Young little mice express a premature cardiovascular aging phenotype

Methods to Utilize Pulse Wave Velocity to Measure Alterations in Cerebral and Cardiovascular Parameters

Alzheimer's Disease (AD) is a global health issue, affecting over 6 million in the United States, with that number expected to increase as the aging population grows. As a neurodegenerative disorder that affects memory and cognitive functions, it is well established that AD is associated with cardiovascular risk factors beyond only cerebral decline. However, the study of cerebrovascular techniques for AD is still evolving. Here, we provide reproducible methods to measure impedance-based pulse wave velocity (PWV), a marker of arterial stiffness, in the systemic vascular (aortic PWV) and in the cerebral vascular (cerebral PWV) systems. Using aortic impedance and this relatively novel technique of cerebral impedance to comprehensively describe the systemic vascular and the cerebral vascular systems, we examined the sex-dependent differences in 5x transgenic mice (5XFAD) with AD under normal and high-fat diet, and in wild-type mice under a normal diet. Additionally, we validated our method for measuring cerebrovascular impedance in a model of induced stress in 5XFAD. Together, our results show that sex and diet differences in wildtype and 5XFAD mice account for very minimal differences in cerebral impedance. Interestingly, 5XFAD, and not wildtype, male mice on a chow diet show higher cerebral impedance, suggesting pathological differences. Opposingly, when we subjected 5XFAD mice to stress, we found that females showed elevated cerebral impedance. Using this validated method of measuring impedance-based aortic and cerebral PWV, future research may explore the effects of modifying factors including age, chronic diet, and acute stress, which may mediate cardiovascular risk in AD.

Blood pressure pulsations modulate central neuronal activity via mechanosensitive ion channels

The transmission of the heartbeat through the cerebral vascular system causes intracranial pressure pulsations. We discovered that arterial pressure pulsations can directly modulate central neuronal activity. In a semi-intact rat brain preparation, vascular pressure pulsations elicited correlated local field oscillations in the olfactory bulb mitral cell layer. These oscillations did not require synaptic transmission but reflected baroreceptive transduction in mitral cells. This transduction was mediated by a fast excitatory mechanosensitive ion channel and modulated neuronal spiking activity. In awake animals, the heartbeat entrained the activity of a subset of olfactory bulb neurons within ~20 milliseconds. Thus, we propose that this fast, intrinsic interoceptive mechanism can modulate perception-for example, during arousal-within the olfactory bulb and possibly across various other brain areas.

Hallmarks of cardiovascular ageing

Normal circulatory function is a key determinant of disease-free life expectancy (healthspan). Indeed, pathologies affecting the cardiovascular system, which are growing in prevalence, are the leading cause of global morbidity, disability and mortality, whereas the maintenance of cardiovascular health is necessary to promote both organismal healthspan and lifespan. Therefore, cardiovascular ageing might precede or even underlie body-wide, age-related health deterioration. In this Review, we posit that eight molecular hallmarks are common denominators in cardiovascular ageing, namely disabled macroautophagy, loss of proteostasis, genomic instability (in particular, clonal haematopoiesis of indeterminate potential), epigenetic alterations, mitochondrial dysfunction, cell senescence, dysregulated neurohormonal signalling and inflammation. We also propose a hierarchical order that distinguishes primary (upstream) from antagonistic and integrative (downstream) hallmarks of cardiovascular ageing. Finally, we discuss how targeting each of the eight hallmarks might be therapeutically exploited to attenuate residual cardiovascular risk in older individuals.

Cardiovascular hemodynamics in mice with tumor necrosis factor receptor-associated factor 2 mediated cytoprotection in the heart

Introduction

Many studies in mice have demonstrated that cardiac-specific innate immune signaling pathways can be reprogrammed to modulate inflammation in response to myocardial injury and improve outcomes. While the echocardiography standard parameters of left ventricular (LV) ejection fraction, fractional shortening, end-diastolic diameter, and others are used to assess cardiac function, their dependency on loading conditions somewhat limits their utility in completely reflecting the contractile function and global cardiovascular efficiency of the heart. A true measure of global cardiovascular efficiency should include the interaction between the ventricle and the aorta (ventricular-vascular coupling, VVC) as well as measures of aortic impedance and pulse wave velocity.

