Role of Macrophage Stimulating Protein 1 (MSP1) in the Development of Glomerulopathy in Sickle Cell Disease

Background

More than 50% patients with sickle cell disease (SCD) develop renal glomerular disease. Its pathophysiology is likely to be multifactorial, being affected by hyperfiltration, glomerular hypertension, ischemia-reperfusion injury, oxidative stress, and endothelial dysfunction. Ischemia-reperfusion is associated with significant recruitment of glomerular and interstitial macrophages. Recently, Macrophage Stimulating Protein 1 (MSP1) was shown to be involved in the development of anti-Thy1 glomerulonephritis in rat model that also associated with renal macrophages infiltration. MSP1 is produced by the liver and secreted into the circulation as a non-active protein. It is cleaved and activated locally by a macrophage membrane-associated proteinase. We hypothesesize that infiltrating macrophages in SCD activate MSP1 protein that accumulates in the renal glomeruli and induces endothelial cell and podocytes injury.

Objective

We analyzed MSP1 expression in vivo in SCD mouse model and the effect of recombinant MSP1 on cultured human podocytes and endothelial cells.

Methods

Transgenic SCD mice were obtained from Jackson Laboratory (B6;129-Hba^tm1(HBA)Tow Hbb^{tm2(HBG1,HBB*)Tow}/Hbb^{tm3(HBG1,HBB)Tow}/J Townes strain). Townes mice produce approximately 94% human sickle (HbS), 6% human fetal hemoglobin (HbF), and no murine hemoglobin. Control animals are carrying two copies of the transgene encoding human α1-globin gene and two copies of the Hbb^{tm3(HBG1,HBB)Tow} mutation (human hemoglobin gamma (^Aγ) gene and the human wildtype hemoglobin beta (β^A) gene). Townes mice spontaneously develop renal glomerular lesions. Kidneys were collected from 5 months old mice and immunohistochemistry (IHC) was carried to detect macrophages, endothelial cells (CD34), podocytes (WT-1) and MSP1. Human glomerular endothelial cell line (HGEC) and two human podocyte lines (PD1 and PD2) were treated with recombinant MCP1 and the cellular motility, permeability, growth and capillary formation were analyzed.

Results

SCD mice developed focal segmental glomerulosclerosis. It was associated with glomerular capillary aneurisms, loss of podocytes and increased macrophages infiltration. IHC demonstrated accumulation of MSP1 in the capillaries of affected glomeruli. In vitro, MSP1 treatment increased motility of both endothelial cells and podocytes. In addition, MSP1 significantly reduced podocytes growth and viability. MSP1 also inhibited capillary formation by endothelial cells on Matrigel.

Conclusion

Activated MSP1 is likely to be involved in the development of glomerular lesions in SCD which could be due to the modulation of endothelial cell and podocytes function. Further analysis is needed to elucidate the role of MSP1 in the development of glomerular disease in humans.

Acknowledgments

This work was supported by NIH Research Grants (1P50HL118006, 1R01HL125005 and 5G12MD007597). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.