Age-related changes in total protein and collagen metabolism in rat liver

Liver collagen levels are determined by a balance between synthesis and degradation, processes known to have rapid rates in growing animals. We report age-related changes in liver collagen synthesis and degradation rates, as well as protein synthesis rates, in rats at five ages from 1 to 24 mo. Fractional collagen synthesis rates were determined after injection of [14C]proline with a flooding dose of unlabeled proline and its incorporation as hydroxy-[14C]proline into proteins. Fractional protein synthesis rates were based on the uptake of [14C]proline into proteins. Fractional collagen degradation rates were calculated from the difference between collagen fractional synthesis and deposition rates. Fractional rates of collagen synthesis were similar between 1 mo (23.0% +/- 4.6%/day) and 24 mo (19.6% +/- 3.4%/day) of age. Collagen deposition into the extracellular matrix was extremely low at every age studied; therefore degradation pathways accounted for the bulk of the collagen synthesized. The mean fractional synthesis rate for the total protein pool was unaltered between 1 mo (105.0% +/- 7.2%/day) and 15 mo (89.9% +/- 6.0%/day) of age, after which it increased to 234.9% +/- 33.0%/day (p less than 0.05) by 24 mo of age. These results indicate that liver collagen and total protein synthesis rates were maintained at relatively high levels during development and maturity but that protein synthesis rates were highest in senescent animals.     

Age-related fluorescence in rat lung collagen

Mechanical lung properties are impaired with age. In other organs an age-related increase in collagen-linked fluorescence, attributable to advanced glycation endproducts (AGE), or other nonenzymatic reactions such as those related to lipid peroxidation derivatives has been described. Moreover, oxidative processes accelerate some of these reactions. In several tissues, these AGE products have been found to be responsible for protein cross-linking and lack of elasticity. We have evaluated the fluorescence levels of lung collagen in rats aged from 1 to 25 months at two distinct wavelengths: the standard AGE fluorescence (Exc 370 nm/Em 440 nm) and the pentosidine fluorescence (Exc 335 nm/Em 395 nm). In pulmonary tissue, fluorescence at both 370/440 nm (p < 0.05) and 335/395 nm (p < 0.001) increases with age. However, a relative stabilization of values is seen in the 25 months group that could be related to the kinetics of fluorescent products in vivo. So, as observed in other tissues, AGE products may increase in pulmonary tissues with time. This may explain the age-associated decline in pulmonary compliance. Offprint requests to: Maria Josep Bellmunt     

Age-related changes in collagen of human intervertebral disks.

Age-related changes of human intervertebral disk collagen have been investigated. A progressive, age-related accumulation of collagen, both in annulus fibrosus and in nucleus pulposus was found. A decrease in collagen solubility was observed during physiological aging. Up to the 3rd-4th decades of life, a significant increase in the aldehyde content in disk collagen has been observed. Nuclei pulposi of the prolapsed disk contain more collagen, and its solubility was higher in comparison to corresponding necropsy material. Some alterations in the collagen of prolapsed disks may be considered as symptomatic of accelerated aging.     

Age-related changes in pyridinoline content of rabbit collagen

The age related changes in the content of pyridinoline were followed for collagen from rabbit muscles. Pyridinoline content of the muscle collagen in 2-week-old rabbits is very low and increases markedly with growth of the animals. However, it decreases after maturation in cardiac muscle but not in red & white muscle. Pyridinoline may serve as an interesting index for aging in connective tissue.     

Age-related changes in elastic fibers and elastin of lung.

The effect of age on the lung elastic tissue of inbred BALB/c mice were studied. Static compliance of excised lungs increased with age. Morphometrically determined total elastic fiber length increased with lung expansion in age- and sex-matched mice (r = 0.83, P smaller than 0.001), indicating an axial extension of elastic fibers. However, total elastic fiber length of aging lungs fixed at a distending pressure of 15 cm H2O showed no significant change despite an age-related increase in lung volume (male, r = 0.96, P smaller than 0.001; female, r = 0.95 P smaller than 0.001). The correlative finding of decreased elastin content (r = -0.87, P smaller than 0.001) indicates that there is a loss of elastic fibers in the aging lung. It is suggested that the absence of pseudoelastin fibers, as demonstrated by histochemical techniques, accounts for the observed differences in elastin content of aging human and mouse lungs.     

Age-related changes of bile acid metabolism in rats

Cholesterol and bile acid leves were examined in young (8 weeks), middle-aged (12 months) and old (24 months) germ-free male rats, and young (8 weeks) and middle-aged (12 months) conventional male rats. The plasma cholesterol levels were higher in the aged rats, being more marked in the conventional rats. The liver cholesterol levels also increased with age and the increases were almost identical for both groups. No age-related changes were found in the biliary bile acid secretion, the pool size and distribution of bile acids in the bile, small intestine and large intestine, nor in the turnover frequency of bile acids, but the pool size in the young and middle-aged germ-free rats was much larger than that in the conventional rats. The turnover frequency was less in the germ-free rats. The bile acid synthesis presumed from the fecal bile acid excretion decreased in the aged germ-free rats but not in the conventional rats. A most remarkable age-related change was found in the bile acid composition; cholic acid increased and beta-muricholic acid derived from chenodeoxycholic acid in the rat decreased by aging, resulting in an increase of the CA/CDCA ratio (bile acids belonging to the cholic acid group/bile acids to the chenodeoxycholic acid group) in the bile, feces and pool. These results suggest that cholic acid synthesis increases while chenodeoxycholic acid synthesis is impaired by aging in rats.     

