Effect of the First Feeding on Enterocytes of Newborn Rats

During Postnatal Ontogenesis, the Development of a Microvascular Bed in an Intestinal Villus Depends on Intussusceptive Angiogenesis

The mechanisms responsible for the growth and development of vascular beds in intestinal villi during postnatal ontogenesis remain enigmatic. For instance, according to the current consensus, in the sprouting type of angiogenesis, there is no blood flow in the rising capillary sprout. However, it is known that biomechanical forces resulting from blood flow play a key role in these processes. Here, we present evidence for the existence of the intussusception type of angiogenesis during the postnatal development of micro-vessel patterns in the intestinal villi of rats. This process is based on the high-level flattening of blood capillaries on the flat surfaces of intestinal villi, contacts among the opposite apical plasma membrane of endothelial cells in the area of inter-endothelial contacts, or the formation of bridges composed of blood leucocytes or local microthrombi. We identified factors that, in our opinion, ensure the splitting of the capillary lumen and the formation of two parallel vessels. These phenomena are in agreement with previously described features of intussusception angiogenesis.

New Interpretations for Sprouting, Intussusception, Ansiform, and Coalescent Types of Angiogenesis

Angiogenesis, or the development of blood vessels by growing from already-formed vessels, is observed in embryonic development, physiological cyclical processes such as wound healing, the encapsulation of foreign bodies, tumor growth, and some other situations. In this review, we analyze the cellular mechanisms of angiogenesis, namely, angiogenesis by sprouting, ansiform (by loop formation) angiogenesis, coalescent angiogenesis, and angiogenesis by intussusception (splitting the capillary into two channels). The analysis of data revealed a lot of unanswered questions and contradictions. Here, we propose several new models of angiogenesis explaining these contradictions.

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.

The Regulated Secretion and Models of Intracellular Transport: The Goblet Cell as an Example

Transport models are extremely important to map thousands of proteins and their interactions inside a cell. The transport pathways of luminal and at least initially soluble secretory proteins synthesized in the endoplasmic reticulum can be divided into two groups: the so-called constitutive secretory pathway and regulated secretion (RS) pathway, in which the RS proteins pass through the Golgi complex and are accumulated into storage/secretion granules (SGs). Their contents are released when stimuli trigger the fusion of SGs with the plasma membrane (PM). In specialized exocrine, endocrine, and nerve cells, the RS proteins pass through the baso-lateral plasmalemma. In polarized cells, the RS proteins secrete through the apical PM. This exocytosis of the RS proteins increases in response to external stimuli. Here, we analyze RS in goblet cells to try to understand the transport model that can be used for the explanation of the literature data related to the intracellular transport of their mucins.

COVID-19 Biogenesis and Intracellular Transport

SARS-CoV-2 is responsible for the COVID-19 pandemic. The structure of SARS-CoV-2 and most of its proteins of have been deciphered. SARS-CoV-2 enters cells through the endocytic pathway and perforates the endosomes' membranes, and its (+) RNA appears in the cytosol. Then, SARS-CoV-2 starts to use the protein machines of host cells and their membranes for its biogenesis. SARS-CoV-2 generates a replication organelle in the reticulo-vesicular network of the zippered endoplasmic reticulum and double membrane vesicles. Then, viral proteins start to oligomerize and are subjected to budding within the ER exit sites, and its virions are passed through the Golgi complex, where the proteins are subjected to glycosylation and appear in post-Golgi carriers. After their fusion with the plasma membrane, glycosylated virions are secreted into the lumen of airways or (seemingly rarely) into the space between epithelial cells. This review focuses on the biology of SARS-CoV-2's interactions with cells and its transport within cells. Our analysis revealed a significant number of unclear points related to intracellular transport in SARS-CoV-2-infected cells.

The Diffusion Model of Intra-Golgi Transport Has Limited Power

The Golgi complex (GC) is the main station along the cell biosecretory pathway. Until now, mechanisms of intra-Golgi transport (IGT) have remained unclear. Herein, we confirm that the goodness-of-fit of the regression lines describing the exit of a cargo from the Golgi zone (GZ) corresponds to an exponential decay. When the GC was empty before the re-initiation of the intra-Golgi transport, this parameter of the curves describing the kinetics of different cargoes (which are deleted in Golgi vesicles) with different diffusional mobilities within the GZ as well as their exit from the GZ was maximal for the piecewise nonlinear regression, wherein the first segment was horizontal, while the second segment was similar to the exponential decay. The kinetic curve describing cargo exit from the GC per se resembled a linear decay. The Monte-Carlo simulation revealed that such curves reflect the role of microtubule growth in cells with a central GC or the random hovering of ministacks in cells lacking a microtubule. The synchronization of cargo exit from the GC already filled with a cargo using the wave synchronization protocol did not reveal the equilibration of cargo within a Golgi stack, which would be expected from the diffusion model (DM) of IGT. Moreover, not all cisternae are connected to each other in mini-stacks that are transporting membrane proteins. Finally, the kinetics of post-Golgi carriers and the important role of SNAREs for IGT at different level of IGT also argue against the DM of IGT.

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.