Enhanced notch signaling modulates unproductive revascularization in response to nitric oxide-angiopoietin signaling in a mouse model of peripheral ischemia

Effect of four weeks of repeated sprint training with blood flow restriction on upper limb microcirculation in boxers

This study evaluates the impact of 4 weeks of 40% arterial occlusion pressure (AOP) blood flow restriction (BFR) combined with repeated sprint training (RST) on the microcirculation function of upper limbs in boxers and investigates the potential mechanisms underlying improvements in microcirculation from the perspective of blood factor changes. Thirty-six healthy male collegiate boxers were assigned to either a blood flow restriction training group (Experimental Group, EG, n = 18) or a conventional training group (Control Group, CG, n = 18), completing 12 sessions over 4 weeks (three sessions per week). The training regimen for EG and CG was identical, except EG underwent BFR during the training sessions. Measurements of arm circumference, muscle strength, microcirculation function (4 indicators), and blood factor (4 indicators) were taken one day before training began and the day after the final training session. Using two-factor repeated measures ANOVA, significant differences were observed in EG's arm circumference at tension, muscle strength, microvascular blood flow perfusion, transcutaneous oxygen pressure, muscle oxygen saturation, nitric oxide levels, endothelial nitric oxide synthase, endothelin-1, and vascular endothelial growth factor, all showing improvements from baseline. In contrast, CG only demonstrated increased upper limb strength, with no significant changes in the other indicators. These findings suggest that while both training protocols may enhance muscle strength, the addition of BFR notably improves upper limb microcirculation and muscle strength in collegiate boxers by modulating the secretion of blood factors such as endothelial nitric oxide synthase, endothelin-1, and vascular endothelial growth factor.

Hypoxia preconditioning increases Notch1 activity by regulating DNA methylation in vitro and in vivo

BACKGROUND

Our previous research has demonstrated that hypoxic preconditioning (HPC) can improve spatial learning and memory abilities in adult mice. Adult hippocampal neurogenesis has been associated with learning and memory. The Neurogenic locus notch homolog protein (Notch) was involved in adult hippocampal neurogenesis, as well as in learning and memory. It is currently unclear whether the Notch pathway regulates hippocampal neuroregeneration by modifying the DNA methylation status of the Notch gene following HPC.

METHOD

The HPC animal model and cell model were established through repeated hypoxia exposure using mice and the mouse hippocampal neuronal cell line HT22. Step-down test was conducted on HPC mice. Real-time PCR and Western blot analysis were used to assess the mRNA and protein expression levels of Notch1 and hairy and enhancer of split1 (HES1). The presence of BrdU-positive cells and Notch1 expression in the hippocampal dental gyrus (DG) were examined with confocal microscopy. The methylation status of the Notch1 was analyzed using methylation-specific PCR (MS-PCR). HT22 cells were employed to elucidate the impact of HPC on Notch1 in vitro.

RESULTS

HPC significantly improved the step-down test performance of mice with elevated levels of mRNA and protein expression of Notch1 and HES1 (P < 0.05). The intensities of the Notch1 signal in the control group, the H group and the HPC group were 2.62 ± 0.57 × 107, 2.87 ± 0.84 × 107, and 3.32 ± 0.14 × 107, respectively, and the number of BrdU (+) cells in the hippocampal DG were 1.83 ± 0.54, 3.71 ± 0.64, and 7.29 ± 0.68 respectively. Compared with that in C and H group, the intensity of the Notch1 signal and the number of BrdU (+) cells increased significantly in HPC group (P < 0.05). The methylation levels of the Notch1 promoter 0.82 ± 0.03, 0.65 ± 0.03, and 0.60 ± 0.02 in the C, H, and HPC groups, respectively. The methylation levels of Notch1 decreased significantly (P < 0.05). The effect of HPC on HT22 cells exhibited similarities to that observed in the hippocampus.

CONCLUSION

HPC may confer neuroprotection by activating the Notch1 signaling pathway and regulating its methylation level, resulting in the regeneration of hippocampal neurons.

