Microvascular changes in estrogen-α sensitive brainstem structures of aging female hamsters

Estradiol Inhibits Human Brain Vascular Pericyte Migration Activity: A Functional and Transcriptomic Analysis

Stroke is the third leading cause of mortality in women and it kills twice as many women as breast cancer. A key role in the pathophysiology of stroke plays the disruption of the blood–brain barrier (BBB) within the neurovascular unit. While estrogen induces vascular protective actions, its influence on stroke remains unclear. Moreover, experiments assessing its impact on endothelial cells to induce barrier integrity are non-conclusive. Since pericytes play an active role in regulating BBB integrity and function, we hypothesize that estradiol may influence BBB by regulating their activity. In this study using human brain vascular pericytes (HBVPs) we investigated the impact of estradiol on key pericyte functions known to influence BBB integrity. HBVPs expressed estrogen receptors (ER-α, ER-β and GPER) and treatment with estradiol (10 nM) inhibited basal cell migration but not proliferation. Since pericyte migration is a hallmark for BBB disruption following injury, infection and inflammation, we investigated the effects of estradiol on TNFα-induced PC migration. Importantly, estradiol prevented TNFα-induced pericyte migration and this effect was mimicked by PPT (ER-α agonist) and DPN (ER-β agonist), but not by G1 (GPR30 agonist). The modulatory effects of estradiol were abrogated by MPP and PHTPP, selective ER-α and ER-β antagonists, respectively, confirming the role of ER-α and ER-β in mediating the anti-migratory actions of estrogen. To delineate the intracellular mechanisms mediating the inhibitory actions of estradiol on PC migration, we investigated the role of AKT and MAPK activation. While estradiol consistently reduced the TNFα-induced MAPK and Akt phosphorylation, only the inhibition of MAPK, but not Akt, significantly abrogated the migratory actions of TNFα. In transendothelial electrical resistance measurements, estradiol induced barrier function (TEER) in human brain microvascular endothelial cells co-cultured with pericytes, but not in HBMECs cultured alone. Importantly, transcriptomics analysis of genes modulated by estradiol in pericytes showed downregulation of genes known to increase cell migration and upregulation of genes known to inhibit cell migration. Taken together, our findings provide the first evidence that estradiol modulates pericyte activity and thereby improves endothelial integrity.

3D Image Analysis of the Complete Ventricular-Subventricular Zone Stem Cell Niche Reveals Significant Vasculature Changes and Progenitor Deficits in Males Versus Females with Aging

With age, neural stem cell (NSC) function in the adult ventricular-subventricular zone (V-SVZ) declines, reducing memory and cognitive function in males; however, the impact on females is not well understood. To obtain a global view of how age and sex impact the mouse V-SVZ, we constructed 3D montages after multiplex immunostaining, and used computer-based 3D image analysis to quantify data across the entire niche at 2, 18, and 22 months. We discovered dramatic sex differences in the aging of the V-SVZ niche vasculature, which regulates NSC activity: females showed increased diameter but decreased vessel density with age, while males showed decreased diameter and increased tortuosity and vessel density. Accompanying these vascular changes, males showed significant decline in NSC numbers, progenitor cell proliferation, and more disorganized migrating neuroblast chains with age; however, females did not. By examining the entire 3D niche, we found significant sex differences, with females being relatively spared through very old age.

miR-195 regulates SIRT1-mediated changes in diabetic retinopathy

AIMS/HYPOTHESIS

Endothelial cell (EC) damage is a key mechanism causing retinal microvascular injury in diabetes. Several microRNAs (miRNAs) have been found to regulate sirtuin 1 (SIRT1, which is involved in regulation of the cell cycle, survival and metabolism) in various tissues and disease states, but no studies have been conducted on the role of miRNA in regulation of SIRT1 in diabetic retinopathy. Here we investigated the effect of miRNA-195 (miR-195), a SIRT1-targeting miRNA, on the development of diabetes-induced changes in ECs and retina.

METHODS

The level of miR-195 was measured in human retinal and dermal microvascular ECs (HRECs, HMECs) following exposure to 25 mmol/l glucose (high glucose, HG) and 5 mmol/l glucose (normal glucose, NG). SIRT1 and fibronectin levels were examined following transfection with miR-195 mimic or antagomir or forced expression of SIRT1. Retinal tissues from diabetic rats were similarly studied following intravitreal injection of an miR-195 antagomir or mimic. In situ hybridisation was used to localise retinal miR-195.

