Transdifferentiation of epithelial cells into mesenchymal cells is important to the development of fibrosis and cancer progression. In the kidneys, EMT is a classic source of myofibroblasts and fibroblasts throughout renal fibrogenesis. However , little is known regarding the roles carried out by and regulation of EpMyT during skin injury healing. Recent studies using rat kidney epithelial cellular lines have shown that P311 may promote IL-1α -induced EMT via a TGFβ 1-independent pathway [ 31 ] and that it may inhibit TGFβ 1-induced EMT by preventing the Smad/ILK pathways [ 32 ]. Furthermore, our latest in-vivo study showed that P311 promotes renal fibrosis via the TGFβ 1/Smad signaling [ 33 ]. These questionable results revealed that the roles played by and systems involving P311 in cell biology might be cell plus microenvironment specific. However , it remains unclear whether P311 directly induces EpSCs to transdifferentiate into MFLCs. To the knowledge, this is the first study to link P311 using the differentiation potential of stem cells, in which it boosts the transdifferentiation of EpSCs into MFLCs. Accordingly, we discovered that P311 induced EpSCs to transdifferentiate into MFLCs via a TGFβ 1-mediated process in vitro. Furthermore, the study also suggests that P311 might regulate TGFβ one expression by promoting TGFβ 1 promoter methylation in the transcriptional level and by activating the TGFβ 1 5′ /3′ UTRs at the translational level. Moreover, we provide proof showing that common injury signals (including cytokines plus hypoxia) might also promote the expression of P311. Significantly, the deletion of P311 resulted in delayed burn injury healing. We therefore propose that P311 is a novel limiter of the transdifferentiation of EpSCs during skin wound recovery (Fig. 7b ).
In skin, the majority of research upon EMT has focused on tumor progression and skin fibrosis, while only a few studies have shown that EMT may be associated with wound healing [ 34 ]. Although EpSCs act as one of the primary functional cells in wound healing, it is unclear whether or not and how EpSCs transdifferentiate into myofibroblasts or MFLCs. With this study, our results indicated that EpSCs were effective at transdifferentiating into MFLCs in vitro and that this process could be regulated by P311. P311-expressing mouse and human EpSCs lost their typical cobblestone morphology and exhibited the myofibroblast-like fusiform morphology. Moreover, P311 upregulated myofibroblast guns (such as vimentin and α -SMA) and downregulated EpSC markers (such as β 1-integrin and E-cadherin). Moreover, P311 reorganized the cortical cytoskeleton into filamentous stress fibers. However , functional tests showed that P311 promoted the EpSC migration and the collagen I plus MMP2 expression but did not enable EpSCs to develop solid contractility (Additional file 2 : Figure S5). One possible explanation for this result would be that the EMT program involving P311 might be limited to the early myogenic program, although P311 could induce other programs, like de-epithelialization (via the loss of E-cadherin), fibrogenesis (via vimentin plus collagen I), possible disruption of the basement membrane (via MMP2), and enhanced cell migration. Another possible description is that, as reported previously (Additional file 1 : Table S2), EMT-sourced myofibroblasts may become the MFLCs that mainly feature motility and secretory abilities, but that are not the same as the classic myofibroblasts which usually feature both contractility and secretory abilities. Furthermore, all of us show here that the physiological significance of EpMyT would be to enable EpSCs to secrete collagen I and MMP2 and obtain a higher degree of motility [ 35 ], but not to create contractions. Hence, in this study, we defined the transdifferentiated EpSCs as MFLCs to distinguish from the typical myofibroblasts. A lot more studies are needed to determine the mechanisms underlying this interesting sensation.
In this study, we discovered that P311 may activate and amplify TGFβ 1/Smad signaling in EpSCs. Specifically, the phosphorylation of Smad2 and Smad3 was increased in P311-overexpressing EpSCs plus decreased in the P311 KO EpSCs. To conclusively verify the role of TGFβ 1/Smad signaling in P311-induced EpMyT, loss-of-function and rescue strategies were used. LY2109761, a specific inhibitor of Tβ RII and Tβ RI, and the specific Smad3 siRNA almost completely blocked P311-induced EpMyT. Furthermore, the application of exogenous TGFβ 1 restored EpMyT in P311 KO EpSCs. The level of α -SMA manifestation dropped only slightly in P311 KO cells, plus exogenous TGFβ 1 had a smaller effect on α -SMA in P311 KO cells, suggesting that other factors (such as Rock pathway) may also contribute to this process. These inhibited and rescue experiments further support our hypothesis that will P311 promotes EpMyT partly via a TGFβ 1-mediated signaling.
