光周期对春石斛开花及多胺含量的影响

以春石斛为试材,研究光周期对其开花及多胺（腐胺、亚精胺和精胺）含量的影响,以期了解春石斛开花的光周期特性以及期间能源物质多胺的变化规律。结果显示,春石斛短日照处理植株开花较长日照处理的提前约18d,为称量性短日照植物;同时,短日照处理植株的花芽多,开花量犬,花径较长日照大。不同光周期诱导开花过程中,春石斛叶片内腐胺含量最高,波动较大,短日照处理下基本维持比长日照高的水平。亚精胺含量其次,且随生长发育逐渐升高,短日照处理下一直保持比长日照高的水平。精胺含量最低,变化不大,短日照下保持与长日照相同或略高的水平。由此推测,春石斛为称量性短日照植物,高水平的腐胺和亚精胺可能与春石斛花芽的形成有关。     

Neuroprotective effects of blockers for T-type calcium channels

Background

Activation of the liver × receptors (LXRs) by exogenous ligands stimulates the degradation of β-amyloid 1–42 (Aβ42), a peptide that plays a central role in the pathogenesis of Alzheimer's disease (AD). The oxidized cholesterol products (oxysterols), 24-hydroxycholesterol (24-OHC) and 27-hydroxycholesterol (27-OHC), are endogenous activators of LXRs. However, the mechanisms by which these oxysterols may modulate Aβ42 levels are not well known.

Results

We determined the effect of 24-OHC and/or 27-OHC on Aβ generation in SH-SY5Y cells. We found that while 27-OHC increases levels of Aβ42, 24-OHC did not affect levels of this peptide. Increased Aβ42 levels with 27-OHC are associated with increased levels of β-amyloid precursor protein (APP) as well as β-secretase (BACE1), the enzyme that cleaves APP to yield Aβ. Unchanged Aβ42 levels with 24-OHC are associated with increased levels of sAPPα, suggesting that 24-OHC favors the processing of APP to the non-amyloidogenic pathway. Interestingly, 24-OHC, but not 27-OHC, increases levels of the ATP-binding cassette transporters, ABCA1 and ABCG1, which regulate cholesterol transport within and between cells.

Conclusion

These results suggest that cholesterol metabolites are linked to Aβ42 production. 24-OHC may favor the non-amyloidogenic pathway and 27-OHC may enhance production of Aβ42 by upregulating APP and BACE1. Regulation of 24-OHC: 27-OHC ratio could be an important strategy in controlling Aβ42 levels in AD.     

Immune correlates of herpes zoster in HIV-infected children and youth

To identify immunologic factors that modulate the risk of herpes zoster (HZ), we compared varicella-zoster virus (VZV)-specific and nonspecific T-cell subpopulations of 47 HIV-infected children before they developed HZ with those of 141 VZV-positive HZ-negative matched controls. Compared with controls, HZ cases had lower VZV-specific CD8(+) CD107a(+) cell percentages independently of CD4(+) percentages or HIV loads, suggesting that VZV-specific cytotoxic T cells are protective against HZ. In contrast, high nonspecific regulatory and activated T cells were associated with an increased risk of HZ.