Effect of age on liver protein synthesis and degradation

Altered Proteasome Composition in Aging Brains, Genetic Proteasome Augmentation Mitigates Age-Related Cognitive Declines, and Acute Proteasome Agonist Treatment Rescues Age-Related Cognitive Deficits in Mice

The aging brain experiences a significant decline in proteasome function, The proteasome is critical for many key neuronal functions including neuronal plasticity, and memory formation/retention. Treatment with proteasome inhibitors impairs these processes. Our study reveals a marked reduction in 20S and 26S proteasome activities in aged mice brains driven by reduced functionality of aged proteasome. This is matched by a decline in 20S proteasome but an increase in 26S proteasome. Our data suggests this may be a compensatory response to reduced functionality. By overexpressing the proteasome subunit PSMB5 in the neurons of mice, enhancing proteasome function, we slowed age-related declines in spatial learning and memory as well neuromuscular declines. We then showed acute treatment with a proteasome activator to rescue spatial learning and memory deficits in aged mice. These findings highlight the potential of proteasome augmentation as a therapeutic strategy to mitigate age-related cognitive declines.

Management of Portal Hypertension in the Older Patient

PURPOSE OF THIS REVIEW

Aging is a process of physiological slowing, reduced regenerative capacity and inability to maintain cellular homeostasis. World Health Organisation declared the commencement of population aging globally, largely attributed to improvement in the healthcare system with early diagnosis and effective clinical management. Liver ages similar to other organs, with reduction in size and blood flow. In this review we aim to evaluate the effect of aging in liver disease.

RECENT FINDINGS

Aging causes dysregulation of major carbohydrate, fat and protein metabolism in the liver. Age is a major risk factor for liver fibrosis accelerated by sinusoidal endothelial dysfunction and immunological disharmony. Age plays a major role in patients with liver cirrhosis and influence outcomes in patients with portal hypertension. Transient elastography may be an useful tool in the assessment of portal hypertension. Hepatic structural distortion, increased vascular resistance, state of chronic inflammation, associated comorbidities, lack of physiological reserve in the older population may aggravate portal hypertension in patients with liver cirrhosis and may result in pronounced variceal bleed. Cut-offs for other non-invasive markers of fibrosis may differ in the elderly population. Non-selective beta blockers initiated at lower dose followed by escalation are the first line of therapy in elderly patients with cirrhosis and portal hypertension, unless contraindicated. Acute variceal bleed in the elderly cirrhotic patients can be life threatening and may cause rapid exsanguination due to poor reserve and associated comorbidities. Vasoactive drugs may be associated with more adverse reactions. Early endoscopy may be warranted in the elderly patients with acute variceal bleed. Role of TIPS in the elderly cirrhotics discussed. Management of portal hypertension in the older population may pose significant challenges to the treating clinician.

Preparation of polyclonal antibodies to chicken P62 protein and its application in nephropathogenic infectious bronchitis virus-infected chickens

p62, also known as SQSTM1, has been shown to be closely related to the coronavirus. However, it remains unclear on the relationship between p62 and NIBV infection. Moreover, there are no available antibodies against the chicken p62 protein. Thus, this study aimed to prepare p62 polyclonal antibody and investigate the correlation between the p62 protein and NIBV infection. Here, PET-32a-p62 prokaryotic fusion expression vector was constructed for prokaryotic protein expression, and then p62 polyclonal antibody was prepared by immunizing rabbits. Lastly, these antibodies were then utilized in Western blotting (WB), immunohistochemistry (IHC), and immunofluorescence (IF) assays. The results showed that we successfully prepared chicken p62 polyclonal antibody. Meanwhile, WB and IF demonstrated that the expression of p62 showed a trend of first increase and then decrease after NIBV infection. IHC showed that the expression of p62 in the spleen, lung, kidney, bursa of Fabricius and trachea of chickens infected with NIBV in 11 dpi was significantly higher than that of normal chickens. Taken together, this study successfully prepared a polyclonal antibody for chicken p62 protein and confirmed its application and expression in chickens, as well as the expression of p62 in tissues after NIBV infection.

Early Life Androgen Administration Attenuates Aging Related Declines in Muscle Protein Synthesis

PURPOSE

This study examined the acute and long-term effects of nandrolone decanoate (ND) on fractional synthetic rates (FSR).

METHODS

Male C57BL/6 mice were randomized into ND ( n = 20) or sham ( n = 20) groups. ND injections (10 g·kg -1 ·wk -1 ) started at 7 months of ages and continued for 6 wk. Ten animals from each group were randomly separated and examined 1 wk following drug cessation. The remaining animals were examined at 16 months of age. Animals were injected IP with 1.5 mL of deuterated water 24 h before euthanasia. The kidney, liver, heart, gastrocnemius, and soleus were extracted. Samples were analyzed for deuterated alanine enrichment in the bound protein and intracellular fraction by liquid chromatography tandem mass spectrometry to measure estimated FSR (fraction/day (F/D)) of mixed tissue.

RESULTS

One-way ANOVA, with treatment and age as fixed factors, indicated that kidney FSR was greater ( P = 0.027) in ND (0.41 ± 0.02 F/D) than sham (0.36 ± 0.014F/D) and higher ( P = 0.003) in young (0.42 ± 0.2 F/D) than old (0.35 ± 0.01 F/D). Liver and heart FSR values were greater ( P ≤ 0.001) in young (0.79 ± 0.06 F/D and 0.13 ± 0.01 F/D, respectively) compared with old (0.40 ± 0.01 F/D and 0.09 ± 0.01 F/D, respectively), but not between ND and sham. Gastrocnemius FSR was ( P ≤ 0.001) greater in young (0.06 ± 0.01 F/D) compared with old (0.03 ± 0.002 F/D), and greater ( P = 0.006) in ND (0.05 ± 0.01 F/D) compared with sham (0.04 ± 0.003 F/D). Soleus FSR rates were greater ( P = 0.050) in young (0.13 ± 0.01 F/D) compared with old (0.11 ± 0.003 F/D), but not between ND (0.12 ± 0.01 F/D) and sham (0.12 ± 0.01 F/D). Old animals who had received ND displayed elevated FSR in the gastrocnemius ( P = 0.054) and soleus ( P = 0.024).

