BSCD Summer Undergraduate Research Fellowship in Pathophysiology, Biology, and Bioenergetics of Renal Diseases - 2021

Mentors: Arlene Chapman, MD, Alex Muir, PhD, Peili Chen, PhD, Departments of Medicine and Molecular Biology. Drs. Chapman, Muir and Chen will be available and committed to fully mentor the students, including guidance about overall career development. 

Autosomal dominant polycystic kidney disease (ADPKD), the most common hereditary kidney disease, is caused by mutations in the PKD1 or PKD2 gene which encode polycystin-1 and polycystin-2 transmembrane heterodimer proteins. Multiple signaling pathways are affected by mutated polycystin1 and polycystin 2, including primary ciliary signaling and Ca2+/cAMP cascade that contribute to the abnormal proliferation of epithelial cells and cyst formation in ADPKD. Initiated in early childhood, progression of renal cysts gradually damages kidney structure and function, eventually leading to renal failure typically in the 5 to 6th decade of life. Despite promising results from recent studies and trials, therapies that cure or slow the progression of disease are limited. The slow progressive nature of ADPKD make it difficult to diagnose and treat at early stage as the estimated glomerular filtration rate (eGFR) is normal for decades. Height corrected total kidney volume (htTKV), an accurate and reproducible FDA approved imaging prognostic biomarker can increase several-fold prior to loss of kidney function and represents cyst burden and epithelial proliferation. However, measurement cyst burden through HtTKV using magnetic resonance imaging (MRI) is only useful in the setting of macroscopic cysts which have been developing for decades. Candidate biomarkers have been evaluated in urine and plasma from ADPKD patients including neutrophil gelatinase-associated lipocalin (NGAL), monocyte chemotactic protein (MCP)1 and CD14, as well as non-targetted profiling of urinary proteome and miRNAs however their contribution to understanding the progression of ADPKD or strength as a biomarker are not additive to htTKV.

Increasing understanding of the signaling and pathological derangements characteristic of ADPKD has revealed marked similarities to those of cancers at the cellular and molecular level. ADPKD shares most of cancer hallmarks including sustained proliferative signaling, evasion of growth suppressors, induction of angiogenesis, deregulation of cellular energetics, tumor-promoting inflammation, genomic instability and mutation and abnormally reprogrammed metabolism. Metabolic reprogramming provides energy and substrates that is necessary to support tumor growth, survival, immune evasion, and metastasis. Recent studies in PKD1 cells demonstrate a Warburg-like effect as observed in cancer cells, which when inhibited results in inhibited cell proliferation and decreased cyst growth and TKV. This metabolic change is also observed in cystic epithelia in ADPKD patient kidneys, indicating altered bioenergetics and adaptation supporting a proliferative cystic phenotype in ADPKD.

We have demonstrated comprehensive abnormalities in multiple amino acid concentrations and metabolic pathways in our studies in urine and plasma in ADPKD patients with normal kidney function, particularly the histidine pathway. Furthermore, levels of histidine metabolites correlate with cyst burden (htTKV) and kidney function (eGFR). In ADPKD cyst fluids, concentrations of all amino acids, except for Glutamine and Proline, are elevated compared to those in plasma and urine, suggesting that active accumulation of amino acids on the apical surface of cystic epithelia occur. Pharmacologically targeting histidine metabolism at histidine decarboxylase or histidine ammino-lysase affects cystic cell proliferation but not healthy non-cystic human epithelia, indicating a possible therapeutic role in the treatment of this disorder. 

Mentor: Hatim Hassan, MD, PhD, John Alverdy, MD, and Matthew Tirrell, Departments of Medicine and Surgery and Institute of Molecular Engineering. Drs. Hassan, Alverdy, and Tirrell will be available and committed to fully mentor the students, including guidance about overall career development. 

Kidney stones (KS) affect ~1 in 5 men and ~1 in 11 women, are costly (>$10B annually), and are associated with CKD and ESRD. High recurrence rates (50% in 5 years and up to 80% in 10 years), indicate that current interventions are inadequate and alternative therapies are needed. Most KS are composed of calcium oxalate and very small increases in urine oxalate concentration increase the risk for stone formation. Lower urinary CaOx supersaturation definitively reduces KS formation. Currently, no FDA approved drugs reduce urinary oxalate excretion. The gut bacterium Oxalobacter formigenes (Of) induces colonic oxalate secretion and reduces urinary oxalate excretion via an unknown secretagogue. Given the difficulties with recolonization, Of alone is not therapeutically feasible and underscores the need to identify the secretagogue that induces colonic oxalate secretion. To this end, we have identified Of-derived factors secreted in its culture conditioned medium (CM) that significantly stimulate (>2.8-fold) oxalate transport by human intestinal Caco2-BBE (C2) cells through PKA activation and stimulation of the oxalate transporters SLC26A6 (A6) and SLC26A2 (A2). In vivo, rectal administration of Of CM reduced urinary oxalate excretion > 32.5% in hyperoxaluric mice, and stimulated colonic oxalate secretion >42%, reflecting the potential therapeutic impact of these factors. We identified a family of a signaling protein as the major Of-derived factors. These proteins closely recapitulate the effects of the Of-derived factors and similarly stimulate (1.4-2.4-fold) oxalate transport by C2 cells. We also identified 35-amino acid peptides (P7-10) within one protein that significantly stimulate (1.5-fold individually and >2.4-fold by P8+9) oxalate transport by C2 cells. Importantly, P8+9 peptides significantly stimulated oxalate transport by HUMAN sigmoid colon (1.8-fold), distal colon (1.7-fold), and ileum (2-fold) organoids (ex vivo intestinal epithelia models fully mimicking the in vivo physiological responses), confirming that P8+9 peptides work in human tissues and that they will likely stimulate oxalate secretion in human colonic and ileal epithelia in vivo. Identification and characterization of the active motifs responsible for colonic oxalate transport can ultimately be translated into an effective novel therapeutic targeting the reduction of plasma and urine oxalate levels. I founded a startup company (Oxalo Therapeutics) to help with developing these peptides into a peptide-based therapeutic and obtained an NIH fast-track STTR grant to optimize our lead peptides through structural modifications (some of which had already being completed). We also obtained phase I NSF STTR grant to develop an innovative drug delivery system consisting of peptide-loaded hydrogel nanoparticles (PLHN) as a vehicle to deliver novel peptides to the intestinal epithelium. Once delivered, the nanoparticles will adhere to the intestinal mucosa and slowly release the peptides, stimulating intestinal oxalate secretion, thereby lowering plasma and urine oxalate and hence preventing KS formation. Such delivery will enable P8+9 peptides to immediately act on the intestinal epithelium to induce oxalate secretion, before being degraded by proteolytic enzymes, mimicking of behavior. In collaboration with Dr. Matthew Tirrell, we are also developing P8 and P9 peptide amphiphiles (peptide-based micellar constructs which can be an effective carrier vehicle for therapeutic drugs) for in vivo testing. 

