Rat liver fat-storing cell lines express sarcomeric myosin heavy chain mRNA and protein

Fat-storing cells (FSC, lipocytes, or Ito cells) of liver store vitamin A and are the main producers of extracellular matrix in normal and cirrhotic liver. During liver injury, FSC undergo an activation process characterized by a decrease in vitamin A storage and an increase in cell proliferation and extracellular matrix deposition. This activation process also occurs upon culturing FSC from normal liver. In contrast to most cells of nonmuscle origin, activated FSC express two cytoskeletal proteins normally found in muscle, desmin, and smooth muscle alpha-actin. Based on their strategic perisinusoidal location, it has been hypothesized that FSC play a role in regulating blood flow. However, the nature of the contractile elements involved in this process remains to be determined. In this communication we demonstrate the presence of a sarcomeric myosin in proteins solubilized from liver biomatrix. In addition we demonstrate the expression of sarcomeric myosin heavy chain (MHC) mRNA and protein in two FSC clones derived from a CCl4-cirrhotic rat liver (CFSC). Through cloning the cDNA corresponding to the MHC gene expressed in these cells we demonstrate that it encodes fast IId skeletal MHC and thus represents a marker normally seen in adult muscle. The unexpected expression of an adult stage skeletal muscle molecular motor in FSC from cirrhotic liver is consistent with the proposed specialized contractile capacity of these cells.