Whole brain irradiation-induced endothelial dysfunction in the mouse brain.

Whole brain irradiation (WBI), also known as whole brain radiation therapy (WBRT), is a well-established treatment for multiple brain metastases and as a preventive measure to reduce the risk of recurrence after surgical removal of a cerebral metastasis. However, WBI has been found to lead to a gradual decline in neurocognitive function in approximately 50% of patients who survive the treatment, significantly impacting their overall quality of life. Recent preclinical investigations have shed light on the underlying mechanisms of this adverse effect, revealing a complex cerebrovascular injury that involves the induction of cellular senescence in various components of the neurovascular unit, including endothelial cells. The emergence of cellular senescence following WBI has been implicated in the disruption of the blood-brain barrier and impairment of neurovascular coupling responses following irradiation. Building upon these findings, the present study aims to test the hypothesis that WBI-induced endothelial injury promotes endothelial dysfunction, which mimics the aging phenotype. To investigate this hypothesis, we employed a clinically relevant fractionated WBI protocol (5 Gy twice weekly for 4 weeks) on young mice. Both the WBI-treated and control mice were fitted with a cranial window, enabling the assessment of microvascular endothelial function. In order to evaluate the endothelium-dependent, NO-mediated cerebral blood flow (CBF) responses, we topically administered acetylcholine and ATP, and measured the resulting changes using laser Doppler flowmetry. We found that the increases in regional CBF induced by acetylcholine and ATP were significantly diminished in mice subjected to WBI. These findings provide additional preclinical evidence supporting the notion that WBI induces dysfunction in cerebrovascular endothelial cells, which in turn likely contributes to the detrimental long-term effects of the treatment. This endothelial dysfunction resembles an accelerated aging phenotype in the cerebrovascular system and is likely causally linked to the development of cognitive impairment. By integrating these findings with our previous results, we have deepened our understanding of the lasting consequences of WBI. Moreover, our study underscores the critical role of cerebromicrovascular health in safeguarding cognitive function over the long term. This enhanced understanding highlights the importance of prioritizing cerebromicrovascular health in the context of preserving cognitive abilities.

A role for the cystathionine-ß-synthase /H2S axis in astrocyte dysfunction in the aging brain.

Astrocytic dysfunction is central to age-related neurodegenerative diseases. However, the mechanisms leading to astrocytic dysfunction are not well understood. We identify that among the diverse cellular constituents of the brain, murine and human astrocytes are enriched in the expression of CBS. Depleting CBS in astrocytes causes mitochondrial dysfunction, increases the production of reactive oxygen species (ROS) and decreases cellular bioenergetics that can be partially rescued by exogenous H2S supplementation or by re-expressing CBS. Conversely, the CBS/H2S axis, associated protein persulfidation and proliferation are decreased in astrocytes upon oxidative stress which can be rescued by exogenous H2S supplementation. Here we reveal that in the aging brain, the CBS/H2S axis is downregulated leading to decreased protein persulfidation, together augmenting oxidative stress. Our findings uncover an important protective role of the CBS/H2S axis in astrocytes that may be disrupted in the aged brain.

Elimination of senescent cells by treatment with Navitoclax/ABT263 reverses whole brain irradiation-induced blood-brain barrier disruption in the mouse brain.

Whole brain irradiation (WBI), a commonly employed therapy for multiple brain metastases and as a prophylactic measure after cerebral metastasis resection, is associated with a progressive decline in neurocognitive function, significantly impacting the quality of life for approximately half of the surviving patients. Recent preclinical investigations have shed light on the multifaceted cerebrovascular injury mechanisms underlying this side effect of WBI. In this study, we aimed to test the hypothesis that WBI induces endothelial senescence, contributing to chronic disruption of the blood-brain barrier (BBB) and microvascular rarefaction. To accomplish this, we utilized transgenic p16-3MR mice, which enable the identification and selective elimination of senescent cells. These mice were subjected to a clinically relevant fractionated WBI protocol (5 Gy twice weekly for 4 weeks), and cranial windows were applied to both WBI-treated and control mice. Quantitative assessment of BBB permeability and capillary density was performed using two-photon microscopy at the 6-month post-irradiation time point. The presence of senescent microvascular endothelial cells was assessed by imaging flow cytometry, immunolabeling, and single-cell RNA-sequencing (scRNA-seq). WBI induced endothelial senescence, which associated with chronic BBB disruption and a trend for decreased microvascular density in the mouse cortex. In order to investigate the cause-and-effect relationship between WBI-induced senescence and microvascular injury, senescent cells were selectively removed from animals subjected to WBI treatment using Navitoclax/ABT263, a well-known senolytic drug. This intervention was carried out at the 3-month post-WBI time point. In WBI-treated mice, Navitoclax/ABT263 effectively eliminated senescent endothelial cells, which was associated with decreased BBB permeability and a trend for increased cortical capillarization. Our findings provide additional preclinical evidence that senolytic treatment approaches may be developed for prevention of the side effects of WBI.

