Nonenzymatic glycation is a multistep, slow reaction between reducing sugars and free amino groups of long-lived proteins, which affects the structural and mechanical properties of collagen-rich tissues via accumulation of advanced glycation end products (AGEs). Dental collagen is exposed to glycation as part of the natural aging process. However, in case of chronically high blood glucose, the process can be accelerated, resulting in premature stiffening of dentin, leading to tooth fragility. The molecular mechanisms whereby collagen glycation evokes the loss of mechanical stability in teeth are currently unknown. In this study, we used 2-photon and atomic force microscopies to correlate structural and mechanical changes in dental collagen induced by in vitro glycation. Young tooth samples were demineralized and cut longitudinally into 30-µm sections, then artificially glycated in 0.5 M ribose solution for 10 wk. Two-photon microscopy analysis showed that both the autofluorescence and second harmonic-generated (SHG) signal intensities of glycated samples were significantly greater than those of the controls. Regarding the structural alteration of individual collagen fibers, a remarkable increase could be measured in fiber length of ribose-treated sections. Furthermore, nanoindentation of intertubular dentin regions revealed significantly higher stiffness in the ribose-treated samples, which points at a significant accumulation of AGEs. Thus, collagen glycation occurring during sustained exposure to reducing sugars leads to profound structural and mechanical changes in dentin. Besides the numerous oral complications associated with type 2 diabetes, the premature structural and mechanical deterioration of dentin may also play an important role in dental pathology.

Objective: Hypertension in the elderly can lead to dysfunctional autoregulation of cerebral blood flow (CBF), leading to increased risk of stroke and the development of Alzheimer's disease (AD), but the underlying mechanisms are still unknown. We hypothesized that hypertension and aging synergistically impair the myogenic constrictor response of cerebral arteries (CA), known to be involved in the autoregulation of CBF and as a consequence, an altered gene expression in the hippocampus will be observable. Design and method: Hypertension was induced in young (3 mo) and aged (24 mo) C57BL/6 mice with chronic (4 wk) infusion of angiotensin II and changes in myogenic response of CA) and hippocampal mRNA expression of genes involved in amyloid precursor protein (APP)-dependent signaling, APP cleavage, A-beta processing and A-beta-degradation, synaptic function were assessed. Results: In MCAs from young hypertensive mice, pressure-induced increases in SMC Ca-signal and myogenic tone were increased, both of which were inhibited by the cytochrome P-450 omega-hydroxylase inhibitor HET0016 and the transient receptor potential (TRP) channel blocker SKF96365. MCAs from aged hypertensive mice did not show adaptive increases in pressure-induced Ca-signal and myogenic tone and responses to HET0016 and SKF96365 were blunted. Aged hypertensive mice exhibited spatial memory impairments in the Y-maze and impaired performance in the novel object recognition assay. Hypertension in aging was associated with changes in hippocampal expression of APP-binding proteins, e.g., [Mint3/amyloid beta A4 precursor protein-binding family. A member 3 (APBA3), Fe65/amyloid beta A4 precursor protein-binding family B member 1 (APBB1)], amyloid beta (A4) precursor-like protein 1 (APLP1), muscarinic M1 receptor, and serum amyloid P component, all of which may have a role in the pathogenesis of late-onset AD. Conclusions: Thus functional maladaptation of aged cerebral arteries to hypertension is due to the dysregulation of pressure-induced 20-HETE and TRP channel-mediated SMC calcium signaling, whereas the hippocampal gene expression signature observed in aged hypertensive mice provides important clues for future studies to elucidate the mechanisms by which hypertension may contribute to the pathogenesis of Alzheimer's disease.

Traumatic brain injuries (TBIs) have a devastating global epidemiological importance since they contribute to the mortality and morbidity in the society with a considerably large extent. After TBI the injured brain tissue tends to swell leading to the increment of the intracranial pressure (ICP) which can cause serious neurological damage and death. Therefore, a main goal of the neurosurgical procedure is the reduction of ICP which is possible via decompressive craniectomy (DC). However, its optimal execution regarding the size and the location of the skull opening is controversial. In this paper the reconstruction of DC is performed by finite element (FE) simulations. The applied modelling strategy is presented and patient-specific FE models are constructed with different levels of anatomic details which can predict the post-operative response of the brain tissue for a given pre-operative state. These models are validated by reconstructing real life DC case, where the predicted displacements and ICP are compared to their observed value measured by neurosurgeons. Results confirm the applicability of the above described modelling procedure, implying that such models can be used to optimize DC in the future based on the biomechanical response of the highly deformable brain tissue.