The role of plus mechanisms involving P311 in the expression of TGFβ one might be cell specific. In NIH3T3 fibroblasts, P311 inhibited the production of the TGFβ 1 mRNA and protein in the post-translational level. Specifically, P311 bound to LAP, which resulted in a decrease in TGFβ 1 auto-induction [ 36 ]. Within vascular smooth muscle cells, P311 inhibited the transcribing of the TGFβ 1 mRNA but promoted the production from the TGFβ 1 protein at the translational level. In particular, P311 directly bound to the 5′ UTRs of TGFβ one and eIF3b to stimulate the translation of TGFβ 1 [ 24 , 37 ]. However , these data do not completely explain the observed decrease in TGFβ 1 mRNA amounts, and the mechanism by which P311 regulates TGFβ 1 within EpSCs remains unclear. Our results show that the reduction in TGFβ 1 mRNA levels and the increase in TGFβ one protein levels observed in P311-overexpressing EpSCs are most likely caused by the particular inhibition of its transcription, which is the result of enhanced promoter methylation and the improved translation of activated 5′ and 3′ UTRs. The current study therefore indicates that P311 manages TGFβ 1 expression not only at the translational level but additionally at the transcriptional level. This conclusion is also partly backed by our recent finding that eIF6, a partner of P311, downregulates TGFβ 1 mRNA and protein expression ranges at the transcriptional level via H2A. Z occupancy plus Sp1 recruitment in fibroblasts [ 38 ]. However , more studies are needed to determine the mechanism by which P311 enhances the particular methylation of the TGFβ 1 promoter and which particular sites of the TGFβ 1 5′ /3′ UTRs are usually bound by P311.
In-vivo experiments provided indirect and weak evidence showing that will P311 mediates the induction of EpMyT. P311 + α -SMA + cells and P311 + vimentin + cells were observed in the epidermis associated with human burn wounds. Furthermore, the mesenchymal features of these types of cells were reduced in the P311 KO mouse burn off wounds. In this study, we found that superficial second-degree thermal burn wounds in mice healed within 10 days and α -SMA + cells were not detected in the epidermis of these mice, in line with the results of previous studies [ 14 , 15 ]. However , the particular burn wounds obtained from patients who needed skin graft surgery healed slower than the mouse wounds, and α -SMA + cells were noticed in the wounds of these patients. Interestingly, α -SMA is detected in the epidermis of the wounds of Buruli ulcer patients [ 39 ]. Thus, given the results of this research, we concluded that the severity of the injury and the period of time required for wound healing might be related to α -SMA manifestation. However , there are natural limitations to the detection methods which were used in this study. For example , histological “ snapshots” could possibly show nonspecifically bound antibodies, and using full-thickness skin examples means that the mRNA and protein detection methods used do not exclude a contribution of the dermis. As a result, we’re able to not determine whether the α -SMA + cells or vimentin + cells did indeed originate from EpSCs in vivo or even whether EpMyT was actually reduced in P311 KO mice. Our results only hint that P311 may have a possible relationship with the mesenchymal features of the epidermis in vivo. However , the in-vitro experiments provide direct evidence displaying that P311 induced EpMyT. To strengthen the evidence intended for EpMyT induction in vivo, new fate-mapping studies are essential, and related research is currently being performed in our program.
Cytokines, growth factors, and EMT-related transcription factors are the main reported regulators of EMT [ 40 ]. In this study, the relationship between P311 along with other EMT inducers (which are also common injury signals), which includes IL-1β [ 15 ], IL-6 [ 41 ], TNFα [ 15 ], and hypoxia [ 42 ], were also looked into. Our results showed that P311 expression was raised by the investigated injury and EMT inducers, especially IL-1β and TNFα. These results indicate that P311 may be a common pathway for cytokine-induced EMT, and our research adds novel regulators of P311 to previously documented results in the kidney and neural and smooth muscle tissue cells. However , identifying the mechanisms underlying these procedures requires further study.