CONCLUSIONS

ND use in young adult animals appeared to maintain long-term elevations in FSR in muscle during aging.

PCSK9: an emerging player in cardiometabolic aging and its potential as a therapeutic target and biomarker

Proprotein convertase subtilisin/kexin type 9 (PCSK9), renowned for its pivotal role in low-density lipoprotein (LDL) regulation, has emerged as a compelling regulator of cardiometabolic aging. Beyond its well-established involvement in cholesterol metabolism, PCSK9's multifaceted influence on the aging processes of the cardiovascular and metabolic systems is garnering increasing attention. This review delves into the evolving landscape of PCSK9 in the context of cardiometabolic aging, offering fresh insights into its potential implications. Drawing inspiration from pioneering research conducted by the Pacher laboratory (Arif et al., Geroscience, 2023, PMID: 37726433), we delve into the intricate interplay of PCSK9 within the aging heart and liver, shedding light on its newfound significance. Recent studies underscore PCSK9's pivotal role in liver aging, suggesting intriguing connections between hepatic aging, lipid metabolism, and cardiovascular health. Additionally, we explore the therapeutic potential of PCSK9 as both a target and a biomarker, within the context of age-related cardiovascular disease.

Data-driven transcriptomics analysis identifies PCSK9 as a novel key regulator in liver aging

The liver, as a crucial metabolic organ, undergoes significant pathological changes during the aging process, which can have a profound impact on overall health. To gain a comprehensive understanding of these alterations, we employed data-driven approaches, along with biochemical methods, histology, and immunohistochemistry techniques, to systematically investigate the effects of aging on the liver. Our study utilized a well-established rat aging model provided by the National Institute of Aging. Systems biology approaches were used to analyze genome-wide transcriptomics data from liver samples obtained from young (4-5 months old) and aging (20-21 months old) Fischer 344 rats. Our findings revealed pathological changes occurring in various essential biological processes in aging livers. These included mitochondrial dysfunction, increased oxidative/nitrative stress, decreased NAD + content, impaired amino acid and protein synthesis, heightened inflammation, disrupted lipid metabolism, enhanced apoptosis, senescence, and fibrosis. These results were validated using independent datasets from both human and rat aging studies. Furthermore, by employing co-expression network analysis, we identified novel driver genes responsible for liver aging, confirmed our findings in human aging subjects, and pointed out the cellular localization of the driver genes using single-cell RNA-sequencing human data. Our study led to the discovery and validation of a liver-specific gene, proprotein convertase subtilisin/kexin type 9 (PCSK9), as a potential therapeutic target for mitigating the pathological processes associated with aging in the liver. This finding envisions new possibilities for developing interventions aimed to improve liver health during the aging process.

Early-adulthood spike in protein translation drives aging via juvenile hormone/germline signaling

Protein translation (PT) declines with age in invertebrates, rodents, and humans. It has been assumed that elevated PT at young ages is beneficial to health and PT ends up dropping as a passive byproduct of aging. In Drosophila, we show that a transient elevation in PT during early-adulthood exerts long-lasting negative impacts on aging trajectories and proteostasis in later-life. Blocking the early-life PT elevation robustly improves life-/health-span and prevents age-related protein aggregation, whereas transiently inducing an early-life PT surge in long-lived fly strains abolishes their longevity/proteostasis benefits. The early-life PT elevation triggers proteostatic dysfunction, silences stress responses, and drives age-related functional decline via juvenile hormone-lipid transfer protein axis and germline signaling. Our findings suggest that PT is adaptively suppressed after early-adulthood, alleviating later-life proteostatic burden, slowing down age-related functional decline, and improving lifespan. Our work provides a theoretical framework for understanding how lifetime PT dynamics shape future aging trajectories.

Protein translation paradox: Implications in translational regulation of aging

Protein translation is an essential cellular process playing key roles in growth and development. Protein translation declines over the course of age in multiple animal species, including nematodes, fruit flies, mice, rats, and even humans. In all these species, protein translation transiently peaks in early adulthood with a subsequent drop over the course of age. Conversely, lifelong reductions in protein translation have been found to extend lifespan and healthspan in multiple animal models. These findings raise the protein synthesis paradox: age-related declines in protein synthesis should be detrimental, but life-long reductions in protein translation paradoxically slow down aging and prolong lifespan. This article discusses the nature of this paradox and complies an extensive body of work demonstrating protein translation as a modulator of lifespan and healthspan.

Age-related changes in tau and autophagy in human brain in the absence of neurodegeneration

Tau becomes abnormally hyper-phosphorylated and aggregated in tauopathies like Alzheimers disease (AD). As age is the greatest risk factor for developing AD, it is important to understand how tau protein itself, and the pathways implicated in its turnover, change during aging. We investigated age-related changes in total and phosphorylated tau in brain samples from two cohorts of cognitively normal individuals spanning 19-74 years, without overt neurodegeneration. One cohort utilised resected tissue and the other used post-mortem tissue. Total soluble tau levels declined with age in both cohorts. Phosphorylated tau was undetectable in the post-mortem tissue but was clearly evident in the resected tissue and did not undergo significant age-related change. To ascertain if the decline in soluble tau was correlated with age-related changes in autophagy, three markers of autophagy were tested but only two appeared to increase with age and the third was unchanged. This implies that in individuals who do not develop neurodegeneration, there is an age-related reduction in soluble tau which could potentially be due to age-related changes in autophagy. Thus, to explore how an age-related increase in autophagy might influence tau-mediated dysfunctions in vivo, autophagy was enhanced in a Drosophila model and all age-related tau phenotypes were significantly ameliorated. These data shed light on age-related physiological changes in proteins implicated in AD and highlights the need to study pathways that may be responsible for these changes. It also demonstrates the therapeutic potential of interventions that upregulate turnover of aggregate-prone proteins during aging.

