Research
We aspire to a future where we can drive the growth, repair, and renewal of any organ. To achieve this, we develop and apply novel technologies to understand and modulate regeneration directly within the living organism.
Overview
The loss of specialized cells in organs such as the heart, brain, and pancreas underlies the lifelong morbidity of numerous diseases including heart attack, stroke, neurodegeneration, and diabetes. In these organs, cell loss begets permanent organ impairment because these tissues have no means of replacing lost cells and restoring organ function. Unlike continuously renewing tissues, these organs lack stem cell populations to replace lost cells. Moreover, any remaining specialized cells cannot replenish lost cells as the specialized cells have permanently exited the cell cycle as part of their differentiation process. A means of restoring proliferative capacity to these specialized cells could enable these organs to regenerate after injury and provide desperately needed cures for numerous diseases.
Although cellular differentiation and proliferative capacity are typically mutually exclusive, the liver, and the hepatocytes responsible for its many functions, exist as remarkable and informative exceptions. Unlike any other solid organ, the liver can completely regenerate itself after injury. Moreover, this regeneration is driven not by a stem cell population but rather by proliferation of the differentiated hepatocytes. This unique property of hepatocytes demonstrates that cell cycle arrest is not an obligate consequence of differentiation and that organ regeneration is possible without a stem cell population. The liver thus contains the instructions for enabling endogenous organ regeneration, however we still lack a molecular explanation for this remarkable regenerative ability.
Our mission is to uncover the molecular rules governing permissive and restrictive contexts for regeneration so that we can ultimately unlock regenerative capacity in any organ. To make this possible, we develop and apply new technologies for high-throughput genetic perturbation directly within the living organism.
Functional genomics
Bringing high-throughput functional genomics into the organism
Our ability to understand mammalian physiology and disease has long been limited by the availability of tools for high-throughput genetic dissection within a living organism. Historically, methods for interrogating gene function in living mammals were largely restricted to single-gene knockout mice, effectively precluding unbiased and comprehensive investigation of physiology and disease. To overcome this technical barrier, we recently established genome-wide CRISPR screening in the mouse liver (Keys and Knouse 2022). Although genome-wide screening in the liver alone will afford novel insights into diverse phenomena, the full potential of high-throughput screening in the organism rests on expanding this technology to other organs and CRISPR applications. We are now working to establish efficient and stable transgene delivery and genome-scale CRISPR screening in any cell type of interest in the living mouse. We aspire to bring the experimental tractability once restricted to cell culture into the living organism, enabling unprecedented insight into mammalian physiology and disease.
Cell biology
What are the molecular requirements for organ regeneration?
The liver’s remarkable regenerative capacity has at its core a fundamental distinction of cell cycle states: the reversible dormancy that defines quiescent cells as opposed to the permanent cell cycle arrest that defines most other differentiated cell types. Importantly, this critical functional difference between quiescence and permanent arrest lacks a molecular explanation. It is unclear why a quiescent cell can receive a proliferative stimulus and re-enter the cell cycle while a permanently arrested cell cannot. We are leveraging our genome-wide screening platform to identify the genes required for quiescent hepatocytes to re-enter the cell cycle and regenerate the liver. In parallel, we are expanding our genome-wide screening platforms to non-regenerative organs in order to identify barriers to regeneration those tissues. By defining the molecular rules governing permissive and restrictive contexts for regeneration, we will bring our goal of unlocking regenerative capacity across tissues into the realm of possibility.
Organismal physiology
How does the organism monitor organ size and function?
In order for regeneration to be effective, cell cycle re-entry must occur only when and as long as required to restore organ size and function. Although many of the signaling pathways involved in the initiation and completion of liver regeneration have been identified, it is unclear how these pathways sense liver size and function. We are working to understand how organ size and function are transduced at the molecular level to ensure that regeneration commences and ceases at the appropriate times. By understanding how the organism monitors organ size and function, we will improve our capacity to modulate organ growth and regeneration for therapeutic purposes.
Disease
From regeneration to cancer
The ability of cells to re-enter the cell cycle after prolonged dormancy is true not only for hepatocytes in the liver but also for disseminated cancer cells. Cancer cells that disseminate from the primary tumor can lie dormant in distant tissues and evade traditional chemotherapies for years before re-entering the cell cycle to form a metastasis. As we uncover the molecular requirements for cell cycle re-entry from dormancy, we will apply this knowledge to modulate proliferative capacity in disease states ranging from organ degeneration to cancer.
