Cyclin-Dependent Kinase 2 Regulates Foxp3 and Regulatory T Cell Function

Foxp3 is a transcription factor required for the development and function of regulatory T cells (Treg). Humans lacking functional Foxp3 are afflicted with uncontrolled systemic autoimmunity. How the Foxp3 protein is regulated post-translationally is unclear. Our previous studies demonstrate cyclin-dependent kinase 2 (CDK2) controls Foxp3+Treg function, but the mechanism by which this occurred was not identified. The CDKs are primarily thought to control cell cycle progression. However, recent studies suggest only CDK1 is required for normal mammalian cell cycle, raising questions about the biological role of the other CDKs. Specifically, mice genetically deficient in CDK2 are viable with no significant defects in cell cycle. We probed the Foxp3 sequence for the presence of CDK motifs, finding four such sites in the amino terminus. We confirmed that Foxp3 is phosphorylated by CDK2 using an in vitro kinase assay and mass spectrometry, as well as a phospho-specific antibody that recognizes one of the phosphorylated Foxp3-CDK motifs. We generated a mutant of Foxp3 lacking all four CDK motifs, which has increased half-life compared to wild-type Foxp3. CD4+ T cells transduced with a Foxp3-CDK motif mutant have increased function compared to cells transduced with wild-type Foxp3 as measured by induction and repression of canonical Foxp3 target genes, as well as the ability to suppress conventional T cell proliferation. These data suggest CDKs negatively regulate Foxp3 protein stability, which has an impact on Foxp3 function. To determine when the CDK cascade was actively regulating Foxp3 in vivo we investigated the role of the CDK2 inhibitor, p27kip1. Recent data shows TGFβ signaling drives expression of p27kip1 in B cells. TGFβ is also required for extrathymic induction of Foxp3 in conventional CD4+ T cells. We show that conventional T cells, which have high CDK2 activity and minimal p27kip1 expression, induce large amounts of p27kip1 along with Foxp3 in the presence of TGFβ. Additionally, T cells lacking p27kip1 have defective TGFβ-dependent Foxp3 induction. We hypothesize that TGFβ signaling is required to activate p27kip1 and stabilize Foxp3 protein levels in developing iTreg by repressing CDK2

High iron and iron household protein contents in perineuronal net-ensheathed neurons ensure energy metabolism with safe iron handling

A subpopulation of neurons is less vulnerable against iron-induced oxidative stress and neurodegeneration. A key feature of these neurons is a special extracellular matrix composition that forms a perineuronal net (PN). The PN has a high affinity to iron, which suggests an adapted iron sequestration and metabolism of the ensheathed neurons. Highly active, fast-firing neurons—which are often ensheathed by a PN—have a particular high metabolic demand, and therefore may have a higher need in iron. We hypothesize that PN-ensheathed neurons have a higher intracellular iron concentration and increased levels of iron proteins. Thus, analyses of cellular and regional iron and the iron proteins transferrin (Tf), Tf receptor 1 (TfR), ferritin H/L (FtH/FtL), metal transport protein 1 (MTP1 aka ferroportin), and divalent metal transporter 1 (DMT1) were performed on Wistar rats in the parietal cortex (PC), subiculum (SUB), red nucleus (RN), and substantia nigra (SNpr/SNpc). Neurons with a PN (PN+) have higher iron concentrations than neurons without a PN: PC 0.69 mM vs. 0.51 mM, SUB 0.84 mM vs. 0.69 mM, SN 0.71 mM vs. 0.63 mM (SNpr)/0.45 mM (SNpc). Intracellular Tf, TfR and MTP1 contents of PN+ neurons were consistently increased. The iron concentration of the PN itself is not increased. We also determined the percentage of PN+ neurons: PC 4%, SUB 5%, SNpr 45%, RN 86%. We conclude that PN+ neurons constitute a subpopulation of resilient pacemaker neurons characterized by a bustling iron metabolism and outstanding iron handling capabilities. These properties could contribute to the low vulnerability of PN+ neurons against iron-induced oxidative stress and degeneration