Methods

We measured cardiac Doppler velocities, blood pressures, along with VVC, aortic impedance, and pulse wave velocity to evaluate global cardiac function in a mouse model of cardiac-restricted low levels of TRAF2 overexpression that conferred cytoprotection in the heart.

Results

While previous studies reported that response to myocardial infarction and reperfusion was improved in the TRAF2 overexpressed mice, we found that TRAF2 mice had significantly lower cardiac systolic velocities and accelerations, diastolic atrial velocity, aortic pressures, rate-pressure product, LV contractility and relaxation, and stroke work when compared to littermate control mice. Also, we found significantly longer aortic ejection time, isovolumic contraction and relaxation times, and significantly higher mitral early/atrial ratio, myocardial performance index, and ventricular vascular coupling in the TRAF2 overexpression mice compared to their littermate controls. We found no significant differences in the aortic impedance and pulse wave velocity.

Discussion

While the reported tolerance to ischemic insults in TRAF2 overexpression mice may suggest enhanced cardiac reserve, our results indicate diminished cardiac function in these mice.

Aortic acceleration as a noninvasive index of left ventricular contractility in the mouse

The maximum value of the first derivative of the invasively measured left ventricular (LV) pressure (+ dP/dtmax or P') is often used to quantify LV contractility, which in mice is limited to a single terminal study. Thus, determination of P' in mouse longitudinal/serial studies requires a group of mice at each desired time point resulting in "pseudo" serial measurements. Alternatively, a noninvasive surrogate for P' will allow for repeated measurements on the same group of mice, thereby minimizing physiological variability and requiring fewer animals. In this study we evaluated aortic acceleration and other parameters of aortic flow velocity as noninvasive indices of LV contractility in mice. We simultaneously measured LV pressure invasively with an intravascular pressure catheter and aortic flow velocity noninvasively with a pulsed Doppler probe in mice, at baseline and after the administration of the positive inotrope, dobutamine. Regression analysis of P' versus peak aortic velocity (vp), peak velocity squared/rise time (vp2/T), peak (+ dvp/dt or v'p) and mean (+ dvm/dt or v'm) aortic acceleration showed a high degree of association (P' versus: vp, r2 = 0.77; vp2/T, r2 = 0.86; v'p, r2 = 0.80; and v'm, r2 = 0.89). The results suggest that mean or peak aortic acceleration or the other parameters may be used as a noninvasive index of LV contractility.

Autophagy in Cardiovascular Aging

Cardiovascular diseases are the most prominent maladies in aging societies. Indeed, aging promotes the structural and functional declines of both the heart and the blood circulation system. In this review, we revise the contribution of known longevity pathways to cardiovascular health and delineate the possibilities to interfere with them. In particular, we evaluate autophagy, the intracellular catabolic recycling system associated with life- and health-span extension. We present genetic models, pharmacological interventions, and dietary strategies that block, reduce, or enhance autophagy upon age-related cardiovascular deterioration. Caloric restriction or caloric restriction mimetics like metformin, spermidine, and rapamycin (all of which trigger autophagy) are among the most promising cardioprotective interventions during aging. We conclude that autophagy is a fundamental process to ensure cardiac and vascular health during aging and outline its putative therapeutic importance.

IGF-1 Deficiency Promotes Pathological Remodeling of Cerebral Arteries: A Potential Mechanism Contributing to the Pathogenesis of Intracerebral Hemorrhages in Aging

