Arteriolar Diameter Research Articles

Whisker-evoked neurovascular coupling is preserved during hypoglycemia in mouse cortical arterioles and capillaries

Hypoglycemia is a serious complication of insulin treatment of diabetes that can lead to coma and death. Neurovascular coupling, which mediates increased local blood flow in response to neuronal activity, increases glucose availability to active neurons. This mechanism could be essential for neuronal health during hypoglycemia, when total glucose supplies are low. Previous studies suggest, however, that neurovascular coupling (a transient blood flow increase in response to an increase in neuronal activity) may be reduced during hypoglycemia. Such a reduction in blood flow increase would exacerbate the effects of hypoglycemia, depriving active neurons of glucose. We have reexamined the effects of hypoglycemia on neurovascular coupling by simultaneously monitoring neuronal and vascular responses to whisker stimulation in the awake mouse somatosensory cortex. We find that neurovascular coupling at both penetrating arterioles and at 2nd order capillaries did not change significantly during insulin-induced hypoglycemia compared to euglycemia. In addition, we show that the basal diameter of both arterioles and capillaries increases during hypoglycemia (10.3 and 9.7% increases, respectively). Our results demonstrate that both neurovascular coupling and basal increases in vessel diameter are active mechanisms which help to maintain an adequate supply of glucose to the brain during hypoglycemia.

Astrocytic GPCR-Induced Ca2+ Signaling Is Not Causally Related to Local Cerebral Blood Flow Changes.

Activation of Gq-type G protein-coupled receptors (GPCRs) gives rise to large cytosolic Ca2+ elevations in astrocytes. Previous in vitro and in vivo studies have indicated that astrocytic Ca2+ elevations are closely associated with diameter changes in the nearby blood vessels, which astrocytes enwrap with their endfeet. However, the causal relationship between astrocytic Ca2+ elevations and blood vessel diameter changes has been questioned, as mice with diminished astrocytic Ca2+ signaling show normal sensory hyperemia. We addressed this controversy by imaging cortical vasculature while optogenetically elevating astrocyte Ca2+ in a novel transgenic mouse line, expressing Opto-Gq-type GPCR Optoα1AR (Astro-Optoα1AR) in astrocytes. Blue light illumination on the surface of the somatosensory cortex induced Ca2+ elevations in cortical astrocytes and their endfeet in mice under anesthesia. Blood vessel diameter did not change significantly with Optoα1AR-induced Ca2+ elevations in astrocytes, while it was increased by forelimb stimulation. Next, we labeled blood plasma with red fluorescence using AAV8-P3-Alb-mScarlet in Astro-Optoα1AR mice. We were able to identify arterioles that display diameter changes in superficial areas of the somatosensory cortex through the thinned skull. Photo-stimulation of astrocytes in the cortical area did not result in noticeable changes in the arteriole diameters compared with their background strain C57BL/6. Together, compelling evidence for astrocytic Gq pathway-induced vasodiameter changes was not observed. Our results support the notion that short-term (<10 s) hyperemia is not mediated by GPCR-induced astrocytic Ca2+ signaling.

Abstract 083: Neurovascular And Cognitive Dysfunction In Middle-Aged Mice With High Blood Pressure Variability

Blood pressure variability (BPV) is a novel risk factor for cognitive decline. This study tested the hypothesis that BPV disrupts cellular function and communication at the neurovascular complex (vascular, glia, and neuron) contributing to BPV-induced neurovascular dysfunction. A main goal of the study was to establish a murine BPV model and examine how this risk factor impacts key functional outputs of the neurovascular complex. Middle-aged C57BL6 mice were implanted a cranial window and injected GCaMP viral vectors to monitor Ca 2+ activity in cortical neurons or astrocytes. DSI telemetry was used to monitor cardiovascular variables simultaneously ( in vivo ) with arteriole diameter and astrocyte/neuronal Ca 2+ responses via two-photon imaging. In addition, mice were implanted a programmable pump and infused 6-8 pulses/day of saline (Control) or angiotensin II (Ang II, 18 μg/day) for 20-25 days. Ang II infusions evoked transient BP increases (Δ 23±2 mmHg, mean arterial pressure (MAP, P=0.0001, n=14)), and increased BPV (P=0.04, n=12) measured by the average real variability. The 24-hour MAP was not different compared to Controls, allowing for the investigation of BPV-evoked changes in neurovascular function in the absence of hypertension. BPV mice displayed cognitive decline (NOR, P=0.006, n=10). Myogenic responses were lost in parenchymal arterioles of BPV mice but preserved in Controls (P&lt;0.01 n=6). In addition to impaired vascular function, during Ang II-induced BP increases, astrocytes of BPV mice exhibited greater Ca 2+ event frequency (P&lt;0.0001, n=4-6), but of lesser amplitude and reduced area (P=0.02, n=4-6). Furthermore, the neurovascular coupling response, evoked via whisker stimulation, was blunted in mice with high BPV (P&lt;0.0001, n=6-10). Relevant to inflammation, microglial cells from BPV mice had elevated Iba1 (P=0.03, n=4-5) and CD68+ (P=0.003), an inflammatory marker. These findings show that BPV, in the absence of hypertension, result in a loss of cerebral autoregulation, a shift in spontaneous astrocyte Ca 2+ dynamics during blood pressure fluctuations, and increased microglia reactivity. Future mechanistic studies are needed to determine how BPV contributes to cognitive decline.

