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Li-Qun
Ren, Xiang-Jun Li, Guang-Sheng Li, Zhi-Tao Zhao, Bo Sun, Department
of Pathology, Institute of Frontier Medical Science, Jilin
University, Changchun 130021, Jilin Province, China
Fei Sun, Department of Cellular Biology, Institute of
Frontier Medical Science, Jilin University, Changchun 130021, Jilin
Province, China
Supported by National Natural Science Foundation of China,
No. 39870668
Correspondence to: to Professor Guang-Sheng Li, Department of
Pathology, Institute of Frontier Medical Science, Jilin University,
Changchun 130021, Jilin Province, China.
ligs@public.cc.jl.cn
Telephone: +86-431-5619287
Received: 2003-12-28
Accepted: 2004-02-10
Abstract
AIM: To investigate coxsackievirus B3 infection and
its gene mutation in Keshan disease.
METHODS: The expression of Coxsackievirus B3 RNA was
detected in autopsy specimens of acute (12 cases), sub-acute (27
cases) and chronic (15 cases) Keshan disease by in situ
hybridization. In sub-acute Keshan disease specimens, 3 cases with
positive result by in situ hybridization were selected RT-PCR
analysis. The DNA segments were then sequenced.
RESULTS: Coxsackievirus B3 RNA was detected in the
cytoplasm of myocardiocyte. The positive rate was 83% in acute, 67%
in sub-acute and 80% in chronic Keshan disease. In the conservative
region of Coxsackievirus B3 genome, there was a mutation
in 234 (C-T) compared to the non-cardiovirulent strain, CVB3/0.
CONCLUSION: Coxsackievirus B3 RNA can survive and
replicate in heart muscle of Keshan disease, which may play an
important role in the occurrence of Keshan disease. The possible
mechanism of occurrence of Keshan disease is associated with point a
mutation in Coxsackievirus B3 genome.
Ren LQ, Li XJ, Li GS,
Zhao ZT, Sun B, Sun F. Coxsackievirus B3 infection and
its mutation in Keshan disease. World J Gastroenterol
2004; 10(22): 3299-3302
http://www.wjgnet.com/1007-9327/10/3299.asp
INTRODUCTION
Enteroviruses,
particularly Coxsackie B viruses (CVB), are the most common cause of
human viral myocarditis and are associated with dilated
cardiomyopathy (DCM)[1-3]. In general, neonates and
children suffer more severe clinical syndromes due to CVB infection,
often severe or life threatening, because of inflammation and
necrosis of heart muscle[4]. Many diseases are considered
to have relationship with CVB3 infect, but the mechanism
is still not well understood. Although the immune response of the
host undoubtedly plays an important role in the pathogenesis of
viral heart disease[5], direct viral cytotoxicity has
been found to be crucial for organ pathology both during acute and
persistent heart muscle infection. Coxsackievirus B3 (CVB3),
one of six CVB serotypes, is a member of the genus enterovirus
within the family Picornaviridae and its structure is well
understood[6,7]. Some studies suggest that the 5'NTR
of enteroviruses maybe play an important role in producing or
sustaining the myocardial virulence[8-14].
Keshan disease is endemic exclusively in selenium-deficient
rural areas of China, including 14 provinces and autonomous regions[15].
Its clinical features are low body selenium content and acute or
chronic episodes of heart disorder characterized by cardiogenic
shock, arrhythmia, ECG changes (for example, right branch block),
and/or congestive heart failure, with an enlarged heart. Four types
of the disease are seen: acute, subacute, chronic, and latent or
compensated. The basic pathological change is multifocal myocardial
necrosis and fibrous replacement throughout the myocardium, with
various degrees of cellular infiltration and calcification,
depending upon the type of disease[16,17]. Research
suggests that not a single but several more factors may have a
relationship with the occurrence of Keshan disease. The reasons are
often considered as global, biological chemical factors (selenium
deficiency), dietary nutritional factors (vitamin E deficiency) and
infection (virus, especially enteroviruses). This hypothesis can
explain both endemic and seasonal features of Keshan disease. Recent
studies have also demonstrated a possible etiological role of
enterovirus infection in a particular form of heart muscle disease,
selenium deficiency-related endemic cardiomyopathy (Keshan disease),
seen in China[18,19]. Presently, patients of Keshan
disease are rare and there is no ideal animal model, research of
viral etiology of Keshan disease is relatively few. In this study,
we detected all the four types of Keshan disease using in situ
hybridization and sequenced the 5’NTR of CVB3 from subacute Keshan
disease in order to investigate the relationship between Keshan
disease and CVB3 infection.
