Regional Blood Flow Research Articles

Data-based modeling of cerebral hemodynamics quantifies impairment of cerebral blood flow regulation in type-2 diabetes

We studied the regulation dynamics of cerebral blood velocity (CBv) at middle cerebral arteries (MCA) in response to spontaneous changes of arterial blood pressure (ABP), termed dynamic cerebral autoregulation (dCA), and end-tidal CO2 as proxy for blood CO2 tension, termed dynamic vasomotor reactivity (DVR), by analyzing time-series data collected at supine rest from 36 patients with Type-2 Diabetes Mellitus (T2DM) and 22 age/sex-matched non-diabetic controls without arterial hypertension. Our analysis employed a robust dynamic modeling methodology that utilizes Principal Dynamic Modes (PDM) to estimate subject-specific dynamic transformations of spontaneous changes in ABP and end-tidal CO2 (viewed as two “inputs”) into changes of CBv at MCA measured via Transcranial Doppler ultrasound (viewed as the “output”). The quantitative results of PDM analysis indicate significant alterations in T2DM of both DVR and dCA in terms of two specific PDM contributions that rise to significance (p < 0.05). Our results further suggest that the observed DVR and dCA alterations may be due to reduction of cholinergic activity (based on previously published results from cholinergic blockade data) that may disturb the sympatho-vagal balance in T2DM. Combination of these two model-based “physio-markers” differentiated T2DM patients from controls (p = 0.0007), indicating diabetes-related alteration of cerebrovascular regulation, with possible diagnostic implications.

A new model of portal vein thrombosis in rats with cirrhosis induced by partial portal vein ligation plus carbon tetrachloride and intervened with rivaroxaban

Background and aimsPortal vein thrombosis (PVT) is a common complication of liver cirrhosis that can aggravate portal hypertension. However, there are features of both PVT and cirrhosis that are not recapitulated in most current animal models. In this study, we aimed to establish a stable animal model of PVT and cirrhosis, intervene with anticoagulant, and explore the related mechanism.MethodsFirst, 49 male SD rats received partial portal vein ligation (PPVL), and 44 survival rats were divided into 6 groups: PPVL control group; 4-week, 6 -week, 8-week, and 10-week model group; and the rivaroxaban (RIVA)-treated group. The rats were intoxicated with or without carbon tetrachloride (CCl4) for 4–10 weeks. Seven normal rats were used as the normal controls. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels and parameters for blood coagulation were all assayed with kits. Liver inflammation, collagen deposition and hydroxyproline (Hyp) levels were also measured. The extrahepatic macro-PVT was observed via portal vein HE staining, etc. The intrahepatic microthrombi was stained via fibrin immunohistochemistry. The portal blood flow velocity (PBFV) and diameter were detected via color Doppler ultrasound. Vascular endothelial injury was evaluated by von Willebrand Factor (vWF) immunofluorescence. Fibrinolytic activity was estimated by western blot analysis of fibrin and plasminogen activator inhibitor-1 (PAI-1).ResultsAfter PPVL surgery and 10 weeks of CCl4 intoxication, a rat model that exhibited characteristics of both cirrhosis and extra and intrahepatic thrombi was established. In cirrhotic rats with PVT, the PBFV decreased, both factors of pro- and anti-coagulation decreased, but with relative hypercoagulable state, vascular endothelial injured, and fibrinolytic activity decreased. RIVA-treated rats had improved coagulation function, increased PBFV and attenuated thrombi. This effect was related to the improvements in endothelial injury and fibrinolytic activity.ConclusionsA new rat model of PVT with cirrhosis was established through partial portal vein ligation plus CCl4 intoxication, with the characteristics of macrothrombi at portal veins and microthrombi in hepatic sinusoids, as well as liver cirrhosis. Rivaroxaban could attenuate PVT in cirrhosis in the model rats. The underlying mechanisms of PVT formation in the rat model and pharmacological action of rivaroxaban are related to the regulation of portal blood flow, coagulant factors, and vascular endothelial cell function.

Cerebral blood flow regulation and cognitive performance in hypertension

We examined the relation between transcranial Doppler (TCD) markers of cerebral blood flow regulation and cognitive performance in hypertension (HT) patients to evaluate the predictive value of these markers for cognitive decline. We assessed dynamic cerebral autoregulation (dCA), vasoreactivity to carbon dioxide, and neurovascular coupling (NVC) in the middle (MCA) and posterior (PCA) cerebral arteries of 52 patients. Neuropsychological evaluation included the Montreal Cognitive Assessment and tests covering attention, executive function, processing speed, and memory. Notably, reduced rate time in the PCA significantly predicted better processing speed (p = 0.003). Furthermore, reduced overshoot systolic cerebral blood velocity in the PCA and reduced phase in the VLF range in the MCA (p = 0.021 and p = 0.017, respectively) significantly predicted better memory. Intriguingly, enhanced dCA in the MCA predicted poorer memory performance, while reduced NVC in the PCA predicted both superior processing speed and memory performance. These findings suggest that HT-induced changes in cerebral hemodynamics impact cognitive performance. Further research should verify these observations and elucidate whether these changes represent adaptive responses or neurovascular inefficiency. TCD markers might provide insights into HT-related cognitive decline.

Tissue-Engineered Microvessels: A Review of Current Engineering Strategies and Applications.

Microvessels, including arterioles, capillaries, and venules, play an important role in regulating blood flow, enabling nutrient and waste exchange, and facilitating immune surveillance. Due to their important roles in maintaining normal function in human tissues, a substantial effort has been devoted to developing tissue-engineered models to study endothelium-related biology and pathology. Various engineering strategies have been developed to recapitulate the structural, cellular, and molecular hallmarks of native human microvessels in vitro. In this review, recent progress in engineering approaches, key components, and culture platforms for tissue-engineered human microvessel models is summarized. Then, tissue-specific models, and the major applications of tissue-engineered microvessels in development, disease modeling, drug screening and delivery, and vascularization in tissue engineering, are reviewed. Finally, future research directions for the field are discussed.

