| As one of the most important organs of our body, lung is susceptible to various injuriesdue to its unique anatomic structure and the character of directly connected with the outsideworld. Trauma patients, particularly severe trauma patients, are often accompanied withacute lung injury (ALI). ALI and its severe form acute respiratory distress syndrome(ARDS), are major cause of death in trauma patients. Lung will start endogenous repairafter ALI. It has been found that a relatively small content of various types of cells locatedin special microenvironment play very important role in the process of repair after injury,including endogenous and exogenous stem/progenitor cells. In addition to the possibilityof the role of stem/progenitor cells in repairing, more and more studies also showed thatthe terminally differentiated cells may also play a vital role in tissue repair after injury. Inrecent years, many studies have demonstrated that various kinds of terminallydifferentiated cells can dedifferentiate into stem/progenitor cells in multiple organs undercertain conditions. However, it has not been reported whether type â… alveolar epithelialcell (ATâ… ) can dedifferentiate to mediate the repair of ALI.ATâ… s are very large, thin cells which extend across several air sacs and cover morethan95%of the entire alveolar surface area. ATâ… s are the targets of many lung insults,such as ventilator-associated lung injury. It is generally accepted that alveolar epithelialwounds are repaired by alveolar type â…¡ cell (AT â…¡) hyperplasia and subsequenttransdifferentiation of ATâ…¡ to an ATâ… phenotype. ATâ… s are considered as terminallydifferentiated cells, and only have a passive barrier function without activefeatures.However, recent studies have found that ATâ… s may have a variety of biologicalfunctions. In addition to participating in the formation of air-blood barrier (ABB), ATâ… sare also capable of transporting ions and water,meanwhile participating in the immuneresponse. However, in case of ALI, whether the biological behavior of ATâ… s will be changed or whether dedifferentiation will occur is unclear.On the basis of successfully established the rat model of ALI induced by hemorrhagicshock and LPS inhalation and AT â… isolation and culture methods, we usedbronchoalveolar lavage fluid (BALF) and lung tissue homogenates (LTH) from the rat ALImodel to represent the acute lung injury milieu. We observe the biological effects of theALI milieu on primary cultured ATâ… s, including cell proliferation and the phenotyperelated marker expression, in order to preliminarily study the possible repair effects of ATâ… s.The main findings are as follows:1. We successfully isolated ATâ… s of high purity from rat lungs by using a three-stepmethod, including neutral protease digestion, IgG adherent and magnetic sorting. Thismethod proved highly efficient and stable.2. The cultured cells expressed ATâ… cell-specific markers, including PDPN, AQP5and Cav-1,barely expressed ATâ…¡ cell-specific marker pro-SPC, which indicated that thesecultured cells were ATâ… s.3. We used the ALI milieu(BALF and LTH) to stimulate primary cultured ATâ… s invitro and observed that day-3BALF, day-3and day-5LTH from rat ALI model couldsignificantly promote the proliferation of ATâ… s.4. For further analysis, we used ALI-D3-LTH to stimulate ATâ… s and then detectedthe expression levels of phenotype related genes. We found that AQP5and RAGE mRNAexpression levels were decreasd to some extent. Klf2gene expression was significantlydecreasd.On the other hand, the expression level of SPC and Nkx2.1mRNA weresignificantly increased. Then we confirmed the protein expression of pro-SPC byimmunofluorescence method and Western Blot. It indicated that the milieu of ALI couldinduce dedifferentiation of ATâ… s. |
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