Endoplasmic reticulum and autophagy in rat hepatocytes.

Abstract

Electron microscopy of hepatocytes in both normal rat liver and rat liver treated to induce hyperplasia of smooth endoplasmic reticulum shows that autophagic vacuoles and residual bodies (types of lysosomes) are continuous with endoplasmic reticulum. Our laboratory has emphasized the diverse activities of GERL (1, 2) and other regions of the endoplasmic reticulum (ER) in hepatocytes (ref. 3; A. B. Novikoff, P. M. Leuenberger, P. M. Novikoff, and M. Quintana, unpublished results). In 1964 we suggested that in hepatocytes the ER is involved in forming autophagic vacuoles-lysosomes in which intracellular material is degraded: "Smooth endoplasmic reticulum appears to wrap around bits of cytoplasm, often becoming 'compacted' in the process. This may reflect an altered permeability and release of acid hydrolases and other materials to the interior of the autophagic vacuoles. The electron micrographs suggest, but do not firmly establish, that the endoplasmic reticulum thus altered becomes the delimiting membranes of the vacuoles" (ref. 4, p. 188).The growing knowledge of proteolysis in cells (reviewed in ref. 5) has revived interest in the degree to which autophagy is involved in such protein breakdown in liver. Biochemical studies on perfused rat livers, reported recently by Mortimore and his colleagues (listed in ref. 6), implicate lysosomes in the proteolysis subsequent to withdrawal of amino acids from the perfusing medium. Mortimore and Schworer (6) quantitated the "fractional cytoplasmic volumes" of the autophagic vacuoles with various constituents that rapidly develop after amino acid deprivation; the vacuoles containing glycogen were especially emphasized. The purposes of this communication are (i) to show the relation of such autophagic vacuoles to the ER in rat hepatocytes; and (ii) to present a three-dimensional model reconstructed from consecutive serial sections. MATERIALS AND METHODSSprague-Dawley rats of both sexes, 150-250 g in weight, were used for the observations on the normal rat. They were fed Purina rat chow ad lib. To induce hyperplasia of the smooth ER, we fed male Sprague-Dawley rats the Miller et al. diet (7) containing 0.06% 4-dimethylaminobenzine for 7 days, and then we partially hepatectomized the rats by the procedure of Higgins and Anderson (8). The rats were fed the 4-dimethylaminobenzine diet for an additional 5 days and then killed.The animals were anesthetized by ether, and thin slices of liver were placed into cold 1% OS04 in 0.1 M phosphate buffer containing 5% sucrose. Cubes, ca. 1 mm in each dimension, were dissected and transferred to fresh fixative. After 2 hr of fixation, the cubes were rapidly dehydrated in alcohols, treated with propylene oxide, and embedded in Epon 812. Sections, about 500-600 A thick, were cut with an LKB Ultratome and mounted on copper grids. After they were stained with lead citrate, they were examined in the Siemens Elmiskop I microscope.Serial sections were mounted on parlodion-coated single slit grids. Serial sections were prepared from four ...

Starvation and ULK1-dependent cycling of mammalian Atg9 between the TGN and endosomes

“…The source of the AV membranes in mammalian cells is controversial: some studies (Dunn, Jr, 1990;Ericsson, 1969;Novikoff and Shin, 1978;Ueda et al, 1991) have identified endoplasmic reticulum (ER) proteins on the AVi, others detected Golgi membrane proteins (Locke and Sykes, 1975;Yamamoto et al, 1990). The unusual morphological properties of AVs has also led to the hypothesis that these membranes are derived from a unique type of membrane, called a phagophore (Seglen et al, 1990), or isolation membrane ).…”

Regulatory factors of intracellular lysosomal activity associated with heterophagy and autophagy.

“…The origin of the segregating membrane of autophagic vacuoles is still a matter of debate in various cells. In hepatocytes, the majority of reports favors the membranes of ER and Golgi apparatus as the original membrane of autophagic vacuoles from the evidence such as occasional direct continuity of ER membranes with the outer limiting membrane of autophagic vacuoles (14) and the osmium-staining common property of the autophagic vacuole membrane with ER and Golgi apparatus membranes (9). In contradicton, it has been recently reported that the limiting membranes of autophagic vacuoles possess characteristics distinct from the ER and Golgi membranes with respect to the density of intramembranous particles (8,19) and the concentration of cholesterol and unsaturated fatty acids (18).…”

L’autophagie, dégrader plus pour vivre plus… mais attention !

“…Récemment, le rôle dans la première étape de la formation de l'autophagosome d'une structure membranaire, baptisée omégasome, issue de la membrane du réticulum endoplasmique, a été élégamment montré [21]. Finalement, il n'y pas que le Fou d'Elsa qui réinvente le passé pour voir la beauté de l'avenir puisque dès 1964 le microscopiste américain Alex Novikoff suggérait le rôle primordial du réticulum endoplasmique dans l'initiation de l'autophagie [22]. ‡ Autophagy: time to degrade to go on living P. Codogno Inserm U756, Université Paris-Sud 11 5, rue Jean Baptiste Clément 92296 Châtenay-Malabry Cedex, France.…”