Altered pericyte-endothelial relations in the rat retina during aging: implications for vessel stability

Single-cell RNA sequencing analysis of the retina under acute high intraocular pressure

JOURNAL/nrgr/04.03/01300535-202419110-00032/figure1/v/2024-03-08T184507Z/r/image-tiff High intraocular pressure causes retinal ganglion cell injury in primary and secondary glaucoma diseases, yet the molecular landscape characteristics of retinal cells under high intraocular pressure remain unknown. Rat models of acute hypertension ocular pressure were established by injection of cross-linked hyaluronic acid hydrogel (Healaflow®). Single-cell RNA sequencing was then used to describe the cellular composition and molecular profile of the retina following high intraocular pressure. Our results identified a total of 12 cell types, namely retinal pigment epithelial cells, rod-photoreceptor cells, bipolar cells, Müller cells, microglia, cone-photoreceptor cells, retinal ganglion cells, endothelial cells, retinal progenitor cells, oligodendrocytes, pericytes, and fibroblasts. The single-cell RNA sequencing analysis of the retina under acute high intraocular pressure revealed obvious changes in the proportions of various retinal cells, with ganglion cells decreased by 23%. Hematoxylin and eosin staining and TUNEL staining confirmed the damage to retinal ganglion cells under high intraocular pressure. We extracted data from retinal ganglion cells and analyzed the retinal ganglion cell cluster with the most distinct expression. We found upregulation of the B3gat2 gene, which is associated with neuronal migration and adhesion, and downregulation of the Tsc22d gene, which participates in inhibition of inflammation. This study is the first to reveal molecular changes and intercellular interactions in the retina under high intraocular pressure. These data contribute to understanding of the molecular mechanism of retinal injury induced by high intraocular pressure and will benefit the development of novel therapies.

Ultrasound Modulates Calcium Activity in Cultured Neurons, Glial Cells, Endothelial Cells and Pericytes

OBJECTIVE

Ultrasound is being researched as a method to modulate the brain. Studies of the interaction of sound with neurons support the hypothesis that mechanosensitive ion channels play an important role in ultrasound neuromodulation. The response of cells other than neurons (e.g., astrocytes, pericytes and endothelial cells) have not been fully characterized, despite playing an important role in brain function.

METHODS

To address this gap in knowledge, we examined cultured murine primary cortical neurons, astrocytes, endothelial cells and pericytes in an in vitro widefield microscopy setup during application of a 500 ms burst of 250 kHz focused ultrasound over a pressure range known to elicit neuromodulation. We examined cell membrane health in response to a range of pulses and used optical calcium indicators in conjunction with pharmacological antagonists to selectively block different groups of thermo- and mechanosensitive ion channels known to be responsive to ultrasound.

RESULTS

All cell types experienced an increase in calcium fluorescence in response to ultrasound. Gadolinium (Gad), 2-aminoethoxydiphenyl borate (2-APB) and ruthenium red (RR) reduced the percentage of responding neurons and magnitude of response. The percentage of astrocytes responding was significantly lowered only by Gad, whereas both 2-APB and Gad decreased the amplitude of the fluorescence response. 2-APB decreased the percentage of responding endothelial cells, whereas only Gad reduced the magnitude of responses. Pericytes exposed to RR or Gad were less likely to respond to stimulation. RR had no detectable effect on the magnitude of the pericyte responses while 2-APB and Gad significantly decreased the fluorescence intensity, despite not affecting the percentage responding.

CONCLUSION

Our study highlights the role of non-neuronal cells during FUS neuromodulation. All of the investigated cell types are sensitive to mechanical ultrasound stimulation and rely on mechanosensitive ion channels to undergo ultrasound neuromodulation.

The stromal microenvironment and ovarian aging: mechanisms and therapeutic opportunities

For decades, most studies of ovarian aging have focused on its functional units, known as follicles, which include oocytes and granulosa cells. However, in the ovarian stroma, there are a variety of somatic components that bridge the gap between general aging and ovarian senescence. Physiologically, general cell types, microvascular structures, extracellular matrix, and intercellular molecules affect folliculogenesis and corpus luteum physiology alongside the ovarian cycle. As a result of damage caused by age-related metabolite accumulation and external insults, the microenvironment of stromal cells is progressively remodeled, thus inevitably perturbing ovarian physiology. With the established platforms for follicle cryopreservation and in vitro maturation and the development of organoid research, it is desirable to develop strategies to improve the microenvironment of the follicle by targeting the perifollicular environment. In this review, we summarize the role of stromal components in ovarian aging, describing their age-related alterations and associated effects. Moreover, we list some potential techniques that may mitigate ovarian aging based on their effect on the stromal microenvironment.

Pericyte dysfunction is a key mediator of the risk of cerebral ischemia

Pericytes are critical yet understudied cells that are a central component of the neurovascular unit. They are connected to the cerebrovascular endothelium and help control vascular contractility and maintain the blood-brain barrier. Pericyte dysfunction has the potential to mediate many of the deleterious vascular consequences of ischemic stroke. Current therapeutics are designed to be administered after stroke onset and limit damage, but there are few options to target vascular risk factors pre-ischemia which likely contribute to stroke outcomes. Here, we focus on the role of pericytes in health and disease, and discuss how pericyte dysfunction can increase the risk of ischemic injury. Additionally, we note that despite the importance of pericytes in cerebrovascular disease, there are relatively few current therapeutic options that target pericyte function.

Retinal gliosis and phenotypic diversity of intermediate filament induction and remodeling upon acoustic blast overpressure (ABO) exposure to the rat eye

Traumatic brain injury (TBI) caused by acoustic blast overpressure (ABO) is frequently associated with chronic visual deficits in military personnel and civilians. In this study, we characterized retinal gliotic response in adult male rats following a single ABO exposure directed to one side of the head. Expression of gliosis markers and intermediate filaments was assessed at 48 h and 1 wk post-ABO exposure, in comparison to age-matched non-exposed control retina. In response to a single ABO exposure, type III IF, glial fibrillary acidic protein (GFAP) was variably induced in a subpopulation of retinal Müller glia in ipsilateral eyes. ABO-exposed eyes exhibited radial Müller glial GFAP filament extension through the inner plexiform layer (IPL) and the inner nuclear layer (INL) through the retina in both the nasal quadrant and juxta-optic nerve head (jONH) eye regions at 1 wk post-ABO. We observed an ∼6-fold increase (p ≤ 0.05) in radial glial GFAP immunolabeling in the IPL in both eye regions, in comparison to regionally matched controls. Similarly, GFAP extension through the INL into the outer retina was elevated ∼3-fold, p ≤ 0.05 in the nasal retina, but exhibited wider variability in the jONH retina. In contrast, constitutive type III IF vimentin exhibited greater remodeling in retinal Müller glia through the jONH retina compared to the nasal retina in response to ABO. We observed areas of lateral vimentin remodeling through the Müller glial end-feet, and greater mid-outer retinal radial vimentin IF extension in a subpopulation of glia at 1 wk post-ABO. We also observed a significant increase in total retinal levels of the type III IF desmin in ABO-exposed retina vs. controls (∼1.6-fold, p ≤ 0.01). In addition, ABO-exposure elicited varied glial induction of developmentally regulated type VI family IFs (nestin and synemin) in subpopulations of Müller cells at 48 h and 1 wk post-ABO. We demonstrate that multiple glial phenotypes emerge in the rat retina following a single ABO exposure, rather than a global homogeneous retinal glial response, involving less well characterized IF protein forms which warrant further investigation in the context of ABO-induced retinal gliosis.