MATERIALS
AND METHODS
Case selected
All the samples were cardiac tissue isolated at post mortem
and fixed in formaldehyde and embedded in paraffin wax and preserved
in Institute of Keshan Disease, Jilin University from 1959-1985. The
samples included 12 acute patients (7 males, 5 females, average age
16.3 years), 27 subacute patients (12 males, 15 females, average age
4.3 years) and 15 chronic patients (9 males, 6 females, average age
23.8 years). We used three non-Keshan disease patients as controls,
including two normal and one perinatal period cardiomyopathy. The
cultured human amniotic cell containing a cardiovirulent strain of
CVB3 served as positive control and by RT-PCR.
In situ Hybridization
An obligonucleotide probe was purchased from Shanghai Sangon
Biological Engineering Company. This probe, labeled with biotin, was
designed to detect coxsackievirus B3, whose sequence was
5’-GTC CGC AAT GGC GGG CGG TGG TGG TGT CTC-3’.
All slides were treated by APES solution
(1:50 acetone) in order to prevent the section slipping from the
slide. The 5 mm
thick section was baked 3-4 h at 80 °C and overnight at 60 °C.
The paraffin wax was removed by immersing the slide in xylene.
The slides were then rehydrated, treated with 0.1 g/L Triton X-100
for 2 min, digested with proteinase K (0.25 mg/mL) in PBS for 5 min
at room temperature, then sealed with histidine (2 mg/mL) for 2 min,
and then dehydrated in graded concentrated ethyl alcohol. The tissue
sections were denatured on heating block for 2 min at 80 °C and then cooled on ice immediately. They were pre-hybridized
for 3-4 h at 42 °C by covering them with pre-hybridization liquid (6×SSC,
5×Denhardt,
5 g/L SDS, 100 mg/mL
herring sperm DNA, 500 g/L deionized formamide) in a wet chamber.
After removal of the pre-hybridization liquid, the sections were
allowed to hybridize overnight under the same conditions as
described above.
Following the hybridization, the slides were rinsed twice
with 2×SSC
containing 500 g/L deionized formamide, twice with 2×SSC,
treated with 1 g/L Triton X-100 for 2 min and washed twice with
buffer I (1 mol/L NaCl, 0.1 mol/L Tris, pH 7.5). Buffer II (3 g
bovine serum albumin dissolved in buffer I) was added to each
section and incubated for 1 h. After pouring off buffer II, the
SA-AP (streptavidin-alkaline phosphatase conjugation) was added onto
the tissue sections, and allowed to react in this mixture for 20
min, rinsed with buffer I and then with buffer III (0.1 mol/L NaCl,
0.1 mol/L Tris-Cl, 50 mmol/L MgCl2, pH 9.5). Finally,
freshly prepared developer solution (BCIP/NBT) was applied to the
slides and incubated for 30 min to 4 h. A brownish blue color
reaction was produced. Following routine dehydration, the sections
were cleared and mounted.
To assess the specificity of the hybridization signal, the
culture cell infected by CVB3 were alternatively hybridized with the
labeled obligonucleotide probe encoding CVB3 before and after
digestion by Rnase, and hybridization solution without containing
the labeled obligonucleotide probe encoding CVB3 was also used as
negative control.
