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Myofibroblastic transformation of rat hepatic stellate cells: the role of Notch signaling and epithelial-mesenchymal transition regulation.

OBJECTIVE
The development of liver fibrosis has been shown to be associated with the transition of quiescent hepatic stellate cells (HSCs) into myofibroblastic HSCs, and the Notch signaling system has been shown to be activated in this process. The Notch signaling pathway is also known to regulate epithelial-mesenchymal transition (EMT).


MATERIALS AND METHODS
In the current study, quiescent HSCs were examined for expression of EMT markers, and experiments were performed to determine whether these markers change as quiescent HSCs transition into myofibroblastic HSCs and whether the process is modulated by Notch signaling. To promote myofibroblastic transition under experimental conditions, enzymatic perfusion and density gradient centrifugation were used to isolate rat HSCs, which were then cultured. A γ-secretase inhibitor was used to inhibit Notch signaling pathway activity in primary rat HSCs.


RESULTS
Upregulated expression of myofibroblastic markers was observed, but expression of quiescent HSC markers and epithelial markers was downregulated during the transition of HSC in vitro. Data indicate that expression of the classical EMT marker; i.e., E-cadherin, was decreased and that of N-cadherin and snail 1 increased. Notch 2 and Notch 3 receptors and Hey2 and HeyL target genes expression increased significantly as quiescent HSCs transitioned into myofibroblastic HSCs. When Notch signaling was blocked, however, the myofibroblastic transition of HSCs reverted, and epithelial marker expression was restored.


CONCLUSIONS
Thus, targeting Notch signaling may provide new insights into the mechanism of HSC transition and may offer a possible therapeutic target for the treatment of hepatic injury.