Leptin levels recover normally in healthy older adults after acute diet-induced weight loss.

OBJECTIVES: Involuntary weight loss affects 20% of community dwelling older adults. The underlying mechanism for this disorder is unknown. Objective is to determine if failure of older persons to regain weight is associated with elevated pro-inflammatory cytokine and leptin levels. DESIGN: Prospective diet intervention study. SETTING: University of Washington Medical Center from 2001-2005. PARTICIPANTS: Twenty-one younger (18-35 years old) and nineteen older (>or= 70 years old) men and women. INTERVENTION: Each subject was placed for two weeks on a weight-maintaining diet, followed in sequence by 2 weeks of 30% caloric restriction, then 4 weeks of ad libitum food intake. MEASUREMENTS: Plasma leptin levels, fasting serum pro-inflammatory cytokine levels, and peripheral blood mononuclear cell cytokine levels were measured. RESULTS: Leptin levels in the two cohorts decreased after caloric restriction and increased after ad-libitum food consumption resumed. Plasma TNF alpha levels were higher in older subjects compared to younger adults. However, there was no association between changes in TNF alpha levels and changes in AUC leptin. CONCLUSION: Leptin levels in healthy older individuals responded appropriately in a compensatory manner to changes in body weight. These data do not support a cytokine dependent elevation in leptin levels as being responsible for the failure of older adults to regain weight.

Circulating TNF alpha receptor levels identify older adults who fail to regain weight after acute weight loss.

OBJECTIVE: Some healthy older adults have difficulty regaining weight after acute weight loss, and the reason for this failure to regain weight is unknown. The objective of this study was to determine if elevated leptin or pro-inflammatory cytokine levels are associated with failure to regain weight over two years after an acute weight loss intervention. DESIGN: Two year prospective study after an acute weight loss intervention. SETTING: University of Washington Medical Center from 2001-2006. PARTICIPANTS: Nineteen older (≥ 70 years old) men and women. MEASUREMENTS: Body weights, health status questionnaire, body composition data, serum leptin, glucose, insulin, C- reactive protein and pro-inflammatory cytokine levels were measured every six months for two years. RESULTS: Five subjects out of 19 failed to regain weight after two years. The subjects who failed to regain weight after 2 years had higher circulating levels of tumor necrosis factor receptor particle 55 (TNFRp55) at baseline and at 6, 12, 18 and 24 months of follow up compared to subjects who regained weight after 2 years (P = 0.02 ). CONCLUSION: Five out of 19 older subjects had difficulty regaining weight for up to 2 years following an acute weight loss intervention, and their TNFRp55 levels were persistently higher than in subjects who regained weight. Greater TNF α action, as reflected by higher circulating levels of TNFRp55, could be contributing towards inability of some older persons to regain weight after acute weight loss.

Indirect consequences of artificial selection on plasticity to light quality in Arabidopsis thaliana.

Covariation between light quality- and photoperiod-mediated phenotypic plasticity was investigated using Arabidopsis thaliana. Three episodes of artificial selection were imposed on an index that quantified the plastic response to reduced red to far-red ratios (R:FR), with higher index values indicating greater plasticity. Relative to control lines, two high plasticity (HP) lines showed 1.6- and 2.4-fold increases in the index; low plasticity (LP) lines showed 1.4- and 1.1-fold decreases. A factorial experiment combining high and low R:FR conditions with long and short photoperiods assessed indirect consequences of selection on plasticity. Despite divergent R:FR-mediated plasticities in HP vs. LP lines, all four lines showed increases in photoperiod-mediated responses and decreases in mean leaf number. Complex relationships among trait means, plasticities and underlying mechanisms caution against generalizing about the genetic architecture of plastic traits. Partially independent developmental and evolutionary responses to R:FR and photoperiod are somewhat unsurprising, given this species' cosmopolitan nature.

Developmental phenotypic plasticity: where ecology and evolution meet molecular biology.

The plastic response of phenotypic traits to environmental change is a common research focus in several disciplines-from ecology and evolutionary biology to physiology and molecular genetics. The use of model systems such as the flowering plant Arabidopsis thaliana has facilitated a dialogue between developmental biologists asking how plasticity is controlled (proximate causes) and organismal biologists asking why plasticity exists (ultimate causes). Researchers studying ultimate causes and consequences are increasingly compelled to reject simplistic, 'black box' models, while those studying proximate causes and mechanisms are increasingly obliged to subject their interpretations to ecological 'reality checks.' We review the successful multidisciplinary efforts to understand the phytochrome-mediated shade-avoidance and light-seeking responses of flowering plants as a pertinent example of convergence between evolutionary and molecular biology. In this example, the two-way exchange between reductionist and holist camps has been essential to rapid and sustained progress. This should serve as a model for future collaborative efforts towards understanding the responses of organisms to their constantly changing environments.