Biomedical subjects

Juan G Reyes

Publications and source records attributed to Juan G Reyes.

9 recordsLinked to original sources

PubMed2006

Up-regulation of CD95 (Apo-1/Fas) is associated with spermatocyte apoptosis during the first round of spermatogenesis in the rat.

Apoptosis plays a major role in controlling both the rate of sperm production and chromosomal abnormalities in adult male testes. However, little is known on the mechanisms controlling induction and execution of apoptosis under physiological conditions. In this work we have uncovered a major role for the cell death receptor Fas in both the extrinsic and intrinsic pathways in normal germ cell apoptosis. We show here that Fas levels increased significantly in a group of germ cell in 25 d old rats, which were identified as spermatocytes and only a few spermatogonia. In addition, we show that isolated spermatocytes expressing high levels of Fas display activation of caspase-8, -9, -3, -6 and -2, as well as increased levels of intracellular calcium and decreased pH, which coincides with stabilization of p53, and transcriptional activation of PUMA and Fas. Therefore, our data strongly suggests that transcriptional up regulation of Fas could predispose a group of spermatocytes to Fas ligand triggering apoptosis by the extrinsic and intrinsic pathway.

Animals↗

PubMed2006

Apoptosis induced by prolonged exposure to odorants in cultured cells from rat olfactory epithelium.

Multicellular organisms undergo programmed cell death (PCD) as a mechanism for tissue remodeling during development and tissue renewal throughout adult life. Overdose of some neuronal receptor agonists like glutamate can trigger a PCD process termed excitotoxicity in neurons of the central nervous system. Calcium has an important role in PCD processes, especially in excitotoxicity. Since the normal turnover of olfactory receptor neurons (ORNs) relies, at least in part, on an apoptotic mechanism and odor transduction in ORNs involves an increase in intracellular Ca2+ concentration ([Ca2+]i), we investigated the possibility that long-term exposures to odorants could trigger an excitotoxic process in olfactory epithelial cells (EC). We used single-cell [Ca2+]i determinations and fluorescence microscopy techniques to study the effects of sustained odorant exposures in olfactory EC in primary culture. Induction of PCD was evaluated successively by three independent criteria: (1) measurements of DNA fragmentation, (2) translocation of phosphatidylserine to the external leaflet of the plasma membrane, and (3) caspase-3 activation. Our results support the notion of an odorant-induced PCD in olfactory EC. This odorant-induced PCD was prevented by LY83583, an odorant response inhibitor, suggesting that ORNs are the main epithelial cell population undergoing odorant-induced PCD.

Aminoquinolines↗

PubMed2006

Caspase activation throughout the first wave of spermatogenesis in the rat.

Early in postnatal life, the first wave of spermatogenesis is accompanied by an initial wave of germ cell apoptosis. This may reflect an adjustment in the number of germ cells that can be adequately maintained by Sertoli cells. Two major pathways (intrinsic and extrinsic) are involved in the process of caspase activation and apoptosis in mammalian cells. The extrinsic pathway is characterized by the oligomerization of death receptors such as FAS or tumor necrosis factor, followed by the activation of caspase-8 and caspase-3. The intrinsic pathway involves the activation of procaspase-9, which in turn activates caspase-3. Extensive information is available concerning apoptotic inducers and their possible mechanisms in the adult rat. However, no data exist regarding the molecular and cellular mechanisms governing physiological cell death during puberty in the male rat. We have studied caspase activation throughout the first wave of spermatogenesis in the rat under physiological conditions, by combining the TUNEL procedure with the localization of active caspases in germ cells. We observed TUNEL-positive germ cells in rats of 5-40 days of age, the highest number being found in 25-day-old rats. TUNEL-positive and caspase-3-positive germ cells appeared as long chains of interconnected germ cells in 25-day-old rats. Caspase activation was assayed by either immunohistochemistry with antibodies against active caspase-3, -8, and -9, or by determining enzymatic activity in seminiferous tubules extracts. Both techniques showed activation of caspase-3, -8, and -9 in 25-day-old rats and low enzymatic activity at other ages. Confocal scanning laser microscopy indicated that active caspase-3, -8, and -9 co-localized with TUNEL-positive cells. Thus, caspase-3, -8, and -9 are active in apoptotic germ cells during the first wave of rat spermatogenesis. The extrinsic pathway of apoptosis may therefore play an important role in germ cell apoptosis during puberty in the rat.