Impaired angiogenesis in ageing: the central role of the extracellular matrix

Each step in angiogenesis is regulated by the extracellular matrix (ECM). Accumulating evidence indicates that ageing-related changes in the ECM driven by cellular senescence lead to a reduction in neovascularisation, reduced microvascular density, and an increased risk of tissue ischaemic injury. These changes can lead to health events that have major negative impacts on quality of life and place a significant financial burden on the healthcare system. Elucidating interactions between the ECM and cells during angiogenesis in the context of ageing is neceary to clarify the mechanisms underlying reduced angiogenesis in older adults. In this review, we summarize ageing-related changes in the composition, structure, and function of the ECM and their relevance for angiogenesis. Then, we explore in detail the mechanisms of interaction between the aged ECM and cells during impaired angiogenesis in the older population for the first time, discussing diseases caused by restricted angiogenesis. We also outline several novel pro-angiogenic therapeutic strategies targeting the ECM that can provide new insights into the choice of appropriate treatments for a variety of age-related diseases. Based on the knowledge gathered from recent reports and journal articles, we provide a better understanding of the mechanisms underlying impaired angiogenesis with age and contribute to the development of effective treatments that will enhance quality of life.

An Altered Neurovascular System in Aging-Related Eye Diseases

The eye has a complex and metabolically active neurovascular system. Repeated light injuries induce aging and trigger age-dependent eye diseases. Damage to blood vessels is related to the disruption of the blood-retinal barrier (BRB), altered cellular communication, disrupted mitochondrial functions, and exacerbated aggregated protein accumulation. Vascular complications, such as insufficient blood supply and BRB disruption, have been suggested to play a role in glaucoma, age-related macular degeneration (AMD), and Alzheimer's disease (AD), resulting in neuronal cell death. Neuronal loss can induce vision loss. In this review, we discuss the importance of the neurovascular system in the eye, especially in aging-related diseases such as glaucoma, AMD, and AD. Beneficial molecular pathways to prevent or slow down retinal pathologic processes will also be discussed.

cGMP Signaling in the Neurovascular Unit—Implications for Retinal Ganglion Cell Survival in Glaucoma

Glaucoma is a progressive age-related disease of the visual system and the leading cause of irreversible blindness worldwide. Currently, intraocular pressure (IOP) is the only modifiable risk factor for the disease, but even as IOP is lowered, the pathology of the disease often progresses. Hence, effective clinical targets for the treatment of glaucoma remain elusive. Glaucoma shares comorbidities with a multitude of vascular diseases, and evidence in humans and animal models demonstrates an association between vascular dysfunction of the retina and glaucoma pathology. Integral to the survival of retinal ganglion cells (RGCs) is functional neurovascular coupling (NVC), providing RGCs with metabolic support in response to neuronal activity. NVC is mediated by cells of the neurovascular unit (NVU), which include vascular cells, glial cells, and neurons. Nitric oxide-cyclic guanosine monophosphate (NO-cGMP) signaling is a prime mediator of NVC between endothelial cells and neurons, but emerging evidence suggests that cGMP signaling is also important in the physiology of other cells of the NVU. NO-cGMP signaling has been implicated in glaucomatous neurodegeneration in humans and mice. In this review, we explore the role of cGMP signaling in the different cell types of the NVU and investigate the potential links between cGMP signaling, breakdown of neurovascular function, and glaucoma pathology.

Pathological changes within the cerebral vasculature in Alzheimer's disease: New perspectives

Cerebrovascular disease underpins vascular dementia (VaD), but structural and functional changes to the cerebral vasculature contribute to disease pathology and cognitive decline in Alzheimer's disease (AD). In this review, we discuss the contribution of cerebral amyloid angiopathy and non‐amyloid small vessel disease in AD, and the accompanying changes to the density, maintenance and remodelling of vessels (including alterations to the composition and function of the cerebrovascular basement membrane). We consider how abnormalities of the constituent cells of the neurovascular unit – particularly of endothelial cells and pericytes – and impairment of the blood‐brain barrier (BBB) impact on the pathogenesis of AD. We also discuss how changes to the cerebral vasculature are likely to impair Aβ clearance – both intra‐periarteriolar drainage (IPAD) and transport of Aβ peptides across the BBB, and how impaired neurovascular coupling and reduced blood flow in relation to metabolic demand increase amyloidogenic processing of APP and the production of Aβ. We review the vasoactive properties of Aβ peptides themselves, and the probable bi‐directional relationship between vascular dysfunction and Aβ accumulation in AD. Lastly, we discuss recent methodological advances in transcriptomics and imaging that have provided novel insights into vascular changes in AD, and recent advances in assessment of the retina that allow in vivo detection of vascular changes in the early stages of AD.

Evaluation of Macular Retinal Vessels and Histological Changes in Two Cases of COVID-19

The purpose of this study was to assess vascular and histological alterations in two COVID-19 and three control post-mortem retinas. The macular areas of flat-mounted samples were processed for immunofluorescence. Lectin and collagen IV positive vessels were captured under confocal microscopy, and endothelium loss and tortuosity were analyzed. Expression of ACE2 (angiotensin-converting enzyme 2) (the receptor for SARS-CoV-2), Iba1 (ionized calcium-binding adaptor molecule 1) and GFAP (glial fibrillary acidic protein) were quantified in retinal sections. The number of lectin vessels in COVID-19 retinas decreased by 27% compared to the control (p < 0.01) and the tortuosity increased in COVID-19 retinas (7.3 ± 0.2) vs. control retinas (6.8 ± 0.07) (p < 0.05). Immunofluorescence analysis revealed an increase in ACE2 (2.3 ± 1.3 vs. 1.0 ± 0.1; p < 0.0001) and Iba1 expression (3.06 ± 0.6 vs. 1.0 ± 0.1; p < 0.01) in COVID-19 sections whereas no changes in GFAP were observed. Analysis of the COVID-19 macular retinal tissue suggested that endothelial cells are a preferential target of SARS-CoV-2 with subsequent changes through their ACE2 receptor expression and morphology. Thus, microglial activation was hyperactive when facing an ensuing immunological challenge after SARS-CoV-2 infection.

Aging of the human choriocapillaris: Evidence that early pericyte damage can trigger endothelial changes

The choriocapillaris (CC), the capillary bed in the choroid, essentially nourishes the photoreceptor cells. Its damage in aging and age-related diseases significantly influences the survival of the photoreceptor cells. Earlier reports implicated endothelial loss in aged and diseased CC; however, age-related pericyte changes and their contribution in CC death remain unknown. We examined human donor eyes (age: 56-94 years; N = 24), and found that CC pericyte damage preceded endothelial changes. With aging (>70 years), the sub-macular choroid accumulated debris in Bruch's membrane (BM). Of the debris content, the long-spaced collagens had a tendency to settle over the capillary basal lamina (BL), and this often resulted in endothelial projection into capillary lumen. Between 75 and 83 years, pericytes contained dark mitochondria, and their processes facing the BM debris showed partial loss of BL and intermediate filaments (IFs), when the endothelium remained unaltered. The endothelial changes appeared beyond 83 years, the abundance of IFs and autophagy reinforced their survival until late aging. TUNEL⁺ pericytes, and immunoreactivity to carboxymethyl lysine and 4-hydroxy 2-nonenal, but no nitro-tyrosine, was detected in aged CC walls. Iba-1⁺ dystrophic microglia were present in the vicinity of the CC. Our data indicate that (1) BM debris exerts pressure on the CC, leading to the damage of the capillary BL and pericyte processes (2) loss of IFs results in early pericyte destabilization (3) capillary wall undergoes lipid peroxidative and glycative damage, and (4) pericyte damage leads to late endothelial changes and ultimately CC loss. Future research should explore the normal ways of pericyte maintenance in the aging nervous system.

