To investigate the effect of the transplantation of human amniotic mesenchymal stem cell (hAMSCs) on the expressions of Aquaporin 1 (AQP1) and phosphorylated p38 mitogen activated protein kinase (p-p38MAPK) in lung tissue of rats with acute lung injury (ALI), and to further explore whether it can alleviate lung injury and its possible mechanism.

84 male SD rats were divided into 4 groups (n=21): normal saline control group (NS group), LPS induced ALI model group (LPS group), hAMSCs control group (NH group) and hAMSCs intervention group (LH group). The rats in LPS group and LH group were injected with LPS (4 mg/kg) through a sublingual vein to create models. NS group and NH group were injected with 250μl normal saline through a sublingual vein, and two hours later NH group and LH group were injected with 250μl DAP-labeled hAMSCs (2.5×10⁶) through a caudal vein. NS group and LPS group were injected with 250μl normal saline through a caudal vein. Seven rats in each group were killed at 6 h, 12 h and 72 h in order to observe the colonization of hAMSCs in the lung tissue of rats, the pathological morphology of lung tissue and the lung wet/dry weight (W/D) ratio. Furthermore, the levels of tumor necrosis factor-α (TNF-α) and interleukin- 1β (IL-1β) in bronchoalveolar lavage fluid(BALF) of rats in each group were detected by enzyme linked immunosorbent assay (ELISA). Immunohistochemistry (IHC) and western blot (WB) was used to detect the expressions of AQP1, p38 MAPK and p-p38 MAPK in the lung tissue of each group.

①Under the fluorescence microscope, it could be observed that there were blue fluorescent labeled hAMSCs around the alveoli of rats in NH and LH groups. Among them, the distribution of hAMSCs in LH group is more than that in NH group, indicating that hAMSCs can " homing" and colonize in the injured lung tissue. ②There was no significant difference in lung histopathological score, W/D ratio, TNF-α and IL-1 β levels in BALF, AQP1 and p-p38 MAPK protein expressions between NS group and NH group at each time point (P>0.05). ③Compared with the NS group and NH group at each time point, the LPS group and LH group showed an increase in lung histopathological score, W/D ratio, TNF-α and IL- 1 β levels in BALF, and p-p38 MAPK protein expression, and decrease in AQP1 expression at corresponding time points (P<0.05). ④Intra-group comparison of the LPS group revealed that there was no significant difference in lung histopathological score, W/D ratio, TNF-α and IL- 1 β levels in BALF, AQP1 and p-p38 MAPK protein expressions at the time points of 6 h and 12 h (P>0.05). Compared with LPS 6 h group and the LPS 12 h group, LPS 72 h group exhibited a decrease in lung histopathological score, W/D ratio, TNF-α and IL- 1 β levels in BALF, and p-p38 MAPK protein expression, and increase in AQP1 expression (P<0.05). Furthermore, there was no significant difference in lung histopathological score, W/D ratio, TNF-α and IL- 1 β levels in BALF, AQP1 and p-p38 MAPK protein expression between LH 6 h group and LH 12 h group (P>0.05). Compared with the 6 h and 12 h LH groups, LH 72 h group revealed a decrease in lung histopathological score, W/D ratio, TNF-α and IL- 1 β levels in BALF, and p-p38 MAPK protein expression, while the expression level of AQP1 was increased (P<0.05). Compared with the LPS group at each time point, lung histopathological score, W/D ratio, levels of TNF-α and IL-1β in BALF and expression of P-P38 MAPK protein were decreased in LH group, while AQP1 expression was increased (P<0.05). ⑤There were no significant difference in the expression of p38 MAPK in lung tissue at each time point among all groups (P>0.05).

①There is a homing and colonization of exogenous hAMSCs in the injured lung tissue. ②hAMSCs can inhibit the activation of p38 MAPK, decrease the release of inflammatory factors TNF-α and IL- 1β, and alleviate pulmonary inflammatory response. ③Intravenous transplantation of hAMSCs can upregulate the expression of AQP1 in lung tissue to enhance alveolar fluid clearance, so as to alleviate lung injury.