TNF-α Stimulates Matrix Metalloproteinase Expression in Myelodysplastic Syndromes (MDS): Therapeutic Potential for Inhibitors of TNF-α and MMPs.

MDS is characterized by ineffective hematopoiesis with increased intramedullary apoptosis which has been correlated in turn with high levels of tumor necrosis factor (TNF)- α. Previously, we showed that TNF-α strongly upregulates the secretion of the matrix metalloproteinases (MMP)-2 and -9 in normal CD34⁺ cells. Elevated expression of MMPs has been suggested to contribute to cancer progression and leukemic dissemination and MMPs also facilitate the secretion of TNF-α. In this work, we hypothesized that TNF-α-induced MMP production plays a role in the progression of MDS. We therefore examined the effects of recombinant human (rh) TNF-α on the expression and secretion of MMP-2, MMP-9 and membrane type (MT) 1-MMP (known activator of MMP-2), by MNC from MDS patients (using RT-PCR, zymography and Western blotting), as well as the effects of TNF-α on migration of MDS MNC across the reconstituted basement membrane Matrigel. We observed higher mean levels of TNF-α in media conditioned by mononuclear cells (MNC) obtained from 20 patients diagnosed with MDS (RAEB-T (4); RAEB (5), RA (10) and RARS (1)) in comparison to normal controls. We found that (i) MMP-9 is secreted by MDS MNC and this secretion is increased by TNF-α, (ii) MT1-MMP is expressed by the majority of MDS MNC and this expression is upregulated by TNF-α, and (iii) MMP-2 is detectable only in RAEB-T MNC samples and is activated by TNF-α. TNF-α also stimulated the migration of MDS MNC across Matrigel, which was inhibited by the inhibitor of MT1-MMP, epigallocatechin-3-gallate. Moreover, Enbrel (soluble TNF receptor fusion protein), which blocks TNF-α, also inhibited the expression of MT1-MMP and secretion of MMP-9 by MDS MNC as well as their migration across Matrigel. In addition, we observed increased activation of the latent form of MMP-2 in co-cultures of MDS MNC with bone marrow fibroblastic cells. We suggest that in MDS patients, TNF-α stimulates the expression of MMP-9 and MT1-MMP, inducing a highly proteolytic environment in bone marrow which could further increase processing and secretion of endogenous TNF-α. Therefore, we suggest that use of TNF-α inhibitors combined with MMP inhibitors could have therapeutic value in abrogating the progression of MDS.