Reciprocal control of G1-phase progression is required for Th-POK/Runx3-mediated CD4/8 thymocyte cell fate decision.

After receiving a TCR-mediated differentiation signal, CD4 and CD8 double-positive thymocytes diverge into CD4 or CD8 single-positive T cells, for which Th-POK and Runx3 have been identified as pivotal transcription factors, respectively. The cross-antagonistic regulation of Th-POK and Runx3 seems to be essential for CD4/8 thymocyte lineage commitment. However, the process for determining which pivotal factor acts dominantly has not been established. To explore the determining process, we used an in vitro culture system in which CD4 or CD8 single-positive cells are selectively induced from CD4/8 double-positive cells. Surprisingly, we found that control of G(1) cell cycle phase progression is critical for the determination. In the CD4 pathway, sustained TCR signal, as well as Th-POK, induces G(1)-phase extension and represses CD8 expression in a G(1) extension-dependent manner. In the CD8 pathway, after receiving a transient TCR signal, the IL-7R signal, as well as Runx3, antagonizes TCR signal-mediated G(1) extension and CD8 repression. Importantly, forced G(1) extension cancels the functions of Runx3 to repress Th-POK and CD4 and to reactivate CD8. In contrast, it is suggested that forced G(1) progression inhibits Th-POK function to repress CD8. Collectively, Th-POK and Runx3 are reciprocally involved in the control of G(1)-phase progression, on which they exert their functions dependently. These findings may provide novel insight into how CD4/CD8 cell lineages are determined by Th-POK and Runx3.

Dietary cis-9, trans-11-conjugated linoleic acid reduces amyloid ß-protein accumulation and upregulates anti-inflammatory cytokines in an Alzheimer's disease mouse model.

Conjugated linoleic acid (CLA) is an isomer of linoleic acid (LA). The predominant dietary CLA is cis-9, trans-11-CLA (c-9, t-11-CLA), which constitutes up to ~ 90% of total CLA and is thought to be responsible for the positive health benefits associated with CLA. However, the effects of c-9, t-11-CLA on Alzheimer's disease (AD) remain to be elucidated. In this study, we investigated the effect of dietary intake of c-9, t-11-CLA on the pathogenesis of an AD mouse model. We found that c-9, t-11-CLA diet-fed AD model mice significantly exhibited (1) a decrease in amyloid-ß protein (Aß) levels in the hippocampus, (2) an increase in the number of microglia, and (3) an increase in the number of astrocytes expressing the anti-inflammatory cytokines, interleukin-10 and 19 (IL-10, IL-19), with no change in the total number of astrocytes. In addition, liquid chromatography-tandem mass spectrometry (LC-MS/MS) and gas chromatographic analysis revealed that the levels of lysophosphatidylcholine (LPC) containing c-9, t-11-CLA (CLA-LPC) and free c-9, t-11-CLA were significantly increased in the brain of c-9, t-11-CLA diet-fed mice. Thus, dietary c-9, t-11-CLA entered the brain and appeared to exhibit beneficial effects on AD, including a decrease in Aß levels and suppression of inflammation.

Engulfment of Toxic Amyloid ß-protein in Neurons and Astrocytes Mediated by MEGF10.

Amyloid-ß proteins (A ß), including Aß42 and A ß 43, are known pathogenesis factors of Alzheimer's disease (AD). Unwanted substances in the brain, including A ß, are generally removed by microglia, astrocytes, or neurons via a phagocytosis receptor. We observed that neurons and astrocytes engulfed A ß 42 and A ß 43, which are more neurotoxic than A ß 40. We previously showed that multiple-EGF like domains 10 (MEGF10) plays an important role in apoptotic cell elimination and is expressed in mammalian neurons and astrocytes. Therefore, we assessed whether MEGF10 is involved in A ß42 and A ß43 engulfment in MEGF10-expressing neurons and astrocytes. We found that MEGF10-expressing astrocytes and neurons engulfed A ß42 and A ß43 but not A ß40. Furthermore, incubation of the neurons and astrocytes with A ß42 and A ß43a ugmented MEGF10 phosphorylation; however, incubation with A ß40 did not have this augmenting effect. Our findings suggest that MEGF10 plays a phagocytosis receptor function for A ß42 and A ß43 in neurons and astrocytes.

Dual functions of Runx proteins for reactivating CD8 and silencing CD4 at the commitment process into CD8 thymocytes.

To understand how CD8 expression is regulated during the transition process from CD4+8+ (CD4 and CD8 double positive, DP) to CD4-8+ (CD8 single positive, CD8SP) cells in the thymus, the involvement of Runx proteins in the alteration of chromatin configuration was investigated. Using the chromatin immunoprecipitation assay, we first demonstrated that Runx proteins bind to the stage-specific CD8 enhancer, as well as the CD4 silencer, in CD8SP thymocytes. Among Runx family members, Runx3 expression was initiated in DP thymocytes receiving a positive selection signal and increased in concert with differentiation to the CD8SP stage. Furthermore, reactivation of the CD8 gene, as well as CD4 silencing, was suppressed in positively selected thymocytes of Runx dominant-negative transgenic mice. These results suggest that Runx proteins, especially Runx3, are involved in lineage specification of CD8 T cells and provide important information for understanding the mechanism for the mutually exclusive expression of coreceptors in mature thymocytes.