Rat age-related benign prostate hyperplasia is concomitant with an increase in the secretion of low ramified α-glycosydic polysaccharides

This work analysed the expression of prostate polysaccharides in rats with age-related benign prostatic hyperplasia (BPH) for a better understanding of the possible relationship between prostate polysaccharides secretion and BPH onset. For this, prostatic glands from 1 month-old, 3 months-old, 6 months-old and 12 months-old Sprague-Dawley rats were processed in order to identify their overall polysaccharide content. Additionally, serum testosterone was also determined. One-month old rats showed significantly (P < 0.05) lower testosterone levels (0.77 ng/mL±0.12 ng/mL) compared with the other groups, which showed no significant difference among them. PAS staining showed positive polysaccharides markings in both the prostatic lumen and inside of luminal prostatic cells in all groups. Semiquantitative analysis of intraluminal PAS showed that one month-old rats had significantly (P < 0.005) lower PAS intensity when compared with all other groups (100.0 ± 0.5, arbitrary units vs. 107.3 ± 0.6, arbitrary units in 3 months-old ones), whereas 12 months-old ones showed significantly (P < 0.005) higher values when compared with all other groups (133.6 ± 3.5, arbitrary units in 12 months-old rats vs. 108.6 ± 1.4, arbitrary units in 6 months-old ones). The PAS + content practically disappeared when tissues were pre-incubated with either α-amylase or amyloglucosidase, regardless of a previous incubation with proteinase K. Incubation of prostate extracts from 12 months-old rats for 2 h with α-amylase yielded a significantly higher amount of free glucose (1.47 nmol/mg protein±0.23 nmol/mg protein vs. 0.32 nmol/mg protein±0.01 nmol/mg protein in untreated extracts). Similar results were obtained when extracts were pre-incubated with amyloglucosidase. Contrarily, pre-incubation with N-glycosidase induced a significantly (P < 0.05), much lower increase of free glucose. Pre-treatment with proteinase K did not significantly modify these results, which indicate that BPH is related to an increase in the secretion of low ramified ductal α-glycosydic polysaccharides that were not protected against lysis by any type of protein protective core. These changes seem to not be related with concomitant variations in serum testosterone levels.

Immunochemical Study of the Effect of F2Glc on Glycogen Synthase Translocation and Glycogen Synthesis in Isolated Rat Hepatocytes

The compound 2-deoxy-2-fluoro-α-D-glucopyranosyl fluoride (F₂Glc), which is a nonmetabolized superior glucose analogue, is a potent inhibitor of glycogen phosphorylase and pharmacological properties are reported. Glycogen phosphorylase (GP) and glycogen synthase (GS) are responsible of the degradation and synthesis, respectively, of glycogen which is a polymer of glucose units that provides a readily available source of energy in mammals. GP and GS are two key enzymes that modulate cellular glucose and glycogen levels; therefore, these proteins are suggested as potential targets for the treatment of diseases related to glycogen metabolism disorders. We studied by Western Blot technique that F₂Glc decreased GP activity, and we also showed that F₂Glc did not affect GS activity and its translocation from a uniform cytosolic distribution to the hepatocyte periphery, which is crucial for glycogen synthesis, using immunoblotting and immunofluorescence labeling techniques. F₂Glc specifically inhibits glycogenolysis pathway and permits a greater deposition of glycogen. These observations open up the possibility of further develop drugs that act specifically on GP. The ability to selectively inhibit GP, which is a key enzyme for the release of glucose from the hepatic glycogen reserve, may represent a new approach for the treatment of hyperglycemia in type 2 diabetes.

