Efficiency of spermatogonial dedifferentiation during aging

Background

Adult stem cells are critical for tissue homeostasis; therefore, the mechanisms utilized to maintain an adequate stem cell pool are important for the survival of an individual. In Drosophila, one mechanism utilized to replace lost germline stem cells (GSCs) is dedifferentiation of early progenitor cells. However, the average number of male GSCs decreases with age, suggesting that stem cell replacement may become compromised in older flies.

Methodology/Principal Findings

Using a temperature sensitive allelic combination of Stat92E to control dedifferentiation, we found that germline dedifferentiation is remarkably efficient in older males; somatic cells are also effectively replaced. Surprisingly, although the number of somatic cyst cells also declines with age, the proliferation rate of early somatic cells, including cyst stem cells (CySCs) increases.

Conclusions

These data indicate that defects in spermatogonial dedifferentiation are not likely to contribute significantly to an aging-related decline in GSCs. In addition, our findings highlight differences in the ways GSCs and CySCs age. Strategies to initiate or enhance the ability of endogenous, differentiating progenitor cells to replace lost stem cells could provide a powerful and novel strategy for maintaining tissue homeostasis and an alternative to tissue replacement therapy in older individuals.     

Changes in Ca, Cu, Fe, Mg, and Zn contents in mouse brain tissues after prolonged oral ingestion of brick tea liquor containing a high level of Al

A study was conducted to analyze the regional distribution of Ca, Cu, Fe, Mg, and Zn contents in brain tissues after animals were given liquor of brick tea that contained a high Al content. In 25 normal adult male mice given either water or 0.9% NaCl for 1 mo or 2 mo, the metal concentrations in the serum, liver, frontal cortex, hippocampus, cerebellum, and brain stem were comparable (p>0.05). When the drinking water was replaced by a 1% brick tea liquor, which contained a high Al content, serum Al concentration was increased significantly 1 mo after the onset of the experiment and remained high at the end of the second month. The level of Al was also elevated in both the cortex and hippocampus at 1 mo after replacing tea for drinking water. In addition to Al, there were a significant increase in hippocampal Zn and a decrease in Cu contents. There was no change in tissue Mg or Fe contents, but there was a significant increase in Ca content in every brain region studied. It was suggested that the increase in Ca might be the result of the effect of other components in tea. Unlike the brain, there was no change in the concentration of any of the metals, including Al, in the liver, which further demonstrated that the changes observed in the brain was specific. The results of the present study confirmed that Al, when given orally in the form of tea, could be absorbed into the bloodstream. The absorbed Al could accumulate in selected brain regions. The presence of Al might also change the tissue content of endogenous trace metals.     

CD44-initiated cell spreading induces Pyk2 phosphorylation, is mediated by Src family kinases, and is negatively regulated by CD45

CD44 is a cell adhesion molecule implicated in leukocyte adhesion and migration, co-stimulation of T cells, and tumor metastasis. CD45 is a leukocyte-specific protein tyrosine phosphatase that dephosphorylates the Src family kinases, Lck and Fyn, in T cells. Positive regulation of Lck by CD45 is required for its effective participation in T cell receptor signaling events. Here, immobilized CD44 antibody induced a distinctive cell spreading in CD45(-), but not CD45(+), T cells, and this correlated with the induction of tyrosine-phosphorylated proteins. Two focal adhesion family kinases, Pyk2 and, to a lesser extent, FAK were inducibly phosphorylated, as was a potential substrate, Cas. CD44-mediated cell spreading and induced tyrosine phosphorylation were prevented by the Src family kinase inhibitor, PP2. Furthermore, 2-fold more Lck associated with CD44 in the low density sucrose fraction from CD45(-) T cells compared with CD45(+) T cells, suggesting that CD45 may regulate the association of Lck with CD44 in this fraction. Therefore, in CD45(-) T cells, CD44 signaling is mediated by Src family kinases, and this leads to Pyk2 phosphorylation, cytoskeletal changes, and cell spreading. This implicates CD45 in the negative regulation of Src family kinase-mediated CD44 signaling leading to T cell spreading.     

Inhibition of serotonin reuptake.

An uptake system on the serotonin neuronal membrane apparently functions to inactivate serotonin that has been released into the synaptic cleft. Various inhibitors of this active transport system on serotonin neurons are known, and some are specific in the sense that they do not inhibit the active uptake system on norepinephrine neurons. The most widely studied specific inhibitor of the serotonin neuron pump is fluoxetine, 3-(p-trifluoromethylphenoxy-N-methyl-3-phenyl propylamine (Lilly 110140). When fluoxetine or other effective but less specific serotonin uptake inhibitors are given, a rapid decrease in serotonin turnover occurs and the rate of firing of single neural units in the serotonin rich raphe area of brain is reduced. This decrease in serotonin turnover and release may be a compensatroy mechanism in response to an enhanced action of serotonin on synaptic receptors. Through the use of fluoxetine and other serotonin uptake inhibitors, the role of serotonin neurons in various brain functions--behavior, sleep, regulation of pituitary hormone release, thermoregulation, pain responsiveness, and so on--can be studied.     

