Biology subjects

Madden, E.

Publications and source records attributed to Madden, E..

3 recordsLinked to original sources

bioRxiv2025

Hypoxia responses in arginase 2 deficient mice enhance cardiovascular health

RATIONALEPhysiological responses to hypoxia involve adaptations in the hematopoietic and cardiovascular systems, which work together to ensure adequate oxygen delivery to tissues for energy production. The arginine/nitric oxide (NO) pathway regulates both systems through its effects on erythropoiesis and vasodilation. In Tibetan populations native to high-altitude hypoxia, increased NO production from arginine and decreased arginine metabolism by arginase contribute to these adaptive mechanisms. These metabolic changes enhance tissue oxygen delivery and reduce the risk of hypoxic pulmonary hypertension. Here, we hypothesize that genetic deletion of mitochondrial arginase 2 (Arg2) in mice will enhance cardiovascular effects and mitigate hypoxia-induced pulmonary hypertension. METHODSComplete blood counts, bone marrow erythroid differentiation, plasma arginine and NO (measured as nitrite), right ventricular systolic pressure (RVSP), heart rate, heart weight, and blood pressure were measured in wild-type (WT) and Arg2 knockout (Arg2KO) mice exposed to short-term (6, 12, 48, or 72 hours) or long-term (3 weeks) hypoxia. RESULTSUnder normoxic conditions, Arg2KO and WT mice exhibit similar RBC counts, hemoglobin levels, hematocrit, heart rate, systolic and diastolic blood pressures, and heart weight (all P > 0.05). WT mice increase erythropoiesis at 12 hours of hypoxia, including proerythroblasts (stage I, P = 0.004), polychromatic erythroblasts (stage III, P = 0.0004), and orthochromatic erythroblasts (stage IV, P = 0.03), but Arg2KO mice do not increase erythropoiesis. After 48 hours of hypoxia, Arg2KO mice increase proerythroblasts (stage I, P = 0.0008), but levels remain significantly lower than in WT mice. Plasma arginine and NO levels increase under hypoxia. NO levels peak at 12 hours of hypoxia in WT mice, then decline rapidly. In contrast, NO levels in Arg2KO mice are higher than in WT mice, with sustained elevations at 48 hours of hypoxia (P = 0.03). Arg2KO mice have significantly higher plasma arginine levels than WT at 6, 12, and 72 hours of hypoxia (all P < 0.05). Under chronic hypoxia, Arg2KO and WT mice show similar RBC counts, hemoglobin levels, hematocrit, and NO levels. Unlike WT, Arg2KO mice do not increase RVSP (P = 0.4) and have lower mean arterial (P = 0.03) and diastolic blood pressures (P = 0.01), as well as much lower heart rates (P < 0.0001). Additionally, small blood vessels increase in lungs of Arg2KO mice (CD31, P = 0.02; vWF, P = 0.6). CONCLUSIONSArginine metabolism in the mitochondria plays a key role in modulating adaptive responses to hypoxia. Deletion of Arg2 results in delayed erythropoiesis under acute hypoxia, but better cardiovascular health, as indicated by higher levels of nitrite and arginine, and lower RVSP, blood pressure, and heart rate with chronic hypoxia.

physiology↗

bioRxiv2024

Dysfunctional mechanotransduction regulates the progression of PIK3CA-driven vascular malformations

Somatic activating mutations in PIK3CA are common drivers of vascular and lymphatic malformations. Despite common biophysical signatures of tissues susceptible to lesion formation, including compliant extracellular matrix and low rates of perfusion, lesions vary in clinical presentation from localized cystic dilatation to diffuse and infiltrative vascular dysplasia. The mechanisms driving the differences in disease severity and variability in clinical presentation and the role of the biophysical microenvironment in potentiating progression are poorly understood. Here, we investigate the role of hemodynamic forces and the biophysical microenvironment in the pathophysiology of vascular malformations, and we identify hemodynamic shear stress and defective endothelial cell mechanotransduction as key regulators of lesion progression. We found that constitutive PI3K activation impaired flow-mediated endothelial cell alignment and barrier function. We show that defective shear stress sensing in PIK3CAE542Kendothelial cells is associated with reduced myosin light chain phosphorylation, junctional instability, and defective recruitment of vinculin to cell-cell junctions. Using 3D microfluidic models of the vasculature, we demonstrate that PIK3CAE542Kmicrovessels apply reduced traction forces and are unaffected by flow interruption. We further found that draining transmural flow resulted in increased sprouting and invasion responses in PIK3CAE542K microvessels. Mechanistically, constitutive PI3K activation decreased cellular and nuclear elasticity resulting in defective cellular tensional homeostasis in endothelial cells which may underlie vascular dilation, tissue hyperplasia, and hypersprouting in PIK3CA-driven venous and lymphatic malformations. Together, these results suggest that defective nuclear mechanics, impaired cellular mechanotransduction, and maladaptive hemodynamic responses contribute to the development and progression of PIK3CA-driven vascular malformations.

bioengineering↗

bioRxiv2022

Fc mediated pan-sarbecovirus protection after alphavirus vector vaccination

Two group 2B {beta}-coronaviruses (sarbecoviruses) have caused regional and global epidemics in modern history. The mechanisms of cross protection driven by the sarbecovirus spike, a dominant immunogen, are less clear yet critically important for pan-sarbecovirus vaccine development. We evaluated the mechanisms of cross-sarbecovirus protective immunity using a panel of alphavirus-vectored vaccines covering bat to human strains. While vaccination did not prevent virus replication, it protected against lethal heterologous disease outcomes in both SARS-CoV-2 and clade 2 bat sarbecovirus HKU3-SRBD challenge models. The spike vaccines tested primarily elicited a highly S1-specific homologous neutralizing antibody response with no detectable cross-virus neutralization. We found non-neutralizing antibody functions that mediated cross protection in wild-type mice were mechanistically linked to FcgR4 and spike S2-binding antibodies. Protection was lost in FcR knockout mice, further supporting a model for non-neutralizing, protective antibodies. These data highlight the importance of FcR-mediated cross-protective immune responses in universal pan-sarbecovirus vaccine designs.

microbiology↗