Department of Physiology and Biophysics, University of California, Irvine, California 92697
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ABSTRACT |
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This study
examined nuclear thyroid receptor (TR) maximum binding capacity
(Bmax), dissociation constant
(Kd), and TR
isoform (1,
2,
1) mRNA expression in rodent
cardiac, "fast-twitch white," "fast-twitch red," and
"slow-twitch red" muscle types as a function of
thyroid state. These analyses were performed in the context of
slow-twitch type I myosin heavy-chain (MHC) expression, a
3,5,3'-triiodothyronine (T3)-regulated gene that
displays varying responsiveness to
T3 in the above tissues. Nuclear
T3 binding analyses show that the skeletal muscle types express more TRs per unit DNA than cardiac muscle, whereas the latter has a lower
Kd than the
former. Altered thyroid state had little effect on either cardiac
Bmax or
Kd, whereas
hypothyroidism increased Bmax in
the skeletal muscle types without affecting its
Kd. Cardiac
muscle demonstrated the greatest mRNA signal of
TR-
1 compared with the other
muscle types, whereas the TR-
1
mRNA signals were more abundant in the skeletal muscle types,
especially fast-twitch red. Hyperthyroidism increased the ratio of
1 to
1 and decreased the ratio of
2- to
1+
1-mRNA signal across the muscle types, whereas hypothyroidism caused the
opposite effects. The nuclear T3
affinity correlated significantly with the
TR-
1 mRNA expression but not
with TR-
1 mRNA expression. Collectively, these findings suggest that, despite a divergent pattern
of TR mRNA expression in the different muscle types, these patterns
follow similar qualitative changes under altered thyroid state.
Furthermore, TR expression pattern cannot account for the quantitative
and qualitative changes in type I MHC expression that occur in the
different muscle types.
heart; slow-twitch muscle; fast-twitch muscle; maximum binding capacity; hyperthyroidism; hypothyroidism; thyroid receptor mRNA
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INTRODUCTION |
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THYROID HORMONES exert profound effects on striated
muscle, and they produce alterations in gene and isoform expression
that result in modified contractile/mechanical and metabolic
characteristics (2, 3, 8, 22, 24, 27). The biological action of thyroid
hormones is thought to be mediated in part via interaction of
3,5,3'-triiodothyronine
(T3) with high-affinity
receptors [thyroid receptors (TRs)] located in the nucleus
(7, 8, 10, 11, 23, 35). The TRs are ligand-dependent transcription
factors that regulate gene transcription via interaction with specific DNA sequences known as thyroid-responsive elements (TREs) located in
the promoter of T3-responsive
genes (3, 11). Nuclear TRs are products of the cellular
erythroblastosis A (c-erbA) protooncogene and are members of a
superfamily of nuclear receptors that includes the steroid hormones,
vitamin D, and retinoic acids (3, 7, 10, 11, 23, 35). These receptors
collectively regulate the transcription of complex gene networks and
subsequently control diverse aspects of growth, development, and
differentiation (3, 7, 10, 11, 17, 23, 35). To date, two distinct TR genes have been characterized, namely the - and
-genes (3, 7, 10,
11, 23, 28). The TR-
gene produces two alternatively spliced mRNA
isoforms,
1 and
2, which are translated into a functional receptor, TR-
1, and
a non-ligand-binding protein, erbA-
2, respectively (7, 10,
11, 17, 19). The TR-
gene also produces two alternatively spliced
mRNA isoforms,
1 and
2, both of which are translated
into functional TRs, but TR-
2
is expressed primarily in the anterior pituitary gland (10, 11, 17, 23,
28). TR-
1,
TR-
1, and
erbA-
2 mRNA are widely distributed among tissues, including striated muscle, and their expression is developmentally regulated in a tissue-specific manner (11, 14, 15, 23).
Thyroid hormones are among the most potent regulators of muscle gene
expression, and their effects appear to dominate other regulatory
factors such as mechanical activity and metabolic state (3). TREs have
been identified on several muscle genes including the glucose
transporter (GLUT-4) gene, the sarcoplasmic reticulum calcium-ATPase
(SERCA) genes, the -actin gene, and the
- and
- (type I)
myosin heavy-chain (MHC) genes (see Ref. 3 for review). For example,
the type I MHC gene is the most widely expressed MHC isoform in
striated muscle, and its expression in the heart and skeletal muscle
appears to be tightly regulated by thyroid hormone at the
pretranslational level (2, 12, 16) as well as at the transcriptional
level (9, 29, 31). Specifically, type I MHC expression is downregulated
by T3, and this repression has
been linked to a putative negative TRE located in proximity to the TATA
box of the gene (9).