Intracellular calcium movements of boar spermatozoa during 'in vitro' capacitation and subsequent acrosome exocytosis follow a multiple-storage place, extracellular calcium-dependent model

This work analysed intracellular calcium stores of boar spermatozoa subjected to 'in vitro' capacitation (IVC) and subsequent progesterone-induced acrosome exocytosis (IVAE). Intracellular calcium was analysed through two calcium markers with different physico-chemical properties, Fluo-3 and Rhod-5N. Indicative parameters of IVC and IVAE were also evaluated. Fluo-3 was located at both the midpiece and the whole head. Rhod-5N was present at the sperm head. This distribution did not change in any of the assayed conditions. Induction of IVC was concomitant with an increase in both head and midpiece Ca(2+) signals. Additionally, while IVC induction was concurrent with a significant (p < 0.05) increase in sperm membrane permeability, no significant changes were observed in O2 consumption and ATP levels. Incubation of boar spermatozoa in the absence of calcium showed a loss of both Ca(2+) labellings concomitantly with the sperm's inability to achieve IVC. The absence of extracellular calcium also induced a severe decrease in the percentage of spermatozoa exhibiting high mitochondrial membrane potential (hMMP). The IVAE was accompanied by a fast increase in both Ca(2+) signalling in control spermatozoa. These peaks were either not detected or much lessened in the absence of calcium. Remarkably, Fluo-3 marking at the midpiece increased after progesterone addition to sperm cells incubated in a medium without Ca(2+) . The simultaneous addition of progesterone with the calcium chelant EGTA inhibited IVAE, and this was accompanied by a significant (p < 0.05) decrease in the intensity of progesterone Ca(2+) -induced peak, O2 consumption and ATP levels. Our results suggest that boar spermatozoa present different calcium deposits with a dynamic equilibrium among them and with the extracellular environment. Additionally, the modulation role of the intracellular calcium in spermatozoa function seems to rely on its precise localization in boar spermatozoa.

Glucose and fructose as functional modulators of overall dog, but not boar sperm function

The main aim of the present work was to test the effects of glucose and fructose on the phosphorylation levels of proteins linked to the control of overall sperm function in two species with very different metabolic characteristics, dog and boar. Incubation of dog spermatozoa with 10mM glucose increased serine phosphorylation of proteins related to cell cycle and signal transduction including cyclins B and E, Cdk2, Cdk6, Cdc6, PYK2, c-kit, Raf-1, TRK and several protein phosphatases. Incubation of dog spermatozoa with 10mM fructose decreased serine phosphorylation levels of cyclins B and D3, Cdk1/Cdc2, Cdk2, Cdk6, Akt, PI3 kinase, ERK-1 and protein kinase C. Incubation of boar spermatozoa with glucose or fructose did not modify any of the phosphorylation patterns studied. Given that one important difference between dog and boar spermatozoa is the presence of glucokinase (GK) in dog but not in boar, GK-transfected COS7 cells were incubated with either 10mM glucose or 10mM fructose. Incubation of GK-transfected cells with fructose decreased serine phosphorylation of cyclin A, ERK-2 and Hsp-70. In contrast, incubation of control COS7 cells with fructose increased serine phosphorylation of Cdk6, Cdk1/Cdc2, protein kinase C and Hsp-70. Incubation with glucose did not induce any significant effect. Our results indicate that monosaccharides act as signalling compounds in dog spermatozoa after ejaculation through changes in the phosphorylation levels of specific proteins. One of the factors that may be related to the action of sugars is the equilibrium of the total sperm hexokinase activity, in which the presence or absence of GK appears to be relevant.

Cryopreservation-induced alterations in boar spermatozoa mitochondrial function are related to changes in the expression and location of midpiece mitofusin-2 and actin network

The authors analyzed changes in mitochondrial activity of boar semen during a standard cryopreservation protocol. For this purpose, mitochondrial activity was evaluated simultaneously with the rhythm of mitochondrial formation of reactive oxygen species (mROS) through a double MitoTracker Red/proxylfluorescamine stain. Moreover, we analyzed changes in the expression and location of two key regulatory elements of mitochondrial function, namely mitofusin-2 (Mfn2) and actin, during the freezing-thawing protocol. Our results indicate that mitochondrial activity and mROS formation decreased during cyropreservation, with an initial decrease during the cooling phase of the protocol. This decrease was accompanied by an increase in the amount of solubilized Mfn2, which was concomitant with a progressive extension of Mfn2 location from the apical zone of the midpiece to the whole midpiece. Simultaneously, cryopreservation induced a decrease in solubilized actin, which was concurrent with significant changes in the midpiece actin location. The observed changes in the expression and location of both Mfn2 and actin were already present after the cooling phase of the cryopreservation protocol. Our results suggest that freezing-thawing impaired mitochondrial function. This impairment was concomitant with a decrease in the mitochondrial capacity to synthesize mROS. This impairment is attributed to changes in mitochondrial volume as a result of alterations in the expression and location of both Mfn-2 and the actin network. Finally, the alterations of mitochondrial function induced by the cryopreservation protocol were already apparent at the cooling phase. This observation indicates that the cooling phase is a crucial stage in which mitochondrial alterations occur during cryopreservation.

