(I-326) Effects of Matrix Stiffness-induced Hepatic Stellate Cell Activation on Adhesion Region Stiffening

Activated hepatic stellate cells (HSCs) produce excessive amounts of collagen I protein, which can lead to liver fibrosis. Further development of fibrosis results in an increase in the elasticity of liver tissue and leads to serious diseases such as cirrhosis and liver cancer. However, these developments are not uniformly induced in the liver and the distribution of stiffness is not constant. Understanding the relationship between HSC activation and local stiffening of liver tissue is essential for the development of effective therapeutic strategies.

The activation of HSCs is known to be affected by the elasticity of the surrounding scaffold. Previous studies have shown that HSCs cultured on scaffolds with high elasticity exhibited an upregulation of activation markers, such as α-SMA, collagen I⁽¹⁾, and collagen cross-linking molecule LOXL1⁽²⁾. Furthermore, activated HSCs cultured on scaffolds with low elasticity tend to revert to their resting state. These findings suggest that the local stiffening of the surrounding matrix accelerates the progression of fibrosis in HSCs.

In this study, we focused on the effects of HSC activation induced by scaffold elasticity on the stiffening of the scaffold to which the HSCs adhere. To achieve this, we used collagen-coated polyacrylamide (PAA) gels to allow HSC-induced changes in scaffold elastic modulus and evaluated scaffold stiffening by adding the supernatant containing substances secreted by HSCs cultured on the different elastic scaffolds to scaffolds without cells.

PAA gel preparation: 8% (w/v) polyacrylamide (PAA) was cross-linked with UV cross-linker (0.6% (w/v) N,N’-Methylenebis (acrylamide)，1.5% (w/v) Omnirad2959) on a 10×10 mm grass slide and the elasticity of PAA gel was controlled by UV exposure time. Considering the early stage and the severe stage of liver fibrosis, 12 kPa and 45 kPa of elastic moduli of PAA gels were used after coating with 9.1% type Ⅰ collagen (Cellmatrix TypeⅠ-C, Nita Gelatin Inc.).

Cell culture and supernatant collection: LX-2 cells were seeded on the collagen-coated PAA gels at a concentration of 5.55×10³ cells/cm² and cultured with 2 mL of Dulbecco's modified Eagle's medium (045-30285, Fujifilm wako pure chemical corporation) containing 10% (v/v) fetal bovine serum (FBS) and 1% antibiotics. The gel without cells was prepared for the control group. The supernatant of the culture medium was collected every 24 hours.

Evaluation of elasticity changes: Each collected supernatant at 48, 72 and 120 hours after cell seeding was added to the collagen-coated PAA gel with the same elastic modulus, and the gels were incubated for 24 hours. The elastic moduli of the gels were measured by scanning probe microscope (SPM) (SPM-9700, Shimadzu corporation) in contact mode.

Evaluation of cell growth: The LX-2 cells on each gel were stained with DAPI at 1, 4, and 7 days after seeding, and the entire cell culture area was imaged by fluorescence microscopy. The fluorescence-stained images were then subjected to particle analysis using ImageJ software to determine the total cell number.

The results of cell proliferation on each gel are shown in Figure 1. The proliferation rate at 12 and 45 kPa showed a 1.31-fold and 2.07-fold increase during 1 week, respectively. The number of cells cultured on the 12-kPa elastic modulus gel tended to increase gradually with culture time, although there were no significant differences. On the other hand, those cultured on the 45-kPa elastic modulus gel showed significant increases. These results suggest that the activated LX-2 cells responded to the elastic modulus of the scaffold, resulting in enhanced proliferative capacity.

The results of changes in the elastic modulus of the PAA gels immersed in the supernatant collected from the culture medium are shown in Figure 2. No changes in elastic modulus were observed in the acellular group of either elastic condition. However, it was found that the supernatants collected from the cellular group had the ability to increase the elasticity of the collagen-coated PAA gel in both elastic conditions. Particularly in the early 24 hours from 48 to 72 hours, the supernatants of the higher elastic modulus in the cellular group appeared to contain many substances that could stiffen the scaffold. As reported by Stefano et al. in the studies of myogenesis using collagen-coated gels⁽³⁾, the amount of LOXL1 in the supernatants could be one of the candidate factors for facilitating the cross-linking of the collagen scaffold. However, because of our results might be affected by the number of cells, further studies on the cell activation by the scaffold elasticity using RT-qPCR to evaluate the expression of activation marker genes would be necessary.

The results of this study indicate that the elasticity of the liver tissue to which HSCs adhere directly affects their activation. In particular, when HSCs are present on a hard tissue, they demonstrate the ability to induce local stiffening in their adhesion areas. Such local stiffening may contribute to the accelerated progression of liver fibrosis. These findings emphasize the significance of the tissue microenvironment in regulating HSC behavior and fibrosis development.

1. 
   

   Jan Görtzen, Robert Schierwagen, Jeanette Bierwolf, Sabine Klein, Frank E. Uschner, Peter F. van der Ven, Dieter O. Fürst, Christian P. Strassburg, Wim Laleman, Jörg-Matthias Pollok, Jonel Trebicka, Interplay of Matrix Stiffness and c-SRC in Hepatic Fibrosis, Frontuers in Physiology, 6(359), 2015, PMC4667086.

   
   


2. 
   

   Wenshan Zhao , Aiting Yang, Wei Chen, Ping Wang, Tianhui Liu, Min Cong, Anjian Xu, Xuzhen Yan. Jidong Jia, HongYou, Inhibition of lysyl oxidase-like 1 (LOXL1) expression arrests liver fibrosis progression in cirrhosis by reducing elastin crosslinking, Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, 1864(4), 2018, pp.1129-1137.

   
   


3. 
   

   Vitalba Di Stefano, Barbara Torsello, Cristina Bianchi, Ingrid Cifola, Eleonora Mangano, Giorgio Bovo, Valeria Cassina, Sofia De Marco, Roberta Corti, Chiara Meregalli, Silvia Bombelli, Paolo Viganò, Cristina Battaglia, Guido Strada, Roberto A. Perego, Major Action of Endogenous Lysyl Oxidase in Clear Cell Renal Cell Carcinoma Progression and Collagen Stiffness Revealed by Primary Cell Cultures, The American Journal of Pathology, 186(9), 2016, pp. 2473-2485.