Cerebrovascular miRNAs Track Early Development of Alzheimer's Disease and Target Molecular Markers of Angiogenesis and Blood Flow Regulation.

Alzheimer's disease (AD) is associated with impaired cerebral circulation which underscores diminished delivery of blood oxygen and nutrients to and throughout the brain. In the 3xTg-AD mouse model, we have recently found that > 10 cerebrovascular miRNAs pertaining to vascular permeability, angiogenesis, and inflammation (e.g., let-7d, miR-99a, miR-132, miR-133a, miR-151-5p, and miR-181a) track early development of AD. Further, endothelial-specific miRNAs (miR-126-3p, miR-23a/b, miR-27a) alter with onset of overall AD pathology relative to stability of smooth muscle/pericyte-specific miRNAs (miR-143, miR-145). We tested the hypothesis that cerebrovascular miRNAs indicating AD pathology share mRNA targets that regulate key endothelial cell functions such as angiogenesis, vascular permeability, and blood flow regulation. As detected by NanoString nCounter miRNA Expression panel for 3xTg-AD mice, 61 cerebrovascular miRNAs and respective mRNA targets were examined using Ingenuity Pathway Analysis for canonical Cardiovascular (Cardio) and Nervous System (Neuro) Signaling. The number of targets regulated per miRNA were 21±2 and 33±3 for the Cardio and Neuro pathways respectively, whereby 14±2 targets overlap among pathways. Endothelial miRNAs primarily target members of the PDE, PDGF, SMAD, and VEGF families. Individual candidates regulated by≥4 miRNAs that best mark AD pathology presence in 3xTg-AD mice include CFL2, GRIN2B, PDGFB, SLC6A1, SMAD3, SYT3, and TNFRSF11B. miRNAs selective for regulation of endothelial function and respective downstream mRNA targets support a molecular basis for dysregulated cerebral blood flow regulation coupled with enhanced cell growth, proliferation, and inflammation.

Photoactivated Formation of an Extravascular Dynamic Hydrogel as an Intelligent Blood Flow Regulator to Reprogram the Immunogenic Landscape.

Long-term tumor starvation may be a potential strategy to elevate the antitumor immune response by depriving nutrients. However, combining long-term starvation therapy with immunotherapy often yields limited efficacy due to the blockage of immune cell migration pathways. Herein, an intelligent blood flow regulator (BFR) is first established through photoactivated in situ formation of the extravascular dynamic hydrogel to compress blood vessels, which can induce long-term tumor starvation to elicit metabolic stress in tumor cells without affecting immune cell migration pathways. By leveraging methacrylate-modified nanophotosensitizers (HMMAN) and biodegradable gelatin methacrylate (GelMA), the developed extravascular hydrogel dynamically regulates blood flow via enzymatic degradation. Additionally, aPD-L1 loaded into HMMAN continuously blocks immune checkpoints. Systematic in vivo experiments demonstrate that the combination of immune checkpoint blockade (ICB) and BFR-induced metabolic stress (BIMS) significantly delays the progression of Lewis lung and breast cancers by reshaping the tumor immunogenic landscape and enhancing antitumor immune responses.

The Impact of Aging and Biological Sex on Diaphragm Hyperemia and Blood Flow Distribution

INTRODUCTION: Age-related respiratory muscle dysfunction (i.e., the diaphragm) diminishes physical capacity and increases the susceptibility to respiratory failure. The diaphragm dysfunction associated with old age is characterized by decreased diaphragm muscle mass and strength, and increased fatiguability. While inadequate perfusion and diminished microvascular function are well recognized to play a central role in age-related peripheral skeletal muscle dysfunction, the impact of aging on diaphragm hyperemia and blood flow distribution, and whether sex differences exist, has not been investigated. METHODS: Young (Y; 4-6 months) and Old (O; 22-24 months) Fischer 344 rats (n=34) were divided into four groups: 1) Young female (YF; n=8), 2) Young male (YM; n=8), 3) Old female (OF; n=9), and 4) Old male (OM; n=9). Fluorescent microspheres were used to assess bulk and regional diaphragm blood flow at rest and during electrically-induced 1Hz contractions. RESULTS: There were no age-related or sex differences in quiescent diaphragm blood flow (BF) or vascular conductance (VC) ( P&gt;0.05). Age-related differences during 1Hz contractions: The increase in total diaphragm BF was significantly lower in OM (98 ± 11 ml/min/100g) compared to YM (141 ± 7 ml/min/100g; p&lt;0.05). Total and regional diaphragm BF was not different in F rats ( P&gt;0.05); however, medial costal diaphragm VC was decreased in OF (1.2 ± 0.1 ml/mmHg/min/100g) compared to YF (1.8 ± 0.2 ml/mmHg/min/100g; p&lt;0.05). Sex differences during 1Hz contractions: Total diaphragm BF and VC were similar in YF and YM ( P &gt; 0.05). While both ventral and medial costal diaphragm BF responses were not different between YF and YM, dorsal costal diaphragm BF was higher in YF (144 ± 27 ml/min/100g) versus YM (84 ± 11 ml/min/100g; p&lt;0.05). Total and regional (ventral, medial, and dorsal costal) diaphragm BF was significantly higher in OF compared to OM ( p&lt;0.05). CONCLUSION: These data demonstrate that aging impaired the ability of the diaphragm to augment BF in response to contractile activity in M rats and decreased medial costal diaphragm VC during contractions in F rats with no significant effect on diaphragmatic hyperemia. In regards to sex differences, these data suggest that both YF and OF may have a greater regional recruitment of the diaphragm compared to YM and OM. The data herein provide a putative mechanism for age-related diaphragm contractile dysfunction and future studies are needed to investigate the impact of aging and biological sex on diaphragm vascular function. National Institute of Aging 1R15AG078060, Ruth L. Kirschstein National Research Service Awards from the National Heart, Lung, and Blood Institute 1F31HL167618-01 and 1F31HL170643-01, and Sustained Momentum for Investigators with Laboratories Established (SMILE) Grants at Kansas State University. This is the full abstract presented at the American Physiology Summit 2024 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.

