SYNTHESIS OF SULFATED PROTEOGLYCANS BY PRIMARY CULTURES OF RAT HEPATOCYTES - MODULATION BY MATRIX SUBSTRATUM

Primary cultures of rat hepatocytes maintained on different matrix pro teins such as collagen (Co IV) fibronectin (Fn), Laminin (Ln) or diffe rent tissue biomatrices were metabolically labelled with (35)[S]-SO4 a nd the synthesis of sulphated proteoglycans was studied. The incorpora tion of the label into total glycosaminoglycan (GAG) was significantly higher in cells maintained on Co IV compared to those maintained on F n or Ln. Similarly the incorporation of label was maximum in those cel ls maintained on the aortic biomatrix compared to liver or mammary gla nd biomatrix. About 80-95% of the GAG synthesised and secreted by cell s maintained on individual matrix proteins and liver biomatrix was hep aran sulphate (HS). But in the case of cells maintained on collagen IV aortic or mammary biomatrix in addition to HS, significant amount of chondroitin sulphate (CS) was also found. Nearly 50% of the total (35) [S]-GAG was associated with the cell layer after 24 h in culture in th e case of cells maintained on individual matrix protein while those ma intained on tissue biomatrix, retained about 70% of the (35)[S]-labell ed proteoglycans (PG) with the cell layer. Analysis of the cell surfac e (35)[S]-labelled proteoglycans isolated from cells maintained on dif ferent biomatrix showed that it is a hybrid proteoglycan consisting of CS and HS. While the PG isolated from cells maintained on liver bioma trix consists of HS and CS in the ratio of 3:2 that from cells maintai ned on aorta or mammary gland matrix was about 2:3 indicating an alter ation in the nature of the cell surface PGs produced by cells maintain ed on different tissue biomatrix. These results indicate that dependin g on the nature of the matrix substratum with which the cells are in c ontact, the nature and quantity of sulphated proteoglycans produced by hepatocytes vary.