Interaction of Clusterin and Matrix Metalloproteinase-9 and Its Implication for Epithelial Homeostasis and Inflammation

• DOI: 10.1016/j.ajpath.2012.01.025
• Publication Date: 2012-03-20T07:18:45Z
• Authors: Shinwu Jeong; Dolena R. Ledee; Gabriel M. Gordon; Tatsuo Itakura; Nitin Patel; Aaron Martin; M. Elizabeth Fini
• Keywords: Inflammation; 0301 basic medicine; Epithelium, Corneal; Down-Regulation; Epithelial Cells; Matrix Metalloproteinase Inhibitors; Recombinant Proteins; Pathology and Forensic Medicine; Cell Line; Enzyme Activation; Mice; 03 medical and health sciences; Clusterin; Matrix Metalloproteinase 9; Cell Line, Tumor; Animals; Cytokines; Homeostasis; Humans; Protease Inhibitors; Desiccation; Inflammation Mediators; Protein Binding

Uncontrolled increases of matrix metalloproteinase-9 (MMP-9) activity have been causally linked to epithelial barrier disruption and severe symptoms of inflammatory diseases such as dry eye (DE). The data presented here show that the anti-inflammatory, cytoprotective intracellular and extracellular chaperone protein clusterin (CLU) interacts with MMP-9 both inside and outside epithelial cells. CLU bound very strongly to active MMP-9, with an affinity constant K(D) of 2.63 nmol/L. Unexpectedly, CLU had a much higher affinity for pro-MMP-9 than for active MMP-9 or pro-MMP-2, requiring the N-terminal propeptide domain of pro-MMP-9. The significance of the interaction between CLU and MMP-9 was demonstrated by the observation that CLU prevents stress-induced MMP-9 aggregation and inhibits MMP-9 enzymatic activity. Furthermore, CLU inhibited MMP-9-mediated disintegration of the tight junction structure formed between human epithelial cells. Additionally, CLU inhibited enzymatic activities of MMP-2, MMP-3, and MMP-7. Treatment with proinflammatory cytokines, which are known to increase MMP-9 transcription under inflammatory conditions, reduced the expression of CLU in human epithelial cells. Similarly, in a mouse model of human DE, inflammatory stress depleted CLU in the ocular surface epithelium but allowed MMP-9 to prevail therein. The present results thus provide novel insights into previously unrecognized mechanisms by which CLU maintains fluid-epithelial interface homeostasis, thereby preventing the onset of inflammatory conditions, especially where MMP-9 is actively involved.