Quantification of tissue-specific protein translation in whole C. elegans using O-propargyl-puromycin labeling and fluorescence microscopy

The regulation of gene expression via protein translation is critical for growth, development, and stress response. While puromycin-based techniques have been used to quantify protein translation in C. elegans, they have been limited to using lysate from whole worms. To achieve tissue-specific quantification of ribosome activity in intact C. elegans, we report the application of O-propargyl-puromycin in a cuticle defective mutant followed by conjugation of an azide fluorophore for detection using fluorescent confocal microscopy. We apply this technique to quantify translation in response to heat shock, cycloheximide, or knockdown of translation factors. Furthermore, we demonstrate that O-propargyl-puromycin can be used to quantify translation between tissues or within a tissue like the germline. This technique is expected to have a broad range of applications in determining how protein translation is altered in different tissues in response to stress or gene knockdowns or with age.

In vivo assay and modelling of protein and mitochondrial turnover during aging

To maintain homoeostasis, cells must degrade damaged or misfolded proteins and synthesize functional replacements. Maintaining a balance between these processes, known as protein turnover, is necessary for stress response and cellular adaptation to a changing environment. Damaged mitochondria must also be removed and replaced. Changes in protein and mitochondrial turnover are associated with aging and neurodegenerative disease, making it important to understand how these processes occur and are regulated in cells. To achieve this, reliable assays of turnover must be developed. Several methods exist, including pulse-labelling with radioactive or stable isotopes and strategies making use of fluorescent proteins, each with their own advantages and limitations. Both cell culture and live animals have been used for these studies, in systems ranging from yeast to mammals. In vivo assays are especially useful for connecting turnover to aging and disease. With its short life cycle, suitability for fluorescent imaging, and availability of genetic tools, Drosophila melanogaster is particularly well suited for this kind of analysis.

Translation elongation rate varies among organs and decreases with age

There has been a surge of interest towards targeting protein synthesis to treat diseases and extend lifespan. Despite the progress, few options are available to assess translation in live animals, as their complexity limits the repertoire of experimental tools to monitor and manipulate processes within organs and individual cells. It this study, we developed a labeling-free method for measuring organ- and cell-type-specific translation elongation rates in vivo. It is based on time-resolved delivery of translation initiation and elongation inhibitors in live animals followed by ribosome profiling. It also reports translation initiation sites in an organ-specific manner. Using this method, we found that the elongation rates differ more than 50% among mouse organs and determined them to be 6.8, 5.0 and 4.3 amino acids per second for liver, kidney, and skeletal muscle, respectively. We further found that the elongation rate is reduced by 20% between young adulthood and mid-life. Thus, translation, a major metabolic process in cells, is tightly regulated at the level of elongation of nascent polypeptide chains.

Alterations of the translation apparatus during aging and stress response

Aging is a biological process characterized by the irreversible and time-dependent deterioration of cell functions, tissues, and organs. Accumulating studies in a wide range of species from yeast to human revealed changes associated with the aging process to be conserved throughout evolution. The main characteristics of aging are (i) genomic instability, (ii) loss of telomere function, (iii) epigenetic changes,(iv) increased cellular senescence, (v) depletion of the stem cell pool, (vi) altered intercellular communication and (vii) loss of protein homeostasis. Among the multiple molecular mechanisms underlying aging, alterations of the translation machinery affecting the rate and selectivity of protein biosynthesis seem to play a central role. At the very heart of translation is the ribosome, a multifaceted and universally conserved RNA-protein particle responsible for accurate polypeptide synthesis and co-translational protein folding. Here we summarize and discuss recent developments on the contribution of altered translation and age-dependent modifications on the ribosome structure to aging and cellular senescence.

Effect of dietary restriction and subsequent re-alimentation on the transcriptional profile of hepatic tissue in cattle

Background

Compensatory growth (CG) is an accelerated growth phenomenon observed in animals upon re-alimentation following a period of dietary restriction. It is typically utilised in livestock systems to reduce feed costs during periods of reduced feed availability. The biochemical mechanisms controlling this phenomenon, however, are yet to be elucidated. This study aimed to uncover the molecular mechanisms regulating the hepatic expression of CG in cattle, utilising RNAseq. RNAseq was performed on hepatic tissue of bulls following 125 days of dietary restriction (RES) and again following 55 days of subsequent re-alimentation during which the animals exhibited significant CG. The data were compared with those of control animals offered the same diet on an ad libitum basis throughout (ADLIB). Elucidation of the molecular control of CG may yield critical information on genes and pathways which could be targeted as putative molecular biomarkers for the selection of animals with improved CG potential.

Results

Following a period of differential feeding, body-weight and liver weight were 161 and 4 kg higher, respectively, for ADLIB compared with RES animals. At this time RNAseq analysis of liver tissue revealed 1352 significantly differentially expressed genes (DEG) between the two treatments. DEGs indicated down-regulation of processes including nutrient transport, cell division and proliferation in RES. In addition, protein synthesis genes were up-regulated in RES following a period of restricted feeding. The subsequent 55 days of ad libitum feeding for both groups resulted in the body-weight difference reduced to 84 kg, with no difference in liver weight between treatment groups. At the end of 55 days of unrestricted feeding, 49 genes were differentially expressed between animals undergoing CG and their continuously fed counterparts. In particular, hepatic expression of cell proliferation and growth genes were greater in animals undergoing CG.

Conclusions

Greater expression of cell cycle and cell proliferation genes during CG was associated with a 100 % recovery of liver weight during re-alimentation. Additionally, an apparent up-regulation in capacity for cellular protein synthesis during restricted feeding may contribute to and sustain CG during re-alimentation. DEGs identified are potential candidate genes for the identification of biomarkers for CG, which may be incorporated into future breeding programmes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2578-5) contains supplementary material, which is available to authorized users.