Blood-Brain Barrier Breakdown: An Emerging Biomarker of Cognitive Impairment in Normal Aging and Dementia

The blood–brain barrier (BBB) plays a vital role in maintaining the specialized microenvironment of the neural tissue. It separates the peripheral circulatory system from the brain parenchyma while facilitating communication. Alterations in the distinct physiological properties of the BBB lead to BBB breakdown associated with normal aging and various neurodegenerative diseases. In this review, we first briefly discuss the aging process, then review the phenotypes and mechanisms of BBB breakdown associated with normal aging that further cause neurodegeneration and cognitive impairments. We also summarize dementia such as Alzheimer's disease (AD) and vascular dementia (VaD) and subsequently discuss the phenotypes and mechanisms of BBB disruption in dementia correlated with cognition decline. Overlaps between AD and VaD are also discussed. Techniques that could identify biomarkers associated with BBB breakdown are briefly summarized. Finally, we concluded that BBB breakdown could be used as an emerging biomarker to assist to diagnose cognitive impairment associated with normal aging and dementia.

Systemic cell therapy for muscular dystrophies : The ultimate transplantable muscle progenitor cell and current challenges for clinical efficacy

The intrinsic regenerative capacity of skeletal muscle makes it an excellent target for cell therapy. However, the potential of muscle tissue to renew is typically exhausted and insufficient in muscular dystrophies (MDs), a large group of heterogeneous genetic disorders showing progressive loss of skeletal muscle fibers. Cell therapy for MDs has to rely on suppletion with donor cells with high myogenic regenerative capacity. Here, we provide an overview on stem cell lineages employed for strategies in MDs, with a focus on adult stem cells and progenitor cells resident in skeletal muscle. In the early days, the potential of myoblasts and satellite cells was explored, but after disappointing clinical results the field moved to other muscle progenitor cells, each with its own advantages and disadvantages. Most recently, mesoangioblasts and pericytes have been pursued for muscle cell therapy, leading to a handful of preclinical studies and a clinical trial. The current status of (pre)clinical work for the most common forms of MD illustrates the existing challenges and bottlenecks. Besides the intrinsic properties of transplantable cells, we discuss issues relating to cell expansion and cell viability after transplantation, optimal dosage, and route and timing of administration. Since MDs are genetic conditions, autologous cell therapy and gene therapy will need to go hand-in-hand, bringing in additional complications. Finally, we discuss determinants for optimization of future clinical trials for muscle cell therapy. Joined research efforts bring hope that effective therapies for MDs are on the horizon to fulfil the unmet clinical need in patients.

Lamina Cribrosa Capillaries Straighten as Intraocular Pressure Increases

Purpose

The purpose of this study was to visualize the lamina cribrosa (LC) capillaries and collagenous beams, measure capillary tortuosity (path length over straight end-to-end length), and determine if capillary tortuosity changes when intraocular pressure (IOP) increases.

Methods

Within 8 hours of sacrifice, 3 pig heads were cannulated via the external ophthalmic artery, perfused with PBS to remove blood, and then perfused with a fluorescent dye to label the capillaries. The posterior pole of each eye was mounted in a custom-made inflation chamber for control of IOP with simultaneous imaging. Capillaries and collagen beams were visualized with structured light illumination enhanced imaging at IOPs from 5 to 50 mm Hg at each 5 mm Hg increment. Capillary tortuosity was measured from the images and paired two-sample t-tests were used to assess for significant changes in relation to changes in IOP.

Results

Capillaries were highly tortuous at 15 mm Hg (up to 1.45). In all but one eye, tortuosity decreased significantly as IOP increased from 15 to 25 mm Hg (P < 0.01), and tortuosity decreased significantly in every eye as IOP increased from 15 to 40 mm Hg (P < 0.01). In only 16% of capillaries, tortuosity increased with elevated IOP. Capillaries had a surprisingly different topology from the collagen beams.

Conclusions

Although high capillary tortuosity is sometimes regarded as potentially problematic because it can reduce blood flow, LC capillary tortuosity may provide slack that mitigates against reduced flow and structural damage caused by excessive stretch under elevated IOP. We speculate that low capillary tortuosity could be a risk factor for damage under high IOP.

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.

OCT angiography metrics predict intradialytic hypotension episodes in chronic hemodialysis patients: a pilot, prospective study

In chronic hemodialysis (HD) patients, intradialytic hypotension (IDH) is a complication that increases mortality risk. We run a pilot study to analyzing possible relationships between optical coherence tomography angiography (OCT-A) metrics and IDH with the aim of evaluating if OCT-A could represent a useful tool to stratify the hypotensive risk in dialysis patients. A total of 35 eyes (35 patients) were analyzed. OCT-A was performed before and after a single dialysis session. We performed OCT-A 3 × 3 mm and 6 × 6 mm scanning area focused on the fovea centralis. Patients were then followed up to 30 days (10 HD sessions) and a total of 73 IDHs were recorded, with 12 patients (60%) experiencing at least one IDH. Different OCT-A parameters were reduced after dialysis: central choroid thickness (CCT), 6 × 6 mm foveal whole vessel density (VD) of superficial capillary plexus (SPC) and 6 × 6 mm foveal VD of deep capillary plexus (DCP). At logistic regression analysis, IDH was positively associated with baseline foveal VD of SCP and DCP, while an inverse association was found with the choroid. In Kaplan–Meier analyses of patients categorized according to the ROC-derived optimal thresholds, CCT, the 3 × 3 foveal VD of SCP, the 3 × 3 mm and 6 × 6 mm foveal VD of DCP and the 6 × 6 mm foveal VD of SCP were strongly associated with a higher risk of IDH over the 30-days follow-up. In HD patients, a single OCT-A measurement may represent a non-invasive, rapid tool to evaluate the compliance of vascular bed to HD stress and to stratify the risk of IDH in the short term.

Pericytes Across the Lifetime in the Central Nervous System

The pericyte is a perivascular cell type that encapsulates the microvasculature of the brain and spinal cord. Pericytes play a crucial role in the development and maintenance of the blood-brain barrier (BBB) and have a multitude of important functions in the brain. Recent evidence indicates that pericyte impairment has been implicated in neurovascular pathology associated with various human diseases such as diabetes mellitus, Alzheimer's disease (AD), and stroke. Although the pericyte is essential for normal brain function, knowledge about its developmental trajectory and anatomical distribution is limited. This review article summarizes the scientific community's current understanding of pericytes' regional heterogeneity in the brain and their changes during major life stages. More specifically, this review article focuses on pericyte differentiation and migration during brain development, regional population differences in the adult brain, and changes during normal and pathological aging. Most of what is known about pericytes come from studies of the cerebral cortex and hippocampus. Therefore, we highlight the need to expand our understanding of pericyte distribution and function in the whole brain to better delineate this cell type's role in the normal brain and pathological conditions.

