Biomedical Sciences ETDs

Publication Date

Spring 5-10-2019

Abstract

Chronic hypoxia (CH)-induced vasoconstriction has been implicated in the pathogenesis of pulmonary hypertension (pHTN) in infants with chronic cardiorespiratory disorders. Although endothelial dysfunction, reduced nitric oxide (NO) bioavailability and oxidative stress contribute to a variety of cardiovascular disorders, their contribution to enhanced vasoconstrictor reactivity in neonatal pHTN is poorly understood. We therefore hypothesized that neonatal CH augments pulmonary vasoconstrictor reactivity by limiting NO-dependent pulmonary vasodilation and by promoting the generation of reactive oxygen species (ROS).

Enzymatic sources of ROS in the vasculature include NADPH oxidase isoforms, xanthine oxidase, and uncoupled endothelial nitric oxide synthase (eNOS). The mitochondria are also a major source of cellular ROS, but surprisingly little is known about the role of mitochondrial-derived ROS (mitoROS) in neonatal pHTN. Based on preliminary studies from our laboratory and evidence that protein kinase Cβ (PKCβ) mediates mitochondrial dysfunction and oxidative stress in neurodegenerative diseases, we further hypothesized that neonatal CH enhances pulmonary vasoconstrictor sensitivity via PKCβ-dependent activation of mitoROS generation.

To test these hypotheses, we employed pharmacologic approaches to assess the role of NO, mitoROS and PKCβ on basal vascular tone and agonist-induced vasoconstrictor sensitivity in both isolated (in situ) lungs and pressurized pulmonary arteries (~150 μm) from control and CH (2 weeks at 380 mmHg) neonatal rats. CH neonates displayed elevated right ventricular (RV) systolic pressure (in vivo) and RV hypertrophy, indicative of pHTN. CH increased both basal pulmonary arterial tone and vasoconstrictor reactivity to the thromboxane analog, U-46619. Interestingly, we observed that endogenous NO limits CH-dependent increases in pulmonary vasoconstriction. Exposure to CH also enhanced NO-dependent vasodilation to arginine vasopressin (AVP), pulmonary expression of NOS III (eNOS), and eNOS phosphorylation at activation residue serine-1177. Additional studies using in situ lungs revealed an effect of scavenging ROS or inhibition of PKCβ to attenuate CH-dependent increases in basal tone and agonist-induced pulmonary vasoconstrictor sensitivity. Selective inhibitors of PKCβ or mitoROS similarly reduced basal tone in arteries from CH rats, while having no effect in control arteries.

We conclude that, in contrast to our hypothesis, enhanced basal tone and agonist-induced vasoconstriction following neonatal CH is limited by increased NO-dependent pulmonary vasodilation resulting from greater eNOS expression and phosphorylation at activation residue serine-1177. Furthermore, both PKCβ and mitoROS contribute to enhanced pulmonary vasoconstrictor sensitivity following CH in neonates. These signaling mediators represent new potential therapeutic targets in the treatment of neonatal pHTN.

Keywords

Neonatal pulmonary hypertension, PKCbeta, mitochondrial reactive oxygen species, nitric oxide

Document Type

Dissertation

Language

English

Degree Name

Biomedical Sciences

Level of Degree

Doctoral

Department Name

Biomedical Sciences Graduate Program

First Committee Member (Chair)

Thomas C. Resta

Second Committee Member

Mary Beth Goens

Third Committee Member

Nancy L. Kanagy

Fourth Committee Member

Nikki L. Jernigan

Fifth Committee Member

Diane S. Lidke

Download

Share

COinS