Endothelial cells signaling and patterning under hypoxia: a mechanistic integrative computational model including the Notch-Dll4 pathway

Introduction: Several signaling pathways are activated during hypoxia to promote angiogenesis, leading to endothelial cell patterning, interaction, and downstream signaling. Understanding the mechanistic signaling differences between endothelial cells under normoxia and hypoxia and their response to different stimuli can guide therapies to modulate angiogenesis. We present a novel mechanistic model of interacting endothelial cells, including the main pathways involved in angiogenesis. Methods: We calibrate and fit the model parameters based on well-established modeling techniques that include structural and practical parameter identifiability, uncertainty quantification, and global sensitivity. Results: Our results indicate that the main pathways involved in patterning tip and stalk endothelial cells under hypoxia differ, and the time under hypoxia interferes with how different stimuli affect patterning. Additionally, our simulations indicate that Notch signaling might regulate vascular permeability and establish different Nitric Oxide release patterns for tip/stalk cells. Following simulations with various stimuli, our model suggests that factors such as time under hypoxia and oxygen availability must be considered for EC pattern control. Discussion: This project provides insights into the signaling and patterning of endothelial cells under various oxygen levels and stimulation by VEGFA and is our first integrative approach toward achieving EC control as a method for improving angiogenesis. Overall, our model provides a computational framework that can be built on to test angiogenesis-related therapies by modulation of different pathways, such as the Notch pathway.

Emerging topics in microvascular research: Advancing our understanding by interdisciplinary exploration

Historically, major advances in microvascular research have been made by integrating physiology and bioengineering approaches. This Special Topics Issue focuses on providing a spotlight on emerging areas of microvascular research, showcasing how interdisciplinary collaborations and application of novel techniques can impact our understanding of tissue‐specific microvascular remodeling by integrating cell behaviors across scales. The authors in this issue investigate pericyte physiology, perturbations to uteroplacental blood flow, bone microvascular alterations in aging, molecular markers of revascularization, and microfluidic devices to mimic the lymphatic system. The articles highlight the continued importance of expanding our understanding of the microvascular system in health, and disease extends microvascular boundaries in the face of current paradigms, and illustrates how emerging leaders in the field are creating new scientific niches.

MicroRNA-24-3p Targets Notch and Other Vascular Morphogens to Regulate Post-ischemic Microvascular Responses in Limb Muscles

MicroRNAs (miRs) regulate complex processes, including angiogenesis, by targeting multiple mRNAs. miR-24-3p-3p directly represses eNOS, GATA2, and PAK4 in endothelial cells (ECs), thus inhibiting angiogenesis during development and in the infarcted heart. miR-24-3p is widely expressed in cardiovascular cells, suggesting that it could additionally regulate angiogenesis by acting on vascular mural cells. Here, we have investigated: 1) new miR-24-3p targets; 2) the expression and the function of miR-24-3p in human vascular ECs; 3) the impact of miR-24-3p inhibition in the angiogenesis reparative response to limb ischemia in mice. Using bioinformatics target prediction platforms and 3'-UTR luciferase assays, we newly identified Notch1 and its Delta-like ligand 1 (Dll1) to be directly targeted by miR-24-3p. miR-24-3p was expressed in human ECs and pericytes cultured under normal conditions. Exposure to hypoxia increased miR-24-3p in ECs but not in pericytes. Transfection with a miR-24-3p precursor (pre-miR-24-3p) increased miR-24-3p expression in ECs, reducing the cell survival, proliferation, and angiogenic capacity. Opposite effects were caused by miR-24-3p inhibition. The anti-angiogenic action of miR-24-3p overexpression could be prevented by simultaneous adenovirus (Ad)-mediated delivery of constitutively active Notch intracellular domain (NICD) into cultured ECs. We next demonstrated that reduced Notch signalling contributes to the anti-angiogenic effect of miR-24-3p in vitro. In a mouse unilateral limb ischemia model, local miR-24-3p inhibition (by adenovirus-mediated miR-24-3p decoy delivery) restored endothelial Notch signalling and increased capillary density. However, the new vessels appeared disorganised and twisted, worsening post-ischemic blood perfusion recovery. To better understand the underpinning mechanisms, we widened the search for miR-24-3p target genes, identifying several contributors to vascular morphogenesis, such as several members of the Wingless (Wnt) signalling pathway, β-catenin signalling components, and VE-cadherin, which synergise to regulate angiogenesis, pericytes recruitment to neoformed capillaries, maturation, and stabilization of newly formed vessels. Among those, we next focussed on β-catenin to demonstrate that miR-24-3p inhibition reduces β-catenin expression in hypoxic ECs, which is accompanied by reduced adhesion of pericytes to ECs. In summary, miR-24-3p differentially targets several angiogenesis modulators and contributes to autonomous and non-autonomous EC crosstalk. In ischemic limbs, miR-24-3p inhibition increases the production of dysfunctional microvessels, impairing perfusion. Caution should be observed in therapeutic targeting of miR-24-3p.

