Hypoxic modulation of fetal vascular MLCK abundance, localization, and function

Abstract

Changes in vascular contractility are among the most important physiological effects of acute and chronic fetal hypoxia. Given the essential role of Myosin Light Chain Kinase (MLCK) in smooth muscle contractility, and its heterogeneous distribution, this study explores the hypothesis that subcellular changes in MLCK distribution contribute to hypoxic modulation of fetal carotid artery contractility. Relative to common carotid arteries from normoxic term fetal lambs (FN), carotids from fetal lambs gestated at high altitude (3802m) (FH) exhibited depressed contractility without changes in MLCK mRNA or protein abundance. Patterns of confocal colocalization of MLCK with aActin and MLC20 enabled calculation of subcellular MLCK fractions: 1) colocalized with the contractile apparatus; 2) colocalized with aActin distant from the contractile apparatus; 3) not colocalized with aActin. Chronic hypoxia did not affect MLCK abundance in the contractile fraction, despite a concurrent decrease in contractility. Organ culture for 72h under 1% O2 decreased total MLCK abundance in FN and FH carotid arteries, but decreased the contractile MLCK abundance only in FH carotid arteries. Correspondingly, culture under 1% O2 depressed contractility more in FH than FN carotid arteries. In addition, hypoxia appeared to attenuate ubiquitin-independent proteasomal degradation of MLCK, as reported for other proteins. In aggregate, these results demonstrate that the combination of chronic hypoxia followed by hypoxic culture can induce MLCK translocation among at least three subcellular fractions with possible influences on contractility, indicating that changes in MLCK distribution are a significant component of fetal vascular responses to hypoxia.

Maternal Undernutrition Modulates Neonatal Rat Cerebrovascular Structure, Function, and Vulnerability to Mild Hypoxic-Ischemic Injury via Corticosteroid-Dependent and -Independent Mechanisms

“…MUN during late gestation produced a programming effect evident in P11/P12 neonates that increased cerebrovascular smooth muscle contractile differentiation, as revealed by increased NM-MHC and SM-MHC colocalization with αActin (Figure 4B,D). This finding, together with previous reports that expression of non-muscle myosin heavy chain decreases with vascular maturation [32,34], emphasizes that contractile protein abundance and colocalization are not always tightly coupled [56,57]. Simultaneous administration of MET during late gestation MUN significantly enhanced αActin colocalization with both SM-MHC and NM-MHC (Figure 4B,D), revealing a lasting, but modest effect of corticosteroids on basal levels of smooth muscle differentiation in neonatal cerebral arteries.…”