The Role of Integrin-linked Kinase in Liver Wound Healing

Abstract

Liver wound healing is an integrated process in which hepatic stellate cells play a major role. We hypothesized that the cellextracellular signaling protein integrin-linked kinase (ILK) is important in transducing signals from the extracellular matrix to stellate cells and thus plays a critical role in stellate cell activation and fibrogenesis during liver injury. Liver injury and subsequent stellate cell activation led to a 3-fold increase in ILK expression and increased kinase activity. Overexpression of ILK in isolated stellate cells led to enhanced motility and adhesion as well as increases in smooth muscle ␣-actin and type I collagen mRNA expression. The effects of ILK on stellate cell phenotypes were phosphatidylinositol 3-kinase-dependent. Forced expression of ILK in vivo led to increases in type I collagen, smooth muscle ␣-actin, transforming growth factor-␤, and extra domain A (EDA) fibronectin mRNAs (by 3.2-, 3.5-, 2.5-, and 2.2-fold, respectively; n ‫؍‬ 8, p < 0.05 for each versus the control), whereas inhibition of ILK in vivo led to significant reductions in these mRNAs. Morphometric analysis revealed that ILK overexpression led to a 31.4% increase in liver collagen content (n ‫؍‬ 8, p < 0.05 versus the control); in contrast ILK knockdown in vivo led to a significant reduction in fibrogenesis. We conclude that ILK plays an important pathophysiological role in vivo in liver wound healing.The liver responds to injury by wound healing, leading to fibrosis. The multiple integrated systems leading to fibrosis are complex and are similar mechanistically to that in skin and other parenchymal organs. A remarkable increase in extracellular matrix production after wounding is characteristic and is typified by a 4 -6-fold increase in collagens (i.e. types I, III, and IV, etc.) as well as an increase in many other extracellular matrix constituents (1). Investigation over the past two decades has helped to establish a cellular mechanism for the woundhealing response to liver injury (2). A critical feature of this wounding response is the transformation of resident stellate cells (also known as lipocytes, Ito cells, or perisinusoidal cells) from the "quiescent" state in the normal liver to an "activated" state in the injured liver. This transition is characterized by both morphologic and functional changes, including loss of vitamin A, acquisition of stress bundles, development of prominent rough endoplasmic reticulum, and a striking increase in the secretion of extracellular matrix proteins, as well as enhanced stellate cell contractility, motility, proliferation, adhesion, and responsiveness to various cytokines and peptides found in the wounding milieu (3).Integrin-linked kinase (ILK) 2 is a newly described signaling molecule important in transducing signals from the extracellular matrix to cellular machinery through the cytoplasmic portion of integrins and adaptor proteins to a variety of signaling cascades (4 -8). For example, ILK interaction with integrins is important in cell growth, differentiation, cell ...

Loss of integrin linked kinase from mouse hepatocytesin vitro andin vivo results in apoptosis and hepatitis

“…49 Altogether, our results clearly show that elimination of integrin signaling by removal of ILK causes apoptosis in primary cultured hepatocytes, as well as in hepatocytes in the whole liver. Thus, ILK is of great importance for the liver in general, consistent with recent work by Shafiei and Rockey 50 highlighting the importance of ILK in liver wound healing.…”

Transforming growth factor-β and substrate stiffness regulate portal fibroblast activation in culture

“…Potential mechanosensors such as integrins along with their downstream signaling pathways might be attractive therapeutic targets. 48,49 In summary, we have characterized portal fibroblast activation in vitro and have demonstrated that both TGF-␤ and matrix stiffness are critical for activation to occur. The demonstration that PFs and HSCs are morphologically, geographically, and functionally distinct may have important implications for both the study and treatment of fibrosis.…”

Adiponectin Regulation of Stellate Cell Activation via PPARγ-Dependent and -Independent Mechanisms

“…23 Adenovirus encoding Cre recombinase (Ad-Cre) was purchased from Vector Biolabs (Philadelphia, PA). Viruses were amplified and titered according to the manufacturer's instructions (BD Biosciences, San Jose, CA).…”

“…Stellate cells were isolated as described above, plated on 35-mm dishes at approximately 85% confluency and at the specified stage of culture were routinely infected as described previously. 23 Infection efficiency was monitored by the expression of GFP and typically reached 80% to 90% within 48 hours.…”