Anti-Cancer Effect of Melatonin via Downregulation of Delta-like Ligand 4 in Estrogen-Responsive Breast Cancer Cells

BACKGROUND

The Notch signaling pathway has a key role in angiogenesis and Delta - Like Ligand 4 (DLL4) is one of the main ligands of Notch involved in cell proliferation in sprouting vessels.

OBJECTIVE

In this study, we aimed to evaluate the expression of DLL4 in primary breast tumors and to examine the effect of melatonin on DLL4 expression in vitro.

METHODS

Eighty-five breast tumor and paired adjacent non-tumor tissue samples were collected. Apoptosis assay was performed on breast cancer cells to evaluate melatonin effects. Western blot and quantitative RT-PCR were used to measure DLL4 expression. Then, we investigated the effect of melatonin on the expression of DLL4 in four breast cancer cell lines at RNA and protein levels. We also performed a probabilistic neural network analysis to study genes closely associated with DLL4 expression.

RESULTS

Our results showed a significantly higher expression of DLL4 in tumor tissues compared to non-tumor tissues (P = 0.027). Melatonin treatment substantially attenuated DLL4 expression in BT474 and MCF-7 cells, but not in SK-BR-3 and MDA-MB-231 cells. Also, melatonin induced apoptosis in all four cell lines. Network analysis revealed a set of 15 genes that had close association and interaction with DLL4. DLL4 was overexpressed in breast cancer tissues as compared to the non-tumor tissues.

CONCLUSION

It can be concluded that melatonin treatment attenuated DLL4 expression only in estrogen- responsive breast cancer cells and is able to induce apoptosis in breast cancer cells.

Enhanced notch signaling modulates unproductive revascularization in response to nitric oxide-angiopoietin signaling in a mouse model of peripheral ischemia

INTRODUCTION

Arteriolargenesis can be induced by concomitant stimulation of nitric Oxide (NO)-Angiopoietin receptor (Tie)-Vascular Endothelial Growth Factor (VEGF) signaling in the rat mesentery angiogenesis assay. We hypothesized that the same combination of exogenously added growth factors would also have a positive impact on arteriolargenesis and, consequently, the recovery of blood flow in a model of unilateral hindlimb ischemia.

RESULTS AND METHODS

NO-Tie mice had faster blood flow recovery compared to control mice, as assessed by laser speckle imaging. There was no change in capillary density within the ischemic muscles, but arteriole density was higher in NO-Tie mice. Given the previously documented beneficial effect of VEGF signaling, we tested whether NO-Tie-VEGF mice would show further improvement. Surprisingly, these mice recovered no differently from control, arteriole density was similar and capillary density was lower. Dll4 is a driver of arterial specification, so we hypothesized that Notch1 expression would be involved in arteriolargenesis. There was a significant upregulation of Notch1 transcripts in NO-Tie-VEGF compared with NO-Tie mice. Using soluble Dll4 (sDll4), we stimulated Notch signaling in the ischemic muscles of mice. NO-Tie-sDll4 mice had significantly increased capillary and arteriole densities, but impaired blood flow recovery.

CONCLUSION

These results suggest that Dll4 activation early on in revascularization can lead to unproductive angiogenesis and arteriolargenesis, despite increased vascular densities. These results suggest spatial and temporal balance of growth factors needs to be perfected for ideal functional and anatomical revascularisation.