3.3.1 JAK-STAT related cytokine release and immune response
IL-6 is a vital factor in ARDS which relays on JAK/STAT transfer the signaling. IL-6 related JAK-STAT activation has a negative impact on the disease progression of ARDS (caused by tobacco, ventilator, etc.). In the VILI (ventilator-induced lung injury), intratracheal IL-6 administration in C57BL/6J mice increased protein content and cell count in bronchoalveolar lavage fluid, which was associated with activation of JAK signal transducers, activators of transcription, p38 MAP kinase, and NF-κB signaling(Birukova, Tian, Meliton, Leff, Wu & Birukov, 2012). Moreover, IL-6 can enlarge the endothelial cell (EC) permeability in the situation of pathologically relevant cyclic stretch (CS) magnitudes, increase ICAM-1 expression of pulmonary EC and neutrophil adhesion. However, Rho kinase inhibitor Y-27632 suppressed the synergistic effect. That is evidence of Rho taking part in the endothelial integrity(Gudipaty & Rosenblatt, 2017). Other study also shows that influenza A virus infection induced muscle wasting via IL-6 regulation of the E3 ubiquitin ligase atrogin-1(Radigan et al., 2019). Glucocorticoids like betamethasone (BTM) and dexamethasone (DXM), potentiate IL-6-induced SP-B expression in H441 cells by enhancing the JAK-STAT signaling pathway, so make a negative impact on ARDS(Ladenburger et al., 2010a).
In the mouse model of severe influenza A pneumonia, IL-6 promoted muscle degradation via the E3 Ubiquitin Ligase atrogin-1, STAT3, FOXO3a(Shaikh, Bhat & Bhandary, 2020). There is also study shows that glucocorticoids potentiate IL-6-induced SP-B expression in H441 cells by enhancing the JAK-STAT signaling pathway and that phenomenon is reversed by JAK1 inhibitor(Ladenburger et al., 2010b). Not only IL-6, there are many other cytokines, like IL-17A participated in the in vivo mice model of ALI, may related to ARDS(Shaikh, Bhat & Bhandary, 2020).
As to STAT (1/3) is activated in ARDS, targeting STAT3 may be therapeutical to ALI and ARDS patients(Severgnini et al., 2004). In LPS-induced ALI mouse model STAT3 was activated in CD45+CD11b+ cells from BALF and in LPS treated macrophages in vitro. STAT3 inhibitor LLL12 decreased IL-1β, IL-6, TNF-α, iNOS, CCL2, and MHC class II in macrophages and inflammatory cells from BALF and serum determined by ELISA. Hyperactivation of STAT3 in LysMCre-SOCS3fl/fl mice accelerated the severity of inflammation in the ALI model(Zhao et al., 2016). Myeloid, Ly6C (+) macrophage, lack of SOCS3 resulted in more expression of STAT3 and increased LPS-induced murine acute lung injury(Jiang, Chen, Li, Zhou & Zhu, 2017).
In recent research about alveolar macrophage transcriptional program in patients, cell-specific AM (alveolar macrophage) proinflammatory and M1-like(IL-6/JAK/STAT5 activation) at the time of ARDS onset were associated with better clinical outcomes(Morrell et al., 2019). Decreasing of p-JAK1, p-STAT1, p-STAT3, and PKM2-mediated glycolytic pathways could reverse lipopolysaccharide-induced inflammatory responses of macrophages(Ying, Li, Yu & Yu, 2021). Not only macrophages, there was also study about the mesenchymal stem cells (MSCs). They affected ARDS in newborn swine via JAK-STAT signaling pathway. MSCs increased interleukins (IL-2, IL-6, IL-8), and tumor necrosis factor-α (TNF-α) expression levels and decreased IL-10 and IL-13.
