Smooth Muscle α-Actin Expression in Mitral Valve Interstitial Cells is Important for Mediating Extracellular Matrix Remodeling

Background: Mitral valve prolapse (MVP) affects 3–6% of the total population including those with connective tissue disorders. Treatment is limited, and patients commonly require surgery which can be impermanent and insuperable. Abnormal prolapse of mitral valve leaflets into the left atria is cause...

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Main Authors: Bailey K. Dye, Catalina Butler, Joy Lincoln
Format: Article
Language:English
Published: MDPI AG 2020-08-01
Series:Journal of Cardiovascular Development and Disease
Subjects:
Online Access:https://www.mdpi.com/2308-3425/7/3/32
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spelling doaj-0503f6c61b4d4596b229bd977eb50b342020-11-25T03:42:25ZengMDPI AGJournal of Cardiovascular Development and Disease2308-34252020-08-017323210.3390/jcdd7030032Smooth Muscle α-Actin Expression in Mitral Valve Interstitial Cells is Important for Mediating Extracellular Matrix RemodelingBailey K. Dye0Catalina Butler1Joy Lincoln2Biomedical Sciences Graduate Program, The Ohio State University, Columbus, OH 43217, USAHarvard College, Boston, MA 02138, USADepartment of Pediatrics, Medical College of Wisconsin, Milwaukee, WI 53226, USABackground: Mitral valve prolapse (MVP) affects 3–6% of the total population including those with connective tissue disorders. Treatment is limited, and patients commonly require surgery which can be impermanent and insuperable. Abnormal prolapse of mitral valve leaflets into the left atria is caused by disturbances to the composition and organization of the extracellular matrix (ECM), that weaken biomechanics. This process, known as myxomatous degeneration is characterized by an abnormal accumulation of proteoglycans, in addition to collagen fiber disruption and elastic fiber fragmentation. The underlying mechanisms that promote myxomatous degeneration to the point of biomechanical failure are unknown, but previous histological studies of end-stage diseased tissue have reported abnormal α-smooth muscle actin (SMA) in a subset of heart valve interstitial cells (VICs); however, the contribution of these abnormal cells to MVP pathogenesis has not been extensively examined. Methods: In vivo and in vitro approaches were used. Mice harboring a <i>Fbn1<sup>C1039G</sup></i> mutation mimic human Marfan Syndrome and develop MVP. Using these mice, temporal and spatial changes in SMA expression relative to myxomatous degeneration were examined using histological techniques. In parallel in vitro experiments, SMA expression was downregulated in primary porcine mitral VICs directly using siRNA, and indirectly using the actin depolymerizing agent Latrunculin A. In addition, the regulation of SMA in VICs by mechanical stiffness was explored relative to ECM remodeling. Results: We show, in mitral valves from <i>Fbn1<sup>C1039G/+</sup></i> mice, that abnormal increases in SMA expression in VICs are evident during early postnatal stages of disease, prior to significant myxomatous degeneration as indicated at later stages by increased proteoglycans and collagen type I (Col1a1). Furthermore, abnormal SMA expression continues to increase during the course of pathogenesis and is localized to the mid belly region of the mitral valve leaflets from 10 weeks. Using an in vitro approach, we demonstrate that reduced SMA function by direct siRNA or indirect Latrunculin A treatment attenuates proteoglycan and Col1a1 expression in porcine mitral VICs. While upstream, we provide insights to show that SMA is regulated by mechanical tension in VICs to promote changes in ECM homeostasis. Conclusions: Together, our data show that in VICs, SMA, an actin binding protein, is important for mediating ECM remodeling associated with phenotypes observed in myxomatous degeneration, and its expression is regulated by mechanical tension. These novel insights could inform the development of future non-surgical therapeutics to halt the progression of mitral valve degeneration thereby avoiding end-stage prolapse.https://www.mdpi.com/2308-3425/7/3/32heart valveextracellular matrixheart valve interstitial cellsmyxomatous degeneration
collection DOAJ
language English
format Article
sources DOAJ
author Bailey K. Dye
Catalina Butler
Joy Lincoln
