Integral to the development of embryonic stem cell therapeutic strategies for hepatic disorders is the identification and establishment of a controllable hepatic differentiation strategy. In order to address this issue we have established an alginate microencapsulation approach which provides a means to modulate the differentiation process through changes in key encapsulation parameters. We report that a wide array of hepatocyte specific markers is expressed by cells differentiated during a 23-day period within an alginate bead microenvironment. These include urea and albumin secretion, glycogen storage, and cytochrome P450 transcription factor activity. In addition, we demonstrate that cellular aggregation is integral to the control of differentiation within the bead environment and this process is mediated by the E-cadherin protein. The temporal expression of surface E-cadherin and hepatocyte functional expression occur concomitantly and both cellular aggregation and albumin synthesis are blocked in the presence of anti E-cadherin immunoglobulin. Furthermore, by establishing a compartmental model of differentiation, which incorporates this aggregation phenomenon, we can optimize key encapsulation parameters.

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Cell replacement therapies, which utilize renewable stem cell sources, hold tremendous potential to treat a wide range of degenerative diseases. Although many studies have established techniques to successfully differentiate stem cells into different mature cell lineages, their practicality is limited by the lack of control during the differentiation process and low yields of differentiated cells. In order to address these issues, we have previously established a murine embryonic stem cell alginate-poly-L-lysine microencapsulation differentiation system [1]. We demonstrated that ES cell differentiation could be mediated by cell-cell aggregation in the encapsulation microenvironment. We have demonstrated that both cell aggregation and hepatocyte functions, such as urea and albumin secretions, as well as increased expression of cytokeratin 18 and cyp4507a, occur concomitantly with surface E-cadherin expression [2]. In the present studies, we assessed the feasibility of inducing neuronal lineage differentiation in the alginate microenvironment by incorporating soluble inducers, such as retinoic acid, into the permeable microcapsule system. We demonstrated decreased cell aggregation and enhanced neuronal lineage differentiation with the expression of various neuronal specific markers, including neurofilament, A2B5, O1 and glial fibrillary acidic protein (GFAP). In addition, we demonstrated that, by blocking the cell aggregation using anti-E-cadherin antibody, encapsulated cells increased neuronal marker expression at a later stage of the encapsulation, even in the absence of retinoic acid. In conjunction with the mechanical and physical characterizations of the alginate crosslinking network, we show that 2.2% alginate concentration is most conducive to neuronal differentiation from embryonic stem cells in the presence of retinoic acid.