Age as a determinant of inflammatory response and survival of glia and axons after human traumatic spinal cord injury

Despite the shift in the demographics of traumatic spinal cord injury (SCI) with increased proportion of injuries in the elderly, little is known on the potential effects of old age on the pathobiology of SCI. Since there is an assumption that age adversely affects neural response to SCI, this study examines the clinically relevant question on whether age is a key determinant of inflammatory response, oligodendroglial apoptosis and axonal survival after traumatic SCI. This unique study includes post-mortem spinal cord tissue from 64 cases of SCI (at cervical or high-thoracic levels) and 38 control cases without CNS injury. Each group was subdivided into subgroups of younger and elderly individuals (65 years of age or older at the SCI onset). The results of this study indicate that age at the SCI onset does not adversely affect the cellular inflammatory response to, oligodendroglial apoptosis and axonal survival after SCI. These results support the conclusion that elderly individuals have similar neurobiological responses to SCI as younger people and, hence, treatment decisions should be based on an assessment of the individual patient and not an arbitrary assumption that "advanced age" should exclude patients with an acute SCI from access to advanced care and translational therapies.

Retinal Vascular Pathology in a Rat Model of Cerebral Small Vessel Disease

Introduction: The initial disease stages of hypertensive arteriopathy (HA) and cerebral amyloid angiopathy (CAA), the two main forms of sporadic human cerebral small vessel diseases (CSVD), are too subtle to be detectable on clinical routine imaging. Small vessel disease (SVD) is a systemic condition, affecting not only the brain, but also other organs. The retina appears as an ideal marker for the early detection of incipient CSVD. We therefore investigated the retinal microvasculature of the spontaneously hypertensive stroke-prone rat (SHRSP), an animal model of sporadic CSVD.

Materials and Methods: The brains and retinas of 26 male SHRSP (18–44 weeks) were examined histologically and immunohistochemically for the presence of HA phenomena (erythrocyte thrombi, small perivascular bleeds) and amyloid angiopathy (AA).

Results: CAA and AA in the retina showed a significant correlation with age (CAA: rho = 0.55, p = 0.005; AA: rho = 0.89, p < 0.001). The number of erythrocyte thrombi in the brain correlated with the severity of retinal erythrocyte thrombi (rho = 0.46, p = 0.023), while the occurrence of CAA correlated with the appearance of AA in the retina (rho = 0.51, p = 0.012). Retinal SVD markers predicted CSVD markers with good sensitivity.

Conclusions: These results indicate that SVD also occurs in the retinal microvasculature of SHRSP and the prediction of cerebral erythrocyte thrombi and CAA might be possible using retinal biomarkers. This underlines the important role of the investigation of the retina in the early diagnosis of CSVD.

The Neurovascular Unit in Glaucomatous Neurodegeneration

Glaucoma is a neurodegenerative disease of the visual system and leading cause of blindness worldwide. The disease is associated with sensitivity to intraocular pressure (IOP), which over a large range of magnitudes stresses retinal ganglion cell (RGC) axons as they pass through the optic nerve head in forming the optic projection to the brain. Despite clinical efforts to lower IOP, which is the only modifiable risk factor for glaucoma, RGC degeneration and ensuing loss of vision often persist. A major contributor to failure of hypotensive regimens is the multifactorial nature of how IOP-dependent stress influences RGC physiology and structure. This stress is conveyed to the RGC axon through interactions with structural, glial, and vascular components in the nerve head and retina. These interactions promote pro-degenerative pathways involving biomechanical, metabolic, oxidative, inflammatory, immunological and vascular challenges to the microenvironment of the ganglion cell and its axon. Here, we focus on the contribution of vascular dysfunction and breakdown of neurovascular coupling in glaucoma. The vascular networks of the retina and optic nerve head have evolved complex mechanisms that help to maintain a continuous blood flow and supply of metabolites despite fluctuations in ocular perfusion pressure. In healthy tissue, autoregulation and neurovascular coupling enable blood flow to stay tightly controlled. In glaucoma patients evidence suggests these pathways are dysfunctional, thus highlighting a potential role for pathways involved in vascular dysfunction in progression and as targets for novel therapeutic intervention.

Microglial changes in the early aging stage in a healthy retina and an experimental glaucoma model

Glaucoma is an age-related neurodegenerative disease that begins at the onset of aging. In this disease, there is an involvement of the immune system and therefore of the microglia. The purpose of this study is to evaluate the microglial activation using a mouse model of ocular hypertension (OHT) at the onset of aging. For this purpose, we used both naive and ocular hypertensives of 15-month-old mice (early stage of aging). In the latter, we analyzed the OHT eyes and the eyes contralateral to them to compare them with their aged controls. In the eyes of aged naive, aged OHT and aged contralateral eyes, microglial changes were observed compared to the young mice, including: (i) aged naive vs young naive: An increased soma size and vertical processes; (ii) aged OHT eyes vs young OHT eyes: A decrease in the area of the retina occupied by Iba-1 cells and in vertical processes; and (iii) aged contralateral vs young contralateral: A decrease in the soma size and arbor area and an increase in the number of microglia in the outer segment layer. Aged OHT eyes and the eyes contralateral to them showed an up-regulation of the CD68 expression in the branched microglia and a down-regulation in the MHCII and P2RY12 expression with respect to the eyes of young OHT mice. Conclusion: in the early phase of aging, morphological microglial changes along with changes in the expression of MHCII, CD68 and P2RY12, in both naive and OHT mice. These changes appear in aged OHT eyes and the eyes contralateral to them eyes.

Research advances in pericyte function and their roles in diseases

Pericyte, a kind of pluripotent cell, may regulate the irrigation flow and permeability of microcirculation. Pericytes are similar to the smooth muscle cells, which express several kinds of contractile proteins and have contractility. The dysfunction of pericytes is related to many microvascular diseases, including hypoxia, hypertension, diabetic retinopathy, fibrosis, inflammation, Alzheimer's disease, multiple sclerosis, and tumor formation. For a long time, their existence and function have been neglected. The distribution, structure, biomarker, related signaling pathways as well as the roles of pericytes on vascular diseases will be introduced in this review.

Age-related changes in retrobulbar circulation: a literature review

Introduction

The advances in research methods used in ophthalmology allow for an increasingly accurate examination of the eyes, as well as the morphology and function of the vessels. Colour Doppler imaging is still the first-line method for the analysis of parameters of retrobulbar circulation. Therefore, the aim of this work was to present the current state of knowledge about anatomical and functional age-related changes in retrobulbar arteries.

Methods

A literature search was performed mainly based on the PubMed database.

Results

The anatomy of retrobulbar arteries, histological background of age-related vascular changes, age-related changes in retrobulbar blood flow in the ophthalmic artery, central retinal artery, short posterior ciliary arteries, and the reference values for the age-dependent retrobulbar circulation parameters measured by colour Doppler imaging are discussed in this review.

Conclusion

The age of the subject should always be taken into account when interpreting the parameters of retrobulbar blood flow measured by colour Doppler imaging.

Optical Coherence Tomography Angiography in Mice: Quantitative Analysis After Experimental Models of Retinal Damage

Purpose

We implemented optical coherence tomography angiography (OCT-A) in mice to: (1) develop quantitative parameters from OCT-A images, (2) measure the reproducibility of the parameters, and (3) determine the impact of experimental models of inner and outer retinal damage on OCT-A findings.