Machine learning techniques for predicting microvascular network hemodynamics

Existing techniques to image microvascular networks in vivo do not allow a direct and accurate measurement of several hemodynamic variables such as the wall shear stress (WSS). They cannot also provide a full 3D characterization of blood velocity and red blood cell (RBC) concentration profiles in every vessel in a microvascular network. Such physiological parameters however play critical roles in blood flow regulation, disease progression, angiogenesis, and hemostasis. Theoretical models of network blood flow, often used for hemodynamic predictions in experimentally acquired images of the microvascular network, cannot provide the full 3D blood velocity, RBC concentration and WSS profiles as these models assume one-dimensional flow governed by Poiseuille’s law. In contrast, high-fidelity computational models that simulate flow of blood as a suspension of deformable RBCs and model the 3D vessel geometry can readily predict such physiological variables with high accuracy. Such high-fidelity computational models have recently been applied to predict hemodynamic variables in microvascular networks in silico composed of many vessels and vascular junctions. Such models, however, tend to become computationally expensive with increasing size of the network; therefore, they are not feasible for use in large networks at organ scale. To overcome this limitation, we developed a machine learning (ML) approach that can predict hemodynamic variables in 3D and with high accuracy. The ML models are based on artificial neural network and convolution-based U-net models. Using experimentally acquired images of the microvascular networks, inputs at a few inlets, and a “bank” of database that we have developed, these ML models can predict flow and RBC distribution in all vessels in the network, 3D blood velocity and RBC concentration profiles over the cross-section of every vessel, 3D WSS profiles, and time-dependent variations in blood flow in any vessel. The prediction from the ML models compare very well against the true data. Also, the prediction time using ML is significantly less than that of the high-fidelity models. The current ML models, which to our knowledge are the first of their kind, are highly promising for image-based predictions of sub-cellular resolved capillary hemodynamics in organ-scale networks. This study paves the way for AI to make hemodynamic predictions in organ-scale capillary vessel networks while retaining the sub-cellular scale details and overcoming the limitations of the in vivo imaging techniques, with potential applications in hematological and microvascular disorders, angiogenesis, and vascular-mediated drug delivery. Funded by NIH (R01-EY033003) and NSF (CBET 2302212). This is the full abstract presented at the American Physiology Summit 2024 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.

Calcium-activated chloride channels in pericytes shape capillary electrical signaling

The brain vasculature, composed of penetrating arterioles (PAs) giving rise to the dense capillary network, facilitates continuous energy substrate delivery to neurons and glia by tightly controlling blood flow. The capillaries are covered by perivascular cells known as pericytes, which exhibit varying morphological and physiological properties based on their location in relation to the terminal arteriole, and these contribute to blood flow control within the capillary network in distinct ways. Thin-strand pericytes —the focus of this study—are located in the deep capillary bed. Serendipitously, we have discovered a robust chloride current during perforated patch clamp experiments on these thin-strand pericytes. We hypothesized that this current is mediated by calcium-activated chloride channels (CaCCs), which may influence electrical signaling and thereby regulate blood flow. Our data reveal that this robust current is dependent on external calcium concentration and can be blocked by voltage-gated calcium channel blockers, depletion of endoplasmic reticulum calcium stores, and calcium-activated chloride channel blockers. This suggests a mechanism wherein calcium entry into the cytosol via voltage-gated channels and intracellular calcium release govern the activity of CaCCs in the thin-strand pericyte membrane. Using two-photon microscopy, we further observed that blocking CaCCs led to PA dilation and hyperemia. Together, our data indicate a novel role for CaCCs in thin-strand pericytes, where they modulate electrical signaling across the capillary bed in response to intracellular calcium activity. By providing a depolarizing signal countering hyperpolarizing electrical signaling, these channels contribute to the intricate regulation of blood flow and vessel dilation. This work was supported by the NIH (grants 1R01AG066645, 5R01NS115401, 1DP2NS121347-01), and the American Heart Association (19IPLOI34660108). This is the full abstract presented at the American Physiology Summit 2024 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.

Postmenopausal Women with Obesity have Reduced Leg Endothelial Function and Exercise Vasodilatory Capacity

