Chromatin clearance in C57Bl/10 mice: interaction with heparan sulphate proteoglycans and receptors on Kupffer cells

Chromatin is an important autoantigen in the pathogenesis of systemic lupus erythematosus (SLE) as an immunogen and as a part of nephritogenic immune complexes. Earlier studies focused on clearance of DNA. However, DNA releas ed into the circulation from dying cells is found associated with histones in nucleosomes. The liver is the major organ involved in clearance of chrom atin from the circulation of mice. Heparan sulphate proteoglycans (HSPG) ha ve been implicated in the clearance of various charged molecules. Receptor- mediated clearance of ssDNA by the liver has also been reported. Because ch romatin contains positively charged histones in addition to DNA, we wished to determine if HSPG and/or DNA receptors are involved in chromatin clearan ce. The rate of clearance of HI-stripped chromatin from the bloodstream of C57B1/10 mice was markedly decreased by prior treatment of mice with Hepari nase I. Clearance was also inhibited by heparin, heparan sulphate, and DNA, but not by colominic acid. DNA was the most effective inhibitor of clearan ce and released chromatin from sites of clearance. Depletion of Kupffer cel ls and splenic macrophages using liposome-encapsulated Clodronate (dichloro methylene bisphosphonate) markedly inhibited chromatin clearance. These dat a suggest that chromatin clearance is mediated by charge interactions with cell surface HSPG and by DNA receptors. Clearance and degradation of chroma tin require functional macrophages in the liver and spleen.