Accelerated cerebromicrovascular senescence contributes to cognitive decline in a mouse model of paclitaxel (Taxol)-induced chemobrain.

Chemotherapy-induced cognitive impairment ("chemobrain") is a frequent side-effect in cancer survivors treated with paclitaxel (PTX). The mechanisms responsible for PTX-induced cognitive impairment remain obscure, and there are no effective treatments or prevention strategies. Here, we test the hypothesis that PTX induces endothelial senescence, which impairs microvascular function and contributes to the genesis of cognitive decline. We treated transgenic p16-3MR mice, which allows the detection and selective elimination of senescent cells, with PTX (5 mg/kg/day, 2 cycles; 5 days/cycle). PTX-treated and control mice were tested for spatial memory performance, neurovascular coupling (NVC) responses (whisker-stimulation-induced increases in cerebral blood flow), microvascular density, blood-brain barrier (BBB) permeability and the presence of senescent endothelial cells (by flow cytometry and single-cell transcriptomics) at 6 months post-treatment. PTX induced senescence in endothelial cells, which associated with microvascular rarefaction, NVC dysfunction, BBB disruption, neuroinflammation, and impaired performance on cognitive tasks. To establish a causal relationship between PTX-induced senescence and impaired microvascular functions, senescent cells were depleted from PTX-treated animals (at 3 months post-treatment) by genetic (ganciclovir) or pharmacological (treatment with the senolytic drug ABT263/Navitoclax) means. In PTX treated mice, both treatments effectively eliminated senescent endothelial cells, rescued endothelium-mediated NVC responses and BBB integrity, increased capillarization and improved cognitive performance. Our findings suggest that senolytic treatments can be a promising strategy for preventing chemotherapy-induced cognitive impairment.

Measurements of cerebral microvascular blood flow, oxygenation, and morphology in a mouse model of whole-brain irradiation-induced cognitive impairment by two-photon microscopy and optical coherence tomography: evidence for microvascular injury in the cerebral white matter.

Whole-brain irradiation (WBI, also known as whole-brain radiation therapy) is a mainstay treatment modality for patients with multiple brain metastases. It is also used as a prophylactic treatment for microscopic tumors that cannot be detected by magnetic resonance imaging. WBI induces a progressive cognitive decline in ~ 50% of the patients surviving over 6 months, significantly compromising the quality of life. There is increasing preclinical evidence that radiation-induced injury to the cerebral microvasculature and accelerated neurovascular senescence plays a central role in this side effect of WBI. To better understand this side effect, male C57BL/6 mice were first subjected to a clinically relevant protocol of fractionated WBI (5 Gy, two doses per week, for 4 weeks). Nine months post the WBI treatment, we applied two-photon microscopy and Doppler optical coherence tomography to measure capillary red-blood-cell (RBC) flux, capillary morphology, and microvascular oxygen partial pressure (PO2) in the cerebral somatosensory cortex in the awake, head-restrained, WPI-treated mice and their age-matched controls, through a cover-glass-sealed chronic cranial window. Thanks to the extended penetration depth with the fluorophore - Alexa680, measurements of capillary blood flow properties (e.g., RBC flux, speed, and linear density) in the cerebral subcortical white matter were enabled. We found that the WBI-treated mice exhibited a significantly decreased capillary RBC flux in the white matter. WBI also caused a significant reduction in capillary diameter, as well as a large (although insignificant) reduction in segment density at the deeper cortical layers (e.g., 600-700 µm), while the other morphological properties (e.g., segment length and tortuosity) were not obviously affected. In addition, we found that PO2 measured in the arterioles and venules, as well as the calculated oxygen saturation and oxygen extraction fraction, were not obviously affected by WBI. Lastly, WBI was associated with a significant increase in the erythrocyte-associated transients of PO2, while the changes of other cerebral capillary PO2 properties (e.g., capillary mean-PO2, RBC-PO2, and InterRBC-PO2) were not significant. Collectively, our findings support the notion that WBI results in persistent cerebral white matter microvascular impairment, which likely contributes to the WBI-induced brain injury and cognitive decline. Further studies are warranted to assess the WBI-induced changes in brain tissue oxygenation and malfunction of the white matter microvasculature as well.