Abstract P397: Preservation Of Renal Microvascular Function In Ischemia-reperfusion Induced Kidney Injury In Rats

Proper renal blood flow and glomerular filtration rate are critical for maintaining normal kidney function by precisely adjusting preglomerular microvascular resistance. Renal ischemia-reperfusion (IR) insult markedly increased mRNA expression of the inflammatory chemokine (C-C motif) Ligand 2 (CCL2) in rat kidney tissues. We hypothesized that depletion of macrophages prevented IR-induced renal autoregulatory impairment via reduction of CCL2 in preglomerular microvessels (PGMV). IR was induced in male rats by 60-minute bilateral renal artery occlusion followed by reperfusion. Some IR rats were treated with the selective macrophage inhibitor, Liposome-encapsulated clodronate (LC) following reperfusion and repeated 72 hours post-IR. Afferent arteriolar autoregulatory reactivity was assessed using the in vitro blood-perfused juxtamedullary nephron preparation in sham, IR, and IR+LC rats on day 7. Afferent arterioles from sham-operated rats exhibited pressure-dependent vasoresponsiveness. The baseline arteriolar diameter averaged 13.4 ± 0.5 μm at renal perfusion pressure (RPP) of 100 mmHg. Diameter increased to 117 ± 4% of baseline at RPP of 65 mmHg and decreased to 69 ± 2% at 170 mmHg, respectively. In contrast, afferent arterioles from IR rats only increased to 104 ± 2% and decreased to 91 ± 5% of baseline at 65 and 170 mmHg, respectively (P &lt; 0.05 vs sham), indicating the impaired autoregulatory capacity in IR rats. LC-treated IR rats, however, markedly improved the pressure-dependent vasoresponsiveness. A decrease in RPP to 65 mmHg resulted in a 124 ± 17% increase in the baseline diameter, whereas increasing RPP to 170 mmHg led to a 74 ± 7% decrease in diameter. Additionally, IR markedly increased CCL2 mRNA expression in isolated PGMV by 10-fold 7 days post-IR. IR also elevated NADPH oxidase subunits (gp91 phox , P67 phox , and P47 phox ). Significantly, LC treatment suppressed mRNA expression of CCL2, gp91 phox , P67 phox , and P47 phox in IR-PGMV. In conclusion, depletion of macrophages preserves afferent arteriolar autoregulatory capacity and reduces PGMV CCL2 mRNA expression in IR rats, suggesting a critical role of macrophages in mediating renal microvascular autoregulatory impairment in IR-induced kidney injury via the increase of CCL2 in PGMV.

Abstract 120: Greater 24-hour Blood Pressure Variability Is Associated With Higher Retinal Microvascular Resistance And Smaller Lumen Diameter In Healthy Normotensive Adults

Introduction: Elevated blood pressure (BP) is associated with damage to high flow, low resistance target organs such as the retina. Recent evidence suggests that 24-hour BP variability (BPV) is a novel risk factor for cardiovascular disease, independent of 24-hour average BP. However, whether 24-hour BPV is related to concentric retinal arteriole remodeling in healthy adults is unknown. Thus, the purpose of our study was to determine the degree to which 24-hour BPV is associated with retinal lumen diameter and vascular resistance in healthy young/middle-aged adults, independent of 24-hour average BP. Methods: Healthy, normotensive adults aged 25 to 60 years (n=40; 50% female) underwent measurements of retinal arteriole diameter and flow using laser speckle flowgraphy. 24-hour brachial BP was determined using ambulatory BP monitoring. BPV was calculated as the standard deviation of all BP recordings for systolic and diastolic BP. Retinal vascular resistance was calculated as ocular perfusion pressure divided by mean retinal flow across 4 arterioles. Aortic stiffness was measured as carotid-femoral pulse wave velocity (cfPWV). Results: Higher 24-hour systolic and diastolic average BP were associated with smaller retinal lumen diameter and elevated vascular resistance (P&lt;0.05). Although both systolic BPV (r=0.391, P=0.012) and diastolic BPV (r=0.315, P=0.048) were associated with higher retinal vascular resistance, only diastolic BPV was associated with smaller retinal arteriole lumen diameter (r=-0.393, P=0.012). The association of greater diastolic BPV with smaller retinal arteriole lumen diameter (β=-0.363, P=0.01) and higher retinal vascular resistance (β=0.395, P=0.007) remained after adjusting for age, body mass index, cfPWV, and 24-hour average diastolic BP. Conclusion: Higher diastolic BPV may contribute to adverse remodeling of retinal arterioles in healthy normotensive adults independent of arterial stiffness and traditional cardiovascular disease risk factors. Future studies could utilize local metabolic vasodilation via diffuse luminance flicker to examine whether retinal arteriole autoregulatory mechanisms are impaired in individuals with higher BPV.

