Native and fragmented fibronectin oppositely modulate monocyte secretion of MMP-9

Barak Marom^*^,^,1, Michal A. Rahat^*^,1^,2, Nitza Lahat^*, Lea Weiss-Cerem, Amalia Kinarty^* and Haim Bitterman

^* Immunology Research Unit and
Ischemia-Shock Research Laboratory, Carmel Medical Center, Rappaport Family Institute for Research in the Medical Sciences, and Bruce Rappaport Faculty of Medicine, Technion, Haifa, Israel

² Correspondence: Immunology Research Unit, Carmel Medical Center, 7 Michal St., Haifa, 34362, Israel. E-mail: rahat_miki{at}clalit.org.il

Monocytes remodel the extracellular matrix (ECM) by secretingproteins composing the ECM such as fibronectin (FN) and degradingproteases such as matrix metalloproteinase-9 (MMP-9), whichcleaves FN into fragments. The effects of FN and its fragmentedproducts on the expression of monocyte MMP-9 are controversialand largely unknown. We showed that in human monocytes, theproinflammatory cytokine TNF- ${alpha}$ induced MMP-9 secretion and increasedfragmentation of FN into distinct fragments. When primary monocytesor the U937 monocytic cell line were incubated on a plasticsubstrate, plastic-coated with native FN, and plastic-coatedwith fragmented FN (frag-FN), native FN inhibited TNF- ${alpha}$ -inducedproMMP-9 secretion by twofold (P<0.01) compared with plasticor frag-FN. Exploration of the dynamics of inflammation by incubatingcells sequentially on the three substrates showed that frag-FNopposed the inhibitory effect of native FN. Inhibition of proMMP-9by native FN was exerted at the translational level, as no changein MMP-9 mRNA, intracellular protein accumulation, or proteomicdegradation was observed, and when degradation was blocked,no de novo translation of MMP-9 could be measured. We also showedthat the reduction of MMP-9 secretion by native FN was responsiblefor attenuated migration of U937 cells (P<0.05). We suggestthat in the inflammatory tissue, intact, native FN has a homeostaticrole in harnessing MMP-9 activity. However, as fragmented productsaccumulate locally, they alleviate the inhibition and enablefaster migration of the monocytes through the degraded ECM.

Key Words: human • macrophages • inflammation