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Abnormalities in lipoprotein metabolism are common in diabetes. It is unknown whether variations in form or concentration of lipoproteins influence the function of pancreatic β cells. This study investigates whether low density lipoproteins (LDL) exhibit specific interactions with islet β cells. Radioactively labeled LDL (125I-LDL) and fluorescently labeled LDL (DiI-LDL) were used as tracers. Rat islet cells express high affinity LDL binding sites (Kd = 9 nm), which are also recognized by very low density lipoproteins and which are down-regulated by LDL. Binding of LDL appears restricted to the β cells, as it was not detected on islet endocrine non-β cells. At 37 C, LDL is taken up and lysosomally degraded by islet β cells but not by islet non-β cells. Human islet cells were also found to present LDL binding, uptake, and degradation. Compared with rat islet cells, human islet cells exhibit 10-fold less binding sites (2.107vs. 2.108 per 103 cells) with a 2-fold lower Kd value (5 nm) and an equal sensitivity to LDL-induced down-regulation. In conclusion, human and rat islet β cells express LDL receptors that can internalize the lipoprotein. This pathway should be examined for its potential role in (dys)regulating pancreatic β cell functions.

Low Density Lipoprotein Binding and Uptake by Human and Rat Isletβ Cells*