SummaryCombating the social and economic consequences of a growing elderly population will require the identification of interventions that slow the development of age‐related diseases. Preserved cellular homeostasis and delayed aging have been previously linked to reduced cell proliferation and protein synthesis rates. To determine whether changes in these processes may contribute to or predict delayed aging in mammals, we measured cell proliferation rates and the synthesis and replacement rates (RRs) of over a hundred hepatic proteins in vivo in three different mouse models of extended maximum lifespan (maxLS): Snell Dwarf, calorie‐restricted (CR), and rapamycin (Rapa)‐treated mice. Cell proliferation rates were not consistently reduced across the models. In contrast, reduced hepatic protein RRs (longer half‐lives) were observed in all three models compared to controls. Intriguingly, the degree of mean hepatic protein RR reduction was significantly correlated with the degree of maxLS extension across the models and across different Rapa doses. Absolute rates of hepatic protein synthesis were reduced in Snell Dwarf and CR, but not Rapa‐treated mice. Hepatic chaperone levels were unchanged or reduced and glutathione S‐transferase synthesis was preserved or increased in all three models, suggesting a reduced demand for protein renewal, possibly due to reduced levels of unfolded or damaged proteins. These data demonstrate that maxLS extension in mammals is associated with improved hepatic proteome homeostasis, as reflected by a reduced demand for protein renewal, and that reduced hepatic protein RRs hold promise as an early biomarker and potential target for interventions that delay aging in mammals.

Bruss MD, Thompson AC, Aggarwal I, Khambatta CF, Hellerstein MK. The effects of physiological adaptations to calorie restriction on global cell proliferation rates. Am J Physiol Endocrinol Metab 300: E735-E745, 2011. First published February 1, 2011 doi:10.1152/ajpendo.00661.2010 reduces the rate of cell proliferation in mitotic tissues. It has been suggested that this reduction in cell proliferation may mediate CR-induced increases in longevity. However, the mechanisms that lead to CRinduced reductions in cell proliferation rates remain unclear. To evaluate the CR-induced physiological adaptations that may mediate reductions in cell proliferation rates, we altered housing temperature and access to voluntary running wheels to determine the effects of food intake, energy expenditure, percent body fat, and body weight on proliferation rates of keratinocytes, liver cells, mammary epithelial cells, and splenic T-cells in C57BL/6 mice. We found that ϳ20% CR led to a reduction in cell proliferation rates in all cell types. However, lower cell proliferation rates were not observed with reductions in 1) food intake and energy expenditure in female mice housed at 27°C, 2) percent body fat in female mice provided running wheels, or 3) body weight in male mice provided running wheels compared with ad libitum-fed controls. In contrast, reductions in insulin-like growth factor I were associated with decreased cell proliferation rates. Taken together, these data suggest that CR-induced reductions in food intake, energy expenditure, percent body fat, and body weight do not account for the reductions in global cell proliferation rates observed in CR. In addition, these data are consistent with the hypothesis that reduced cell proliferation rates could be useful as a biomarker of interventions that increase longevity. food intake; energy expenditure; percent body fat; body weight CALORIE RESTRICTION (CR), defined as a reduction in caloric intake without malnutrition, increases lifespan, delays the onset of age-related diseases, and slows the functional decline of various organs (42). Although the mechanisms mediating these effects are unclear, one of the most rapid and robust effects of CR is a reduction in the rate of cell proliferation in mitotic tissues (25,28,38). The turnover rates of keratinocytes, liver cells, mammary epithelial cells (MECs), splenic T cells, and prostate cells are decreased by 30 -50% following several weeks of CR, and the effects persist throughout the intervention period (25). It has been suggested that this reduction in cell proliferation could mediate many of the longevity and anticancer effects of CR by delaying replicative senescence and reducing the promotional phase of carcinogenesis (11,42). Considering that the rate of cell proliferation is an integrated response that comprises many genetic and hormonal signals and appears to be mechanistically linked to aging, this cellular process represents a potential target for monitoring therapeutic interventions aimed at delaying the onset of age-relate...

To determine the metabolic effects of grapefruit juice consumption we established a model in which C57Bl/6 mice drank 25–50% sweetened GFJ, clarified of larger insoluble particles by centrifugation (cGFJ), ad libitum as their sole source of liquid or isocaloric and sweetened water. cGFJ and control groups consumed similar amounts of liquids and calories. Mice fed a high-fat diet and cGFJ experienced a 18.4% decrease in weight, a 13–17% decrease in fasting blood glucose, a three-fold decrease in fasting serum insulin, and a 38% decrease in liver triacylglycerol values, compared to controls. Mice fed a low-fat diet that drank cGFJ experienced a two-fold decrease in fasting insulin, but not the other outcomes observed with the high-fat diet. cGFJ consumption decreased blood glucose to a similar extent as the commonly used anti-diabetic drug metformin. Introduction of cGFJ after onset of diet-induced obesity also reduced weight and blood glucose. A bioactive compound in cGFJ, naringin, reduced blood glucose and improved insulin tolerance, but did not ameliorate weight gain. These data from a well-controlled animal study indicate that GFJ contains more than one health-promoting neutraceutical, and warrant further studies of GFJ effects in the context of obesity and/or the western diet.

The intracellular accumulation of aggregated misfolded proteins is a cytopathological hallmark of neurodegenerative diseases. However, the functional relationship between protein misfolding or aggregation and the cellular proteostasis network that monitors and maintains proteome health is poorly understood. Previous studies have associated translational suppression and transcriptional remodeling with the appearance of protein aggregates, but whether these responses are induced by aggregates or their misfolded monomeric or oligomeric precursors remains unclear. Because aggregation in cells is rapid, nonlinear, and asynchronous, it has not been possible to deconvolve these kinetically linked processes to determine the earliest cellular responses to misfolded proteins. Upon removal of the synthetic, biologically inert ligand shield-1 (S1), AgDD, an engineered variant FK506-binding protein (FKBP1A), rapidly (t1 ⁄ 2 ϳ5 min) unfolds and self-associates, forming detergent-insoluble, microscopic cytoplasmic aggregates. Using global diglycine-capture (K-GG) proteomics, we found here that this solubility transition is associated with immediate increases in ubiquitylation of AgDD itself, along with that of endogenous proteins that are components of the ribosome and the 26S proteasome. We also found that the earliest cellular responses to acute S1 removal include recruitment of ubiquitin protein ligase E3C (UBE3C) to the 26S proteasome and ubiquitylation of two key proteasomal ubiquitin receptors, 26S proteasome regulatory subunit RPN10 (RPN10) and Rpn13 homolog (RPN13 or ADRM1). We conclude that these proteasomal responses are due to AgDD protein misfolding and not to the presence of detergent-insoluble aggregates.

RDH1 is one of several enzymes that catalyze the first of two reactions to convert retinol into alltrans-retinoic acid (atRA). Here we show that Rdh1-null mice fed a low-fat diet gain more weight as adiposity (17% males, 13% females) than wild-type mice by 20 weeks old, despite not consuming more calories nor decreasing activity. Glucose intolerance and insulin resistance develops following increased adiposity. Despite the increase in white fat pads, epididymal white adipose does not express Rdh1, nor does muscle. Brown adipose tissue (BAT) and liver express 3