75 GLUCOSE CONCENTRATION OF FREEZING EXTENDER MODULATES THE TYROSINE PHOSPHORYLATION PATTERN OF FROZEN-THAWED BOAR SPERMATOZOA

The optimization of freezing extenders is an essential issue for enhancing boar sperm cryosurvival. The aim of the present study was to disclose the role of glucose concentration of freezing extender on the metabolic activity of frozen–thawed spermatozoa. To achieve it, pooled sperm-rich ejaculate fractions from 5 mature and fertile boars (3 ejaculates per boar) were collected using the gloved-hand method. After centrifugation (2400g for 3 min), the sperm pellet was split into 7 aliquots. The aliquots were diluted to a final concentration of 1 × 109 sperm mL–1, in a Tris-citric extender supplemented with 20% egg-yolk, 3% glycerol, and 0, 0.05, 2, 4, 10, 55, or 185 mm glucose. All the extenders were adjusted to a pH of 6.8 and 310 mOsm kg–1 to avoid osmolarity effects. Extended semen samples were dispensed into 0.5-mL straws, and frozen in a programmable cell freezer at 20°C min–1. Thawing was carried out in a water bath at 37°C for 20 s. Afterward, an analysis of protein phosphorylation in tyrosine residues was carried out through bi-dimensional electrophoresis followed by a Western blot analysis. This analysis indicated that sperm samples frozen in extenders without glucose showed specific changes in the tyrosine phosphorylation pattern compared with fresh sperm. Furthermore, the addition of glucose in increasing concentrations to the freezing extender was accompanied by a concentration-dependent decrease in the overall tyrosine phosphorylation pattern, especially in proteins with a molecular weight ranging from 150 to 200 kDa and an acidic isoelectric point (pI). The maximal decrease was observed in spermatozoa frozen in the extender containing 185 mm glucose, in which an additional decrease in the tyrosine phosphorylation of proteins ranging from 60 to 80 kDa, and a basic pI was also observed. These results suggest that glucose is a modulator in the resistance of boar sperm to support freezing and thawing process, because the precise protein phosphorylation pattern of spermatozoa is directly linked to their functional status. In this way, a precise control of the glucose concentration of the freezing extender would be required to improve boar sperm cryoresistance. Supported by CICYT (AGL2005-00760 and AGL2004-04756-C02-02/GAN), Madrid and GERM (04543/07), Murcia, Spain.

A biochemistry and molecular biology course for secondary school teachers*

This article describes a course for reinforcing the knowledge of biochemistry in secondary school science teachers. The Department of Biochemistry and Molecular Biology of the University of Barcelona designed a course to bring these teachers up to date with this discipline. In addition to updating their knowledge of biochemistry and molecular biology, this course aims to provide teachers with a set of relevant laboratory practices that can be applied in their practical lessons.

Gluconeogenesis-Linked Glycogen Metabolism Is Important in the Achievement of In Vitro Capacitation of Dog Spermatozoa in a Medium Without Glucose1