Previous studies demonstrate that aging and pathological conditions associated with accelerated cerebromicrovascular aging (e.g. hypertension, obesity) promote cerebrovascular dysfunction by decreasing bioavailability of NO and increasing production of O2. − and reactive nitrogen species. 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 cognitive impairment associated with the aforementioned conditions and previous studies demonstrate that endothelial dysfunction plays a critical role in neurovascular uncoupling in these conditions. Despite these advances, the role of endothelial NO mediation in neurovascular coupling responses is not well understood. To establish the link between endothelial function and functional hyperemia, neurovascular coupling responses were studied in mutant mice overexpressing or deficient in eNOS and the role of P2Y1 receptors in purinergic glioendothelial coupling was assessed. We found that genetic depletion of eNOS (eNOS−/−) and pharmacological inhibition of NO synthesis significantly decreased the CBF responses in the somatosensory cortex evoked by whisker stimulation and by administration of ATP, mimicking oxidative/nitrative stress‐mediated impairment of functional hyperemia and microvascular endothelial responses observed in aged mice. Overexpression of eNOS enhanced NO mediation of functional hyperemia. In control mice the selective and potent P2Y1 receptor antagonist MRS2179 attenuated both whisker stimulation‐induced and ATP‐mediated CBF responses, whereas in eNOS−/− mice the inhibitory effects of MRS2179 were blunted. Collectively, our findings provide additional evidence for purinergic glio‐endothelial coupling during neuronal activity, highlighting the role of ATP‐mediated activation of eNOS via P2Y1 receptors in functional hyperemia.Support or Funding InformationThis work was supported by grants from the American Heart Association, the National Center for Complementary and Alternative Medicine, and the National Institute on Aging

There is increasing evidence that vascular risk factors, including aging, hypertension, diabetes mellitus and obesity, promote cognitive impairment, however, the underlying mechanisms remain obscure. Cerebral blood flow (CBF) is adjusted to neuronal activity via neurovascular coupling (NVC) and this mechanism is known to be impaired in the aforementioned pathophysiological conditions. To establish a direct, causal relation between impaired NVC and cognitive decline, we induced neurovascular uncoupling pharmacologically in mice by inhibiting the synthesis of vasodilator mediators involved in NVC. Treatment of mice with the epoxygenase inhibitor MS‐PPOH, the NOS inhibitor L‐NAME and the COX inhibitor indomethacin decreased NVC by 75% mimicking the aging phenotype, which was associated with significantly impaired spatial working memory (Y‐maze), recognition memory (Novel object recognition) and impairment in motor coordination (Rotarod). Blood pressure (tail cuff), basal cerebral perfusion (arterial spin labeling perfusion MRI) and synaptic activity (evoked field potential) were unaffected. Thus, targeted experimental disruption of NVC per se leads to significant impairment of cortical function, including cognitive decline, recapitulating neurological symptoms and signs observed in brain aging and pathophysiological conditions associated with accelerated cerebromicrovascular aging.

Stability of myogenic tone in middle cerebral arteries (MCA) is essential for adequate control over penetration of pressure waves into the distal portion of the cerebral microcirculation. Because the increased pulse pressure observed in advanced aging is associated with cerebromicrovascular injury, the effect of aging on myogenic response of mouse MCAs was determined. Aging did not affect the myogenic constriction in response to static increases in pressure, whereas it significantly impaired pulsatile pressure-induced myogenic tone. Impaired myogenic adaptation of MCAs to pulsatile pressure may allow high pressure to penetrate the distal portion of the cerebral microcirculation, contributing to microvascular damage.