spellingShingle Bailey K. Dye
Catalina Butler
Joy Lincoln
Smooth Muscle α-Actin Expression in Mitral Valve Interstitial Cells is Important for Mediating Extracellular Matrix Remodeling
Journal of Cardiovascular Development and Disease
heart valve
extracellular matrix
heart valve interstitial cells
myxomatous degeneration
author_facet Bailey K. Dye
Catalina Butler
Joy Lincoln
author_sort Bailey K. Dye
title Smooth Muscle α-Actin Expression in Mitral Valve Interstitial Cells is Important for Mediating Extracellular Matrix Remodeling
title_short Smooth Muscle α-Actin Expression in Mitral Valve Interstitial Cells is Important for Mediating Extracellular Matrix Remodeling
title_full Smooth Muscle α-Actin Expression in Mitral Valve Interstitial Cells is Important for Mediating Extracellular Matrix Remodeling
title_fullStr Smooth Muscle α-Actin Expression in Mitral Valve Interstitial Cells is Important for Mediating Extracellular Matrix Remodeling
title_full_unstemmed Smooth Muscle α-Actin Expression in Mitral Valve Interstitial Cells is Important for Mediating Extracellular Matrix Remodeling
title_sort smooth muscle α-actin expression in mitral valve interstitial cells is important for mediating extracellular matrix remodeling
publisher MDPI AG
series Journal of Cardiovascular Development and Disease
issn 2308-3425
publishDate 2020-08-01
description Background: Mitral valve prolapse (MVP) affects 3–6% of the total population including those with connective tissue disorders. Treatment is limited, and patients commonly require surgery which can be impermanent and insuperable. Abnormal prolapse of mitral valve leaflets into the left atria is caused by disturbances to the composition and organization of the extracellular matrix (ECM), that weaken biomechanics. This process, known as myxomatous degeneration is characterized by an abnormal accumulation of proteoglycans, in addition to collagen fiber disruption and elastic fiber fragmentation. The underlying mechanisms that promote myxomatous degeneration to the point of biomechanical failure are unknown, but previous histological studies of end-stage diseased tissue have reported abnormal α-smooth muscle actin (SMA) in a subset of heart valve interstitial cells (VICs); however, the contribution of these abnormal cells to MVP pathogenesis has not been extensively examined. Methods: In vivo and in vitro approaches were used. Mice harboring a <i>Fbn1<sup>C1039G</sup></i> mutation mimic human Marfan Syndrome and develop MVP. Using these mice, temporal and spatial changes in SMA expression relative to myxomatous degeneration were examined using histological techniques. In parallel in vitro experiments, SMA expression was downregulated in primary porcine mitral VICs directly using siRNA, and indirectly using the actin depolymerizing agent Latrunculin A. In addition, the regulation of SMA in VICs by mechanical stiffness was explored relative to ECM remodeling. Results: We show, in mitral valves from <i>Fbn1<sup>C1039G/+</sup></i> mice, that abnormal increases in SMA expression in VICs are evident during early postnatal stages of disease, prior to significant myxomatous degeneration as indicated at later stages by increased proteoglycans and collagen type I (Col1a1). Furthermore, abnormal SMA expression continues to increase during the course of pathogenesis and is localized to the mid belly region of the mitral valve leaflets from 10 weeks. Using an in vitro approach, we demonstrate that reduced SMA function by direct siRNA or indirect Latrunculin A treatment attenuates proteoglycan and Col1a1 expression in porcine mitral VICs. While upstream, we provide insights to show that SMA is regulated by mechanical tension in VICs to promote changes in ECM homeostasis. Conclusions: Together, our data show that in VICs, SMA, an actin binding protein, is important for mediating ECM remodeling associated with phenotypes observed in myxomatous degeneration, and its expression is regulated by mechanical tension. These novel insights could inform the development of future non-surgical therapeutics to halt the progression of mitral valve degeneration thereby avoiding end-stage prolapse.
topic heart valve
extracellular matrix
heart valve interstitial cells
myxomatous degeneration
url https://www.mdpi.com/2308-3425/7/3/32
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