The rodent heart is most unique in its properties in the euthyroid state. It is characterized by a high intrinsic contractility state, high myosin ATPase activity, and high oxidative capacity that can only be mimicked in larger animals under a hyperthyroid state (27). Hypothyroidism severely alters these properties and transforms the rodent heart into a hypokinetic state (8). These changes involve a large number of genes expressed in the heart, including the myofibrillar proteins, metabolic enzymes, transporters, receptors, channels, and other regulatory genes (see Ref. 3 for review; Ref. 8). In contrast, in response to hyperthyroidism, the hyperkinetic functional state of the rodent heart is upregulated even further, but the magnitude of change is much smaller than that seen in the hypothyroid-induced transformations. Thus these observations suggest that the rodent heart is more sensitive to a hypothyroid state than to a hyperthyroid state. In contrast, studies examining the effects of thyroid hormone on gene expression in skeletal muscles suggest that T3 exerts a differential effect on gene expression in different types of muscle fibers (3, 12, 16). Other studies suggest that, among skeletal muscle types, slow-twitch muscle is more sensitive than fast-twitch muscle to the effects of thyroid hormone (22, 24). The molecular basis of these differences is not clear, but they suggest differences in the thyroid hormone receptors expressed in these muscles.
Presently, relatively little is known concerning 1) the relative level of expression of TRs and their isoform species and 2) the plasticity of TR levels in response to altered thyroid states in different types of striated muscle. Therefore, in view of the key role that TRs play as a transcriptional factor in muscle gene regulation, the present study was undertaken to examine nuclear T3 binding capacity and the pattern of TR mRNA expression in the rodent heart and skeletal muscles of varying fiber type as a function of thyroid state. Also, we investigated the possible existence of differential regulation of TR mRNA expression by T3 in the different types of striated muscle. These determinations were performed in the context of analyses of type I MHC expression, which served as a marker gene that is highly sensitive to thyroid state in different types of skeletal muscle.
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METHODS |
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Animal care and experimental groups. Seventy-two adult female Sprague-Dawley rats (240-250 g; Taconic Farms, Germantown, NY) were randomly separated into three groups (n = 24 each) designated as normal control (NC), hypothyroid (PTU), and hyperthyroid (T3). The animals were housed in groups of four in light- and temperature-controlled quarters and were fed food and water ad libitum. Hypothyroidism was induced with propylthiouracil (PTU; 12 mg/kg ip daily), whereas hyperthyroidism was induced with T3 (150 µg/kg ip). The protocols used in this study were approved by our institutional animal review committee.
At the end of 3 wk, the animals were deeply sedated with a lethal dose of pentobarbital sodium. For each animal, the chest was opened to obtain a blood sample via direct cardiac puncture using a vacucontainer containing EDTA. The plasma was separated by centrifugation and analyzed for T3 and thyroxine (T4) with the use of commercially available radioimmunoassay kits (ICN, Costa Mesa, CA). Next, each heart was rapidly excised, and the ventricles were dissected out free of atria and major blood vessels, rinsed in cold saline, blotted dry, quickly weighed, frozen on dry ice, and stored atIsolation of cardiac and skeletal muscle nuclei. The isolation of cardiac nuclei was based on a method previously described (37, 25), with the modifications as described in Haddad et al. (13). Skeletal muscle nuclei were isolated according to the same method as that used for cardiac tissue, with the exception that after the Triton X-100 wash (13), the pellet was suspended in 2.0 M sucrose buffer and layered over 2.0 M sucrose in the ultracentrifuge tube (4). The rest of the procedure and the storage were the same as for cardiac muscle nuclei.
DNA determination. DNA concentration in the total homogenate as well as in the nuclei suspension was determined by fluorometry using a minifluorometer (TK0100; Hoeffer Sci). Bisbenzimide Hoechst No. 33258 was used as the fluorescent dye (20), and calf thymus DNA was used as a standard.
T3 binding assay. Nuclear T3 maximum binding capacity (Bmax) and dissociation constant (Kd) were determined by in vitro saturation analysis according to the method described by Swoap et al. (37), with modifications as described by Haddad et al. (13). Nuclei from all three groups (NC, PTU, and T3) for a specific muscle type were assayed simultaneously on the same day to eliminate day-to-day intergroup variability. Binding data were analyzed with the use of GraphPad Prism Software. Saturation data were analyzed with the use of nonlinear regression for one-site binding (hyperbola). The program calculates Bmax and the Kd for nuclear receptors in each individual set of data. For each individual sample, the reaction was run in duplicate for each of the tested [125I]T3 concentrations. Bmax was expressed in both femtomoles per milligram nuclear DNA and femtomoles per gram tissue. For the latter, tissue total DNA concentration was used in the conversion.
