Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biochemistry

Supervisor

Dr. Victor Han

Abstract

The human placenta of different gestational ages is a readily available source for isolation of adult mesenchymal stem cell (MSC) for potential use in regenerative therapies. The chorionic villous region, the largest component of a placenta that interfaces with the maternal circulation, is a rich source of placental MSCs (PMSCs). To remain multipotent, PMSCs are best maintained in culture conditions that mimic the in vivo microenvironment. Insulin like growth factors (IGFs, IGF-I and -II) and oxygen tension are two of the most important microenvironmental factors in the placenta. They are of low concentration or tension respectively, at early gestation, and increase as pregnancy progresses. In this thesis, we investigated the role and cellular mechanisms by which IGFs and low oxygen tension determine PMSC fate. The main hypothesis is that the interaction between IGFs and oxygen tension determines PMSC fate towards self-renewal or differentiation. We used cell proliferation assay, immunoblotting, real-time PCR, and cell monolayer staining to evaluate the role of IGF and oxygen tension on PMSC multipotency and differentiation. We found that low oxygen tension was a major determinant of PMSCs proliferation and multipotency, and to delay differentiation. Also, PMSC response to IGF stimulation and low oxygen tension was gestational age dependent — preterm PMSCs being more multipotent and proliferative than term PMSCs. IGF-I and IGF-II promoted PMSC proliferation and multipotency via IGF-IR or IR, depending on oxygen tension. IGFs enhanced PMSC differentiation towards the osteogenic lineage which was transduced by ERK1/2 and AKT signaling cascades. We conclude that IGFs and oxygen tension act synergistically or antagonistically, mimicking in vivo microenvironmental conditions, to determine PMSC fate towards multipotency or differentiation. The appropriate combination of IGFs and oxygen tension can be used to maintain stem cells in multipotency, or to be induced towards a specific progenitor cell lineage for successful use in tissue regeneration therapies.

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