Pericytes control key neurovascular functions and neuronal phenotype in the adult brain and during brain aging

Pericytes play a key role in the development of cerebral microcirculation. The exact role of pericytes in the neurovascular unit in the adult brain and during brain aging remains, however, elusive. Using adult viable pericyte-deficient mice, we show that pericyte loss leads to brain vascular damage by two parallel pathways: (1) reduction in brain microcirculation causing diminished brain capillary perfusion, cerebral blood flow, and cerebral blood flow responses to brain activation that ultimately mediates chronic perfusion stress and hypoxia, and (2) blood-brain barrier breakdown associated with brain accumulation of serum proteins and several vasculotoxic and/or neurotoxic macromolecules ultimately leading to secondary neuronal degenerative changes. We show that age-dependent vascular damage in pericyte-deficient mice precedes neuronal degenerative changes, learning and memory impairment, and the neuroinflammatory response. Thus, pericytes control key neurovascular functions that are necessary for proper neuronal structure and function, and pericyte loss results in a progressive age-dependent vascular-mediated neurodegeneration.     

Levels of alpha-inhibin in aging female mice.

alpha-inhibin was immunocytochemically localized in granulosa cells of different stages of developing follicles, freshly formed corpora lutea, and scattered interstitial cells (pigmented or ceroid cells) in ovaries of 6-, 14-, and 23-25-mo-old C57BL/6NNia mice. Developing follicles exhibited the greatest amount of staining. Quantitation of the stain using an image analysis system indicated the staining intensity within ovarian follicles of 14-mo-old mice was greater than that in 23-25-mo-old mice. The levels of plasma alpha-inhibin and estradiol (E2) decreased with age. The number of follicles present in ovaries of middle-aged mice was comparable to those of 6-mo-old mice, yet plasma levels of FSH were significantly higher than those of 6-mo-old mice. This may be due to an age-related loss in the sensitivity of the hypothalamus and/or pituitary of middle-aged mice to ovarian hormones. In contrast, ovaries of 23-25-mo-old mice contained few antral follicles and consequently produced little alpha-inhibin. There appeared to be little negative feedback regulation of FSH secretion in 23-25-mo-old mice as a result of age-related ovarian impairments. This study supports an earlier hypothesis from our laboratory [Biol Reprod 1985; 32:989-997] that the primary defect(s) limiting age-related reproductive performance in mice appears to reside within the hypothalamo-hypophyseal axis, whereas secondary defects arise from the ovary.     

Weight-bearing exercise and markers of bone turnover in female athletes.

Weight-bearing activity provides an osteogenic stimulus, while effects of swimming on bone are unclear. We evaluated bone mineral density (BMD) and markers of bone turnover in female athletes (n = 41, age 20.7 yr) comparing three impact groups, high impact (High, basketball and volleyball, n = 14), medium impact (Med, soccer and track, n = 13), and nonimpact (Non, swimming, n = 7), with sedentary age-matched controls (Con, n = 7). BMD was assessed by dual-energy X-ray absorptiometry at the lumbar spine, femoral neck (FN), Ward's triangle, and trochanter (TR); bone resorption estimated from urinary cross-linked N-telopeptides (NTx); and bone formation determined from serum osteocalcin. Adjusted BMD (g/cm; covariates: body mass index, weight, and calcium and calorie intake) was greater at the FN and TR in the High group (1.27 +/- 0.03 and 1.05 +/- 0.03) than in the Non (1.05 +/- 0.04 and 0.86 +/- 0.04) and Con (1.03 +/- 0.05 and 0.85 +/- 0.05) groups and greater at the TR in the Med group (1.01 +/- 0.03) than in the Non (0.86 +/- 0.04) and Con (0.85 +/- 0.05) groups. Total body BMD was higher in the High group (4.9 +/- 0.12) than in the Med (4.5 +/- 0.12), Non (4.2 +/- 0.14), and Con (4.1 +/- 0.17) groups and greater in the Med group than in the Non and Con groups. Bone formation was lower in the Non group (19.8 +/- 2.6) than in the High (30.6 +/- 3.0) and Med (32.9 +/- 1.9, P < or = 0.05) groups. No differences in a marker of bone resorption (NTx) were noted. This indicates that women who participate in impact sports such as volleyball and basketball had higher BMDs and bone formation values than female swimmers.     