RT-PCR
Total RNA was extracted from paraffin-embedded heart tissue
of patients with Keshan disease according to the following
procedures. Several section slices (5-10 mm)
were put into a 1.5 mL Eppendorf tube in which approximately 1 mL
xylene was added in order to exclude paraffin. The xylene was
changed every 2 h and the last time it was kept overnight at room
temperature. After being centrifuged at 5 000 r/min for 5 min, the
tissue was washed with non-water ethanol and then baked at 55 °C. The total RNA from the dried tissue was then extracted using
Trizol regent (GIBCO). Positive controls were the cultured human
amniotic cells containing CVB3. The RNA precipitate was
dissolved in 10 mL
of diethyl pyrocarbonate-treated H2O.
The
enterovirus specific primers used for RT-PCR and sequencing of the 5'NTR
were purchased from Sigma Genosys Australia Pty. Ltd. The sequence
of the primers was 3P: 5’-TCA ATT GTC ACC ATA AGC AGC AGC CA-3’
and 5P: 5’-CGG TAC CTT TGT GCC CCT GTT TT-3’.
RT was carried out following the manufacturer’s
instructions. A 2 mL
of specific primer 3P and 1 mL
of 10 mmol/L dNTPs were mixed with 8 mL
of RNA template. The mixture was immediately put on ice after
incubated at 65 °C for 5 min. Then the mixture of 4 mL
of 5×first
strand buffer, 1 mL
of Rnase inhibitor, 1 mL
Superscript II Rnase H-free reverse transcriptase and 3 mL
of diethyl pyrocarbonate-treated H2O was added to the
reaction tube, followed by incubation at 42 °C for 5 min, and at 70 °C for 15 min in order to inactivate the reverse transcriptase.
PCR was carried out with a 25 mL
mixture containing 10 pmoL deoxynucleotide triphosphates, 15 pmoL
forward primer (5P), 15 pmoL reverse primer (3P), 1×reaction
buffer (Dingguo Biocompany), and 3 mL
of the RT reaction product. The PCR reaction mixture was
pre-denatured at 95 °C for 2 min, and then amplified through 30 cycles, each cycle
consisting of denaturation at 95 °C for 45 s, annealing at 55 °C for 45 s, and extension at 72 °C for 45 s. Finally, an additional extension was carried out at
72 °C for 10 min. A negative control containing 22 mL
of the reaction mixture plus 3 mL
of autoclaved H2O and a positive control containing 22 mL
of the reaction mixture plus 3 mL
of the RT reaction product from cells infected with the virulent
laboratory strain of CVB3 were included in each set of
PCR.
The amplification products of PCR were analyzed on 17 g/L
agarose gel by electrophoresis and stained with ethidium bromide. To
assess the specificity of RT-PCR, the extracted total RNA were
digested by Rnase then used for PCR as template. The distilled water
was also used as template in PCR reaction as negative control.
DNA
sequencing
The sequencing reaction cycle was carried out using 4 mL
of DNA polymerase FS-terminator mix (PE-ABI), 3.2
mmol/L primer, and 5 ng of PCR product per 100 bp length of
template DNA with the volume made up to 10 mL
with H2O. Reactions were run for 25 cycles as follows: 96
°C for 30 s, 50 °C for 15 s, and 60 °C for 4 min. DNA was precipitated, dissolved in loading buffer
(167 g/L formamide, 733 g/L dextran), and separated on 41 g/L
denaturing polyacrylamide gel on an ABI model 377 DNA sequencer.
This procedure was performed by Shanghai Sangon Biological
Engineering Company.
RESULTS
In situ Hybridization
According to the feature of positive signal of the culture
cell, the positive hybridization signals of the Coxsackievirus RNA
appeared as deep brownish blue mass or granules (Figure 1). This
criterion was applied to the tissue sample. In longitudinal
sections, they were seen to adhere to myofibrils in one or several
strings of beads (Figure 2A). They varied in size and, in cross
section, were usually localized in the sarcoplasm in proximity to
myocyte nuclei, but no signals were found in the nuclei themselves.