Background: Aging is associated with increased incidence of cerebrovascular disorders, but the age-dependent changes in local vasomotor mechanisms are not completely understood. Myogenic autoregulation of cerebral vessels in response to static changes in perfusion pressure protects the microcirculation from high pressure and volume. However, it was recently shown that aging impairs static myogenic regulation of cerebral blood flow, responses of cerebral vessels to pulsatile pressure, especially in aging are not known. Thus, we tested the hypotheses that aging impairs myogenic responses of cerebral arteries to pulsatile pressure. Methods and Results: Isolated and cannulated middle cerebral arteries (MCA) were isolated from young (3 mo) and aged (24 mo) C57BL/6 mice. Both young and aged MCAs developed similar myogenic tone in response to stepwise, steady-state increases in intraluminal P. Also, young MCAs exhibited significant myogenic adaptation to sinusoidal pulsatile P (amplitude: 40 mmHg, frequency: 450/min). While in myogenic-inactive MCAs each P pulse elicited a ∼7% distension in synchrony with the pulsatile P, in young myogenic-active MCAs the amplitude of the diameter changes induced by the P pulses in the autoregulated P range was significantly attenuated (∼2%). The mean P-myogenic tone curve was similar in young MCAs exposed to constant and pulsatile P. In aged MCAs the cyclic changes in diameter induced by the P pulses were increased (∼4%) and development of myogenic tone in response to pulsatile P was impaired. Conclusion: Collectively, aging impairs myogenic adaptation of cerebral arteries to pulsatile P, which likely promotes the development of cerebromicrovascular injury, such as cerebral microbleeds and blood brain barrier disruption by allowing high P to penetrate the distal portion of the cerebral microcirculation.

Hypertension in the elderly substantially contributes to cerebromicrovascular damage and promotes the development of vascular cognitive impairment. Despite the importance of the myogenic mechanism in cerebromicrovascular protection, it is not well understood how aging affects the functional adaptation of cerebral arteries to high blood pressure. Hypertension was induced in young (3 mo) and aged (24 mo) C57/BL6 mice by chronic infusion of angiotensin II. In young hypertensive mice, the range of cerebral blood flow autoregulation was extended to higher pressure values and the pressure‐induced tone of MCA was increased. In aged hypertensive mice autoregulation was markedly disrupted, and MCAs did not show adaptive increases in myogenic tone. In young mice the mechanism of adaptation to hypertension involved up‐regulation of the 20‐HETE/TRPC6 pathway and this mechanism was impaired in aged hypertensive mice. Downstream consequences of cerebrovascular autoregulatory dysfunction in aged angiotensin II‐induced hypertensive mice include exacerbated disruption of the blood‐brain barrier and neuroinflammation (microglia activation, up‐regulation of pro‐inflammatory cytokines and chemokines), which were associated with impaired hippocampal cognitive function. Collectively, aging impairs autoregulatory protection in the brain of mice with angiotensin II‐induced hypertension, potentially exacerbating cerebromicrovascular injury and neuroinflammation.Grant Funding Source: Supported by the American Federation for Aging Research and the Nemzeti Fejlesztési Ügynökség

There is growing evidence that obesity has deleterious effects on the brain and cognitive function in the elderly population. However, the specific mechanisms through which aging and obesity interact to promote cognitive decline remain unclear. To test the hypothesis that aging exacerbates obesity-induced cerebromicrovascular damage and neuroinflammation, we compared young (7 months) and aged (24 months) high fat diet-fed obese C57BL/6 mice. Aging exacerbated obesity-induced systemic inflammation and blood-brain barrier disruption, as indicated by the increased circulating levels of proinflammatory cytokines and increased presence of extravasated immunoglobulin G in the hippocampus, respectively. Obesity-induced blood-brain barrier damage was associated with microglia activation, upregulation of activating Fc-gamma receptors and proinflammatory cytokines, and increased oxidative stress. Treatment of cultured primary microglia with sera derived from aged obese mice resulted in significantly more pronounced microglia activation and oxidative stress, as compared with treatment with young sera. Serum-induced activation and oxidative stress were also exacerbated in primary microglia derived from aged animals. Hippocampal expression of genes involved in regulation of the cellular amyloid precursor protein-dependent signaling pathways, beta-amyloid generation, and the pathogenesis of tauopathy were largely unaffected by obesity in aged mice. Collectively, obesity in aging is associated with a heightened state of systemic inflammation, which exacerbates blood-brain barrier disruption. The resulting neuroinflammation and oxidative stress in the mouse hippocampus likely contribute to the significant cognitive decline observed in aged obese animals.

