Lang, Florian, Gillian L. Busch, Markus Ritter, Harald Volkl, Siegfried Waldegger, Erich Gulbins, and Dieter Haussinger. Functional Significance of Cell Volume Regulatory Mechanisms. Physiol. Rev. ...

Functional Significance of Cell Volume Regulatory Mechanisms

Fructose is now such an important component of human diets that increasing attention is being focused on the fructose transporter GLUT5. In this review, we describe the regulation of GLUT5 not only in the intestine and testis, where it was first discovered, but also in the kidney, skeletal muscle, fat tissue, and brain where increasing numbers of cell types have been found to have GLUT5. GLUT5 expression levels and fructose uptake rates are also significantly affected by diabetes, hypertension, obesity, and inflammation and seem to be induced during carcinogenesis, particularly in the mammary glands. We end by highlighting research areas that should yield information needed to better understand the role of GLUT5 during normal development, metabolic disturbances, and cancer.

/pdf/regulation-of-the-fructose-transporter-glut5-in-health-and-21cb1rm3kd.pdf

Regulation of the fructose transporter GLUT5 in health and disease.

Mammalian sperm cells are activated prior to fertilization by high bicarbonate levels, which facilitate lipoprotein-mediated cholesterol efflux. The role of bicarbonate and cholesterol acceptors on the cholesterol organization in the sperm plasma membrane was tested. Bicarbonate induced an albumin-independent change in lipid architecture that was detectable by an increase in merocyanine staining (due to protein kinase A-mediated phospholipid scrambling). The response was limited to a subpopulation of viable sperm cells that were sorted from the non-responding subpopulation by flow cytometry. The responding cells had reduced cholesterol levels (30% reduction) compared with non-responding cells. The subpopulation differences were caused by variable efficiencies in epididymal maturation as judged by cell morphology. Membrane cholesterol organization was observed with filipin, which labeled the entire sperm surface of non-stimulated and non-responding cells, but labeled only the apical surface area of bicarbonate-responding cells. Addition of albumin caused cholesterol efflux, but only in bicarbonate-responding cells that exhibited virtually no filipin labeling in the sperm head area. Albumin had no effect on other lipid components, and no affinity for cholesterol in the absence of bicarbonate. Therefore, bicarbonate induces first a lateral redistribution in the low cholesterol containing spermatozoa, which in turn facilitates cholesterol extraction by albumin. A model is proposed in which phospholipid scrambling induces the formation of an apical membrane raft in the sperm head surface that enables albumin mediated efflux of cholesterol.

Bicarbonate stimulated phospholipid scrambling induces cholesterol redistribution and enables cholesterol depletion in the sperm plasma membrane

Sperm cryopreservation update: Cryodamage, markers, and factors affecting the sperm freezability in pigs.

Cryopreservation and post-thawed fertility of ram semen frozen in different trehalose concentrations.

Freezability prediction of boar ejaculates assessed by functional sperm parameters and sperm proteins.

Semen quality of postpubertal boars during increasing and decreasing natural photoperiods

Sperm quality in the caput, corpus, and cauda regions of the epididymis of healthy and sexually mature Landrace boars was studied. Epididymal sperm characteristics were examined by light microscopy (LM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Sperm vitality decreased very slightly although progressively with the transport of sperm through the epididymis. Osmotic resistance of acrosomes was very low in the sperm from the caput and approximately 100% in the corpus and cauda. The incidence of spermatozoa with the head detached from the tail remained stable in the first two regions of the epididymis, increasing notably in the cauda. Sperm agglutination increased progressively as sperm progressed along the epididymal duct. The percent of mature spermatozoa and aberrant spermatozoa increased from the caput to the cauda, whereas the percent of immature spermatozoa decreased. In the caput and corpus the percent of immature spermatozoa was similar, although in the caput they were characterized by the presence of a proximal cytoplasmic droplet; in the corpus the cytoplasmic droplet was distal. The acrosomal protuberance was highly developed in spermatozoa from the epididymal caput, but its volume was considerably reduced in those from the epididymal cauda. The electron density of the acrosomal content was lower in spermatozoa from the caput than in those from the epididymal cauda. The mitochondrial sheath of spermatozoa from the caput was made of voluminous mitochondria of unequal size, with a low electron-dense matrix. In the cauda region, the mitochondria were smaller in diameter, homogeneous in size, and with greater matrix electron density. This last fact is related to the loss of the capacity of spermatozoa to fold their tail by the midpiece as they progress along the epididymal duct. The complex epididymal maturation process of the sperm results in quantitative and qualitative changes that can be characterized in each of the three epididymal regions. The presence in the ejaculate of one or more gamete forms belonging to the epididymal caput, corpus, or cauda will allow workers to better establish the intensity of stress produced by a high frequency of semen collection.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.1939-4640.1995.tb01751.x

Comparative study of boar sperm coming from the caput, corpus, and cauda regions of the epididymis.

The HSP90AA1 sperm content and the prediction of the boar ejaculate freezability.

This study evaluated the effects of cooling, freezing and thawing on the plasma membrane integrity, kinetics and expression of two sugar transporters glucose transporter-3 and -5 (GLUT-3 and GLUT-5) in spermatozoa from Iberian boars. Semen samples were collected twice weekly from eight young, fertile Iberian boars of the 'Entrepelado' and 'Lampino' breeds. The samples were suspended in a commercial extender and refrigerated to 17 degrees C for transport to the laboratory (step A), where they were further extended with a lactose-egg yolk-based extender and chilled to 5 degrees C (step B) prior to freezing in the presence of glycerol (3%). Spermatozoa were assessed for plasma membrane integrity and sperm motility at each of the steps, including post-thaw (step C). Aliquots were also prepared for immunocytochemical localisation of the sugar transporters (fixed and thin smears for transmission and scanning electron microscopy levels respectively) and for SDS-PAGE electrophoresis and subsequent western blotting, using the same antibodies (rabbit anti-GLUT-3 and anti-GLUT-5 polyclonal antibodies). The results showed lower percentages of progressively motile spermatozoa at step C in both breeds, while the percentage of live spermatozoa was significantly lower only in the 'Entrepelado' breed. The results obtained from electron microscopy clearly showed that Iberian boar spermatozoa expressed the hexose transporters, GLUT-3 and GLUT-5. The pattern of expression, in terms of location and concentration, was characteristic in each case but, in the case of isoform GLUT-5, it remained constant during the different steps of freezing-thawing protocol. These results indicate that cryopreservation affects the status of sperm cells of Iberian boars by altering the distribution of some membrane receptors and decreasing the percentage values of parameters linked to sperm quality.

/pdf/effects-of-cryopreservation-on-semen-quality-and-the-5dcpnlmnel.pdf

M.D. Briz

Papers

Freezability prediction of boar ejaculates assessed by functional sperm parameters and sperm proteins.

Semen quality of postpubertal boars during increasing and decreasing natural photoperiods

Comparative study of boar sperm coming from the caput, corpus, and cauda regions of the epididymis.

The HSP90AA1 sperm content and the prediction of the boar ejaculate freezability.

Effects of cryopreservation on semen quality and the expression of sperm membrane hexose transporters in the spermatozoa of Iberian pigs