الفهرس 
TitleOnly 14 pages are availabe for public view
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Abstract
Schistosomiasis is a chronic water-borne helminthic disease with a major health and
economic burden in tropical and sub-tropical areas, especially without access to safe
drinking water and adequate sanitation. In Egypt, schistosomiasis is the most important
endemic parasitic disease. S. mansoni is the causative agent for over 90% of all human
schistosomiasis. In the definitive host, including man, adult male and female worms
produce large numbers of eggs. Many eggs leave the body in feces, but some are trapped in
tissues and induce a granulomatous immune response, leading to progressive tissue fibrosis
and organ damage.
miRNAs comprise a family of non-coding RNAs with approximately 21-25
nucleotides that can be detected in a wide range of body fluids and tissues. They downregulate
gene expression at the post-transcriptional level and play an important role in
controlling diverse biological functions including cell differentiation, development,
proliferation and signal transduction. In schistosomiasis, it was found that the miRNA
plays a variety of regulatory roles in the immunological responses occuring during the
development of schistosoma.
The present study aimed to assess the expression of host miRNA in serum and liver
in mice experimentally infected with S. mansoni at different time intervals.
In the present study blood and liver tissue samples were collected from control non
infected mice (group I) and S. mansoni infected mice sacrificed at 4 , 8 and 12 weeks p.i.
(groups II-IV) and from mice treated with PZQ eight weeks p.i. and sacrificed four weeks
later (group V). At each time point, serum and liver tissue samples were processed for
miRNAs extraction, reverse transcription and real time PCR analysis of miRNAs 223 &
146b expression. Liver sections were subjected to egg count estimation and
histopathological examination.
Parasitological assessment of hepatic egg count in the S. mansoni infected mice groups
revealed no eggs in mice examined four weeks p.i. (group II) and a significantly higher mean
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egg count ∕ gm of liver tissue in group IV (12 weeks p.i.) compared to group III (eight weeks
p.i.) with 142.4 % elevation. Treated mice (group V) showed the least mean egg counts with
reduction percentages of 74.6 % compared to group III and 89.72 % compared to group IV.
Examination of H&E stained liver sections revealed inflammation in the portal tracts
as well as apoptosis in some hepatocytes four weeks p.i. On the other hand, large
granulomas, more inflammation and appearance of fibroblasts and fibrocytes were
observed eight weeks p.i. The changes become more obvious 12 weeks p.i with distorted
hepatic architecture, chronic granulomatous lesions and fibrous transformation of
granuloma around mature egg.
It was observed that administration of praziquantel eight weeks p.i. improved the
hepatic tissue pathology in S. mansoni infected mice. The hepatic granuloma size in the
treated mice was significantly lower than that of the untreated mice (groups III and IV).
Moreover, the treated group recorded the least inflammatory reaction. The decrease in
granulomas size after treatment went hand in hand with diminished egg counts in the liver.
Regarding miRNA-223, results of this study revealed that miRNA-223 expression in
liver tissue in the early stage of infection (four weeks p.i.) was not significantly different
from that of the uninfected mice. Significant down regulation was detected in mice
examined 8 and 12 weeks p.i with more marked down-regulation in the latter. Moreover,
the expression at 12 weeks was significantly lower than that observed at four weeks p.i.
Expression is specifically associated with the hepatic egg count and the extent of hepatic
pathological changes. It correlated negatively with tissue egg count.
Serum miRNA 223 expression showed significant down regulation 8 and 12 weeks
p.i, following the same pattern as tissue level. The levels of serum and tissue miRNA-223
were positively correlated and both were inversely related to the histopathological changes.
Regarding liver expression of miRNA-146b, the present study showed nonsignificant
difference between infected and control mice. However, expression increased
gradually with progression of infection resulting in a significant higher level in mice
examined in the later stage of infection (12 weeks p.i ) compared to mice examined earlier
(4 weeks p.i.). Unlike miRNA- 223, expression of serum and tissue miRNA-146b
correlated positively with egg count and pathological changes. Studying the expression
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profile of miRNA-146b in serum samples revealed a positive correlation with liver
expression levels. The serum level was significantly elevated in the late stage (12 weeks
p.i.) compared to the two earlier follow up periods (four & eight weeks p.i.).
Regarding the effect of treatment, it was found that tissue and serum miRNA-223
expression levels nearly returned to normal level in infected mice within one month after
PZQ treatment. Importantly, tissue miRNA 223 expression was significantly higher in the
treated mice compared to the untreated groups examined 8 or 12 weeks p.i. (groups III and
IV). PZQ treated mice also showed significant reduction in liver and serum miRNA-146b
expression compared to the group with untreated advanced infection (group IV).
Restoration of normal miRNAs expression in treated mice was accompanied by
significantly lower hepatic egg counts, smaller hepatic granuloma size and diminished
inflammatory cellular infiltration.
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Conclusions
from the present study, it can be concluded that:
- Down-regulation of miRNA-223 and up-regulation of miRNA-146b occurs in the
liver tissue of mice experimentally infected with S. mansoni. Serum expression
level of these two miRNAs follows the same pattern as the tissue expression level
with significant positive correlation.
- Expression levels of the studied miRNAs do not change until four weeks p.i. in
mice. They may be useful as diagnostic markers of infection after the start of egg
deposition.
- Dysregulation of miRNAs expression correlates with liver egg count and becomes
more obvious with the progression of infection and detection of more chronic
granulomatous lesions, fibrous transformation and distorted hepatic architecture in
liver sections. The expression level of these miRNAs can, thus, be used as a marker
to reflect the extent of liver pathology.
- The expression level miRNA146b in serum is sensitive to chemotherapy.
Therefore, it could be potentially useful to monitor the therapeutic effects of PZQ
in terms of improvement of sever hepatic histopathological damage.
- Collectively, these findings provide new insights for further understanding of the
mechanisms of host-parasite interaction in schistosomiasis mansoni. This may
facilitate development of novel interventions for management of schistosomiasis
associated morbidity.
Recommendations
- Further research is needed to investigate the molecular and functional role of
miRNA-223 and miRNA-146b in the inhibition or activation of the immune system
cells and HSC during the course of schistosomiasis
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- Further studies are needed to study the potential value of using a combination of
miRNA-223 and miRNA-146b as well as other miRNAs as biomarkers to evaluate
hepatopathology progression in patients with schistosomiasis.
- It is also important to identify more potential miRNAs specific for schistosomiasis
fibrosis.
- Effective therapeutic methods for treating schistosomiasis-associated hepatic
fibrosis are urgently needed as PZQ cannot completely reverse the progression of
chronic liver fibrosis.
- Considering the role of miRNAs in the hepatic immunopathology induced by
schistosoma eggs, there is a need to explore the effectiveness of therapeutic
strategies based on manipulating miRNA expression to prevent and/or treat the
chronic complications of schistosomiasis. Safety issues of miRNA therapeutics in
schistosomiasis require further studies.