Lymphocytes in Alzheimer’s Disease Pathology: Altered Signaling Pathways

Alzheimer's disease (AD) is a neurodegenerative disorder marked by progressive impairment of cognitive ability. Patients with AD display neuropathological lesions including plaques, neurofibrillary tangles, and neuronal loss in brain regions linked to cognitive functions. Despite progress in uncovering many of the factors that contribute to the etiology of this disease, the cause of neuronal death is largely unknown. Neuroinflammation seems to play a critical role in the pathogenesis of AD. Inflammatory processes in the brain are mainly mediated by the intrinsic innate immune system consisting of astrocytes and microglial cells, and cytokine, chemokine, and growth factor signaling molecules. However mounting evidence suggest that the Central Nervous System (CNS) is accessible to lymphocytes and monocytes from the blood stream, indicating that there is an intense crosstalk between the immune and the CN systems. On the other hand, some AD-specific brain-derived proteins or metabolites may enter the plasma through a deficient blood-brain barrier, and exert some measurable signaling properties in peripheral cells. The goals of this review are: 1) to explore the evidences of changes in signaling pathways that could mediate both central and peripheral manifestations of AD, and 2) to explore whether changes in immune cells, particularly lymphocytes, could contribute to AD pathogenesis

Inactivation of CDK/pRb Pathway Normalizes Survival Pattern of Lymphoblasts Expressing the FTLD-Progranulin Mutation c.709-1G>A

8 figuras, 2 tablasBackground Mutations in the progranulin (PGRN) gene, leading to haploinsufficiency, cause familial frontotemporal lobar degeneration (FTLD-TDP), although the pathogenic mechanism of PGRN deficit is largely unknown. Allelic loss of PGRN was previously shown to increase the activity of cyclin-dependent kinase (CDK) CDK6/pRb pathway in lymphoblasts expressing the c.709-1G>A PGRN mutation. Since members of the CDK family appear to play a role in neurodegenerative disorders and in apoptotic death of neurons subjected to various insults, we investigated the role of CDK6/pRb in cell survival/death mechanisms following serum deprivation. Methodology/Principal Findings We performed a comparative study of cell viability after serum withdrawal of established lymphoblastoid cell lines from control and carriers of c.709-1G>A PGRN mutation, asymptomatic and FTLD-TDP diagnosed individuals. Our results suggest that the CDK6/pRb pathway is enhanced in the c.709-1G>A bearing lymphoblasts. Apparently, this feature allows PGRN-deficient cells to escape from serum withdrawal-induced apoptosis by decreasing the activity of executive caspases and lowering the dissipation of mitochondrial membrane potential and the release of cytochrome c from the mitochondria. Inhibitors of CDK6 expression levels like sodium butyrate or the CDK6 activity such as PD332991 were able to restore the vulnerability of lymphoblasts from FTLD-TDP patients to trophic factor withdrawal. Conclusion/Significance The use of PGRN-deficient lymphoblasts from FTLD-TDP patients may be a useful model to investigate cell biochemical aspects of this disease. It is suggested that CDK6 could be potentially a therapeutic target for the treatment of the FTLD-TDPThis work has been supported by grants from Ministry of Education and Science (SAF2007-61701, SAF2010-15700, SAF2011-28603), Fundación Eugenio Rodríguez Pascual, and Basque Government (Saiotek program 2008–2009). NE holds a fellowship of the JAE predoctoral program of the CSICPeer reviewe