The influence of exercise on brain aging and dementia

Physical activity has been recognized as an important protective factor reducing disability and mortality and therefore it is focus of many health promotion activities at all ages. More recently a growing body of literature is focusing whether physical activity could also have a positive impact on brain aging with exploring healthy brain aging as well as on cognitive impairment and dementia. An increasing number of prospective studies and randomized controlled trials involving humans take place both with older adults with normal cognition as well as with mild cognitive impairment or dementia. However, the body of evidence is still sparse and many methodological issues make comparisons across studies challenging. Increasingly research into underlying mechanisms in relation to physical activity and brain aging identify biomarker candidates with especially neuroimaging measurements being more used in trials with humans. Whilst the evidence base is slowly growing more detailed research is needed to address methodological issues to finally achieve clinical relevance. This article is part of a Special Issue entitled: Imaging Brain Aging and Neurodegenerative disease.     

Antioxidant enzymatic systems in neuronal and glial cell-enriched fractions of rat brain during aging

The activities of Cu,Zn superoxide dismutase, glutathione peroxidase, catalase and glutathione reductase in neuronal and glial cell-enriched fractions obtained from the cerebral cortex of rat brain during aging (15, 30, 90, 350, 750 days of age) were assayed. Our results showed that glutathione peroxidase, catalase and glutathione reductase activities varied little during the examined periods. Only the Cu,Zn superoxide dismutase activity decreased notably from 15th to 750th day of age in both neuronal and glial cells, moreover the activities of all enzymes studied were always detected at lower levels in neuronal cells with respect to glial cells. In agreement with diminished SOD activity, the lipid peroxidation showed an elevated increase with aging; this fact is more evident in neuronal than in glial cells. In conclusion our data show that Cu,Zn superoxide dismutase is the most affected antioxidant enzymatic system of brain aging and it could be responsible for the increased lipid peroxidation in both cell types examined.A preliminary report of these results was presented at the 19th Meeting F.E.B.S. Rome July 2–7, 1989.     

Pre- and post-implantation losses of embryos in aging female IVCS mice

Mated female mice of the IVCS strain, aged 90 (control group), 180, 210, 240, 270, 300, 330, 360 and 420 days old, were studied for pre- and post-implantation loss of embryos. The percentage of pre-implantation loss in mice aged 90 to 210 days was 1.7/11.8 (14.4%) to 2.7/11.7 (23.1%). In mice aged 240 to 300 days it increased significantly as compared to the controls (46.5-90.2% versus 14.4%). It reached 100% in 300-days-old mice. The post-implantation loss of embryos and/or fetuses in mice aged 90 to 240 days was 1.0/10.2 (9.8%) to 2.5/9.0 (27.8%). In mice aged 270 to 300 days it increased significantly compared to the controls (100% versus 9.8%). The decrease in reproductive activity appeared first in a decrease in litter size, followed by a decrease in the number of blastocyst and implantation sites, and finally by anovulation during the process of aging in IVCS mice.     

Drosophila brain tumor metastases express both neuronal and glial cell type markers

Loss of either lgl or brat gene activity in Drosophila larvae causes neoplastic brain tumors. Fragments of tumorous brains from either mutant transplanted into adult hosts over-proliferate, and kill their hosts within 2 weeks. We developed an in vivo assay for the metastatic potential of tumor cells by quantifying micrometastasis formation within the ovarioles of adult hosts after transplantation and determined that specific metastatic properties of lgl and brat tumor cells are different. We detected micrometastases in 15.8% of ovarioles from wild type host females 12 days after transplanting lgl tumor cells into their abdominal cavities. This frequency increased significantly with increased proliferation time. We detected micrometastases in 15% of ovarioles from wild type host females 10 days after transplanting brat tumor cells into their abdominal cavities. By contrast, this frequency did not change significantly with increased proliferation time. We found that nearly all lgl micrometastases co-express the neuronal cell marker, ELAV, and the glial cell marker, REPO. These markers are not co-expressed in normal brain cells nor in tumorous brain cells. This indicates deregulated gene expression in these metastatic cells. By contrast, most of the brat micrometastases expressed neither marker. While mutations in both lgl and brat cause neoplastic brain tumors, our results reveal that metastatic cells arising from these tumors have quite different properties. These data may have important implications for the treatment of tumor metastasis.     

