Maturation of the developing renal glomerulus with respect to basement membrane proteoglycans

Maturation of extracellular matrices in relation to heparan sulfate proteoglycans was investigated during glomerular development. Antibodies directed against the core-protein (M(r) = 18,000) of the basement membrane heparan sulfate-proteoglycan were utilized. The IgG fraction of the antibodies was conjugated with either fluorescein or rhodamine or ¹²⁵I-iodine. The fluoresceinated and radioiodinated antibodies were given intravenously to three-day-old rats; their kidneys were obtained 6, 48, and 120 hours later and processed for immunohistochemical and tissue autoradiographic studies. At six hours (day 0), matrices of all the stages were labeled. The labeling was lowest in the vesicle stage and highest in the capillary stage. The autoradiographic grain-densities of vesicle, S-shaped, precapillary, and capillary stages were 10.62 ± 0.54, 7.44 ± 0.65, 11.37 ± 1.03, and 18.35 ± 1.97, respectively. After 48 hours (day 5), the grain-density for S-shaped body decreased from 7.44 ± 0.65 to 4.38 ± 0.61, while no appreciable change in the precapillary and capillary stages was observed. At this time interval, the fluorescein-labeled glomeruli were seen in the deeper cortex only. After 120 hours (day 8), the grain-density for the capillary stage decreased from 18.35 ± 1.97 to 2.82 ± 0.92. The double-labeling experiments included a second injection of rhodaminated antibody at 48 hours (day 5). In these experiments, newly developed glomeruli of varying stages were seen in the superficial cortex. With the use of double filters, the immature glomeruli in the superficial cortex and mature ones in the deeper cortex were visualized. These data indicate the following: (a) during development, there is a concomitant appearance of extracellular matrices and proteoglycans; (b) the concentration of proteoglycans, as measured in terms of absolute number of autoradiographic grains, seems to rise dramatically at the time of epithelial-mesenchymal cells interaction, that is, at the S-shaped body stage; and (c) removal of the antibody bound to the core-protein or, alternatively, the turnover of the core-peptide of proteoglycan appears to be of a few days' duration.