Background: Obesity (OB) is highly prevalent in postmenopausal women; particularly increased abdominal visceral adipose tissue contributes to endothelial dysfunction and cardiovascular risk. The endothelium plays an important role on blood flow (BF) and pressure control at rest and during exercise. However, it is unknown how different body mass index (BMI) categories influence upper and lower limb endothelial function and BF responses to exercise in postmenopausal women. Purpose: The purpose was to examine upper and lower limb endothelial function at rest and BF regulation during low-intensity exercises in OB, overweight (OW), and lean (LN) postmenopausal women. We hypothesized that endothelial function and BF responses to submaximal exercise in both limbs will be attenuated in OB compared to the OW and LN groups. Methods: Women were classified as OB (30.0-39.9 kg/m2; n = 13), OW (25.0-29.9 kg/m2; n = 15), and LN (18.5-24.9 kg/m2; n = 11) by BMI. Flow-mediated dilation (FMD) of the brachial (BA-FMD) and superficial femoral arteries (FA-FMD) were measured using ultrasound. BF and vascular conductance (VC) in the brachial (BA-BF and BA-VC) and femoral (FA-BF and FA-VC) arteries were measured during separate 3-stage incremental rhythmic handgrip and plantarflexion exercises (PFE) at 5, 15, and 30 % of maximal strength and calculated 1-repetition max (1RM), respectively. Results: No differences in BA-FMD were observed among the groups. FA-FMD was significantly lower in OB (2.6 ± 1.4%) compared to OW (4.3 ± 1.9%) and LN (4.2 ± 0.7%) groups (P &lt; 0.05). Increases in FA-BF (OB: 462 ± 229 vs. OW: 616 ± 173 vs. LN: 640 ± 141 mL/min; P &lt; 0.001) and FA-VC (OB: 410 ± 176 vs. OW: 585 ± 155 vs LN: 623 ± 153 mL/min*100mmHg; P &lt; 0.001) were attenuated during PFE at 30% of 1RM in OB compared to OW and LN. Upper-body exercise vasodilation was not attenuated by OB. FA-BF and FA-VC during PFE at 30% of 1RM were correlated with FA-FMD (FA-BF: r = 0.423, P = 0.007, FA-VC: r = 0.367, P = 0.021) and BMI (FA-BF: r = -.386, P = 0.015, FA-VC: r = -.456, P = 0.004). Conclusion: Postmenopausal women with OB have blunted leg endothelial function and exercise vasodilator function during submaximal dynamic plantarflexion exercise compared to LN and OW. These findings suggest that OB may contribute to reduce leg endothelial function, and vasodilator function during exercise in postmenopausal women. No support of funding information to disclose. This is the full abstract presented at the American Physiology Summit 2024 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.

Novel regulation of kidney function by gastrointestinal hormones

The control of whole-body energy metabolism involves intricate crosstalk between multiple organ systems including the gut and the brain that play well-recognized roles in this process. However, the important contributions and mechanisms by other organs are poorly understood. Errors in metabolic regulation can lead to human metabolic diseases including diabetes and obesity that affect 75% of the population and can lead to significant comorbidities. Improving our mechanistic understanding of multi-organ metabolic crosstalk in health and disease is essential for developing highly effcient and new therapeutic approaches. Macula densa (MD) cells in the kidney are chief regulators of renal blood flow and tissue remodeling. We hypothesized that the kidney is a major player in body metabolism via a new mechanism of gut-kidney crosstalk that involves the gut hormones gastrin and cholecystokinine (CCK) activating intrarenal, MD-specific mechanisms to increase blood flow and filtration, progenitor cells and tissue growth factors. High-resolution MD bulk and single-cell transcriptome analysis was performed from freshly isolated, enriched MD cells using MD-GFP mouse kidneys. Single cell MD Ca2+ signaling was analyzed in vivo using intravital multiphoton microscopy (MPM) of Sox2-GT mice that express the ratiometric Ca2+ reporter GCaMP6f/tdTomato in all renal cells. The altered expression of MD specific markers in response to gastrin/CCK8 stimuli was studied using western blot and the novel MDgeo immortalized cell line cultured in vitro. RNA sequencing and transcriptome analysis identified the gastrin/CCK receptor Cckbr as one of the highest expressed genes in MD versus control kidney cells. Intravital multiphoton imaging of Sox2-GCaMP6 reporter mouse kidneys revealed robust and entirely MD cell-specific calcium signaling in response to systemic gastrin/CCK injection. Using the novel MDgeo immortalized cell line cultured in vitro, CCK8 treatment led to 3-fold increases in MD cell synthesis of Prostaglandin E2 (PGE2)-generating COX2 and CCN1 that are established mediators of MD-induced glomerular hyperfiltration and tissue remodeling, respectively. Chronic treatment of Ren1d-Confetti mice with Darunavir, an HIV protease inhibitor significantly increased plasma CCK levels, Ren+ mesenchymal progenitor cell number and clonality, renal cell proliferation and tissue hypertrophy. This study uncovered new regulatory mechanisms of systemic metabolism especially the role of MD cells in the kidney. Repurposing the commonly used HIV drug Darunavir for kidney and metabolic diseases may provide therapeutic benefit for millions of patients worldwide. DK064234, DK123564, DK135290. This is the full abstract presented at the American Physiology Summit 2024 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.

Pharmacological Targeting of Endothelial KCa Channels In Vivo Augments Vasodilatory Responses in Rat Femoral and Coronary Arteries in Health and Disease