Response of hepatic antioxidant system to exercise training in aging female rat

This study was undertaken to investigate the effect of exercise training on aging in the hepatic oxidative status and antioxidant defense of female albino rat. Two age groups of 3 months and 12 months old Wistar strain female albino rats were given chronic exercise training for a period of 12 weeks. The antioxidant enzyme assays were carried out by the standard methods. Lower (P<0.01) activities of the antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and glutathione reductase (GR) by 21%, 44% and 63% respectively was observed in the older rats when compared to younger rats. Also, glutathione (GSH) levels were 42% lower (P<0.01) in older than younger animals. Exercise training to the 12 months aged rats significantly (P<0.01) elevated these antioxidant enzyme activities and GSH content, when compared to older control rats. These levels are almost equal to the values observed in the younger control rats. The levels of lipid peroxidation end product, malondialdehyde (MDA) the major indicator of oxidative stress, was found to increase with age (11%) and exercise training caused further elevation (28% of control). The present findings imply that the reactive oxygen species that are generated due to aging process were detoxified by the exercise induced antioxidant system in the liver tissue. These findings are also in agreement with similar changes in male animals, which clearly envisage no gender difference in the amelioration of the antioxidant enzyme system in older age due to exercise. In conclusion, it can be stated that twelve weeks treadmill exercise training has beneficial effect in improving antioxidant defense capacity by augmenting SOD, CAT and GR activities and GSH levels of older rats, thereby preventing oxidative damage to the liver tissue.     

Effect of exercise and calorie restriction on biomarkers of aging in mice

Unlike calorie restriction, exercise fails to extend maximum life span, but the mechanisms that explain this disparate effect are unknown. We used a 24-wk protocol of treadmill running, weight matching, and pair feeding to compare the effects of exercise and calorie restriction on biomarkers related to aging. This study consisted of young controls, an ad libitum-fed sedentary group, two groups that were weight matched by exercise or 9% calorie restriction, and two groups that were weight matched by 9% calorie restriction + exercise or 18% calorie restriction. After 24 wk, ad libitum-fed sedentary mice were the heaviest and fattest. When weight-matched groups were compared, mice that exercised were leaner than calorie-restricted mice. Ad libitum-fed exercise mice tended to have lower serum IGF-1 than fully-fed controls, but no difference in fasting insulin. Mice that underwent 9% calorie restriction or 9% calorie restriction + exercise, had lower insulin levels; the lowest concentrations of serum insulin and IGF-1 were observed in 18% calorie-restricted mice. Exercise resulted in elevated levels of tissue heat shock proteins, but did not accelerate the accumulation of oxidative damage. Thus, failure of exercise to slow aging in previous studies is not likely the result of increased accrual of oxidative damage and may instead be due to an inability to fully mimic the hormonal and/or metabolic response to calorie restriction.     

IGF‐1 deficiency impairs neurovascular coupling in mice: implications for cerebromicrovascular aging

Aging is associated with marked deficiency in circulating IGF‐1, which has been shown to contribute to age‐related cognitive decline. Impairment of moment‐to‐moment adjustment of cerebral blood flow (CBF) via neurovascular coupling is thought to play a critical role in the genesis of age‐related cognitive impairment. To establish the link between IGF‐1 deficiency and cerebromicrovascular impairment, neurovascular coupling mechanisms were studied in a novel mouse model of IGF‐1 deficiency (Igf1^f/f‐TBG‐Cre‐AAV8) and accelerated vascular aging. We found that IGF‐1‐deficient mice exhibit neurovascular uncoupling and show a deficit in hippocampal‐dependent spatial memory test, mimicking the aging phenotype. IGF‐1 deficiency significantly impaired cerebromicrovascular endothelial function decreasing NO mediation of neurovascular coupling. IGF‐1 deficiency also impaired glutamate‐mediated CBF responses, likely due to dysregulation of astrocytic expression of metabotropic glutamate receptors and impairing mediation of CBF responses by eicosanoid gliotransmitters. Collectively, we demonstrate that IGF‐1 deficiency promotes cerebromicrovascular dysfunction and neurovascular uncoupling mimicking the aging phenotype, which are likely to contribute to cognitive impairment.     

