Ultrastructural changes in microvessel with age in the hippocampus of senescence-accelerated mouse (SAM)-P/10

Age-related ultrastructural neurovascular changes in the female mouse cortex and hippocampus

Blood-brain barrier (BBB) breakdown occurs in aging and neurodegenerative diseases. Although age-associated alterations have previously been described, most studies focused in male brains; hence, little is known about BBB breakdown in females. This study measured ultrastructural features in the aging female BBB using transmission electron microscopy and 3-dimensional reconstruction of cortical and hippocampal capillaries from 6- and 24-month-old female C57BL/6J mice. Aged cortical capillaries showed more changes than hippocampal capillaries. Specifically, the aged cortex showed thicker basement membrane, higher number and volume of endothelial pseudopods, decreased endothelial mitochondrial number, larger pericyte mitochondria, higher pericyte-endothelial cell contact, and increased tight junction tortuosity compared with young animals. Only increased basement membrane thickness and pericyte mitochondrial volume were observed in the aged hippocampus. Regional comparison revealed significant differences in endothelial pseudopods and tight junctions between the cortex and hippocampus of 24-month-old mice. Therefore, the aging female BBB shows region-specific ultrastructural alterations that may lead to oxidative stress and abnormal capillary blood flow and barrier stability, potentially contributing to cerebrovascular diseases, particularly in postmenopausal women.

Resveratrol preserves cerebrovascular density and cognitive function in aging mice

Resveratrol, a natural polyphenol abundant in grapes and red wine, has been reported to exert numerous beneficial health effects. Among others, acute neuroprotective effects of resveratrol have been described in several models of neurodegeneration, both in vitro and in vivo. In the present study we examined the neuroprotective effects of long-term dietary supplementation with resveratrol in mice on behavioral, neurochemical and cerebrovascular level. We report a preserved cognitive function in resveratrol-treated aging mice, as shown by an enhanced acquisition of a spatial Y-maze task. This was paralleled by a higher microvascular density and a lower number of microvascular abnormalities in comparison to aging non-treated control animals. We found no effects of resveratrol supplementation on cholinergic cell number or fiber density. The present findings support the hypothesis that resveratrol exerts beneficial effects on the brain by maintaining cerebrovascular health. Via this mechanism resveratrol can contribute to the preservation of cognitive function during aging.

Capillary injury in the ischemic brain of hyperlipidemic, apolipoprotein B-100 transgenic mice

AIMS

Apolipoprotein B-100 (apoB-100) has been implicated in hyperlipidemia, which contributes to the pathogenesis of vascular disorders. Our aim was to investigate whether the expression of human apoB-100 in transgenic mice and/or a high-cholesterol diet cause cerebral microvascular lesions, and whether these conditions augment ischemia-related capillary damage.

MAIN METHODS

Human apoB-100 overexpressing transgenic (Tg(apoB-100), n=23) and wild-type mice (C5/B6, Wt, n=26) were supplied with standard or 2% cholesterol-enriched diet for 17-19 weeks. Cerebral ischemia was induced by unilateral common carotid artery occlusion. Cortical samples were embedded for electron microscopy. Microvascular density (number of microvascular profiles/examined area), lumen diameter, the swelling of astrocytic endfeet, the occurrence of endothelial microvilli (affected capillaries expressed as ratio of all capillaries encountered), and the ratio of intact capillaries (devoid of all the above pathology) were calculated.

KEY FINDINGS

The expression of apoB-100 coincided with decreased cortical microvascular density (195+/-7 vs. 223+/-8 vessels/mm(2), vs. Wt; P<0.008) and increased capillary lumen diameter (3.16+/-0.5 vs. 2.88+/-0.6 microm, vs. Wt; P<0.001). Cerebral ischemia promoted the swelling of perivascular astrocytes (62.1+/-4.2 vs. 36.5+/-4.0%, vs. contralateral, Wt; P<0.001), and reduced the ratio of intact capillaries (32.1+/-5.6 vs. 65.2+/-3.7%, vs. contralateral, Wt; P<0.001). Hyperlipidemia did not exacerbate the injury.

SIGNIFICANCE

The overexpression of human apoB-100 alters the density of the microvascular network and the diameter of capillaries, which may compromise cerebrovascular reactivity during ischemia.