Cardiac isomyosin analysis. Cardiac isomyosins were separated by native gel electrophoresis, and cardiac MHC isoform composition was determined as described previously (13, 37).
RNA and protein extraction.
Total cellular RNA and total muscle proteins were simultaneously
coextracted from frozen muscle samples by using the TRI Reagent (Molecular Research Center, Cincinnati, OH) according to the company's protocol, which is based on the method described by Chomczynski (6).
Total proteins were separated in the organic phase and subsequently
precipitated with isopropanol, washed with guanidine hydrochloride and
ethanol, and suspended in 1% SDS. Protein concentration was adjusted
to 1 mg/ml with 1% SDS, and samples were subsequently analyzed for MHC
isoform distribution pattern by SDS-PAGE (38). Extracted RNA was
precipitated from the aqueous phase with isopropanol, and after washing
with ethanol, it was dried and suspended in a small volume of 0.5% SDS
in TE buffer (10 mM Tris, pH 8.0, and 1 mM EDTA). The RNA concentration
was determined by optical density at 260 nm (using an
OD260 unit equivalent to 40 µg/ml). The RNA samples were stored frozen at 80°C until
subsequent analysis for MHC and TR mRNA expression by Northern
hybridization.
Northern analysis for mRNA.
The Northern procedure used to identify MHC and TR mRNA isoforms was
essentially as reported previously (13). For the MHC mRNA analyses,
32P-labeled 5'-end-labeled
oligonucleotides, highly specific for each MHC isoform, were used in
the hybridization (12). For TR mRNA analyses,
32P-labeled random-primed cDNA
probes were used. Plasmids for the 1-,
2-, and
1-TR mRNA isoforms were kind
gifts from Dr. Ronald Evans (The Salk Institute, San Diego, CA), Dr.
Mitchell Lazar (Harvard Medical School, Boston, MA), and Dr. Howard
Towle (Univ. of Minnesota, Minneapolis, MN), respectively. After
hybridization, band intensities on the autoradiogram were quantified
using a laser-scanning densitometer (Molecular Dynamics, Sunnyvale,
CA), and each specific mRNA signal (MHC or TR) was normalized to its corresponding 18S rRNA signal.
Statistical analyses. All data are reported as means ± SE. All statistical analyses were performed using a computer software package (Prism, GraphPad Software). For each variable analyzed, differences among groups were determined using one-way ANOVA and Newman-Keuls post hoc tests. Statistical significance was set at the 0.05 probability level.
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RESULTS |
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Confirmation of altered thyroid state. The PTU group exhibited a marked, significant reduction in circulating T3 and T4 levels relative to the euthyroid group (NC), whereas the T3 group responded with elevated levels of plasma T3 obtained 24 h after the last injection (Table 1). The low T4 levels in this group were attributed to a T3-induced inhibition in T4 production due to the high levels of circulating T3. The absolute and relative heart weight data paralleled the T3 data (Table 1), which provides strong evidence of an altered thyroid state, as the increases and decreases in these values relative to the euthyroid state are characteristics of a hyperthyroid and hypothyroid state, respectively, in rodents (18, 30).
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Type I MHC mRNA and protein expression.
Type I MHC (-MHC) is negatively regulated by
T3 at the transcriptional level
(3, 9, 31), and the results presented in the current study agree with
this notion in that hypothyroidism upregulated type I MHC (
-MHC)
mRNA expression, whereas hyperthyroidism resulted in the opposite
response (Fig. 1). This regulation was observed in both heart and skeletal muscle, with the former showing much greater sensitivity, as the type I mRNA signal in the heart varied
10-fold because of extremes in thyroid state (Fig. 1). The type I MHC
protein data do not fully reflect the impact of altered thyroid state
on this phenotype, especially in the soleus and VI muscles (Fig. 1).
This discrepancy likely has to do with the duration of the experimental
manipulation. With consideration that the MHC protein half-life is
~7-10 days, a steady state at the protein level cannot be
reached in 3 wk. However, it has been previously shown that a longer
duration of hypothyroidism compared with that used herein transformed
the soleus MHC protein profile to 100% type I (3), whereas
hyperthyroidism decreased type I MHC expression by ~60% (24).
