Abstract
Objective: Physiological liver regeneration requires adequate microvascular perfusion after partial hepatectomy. Although Kupffer cells (KCs) are known to play a key role in modulating hepatocyte proliferation, their impact on regulating hepatic microcirculation during liver regeneration has so far been disregarded. With respect to their expression and modulation of vasoactive mediators, KCs may provide important signals that regulate hepatic perfusion during liver regeneration.
Methods: Intravital fluorescence microscopy, immunohistochemistry, Western blot analysis, and RT-PCR were used to analyze livers of KC-depleted mice (liposome-encapsulated clodronate application) and KC-competent mice at days 3, 5, and 8 after 68% hepatectomy.
Results: Selective and long-lasting KC elimination limited the resection-associated hyperperfusion, as evidenced by an only 1.7- to 2-fold increase of sinusoidal volumetric blood flow and shear stress in contrast to a 3.5- to 5-fold increase in KC-competent mice. In accordance to that livers of KC-depleted mice showed an altered pattern of vasoregulatory gene expression. KC-depleted mice failed to show resection-induced increase of HO-1 and eNOS protein expression, but revealed a reduction of hepatic eNOS and HO-1 protein levels to 22 and 12% of the corresponding values in KC-competent mice. In addition, the eNOS inhibitory protein caveolin-1 was increased in KC-depleted animals prior to as well as after resection. Furthermore, resection-associated accumulation of ET-1 mRNA was absent in KC-depleted livers. Finally, liver mass restoration was impaired, with a regain of only 79% weight within 8 days after resection in KC-depleted mice.
Conclusion: The present study documents a remarkable change of the vasoactive mediator profile upon KC-depletion and liver resection, limiting intrahepatic hyperperfusion. Therefore, KC-dependent molecular mechanisms seem to be mandatory in regulating vasotonus during the process of liver regeneration and therewith maintaining intrahepatic shear stress as a trigger of hepatic proliferation.
The authors kindly thank Katrin Sievert, Dorothea Frenz, Maren Nerowski, Berit Blendow, and Doris Butzlaff (Institute for Experimental Surgery, University of Rostock) for their excellent technical assistance. This study is supported by a grant from the Deutsche Forschungsgemeinschaft, Bonn, Germany (Vo 450/7-3) and by a FORUN grant of the Medical Faculty, University of Rostock.