Temporary opening of the blood-brain barrier with the nitrone compound OKN-007.

The blood-brain barrier (BBB) is usually impermeable to several drugs, which hampers treatment of various brain-related diseases/disorders. There have been several approaches to open the BBB, including intracarotid infusion of hyperosmotic concentrations of arabinose, mannitol, oleic or linoleic acids, or alkylglycerols, intravenous infusion of bradykinin B2, administration of a fragment of the ZO toxin from vibrio cholera, targeting specific components of the tight junctions (e.g. claudin-5) with siRNA or novel peptidomimetic drugs, or the use of ultrasound with microbubbles. We propose the use of a low molecular weight (MW), nitrone-type compound, OKN-007, which can temporarily open up the BBB for 1-2 hours. Gadolinium (Gd)-based compounds assessed ranged in MW from 546 (Gd-DTPA) to 465 kDa (ß-galactosidase-Gd-DOTA). We also included an albumin-based CA (albumin-Gd-DTPA-biotin) for assessment, as well as an antibody (Ab) against a neuron-specific biomarker conjugated to Gd-DOTA (anti-EphB2-Gd-DOTA). For the anti-EphB2 (goat Ab)-Gd-DOTA assessment, we utilized an anti-goat Ab conjugated with horse radish peroxidase (HRP) for confirmation of the presence of the anti-EphB2-Gd-DOTA probe. In addition, a Cy5 labeled anti-EphB2 Ab was co-administered with the anti-EphB2-Gd-DOTA probe, and assessed ex vivo. This study demonstrates that OKN-007 may be able to temporarily open up the BBB to augment the delivery of various compounds ranging in MW from as small as ~550 to as large as ~470 kDa. This compound is an investigational new drug for glioblastoma (GBM) therapy in clinical trials. The translational capability for human use to augment the delivery of non-BBB-permeable drugs is extremely high.

Treatment with the BCL-2/BCL-xL inhibitor senolytic drug ABT263/Navitoclax improves functional hyperemia in aged mice.

Moment-to-moment adjustment of regional cerebral blood flow to neuronal activity via neurovascular coupling (NVC or "functional hyperemia") has a critical role in maintenance of healthy cognitive function. Aging-induced impairment of NVC responses importantly contributes to age-related cognitive decline. Advanced aging is associated with increased prevalence of senescent cells in the cerebral microcirculation, but their role in impaired NVC responses remains unexplored. The present study was designed to test the hypothesis that a validated senolytic treatment can improve NVC responses and cognitive performance in aged mice. To achieve this goal, aged (24-month-old) C57BL/6 mice were treated with ABT263/Navitoclax, a potent senolytic agent known to eliminate senescent cells in the aged mouse brain. Mice were behaviorally evaluated (radial arms water maze) and NVC was assessed by measuring CBF responses (laser speckle contrast imaging) in the somatosensory whisker barrel cortex evoked by contralateral whisker stimulation. We found that NVC responses were significantly impaired in aged mice. ABT263/Navitoclax treatment improved NVC response, which was associated with significantly improved hippocampal-encoded functions of learning and memory. ABT263/Navitoclax treatment did not significantly affect endothelium-dependent acetylcholine-induced relaxation of aorta rings. Thus, increased presence of senescent cells in the aged brain likely contributes to age-related neurovascular uncoupling, exacerbating cognitive decline. The neurovascular protective effects of ABT263/Navitoclax treatment highlight the preventive and therapeutic potential of senolytic treatments (as monotherapy or as part of combination treatment regimens) as effective interventions in patients at risk for vascular cognitive impairment (VCI).

Whole brain irradiation in mice causes long-term impairment in astrocytic calcium signaling but preserves astrocyte-astrocyte coupling.