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TR protein expression. Striated muscle TR expression was examined at both the protein and mRNA levels (Tables 2 and 3). Muscle nuclei T3 Bmax was used as an index of TR number and was expressed on the basis of nuclear DNA as well as per unit muscle mass. These data (Table 2) revealed collectively that the three types of skeletal muscle have a greater Bmax than cardiac muscle as expressed per milligram of nuclear DNA, whereas cardiac nuclei had a greater T3 affinity (lower Kd) than skeletal muscle nuclei. However, when Bmax is expressed on the basis of muscle mass, the data show that slow-twitch skeletal muscle contains a greater density of TRs than the fast-twitch types (Table 2). This difference likely has to do with slow-twitch skeletal muscles having more nuclei per cell volume compared with their fast-twitch counterparts (1).
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TR mRNA expression.
Although it is known that TRs exist as different isoforms, our binding
assays did not involve a technique that differentiates between the
various TR isoforms at the protein level. Thus the reported
Bmax consists of both
TR-1 and
TR-
1 binding
activities, not considering the expression of the
2-isoform, which does not bind
T3 (3, 23). Also it is not quite
clear how the Kd
would be affected by the different isoform composition within a given muscle type. Therefore, in an attempt to gain some insight on this
issue in the context of the present study, analyses concerning TR
isoforms were performed using Northern analyses with cDNA probes specific for the TR-
1,
TR-
1, and
erbA-
2 isoforms. Figure
2 depicts TR isoform mRNA signals for the
different muscle types under the euthyroid state. In the performance of
these analyses, the soleus and VI muscles were analyzed individually as
separate representatives of the slow-twitch type. The mRNA data
analyses show that the expression pattern of the three TR mRNA isoforms in the soleus and VI was not different. Furthermore, TR-
mRNA is
most abundant in the heart, i.e., the signal was two- to threefold greater compared with that of the skeletal muscles (Fig.
2B). In contrast,
TR-
1 is most abundant in the
RMG fast-twitch skeletal muscle type and least abundant in the heart.
Also, these results clearly show that the ratio of
2- to
1+
-mRNA is relatively constant across the striated muscle types, whereas the ratio of the
- to
1-signal was
significantly higher in the heart compared with skeletal muscle (Fig.
2C). Slow muscles (soleus, VI) also exhibited a larger ratio of TR-
to
TR-
1 mRNA than fast-twitch muscles (RMG, white MG).
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DISCUSSION |
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Thyroid hormone exerts its biological effects largely by influencing gene expression via interactions with the high-affinity TRs located in the nucleus. Both the concentration of the nuclear receptors and T3 affinity play a major role in determining T3 responsiveness of a given tissue. However, other factors are also involved. For example, T3 transport from the bloodstream to the nucleus could play a critical role in determining the sensitivity to T3. A cytosolic protein has been shown to bind T3 and thus modulate its availability to the nucleus (5). This cytosolic T3 binding protein has been shown to be expressed and regulated by T3 in a tissue-specific fashion (5). Also, TR activation or repression of transcription is not a simple process. Rather, it involves complex multilevel interactions with other nuclear factors that could also be tissue specific and may affect the T3 response (26). Despite this complexity and as a first approach to studying this problem, it seemed logical to examine TR expression in striated muscle types and how this expression is altered by extremes in thyroid state.
Although previous reports have established that heart and skeletal
muscle express the TR-1,
TR-
1, and
erbA-
2 forms (2, 3, 11, 15),
relatively little is known about the pattern of TR expression in
specific skeletal muscle types and whether TR isoform expression is
sensitive to altered thyroid state in a muscle type-specific fashion.
Thus one of the goals of the present study was to examine the
expression of TR isoforms both in different muscle types and as a
function of thyroid state. We examined the TR protein expression using
T3 binding assays, which give the nuclear T3
Bmax and affinity. Surprisingly,
these assays demonstrated that the rodent heart expresses the fewest
nuclear receptors based on its lower
Bmax when expressed per milligram
DNA, but it exhibited a higher affinity to
T3 than any of the skeletal muscle
types. Both slow-twitch and fast-twitch skeletal muscles have similar T3 affinity and similar
Bmax as expressed per milligram
DNA. However, slow-twitch skeletal muscle had a higher
Bmax when expressed per unit
muscle mass. This difference likely has to do with slow-twitch muscle
having more DNA, i.e., more nuclei per muscle mass (1), and is
consistent with slow-twitch muscles being more responsive to altered
thyroid state than fast-twitch muscles (3, 22, 24). Under an altered
thyroid state, the heart Bmax did
not change, whereas skeletal muscle
Bmax increased in the hypothyroid state and tended to decrease somewhat in the slow-twitch (19%) and RMG
(13%) muscles in the hyperthyroid state (Table 2). Although these
binding assays do not differentiate among the different receptor
isoforms that are expressed or account for
2-isoform expression, they
suggest both a qualitative and quantitative difference between
T3 binding properties of cardiac
vs. skeletal muscle nuclei. Also, they show a differential response to
altered thyroid state, with the heart being the least sensitive in
terms of altering its binding capacity. In agreement with previous
reports, we show that altered thyroid state does not alter the binding
affinity in striated muscles (21).
