Lysosomal compartment of macrophages: extending the definition of GERL

Decellularized human placenta supports hepatic tissue and allows rescue in acute liver failure

Tissue engineering with scaffolds to form transplantable organs is of wide interest. Decellularized tissues have been tested for this purpose, although supplies of healthy donor tissues, vascular recellularization for perfusion, and tissue homeostasis in engineered organs pose challenges. We hypothesized that decellularized human placenta will be suitable for tissue engineering. The universal availability and unique structures of placenta for accommodating tissue, including presence of embedded vessels, were major attractions. We found decellularized placental vessels were reendothelialized by adjacent native cells and bridged vessel defects in rats. In addition, implantation of liver fragments containing all cell types successfully hepatized placenta with maintenance of albumin and urea synthesis, as well as hepatobiliary transport of ^99m Tc-mebrofenin, up to 3 days in vitro. After hepatized placenta containing autologous liver was transplanted into sheep, tissue units were well-perfused and self-assembled. Histological examination indicated transplanted tissue retained hepatic cord structures with characteristic hepatic organelles, such as gap junctions, and hepatic sinusoids lined by endothelial cells, Kupffer cells, and other cell types. Hepatocytes in this neo-organ expressed albumin and contained glycogen. Moreover, transplantation of hepatized placenta containing autologous tissue rescued sheep in extended partial hepatectomy-induced acute liver failure. This rescue concerned amelioration of injury and induction of regeneration in native liver. The grafted hepatized placenta was intact with healthy tissue that neither proliferated nor was otherwise altered.

CONCLUSION

The unique anatomic structure and matrix of human placenta were effective for hepatic tissue engineering. This will advance applications ranging from biological studies, drug development, and toxicology to patient therapies. (Hepatology 2018;67:1956-1969).

Decellularized human placenta supports hepatic tissue and allows rescue in acute liver failure

Tissue engineering with scaffolds to form transplantable organs is of wide interest. Decellularized tissues have been tested for this purpose, although supplies of healthy donor tissues, vascular recellularization for perfusion, and tissue homeostasis in engineered organs pose challenges. We hypothesized that decellularized human placenta will be suitable for tissue engineering. The universal availability and unique structures of placenta for accommodating tissue, including presence of embedded vessels, were major attractions. We found decellularized placental vessels were reendothelialized by adjacent native cells and bridged vessel defects in rats. In addition, implantation of liver fragments containing all cell types successfully hepatized placenta with maintenance of albumin and urea synthesis, as well as hepatobiliary transport of ^99m Tc-mebrofenin, up to 3 days in vitro. After hepatized placenta containing autologous liver was transplanted into sheep, tissue units were well-perfused and self-assembled. Histological examination indicated transplanted tissue retained hepatic cord structures with characteristic hepatic organelles, such as gap junctions, and hepatic sinusoids lined by endothelial cells, Kupffer cells, and other cell types. Hepatocytes in this neo-organ expressed albumin and contained glycogen. Moreover, transplantation of hepatized placenta containing autologous tissue rescued sheep in extended partial hepatectomy-induced acute liver failure. This rescue concerned amelioration of injury and induction of regeneration in native liver. The grafted hepatized placenta was intact with healthy tissue that neither proliferated nor was otherwise altered.

CONCLUSION

The unique anatomic structure and matrix of human placenta were effective for hepatic tissue engineering. This will advance applications ranging from biological studies, drug development, and toxicology to patient therapies. (Hepatology 2018;67:1956-1969).

Urban planning of the endoplasmic reticulum (ER): how diverse mechanisms segregate the many functions of the ER

The endoplasmic reticulum (ER) is the biggest organelle in most cell types, but its characterization as an organelle with a continuous membrane belies the fact that the ER is actually an assembly of several, distinct membrane domains that execute diverse functions. Almost 20 years ago, an essay by Sitia and Meldolesi first listed what was known at the time about domain formation within the ER. In the time that has passed since, additional ER domains have been discovered and characterized. These include the mitochondria-associated membrane (MAM), the ER quality control compartment (ERQC), where ER-associated degradation (ERAD) occurs, and the plasma membrane-associated membrane (PAM). Insight has been gained into the separation of nuclear envelope proteins from the remainder of the ER. Research has also shown that the biogenesis of peroxisomes and lipid droplets occurs on specialized membranes of the ER. Several studies have shown the existence of specific marker proteins found on all these domains and how they are targeted there. Moreover, a first set of cytosolic ER-associated sorting proteins, including phosphofurin acidic cluster sorting protein 2 (PACS-2) and Rab32 have been identified. Intra-ER targeting mechanisms appear to be superimposed onto ER retention mechanisms and rely on transmembrane and cytosolic sequences. The crucial roles of ER domain formation for cell physiology are highlighted with the specific targeting of the tumor metastasis regulator gp78 to ERAD-mediating membranes or of the promyelocytic leukemia protein to the MAM.

