Hypercholesterolemia aggravates experimental progressive glomerular injury. Evidence suggests the infiltrating glomerular macrophage (M phi) is a potential effector mechanism for the noxious effects of hypercholesterolemia. Because transforming growth factor (TGF)-beta 1 is secreted by activated M phi s and also stimulates fibronectin production by glomerular cells, we evaluated the kinetics of gene expression for these moieties in glomeruli isolated from nephrotic rats at 3, 7, 11, and 42 days after the delivery of puromycin aminonucleoside (PA). We also assessed whether cholesterol feeding, which raises the glomerular M phi number, alters the glomerular mRNA levels for TGF-beta 1 and fibronectin. Glomerular mRNA levels for TGF-beta 1 and fibronectin in nephrotic rats exhibited a biphasic temporal pattern, decreasing significantly below control at 3 and 7 days after PA but increasing significantly at 11 and 42 days after PA. The upregulated gene expression for TGF-beta 1 and fibronectin at 11 days after PA temporally corresponded to the phase of mesangial M phi infiltration in this model. Cholesterol feeding to both normal and nephrotic rats significantly increased glomerular TGF-beta 1 and fibronectin mRNA levels at 11 days after PA. Immunohistochemical labeling for M phi s and intracellular TGF-beta 1 demonstrated both mesangial and cortical interstitial localization with the TGF-beta1-positive cells possessing M phi nuclear morphology. These findings identify a novel interaction between hypercholesterolemia, augmented glomerular M phi accumulation, and upregulated glomerular TGF-beta 1 and fibronectin gene expression. These perturbations within the acutely injured glomerulus constitute an early pathobiological determinant for the later development of mesangial matrix expansion and glomerulosclerosis.