Cardiorespiratory fitness and development of childhood cardiovascular risk: The EXAMIN YOUTH follow-up study.

Background: Obesity- and hypertension-related cardiovascular (CV) risk has been shown to originate in childhood. Higher body mass index (BMI) and blood pressure (BP) have been associated with increased large artery stiffness and a lower microvascular arteriolar-to-venular diameter ratio (AVR) in children. This study aimed to investigate the association of cardiorespiratory fitness (CRF) with development of BMI, BP and vascular health during childhood. Methods: In our prospective cohort study, 1,171 children aged 6-8years were screened for CRF, BMI, BP, retinal vessel diameters and pulse wave velocity using standardized protocols. Endurance capacity was assessed by 20m shuttle run test. After 4years, all parameters were assessed in 664 children using the same protocols. Results: Children with a higher CRF at baseline developed a significantly lower BMI (β [95% CI] -0.09 [-0.11 to -0.06] kg/m2, p < 0.001), a lower systolic BP (β [95% CI] -0.09 [-0.15 to -0.03]mmHg, p = 0.004) and a higher AVR (β [95% CI] 0.0004 [0.00004 to 0.0007] units, p = 0.027) after 4years. The indirect association of CRF with development of retinal arteriolar diameters was mediated by changes in BMI. Conclusion: Our results identify CRF as a key modulator for the risk trajectories of BMI, BP and microvascular health in children. Obesity-related CV risk has been shown to track into adulthood, and achieving higher CRF levels in children may help counteract the development of CV risk and disease not only in pediatric populations, but may also help reduce the burden of CVD in adulthood. Registration: http://www.clinicaltrials.gov/ (NCT02853747).

Effects of Gold Nanoparticles Phytoreduced with Rutin in an Early Rat Model of Diabetic Retinopathy and Cataracts.

Diabetic retinopathy (DR) and cataracts (CA) have an early onset in diabetes mellitus (DM) due to the redox imbalance and inflammation triggered by hyperglycaemia. Plant-based therapies are characterised by low tissue bioavailability. The study aimed to investigate the effect of gold nanoparticles phytoreduced with Rutin (AuNPsR), as a possible solution. Insulin, Rutin, and AuNPsR were administered to an early, six-week rat model of DR and CA. Oxidative stress (MDA, CAT, SOD) was assessed in serum and eye homogenates, and inflammatory cytokines (IL-1 beta, IL-6, TNF alpha) were quantified in ocular tissues. Eye fundus of retinal arterioles, transmission electron microscopy (TEM) of lenses, and histopathology of retinas were also performed. DM was linked to constricted retinal arterioles, reduced endogen antioxidants, and eye inflammation. Histologically, retinal wall thickness decreased. TEM showed increased lens opacity and fibre disorganisation. Rutin improved retinal arteriolar diameter, while reducing oxidative stress and inflammation. Retinas were moderately oedematous. Lens structure was preserved on TEM. Insulin restored retinal arteriolar diameter, while increasing MDA, and amplifying TEM lens opacity. The best outcomes were obtained for AuNPsR, as it improved fundus appearance of retinal arterioles, decreased MDA and increased antioxidant capacity. Retinal edema and disorganisation in lens fibres were still present.

Increased retinal venule diameter as a prognostic indicator for recurrent cerebrovascular events: a prospective observational study.

Microvasculature of the retina is considered an alternative marker of cerebral vascular risk in healthy populations. However, the ability of retinal vasculature changes, specifically focusing on retinal vessel diameter, to predict the recurrence of cerebrovascular events in patients with ischemic stroke has not been determined comprehensively. While previous studies have shown a link between retinal vessel diameter and recurrent cerebrovascular events, they have not incorporated this information into a predictive model. Therefore, this study aimed to investigate the relationship between retinal vessel diameter and subsequent cerebrovascular events in patients with acute ischemic stroke. Additionally, we sought to establish a predictive model by combining retinal veessel diameter with traditional risk factors. We performed a prospective observational study of 141 patients with acute ischemic stroke who were admitted to the First Affiliated Hospital of Jinan University. All of these patients underwent digital retinal imaging within 72 hours of admission and were followed up for 3 years. We found that, after adjusting for related risk factors, patients with acute ischemic stroke with mean arteriolar diameter within 0.5-1.0 disc diameters of the disc margin (MAD0.5-1.0DD) of ≥ 74.14 μm and mean venular diameter within 0.5-1.0 disc diameters of the disc margin (MVD0.5-1.0DD) of ≥ 83.91 μm tended to experience recurrent cerebrovascular events. We established three multivariate Cox proportional hazard regression models: model 1 included traditional risk factors, model 2 added MAD0.5-1.0DD to model 1, and model 3 added MVD0.5-1.0DD to model 1. Model 3 had the greatest potential to predict subsequent cerebrovascular events, followed by model 2, and finally model 1. These findings indicate that combining retinal venular or arteriolar diameter with traditional risk factors could improve the prediction of recurrent cerebrovascular events in patients with acute ischemic stroke, and that retinal imaging could be a useful and non-invasive method for identifying high-risk patients who require closer monitoring and more aggressive management.

