Developmental Approaches to in Vitro Engineering of Kidney-Like Tissues

Many tissue engineering strategies are being pursued to alleviate chronic kidney disease. This thesis presents two developmental approaches that aim to use progenitor tissues to engineer kidney-like tissues capable of providing significant renal functionality. If this can be done, and cells can be used to construct these progenitor tissues, then it may be possible to make kidney-like tissues from cells. In one approach, the Wolffian duct (WD) is guided through the stages of kidney development, in vitro, and then recombined with metanephric mesenchyme (MM) to produce a kidney-like tissue. In the second approach, a small segment of WD is directly surrounded by MM recreating an embryonic kidney-like structure that may then be cultured in a three dimensional (3D) matrix to yield a kidney-like tissue. These strategies are advantageous because they; (1) potentially can begin with only two cell types; (2) require the construction of relatively small, simple tissues; (3) offer opportunities for tissue propagation; and (4) result in tissues with a 3D structure known to be important for kidney function. The objective of this dissertation is to examine the hypothesis that the developmental approaches to in vitro engineering of kidney tissues presented here are potentially feasible. Using in vitro models of kidney development, it was demonstrated that a WD tissue could (in the context of appropriate growth factors and extracellular matrix molecules) be induced to recapitulate key stages of kidney development and ultimately be recombined with MM, resulting in a kidney-like tissue containing functional transporters and, following implantation into a host animal, markers of vascularization. Next, it was found that a homogenous cell line has the potential to be used in the construction of an epithelial tubule that can be used in the developmental strategies described; however, the MM may require an earlier cell lineage than currently available. Ideally, in vitro-formed kidney tissue would have a 3D structure comparable to the in vivo kidney. A type IV collagen suspension culture was shown to enable 3D embryonic kidney growth, resulting in a branching structure similar to in vivo ureteric bud branching morphogenesis. Differentiation factors may enhance the functionality of the in vitro engineered kidney-like tissue. A biocompatible polymer, hyaluronic acid, was found to be a potential regulator of both UB and MM growth and differentiation, with the ability to strongly promote both branching morphogenesis and tubular differentiation of in vitro embryonic kidney cultures. This raises the possibility that HA can be used as a growth and differentiation enhancing scaffold material for in vitro kidney engineering. Together, these findings represent important advances towards engineering kidney tissues via developmental approaches.