Simultaneous PET-MRI: a new approach for functional and morphological imaging

Noninvasive imaging at the molecular level is an emerging field in biomedical research. This paper introduces a new technology synergizing two leading imaging methodologies: positron emission tomography (PET) and magnetic resonance imaging (MRI). Although the value of PET lies in its high-sensitivity tracking of biomarkers in vivo, it lacks resolving morphology. MRI has lower sensitivity, but produces high soft-tissue contrast and provides spectroscopic information and functional MRI (fMRI). We have developed a three-dimensional animal PET scanner that is built into a 7-T MRI. Our evaluations show that both modalities preserve their functionality, even when operated isochronously. With this combined imaging system, we simultaneously acquired functional and morphological PET-MRI data from living mice. PET-MRI provides a powerful tool for studying biology and pathology in preclinical research and has great potential for clinical applications. Combining fMRI and spectroscopy with PET paves the way for a new perspective in molecular imaging.     

Species distribution and <Emphasis Type="Italic">in vitro</Emphasis> antifungal susceptibility of oral yeast isolates from Tanzanian HIV-infected patients with primary and recurrent oropharyngeal candidiasis

Background  

In Tanzania, little is known on the species distribution and antifungal susceptibility profiles of yeast isolates from HIV-infected patients with primary and recurrent oropharyngeal candidiasis.     

Radiolabeling rhesus monkey CD34+ hematopoietic and mesenchymal stem cells with 64Cu-pyruvaldehyde-bis(N4-methylthiosemicarbazone) for microPET imaging

Noninvasive positron emission tomography (PET) provides a potential method for in vivo tracking of radiolabeled cells. The goal of this study was to assess the potential toxicity of 64Cu-pyruvaldehyde-bis(N4-methylthiosemicarbazone) (PTSM) on rhesus monkey CD34+ hematopoietic and mesenchymal stem cells in vitro in preparation for developing imaging protocols posttransplantation. CD34+ hematopoietic cells were radiolabeled with 0 to 40 microCi/mL 64Cu-PTSM and viability and colony formation were assessed. Rhesus monkey mesenchymal stem cells (rhMSCs) were placed in culture postradiolabeling for assessments of growth and differentiation toward adipogenic, osteogenic, and chondrogenic lineages. The results indicated that CD34+ cells radiolabeled with 20 microCi/mL and rhMSCs radiolabeled with 10 microCi/mL 64Cu-PTSM did not result in adverse effects on growth or differentiation. Nonradioactive copper was also evaluated and showed that the presence of copper was not harmful to the cells. CD34+ cells and rhMSCs radiolabeled with the optimized concentrations of 20 and 10 microCi/mL, respectively, were also assessed using the microPET scanner. Studies showed that a minimum of 2.50x10(4) CD34+ cells (1.1 pCi/cell) and 6.25x10(3) rhMSCs (4.4 pCi/cell) could be detected. These studies indicate that CD34+ hematopoietic cells and rhMSCs can be safely radiolabeled with 64Cu-PTSM without adverse cellular effects.     

Trade-offs in plant responses to herbivory influence trophic routes of production in a freshwater wetland

Responses of aquatic macrophytes to leaf herbivory may differ from those documented for terrestrial plants, in part, because the potential to maximize growth following herbivory may be limited by the stress of being rooted in flooded, anaerobic sediments. Herbivory on aquatic macrophytes may have ecosystem consequences by altering the allocation of nutrients and production of biomass within individual plants and changing the quality and quantity of aboveground biomass available to consumers or decomposers. To test the effects of leaf herbivory on plant growth and production, herbivory of a dominant macrophyte, Nymphaea odorata, by chrysomelid beetles and crambid moths was controlled during a 2-year field experiment. Plants exposed to herbivory maintained, or tended to increase, biomass and aboveground net primary production relative to controls, which resulted in 1.5 times more aboveground primary production entering the detrital pathway of the wetland. In a complementary greenhouse experiment, the effects of simulated leaf herbivory on total plant responses, including biomass and nutrient allocation, were investigated. Plants in the greenhouse responded to moderate herbivory by maintaining aboveground biomass relative to controls, but this response occurred at the expense of belowground growth. Results of these studies suggest that N. odorata may tolerate moderate levels of herbivory by reallocating biomass and resources aboveground, which in turn influences the quantity, quality and fate of organic matter available to herbivores and decomposers.     

