Single-cell sequencing technology reveals key processes in acute kidney injury

Acute kidney injury (AKI) is a common complication associated with a variety of conditions, particularly affecting patients in intensive care units
.
However, the underlying mechanisms of AKI are not fully understood
.
Just recently, an interdisciplinary team of researchers used single-cell sequencing techniques to reveal molecular processes associated with AKI, and researchers described new patterns of gene expression that damage kidney cells that could lead to new therapeutic approaches and biomarker discovery strategies
。 The studies were carried out in close collaboration with Charité-Universit tsmedizin Berlin; Max Delbrück Center of the Institute for Medical Systems Biology (BIMSB) in Berlin; Leibniz Institute, Berlin Rheumatology Research Center (DRFZ), Germany; and Hannover Medical School

The kidneys are one of the most important organs of the
human body.
They filter waste products from the bloodstream, control fluid composition and blood pressure, affect energy metabolism, and produce important hormones
.
If kidney function is impaired – as is the case with AKI – there can be serious consequences
.
"AKI is a common serious complication for critically ill patients and affects about half of our patients in intensive care units," said
Dr.
Jan Klocke of Charité's Department of Nephrology and Medical Intensive Care.
"This condition is often underestimated, although AKI is associated with increased mortality and patients may suffer permanent damage or even complete loss of kidney function
.
"

AKI can be associated with a variety of diseases
.
It usually occurs in conjunction with cardiovascular disease or serious infectious diseases such as COVID-19, but is also after surgical intervention or in connection
with medication.
There is usually no specific treatment plan
.
"We tried to stabilize affected patients, but until now, it has not been possible to reverse destructive processes in the kidneys with targeted therapy," Dr.
Hinch said
.
He played a key supervisory role in a study at the Charité and Max Delbrück Centers and currently works
at the Hannover Medical School.
"Until now, little
is known about the mechanisms by which it plays in kidney cells.
The purpose of our research is to illustrate this, and our long-term goal is to improve the treatment
offered to clinical patients.
”

AKI is usually caused by insufficient blood supply to the kidneys, causing kidney cells to no longer receive enough oxygen and nutrients and react
with stress.
The cell enters an alarm mode and produces signaling substances that can lead to inflammation and remodeling processes (fibrosis)
of the surrounding tissues.
We know from animal model studies that epithelial cells – cells that line the fine renal tubules – are involved in these inflammatory and fibrotic processes
.
This is demonstrated by a state-of-the-art new method known as single-cell sequencing, which enables researchers to create detailed profiles of molecular gene expression profiles
of thousands of individual cells.
But what's happening at the cellular level of human AKI?

This is the question that the research team led by Dr.
Hincher and Dr.
Crocker set out to investigate
.
The two recently published studies are the first to use single-cell technology to study the molecular processes
of AKI in human kidney cells.
The scientists examined cells extracted from tissue and urine samples from more than 40 patients and analyzed the molecular patterns
of more than 140,000 cells using state-of-the-art bioinformatics methods.
Dr.
Hinze explains: "Single-cell sequencing allows us to zoom in on each cell and see which gene is active in that cell at that point in time
.
" "From this, we can determine whether a particular kidney cell is currently functioning normally, under stress, or is about to die
.
" This cutting-edge technology gives us an unprecedented level of detail about
AKI.
”

The team also found that different types of cells in the kidneys respond very differently to AKI, with the strongest response observed in epithelial cells of the renal tubules
.
The kidneys are the smallest function in the kidneys and consist of several segments
.
Animal models know that AKI primarily affects epithelial cells
in specific early tubular segments.
However, the latest findings on human kidney cells suggest that almost all epithelial cells of the tubular segments of the kidney are involved in the injury process
.
Dr Hinze said: "This shows once again how important
it is for us to study human systems and learn to better understand them.
" "In different types of epithelial cells, we were able to identify specific molecular patterns that occur in all AKI patients, but at
individual abundance.
In the future, these findings could help doctors better assess the risk of
serious disease progression.
”

In clinical practice, doctors ideally need a rapid, non-invasive, and accurate test to confirm the diagnosis of AKI
at an early stage.
To get closer to this vision for the future, Dr.
Klocke set out to look for epithelial cells
in urine samples.
Healthy people can hardly find any cells
in their urine.
But in patients with AKI, epithelial cells are isolated from the renal tubules and excreted into the
urine.
However, because the cells could not survive in the urine for very long, there were initially doubts about whether the cells were still intact and even whether their molecular state could be measured
with single-cell sequencing.
Dr Klocke said: "We processed the urine sample in 4 to 6 hours and it actually worked very well
.
" The researchers were able to determine which part of the tubule these cells came from, and which genetic programs
they activated in the event of kidney damage.
"The information provided by the cells in the urine sample matches the corresponding cells in the tissue sample," Dr.
Klocke said
.
"Thus, urine provides us with a simple and patient-friendly way to obtain sample material for further research in order to identify biomarkers that, in the long run, may reduce or even replace kidney biopsies
.
"

Through the two current studies, the research team used single-cell sequencing to provide a completely new insight into the cellular mechanisms of AKI and a promising approach
to future diagnostic procedures and personalized treatments.
In further research, they plan to recruit more patients, study cell responses to different underlying diseases, and use cell culture to discover other fundamental molecular mechanisms of
AKI.