Mechanisms of Formation of Antibodies against Blood Group Antigens That Do Not Exist in the Body.

The system of the four different human blood groups is based on the oligosaccharide antigens A or B, which are located on the surface of blood cells and other cells including endothelial cells, attached to the membrane proteins or lipids. After transfusion, the presence of these antigens on the apical surface of endothelial cells could induce an immunological reaction against the host. The final oligosaccharide sequence of AgA consists of Gal-GlcNAc-Gal (GalNAc)-Fuc. AgB contains Gal-GlcNAc-Gal (Gal)-Fuc. These antigens are synthesised in the Golgi complex (GC) using unique Golgi glycosylation enzymes (GGEs). People with AgA also synthesise antibodies against AgB (group A [II]). People with AgB synthesise antibodies against AgA (group B [III]). People expressing AgA together with AgB (group AB [IV]) do not have these antibodies, while people who do not express these antigens (group O [0; I]) synthesise antibodies against both antigens. Consequently, the antibodies are synthesised against antigens that apparently do not exist in the body. Here, we compared the prediction power of the main hypotheses explaining the formation of these antibodies, namely, the concept of natural antibodies, the gut bacteria-derived antibody hypothesis, and the antibodies formed as a result of glycosylation mistakes or de-sialylation of polysaccharide chains. We assume that when the GC is overloaded with lipids, other less specialised GGEs could make mistakes and synthesise the antigens of these blood groups. Alternatively, under these conditions, the chylomicrons formed in the enterocytes may, under this overload, linger in the post-Golgi compartment, which is temporarily connected to the endosomes. These compartments contain neuraminidases that can cleave off sialic acid, unmasking these blood antigens located below the acid and inducing the production of antibodies.

Effect of the First Feeding on Enterocytes of Newborn Rats.

The transcytosis of lipids through enterocytes occurs through the delivery of lipid micelles to the microvilli of enterocytes, consumption of lipid derivates by the apical plasma membrane (PM) and then their delivery to the membrane of the smooth ER attached to the basolateral PM. The SER forms immature chylomicrons (iChMs) in the ER lumen. iChMs are delivered at the Golgi complex (GC) where they are subjected to additional glycosylation resulting in maturation of iChMs. ChMs are secreted into the intercellular space and delivered into the lumen of lymphatic capillaries (LCs). The overloading of enterocytes with lipids induces the formation of lipid droplets inside the lipid bilayer of the ER membranes and transcytosis becomes slower. Here, we examined components of the enterocyte-to-lymphatic barriers in newly born rats before the first feeding and after it. In contrast to adult animals, enterocytes of newborns rats exhibited apical endocytosis and a well-developed subapical endosomal tubular network. These enterocytes uptake membranes from amniotic fluid. Then these membranes are transported across the polarized GC and secreted into the intercellular space. The enterocytes did not contain COPII-coated buds on the granular ER. The endothelium of blood capillaries situated near the enterocytes contained only a few fenestrae. The LCs were similar to those in adult animals. The first feeding induced specific alterations of enterocytes, which were similar to those observed after the lipid overloading of enterocytes in adult rats. Enlarged chylomicrons were stopped at the level of the LAMP2 and Neu1 positive post-Golgi structures, secreted, fused, delivered to the interstitial space, captured by the LCs and transported to the lymph node, inducing the movement of macrophages from lymphatic follicles into its sinuses. The macrophages captured the ChMs, preventing their delivery into the blood.

Role of Endothelial Regeneration and Overloading of Enterocytes with Lipids in Capturing of Lipoproteins by Basement Membrane of Rat Aortic Endothelium.

Atherosclerosis is a complex non-monogenic disease related to endothelial damage in elastic-type arteries and incorrect feeding. Here, using cryodamage of endothelial cells (ECs) of rat abdominal aorta, we examined the role of the EC basement membrane (BM) for re-endothelization endothelial regeneration and its ability to capture low density lipoproteins (LDLs). Regeneration of endothelium induced thickening of the ECBM. Secretion of the BM components occurred in the G2-phase. Multiple regenerations, as well as arterial hypertension and aging, also led to the thickening of the BM. Under these conditions, the speed of re-endothelialization increased. The thick BM captured more LDLs. LDLs formed after overloading of rats with lipids acquired higher affinity to the BM, presumably due to the prolonged transport of chylomicrons through neuraminidase-positive endo-lysosomes. These data provide new molecular and cellular mechanisms of atherogenesis.