Glial responses to steroids as markers of brain aging.

Glia mediate neuroendocrine and neuroimmune functions that are altered during the process of normal aging. The biological functions of glia are also important in synaptic remodeling and the loss of synaptic connections that occur during aging. These functions are carried out by changes in glia, including changes in shape, interactions with neurons and other glia, and gene expression. The predominant change that occurs in glia during aging is glial activation, which can progress to reactive gliosis in response to neurodegeneration. More markers are needed to distinguish normal and reactive glia. During aging, astrocytes hypertrophy and exhibit signs of metabolic activation, and astrocytic processes surround neurons. Microglia also become activated and subsets of activated microglial increase in number and may enter the phagocytic or reactive stage. Glial markers of brain aging and glial activation include glial fibrillary acidic protein (GFAP) and transforming growth factor (TGF)-beta1, which are increased in astrocytes and microglia, respectively. Steroids regulate the interactions between glia and neurons and glial gene expression, including GFAP and TGF-beta1. Therefore, changes in these parameters during aging may be due to altered steroid regulation. In general, the effects of steroids oppose the effects of aging. Recent data indicate that steroid treatment can decrease the expression of GFAP in the aged brain, yet GFAP is resistant to down-regulation by endogenous glucocorticoids. Cellular and molecular markers of glial activation are being used to determine how changes in neuroendocrine and neuroimmune regulation contribute to repair and functional recovery that may reverse synaptic loss and cognitive impairment during aging.     

Severe pulmonary hypertension in aging female apolipoprotein E-deficient mice is rescued by estrogen replacement therapy

Corticotropin-releasing factor overexpressing (CRF-OE) male mice showed an inhibited feeding response to a fast, and lower plasma acyl ghrelin and Fos expression in the arcuate nucleus compared to wild-type (WT) mice. We investigated whether hormones and hypothalamic feeding signals are impaired in CRF-OE mice and the influence of sex. Male and female CRF-OE mice and WT littermates (4–6 months old) fed ad libitum or overnight fasted were assessed for body, adrenal glands and perigonadal fat weights, food intake, plasma hormones, blood glucose, and mRNA hypothalamic signals. Under fed conditions, compared to WT, CRF-OE mice have increased adrenal glands and perigonadal fat weight, plasma corticosterone, leptin and insulin, and hypothalamic leptin receptor and decreased plasma acyl ghrelin. Compared to male, female WT mice have lower body and perigonadal fat and plasma leptin but higher adrenal glands weights. CRF-OE mice lost these sex differences except for the adrenals. Male CRF-OE and WT mice did not differ in hypothalamic expression of neuropeptide Y (NPY) and proopiomelanocortin (POMC), while female CRF-OE compared to female WT and male CRF-OE had higher NPY mRNA levels. After fasting, female WT mice lost more body weight and ate more food than male WT, while CRF-OE mice had reduced body weight loss and inhibited food intake without sex difference. In male WT mice, fasting reduced plasma insulin and leptin and increased acyl ghrelin and corticosterone while female WT showed only a rise in corticosterone. In CRF-OE mice, fasting reduced insulin while leptin, acyl ghrelin and corticosterone were unchanged with no sex difference. Fasting blood glucose was higher in CRF-OE with female > male. In WT mice, fasting increased hypothalamic NPY expression in both sexes and decreased POMC only in males, while in CRF-OE mice, NPY did not change, and POMC decreased in males and increased in females. These data indicate that CRF-OE mice have abnormal basal and fasting circulating hormones and hypothalamic feeding-related signals. CRF-OE also abolishes the sex difference in body weight, abdominal fat, and fasting-induced feeding and changes in plasma levels of leptin and acyl ghrelin.     

