Cardiovascular Research 2000 45(3):560-569; doi:10.1016/S0008-6363(99)00372-7
© 2000 by European Society of Cardiology
Copyright © 2000, European Society of Cardiology
Apoptosis in cardiac diseases: stress- and mitogen-activated signaling pathways
Giora Z. Feuerstein* and
Peter R. Young
Cardiovascular Disease Research, DuPont Pharmaceuticals Corporation, Wilmington, DE 19880-0400, USA
* Corresponding author. Tel.: +1-302-695-1840; fax: +1-302-695-4162
Received 3 August 1999; accepted 18 October 1999
 |
Abstract
|
|---|
Apoptosis is a form of cell death that involves discrete genetic
and molecular programs, de novo protein expression and a unique
cellular phenotype. Evidence for the existence of apoptosis
in the human heart has been reported in various cardiac diseases,
including ischemic and non-ischemic heart failure, myocardial
infarction and arrhythmias. Among the most potent stimuli that
elicit cardiomyocyte apoptosis are: oxygen radicals (including
NO), cytokines (FAS/TNF
-receptor signaling), stress conditions
(chemical or physical, e.g., radiation), sphingolipid metabolites
(ceramide) and autocoids, e.g., angiotensin II. Apoptosis of
cardiac myocytes may contribute to progressive pump-failure,
arrhythmias and cardiac remodeling. The recognition of numerous
molecular targets associated with cardiomyocyte apoptosis may
provide novel therapeutic strategies for diverse cardiac ailments,
as recently suggested by pharmacologic studies in experimental
animals. This review paper is aimed to highlight the role of
protein kinase signaling pathways in apoptosis with special
attention to the stress-activated protein kinases (SAPK) and
mitogen-activated protein kinases (MAPK) systems.
KEYWORDS Heart failure; Protein kinases; Signal transduction
|
1 Introduction
|
|---|
Apoptosis was first reported in a seminal paper by a group of
pathologists studying cell population regulation
[1]. In this
paper, the authors described a form of cell death marked by
its singularity, unique morphology and resolution without apparent
‘traces’ (e.g., inflammation) in the tissue of origin.
These features of cell death were contrasted to necrosis, a
form of cell death, due to noxious stimuli that leads to cell
membrane disruption, swelling, disintegration, cell-content
leakage and local inflammation. Featuring prominently in the
apoptotic process are the ‘apoptotic bodies’ (fragments
of dense DNA surrounded by apparently intact plasma membrane)
and DNA condensation and fragmentation (the latter noted as
a ‘ladder’ when separated on DNA-gel electrophoresis).
The apoptosis phenotype has been associated later on with ‘programmed
cell death’ (PCD) described first in the nematode,
C. elegans, where genetically specified deletions of cells during
development followed a timed-activation of specific genes (
ced-3/4)
[2]. It is now quite common to use apoptosis and PCD interchangeably.
In this review, apoptosis represents the cellular phenotype
resulting from activation of genomic programs that lead to DNA
damage and cell death. Reports on cardiomyocyte apoptosis in
human cardiac disease were only recently published
[3,4]. Using
two key markers of apoptosis that monitor the breakup of nuclear
DNA: DNA ‘ladder’ and TUNEL (terminal deoxy-uridine-nick-end-labeling)
histochemistry, apoptosis of cardiomyocytes and non-myocytes
were identified in the following cardiac diseases: (1) ischemic
and idiopathic dilated cardiomyopathy, associated with clinical
heart failure; (2) acute myocardial infarction; (3) congenital
arrhythmogenic dysplasias; (4) myocarditis; (5) arrhythmias.
The reported incidence of cardiac myocyte apoptosis in these
conditions varied considerably with estimates of 0.1% to 30%,
depending on the disease specimen, methodology, and area of
sampling. The rate of cardiac cell deletion of both myocytes
and non-myocytes by apoptosis is difficult to assess in vivo
especially in the human situation; in vitro, the resolution
of the apoptotic process from initiation to complete engulfment
is quite rapid (hours or a few days) and therefore even a low
prevalence, e.g., 0.1%, recycled over years may lead to substantial
depletion of cardiac cells. At the present time, the contribution
of cardiac myocyte apoptosis to initiation and progression of
the above-cited heart diseases cannot be accurately estimated.
|
2 Stimuli that elicit cardiomyocyte apoptosis
|
|---|
Significant research has been launched over the past 5 years
to identify stimuli that elicit cardiomyocyte apoptosis and
to decipher their signal transduction pathways
[5]. It is important
to note that much of the information is derived from (1) in
vitro studies; (2) non-human (and often non-adult) cardiomyocytes,
and (3) highly controlled (artificial) conditions. Nevertheless,
circumstantial evidence supports the existence of many of the
same stimuli in human cardiac disease as enumerated below. (1)
Stress conditions such as ischemia (especially when followed
by reperfusion) and oxygen radicals can elicit cardiomyocyte
apoptosis, as has been demonstrated in both cell cultures and
isolated cardiac perfusion studies
[6,7]. In the former condition,
deprivation of growth factors, energy sources (glucose) occurs,
and endogenous antioxidants are usually present. (2) Cytokines,
such as TNF
, have been shown to produce cardiomyocyte apoptosis
in culture. Cytokines may figure prominently especially in advanced
heart failure where very high levels of circulating TNF
(and
other cytokines) are present
[8–10]. Endogenous synthesis
of TNF
in the heart (where its receptors are present) may be
equally important. (3) Nitric oxide (NO) produced primarily
by the Type II NOS (inducible nitric oxide synthase) elicits
cardiomyocyte apoptosis possibly in association with peroxynitrite
(ONOO
–) production. Activation of iNOS in heart failure
has been established. (4) Neurohormonal factors such as angiotensin
II (ATII) acting via the AT-receptors, have been shown to produce
cardiomyocyte apoptosis
[11]. Elevated circulating levels of
ATII, correlating to disease stage, and in situ cardiac ATII
production, possibly by a non-ACE pathway, may play an important
role in this respect. (5) Mechanical stress has been shown to
elicit apoptosis in cardiac muscle preparations in vitro. This
physical form of stress is likely to exist in situations of
cardiac remodeling leading to dilated myopathy and sphericity
where increase in wall tension/stress is fundamental to the
heart failure condition. Taken together, diverse stimuli are
capable of producing apoptosis in cardiac myocytes, many of
which co-exist in advanced heart failure. It is difficult at
this time to dissect out the most important contributing factors
in chronic human cardiac diseases where multiple humoral and
local pro-apoptotic stimuli exist.
