REGULATORY ROLE OF TRIIODOTHYRONINE IN THE DEGRADATION OF LOW DENSITY LIPOPROTEIN BY CULTURED HUMAN SKIN FIBROBLASTS

Abstract

Degradation of [¹²⁵I]-labeled low density lipoprotein (LDL) by cultured normal human skin fibroblasts was enhanced by exposure to concentrations of L-triiodothyronine (T₃) spanning the physiological range. Analysis of LDL concentration curves suggests that To may increase LDL receptor number rather than alter the affinity of LDL for its receptor. No effect of T₃ on LDL degradation was observed in receptor negative cells. Thus thyroid hormone appears to regulate receptor-mediated LDL degradation by increasing the binding of the lipoprotein to its cell-surface receptor.