CONTRIBUTION OF A SPERM PROTEIN, PAWP, TO THE SIGNAL TRANSDUCT PATHWAY DURING VERTEBRATE FERTILIZATION

PAWP, postacrosomal sheath WW domain binding protein, is a novel sperm protein identified as a candidate sperm borne, oocyte-activating factor (SOAF). PAWP induces both early and later egg activation events including meiotic resumption, pronuclear formation and egg cleavage. Based on the fact that calcium increase is universally accepted as the sole requirement for egg activation, we hypothesized that PAWP is an upstream regulator of the calcium signaling pathway during fertilization. Intracellular calcium increase was detected by two-photon laser scanning fluorescence microscopy following microinjection of recombinant PAWP into Xenopus oocytes, bolstering our hypothesis and suggesting the involvement of a novel PAWP-mediated signaling pathway during fertilization. The N-terminal of PAWP shares a high homology to WW domain binding protein while the C-terminal half contains a functional PPXY motif, which allows it to interact with group I WW domain proteins. These structural considerations together with published data indicating that PPXY synthetic peptide derived from PAWP inhibits ICSI-induced fertilization led to the hypothesis that PAWP triggers egg activation by binding to a group I WW domain protein in the oocyte. By far-Western analysis of oocyte cytoplasmic fraction, PAWP was found to bind to a 52 kDa protein. The competitive inhibition studies with PPXY synthetic peptide, WW domain constructs, and their point mutants demonstrated that the interaction between PAWP and its binding partner is specifically via the PPXY-WW domain module. The 52 kDa protein band crossreacted with antibodies against group I WW domain protein YAP in Western blot assay, indicating that this 52 kDa PAWP binding partner is either YAP or a YAP-related protein. In addition, the far-Western competitive inhibition studies with recombinant GST fusion protein YAP and another WW domain-containing protein, TAZ, demonstrated that the binding of PAWP to its binding partner was significantly reduced by TAZ, providing evidence that TAZ could be the 52 kDa protein candidate. Mass spectrometry was employed to identify this PAWP binding partner candidate. However, due to the low abundance of the candidate protein and the complexity of the sample, several strategies are still needed to enrich this protein. This study correlates PAWP induced meiotic resumption and calcium efflux at fertilization and uncovers a 52 kDa candidate WW domain protein in the oocyte cytoplasm that most likely interacts with PAWP to trigger egg activation.

Tissue-specific bioscaffolds for adipose-derived stem/stromal cell expansion and delivery

Decellularized adipose tissue (DAT) is a promising biomaterial for soft tissue regeneration, and it provides a highly conducive microenvironment for human adipose-derived stem/stromal cell (ASC) attachment, proliferation, and adipogenesis. This thesis focused on developing techniques to fabricate 3-D bioscaffolds from enzymatically-digested DAT as platforms for ASC culture and delivery in adipose tissue engineering and large-scale ASC expansion. Initial work investigated chemically crosslinked microcarriers fabricated from pepsin-digested DAT as injectable adipo-inductive substrates for ASCs. DAT microcarriers highly supported ASC adipogenesis compared to gelatin microcarriers in a CELLSPIN system, as confirmed by glycerol-3-phosphate dehydrogenase (GPDH) enzyme activity, lipid accumulation, and endpoint RT-PCR. ASCs cultured on DAT microcarriers in proliferation medium also had elevated PPARγ, C/EBPα, and LPL expression which suggested adipo-inductive properties. In vivo testing of the DAT microcarriers exhibited stable volume retention and enhanced cellular infiltration, tissue remodeling, and angiogenesis. Building from this work, non-chemically crosslinked porous foams and bead foams were fabricated from α-amylase-digested DAT for soft tissue regeneration. Foams were stable and strongly supported ASC adipogenesis based on GPDH activity and endpoint RT-PCR. PPARγ, C/EBPα, and LPL expression in ASCs cultured on the foams in proliferation media indicated adipo-inductive properties. Foams with Young’s moduli similar to human fat also influenced ASC adipogenesis by enhanced GPDH activity. In vivo adipogenesis accompanied by a potent angiogenic response and rapid resorption showed their potential use in wound healing applications. Finally, non-chemically crosslinked porous microcarriers synthesized from α-amylase-digested DAT were investigated for ASC expansion. DAT microcarriers remained stable in culture and supported significantly higher ASC proliferation compared to Cultispher-S microcarriers in a CELLSPIN system. ASC immunophenotype was preserved for all expanded groups, with reduced adhesion marker expression under dynamic conditions. DAT microcarrier expansion upregulated ASC expression of early adipogenic (PPARγ, LPL) and chondrogenic (COMP) markers without inducing a mature phenotype. DAT microcarrier expanded ASCs also showed similar levels of adipogenesis and osteogenesis compared to Cultispher-S despite a significantly higher population fold-change, and had the highest level of chondrogenesis among all groups. This study demonstrates the promising use of DAT microcarriers as a clinically relevant strategy for ASC expansion while maintaining multilineage differentiation capacity.