Hepatic blood flow regulation by stellate cells in normal and injured liver

Hepatic stellate cells have received considerable attention as key components of the fibrogenic response to injury. Beyond this feature, they also have been implicated as regulators of sinusoidal vascular tone, and in disease states, in the pathogenesis of intrahepatic portal hypertension. The basis for this latter concept is derived from the following: (a) stellate cells are situated in a perisinusoidal orientation within the sinusoid, optimized for sinusoidal constriction; (b) a series of studies performed over the past decade have demonstrated that perisinusoidal stellate cells exhibit a remarkable capacity for cellular contraction, a characteristic that is most prominent after liver injury and stellate cell activation; and (c) in vivo microscopy studies have revealed that stellate cells can mediate sinusoidal constriction. Available evidence indicates that liver injury leads to a vascular disorder in which endothelin-1 is overproduced by stellate cells and endothelial cell-derived nitric oxide production is reduced. These abnormalities, in the context of exaggerated stellate cell contractility after liver injury, set up a paradigm in which stellate cells contribute to the increased intrahepatic resistance typical of portal hypertension. Furthermore, because stellate cell contractility and the mediators that control this function are dynamic processes, strategies that target exaggerated contractility provide an opportunity for novel therapeutics in intrahepatic portal hypertension.