As the primary interface between the blood and organs, the vascular endothelium functions as a key regulator of tissue blood flow by sensing chemical and mechanical stimuli and producing vasoactive signals to dynamically control intraluminal diameter in local arterioles and upstream arteries. Flow-mediated dilation (FMD) is an important physiological mechanism to modify local tissue perfusion in response to dynamic metabolic conditions, and reduced FMD responses are indicative of endothelial dysfunction, the latter being a major risk factor for cardiovascular disease. We have previously reported that pharmacological enhancement of endothelial KCa2.3 and KCa3.1 channel activity by SKA-31 augmented vasodilatory responses in small resistance arteries and intact hearts isolated from healthy and Type 2 Diabetic (T2D) rats (RC Mishra et al, 2014, 2021). In the present study, we have investigated the ability of SKA-31 to enhance endothelium-dependent vasodilation in vivo in femoral and coronary arteries of healthy and T2D male rats. Methods: FMD responses associated with reactive hyperemia were measured in a side branch of the femoral artery by high sensitivity Doppler ultrasound following release of an inflated pressure cuff placed on the distal hind limb of male Sprague Dawley (SD) and T2D Goto-Kakizaki (GK) rats (26-32 weeks of age). Rats were injected i.p. with either 10 mg/kg SKA-31 or drug vehicle ~ 3 hours prior to cuff inflation. M-mode echocardiographic imaging was used to visualize intraluminal diameter changes in the left main coronary artery in the same four treatment groups in response to an increase in inhalational isoflurane from 2% to 5%. Results: Femoral artery blood flow increased ~2-fold during reactive hyperemia in vehicle treated SD rats, as quantified by velocity-time integral, and did not increase further with SKA-31 treatment. In contrast, the FMD response in vehicle treated T2D GK rats was substantially blunted vs. SD rats, and SKA-31 administration restored this response to the level observed in healthy controls, which was still observable 15-24 hours later. In vehicle treated SD rats, exposure to 5% isoflurane increased left main coronary arterial diameter by 50-60%, which reversed to baseline following return to the original 2% isoflurane condition. SKA-31 treatment of SD rats increased basal arterial diameter by ~30%, but did not significantly modify the observed increase in arterial diameter evoked by 5% isoflurane inhalation, compared with vehicle treatment. In vehicle treated T2D GK rats, exposure to 5% isoflurane did not increase coronary artery diameter over a 10 min period, which is suggestive of endothelial dysfunction. However, SKA-31 treatment significantly increased basal coronary arterial diameter by 40-50%, and promoted a rapid and robust increase in diameter following exposure to 5% isoflurane (80-90% increase above that observed in vehicle treated T2D rats), which reversed to baseline upon return to 2% isoflurane inhalation. No enhancement of isoflurane evoked coronary vasodilation was observable in T2D GK rats 15-24 hrs post-SKA-31 treatment. In summary, these data provide the first direct demonstration that low dose administration of a KCa channel activator can enhance vasodilatory responses in vivo. This study was supported by research funding to APB from the Canadian Institutes of Health Research (MOP-142467) and NSERC (RGPIN 2017-04116). This is the full abstract presented at the American Physiology Summit 2024 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.

Signaling switches maintain intercellular communication in the vascular endothelium

The endothelium is a sophisticated coordination center that controls a wide range of vascular functions, which include the regulation of blood pressure and blood flow via changes in vascular contractility. To coordinate vascular function, cell communication and interactions are required for tissue level responses to emerge. A significant form of cell-cell communication occurs by the propagation of Ca2+ signals between cells (‘Ca2+ waves’). The objective of our study was to tease apart the mechanisms driving these intercellular Ca2+ waves in the vascular endothelium. We hypothesised that diffusion of free Ca2+ would drive endothelial Ca2+ wave propagation and effect vessel diameter changes. To investigate the mechanisms, intact mesenteric arteries from male Sprague Dawley rats were mounted in an en face preparation, stained with the Ca2+ indicator Cal-520/AM and were imaged on specialised epifluorescence microscopes. Intercellular endothelial signaling was manipulated using caged compounds in concert with precise spatial and temporal control of UV illumination, as well as global or localized drug application. We show that multiple mechanisms maintain communication so that Ca2+ wave propagation occurs irrespective of the status of cell connectivity. Contrary to our hypothesis, regenerative IP3-induced IP3 production transmits Ca2+ signals between adjoining cells and explains the propagated vasodilation that underlies the increased blood flow accompanying tissue activity. By controlling the production of IP3, the inositide is itself suffcient to evoke a regenerative phospholipase C-dependent Ca2+ wave across coupled cells. None of gap junctions, Ca2+ diffusion nor the release of extracellular messengers are required to support this type of intercellular Ca2+ signaling. Surprisingly, when a discontinuity between cells was created using a fire-polished pipette tip, signal was propagated to the other side of the discontinuity and was able to drive propagated vasodilation. Experiments using counter flow and localised perfusion in the absence and presence of P2Y inhibitors revealed that it is ATP released as a diffusible extracellular messenger that transmits Ca2+ signals across endothelial discontinuities. These results show that signaling switches underlie endothelial cell-cell signal transmission, and reveal how communication is maintained in the face of endothelial damage. The findings provide a new framework for understanding Ca2+ wave propagation and cell-cell signaling in the endothelium. This work was funded by the British Heart Foundation (RG/F/20/110007; PG/20/9/34859 ). This is the full abstract presented at the American Physiology Summit 2024 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.

Chronic Hypoxia during Gestation Disrupts Spontaneous Ca2+ Oscillations in Middle Cerebral Arterial Myocytes of Fetal Sheep

Long Term Hypoxic (LTH) stress is associated with an elevated risk of intracranial hemorrhage and stroke in newborns. Existing evidence illustrates that fetal sheep subjected to LTH conditions exhibit compromised cerebrovascular reactivity and arterial development, leading to perturbations in cerebral blood flow. Given the critical role of whole-cell Ca2+ waveforms in the contraction of middle cerebral arterial (MCA) myocytes and the regulation of cerebral blood flow, a comprehensive understanding of Ca2+ signaling patterns can provide insight into hypoxia-related cerebrovascular disease in neonates. This study was designed to test the hypothesis that intrauterine LTH disrupts whole-cell Ca2+ oscillations in fetal MCA myocytes. The hypothesis was addressed using MCAs isolated from term fetal sheep (approximately 140 days of gestation) delivered by cesarean section. These fetuses were carried by ewes residing at low-altitude (700 m) or high-altitude conditions (3801 m) for over 100 days of gestation. Ca2+ oscillatory activity was recorded using confocal fluorescence imaging techniques in an en face myocyte preparation. Spontaneous Ca2+ oscillations were evaluated in the presence and absence of 30 mM K+ to depolarize the myocytes, with or without 10 μM ryanodine, which blocks ryanodine receptor mediated Ca2+ release. The results of the study reveal that LTH decreases oscillatory activity and restricts the augmentation of activity following membrane depolarization. Furthermore, LTH induces dysregulation in spatial and temporal Ca2+ signals, manifesting as reduced event amplitude, shortened event duration, and decreased area under the curve (AUC). These findings highlight the impact of gestational hypoxia on multiple aspects of Ca2+ signaling in fetal lamb MCA, which may contribute to cerebrovascular dysfunction in the newborn. R01HL155295, R01HL149608, Advanced Imaging and Microscopy Core Loma Linda University School of Medicine. This is the full abstract presented at the American Physiology Summit 2024 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.