Methods

OCT-A images were acquired with a customized system (Spectralis Multiline OCT2). To assess reproducibility, imaging was performed five times over 1 month. Inner retinal damage was induced with optic nerve transection, crush, or intravitreal N-methyl-d-aspartic acid injection in transgenic mice with fluorescently labeled retinal ganglion cells (RGCs). Light-induced retinal damage was induced in albino mice. Mice were imaged at baseline and serially post injury. Perfusion density, vessel length, and branch points were computed from OCT-A images of the superficial, intermediate, and deep vascular plexuses.

Results

The range of relative differences measured between sessions across the vascular plexuses were: perfusion density (2.8%-7.0%), vessel length (1.9%-4.1%), and branch points (1.9%-5.0%). In mice with progressive RGC loss, imaged serially and culminating in around 70% loss in the fluorescence signal and 18% loss in inner retinal thickness, there were no measurable changes in any OCT-A parameter up to 4 months post injury that exceeded measurement variability. However, light-induced retinal damage elicited a progressive loss of the deep vascular plexus signal, starting as early as 3 days post injury.

Conclusions

Vessel length and branch points were generally the most reproducible among the parameters. Injury causing RGC loss in mice did not elicit an early change in the OCT-A signal.

Novel morphometric analysis of higher order structure of human radial peri-papillary capillaries: relevance to retinal perfusion efficiency and age

We apply novel analyses to images of superficial capillaries that are located near and around the optic disc of the human retina: the radial peri-papillary capillaries (RPCs). Due to their unique perfusion of the nerve fibre layer the RPCs are particularly significant for optic-neuropathies. The inputs to the analysis were z-stacks from 3D confocal fluorescence microscopy from 62 human retinas aged 9 to 84 years. Our aim was to find morphometric correlates of age. The retinas had no ophthalmic history. The analysis was undertaken in two stages: (1) converting the z-stacks to 3D tubular networks of vessels, and (2) characterizing the tubular networks using features derived from the Minkowski functionals (MFs). The MFs measure: the capillary volume, surface area, mean breadth, and Euler number. The mean breadth is related to tortuosity, wall shear stress and resistance to flow, and the Euler number is related to the density of loops (collaterals). Features derived from the surface area, mean breadth and Euler number were most related to age (all p ≤ 0.006). The results indicate the importance of pressure-equalizing loops and tortuosity as quantitative measures related to perfusion efficiency. The novel morphometric analysis could quantify disease-related accelerated aging and vessel malformation.

Intrinsic Myogenic Potential of Skeletal Muscle-Derived Pericytes from Patients with Myotonic Dystrophy Type 1

Pericytes are multipotent, vessel-associated progenitors that exhibit high proliferative capacity, can cross the blood-muscle barrier, and have the ability to home to muscle tissue and contribute to myogenesis. Consequently, pericyte-based therapies hold great promise for muscular dystrophies. A complex multi-system disorder exhibiting muscular dystrophy for which pericytes might be a valuable cell source is myotonic dystrophy type 1 (DM1). DM1 is caused by an unstable (CTG)n repeat in the DMPK gene and characterized by skeletal muscle weakness, muscle wasting, and myotonia. We have successfully isolated alkaline phosphatase-positive pericytes from skeletal muscle of DM1 patients and a transgenic mouse model. Intranuclear (CUG)n RNA foci, a pathogenic DM1 hallmark, were identified in human and mouse pericytes. Notably, pericytes from DM1 patients maintained similar growth parameters and innate myogenic characteristics in vitro compared to cells from unaffected controls. Our in vitro results thus demonstrate the potential of pericytes to ameliorate muscle features in DM1 in a therapeutic setting.

Endothelial dysfunction and angiogenesis impairment in the ageing vasculature

Ageing is the main risk factor for the development of cardiovascular diseases. A central mechanism by which ageing promotes vascular pathologies is compromising endothelial health. The age-related attenuation of endothelium-dependent dilator responses (endothelial dysfunction) associated with impairment of angiogenic processes and the subsequent pathological remodelling of the microcirculation contribute to compromised tissue perfusion and exacerbate functional decline in older individuals. This Review focuses on cellular, molecular, and functional changes that occur in the endothelium during ageing. We explore the links between oxidative and nitrative stress and the conserved molecular pathways affecting endothelial dysfunction and impaired angiogenesis during ageing. We also speculate on how these pathological processes could be therapeutically targeted. An improved understanding of endothelial biology in older patients is crucial for all cardiologists because maintenance of a competently functioning endothelium is critical for adequate tissue perfusion and long-term cardiac health.

Aging Neurovascular Unit and Potential Role of DNA Damage and Repair in Combating Vascular and Neurodegenerative Disorders

Progressive neurological deterioration poses enormous burden on the aging population with ischemic stroke and neurodegenerative disease patients, such as Alzheimers’ disease and Parkinson’s disease. The past two decades have witnessed remarkable advances in the research of neurovascular unit dysfunction, which is emerging as an important pathological feature that underlies these neurological disorders. Dysfunction of the unit allows penetration of blood-derived toxic proteins or leukocytes into the brain and contributes to white matter injury, disturbed neurovascular coupling and neuroinflammation, which all eventually lead to cognitive dysfunction. Recent evidences suggest that aging-related oxidative stress, accumulated DNA damage and impaired DNA repair capacities compromises the genome integrity not only in neurons, but also in other cell types of the neurovascular unit, such as endothelial cells, astrocytes and pericytes. Combating DNA damage or enhancing DNA repair capacities in the neurovascular unit represents a promising therapeutic strategy for vascular and neurodegenerative disorders. In this review, we focus on aging related mechanisms that underlie DNA damage and repair in the neurovascular unit and introduce several novel strategies that target the genome integrity in the neurovascular unit to combat the vascular and neurodegenerative disorders in the aging brain.

Age-related changes of the human retinal vessels: Possible involvement of lipid peroxidation

BACKGROUND

Aging of the human retina is accompanied by oxidative stress that exerts profound changes in the retinal neurons. It is unknown if oxidative stress influences the cellular components of the retinal vessels in some ways.

METHODS

We examined changes in retinal vessels in human donor eyes (age: 35-94 years; N=18) by light and transmission electron microscopy, TUNEL and immunohistochemistry for biomarkers of vascular smooth muscle cells (SMC; actin), oxidative stress (4-hydroxy 2-nonenal [HNE] and nitrotyrosine), microglia (Iba-1) and vessels (isolectin B₄).

RESULTS

The earliest changes in the endothelium and pericytes of capillaries are apparent from the seventh decade. With aging, there is clear loss of organelles and cytoplasmic filaments, and a progressive thickening of the endothelial and pericyte basal lamina. Loss of filaments, accumulation of lipofuscin and autophagic vacuoles are significant events in aging pericytes and SMC. Actin immunolabelling reveals discontinuity in arterial SMC layers during eighth decade, indicating partial degeneration of SMC. This is followed by hyalinization, with degeneration of the endothelium and SMC in arteries and arterioles of the nerve fibre layer (NFL) and ganglion cell layer in ninth decade. Iba-1 positive microglia were in close contact with the damaged vessels in inner retina, and their cytoplasm was rich in lysosomes. HNE immunoreactivity, but not of nitrotyrosine, was detected in aged vessels from seventh decade onwards, suggesting that lipid peroxidation is a major problem of aged vessels. However, TUNEL positivity seen during this period was limited to few arteries and venules of NFL.