The reported TR mRNA data demonstrated that cardiac muscle expresses
the greatest proportions of TR- mRNA, whereas the RMG, a fast-twitch
skeletal muscle, expresses greater
TR-
1 than the other muscle
types (Table 3). Our findings are in general agreement with previous
studies dealing with TR mRNA expression in a broad tissue spectrum that
suggested that TR-
mRNA expression in the heart is greater than that
in skeletal muscle, whereas skeletal muscles have higher content of
TR-
mRNA (11). Also, our results agree with a previous study in
which TR mRNA isoform expression was studied during development of rat
soleus, extensor digitorum longus, and diaphragm muscles (15). This
study showed that extensor digitorum longus muscle has higher
expression of TR-
1, whereas the
soleus and diaphragm muscles have a higher expression of TR-
.
Previous studies focusing on a broad tissue spectrum suggest that
TR- and TR-
mRNA species are differentially regulated by
T3, with TR-
being upregulated
and TR-
mRNA being downregulated by elevations in
T3 (14). Our findings dealing with
various muscle types are consistent with this notion (Table 3, Fig. 3). Interestingly, our findings suggest that
1- and
2-mRNAs vary in the same
direction, which is probably due to both being a different splice of
the same gene. Furthermore, our data show that the ratio of
2- to
1+
1-mRNA
species appears to be reciprocally regulated by thyroid state, i.e.,
increased in response to hypothyroidism and vice versa. On the other
hand, the ratio of
- to
1-mRNA species appears to be
regulated by thyroid state in the opposite direction of the
2- to
1+
1-mRNA
ratio. Although these results are interesting and suggest a subtle
plasticity in the control of TR expression, the physiological
significance of these changes at the message level remains uncertain.
With the assumption that TR mRNA and protein expressions follow the
same directional shifts, the findings on
c-erbA-
2 mRNA plasticity are
interesting. Although this species does not bind
T3, it interacts with the TRE and
has been shown in transfection assays to inhibit TR-mediated
T3 regulation of targeted reporter
genes (11, 19, 23). Interestingly, it would appear that this inhibition
would be expected to be diminished under the state of hyperthyroidism
(Fig. 3), and hence the influence of
T3 would be augmented in this
state on thyroid-sensitive genes. Conversely, during hypothyroidism,
the increased relative expression of the
erbA-
2 would likely potentiate
the effects of any reduction in the availability of
T3. Clearly, more studies are
needed to address these issues.
With regard to the relationship between TR mRNA pattern, TR isoform
protein composition, and T3
binding properties, previous studies suggest that the
TR-1 has a lower
Kd than
TR-
1 when analyzed in purified
forms (33). However, other studies suggest that TR isoform composition
cannot predict the
Kd when TRs are analyzed as a component of the nuclear extract (34). Also, it has been
proposed that tissue thyroid responsiveness (rather than Bmax) correlates better with
TR-
mRNA expression in a broad spectrum of mammalian tissue,
including liver, kidney, brain, and heart (36). However, in this study
(36), the Kd of
the binding in the different tissue was not reported. In the present
study, our findings agree with the notion that there is no definitive
relationship between Bmax and TR
mRNA expression; however, a somewhat different perspective can be drawn
from the relationship between
Kd and TR-
mRNA expression. For example, in the euthyroid animals, the mean
Kd values
negatively correlated with the mean TR-
mRNA signals, with a
correlation coefficient of
0.79. However, because of the low
number of rats included for the analyses, the statistical significance was low (P = 0.10). When
the different Kd
values were correlated with TR mRNA expression across all of the muscle types and under altered T3 state,
a significant negative correlation (P = 0.03) was found between
Kd and TR-
mRNA, with a correlation coefficient
(r) of
0.56. However, when
TR-
1 mRNA was used instead of
TR-
, this correlation was very poor
(r =
0.024,
P = 0.47). These findings suggest that
the higher affinity for T3 in
cardiac nuclei could be due in part to its disproportionately greater expression of the TR-
isoform (especially in the euthyroid state), assuming that cardiac vs. skeletal muscle TR proteins are expressed to
the same relative proportions as their respective mRNA levels.
