[Critical roles of matrix metalloproteinases secreted by leukemic cells in the pathogenesis of central nervous system leukemia]

Objective: To observe the effects of matrix metalloproteinases (MMP)-2 and MMP-9 secreted by leukemic cells on tight junction proteins ZO-1, claudin-5 and occluding and the permeability of the blood-brain barrier (BBB) and explore the mechanisms of MMP-2 and MMP-9 in leukemic cell infiltration of the central nervous system (CNS). Methods: The mRNA expressions of MMP-2 and MMP-9 in leukemic cell lines SHI-1, HL-60 and U937 were detected by quantitative RT-PCR. The MMP inhibitor GM6001 was used to inhibit the secretion of MMP-2 and MMP-9. RNA interference (RNAi) was used to knock down the expression of MMP-2 and MMP-9. Zymography was used to analyze the secretion of MMP-2 and MMP-9 in the supernatant of different leukemia cell lines treated or untreated with drugs, as well as the RNAi-treated cells. An in vitro BBB model composed of human brain microvascular endothelial cells (BMVECs) was developed on a Matrigel-based insert. Cell invasion through a barrier of Matrigel-based human basement membrane and the BMVECs-based human BBB barrier was assayed to measure the invasive capacity and the capacity to breakdown the BBB of different leukemia cell lines treated or untreated with drugs, as well as the RNAi-treated cells. The morphologic changes of BMVECs after co-culture with different leukemia cell lines treated or untreated with drugs, as well as the RNAi-treated cells in vitro BBB models were observed by invert microscopy and tight junction proteins in these BMVECs were analyzed with a laser-scanning confocal microscope. Results: ①The mRNA expression in different leukemic cell lines shown a pronounced transcription of MMP-2 and - 9, and the transcriptional level in SHI-1 cells was the highest among all leukemic cell lines tested (P<0.01). The data of activities of MMP-2 and -9 were consistent with the results of mRNA expression and SHI-1 displayed higher capacity of invasion (P<0.01). ②After incubation 24h with different leukemic cells, the BMVECs disrupted to loss cell-cell contacts and grew in single cell. Confocal imaging showed down-regulations of ZO-1, claudin-5 and occluding accompanied by the disruption of BBB in vitro models. SHI-1 cells had stronger alterations to BMVECs, tight junction proteins and the permeability of the BBB than HL-60 and U937 cells. However, GM6001 and the knock-down of MMP-2 and MMP-9 altered the responses of BBB. They reduced the degradation of three tight junction proteins with a decreased permeability of BBB. Conclusion: MMP-2 and MMP-9 secreted by leukemic cells could disrupt the BBB by degrading the tight junction proteins ZO-1, claudin-5 and occluding, which contributed the infiltration of leukemic cell into CNS.