CONCLUSION

This study shows prominent age-related alterations of the pericytes and SMC of retinal vessels. These changes may limit the energy supply to the neurons and be responsible for age-related loss of neurons of the inner retina.

The effects of endothelium-specific CYP2J2 overexpression on the attenuation of retinal ganglion cell apoptosis in a glaucoma rat model

Glaucoma is a leading cause of irreversible blindness worldwide. Vascular factors play a substantial role in the pathogenesis of glaucoma. Expressed in the vascular endothelium, cytochrome P450 (CYP) 2J2 is one of the CYP epoxygenases that metabolize arachidonic acid to produce epoxyeicosatrienoic acids and exert pleiotropic protective effects on the vasculature. In the present study, we investigated whether endothelium-specific overexpression of CYP2J2 (tie2-CYP2J2-Tr) protects against retinal ganglion cell (RGC) loss induced by glaucoma and in what way retinal vessels are involved in this process. We used a glaucoma model of retinal ischemia-reperfusion (I/R) injury in rats and found that endothelium-specific overexpression of CYP2J2 attenuated RGC loss induced by retinal I/R. Moreover, retinal I/R triggered retinal vascular senescence, indicated by up-regulated senescence-related proteins p53, p16, and β-galactosidase activity. The senescent endothelial cells resulted in pericyte loss and increased endothelial secretion of matrix metallopeptidase 9, which further contributed to RGC loss. CYP2J2 overexpression alleviated vascular senescence, pericyte loss, and matrix metallopeptidase 9 secretion. CYP2J2 suppressed endothelial senescence by down-regulating senescence-associated proteins p53 and p16. These 2 proteins were positively regulated by microRNA-128-3p, which was inhibited by CYP2J2. These results suggest that CYP2J2 protects against endothelial senescence and RGC loss in glaucoma, a discovery that may lead to the development of a potential treatment strategy for glaucoma.-Huang, J., Zhao, Q., Li, M., Duan, Q., Zhao, Y., Zhang, H. The effects of endothelium-specific CYP2J2 overexpression on the attenuation of retinal ganglion cell apoptosis in a glaucoma rat model.

Pericytes in Alzheimer's Disease: Novel Clues to Cerebral Amyloid Angiopathy Pathogenesis

Pericytes in the central nervous system attract growing attention of neurobiologists because of obvious opportunities to use them as target cells in numerous brain diseases. Functional activity of pericytes includes control of integrity of the endothelial cell layer, regeneration of vascular cells, and regulation of microcirculation. Pericytes are well integrated in the so-called neurovascular unit (NVU) serving as a platform for effective communications of neurons, astrocytes, endothelial cells, and pericytes. Contribution of pericytes to the establishment and maintaining the structural and functional integrity of blood-brain barrier is confirmed in numerous experimental and clinical studies. The review covers current understandings on the role of pericytes in molecular pathogenesis of NVU/BBB dysfunction in Alzheimer's disease with the special focus on the development of cerebral amyloid angiopathy, deregulation of cerebral angiogenesis, and progression of BBB breakdown seen in Alzheimer's type neurodegeneration.

Immune regulation in the aging retina

The retina is an immune privileged tissue, which is protected from external and internal insults by its blood-retina barriers and immune suppressive microenvironment. Apart from the avoidance and tolerance strategies, the retina is also protected by its own defense system, i.e., microglia and the complement system. The immune privilege and defense mechanisms work together to maintain retinal homeostasis. During aging, the retina is at an increased risk of developing various degenerative diseases such as age-related macular degeneration, diabetic retinopathy, and glaucomatous retinopathy. Previously, we have shown that aging induces a para-inflammatory response in the retina. In this review, we explore the impact of aging on retinal immune regulation and the connection between homeostatic control of retinal immune privilege and para-inflammation under aging conditions and present a view that may explain why aging puts the retina at risk of developing degenerative diseases.

Designing in vitro Blood-Brain Barrier Models Reproducing Alterations in Brain Aging

Blood-brain barrier (BBB) modeling in vitro is a huge area of research covering study of intercellular communications and development of BBB, establishment of specific properties that provide controlled permeability of the barrier. Current approaches in designing new BBB models include development of new (bio) scaffolds supporting barriergenesis/angiogenesis and BBB integrity; use of methods enabling modulation of BBB permeability; application of modern analytical techniques for screening the transfer of metabolites, bio-macromolecules, selected drug candidates and drug delivery systems; establishment of 3D models; application of microfluidic technologies; reconstruction of microphysiological systems with the barrier constituents. Acceptance of idea that BBB in vitro models should resemble real functional activity of the barrier in different periods of ontogenesis and in different (patho) physiological conditions leads to proposal that establishment of BBB in vitro model with alterations specific for aging brain is one of current challenges in neurosciences and bioengineering. Vascular dysfunction in the aging brain often associates with leaky BBB, alterations in perivascular microenvironment, neuroinflammation, perturbed neuronal and astroglial activity within the neurovascular unit, impairments in neurogenic niches where microvascular scaffold plays a key regulatory role. The review article is focused on aging-related alterations in BBB and current approaches to development of “aging” BBB models in vitro.

Age-related focal loss of contractile vascular smooth muscle cells in retinal arterioles is accelerated by caveolin-1 deficiency

Cerebral microcirculation is critical for the preservation of brain health, and vascular impairment is associated with age-related neurodegenerative diseases. Because the retina is a component of the central nervous system, cellular changes that occur in the aging retina are likely relevant to the aging brain, and the retina provides the advantage that the entire vascular bed is visible, en face. In this study, we tested the hypothesis that normal, healthy aging alters the contractile vascular smooth muscle cell (VSMC) coverage of retinal arterioles. We found that aging results in a significant reduction of contractile VSMCs in focal patches along arterioles. Focal loss of contractile VSMCs occurs at a younger age in mice deficient in the senescence-associated protein, caveolin-1. Age-related contractile VSMC loss is not exacerbated by genetic depletion of insulin-like growth factor-1. The patchy loss of contractile VSMCs provides a cellular explanation for previous clinical studies showing focal microirregularities in retinal arteriolar responsiveness in healthy aged human subjects and is likely to contribute to age-related retinal vascular complications.

Retinal Vascular Degeneration in the Transgenic P23H Rat Model of Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a group of inherited retinal degenerative diseases involving a progressive degeneration of photoreceptor cells. Following the loss of photoreceptors, retinal vascularization tends to decrease, which seems to play a role in the degenerative process of retinal cells. This study reports changes in retinal vascular network architecture in the P23H rat model of RP at different stages of retinal degeneration. Homozygous P23H line-3 rats of ages ranging from 18 days to 16 months were used in this study. Age-matched Sprague-Dawley (SD) rats were used as control animals. Vertical sections and wholemount retinas were immunolabeled for type IV collagen or stained using NADPH diaphorase histochemistry, and retinal vascular networks were drawn using a camera lucida. The superficial and deep capillary plexus (DCP) were fully developed at P18 in P23H rat retinas and showed no differences from the control animals. In 4-month-old P23H rat retinas, the superficial and intermediate capillary plexus were similar to those observed in age-matched SD rats, but a reduction in the DCP could be observed in these animals, with a significant decrease in both capillary density and capillary loops. At 16 months, the DCP was completely lost, and only vessels exhibiting an abnormal, tortuous dead-end could be observed. The middle capillary plexus had virtually disappeared at this age. Only perpendicular vessels connecting the superficial and DCP were found. The superficial plexus showed no changes in the vascular surface with age. In RP, photoreceptor loss is accompanied by degenerative changes in the retinal vascular network. The disruption of the capillary plexus, with loss of capillary density and capillary loops, can hamper the normal supply of oxygen and nutrients to retinal cells, thus accelerating retinal degeneration. Therefore, changes in retinal vascularization must be taken into account in the design of therapies targeting retinal degenerative diseases.