It is clear from this study that the diversity in type I MHC expression in striated muscle and its regulation under altered thyroid state (Fig. 1) do not correlate well with either the T3 binding capacity of the tissue or TR mRNA isoform expression in the spectrum of muscles examined in the present study. For example, in the heart, type I MHC expression varies from 0 to 100% depending on the T3 state, whereas Bmax does not change significantly. These observations suggest that the level of circulating T3 and hence its availability to the cardiac myocyte nuclei are critically important in cardiac myosin isoform regulation. In skeletal muscle, type I MHC expression also does not correlate well with the T3 Bmax or with TR mRNA expression. For example, in the comparison of the fast-twitch white with the slow-twitch red muscle, type I MHC expression goes from being undetectable in the white muscle to accounting for >80% of the MHC pool in the slow-twitch muscle (Fig. 1). However, Bmax is approximately equal in these two muscle types as expressed per milligram DNA. Also, although white muscle is not responsive to T3 state in terms of type I MHC expression, it was highly plastic in terms of TR expression. In fact, white muscle showed more plasticity than slow-twitch muscles in TR mRNA expression under altered T3 state (Fig. 3). It should be emphasized that although TR expression did not account for the changes in MHC expression, this may not be generalized to all T3-regulated genes, i.e., MHC regulation may not be the best marker in this case. These observations suggest that although the TR is a transcription factor involved directly with transcriptional regulation of MHC expression in striated muscle, it would appear that other muscle-specific factors are also important in this regulation. The TRs appear to be widely expressed transcription factors affecting the expression of different genes in a different fashion. Of further interest, TRs may affect the same gene differently depending on the muscle type (3, 12, 16). Therefore, because of their diverse action, TRs must work in concert with other factors or cofactors, which in turn must be more muscle type specific. This latter concept can be illustrated by the fact that the fast-twitch IIb MHC gene is sensitive to thyroid state even though no TRE has been reported on its promoter (3).
In summary, the present study has provided information to suggest that 1) TRs are differentially expressed, both quantitatively and qualitatively, in skeletal vs. cardiac muscle types; 2) this pattern of expression does not necessarily correspond to the differences in responsiveness between cardiac and skeletal muscle to altered thyroid state, in which the former is markedly greater than the latter; 3) there is a differential quantitative response between cardiac vs. skeletal muscle concerning the pattern of TR adaptation to altered thyroid state; and 3) all striated muscle types share a similar pattern of adaptation concerning TR isoform plasticity as examined at the mRNA level (Fig. 3). Despite the new findings reported herein, more research is necessary to establish the physiological context of these adaptations in terms of thyroid-responsive gene regulation.
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ACKNOWLEDGEMENTS |
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We acknowledge the technical assistance of Paul W. Bodell, Megha Agarwal, Sepideh Najaran, and Terri Rembuskos.
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FOOTNOTES |
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This work was supported by National Heart, Lung, and Blood Institute Grant HL-38819 and National Institute of Arthritis and Musculoskeletal and Skin Diseases Grant AR-30346.
Address for reprint requests: K. M. Baldwin, Dept. of Physiology and Biophysics, Univ. of California, Irvine, CA 92697-4560.
Received 21 November 1997; accepted in final form 26 February 1998.
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REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Allen, D. L.,
S. R. Monke,
R. J. Talmadge,
R. R. Roy,
and
V. R. Edgerton.
Plasticity of myonuclear number in hypertrophied and atrophied mammalian skeletal muscle fibers.
J. Appl. Physiol.
78:
1969-1976,
1995
2.
Balkman, C.,
K. Ojama,
and
I. Klein.
Time course of the in vivo effects of thyroid hormone on cardiac gene expression.
Endocrinology
130:
2001-2006,
1992[Abstract].
3.
Caiozzo, V. J.,
and
F. Haddad.
Thyroid hormone: modulation of muscle structure, function, and adaptive responses to mechanical loading.
Exerc. Sport Sci. Rev.
24:
321-361,
1996[Medline].
4.
Carson, J. A.,
R. J. Schwartz,
and
F. W. Booth.
SRF and TEF-1 control of chicken skeletal -actin gene during slow muscle hypertrophy.
Am. J. Physiol.
270 (Cell Physiol. 39):
C1624-C1633,
1996
5.
