Biology Reference
In-Depth Information
Chapter 9
Consequences of Elastolysis
A. McGarry Houghton, Majd Mouded, and Steven D. Shapiro
Abstract Elastic fibers are an essential and irreplaceable structural component of
lung tissue, blood vessels, and skin. Degradation of elastic fibers in these organs
results in emphysema, aortic aneurysm, and solar elastosis (aging skin), respec-
tively. Enzymes capable of degrading elastin have been termed elastases. This
chapter will discuss the properties of the elastases, discuss the consequences of
elastic fiber breakdown (elastolysis), and review the emerging reports of none-
lastolytic functions of elastases in health and disease.
9.1
Introduction
Elastin is one of the most long-lived and inert substances known. Few proteinases
have the capacity to degrade elastin, and many that do are termed “elastases,” to
highlight their potency. The name should not suggest that elastin degradation is a
physiologic function of the enzyme. For one, it is difficult to understand under what
circumstances degrading elastin would be beneficial given the importance of elastin
to the structural and functional integrity of the vascular system, lung, and skin.
Second, elastases have been around quite a long time, being present in prokaryotes.
Elastin, on the other hand, has evolved relatively recently. Elastin is a vertebrate-
specific protein dating to time of the sharks that allowed for the transition from an
open to a closed, pulsatile circulatory system. Elastin also was critical for the lung
to evolve from itself being a muscular pump to being an elastic organ that functions
within a pump (the diaphragm and other respiratory muscles). Hence, it is unlikely
that elastases were meant to degrade a protein yet to evolve. Luckily, it is difficult to
degrade elastin, and its proteinase inhibitors, such as alpha
1
-antitrypsin (A1AT), are
highly expressed in the blood and tissues to prevent uncontrolled elastolysis. As a
A. McGarry Houghton (
*
), M. Mouded, and S.D. Shapiro
Division of Pulmonary, Allergy, and Critical Care Medicine, Department of Medicine, University
of Pittsburgh School of Medicine, NW628 Montefiore, 3459 Fifth Avenue, Pittsburgh, PA 15261,
USA
e-mail: houghtonm@dom.pitt.edu