|
3 Signaling pathways of apoptosis in cardiac myocytes
|
|---|
Five possible pro-apoptotic signaling pathways in cardiac myocytes
have emerged which may provide opportunities for specific pharmacological
interventions. The data on these signal transduction pathways
are largely derived from in vitro and mostly cultured neonatal
cardiomyocytes. Discrete stimuli may activate multiple signal
transduction pathways and ‘cross talk’ between various
pathways is likely to be the common situation. Activation of
apoptotic pathways may be ‘intercepted’ and aborted
by anti-apoptotic regulatory mechanisms; thus, checkpoints that
provide ‘rescue’ opportunities may be important
in determining execution of the apoptotic programs.
The five major signaling pathways that have been suggested to convey apoptotic stimuli in cardiac myocytes are:
- 1. Redox-regulated systems (activated by oxygen radicals and NO/ONOO). [12,13]
- 2. The Fas/TNF family of cytokine receptors operating via unique ‘death domains’ that are linked to several intracellular signaling pathways. [14,15]
- 3. Caspases, a family of cysteine-proteases operating in a cascade that is activated either by receptor originating signals or mitochondrial-associated cytochrome C. [5,10,16,17].
- 4. G-protein-coupled receptor (GPCR)-dependent stimulation induced by ligands/agonists. One such system is ATII and its receptor signaling system Gi/Gq, but other, novel GPCR pathways associated with Gq have also been recently described [18,19].
- 5. Phospholipase-C type biochemical reactions that lead to sphingomyelinase activation and generation of sphingolipids like ceramide [20].
The scope of this brief
review may not accommodate detailed deliberations on each of
the discrete signaling events enumerated above, for which the
reader is encouraged to resort to recent reviews
[5]. More important
though, are emerging principles that can be summarized as follows:
(a) a single pro-apoptotic stimulus may lead to activation of
single or multiple pathways of apoptosis; (b) the final common
pathway of apoptotic signaling pathways involves breakdown of
numerous nuclear proteins of cytoarchitectural function, transcription
modulation and cell cycle regulation; (c) ‘checkpoints’
that regulate the apoptotic process are present in cardiomyocytes
as is also the case for other cells; in this respect, the Bcl-2
family of proteins and the Bax-associated proteins may modulate
both cell membrane or mitochondrial-activated apoptosis
[21].
|
4 Phospholipids as secondary messengers in apoptosis
|
|---|
Ceramides have been implicated as key mediators in numerous
signaling pathways leading to diverse cellular phenotypes including
cell proliferation, differentiation and apoptosis. Ceramides,
along with phosphocholine, are products of sphingomyelin hydrolysis
by sphingomyelinases (which are sphingomyelin-specific type
C phospholipases). Accumulation of ceramides in response to
various stimuli such as interferon-
, tumor necrosis factor
(TNF
), IL-1β, FAS/APO-1 (CD95) and other cytokines is well
established (for review see
[22]). Furthermore, sphingomyelin
hydrolysis is also induced by cellular stresses such as nutritional
withdrawal or irradiation, two known pro-apoptotic conditions.
Ceramides were shown to activate ceramide-activated protein
kinases (CAPK) that phosphorylate
raf-1 which in turn activates
extracellular-signal regulated kinase-2 (ERK2) type of MAPK
via phosphorylation of MAPK/ERK kinase (MEK)
[23] (see
Fig. 1).
Ceramide may also serve as upstream activator of
ras possibly
through vav exchange factor
[24]. Ceramide may also activate
the stress–response kinase cascade via MEKK, resulting
in activation of JNK-1 via SEK (See
Fig. 1)
[25], thereby activating
nuclear transcriptional mechanisms. Finally, it has been suggested
that ceramides induce NF-
B translocation and activation possibly
by indirect pathways that result in phosphorylation (by PKC)
of the cytosolic I
B
inhibitor
[26]. The subsequent activation
of many transcriptional events including genes known to be associated
with cardiac apoptosis (iNOS, TNF
) may provide a key link of
ceramides to apoptosis.
However, the stimulation of numerous signaling pathways by ceramide
may result in opposing biological outcomes depending on cell
type, stimuli and conditions such as pH, ions and nutrition.
It is believed that key stimuli and receptor signaling pathways
leading to apoptosis are CD95 and TNF-R1. Both receptors have
‘death domains’ which are critical for the rapid,
transient sphingomyelin hydrolysis by the acidic sphingomyelinase
[27] which results in apoptosis.
In conclusion, stimuli that are know to impact on failing cardiac myocytes (e.g.TNF) activate specific sphingomyelinases that result in ceramide production and activation of apoptotic programs within the cells. However, the precise role of these phospholipids in cardiac apoptosis awaits further investigation with selective chemical tools that allow highly specific inhibition of selected elements of the ceramide synthesis and action.
|
5 MAP kinase signaling pathways
|
|---|
Cells respond to various stimuli by activating one or more intracellular
signaling pathways that in turn can result in alterations in
gene expression, cytoskeleton and motility and can lead to apoptosis,
proliferation or differentiation. One of the pathways that has
been extensively studied for its role in apoptosis is the MAP
kinase pathway. The MAP kinases, or mitogen-activated protein
kinases, phosphorylate target proteins on serine or threonine
residues adjacent to a proline. The name of the family comes
from the observation that the first discovered member responded
to mitogens, but it has since been established that the MAP
kinases can respond to a range of stimuli
[18].