Heme oxidation of NO-receptor soluble guanylyl cyclase is an important contributor to cerebrovascular and cognitive dysfunctions

Introduction: Decreased cerebral blood flow (CBF) is one of the major hemodynamic alterations leading to neurodegeneration and age-related cognitive decline. Nitric Oxide (NO)-dependent vasomotor reactivity is central in regulating cerebrovascular hemodynamics and adequate brain blood perfusion. NO receptor Soluble Guanylyl Cyclase (sGC) is the primary mediator of NO-dependent vasodilation. Oxidative stress, often persisting in diseased vasculature, renders sGC insensitive to NO and impairs the NO signaling. The objective of our study was to investigate the role of sGC oxidation in regulation CBF and brain function. Hypothesis: Oxidative stress disrupts NO/cGMP signaling in brain by decreasing sGC activity via oxidation of sGC heme. Approach: To assess causal effect of sGC oxidation on NO signaling function we administered ODQ, a sGC-specific heme oxidizing agent, to simulate long-term effect of sGC oxidation in cerebral vasculature. Two groups of young wild-type male and female mice (4 months old C57BL/6) were treated intraperitoneally (IP) twice a week for one month with ODQ (20 mg/kg) or a solvent as control. Changes in cerebrovascular reactivity and memory function were assessed and compared in treated and control groups. Using a non-invasive pulsed Doppler ultrasound-based system we assessed the changes in blood flow velocity (PVF, % of baseline) in the mouse middle cerebral artery (MCA) of male and female groups. MCA vasodilation was induced by bolus IP injection of NO-donor sodium nitroprusside (SNP) or BAY 58-2667, an allosteric NO-independent sGC activator. Memory function was assessed by the Novel Object Recognition Task (NORT, RI, recognition index) in all experimental groups. Western blotting and densitometry assessed the expression of major sGC subunits (α1, α2 and β1) in cleared brain lysates from ODQ-treated and control groups. Results: We observed a significantly blunted vasodilative response to SNP (1 mg/kg) in ODQ-treated mice vs controls of both genders (PVF, max response at 2 min post-injection, males 73.9 ± 10.4% (n=7/7) vs 58.5 ± 8.6 %, p=0.01; females (n=6/6) 77.4 ± 10.6 % vs 61.9 ± 5.4 %, p=0.01). Changes in response to NO-donor were more pronounced in males than females. The difference in BAY 58-2667 response between ODQ-treated and control groups was not statistically significant. ODQ significantly reduced the long-term memory in males but not female, according to NORT (RI, males (n=7/7) 0.58 ± 0.13 vs 0.69 ± 0.05; p=0.01; females (n=6/6) ODQ 0.59 ± 0.17 vs 0.73 ± 0.1, p=0.13). No statistically significant difference in expression of sGC subunits between control and ODQ-treated (n= 4/4) of male and female groups was determined. Conclusions: ODQ treatment significantly impairs vasodilation response to NO-donor but not to NO-independent sGC activator in mice MCA. ODQ treatment negatively affects long-term memory function in male, but not female mice. ODQ treatment does not significantly affect the expression of sGC subunits. Together our data suggest that the oxidation of sGC heme moiety impairs the regulation of cerebral blood flow of both genders and impairs long-term memory function gender-specifically in young mice. This research was supported by National Institute of Health grants RAG071999A (Iraida Sharina), HL139838, and American Heart Association 23TPA1070711 (Emil Martin). This is the full abstract presented at the American Physiology Summit 2024 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.

Heat-related changes in the velocity and kinetic energy of flowing blood influence the human heart's output during hyperthermia.

Passive whole-body hyperthermia increases limb blood flow and cardiac output ( ), but the interplay between peripheral and central thermo-haemodynamic mechanisms remains unclear. Here we tested the hypothesis that local hyperthermia-induced alterations in peripheral blood flow and blood kinetic energy modulate flow to the heart and . Body temperatures, regional (leg, arm, head) and systemic haemodynamics, and left ventricular (LV) volumes and functions were assessed in eight healthy males during: (1) 3h control (normothermic condition); (2) 3h of single-leg heating; (3) 3h of two-leg heating; and (4) 2.5h of whole-body heating. Leg, forearm, and extracranial blood flow increased in close association with local rises in temperature while brain perfusion remained unchanged. Increases in blood velocity with small to no changes in the conduit artery diameter underpinned the augmented limb and extracranial perfusion. In all heating conditions, increased in association with proportional elevations in systemic vascular conductance, related to enhanced blood flow, blood velocity, vascular conductance and kinetic energy in the limbs and head (all R2≥0.803; P<0.001), but not in the brain. LV systolic (end-systolic elastance and twist) and diastolic functional profiles (untwisting rate), pulmonary ventilation and systemic aerobic metabolism were only altered in whole-body heating. These findings substantiate the idea that local hyperthermia-induced selective alterations in peripheral blood flow modulate the magnitude of flow to the heart and through changes in blood velocity and kinetic energy. Localised heat-activated events in the peripheral circulation therefore affect the human heart's output. KEY POINTS: Local and whole-body hyperthermia increases limb and systemic perfusion, but the underlying peripheral and central heat-sensitive mechanisms are not fully established. Here we investigated the regional (leg, arm and head) and systemic haemodynamics (cardiac output: ) during passive single-leg, two-leg and whole-body hyperthermia to determine the contribution of peripheral and central thermosensitive factors in the control of human circulation. Single-leg, two-leg, and whole-body hyperthermia induced graded increases in leg blood flow and . Brain blood flow, however, remained unchanged in all conditions. Ventilation, extracranial blood flow and cardiac systolic and diastolic functions only increased during whole-body hyperthermia. The augmented with hyperthermia was tightly related to increased limb and head blood velocity, flow and kinetic energy. The findings indicate that local thermosensitive mechanisms modulate regional blood velocity, flow and kinetic energy, thereby controlling the magnitude of flow to the heart and thus the coupling of peripheral and central circulation during hyperthermia.