The color of signal was the darkest in the myocardium of papillary
muscles, trabeculae carneae and subendocardial muscle. It was
lighter and less intense in the cells of the outer layers than those
in the middle layers of ventricular walls. The myocardial cells
surviving in fresh lesions and surrounding old necrotic foci often
showed the hybridization signal. No signal was found in necrotic
foci, and there were slight differences in the distribution and
manifestation of positive hybrid signals in several types of Keshan
disease. In most acute and subacute cases, the signal appeared
predominantly in the myocyte surrounding foci and surviving in fresh
foci as well as cells beneath the endocardium and of papillary
muscles. The hybridization-positive granules were thick, and had
clear border. The sarcoplasm appeared dark, and sometimes,
homogeneously blue (Figure 2B). In most of the chronic cases, the
granules were usually distributed in all parts of the myocardium,
and were small and without clear borders, like dirt. The detection
rate in subacute specimens was the highest, and the rate in acute
specimens was higher than that in chronic specimens, but there were
no significant differences among the three types of Keshan disease.
The positive rate of hybridization in the three
type of Keshan disease was 83% (10/12) in acute, 67% (18/27) in
sub-acute and 80% (12/15) in chronic Keshan disease. No positive
signals were found in any negative controls.
Results of 3 myocardial control specimens
investigated with in situ hybridization were negative.
RT-PCR
RT-PCR revealed that the RNA extracted from the myocardial
tissue with positive control of in situ hybridization amplified a
DNA fragment about 541 bp, while the three negative controls did not
amplify (Figure 3). The RNA extracted from cultured cell infected by
CVB3 were also amplified the DNA fragment about 541 bp.
Sequence analysis
The DNA segments from RT-PCR were sequenced and compared
to the non-cardiovirulent control, CVB3/0, and the
cardiovirulent strain, CVB3/Nancy and CVB3/20.
We found that the sequence of the amplified segment had one
nucleotide different compared to that of CVB3/0. The
234th nucleotide in the genome of CVB3/0 was C while ours
was T. But the sequence of our segment was similar that of CVB3/Nancy,
CVB3/20 and the positive control (Figure 4).
Figure 1 Positive
signal in cultured cell A: the positive hybridization signals of the
Coxsackievirus RNA appeared as deep brownish blue mass or granules
(arrow) B: control, only hybridization solution was applied.
Figure
2 Positive signal
of in situ hybridization in subacute myocardial tissue A: Feature
positive signal of in situ hybridization with cardiac tissue is seen
as deep brownish blue and seems to adhere onto myofibril, linked
together in one or several strings of beads, when observed
longitudinally (×400). B: The granules of positive signal were thick and with
clear border in varying size and localized in the sarcoplasm.
Figure
3(PDF) Agarose gel
electrophoresis results Lanes 1, 2, 3: negative control; Lanes 4-6:
subacute Keshan disease; Lanes 7: positive control; Lane 8: DL-2000
DNA Marker. A 541 bp DNA segment can be seen in lanes 4-7.
Figure
4(PDF)
Sequence of segment of RT-PCR Compared to the nonvirulent strain of
CVB3/0,
there was one nucleotide different (arrow). The nonvirulent strain
of CVB3/0
was C while ours was T.
DISCUSSION
Keshan disease has been studied for over 60 years in China. One
of the key issues is the complex etiology of this endemic disease,
with a focus on environmental nutritional factors and infectious
agents. Selenium deficiency in the food chain has been recognized as
a major but not exclusive environmental-nutritional factor, and
increasing evidence supports an etiological role of enteroviruses in
Keshan disease. Recently, Peng et al.[20]
determined the sequences of the 5’NTR and the 3’ end of the VP1
coding region from six enteroviruses isolate from cases of Keshan
disease or outbreak myocarditis. From their results, they drew a
conclusion that the sequence data confirm that coxsackievirus group
B serotypes are predominant in the region where Keshan disease is
endemic, and may be the etiological factors in outbreaks of
myocarditis, and VP1 genotyping of enteroviruses is accurate and
reliable. Animal experiments indicate that isolates may differ in
pathogenicity. Virus infection combined with selenium deficiency in
environments and vitamin E deficiency in dietary can illustrate both
endemic and seasonal features of Keshan disease. The hypothesis of
virus infection was accepted once it appeared, but the methods used
in virology limited the development of a virus infection hypothesis
of Keshan disease. The rapid development in molecular biology brings
vitality to virology.
