Expression of fibroblast growth factors and their receptors in rat glomeruli

Fibroblast growth factors (FGFs) regulate cell proliferation and differentiation, and are also important regulators of extracellular matrix. They are among the most potent angiogenic factors known. Evidence suggests the FGFs play a role in glomerular development and pathology. The aim of the present study was to determine whether FGF-1 (acidic FGF) and FGF-2 (basic FGF) and their receptors (FGFRs) were expressed in normal adult rat glomeruli, using reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. For RT-PCR studies, the kidneys of 200 g female Sprague-Dawley rats were perfused with buffer and glomeruli isolated using conventional sieving techniques followed by micropipetting. FGF-1 and FGF-2 were expressed in cortex and in glomeruli. All seven receptor isoforms assayed (FGFR1, 2 and 3 IIIb and IIIc splice variants, and FGFR4) were expressed in whole cortex. However, only the IIIc variants and FGFR4 were expressed in glomeruli. The relative levels of glomerular expression of these isoforms were determined using a semiquantitative RT-PCR assay using primers designed against three transmembrane regions; FGFR1 (100%); FGFR2 (0.1%); and FGFR4 (6%). Immunohistochemistry revealed specific immunostaining for all four FGFRs within glomeruli. The differential expression pattern of FGFR isoforms between glomeruli and whole cortex, and the mutually exclusive nature of the expression of IIIc but not IIIb isoforms within glomeruli, indicates that FGFR expression and thereby FGF activity is tightly regulated in glomeruli. These findings have important implications for the roles of the FGFs in glomerular health and disease.