Abdominal aortic aneurysm (AAA) is a chronic inflammatory disease with no available pharmacological treatment. AAA formation reduces the structural integrity of the vessel and increases the susceptibility to rupture. The inflammatory response within human aneurysmal tissue is characterized by increased expression of cyclooxygenase-2 (COX-2). Similarly, in a mouse model of the disease induced by chronic Angiotensin II (AngII) infusion, we have shown that COX-2 expression in the abdominal aortic smooth muscle layer increases early in the development of the disease. Furthermore, genetic or pharmacological inactivation of COX-2 prior to disease initiation reduces AAA incidence. The current study utilized nonhyperlipidemic mice to determine the effectiveness of COX-2 inhibition initiated after AAA formation. COX-2 inhibitor treatment was initiated 5 days after beginning the AngII infusion, a time-point where significant aneurysmal pathology is observed. COX-2 inhibition with celecoxib significantly reduced the incidence as well as severity of AAAs as compared to the control group. Celecoxib treatment also protected the mice from aortic rupture and death. AAA development is characterized by degradation of the aortic smooth muscle layer with loss of the contractile phenotype. We found that the effectiveness of celecoxib was associated with significantly increased mRNA expression of alpha-actin, SM22alpha and desmin, all of which are markers of a differentiated smooth muscle cell phenotype. Celecoxib treatment also decreased mRNA expression of a marker of dedifferentiated smooth muscle (hyaluronic acid synthase 2). We also examined the role of altered expression of COX-2 in the increased susceptibility of the abdominal segment to AAA formation. We found a prolonged and greater induction of COX-2 in the abdominal aortic smooth muscle layer in contrast to a transient induction of COX-2 in the other regions of the aorta throughout disease progression. Overall, these findings suggest that COX-2 plays an important role in AAA development in mice, and COX-2 inhibition with celecoxib attenuates progression of aneurysm development by maintaining a differentiated phenotype in abdominal aortic smooth muscle cells.

[Truncated abstract] Hepatocellular carcinoma (HCC) is the major malignancy complicating chronic liver disease. New therapies for the prevention of HCC are required due to the limited success and high tumour recurrence rates of existing treatments. Emerging evidence suggests that HCC arise from the transformation of adult liver progenitor cells (LPCs), which have the capacity to differentiate into hepatocytes and biliary cells during liver regeneration. LPC activation precedes neoplasia in experimental hepatocarcinogenesis. LPCs share antigenic epitopes with HCCs, including α-fetoprotein (AFP) and M2- pyruvate kinase (M2PK). In animal models of hepatocarcinogenesis, attenuation of the LPC response reduces the incidence of HCC following prolonged liver injury via a tumour necrosis factor (TNF) dependent mechanism. As TNF is a pro-inflammatory cytokine, these data suggest that anti-inflammatory agents may be effective in inhibiting LPC activation and hepatocarcinogenesis. Cyclo-oxygenase-2 (COX-2) is an inducible enzyme that mediates the production of many prostaglandins during inflammation and carcinogenesis. Recent investigations show that the administration of selective COX-2 inhibitors (SC2Is) may reduce the incidence of a variety of tumours including breast, colon and skin. The broad aim of this thesis was to conduct a series of detailed studies on the effects of a SC2I on LPC activation and the hepatic pathologies associated with hepatocarcinogenesis in order to test the hypothesis that S2CIs may be a beneficial therapy that can reduce liver injury and pre-neoplastic changes in the choline-deficient, ethionine supplemented (CDE) murine model of hepatocarcinogenesis. Administration of a SC2I (SC-236) significantly inhibited a variety of hepatic cell populations that expand during the first month of the CDE mouse model of hepatocarcinogenesis (a choline deficient, ethionine supplemented diet). Numbers of M2PK-positive LPCs (which are more hepatocytic in morphology and are also COX-2 positive) and inflammatory cells were all significantly reduced by SC-236. In contrast, numbers of A6-positive LPCs (which are more biliary cell-like in morphology and do not express COX-2) were unchanged. ... In summary, these data suggest that COX-2 inhibitors such as SC-236 inhibit LPC activation and a variety of pre-neoplastic liver pathologies as a result of COX-2 dependent and independent mechanisms that may be mediated through inhibition of Akt phosphorylation and induction of apoptosis. Moreover, SC2Is may be useful as preventative treatment strategies for HCC in patients with chronic liver disease.