Bivariate relation of vascular health and blood pressure progression during childhood

Background and aimsHypertension is a major risk factor for the development of cardiovascular disease (CVD) in adulthood. High blood pressure (BP) is associated with subclinical vascular impairments as early as childhood. We aimed to assess the association of retinal microvascular diameters and large artery pulse wave velocity (PWV) with progression of childhood BP. MethodsIn our prospective Basel cohort study, 1171 children aged 6–8 years were screened for BP, body mass index, retinal vessel diameters and PWV using standardized protocols. After 4 years, all parameters were assessed in 749 children using the same protocols. ResultsChildren with narrower central retinal arteriolar diameters (CRAE) and higher PWV at baseline developed higher systolic BP after 4 years (β [95% CI] 0.6 [0.072 to 1.164] mmHg per 10 μm decrease, p = 0.026 and β [95% CI] 0.6 [0.331 to 0.838] mmHg per 0.1 m/s increase, p < 0.001, respectively). Children with increased systolic BP at baseline developed narrower CRAE and higher PWV at follow-up (β [95% CI] −3.3 [-4.43 to −2.09] μm per 10 mmHg increase, p < 0.001 and β [95% CI] 0.13 [0.10 to 0.16] m/s per 10 mmHg increase, p < 0.001, respectively). ConclusionsRetinal arteriolar diameter and PWV independently predict progression of childhood BP, while initial BP is linked to development of micro- and macrovascular impairments, describing a bivariate temporal relationship between vascular health and BP. Childhood may present a window of opportunity for initiation of primary prevention strategies for the treatment of high BP to help prevent manifestation of CVD later in life.

Abstract P3008: A Computational Model Predicts Sex-specific Responses To Calcium Channel Blockers In Mesenteric Vascular Smooth Muscle

The electrical activity of smooth muscle cells underlies the regulation of the diameter of small resistance arteries and arterioles to control blood flow and blood pressure. Historically, measurements of pressure in blood vessels and their responses to drug interventions have been based entirely on data from male animals. Recently, experiments have indicated sex-specific differences in smooth muscle. We hypothesize that the fundamental differences in ion channel expression measured in male and female cells may underlie variable responses to antihypertensive drugs between males and females. To determine if this hypothesis is plausible, we developed a computational model to investigate the effects of measured sex-specific differences in the electrophysiology and Ca 2+ signaling of vascular smooth muscle cells. Contrary to established models suggesting that K V 1.5 channels are the most prominent K V channels regulating membrane potential, our model predicts that K V 2.1 channels play an unexpectedly primary role in the control of membrane potential in female but not in male cells. In addition, we found that sex-specific differences in the amplitude and voltage dependencies of L-type Ca V 1.2 currents between males and females cause higher Ca 2+ influx and higher [Ca 2+ ] i , in female than in male mesenteric smooth muscle cells. To simulate sex differences in the regulation of resistance arteries and arterioles, we developed an idealized vessel model by connecting smooth muscle cells through simulated resistances to represent gap junctional coupling. The model predictions suggest that female arterial smooth muscle is more sensitive to clinically used Ca 2+ channel blockers than male smooth muscle. Our computational framework initiates the first steps toward the investigation of the potential sex-specific impact of antihypertensive drugs, which may lead to more effective treatment for hypertension.

Abstract P3107: Sexual Dimorphism In Diastolic Dysfunction And Cardiac Small Vessel Disease In Heart Failure With Preserved Ejection Fraction Mouse Models

Introduction: Coronary microvascular disease has been proposed to be responsible for heart failure with preserved ejection fraction (HFpEF) about 10 years ago. However, to date the role and phenotype of the coronary microvasculature has still been poorly investigated in animal models of HFpEF and sex differences are not always considered. Objective: To characterize the phenotype of the coronary microvasculature in male and female mice with diastolic dysfunction in two HFpEF mouse models. Method: We assessed cardiac function and characterized the coronary microvasculature in mice fed with a high fat diet (HFD) + L-NAME regimen and in Leptin receptor deficient ( Lepr db/db ) mice. Notably, our study was done in males, females and ovariectomized (OVX) female mice in order to search for possible sexual dimorphisms. Results: Upon a HFD + L-NAME regimen, both males and OVX females but not non OVX females develop diastolic dysfunction attested by an increased end diastolic pressure. In Lepr db/db mice, both Male and non OVX female mice develop diastolic dysfunction. Notably female mice have reduced estradiol and progesterone level mice mimicking ovariectomy. We found that both OVX and non OVX females but not males display increased endothelial activation attested by increased ICAM1 expression, endothelium leakage attested by increased Fibrinogen and IgG extravasation and decreased arteriole diameter suggesting vasoconstriction. The same results were found in Lepr db/db mice. Conclusion: Diastolic dysfunction is not always associated with cardiac small vessel disease since Lepr db/db males and C57BL/6J males fed with a high fat diet (HFD) + L-NAME regimen develop diastolic dysfunction in the absence of endothelial dysfunction. Also endothelial dysfunction may not be sufficient to induce diastolic dysfunction since non OVX female mice fed with a high fat diet (HFD) + L-NAME regimen display endothelial dysfunction while they do not develop diastolic dysfunction.