Cheng, S.-Y.
Interaction of thyroid hormone with cytosol proteins.
In: Thyroid Hormone Metabolism, edited by S.-Y. Wu. Boston: Blackwell, 1991, p. 145-166.
6.
Chomczynski, P.
A reagent for the single-step simultaneous isolation of RNA, DNA, and proteins from cell and tissue samples.
Biotechniques
15:
532-537,
1993[Medline].
7.
DeGroot, L. J.,
A. Nakai,
A. Sakurai,
and
E. Macchia.
The molecular basis of thyroid hormone action.
J. Endocrinol. Invest.
12:
843-861,
1989[Medline].
8.
Dillmann, W. H.
Biochemical basis of thyroid hormone action in the heart.
Am. J. Med.
88:
626-630,
1990[Medline].
9.
Edwards, J. G.,
J. J. Bahl,
I. L. Flink,
S. Y. Cheng,
and
E. Morkin.
Thyroid hormone influences beta myosin heavy chain (MHC) expression.
Biochem. Biophys. Res. Commun.
199:
1482-1488,
1994[Medline].
10.
Evans, R. M.
The steroid and thyroid hormone receptor superfamily.
Science
240:
889-895,
1988[Medline].
11.
Glass, C. K.,
and
J. M. Holloway.
Regulation of gene expression by the thyroid hormone receptor.
Biochim. Biophys. Acta
1032:
157-176,
1990[Medline].
12.
Gustafson, T. A.,
B. E. Markham,
and
E. Morkin.
Effects of thyroid hormone on -actin and myosin heavy chain gene expression in cardiac and skeletal muscles of the rat: measurement of mRNA content using synthetic oligonucleotide probes.
Circ. Res.
59:
194-201,
1986[Abstract].
13.
Haddad, F.,
P. W. Bodell,
S. A. McCue,
and
K. M. Baldwin.
Effects of diabetes on rodent cardiac thyroid hormone receptor and isomyosin expression.
Am. J. Physiol.
272 (Endocrinol. Metab. 35):
E856-E863,
1997
14.
Hodin, R. A.,
M. A. Lazar,
and
W. W. Chin.
Differential and tissue-specific regulation of the multiple rat c-erbA messenger RNA species by thyroid hormone.
J. Clin. Invest.
85:
101-105,
1990[Medline].
15.
Hoffman, R.,
M. Lazar,
N. Rubinstein,
and
A. Kelly.
Differential expression of 1,
2 and
1 thyroid hormone genes in developing rat skeletal muscle (Abstract).
J. Cell. Biochem.
18D:
517,
1994.
16.
Izumo, S.,
B. Nadal-Ginard,
and
V. Mahdavi.
All members of the MHC multigene family respond to thyroid hormone in a highly tissue-specific manner.
Science
231:
597-600,
1986[Medline].
17.
Karin, M., H. F. Yang-Yen, J. C. Chambard, T. Deng, and F. Saatcioglu. Various modes of gene regulation by
nuclear receptors for steroid and thyroid hormones.
Eur. J. Clin. Pharmacol. 5, Suppl. 1: S9-S15, 1993.
18.
Klein, I.
Thyroxine-induced cardiac hypertrophy: time course of development and inhibition by propranolol.
Endocrinology
123:
203-210,
1988[Abstract].
19.
Koenig, R. J.,
M. A. Lazar,
R. A. Hodin,
G. A. Brent,
P. R. Larsen,
W. W. Chin,
and
D. D. Moore.
Inhibition of thyroid hormone action by a non-hormone binding c-erbA protein generated by alternative mRNA splicing.
Nature
337:
659-661,
1989[Medline].
20.
Labarca, C.,
and
K. Paigen.
A simple, rapid, and sensitive DNA assay procedure.
Anal. Biochem.
102:
344-352,
1980[Medline].
21.
Ladenson, P. W.,
J. D. Kieffer,
A. P. Farwell,
and
E. C. Ridgway.
Modulation of myocardial L-triiodothyronine receptors in normal, hypothyroid, and hyperthyroid rats.
Metab. Clin. Exp.
35:
5-12,
1986[Medline].
22.
Larsson, L.,
X. Li,
A. Teresi,
and
G. Salviati.
Effects of thyroid hormone on fast- and slow-twitch skeletal muscles in young and old rats.
J. Physiol. (Lond.)
481:
149-161,
1994[Abstract].
23.
Lazar, M. A.
Steroid and thyroid hormone receptors.
Endocrinol. Metab. Clin. North Am.