HTLV-1 infection in solid organ transplant donors and recipients in Spain

HTLV-1 infection is a neglected disease, despite infecting 10-15 million people worldwide and severe illnesses develop in 10% of carriers lifelong. Acknowledging a greater risk for developing HTLV-1 associated illnesses due to immunosuppression, screening is being widely considered in the transplantation setting. Herein, we report the experience with universal HTLV testing of donors and recipients of solid organ transplants in a survey conducted in Spain. All hospitals belonging to the Spanish HTLV network were invited to participate in the study. Briefly, HTLV antibody screening was performed retrospectively in all specimens collected from solid organ donors and recipients attended since the year 2008. A total of 5751 individuals were tested for HTLV antibodies at 8 sites. Donors represented 2312 (42.2%), of whom 17 (0.3%) were living kidney donors. The remaining 3439 (59.8%) were recipients. Spaniards represented nearly 80%. Overall, 9 individuals (0.16%) were initially reactive for HTLV antibodies. Six were donors and 3 were recipients. Using confirmatory tests, HTLV-1 could be confirmed in only two donors, one Spaniard and another from Colombia. Both kidneys of the Spaniard were inadvertently transplanted. Subacute myelopathy developed within 1 year in one recipient. The second recipient seroconverted for HTLV-1 but the kidney had to be removed soon due to rejection. Immunosuppression was stopped and 3 years later the patient remains in dialysis but otherwise asymptomatic. The rate of HTLV-1 is low but not negligible in donors/recipients of solid organ transplants in Spain. Universal HTLV screening should be recommended in all donor and recipients of solid organ transplantation in Spain. Evidence is overwhelming for very high virus transmission and increased risk along with the rapid development of subacute myelopathy

On the mechanism of glucagon stimulation of hepatic gluconeogenesis

The addition of L-alanine as substrate to a perfused rat liver preparation produced a five-fold increase in the rate of glucose production. This enhancement of the gluconeogenic flux seems to be a consequence of a rise in the steady-state levels of pyruvate and oxaloacetate subsequent to the rise in alanine concentration. Glucagon (2 x 10-9 M) increased the gluconeogenic flux from alanine (10 mM) by 50 percent, even though the concentration of the substrate in the perfusion fluid was at saturation. This effect was accompanied by a rise in the intracellular concentration of alanine. However, the steady-state concentrations of pyruvate and oxaloacetate were decreased, probably as a consequence of a more reduced state of the nicotinamide-nucleotide system. In vivo, the intraperitoneal administration of glucagon to starved rats was accompanied by a decrease in the hepatic alanine and pyruvate concentrations despite the striking effects raising the plasma glucose levels. These observations seem to indicate that the effect of the hormone increasing the hepatic glucose output must be mediated through some other mechanism(s) independent of the intracellular variations in the hepatic amino acids levels.This work has been supported by grants from Comisión Asesora para el Desarrollo de la Investigación Científica, Lilly Indiana de Espafia, S. A. and Essex Espafia. A.M.R. is a recipient of a fellowship from the Spanish Secretary of Science and Education

On the mechanism of the glucagon-induced inhibition of hepatic protein synthesis

The intraperitoneal administration of glucagon (200 μg) to rats produced a transient increase of the hepatic polypeptide chain completion time, the increase being maximum at 5 min returning to control values at 20 min. This inhibitory effect was sustained when glucagon was constantly supplied by continuous infusion. Postmitochondrial supernatants from livers of the control group or rats treated with glucagon for 5 min showed no difference in their protein synthetic activity. After 20 min of intraperitoneal administration of the hormone, that is, when the effect on protein synthesis had vanished, the levels of cAMP were still 40% above those of the control group, and the ribosomal proteins were 110% more phosphorylated. These results suggest that the observed effect of glucagon is not due to its direct action on the protein synthesis machinery. On the other hand, the variations in the hepatic amino acid content brought about by glucagon do not appear to be quantitatively significant to account for the observed inhibition of protein synthesis. The effect of glucagon was always paralleled by a decrease in the [ATP] [ADP] ratio which may be responsible for the observed decrease in the rates of elongation and/or termination steps of protein synthesis. Glucagon also produced a rise in the [NADH] [NAD+] ratio in both cellular compartments, cytosol and mitochondria, as reflected by the rise in the lactate to pyruvate and the β-hydroxybutyrate to acetoacetate ratios. This shift of the NAD+ couple to a more reduced state seems to be the result of an increased mobilization and oxidation of fatty acids brought about by the hormone. It is postulated then that the primary effect of glucagon leading to a decrease in protein synthesis is probably to increase the state of reduction of the hepatic nicotinamide nucleotide system. This point of view is supported by the fact that the nicotinamide and adenine nucleotide systems in rat liver are in equilibrium through cytosolic equilibrium reactions, so that a decrease in the [ATP] [ADP] ratio brought about by glucagon may be secondary to the increase in the [NADH] [NAD+] ratio. This hypothesis is supported by the fact that glucagon was not effective in inhibiting hepatic protein synthesis in rats pretreated with a drug, 2-benzene-sulfonamido-5-(β-methoxy-ethoxy)pyrimidine, that prevents fatty acid mobilization and the subsequent changes in the [NADH] [NAD+] and [ATP] [ADP] ratios. Furthermore, the administration of exogenous fatty acid brings about an inhibition of the rate of hepatic protein synthesis accompanied by a decrease in the ATP levels and an increase in the state of reduction of the NAD+ system.This work has been supported by a grant from the “Comisión Asesora para el Desarrollo de la Investigación” and a research grant from Essex Esptia, S. A. (Madrid, Spain). A.M.R. and J.P.D. were recipients of fellowships from the Spanish Ministry of Education and Science

