Angiopoietin-like proteins: emerging targets for treatment of obesity and related metabolic diseases

Obesity and related metabolic diseases, such as type 2 diabetes, hypertension and hyperlipidemia are an increasingly prevalent medical and social problem in developed and developing countries. These conditions are associated with increased risk of cardiovascular disease, the leading cause of death. Therefore, it is important to understand the molecular basis underlying obesity and related metabolic diseases in order to develop effective preventive and therapeutic approaches against these conditions. Recently, a family of proteins structurally similar to the angiogenic-regulating factors known as angiopoietins was identified and designated 'angiopoietin-like proteins' (ANGPTLs). Encoded by seven genes, ANGPTL1-7 all possess an N-terminal coiled-coil domain and a C-terminal fibrinogen-like domain, both characteristic of angiopoietins. ANGPTLs do not bind to either the angiopoietin receptor Tie2 or the related protein Tie1, indicating that these ligands function differently from angiopoietins. Like angiopoietins, some ANGPTLs potently regulate angiogenesis, but ANGPTL3, -4 and ANGPTL6/angiopoietin-related growth factor (AGF) directly regulate lipid, glucose and energy metabolism independent of angiogenic effects. Recently, we found that ANGPTL2 is a key adipocyte-derived inflammatory mediator that links obesity to systemic insulin resistance. In this minireview, we focus on the roles of ANGPTL2 and ANGPTL6/AGF in obesity and related metabolic diseases, and discuss the possibility that both could function as molecular targets for the prevention and treatment of obesity and metabolic diseases.     

Effects of walking speed and step frequency on estimation of physical activity using accelerometers

This study evaluated the accuracy of assessing step counts and energy costs under walking conditions altered by step frequency changes at given speeds using uni- (LC) and tri-axial accelerometers (AM, ASP). Healthy young men and women (n=18) volunteered as subjects. Nine tests were designed to manipulate three step frequencies, low (-15% of normal), normal, and high (+15%), at each walking speed (55, 75, and 95 m/min). A facemask connected to a Douglas bag was attached to subjects, who wore accelerometers around their waist. LC underestimated the step counts at normal or high step frequency at 55 m/min and AM also at all step frequencies at 55 m/min, whereas ASP did not in all trials. LC underestimated metabolic equivalents (METs) at low or normal step frequency at all walking speeds. AM underestimated METs at low step frequency at all walking speeds and at high step frequency of 95 m/min. ASP gave underestimates only at low step frequency of 95 m/min. The degree of the percentage error of METs for AM and ASP was affected by step frequency. Significant interaction between step frequency and speed was found that for LC. These results suggest that LC and AM can cause errors in step-count functions at a low walking speed. Furthermore, LC may show low accuracy of the METs measurement during walking altered according to step frequency and speed, whereas AM and ASP, which are tri-axial accelerometers, are more accurate but the degree of the percentage error is affected by step frequency.     

Sex- and age-related differences in morbidity rates of 2009 pandemic influenza A H1N1 virus of swine origin in Japan

Background

The objective of the present study was to determine whether the morbidity rates of the 2009 pandemic influenza A H1N1 virus (pdmH1N1) varied by age and/or sex.

Methods and Findings

Retrospective analysis of 2,024,367 cases of pdmH1N1 was performed using the national surveillance data from influenza sentinel points in Japan. The male-to-female morbidity ratios (M/F ratios) in nineteen age groups were estimated as the primary outcome. The M/F ratios for pdmH1N1 influenza were: >1 in age groups <20 years and ≥80 years (p<0.001); <1 in age groups 20–79 years (p<0.001). This data suggests that males <20 years of age may be more likely to suffer from pdmH1N1 influenza than females in the same age categories. When the infection pattern for pdmH1N1was compared with that of seasonal influenza outbreaks between 2000 and 2008, the M/F ratio for pdmH1N1 influenza was higher in ages 3–29 years and lower in ages 40–79 years. Because the present study was based on the national surveillance, it was impossible to estimate the morbidity rate for the Japanese population. It is also likely that the data did not capture asymptomatic or mild infections.