Prevalence and Associations of Nonglaucomatous Optic Nerve Atrophy in High Myopia: The Ural Eye and Medical Study

To assess the prevalence of non-glaucomatous optic nerve atrophy (NGOA) and its associations in highly myopic individuals. Population-based study. The Ural Eye and Medical Study included 5899 (80.5%) out of 7328 eligible individuals. The participants underwent an ophthalmological and general examination. NGOA, graded into five arbitrary stages, was characterized by decreased visibility of the retinal nerve fiber layer (RNFL) on fundus photographs and on red-free fundus photographs, neuroretinal rim pallor, abnormally thin retinal arteriole diameter, and abnormally thin peripapillary RNFL as measured by optical coherence tomography. NGOA prevalence and degree. Out of 5709 (96.9%) participants with axial length measurements, 130 (2.3%) individuals were highly myopic, of which 116 (89.2%) participants (age:57.8±11.1 years; range:41.0-84.2 years; axial length:27.0±1.2mm; range:26.01-32.87mm) had available fundus photographs and OCT images and were included into the present study. NGOA prevalence was 34/116 (29.3%;95%CI:21.0,38.0), and mean NGOA degree in eyes with NGOA was 1.7±1.0 arbitrary units. Higher NGOA degree correlated (multivariable analysis; regression coefficient r2:0.59) with longer axial length (beta:0.22; B:0.18; 95%CI:0.05,0.31; P=0.007), wider temporal parapapillary gamma zone width (beta:0.50; B:0.45; 95%CI:0.30,0.59; P<0.001), higher prevalence of diabetes (beta:0.20; B:0.63; 95%CI:0.20,1.06; P=0.005), and higher systolic blood pressure (beta:0.15; B:0.01; 95%CI:0.001,0.02; P=0.03). Higher NGOA prevalence was associated with longer axial length (odds ratio (OR):7.45; 95%CI:2.15,25.7; P=0.002), wider temporal parapapillary gamma zone (OR:6.98; 95%CI:2.61,18.7; P<0.001), and higher systolic blood pressure (OR:1.05; 95%CI:1.01,1.10; P=0.02). In this ethnically mixed population from Russia with an age of 40+ years, high axial myopia showed a relatively high prevalence of NGOA, increasing with longer axial length and wider temporal parapapillary gamma zone. For each millimeter of axial elongation and widening of gamma zone, the odds for NGOA increased 7.45-fold and 6.98-fold, respectively. The axial elongation-associated and gamma zone-related increase in the distance between the retinal ganglion cells and the optic disc may lead to a lengthening and stretching of the retinal ganglion cell axons and may pathogenetically be of importance. In highly myopic eyes, NGOA may be a reason for visual field and central visual acuity loss, unexplainable by myopic macular pathologies.

Differential effects of purines and prostaglandins on hypoxia induced dilatation of porcine retinal vessels at different branching level ex vivo

The metabolic pathways leading from hypoxia to retinal vasodilatation can involve effects of both purines and prostaglandins, but the effects of these compounds at different vascular branching levels are unknown. The purpose of the present study was to investigate differential effects of purines and prostaglandins in hypoxia-induced dilatation of retinal arterioles, precapillary arterioles and capillaries ex vivo.Porcine hemiretinas were mounted in a tissue chamber while monitoring temperature, pH, and oxygen tension. The effect of hypoxia on the diameter of larger arterioles, precapillary arterioles and capillaries was studied in the presence of the ecto-nucleotidase inhibitor AOPCP, the nonselective P2 purinoreceptor antagonist PPADS, the A2B adenosine receptor antagonist MRS 1754, the A3 adenosine receptor antagonist MRS 1523, the EP1 receptor antagonist SC-19220, the EP2 receptor antagonist PF-04418948, the EP3 receptor antagonist L-798,106, the EP4 receptor antagonist L-161-982, the prostaglandin synthesis inhibitor ibuprofen, and ibuprofen combined with AOPCP or ATP.Hypoxia-induced dilatation in arterioles was reduced by the A2B adenosine receptor antagonist (p < 0.01) and increased by the EP2 and the EP3 receptor antagonists (p < 0.01 for both comparisons). In precapillary arterioles the dilatation was reduced by the EP2 receptor antagonist (p < 0.04) and increased by the EP1 receptor antagonist (p < 0.03), whereas in capillaries the dilatation was increased by both the A3 adenosine receptor antagonist (p < 0.01), by ibuprofen in combination with the unspecific ecto-nucleotidase inhibitor AOPCP (p = 0.04) and by the prostaglandin EP3 receptor antagonist.Hypoxia-induced dilatation of retinal vessels is influenced by adenosine A2B and A3 receptors, and by the prostaglandin EP1, EP2 and EP3 receptors. The effects mediated by these receptors differ at different branching levels of the resistance vessels.