RESULTS

HG caused increased miR-195 levels and decreased SIRT1 expression (compared with NG) in both HRECs and HMECs. Transfection with miR-195 antagomir and forced expression of SIRT1 prevented such changes, whereas transfection with miR-195 mimic produced HG-like effects. A luciferase assay confirmed the binding of miR-195 to the 3' untranslated region of SIRT1. miR-195 expression was upregulated in retinas of diabetic rats and intravitreal injection of miR-195 antagomir ameliorated levels of SIRT1.

CONCLUSIONS/INTERPRETATION

These studies identified a novel mechanism whereby miR-195 regulates SIRT1-mediated tissue damage in diabetic retinopathy.

Age-related changes in brain support cells: Implications for stroke severity

Stroke is one of the leading causes of adult disability and the fourth leading cause of mortality in the US. Stroke disproportionately occurs among the elderly, where the disease is more likely to be fatal or lead to long-term supportive care. Animal models, where the ischemic insult can be controlled more precisely, also confirm that aged animals sustain more severe strokes as compared to young animals. Furthermore, the neuroprotection usually seen in younger females when compared to young males is not observed in older females. The preclinical literature thus provides a valuable resource for understanding why the aging brain is more susceptible to severe infarction. In this review, we discuss the hypothesis that stroke severity in the aging brain may be associated with reduced functional capacity of critical support cells. Specifically, we focus on astrocytes, that are critical for detoxification of the brain microenvironment and endothelial cells, which play a crucial role in maintaining the blood brain barrier. In view of the sex difference in stroke severity, this review also discusses studies of middle-aged acyclic females as well as the effects of the estrogen on astrocytes and endothelial cells.

High glucose induced alteration of SIRTs in endothelial cells causes rapid aging in a p300 and FOXO regulated pathway

In diabetes, some of the cellular changes are similar to aging. We hypothesized that hyperglycemia accelerates aging-like changes in the endothelial cells (ECs) and tissues leading to structural and functional damage. We investigated glucose-induced aging in 3 types of ECs using senescence associated β-gal (SA β-gal) staining and cell morphology. Alterations of sirtuins (SIRTs) and their downstream mediator FOXO and oxidative stress were investigated. Relationship of such alteration with histone acetylase (HAT) p300 was examined. Similar examinations were performed in tissues of diabetic animals. ECs in high glucose (HG) showed evidence of early senescence as demonstrated by increased SA β-gal positivity and reduced replicative capacities. These alterations were pronounced in microvascular ECs. They developed an irregular and hypertrophic phenotype. Such changes were associated with decreased SIRT (1–7) mRNA expressions. We also found that p300 and SIRT1 regulate each other in such process, as silencing one led to increase of the others’ expression. Furthermore, HG caused reduction in FOXO1’s DNA binding ability and antioxidant target gene expressions. Chemically induced increased SIRT1 activity and p300 knockdown corrected these abnormalities slowing aging-like changes. Diabetic animals showed increased cellular senescence in renal glomerulus and retinal blood vessels along with reduced SIRT1 mRNA expressions in these tissues. Data from this study demonstrated that hyperglycemia accelerates aging-like process in the vascular ECs and such process is mediated via downregulation of SIRT1, causing reduction of mitochondrial antioxidant enzyme in a p300 and FOXO1 mediated pathway.

Reduced aging defects in estrogen receptive brainstem nuclei in the female hamster

The nucleus pararetroambiguus (NPRA) and the commissural nucleus of the solitary tract (NTScom) show estrogen nuclear receptor-α immunoreactivity (nuclear ER-α-IR). Both cell groups are involved in estrous cycle related adaptations. We examined in normally cycling aged hamsters the occurrence/amount/frequency of age-related degenerative changes in NPRA and NTScom during estrus and diestrus. In 2640 electron microscopy photomicrographs plasticity reflected in the ratio of axon terminal surface/dendrite surface (t/d) was morphometrically analyzed. Medial tegmental field (mtf, nuclear ER-α-IR poor), served as control. In aged animals, irrespective of nuclear ER-α-IR+ or nuclear ER-α-IR- related cell groups, extensive diffuse degenerative structural aberrations were observed. The hormonal state had a strong influence on t/d ratios in NPRA and NTScom, but not in mtf. In NPRA and NTScom, diestrous hamsters had significantly smaller t/d ratios (NPRA, 0.750 ± 0.050; NTScom, 0.900 ± 0.039) than the estrous hamsters (NPRA, 1.083 ± 0.075; NTScom, 1.204 ± 0.076). Aging affected axodendritic ratios only in mtf (p < 0.001).

IN CONCLUSION

in the female hamster brain, estrous cycle-induced structural plasticity is preserved in NPRA and NTScom during aging despite the presence of diffuse age-related neurodegenerative changes.