3.3.2 JAK-STAT in epithelial function/ smooth muscle proliferation and surplus fluid absorption
JAK is vital for the epithelial functions. JAK3 was found interacts with cytoskeletal proteins so play an essential role in cytoskeletal remodeling and epithelial wound repair(Kumar, Mishra, Narang & Waters, 2007). In mucosal homeostasis, JAK3 interacted with adapter protein p52ShcA and regulated the expression of differentiation markers, formation of mucus in mice, and facilitated barrier functions through its interactions and adherent junction (AJ) localization. In DSS mouse model, knockdown of JAK3 decreased TEER and AJ localizations of β-catenin induced increasing of severity in DSS-induced colitis. JAK3 activation led to β-catenin phosphorylation at Tyr-654, which promoted β-catenin interaction with E-cadherin, thereby facilitated AJ formation and enhanced the IEC barrier functions. The expression of differentiation markers of human intestinal epithelial cells (IEC) depended on the nuclear translocation of phosphorylated form of JAK3(Mishra, Verma, Alpini, Meng & Kumar, 2013). In the region of SHC, the CH1 and PID domains were responsible for binding to JAK3. In situation of IL-2 stimulated of epithelial cells, JAK3 was auto-phosphorylated. However, SHC recruited tyrosine phosphatases SHP2 and PTP1B to JAK3, thereby dephosphorylated JAK3(Mishra & Kumar, 2014).
Additionally, Surfactant protein C, a key component of pulmonary surfactant, which is a specific marker of type II alveolar epithelial cells, is convinced has a connection with JAK/STAT. Misfolded proSP-C caused subsequently type II alveolar cell injury and inflammation(Hamvas et al., 2004). The SPC-TK/SPC-KO (surfactant protein C-thymidine kinase/surfactant protein C knockout) mice showed enhancing Janus kinase (JAK)/STAT activation which is associated with increased inflammation and delayed repair(Alsulaimani, 2018). Clinical trials about ARDS patients’ treatment with exogenous recombinant surfactant protein C(rSP-C)-based surfactant resulted in improvement in blood oxygenation and suggested a potential benefit(Spragg et al., 2004).
JAK3 plays a critical role in smooth muscle proliferation and injury-induced neointima formation. Despite JAK3 has a low level of expression in normal vascular SMCs, the expression and activity of JAK3 are dramatically induced by PDGF-BB in vitro and by balloon injury in vivo(Wang, Cui, Chuang & Chen, 2017a). Thus, JAK3 is potential a therapeutic target to preventing neointimal hyperplasia in proliferative vascular diseases. Moreover, JAK2 is reported regulating angiotensin II induced smooth muscle proliferation and vascular remodeling(Wang, Cui, Chuang & Chen, 2017b). In vitro ALI model, LPS-induced upregulation of the PI3K/AKT and JAK/STAT signaling pathways in human lung fibroblast, was further inhibited by KLF4 knockdown(Li, Zhang & Yang, 2019). Muscle dysfunction, associated with JAK/STAT activation, is related to the low mobility of ARDS(Files, Sanchez & Morris, 2015).
JAK2 and JAK3 are both potent regulators of Na+/K+ ATPase(Bhavsar et al., 2014; Hosseinzadeh et al., 2015). That reveals JAK/STAT may participate in the absorption of surplus fluid during ARDS process by the Na+/K+-ATPase. In energy depletion model of DCs and Xenopus laevis oocytes which treated with 2,4-dinitro-phenol, JAK3 was phosphorylated (and therefore activated), and JAK3 downregulated the Na+/K+-ATPase. Pharmacological inhibition of JAK3 significantly increased Na+/K+-ATPase(Hosseinzadehet al., 2015). Recent studies found that JAK3 directly affected the transport proteins in partial, including various ion channels, a number of cellular carriers and the Na+/K+pump including the high-affinity Na+ coupled glucose transporter SGLT1, the excitatory amino acid transporters EAAT1, EAAT2, EAAT3 and EAAT4, the peptide transporters PepT1 and PepT2, CreaT1 and the Na+/K+-ATPase(Sopjani, Thaci, Krasniqi, Selmonaj, Rinnerthaler & Dermaku-Sopjani, 2017). There need additional experiments to elucidate the mechanisms and prerequisites of up- or down-regulation of Na+/K+-ATPase by JAK3 or JAK2.
Moreover, JAKs also phosphate SHP-2 or PI3K, thus play an important part in other signal transduction pathways such as Ras/Raf/MAPK/ERK pathway and PI3K-AKT pathway(Saxena et al., 2007; Wit & de Luca, 2016). Besides, ROS is revealed participated in the activation of JAK-STAT signaling and in the pathogenesis of ARDS. In fibroblasts and A-431 carcinoma cells, treatment of H2O2 can activated STAT1, STAT3 and STAT kinases JAK2 and TYK2 within 5min. And PDGF uses ROS as a second messenger to regulate STAT activation(Simon, Rai, Fanburg & Cochran, 1998).