Comparison of the Cisterna Maturation-Progression Model with the Kiss-and-Run Model of Intra-Golgi Transport: Role of Cisternal Pores and Cargo Domains.

The Golgi complex is the central station of the secretory pathway. Knowledge about the mechanisms of intra-Golgi transport is inconsistent. Here, we compared the explanatory power of the cisterna maturation-progression model and the kiss-and-run model. During intra-Golgi transport, conventional cargoes undergo concentration and form cisternal distensions or distinct membrane domains that contain only one membrane cargo. These domains and distension are separated from the rest of the Golgi cisternae by rows of pores. After the arrival of any membrane cargo or a large cargo aggregate at the Golgi complex, the cis-Golgi SNAREs become enriched within the membrane of cargo-containing domains and then replaced by the trans-Golgi SNAREs. During the passage of these domains, the number of cisternal pores decreases. Restoration of the cisternal pores is COPI-dependent. Our observations are more in line with the kiss-and-run model.

Cellular and sub-cellular mechanisms of lipid transport from gut to lymph.

Although the general structure of the barrier between the gut and the blood is well known, many details are still missing. Here, we analyse the literature and our own data related to lipid transcytosis through adult mammalian enterocytes, and their absorption into lymph at the tissue level of the intestine. After starvation, the Golgi complex (GC) of enterocytes is in a resting state. The addition of lipids in the form of chyme leads to the initial appearance of pre-chylomicrons (ChMs) in the tubules of the smooth endoplasmic reticulum, which are attached at the basolateral plasma membrane, immediately below the 'belt' of the adhesive junctions. Then pre-ChMs move into the cisternae of the rough endoplasmic reticulum and then into the expansion of the perforated Golgi cisternae. Next, they pass through the GC, and are concentrated in the distensions of the perforated cisternae on the trans-side of the GC. The arrival of pre-ChMs at the GC leads to the transition of the GC to a state of active transport, with formation of intercisternal connections, attachment of cis-most and trans-most perforated cisternae to the medial Golgi cisternae, and disappearance of COPI vesicles. Post-Golgi carriers then deliver ChMs to the basolateral plasma membrane, fuse with it, and secret ChMs into the intercellular space between enterocytes at the level of their interdigitating contacts. Finally, ChMs are squeezed out into the interstitium through pores in the basal membrane, most likely due to the function of the actin-myosin 'cuff' around the interdigitating contacts. These pores appear to be formed by protrusions of the dendritic cells and the enterocytes per se. ChMs are absorbed from the interstitium into the lymphatic capillaries through the special oblique contacts between endothelial cells, which function as valves through the contraction-relaxation of bundles of smooth muscle cells in the interstitium. Lipid overloading of enterocytes results in accumulation of cytoplasmic lipid droplets, an increase in diameter of ChMs, inhibition of intra-Golgi transport, and fusion of ChMs in the interstitium. Here, we summarise and analyse recent findings, and discuss their functional implications.

Intracellular transports and atherogenesis.

There is a great progress in understanding the cellular and molecular aspects of atherosclerosis, which is one of the leading causes of death. Yet, there are questions regarding the cellular and metabolic mechanisms that lead to atherogenesis. Among the many factors that influence this process, food plays a significant role. Among other factors that play a paramount role in atherogensis are alterations of the transport of food in enterocytes, oxysterols, development of an atherogenic serum, endothelial damage, accumulation of foam cells within the vessel wall, lysosome-ER transport, and hypertension. Here, we discuss the contribution of secretion, transcytosis, endocytosis of chylomicrons, low-density lipoproteins (LDL), very LDL, and high-density lipoproteins to atherogenesis.

