Research

The focus of the Humphreys Lab is to understand the cellular and molecular mechanisms of adult kidney repair. The mammalian kidney has the intrinsic to repair itself after even severe injury. If we can understand the molecular events regulating this repair process, we should be able to harness it therapeutically to either prevent injury or accelerate repair in humans. We use knowledge of the developmental program during nephrogenesis to inform our investigations of adult kidney repair, which in some ways recapitulates kidney development. Current work encompasses on two main areas: identifying and characterizing adult kidney stem cells and understanding the genetic and epigenetic regulation of epithelial cell dedifferentiaion and proliferation after injury.


Genetic Analysis of Kidney Repair

Lineage tracing during renal repair. There are two primary obstacles to studying stem cells. First, no matter how many markers are used, it is not possible to obtain a pure population of cells. Second, any in vitro assay used to quantitate and characterize stem cell number will necessarily be imperfect because it cannot faithfully recapitulate the in vivo stem cell environment, or niche (Jones, Simons and Watt, 2007). These challenges are particularly applicable to kidney, because there are few if any validated stem cell markers to begin with, and the cellular complexity of the kidney makes any attempt to recapitulate the cellular environment in vitro more difficult. Therefore our laboratory utilizes in vivo lineage tracing to reveal the fate of putative kidney stem cells as well as epithelial progenitors, during homeostasis and repair. Lineage analysis is a powerful tool that is made possible by Cre/Lox recombination technologies and it allows visualization of cellular function in a normal context without disrupting the cellular environment as would be required for in vitro culture or transplantation assays.

We have carried out lineage analysis of renal epithelial cells to determine the origin of reparative cells in adult kidney. These studies indicate that intrinsic renal epithelial cells are responsible for renal repair. Current studies are aimed at developing novel Cre driver lines for the inducible expression of Cre recombinase in either terminally differentiated, or in injured and dedifferentiated epithelial cells. These genetic tools will also allow dissection of the signaling pathways that regulate the renal repair process in epithelial cells. In other studies, we have used a DNA analog lineage tracing technique to distinguish between epithelial proliferation from a multipotent, intratubular progenitor, and repair by self-duplication of terminally differentiated cells.

Multipotent Intratubular Stem Cells

Telomerase expression in kidney. In other studies, we are characterizing a transgenic mouse expressing GFP under control of the Telomerase promoter (D. Breault, CHB) to identify adult kidney stem cell populations. Finally, we are generating additional transgenic and knock-in mice that will serve as useful tools in genetic fate-mapping and cell ablation models for renal injury. Collectively, these studies will help to answer the question of whether adult tubular epithelia regenerate by self-duplication or by replacement from a stem cell population. Ultimately, this knowledge will help to focus future efforts at renal regenerative medicine.

Mechanisms of Renal Fibrosis

Interstitial fibrosis is the final common pathway of all progressive nephropathies, and we are interested in the origin of the cells that produce matrix proteins, the activated myofibroblast. A related question concerns the nature of the signals originating from the tubular epithelial cell that trigger the fibrotic process. We have generated a transgenic model for conditional overexpression of genes that might trigger a progressive fibrotic phenotype. Current efforts are aimed at defining the signals regulating this effect.
Smooth Muscle Actin

Recent Publications