Katharina Hopp, Ph.D. - US grants

PROJECT SUMMARY/ABSTRACT This NIDDK K01 application is designed to provide Dr. Katharina Hopp with the scientific, technical, and career training to enable her transition into an independent investigator studying mechanisms controlling Autosomal Dominant Polycystic Kidney Disease (ADPKD) cystogenesis. The project builds on Dr. Hopp's expertise in the genetics and cell biology of ADPKD, and extends her training in the immunological and microenvironmental aspects of this disease. The proposal encompasses a five-year training plan under the primary mentorship of Dr. Raphael Nemenoff, an expert in the cancer microenvironment, and an Advisory Committee comprised of accomplished immunologists and PKD physician/scientists. The project will investigate the functional role of T- cells in cyst initiation and progression, underlying mechanisms, and novel therapeutic approaches. Features of ADPKD parallel those of cancer, including induction of proliferation, genomic instability, and increased inflammation. In cancer, targeting T-cells in the tumor microenvironment has shown clinical success; however, the functional role of T-cells in PKD is poorly understood. Preliminary data generated by Dr. Hopp showed that, in a well-established murine ADPKD mouse model developed by Dr. Hopp, distinct T-cell subpopulations increased correlative to disease severity and localized specifically to cystic lesions. Importantly, depletion of CD8+ T-cell, which are generally anti-tumorgenic, increased disease progression, highlighting the functional importance of these cells in halting cyst progression. However, regulatory T-cells, which are generally pro- tumorgenic, rose early in disease, suggesting that distinct T-cell subpopulations may have opposing effects on cystogenesis. In addition, both PD-L1 and PD-1, components of an immune checkpoint pathway, were significantly increased in the mouse model and PKD patient kidney sections. Targeting this pathway has been therapeutically effective in numerous cancers. Thus the central hypothesis of this project is that interactions of distinct T-cell populations with the cystic microenvironment/epithelium result in both anti- and pro- cystogenic effects, and targeting T-cells represents a novel therapeutic strategy for APDKD. The specific aims of this project are (1) Define the functional role of T-cell subpopulations in cyst initiation and progression; (2) Elucidate the mechanisms how T-cells alter cellular pathways in the cystic epithelium; and (3) Evaluate the efficacy of checkpoint inhibitors in ADPKD. The project will be supported by the University of Colorado, Denver's outstanding PKD Program, the Renal Division, and the Immunology Department. The PKD Program has been successful in translating preclinical data into clinical trials and is motivated to incorporate results of this project into future clinical trial designs. In addition to the above aims, Dr. Hopp will (1) develop a strong knowledge of immunology and related novel technique/model systems; (2) expand her professional proficiencies in manuscript/grant writing, mentoring, and reviewing duties; and (3) submit a competitive R01 application towards the end of this K01 expanding upon findings from this application.

PROJECT SUMMARY Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the most common, monoallelic nephropathy worldwide, characterized by continuous renal cysts growth leading to end stage kidney disease. A single FDA approved therapy is available, but it merely slows cyst growth and impacts quality of life, highlighting the urgent need for new treatment options. ADPKD presents with high phenotypic variability, suggesting that mechanisms beyond the genetic mutation to either PKD1 or PKD2 influence disease severity. Recent data have implicated immune cells as modulators of disease severity. Multiple publications highlight that M2-like renal macrophages promote cystic progression. Conversely, data from my K01, using the slowly progressive, orthologous Pkd1 p.R3277C (Pkd1RC/RC) ADPKD model, show that CD8+ T cells can inhibit renal cyst growth. We further found that the renal cystic microenvironment displays multiple features of immunosuppression such as increased numbers of CD4+ regulatory T cells, metabolic reprogramming, and engagement of immune checkpoints. Indeed, immune checkpoint inhibitors, which lead to reactivation of CD8+ T cells, alleviate cystic disease in the Pkd1RC/RC model. What remains unknown are the mechanisms that drive immunosuppression, which may present important/novel therapeutic targets. In cancer, a disease that parallels PKD at the cellular and molecular level, activation of the complement pathway has been shown to promote an immunosuppressive microenvironment. The complement cascade is a central part of the innate immune system that regulates adaptive immunity. Complement has been shown to be upregulated in PKD cells, patient kidneys/cyst fluid, and murine models, including the Pkd1RC/RC mouse as shown by our preliminary data. Further, genetic loss or non-selective inhibition of the complement protein C3 slows cyst growth in murine PKD models. We hypothesize that complement signaling drives PKD, in part, by creating an immunosuppressive microenvironment which impairs the adaptive immune system to halt cyst growth. This project has two aims. In Aim 1, we will utilize fluorescent-activated cell sorting, flow cytometry, and multispectral immunofluorescent imaging to determine which cells are key producers and responders of complement signaling in the Pkd1RC/RC kidney. We will further correlate these findings to disease severity. In Aim 2, we will test if targeted complement inhibition alleviates cystic disease. This will be the first of such studies using a clinically relevant, specific complement inhibitor in a model orthologous to ADPKD, the Pkd1RC/RC mouse. We will further utilize sophisticated 64-fluorophore capable flow cytometry methods to investigate how complement inhibition alters the cystic immune microenvironment with specific focus on immunosuppressive features. These investigations directly expand upon my NIDDK K01 work and will provide key preliminary data for a competitive R01 application. Obtaining this R03 will further facilitate my transition into an independent investigator with an innovative, preclinical, and translational research program that focuses on the role of the cystic microenvironment as modulator of and therapeutic target for PKD.