Molecular Mechanism Responsible for Fibronectin-controlled Alterations in Matrix Stiffness in Advanced Chronic Liver Fibrogenesis

Abstract

Fibrosis is characterized by extracellular matrix (ECM) remodeling and stiffening. However, the functional contribution of tissue stiffening to noncancer pathogenesis remains largely unknown. Fibronectin (Fn) is an ECM glycoprotein substantially expressed during tissue repair. Here we show in advanced chronic liver fibrogenesis using a mouse model lacking Fn that, unexpectedly, Fn-null livers lead to more extensive liver cirrhosis, which is accompanied by increased liver matrix stiffness and deteriorated hepatic functions. Furthermore, Fnnull livers exhibit more myofibroblast phenotypes and accumulate highly disorganized/diffuse collagenous ECM networks composed of thinner and significantly increased number of collagen fibrils during advanced chronic liver damage. Mechanistically, mutant livers show elevated local TGF-␤ activity and lysyl oxidase expressions. A significant amount of active lysyl oxidase is released in Fn-null hepatic stellate cells in response to TGF-␤1 through canonical and noncanonical Smad such as PI3 kinase-mediated pathways. TGF-␤1-induced collagen fibril stiffness in Fn-null hepatic stellate cells is significantly higher compared with wild-type cells. Inhibition of lysyl oxidase significantly reduces collagen fibril stiffness, and treatment of Fn recovers collagen fibril stiffness to wild-type levels. Thus, our findings indicate an indispensable role for Fn in chronic liver fibrosis/cirrhosis in negatively regulating TGF-␤ bioavailability, which in turn modulates ECM remodeling and stiffening and consequently preserves adult organ functions. Furthermore, this regulatory mechanism by Fn could be translated for a potential therapeutic target in a broader variety of chronic fibrotic diseases.

The role of extracellular matrix on liver stem cell fate: A dynamic relationship in health and disease

“…On the other hand, FN is a glycoprotein that can be found in the liver capsule, portal stroma, and space of Disse. FN levels increase during liver regeneration (Aziz-Seible and Casey, 2011), while the absence of that is correlated with cirrhosis, liver stiffness, and disorganized COL network (Iwasaki et al, 2016). Cell-cell interaction and also cell-matrix interplay are essential in the regulation of the stem cell behavior within niches (Spradling et al, 2001).…”

Lysyl Oxidase Isoforms and Potential Therapeutic Opportunities for Fibrosis and Cancer

“…Thus, if BAPN appears to not inhibit a LOX isoform in vivo, then it is likely that (1) either BAPN has been metabolized, or (2) that the activity in question occurs as a result of a non-enzymatic function of LOX or LOX isoform. Data consistently show LOX up-regulated in a variety of fibrotic conditions, sometimes accompanied by additional LOX isoforms, including lung- 49-53 , liver- 43, 54-56 , and heart- 57, 58 , and skin- 59-61 fibrosis, and hypertension 47, 58 . One notable exception is phenytoin-induced gingival overgrowth which appears to be accompanied by LOXL2 elevations and not LOX 62, 63 .…”

Periostin promotes liver fibrogenesis by activating lysyl oxidase in hepatic stellate cells

“…Our current data indicate fibrotic liver sections of periostin -/-mice were less stiff than liver sections of WT mice and also have lower levels of collagen I expression. Liver stiffness is a multifaceted phenomenon which makes outside-in-myofibroblast signal transduction (19,20,27) …”

“…Lysyl oxidase (LOX) is a copper-dependent extracellular, matrix-embedded amine oxidase protein that plays a critical role in covalent cross-linking of fibrillar collagens and elastin (17,18). There are a total of five LOX isoforms identified to date: LOX and the LOX-like (LOXL) enzymes 1 to 4, which share a conserved enzymatic domain with divergent N-termini (19,20).…”