Team:UCL/Sensors
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The physiological conditions underlying mental illnesses vary between patients resulting in a need for individualized treatments.We have evaluated potential biomarkers linked to mood disorders and developed a set of bacterial sensors that could detect mood-related symptoms in the gut.
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Background
In order to target mental health issues such as depression and anxiety in a responsive manner it is necessary to design sensors that respond only when triggered by specific biomarkers. This means that mood sensing probiotics designed by our team will only release neuroactive compounds when a patient actually goes through clinical depression or a panic attack instead of being constitutively active. This is achieved by transforming bacteria with plasmids with signal sensing promoters upstream of the effector genes.
Constructs
Clinical depression is likely caused by a chronic low grade-response to inflammation
M. Berk et al. So depression is an inflammatory disease, but where does the inflammation come from? in European Journal for Medical Research, 2013 [Link][1].
Although the pathway from inflammation to depression is complex and not fully understood it has been shown that the immune response is often accompanied by symptoms such as oxidative and nitrosative stress in the gut.
Leonard B. and Maes M. Mechanistic explanations how cell-mediated immune activation, inflammation and oxidative and nitrosative stress pathways and their sequels and concomitants play a role in the pathophysiology of unipolar depression in Neuroscience & Biobehavioral Reviews Volume 36, Issue 2, February 2012, Pages 764–785
[Link][2].
Therefore, one of the promoters we have used is PyeaR which is sensitive to nitric oxide in the cell and was inserted upstream of different effectors. This promoter uses the E. coli native enzyme NsrR which inhibits the expression of the PyeaR promoting sequence.
HJ Beaumont et al. Expression of nitrite reductase in Nitrosomonas europaea involves NsrR, a novel nitrite-sensitive transcription repressor in Molecular Microbiology Volume 54, Issue 1, October 2004, Pages 148-58[Link][3]
Nitric oxide in the cell inactivates this enzyme, thus increasing the rate of transcription of any downstream genes.
Epinephrine sensor
There are several different kinds of anxiety and panic disorders. One common feature of these diseases is the occurrence of panic attacks which are caused by a sudden surge in adrenaline. It has also been shown that patients with panic disorder have an elevated level of arterial adrenaline even at rest. Sympathetic Activity in Patients With Panic Disorder at Rest, Under Laboratory Mental Stress, and During Panic Attacks[Link][4]
As the gut is strongly innervated by the sympathetic nervous system and plays an important role in inflammation The role of the sympathetic nervous system in intestinal inflammation[Link][5]and because many E. coli strains have an inbuilt system for response to adrenaline we designed a construct with an adrenaline sensitive promoter, flhDC. This promoter is controlled by the transcription factor QseB which is activated by the adrenaline sensing membrane bound protein QseC. Transcriptional regulation of flhDC by QseBC and sigma (FliA) in enterohaemorrhagic Escherichia coli.[Link][6]
In a study with rats researchers have already tested whether QseC could sense adrenaline. QseC-loaded liposomes were treated with the physiologically intestinal-relevant concentration of 5–50 μM adrenaline. The QseC sensor kinase: A bacterial adrenergic receptor.[Link][7]
The flhDC promoter can therefore be useful for immediate response in the case of a sudden surge in adrenaline during a panic attack.
The flhDC promoter BBa_K554001 biobrick from the 2011 UNICAMP-EMSE Brazil iGEM team was characterised.
Figure 1. Fluorescence per OD600 of flhDC induced at varying concentrations of (-)-epinephrine.