The zona-pellucida (zona, ZP) is an adhesion-refractory, acellular coat enclosing the rapidly growing, free-living mammalian preimplantation embryo which undergoes successive cleavage divisions to form the blastocyst, composed of ICM-cells surrounded by outer TE-cells. For further development, the blastocyst must ‘hatch’ or ‘escape’ out of the zona before it can implant into the endometrium for further development (Fig. 5.1A). Hence, the event of hatching or ‘zona escape’ assumes critical importance for the establishment of a successful pregnancy. The golden-hamster blastocyst offers a very unique paradigm to understand hatching, whereby upon attainment of a fully-expanded state, the blastocyst undergoes a dramatic (and molecularly unexplained) deflation event, followed by appearance of TE-derived dynamic cellular projections called TE-projections, whose appearance in an embryonic-stage and -time dependant manner suggest an intimate association with the hatching phenomenon (Fig. 5.1B). Thirdly, embryo-derived zonalytic proteases have been shown to bring about a focal-lysis of the ZP followed by global zona dissolution. Earlier work in the laboratory had demonstrated the intimate involvement of signaling molecules like LIF, HB-EGF, TGF-β and (ER)-α with hatching (Seshagiri et al., 2002, 2009). Investigations also revealed the involvement of cysteine-proteases of the cathepsin (cts) family, especially cts-L, -B and-P to be involved in zona lysis (Sireesha et al., 2008). In order to achieve a better understanding of mammalian preimplantation development, especially hatching, it was important to investigate the role and impact of other critical regulators of developmental and reproductive physiology. COX-2 is one such key signaling moiety and it was decided to investigate the role, if any, of COX-2 and its derived PGs in hamster peri-implantation events. COX-2 transcripts and immunoreactive COX-2 protein were detected in the different preimplantation stages, from 8-cell onwards. COX-2 protein was abundant in both the ICM and TE, but was especially enriched in the TE-cells of the late blastocyst. In order to investigate the function of this enzyme in preimplantation development and hatching, two very-specific inhibitors of COX-2 catalytic action, NS-398 and CAY-10404, were tested in identical concentrations of 25, 50 and 75 μM on in vitro cultured hamster blastocysts. In order to assess the impact of COX-2 inhibition on an embryo-stage and time-dependant manner, inhibitors were tested on freshly recovered 8-cell embryos or early blastocysts, continuously for 72 h or 48 h, respectively. COX-2-selective inhibitors inhibited hamster blastocyst hatching in a dose-dependant manner with maximum inhibition observed in the 75 μM dose. Surprisingly, there was a profound dose-dependent failure of deflation of late-blastocysts upon inhibitor treatment and embryos which hatched, did so in an inflated state and retained intact zonae in cultures. Moreover, embryos subjected to NS-398 treatment phenocopied those subjected to CAY-10404 treatment. Results demonstrate that the effect of inhibitors, and hence the need for COX-2 mediated signaling events is more pronounced in 8¬cell embryos than with early-blastocysts, indicating that COX-2 dependant molecular and cellular processes required for blastocyst morphogenesis and ZP-lysis may have been initiated prior to compaction and cavitation. The reversal of effects of COX-2 inhibition on hatching with exogenous addition of PGE2 and Iloprost (a stable PGI2 analogue) to inhibitor cultures, show that COX-2-derived eicosanoids could, in effect bring about hamster hatching, which is in agreement with previous reports (Davis et al., 1999) and augment peri-implantation development including hatching (Huang et al., 2003). Additionally, it has been successfully demonstrated that PGE2 was superior to PGI2 in augmenting blastocyst hatching in inhibitor-cultures. In this study, the modulation of critical cts-L, -B, -P proteases in COX-2 mediated hamster zona hatching has been verified by quantifying cts in transcripts in control and inhibitor-subjected embryonic samples which was further substantiated by the decreased intra-embryonal protein levels of cts-L and -P. These results demonstrate that COX-2 mediated signaling components directly and effectively modulate hamster preimplantation development, especially zona-hatching phenomenon by transcriptional-regulation of the critical zonalytic proteases. Another potential hatching-associated molecule i.e., NF-κB which is known to exert a great deal of influence on overall reproductive and developmental biology, was investigated in this study. Its specific effects on mammalian preimplantation development, especially hatching, remain totally uninvestigated. This formed the rationale to investigate the reach and impact of NF-κB signaling network in the modulation of peri-hatching events. Transcripts and immunoreactive NF-κB protein of crucial pathway-components like IKK, IκB-β and RelA were detected from 8-cell embryo to the zona-free blastocyst. In order to ascertain the impact of NF-κB signaling on peri-hatching events, two very-specific inhibitors of the NF-κB pathway, BAY-11-7082 and JSH-23 were employed which acted at two strategic signaling points. In order to assess the impact of NF-κB inhibition on an embryo-stage and time-dependant manner, inhibitors were tested on freshly recovered 8-cell embryos or early blastocysts, continuously for 72 h or 48 h, respectively. NF-κB-selective