Hepatic stellate cells and portal fibroblasts are the major cellular sources of collagens and lysyl oxidases in normal liver and early after injury

Abstract

Perepelyuk M, Terajima M, Wang AY, Georges PC, Janmey PA, Yamauchi M, Wells RG. Hepatic stellate cells and portal fibroblasts are the major cellular sources of collagens and lysyl oxidases in normal liver and early after injury. Am J Physiol Gastrointest Liver Physiol 304: G605-G614, 2013. First published January 17, 2013 doi:10.1152/ajpgi.00222.2012.-Liver fibrosis is characterized by excessive deposition of extracellular matrix proteins by myofibroblasts derived from hepatic stellate cells and portal fibroblasts. Activation of these precursors to myofibroblasts requires matrix stiffness, which results in part from increased collagen crosslinking mediated by lysyl oxidase (LOX) family proteins. The aims of this study were to characterize the mechanical changes of early fibrosis, to identify the cells responsible for LOX production in early injury, and to determine which cells in normal liver produce collagens and elastins, which serve as substrates for LOXs early after injury. Hepatocytes and liver nonparenchymal cells were isolated from normal and early-injured liver and examined immediately for expression of LOXs and matrix proteins. We found that stellate cells and portal fibroblasts were the major cellular sources of fibrillar collagens and LOXs in normal liver and early after injury (1 day after bile duct ligation and 2 and 7 days after CCl 4 injury). Activity assays using stellate cells and portal fibroblasts in culture demonstrated significant increases in LOX family enzymatic activity as cells became myofibroblastic. LOX family-mediated deoxypyridinoline and pyridinoline cross-links increased after CCl 4-mediated injury. There was a significant association between liver stiffness (as quantified by the shear storage modulus G=) and deoxypyridinoline levels; increased deoxypyridinoline levels were also coincident with significantly increased elastic resistance to large strain deformations, consistent with increased cross-linking of the extracellular matrix. These data suggest a model in which the liver is primed to respond quickly to injury, activating potential mechanical feed-forward mechanisms.collagen cross-linking; liver fibrosis; pyridinoline; deoxypyridinoline; extracellular matrix PATHOLOGICAL FIBROSIS is characterized by excessive accumulation of extracellular matrix (ECM) proteins, most notably fibrillar collagens. The majority of ECM in organ fibrosis is deposited by myofibroblasts, proliferative and motile cells characterized by expression of ␣-smooth muscle actin (␣-SMA), which migrate to the site of injury or differentiate from preexisting cells in the organ. In the liver, the major myofibroblast precursor cells are hepatic stellate cells and portal fibroblasts.Myofibroblast differentiation from precursor cells requires mechanical tension. This has been shown in vitro for general fibroblast-to-myofibroblast activation (14), as well as for hepatic stellate cell and portal fibroblast activation to myofibroblasts in the liver (19,36) and suggests that increases in liver stiffness precede myofi...

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