Reference intervals, longitudinal analyses, and index of individuality of commonly measured laboratory variables in captive bald eagles (Haliaeetus leucocephalus)

The objectives of this study were to determine reference intervals, perform longitudinal analyses, and determine the index of individuality (IoI) of 8 hematologic, and 13 biochemical and electrophoretic variables for a group of captive bald eagles (Haliaeetus leucocephalus). Reference intervals were determined from blood samples collected during annual wellness examinations for 41 eagles (23 male and 18 female) with ages ranging between 6 and 43 years (18.7 +/- 7.4, mean +/- SD) at the time of sample collection. Longitudinal analyses and IoI were determined for measured hematologic, biochemical, and protein electrophoretic variables, both individually and as a group, for a subset of 16 eagles (10 male and 6 female) during a 12-year period. This smaller group of eagles ranged in age between 2 and 20 years at the start of the study period, and between 14 and 32 years (21.9 +/- 5.0, mean +/- SD) at the end of the study period. Significant increases with age within the group of 16 eagles were observed only for red blood cells, percent heterophils, total protein, and beta-globulin protein fraction, while albumin:globulin decreased significantly with age. A low IoI (> or = 1.4) was determined for all hematologic and biochemical variables except gamma globulins, which had high IoI (< or = 0.6) for 3 individuals within the subset of 16.

Molecular alterations in proteasomes of rat liver during aging result in altered proteolytic activities

Aging induces alterations of tissue protein homoeostasis. To investigate one of the major systems catalysing intracellular protein degradation we have purified 20S proteasomes from rat liver of young (2 months) and aged (23 months) animals and separated them into three subpopulations containing different types of intermediate proteasomes with standard- and immuno-subunits. The smallest subpopulation ΙΙΙ and the major subpopulation Ι comprised proteasomes containing immuno-subunits β1i and β5i beside small amounts of standard-subunits, whereas proteasomes of subpopulation ΙΙ contained only β5i beside standard-subunits. In favour of a relative increase of the major subpopulation Ι, subpopulation ΙΙ and ΙΙΙ were reduced for about 55 % and 80 %, respectively, in aged rats. Furthermore, in all three 20S proteasome subpopulations from aged animals standard-active site subunits were replaced by immuno-subunits. Overall, this transformation resulted in a relative increase of immuno-subunit-containing proteasomes, paralleled by reduced activity towards short fluorogenic peptide substrates. However, depending on the substrate their hydrolysing activity of long polypeptide substrates was significantly higher or unchanged. Furthermore, our data revealed an altered MHC class I antigen-processing efficiency of 20S proteasomes from liver of aged rats. We therefore suggest that the age-related intramolecular alteration of hepatic proteasomes modifies its cleavage preferences without a general decrease of its activity. Such modifications could have implications on protein homeostasis as well as on MHC class I antigen presentation as part of the immunosenescence process.

The effect of old age on apolipoprotein E and its receptors in rat liver

Apolipoprotein E (apoE) is associated with aging and some age-related diseases. The majority of apoE is produced by hepatocytes for the receptor-mediated uptake of lipoproteins. Here, the effects of age on the hepatic expression and distribution of apoE and its receptors were determined using immunofluorescence, Western blots, and quantitative PCR in rat liver tissue and isolated hepatocytes. The expression of apoE mRNA and protein was not influenced significantly by aging. Immunofluorescence studies in isolated hepatocytes showed that apoE was more likely to be co-localized with early endosomes, golgi, and microtubules in isolated old hepatocytes. The mRNA expression of the receptor involved in sequestration of apoE, heparan sulfate proteoglycan was reduced in old age, without any significant effect on the expression of either the low-density lipoprotein receptor or low density-lipoprotein receptor-related protein. Old age is associated with changes in hepatic apoE intracellular trafficking and heparan sulfate proteoglycan expression that might contribute to age-related disease.

A comparative analysis of the cell biology of senescence and aging

Various intracellular organelles, such as lysosomes, mitochondria, nuclei, and cytoskeletons, change during replicative senescence, but the utility of these changes as general markers of senescence and their significance with respect to functional alterations have not been comprehensively reviewed. Furthermore, the relevance of these alterations to cellular and functional changes in aging animals is poorly understood. In this paper, we review the studies that report these senescence-associated changes in various aging cells and their underlying mechanisms. Changes associated with lysosomes and mitochondria are found not only in cells undergoing replicative or induced senescence but also in postmitotic cells isolated from aged organisms. In contrast, other changes occur mainly in cells undergoing in vitro senescence. Comparison of age-related changes and their underlying mechanisms in in vitro senescent cells and aged postmitotic cells would reveal the relevance of replicative senescence to the physiological processes occurring in postmitotic cells as individuals age.

Parathyroid hormone stimulation of the renal 25-hydroxyvitamin D-1alpha-hydroxylase--effect of age and free radicals

The capacity of parathyroid hormone (PTH) to increase serum 1,25(OH)(2)D levels declines with age in both rats and humans. In young rats, PTH stimulates renal 1,25(OH)(2)D production and increases mRNA levels for the terminal mitochondrial P450 of the 1alpha-hydroxylase complex (CYP27B1 or CYP1alpha). However, in older rats PTH increases mRNA levels but not 1,25(OH)(2)D production. This suggests that in old animals there is either decreased CYP1alpha protein levels in response to PTH or that the protein produced lacks functionality. The CYP1alpha protein is located on the inner mitochondrial membrane, the site of increased free radical production with age. To study these possibilities, we examined the effect of PTH and free radicals on CYP1alpha expression in a model system-AOK-B50 renal tubular cells. PTH increased CYP1alpha mRNA and protein in a similar time-dependent manner, suggesting that CYP1alpha protein levels were largely regulated by mRNA levels. The effect of free radicals was determined by preincubation with hydrogen peroxide (H(2)O(2)), a standard model for studying free radical damage. H(2)O(2) inhibited PTH-stimulated CYP1alpha protein levels and 1,25(OH)(2)D production in a dose dependent manner. However, 1,25(OH)(2)D production was more sensitive to H(2)O(2) than was CYP1alpha protein levels. This suggests that the catalytic activity of the CYP1alpha protein may be reduced by free radical damage in these cells. Future studies will focus on detecting oxidative damage in this model system and in vivo.

Impact of donor age on the growth of young recipient rats after liver transplantation

PURPOSE

We studied the age-related changes in graft livers, and their impact on post-transplantation liver function and the growth of young recipient rats.

METHODS

Rats aged 11-68 weeks old were studied as controls to assess liver histology, liver function, and body weight. We performed orthotopic liver transplantation using Kamada's cuff technique without arterial reconstruction. Young rats aged 11 weeks were randomized to receive livers from either 11-week-old donors (YD group) or 52-week-old donors (OD group). Recipient rats were killed 0, 8, or 16 weeks after surgery and we assessed the same variables as in the controls.