Conclusions

Although exposure to the pdmH1N1 virus is assumed to be similar in both boys and girls, M/F ratios were >1 in those younger than 20 years. The subsequent reversal of the M/F ratio in the adult generation could be due to several possibilities, including: greater immunity among adult males, more asymptomatic infections among males, less reporting of illness by males, or differences in exposure to the virus and probability of visiting a clinic. These results suggest that the infection and virulence patterns of pdmH1N1 are more complex than previously considered.     

Differential regulation of periplasmic nitrate reductase gene (napKEFDABC) expression between aerobiosis and anaerobiosis with nitrate in a denitrifying phototroph Rhodobacter sphaeroides f. sp. denitrificans

A denitrifying phototroph, Rhodobacter sphaeroides f. sp. denitrificans, has the ability to denitrify by respiring nitrate. The periplasmic respiratory nitrate reductase (Nap) catalyses the first step in denitrification and is encoded by the genes, napKEFDABC. By assaying the ss-galactosidase activity of napKEFD-lacZ fusions in wild type and nap mutant cells grown under various growth conditions, the environmental signal for inducing nap expression was examined. Under anoxic conditions with nitrate, nap genes expression in the wild-type strain was highest in the dark, and somewhat lowered by incident light, but that of the napA, napB, and napC mutant strains was low, showing that nap expression is dependent on nitrate respiration. Under oxic conditions, both the wild type and nap mutant cells showed high ss-galactosidase activities, comparable to the wild-type grown under anoxic conditions with nitrate. Myxothiazol, a specific inhibitor of the cytochrome bc (1) complex, did not affect the beta-galactosidase activity in the wild-type cells grown aerobically, suggesting that the redox state of the quinone pool was not a candidate for the activation signal for aerobic nap expression. These results suggested that the trans-acting regulatory signals for nap expression differ between anoxic and oxic conditions. Deletion analysis showed that the nucleotide sequence from -135 to -88 with respect to the translational start point is essential for nap expression either under anoxic or oxic conditions, suggesting that the same cis-acting element is involved in regulating nap expression under either anoxic with nitrate or oxic conditions.     

Insulin-like growth factor-I stimulates cell proliferation in the outer layer of Hertwig’s epithelial root sheath and elongation of the tooth root in mouse molars in vitro

To elucidate the mechanism of root formation in tooth development, we examined the role of insulin-like growth factor I (IGF-I) on early root formation in mandibular first molar teeth from 5-day-old mice. Immunohistochemistry revealed the specific localization of the IGF-I receptor in Hertwigs epithelial root sheath (HERS) in the tooth root. The effect of IGF-I on root development, especially on HERS, was subsequently examined in vitro. The control culture showed normal development of HERS and the periodontium, resembling that in vivo. However, the presence of 100 ng/ml IGF-I resulted in elongation of HERS and increased cell proliferation in its outer layer. These effects were negated by the addition of antibodies specific for IGF-I. Thus, we propose that IGF-I is involved in early root formation by regulating the mitotic activity in the outer layer of HERS.This study was partly supported by grants to N.F. from KAKENHI (no. 13671909), to N.F. and M.J.T. from the Promotion of 2001-Multidisciplinary Research Projects in 2001–2005, and to N.F. and K.I. from Iwate Medical University—Keiryokai Research Foundation (no. 64).     

Roles of Arabidopsis AtREV1 and AtREV7 in translesion synthesis

Plants have mechanisms for repairing and tolerating detrimental effects by various DNA damaging agents. A tolerance pathway that has been predicted to be present in higher plants is translesion synthesis (TLS), which is catalyzed by polymerases. In Arabidopsis (Arabidopsis thaliana), however, the only gene known to be involved in TLS is the Arabidopsis homolog of REV3, AtREV3, which is a putative catalytic subunit of Arabidopsis DNA polymerase zeta. A disrupted mutant of AtREV3, rev3, was previously found to be highly sensitive to ultraviolet-B (UV-B) and various DNA damaging agents. REV1 and REV7 are thought to be components of translesion synthesis in plants. In this study, we identified the Arabidopsis homologs of REV1 and REV7 (AtREV1 and AtREV7). Several mutants carrying disrupted AtREV1 and AtREV7 genes were isolated from Arabidopsis T-DNA-inserted lines. An AtREV1-disrupted mutant, rev1, was found to be moderately sensitive to UV-B and DNA cross-linkers. A rev1rev3 double mutant, like rev3, showed high sensitivity to UV-B, gamma-rays, and DNA cross-linkers. An AtREV7-disrupted mutant, rev7, was possibly sensitive to cis-diamminedichloroplatinum(II), a kind of DNA cross-linker, but it was not sensitive to acute UV-B and gamma-ray irradiation. On the other hand, the aerial growth of rev7, like the aerial growth of rev1 and rev3, was inhibited by long-term UV-B. These results suggest that a TLS mechanism exists in a higher plant and show that AtREV1 and AtREV7 have important roles in tolerating exposure to DNA-damaging agents.     

