Heterogeneity of the intrahepatic biliary epithelium

The objectives of this review are to outline the recent findings related to the morphological heterogeneity of the biliary epithelium and the heterogeneous pathophysiological responses of different sized bile ducts to liver gastrointestinal hormones and peptides and liver injury/toxins with changes in apoptotic, proliferative and secretory activities. The knowledge of biliary function is rapidly increasing because of the recognition that biliary epithelial cells （cholangiocytes） are the targets of human cholangiopathies, which are characterized by proliferation/damage of bile ducts within a small range of sizes. The unique anatomy, morphology, innervation and vascularization of the biliary epithelium are consistent with function of cholangiocytes within different regions of the biliary tree. The in vivo models [e.g., bile duct ligation （BDL）, partial hepatectomy, feeding of bile acids,carbon tetrachloride （CCI4） or α-naphthylisothiocyanate（ANIT）] and the in vivo experimental tools [e.g., freshly isolated small and large cholangiocytes or intrahepatic bile duct units （IBDU） and primary cultures of small and large murine cholangiocytes] have allowed us to demonstrate the morphological and functional heterogeneity of the intrahepatic biliary epithelium.These models demonstrated the differential secretory activities and the heterogeneous apoptotic and proliferative responses of different sized ducts. Similar to animal models of cholangiocyte proliferation/injury restricted to specific sized ducts, in human liver diseases bile duct damage predominates specific sized bile ducts.Future studies related to the functional heterogeneity of the intrahepatic biliary epithelium may disclose new pathophysiological treatments for patients with cholangiopathies.

Estrogens and the pathophysiology of the biliary tree

The scientific framework concerning estrogen effects on different tissues has expanded enormously during the last decades, when estrogen receptor （ER） subtypes were identified. Estrogens are not only essential for the female reproductive system, but they also control fundamental functions in other tissues including the cardiovascular system, bone, brain and liver. Recently, estrogens have been shown to target the biliary tree, where they modulate the proliferative and secretory activities of cholangiocytes, the epithelial cells lining bile ducts. By acting on both estrogen receptors （ER-α） and （ER-β） subtypes, and by activating either genomic or non-genomic pathways, estrogens play a key role in the complex loop of growth factors and cytokines, which modulates the proliferative response of cholangiocytes to damage. Specifically, estrogens activate intracellular signalling cascades JERK1/2 （extracellular regulated kinases 1/2, PI3-kinase/AKT （phosphatidylinositol-3＇ kinase/AKT）] typical of growth factors such as insulin like growth factor （IGF1）, nerve growth factor （NGF） and vascular endothelial growth factor （VEGF）, thus potentiating their action. In addition, estrogens stimulate the secretion of different growth factors in proliferating cholangiocytes. This review specifically deals with the recent advances related to the role and mechanisms by which estrogens modulate cholangiocyte functions in normal and pathological conditions.

Mechanisms of biliary carcinogenesis and growth

Cholangiocarcinoma is a rare cancer originating from the neoplastic transformation of the epithelial cells (i.e. cholangiocytes) that line the biliary tract. The prognosis for patients with cholangiocarcinoma is grim due to lack of viable treatment options. The increase in world-wide incidence and mortality from cholangiocarcinoma highlights the importance of understanding the intracellular mechanisms that trigger the neoplastic transformation of cholangiocytes and the growth of biliary cancers. The purpose of the following review is to address what has been learned over the past decade concerning the molecular basis of cholangiocarcinogenesis. The material presented is divided into two sections:(1) mechanisms regulating neoplastic transformation of cholangiocytes; and (2) factors regulating cholangiocarcinoma growth. An understanding of the growth regulatory mechanisms of cholangiocarcinoma will lead to the identification of therapeutic targets for this devastating cancer.

TRAF2-MLK3 interaction is essential for TNF-α-induced MLK3 activation

Mixed lineage kinase 3 （MLK3） is a mitogen-activated protein kinase kinase kinase that is activated by tumor necrosis factor-α （TNF-α） and specifically activates c-Jun N-terminal kinase （JNK） on TNF-a stimulation. The mecha- nism by which TNF-α activates MLK3 is still not known. TNF receptor-associated factors （TRAFs） are adapter molecules that are recruited to cytoplasmic end of TNF receptor and mediate the downstream signaling, including activation of JNK. Here, we report that MLK3 associates with TRAF2, TRAF5 and TRAF6; however only TRAF2 can significantly induce the kinase activity of MLK3. The interaction domain of TRAF2 maps to the TRAF domain and for MLK3 to its C-terminal half （amino acids 511-847）. Endogenous TRAF2 and MLK3 associate with each other in response to TNF-α treatment in a time-dependent manner. The association between MLK3 and TRAF2 mediates MLK3 activation and competition with the TRAF2 deletion mutant that binds to MLK3 attenuates MLK3 kinase activity in a dose-dependent manner, on TNF-α treatment. Furthermore the downstream target of MLK3, JNK was activated by TNF-α in a TRAF2-dependent manner. Hence, our data show that the direct interaction between TRAF2 and MLK3 is required for TNF-α-induced activation of MLK3 and its downstream target, JNK.

