Embryonic Expression of Cytokines: Functional Role of Il-1β During Blastocyst Hatching
The detailed investigation on the embryo-endometrial cytokine expression, in both mouse and hamster, was carried out during the peri-hatching development and it is described in chapter 2. We hypothesize that, for a successful implantation, a balance of embryonic expression and function of pro-inflammatory and anti-inflammatory cytokines are necessary to maintain proper homeostasis of cytokine expression, compatible with peri- hatching embryonic development and hatching, eventually enabling the establishment of early pregnancy. Our cytokine expression studies along with various other reports have successfully established that a number of implantation-associated cytokines are expressed during peri- hatching development and therefore, could be critical for blastocyst to become implantation- competent. One of the cytokines, IL-1β was found to be strongly expressed during the peri- hatching development. The human clinical reports have established that IL-1β is as a potential embryonic biomarker for successful implantation. Besides, there are controversial reports probing its significance in implantation process (Chapter 1, section 3.2.3). Much of the functional data on the critical requirement of IL-1β and their signaling system during the peri-implantation development comes from gene-knockout studies involving the cytokine and their cognate receptor (Chapter 1, Table IV). Due to the redundancy and cross-talk, the IL-1β knock- out mouse does not exhibit profound implantation failure and the least known is the hatching phenotype. In view of the above, the functional involvement of strategically identified pro- inflammatory cytokine, IL-1β along with its natural antagonist and anti- inflammatory cytokine i.e., IL-1ra were investigated in hatching process of both the hamster (Chapter 3) and the mouse (Chapter 4), for comparison. Previous reports on hamster and mouse have established the participation of species- specific proteases associated with blalstocyst hatching. Of relevance, here, is the observation that both IL-1β and IL-1ra are known, in non-embryonic context, to modulate generally proteases (Chapter 1, section 3.2.5). These reports are significant in the context of hatching and therefore, the expression and functional correlation of IL- 1β and hatching promoting proteases during peri- hatching blastocyst development in the hamster and mouse were examined in this study (Chapters 3 and 4). Besides, the involvement of species-specific proteases in the hatching process is examined further at the structural level. In this computational study, the interaction of proteases with individual ZP protein(s) of the hamster and the mouse were analyzed. We studied the sequential and structural variations potentially responsible for the differential susceptibility of zona protein of the mouse and hamster towards different proteases examined (Chapter 5). The defined objectives and implications of the proposed study are depicted in Fig 1. This study is significant in our understanding of cytokines-mediated cellular and molecular regulation of blastocyst hatching phenomenon. The new and improved formulation of culture systems with a possible cytokine supplements could be exploited for sustained in vitro potentially viable development of blastocysts through hatching. The data on the cytokine (IL-1β) expression and function, described here, could be potentially a quality/viable embryo biomarker (i) as a tool to improve efficacy of peri-hatching blastocyst development and importantly, (ii) in the human, it could be exploited for improving the pregnancy outcome of the IVF-ET program in the ART clinic setting.