Metformin slows down aging and extends life span of female SHR mice

Studies in mammals have led to the suggestion that hyperglycemia and hyperinsulinemia are important factors both in aging and in the development of cancer. It is possible that the life-prolonging effects of calorie restriction are due to decreasing IGF-1 levels. A search of pharmacological modulators of insulin/IGF-1 signaling pathway (which resemble effects of life span extending mutations or calorie restriction) could be a perspective direction in regulation of longevity. Antidiabetic biguanides are most promising among them. Here we show the the chronic treatment of female outbred SHR mice with metformin (100 mg/kg in drinking water) slightly modified the food consumption but decreased the body weight after the age of 20 months, slowed down the age-related switch-off of estrous function, increased mean life span by 37.8%, mean life span of last 10% survivors by 20.8%, and maximum life span by 2.8 months (+10.3%) in comparison with control mice. On the other side, treatment with metformin failed influence blood estradiol concentration and spontaneous tumor incidence in female SHR mice. Thus, antidiabetic biguanide metformin dramatically extends life span, even without cancer prevention in this model.     

Reversal of epigenetic aging and immunosenescent trends in humans

Epigenetic “clocks” can now surpass chronological age in accuracy for estimating biological age. Here, we use four such age estimators to show that epigenetic aging can be reversed in humans. Using a protocol intended to regenerate the thymus, we observed protective immunological changes, improved risk indices for many age‐related diseases, and a mean epigenetic age approximately 1.5 years less than baseline after 1 year of treatment (?2.5‐year change compared to no treatment at the end of the study). The rate of epigenetic aging reversal relative to chronological age accelerated from ?1.6 year/year from 0–9 month to ?6.5 year/year from 9–12 month. The GrimAge predictor of human morbidity and mortality showed a 2‐year decrease in epigenetic vs. chronological age that persisted six months after discontinuing treatment. This is to our knowledge the first report of an increase, based on an epigenetic age estimator, in predicted human lifespan by means of a currently accessible aging intervention.     

The effect of aging on the mineral status of female mice

To clarify the effect of aging on the mineral status of female mice, mineral concentrations in their tissues were determined. Five 2-mo-old, five 6-mo-old, and five 10-mo-old female B10BR mice were fed a commercial diet. Iron, zinc, copper, calcium, magnesium, sodium, and potassium concentrations in the blood, liver, kidney, heart, brain, lung, and spleen of the mice were determined using a flame atomic absorption spectrophotometer. Iron concentrations in the liver, kidney, heart, brain, and spleen increased with age. Significant differences were detected between mice 2 and 6 mo of age and between mice 2 and 10 mo of age. Zinc concentrations in the heart and lung decreased significantly with age. Zinc concentrations in the heart and lung of 10-mo-old mice were significantly lower than those of 2-mo-old mice. It is noteworthy that the copper concentration in the brain of 10-mo-old mice was markedly higher compared with that of younger mice. Calcium accumulation was apparent in the kidney of mice at 10 mo.     

Protein synthesis and antioxidant capacity in aging mice: effects of long-term voluntary exercise

Exercise increases metabolic rate and the production of reactive oxygen species (ROS) but also elevates protein turnover. ROS cause damage to macromolecules (e.g., proteins) and thereby contribute to aging. Protein turnover removes and replaces damaged proteins. The balance between these two responses may underlie beneficial effects of physical activity on aging. Effects of lifelong exercise on antioxidant enzyme activities and fractional synthesis rate of protein (FSRP) were examined at various ages (2-26 mo) in heart, liver, and muscle of mice that had been selectively bred for high wheel-running activity, housed with (S+) or without (S-) a running wheel, and their random-bred controls (C+) housed with running wheels. FSRP decreased with age and increased in muscle of young, but not old, activity-selected mice. Enzyme activity of superoxide dismutase and glutathione peroxidase decreased with age and showed a peak at 10 mo of age in liver. Selection for wheel-running activity did not affect antioxidant enzyme activity. Daily energy expenditure correlated positively with antioxidant levels in liver. This might indicate that oxidative stress (ROS production) increases with metabolic rate, driving upregulation of antioxidant enzymes. Alternatively, the elevated energy expenditure may reflect the energetic cost of elevated protection, consistent with the disposable-soma hypothesis and with other studies showing positive links between energy expenditure and life span. Long-term elevations in voluntary exercise did not result in elevations in antioxidant enzyme activities or protein synthesis rates.