Whole brain irradiation (WBI) therapy is an important treatment for brain metastases and potential microscopic malignancies. WBI promotes progressive cognitive dysfunction in over half of surviving patients, yet, the underlying mechanisms remain obscure. Astrocytes play critical roles in the regulation of neuronal activity, brain metabolism, and cerebral blood flow, and while neurons are considered radioresistant, astrocytes are sensitive to γ-irradiation. Hallmarks of astrocyte function are the ability to generate stimulus-induced intercellular Ca2+ signals and to move metabolic substrates through the connected astrocyte network. We tested the hypothesis that WBI-induced cognitive impairment associates with persistent impairment of astrocytic Ca2+ signaling and/or gap junctional coupling. Mice were subjected to a clinically relevant protocol of fractionated WBI, and 12 to 15 months after irradiation, we confirmed persistent cognitive impairment compared to controls. To test the integrity of astrocyte-to-astrocyte gap junctional coupling postWBI, astrocytes were loaded with Alexa-488-hydrazide by patch-based dye infusion, and the increase of fluorescence signal in neighboring astrocyte cell bodies was assessed with 2-photon microscopy in acute slices of the sensory-motor cortex. We found that WBI did not affect astrocyte-to-astrocyte gap junctional coupling. Astrocytic Ca2+ responses induced by bath administration of phenylephrine (detected with Rhod-2/AM) were also unaltered by WBI. However, an electrical stimulation protocol used in long-term potentiation (theta burst), revealed attenuated astrocyte Ca2+ responses in the astrocyte arbor and soma in WBI. Our data show that WBI causes a long-lasting decrement in synaptic-evoked astrocyte Ca2+ signals 12-15 months postirradiation, which may be an important contributor to cognitive decline seen after WBI.

Companion animals likely do not spread COVID-19 but may get infected themselves.

Coronavirus disease 2019 (COVID-19) is a highly contagious infectious disease caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). From the epidemiological data, the picture emerges that the more severe etiopathologies among COVID-19 patients are found in elderly people. The risk of death due to COVID-19 increases exponentially with age. Eight out of 10 COVID-19 related deaths occur in people older than 65 years of age. Older patients with comorbid conditions such as hypertension, heart failure, diabetes mellitus, asthma, chronic obstructive pulmonary disease, and cancer have a much higher case fatality rate. Governments and public health authorities all over the world have realized that protections of vulnerable older adults should be a priority during the COVID-19 pandemic. COVID-19 is a zoonotic disease. The SARS-CoV-2 virus was originally transmitted likely from a bat or a pangolin to humans. Recent evidence suggests that SARS-CoV-2, similar to other coronaviruses, can infect several species of animals, including companion animals such as dogs, cats, and ferrets although their viral loads remain low. While the main source of infection transmission therefore is human to human, there are a few rare cases of pets contracting the infection from a SARS-CoV-2-infected human. Although there is no evidence that pets actively transmit SARS-CoV-2 via animal-to-human transmission, senior pet ownership potentially may pose a small risk to older adults by (1) potentially enabling animal-to-human transmission of SARS-CoV-2 in the most vulnerable population and (2) by increasing the exposition risk for the elderly due to the necessity to care for the pet and, in the case of dogs, to take them outside the house several times per day. In this overview, the available evidence on SARS-CoV-2 infection in pets is considered and the potential for spread of COVID-19 from companion animals to older individuals and the importance of prevention are discussed.

Pharmacological or genetic depletion of senescent astrocytes prevents whole brain irradiation-induced impairment of neurovascular coupling responses protecting cognitive function in mice.

