The Response to Exercise with Constant Energy Intake in Identical Twins

Seven pairs of young adult male identical twins completed a negative energy balance protocol during which they exercised on cycle ergometers twice a day, 9 out of 10 days, over a period of 93 days while being kept on a constant daily energy and nutrient intake. The total energy deficit caused by exercise above the estimated energy cost of body weight maintenance reached 244 ± 9.8 MJ (Mean ± SEM). Baseline energy intake was estimated over a period of 17 days preceding the negative energy balance protocol. Mean body weight loss was 5.0 kg (SEM = 0.6) (p <0.001) and it was entirely accounted for by the loss of fat mass (p <0.001). Fat-free mass was unchanged. Body energy losses reached 191 MJ (SEM = 24) (p <0.001) which represented about 78% of the estimated energy deficit. Subcutaneous fat loss was slightly more pronounced on the trunk than on the limbs as estimated from skinfolds, circumferences, and computed tomography (CT). The reduction in CT-assessed abdominal visceral fat was quite striking, from 81 cm² (SEM = 5) to 52 cm² (SEM = 6) (p <0.001). At the same submaximal power output level, subjects oxidized more lipids than carbohydrates after the program as indicated by the changes in the respiratory exchange ratio (p <0.05). Intrapair resemblance was observed for the changes in body weight (p <0.05), fat mass (P <0.01), percent fat (p <0.01), body energy content (p <0.01), sum of 10 skinfolds (p <0.01), abdominal visceral fat (p <0.01), fasting plasma triglycerides (p <0.05) and cholesterol (p <0.05), maximal oxygen uptake (p <0.05), and respiratory exchange ratio during submaximal work (p <0.01). We conclude that even though there were large individual differences in response to the negative energy balance and exercise protocol, subjects with the same genotype were more alike in responses than subjects with different genotypes particularly for body fat, body energy, and abdominal visceral fat changes. High lipid oxidizers and low lipid oxidizers during sub-maximal exercise were also seen despite the fact that all subjects had experienced the same exercise and nutritional conditions for about three months.     

蛋白质组学在干细胞研究中的应用

蛋白质组学技术通过整合多项技术来分析生物体的全部蛋白质成分,通过考察不同状态下细胞或组织蛋白质组的变化情况来了解细胞活动的分子机理。干细胞分化过程中受外界条件的影响其蛋白表达模式也表现出一定的差异,对干细胞分化过程中进行蛋白质组学研究将有利于从蛋白质分子水平上阐明干细胞的分化机理。本文对蛋白质组学及其在干细胞研究中的应用加以评述。     

REJUVENATION OF MELOSIRA GRANULATA (BACILLARIOPHYCEAE) RESTING CELLS FROM THE ANOXIC SEDIMENTS OF DOUGLAS LAKE,MICHIGAN, II. ELECTRON MICROSCOPY 1

Detailed cytological changes that accompany the rejuvenation of resting cells of Melosira granulata were studied with the electron microscope. Dormant and viable cells that we previously classified as the condensed state generally contain definable chloroplasts, mitochondria, a nucleus and other cytoplasmic remnants. However, there appears to be a continuous cytoplasmic degradation spectrum and some cells which appear intensely colored with the light microscope have discontinuous chloroplast membranes and few other cytoplasmic remnants. Rejuvenation of viable dormant cells is initially accompanied by the accumulation of both lipids and polyphosphates. In the earliest stages of expansion, these storage products are dispersed throughout the cell. In later stages of expansion, the lipids appear to be coalesced into larger droplets which are easily identified at the light microscope level. The fully expanded stage is characterized by the normal complement of organelles and their arrangement at the periphery of the cells and central cytoplasmic bridge. These cells appear both anabolically and catabolically active as evidenced by the abundance of endoplasmic reticulum, ribosomes and secretory and lytic vesicles. Prior to cell division, both lipids and polyphosphates a re reduced or absent in the cells. The ultrastructural features of the dormant, condensed state in resting cells of M, granulata are similar to those described for hypnospores. A rejuvenation sequence that produces cytological features common to resting state formation could provide a population of cells which could easily revert should environmental conditions become adverse.     

Ultrastructure of the putative stem cell niche in rat mammary epithelium

There is now strong evidence that the stem cells of many tissues reside in specialized structures termed niches. The stem cell niche functions to house and regulate symmetric and asymmetric mitosis of stem cells in mammalian skin, mouse and human bone marrow, mouse brain, gut, and hair follicle, and Drosophila ovary and testis. This regulation is effected through the action of various signaling pathways such as Notch, Hedgehog, Wnt and others. The hormones of the estrous cycle, pregnancy and lactation that initiate growth in mouse mammary epithelium appear to act at a paracrine level to regulate mitosis through Notch receptors. Previous work has established that the putative stem cells of the mammary epithelium in several animal species reside near the basement membrane and never make contact with the ductal lumen. We show that these putative stem cells are found in anatomically specialized places created by the cytoplasmic extensions and modifications of neighboring differentiated cells. Such specializations may help to regulate stem cell activity by modulating molecular traffic to putative stem cells and contact with signaling molecules in the basement membrane. The histological characteristics of these putative niches vary as to the kinds of relationships the cells can have with the basement membrane and neighboring cells and as to how many stem or progenitor cells they may contain. This suggests a plasticity that may be relevant to the response of niches to tissue demands, such as wound healing, the periodic growth and regression of mammary epithelium, the process of mammary tumorigenesis therapeutic strategies for breast cancer.     