Mentors: Fredric Coe, MD, Elaine Worcester, MD, Ben Ko, MD, Anna Zisman, MD, Megan Prochaska, MD. Department of Medicine. Drs. Coe, Worcester, Ko, Zisman and Prochaska will be available and committed to fully mentor the students, including guidance about overall career development.

 

Diet sodium and acid intake strongly affect mineral metabolism and risk for kidney stone formation. Acid loads raise urine calcium losses, saturating urine with stone forming calcium salts, and foster bone mineral loss. The effects are most severe in those people with inherited hypercalciuria, a polygenic trait that makes calcium balance and urine calcium loss abnormally responsive to both salt and acid load. We have found that patients who make calcium phosphate stones, and women who make calcium oxalate stones, have abnormalities of acid-base status, compared to same-sex normal subjects. We have also discovered differences in acid-base handling that involve both gastrointestinal system and kidney in normal men and women. Funded by an NIH Program Project grant (Worcester, PI) the group presently studies effects of varying diet sodium and alkali supplementation on renal calcium handling in the University of Chicago Clinical Research Center.

A full understanding of acid-base balance requires a complete accounting for all renal acid excretion, which is not obtainable from standard urine measurements. In order to better understand the abnormalities we have seen in various types of stone formers, as well as the differences in acid-base handling between normal men and women, we have added novel measurements of urine anion excretion that are the effectors of acid production from diet. We are studying these anions in response to altered diet sodium and alkali, in both types of calcium stone formers and normal subjects. To complement our new measurements, we plan metabolomic measurements of urine anion patterns in collaboration with Dr. Arlene Chapman’s group.

Our previous work has shown differences in segmental renal tubule handling of sodium and calcium between normal subjects and stone formers, which foster loss of calcium in the urine. As there is no appropriate animal model of human stone formation, it has been difficult to examine the possible differences in renal tubule transporter abundance or function that may create the altered mineral handling. Dr. Ko has recently applied the techniques of urine exosome analysis to characterize how nutrient ingestion alters renal transporters, by measuring the levels of transporters of interest in urine exosomes during nutrient challenges. 

 

 

4. Hatim Hassan, MD, PhD, Associate Professor of Medicine: A well trained investigator in epithelial transport (with specific expertise in gastrointestinal oxalate transport and its relevance to overall oxalate homeostasis), cell signaling, biochemistry, and molecular biology. He will lead the conceptual development of projects with the investigative team along where the students will participate.

5. John Alverdy, MD, Sarah and Harold Lincoln Thompson Professor of Surgery and Executive Vice-Chair of the department of surgery at UOC. Dr. Alverdy is the director of the Center for Surgical Infection Research at UOC that studies the microbial pathogenesis of infections that develop following surgery including sepsis, wound infection, and anastomotic leak. He has been funded by the NIH for this work since 1999. He will provide mentorship in studies related to the in vivo administration of peptide-loaded hydrogel nanoparticles.

8. Elaine Worcester, MD, Professor of Medicine, is an NIH-funded clinical investigator leading studies of altered renal mineral handling in patients with kidney stones and normal subjects and will mentor the students in the design, performance and analysis of human studies, and the ethical implications of human research.

 

9. Ben Ko, MD, Associate Professor of Medicine, has expertise in isolation of urine exosomes and their use to understand alterations of renal tubule specific transport activity in humans under varying dietary conditions. He will provide mentorship in the relevant laboratory techniques and their interpretation as part of studies of human renal mineral handling in health and disease.

 

10. Anna Zisman, MD, Associate Professor of Medicine, is a funded investigator with active clinical and research interests in kidney stones and chronic renal disease. She has been recognized for her excellence in teaching and clinical care with several awards, and is the director of the Nephrology Fellowship Program.

 

11. Megan Prochaska, MD, MPH, Instructor of Medicine, is a young investigator with clinical and research focus in kidney stones. She has a background in epidemiology, and is now studying the effects of the microbiome on risks for kidney stone disease.