All of the MAPK members are catalytically inactive in unstimulated cells, and are activated in response to the appropriate stimulus by phosphorylation on both a threonine and tyrosine that appear in a threonine-X-tyrosine motif close to the active site. This phosphorylation is carried out by a dual specificity MAPKK (MAP kinase kinase), which in turn is activated through phosphorylation by a MAPKKK (MAP kinase kinase kinase). As illustrated in Fig. 1, the MAP kinases fall into three main families, the ERKs (extracellular regulated kinases), the JNK/SAPKs (c-jun amino-terminal kinase/stress-activated protein kinases) and the p38 MAPKs. Each family contains multiple isoforms encoded by different genes and splice variants, and differs from other family members in the amino acid X in the threonine-X-tyrosine activation motif (ERK has Thr-Glu-Tyr, JNK has Thr-Pro-Tyr, p38 has Thr-Gly-Tyr) and the size of the loop that contains it. This reflects the finding that each MAPK family is activated by a different MAPKK. In contrast, each MAPKK can be activated by several different MAPKKKs.
The stimuli that trigger each MAPK pathway differ. While ERKs respond primarily to mitogenic stimuli such as growth factors and PMA, the JNKs and p38 MAPKs respond to physiological stresses such as heat, chemical, oxidative, osmotic, pH, hypoxia, growth factor withdrawal and UV. This has led to the latter two being often referred to as stress-activated protein kinases (SAPKs) [29]. However, there are many stimuli that can activate more than one pathway at a time. Thus LPS and the two proinflammatory cytokines IL-1 and TNF can stimulate all three pathways, albeit to differing extents [30,31], and similar results are seen with several cytokines and with G-protein-coupled receptor ligands. The particular MAPK pathways stimulated may be determined by the choice of MAPKKK, since some of these appear to be more promiscuous than the MAPKK and MAPKs.
Our understanding of the role of the different MAPKs in the physiological responses of cells to various stimuli has been aided by the use of dominant negative fragments of several components of the MAPK pathways and through the use of low molecular weight, cell permeable inhibitors of two of the MAPK pathways (Fig. 2). MEK 1 and 2 are two MAPKK that phosphorylate and activate ERK in response to mitogenic stimuli (Fig. 1). Two inhibitors of MEK were discovered. PD98059 was discovered by screening for inhibitors of a mutant, constitutively active form of the enzyme, but the inhibitor actually inhibits the activation of MEK1 by binding to the inactive form and is ten-fold less effective on MEK2 [32]. In contrast, U0126 was discovered in a screen for compounds that inhibited AP-1 dependent transcription, and was subsequently characterized as an inhibitor of both MEK1 and MEK2 [33]. Both are non-ATP competitive inhibitors but compete with each other for the same binding site on MEK. When added to cells, both MEK inhibitors block the activation of ERKs in response to various mitogenic stimuli.
View larger version (19K):
[in this window]
[in a new window]
[Download PowerPoint slide]
|
Fig. 2 Interaction of the various protein-kinase signaling pathways and site of inhibitor action. Inhibitors and kinase abbreviations are provided in text and in reviews [29,66]. CREB=cAMP response element binding protein. Hsp27=Heat shock protein 27.
|
|
The p38 inhibitors, exemplified by the pyridinyl imidazole SB203580,
were discovered by their ability to inhibit LPS-stimulated production
of IL-1 and TNF
from human monocytes, and were subsequently
used to identify and clone the molecular target, which turned
out to be p38 MAP kinase
[34]. SB203580 inhibits the kinase
activity of p38 and its nearest homologue, p38β/β2,
but does not inhibit the more distantly related homologues p38
and p38
[35,36]. When added to cells, SB203580 blocks the activation
of MAPKAP kinase-2, a direct substrate of p38, in response to
various stress and cytokine stimuli
[37].
The physiological pathways regulated by the ERK, p38 MAP kinase and JNK pathways as determined through inhibitor and dominant negative studies have been recently reviewed [29,38,39]. From many studies, it is clear that MAP kinase pathways can regulate gene expression at the transcription, mRNA stabilization and translation levels [40,41]. In the case of transcription regulation, this can be directly correlated with the ability of the MAPKs or their substrate MAPKAPK/RSKs to phosphorylate specific transcription factors [42,43]. MAPKs can modulate the enzyme activity of targets such as PLA2, tyrosine hydroxylase and the RSK/MAPKAP kinases through direct phosphorylation [44]. P38 MAPK activation can also lead to structural changes in the cell through alterations in hsp27 phosphorylation [45]. Finally, there is evidence that the MAPK pathways can influence proliferation, apoptosis, differentiation, aggregation and migration in different cell types [46–49].
The specific contribution of each MAPK pathway to a physiological response varies from cell to cell, and also depends on stimulus. In some cases MAPK pathways can cooperate, and in other cases they antagonize [28,46]. However, in several of these cases, inhibition of just one of the pathways has a physiological effect. Further obscuring this picture has been the reliability of extending studies using transformed cell lines to primary cultures and in vivo physiology. An example of this confusion emerges from studies of apoptosis. In neural cells, p38 is proapoptotic [46] whereas it is anti-apoptotic in TNF treated fibroblast cell lines [50].
|
6 SAPK and MAPK in cardiac cell hypertrophy and apoptosis
|
|---|
Evidence in support for linkage between SAPK/MAPK activation
and cardiac cell hypertrophy and apoptosis has been derived
from several lines of investigations in in vitro and in vivo
systems. Wang et al.