Metabolic features of isolated rat lung cells. I. Factors controlling glucose utilization

Isolated rat lung cell suspensions were prepared by collagenase digestion of the lung stroma. These cells were functionally competent as judged, among other criteria, by their constant rates of oxygen uptake and glucose utilization. An important metabolic feature of these cells is that they display very high glycolytic rates. At least 60% of the glucose utilized was converted to lactate, regardless of the glucose concentration in the medium. The state of reduction of the nicotinamide system, as indicated by the lactate-to-pyruvate ratio, was normal, thus indicating that the high glycolytic fluxes are not related to poor oxygenation of the preparation. Utilization of glucose displayed Michaelis-Menten saturation type kinetics with a V(max) of 331 nmol/106 cells per h and an apparent K(m) of 2.4 mM. These values were not affected by the presence of ouabain (0.1 mM), mannoheptulose (5 mM), or insulin (1 mU/ml), whereas phloridzin produced a drastic inhibition of glucose utilization showing an apparent K(i) of 0.4 mM. The substitution of sodium by K+ or Li+ as the predominant cations in the incubation medium does not alter rates of glucose utilization. Optimal pH for glucose utilization was within the physiological range with a more pronounced inhibitory effect at alkaline pH's. The intracellular concentration of glucose was found to be low. This finding, in conjunction with a Q10 (27-37°C) for glucose utilization above 2.0 and the differential effects of D- and L-glucose on lactate production, seems to indicate that a stereospecific glucose transport system exists in lung cells. Several findings point to glucose transport into the lung cells as a probable rate-limiting step for its metabolism: 1) the activity of the glycolytic enzymes largely exceeded the observed rate of glucose utilization; 2) the decrease in enzyme activity during starvation was not accompanied by a decreased glycolytic flux, suggesting that factors other than enzyme activity, perhaps the supply of fuel, are rate limiting in the overall process of glucose breakdown; 3) fructose was able to increase lactate production in the presence of saturating concentrations of glucose. These additive effects of glucose and fructose seem to support the point of view that it is not the glycolytic machinery but the supply of fuel which is rate limiting for glucose utilization by isolated rat lung cells

On the mechanism of stimulation of ureagenesis by gluconeogenic substrates: Role of pyruvate carboxylase

Gluconeogenic substrates, lactate or pyruvate, or ornithine produced 100% increase of urea synthesis from NH4Cl. The combined administration of ornithine and lactate (or pyruvate) produced more than additive effects, indicating that they acted at different steps in a potentiating manner. The uptake of ornithine was enhanced by gluconeogenic substrates. This finding may explain, at least in part, the stimulating effect of these substrates on ureagenesis from NH4Cl and ornithine. The gluconeogenic substrate-induced stimulation of ureagenesis from NH4Cl was still observed under conditions of reduced flux through pyruvate carboxylase, ruling out that their action was exclusively mediated by the anaplerotic effect of this enzyme. Pyruvate was a more potent stimulator of ureagenesis than lactate and its effect less sensitive to pyruvate carboxylase inhibition. These observations indicate that a correlation exists between stimulation of ureagenesis by gluconeogenic substrates and flux through pyruvate dehydrogenase. It is concluded that gluconeogenic substrates may stimulate ureagenesis from NH4Cl by 1) increasing intracellular ornithine availability and/or 2) enhancing flux through pyruvate dehydrogenase and consequently the tricarboxylic acid cycle activity.Peer reviewe