Mitochondrial oxygen consumption inhibition importance for TMT-dependent cell death in undifferentiated PC12 cells

The evolving role of mitochondria as a target for different death-inducing noxae prompted us to investigate trimethyltin (TMT)-dependent effects on mitochondrial functionality. For this purpose, we used a homogeneous cell culture model represented by undifferentiated PC12 cells. Mitochondria isolated from PC12 cells treated with TMT for 6, 12 and 24h, showed a time-dependent inhibition of ADP-stimulated oxygen consumption using succinate or glutamate/malate as substrate. Using a fluorescent assay, the effect of TMT on mitochondrial membrane potential (delta Psi) in PC12 cells was also determined. After 24h in culture, a strong loss of mitochondrial membrane potential (delta Psi) was observed in TMT-treated cells. Collapse of mitochondrial membrane potential correlated with an increased expression of bax/bcl-2 ratio, as evaluated by polymerase chain reaction. Western blotting and spectrophotometric analysis showed that cytochrome c release and activation of caspase 3 were concurrently induced. Our findings suggest that inhibition of mitochondrial respiration represents the early toxic event for cell death in PC12 due to trimethyltin.     

Participation of the chaperone Hsc70 in the trafficking and functional expression of ASIC2 in glioma cells

High-grade glioma cells express subunits of the ENaC/Deg superfamily, including members of ASIC subfamily. Our previous work has shown that glioma cells exhibit a basally active cation current, which is not present in low-grade tumor cells or normal astrocytes, and that can be blocked by amiloride. When ASIC2 is present within the channel complex in the plasma membrane, the channel is rendered non-functional because of inherent negative effectors that require ASIC2. We have previously shown that high-grade glioma cells functionally express this current because of the lack of ASIC2 in the plasma membrane. We now hypothesize that ASIC2 trafficking in glioma cells is regulated by a specific chaperone protein, namely Hsc70. Our results demonstrated that Hsc70 co-immunoprecipitates with ASIC2 and that it is overexpressed in glioma cells as compared with normal astrocytes. In contrast, there was no difference in the expression of calnexin, which also co-immunoprecipitates with ASIC2. In addition, glycerol and sodium 4-phenylbutyrate reduced the amount of Hsc70 expressed in glioma cells to levels found in normal astrocytes. Transfection of Hsc70 siRNA inhibited the constitutively activated amiloride-sensitive current, decreased migration, and increased ASIC2 surface expression in glioma cells. These results support an association between Hsc70 and ASIC2 that may underlie the increased retention of ASIC2 in the endoplasmic reticulum of glioma cells. The data also suggest that decreasing Hsc70 expression promotes reversion of a high-grade glioma cell to a more normal astrocytic phenotype.     

Basal activation of p70S6K results in adipose-specific insulin resistance in protein-tyrosine phosphatase 1B -/- mice

Although protein-tyrosine phosphatase 1B (PTP-1B) is a negative regulator of insulin action, adipose tissue from PTP-1B-/- mice does not show enhanced insulin-stimulated insulin receptor phosphorylation. Investigation of glucose uptake in isolated adipocytes revealed that the adipocytes from PTP-1B-/- mice have a significantly attenuated insulin response as compared with PTP-1B+/+ adipocytes. This insulin resistance manifests in PTP-1B-/- animals older than 16 weeks of age and could be partially rescued by adenoviral expression of PTP-1B in null adipocytes. Examination of adipose signaling pathways found that the basal p70S6K activity was at least 50% higher in adipose from PTP-1B-/- mice compared with wild type animals. The increased basal activity of p70S6K in PTP-1B-/- adipose correlated with decreases in IR substrate-1 protein levels and insulin-stimulated Akt/protein kinase B activity, explaining the decrease in insulin sensitivity even as insulin receptor phosphorylation was unaffected. The insulin resistance of the of the PTP-1B-/- adipocytes could also be rescued by treatment with rapamycin, suggesting that in adipose the loss of PTP-1B results in basal activation of mTOR (mammalian target of rapamycin) complex 1 leading to a tissue-specific insulin resistance.     

Ticks and mosquitoes as vectors of Borrelia burgdorferi s. l. in the forested areas of Szczecin

The aim of the study was to determine the infection level of adult forms and larvae of ticks and mosquitoes with Borrelia burgdorferi in the forested areas of Szczecin. A total of 1699 ticks Ixodes ricinus, including 1422 nymphs, 277 adult forms and 2862 mosquito females representing the genera Aedes (89.6%) and Culex (10.4%) were collected between the years 2004 and 2005. A further 3746 larvae and 1596 pupae of Culex pipiens pipiens were colleted from water bodies. Borrelia burgdorferi s. l. was detected in the arthropods by the method of indirect immunofluorescence assay (IFA). A positive immunological reaction was detected in 16.6% of the adult forms and in 16.5% of the nymphs of Ixodes ricinus. Spirochetes were also detected in 1.7% of mosquito females, 3.2% of larvae and in 1.6% of pupae of Culex pipiens pipiens. The results of the present study confirm that contact with ticks constitutes the main risk of contracting Lyme disease, although mosquitoes play a role as vectors as well.     

Measurements of Na+-occluded intermediates during the catalytic cycle of the Na+/K+-ATPase provide novel insights into the mechanism of Na+ transport

The Na⁺/K⁺-ATPase is an integral plasma membrane glycoprotein of all animal cells that couples the exchange of intracellular Na⁺ for extracellular K⁺ to the hydrolysis of ATP. The asymmetric distribution of Na⁺ and K⁺ is essential for cellular life and constitutes the physical basis of a series of fundamental biological phenomena. The pumping mechanism is explained by the Albers–Post model. It involves the presence of gates alternatively exposing Na⁺/K⁺-ATPase transport sites to the intracellular and extracellular sides and includes occluded states in which both gates are simultaneously closed. Unlike for K⁺, information is lacking about Na⁺-occluded intermediates, as occluded Na⁺ was only detected in states incapable of performing a catalytic cycle, including two Na⁺-containing crystallographic structures. The current knowledge is that intracellular Na⁺ must bind to the transport sites and become occluded upon phosphorylation by ATP to be transported to the extracellular medium. Here, taking advantage of epigallocatechin-3-gallate to instantaneously stabilize native Na⁺-occluded intermediates, we isolated species with tightly bound Na⁺ in an enzyme able to perform a catalytic cycle, consistent with a genuine occluded state. We found that Na⁺ becomes spontaneously occluded in the E1 dephosphorylated form of the Na⁺/K⁺-ATPase, exhibiting positive interactions between binding sites. In fact, the addition of ATP does not produce an increase in Na⁺ occlusion as it would have been expected; on the contrary, occluded Na⁺ transiently decreases, whereas ATP lasts. These results reveal new properties of E1 intermediates of the Albers–Post model for explaining the Na⁺ transport pathway.