Biological clock dysfunction exacerbates contact hypersensitivity in mice.

BACKGROUND: Immediate-type skin allergic reactions, such as passive cutaneous anaphylactic reaction, are associated with circadian rhythm, but the role of circadian mechanisms on delayed-type skin allergic reactions, such as contact hypersensitivity (CHS), remains uncertain. In mice, CHS, a T-cell-mediated immune response, is a classic model of human allergic contact dermatitis. OBJECTIVES: We investigated whether biological clock dysfunction affects CHS pathogenesis in CLOCK mutant mice compared with wild-type (WT) mice. METHODS: Mice were treated with 2,4,6-trinitro-1-chlorobenzene (TNCB) on the abdominal skin on day 0 (sensitization) and then treated with TNCB on the ears on day 5 (challenge). RESULTS: We found that biological clock dysfunction resulted in severe inflammation. Ear swelling, serum immunoglobulin E level and mast cell number were significantly increased in CLOCK mutant mice compared with WT mice. These results provide evidence that CLOCK mutation promotes the T-helper type 2 immune response and exacerbates CHS. Corticosterone has a protective effect on CHS. The serum corticosterone level lost rhythmicity and showed a decreased daily level in CLOCK mutant mice compared with WT mice, supporting the exacerbating effect of CLOCK mutation on CHS. Adrenalectomy markedly worsened TNCB-induced CHS in WT mice but not in CLOCK mutant mice. In addition, dramatic dexamethasone-induced protection of CHS was observed in CLOCK mutant mice compared with WT mice. CONCLUSIONS: The present results suggest that circadian rhythm might be an important factor in the regulation of CHS via corticosterone rhythmicity and/or level.

Overexpression of mitochondrial citrate synthase in Arabidopsis thaliana improved growth on a phosphorus-limited soil.

The gene for mitochondrial citrate synthase (CS) was isolated from Daucus carota (DcCS) and introduced into Arabidopsis thaliana (strain WS) using Agrobacterium tumefaciens-mediated transformation. Characteristics of citrate excretion were compared between T3 transgenic plants, which were derived from the initial transgenic plants by self-fertilization and homozygous for DcCS, and the control plants that had no DcCS. The highest CS activity 0.78 micromol protein min(-1) exhibited by the transgenic plants was about threefold greater than that found in the control plants (0.23-0.28 micromol protein min(-1)). Western analysis of the transgenic plants showed two CS signals corresponding to signals obtained from both D. carota and A. thaliana. Thus, it appears that the CS polypeptides by ectopic expression of DcCS were processed into the mature form and localized in the mitochondria of A. thaliana. The signal corresponding to the mature form of DcCS were greater in the transgenic plants having higher levels of CS activity. When the transgenic plants were grown in Al-phosphate media, a correlation between the levels of CS activity and the amounts of citrate excreted into the medium. The highest value (5.1 nmol per plant) was about 2.5-fold greater than that from control plants (1.9 nmol per plant). Both growth and P accumulation were greater in transgenic plants with high CS activity than that in control plants when they were grown on an acid soil where the availability of phosphate was low due to the formation of Al-phosphate. It appears that the overexpression of CS in A. thaliana improves the growth in phosphorous limited soil as a result of enhanced citrate excretion from the roots.

Over expression of mitochondrial citrate synthase gene improves the growth of carrot cells in Al-phosphate medium.

A mitochondrial citrate synthase (CS) of Arabidopsis thaliana was introduced into carrot (Daucus carota L. cv. MS Yonsun) cells by Agrobacterium tumefaciens-mediated transformation. Transgenic cell lines had high CS activity, the highest value observed was 0.24 mumol (mg protein)-1 min-1 which was 1.9-fold of that in wild-type cells. Transcript levels of DcCS were similar between transgenic lines, but those of AtCS were increased as the CS activity of cells was increased. Isoelectric focussing revealed that the CS polypeptide of the transgenic lines had a pI value different from that of the wild-type cells, although the molecular mass was the same. These results indicate that the CS polypeptides of A. thaliana were expressed and processed to the mature form in carrot cells. The growth rate and excretion was 2.2-2.8 and 2.8-4.0 fold greater in the transgenic cells than in the wild type cells, respectively. Phosphate uptake from Al-phosphate also increased in transgenic cells. It appears, the overexpression of mitochondrial citrate synthase in carrot cells improves the growth rate in Al-phosphate medium possibly as a result of increased citrate excretion.