RESULTS

We confirmed an age-related increase in the average size of hepatocytes and their nuclei. These age-related changes persisted and progressed in the graft liver after transplantation. There were no significant differences in the levels of serum transaminases or total bilirubin between the YD and OD groups, but the serum albumin level was significantly lower in the OD group. The YD group grew normally, whereas the OD group recipients lagged significantly in gaining body weight.

CONCLUSION

We found that 52-week-old grafts transplanted into 11-week-old recipients resulted in deficient growth and a decline in serum albumin, suggesting that grafted old livers fail to produce enough protein to meet the demands of growth adequately.

Programming of hepatic antioxidant capacity and oxidative injury in the ageing rat

Exposure to undernutrition in fetal life increases the susceptibility of humans and animals to major disease states in adult life. Studies of rodents exposed to protein restriction during fetal life indicate that lifespan is reduced, a finding that is the opposite of the well-documented improvement in longevity noted with post-weaning caloric restriction. The maternal low-protein (MLP) model of rat pregnancy therefore provides a suitable vehicle to consider how nutrition in fetal life may programme mechanisms of ageing. Pregnant rats were fed control (n = 7) or MLP diet (n = 7) throughout pregnancy. At birth, increased oxidation of hepatic proteins was noted, and this appeared related to activity of glutathione reductase. Older offspring were studied at 4, 16, 30 and 44 weeks of age and analyses revealed that MLP exposure in utero produced sex-specific differences in oxidant:antioxidant balance. In male offspring, MLP increased protein carbonyl concentrations in the liver (P = 0.013) and increased glutathione peroxidase activity (P = 0.018). These programmed changes were absent in the female offspring. The data support the hypothesis that reduced lifespan in rats subject to prenatal protein restriction is a consequence of enhanced oxidative processes promoting apoptosis and loss of tissue function. Mechanisms of ageing appear to be subject to nutritional programming during early development.

Anti-aging effects of anti-lipolytic drugs

Genetic disruption of insulin and insulin-like signaling pathways may extend lifespan. Hyperinsulinemia and insulin resistance may accelerate aging. The hypothesis was tested that a once-a-week life-long inhibition of insulin secretion by the administration of anti-lipolytic drugs might have anti-aging effects. Groups of 3-month-old male Sprague-Dawley rats were (a) given standard laboratory food ad libitum (AL); (b) fed AL 6 days and fasted 1 day every week (FW); (c) fed AL every other day (EOD), (d) fed like FW and given Acipimox (50 mg/kg b.w.) on the day of fasting (FWA) by the gastric tube. The AL, FW and EOD groups received saline intragastrically. Treatment with ACIPIMOX transiently decreased plasma free fatty acids, glucose and insulin and increased valine plasma levels, and had no long-term effect on food consumption and body weight. By age 6, 12 and 24 months subgroups were taken and the age-related changes in liver dolichol and autophagic proteolysis--which are correlated with life-expectancy--were measured. Liver dolichol levels increased and autophagic proteolysis decreased in mature and older AL rats; EOD and FWA fully counteracted these changes; FW rats had significant but smaller beneficial effects. It is concluded that life-long weekly-repeated transient inhibition of insulin secretion by antilipolytic drugs may have an anti-aging effect, additive to the anti-aging effect of a milder caloric restriction. Speculation is that transiently lower plasma insulin levels might stimulate the anti-aging cell-repair mechanism autophagy, which has longer lasting effects on cell housekeeping.

Experimental diabetes accelerates accumulation of fluorescent pigments in rat trigeminal neurons

The purpose of this study was to investigate autofluorescent pigment granules (lipofuscin, ceroid) in the trigeminal neurons (TN) during aging and streptozotocin-induced diabetes. Four young adult male rats were injected with streptozotocin (STZ; 50 mg/kg) to produce diabetes (DM), for comparison with four young uninjected control rats and four aged rats (90 weeks old). Eight weeks after STZ injection, all rats were fixed with 4% paraformaldehyde, and paraffin sections of TN were prepared and observed by fluorescence microscopy. We found the number of neurons with autofluorescent pigments had increased to 30.38% of the total in DM compared to 8.98% in the control group, and 25.36% in the aged rats. The area of autofluorescence within those neurons was 16.84% in aged rats, 13.02% in DM and 4.45% in the controls. Thus, DM caused accelerated accumulation of fluorescent granules in trigeminal neurons, and this change may show that premature aging contributes to neuronal functional decline and morphological change.

The ageing heart: influence of cellular and tissue ageing on total content and distribution of the variants of elongation factor-2

The involvement of elongation factor-2 (EEF-2), a key-protein of peptide-chain elongation, in the slowing down of protein synthesis during cardiac ageing was addressed. EEF-2 was measured in rat heart extracts and isolated rat cardiomyocytes (CM) from newborn and adult rats using sodium-dodecylsulphate polyacrylamide gel electrophoresis after specific labeling with [32P]ADP-ribosylation or immunoblot. The age-dependent proportional content of several eucaryotic elongation factor-2 (eEF-2) subtypes in rat CM and rat heart extracts was compared using one-dimensional isoelectric focusing. EEF-2 was considerably reduced in the hearts of adult compared to neonatal rats (P<0.01). EEF-2 was also significantly decreased in isolated CM from adult versus newborn rats and during prolonged cultivation of neonatal CM. Cellular ageing was combined with reduced protein synthesis. During adolescence the eEF-2 variants shifted to acidic subtypes. Young adult and old rats revealed similar amounts and subtype distribution of cardiac eEF-2. Only the more acidic eEF-2 variants appeared to contain phosphorylated eEF-2. We concluded that total cardiac eEF-2 and its subtype pattern might play an important role in developmental and age-related proteomic changes.