Bone marrow mesenchymal stem cells differentiate into urothelial cells and the implications for reconstructing urinary bladder mucosa

To determine the ability of cultured bone marrow-derived mesenchymal stem cells (BMSCs) to differentiate into functional urothelium. BMSCs were isolated from the long bones of aborted fetal limbs by Percoll density gradient centrifugation and characterized by flow cytometry. Human fetal urinary bladders were cut into small pieces and cultured for 3–5 days until the growth of urothelial cells was established. BMSCs were then cocultured with neonatal urothelial cells and subsequently evaluated for antigen expression and ultramicrostructure, by immunocytochemistry and electron microscopy, respectively. A subset of BMSCs expressed the differentiation marker CD71. The BMSC markers CD34, CD45, and HLA-DR were barely detectable, confirming that these cells were not derived from hematopoietic stem cells or differentiated cells. In contrast, the stem cell markers CD29, CD44, CD105, and CD90 were highly expressed. BMSCs possessed the ability to differentiate into a variety of cellular subtypes, including osteocytes, adipocytes, and chondrocytes. The shapes of BMSCs changed, and the size of the cells increased, following in vitro coculture with urothelial cells. After 2 weeks of coculture, immunostaining of the newly differentiated BMSCs positively displayed the urothelial-specific keratin marker. Electron microscopy revealed that the cocultured BMSCs had microstructural features characteristic of epithelial cells. Pluripotent BMSCs can transdifferentiate into urothelial cells in response to an environment conditioned by neonatal urothelial cells, providing a means for the time-, labor- and cost-effective reconstruction of urinary bladder mucosa.     

Breast cancer cells attract the migration of adipose tissue-derived stem cells via the PDGF-BB/PDGFR-β signaling pathway

The origin of vascular cells in tumors is unknown, but it is believed that tumors use cells from the host to build new vessels. To determine whether adipose tissue stem cells (ASCs) could be attracted by cancer cells, we performed migration assays in which ASCs were seeded on a transwell migration system top chamber and tumor-conditioned medium was placed in the bottom chamber. Our data showed that a significant number of ASCs migrated toward the tumor-conditioned medium (p < 0.0001), and migration of human ASCs significantly (p < 0.0001) increased in response to increased concentrations of recombinant PDGF-BB. In addition, neutralizing antibodies to PDGF receptor (PDGFR)-β decreased migration of ASCs toward a breast cancer-conditioned medium to the level of serum-free control. These data suggest that tumor cell-derived PDGF-BB is an important factor in governing the microenvironment interaction between tumor cells and local tissue-resident stem cells.     

绵羊羊膜上皮细胞治疗兔桡骨缺损模型的研究

为了确定绵羊羊膜上皮细胞在体内向骨组织的分化能力,实验在分离培养绵羊羊膜上皮细胞并对其进行干细胞特性的鉴定的基础上,制作新西兰大白兔桡骨13mm骨缺损模型,随机分组对其进行注射绵羊羊膜上皮细胞实验。高剂量组:移植细胞5×107个;低剂量组:移植细胞5×106个;对照组:生理盐水。细胞移植后2、4、8周拍摄X光片观察骨缺损部位的缺损修复情况;相应时段取骨缺损部位新生骨进行组织学观察:分析骨小梁生成数量和骨的改建时期。实验结果显示,高剂量实验组在移入细胞第8周,骨缺损完全修复,且同期高剂量组新骨生成的数量和质量明显高于低剂量组,低剂量组优于对照组。由此可见,绵羊羊膜上皮细胞不仅可以在不同种动物间进行移植,而且对骨缺损有良好的修复能力。     

Role of the cellular environment in interstitial stem cell proliferation in Hydra

Summary The role of the cellular environment on hydra stem cell proliferation and differentiation was investigated by introduction of interstitial cells into host tissue of defined cellular composition. In epithelial tissue lacking all non-epithelial cells the interstitial cell population did not grow but differentiated into nerve cells and nematocytes. In host tissue with progressively increased numbers of nerve cells growth of the interstitial cell population was positively correlated to the nerve cell density. In agreement with previous observations (Bode et al. 1976), growth of the interstitial cell population was also found to be negatively correlated to the level of interstitial cells present. The strong correlation between the growth of the interstitial cell population and the presence of interstitial cells and nerve cells implies that interstitial cell proliferation is controlled by a feedback signal from interstitial cells and their derivatives. Our results suggest that the cellular environment of interstitial cells provides cues which are instrumental in stem cell decision making. Offprint requests to: T.C.G. Bosch