Background: Aging is associated with increased incidence of cerebrovascular disorders, but the age-dependent changes in local vasomotor mechanisms are not completely understood. Myogenic autoregulation of cerebral vessels in response to static changes in perfusion pressure protects the microcirculation from high pressure and volume. Recently it was shown that aging impairs static myogenic regulation of cerebral vessels, however effects of aging on responses of cerebral arteries to pulsatile pressure are not known. Thus, we tested the hypothesis that aging impairs myogenic responses of cerebral arteries to increases in pulsatile pressure. Methods and Results: Middle cerebral arteries (MCA) were isolated from young (3 mo) and aged (24 mo) C57BL/6 mice and then cannulated. Young and aged MCAs developed similar myogenic tone in response to stepwise, steady-state increases in intraluminal P. Young MCAs exhibited significant myogenic adaptation to sinusoidal pulsatile pressure (PP, amplitude: 40 mmHg, frequency: 450/min). While in myogenic-inactive MCAs each PP elicited a ~7% distension in synchrony with the PP, in young myogenic-active MCAs the amplitude of the diameter changes induced by the PP was significantly attenuated (~2%) in the range of autoregulation. The myogenic tone curves of young MCAs were similar to steady and pulsatile pressures. In aged MCAs, the cyclic changes in diameter induced by the PP were increased, but the development of myogenic tone in response to PP was impaired. Conclusion: Collectively, aging impairs myogenic adaptation of cerebral arteries to pulsatile pressure, which likely promotes the development of cerebromicrovascular injury, such as cerebral microbleeds and blood brain barrier disruption by allowing the high pressure to penetrate the distal portion of the cerebral microcirculation.

Aging is associated with high prevalence of cerebral microbleeds (CMBs) in the elderly, which contribute to the age‐related decline in higher cortical function. Despite its clinical significance, the pathophysiology of CMBs is poorly understood. To establish a novel model of CMB hypertension was induced in young (3 mo) and aged (24 mo) C57B/6 mice (s.c AngII, p.o. L‐NAME). Neurological examination and gait analysis followed by histological analysis of CMBs in serial sections of the brain showed that in the aged mice the same level of hypertension lead to significantly earlier onset and increased incidence of CMBs (incidence: young:27%, aged:90% of the animals; average number of CMBs: young:15±3, aged:28±2). Aging exacerbated hypertension‐induced cerebral oxidative stress, NADPH oxidase expression (Nox2 mRNA: 2±0.1 fold increase in aged vs. young) and activation of MMPs (6±0.9 fold increase in aged vs. young). Treatment of aged mice with the dietary polyphenol resveratrol (200 mg/kg for 20 days) significantly attenuated oxidative stress, down‐regulated NADPH oxidase, decreased MMP activity and prevented/delayed the development of CMBs. Collectively, aging exacerbates hypertension‐induced intracerebral microbleeds in mice likely by increasing oxidative stress and MMP activation. Therapeutic strategies to reduce microvascular oxidative stress and MMP activity should be considered for the prevention of CMBs in the elderly.Grant Funding Source: Supported by the Oklahoma Center for the Advancement of Science and Technology

Obesity in the elderly promotes the development of vascular cognitive impairment, which develops in the absence of Alzheimer‐type senile plaques as a result of cerebromicrovascular alterations. To elucidate the mechanisms by which aging exacerbates the deleterious cerebrovascular effects of obesity, young (7 mo) and aged (24 mo) C57/BL6 mice were fed a high fat diet for 5 months. Compared to young obese mice, aged obese mice exhibited impaired pressure‐induced myogenic constriction and flow‐induced constriction of middle cerebral arteries, disruption of the blood‐brain barrier, hippocampal microvascular rarefaction, microglia activation, up‐regulated hippocampal expression of pro‐inflammatory cytokines and chemokines and impaired performance in tests relevant for hippocampally ‐ dependent tasks of learning and memory. Taken together, aging exacerbates obesity‐induced cerebromicrovascular injury and neuroinflammation, which likely promote the development of vascular cognitive impairment in aged obese individuals.