Association of Apolipoprotein E4-related Microvascular Disease in the Alzheimer’s Disease Hippocampal CA1 Stratum Radiatum

Current data suggest a hypothesis of vascular pathogenesis for the development and progression of Alzheimer’s disease (AD). To investigate this, we studied the association of apolipoprotein E4 (APOE4) gene on microvessels in human autopsy-confirmed AD with and without APOE4, compared with age/sex-matched control (AC) hippocampal CA1 stratum radiatum. AD arterioles (without APOE4 gene) had mild oxidative stress and loss of vascular endothelial growth factor (VEGF) and endothelial cell density, reflecting aging progression. In AD + APOE4, an increase in strong oxidative DNA damage marker 8-hydroxy-2′-deoxyguanosine (8-OHdG), VEGF, and endothelial cell density were associated with increased diameter of arterioles and perivascular space dilation. In cultured human brain microvascular cells (HBMECs), treatment of ApoE4 protein plus amyloid-β (Aβ) oligomers increased superoxide production and the apoptotic marker cleaved caspase 3, sustained hypoxia inducible factor-1α (HIF-1α) stability that was associated with an increase in MnSOD, VEGF, and cell density. This cell over-proliferation was inhibited with the antioxidants N-acetyl cysteine and MnTMPyP, the HIF-1α inhibitor echinomycin, the VEGFR-2 receptor blocker SU1498, the protein kinase C (PKC) ε knock-down (KD) and the extracellular signal-regulated kinase 1/2 (ERK) inhibitor FR180204. The PKCε KD and echinomycin decreased VEGF and/or ERK. In conclusion, AD capillaries and arterioles in hippocampal CA1 stratum radiatum of non-APOE4 carriers are related with aging, while those in APOE4 carriers with AD are related with pathogenesis of cerebrovascular disease.

Insights into the Regulation of GFR by the Keap1-Nrf2 Pathway.

Literature data suggest that the activation of the Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathway increases glomerular filtration rate (GFR) in patients with type 2 diabetes and chronic kidney disease. However, the mechanisms whereby the Keap1-Nrf2 pathway regulates GFR are unknown. Methods: Various renal physiological parameters were assessed in C57BL/6 mice (WT), Nrf2-deficient mice, and Nrf2-activated Keap1-knockdown mice. Also, these parameters were assessed following the administration of RTA dh404 (CDDO-dhTFEA), a Nrf2 activator. Pharmacological and genetic Keap1-Nrf2 activation increased renal blood flow (p <0.05), glomerular volume (p <0.05) and GFR (p <0.05), but did not alter the afferent-to-efferent arteriolar diameter ratio or glomerular permeability. Calcium influx into the podocytes through TRPC channels in response to H2O2 was suppressed by Keap1-Nrf2 activation and TRPCs inhibition. Treatment with a TRPC6 and TRPC5 inhibitors increased single-nephron GFR in WT mice. In conclusion, the Keap1-Nrf2 pathway regulates GFR through changes in ultrafiltration by modulating redox-sensitive intracellular calcium signaling and cellular contractility, mediated through TRPC activity, in glomerular cells, in particular the podocytes.

Retinal Microvascular Diameters are Associated with Diabetic Kidney Disease in Patients with Type 2 Diabetes Mellitus.

To investigate the association between retinal microvascular diameters and diabetic kidney disease (DKD) in patients with type 2 diabetes mellitus (T2DM). A total of 690 patients with T2DM were included in this retrospective study. Patients were divided into DKD and non-DKD groups according to urine microalbumin/creatinine ratio and estimated glomerular filtration rate. Retinal microvascular diameters were measured by the automated retinal image analysis system. Multivariate logistic regression analysis and restricted cubic splines were used to assess the relationships between the retinal microvascular diameters and DKD in patients with T2DM. Multivariate logistic regression showed that widened diameters of retinal venules and narrowed diameters of retinal arterioles were associated with DKD after adjusting for potential confounding variables. There was a significant linear trend between the diameters of superior temporal retinal venula (P for trend < 0.001, P for non-linearity = 0.080), inferior temporal retinal venula (P for trend < 0.001, P for non-linearity = 0.111) and central retinal venular equivalent (CRVE) (P for trend < 0.001, P for non-linearity = 0.392) and risk of DKD in patients with T2DM. The restricted cubic splines showed that narrowed retinal arteriolar diameters, superior and inferior nasal retinal venulas were associated with the risk of DKD in a non-linear fashion (all P for non-linearity < 0.001). Wider retinal venular diameters and narrower retinal arteriolar diameters were associated with an increased risk of DKD in patients with T2DM. Widened retinal venular diameters, especially CRVE, superior and inferior temporal retinal venula, were positively associated with an increased risk of DKD in a linear fashion. In contrast, narrowed retinal arteriolar diameters were associated with the risk of DKD in a non-linear fashion.