Oxysterol binding proteins: in more than one place at one time?

Oxysterols are potent signalling lipids that directly bind liver X receptors (LXRs) and a subset of oxysterol binding protein (OSBP) related proteins (ORPs). It is relatively well established that the oxysterol-regulated function of LXRs is to control the expression of genes involved in reverse cholesterol transport, catabolism of cholesterol, and lipogenesis. In contrast, the mechanisms by which oxysterols and ORPs affect cellular lipid metabolism have remained poorly understood. In this review, we summarize the information available on function of the ORPs and compare the two families of proteins binding oxysterol to demonstrate the different responses that similar lipids can elicit within cells. The other focus is on the membrane targeting determinants and the protein interaction partners of ORPs, which provide interesting clues to the mode(s) of ORP action. Specifically, we suggest a model in which a general property of ORPs is to function at membrane contact sites, specialized zones of communication between two different organelles.

FTY720 pretreatment reduces warm hepatic ischemia reperfusion injury through inhibition of T-lymphocyte infiltration

Ischemia and reperfusion (IR) injury remains a significant problem in clinical liver transplantation. We investigated the effects of lymphocyte depletion with FTY720 in models of warm hepatic IR. Using 60-min partial warm hepatic IR, three groups of rats were studied: Sham--laparotomy alone; Control--water p.o. x 3 d before ischemia; Treatment--FTY720 p.o. x 3 d before ischemia. Animals were sacrificed for analysis at 6 h and 24 h post reperfusion. The effect of FTY720 pretreatment on survival was also studied using 150 min total hepatic IR with portojugular shunt. FTY720 treatment significantly reduced serum glutamic pyruvic transaminase and peripheral blood lymphocytes compared to controls at 6h and 24h (p < 0.0005). Histological grade was significantly improved in treated livers vs. controls (p < 0.05). CD3 immunocytochemical analysis revealed a significant reduction in T-cell infiltration in FTY720-treated livers (p < 0.0002). No difference in tissue myeloperoxidase levels was observed. Seven-day survival was significantly improved in treated rats vs. controls following total hepatic ischemia (p < 0.05). In conclusion, FTY720 ameliorates the biochemical and histological manifestations of hepatic IR by preventing T-lymphocyte infiltration and prolongs survival following a more severe ischemic insult. Myeloperoxidase data suggest this mechanism is independent of neutrophil activation. These results indicate that T lymphocytes are pivotal mediators in hepatic IR and may have important implications in liver transplantation.

Cyclophosphamide disrupts hepatic sinusoidal endothelium and improves transplanted cell engraftment in rat liver

To determine whether disruption of the hepatic sinusoidal endothelium will facilitate engraftment of transplanted cells, we treated Fischer 344 (F344) rats lacking dipeptidyl peptidase IV (DPPIV) activity with cyclophosphamide (CP). Electron microscopy showed endothelial injury within 6 hours following CP, and, after 24 and 48 hours, the endothelium was disrupted in most hepatic sinusoids. CP did not affect Kupffer cell function. Similarly, CP had no obvious effects on hepatocytes. Intrasplenic transplantation of F344 rat hepatocytes followed by their localization with DPPIV histochemistry showed 3- to 5-fold increases in the number of transplanted cells in CP-treated animals. Transplanted cells integrated in the liver parenchyma more rapidly in CP-treated animals, and hybrid bile canaliculi developed even 1 day after cell transplantation, which was not observed in control animals. To demonstrate whether improved cell engraftment translated into superior liver repopulation, recipient animals were conditioned with retrorsine and two-thirds partial hepatectomy (PH), which induces transplanted cell proliferation. CP treatment of these animals before cell transplantation significantly increased the number and size of transplanted cell foci. In conclusion, disruption of the hepatic sinusoidal endothelium was associated with accelerated entry and integration of transplanted cells in the liver parenchyma. These results provide insights into hepatocyte engraftment in the liver and will help in optimizing liver-directed cell therapy.

Lysosomal movements during heterophagy and autophagy: with special reference to nematolysosome and wrapping lysosome

Recent studies on lysosomal movements during heterophagy and autophagy performed in our laboratory for the past several years were reviewed; methods for the investigation of lysosomes and the cytoskeleton in these studies mainly involved electron microscopic cytochemistry. Lysosomal movements during heterophagy were observed in cultured rat alveolar macrophages taking up horseradish peroxidase (HRP) and rat peroxidase-antiperoxidase (PAP) by fluid-phase pinocytosis and adsorptive pinocytosis, respectively. A characteristic lysosomal change which was induced by the pinocytosis was the appearance of long, threadlike lysosomes (nematolysosomes) in the cytoplasm. The effects of actin filament destabilizer and antimicrotubular drug on lysosomal changes revealed that the appearance of nematolysosomes was dependent on the presence of both actin filaments and microtubules. The close morphological relationship between lysosomes and cytoskeletal elements, such as actin filaments and microtubules in the alveolar macrophages, supports the participation of the cytoskeletal system in the regulatory mechanism of lysosomal movements. In the study of the lysosomal wrapping mechanism (LWM), which is one type of lysosomal movement that occurs during autophagy, it was found that the occurrence of LWM was dependent on energy--namely, the supply of ATP--and on the presence of actin filaments. However, deconstruction of microtubules induced or favored the occurrence of LWM. It is conceivable that the LWM is also related to the cytoskeletal system. We conclude that intracellular dynamics of lysosomes during heterophagy and autophagy are largely a consequence of complicated modulation by the cytoskeletal system.