[51,52] used in vitro gene transfer technology
to over-express wild type and constitutively active forms of
MKK7 (or JNKK2) in neonatal rat cardiomyocytes. This procedure
resulted in activation of JNK without affecting other mitogen-activated
protein kinases, including extracellular signal-regulated protein
kinase and p38 (see
Fig. 2 for orientation). Specific activation
of the JNK pathway in cardiac myocytes induced characteristic
features of cardiomyocyte hypertrophy along with increased expression
of atrial natriuretic factor and changes in sarcomeric organization.
Similarly, activation of JNKs through transfection of MEKK1
and MKK4 also led to hypertrophy
[53]. In contrast, co-activation
of both JNK (via MKK7) and p38 (by dual expression of MKK3 or
MKK6) induced phenotypic alterations compatible with apoptosis
without hypertrophy. While gene overexpression studies harbor
the caveat of possibly non-physiological levels of products,
these data provide strong direct evidence that activation of
JNK alone is sufficient to induce cardiac cell hypertrophy.
Because co-activation pathways (JNK+p38) induced apoptosis with
a lack of hypertrophy, this suggests that interaction or convergence
of SAPK/MAPK pathways may ultimately lead to apoptosis possibly
following a hypertrophic phase. These in vitro derived data
support a role for SAPK/MAPK in the pathophysiology of cardiac
injury in response to various conditions, including ischemia
and reperfusion injury and hypertrophy in vivo
[53–55].
Wang et al. 1998 [52] have shown that the p38 MAPK pathway is activated in cardiac tissue of murine hearts subjected to chronic transverse aortic constriction (Fig. 3). In in vitro cultures of neonatal rat cardiomyocytes, the p38 pathway was shown to have complex role in cardiac myocytes. Infection of cardiac myocytes with recombinant adenoviruses encoding up-stream activators of p38 kinases (constitutively active mutants of MKK3b and MKK6b) (see Figs. 1 and 2
for orientation) elicited typical hypertrophic responses including ANF expression [52]. The hypertrophic response was enhanced by co-transfection of p38β (wild type) and suppressed by a dominant-negative p38β mutant. In contrast, MKK3bE-induced cell death was augmented by co-transfection of the p38 isoform and suppressed by a p38 dominant negative mutant. These data suggest a highly differentiated p38 pathway that includes divergent functions for different molecules of the p38 MAPK family.
|
7 p38 MAPK inhibitors in cardiac ischemia and apoptosis
|
|---|
Myocardial ischemia and reperfusion was shown to activate p38
MAPK in vivo (52–54,
Fig. 3). In order to establish whether
activation of p38 MAPK plays a role in myocardial cell apoptosis
and infarction, we have used the potent and selective inhibitor
of p38 MAPK, SB203580
[37] in a rabbit heart (Langendorff preparation)
model of ischemia and reperfusion
[56]. In this model, ischemia
alone caused a moderate increase in p38 MAPK (3.5 fold over
baseline) while reperfusion after ischemia further increased
p38 MAPK by 6.3 fold. Activation of p38 MAPK is a rapid event
occuring over minutes that precedes cellular and organ lesions.
Administration of SB203580 before the ischemic insult resulted
in dose-dependent inhibition of p38 MAPK and markedly diminished
the consequences of the ischemia/reperfusion injury, including
apoptosis (>50%), creatinine kinase loss (34%) and infarct
size (>50%). Confirmation of inhibition of apoptosis was
done by both TUNEL and DNA-‘ladder’ criteria. Most
importantly, the p38 MAPK inhibitor accelerated the recovery
of coronary flow, cardiac contractility and left ventricular
pressure. It is also of interest to note that SB203580 did not
inhibit JNK, another kinase activated by stress/ischemia, indicating
the specific role of p38 MAPK in myocardial injury associated
with ischemia and reperfusion. These data, while preliminary,
should encourage more detailed work in many other models of
cardiac injury, including heart failure. If such studies are
consistently positive, clinical investigations will be warranted
pending on the safety and tolerability of the p38 MAPK inhibitors.
|
8 SAPK inhibition in cardiac ischemia and apoptosis — potential role in adrenergic blockers and antioxidants
|
|---|
Beta-adrenergic receptor blockers (β-blockers) are proven
drugs for cardioprotection in a variety of heart diseases including
myocardial infarction and heart failure
[57,58]. While the primary
mechanism of cardioprotection by β-blockers is believed
to be reduction in cardiac work, new information derived from
studies with the multiple-action β-blocker, carvedilol
and the non-selective β-blocker propranolol, indicate that
these agents may prevent apoptosis of cardiac myocytes subjected
to ischemia and reperfusion injury. In a rabbit model of in
vivo ischemia (30 min) and reperfusion (I/RP, 4 h), robust apoptosis
has been demonstrated by TUNEL and ‘DNA ladder’
markers
[56]. Administration of carvedilol (a multiple action,
β-blocker,
1-blocker and antioxidant) immediately before
reperfusion, reduced the number of apoptotic myocytes by 77%
(
Fig. 4). Most notably, carvedilol significantly reduced infarct
size
[59]. Propranolol, the non-selective β-blocker, administered
at equipotent β-blocking doses as carvedilol also provided
significant protection against I/RP induced apoptosis, although
to a lesser extent (39%). In this model, I/RP resulted in robust
activation of JNK/SAPK in the ischemic myocardium only; this
increase of JNK was significantly diminished by carvedilol (53%)
yet no consistent effect on JNK activation was found in propranolol-treated
rabbits (
Fig. 4). Furthermore, expression of
Fas in the ischemic
myocardium was also significantly reduced by carvedilol
[56].