Analysis of retinal arteriolar and venular parameters in primary open angle glaucoma.

To measure the retinal vessels of primary open angle glaucoma (POAG) patients on spectral domain optical coherence tomography (SD-OCT) with a full-width at half-maximum (FWHM) algorithm to better explore their structural changes in the pathogenesis of POAG. In this retrospective case-control study, the right eyes of 32 patients with POAG and 30 healthy individuals were routinely selected. Images of the supratemporal and infratemporal retinal vessels in the B zones were obtained by SD-OCT, and the edges of the vessels were identified by the FWHM method. The internal and external diameters, wall thickness (WT), wall cross-sectional area (WCSA) and wall-to-lumen ratio (WLR) of the blood vessels were studied. Compared with the healthy control group, the POAG group showed a significantly reduced retinal arteriolar outer diameter (RAOD), retinal arteriolar lumen diameter (RALD) and WSCA in the supratemporal (124.22±12.42 vs 138.32±10.73 µm, 96.09±11.09 vs 108.53±9.89 µm, and 4762.02±913.51 vs 5785.75±1148.28 µm2, respectively, all P<0.05) and infratemporal regions (125.01±15.55 vs 141.57±10.77 µm, 96.27±13.29 vs 110.83±10.99 µm, and 4925.56±1302.88 vs 6087.78±1061.55 µm2, all P<0.05). The arteriolar WT and WLR were not significantly different between the POAG and control groups, nor were the retinal venular outer diameter (RVOD), retinal venular lumen diameter (RVLD) or venular WT in the supratemporal or infratemporal region. There was a positive correlation between the arteriolar parameters and visual function. In POAG, narrowing of the supratemporal and infratemporal arterioles and a significant reduction in the WSCA is observed, while the arteriolar WT and WLR do not change. Among the venular parameters, the external diameter, internal diameter, WT, WLR, and WSCA of the venules are not affected.

High-mobility group box 1 impairs renal microvascular autoregulatory responses in male and female rats

High-mobility group box 1 (HMGB1) is a nuclear protein that functions as a paracrine signaling molecule when released from the nucleus of stressed or injured cells into the interstitial fluid. Secreted HMGB1 can activate toll-like receptor 4 (TLR4) and we showed that activation of renal TLR4 causes autoregulatory dysfunction. In addition, microvascular function is seriously compromised in hypertension but the specific mechanisms involved are poorly defined. We tested the hypothesis that HMGB1 negatively influences renal microvascular autoregulatory capability by activating TLR4. Experiments were performed in male rats using the blood-perfused juxtamedullary nephron technique. Three groups were studied: control, HMGB1 (~1.25 μg/ml in the blood perfusate) and HMGB1+LPS-RS (TLR4 blocker; ~10 μg/ml in the blood perfusate). Afferent arteriole autoregulatory behavior was assessed in these groups by increasing perfusion pressure from 65 to 170 mmHg in 15 mmHg increments. Starting diameters of male arterioles, measured at 100 mmHg, were similar across all three groups (15.3±0.7; 15.1±0.2 and 15.3±0.1 μm, respectively). When perfusion pressure increased from 65 to 170 mmHg, control arteriole diameter decreased to 69±3% of baseline (P&lt;0.05; n=6), exhibiting normal pressure-induced autoregulatory vasoconstriction. Afferent arteriole diameters in kidneys receiving HMGB1 remained unchanged at 97±1% over the same pressure range (n=9; P&gt;0.05 vs. baseline; P&lt;0.05 compared to control kidneys), indicating significant loss of autoregulatory behavior. In the HMGB1+LPS-RS group, afferent arteriole responses were similar to normal controls and decreased to 76±1% (n=6; P&lt;0.05 vs baseline; P&lt;0.05 vs. HMGB1) over the same pressure range, signifying normalization of autoregulatory behavior by TLR4 blockade. There are few published data on the response of female afferent arterioles to the change in perfusion pressure, so we conducted separate experiments using females in two groups of rats, (normal kidneys with or without HMGB1 in the perfusate blood). Baseline diameters of female arterioles (100 mmHg) were similar across both groups (14.7±0.4 and 14.2±0.3 μm, respectively) and were similar to baseline diameters in males (P&gt;0.05). Increasing perfusion pressure from 65 to 170 mmHg decreased female control arteriole diameter to 78±1% (P&lt;0.05 vs baseline; n=6), reflecting normal autoregulatory vasoconstriction resembling that observed in males. Afferent arteriole diameters in female kidneys receiving HMGB1 actually became slightly larger to 103±1% (P&lt;0.05 vs baseline; P&lt;0.05 vs control kidneys; n=6) by 170 mmHg, indicating significant loss of autoregulatory reactivity and that female renal microvessels respond to HMGB1 similarly to males. These data demonstrate that HMGB1 exposure can impair afferent arteriole autoregulatory capability in male and female rats and suggests that impairment involves HMGB1-dependent TLR4 activation. Study supported by NIH (DK044628). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Combining in vivo two-photon microscopy with ex vivo pressure myography as a novel approach to assess neurovascular coupling