Clinical and experimental studies show that age-related decline in circulating insulin-like growth factor-1 (IGF-1) levels promotes the pathogenesis of intracerebral hemorrhages, which critically contribute to the development of vascular cognitive impairment and disability in older adults. Yet, the mechanisms by which IGF-1 deficiency compromises structural integrity of the cerebral vasculature are not completely understood. To determine the role of IGF-1 deficiency in pathological remodeling of middle cerebral arteries (MCAs), we compared alterations in vascular mechanics, morphology, and remodeling-related gene expression profile in mice with liver-specific knockdown of IGF-1 (Igf1f/f + TBG-Cre-AAV8) and control mice with or without hypertension induced by angiotensin-II treatment. We found that IGF-1 deficiency resulted in thinning of the media and decreased wall-to-lumen ratio in MCAs. MCAs of control mice exhibited structural adaptation to hypertension, manifested as a significant increase in wall thickness, vascular smooth muscle cell (VSMC) hypertrophy, decreased internal diameter and up-regulation of extracellular matrix (ECM)-related genes. IGF-1 deficiency impaired hypertension-induced adaptive media hypertrophy and dysregulated ECM remodeling, decreasing elastin content and attenuating adaptive changes in ECM-related gene expression. Thus, circulating IGF-1 plays a critical role in maintenance of the structural integrity of cerebral arteries. Alterations of VSMC phenotype and pathological remodeling of the arterial wall associated with age-related IGF-1 deficiency have important translational relevance for the pathogenesis of intracerebral hemorrhages and vascular cognitive impairment in elderly hypertensive patients.

SRC-1 Regulates Blood Pressure and Aortic Stiffness in Female Mice

Framingham Heart Study suggests that dysfunction of steroid receptor coactivator-1 may be involved in the development of hypertension. However, there is no functional evidence linking steroid receptor coactivator-1 to the regulation of blood pressure. We used immunohistochemistry to map the expression of steroid receptor coactivator-1 protein in mouse brain, especially in regions implicated in the regulation of blood pressure. Steroid receptor coactivator-1 protein was found in central amygdala, medial amygdala, supraoptic nucleus, arcuate nucleus, ventromedial, dorsomedial, paraventricular hypothalamus, and nucleus of the solitary tract. To determine the effects of steroid receptor coactivator-1 protein on cardiovascular system we measured blood pressures, blood flow velocities, echocardiographic parameters, and aortic input impedance in female steroid receptor coactivator-1 knockout mice and their wild type littermates. Steroid receptor coactivator-1 knockout mice had higher blood pressures and increased aortic stiffness when compared to female wild type littermates. Additionally, the hearts of steroid receptor coactivator-1 knockout mice seem to consume higher energy as evidenced by increased impedance and higher heart rate pressure product when compared to female wild type littermates. Our results demonstrate that steroid receptor coactivator-1 may be functionally involved in the regulation of blood pressure and aortic stiffness through the regulation of sympathetic activation in various neuronal populations.

IGF-1 deficiency in a critical period early in life influences the vascular aging phenotype in mice by altering miRNA-mediated post-transcriptional gene regulation: implications for the developmental origins of health and disease hypothesis

Epidemiological findings support the concept of Developmental Origins of Health and Disease, suggesting that early-life hormonal influences during a sensitive period of development have a fundamental impact on vascular health later in life. The endocrine changes that occur during development are highly conserved across mammalian species and include dramatic increases in circulating IGF-1 levels during adolescence. The present study was designed to characterize the effect of developmental IGF-1 deficiency on the vascular aging phenotype. To achieve that goal, early-onset endocrine IGF-1 deficiency was induced in mice by knockdown of IGF-1 in the liver using Cre-lox technology (Igf1 ^f/f mice crossed with mice expressing albumin-driven Cre recombinase). This model exhibits low-circulating IGF-1 levels during the peripubertal phase of development, which is critical for the biology of aging. Due to the emergence of miRNAs as important regulators of the vascular aging phenotype, the effect of early-life IGF-1 deficiency on miRNA expression profile in the aorta was examined in animals at 27 months of age. We found that developmental IGF-1 deficiency elicits persisting late-life changes in miRNA expression in the vasculature, which significantly differed from those in mice with adult-onset IGF-1 deficiency (TBG-Cre-AAV8-mediated knockdown of IGF-1 at 5 month of age in Igf1 ^f/f mice). Using a novel computational approach, we identified miRNA target genes that are co-expressed with IGF-1 and associate with aging and vascular pathophysiology. We found that among the predicted targets, the expression of multiple extracellular matrix-related genes, including collagen-encoding genes, were downregulated in mice with developmental IGF-1 deficiency. Collectively, IGF-1 deficiency during a critical period during early in life results in persistent changes in post-transcriptional miRNA-mediated control of genes critical targets for vascular health, which likely contribute to the deleterious late-life cardiovascular effects known to occur with developmental IGF-1 deficiency.