In vitro capacitation of dog spermatozoa in a medium without sugars and with lactate as the metabolic substrate (l-CCM) was accompanied by a progressive increase of intracellular glycogen during the first 2 h of incubation, which was followed by a subsequent decrease of glycogen levels after up to 4 h of incubation. Lactate from the medium is the source for the observed glycogen synthesis, as the presence of [(14)C]glycogen after the addition to l-CCM with [(14)C]lactate was demonstrated. The existence of functional gluconeogenesis in dog sperm was also sustained by the presence of key enzymes of this metabolic pathway, such as fructose 1,6-bisphophatase and aldolase B. On the other hand, glycogen metabolism from gluconeogenic sources was important in the maintenance of a correct in vitro fertilization after incubation in the l-CCM. This was demonstrated after the addition of phenylacetic acid (PAA) to l-CCM. In the presence of PAA, in vitro capacitation of dog spermatozoa suffered alterations, which translated into changes in capacitation functional markers, like the increase in the percentage of altered acrosomes, a distinct motion pattern, decrease or even disappearance of capacitation-induced tyrosine phosphorylation, and increased heterogeneity of the chlorotetracycline pattern in capacitated cells. Thus, this is the first report indicating the existence of a functional glyconeogenesis in mammalian spermatozoa. Moreover, gluconeogenesis-linked glycogen metabolism seems to be of importance in the maintenance of a correct in vitro capacitation in dog sperm in the absence of hexoses in the medium.

Differential effects of glucose and fructose on hexose metabolism in dog spermatozoa

Incubation of dog spermatozoa with 10 mmol l(-1) glucose or fructose rapidly increased the intracellular content of glucose 6-phosphate and fructose 6-phosphate, although the effect of fructose was greater. These effects were correlated with increases in ATP, ribose 5-phosphate and glycogen contents, and in the rates of formation of L-lactate and CO2. In all cases, except for ATP and glycogen, the effect of fructose was greater than that of glucose. The total hexokinase activity of the crude extracts of dog spermatozoa was more sensitive to fructose than to glucose at lower concentrations (0.1-3.0 mmol l(-1)). Both monosaccharides induced a fast and intense increase in the overall tyrosine phosphorylation of dog spermatozoa, although their specific induced-phosphorylation patterns differed slightly. Glut 3 and Glut 5 hexose transporters were the main hexose transporters in dog spermatozoa; however, other possible SGLT family-related hexose transporters were also localized. These data indicate that, at concentrations from 1 mmol l(-1) to 10 mmol l(-1), fructose has a stronger effect than glucose on hexose metabolism of dog spermatozoa. These differences appear to be related to variations in the sensitivity of hexokinase activity. Moreover, the differential hexose metabolism induced by the two sugars had distinct effects on the function of dog spermatozoa, as revealed by the diverse patterns of tyrosine phosphorylation.

Intracellular distribution of glycogen synthase and glycogen in primary cultured rat hepatocytes

Changes in the intracellular distribution of liver glycogen synthase (GS) might constitute a new regulatory mechanism for the activity of this enzyme at cellular level. Our previous studies indicated that incubation of isolated hepatocytes with glucose activated GS and resulted in its translocation from a homogeneous cytosolic distribution to the cell periphery. These studies also suggested a relationship with insoluble elements of the cytoskeleton, in particular actin. Here we show the translocation of GS in a different experimental model that allows the analysis of this phenomenon in long-term studies. We describe the reversibility of translocation of GS and its effect on glycogen distribution. Incubation of cultured rat hepatocytes with glucose activated GS and triggered its translocation to the hepatocyte periphery. The relative amount of the enzyme concentrated near the plasma membrane increased with time up to 8 h of incubation with glucose, when the glycogen stores reached their maximal value. The lithium-induced covalent activation of GS was not sufficient to cause its translocation to the cell periphery. The intracellular distribution of GS closely resembled that of glycogen. Our results showed an interaction between GS and an insoluble element of the hepatocyte matrix. Although no co-localization between actin filaments and GS was observed in any condition, disruption of actin cytoskeleton resulted in a significantly lower percentage of cells in which the enzyme translocated to the cell periphery in response to glucose. This observation suggests that the microfilament network has a role in the translocation of GS.