20:
681-695,
1991[Medline].
24.
Li, X.,
and
L. Larsson.
Contractility and myosin isoform compositions of skeletal muscles and muscle cells from rats treated with thyroid hormone for 0, 4 and 8 weeks.
J. Muscle Res. Cell Motil.
18:
335-344,
1997[Medline].
25.
Liew, C. C.,
G. Jackowski,
T. Ma,
and
M. J. Sole.
Nonenzymatic separation of myocardial cell nuclei from whole heart tissue.
Am. J. Physiol.
244 (Cell Physiol. 13):
C3-C10,
1983
26.
Lin, K.,
S. L. Chen,
X. G. Zhu,
H. Shieh,
P. McPhie,
and
S. Cheng.
The gene regulating activity of thyroid hormone nuclear receptors is modulated by cell-type specific factors.
Biochem. Biophys. Res. Commun.
238:
280-284,
1997[Medline].
27.
Morkin, E.,
I. L. Flink,
and
S. Goldman.
Biochemical and physiologic effects of thyroid hormone on cardiac performance.
Prog. Cardiovasc. Dis.
25:
435-464,
1983[Medline].
28.
Murray, M. B.,
N. D. Zilz,
N. L. McCreary,
M. J. MacDonald,
and
H. C. Towle.
Isolation and characterization of rat cDNA clones for two distinct thyroid hormone receptors.
J. Biol. Chem.
263:
12770-12777,
1988
29.
Ojamaa, K.,
J. D. Klemperer,
S. S. MacGilvray,
I. Klein,
and
A. Samarel.
Thyroid hormone and hemodynamic regulation of -myosin heavy chain promoter in the heart.
Endocrinology
137:
802-808,
1996[Abstract].
30.
Penney, D. G.,
and
B. G. Barthel.
Effects of thyroid and growth hormone deficiency, and food restriction on heart mass, with and without added stress (carboxyhemoglobinemia).
Can. J. Physiol. Pharmacol.
63:
642-648,
1985[Medline].
31.
Rottman, J. N.,
W. R. Thompson,
B. Nadal-Ginard,
and
V. Mahdavi.
Myosin heavy chain gene expression: interplay of cis and trans factors determines hormonal and tissue specificity.
In: The Dynamic State of Muscle Fibers, edited by D. Pette. New York: Walter de Gruyter, 1990, p. p.3-16.
32.
Roy, R. R.,
K. M. Baldwin,
T. P. Martin,
S. P. Chimarusti,
and
V. R. Edgerton.
Biochemical and physiological changes in overloaded rat fast- and slow-twitch ankle extensors.
J. Appl. Physiol.
59:
639-646,
1985
33.
Schueler, P. A.,
H. L. Schwartz,
K. A. Strait,
C. N. Mariash,
and
J. H. Oppenheimer.
Binding of 3,5,3'-triiodothyronine (T3) and its analogs to the in vitro translational products of c-erbA protooncogenes: differences in the affinity of the - and
-forms for the acetic acid analog and failure of the human testis and kidney
-2 products to bind T3.
Mol. Endocrinol.
4:
227-234,
1990[Abstract].
34.
Schwartz, H. L.,
K. A. Strait,
N. C. Ling,
and
J. H. Oppenheimer.
Quantitation of rat tissue thyroid hormone binding receptor isoforms by immunoprecipitation of nuclear triiodothyronine binding capacity.
J. Biol. Chem.
267:
11794-11799,
1992
35.
Schwartz, H. L.,
K. A. Strait,
and
J. H. Oppenheimer.
Molecular mechanisms of thyroid hormone action. A physiologic perspective.
Clin. Lab. Med.
13:
543-561,
1993[Medline].
36.
Strait, K. A.,
H. L. Schwartz,
A. Perez-Castillo,
and
J. H. Oppenheimer.
Relationship of c-erbA mRNA content to tissue triiodothyronine nuclear binding capacity and function in developing and adult rats.
J. Biol. Chem.
265:
10514-10521,
1990
37.
Swoap, S. J.,
F. Haddad,
P. Bodell,
and
K. M. Baldwin.
Effect of chronic energy deprivation on cardiac thyroid hormone receptor and myosin isoform.
Am. J. Physiol.
266 (Endocrinol. Metab. 29):
E254-E260,
1994
38.
Talmadge, R. J.,
and
R. R. Roy.
Electrophoretic separation of rat skeletal muscle myosin heavy-chain isoforms.
J. Appl. Physiol.
75:
2337-2340,
1993[Abstract].