Brain Endothelial Senescence and Vascular Density in Mid-Life Obesity: Exploring Neurovascular Dysfunction and Cognitive Impairment

The obesity epidemic is a major health challenge in the United States, with more than 42% of American adults being obese. Growing evidence shows that mid-life obesity has detrimental effects on cerebrovasculature, and it compromises cerebral blood flow (CBF) regulation and promotes the pathogenesis of vascular cognitive impairment and dementia (VCID). The cerebral microcirculation and the "neurovascular unit" (NVU) play a key role in maintaining healthy brain function. Our previous studies have shown that obesity-induced NVU dysfunction impairs endothelium-mediated neurovascular coupling (NVC) and contributes to VCID. Although great advances have been made in the last decade, the cellular mechanisms underlying NVU dysfunction, CBF dysregulation and NVC impairment remain not clear and there are no available treatments. Cellular senescence is a typical cellular response that occurs in physiological and pathological conditions. In this context, we found that middle-life obesity promotes cellular senescence in the brain and in the vasculature. Moreover, senescence of cells within the NVU has been linked to cognitive impairment and neuro-vascular dysfunction. To provide proof-of-concept for our studies on obesity induced NVU senescence, we used the novel transgenic mouse model (p16-3MR mouse), which allows the visualization and selective elimination of senescent cells. We evaluated senescence through the expression of RFP (senescent marker) with flow cytometry and through the analysis of single cell transcriptomic. NVC and vascular density was measured with functional ultrasound imaging (ICONEUS) and cognitive function was tested with radial arm water maze test (RAWM). We found increased senescence in endothelial cells in high fat diet-fed (HFD; 60% kcal from fat) mice compared to ones fed with standard diet (SD; 10% kcal from fat). Moreover, we demonstrated the functional significance of senescent cells by treating older HFD-fed obese mice with the well-characterized, potent senolytic compound Navitoclax/ABT263, which selectively kills senescent cells. We found that in obese older mice NVC responses were significantly impaired and were rescued by senolytic treatment. HFD-fed mice had impaired learning plasticity in RAWM. Restoration of NVC responses by ABT263 treatment associated with significant cognitive benefit. Overall, our work is novel in that it will be the first to demonstrate that obesity-induced senescence is a critical contributing factor to the pathogenesis of VCID, providing insights into potential therapeutic interventions. NIH R03AG070479, K01AG073614, R21AG080775, American Heart Association, Hevolution/AFAR. This is the full abstract presented at the American Physiology Summit 2024 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.

Elevated plasma aldosterone impairs functional hyperemia and cognitive function

Aldosterone, a steroid hormone, plays an important role in blood pressure homeostasis and the maintenance of plasma electrolyte levels by activating the mineralocorticoid receptor (MR) in renal distal tubule and collecting duct epithelial cells. Recent studies revealed that MRs are also expressed in other tissues, including cardiac myocytes, vascular smooth muscle cells, and vascular endothelial cells (EC), and that elevated plasma aldosterone, termed hyperaldosteronemia (HA), has deleterious effects on the cardiovascular system. HA is present in 10-30% of hypertensive patients and unrecognized and asymptomatic HA is estimated to occur in &gt; 10% of individuals with normal blood pressure. Despite the high prevalence of HA, little is known about its impact on cerebral blood flow (CBF) regulation and brain health. This study focused on the physiological processes that support the on-demand delivery of blood to regions of heightened neuronal activity (functional hyperemia). Specifically, we examined the impact of HA on the recently discovered novel mechanism, termed capillary-to-arteriole signaling, through which capillaries and their strong inward rectifier K+ (Kir 2.1) channels play a significant role in functional hyperemia. Importantly, early deficits in functional hyperemia are a hallmark of small vessel diseases of the brain, which are significant contributors to cognitive impairment and dementia. Employing HA model mice, we examined the impact of HA on functional hyperemia, capillary-to-arteriole signaling, Kir2.1 channel activity in freshly isolated capillary ECs (cECs), and cognitive function. Functional hyperemia, measured as whisker stimulation-induced CBF increases using laser Doppler flowmetry, was impaired in HA animals compared to vehicle-treated animals. Retrograde capillary-to-arteriole signaling, evaluated as upstream arteriolar dilation in response to capillary stimulation with 10 mM K+ in Capillary-Parenchymal Arteriole (CaPA), preparations was significantly attenuated in HA mice. Furthermore, cEC Kir2.1 channel currents, recorded using the conventional whole-cell configuration of the patch-clamp technique, were significantly smaller in HA mice compared to vehicle-treated mice. Further, HA model animals obtained lower scores in the Novel Object Recognition test, indicating that cognitive function in the form of memory retention may be impacted by elevated plasma aldosterone. These data suggest that HA impairs functional hyperemia and cognitive function, and that HA may be a novel risk factor for vascular cognitive impairment. This work was supported by The National Institute of Health (P20-GM-135007 to MK and R01-HL-142888 to GCW). This is the full abstract presented at the American Physiology Summit 2024 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.