In situ hybridization is a method to detect the nucleic acids
in a tissue or cell using a labeled obligonucleotide chain as probe.
This technique has already been widely used in biology and medicine
because of its high specificity, sensitivity and location precision.
Using a cloned cDNA probe obtained from CVB4 infected cells and
labeled by biotin-11-dUTP, Easton et al.[21] found
that 46% (6/13) patients who had been diagnosed coxsackievirus
myocarditis can be found enterovirus infection in their myocardial
tissue. Archard et al.[22] examined enteroviruses
infection in human myocardial tissue using an enterovirus specific
probe, and found that the rate of enterovirus infection was 45%
(21/47) in myocarditis patients and 43% (35/82) in cured myocarditis
and DMC patients. In our research, the specific obligonucleotide
probe of CVB3 was labeled by biotin on 5’ end, and the specimen
was paraffin-embedded myocardial tissue from autopsy patients of
Keshan disease. The object was to detect the coxsackievirus B3 RNA
by in situ hybridization. Among the three types of Keshan disease
patients, we found the positive rate was 83%, 67%, and 80% in acute,
sub-acute and chronic Keshan disease patients, respectively. Our
results provide a new support to the hypothesis that enterovirus,
especially CVB3, might play an important role in
pathogenesis of Keshan disease. Moreover, the area, range and the
distribution of the positive signal of CVB3 were
associated with the development of Keshan disease. The positive
signals in acute and sub-acute Keshan disease were located in the
surviving myocardiocyte in or around the necrosis foci while they
were dispersed in almost all the myocardiocyte in chronic Keshan
disease. The results of in situ hybridization suggested that
enterovirus could lead to heart muscle lesion when they involved in
the myocardial tissue, and they can dispersed to the normal heart
muscle with increase of time.
Though
there was a high enterovirus infection rate in myocardial tissue of
Keshan disease patients[23,24], it is well known that the
enterovirus could also be detected in many patients who had no heart
muscle lesion. The change of viral cardiovirulence can undoubtedly
play an important role. Some research has demonstrated that under
some conditions, such as selenium deficiency, vitamin deficiency,
the phenotype of enterovirus can be changed, that is, a non-cardiovirulent
strain can change into a cardiovirulent strain, or the
cardiovirulence can be increased in these conditions[25-27].
Beck et al.[28] sequenced the mutated strain, CVB3/0se-,
which was extracted from the heart muscle of selenium deficient
mice, and found that there were six mutation points in CVB3/0se-
and compared to the two-cardiovirulent strains, CVB3/20,
CVB3/M1, all mutated points were turned into that of a
cardiovirulent strain. Can the same episodes also happen in Keshan
disease patients? In our research, we found an about 541 bp DNA
segment by RT-PCR. Compared to CVB3/0, a non-cardiovirulent strain,
the sequence of our segment had only one nucleotide different, which
was 234 T. But the segment had the same sequence as that of
CVB3/Nancy and CVB3/20, cardiovirulent strain. This result can give
us some indications that the mutation of virus genome might play an
important role in the pathogeny of Keshan disease. But this needs to
further investigation.
As we know that RNA is degraded easily, so its detection is
difficult, especially in paraffin-embedded tissue[29,30].
But the paraffin-embedded myocardial tissue we select have been kept
in our institute for a long time (10-50 years), and are generally
thought not to be optimal for RNA research, but our results
displayed that results of both in situ hybridization and RT-PCR were
satisfactory.
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