Project Description

Nowadays, millions of young students and scientists are struggling with severe chronic mental stress, resulting in destructive outcomes such as depression and anxiety, which even leads to suicide.

Stress-related mental conditions in academia have raised broad attention for years. In 2018, Evans et al. showed that 41% of graduate students were under moderate to severe anxiety, and 39% suffered from mild to severe depression (Evans, Bira, Gastelum, Weiss, & Vanderford, 2018) . Similarly, according to Chris Woolston’s survey, 51% of postdoctoral scientists have considered leaving scientific research because of depression, anxiety, or similar work-related stress (Woolston, 2020). Meanwhile, in China, study conducted by Fudan University showed that graduation pressure, depression, and academic pressure were the three leading suicidal causes in graduate students (Cheng, Zhang, Ye, Jin, & Yang, 2020). These data all revealed the severe consequences resulting from the accumulation of chronic mental stress.

As a well-educated group of people, college students and young scientists should be knowledgeable enough to be aware of these potentially destructive outcomes caused by chronic stress; we then wondered whether it was the active ignorance of mental stress or the lack of self-awareness regarding the accumulating stress that eventually led to the high incidence of depression and anxiety in this population.

To answer these questions, we designed a questionnaire to 1) evaluate the self-awareness of stress levels and 2) collect information regarding the stress conditions and how mental stress is commonly dealt with in undergraduate and graduate students (The details of the questionnaire design and data analysis can be found on the Human Practice Page). Briefly speaking, our results obtained from more than 500 participants showed that although our participants have their ways to actively adjust lifestyles upon stress conditions (Figure 1a), they generally lacked proper ways to measure their stress levels (Figures 1c and 1d), which could possibly contribute to the deviation between self-reported stress levels and the levels reported by the clinical assessment scale (Figure 1b). Therefore, tools to detect stress levels prematurely and precisely might be an essential step to help monitor our stress levels and reduce the risk of chronic stress-induced mental diseases.

To select a good stress marker, we first reviewed the endogenous stress-responding process in humans. Numerous studies elucidate that when we are under stress, the sympathetic nervous system (SNS) and hypothalamic-pituitary-adrenal axis (HPA axis) is activated to secrete stress hormones, which triggers a series of neuroendocrine reactions (Monteleone et al., 2015). Upon stress stimulation, the SNS is the first response pathway to respond immediately, leading to a faster heartbeat and higher blood pressure in a short time. Compared with the SNS axis, the HPA axis makes response slower. It originates from the secretion of corticotropin-releasing hormone (CRH) after receiving stimulation from the medial hypothalamic paraventricular nucleus, which causes the release of adrenocorticotrophin (ACTH) in the anterior pituitary. It is eventually accompanied by an increase in glucocorticoid.

Studies have found that cortisol levels can be used as a biomarker for chronic stress. Patients with long-term severe chronic pain showed approximately two-fold higher hair cortisol contents compared to controls (P < 0.01) (Van Uum et al., 2008). Significantly increased glucocorticoid levels were also observed in mouse monkey stress models (Teng et al., 2021). At present, there are various methods to detect cortisol content, including enzyme-linked immunosorbent assay, radioimmunoassay, chemiluminescence immunoassay  (Greaves et al., 2014), gas chromatography MS  (de la Torre et al., 2015), liquid chromatography MS  (Hawley et al., 2016), etc. However, the detection process of these methods is too complicated and requires large and expensive equipment, making it impossible to monitor cortisol content in a real-time manner. Recently, the UCLA research team has developed a class of wearable sensors that can directly detect cortisol concentrations in sweat as a stress-sensing device (Wang et al., 2022).

Compared with these electronic sensors, biological approaches advance in their good biocompatibility, and no need for power supply; cell-based sensors might also allow therapeutic protein expression as an all-in-one platform for both diagnostics and therapeutics. Recently, an important advance has been made to generate visible signals in mammalian cell-based sensors. In 2018, Tastanova et al. from ETH Zurich designed a designer-cell-based hypercalcemia sensor by putting the melanin synthesis gene tyrosinase (Tyrosinase) downstream of the calcium-responsive NFAT promoter, thereby achieving a high blood calcium-triggered melanin synthesis. They referred to this circuit as a diagnostic "biological tattoo" (Tastanova et al., 2018), an excellent example of designer cells based on synthetic biology.

Inspired by these works, our team developed a novel synthetic biomedical tattoo using engineered cells that would monitor the rising glucocorticoid level induced by chronic stress and responds accordingly with a visible output (Figure 2a). To achieve this, we generated a novel transcriptional factor, Tet_stress, that responds to glucocorticoids (Figure 2b). Once glucocorticoids increases, this transcriptional factor would translocate into the nucleus and bind to the promoter region of the reporter gene (Figure 2c), then trigger the activation of reporter gene transcription (See the Engineering Success page for the development of Tet_stress). We finally demonstrated that Tet_stress enabled fluorescent and colorimetric output under glucocorticoid stimulation in a dose-dependent manner (Figure 3). This circuit can be applied via subcutaneous injection of either adeno-associated virus or microencapsulated designer cells. If fully developed in the future, we firmly believe that our project could help our peers monitor their stress levels, thereby helping them adjust their lifestyle in time.