Age-related ultrastructural changes in human embryonic lung fibroblasts

Scanning and transmission electron microscopy were used to examine human embryonic lung fibroblasts at different population doubling levels. Scanning electron microscopy of cells at population doubling levels 26, 45 and 59 did not reveal a significant change in cell size with increasing age. However, transmission electron microscopy of cells at population doubling levels 19 and 45 showed an increase in nuclear lobes, a decrease in the number of ribosomes associated with rough endoplasmic reticulum, and changes to the internal structure of mitochondria on increasing population doubling level. No other previously reported age-related changes were found.     

Age-related changes in collagen synthesis and turnover in porcine heart valves

BACKGROUND AND AIM OF THE STUDY: Although the six-month-old pig is commonly used as a model to study human heart valve biology and various age-specific valve diseases, the correlation of porcine valve biology and development with that of humans has not been thoroughly assessed. Given the important role of the matrix in valve function, the aim of this study was to characterize porcine valve matrix structure and collagen turnover during development and aging. METHODS: Porcine aortic valves (AV) and mitral valves (MV) were examined throughout fetal development and postnatally at six weeks, six months and six years, using Movat pentachrome staining and immunohistochemistry for collagen III, markers of collagen synthesis (molecular chaperone HSP47, hydroxylating enzyme prolyl-4-hydroxylase (P4H), cross-linking enzyme lysyl oxidase (LOX)) and collagen degradation (matrix metalloproteinase (MMP)-13), and a marker of an 'activated' cellular phenotype, smooth muscle alpha-actin (SMalphaA). An analysis of variance was used to compare the staining intensities. RESULTS: Cell density measurements showed layer differentiation in the first trimester (p < 0.003), and this decreased ten-fold from the second trimester to six years of age (p < 0.025). Matrix turnover was identified by the co-localization of P4H, HSP47 and MMP13, and correlated to an 'activated' cellular phenotype. SMalphaA expression was noted on the inflow surface of both valves. P4H and LOX were maximally expressed around mature collagen (p < 0.001). P4H increased during fetal development (p < 0.01) and in the six-year-old AV fibrosa (p < 0.05). Collagen-related markers were consistently higher in the AV than MV (HSP47 in fetal; P4H, Col III, and LOX in six-year-old). CONCLUSION: The substantial matrix changes shown in this porcine study provide further insight into the role of matrix turnover during development and aging and should be considered when using the porcine animal model to study age-specific human diseases.     

Age-related changes in the regulation of cholesterol metabolism in rats

Activities of the hepatic cholesterol synthetic system including initial steps of the pathway and cholesterol 7 alpha-hydroxylase were all lower in adult (8 to 9-month-old) rats than in young (5 week-old) rats. The extent of diurnal fluctuation of 3-hydroxy-3-methylglutaryl coenzyme A reductase was, however, apparently greater in adult animals. When the cholesterol-enriched diet was fed to rats for 1 day, the extent of the depression of the cholesterogenic enzymes was dependent on age of animals. The enzyme activities rapidly increased on refeeding a cholesterol-free diet after the cholesterol challenge. In young rats the activity of cholesterol 7 alpha-hydroxylase exhibited a pattern inverse to that of HMG-CoA reductase whereas in adult rats it increased continuously during the entire experimental period. Cholesterol and triglyceride accumulated in the liver of adult animals, and their response to dietary cholesterol also depended on the age of the animals. The results indicate a specific modification of the cholesterol homeostatic mechanism with age.     

Age-related changes in cognitive domains. A population-based study

BACKGROUND AND AIMS: The aim of the present study is to describe the effects of aging on various cognitive domains (global cognitive function, executive function, motor speed) in a population sample of elderly men, and to describe how their age-related changes are influenced by education, depression, or prevalent cerebrovascular accidents (CEVD). METHODS: A cross-sectional observational study was conducted in a cohort of 334 men, 65 to 95 years old, living in rural communities, participating in the Italian cohort of two population studies--MATISS (Malattie cardiovascolari ATerosclerotiche Istituto Superiore di Sanità) and FINE (Finland, Italy, Netherlands, Elderly). Global cognitive function was measured by the Mini-Mental State Examination (MMSE), executive function by the Stroop test, motor speed by the Purdue Pegboard test, and depression by the CES-D test. Prevalence of cerebrovascular accidents (CEVD), myocardial infarction, and diabetes were evaluated by a questionnaire and a clinical examination. Blood pressure, and total and HDL cholesterol were measured. Current smoking status was self-reported. RESULTS: An age-associated decline in global cognitive functions, executive functions, and motor speed was observed. The decline is more apparent after the age of 85 for the MMSE, and after 75 for executive functions and motor speed. Logistic regression analysis revealed that age was independently associated with altered global cognitive functions, executive functions, and motor speed, even after adjusting for education, depression or prevalent CEVD. CONCLUSIONS: In a cohort of community-living elderly men aged 65 to 95 years, age-associated changes in mental functions are more evident after the age of 85. These changes are independent of education, depression, or prevalent CEVD.     