Bile acid interactions with cholangiocytes

Cholangiocytes are exposed to high concentrations of bile acids at their apical membrane. A selective transporter for bile acids, the Apical Sodium Bile Acid Cotransporter （ASBT） （also referred to as Ibat; gene name Slc10a2） is localized on the cholangiocyte apical membrane. On the basolateral membrane, four transport systems have been identified （t-ASBT, multidrug resistance （MDR）3, an unidentified anion exchanger system and organic solute transporter （Ost） heteromeric transporter, Ostα- Ostβ. Together, these transporters unidirectionally move bile acids from ductal bile to the circulation. Bile acids absorbed by cholangiocytes recycle via the peribiliary plexus back to hepatocytes for re-secretion into bile. This recycling of bile acids between hepatocytes and cholangiocytes is referred to as the cholehepatic shunt pathway. Recent studies suggest that the cholehepatic shunt pathway may contribute in overall hepatobiliary transport of bile acids and to the adaptation to chronic cholestasis due to extrahepatic obstruction. ASBT is acutely regulated by an adenosine 3＇, 5＇monophosphate （cAMP）-dependent translocation to the apical membrane and by phosphorylation-dependent ubiquitination and proteasome degradation. ASBT is chronically regulated by changes in gene expression in response to biliary bile acid concentration and inflammatory cytokines. Another potential function of cholangiocyte ASBT is to allow cholangiocytes to sample biliary bile acids in order to activate intracellular signaling pathways. Bile acids trigger changes in intracellular calcium, protein kinase C （PKC）, phosphoinositide 3-kinase （PI3K）, mitogenactivated protein （MAP） kinase and extracellular signalregulated protein kinase （ERK） intracellular signals. Bile acids significantly alter cholangiocyte secretion,proliferation and survival. Different bile acids have differential effects on cholangiocyte intracellular signals,and in some instances trigger opposing effects on cholangiocyte secretion, proliferation and survival. Based upon these concepts and observations, the cholangiocyte has been proposed to be the principle target cell for bile acids in the liver.

Cholangiocytes and blood supply

The microvascular supply of the biliary tree, the peribiliary plexus （PBP）, stems from the hepatic artery branches and flows into the hepatic sinusoids. A detailed three-dimensional study of the PBP has been performed by using the Scanning Electron Microscopy vascular corrosion casts （SEMvcc） technique. Considering that the PBP plays a fundamental role in supporting the secretory and absorptive functions of the biliary epithelium, their organization in either normalcy and pathology is explored. The normal liver shows the PBP arranged around extra-and intrahepatic biliary tree. In the small portal tract PBP was characterized by a single layer of capillaries which progressively continued with the extrahepatic PBP where it showed a morecomplex vascular network. After common duct ligation （BDL）, progressive modifications of bile duct and PBP proliferation are observed. The PBP presents a three-dimensional network arranged around many bile ducts and appears as bundles of vessels, composed by capillaries of homogeneous diameter with a typical round mesh structure. The PBP network is easily distinguishable from the sinusoidal network which appears normal. Considering the enormous extension of the PBP during BDL, the possible role played by the Vascular Endothelial Growth Factor （VEGF） is evaluated. VEGF-A,VEGF-C and their related receptors appeared highly immunopositive in proliferating cholangiocytes of BDL rats. The administration of anti-VEGF-A or anti-VEGF-C antibodies to BDL rats as well as hepatic artery ligation induced a reduced bile duct mass. The administration of rVEGF-A to BDL hepatic artery ligated rats prevented the decrease of cholangiocyte proliferation and VEGF-A expression as compared to BDL control rats. These data suggest the role of arterial blood supply of the biliary tree in conditions of cholangiocyte proliferation, such as it occurs during chronic cholestasis. On the other hand,the role played by VEGF as a tool of cross-talk between cholangiocytes and PBP endothelial cells suggests that manipulation of VEGF release and function could represent a therapeutic strategy for human pathological conditions characterized by damage of hepatic artery or the biliary tree.

激光扫描共聚焦显微镜在医学研究中的应用

激光扫描共聚焦显微镜(Confocal laser scanning microscope,CLSM)具有高分辨率、高灵敏度、三维重建、动态分析等优点,使图像更为精确清晰和数字化。该仪器现已广泛应用于细胞生物学、生理学、病理学、遗传学和药理学等研究领域中。本文简述了激光扫描共聚焦显微镜的结构、工作原理并归纳了其在医学各领域研究中的应用。

手术中用三维经食道超声心动图测量心输出量的准确性和可行性

背景本研究中，我们试图用三维经食道超声心动图（3DTEE）确定心输出量，并评价其在手术中应用的可行性。方法同时用3DTEE和热稀释．法测定20例行心脏手术的患者在临床上稳定的体外循环前期时的心输出量。结果用这2种方法测定心输出量之间的相关系数是0．86。3DTEE的平均偏差是0．27L／min，范围是一1．64—2．17L／min（一致性为±35％）。平均三维数据采集时间为43秒，数据后处理时间为7分钟。结论可以用3DTEE来测量心输出量，并且这种方法在围手术期是可行的。虽然这种方法同热稀释法相比差异有显著性，且一致性较差，但是与热稀释法有很好的相关性。