Generation and properties of ascorbic acid-overproducing transgenic tobacco cells expressing sense RNA for <Emphasis Type="SmallCaps">l</Emphasis>-galactono-1,4-lactone dehydrogenase

l-Galactono-1,4-lactone dehydrogenase (GalLDH; EC 1.3.2.3) is the last enzyme in the putative l-ascorbic acid (AsA) biosynthetic pathway of plants. Here, we show for the first time that the overexpression of GalLDH can increase AsA content in tobacco (Nicotiana tabacum L.) BY-2 cells. To see the effect, we analyzed the properties of these AsA-overproducing transgenic cell lines, especially in relation to AsA content of cells, cell division, senescence and resistance to oxidative stress. The mitotic index in AsA-overproducing cells was higher than in wild-type cells. Moreover, the browning of these cells was markedly restrained, and the proportion of dead cells was reduced, especially in the later period of culture. These AsA-overproducing cells also acquired resistance to paraquat (methyl viologen), which produces active oxygen species. These results contribute to the previous insights about AsA and raise the possibility of the generation of plants that have resistance to environmental stresses by increasing their AsA content.     

Osteoblastic activity and estrogenic response in the regenerating scale of goldfish, a good model of osteogenesis

Osteogenesis in the teleost was morphologically observed using regenerating scales of goldfish. Histological observations indicated that osteoblasts around the regenerating scales on days 7 to 10 were greater in size and number than those at other stages. Therefore, further experiments were carried out to examine the activity of osteoblasts in the regenerating period. To quantify their osteoblastic activities, scales on the left side of the body were taken, and the regenerating scales were then used to measure the activities of alkaline phosphatase (ALP), a marker of osteoblasts, on days 7, 10, and 15. The ontogenic scales on the right side of the body were also collected and used to measure ALP activity on the same days. Osteoblasts at all stages of regenerating scales were more active than those in the remaining ontogenic scales. The regenerating scales on day 10 had the highest activity. Furthermore, we found that estrogen receptor (ER) mRNA was expressed in the regenerating scales because estrogen participates in osteoblastic growth and differentiation in mammals. Therefore, using a scale culture system reported previously, the estrogenic response was examined in the ontogenic and regenerating scales on day 10. The reactivity was much higher in regenerating scales, although estrogen treatment significantly activated the osteoblastic activities in both scales. We are the first to demonstrate that ER is expressed in regenerating scales and that estrogen participates in osteogenesis as it does in mammalian bone. Our findings strongly suggest that regenerating scales can be used as a model of osteogenesis in vertebrates.     

Symbiotic rhizobium and nitric oxide induce gene expression of non-symbiotic hemoglobin in Lotus japonicus

We characterized the expression profiles of LjHb1 and LjHb2, non-symbiotic hemoglobin (non-sym-Hb) genes of Lotus japonicus. Although LjHb1 and LjHb2 showed 77% homology in their cDNA sequences, LjHb2 is located in a unique position in the phylogenetic tree of plant Hbs. The 5'-upstream regions of both genes contain the motif AAAGGG at a position similar to that in promoters of other non-sym-Hb genes. Expression profiles obtained by using quantitative RT-PCR showed that LjHb1 and LjHb2 were expressed in all tissues of mature plants, and expression was enhanced in mature root nodules. LjHb1 was strongly induced under both hypoxic and cold conditions, and by the application of nitric oxide (NO) donor, whereas LjHb2 was induced only by the application of sucrose. LjHb1 was also induced transiently by the inoculation with the symbiotic rhizobium Mesorhizobium loti MAFF303099. Observations using fluorescence microscopy revealed the induction of LjHb1 expression corresponded to the generation of NO. These results suggest that non-sym-Hb and NO have important roles in stress adaptation and in the early stage of legume-rhizobium symbiosis.