Novel Use of 1-methylhistamine as a Biomarker of the Histamine Response to Exercise

Histamine is released within skeletal muscle during exercise, promoting a sustained post-exercise vasodilation and contributing to adaptive responses to exercise training. Tracking this response is complicated by the short half-life and localization of histamine, requiring invasive methods such as intramuscular microdialysis or arteriovenous catheterization. Surrogates based on regional blood flow to assess post-exercise vasodilation require skilled use of expensive equipment, such as ultrasonography. These approaches may not be available in many research or athletic settings. Therefore, we explored the use of 1-methylhistamine (1-MH), a primary metabolite of histamine, as a novel biomarker of histamine’s release in response to aerobic and resistance exercise. We hypothesized that urinary 1-MH production would increase following exercise and that it would be positively correlated with post-exercise femoral artery blood flow and vascular conductance. Six healthy (1F, 5M; 22±4y; 24.3±1.9 kg·m2) trained participants (VO2peak: 51.8±7.7 ml·kg−1·min−1; back squat 1-repetition maximum, 1-RM: 1.66±0.27 kg·bodyweight−1) completed two exercise sessions separated by 1-wk: Aerobic, 30-min of cycling exercise at 70% VO2peak; Resistance, 6 sets of 10 repetitions of back squat exercise at 70% 1-RM. Femoral artery blood flow and vascular conductance were measured and venous blood samples were obtained before, immediately after, and throughout 2-h of post-exercise recovery. Urine was collected during the 24-h before and 2-, and 24-h post-exercise. Histamine and 1-MH concentrations were measured via high-performance liquid chromatography. Results are presented as mean ± SD and were compared by repeated-measures ANOVA and Pearson’s correlations. Blood flow increased immediately after exercise vs before (Aerobic: 442±60 vs 184±58 mL·min−1, p&lt;0.05; Resistance: 626±190 vs 194±54 mL·min−1, p&lt;0.05) and remained elevated 30-min into recovery (Aerobic: 273±63, p&lt;0.05; Resistance: 396±99 mL·min−1, p&lt;0.05). The area under the curve for blood flow after exercise tended to be greater following resistance (16117±5504 mL) vs aerobic (8732±5360 mL, p=0.06) exercise. When averaged across exercise modes, urine 1-MH production was elevated 2-h post-exercise vs before (23.6±15.9 vs 9.2±5.9 μg/h, p&lt;0.05). Urine 1-MH production tended to correlate with percent elevation in femoral artery blood flow (r=0.59, p=0.09) and correlated with the percent elevation in vascular conductance following exercise (r=0.53, p&lt;0.05). These results demonstrate that both aerobic and resistance exercise elicit a histamine response and support the utility of urinary 1-MH production as a biomarker of histamine’s release in response to exercise. Supported by NIH grant R01 AG072805. This is the full abstract presented at the American Physiology Summit 2024 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.

Effects of Myocardial Infarction-induced Heart Failure on Diaphragm Arteriolar Vasorelaxation

INTRODUCTION: Diaphragm atrophy and contractile dysfunction are prevalent in heart failure (HF), diminishing physical capacity and quality of life. The delivery of blood flow and oxygen necessary to support the metabolic demand of contractions is largely governed by the resistance vasculature (i.e., arterioles) with the endothelium playing a central role in arteriolar vasorelaxation. Adequate perfusion and blood flow distribution, and thus resistance vessel vasodilation, is a major determinate of diaphragm contractile function. While the mechanistic bases of HF-induced diaphragm dysfunction continue to be elucidated, the impact of HF on diaphragm vasomotor control has not been investigated. METHODS: Adult (6 mo) Sprague-Dawley rats (n=7) were divided into two groups: 1) Healthy Control (HC; n=4) and 2) MI-induced heart failure (HF; n=3). First-order arterioles (1A) from the medial costal diaphragm were isolated, cannulated, and pressurized at 90 cmH2O and allowed to equilibrate for 60 min to develop spontaneous tone. Thereafter, endothelium-dependent and -independent vasorelaxation responses to cumulative doses of acetylcholine (ACh; 10−9 to 10−4M) and sodium nitroprusside (SNP; 10−9 to 10−4M) were determined. RESULTS: There were no differences in spontaneous development (%) or maximal diameter (μm) between HC (20 ± 4%; 178 ± 11 μm) and HF (18 ± 2%; 184 ± 29 μm) diaphragm 1As ( P &gt; 0.05). Maximal ACh-mediated relaxation (%) was significantly reduced in HF rats compared to HC rats (52 ± 2 versus 68 ± 5%; P &lt; 0.05). Maximal endothelial-independent vasorelaxation with SNP, was not different between HC and HF rats (71 ± 3 versus 73 ± 1%; P &gt; 0.05). CONCLUSION: The preliminary data herein demonstrate that HF impaired endothelial function and vasomotor function in the medial costal diaphragm resistance vasculature. This suggests that, in HF, there may be a redistribution of blood flow to less effcient regions of the diaphragm (e.g., ventral costal) to sustain contractile function and compensate for the diminished medial costal vasomotor function demonstrated herein. Studies including a larger sample size are warranted to investigate the impact of HF on regional blood flow distribution and resistance vessel function in the diaphragm. Such investigations would yield novel mechanistic insights into HF-induced diaphragm dysfunction. National Institute of Aging 1R15AG078060, Ruth L. Kirschstein National Research Service Awards from the National Heart, Lung, and Blood Institute 1F31HL167618-01, and Sustained Momentum for Investigators with Laboratories Established (SMILE) Grants at Kansas State University. This is the full abstract presented at the American Physiology Summit 2024 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.