Effects of aging on hepatic IGF-I signaling

Little is known regarding hepatic insulin-like growth factor-1 IGF-I signaling with aging despite the observation that other tissues demonstrate resistance to IGF-I with aging and declines in liver mass accompany aging. Our aim was to determine if the IGF-I-induced signaling process changes with aging. Young (5 months) and old (24 months) C57BL/6 mice hepatic tissues and blood samples were taken 20 min after an intraperitoneal injection of desIGF-I. Age had no significant effect on plasma glucose, insulin and total IGF-I levels. IRS-1 protein was significantly decreased (33%) with aging. Basal phosphorylation of IRS-1, PKB and ERK were unaffected whereas basal phosphorylation of CREB and FKHR were significantly increased (37 and 33%, respectively) with aging. desIGF-I caused a significant decrease in plasma glucose concentrations in both young (53%) and old (44%) mice. desIGF-I administration significantly increased the phosphorylation of IRS-1 in both young (104%) and old (89%) hepatic tissues. Similarly, the phosphorylation of PKB was dramatically enhanced in both young (527%) and old (350%) hepatic tissues after desIGF-I stimulation. By contrast, desIGF-I administration had no significant effects on the phosphorylation of ERK and phosphorylation of transcription factors CREB and FKHR in both young and old hepatic tissues. These data suggest that aging dose not impair IGF-I signaling in hepatic tissues.

Caloric restriction and lifespan: a role for protein turnover?

Oxidative damage to cellular macromolecules has been postulated to be a major contributor to the ageing of diverse organisms. Oxidative damage can be limited by maintaining high anti-oxidant defenses and by clearing/repairing damage efficiently. Protein turnover is one of the main routes by which functional proteins are maintained and damaged proteins are removed. Protein turnover rates decline with age, which might contribute to the accumulation of damaged proteins in ageing cells. Interestingly, protein turnover rates are maintained at high levels in caloric restricted animals. Whether changes in protein turnover are a cause or a consequence of ageing is not clear, and this question has not been a focal point of modern ageing research. Here we survey work on protein turnover and ageing and suggest that powerful genetic models such as the nematode Caenorhabditis elegans are well suited for a thorough investigation of this long-standing question.

Energetic cost of protein turnover in healthy elderly humans

OBJECTIVE

Whole body protein turnover (PTO) and resting energy expenditure (REE) are both correlated to fat-free mass (FFM), in young and elderly subjects, and REE is positively correlated to PTO in young adults. Thus, the aim of this study was to compare the energetic cost of PTO in young (n=39, 23.4+/-3.1 y) and elderly (n=41, 67.5+/-3.6 y) healthy volunteers.

MEASUREMENTS

REE (indirect calorimetry), PTO ((13)C-leucine isotopic dilution) and body composition (bioelectrical impedance analysis with age-specific equations) were measured in the postabsorptive state.

RESULTS

Elderly subjects had a higher fatness (30.5+/-7.1 vs 18.2+/-5.5%, elderly vs young, P<0.001), a similar REE (0.97+/-0.13 vs 1.06+/-0.15 kcal min(-1)), and a lower PTO (1.28+/-0.22 vs 1.44+/-0.18 micromol kg(-1) min(-1), P<0.001). PTO, REE and FFM were significantly correlated and after adjustment for FFM, REE was positively correlated to PTO (r=0.61, P<0.001). The slope of this relationship was the same in both groups, while the adjusted mean REE was lower in elderly subjects (0.97+/-0.09 vs 1.05+/-0.07 kcal min(-1), P<0.01).

CONCLUSION

In comparison with young subjects, the energetic cost associated with PTO in elderly subjects is not different, but the proportion of REE not associated with PTO is lower.

Age-related changes in the regulation of autophagic proteolysis in rat isolated hepatocytes

During intervals between meals, autophagy is a major source of nutrients and may remove damaged organelles and membranes. Age-related changes in the regulation of autophagic proteolysis were studied by monitoring the rate of valine release from liver cells of 2-, 6-, 12-, 18-, and 24-month-old male Sprague-Dawley rats fed ad libitum, and incubated in vitro with added amino acids and 10(-7) M of insulin or glucagon. The maximum rate of proteolysis and its maximum inhibition by amino acids were reached at 6 months and declined thereafter. In contrast, the rate of protein degradation in the presence of high concentrations of amino acids was not affected by aging. The inhibitor effect of insulin was additive to that of amino acids and was not altered significantly by age. The conclusion is that altered regulation of autophagic proteolysis decreases susceptibility of older cells to lysosomal degradation, and it may lead to the accumulation of altered organelles and membranes.

The protection of rat liver autophagic proteolysis from the age-related decline co-varies with the duration of anti-ageing food restriction

Restricting caloric intake (CR) well below that of ad libitum (AL) fed animals retards and/or delays many characteristics of ageing and the occurrence and progression of age-associated diseases, efficacy depending on duration. The hypothesis that the anti-ageing effect of CR might involve stimulation of the cell-repair mechanism autophagy was tested. The effects of ageing and duration of anti-ageing CR on liver autophagic proteolysis (AP) were explored in male AL Sprague-Dawley rats aged 2-, 6-, 12- and 24-months; and 24-month-old rats on a CR diet initiated at 2-, 6- and 12-month of age or initiated at age 2-months and interrupted at age 18 months. The age-related changes in the regulation of AP were studied by monitoring the rate of valine release in the incubation medium from isolated liver cells by an HPLC procedure. Results show that the maximum attainable rate and the regulation of AP decline with increasing age; that changes are prevented by anti-ageing CR initiated at young age, that the protective effects of CR change with the duration of diet. It is concluded that the data are compatible with the hypothesis that AP and improved membrane maintenance might be involved in the antiageing mechanism of CR.

Age-related alterations in the activation of heat shock transcription factor 1 in rat hepatocytes

The induction of hsp70 transcription by heat shock is significantly reduced in hepatocytes isolated from old rats compared to hepatocytes isolated from young/adult rats, and the decline in hsp70 transcription is correlated with a decrease in the induction of heat shock transcription factor 1 (HSF1) binding to the heat shock element. However, the decreased HSF1 binding activity to DNA is not due to reduced levels of HSF1 that are available for activation by heat shock. In fact, the levels of HSF1 are two- to threefold higher in hepatocytes from old rats, and the age-related increase in the levels of HSF1 protein in hepatocytes appears to arise from a decrease in the degradation of the HSF1 because HSF1 mRNA levels do not change and the synthesis of HSF1 decreases approximately 50% with age. No evidence was found for an impairment in HSF1 oligomerization in hepatocytes from old rats, e.g., the level of HSF1 trimers, the nuclear translocation of HSF1, and the phosphorylation of HSF1 after heat shock are similar in hepatocytes isolated from young/adult and old rats. However, the thermostability of the DNA binding activity of HSF1 was significantly reduced with age in a cell-free system as well as in isolated hepatocytes.

