John R. Hoyer

Studies on the rat glomerular basement membrane: Age-related changes in composition

To examine the effect of age on the glomerular basement membrane, compositional analyses were performed on membranes isolated in highly purified form from rats at different stages of their growth (35 to 200 days old). Substantial age-related changes were observed in the amino acid composition of the basement membranes. A significant correlation with age (P < 0.01) was evident in the contents of 3- and 4-hydroxyproline, threonine, serine, alanine, valine, half-cystine, hydroxylysine, and lysine. Of these amino acids, hydroxylysine and both isomers of hydroxyproline demonstrated a progressive increase with age, while the others were found to decline. The direct relationship of hydroxylysine content with age (P < 0.001) was associated with an inverse correlation of lysine with age (P < 0.001) so that the ratio of hydroxylysine to lysine increased in a highly significant manner from 0.92 at 35 days to 1.33 at 200 days. This elevation in the hydroxylysine content was accompanied by an augmentation in the number of saccharide units linked to it so that the percentage glycosylation of this amino acid was not significantly affected by age. The relative differences in the hydroxylysine and lysine levels between young and older rats were maintained in sodium dodecyl sulfateextracted membranes. These results suggest that the compositional changes observed during the aging process reflect an alteration in the subunit makeup of the basement membrane, possibly due to an increased synthesis or decreased degradation of the more collagen-like polypeptide components.

Extratubular Tamm-Horsfall protein deposits induced by ureteral obstruction in mice

The effects of unilateral ureteral obstruction were studied in mice. Obstruction for 24 hr led to the formation of extratubular Tamm-Horsfall protein (TH) aggregates within the renal interstitium and at the base of distal convoluted tubular (DCT) cells. These DCT deposits were shown by ultrastructural analysis to be entirely extracellular. They had the fibrillar substructure characteristic of TH and had not been seen after urinary obstruction in other species. As a consequence of retrograde flow of urine to glomeruli, obstruction also caused TH aggregates to form within Bowmans spaces. These glomerular casts of TH were detected throughout the 3-week period of study after the release of unilateral obstruction. High serum titers of IgG antibodies to TH developed in mice intradermally immunized with TH but were not observed after obstruction alone. Circulating anti-TH antibodies combined with TH present on the basal surfaces of the thick ascending limb of the loop of Henle cells and DCT cells to form immune complexes in situ. Interstitial inflammation in the areas surrounding subepithelial tubular immune deposits was not present in the kidneys of immunized mice and was not selectively induced by temporary obstruction. However, foci of inflammation were seen in all obstructed kidneys. At later times, inflammatory foci in previously obstructed kidneys were associated with progressive scarring, primarily in polar regions. The location and severity of these changes within kidneys produced by obstruction in immunized mice did not differ from those in unimmunized mice. The titers of anti-TH antibodies in immunized mice were not enhanced or depressed as a consequence of unilateral ureteral obstruction. These studies demonstrate that complete obstruction of urinary flow in the mouse for periods as short as 24 hr may lead to progressive segmental renal scarring. These studies further indicate that increasing the quantities of extracellular TH by obstruction does not facilitate inflammatory responses to TH immune complexes formed in situ. While exposure of renal tissue to highly toxic components of extravasated urine may play a crucial role in inflammatory responses, autoimmunity to TH was not implicated as a contributing factor by the present studies in mice.

Immunofluorescent localization of factor VIII-related antigen and fibrinogen in hyperacute xenograft rejection and in the Shwartzman reaction in the rat

Abstract Factor VIII-related antigen was localized by immunofluorescent microscopy to endothelial cells of all normal rat tissues in a pattern identical to that observed in human tissues and studied in experimental renal diseases. Glomerular capillaries in rabbit kidneys hyperacutely rejected by presensitized rats showed marked granular deposition of rat fibrinogen and factor VIII-related antigens derived from the host circulation. Renal glomerular capillary thrombi in the Shwartzman reaction induced by endotoxin in pregnant rats and in rats given nephrotoxic serum showed marked deposition of fibrinogen-related and factor VIII-related antigens. Unilateral renal perfusion studies showed that nephrotoxic serum prepares for the Shwartzman reaction by direct renal effects. The parallel deposition of fibrinogen and factor VIII-related antigens in these rat models is similar to observations in human renal disease and suggests participation of platelets and/or plasma coagulation in the evolution of such lesions.

GLOMERULAR CAPILLARY PERMEABILITY AND EXPERIMENTAL NEPHROTIC SYNDROME

Publisher Summary This chapter describes glomerular capillary permeability and experimental nephrotic syndrome. The glomerular capillary is relatively impermeable to most serum proteins. This impermeability that leads to virtual exclusion of proteins like albumen from the glomerular filtrate but permits complete permeation by inulin is thought to be related in part to the molecular dimensions of the protein. The presence of large quantities of serum proteins — principally albumin — in urine is a cardinal feature of the various forms of glomerular disease that affect man. A number of micropuncture studies have demonstrated protein in the proximal tubular fluid containing the glomerular filtrate. Different studies indicate that the glomerular basement membrane impedes filtration of proteins over a wide range of molecular size — with greater restriction for molecules of large size; the slit pore is an additional barrier for larger molecules that permeate the glomerular basement membrane.

Autoimmunity to Tamm-Horsfall Protein

Although interstitial inflammation and fibrosis, and tubular damage are prominent pathologic features in a variety of renal diseases, the pathogenesis of these lesions has received much less attention than have mechanisms of glomerular injury. Recently, clinical and experimental studies have shown that, in addition to well-established roles of immunologic mechanisms in glomerulonephritis, such immune mechanisms can cause tubulointerstitial nephritis also. Primary antibody-mediated tubular and interstitial lesions may be caused by either antibodies to tubular basement membranes (TBM) or by immune complexes. Anti-TBM-mediated nephritis is characterized by a smooth linear pattern of immunoglobulin fixed along the TBM, and the pathogenesis of these lesions has been discussed in detail (McCluskey and Colvin, 1978). In this discussion, features of tubulointerstitial nephritis mediated by immune complexes and having a granular staining pattern will be presented with emphasis on the pathogenesis of renal lesions produced by antibodies to Tamm-Horsfall protein (TH), a urinary glycoprotein of renal origin.