The antioxidant properties of carvedilol might have contributed
to its anti-apoptotic and cardiac protection since propranolol,
an equipotent β-blocker that has much lesser anti-oxidant
actions
[60], displayed less anti-apoptotic capacity. The agents
that have been used in this study are not specific JNK inhibitors,
since no direct inhibition of the JNKs have been demonstrated
with carvedilol or propranolol. However, the association of
JNK suppression to apoptosis inhibition and improved function
suggests a role of these kinases in ischemia induced cardiac
apoptosis and injury. Further investigation with potent and
specific JNK inhibitors will determine if inhibition of JNK
contributes to the effect of carvedilol in cardiac apoptosis.
View larger version (13K):
[in this window]
[in a new window]
[Download PowerPoint slide]
|
Fig. 4 Effect of carvedilol or propranolol on cardiac cell apoptosis and injury following ischemia and reperfusion (see Ref. [59]). Panel A: Effects of carvedilol and propanolol on ischemia/reperfusion-induced activation of JNK/SAPK. CARV=carvedilol; PROP=propranolol; concentration of agents are expressed in µm (micromolar). Panel B: Percentage of nuclei staining positive for TUNEL in heart tissues exposed to 30 min of ischemia and 4 h or reperfusion compared to vehicle treated rabbits. Carvedilol and propanolol were administered intravenously at 1 mg/kg, 5 min before reperfusion. AAR=area at risk; ANAR: area not at risk.
|
|
|
9 The significance of cardiac cell apoptosis in the evolution of heart diseases
|
|---|
The emerging evidence in recent literature on cardiac apoptosis
strongly suggests that this form of cell death indeed exists
in the human heart during various disease conditions. Although
the evidence derived from human specimens is largely based on
histological and phenotypic observations, cell based systems
provide strong support for the existence of pro-apoptotic pathways
in cardiomyocytes. However, a key question that remains unanswered
is whether cardiac cell apoptosis has a significant role in
any of the cardiac diseases where it is found. While this question
cannot be decisively answered at this time, some suggestions
as for possible mechanisms whereby apoptosis contributes to
heart disease can be offered. Loss of cardiomyocytes could lead
to loss of ‘cardiac mass’ and hence ‘diminished
pump power’. This possibility although plausible, is difficult
to assess as the rate and incidence of the apoptotic cycle in
the heart has not been assessed. However, Adams et al.
[18] have shown that robust apoptosis induced by
Gq overexpression
in transgenic mice results in severe heart failure with markedly
dilated chambers and perinatal death, indicating that robust
apoptosis exercised over a brief period may on its own, without
ischemia or growth factor deprivation, result in fulminant heart
failure. Furthermore, in cardiac selective ‘knock out’
mice where the
gpl30 gene was deleted, heart failure develops
following pressure overload by apoptosis without an ischemic
or inflammatory component
[61]. While ‘quantity’
cannot be dismissed as a possible mechanism, other possible
factors such as aberrant electrical conduction at apoptotic
sites may lead to arrhythmias. Apoptosis may also result in
‘cardiac remodeling’ due to ‘re-alignment’
of neighboring cardiomyocytes
[62]. This latter mechanism is
unique to the heart, where function is extremely dependent on
the optimal geometrical and structural alignment. Thus, apoptosis,
even if limited in its local scope, may result in confounding
mechanical and electrical disturbances.
|
10 Novel therapeutic opportunities for heart diseases based on anti-apoptotic agents
|
|---|
The potential for development of cardioprotective agents that
are mechanistically based on modulation of apoptosis is rapidly
emerging. Diverse opportunities may be exploitable, emanating
both from enhancing anti-apoptotic capacities within the cardiac
myocytes such as the
bcl-2 system, or inhibition of key pro-apoptotic
stimuli and their signal transduction pathways. The former option,
enhancing anti-apoptotic pathways may turn out to be a difficult
task as the discrete regulatory pathways of the anti-apoptotic
genes have not been clarified as yet. However, some interesting
‘proof of concept’ studies have been recently reported.
Experiments conducted in
bcl-2 transgenic (TG) mice provided
proof of concept that enhanced expression of anti-apoptotic
pathways may provide protection from ischemic injury
[63]. In
the latter study,
bcl-2 TG mice were exposed to transient cerebral
ischemia and neuronal death followed over extended periods.
The
bcl-2 TG mice demonstrated significant protection against
ischemia induced neuronal loss. While such studies have not
as yet been reported in experimental models of cardiac ischemia
or heart failure, in vitro studies of cardiomyocyte apoptosis
evoked by p53 overexpression have been performed with co-transfection
with
bcl-2 [21]. In this model of cardiac myocyte apoptosis,
bcl-2 provided strong anti-apoptotic action and prevented cell
death. These data suggest that there is a potential for developing
pharmacological strategies aimed at enhancing the expression
and/or action of
bcl-2 as a means of arresting cardiac cell
apoptosis. However, specific strategies that enable this objective
have not as yet been reported. Alternatively, it may be more
plausible to expect that agents acting at critical ‘checkpoints’
downstream of the key ‘final common pathway(s)’
elements leading to apoptosis may prove a superior strategy
to prevent apoptosis. Several anti-apoptotic agents that may
provide cardioprotection due to an anti-apoptotic mechanism
have been reported: (a) p38 MAPK inhibitors; (b) caspase inhibitors;
(c) β-adrenergic receptor blockers; (d) antioxidants and
growth factors that inhibit SAPK
[64,65].
