Effects of Autoantibodies to the Insulin Receptor on Isolated Adipocytes

Abstract

A B S T R A C T Autoantibodies to the insulin receptor have been detected in the sera of several patients with the Type B syndrome of insulin resistance and acanthosis nigricans. In this study we have used three of these sera (B-1, B-2, and B-3) as probes ofthe insulin receptor in isolated rat adipocytes. Preincubation of adipocytes with each of the three sera resulted in an inhibition of subsequent [1251]insulin binding. 50% inhibition of binding occurred with serum dilutions of 1:5 to 1:7,500. As in our previous studies with other tissues, Scatchard analysis of the insulin-binding data was curvilinear consistent with negative cooperativity. Computer analysis suggested that in each case the inhibition of binding was due to a decrease in receptor affinity rather than a change in available receptor number.In addition to the effects on insulin binding, adipocytes pretreated with antireceptor sera also showed alterations in biological responses. All three sera produced some stimulation of basal glucose oxidation. With serum B-3, maximal stimulation of glucose oxidation occurred at a serum concentration that inhibited binding by only 10-15%, whereas with serum B-2 the dilution curves for inhibition of binding and stimulation of glucose oxidation were superimposable. Serum B-1 behaved as a partial agonist; that is, it inhibited binding more effectively than it stimulated glucose oxidation. Cells pretreated with this serum in a concentration which inhibited binding by 80% also showed a five-fold shift to the right in the dose response of insulin-stimulated glucose oxidation, whereas sperminestimulated glucose oxidation was unaffected. Serum B-2, which contained the highest titer of antireceptor

Differing effects of antiinsulin serum and antiinsulin receptor serum on 123I-insulin metabolism in rats.

“…Bovine insulin was iodinated with 125I in a similar manner and also purified by high pressure liquid chromatography. Antiserum to the insulin receptor (AIRS)' was from patient B2 and was previously well characterized (6,8,9). This serum has been shown to contain no detectable anti-insulin antibodies but has a high titer of anti-receptor antibodies.…”

“…To determine to which liver cell type radioactivity was bound, two control and two AIS-treated rats received 0.5 gCi/g '1251-insulin. 9 min later, the animals were sacrificed, their livers were dissected, fixed, and sectioned, and autoradiographs were prepared as previously described (11) (12). Criteria of homoskedasticity were satisfied by log transformation of the variables and statistical differences were determined with the Snedecor (F) test in the BMDP program (12).…”

Protein kinase activity of the insulin receptor

“…1). The dual role of insulin receptors in metabolic regulation and hormone degradation is based on two kinds of experimental evidence: (1) that receptor occupancy elicits biological effects (Gliemann et al, 1975) and leads to insulin degradation (Terris & Steiner, 1975) and (2) that modifications of receptors by trypsin or antibodies to insulin receptors are followed by reduced insulin action (Kono & Barham, 1971;Kahn et al, 1977) and impaired proteolysis of insulin (Terris & Steiner, 1975). Morphological and biochemical studies have provided evidence that receptor-bound insulin is translocated from the surface to the interior of the cell (for reviews see Gorden et al, 1980;Bergeron et al, 1985).…”

“…Thus, under physiological conditions, maximal effects are obtained by receptor occupancies of -90% in liver versus -5-10% in fat cells (Gammeltoft, 1984). Structural differences may also exist because antigenic determinants and glycosylation of insulin receptors in liver and fat cells seem to vary whereas the molecular size and subunit composition are similar (Kahn et al, 1977;Pottick et al, 1981). Insulin receptors are widespread in mammalian brain (Havrankova et al, 1978;Hendricks et al, 1983) and recent observations suggest that they may represent a structural and functional receptor subtype among insulin receptors (for review see Gammeltoft et al, 1985a).…”

Nonbinding inhibitory antiinsulin receptor antibodies. A new type of autoantibodies in human diabetes.

“…In vitro, unlike binding-inhibitory AIRA (24), nonbinding-inhibitory AIRA did not inhibit insulin binding, nor did they stimulate glucose oxidation. As far as in vivo activities are concerned, it is noteworthy that none of the five IDDM patients appeared to be insulin resistant (as judged by their daily insulin requirements), while only one of four NIDDM patients had hyperinsulinemia (not associated with obesity) which was probably indicative of insulin resistance (Table II) …”