De novo expression of glutamine synthetase during transformation of hepatic stellate cells into myofibroblast-like cells

Abstract

The expression of glutamine synthetase (GS) was studied in cultured quiescent hepatic stellate cells (HSC) and during their transformation into myofibroblast-like cells. GS mRNA was detectable in quiescent HSC (1-day culture); however, the enzyme protein was not expressed, as assessed by Western blot analysis, immunocytochemistry and the absence of detectable enzyme activity. Similar findings were obtained after 2 days of culture; in addition, the mRNA levels had dropped by about 70%, but they increased again thereafter during the process of HSC transformation in culture, as indicated by the expression of alpha-smooth-muscle actin. In parallel with the accumulation of alpha-smooth-muscle actin, GS was expressed, as shown by Western blot analysis and immunocytochemistry, and enzyme activity increased from undetectable levels in quiescent cells to 0.13+/-0.01 micromol/h per mg of cell protein within 7-14 days. This value compares with GS activity in liver parenchymal cells of 0.57+/-0.03 micromol/h per mg of cell protein. The findings suggest that activation of HSC results in the de novo expression of GS protein and activity, and this may serve as another marker of HSC transformation.

Ammonia produces pathological changes in human hepatic stellate cells and is a target for therapy of portal hypertension

“…Hence, providing the first indication that ammonia-induced dysfunction of HSCs is reversible. In accordance with prior observations in rat HSCs [17], human HSCs also express GS. Interestingly, although GS gene expression remained unaffected by increasing concentrations of ammonia, a significant reduction in protein levels was observed.…”

“…[13][14][15][16] Previous work showed that rat HSCs express glutamine synthetase leading to our hypothesis that excess ammonia may therefore produce deleterious effects on the activity and function of primary human HSC as it does in astrocytes. [17] Following acute or chronic liver injury, HSCs undergo phenotypic transformation from "quiescent" (non-proliferating and non-contractile) to "activated" (promitogenic, [28,29] in BDL rats was associated with a negative modulation of HSC activation and in the reduction of portal pressure.…”

c-Jun-N-terminal Kinase Dependent Membrane Targeting of CD95 in Rat Hepatic Stellate Cells

“…In line with previous data [3,17], HSC in culture spontaneously transform to myofibroblast-like cells within one week. As shown in fig.…”

All-trans retinoic acid mitigates methotrexate-induced liver injury in rats; relevance of retinoic acid signaling pathway

“…d MTX-ATRA cotreated group: individual sinusoidal dilation (arrow head) Jaskiewicz et al (1996) reported that MTX administration activates HSCs leading to liver fibrosis. On the other hand, another report mentioned that activation of HSCs converts it to myofibroblasts with subsequent loss of its retinoid storage (Abdel-Bakky et al 2011;Bode et al 1998). Results of our study showed that RXR-α and RAR-α expression is downregulated in MTX model of hepatotoxicity.…”