Animals↗

PubMed2006

Hexose transporters GLUT1 and GLUT3 are colocalized with hexokinase I in caveolae microdomains of rat spermatogenic cells.

Postmeiotic spermatogenic cells, but not meiotic spermatogenic cells respond differentially with glucose-induced changes in [Ca2+]i indicating a differential transport of glucose via facilitative hexose transporters (GLUTs) specifically distributed in the plasma membrane. Several studies have indicated that plasma membrane in mammalian cells is not homogeneously organized, but contains specific microdomains known as detergent-resistant membrane domains (DRMDs), lipid rafts or caveolae. The association of these domains and GLUTs isoforms has not been characterized in spermatogenic cells. We analyzed the expression and function of GLUT1 and GLUT3 in isolated spermatocytes and spermatids. The results showed that spermatogenic cells express both glucose transporters, with spermatids exhibiting a higher affinity glucose transport system. In addition, spermatogenic cells express caveolin-1, and glucose transporters colocalize with caveolin-1 in caveolin-enriched membrane fractions. Experiments in which the integrity of caveolae was disrupted by pretreatment with methyl-beta-cyclodextrin, indicated that the involvement of cholesterol-enriched plasma membrane microdomains were involved in the localization of GLUTs and uptake of 2-deoxyglucose. We also observed cofractionation of GLUT3 and caveolin-1 in low-buoyant density membranes together with their shift to higher densities after methyl-beta-cyclodextrin treatment. GLUT1 was found in all fractions isolated. Immunofluorescent studies indicated that caveolin-1, GLUT1, and hexokinase I colocalize in spermatocytes while caveolin-1, GLUT3, and hexokinase I colocalize in spermatids. These findings suggest the presence of hexose transporters in DRMDs, and further support a role for intact caveolae or cholesterol-enriched membrane microdomains in relation to glucose uptake and glucose phosphorylation. The results would also explain the different glucose-induced changes in [Ca2+]i in both cells.

3-O-Methylglucose↗

PubMed2006

Sustained acclimatization in Chilean mine workers subjected to chronic intermittent hypoxia.

Farias, Jorge G., Jorge Osorio, Gustavo Soto, Julio Brito, Patricia Siques, and Juan G. Reyes. Sustained acclimatization in Chilean mine workers subjected to chronic intermittent hypoxia. High Alt. Med. Biol. 7:302-306, 2006--We wanted to know if sea-level mine workers exposed previously to chronic intermittent hypoxia reached a steady acclimatization at 36 months under hypobaric hypoxia. An intermittently exposed group of mine workers (IE, n = 25) were subjected to submaximal exercise (100 W) at 4500 m. Their systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), and hemoglobin oxygen saturation (HbSatO(2)) were monitored. Two comparison groups of unacclimatized sea-level workers (n = 17) were studied. A nonexposed group (NE) performed 5 min of submaximal exercise at sea level. Some kind of exercise was performed both by an acutely exposed group (AE) and IE group at 4500 m. No statistical differences were found for HR, SBP, and DBP (p > 0.05) during exercise between IE and AE groups. Resting HbSatO(2) of IE (87 +/- 6%) was lower than NE (97 +/- 3%) (p < 0.05), but was higher than AE (82 +/- 4%) (p < 0.05). In the exercise condition, HbSatO(2) of IE (85 +/- 5%) was lower than NE (95 +/- 3%) (p < 0.05), but was higher than AE (76 +/- 2%) (p < 0.05). These responses were maintained through the 6 months of the study period. Thus, mine workers subjected to intermittent hypobaric condition for 3 years showed a good degree of acclimatization that was maintained through time.

Acclimatization↗

PubMed2005

Changes of enzyme activity in lipid signaling pathways related to substrate reordering.

The static fluid mosaic model of biological membranes has been progressively complemented by a dynamic membrane model that includes phospholipid reordering in domains that are proposed to extend from nanometers to microns. Kinetic models for lipolytic enzymes have only been developed for homogeneous lipid phases. In this work, we develop a generalization of the well-known surface dilution kinetic theory to cases where, in a same lipid phase, both domain and nondomain phases coexist. Our model also allows understanding the changes in enzymatic activity due to a decrease of free substrate concentration when domains are induced by peptides. This lipid reordering and domain dynamics can affect the activity of lipolytic enzymes, and can provide a simple explanation for how basic peptides, with a strong direct interaction with acidic phospholipids (such as beta-amyloid peptide), may cause a complex modulation of the activities of many important enzymes in lipid signaling pathways.

