1. Introduction
Pulmonary fibrosis is a mostly irreversible lung disease resulted from
acute lung injury, including severe infections such as COVID-19,
radiation, chemotherapy, toxins, COPD, etc(George, Wells & Jenkins,
2020; Meziani et al., 2018; Wijsenbeek, Suzuki & Maher, 2022; Wilson &
Wynn, 2009). The incidence of PF is not easy to estimate. Whereas,
idiopathic pulmonary fibrosis (IPF), a specific chronic and progressive
PF, was once classed as a rare disease but with an incidence rate
continuously increased these years(Hutchinson, Fogarty, Hubbard &
McKeever, 2015; Navaratnam, Fogarty, Glendening, McKeever & Hubbard,
2013). Importantly, the average survival year of IPF is around 3-5 years
after diagnosis(Vancheri, Failla, Crimi & Raghu, 2010). However, the
approved treatments for PF are limited or with low efficacy, including
pirfenidone and nintedanib(Johannson, Chaudhuri, Adegunsoye & Wolters,
2021). Therefore, it is still required efforts to elucidate important
mechanisms for developing efficient strategies to treat PF progression.
With years’ efforts, it has been now well recognized that the
progression of PF shares three common phases, including injury,
inflammation, and tissue repair and contraction(Wilson & Wynn, 2009).
In brief, the lung injury caused by multiple factors mentioned above
would lead to inflammation for replacing the damaged epithelial or
endothelial cells to maintain barrier function and integrity, from which
several cytokines are produced, leading to EMT in AT II cells for tissue
repair but also initiates fibrosis by synthesizing ECM components like
fibronectin and collagen type 1, etc.(Kim et al., 2006; Kim et al.,
2009). EMT has been reported to be an important process for fibrosis in
multiple lung diseases, except IPF with controversial
conclusions(Gauldie, 2002; Strieter, 2002). Recently, a single cell-RNA
Seq analysis identified that EMT process in AT II cells does require for
IPF progression(Xu et al., 2016). These studies together emphasize the
importance of EMT in promotion of pulmonary fibrosis. Till now, multiple
molecular targets modulating EMT have been reported to be effective in
fibrotic lung diseases in mice model, however, no relevant effective
clinic strategies so far have been reported(Bartis, Mise, Mahida,
Eickelberg & Thickett, 2014).
Several animal models have been established to understand the PF
progression, from which PQ poisoning-induced acute lung injury is widely
recognized to induce PF in a short period. Other models, like
bleomycin-induced PF, require a relatively long period (O’Dwyer &
Moore, 2018), which contains EMT, endothelial-to-mesenchymal transition,
fibroblast-to-myofibroblast transition (FMT), etc(Moss, Ryter & Rosas,
2022). Considering others and our previous studies all identify EMT as a
key process in PQ-driven PF(Chowdhury, Zielonka, Kalyanaraman, Hartley,
Murphy & Avadhani, 2020; Su, Cong, Bi & Gao, 2018; Yamada, Aki, Unuma,
Funakoshi & Uemura, 2015), PQ-induced acute lung injury would be an
ideal model to identify potential strategies targeting EMT for treating
PF. PQ has been well recognized to produce ROS that leads to severe
cellular damage, EMT, and thus pulmonary fibrosis(Zheng, Goncalves,
Abiko, Li, Kumagai & Aschner, 2020), which oxidative stress has been
well characterized as a central signal for multiple factors-raised PF.
Interestingly, clinical treatments to eradicate ROS production are not
sufficient to treat PQ-induced PF and following high mortality
(Dinis-Oliveira, Duarte, Sanchez-Navarro, Remiao, Bastos & Carvalho,
2008; Subbiah & Tiwari, 2021), indicating that other important
mechanisms are still required to be elucidated. Recent studies have
identified several other potential mechanisms and relevant new
strategies for treating PQ poisoning, however, the efficacy is limited,
yet exhibiting attenuation of the symptom (Subbiah & Tiwari, 2021),
including metformin treatment only slightly reducing PQ induced
pulmonary fibrosis(Wu et al., 2019) and maintaining an around 30%
survival rate in PQ-poisoned mice model (Algire et al., 2012), rapamycin
treatment exhibiting an increased survival rate on day 2 but almost
losing the efficacy on day 3 in PQ-poisoned zebrafish model (Feng, Bian,
Zhang, Wang & Chen, 2019). Similarly, rapamycin attenuates but not
reverses PQ-induced pulmonary fibrosis in animal models(Tai et al.,
2020; Xu et al., 2017). These observations raised us to identify the
molecular target for PQ-induced EMT. Our previous work has successfully
revealed that STIM1 is another important molecular target of PQ for EMT
in AT II cells(Yang et al., 2022). STIM1 is an essential component for
extracellular calcium entry by association with either ORAI1 or TRP
family members(Soboloff, Rothberg, Madesh & Gill, 2012). We found that
PQ targeting STIM1 promotes the exposure of the poly-lysine (K) region
in the C-terminal of STIM1, which facilitates the association between
STIM1 and TRPC1 for extracellular calcium entry and intracellular
calcium increase(Yang et al., 2022). Note, it has been reported that
intracellular calcium burden is required for EMT in multiple cancer
cells for tumor metastasis. Therefore, we speculated that intracellular
calcium increase is an important signal for PF, targeting intracellular
calcium burden would be a potential strategy to treat PF(Wei et al.,
2021). Herein, we utilized PQ-induced EMT and PF model with combination
of information from mice model, cynomolgus model, and PQ poisoned
patients, to examine the precise restriction of intracellular calcium
burden as a potential strategy to treat PF.