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The role of glucocorticoids in the regulation of the diurnal rhythm of hepatic beta-hydroxy-beta-methylglutaryl-coenzyme A reductase and cholesterol 7 alpha-hydroxylase.

ABSTRACT: The microsomal activities of the hepatic enzymes hydroxymethylglutaryl-CoA reductase and cholesterol 7 alpha-hydroxylase exhibit a diurnal rhythm with maximum activities observed during the dark period and minimum activities around noon (12:00h). This diurnal rhythm was maintained for both enzymes after adrenalectomy, but the amplitude of variation for the activity of both enzymes was greatly decreased. A single injection of cortisol administered to adrenalectomized rats 3h before the expected maximum in enzyme activity resulted in a twofold increase in the activity of both enzymes 3h later, at values similar to those observed for control rats killed at the same time. This response appeared to require protein synthesis, since it was blocked by actinomycin D. However, the administration of cortisol to adrenalectomized rats 3 h before the expected minimum did not result in significant change in the activity of hydroxymethylglutaryl-CoA reductase and cholesterol 7 alpha-hydroxylase 3 h later. Kinetic studies of cholic acid metabolism in vivo demonstrated that adrenalectomy results in a significant decrease in the rate of synthesis of cholic acid and a considerable decrease in the pool size of cholic acid and its metabolic products. Treatment of adrenalectomized rats with cortisol increased the rate oonsistent with the effects of adrenalectomy and cortisol treatment on the activity of cholesterol 7alpha-hydroxylase.

SUBMITTER: Mitropoulos KA

PROVIDER: S-EPMC1164200 | biostudies-other | 1976 Oct

REPOSITORIES: biostudies-other

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Project description:In addition to inducing a self-limited myopathy, statin use is associated with an immune-mediated necrotizing myopathy (IMNM), with autoantibodies that recognize ?200-kd and ?100-kd autoantigens. The purpose of this study was to identify these molecules to help clarify the disease mechanism and facilitate diagnosis.The effect of statin treatment on autoantigen expression was addressed by immunoprecipitation using sera from patients. The identity of the ?100-kd autoantigen was confirmed by immunoprecipitation of in vitro-translated 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) protein. HMGCR expression in muscle was analyzed by immunofluorescence. A cohort of myopathy patients was screened for anti-HMGCR autoantibodies by enzyme-linked immunosorbent assay and genotyped for the rs4149056 C allele, a predictor of self-limited statin myopathy.Statin exposure induced expression of the ?200-kd/?100-kd autoantigens in cultured cells. HMGCR was identified as the ?100-kd autoantigen. Competition experiments demonstrated no distinct autoantibodies recognizing the ?200-kd protein. In muscle biopsy tissues from anti-HMGCR-positive patients, HMGCR expression was up-regulated in cells expressing neural cell adhesion molecule, a marker of muscle regeneration. Anti-HMGCR autoantibodies were found in 45 of 750 patients presenting to the Johns Hopkins Myositis Center (6%). Among patients ages 50 years and older, 92.3% had taken statins. The prevalence of the rs4149056 C allele was not increased in patients with anti-HMGCR.Statins up-regulate the expression of HMGCR, the major target of autoantibodies in statin-associated IMNM. Regenerating muscle cells express high levels of HMGCR, which may sustain the immune response even after statins are discontinued. These studies demonstrate a mechanistic link between an environmental trigger and the development of sustained autoimmunity. Detection of anti-HMGCR autoantibodies may facilitate diagnosis and direct therapy.

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The role of glucocorticoids in the regulation of the diurnal rhythm of hepatic beta-hydroxy-beta-methylglutaryl-coenzyme A reductase and cholesterol 7 alpha-hydroxylase.

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