inhibitors inhibited blastocyst hatching in a dose-dependent manner. Interestingly, a profound dose-dependent failure of deflation of late-blastocysts upon inhibitor treatment was observed and embryos which hatched did so in an inflated state and also retained intact zonae in cultures. Moreover, embryos subjected to BAY-11-7082 treatment phenocopied those subjected to JSH-23 treatment, indicating specificity of inhibitor action. Time-course experiments demonstrated that the need for efficient NF-κB mediated signaling is distinctively more for 8-cell embryos than early-blastocysts, indicating that NF-κB dependant molecular and cellular processes required for blastocyst morphogenesis and ZP-lysis may have been initiated prior to compaction and cavitation. Moreover, modulation of zonalysins cts-L, -B and -P by NF-κB-signaling, during the event of zona lysis, both by real-time quantitation of its transcripts and intracellular protein levels has been demonstrated. These results demonstrate that NF¬κB mediated signaling components directly and effectively modulate hamster preimplantation development, especially zona-hatching phenomenon by transcriptional-regulation of the critical zonalytic proteases. The profound inhibition of hatching and effects on blastocyst morphogenesis observed by inhibition of COX-2 and NF-κB signaling systems demonstrate a fundamental need of the growing embryo for these critical signaling moieties. Moreover, the underlying similarity of consequences obtained upon inhibition of both signaling networks i.e., NF-κB and COX-2, perhaps indicate a linear mode of signaling between these principles. It remains to be tested, though, if it really is the case. A striking observation made in this study was the detection of immunoreactive signals for critical signaling moieties like ER-α, COX-2 and RelA onto TEPs of the deflated hamster blastocyst, in addition to earlier TEP-localisation of cathepsins. A B C (Figure) ENDOMETRIUM ENDOMETRIUM ENDOMETRIUM Fig 5.1. Schematic representation of the role of molecular and cellular factors in the regulation of concordant phenomena of mammalian blastocyst hatching and endometrial implantation. (A) Depicts a zona-intact well-formed blastocyst. Preimplantation embryo development and blastocyst formation involves close cooperation between several molecular principles (discussed in sections 1.3.1 to 1.3.3), (B) as the embryo prepares to hatch, prior to implantation, it initiates egression from the non-adhesive ZP coat by cathepsin (cts) protease-mediated lysis of zona (pink circles); there is concomitant appearance of cellular principles such as TEPs (undulating projections shown in green). Of interest is the intimate association of hatching-promoting molecules such as COX-2, NF-κB, ER-α, Cts etc. with the TEPs. (C) depicts a zona-free, TEP-rich blastocyst initiating implantation into the maternal endometrium. It is possible, that the embryonic TEPs with the associated hatching-regulatory molecules are also critical for implantation phenomena during the embryo-maternal recognition and implantation during the establishment of early pregnancy. Preliminary results indicate that TEPs could be the site of membrane lipid-rafts, focal points of membrane-based signaling. The definitive role of TEPs in peri-hatching events is yet to be confirmed, but it is presumed that these actin-based undulating structures, harboring several key molecules involved in peri-implantation events in the embryo as well as the maternal uterus could be instrumental in successfully bringing about the concomitant processes of hatching and implantation. Interestingly, during rodent implantation (hamster, guinea-pig, mouse and rat), the blastocyst orients in such a way that the ICM is oriented away from the endometrium and, at least in the hamster, the TEP-carrying abembryonic (mural) pole remains closest to the luminal epithelium (LE) (Gonzales et al., 1996b; Seshagiri et al., 2009; Fig. 5.1C). In contrast, in humans and other primates, the embryonic pole is closest to LE before implantation (Kirby, 1971; Lee and DeMayo, 2004). Although direct evidence is lacking, but these observations gives rise to a possibility that both hatching and implantation could be intimately related to the polar appearance of TEPs in the embryo. Several key signaling molecules like ER-α, LIF, HB-EGF and TGF-β have been already demonstrated to play crucial roles in mammalian hatching. In this thesis, we have exemplified the need for COX-2 mediated prostanoid signaling and the pleotropic NF-κB signaling system in bringing about mammalian blastocyst hatching. How exactly do these molecular entities communicate among themselves and with cellular principles like TEPs thereby effectively enabling peri-implantation development, remain to be understood. Taken together, these results demonstrate, for the first time, the involvement of embryo-derived signaling molecules, like COX-2 and NF-κB in an embryo stage-and time-dependant manner in mammalian peri-implantation events, especially blastocyst hatching. The association of TEPs with key molecules common to embryonic and maternal preparation for hatching and implantation, respectively, indicates towards a molecular and cellular continuity between the concomitant events. These fundamental findings on hamster blastocyst biology have profound clinical implications in the management of human infertility. (For figures pl see the abstract file).

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal