Nonmuscle myosin II regulates migration but not contraction in rat hepatic stellate cells

Aim: To identify and characterize the function of nonmu- scle myosin II (NMM II) isoforms in primary rat hepatic stellate cells (HSCs). Methods: Primary HSCs were isolated from male Spra-gue-Dawley rats by pronase/collagenase digestion. Total RNA and protein were harvested from quiescent and culture-activated HSCs. NMM II isoform (II-A, II-B and II-C) gene and protein expression were measured by RealTime polymerase chain reaction and Western blot analyses respectively. NMM II protein localization was visualized in vitro using immunocytochemical analysis. For in vivo assessment, liver tissue was harvested from bile duct-ligated (BDL) rats and NMM IIisoform expression determined by immunohistochemistry. Using a selective myosin II inhibitor and siRNA-mediated knockdown of each isoform, NMM II functionality in primary rat HSCs was determined by contraction and migration assays. Results: NMM II-A and II-B mRNA expression was increased in culture-activated HSCs (Day 14) with significant increases seen in all pair-wise comparisons (II -A: 12.67 ± 0.99 (quiescent) vs 17.36 ± 0.78 (Day 14), P < 0.05; II-B: 4.94 ± 0.62 (quiescent) vs 13.90 ± 0.85 (Day 14), P < 0.001). Protein expression exhibited similar expression patterns (II-A: 1.87 ± 2.50 (quiescent) vs 58.64 ± 8.76 (Day 14), P < 0.05; II-B: 1.17 ± 1.93 (quiescent) vs 103.71 ± 21.73 (Day 14), P < 0.05). No significant differences were observed in NMM II-C mRNA and protein expression between quiescent and activated HSCs. In culture-activated HSCs, NMM II-A and II-B merged with F-actin at the cellular periphery and throughout cytoplasm respectively. In vitro studies showed increased expression of NMM II-B in HSCs activated by BDL compared to sham-operated animals. There were no apparent increases of NMM II-A and II -C protein expression in HSCs during hepatic BDL injury. To determine the contribution of NMM II-A and II-B to migration and contraction, NMM II-A and II-B expression were downregulated with siRNA. NMM II-A and/or II-B siRNA inhibited HSC migration by approximately 25% compared to scramble siRNA-treated cells. Conversely, siRNA-mediated NMM II-A and II-B inhibition had no significant effect on HSC contraction; however, contraction was inhibited with the myosin II inhibitor, blebbistatin (38.7% ± 1.9%). Conclusion: Increased expression of NMM II-A and II-B regulates HSC migration, while other myosin II classes likely modulate contraction, contributing to development and severity of liver fibrosis.