MOCCA-SURVEY Database I: Assessing GW kick retention fractions for BH-BH mergers in globular clusters

Anisotropy of gravitational wave (GW) emission results in a net momentum gained by the black hole (BH) merger product, leading to a recoil velocity up to $\sim10^3\text{ km s}^{-1}$, which may kick it out of a globular cluster (GC). We estimate GW kick retention fractions of merger products assuming different models for BH spin magnitude and orientation (MS0 - random, MS1 - spin as a function of mass and metalicity, MS2 - constant value of $0.5$). We check how they depend on BH-BH merger time and properties of the cluster. We analyze the implications of GW kick retention fractions on intermediate massive BH (IMBH) formation by repeated mergers in a GC. We also calculate final spin of the merger product, and investigate how it correlates with effective spin of the binary. We used data from MOCCA (MOnte Carlo Cluster simulAtor) GC simulations to get a realistic sample of BH-BH mergers, assigned each BH spin value according to a studied model, and calculated recoil velocity and final spin based on most recent theoretical formulas. We discovered that for physically motivated models, GW kick retention fractions are about $30\%$ and display small dependence on assumptions about spin, but are much more prone to cluster properties. In particular, we discovered a strong dependence of GW kick retention fractions on cluster density. We also show that GW kick retention fractions are high in final life stages of the cluster, but low at the beginning. Finally, we derive formulas connecting final spin with effective spin for primordial binaries, and with maximal effective spin for dynamical binaries.Comment: 13 pages, 9 figures, accepted for publication in MNRA

Iron concentrations in neurons and glial cells with estimates on ferritin concentrations

BACKGROUND: Brain iron is an essential as well as a toxic redox active element. Physiological levels are not uniform among the different cell types. Besides the availability of quantitative methods, the knowledge about the brain iron lags behind. Thereby, disclosing the mechanisms of brain iron homeostasis helps to understand pathological iron-accumulations in diseased and aged brains. With our study we want to contribute closing the gap by providing quantitative data on the concentration and distribution of iron in neurons and glial cells in situ. Using a nuclear microprobe and scanning proton induced X-ray emission spectrometry we performed quantitative elemental imaging on rat brain sections to analyze the iron concentrations of neurons and glial cells. RESULTS: Neurons were analyzed in the neocortex, subiculum, substantia nigra and deep cerebellar nuclei revealing an iron level between [Formula: see text] and [Formula: see text]. The iron concentration of neocortical oligodendrocytes is fivefold higher, of microglia threefold higher and of astrocytes twofold higher compared to neurons. We also analyzed the distribution of subcellular iron concentrations in the cytoplasm, nucleus and nucleolus of neurons. The cytoplasm contains on average 73 of the total iron, the nucleolus-although a hot spot for iron-due to its small volume only 6 of total iron. Additionally, the iron level in subcellular fractions were measured revealing that the microsome fraction, which usually contains holo-ferritin, has the highest iron content. We also present an estimate of the cellular ferritin concentration calculating [Formula: see text] ferritin molecules per [Formula: see text] in rat neurons. CONCLUSION: Glial cells are the most iron-rich cells in the brain. Imbalances in iron homeostasis that lead to neurodegeneration may not only be originate from neurons but also from glial cells. It is feasible to estimate the ferritin concentration based on measured iron concentrations and a reasonable assumptions on iron load in the brain

Research on properties of multi-core superconducting wires made from materials based on magnesium and boron (MgB2)

The article presents the results of laboratory research on the production of multi-core superconducting wires. Multicore wires containing boron and magnesium powders in a copper matrix were obtained in the drawing process combined with intermediate heat treatment. The wires contains powder cores were sintered under high isostatic pressure to produce the MgB2 superconducting phase. The critical temperature for the composite’s superconducting state was determined. The macrostructure and energy dispersion (EDX) analysis of multi-core wires was also presented