Immunocytochemical localization of lysosomal beta-galactosidase in rat liver

beta-galactosidase is a ubiquitous lysosomal hydrolase that specifically cleaves terminal beta-galactosyl residues from glycoproteins, glycosaminoglycans, oligosaccharides, and glycolipids. To study the intracellular distribution of this enzyme, we prepared a specific polyclonal antibody to lysosomal beta-galactosidase by immunizing rabbits with a highly purified preparation of beta-galactosidase from rat liver. Using this antibody we employed an immunocytochemical technique (protein A coupled to horseradish peroxidase and diaminobenzidine cytochemistry) and showed that beta-galactosidase is present in all hepatocytes of the rat liver. All types of lysosomes, the rough endoplasmic reticulum, and the specialized region of smooth endoplasmic reticulum known as GERL showed immunoreactivity. This in situ distribution suggests that these organelles are involved in the biosynthesis and intracellular sorting of this lysosomal enzyme.

Ultrastructure of hepatic cholesterol crystals in the hypercholesterolemic - diabetic rat

The cellular morphology of lipid accumulation in the liver was examined in normal rats fed a diet containing cholesterol and cholic acid, and streptozotocin-diabetic rats fed the same diet. The cholesterol-fed non diabetic rats displayed moderate hypercholesterolemia (average cholesterol 317 mg/dl) whereas the cholesterol-fed diabetic rats exhibited severe hypercholesterolemia (cholesterol greater than 1300 mg/dl). Ultrastructural studies were performed on hepatic tissues following in situ fixation and water soluble embedment, which were used to reduce lipid extraction and minimize structural distortions. Although both groups exhibited hepatocyte lipid droplets, the accumulation was markedly accentuated in the diabetic animals. The Kupffer cells of the diabetic animals contained cytosolic lipid crystals that were membrane delimited and showed lattice ordering 3.9 +/- 2.2 nm periodicity. These findings suggest that cholesteryl ester crystals of the cholesteric phase, similar to those found in atherosclerotic lesions, may form in other cellular foci exposed to abnormally high plasma lipid levels.

Phagosome-lysosome interactions related to erythrophagocytosis in Kupffer cells of fetal rat liver

Kupffer cells of fetal rat liver were examined by ultrastructural cytochemical methods to reveal acid phosphatase (AcPase) activity in lysosomes. Elongated cisternae, 940-1150 A in width containing AcPase reaction product, were identified in these cells. These cisternae were sometimes in continuity with phagosomes containing engulfed erythrocytes. Observations suggest that such cisternae may partly encircle these phagosomes. The relationships of these cisternae to GERL (Golgi Endoplasmic Reticulum Lysosomes) is discussed.

Induced autophagocytosis in macrophages. Origin of the segregating membranes

Cultured mouse peritoneal macrophages were exposed for 48 h to a large and toxic dose of polyacrylamide microspheres (previously designed for use as a lysosomotropic carrier for the intracellular delivery of enzymes and other macromolecules). This treatment induced autophagocytosis in the macrophages, which contained abundant autophagic vacuoles at 24 h post exposure. Transmission electron microscopical studies including enzyme cytochemistry showed that the segregating membranes in autophagosome formation consisted of flattened, smooth-surfaced vacuoles with a granular matrix in which reaction product indicating acid phosphatase activity could be demonstrated. The autophagic vacuole formation was apparently effected by wrapping of a portion of the cytoplasm in a sheet formed by flattening and fusion of multiple small vacuoles with acid phosphatase activity in their matrices. The conclusion is drawn that the segregating membranes are derived from lysosomes or GERL structures in this particular system of induced autophagocytosis.

Carbohydrate-specified endocytosis: localization of ligand in the lysosomal compartment

Carbohydrate-directed endocytosis is mediated by a receptor, the hepatic binding protein; it is responsible for the clearance of galactose-terminated glycoproteins from the circulation. This process was investigated by using lactosaminated ferritin which is recognized by this receptor. Ferritin was seen in elements of an extensive "lysosomal compartment" that includes secretory vacuoles, coated vesicles, and GERL. The compartment marked in hepatocytes by the distribution of ligand is similar to that previously described in Kupffer cells (marked by acid phosphatase reaction product and horseradish peroxidase reaction product).