Age‐related impairment of angiogenesis is likely to play a central role in cerebromicrovascular rarefaction and development of vascular cognitive impairment. To test the hypothesis that dysregulation of Dicer1 impairs endothelial angiogenic capacity in aging, primary cerebromicrovascular endothelial cells(CMVEC) were isolated from young (3 mo) and aged (24 mo) F344xBN rats. In aged CMVECs Dicer1 was down‐regulated and its expression was increased by treatment with PEG‐catalase. Compared to young cells aged CMVECs exhibited altered miRNA expression profile, which was associated with impaired proliferation, adhesion to vitronectin, collagen and fibronectin, cellular migration and impaired ability to form capillary‐like structures. Overexpression of Dicer1 in aged CMVECs partially restored miRNA expression profile and significantly improved angiogenic processes. In young CMVECs down‐regulation of Dicer1 (siRNA) resulted in altered miRNA expression profile associated with impaired proliferation, adhesion, migration and tube formation, mimicking the aging phenotype. Collectively, Dicer1 is essential for normal endothelial angiogenic processes, suggesting that age‐related dysregulation of Dicer1‐dependent microRNA expression may be a potential mechanism underlying impaired angiogenesis and cerebromicrovascular rarefaction in aging.

The elderly show a significantly elevated mortality rate during sepsis than younger patients, due to their higher propensity to microvascular dysfunction and consequential multi‐organ failure. We tested whether aging renders vascular endothelial cells more susceptible to damage induced by inflammatory factors present in the circulation during sepsis. Primary microvascular endothelial cells derived from young (3 m.o.) and aged (24 m.o.) F344xBN rats were treated with sera obtained from sepsis patients and healthy controls. Apoptotic cell death (caspase 3 and caspase 8 activities) induced by treatment with septic sera was exacerbated in aged endothelial cells as compared to responses obtained in young cells. In aged endothelial cells, compared to young cells, DAF fluorescence, indicating NO production, was decreased both under basal conditions and after treatment with septic sera. Treatment with septic sera elicited greater increases in mitochondrial production of reactive oxygen species (MitoSox fluorescence) and NF‐kappaB activation (reporter gene assay) in aged endothelial cells, as compared to young cells. Collectively, aging increases sensitivity of microvascular endothelial cells to oxidative stress and cellular damage induced by inflammatory factors present in the circulation, which likely contributes to the increased vulnerability of elderly patients to sepsis.

Moderate caloric restriction (CR) increases healthspan in virtually every species studied, including nonhuman primates. In mice, CR exerts significant microvascular protective effects resulting in increased microvascular density in the heart and the brain, which likely contribute to enhanced tolerance to ischemia and improved cardiac performance and cognitive function. Yet, the underlying mechanisms by which CR confer microvascular protection remain elusive. To test the hypothesis that circulating factors triggered by CR regulate endothelial angiogenic capacity, we treated cultured human endothelial cells with sera derived from Macaca mulatta on long‐term (>;10 years) CR. Cells treated with sera derived from ad libitum fed control monkeys served as controls. We found that factors present in CR sera up‐regulate VEGF signaling and stimulate angiogenic processes, including endothelial cell proliferation and formation of capillary‐like structures. Treatment with CR sera also increased cellular migration and adhesion. Collectively, we find that circulating factors induced by CR promote endothelial angiogenic processes, suggesting that increased angiogenesis may be a potential mechanism by which CR improves cardiac function and prevents vascular cognitive impairment

Diet‐induced obesity in the elderly promotes the development of vascular cognitive impairment, which develops in the absence of Alzheimer‐type senile plaques as a result of decreased cerebral blood flow due to vascular alterations. To test the hypothesis that obesity in aging impairs local vasoregulatory mechanisms in cerebral arteries, young (3 mo) and aged (24 mo) C57BL/6 mice were fed a high fat diet (HFD) or a standard diet (SD) for 6 months. In middle cerebral arteries (MCA) isolated from obese aged mice stepwise increases in transmural pressure (from 10 to 160 mmHg) elicited impaired steady‐state myogenic constriction as compared to responses obtained in vessels of young SD‐ and HFD‐fed and aged SD‐fed mice. MCAs from aged obese mice also exhibited impaired dynamic myogenic responses and flow‐induced constriction. Furthermore, obesity impaired metabolic vasodilation in response to adenosine in young mice, whereas its effect was exacerbated in aged mice. Collectively, aging exacerbates obesity‐induced cerebrovascular autoregulatory dysfunction, which likely promotes microvascular damage contributing to the development of vascular cognitive impairment in aged obese individuals. (Funding: AHA, AFAR, NIH).