Whole brain irradiation (WBI, also known as whole brain radiation therapy or WBRT) is a mainstream therapy for patients with identifiable brain metastases and as a prophylaxis for microscopic malignancies. WBI accelerates brain aging, causing progressive cognitive dysfunction in ~ 50% of surviving patients, thus compromising quality of life. The mechanisms responsible for this WBI side effect remain obscure, and there are no effective treatments or prevention strategies. Here, we test the hypothesis that WBI induces astrocyte senescence, which contributes to impaired astrocytic neurovascular coupling (NVC) responses and the genesis of cognitive decline. To achieve this goal, we used transgenic p16-3MR mice, which allows the detection and selective elimination of senescent cells. We subjected these mice to a clinically relevant protocol of fractionated WBI (5 Gy twice weekly for 4 weeks). WBI-treated and control mice were tested for spatial memory performance (radial arm water maze), astrocyte-dependent NVC responses (whisker-stimulation-induced increases in cerebral blood flow, assessed by laser speckle contrast imaging), NVC-related gene expression, astrocytic release of eicosanoid gliotransmitters and the presence of senescent astrocytes (by flow cytometry, immunohistochemistry and gene expression profiling) at 6 months post-irradiation. WBI induced senescence in astrocytes, which associated with NVC dysfunction and impaired performance on cognitive tasks. To establish a causal relationship between WBI-induced senescence and NVC dysfunction, senescent cells were depleted from WBI-treated animals (at 3 months post-WBI) by genetic (ganciclovir treatment) or pharmacological (treatment with the BCL-2/BCL-xL inhibitor ABT263/Navitoclax, a known senolytic drug) means. In WBI-treated mice, both treatments effectively eliminated senescent astrocytes, rescued NVC responses, and improved cognitive performance. Our findings suggest that the use of senolytic drugs can be a promising strategy for preventing the cognitive impairment associated with WBI.

Microvascular contributions to age-related macular degeneration (AMD): from mechanisms of choriocapillaris aging to novel interventions.

Aging of the microcirculatory network plays a central role in the pathogenesis of a wide range of age-related diseases, from heart failure to Alzheimer's disease. In the eye, changes in the choroid and choroidal microcirculation (choriocapillaris) also occur with age, and these changes can play a critical role in the pathogenesis of age-related macular degeneration (AMD). In order to develop novel treatments for amelioration of choriocapillaris aging and prevention of AMD, it is essential to understand the cellular and functional changes that occur in the choroid and choriocapillaris during aging. In this review, recent advances in in vivo analysis of choroidal structure and function in AMD patients and patients at risk for AMD are discussed. The pathophysiological roles of fundamental cellular and molecular mechanisms of aging including oxidative stress, mitochondrial dysfunction, and impaired resistance to molecular stressors in the choriocapillaris are also considered in terms of their contribution to the pathogenesis of AMD. The pathogenic roles of cardiovascular risk factors that exacerbate microvascular aging processes, such as smoking, hypertension, and obesity as they relate to AMD and choroid and choriocapillaris changes in patients with these cardiovascular risk factors, are also discussed. Finally, future directions and opportunities to develop novel interventions to prevent/delay AMD by targeting fundamental cellular and molecular aging processes are presented.

Chemically induced carcinogenesis in rodent models of aging: assessing organismal resilience to genotoxic stressors in geroscience research.

There is significant overlap between the cellular and molecular mechanisms of aging and pathways contributing to carcinogenesis, including the role of genome maintenance pathways. In the field of geroscience analysis of novel genetic mouse models with either a shortened, or an extended, lifespan provides a unique opportunity to evaluate the synergistic roles of longevity assurance pathways in cancer resistance and regulation of lifespan and to develop novel targets for interventions that both delay aging and prevent carcinogenesis. There is a growing need for robust assays to assess the susceptibility of cancer in these models. The present review focuses on a well-characterized method frequently used in cancer research, which can be adapted to study resilience to genotoxic stress and susceptibility to genotoxic stress-induced carcinogenesis in geroscience research namely, chemical carcinogenesis induced by treatment with 7,12-dimethylbenz(a)anthracene (DMBA). Recent progress in understanding how longer-living mice may achieve resistance to chemical carcinogenesis and how these pathways are modulated by anti-aging interventions is reviewed. Strain-specific differences in sensitivity to DMBA-induced carcinogenesis are also explored and contrasted with mouse lifespan. The clinical relevance of inhibition of DMBA-induced carcinogenesis for the pathogenesis of mammary adenocarcinomas in older human subjects is discussed. Finally, the potential role of insulin-like growth factor-1 (IGF-1) in the regulation of pathways responsible for cellular resilience to DMBA-induced mutagenesis is discussed.

Simultaneous assessment of cognitive function, circadian rhythm, and spontaneous activity in aging mice.