Evidence for a functional glycogen metabolism in mature mammalian spermatozoa

The glycogen content in fresh raw dog spermatozoa was 0.22+/-0.03 micromol/mg protein. This matched with the presence of a glycogen-like staining in the head and midpiece. Glycogen levels lowered to 0.05 micromol/mg protein after incubation for 60 min without sugars. Addition of either 10 mM fructose or 10 mM glucose increased glycogen content to 0.70 micromol/mg protein. On the other hand, glycogen synthase activity ratio of fresh dog sperm (0.35+/-0.07, measured in the absence and the presence of glucose 6-P) increased to 0.55 with 10 mM fructose for 20 min, whereas glucose had a smaller effect. Spermatozoa extracts had also a protein of about 100 Kd, which reacted against a rat liver glycogen synthase antibody. This was located in sperm head and midpiece. Furthermore, glycogen phosphorylase activity ratio measured in presence and absence of AMP (0.25+/-0.03 in fresh samples) decreased to 0.15 by 10 mM glucose for 20 min, whereas fructose was less potent in this regard. The maximal effect of glucose and fructose were observed from 10-20 mM onwards. This work is the first indication for a functional glycogen metabolism in mammal spermatozoa, which could play an important role in regulating sperm survival in vivo.

Lithium's effects on rat liver glucose metabolism in vivo

Oral administration of lithium carbonate to fed-healthy rats strongly decreased liver glycogen content, despite the simultaneous activation of glycogen synthase and the inactivation of glycogen phosphorylase. The effect seemed to be related to a decrease in glucose 6-phosphate concentration and to a decrease in glucokinase activity. Moreover, in these animals lithium markedly decreased liver fructose 2,6-bisphosphate, which could be a consequence of the fall in glucose 6-phosphate and of the inactivation of 6-phosphofructo-2-kinase. Liver pyruvate kinase activity and blood insulin also decreased after lithium administration. Lower doses of lithium carbonate had less intense effects. Lithium administration to starved-healthy and fed-streptozotocin-diabetic rats caused a slight increase in blood insulin, which was simultaneous with increases in liver glycogen, glucose 6-phosphate, and fructose 2, 6-phosphate. Glucokinase, 6-phosphofructo-2-kinase, and pyruvate kinase activities also increased after lithium administration in starved-healthy and fed-diabetic rats. Lithium treatment activated glycogen synthase and inactivated glycogen phosphorylase in a manner similar to that observed in fed-healthy rats. Glycemia was not modified in any group of animals. These results indicate that lithium acts on liver glycogen metabolism in vivo in at least two different ways: one related to changes in insulinemia, and the other related to the direct action of lithium on the activity of some key enzymes of liver glucose metabolism.

Intracellular distribution of hepatic glucokinase and glucokinase regulatory protein during the fasted to refed transition in rats

We have studied the intracellular distribution in vivo of glucokinase (GK) and glucokinase regulatory protein (GKRP) in livers of fasted and refed rats, using specific antibodies against both proteins and laser confocal fluorescence microscopy. GK was found predominantly in the nucleus of hepatocytes from starved rats. GK was translocated to the cytoplasm in livers of 1- and 2-h refed animals, but returned to the nucleus after 4 h. GKRP concentrated in the hepatocyte nuclei and its distribution did not change upon refeeding. These results show that, in physiological conditions, GKRP is present predominantly in the nuclei of hepatocytes and that the translocation of hepatic GK from and to the nucleus is operative in vivo.

Glucose induces the translocation of glycogen synthase to the cell cortex in rat hepatocytes

After incubation with glucose a dramatic change in the intracellular distribution of glycogen synthase was observed in rat hepatocytes. Confocal laser scanning microscopy showed that glycogen synthase existed diffusely in the cytosol of control cells, whereas in cells incubated with glucose it accumulated at the cell periphery. Colocalization analysis between glycogen synthase immunostaining and actin filaments showed that the change in glycogen synthase distribution induced by glucose correlated with a marked increase in the co-distribution of the two proteins, indicating that, in response to glucose, glycogen synthase moves to the actin-rich area close to the membrane. When glycogen synthase was immunostained with rabbit anti-(glycogen synthase) and Protein A-colloidal gold, few particles were observed close to the membrane in control cells. In contrast, in cells incubated with glucose most of the gold particles were found near the membrane, confirming that glycogen synthase had moved to the cell cortex. Furthermore, in agreement with the glycogen synthase distribution, glycogen deposition appeared to be more active at the periphery of the cell.

