Effect of the First Feeding on Enterocytes of Newborn Rats

Abstract

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

“…Earlier, we showed that in newborn rats, when the GC is overloaded, the chylomicrons were delayed in the post-Golgi compartment positive for LAMP2, a marker of lysosomes and late endosomes [ 80 ]. Since we were familiar with the contradiction of desialilyation of modified LDLs [ 5 ], we checked whether in adult animals, after the enterocyte overloading with lipids, post-Golgi carriers pass through LAMP2-positive compartments.…”

“…Under normal conditions, post-Golgi carriers positive for LAPM2 were not found (unpublished results). However, earlier, we found that when the enterocytes of newborn rats were overloaded with lipids, the large chylomicrons were accumulated in the LAMP2-positive post-Golgi compartment [ 80 ]. The overloading of enterocytes with lipids led to an increase in the size of chylomicrons ( Figure 10 D–I quantified in Figure 11 I) and their prolonged stay in the post-Golgi compartments, which in 33% of cases were marked for LAMP2 and Neu-1.…”

The Diffusion Model of Intra-Golgi Transport Has Limited Power

“…Unless otherwise stated, all of the chemicals and reagents were obtained from previously indicated sources [ 55 , 56 ] or from Sigma (Milan, Italy). FUGENE6 transfection reagent was from Roche (Monza, Italy).…”

“…For electron microscopy (EM), the samples were prepared as described previously [ 6 , 9 , 56 , 57 , 58 , 59 , 60 ]. All manipulations were carried out at room temperature (~21 °C) unless otherwise stated.…”

“…For the identification of cells transfected with AFP, PFP, PCIII-GFP, or VFP or after cell microinjection, we used CLEM based on vertical sectioning, as described in [ 55 , 56 ]. For CLEM and cryo-sectioning, the cells on Petri dishes were fixed in 4% paraformaldehyde and 0.05% glutaraldehyde.…”