Distribution of protein turnover changes with age in humans as assessed by whole-body magnetic resonance image analysis to quantify tissue volumes

We tested the hypothesis that nonmuscle lean tissue mass and its rate of protein catabolism remain constant with aging despite changes in the proportional contribution of these tissues to whole-body protein metabolism. Whole-body protein kinetics, using the 60-h oral [(15) N]glycine method, and muscle and nonmuscle protein catabolism, based on protein kinetic data, urinary N(tau)-methylhistine excretion and lean tissue volumes defined by whole-body magnetic resonance imaging, from eight healthy elderly subjects (5 females and 3 males, mean age 71.5 y) were compared with those of seven young persons (3 females and 4 males, mean age 28 y). There were no significant age or gender effects on rates of protein kinetics per L total lean tissue. There was a lower (P < 0.004) rate of muscle protein catabolism in the elderly (1.8 +/- 0.2 vs. 2.6 +/- 0.1 g. L(-1). d(-1)) and a trend (P = 0.08) for lower muscle volume (19.7 +/- 1.5 vs. 25.0 +/- 2.4 L). This contrasted with intraabdominal lean tissue, where the rate of protein catabolism (13. 8 +/- 0.6 vs. 13.2 +/- 0.9 g. L(-1 ). d(-1)) and volume (7.5 +/- 0.3 vs 8.0 +/- 0.5 L) did not differ between age groups. Thus, the decrease in the contribution by muscle to whole-body protein metabolism with age is associated with an increase from 62 to 74% (P < 0.001) in the contribution by nonmuscle lean tissues. These findings have potential implications for the nutrition of both normal and sick elderly persons.

Age effect on fibrinogen and albumin synthesis in humans

A strong association has been reported between atherosclerotic diseases and fibrinogen levels, and a decreased whole body protein synthesis has also been reported with aging. We investigated the effect of age on fractional synthesis rates (FSR) of fibrinogen and albumin in 12 human subjects of young (20-30 yr), middle (45-60 yr), and old (65-79 yr) age by use of L-[1-13C]leucine and L-[15N]phenylalanine as tracers. An age-related decline in FSR of fibrinogen (P < 0.01) was observed with use of both tracers, with the maximal decrease (average 37% with alpha-[13C]ketoisocaproate as the precursor) occurring by middle age and with no further changes thereafter. In contrast, plasma concentrations of fibrinogen increased with age (P < 0.002). There was no age-related change in synthesis rate and concentrations of albumin. An age-related decline in fibrinogen FSR, but not FSR of albumin, indicates a differential effect of age on synthesis rate of these two liver proteins. This study also demonstrated that the increased circulating levels of fibrinogen represent a slower rate of disposal of fibrinogen rather than an increased production rate.

Influence of caloric intake on aging and on the response to stressors

Reducing the food intake of rodents to well below that of ad libitum fed animals increases the life span. This action, which gerontologists often refer to as the antiaging action of dietary restriction (DR), is due to the slowing of the aging processes. DR also maintains most physiological processes in a youthful state and delays the occurrence and/or slows the progression of age-associated disease processes. This antiaging action of DR results from the reduced intake of calories. Reduction of the body fat content does not play a causal role in the antiaging action of DR, nor does reduction in the metabolic rate. Alterations in the characteristics of carbohydrate metabolism and of oxidative metabolism in response to DR have been found that are of such a nature that they could, at least in part, underlie the antiaging action. Several theories have recently been proposed in regard to the mechanisms responsible for the antiaging action of DR, but none has been tested by rigorously designed studies. Of these theories, the one that seems most promising is based on the fact that DR protects rats and mice of all ages against the damaging actions of acute stressors. This protective action against stressors may play a major role in the antiaging action of DR.

The aging liver. Drug clearance and an oxygen diffusion barrier hypothesis

A change in drug clearance with age is considered an important factor in determining the high prevalence of adverse drug reactions associated with prescribing medications for the elderly. Despite this, no general principles have been available to guide drug administration in the elderly, although a substantial body of clearance and metabolism data has been generated in humans and experimental animals. A review of age-related change in drug clearances established that patterns of change are not simply explained in terms of hepatic blood flow, hepatic mass and protein binding changes. In particular, the maintained clearance of drugs subject to conjugation processes while oxygen-dependent metabolism declines, and all in vitro tests of enzyme function have been normal, requires new explanations. Reduction in hepatic oxygen diffusion as part of a general change in hepatocyte surface membrane permeability and conformation does provide one explanation for the paradoxical patterns of drug metabolism, and increased hepatocyte volume would also modify oxygen diffusion path lengths (the 'oxygen diffusion barrier' hypothesis). The reduction in clearances of high extraction drugs does correlate with observed reduction in hepatic perfusion. Dosage guidelines emerge from these considerations. The dosage of high clearance drugs should be reduced by approximately 40% in the elderly while the dosage of low clearance drugs should be reduced by approximately 30%, unless the compound is principally subject to conjugation mechanisms. If the hepatocyte diffusion barrier hypothesis is substantiated, this concept may lead to therapeutic (preventative and/or restorative) approaches to increased hepatocyte oxygenation in the elderly. This may lead to approaches for modification of the aging process in the liver.

Lipofuscin: mechanisms of formation and increase with age

Lipofuscin (age pigment) is a brown-yellow, electron-dense, autofluorescent material that accumulates progressively over time in lysosomes of postmitotic cells, such as neurons and cardiac myocytes. The exact mechanisms behind this accumulation are still unclear. This review outlines the present knowledge of age pigment formation, and considers possible mechanisms responsible for the increase of lipofuscin with age. Numerous studies indicate that the formation of lipofuscin is due to the oxidative alteration of macromolecules by oxygen-derived free radicals generated in reactions catalyzed by redox-active iron of low molecular weight. Two principal explanations for the increase of lipofuscin with age have been suggested. The first one is based on the notion that lipofuscin is not totally eliminated (either by degradation or exocytosis) even at young age, and, thus, accumulates in postmitotic cells as a function of time. Since oxidative reactions are obligatory for life, they would act as age-independent enhancers of lipofuscin accumulation, as well as of many other manifestations of senescence. The second explanation is that the increase of lipofuscin is an effect of aging, caused by an age-related enhancement of autophagocytosis, a decline in intralysosomal degradation, and/or a decrease in exocytosis.

