AHL. This activates the expression of the wanted protein and expression of a kill gene that will induce lysis when a threshold amount of bacteria is present. When the kill switch is triggered the bacteria will be lysed and the protein released in the extracellular matrix (figure 1).
Our heterodimeric scaffold protein can help to control this system even more. By using the small molecule AHL only as an inducer of the expression of the wanted protein and using the heterodimeric T14-3-3 scaffold protein, a bacterial system can be created that controls both expression and release of protein separately from each other. The heterodimeric T14-3-3 scaffold protein can control the interaction of two transcription factors of the kill gene to induce lysis. Because the T14-3-3 is regulated by the small molecule fusicoccin, a system is created that can be controlled with two small molecules.
The main advantage of this system is that it is possible to regulate the protein release. This could be an essential feature when proteins need to be delivered at a very specific location. In such systems the location of the bacteria could be verified before the protein is released
This bacterial system is widely applicable. As mentioned in the article about this transporter bacteria, it could be used to deliver cancer drugs. However, this bacterial system might also be useful in other diseases in which proteins need to be delivered. To illustrate the possibilities this bacterial system can have when it is implemented with our scaffold protein, one application is described.
Alzheimer is the 6th leading cause of death in the United States.2 Accumulation of protein in the brain causes dementia. Alzheimer is a progressive disease which gets worse till the moment you die. Recent research showed that presence of a certain protein could stave off the effects of Alzheimer and thus improve living condition of Alzheimer patients.
Alzheimer is a specific variant of dementia, which effects memory, thinking and behaviour3,4. There are still a lot of things about Alzheimer we do not know. It is proven that Alzheimer is caused by misfolded proteins in the brain that aggregate to plaques. These plaques lead to loss of connections between nerve cells in the brain. Eventually this will result in brain damage.
The main risk factor for Alzheimer is age. Other risk factors, like depression and genetics are still researched. Symptoms of the early stages of Alzheimer are memory loss and loss of concentration. In the later stages of Alzheimer, extra symptoms are behavioural changes, hallucinations and cognitive problems. There is not much known about treatments for Alzheimer. Current research mainly focusses on early detection and cures.
The klotho protein is a known age suppressor protein5,6. In multiple age related disorders, klotho production is (partially) dysregulated. Klotho is produced mostly in the kidneys. Research have shown that increased concentrations of klotho can reduce a part of the implications of Alzheimer disease7. Klotho exists in two different forms in the human body, a transmembrane form and an extracellular form8. Normally klotho occurs as the transmembrane protein with a small intracellular part and a large extracellular part, but when this extracellular part is detached from the membrane you have extracellular klotho. Intracellular klotho regulates phosphate excretion and vitamin D synthesis and extracellular klotho works as the age suppressor as described above.
A possible treatment for Alzheimer would be a treatment in which klotho is present in higher concentration, so it can stave off the effects of Alzheimer. The first problem with this treatment is that you should be able to closely regulate this. A possible usage of our scaffold proteins in a treatment for Alzheimer could be by using our scaffold protein to control the expression of the klotho protein.
The modified bacteria will be placed in the brains of the patients. When AHL is brought in close proximity of the bacteria, expression of the klotho protein will be induced. When fusicoccin is added, the lysis gene becomes active. This means that the Klotho protein will be excreted in the extracellular matrix. This might reduce effects of Alzheimer. This will not cure Alzheimer's disease, it will possibly improve living conditions for Alzheimer patients and extend their life span.
- Din, M., Danino, T., Prindle, A., Skalak, M., Selimkhanov, J., & Allen, K. et al. (2016). Synchronized cycles of bacterial lysis for in vivo delivery. Nature, 536(7614), 81-85. http://dx.doi.org/10.1038/nature18930
-  Latest Facts & Figures Report | Alzheimer's Association. (2013). Latest Alzheimer's Facts and Figures. Available at: http://www.alz.org/facts/overview.asp
-  Alz.org. (2016). Alzheimer's Disease & Dementia | Alzheimer's Association. Available at: http://www.alz.org/alzheimers_disease_what_is_alzheimers.asp
-  O'Brien, J., Ames, D. and Burns, A. (2010). Dementia. London: Hodder Arnold. 389,391,395,396
-  Foster, P., Rosenblatt, K. and Kuljiš, R. (2011). Exercise-Induced Cognitive Plasticity, Implications for Mild Cognitive Impairment and Alzheimers Disease. Frontiers in Neurology, 2.
-  Wang, Y. and Sun, Z. (2009). Current understanding of klotho. Ageing Research Reviews, 8(1), pp.43-51.
-  IFLScience. (2016). Protein Treatment Staves Off Alzheimer’s Disease Symptoms. Available at: http://www.iflscience.com/brain/protein-treatment-staves-alzheimer-s-disease-symptoms
-  Kuro-o, M. (2011). Klotho and the Aging Process. Korean J Intern Med, 26(2), 113.