The influence of cellular patterning on brown adipogenic differentiation from mouse embryonic stem cells

Abstract

A method for fabricating 3D microcapsules via LDW was developed, with excellent size control of encapsulated embryoid bodies. While cells could grow in 3D in these environments, they did not appear to survive differentiation to brown adipocytes, so differentiation will have to be modified for microcapsule environments. Overall, this work demonstrates LDW as a tool for priming and directing differentiation, and for generating novel 3D microenvironments. This work also uniquely applies LDA for the evaluation of stem cell niches.

Our lab has previously shown that cells printed by LDW have high viability, no detectable DNA damage, and mESCs retain the capacity to differentiate into cells whose populations express markers for all three primitive germ layers. In this thesis, LDW was shown to influence the size of embryoid bodies that spontaneously form from mESCs, which has implications on directing differentiation. Moreover, printing mESCs in different patterns, or in other initial seeding configurations, may prime differentiation to favor particular lineages. Linear discriminant analysis (LDA) of quantitative polymerase chain reaction (qPCR) data suggested that patterns could be classified based on gene expression.

Directed differentiation was attempted to brown adipocytes, a clinically relevant cell type for the metabolic syndrome, because of thermogenic consumption of glucose via the uncoupling protein 1 (UCP1) in the mitochondria. Differences in gene expression were observed for different patterns, and gene expression was compared to brown pre-adipocytes and mature brown adipocytes from mouse. Gene expression appeared closer to preadipocytes than mature brown adipocytes in differentiated mESCs, and mapping via LDA suggested that differences in gene expression were primarily due to early differentiation markers rather than adipogenic markers, although some patterns had higher expression than others for key brown adipogenic markers.

Embryonic stem cells can theoretically have regenerative medicine applications for any tissue type, because they can self-renew, and have the potential to differentiate into any somatic cell type. However, harnessing this potential remains challenging, as stem cell fate decisions to specific cell types are difficult to control. Many have previously used morphogens and engineered substrates to direct differentiation, but another aspect of the stem cell microenvironment, that has received considerably less attention, is cellular interactions and signaling. Cell patterning can potentially provide some degree of control over cellular signaling by cell-cell contacts, juxtacrine, and paracrine signaling. The goal of this thesis was to pattern mouse embryonic stem cells (mESCs) using laser direct-write (LDW), and evaluate the influence of patterning on their differentiation.