|
11 Conclusion
|
|---|
Apoptosis is now recognized as a fundamental process in cell
biology that is critical for tissue and organ development, physiologic
adaptation and disease. The heart is like other organs —
apoptosis plays a role in cardiac development, maturation and
diverse disease conditions. The discrete stimuli and the molecular
mechanisms that initiate and propagate apoptosis in human heart
disease are largely unknown. In vitro studies in experimental
models suggest multiple stimuli that activate highly diverse
signaling pathways. The pathways of apoptosis display redundancies,
regulatory ‘checkpoints’ and possibly convergence
into a final common pathway where a ‘point of no return’
completes the process. Three possible consequences of cardiac
myocytes apoptosis are postulated: (1) compromise in cardiac
contractility due to loss of myocytes; (2) conduction disturbances
leading to arrhythmias; (3) cardiac remodeling due to disruption
of the geometrical alignment of cardiac myocytes. If indeed
cardiomyocyte apoptosis plays an important role in initiation
and progression of cardiac diseases, drugs that effectively
and specifically inhibit apoptosis might be useful therapeutic
agents for diverse cardiac diseases. Opportunities may emerge
from either enhancing anti-apoptotic mechanisms (e.g., up-regulation
of
bcl-2) or inhibition of key targets in the pro-apoptotic
pathways such as SAPKs and MAPKs. In conclusion, the recognition
of apoptosis as a discrete, genomically mediated cell death
in the myocardium, has opened new conceptual paradigms in heart
disease research. Most importantly, the understanding on a molecular
basis of the key executioners of apoptosis in cardiac myocytes
may provide new opportunities for development of novel cardioprotective
agents.
Time for primary review 31 days.
|
References
|
|---|
- Kerr J.F.R., Wyllie A.H., Currie A.R. Apoptosis: a basic biological phenomenon with wide ranging implications in tissue kinetics. Br J Cancer (1972) 26:239–257.[ISI][Medline]
- Yuan J., Shaham S., Ledoux S., Ellis H.M., Horvitz H.R. The C. elegans cell death gene ced-3 encodes a protein similar to mammalian interleukin-1β-converting enzyme. Cell (1993) 75:641–652.[CrossRef][ISI][Medline]
- Anversa P., Leri A., Behrami C.A., Guerra S., Kajstura J. Myocyte death and growth in failing heart. Lab Invest (1998) 78:767–786.[ISI][Medline]
- Narula J., Haider N., Virmani R., et al. Apoptosis in myocytes in end-stage heart failure. New Engl J Med (1996) 335:1182–1189.[Abstract/Free Full Text]
- Haunstetter A., Izumo S. Apoptosis-basic mechanisms and implications for cardiovascular disease. Circ Res (1998) 82:1111–1129.[Free Full Text]
- Yaoita H., Ogawa K., MaeLare K., Maruyama Y. Attenuation of ischemia/repercussion injury in rats by a caspase inhibitor. Circulation (1998) 97:276–281.[Abstract/Free Full Text]
- Yue T.-L., Wang X.-K., Romanic A., et al. Possible involvement of stress-activated protein kinase signaling pathway and Fas receptor expression in prevention of ischemia/reperfusion- induced cardiomyocyte apoptosis by carvedilol. Circ Res (1998) 82:166–174.[Abstract/Free Full Text]
- Deswal A., Bozkurt B., Seta Y., et al. Safety and efficacy of a soluble P75 tumor necrosis factor receptor (Enbrel, Entracept) in patients with advanced heart failure. Circulation (1999) 99:3224–3226.[Abstract/Free Full Text]
- Satoh M., Nakamura M., Saitoh H., et al. Tumor necrosis factor -converting enzyme and tumor necrosis factor in human dilated cardiomyopathy. Circulation (1999) 99:3260–3265.[Abstract/Free Full Text]
- van Overbeeke I.C.R., Baan C.C., Niesters H.G.M., et al. The TNF system in heart failure and after heart transplantation. Eur Heart J (1999) 20:833–840.[Abstract/Free Full Text]
- Fortuno M.A., Ravassa S., Etayo J.C., Diez J. Overexpression of Bax protein and enhanced apoptosis in the left ventricle of spontaneously hypertensive rats. Effects of AT- blockade with losartan. Hypertension (1998) 32:280–286.[Abstract/Free Full Text]
- Szaboles M., Michler R.E., Yang X., et al. Apoptosis of cardiac myocytes during cardiac allograft rejection relation to induction of nitric oxide synthase. Circulation (1996) 94:1665–1673.[Abstract/Free Full Text]
- Pinsky D.J., Cai B., Yang X., et al. The lethal effects of cytokine-induced nitric oxide on cardiac myocytes are blocked by nitric oxide synthase antagonism or transforming growth factor β. J Clin Invest (1995) 95:677–685.[ISI][Medline]
- Pulkki K. Cytokines and cardiomyocyte death. Ann Med (1997) 29:339–343.[ISI][Medline]
- Ing D.J., Znag J., Dzau V.J., Webster K.A., Bishopric N.H. Modulation of cytokine-induced cardiac myocyte apoptosis by nitric oxide, BAK and Bcl-X. Circ Res (1999) 84:21–33.[Abstract/Free Full Text]
- Salvesen G.S., Dixit V.M. Caspases: intracellular signaling by proteolysis. Cell (1997) 91:443–446.[CrossRef][ISI][Medline]
- Black S.C., Huang J.Q., Rezaiefar P., et al. Co-localization of the cysteine protease caspase-3 with apoptotic myocytes after in vivo myocardial ischemia and reperfusion in rats. J Mol Cell Cardiol (1998) 30:733–742.[CrossRef][ISI][Medline]
- Adams J.W., Sokata Y., Davis M.G., et al. Enhanced Galphaq signaling: a common pathway mediates cardiac hypertrophy and apopotic heart failure. Proc Natl Acad Sci (1998) 95:10140–10145.[Abstract/Free Full Text]
