Cardiac overexpression of metallothionein rescues cardiac contractile dysfunction and endoplasmic reticulum stress but not autophagy in sepsis

Abstract

Sepsis is characterized by systematic inflammation where oxidative damage plays a key role in organ failure. This study was designed to examine the impact of the antioxidant metallothionein (MT) on lipopolysaccharide (LPS)-induced cardiac contractile and intracellular Ca 2+ dysfunction, oxidative stress, endoplasmic reticulum (ER) stress and autophagy. Mechanical and intracellular Ca 2+ properties were examined in hearts from FVB and cardiac-specific MT overexpression mice treated with LPS. Oxidative stress, activation of mitogen-activated protein kinase pathways (ERK, JNK and p38), ER stress, autophagy and inflammatory markers iNOS and TNFα were evaluated. Our data revealed enlarged end systolic diameter, decreased fractional shortening, myocyte peak shortening and maximal velocity of shortening/relengthening as well as prolonged duration of relengthening in LPS-treated FVB mice associated with reduced intracellular Ca 2+ release and decay. LPS treatment promoted oxidative stress (reduced glutathione/glutathione disulfide ratio and ROS generation). Western blot analysis revealed greater iNOS and TNFα, activation of ERK, JNK and p38, upregulation of ER stress markers GRP78, Gadd153, PERK and IRE1α, as well as the autophagy markers Beclin-1, LCB3 and Atg7 in LPS-treated mouse hearts without any change in total ERK, JNK and p38. Interestingly, these LPS-induced changes in echocardiographic, cardiomyocyte mechanical and intracellular Ca 2+ properties, ROS, stress signaling and ER stress (but not autophagy, iNOS and TNFα) were ablated by MT. Antioxidant N-acetylcysteine and the ER stress inhibitor tauroursodeoxycholic acid reversed LPS-elicited depression in cardiomyocyte contractile function. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. LPS activated AMPK and its downstream signaling ACC in conjunction with an elevated AMP/ATP ratio, which was unaffected by MT. Taken together, our data favor a beneficial effect of MT in the management of cardiac dysfunction in sepsis. DISCLOSURES

Endotoxin Tolerance Represents a Distinctive State of Alternative Polarization (M2) in Human Mononuclear Cells

“…Metallothioneins are a group of small proteins with a variety of functions, including protection from oxidative damage, as well as influencing zinc homeostasis and angiogenesis, all of which may have important roles during endotoxin tolerance. Metallothionein expression has also been linked with protection from acute lung injury and cardiac dysfunction during endotoxemia mainly by modulating inflammation as well as enhancement of endothelial integrity (62,63). Moreover, metallothionein expression has also been shown to be increased with age leading to a low bioavailability of zinc, a consequent thymic involution and a basic level of immunosuppression in the elderly, phenomena that become stabilized at a very old age (64).…”

Autophagy in sepsis: Degradation into exhaustion?

“…8 Accumulating evidence from in vitro and in vivo studies [9][10][11][12][13][14][15] suggest that autophagy plays a protective role in sepsis, although contradictory findings have been reported. 16,17 In support of this notion, newly tested therapeutic agents in animal models have targeted modulation of the same molecular pathway-autophagy. 10,[18][19][20][21][22] In this review, we discuss the role of autophagy in sepsis.…”

Septic cardiomyopathy in rat LPS-induced endotoxemia: relative contribution of cellular diastolic Ca2+ removal pathways, myofibrillar biomechanics properties and action of the cardiotonic drug levosimendan

“…This is in line with reduced intracellular Ca 2? release and transient decay kinetics and amplitudes in LPS-treated mice [4] and rats [12]. Thus, increased SR Ca 2?…”