Oxidized low-density lipoproteins bind to the scavenger receptor, CD36, ofhepatic stellate cells and stimulate extracellular matrix synthesis

Cumulating evidence suggests that oxidative stress resulting in lipid perox idation and protein modification is involved in the pathogenesis of chronic liver injury and fibrogenesis. We investigated the effects of oxidized low -density lipoproteins (oxLDL) on collagen and fibronectin synthesis of cult ured human and rat hepatic stellate cells (HSC). As shown on protein and mR NA levels, oxLDL dose-dependently stimulated the synthesis of collagen type s I and III and fibronectin of cultured HSC. The effect was biphasic, with a maximum between 5 and 25 mug/mL oxLDL (c-fibronectin concentration in HSC supernatants increased 3.9-fold; collagen type I increased 4-fold). Higher oxLDL concentrations were cytotoxic. LDL modified with malondialdehyde (MD A) was not toxic, but stimulated extracellular matrix synthesis as well. As demonstrated by immunofluorescence microscopy (double staining of CD36 and iso-alpha -smooth muscle actin [iso-alpha -sm actin]), immunoblot, and rev erse-transcription polymerase chain reaction (RT-PCR), respectively, cultur ed human HSC express the oxLDL receptor, CD36 (glycoprotein IIIb). Colocali zation of CD36 and iso-a-sm actin on sinusoidal lining cells was further de monstrated using sections of human fibrotic liver. Preincubation of culture d human HSC with the monoclonal antibody, OKM5, known to block CD36-mediate d oxLDL uptake, resulted in a reduction of the oxLDL-stimulated collagen ty pe I synthesis by 56%. In summary, our results demonstrate that low concent rations of modified lipoproteins (oxLDL and MDA-LDL) represent fibrogenic m ediators that bind to CD36 and stimulate matrix synthesis of HSC.