- D’Angel D.D., Sabata Y., Lorentz J.N., et al. Transgenic Gaq overexpression induces cardiac contractile failure in mice. Proc Natl Acad Sci (1997) 94:8121–8126.[Abstract/Free Full Text]
- Hofmann K., Dixit V.M. Ceramide in apoptosis-does it really matter? Trends Biochem Science. (1998) 23:374–377.[CrossRef][ISI][Medline]
- Kirshenbaum L.A., Moissac D. The bcl-2 gene product prevents programmed cell death of ventricular myocytes. Circulation (1997) 96:1580–1585.[Abstract/Free Full Text]
- Testi R. Sphingomyelin breakdown and cell fate. Trends Biochem. Sci. (1996) 21:468–471.[CrossRef][ISI][Medline]
- Yao B., Zhang Y., Delikat S., et al. Phosphorylation of Raf by ceramide-activated protein kinase. Nature (1995) 378:307–310.[CrossRef][Medline]
- Gulbins E., Bissonnette R., Mahboubi A., et al. FAS-induced apoptosis is mediated via a ceramide-initiated RAS signaling pathway. Immunity (1995) 2:341–351.[CrossRef][ISI][Medline]
- Verheij M., Bose R., Lin X.H., et al. Requirement for ceramide-initiated SAPK/JNK signalling in stress-induced apoptosis. Nature (1996) 380:75–79.[CrossRef][Medline]
- Lozano J., Berra E., Municio M.M., et al. Protein kinase C zeta isoform is critical for kappa B-dependent promoter activation by sphingomyelinase. J Biol Chem (1994) 269:19200–19202.[Abstract/Free Full Text]
- Cascino I., Papoff G., De Maria R., Testi R., Ruberti G. Fas/Apo-1 (CD95) receptor lacking the intracytoplasmic signaling domain protects tumor cells from Fas-mediated apoptosis. J Immunol (1996) 156:13–17.[Abstract]
- Robinson M.J., Cobb M.H. Mitogen-activated protein kinase pathways. Curr Opin Cell Biol (1997) 9:180–186.[CrossRef][ISI][Medline]
- Cohen P. The search for physiological substrates of MAP and SAP kinases in mammalian cells. Trends Cell Biol (1997) 7:353–361.[CrossRef][ISI][Medline]
- Kumar A., Middleton A., Chambers T.C., Mehta K.D. Differential roles of extracellular signal-regulated kinase-1/2 and P38(MAPK) in interleukin-1-beta- and tumor necrosis factor-alpha-induced low density lipoprotein receptor expression in HepG2 cells. J Biol Chem (1998) 273:15742–15748.[Abstract/Free Full Text]
- Schumann R.R., Pfeil D., Lamping N., et al. Lipopolysaccharide induces the rapid tyrosine phosphorylation of the mitogen-activated protein kinases ERK-1 and p38 in cultured human vascular endothelial cells requiring the presence of soluble CD14. Blood (1996) 87:2805–2814.[Abstract/Free Full Text]
- Alessi D.A., Cuenda A., Cohen P., Dudley D.T., Saltiel A.R. PD 098059 is a specific inhibitor of the activation of mitogen-activated protein kinase in vitro and in vivo. J Biol Chem (1995) 270:27489–27494.[Abstract/Free Full Text]
- Favata M.F., Horiuchi K.Y., Manos E.J., et al. Identification of a novel inhibitor of mitogen-activated protein kinase kinase. J Biol Chem (1998) 273:18623–18632.[Abstract/Free Full Text]
- Lee J.C., Laydon J.T., McDonnell P.C., et al. A protein kinase involved in the regulation of inflammatory cytokine biosynthesis. Nature (1994) 372:739–746.[CrossRef][Medline]
- Kumar S., McDonnell P.C., Gum R.J., et al. Novel homologues of CSBP/p38 MAP kinase: activation, substrate specificity and sensitivity to inhibition by pyridinyl imidazoles. Biochem Biophys Res Commun (1997) 235:533–538.[CrossRef][ISI][Medline]
- Gum R.J., McLaughlin M.M., Kumar S., et al. Acquisition of sensitivity of stress-activated protein kinases to the p38 inhibitor, SB 203580, by alteration of one or more amino acids within the ATP binding pocket. J Biol Chem (1998) 273:15605–15610.[Abstract/Free Full Text]
- Cuenda A., Rouse J., Doza Y.N., et al. SB 203580 is a specific inhibitor of a MAP kinase homologue which is stimulated by cellular stresses and interleukin-1. FEBS Lett (1995) 364:229–233.[CrossRef][ISI][Medline]
- Ip Y.T., Davis R.J. Signal transduction by the Jun N-terminal kinase (JNK) — from inflammation to development. Curr Opin Cell Biol (1998) 10:205–219.[CrossRef][ISI][Medline]
- Minden A., Karin M. Regulation and function of the JNK subgroup of MAP kinases. Biochim Biophys Acta (1997) 1333:F85–104.[Medline]
- Dean J.L.E., Brook M., Clark A.R., Saklatvala J. p38 Mitogen-activated protein kinase regulates cyclooxygenase-2 mRNA stability and transcription in lipopolysaccharide-treated human monocytes. J Biol Chem (1999) 274:264–269.[Abstract/Free Full Text]
- Young P., McDonnell P., Dunnington D., et al. Pyridinyl imidazoles inhibit IL-1 and TNF production at the protein level. Agents and Actions (1993) 39:C67–C69.[CrossRef][ISI][Medline]
- Han J., Jiang Y., Li Z., Kravchenko V.V., Ulevitch R.J. Activation of the transcription factor MEF2C by the MAP kinase p38 in inflammation. Nature (1997) 386:296–299.[CrossRef][Medline]
- Thuerauf D.J., Arnold N.D., Zechner D., et al. p38 Mitogen-activated protein kinase mediates the transcriptional induction of the atrial natriuretic factor gene through a serum response element. A potential role for the transcription factor ATF6. J Biol Chem (1998) 273:20636–20643.[Abstract/Free Full Text]
- Kramer R.M., Roberts E.F., Um S.L., et al. p38 Mitogen-activated protein kinase phosphorylates cytosolic phospholipase A2 (cPla2) in thrombin-stimulated platelets. Evidence that proline-directed phosphorylation is not required for mobilization of arachidonic acid by cPLA2. J Biol Chem (1996) 271:2723–2772.