Understanding angiogenesis during aging: opportunities for discoveries and new models

Microvascular network growth and remodeling are common denominators for most age-related pathologies. For multiple pathologies (myocardial infarction, stroke, hypertension), promoting microvascular growth, termed angiogenesis, would be beneficial. For others (cancer, retinopathies, rheumatoid arthritis), blocking angiogenesis would be desirable. Most therapeutic strategies, however, are motivated based on studies using adult animal models. This approach is problematic and does not account for the impaired angiogenesis or the inherent network structure changes that might result from age. Considering the common conception that angiogenesis is impaired with age, a need exists to identify the causes and mechanisms of angiogenesis in aged scenarios and for new tools to enable comparison of aged versus adult responses to therapy. The objective of this article is to introduce opportunities for advancing our understanding of angiogenesis in aging through the discovery of novel cell changes along aged microvascular networks and the development of novel ex vivo models.

Cerebral microvascular abnormalities in patients with idiopathic intracranial hypertension

AIM

Idiopathic intracranial hypertension (IIH) is characterized by symptoms indicative of increased intracranial pressure (ICP), such as headache and visual impairment. We have previously reported that brain biopsies from IIH patients show patchy astrogliosis and increased expression of the water channel aquaporin-4 (AQP4) at perivascular astrocytic endfeet.

METHODS

The present study was undertaken to investigate for ultrastructural changes of the cerebral capillaries in individuals with IIH. We examined by electron microscopy (EM) biopsies from the cortical parenchyma of 10 IIH patients and 8 reference subjects (patients, not healthy individuals), in whom tissue was retrieved from other elective and necessary brain surgeries (epilepsy, tumors or vascular diseases). IIH patients were diagnosed on the basis of typical clinical symptoms and abnormal intracranial pressure wave amplitudes during overnight ICP monitoring.

RESULTS

All 10 IIH patients underwent shunt surgery followed by favorable clinical outcome. EM revealed abnormal pericyte processes in IIH. The basement membrane (BM) showed more frequently evidence of degeneration in IIH, but neither the BM dimensions nor the pericyte coverage differed between IIH and reference tissue. The BM thickness increased significantly with increasing age. Reference individuals were older than IIH cases; observations may to some extent be age-related.

CONCLUSION

The present study disclosed marked changes of the cerebral cortical capillaries in IIH patients, suggesting that microvascular alterations are involved in the evolvement of IIH.

Age-related changes in the response of retinal structure, function and blood flow to pressure modification in rats

Age-related changes to the balance between the pressure inside the eye (intraocular pressure, IOP) and the pressure inside the brain (intracranial pressure, ICP) can modify the risk of glaucoma. In this study, we consider whether the optic nerve in older rat eyes is more susceptible to acute IOP and ICP modification. We systematically manipulate both ICP and IOP and quantify their effects on ganglion cell function (electroretinography, ERG), optic nerve structure (optical coherence tomography, OCT) and retinal blood flow (Doppler OCT). We show that ganglion cell function in older eyes was more susceptible to a higher optic nerve pressure difference (ONPD = IOP - ICP). This age-related susceptibility could not be explained by poorer blood flow with elevated ONPD. Rather, as ONPD increased the retinal nerve fibre layer showed greater compression, and the retinal surface showed less deformation in older eyes. Our data suggest that age-related changes to connective tissues in and around the rat optic nerve make it less flexible, which may result in greater strain on ganglion cell axons. This may account for greater functional susceptibility to higher optic nerve pressure differences in older rat eyes. Further studies in a species with a well-developed lamina cribrosa are needed to determine the clinical importance of these observations.

Brain Capillary Ultrastructure in Idiopathic Normal Pressure Hydrocephalus: Relationship With Static and Pulsatile Intracranial Pressure

Idiopathic normal pressure hydrocephalus (iNPH) is a neurodegenerative disease of unknown cause. We investigated the morphology of capillaries in frontal cortex biopsies from iNPH patients and related the observations to overnight intracranial pressure (ICP) scores. A biopsy (0.9×10 mm) was taken from where the ICP sensor subsequently was inserted. Brain capillaries were investigated by electron microscopy of biopsies from 27 iNPH patients and 10 reference subjects, i.e. patients (not healthy individuals) without cerebrospinal fluid circulation disturbances, in whom normal brain tissue was removed as part of necessary neurosurgical treatment. Degenerating and degenerated pericyte processes were identified in 23/27 (85%) iNPH and 6/10 (60%) of reference specimens. Extensive disintegration of pericyte processes were recognized in 11/27 (41%) iNPH and 1/10 (10%) reference specimens. There were no differences in basement membrane (BM) thickness or pericyte coverage between iNPH and reference subjects. The pulsatile or static ICP scores did neither correlate with the BM thickness nor with pericyte coverage. We found increased prevalence of degenerating pericytes in iNPH while the BM thickness and pericyte coverage did not differ from the reference individuals. Observations in iNPH may to some extent be age-related since the iNPH patients were significantly older than the reference individuals.

The aging rat retina: from function to anatomy

In healthy beings, age is the ultimate reason of cellular malfunction and death. In the rat retina, age causes a functional decline and loss of specific neuronal populations. In this regard, controversial conclusions have been reported for the innermost retina. Here, we have studied the albino and pigmented retina for the duration of the rat life-span. Independent of age (21 days-22 months), the electroretinographic recordings and the volume of the retina and its layers are smaller in albinos. Functionally, aging causes in both strains a loss of cone- and rod-mediated responses. Anatomically, cell density decreases with age because the retina grows linearly with time; no cell loss is observed in the ganglion cell layer; and only in the pigmented rat, there is a decrease in cone photoreceptors. In old animals of both strains, there is gliosis in the superior colliculi and a diminution of the area innervated by retinal ganglion cells. In conclusion, this work provides the basis for further studies linking senescence to neurodegenerative retinal diseases.

The effect of age on the response of retinal capillary filling to changes in intraocular pressure measured by optical coherence tomography angiography

PURPOSE

To compare the effect of elevated intraocular pressure (IOP) on retinal capillary filling in elderly vs adult rats using optical coherence tomography angiography (OCTA).

METHODS

The IOP of elderly (24-month-old, N=12) and adult (6-8month-old, N=10) Brown Norway rats was elevated in 10mmHg increments from 10 to 100mmHg. At each IOP level, 3D OCT data were captured using an optical microangiography (OMAG) scanning protocol and then post-processed to obtain both structural and vascular images. Mean arterial blood pressure (MAP), respiratory rate, pulse and blood oxygen saturation were monitored non-invasively throughout each experiment. Ocular perfusion pressure (OPP) was calculated as the difference between MAP for each animal and IOP at each level. The capillary filling index (CFI), defined as the ratio of area occupied by functional capillary vessels to the total scan area but excluding relatively large vessels of >30μm, was calculated at each IOP level and analyzed using the OCTA angiograms. Relative CFI vs IOP was plotted for the group means. CFI vs OPP was plotted for every animal in each group and data from all animals were combined in a CFI vs OPP scatter plot comparing the two groups.

