Defining the role of biased calcium-sensing receptor signalling in kidney stone disease

Overview of the research findings

Find out more about Sarah Howles’ ground-breaking research into kidney stones in her video below.

Following the success of this project, the team hope to continue more detailed laboratory experiments looking at what causes kidney stones and possible ways to prevent kidney stones. They are looking at the effects of DGKD on CaSR-signalling and the use of drugs to restore altered signaling.

They expect to then apply to the NIHR for funding for a large clinical trail.

We’re delighted to have provided the initial funding for this vital research that has the potential to tangibly improve outcomes for people who experience kidney stones.

Full research report

Defining the role of biased calcium-sensing receptor signalling in kidney stone disease

Personnel

Principal Investigator: Sarah Howles, Nuffield Department of Surgical Sciences, University of Oxford.

Post-Doctoral Research Assistant: Michelle Goldsworthy, Nuffield Department of Surgical Sciences, University of Oxford

Project Dates                                                                         Report Date

17^th February 2022-2^nd May 2023                                          1^st July 2023

Background and rationale

Kidney stone disease is a common problem that affects ~20% of men and ~10% of women by 70 years of age. Unfortunately, around 50% of people who have formed a stone will have a second stone episode within 10 years of their first. There are some people who form stones very frequently. Passing a kidney stone can be extremely painful and many people will need an operation to treat their stones. It is well known that there is a need for better treatments to stop kidney stones from forming.

Despite kidney stones being so common, we don’t have a good understanding of the reasons why many people form kidney stones. Our lack of understanding about the causes of kidney stone has made it difficult to design new treatments. To help us understand more about the causes of kidney stone disease, we undertook a study in the UK Biobank that compared the genetic makeup of people who form kidney stones to those who do not. This study suggested that a protein called diacylglcerol kinase delta, or DGKD, might be important in kidney stone pathways. Kidney stones are often made of calcium and disorders of calcium control can cause kidney stones. In our study, we were able to show that DGKD plays a role in how the calcium-sensing receptor (CaSR) signals within a cell; the CaSR controls how the body handles calcium.

Objectives

This project aimed to:

• Help us understand more about how DGKD is important in kidney stone formation and how it effects the CaSR-signaling pathway.
• Find drugs that might be useful to prevent kidney stones by bringing CaSR signaling back to normal when it has been changed by alterations in DGKD.

Study Design

Our investigations had four main parts:

1. Laboratory studies to examine the effects of increased and decreased cellular levels of DGKD on CaSR signaling.
2. Genetic studies in large databases to find kidney stone patients with rare genetic variants in DGKD.
3. Laboratory studies that determine the effects of rare genetic variants in DGKD on the CaSR signaling pathway.
4. Laboratory studies that test out drugs that modulate CaSR signaling as potential new treatments for kidney stone disease.

Problems Encountered

At the time of grant application, we had identified 2 rare variants in DGKD in people with kidney stone disease in the 100,000 genomes database that we wanted to study. After the application was submitted, we found another rare DGKD variant in a kidney stone patient in the 100,000 genomes database. We collaborated with a research group from the Geisinger Institute, USA to look for more variants that might be of interest. This aspect was very successful, and in the Geisinger cohort 6 rare variants of interest were identified. However, this meant that there was more experimental work to be done and some experiments are not yet finished. In addition, some of the experiments we hoped to do did not give reliable results and we have therefore focused on those that gave consistent results.

Key Findings

The key findings for each part of our study are outlined below:

1. Increased and decreased levels of DGKD alter CaSR-signaling in laboratory experiments. The CaSR signaling pathway has two main arms – intracellular calcium release and mitogen-activated protein kinase (MAPK) activation. We found that decreasing cellular levels of DGKD cause a reduction in signal via MAPK signaling, but no change in intracellular calcium release. However, increasing cellular levels of DGKD cause an increase in signal via MAPK signaling, but a reduction in intracellular calcium release.
2. Rare variants in DGKD are associated with kidney stone disease. In the 100,000 genomes project we found 3 people with kidney stones who had rare changes in the genetic code for DGKD. In the Geisinger cohort we found 6 changes in the genetic code for DGKD that were associated with people forming kidney stones.
3. Rare variants in DGKD that are associated with kidney stone disease cause a reduction in CaSR-signaling in laboratory experiments. We have found that rare variants in DGKD that are present in people with kidney stones cause reduced CaSR signaling via MAPK and intracellular calcium pathways.
4. Drugs that increase CaSR-signaling may be useful to prevent kidney stones. We are currently completing our experiments; the data that we have so far shows that a drug called cinacalcet can bring signaling back to normal when it is reduced because of a reduction in DGKD levels or due to kidney stone associated rare variants in DGKD.

Significance of Findings

Studying rare DGKD variants has shown us that it is likely that decreased signaling via the CaSR is a common cause of kidney stone disease. Furthermore, our studies suggest that drugs that act on the CaSR to increase how well it signals may be a new way to prevent people forming kidney stones.

Project Success

Our project has been successful: we have a better understanding of how DGKD might cause an increased risk of kidney stones and what treatments we could try to prevent stone formation.

Potential Clinical Impact

These studies suggest that drugs that target the CaSR may prevent kidney stones.

Future Studies and Plans

We hope to complete some more detailed laboratory experiments of the effects of DGKD on CaSR-signaling and the use of drugs to restore altered signaling. Once these are complete, we expect to apply to the NIHR for funding for a large clinical trial. We hope to be starting the clinical trial in the next 5 years.

 We are very likely to apply to The Urology Foundation for further funding to continue this project.