Effects of BMSCs, hCMSCs and LRMSCs on histopathological changes and PaCO2 in ALI
It could be seen from the pathological sections (H&E staining) that no inflammatory changes were detected in the normal rats (Fig. 1a) while the model group showed swollen lung interstitium and infiltration of many blood cells (Fig. 1a). Treatment with three types of MSCs restored damaged alveolar structure and significantly alleviated pathological damage (Fig. 1a). Compared to those of the normal group, lung injury scores, total protein content and cell count in BALF in the model group were all increased after 24h. However, while those in treatment groups were significantly decreased (Fig. 1b-e). PaCO2 was significantly decreased at 6h, 24h and 48h after inhalation of phosgene (Fig. 1f-h). MSCs treatment resulted in the recovery of PaCO2 (Fig. 2f-h). These changes were more prominent in the BMSCs group compared to the other groups.
Effects of BMSCs, hCMSCs and LRMSCs on reducing inflammatory response and immune regulation in ALI
The expressions of TNF-1α, IL-6 and IL-1β in BALF and serum were increased after phosgene inhalation while their expressions were decreased in three MSCs groups (Fig. 2a-c, e-g). Moreover, the changes of BMSCs were more significant than those of other MSCs groups (Fig. 2a-c, e-g). These results demonstrated that BMSCs could better resist inflammatory response both in the lungs and the entire body. IL-10 possess immunomodulatory properties [25]. After the rats were poisoned, the levels of IL-10 in both BALF and serum were increased and the increase was even higher after MSCs treatment (Fig. 2d, h). The effects of BMSCs were stronger than those of LRMSCs and hCMSCs, indicating that BMSCs had higher immune regulation ability in ALI than LRMSCs and hCMSCs.
Changes in HGF after the treatment of BMSCs, hCMSCs and LRMSCs
The expression of HGF in BALF and serum of each group were detected at 6h, 24h and 48h, respectively (Fig. 3a-f). Compared with healthy rats, the levels of HGF in BALF and serum in the phosgene group were increased. HGF expression was increased in all MSCs treatment groups. BMSCs showed the most significant effects followed by hCMSCs and LRMSCs.
Effects of BMSCs, hCMSCs and LRMSCs on repairing alveolar epithelia and vascular endothelia in ALI
Many red cells were shown to leak into the alveoli in the injured lungs (Fig. 4a). After MSCs treatment, fewer red cells were present in the alveoli indicating that vascular endothelial permeability had been significantly recovered (Fig. 4a). The expression of VE-CAD, a vascular endothelial cell marker, was decreased after lung injury but was increased in rats treated with MSCs (Fig. 4e, f). BMSCs, hCMSCs and LRMSCs were found to have protective effects in repairing vascular endothelia. BMSCs were shown to have the best protective effects followed by hCMSCs and LRMSCs. SP-C expression reflects the secretory function of normal alveolar epithelia [26]. SP-C was significantly reduced due to alveolar epithelial damage caused by phosgene (Fig. 4b-d). The expression of SP-C mRNA in lung tissues in each group was detected by RT-PCR (Fig. 4b-d). SP-C mRNA expression was significantly decreased in the phosgene group. Meanwhile, MSCs treatment significantly increased SP-C mRNA expression, and the BMSCs group showed the highest increase.
Comparison of the proliferation potential of three types of MSCs by CCK8 assay
The proliferation of the three types of MSCs were found not to be significantly different (Fig. 5a). However, the proliferation of BMSCs was slightly higher compared to that of hCMSCs and LRMSCs at 72h. All MSCs entered the logarithmic growth from the second to the fourth day.
Comparison of the migration potential of BMSCs, hCMSCs and LRMSCs
The horizontal migration of MSCs was different based on the wound-healing test (Fig. 5b). The BMSCs group exhibited significantly higher cell migration with obvious cell aggregation at 48h, followed by the hCMSCs group and LRMSCs group. The vertical migration of MSCs was determined using the transwell migration assay (Fig. 5c-d). At 24h, the number of hCMSCs, BMSCs and LRMSCs that migrated to the lower compartment was 181.27±62, 708.75±20 and 106.31±17, respectively. The three types of MSCs exhibited different migration rates and BMSCs showed the highest migration. This finding was consistent with the change in HGF in each treatment group in vivo. It is speculated that the high migration potential of BMSCs may be related to HGF, which may also be important in defining the roles of different MSCs. According to the experimental result (Fig. 5e), the optimal concentration of HGF was 25ng/mL which was added to the MSCs medium for 48h. MSCs with HGF showed a higher migration ability compared to the group without HGF (Fig. 5e). The experimental result indicated that HGF promoted the migration of MSCs in a dose-dependent manner in a certain range. Previous studies have shown that CXCL12 is the most important factor affecting the homing ability of hBMSCs compared with hCMSCs which was determined by PCR array in all the chemokines and receptors [9]. The effect of HGF on BMSCs migration was compared with that of CXCL12. The HGF group was compared with the CXCL12 group (30ng/mL) [20] and the FBS (10%) group (Fig. 5f). HGF was shown to significantly induce migration compared to CXCL12. HGF increased MSCs’ migration by about 2 fold when compared with 10%FBS. These results indicated that HGF was a strong inducer of BMSCs’ migration. Different concentrations of HGF were co-cultured with hCMSCs and LRMSCs for 48 hours (Fig. 6a). The migration of LRMSCs and hCMSCs were increased with different doses of HGF (Fig. 6b, c). The migration ability in HGF (25ng/mL) treatment group was highest, which verified that the optimal concentration of HGF was 25ng/mL. The migration potential of the three types of MSCs after HGF treatment was different (Fig. 6d). BMSCs showed significantly increased migration potential when compared to LRMSCs and hCMSCs. This indicated that BMSCs had the highest HGF sensitivity among the three types of MSCs.
The effect of HGF on the p-GSK-3β/β-catenin signaling pathway.
The expressions of proteins in MSCs were tested by Western blot (Fig. 7a-d) to explore the mechanism of the effect of HGF on MSCs. Compared with the control group, the expressions of p-GSK-3β and β-catenin in MSCs after HGF treatment were significantly increased in a dose-dependent manner that indicated that HGF activated this signaling pathway. Studies have confirmed the MMP-2 gene is an important target gene for the β-catenin signal pathway and its expression is associated with the degree of cell migration [27]. Therefore, the changes in MMP-2 mRNA after treatment were detected to investigate the effect of HGF on the target gene. Compared with the control group, MMP-2 expression after HGF treatment increased significantly (Fig. 7e). MMP-2 transcription was inhibited by the addition of FH535 (20μM), a potent inhibitor of the β-catenin signal pathway [28]. This showed that HGF promoted the transcription of MMP-2 by activating the β-catenin signaling pathway which promoted the migration of MSCs.