Neutralization of Macrophage-Stimulating Protein Ameliorates Renal Injury in Anti–Thy 1 Glomerulonephritis Teresa Rampino,* Grazia Soccio,* Marilena Gregorini,* Cristina Guidetti,* Maddalena Marasa `,* Milena Maggio,* Vincenzo Panichi, † Massimiliano Migliori, † Carmelo Libetta,* and Antonio Dal Canton* *Unit of Nephrology, Dialysis and Transplantation, Istituto di Ricovero e Cura a Carattere Scientifico Policlinico San Matteo and University of Pavia, Pavia, and † Department of Internal Medicine and Neuroscience (Pharmacology Section), University of Pisa, Pisa, Italy Macrophage-stimulating protein (MSP) is a scatter factor that causes cell proliferation and migration, and receptor origin nantaise (RON) is its receptor. RON is expressed in macrophages and mesangial cells, and MSP is produced by renal tubular cells. This study investigated whether MSP/RON participate in the pathogenesis of anti–Thy 1 nephritis, a glomerular disease that is characterized by invasion of circulating monocytes into glomeruli and migration and proliferation of mesangial cells. In vivo, renal function and histopathology were studied in rats that had anti–Thy 1 disease and were untreated and treated with a neutralizing anti-MSP antibody. In vitro, whether monocytes express RON and whether MSP has a chemotactic effect on monocytes were studied. In vivo, in anti–Thy 1 disease, MSP was expressed de novo in glomeruli, and neutralization of MSP attenuated the rise in serum creatinine and proteinuria, stopped glomerular neutrophil and monocyte influx, protected from glomerular injury, and lessened mesangial cell overgrowth. In vitro, unstimulated monocytes did not express RON, but the stimulation with LPS induced de novo RON expression. LPS-stimulated monocytes were attracted by MSP. These results demonstrate a pathogenic role of the MSP/RON system in anti–Thy 1 nephritis. J Am Soc Nephrol 18: 1486 –1496, 2007. doi: 10.1681/ASN.2006060680 M acrophage-stimulating protein (MSP) is a “scatter factor” that is homologous to hepatocyte growth factor (HGF) (1–3). The receptor of MSP is receptor origin nantaise (RON), a proto-oncogene product (4). Informa- tion on the cell source of MSP and the biologic meaning of the MSP/RON system is very limited. Originally, MSP was de- scribed as a serum factor produced by hepatocytes that en- hanced the chemotactic response of macrophages to the C5a fraction of complement (5– 8). It was then demonstrated that MSP induces proliferation, migration, and invasive growth of keratinocytes and epithelial tumor cell lines. These findings have suggested a role of MSP in skin-wound healing and in oncogenesis (8 –15). We have shown that MSP is diffusely expressed in tubular epithelium of human kidney and that proximal tubular cells release MSP. In addition, we have shown that human mesan- gial cells express RON and that MSP induces in human mes- angial cell growth, migration, invasion into an artificial colla- gen matrix, and synthesis of IL-6 (16). These findings suggest that MSP, either circulating or as paracrine product, may par- ticipate in the pathogenesis of mesangial proliferative glomer- ulonephritis (e.g., by inducing mesangial cell proliferation, movement, and invasion into the subendothelial space). An additional mechanism of glomerular endocapillary prolifera- tion that may be induced by MSP is the recruitment of circu- lating monocytes into the glomerulus. In fact, MSP has a che- moattractant action on macrophages that are derived from monocytes. As yet, however, we ignore whether circulating monocytes express RON, and indeed the role of MSP in the pathogenesis of glomerulonephritis or any else inflammatory disease has never been investigated. This study was performed to understand whether the MSP/ RON system plays a pathogenic role in mesangial proliferative glomerulonephritis. We investigated MSP/RON in anti–Thy 1 glomerulonephritis because in this experimental disease, both proliferation of resident mesangial cells and influx of circulating monocytes into the glomerular tuft (17–19) are proven pathogenic mechanisms. We aimed also to demonstrate in vitro that mono- cytes express RON and are attracted by MSP when they are activated, to support the concept that MSP can work in disease as an effector of monocyte recruitment and inflammation. Materials and Methods We performed experiments in vivo and in vitro. In vivo, we investi- gated whether in anti–Thy 1 glomerulonephritis (1) plasma and urinary levels of MSP and glomerular expression of RON and MSP are en- hanced and (2) blockade of MSP prevents glomerular injury, leukocyte influx, and renal failure (rise in plasma creatinine, proteinuria). The experiments in vitro aimed to understand whether monocytes express RON and whether MSP has a chemotactic effect on monocytes. Received June 30, 2006. Accepted February 13, 2007. Published online ahead of print. Publication date available at www.jasn.org. Address correspondence to: Dr. Teresa Rampino, Unit of Nephrology, Dialysis, Transplantation, IRCCS Policlinico San Matteo, Pavia, Italy. Phone: +39-0382- 422037; Fax: +39-0382-526341; E-mail: t.rampino@smatteo.pv.it Copyright © 2007 by the American Society of Nephrology ISSN: 1046-6673/1805-1486