Apoptosisis activated during the early phase of reperfusion after liver ischemia and after liver transplantation in animals. However, the molecular basis of ischemia-induced cell death remains poorly understood. In this study we show that hepatocytes from ischemic liver lobes undergo apoptosis after reperfusion. In vivo pretreatment of rats with a specific inhibitor of caspases abrogates the apoptotic response in ischemic liver lobes. Inhibition of apoptosis can be accounted for by total inhibition of caspase activation as assessed in an enzymatic assay and by specific affinity labeling. Treatment with a caspase inhibitor fully protects rats from death induced by ischemia/reperfusion. These findings indicate that liver injury after ischemia/reperfusion can be prevented by inhibition of caspases. Thus, caspase inhibitors may have important therapeutic implications in liver ischemic diseases and after liver transplantation.

Hepatic ischemia occurs in liver transplantation, hemodynamic or cardiogenic shock, and liver resection associated with trauma or tumor. Ischemia/reperfusion (I/R) injury results in microcirculation failure followed by apoptosis and necrosis. Matrix metalloproteinases (MMPs) are involved in many physiological and pathological processes, but their expression and function during liver I/R remains poorly documented. In this study, we evaluated the expression of nine MMPs and their natural inhibitors, tissue inhibitors of MMPs (TIMPs), in a rat model of liver I/R. Analysis of MMP and TIMP expression show that although most of these genes are not constitutively expressed in the normal liver, they are induced in a specific time-dependent manner following I/R. Stromelysin-1, gelatinase B, and collagenase-3 are induced during the early phase of acute liver injury associated with inflammation and increased necrosis/apoptosis, whereas gelatinase A, membrane type-MMP, stromelysin-3, metalloelastase, TIMP-1, and TIMP-2 are essentially detectable during the recovery phase of liver injury corresponding to hepatocyte regeneration. This observation suggested that MMPs and TIMPs could play both deleterious and beneficial roles following I/R. We thus tested the effect of a specific phosphinic MMP inhibitor on acute liver I/R injury. Inhibition of MMP activity was shown to significantly decrease liver injury in ischemic/reperfused liver tissue as assessed by histological studies and serum hepatic enzyme levels. We therefore propose that MMP inhibitors may be of clinical relevance in liver-associated ischemic diseases or after liver transplantation.

In vivo studies have demonstrated that p63 plays complex and pivotal roles in pluristratified squamous epithelial development, but its precise function and the nature of the isoform involved remain controversial. Here, we investigate the role of p63 in epithelial differentiation, using an in vitro ES cell model that mimics the early embryonic steps of epidermal development. We show that the ΔNp63 isoform is activated soon after treatment with BMP-4, a morphogen required to commit differentiating ES cells from a neuroectodermal to an ectodermal cell fate. ΔNp63 gene expression remains high during epithelial development. P63 loss of function drastically prevents ectodermal cells to commit to the K5/K14-positive stratified epithelial pathway while gain of function experiments show that ΔNp63 allows this commitment. Interestingly, other epithelial cell fates are not affected, allowing the production of K5/K18-positive epithelial cells. Therefore, our results demonstrate that ΔNp63 may be dispensable for some epithelial differentiation, but is necessary for the commitment of ES cells into K5/K14-positive squamous stratified epithelial cells.

In vivo studies, transgenic and knock-out mice have demonstrated that p63 isoforms play pivotal roles in ectodermal and epidermal development but their respective function remains highly controversial. Since embryonic stem (ES) cells can be differentiated into many cell types, they represent an effective tool to recapitulate in vitro the main steps of embryonic development. We recently reported the efficient derivation of ectodermal and epidermal cells from murine ES cells and clarified the function of BMP-4 in the binary neuroectodermal choice by stimulating sox-1(+) neural precursors to undergo specific apoptosis while inducing epidermal differentiation through DeltaNp63 gene activation. DeltaNp63 is not required for ectodermal fate but enhances ES-derived ectodermal cell proliferation and epidermal commitment. This unique cellular model should further provide a powerful tool for identifying the molecular mechanisms controlling normal skin development and in p63-ectodermal dysplasia human congenital pathologies.