RESULTS

The MAP in adult animals was 108±5mmHg (mean±SD), whereas this value in the elderly was 99±5mmHg. All other physiologic parameters for both age groups were uniform and stable. In elderly animals, significant reduction of the CFI was first noted at IOP 40mmHg, as opposed to 60mmHg in adult animals. Individual assessment of CFI as a function of OPP for adult animals revealed a consistent plateau until OPP reached between 40 and 60mmHg. Elderly individuals demonstrated greater variability, with many showing a beginning of gradual deterioration of CFI at an OPP as high as 80mmHg. Overall comparison of CFI vs OPP between the two groups was not statistically significant.

CONCLUSIONS

Compared to adults, some, but not all, elderly animals demonstrate a more rapid deterioration of CFI vs OPP. This suggests a reduced autoregulatory capacity that may contribute to increased glaucoma susceptibility in some older individuals. This variability must be considered when studying the relationship between IOP, ocular perfusion and glaucoma in elderly animal models.

Cell-cell communication in diabetic retinopathy

In diabetic retinopathy, high glucose (HG)-mediated breakdown in cell-cell communication promotes disruption of retinal homeostasis. Several studies indicate that HG condition alters expression of connexin genes and subsequent gap junction intercellular communication (GJIC) in retinal vascular cells and non-vascular cells. A serious consequence of disrupted cell-cell communication is apoptosis and breakdown of the blood-retinal barrier (BRB). More recently, studies suggest adverse effects from HG on retinal Müller cells. This article focuses on HG-mediated changes in connexin expression and GJIC and their subsequent effects on the breakdown of retinal homeostasis, cell death, compromised vascular permeability, and interactions between endothelial cells, pericytes and retinal Müller cells in the pathogenesis of diabetic retinopathy. Additionally, options for rectifying disrupted homeostasis under HG condition associated with diabetic retinopathy are reviewed.

Cerebral Vascular Disease and Neurovascular Injury in Ischemic Stroke

The consequences of cerebrovascular disease are among the leading health issues worldwide. Large and small cerebral vessel disease can trigger stroke and contribute to the vascular component of other forms of neurological dysfunction and degeneration. Both forms of vascular disease are driven by diverse risk factors, with hypertension as the leading contributor. Despite the importance of neurovascular disease and subsequent injury after ischemic events, fundamental knowledge in these areas lag behind our current understanding of neuroprotection and vascular biology in general. The goal of this review is to address select key structural and functional changes in the vasculature that promote hypoperfusion and ischemia, while also affecting the extent of injury and effectiveness of therapy. In addition, as damage to the blood-brain barrier is one of the major consequences of ischemia, we discuss cellular and molecular mechanisms underlying ischemia-induced changes in blood-brain barrier integrity and function, including alterations in endothelial cells and the contribution of pericytes, immune cells, and matrix metalloproteinases. Identification of cell types, pathways, and molecules that control vascular changes before and after ischemia may result in novel approaches to slow the progression of cerebrovascular disease and lessen both the frequency and impact of ischemic events.

Dysfunction of the neurovascular unit in ischemic stroke and neurodegenerative diseases: An aging effect

Current understanding on the mechanisms of brain injury and neurodegeneration highlights an appreciation of multicellular interactions within the neurovascular unit (NVU), which include the evolution of blood-brain barrier (BBB) damage, neuronal cell death or degeneration, glial reaction, and immune cell infiltration. Aging is an important factor that influences the integrity of the NVU. The age-related physiological or pathological changes in the cellular components of the NVU have been shown to increase the vulnerability of the NVU to ischemia/reperfusion injury or neurodegeneration, and to result in deteriorated brain damage. This review describes the impacts of aging on each NVU component and discusses the mechanisms by which aging increases NVU sensitivity to stroke and neurodegenerative diseases. Prophylactic or therapeutic perspectives that may delay or diminish aging and thus prevent the incidence of these neurological disorders will also be reviewed.

Aging is associated with impaired angiogenesis, but normal microvascular network structure, in the rat mesentery

A big problem associated with aging is thought to be impaired microvascular growth or angiogenesis. However, to link the evidence for impaired angiogenesis to microvascular dysfunction in aged tissues, we must compare adult vs. aged microvascular networks in unstimulated scenarios. The objective of this study was to test the hypothesis that aged microvascular networks are characterized by both fewer vessels and the impaired ability to undergo angiogenesis. Mesentery tissues from adult (9-mo) and aged (24-mo) male Fischer 344 rats were harvested and immunolabeled for platelet/endothelial cell adhesion molecule (an endothelial cell marker) according to two scenarios: unstimulated and stimulated. For unstimulated groups, tissues harvested from adult and aged rats were compared. For stimulated groups, tissues were harvested 3 or 10 days after compound 48/80-induced mast cell degranulation stimulation. Unstimulated aged microvascular networks displayed larger mean vascular area per tissue area compared with the unstimulated adult networks. The lack of a decrease in vessel density was supported at the gene expression level with RNA-Seq analysis and with comparison of vessel densities in soleus muscle. Following stimulation, capillary sprouting and vessel density were impaired in aged networks at 3 and 10 days, respectively. Our results suggest that aging associated with impaired angiogenesis mechanisms might not influence normal microvascular function, since unstimulated aged microvascular networks can display a "normal adult-like" vessel density and architecture.

NEW & NOTEWORTHY

Using a multidimensional approach, we present evidence supporting that aged microvascular networks display vessel density and patterning similar to adult networks despite also being characterized by a decreased capacity to undergo angiogenesis. Thus, vessel loss is not necessarily a characteristic of aging.

Pericytes in Brain Injury and Repair After Ischemic Stroke

Pericytes are functional components of the neurovascular unit (NVU). They provide support to other NVU components and maintain normal physiological functions of the blood-brain barrier (BBB). The brain ischemia and reperfusion result in pathological alterations in pericytes. The intimate anatomical and functional interactions between pericytes and other NVU components play pivotal roles in the progression of stroke pathology. In this review, we depict the biology and functions of pericytes in the normal brain and discuss their effects in brain injury and repair after ischemia/reperfusion. Since ischemic stroke occurs mostly in elderly people, we also review age-related changes in pericytes and how these changes predispose aged brains to ischemic/reperfusion injury. Strategies targeting pericyte responses after ischemia and reperfusion may provide new therapies for ischemic stroke.

Pericytes: A newly recognized player in wound healing

Pericytes have generally been considered in the context of stabilizing vessels, ensuring the blood barriers, and regulating the flow through capillaries. However, new reports suggest that pericytes may function at critical times to either drive healing with minimal scarring or, perversely, contribute to fibrosis and ongoing scar formation. Beneficially, pericytes probably drive much of the vascular involution that occurs during the transition from the regenerative to the resolution phases of healing. Pathologically, pericytes can assume a fibrotic phenotype and promote scarring. This perspective will discuss pericyte involvement in wound repair and the relationship pericytes form with the parenchymal cells of the skin. We will further evaluate the role pericytes may have in disease progression in relation to chronic wounds and fibrosis.