- Guay J., Lambert H., Gingras-Breton G., Lavoie J.N., Huot J., Landry L. Regulation of actin filament dynamics by p38 map kinase-mediated phosphorylation of heart shock protein 27. J Cell Sci (1997) 110:357–368.[Abstract]
- Xia Z., Dickens M., Raingeaud J., Davis R.J., Greenberg M.E. Opposing effects of ERK and JNK-p38 MAP kinases on apoptosis. Science (1996) 270:1326–13231.[CrossRef][ISI]
- Ichijo H., Nishida E., Irie K., et al. Induction of apoptosis by ASK1, a mammalian MAPKKK that activates SAPK/JNK and p38 signaling pathways. Science (1997) 275:90–94.[Abstract/Free Full Text]
- Hannigan M., Zhan L., Ai Y., Huang C.K. The role of p38 MAP kinase in TGFβ1-induced signal transduction in human neutrophils. Biochem Biophys Res Commun (1998) 246:55–58.[CrossRef][ISI][Medline]
- Saklatvala J., Rawlinson L., Waller R.J., et al. Role for p38 mitogen-activated protein kinase in platelet aggregation caused by collagen or a thromboxane analogue. J Biol Chem (1996) 271:6586–6589.[Abstract/Free Full Text]
- Roulston A., Reinhard C., Amiri P., Williams L.T. Early activation of c-Jun N-terminal kinase and p38 kinase regulate cell survival in response to tumor necrosis factor alpha. J Biol Chem (1998) 273:10232–10239.[Abstract/Free Full Text]
- Wang Y., Su B., Sah V.P., Heller Brown J., Han J., Chien K.R. Cardiac hypertrophy induced by mitogen-activated protein kinase kinase 7, a specific activator for c-Jun NH2-terminal kinase inventricular muscle cells. J Biol Chem (1998) 273:5423–5426.[Abstract/Free Full Text]
- Wang Y., Huang S., Sah V.P., et al. Cardiac muscle cell hypertrophy and apoptosis induced by distinct members of the p38 mitogen-activated protein kinase family. J Biol Chem (1998) 273:2161–2168.[Abstract/Free Full Text]
- Bogoyevitch M.A., Gillespie-Brown J., Ketterman A.J., et al. Stimulation of the stress-activated mitogen-activated protein kinase subfamilies in perfused heart. p38/RK mitogen-activated protein kinases and c-Jun N-terminal kinases are activated by ischemia/reperfusion. Circ Res (1996) 79:162–173.[Abstract/Free Full Text]
- Yin T., Sandhu G., Wolfgang C.D., et al. Tissue-specific pattern of stress kinase activation in ischemic/reperfused heart and kidney. J Biol Chem (1997) 272:19943–19950.[Abstract/Free Full Text]
- Mackay K., Mochly-Rosen D. An inhibitor of p38 mitogen-activated protein kinase protects neonatal cardiac myocytes from ischemia. J Biol Chem (1999) 274:6272–6279.[Abstract/Free Full Text]
- Ma X.-L., Kumar S., Gao F., et al. Inhibition of p38 mitogen-activated protein kinase decreases and cardiomyocyte apoptosis and improves cardiac function after myocardial ischemia and reperfusion. Circulation (1999) 99:1685–1691.[Abstract/Free Full Text]
- Packer M., Colucci W.S., Sackner-Bernstein J., et al. Double blind, placebo-controlled study of the effects of carvedilol in patients with moderate to severe heart failure. The PRECISE trial. Circulation (1996) 94:2793–2799.[Abstract/Free Full Text]
- Australia/New Zealand Heart Failure Collaborative Group. Randomized, placebo controlled trial of carvedilol in patients with congestive heart failure due to ischemic heart disease. Lancet (1997) 349:375–380.[CrossRef][ISI][Medline]
- Yue T.-L., Ma X.-L., Wong X., et al. Possible involvement of stress-activated protein kinase signaling pathway and Fas receptor expression in prevention of ischemia/reperfusion-induced cardiomyocyte apoptosis by carvedilol. Circ Res (1998) 82:166–179.[Abstract/Free Full Text]
- Yue T.-L., Cheng H.Y., Lyska P.G., et al. Carvedilol, a new vasodilator and β-adenoreceptor antagonist is an antioxidant and free radical scavenger. J Pharmacol Exp Flow (1992) 263:92–98.
- Hirota H., Chen J., Betz U.A.K., et al. Loss of a gp130 cardiac muscle cell survival pathway is a critical event in the onset of heart failure during biomechanical stress. Cell (1999) 97:189–198.[CrossRef][ISI][Medline]
- Feuerstein G.Z. Apoptosis in cardiac diseases — new opportunities for novel therapeutics for heart diseases. Cardiovasc Drugs Ther (1999) 13:289–294.[CrossRef][ISI][Medline]
- Kitogawa K., Matsumoto M., Tsujimoto Y., et al. Amelioration of hippocampal neuronal damage after global ischemia by neuronal over expression of bcl-2 in transgenic mice. Stroke (1998) 29:2616–2621.[Abstract/Free Full Text]
- Wang L., Ma W., Markovich R., Chen J.-W., Wang P.H. Regulation of cardiomyocyte apoptotic signaling by insulin-like growth factor 1. Circ Res (1998) 83:516–522.[Abstract/Free Full Text]
- Okubo Y., Blakesley V.A., Stannard B., Gutkind S., LeRoith D. Insulin-like growth factor I inhibits the stress-activated protein kinase — Jun N-terminal kinase. J Biol Chem (1998) 273:25961–25966.[Abstract/Free Full Text]
- Kyriakis J.M., Avruch J. Sounding the alarm: protein kinase cascades activated by stress and inflammation. J Biol Chem (1996) 271:24313–24316.[Free Full Text]
CiteULike 
Connotea 
Del.icio.us What's this?
Top
Abstract
1 Introduction
