Effect of Diabetes on In Vivo Metabolism of [35S]-labeled Glomerular Basement Membrane

Abstract

Glomerular basement membrane (GBM) was labeled in vivo by the injection of tracer amounts of [35S]-sulfate into normal and streptozotocin-diabetic rats. The biosynthesis and turnover of sulfated glycosaminoglycans in the GBM was determined from the specific activity of [35S] after pronase digestion of basement membranes purified from glomeruli isolated 1-7 days after injection. Peak radiolabeling of both normal and diabetic GBM occurred 24 h after injection and, when corrected for differences in serum sulfate specific activities, was less in diabetic than in normal samples. The specific activity of GBM sulfate, expressed as cpm/microgram uronic acid, progressively diminished over the ensuing period of study in both normal and diabetic samples. The rate of decrease in specific activity of [35S]-labeled GBM was not significantly different in diabetic preparations compared with that in normal controls. The findings are compatible with diminished sulfation and/or production but normal turnover of glycosaminoglycans in the renal GBM in experimental diabetes.

Disturbances in Glomerular Basement Membrane Glycosaminoglycans in Experimental Diabetes

“…Furthermore, our experiments demonstrate that the GAG content of the intracellular material released with osmotic lysis is significantly decreased in diabetic glomeruli. Together with the results of a previous study showing that the in vivo turnover of 35 S-labeled GAG is unchanged in diabetes, although 35 S incorporation is reduced (11), these findings strongly suggest that a decrease in GAG production is responsible for the decrease in anionic sites of GBM associated with diabetes. Although subtle differences in the degree of sulfation of GAGs do not appear to alter their ability to compete in the binding assay (18), our results do not exclude the possibility that such differences exist between the heparan sulfate of normal versus diabetic GBM.…”

“…In this regard, GAGs of the renal glomerular basement membrane (GBM) are of particular interest, because they constitute anionic sites that regulate the chargeselective nature of the glomerular filtration barrier (4)(5)(6)(7)(8) and have been implicated in the pathogenesis of the increased glomerular permeability occurring in diabetes and other proteinuric states (9). The findings that incorporation of [ 35 S]sulfate into basement membrane proteoglycans is diminished in diabetes (10)(11)(12)(13)(14) and that removal of heparan sulfate by an in situ enzymatic digestion leads to a dramatic increase in the permeability of GBM to ferritin (7) and 125 Ilabeled albumin (8) lend support to the hypothesis that alterations in basement membrane GAGs contribute to the defective function of the glomerular filtration barrier in diabetes. It is not clear, however, whether such changes are qualitative or quantitative, because there are conflicting reports regarding the amount of measurable uronic acid or proteoglycan, the latter determined by ELISA with antibody directed against core protein, in basement membranes from diabetic subjects or experimental animals compared with controls (10)(11)(12)14,15).…”

“…The findings that incorporation of [ 35 S]sulfate into basement membrane proteoglycans is diminished in diabetes (10)(11)(12)(13)(14) and that removal of heparan sulfate by an in situ enzymatic digestion leads to a dramatic increase in the permeability of GBM to ferritin (7) and 125 Ilabeled albumin (8) lend support to the hypothesis that alterations in basement membrane GAGs contribute to the defective function of the glomerular filtration barrier in diabetes. It is not clear, however, whether such changes are qualitative or quantitative, because there are conflicting reports regarding the amount of measurable uronic acid or proteoglycan, the latter determined by ELISA with antibody directed against core protein, in basement membranes from diabetic subjects or experimental animals compared with controls (10)(11)(12)14,15). Furthermore, reduced radioactive sulfate incorporation may reflect decreased GAG production or undersulfation of GAG chains in diabetes; there is some support for the latter possibility in at least two reports, which describe fewer sulfate groups in the heparan sulfate proteoglycan isolated from liver plasma membranes of streptozocin-induced diabetic (STZ-D) rats (16) and in the [ 35 S]heparan sulfate prepared from intestinal epithelial cells of diabetic animals (17).…”

Reduced transcapillary escape of albumin during acute blood pressure-lowering in Type 1 (insulin-dependent) diabetic patients with nephropathy

“…A loss of the charge selective properties and increased pore size of the glomerular capillary wall con-tribute to albuminuria in diabetic nephropathy [23,24]. Studies in diabetic animals have suggested a decreased rate of synthesis of acid glycosaminoglycans in the renal and extra-renal microvasculature [25][26][27].…”

Selective proteinuria in diabetic nephropathy in the rat is associated with a relative decrease in glomerular basement membrane heparan sulphate

“…Biochemical quantitation of HS in the GBM, in glomeruli or in renal cortex revealed a decreased [23][24][25][26] or unaltered [27,28] HS content in rats with STZ-induced diabetic nephropathy. Others studied HS synthesis in GBM or glomeruli by in vivo 35S-sulphate incorporation, which revealed either a decreased [25,26,29] or normal [30,31] synthesis of HS. Studies using ex vivo (isolated perfused kidney) or in vitro (short-term culture of glomeruli) 35S-sulphate incorporation suggest a decreased HS synthesis [32,33], although this was not been found by all investigators [30].…”