Evaluation of the activities of eight lysosomal hydrolases in sera of humans, rats and pigs of different ages

The activities of 21 enzymes (belonging to four classes of enzymes) involved in different metabolic pathways were assayed in blood sera of healthy young and adult/elderly groups of humans, rats and pigs, to determine whether activity changes coinciding with changes in age and aging could be detected. In all three species analysed, measurable activities (performed by highly specific and sensitive techniques, generally spectrofluorimetric procedures) were found, usually following a decreasing order of: among glycosidases, beta-N-acetylglucosaminidase (NAG) > alpha-L-fucosidase > alpha-mannosidase > beta-glucuronidase > beta-galactosidase > alpha-galactosidase. In addition, among esterases very high values were found for arylesterase and acid phosphatase. By contrast, no measurable activity was found for the remaining enzymes assayed (8 hydrolases, 1 oxidoreductase, 3 transferases and 1 lyase). In the elderly group of humans, significantly higher activities (P < or = 0.05) were found for NAG, alpha-mannosidase and beta-glucuronidase in comparison to the adult and young groups. However, several activities in rats and all activities in pigs decreased with age. In conclusion, differences in the activities of 6 lysosomal glycosidases and 2 esterases (but no significant differences for another 13 enzymes belonging to several enzyme classes) are found in the sera of healthy humans, rats and pigs. These differences coincide with changes observed in aging.

Dietary calorie restriction in mice induces carbamyl phosphate synthetase I gene transcription tissue specifically

Dietary calorie restriction (CR) delays age-related physiologic changes, increases maximum life span, and reduces cancer incidence. Here, we present the novel finding that chronic reduction of dietary calories by 50% without changing the intake of dietary protein induced the activity of mouse hepatic carbamyl phosphate synthetase I (CpsI) 5-fold. In liver, CpsI protein, mRNA, and gene transcription were each stimulated by approximately 3-fold. Thus, CR increased both the rate of gene transcription and the specific activity of the enzyme. Short-term feeding studies demonstrated that higher cpsI expression was due to CR and not consumption of more dietary protein. Intestinal CpsI activity was stimulated 2-fold, while its mRNA level did not change, suggesting enzyme activity or translation efficiency was stimulated. CpsI catalyzes the conversion of metabolic ammonia to carbamyl phosphate, the rate-limiting step in urea biosynthesis. cpsI induction suggests there is a shift in the metabolism of calorie-restricted animals toward protein catabolism. CpsI induction likely facilitates metabolic detoxification of ammonia, a strong neurotoxin. Enhanced protein turnover and metabolic detoxification may extend life span. Physiologic similarities between calorie-restricted and hibernating animals suggest the effects of CR may be part of a spectrum of adaptive responses that include hibernation.

Synthesis, modifications, and turnover of proteins during aging

Slowing down of bulk protein synthesis is one of the most commonly observed biochemical changes during aging. The implications and consequences of slower rates of protein synthesis are manifold, including a decrease in the availability of enzymes for the maintenance, repair, and normal metabolic functioning of the cell, an inefficient removal of inactive, abnormal, and damaged macromolecules in the cell, the inefficiency of the intracellular and intercellular signalling pathways, and a decrease in the production and secretion of hormones, antibodies, neurotransmitters, and the components of the extracellular matrix. Age-related changes in the activity, specificity, and stability of a large number of proteins have been reported. However, the molecular mechanisms responsible for such alterations are still poorly understood. Studies on various components of the protein synthetic machinery have revealed a decline in the efficiency and accuracy of ribosomes, an increase in the levels of rRNA and tRNA, and a decrease in the amounts and activities of elongation factors. Because posttranslational modifications of proteins determine their activity and stability, alterations in the extent and level of various modifications such as phosphorylation, methylation, ADP-ribosylation, oxidation, glycation, and conformational changes during aging are being studied. Changes in the regulation of protein synthesis, posttranslational modifications, and protein turnover are crucial determinants of age-related decline in the maintenance, repair, and survival of the organism.

Effect of caloric restriction on the expression of heat shock protein 70 and the activation of heat shock transcription factor 1

The regulation of heat shock protein 70 (hsp70) expression is an excellent example of a cellular mechanism that has evolved to protect all living organisms from various types of physiological stresses; therefore, the reported age-related alterations in the ability of cells to express hsp70 in response to stress could seriously compromise the ability of a senescent organism in respond to changes in its environment. Because caloric restriction (CR) is the only experimental manipulation known to retard aging and increase the survival of rodents, it was of interest to analyze the effect of CR on the age-related alteration in the induction of hsp70 expression in rat hepatocytes. The effect of CR on the nuclear transcription of hsp70 gene in rat hepatocytes in response to various levels of heat shock was determined, and it was found that the age-related decline in the transcription of hsp70 at all temperatures studied was reversed by CR. Because the heat shock transcription factor (HSF) mediates the heat-induced transcription of hsp70, the effect of CR on the induction of HSF binding activity by heat shock was studied and found to arise from HSF1, which has been shown to be involved in the induction of HSF binding activity in other cell types. The age-related decrease in the induction of HSF1 binding activity in rat hepatocytes was reversed by CR, and did not appear to be due to an accumulation of inhibitory molecules with age. Interestingly, the level of HSF1 protein was significantly higher in hepatocytes isolated from old rats fed ad libitum compared to hepatocytes obtained from rats fed the CR diet even though the levels of HSF1 binding activity were lower for hepatocytes isolated from the old rats fed ad libitum. The levels of the mRNA transcript for HSF1 was not significantly altered by age or CR. Thus, the changes in HSF1 binding activity with age and CR do not arise from changes in the level of HSF1 protein available for activation.