Cognitive function declines substantially with age in both humans and animal models. In humans, this decline is associated with decreases in independence and quality of life. Although the methodology for analysis of cognitive function in human models is relatively well established, similar analyses in animal models have many technical issues (e.g., unintended experimenter bias, motivational issues, stress, and testing during the light phase of the light dark cycle) that limit interpretation of the results. These caveats, and others, potentially bias the interpretation of studies in rodents and prevent the application of current tests of learning and memory as part of an overall healthspan assessment in rodent models of aging. The goal of this study was to establish the methodology to assess cognitive function in aging animals that addresses many of these concerns. Here, we use a food reward-based discrimination procedure with minimal stress in C57Bl/6J male mice at 6, 21, and 27 months of age, followed by a reversal task to assess behavioral flexibility. Importantly, the procedures minimize issues related to between-experimenter confounds and are conducted during both the dark and light phases of the light dark cycle in a home-cage setting. During cognitive testing, we were able to assess multiple measures of spontaneous movement and diurnal activity in young and aged mice including, distance moved, velocity, and acceleration over a 90-h period. Both initial discrimination and reversal learning significantly decreased with age and, similar to rats and humans, not all old mice demonstrated impairments in learning with age. These results permitted classification of animals based on their cognitive status. Analysis of movement parameters indicated decreases in distance moved as well as velocity and acceleration with increasing age. Based on these data, we developed preliminary models indicating, as in humans, a close relationship exists between age-related movement parameters and cognitive ability. Our results provide a reliable method for assessing cognitive performance with minimal stress and simultaneously provide key information on movement and diurnal activity. These methods represent a novel approach to developing non-invasive healthspan measures in rodent models that allow standardization across laboratories.

Treatment with the mitochondrial-targeted antioxidant peptide SS-31 rescues neurovascular coupling responses and cerebrovascular endothelial function and improves cognition in aged mice.

Moment-to-moment adjustment of cerebral blood flow (CBF) via neurovascular coupling has an essential role in maintenance of healthy cognitive function. In advanced age, increased oxidative stress and cerebromicrovascular endothelial dysfunction impair neurovascular coupling, likely contributing to age-related decline of higher cortical functions. There is increasing evidence showing that mitochondrial oxidative stress plays a critical role in a range of age-related cellular impairments, but its role in neurovascular uncoupling remains unexplored. This study was designed to test the hypothesis that attenuation of mitochondrial oxidative stress may exert beneficial effects on neurovascular coupling responses in aging. To test this hypothesis, 24-month-old C57BL/6 mice were treated with a cell-permeable, mitochondria-targeted antioxidant peptide (SS-31; 10 mg kg-1  day-1 , i.p.) or vehicle for 2 weeks. Neurovascular coupling was assessed by measuring CBF responses (laser speckle contrast imaging) evoked by contralateral whisker stimulation. We found that neurovascular coupling responses were significantly impaired in aged mice. Treatment with SS-31 significantly improved neurovascular coupling responses by increasing NO-mediated cerebromicrovascular dilation, which was associated with significantly improved spatial working memory, motor skill learning, and gait coordination. These findings are paralleled by the protective effects of SS-31 on mitochondrial production of reactive oxygen species and mitochondrial respiration in cultured cerebromicrovascular endothelial cells derived from aged animals. Thus, mitochondrial oxidative stress contributes to age-related cerebromicrovascular dysfunction, exacerbating cognitive decline. We propose that mitochondria-targeted antioxidants may be considered for pharmacological microvascular protection for the prevention/treatment of age-related vascular cognitive impairment (VCI).

Connective tissue growth factor (CTGF) in age-related vascular pathologies.

Connective tissue growth factor (CTGF, also known as CCN2) is a matricellular protein expressed in the vascular wall, which regulates diverse cellular functions including cell adhesion, matrix production, structural remodeling, angiogenesis, and cell proliferation and differentiation. CTGF is principally regulated at the level of transcription and is induced by mechanical stresses and a number of cytokines and growth factors, including TGFß. In this mini-review, the role of age-related dysregulation of CTGF signaling and its role in a range of macro- and microvascular pathologies, including pathogenesis of aorta aneurysms, atherogenesis, and diabetic retinopathy, are discussed. A potential role of CTGF and TGFß in regulation and non-cell autonomous propagation of cellular senescence is also discussed.

IGF-1 has sexually dimorphic, pleiotropic, and time-dependent effects on healthspan, pathology, and lifespan.