Fasting physiology of polar bears in relation to environmental change and breeding behavior in the Beaufort Sea

We examined the use of the ratio of serum urea to serum creatinine as a physiological biomarker of fasting to monitor temporal patterns in the feeding ecology of polar bears (Ursus maritimus). Blood was collected from 436 polar bears in the eastern Beaufort Sea during April and May of 1985–1986 and 2005–2006. The proportions of polar bears fasting were 9.6% in 1985, 10.5% in 1986, 21.4% in 2005, and 29.3% in 2006. We used stepwise logistic regression analysis to evaluate factors that could influence the binary response variable of fasting or not fasting. Significant predictor variables of fasting were: the 2005 and 2006 capture years, solitary adult male bears, and adult male bears that were accompanying an estrous female. The increased number of polar bears in a physiological fasting state from all sex, age, and reproductive classes in 2005 and 2006 corresponded with broad scale changes in Arctic sea ice composition, which may have affected prey availability. The higher proportion of adult males fasting from all years was attributed to spring breeding behavior.     

Meiotic Recombination in Human Oocytes

Studies of human trisomies indicate a remarkable relationship between abnormal meiotic recombination and subsequent nondisjunction at maternal meiosis I or II. Specifically, failure to recombine or recombination events located either too near to or too far from the centromere have been linked to the origin of human trisomies. It should be possible to identify these abnormal crossover configurations by using immunofluorescence methodology to directly examine the meiotic recombination process in the human female. Accordingly, we initiated studies of crossover-associated proteins (e.g., MLH1) in human fetal oocytes to analyze their number and distribution on nondisjunction-prone human chromosomes and, more generally, to characterize genome-wide levels of recombination in the human female. Our analyses indicate that the number of MLH1 foci is lower than predicted from genetic linkage analysis, but its localization pattern conforms to that expected for a crossover-associated protein. In studies of individual chromosomes, our observations provide evidence for the presence of “vulnerable” crossover configurations in the fetal oocyte, consistent with the idea that these are subsequently translated into nondisjunctional events in the adult oocyte.     

Heterosexual and Homosexual Partners Practising Unprotected Sex May Develop Allogeneic Immunity and to a Lesser Extent Tolerance

Background

Epidemiological studies suggest that allogeneic immunity may inhibit HIV-1 transmission from mother to baby and is less frequent in multiparous than uniparous women. Alloimmune responses may also be elicited during unprotected heterosexual intercourse, which is associated ex vivo with resistance to HIV infection.

Methodology/Principal Findings

The investigation was carried out in well-defined heterosexual and homosexual monogamous partners, practising unprotected sex and a heterosexual cohort practising protected sex. Allogeneic CD4⁺ and CD8⁺ T cell proliferative responses were elicited by stimulating PBMC with the partners'' irradiated monocytes and compared with 3^rd party unrelated monocytes, using the CFSE method. Significant increase in allogeneic proliferative responses was found in the CD4⁺ and CD8⁺ T cells to the partners'' irradiated monocytes, as compared with 3^rd party unrelated monocytes (p≤0.001). However, a significant decrease in proliferative responses, especially of CD8⁺ T cells to the partners'' compared with 3^rd party monocytes was consistent with tolerization, in both the heterosexual and homosexual partners (p<0.01). Examination of CD4⁺CD25⁺FoxP3⁺ regulatory T cells by flow cytometry revealed a significantly greater proportion of these cells in the homosexual than heterosexual partners practising unprotected sex (p<0.05). Ex vivo studies of infectivity of PBMC with HIV-1 showed significantly greater inhibition of infectivity of PBMC from heterosexual subjects practising unprotected compared with those practising protected sex (p = 0.02).

Conclusions/Significance

Both heterosexual and homosexual monogamous partners practising unprotected sex develop allogeneic CD4⁺ and CD8⁺ T cell proliferative responses to the partners'' unmatched cells and a minority may be tolerized. However, a greater proportion of homosexual rather than heterosexual partners developed CD4⁺CD25FoxP3⁺ regulatory T cells. These results, in addition to finding greater inhibition of HIV-1 infectivity in PBMC ex vivo in heterosexual partners practising unprotected, compared with those practising protected sex, suggest that allogeneic immunity may play a significant role in the immuno-pathogenesis of HIV-1 infection.     

The WD40 Domain Is Required for LRRK2 Neurotoxicity

Background

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common genetic cause of Parkinson disease (PD). LRRK2 contains an “enzymatic core” composed of GTPase and kinase domains that is flanked by leucine-rich repeat (LRR) and WD40 protein-protein interaction domains. While kinase activity and GTP-binding have both been implicated in LRRK2 neurotoxicity, the potential role of other LRRK2 domains has not been as extensively explored.

Principal Findings

We demonstrate that LRRK2 normally exists in a dimeric complex, and that removing the WD40 domain prevents complex formation and autophosphorylation. Moreover, loss of the WD40 domain completely blocks the neurotoxicity of multiple LRRK2 PD mutations.

Conclusion

These findings suggest that LRRK2 dimerization and autophosphorylation may be required for the neurotoxicity of LRRK2 PD mutations and highlight a potential role for the WD40 domain in the mechanism of LRRK2-mediated cell death.