Abstract

Changes in vascular structure and reactivity are amongst the most important that occur during the transition from fetal to newborn life, and are guided by the principle of ensuring adequate coupling of blood flow to metabolism. A clinical consequence of maladaptive fetal vascular adaptation to hypoxia is an increased probability for loss of cerebral autoregulation, increased risk for neonatal encephalopathy, and hypoxicischemic cerebral injury. MLCK is a very specific calcium-calmodulin dependent enzyme, with its only known substrate being MLC20, and is essential for the ability of VSMCs within resistance arteries to appropriately contract or relax in response to changes in intravascular pressure. Several studies have demonstrated that despite low abundance of MLCK in immature arteries, rates of MLC20 phosphorylation are high, suggesting age-dependent changes in MLCK catalytic activity. Our first study explored the hypothesis that the greater apparent catalytic activity of MLCK in fetal arteries is due to age-dependent changes in intracellular distribution of MLCK relative to pMLC20. Optimization experiments yielded similar estimates of MLCK Vmax and Km in fetal and adult artery homogenates. A custom-designed, computer-controlled apparatus allowed electrical stimulation of intact arterial segments for measurement of rates of MLC20 phosphorylation and confocal analysis of MLCK relative to pMLC20. These experiments revealed that fractional activation of MLCK is greater in the fetus than the adult and that MLCK activation is faster in the peri-luminal region of VSMCs in both groups. The second study explored the hypothesis that subcellular changes in MLCK distribution relative to MLC20 and aActin contribute to hypoxic modulation of fetal artery contractility. As compared to normoxic term fetal lambs, carotid arteries from fetal lambs maintained at high altitude displayed diminished contractility, with no parallel changes in MLCK protein or mRNA. Through integration of confocal analysis and total MLCK mass, we developed a model to calculate subcellular fractions of MLCK. These studies demonstrate that dynamic translocation of contractile MLCK mass accounts for a significant component of diminished contractility in response to hypoxia. Of clinical importance, a better understanding of MLCK translocation will help facilitate future strategies in the treatment of human neonates that exhibit maladaptive arterial remodeling.

LLU Discipline

Physiology

Department

Physiology

School

School of Medicine

First Advisor

William J Pearce

Second Advisor

Olayemi Adeoye

Third Advisor

Erik Behringer

Fourth Advisor

Eugenia Mata-Greenwood

Fifth Advisor

Surya Nauli

Degree Name

Doctor of Philosophy (Medical Science)

Degree Level

Ph.D.

Year Degree Awarded

2021

Date (Title Page)

12-2020

Language

English

Library of Congress/MESH Subject Headings

Myosin-Light-Chain Kinase -- physiology; Epoxomicin; Arteries; Oligopeptides; Ubiquitination

Type

Dissertation

Page Count

xii, 152 p.

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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