Reduced circulating levels of IGF-1 have been proposed as a conserved anti-aging mechanism that contributes to increased lifespan in diverse experimental models. However, IGF-1 has also been shown to be essential for normal development and the maintenance of tissue function late into the lifespan. These disparate findings suggest that IGF-1 may be a pleiotropic modulator of health and aging, as reductions in IGF-1 may be beneficial for one aspect of aging, but detrimental for another. We postulated that the effects of IGF-1 on tissue health and function in advanced age are dependent on the tissue, the sex of the animal, and the age at which IGF-1 is manipulated. In this study, we examined how alterations in IGF-1 levels at multiple stages of development and aging influence overall lifespan, healthspan, and pathology. Specifically, we investigated the effects of perinatal, post-pubertal, and late-adult onset IGF-1 deficiency using genetic and viral approaches in both male and female igf f/f C57Bl/6 mice. Our results support the concept that IGF-1 levels early during lifespan establish the conditions necessary for subsequent healthspan and pathological changes that contribute to aging. Nevertheless, these changes are specific for each sex and tissue. Importantly, late-life IGF-1 deficiency (a time point relevant for human studies) reduces cancer risk but does not increase lifespan. Overall, our results indicate that the levels of IGF-1 during development influence late-life pathology, suggesting that IGF-1 is a developmental driver of healthspan, pathology, and lifespan.

Cerebromicrovascular dysfunction predicts cognitive decline and gait abnormalities in a mouse model of whole brain irradiation-induced accelerated brain senescence.

Whole brain irradiation (WBI) is a mainstream therapy for patients with both identifiable brain metastases and prophylaxis for microscopic malignancies. However, it also promotes accelerated senescence in healthy tissues and leads to progressive cognitive dysfunction in up to 50% of tumor patients surviving long term after treatment, due to γ-irradiation-induced cerebromicrovascular injury. Moment-to-moment adjustment of cerebral blood flow (CBF) via neuronal activity-dependent cerebromicrovascular dilation (functional hyperemia) has a critical role in maintenance of healthy cognitive function. To determine whether cognitive decline induced by WBI associates with impaired cerebromicrovascular function, C56BL/6 mice (3 months) subjected to a clinically relevant protocol of fractionated WBI (5 Gy twice weekly for 4 weeks) and control mice were compared. Mice were tested for spatial memory performance (radial arm water maze), sensorimotor coordination (computerized gait analysis, CatWalk), and cerebromicrovascular function (whisker-stimulation-induced increases in CBF, measured by laser Doppler flowmetry) at 3 to 6 months post-irradiation. We found that mice with WBI exhibited impaired cerebromicrovascular function at 3 months post-irradiation, which was associated with impaired performance in the radial arm water maze. At 6 months, post-irradiation progressive impairment in gait coordination (including changes in the regularity index and phase dispersion) was also evident. Collectively, our findings provide evidence for early and persisting neurovascular impairment after a clinically relevant protocol of fractionated WBI, which predict early manifestations of cognitive impairment.

Association between daily walking and antioxidant capacity in patients with symptomatic peripheral artery disease.

OBJECTIVE: The primary aim of the study was to assess whether both the amount and pace of daily walking were associated with circulating antioxidant capacity in symptomatic patients with peripheral artery disease (PAD). METHODS: Community-based walking was measured in 244 men and women who were limited by symptomatic PAD during a 1-week period in which they wore an ankle-mounted step activity monitor. Patients were further characterized by circulating antioxidant capacity with the OxiSelect (Cell Biolabs Inc, San Diego, Calif) hydroxyl radical antioxidant capacity (HORAC) activity assay. RESULTS: To assess the amount of walking, patients were grouped into low (≤2440 strides/d), middle (2441-3835 strides/d), and high (>3835 strides/d) stride tertiles. HORAC was higher in the middle (P = .03) and high (P = .01) stride tertiles than in the low tertile, but there was no difference between middle and high tertiles (P = .44). To assess the pace of walking, patients were grouped into slow (<25.0 strides/min), middle (25.0-31.6 strides/min), and fast (>31.6 strides/min) cadence tertiles. HORAC was higher in the high cadence tertile than in the low (P < .01) and middle (P < .01) tertiles, but there was no difference between low and middle tertiles (P = .48). Similar findings were obtained on group differences in HORAC after adjusting for age, sex, race, and ankle-brachial index for both the amount and pace of daily walking. CONCLUSIONS: Walking >2440 strides each day and walking at a cadence faster than 31.6 strides/min for 30 minutes each day are both associated with greater circulating antioxidant capacity in symptomatic patients with PAD. The clinical significance is that a home-based walking program may be one approach to increase endogenous antioxidant capacity.

