Thrombospondin secretion by cultured human glomerular mesangial cells.

Thrombospondin is a high-molecular-weight glycoprotein constituent of extracellular matrices of several cells in culture. Immunoreactive thrombospondin is also present within the normal human renal mesangium. To determine whether this thrombospondin could be a synthetic product of the intrinsic glomerular mesangial cells, we examined cultured human glomerular mesangial cells for the ability to synthesize and secrete thrombospondin. Well-characterized human mesangial cells were found to synthesize and secrete thrombospondin, as determined by specific immunostaining at the light- and electron-microscopic levels. Furthermore, metabolically labeled thrombospondin was immunoprecipitated from the conditioned medium of cultured cells. These studies suggest that the thrombospondin present within the normal mesangium is of intrinsic glomerular cell origin. Mesangial thrombospondin may be an important mediator of cellular function, particularly in disease states characterized by intrinsic glomerular cell proliferation.