The senescence-accelerated mouse (SAM-P8) as a model for the study of vascular functional alterations during aging

We studied vascular function in quiescent aortas from senescence-accelerated resistant (SAM-R1) and prone (SAM-P8) mice. Myographical studies of thoracic aorta segments from 6-7 month-old mice showed that the contractility of SAM-P8 aortas was markedly higher than that of SAM-R1 after KCl depolarization or phenylephrine addition. Acetylcholine dose-response relaxation curves revealed that SAM-R1 vessels were slightly more sensitive than those of SAM-P8. In the presence of the NO synthase inhibitor, L-NAME, all vessels displayed contractions to acetylcholine, but these were more distinct in the SAM-R1. Phenylephrine plus L-NAME displayed stronger contractions in both animal strains, but were markedly more pronounced in SAM-R1. The cyclooxygenase inhibitor, indomethacin did not change the vessel responses to acetylcholine or phenylephrine. These data indicate that NO synthase, not cyclooxygenase, was responsible for the differences in contractility. Standard histology and immunohistochemistry of endothelial NO synthase revealed no differences in the expression of this protein. In contrast, increased levels of malondialdehyde were found in SAM-P8 vessels. We conclude that SAM-P8 vessels exhibit higher contractility than those of SAM-R1. Furthermore, our results suggest that the endothelium of SAM-P8 vessels is dysfunctional and lacks normal capability to counteract smooth muscle contraction. Therefore, our findings support SAM-P8 as a suitable model for the study of vascular physiological changes during aging.

Mechanisms of aging in senescence-accelerated mice

BACKGROUND

Progressive neurological dysfunction is a key aspect of human aging. Because of underlying differences in the aging of mice and humans, useful mouse models have been difficult to obtain and study. We have used gene-expression analysis and polymorphism screening to study molecular senescence of the retina and hippocampus in two rare inbred mouse models of accelerated neurological senescence (SAMP8 and SAMP10) that closely mimic human neurological aging, and in a related normal strain (SAMR1) and an unrelated normal strain (C57BL/6J).

RESULTS

The majority of age-related gene expression changes were strain-specific, with only a few common pathways found for normal and accelerated neurological aging. Polymorphism screening led to the identification of mutations that could have a direct impact on important disease processes, including a mutation in a fibroblast growth factor gene, Fgf1, and a mutation in and ectopic expression of the gene for the chemokine CCL19, which is involved in the inflammatory response.

CONCLUSION

We show that combining the study of inbred mouse strains with interesting traits and gene-expression profiling can lead to the discovery of genes important for complex phenotypes. Furthermore, full-genome polymorphism detection, sequencing and gene-expression profiling of inbred mouse strains with interesting phenotypic differences may provide unique insights into the molecular genetics of late-manifesting complex diseases.

Impaired angiogenesis in aging is associated with alterations in vessel density, matrix composition, inflammatory response, and growth factor expression

It is generally accepted that angiogenesis is delayed in aging. To define the effects of age on the neovascular response, polyvinyl alcohol sponges were implanted SC in young (6-8 months old, n=11) and aged (23-25 months old, n=13) mice and sampled at 14 and 19 days. Angiogenic invasion was significantly delayed in aged mice at 14d relative to young at 14d (% area of invasion 9.0 +/- 3.7 vs 19.0 +/- 5.6; p=0.02). Although microvessel morphology and basement membrane composition were similar between the age groups, a significant decrease in capillary density was noted in aged tissues at 14d (7.5 +/- 4.1) and 19d (12.1 +/- 2.8) relative to young at 14d (18.7 +/- 2.3) (p<0.01 A14d vs Y14d). In comparison to young at 14d, the inflammatory response was decreased by 43 +/- 2.9% and 36 +/- 7.8% in aged mice at 14d and 19d, respectively. Tissues of aged mice showed less newly deposited collagen. There was a lack of expression of transforming growth factor-beta1 (TGF-beta1) and vascular endothelial growth factor (VEGF) in aged mice at 14d (0.63 +/- 0.3) and 19d (1.14 +/- 0.5) vs young at 14d (1.92 +/- 0.5) (p< or =0.01 A14d vs Y14d for VEGF). However, similar production of VEGF receptor2 was observed. In contrast to young mice, there was significantly increased expression of thrombospondin-2 (TSP-2) in aged mice from 14d (14.6 x 10(3) +/- 7.3 x 10(3)) to 19d (34.9 x 10(3) +/- 17 x 10(3)). We conclude that angiogenesis in aging is not merely delayed, but is altered due to multiple impairments.