The GH/IGF-1 axis in a critical period early in life determines cellular DNA repair capacity by altering transcriptional regulation of DNA repair-related genes: implications for the developmental origins of cancer.

Experimental, clinical, and epidemiological findings support the concept of developmental origins of health and disease (DOHAD), suggesting that early-life hormonal influences during a sensitive period around adolescence have a powerful impact on cancer morbidity later in life. The endocrine changes that occur during puberty are highly conserved across mammalian species and include dramatic increases in circulating GH and IGF-1 levels. Importantly, patients with developmental IGF-1 deficiency due to GH insensitivity (Laron syndrome) do not develop cancer during aging. Rodents with developmental GH/IGF-1 deficiency also exhibit significantly decreased cancer incidence at old age, marked resistance to chemically induced carcinogenesis, and cellular resistance to genotoxic stressors. Early-life treatment of GH/IGF-1-deficient mice and rats with GH reverses the cancer resistance phenotype; however, the underlying molecular mechanisms remain elusive. The present study was designed to test the hypothesis that developmental GH/IGF-1 status impacts cellular DNA repair mechanisms. To achieve that goal, we assessed repair of γ-irradiation-induced DNA damage (single-cell gel electrophoresis/comet assay) and basal and post-irradiation expression of DNA repair-related genes (qPCR) in primary fibroblasts derived from control rats, Lewis dwarf rats (a model of developmental GH/IGF-1 deficiency), and GH-replete dwarf rats (GH administered beginning at 5 weeks of age, for 30 days). We found that developmental GH/IGF-1 deficiency resulted in persisting increases in cellular DNA repair capacity and upregulation of several DNA repair-related genes (e.g., Gadd45a, Bbc3). Peripubertal GH treatment reversed the radiation resistance phenotype. Fibroblasts of GH/IGF-1-deficient Snell dwarf mice also exhibited improved DNA repair capacity, showing that the persisting influence of peripubertal GH/IGF-1 status is not species-dependent. Collectively, GH/IGF-1 levels during a critical period during early life determine cellular DNA repair capacity in rodents, presumably by transcriptional control of genes involved in DNA repair. Because lifestyle factors (e.g., nutrition and childhood obesity) cause huge variation in peripubertal GH/IGF-1 levels in children, further studies are warranted to determine their persisting influence on cellular cancer resistance pathways.

Circulating IGF-1 deficiency exacerbates hypertension-induced microvascular rarefaction in the mouse hippocampus and retrosplenial cortex: implications for cerebromicrovascular and brain aging.

Strong epidemiological and experimental evidence indicate that both age and hypertension lead to significant functional and structural impairment of the cerebral microcirculation, predisposing to the development of vascular cognitive impairment (VCI) and Alzheimer's disease. Preclinical studies establish a causal link between cognitive decline and microvascular rarefaction in the hippocampus, an area of brain important for learning and memory. Age-related decline in circulating IGF-1 levels results in functional impairment of the cerebral microvessels; however, the mechanistic role of IGF-1 deficiency in impaired hippocampal microvascularization remains elusive. The present study was designed to characterize the additive/synergistic effects of IGF-1 deficiency and hypertension on microvascular density and expression of genes involved in angiogenesis and microvascular regression in the hippocampus. To achieve that goal, we induced hypertension in control and IGF-1 deficient mice (Igf1 f/f  + TBG-Cre-AAV8) by chronic infusion of angiotensin II. We found that circulating IGF-1 deficiency is associated with decreased microvascular density and exacerbates hypertension-induced microvascular rarefaction both in the hippocampus and the neocortex. The anti-angiogenic hippocampal gene expression signature observed in hypertensive IGF-1 deficient mice in the present study provides important clues for subsequent studies to elucidate mechanisms by which hypertension may contribute to the pathogenesis and clinical manifestation of VCI. In conclusion, adult-onset, isolated endocrine IGF-1 deficiency exerts deleterious effects on the cerebral microcirculation, leading to a significant decline in cortical and hippocampal capillarity and exacerbating hypertension-induced cerebromicrovascular rarefaction. The morphological impairment of the cerebral microvasculature induced by IGF-1 deficiency and hypertension reported here, in combination with neurovascular uncoupling, increased blood-brain barrier disruption and neuroinflammation reported in previous studies likely contribute to the pathogenesis of vascular cognitive impairment in elderly hypertensive humans.