Translocation and aggregation of hepatic glycogen synthase during the fasted-to-refed transition in rats

Changes in the activation state and intracellular distribution of liver glycogen synthase have been studied during the fasted-to-refed transition in rats. Glycogen synthase activity and activation state were measured in supernatants and pellets obtained after centrifugation of liver homogenates at 9200 g. Upon refeeding, the glycogen synthase activity ratio increased, in a time-dependent manner, in both fractions. The total activity of the enzyme decreased in supernatants and was quantitatively recovered in the pellets. Therefore, refeeding induced both the activation of glycogen synthase and its translocation from the soluble to the pelletable fraction. Immunocytochemical evidence indicates that refeeding induced the formation of clusters of glycogen synthase, which were recovered in the 9200 g sediments. However, the enzyme clusters did not locate with the glycogen particles in the pelletable fraction. The glycogen synthase activation state responded almost as an of-off switch to changes in the intracellular glucose 6-phosphate concentration in the range 0.2-0.3 mM. The amount of enzyme present in the pellets correlated linearly with the intracellular glucose 6-phosphate levels. These results indicate that glucose 6-phosphate is the key signal for both the activation and changes in intracellular localization of hepatic glycogen synthase in vivo.

Effects of glucose on the activation and translocation of glycogen synthase in diabetic rat hepatocytes

Incubation of hepatocytes from diabetic rats with glucose results in the translocation of glycogen synthase from soluble fractions to fractions which sediment at 9200 g. The extent of the translocation correlates positively with the intracellular concentration of glucose 6-phosphate. No difference was found between healthy and diabetic rats in the capacity of glycogen synthase to translocate to pellets in response to an increase in glucose 6-phosphate. In diabetic hepatocytes, glycogen synthase in the supernatant fractions was not activated upon incubation of the cells with glucose, whereas this sugar was able to activate the enzyme found in the fractions that could be pelleted. In the 9200-g pellets, the glycogen synthase activity ratio (-glucose 6-phosphate/+glucose 6-phosphate) from both healthy and diabetic animals correlated with the intracellular glucose 6-phosphate levels. In the supernatants, the glycogen synthase activity ratio from healthy cells also correlated with glucose 6-phosphate levels. In contrast, in diabetic cells the activation state of the soluble enzyme remained essentially unchanged despite the accumulation of glucose 6-phosphate.

Role of glucose 6-phosphate in the translocation of glycogen synthase in rat hepatocytes

Incubation of rat hepatocytes with glucose induces the translocation of glycogen synthase from soluble fractions to fractions which sediment at 10,000 g. Incubation of the cells with fructose, galactose, 2-deoxyglucose or 5-thioglucose, which activate glycogen synthase, also resulted in the translocation of the enzyme, whereas 3-O-methylglucose, 6-deoxyglucose and 1,5-anhydroglucitol, which do not cause the activation of the enzyme, were ineffective. Adenosine and carbonyl cyanide m-chlorophenylhydrazone, although activating glycogen synthase, did not induce its translocation. Mannoheptulose, which inhibits glucose phosphorylation, impaired the translocation of glycogen synthase induced by glucose. Furthermore, the extent of the translocation of the enzyme triggered by glucose and other sugars showed a high positive correlation with the intracellular concentration of glucose 6-phosphate. Microcystin, which blocks the activation of glycogen synthase by glucose, but not the accumulation of glucose 6-phosphate, did not affect the translocation of the enzyme. These results indicate that glucose 6-phosphate plays a role in the translocation of glycogen synthase in rat hepatocytes.

Glucose induces the translocation and the aggregation of glycogen synthase in rat hepatocytes

Incubation of rat hepatocytes with glucose results in a decrease in the amount of glycogen synthase activity found in supernatants obtained after centrifugation of cell homogenates at 9200 g. The enzymic activity was quantitatively recovered in the sediments. This effect of translocation was dose- and time-dependent and correlated with the amount of immunoreactive enzyme determined by immunoblotting in both fractions. Hydrolysis by alpha-amylase of glycogen accumulated upon incubation with the sugar did not affect the translocation pattern. Translocation was also observed when cells were incubated with 2-deoxyglucose, which did not result in accumulation of glycogen. Immunocytochemical evidence indicates that glucose induces the aggregation of glycogen synthase molecules into clusters which are recovered in the sediments. These results indicate that glucose, in addition to activating glycogen synthase, may trigger changes in the localization of the enzyme in the cell.