The brain’s vascular network maintains cerebral blood flow and crucially, responds neuronal demands by rapidly altering local perfusion. In vivo techniques using cranial windows can visualise this neurovascular communication and measure real-time blood flow changes. In turn, the ex vivo capillary-to-parenchymal-arteriole preparation (CaPA Prep) can examine the mechanisms of signalling between capillaries and arterioles in response to physiological or pharmacological stimuli, and study these in health and disease models. In order to promote the 3R’s of animal research, and reduce the number of animals required in studies of neurovascular function, we wished to examine whether vessels from mice which have undergone cranial window surgery are comparable to vessels from mice without cranial window surgery by using the ex vivo CaPA Prep.C57 mice underwent craniotomies to implant chronic cranial windows and were left to recover. In order to examine capillary-to-arteriole signalling, we utilised the CaPA Prep, where parenchymal arterioles (&lt;45μms) with attached capillary branches were isolated and pressurised. The capillary branch and arteriole are independently stimulated via a micropipette and the arteriole diameter is recorded. This approach enables study of multiple ion channels integral to neurovascular coupling to be assessed.Cranial window implantation did not significantly affect the function of cerebral vessels, compared to control C57 mice. Mice underwent craniotomies and were left to recover for up to 8 weeks before euthanization. Parenchymal arterioles with attached capillary branches were pressurised to 40mmHg. No significant difference in tone was observed between control and implanted animals (32.7 ± 4.7 vs 29.7 ± 2.57, N = 4-6, P= .56). We next examined the capillary-to-arteriolar KIR2.1 signalling mechanism via application of 10mM K+ to the capillary branch. Responses were not significantly different between control and implanted animals (68.1 ± 13.2 vs 75.2 ± 8.4, N = 4, P= .66) and KIR2.1 function via directly stimulating the arteriole was also not significantly different (74.7 ± 9.4 vs 60.7 ± 5.3, N = 4, P= .24). Arteriole responses to NS309 (3mM) and 60mM K+ were also not significantly different between groups (73.5 ± 11.51 vs 104.8 ± 19.6, N = 4-5, P= .23, 60.6 ± 5.5 vs 64.9 ± 5.5, N = 4-5, P= .59, respectively).Moreover, our preliminary data suggests that in vivo imaging in mice with cranial windows also has no effect on vascular function in relation to pressure induced tone, KIR2.1 capillary-to-arteriolar signalling and responses to NS309 and 60mMK+. Overall, our data suggests cranial window implantation and in vivo imaging preserves vascular function and these mice can be utilised for ex vivo analysis of vessel physiology. Minimising the number of animals avoids the need for additional animals for different techniques, and maximises the data obtained per animal. British Heart Foundation This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Measurement of hippocampal arteriolar diameter and blood velocity in awake head-fixed mice

Cerebral hypoperfusion is associated with neurodegeneration. However, the influence of disease on the microcirculation of specific brain regions is poorly understood. In the current study, we validated a technical approach that allows us to simultaneously image arteriolar diameter and blood velocity in the hippocampi of awake, head-fixed mice. The approach involved implanting a gradient-Index (GRIN) lens into the hippocampus and cementing it in place together with a steel head-fixation bar. Imaging was performed after 7-14 days recovery. On the day of imaging, we intravenously administered Alexa Fluor 633 hydrazide (1.25 mg/kg) to label arterioles, and after 90 minutes, secured the mice on a custom-built stage of a widefield fluorescence microscope. We measured blood velocity in parallel with vessel diameter by imaging fluorescent latex beads infused by tail vein cannulation. Vessel diameter and blood velocity were assessed in 14 vessels from 6 mice. Hypercapnia induces cerebral vasodilation and increases cerebral blood flow. In our experiments, inhalation of 10% CO 2 caused a 12.1 ± 6% (mean ± SEM) increase in vessel diameter and a significant (P&lt;0.01, student’s t-test) increase in blood velocity from 1.09 ± 0.1 to 1.73 ± 0.2 cm/s (mean ± SEM). These data demonstrate the feasibility of this approach to assess microvascular function and perfusion in highly localized brain regions. NIH grant (HL142906) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.