Bleomycin-induced pulmonary fibrosis. Effects of steroid on lung collagen metabolism

Using bleomycin-induced pulmonary fibrosis as a model, we have set out to study collagen metabolism in the fibrotic process. As was previously shown, intratracheal administration of bleomycin in the rat caused increased deposition and net synthesis of collagen in the lung. This was accompanied by marked increases in the tissue-free proline pool size and less dramatic increases in the pool's radioactivity when lung mince was pulsed with radioactive proline to measure the net collagen synthesis. Using a technique based on the quantitation of the rate of release of hydroxyproline-containing peptides when lung homogenates were incubated in calcium-containing buffer, lung collagenolytic activity was markedly diminished as a result of bleomycin treatment. Concomitant treatment with the steroid methylprednisolone did not affect significantly this decrease in lung collagenolytic activity. Such steroid treatment, however, prevented the increase in bleomycin-induced lung collagen deposition and partially suppressed total lung collagen synthesis, without affecting the net rate of lung collagen synthesis expressed per mg of DNA. Steroid treatment also inhibited the marked increase in tissue-free proline pool size and radioactivity caused by bleomycin. The mechanism of amelioration of the fibrotic response by the steroid is discussed.     

Age-related changes in cytokine production by leukocytes in rhesus monkeys

Using a variety of experimental rodent and human models, age-related alterations in cytokine production by immune cells have been described extensively. While the precise mechanism(s) responsible for such age-related changes in cytokine responses remain unclear, it seems likely that these changes may have a significant effect on immune cell function. In an attempt to clarify such changes in aging primates, we examined cytokine production by white cells derived from a controlled colony of rhesus monkeys (Macaca mulatta). Non-fractionated whole blood and peripheral blood mononuclear cells (PBMCs) were obtained from male monkeys of different ages (6-28 years), and were subsequently evaluated for their ability to express mRNA and protein for the cytokines, IL-10, IL-6, IFNgamma, IL-1beta, and TNFalpha, following in vitro stimulation with polyclonal mitogens. Our results suggest that white blood cells derived from aged rhesus monkeys exhibit a significant increase in their ability to produce the Th2-associated cytokine, IL-10, upon stimulation with lipopolysaccharide (LPS) when compared to white cells derived from younger counterparts. Similarly, a significant age-related decrease in the expression of the Th1-associated cytokine, IFNgamma, was also observed using phytohemagglutinin (PHA)-stimulated PBMCs. No significant age-related differences in the production of IL-1beta or TNFalpha were observed in response to any stimulation, but there was limited evidence of an age-related increase in IL-6 production. Overall, our results suggest that a possible systemic change from a Th0/Th1 to a Th2-like cytokine profile occurs in circulating leukocytes derived from aging primates. We believe that such age-related alterations in cytokine production may play a role in the reduced immune responses observed in elderly human populations.     

Age-related changes in cholesterol and bile-acid metabolism in spontaneously hypertensive rats

Age-related changes in serum and liver cholesterol, phospholipid and triglyceride levels, serum lipoproteins, biliary secretion of cholesterol, phospholipids and bile acids, fecal excretion of sterols and bile acids, and the pool size of bile acids were examined in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKR). SHR showed distinct age- and sex-related changes when young and marked aged-rat hypercholesterolemia after 1 yr of age. (1) Cholesterol shifted from blood to the liver between 10 and 20 wk only in male SHR and not at all in WKR. (2) Serum lipoprotein percentages changes; α-lipoprotein decreased, pre-β-lipoprotein increased, but β-lipoprotein did not change. These changes appeared only in male SHR and after 13 to 15 wk of age. (3) Liver enlargement in SHR, although not detected at 5 to 6 wk, progressed more rapidly than in WKR, giving values almost double those in WKR after 13 to 15 wk. Liver enlargement in female SHR was much less than in the male. (4) Bile flow, biliary secretion, and the pool size of bile acids increased. However, when expressed on the basis of liver weight, these values were similar to those in WKR, suggesting that the increases were caused by the hepatomegaly. (5) Differences appeared in the bile acid composition. A large amount of β-muricholic acid was present in SHR of both sexes and the cholic acid percentage was low in male SHR. (6) Changes were observed in fecal bile acid excretion. Since the daily amounts in male SHR were similar to those in WKR, the hepatic synthesis activity (mg per day per 10 g liver) in male SHR was almost half that in WKR at all ages.