Structure of the enterocyte transcytosis compartments during lipid absorption.

In spite of tremendous progress in deciphering the molecular mechanisms involved in intracellular transport in cell culture and in the test tube, many aspects of this process in situ remain unclear. Here, we examined lipid transcytosis in enterocytes in adult rats. Apical clathrin-coated buds and the ER exit sites were not found. After starvation, the Golgi complex was in a non-transporting state and contained many vesicles, but no intercisternal connections and typical the cis-most and the trans-most cisternae. Following the addition of the lipids in the form of chyme, pre-chylomicrons (pre-ChMs) were initially found in the tubules of the smooth SER attached to the basolateral plasmalemma below the belt composed of adhesive junctions (AJ) and always connected with other cisternae. However, the ER exit sites were still absent. Pre-ChMs moved into the cis-most cisterna and were concentrated in cisternal distensions at the trans-side of the Golgi complex. This induced attachment of the cis-most and the trans-most cisternae to the Golgi complex. Post-Golgi carriers fused with the basolateral plasmalemma and delivered ChMs outside. Overloading of enterocytes with lipids resulted in an accumulation of lipid droplets, an increase of the diameter of ChMs, and shift of the Golgi complex to the transporting state with the formation of intercisternal connections, attachment of the cis-most and the trans-most cisternae and disappearance of vesicles. These data are discussed from the functional point of view. In spite of tremendous progress in deciphering the molecular mechanisms involved in intracellular transport in cell culture and in the test tube, many aspects of this process in situ remain unclear. Here, we examined lipid transcytosis in enterocytes in adult rats. Apical clathrin-coated buds and the ER exit sites were not found. After starvation, the Golgi complex was in a non-transporting state and contained many vesicles, but no intercisternal connections and typical the cis-most and the trans-most cisternae. Following the addition of the lipids in the form of chyme, pre-chylomicrons (pre-ChMs) were initially found in the tubules of the smooth SER attached to the basolateral plasmalemma below the belt composed of adhesive junctions (AJ) and always connected with other cisternae. However, the ER exit sites were still absent. Pre-ChMs moved into the cis-most cisterna and were concentrated in cisternal distensions at the trans-side of the Golgi complex. This induced attachment of the cis-most and the trans-most cisternae to the Golgi complex. Post-Golgi carriers fused with the basolateral plasmalemma and delivered ChMs outside. Overloading of enterocytes with lipids resulted in an accumulation of lipid droplets, an increase of the diameter of ChMs, and shift of the Golgi complex to the transporting state with the formation of intercisternal connections, attachment of the cis-most and the trans-most cisternae and disappearance of vesicles. These data are discussed from the functional point of view.

Different Golgi ultrastructure across species and tissues: Implications under functional and pathological conditions, and an attempt at classification.

The Golgi complex (GC) is the central station of the secretory pathway, through which several paths of intracellular transport are connected. The main function of the GC is glycosylation of proteins and lipids, and their subsequent sorting. The structure of the GC is extremely complicated, although in general it is unbelievably similar across different cells types and under different functional and pathological conditions. However, there are also a lot of differences between the GCs in different cells and under different normal and pathological conditions. Here, we compare the phenotypes of the GCs in different organisms under these different conditions, in particular according to morphological criteria. We propose a classification of the GC types that reflects the different features of the GC, and that depends on the different molecular machines.

Evolution of the endoplasmic reticulum and the Golgi complex.

By analyzing the morpho-physiological features of the Golgi complex, its relationship with the endoplasmic reticulum in different species, and the molecular machineries involved in intracellular transport, we conclude that; (1) all eukaryotic cells have either Golgi complexes or remnants thereof; (2) all eukaryotic cells have a large minimal set of proteins that are involved in intracellular transport; and (3) several indispensable molecular machines are always present in secreting eukaryotic cells. Using this information, our data about mechanisms of intra-Golgi transport and phylogenetic analysis of several molecular machines, we propose a model for the evolution of the Golgi complex and the endoplasmic reticulum.