Magnetic Resonance Water Proton Relaxation in Protein Solutions and Tissue: T1ρ Dispersion Characterization

BACKGROUND: Image contrast in clinical MRI is often determined by differences in tissue water proton relaxation behavior. However, many aspects of water proton relaxation in complex biological media, such as protein solutions and tissue are not well understood, perhaps due to the limited empirical data. PRINCIPAL FINDINGS: Water proton T(1), T(2), and T(1rho) of protein solutions and tissue were measured systematically under multiple conditions. Crosslinking or aggregation of protein decreased T(2) and T(1rho), but did not change high-field T(1). T(1rho) dispersion profiles were similar for crosslinked protein solutions, myocardial tissue, and cartilage, and exhibited power law behavior with T(1rho)(0) values that closely approximated T(2). The T(1rho) dispersion of mobile protein solutions was flat above 5 kHz, but showed a steep curve below 5 kHz that was sensitive to changes in pH. The T(1rho) dispersion of crosslinked BSA and cartilage in DMSO solvent closely resembled that of water solvent above 5 kHz but showed decreased dispersion below 5 kHz. CONCLUSIONS: Proton exchange is a minor pathway for tissue T(1) and T(1rho) relaxation above 5 kHz. Potential models for relaxation are discussed, however the same molecular mechanism appears to be responsible across 5 decades of frequencies from T(1rho) to T(1)

The RNA Helicase Rm62 Cooperates with SU(VAR)3-9 to Re-Silence Active Transcription in Drosophila melanogaster

Gene expression is highly dynamic and many genes show a wide range in expression over several orders of magnitude. This regulation is often mediated by sequence specific transcription factors. In addition, the tight packaging of DNA into chromatin can provide an additional layer of control resulting in a dynamic range of gene expression covering several orders of magnitude. During transcriptional activation, chromatin barriers have to be eliminated to allow an efficient progression of the RNA polymerase. This repressive chromatin structure has to be re-established quickly after it has been activated in order to tightly regulate gene activity. We show that the DExD/H box containing RNA helicase Rm62 is targeted to a site of rapid induction of transcription where it is responsible for an increased degree of methylation at H3K9 at the heat shock locus after removal of the heat shock stimulus. The RNA helicase interacts with the well-characterized histone methyltransferase SU(VAR)3-9 via its N-terminus, which provides a potential mechanism for the targeting of H3K9 methylation to highly regulated genes. The recruitment of SU(VAR)3-9 through interaction with a RNA helicase to a site of active transcription might be a general mechanism that allows an efficient silencing of highly regulated genes thereby enabling a cell to fine tune its gene activity over a wide range

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Autopercepção corporal de variáveis da aptidão física relacionada à saúde Bodily self-perception of health-related physical fitness variables

FUNDAMENTAÇÃO: A aptidão física apresenta duas dimensões, uma relacionada à saúde e outra ao desempenho. Não é sabido se adultos não-atletas possuem autopercepção corporal (ApC) apropriada sobre a sua aptidão física relacionada à saúde. OBJETIVOS: a) testar a ApC de indivíduos não-atletas em algumas variáveis morfofuncionais constituintes da aptidão física, b) verificar se a margem de acerto ou de erro nessa ApC depende dos resultados obtidos; e c) verificar se aqueles com maior ApC são mais aptos fisicamente. MÉTODOS: Foram obtidos dados em 63 adultos (51 homens), com idade entre 22 e 85 anos, tendo sido medida e testada a ApC das seguintes variáveis: VO2 máximo, flexibilidade, força de preensão manual, potência muscular máxima absoluta e relativa, localização predominante de gordura corporal e peso de referência, habilidade de sentar e levantar do solo e relação peso/altura, além da altura e do peso corporal. A influência da magnitude das variáveis sobre o escore de ApC (soma dos acertos nas 12 variáveis testadas) foi testada pela comparação entre os resultados do primeiro e do quinto quintis da distribuição e por correlações. RESULTADOS: Os indivíduos tendem a errar mais do que a acertar, em média, a ApC: 60 vs. 40%. A ApC é mais incorreta para a variável flexibilidade 84% de erro - e mais precisa para a habilidade de levantar do solo 66% de acerto. O escore de ApC foi maior nos indivíduos mais flexíveis (p = 0,01) e nos que possuíam maior força de preensão manual (p = 0,04) e tendia a ser maior nos que alcançavam percentual mais elevado do VO2 máximo previsto (p = 0,08). O sedentarismo era quase três vezes mais prevalente nos indivíduos com pior ApC. Os 20% com maiores escores de ApC tendiam a melhores resultados nas variáveis da aptidão física (p entre 0,03 e 0,11). CONCLUSÕES: O nível global de ApC de variáveis da aptidão física é baixo, dependendo dos níveis de flexibilidade e de força de preensão manual e pelo padrão de atividade física regular no passado e no presente. Os que apresentam melhor ApC tendem a ser mais aptos. É possível que o aumento do conhecimento sobre os níveis de aptidão física influenciem positivamente para a adoção de um estilo de vida mais ativo.<br>BACKGROUND: Physical fitness has two dimensions, one related to health and the other, to performance. However, it is still unknown if non-athlete adults present an appropriate level of self-perception (SP) about their health-related physical fitness. OBJECTIVES: a) to assess the SP of non-athlete subjects in some morphofunctional variables related to physical fitness; b) to check if the degree of SP correctness is related to those variables; and c) to check if those with higher SP levels are more physically fit. METHODS: SP data from 63 adults (51 men), ages ranging from 22 to 85, were measured and assessed regarding the following variables: maximum VO2, flexibility, handgrip, absolute and relative maximal muscular power, largest fat deposition site and reference body weight, ability to sit and stand up from the floor and weight/height ratio, and height and body weight. The influence of variable magnitude on the SP score (sum total of correct answers in the 12 variables assessed) was tested by comparison between the first and fifth quintiles and by correlation. RESULTS: On the average, subjects more often provided wrong answers for the SP 60 vs 40%. SP was more incorrect regarding flexibility 84% of mistakes and more precise as to the ability to stand up from the floor 66% of correct answers. SP score was higher for more flexible subjects (p = 0.01) and for those that showed higher values of grip strength (p = 0.04) and those who achieved a higher % of predicted maximal VO2 (p = 0,08) tended to present a higher SP. Physical inactivity was almost three times more common for those with lower SP. The 20% with higher SP levels tended to present higher values in the physical fitness variables (p between 0.03 and 0.11). On the other hand, when the authors compared subjects with levels above the average for aerobic condition, flexibility and muscle strength and power with those with values below average in the four variables, there was no differences in SP. CONCLUSIONS: The overall level of SP of health-related physical fitness is low, being related to levels of flexibility, grip strength, and by past and current physical activity pattern. Subjects with higher SP tended to be more physically fit. It is possible that higher awareness about physical fitness levels will induce positive behaviors leading to the adoption of a more active lifestyle