“Engineering Pluripotent Trophic Factor Delivery to Stimulate Adult Stem Cell Populations”

Advisor:
Todd McDevitt, Ph.D.

Committee:
Edward Botchwey, Ph.D.
Krishnendu Roy, Ph.D.
Athanassios Sambanis, Ph.D.
Edmund Waller, M.D., Ph.D. (Emory University)

A reduced capacity for regeneration often accompanies illness, injury, or aging, a decline that is associated with the diminished function of adult stem cell populations. Increasing evidence indicates that the decreased ability of adult stem cell populations to properly repair deteriorating tissues is due to a failure of the surrounding microenvironment to provide adequate support. Furthermore, it has been demonstrated that the application of systemic factors from young individuals can improve adult stem cell function and restore regenerative capacity in aged individuals. The in vivo equivalents of pluripotent embryonic stem cells (ESCs) are present transiently in the early stages of development, and they have powerful roles in stimulating tissue specification and morphogenesis through their secretion of growth factors, cytokines, chemokines, and mitogens. Additionally, the regenerative capacity of fetal tissue, such as its ability for scarless wound-healing, may be related to endogenous signals present during the growth and maturation of developing mammals. Therefore, the paracrine actions of ESC trophic factors may provide analogous signals required for dysfunctional adult stem cells to regain their regenerative capability. However, there are significant challenges with employing an ESC paracrine-based approach to regeneration, as the differentiation of ESCs has proven difficult to control and pluripotent cells can form teratomas when delivered in vivo. A platform that both provides a defined environment to control ESC morphogen secretion and offers a means to deliver ESC-derived trophic factors without cell transplantation would transform the field of tissue regeneration. Due to the number of disorders that can be attributed to deficient hematopoietic function, the application of pluripotent trophic factors (pTFs) to the bone marrow compartment may stimulate improved function of a cell population which undergoes age-related decline, is sensitive to damage following radiation exposure, and is comprised of multipotent cell populations that are difficult to expand ex vivo.

The primary objective of this thesis proposal is to develop a microencapsulation-based bioreactor system for modulating and delivering pTFs to regenerate cell populations present in the bone marrow niche. The central hypothesis is that providing a defined environment via encapsulation and bioreactor parameters will allow the trophic secretion of ESCs to be controlled and concentrated such that the delivery of pTFs will enhance the function of adult bone marrow populations ex vivo and in vivo. The hypothesis will be assessed through (1) development of a microencapsulation-based platform for ESC culture, (2) examination of strategies to promote hemogenic-specific and concentrated trophic secretion profiles, and (3) investigation of the effects of ESC trophic factors on bone marrow populations ex vivo and in vivo.