Animals↗

PubMed2004

Kinetics, molecular basis, and differentiation of L-lactate transport in spermatogenic cells.

Round spermatid energy metabolism is closely dependent on the presence of L-lactate in the external medium. This L-lactate has been proposed to be supplied by Sertoli cells in the seminiferous tubules. L-Lactate, in conjunction with glucose, modulates intracellular Ca(2+) concentration in round spermatids and pachytene spermatocytes. In spite of this central role of L-lactate in spermatogenic cell physiology, the mechanism of L-lactate transport, as well as possible differentiation during spermatogenesis, has not been studied in these cells. By measuring radioactive L-lactate transport and intracellular pH (pH(i)) changes with pH(i) fluorescent probes, we show that these cells transport L-lactate using monocarboxylate-H(+) transport (MCT) systems. RT-PCR, in situ mRNA hybridization, and immunocyto- and immunohistochemistry data show that pachytene spermatocytes express mainly the MCT1 and MCT4 isoforms of the transporter (intermediate- and low-affinity transporters, respectively), while round spermatids, besides MCT1 and MCT4, also show expression of the MCT2 isoform (high-affinity transporter). These molecular data are consistent with the kinetic data of L-lactate transport in these cells demonstrating at least two transport components for L-lactate. These separate transport components reflect the ability of these cells to switch between the generation of glycolytic L-lactate in the presence of external glucose and the use of L-lactate when this substrate is available in the external environment. The supply of these substrates is regulated by the hormonal control of Sertoli cell glycolytic activity.

Animals↗

PubMed2002

Permeability changes induced by polylysines in rat spermatids.

High molecular weight (HMW, >15 kDa) but not low molecular weight (LMW, <15 kDa) polylysines (PLs) bound and induced permeability changes in rat spermatid plasma membranes, estimated by Mn2+ quenching of intracellular indo-1 fluorescence (K(1/2) = 3.3 +/- 0.5 microg/ml) and Co2+ quenching of intracellular calcein. The pharmacology of the Mn2+ entry pathway activated by HMW PL does not suggest that Ca2+ channels are involved in this phenomenon. Concentrations of HMW PL that induced divalent ion entry did not induce the entry of ethidium bromide, suggesting that HMW PL first bound and perturbed the plasma membrane structure inducing a non-specific increase in membrane permeability. High concentrations of HMW PL induced cell lysis (K(1/2) = 23 microg/ml). The binding of HMW PL, initially homogenous on the cell surface, subsequently progressed to a segregated pattern resembling a clustering phenomenon.

Animals↗

PubMedDate not supplied

Increase in testicular temperature and vascularization induced by hypobaric hypoxia in rats.

The exposure of male rats to continuous chronic hypobaric hypoxia (HH) and intermittent chronic hypobaric hypoxia induced evident changes in testicular morphology and spermatogenic cell metabolism. The mechanisms that underlie these changes under HH are not known. In this work, we have tested the hypothesis that in rats subjected to HH, the testis undergoes changes in vascularization leading to changes in temperature homeostasis. Male Wistar rats (247 +/- 16 g) were maintained in normobaric or hypobaric (428 torr, equivalent to 4600 m a.s.l) conditions. At days 0, 5, 15, and 30 postexposure, 12 rats were anesthetized with ketamine, and the intratesticular temperature was determined. These rats were subsequently sacrificed and the testicles were fixed in formaldehyde and processed for routine histological analysis. Our results showed that the height of the seminiferous epithelium decreased significantly at day 5 posthypoxia and thereafter, indicating a decreased spermatogenesis. Intratesticular temperature increased (1.5 degrees C) and remained high after 5 days of hypoxia exposure. Correlated with these changes, histometrical analysis of the number of blood vessels in the testicular interstitium was significantly increased by day 5 and afterwards. Morphological classification of interstitial blood vessels indicates a transition from capillaries to larger vessels as the hypoxia exposure progresses.

Altitude↗