Twist function is required for the morphogenesis of the cephalic neural tube and the differentiation of the cranial neural crest cells in the mouse embryo

Loss of Twist function in the cranial mesenchyme of the mouse embryo causes failure of closure of the cephalic neural tube and malformation of the branchial arches. In the Twist(-/-) embryo, the expression of molecular markers that signify dorsal forebrain tissues is either absent or reduced, but those associated with ventral tissues display expanded domains of expression. Dorsoventral organization of the mid- and hindbrain and the anterior-posterior pattern of the neural tube are not affected. In the Twist(-/-) embryo, neural crest cells stray from the subectodermal migratory path and the late-migrating subpopulation invades the cell-free zone separating streams of cells going to the first and second branchial arches. Cell transplantation studies reveal that Twist activity is required in the cranial mesenchyme for directing the migration of the neural crest cells, as well as in the neural crest cells within the first branchial arch to achieve correct localization. Twist is also required for the proper differentiation of the first arch tissues into bone, muscle, and teeth.     

The soft metal ion binding sites in the Staphylococcus aureus pI258 CadC Cd(II)/Pb(II)/Zn(II)-responsive repressor are formed between subunits of the homodimer

The Staphylococcus aureus plasmid pI258 CadC is a homodimeric repressor that binds Cd(II), Pb(II), and Zn(II) and regulates expression of the cadAC operon. CadC binds two Cd(II) ions per dimer, with a tetrathiolate binding site composed of residues Cys(7), Cys(11), Cys(58), and Cys(60). It is not known whether each site consists of residues from a single monomer or from residues contributed by both subunits. To examine whether Cys(7) and Cys(11) are spatially proximate to Cys(58) and Cys(60) of the same subunit or of the other subunit, homodimers with the same cysteine mutation in each subunit and heterodimers containing different cysteine mutations in the two subunits were reacted with 4,6-bis(bromomethyl)-3,7-dimethyl-1,5-diazabicyclo[3.3.0]octa-3,6-diene-2,8-dione, which cross-links thiol groups that are within 3-6 A of each other. Cys(7) or Cys(11) cross-linked only with Cys(58) or Cys(60) on the other subunit. The data demonstrate that Cys(7) and Cys(11) from one monomer are within 3-6 A of either Cys(58) or Cys(60) in the other monomer. The results of this study strongly indicate that each of the two Cd(II) binding sites in the CadC homodimer is composed of Cys(7) and Cys(11) from one monomer and Cys(58) and Cys(60) from the other monomer.     

Utility of a Histone Deacetylase Inhibitor (PXD101) for Thyroid Cancer Treatment

Background

We evaluated the therapeutic effects of the histone deacetylase inhibitor PXD101 alone and in combination with conventional chemotherapy in treating thyroid cancer.

Methodology/Principal Findings

We studied eight cell lines from four types of thyroid cancer (papillary, follicular, anaplastic and medullary). The cytotoxicity of PXD101 alone and in combination with three conventional chemotherapeutic agents (doxorubicin, paclitaxel and docetaxel) was measured using LDH assay. Western blot assessed expression of acetylation of histone H3, histone H4 and tubulin, proteins associated with apoptosis, RAS/RAF/ERK and PI3K/AKT/mTOR signaling pathways, DNA damage and repair. Apoptosis and intracellular reactive oxygen species (ROS) were measured by flow cytometry. Mice bearing flank anaplastic thyroid cancers (ATC) were daily treated with intraperitoneal injection of PXD101 for 5 days per week. PXD101 effectively inhibited thyroid cancer cell proliferation in a dose-dependent manner. PXD101 induced ROS accumulation and inhibited RAS/RAF/ERK and PI3K/mTOR pathways in sensitive cells. Double-stranded DNA damage and apoptosis were induced by PXD101 in both sensitive and resistant cell lines. PXD101 retarded growth of 8505C ATC xenograft tumors with promising safety. Combination therapy of PXD101with doxorubicin and paclitaxel demonstrated synergistic effects against four ATC lines in vitro.

Conclusions

PXD101 represses thyroid cancer proliferation and has synergistic effects in combination with doxorubicin and paclitaxel in treating ATC. These findings support clinical trials using PXD101 for patients with this dismal disease.