Posts

NephCure Kidney International logo

Marva Moxey-Mims, M.D., named NephCure Kidney International scientific adviser

NephCure Kidney International logo

Marva Moxey-Mims, M.D., chief of the Division of Nephrology at Children’s National Health System, has been named to the Scientific Advisory Board for NephCure Kidney International, a non-profit that aims to accelerate research for rare forms of nephrotic syndrome.

Dr. Moxey-Mims and two additional scientific advisers were selected for their commitment to improving care for patients with glomerular disease, diseases that impair kidney function by attacking blood cleaning units within the kidney.

During her tenure at the National Institute of Diabetes and Digestive and Kidney Diseases at the National Institutes of Health, Dr. Moxey-Mims launched the Chronic Kidney Disease in Children Cohort Study, a prospective study to investigate chronic kidney disease risk factors and outcomes, and helped launch the Cure Glomerulonephropathy Network, a multi-site study with the overarching aim to advance the diagnosis and care of patients with four different glomerular diseases.

“I am truly honored to join this distinguished group of scientific advisers and look forward to leveraging our combined strengths and research knowledge in order to deliver cures for kidney diseases faster,” says Dr. Moxey-Mims.

mitochondria

Treating nephrotic-range proteinuria with tacrolimus in MTP

mitochondria

Mitochondria are the cell’s powerplants and inside them the MTP enzymatic complex catalyzes three steps in beta-oxidation of long-chain fatty acids.

In one family, genetic lightning struck twice. Two sisters were diagnosed with mitochondrial trifunctional protein (MTP) deficiency. This is a rare condition that stops the body from converting fats to energy, which can lead to lactic acidosis, recurrent breakdown of muscle tissue and release into the bloodstream (rhabdomyolysis), enlarged heart (cardiomyopathy) and liver failure.

Mitochondria are the cell’s powerplants and inside them the MTP enzymatic complex catalyzes three steps in beta-oxidation of long-chain fatty acids. MTP deficiency is so rare that fewer than 100 cases have been reported in the literature says Hostensia Beng, M.D., who presented an MTP case study during the American Society of Nephrology’s Kidney Week.

The 7-month-old girl with known MTP deficiency arrived at Children’s National lethargic with poor appetite. Her laboratory results showed a low corrected serum calcium level, elevated CK level and protein in the urine (proteinuria) at a nephrotic range. The infant was treated for primary hypoparathyroidism and rhabdomyolysis.

Even though the rhabdomyolysis got better, the excess protein in the girl’s urine remained at worrisome levels. A renal biopsy showed minimal change disease and foot process fusion. And electron microscopy revealed shrunken, dense mitochondria in visceral epithelial cells and endothelium.

“We gave her tacrolimus, a calcineurin inhibitor that we are well familiar with because we use it after transplants to ensure patient’s bodies don’t reject the donated organ. By eight months after treatment, the girl’s urine protein-to-creatinine (uPCR) ratio was back to normal. At 35 months, that key uPCR measure rose again when tacrolimus was discontinued. When treatment began again, uPCR was restored to normal levels one month later,” Dr. Beng says.

The girl’s older sister also shares the heterozygous deletion in the HADHB gene, which provides instructions for making MTP. That missing section of the genetic how-to guide was predicted to cause truncation and loss of long-chain-3-hydroxyacl CoA dehydrogenase function leading to MTP deficiency.

The older sister was diagnosed with nephrotic syndrome and having scar tissue in the kidney’s filtering unit (focal segmental glomerulosclerosis) when she was 18 months old. By contrast, she developed renal failure and progressed to end stage renal disease at 20 months of age.

“Renal involvement has been reported in only one patient with MTP deficiency to date, the older sister of our patient,” Dr. Beng adds.

Podocytes are specialized cells in the kidneys that provide a barrier, preventing plasma proteins from leaking into the urine. Podocytes, however, need energy to function and are rich in mitochondria.

“The proteinuria in these two sisters may be related to their mitochondrial dysfunction. Calcineurin inhibitors like tacrolimus have been reported to reduce proteinuria by stabilizing the podocyte actin cytoskeleton. Tacrolimus was an effective treatment for our patient, who has maintained normal renal function, unlike her sister,” Dr. Beng says.

American Society of Nephrology’s Kidney Week presentation

  • “Treatment of nephrotic-range proteinuria with tacrolimus in mitochondrial trifunctional protein deficiency

Hostensia Beng, M.D., lead author; Asha Moudgil, M.D., medical director, transplant, and co-author; Sun-Young Ahn, M.D., MS, medical director, nephrology inpatient services, and senior author, all of Children’s National Health System.

Zhe Han

Research led by Zhe Han featured on cover of JASN, leading kidney disease journal

Journal of the American Society of Nephrology September 2017 cover

Coenzyme Q10, one of the best-selling nutrient supplements to support heart health also could be beneficial for kidney health, according to research conducted in transgenic fruit flies that was led by Zhe Han, Ph.D., associate professor at Children’s Center for Cancer and Immunology Research.

Nephrocytes, filtration kidney cells in Drosophila, require the Coq2 gene for protein reabsorption, toxin sequestration and critical cell ultrastructure.  Silencing the Coq2 gene results in aberrantly localized nephrocyte slit diaphragms and deformed lacunar channels, Han and co-authors found. Nephrocytes closely resemble the podocytes of the human kidney.

The research team’s paper, published online April 2017, this fall was featured on the cover of Journal of the American Society of Nephrology, the No. 1 kidney disease journal.

“I am honored that the JASN editors chose to feature my lab’s work on the cover of this prestigious journal,” Han says. “This underscores the utility of our gene-replacement approach, which silenced the fly homolog in the tissue of interest – here, the kidney cells – and provided a human gene to supply the silenced function.”

Coenzyme Q10

Supplement might help kidney disease

Coenzyme Q10

A research team was able to “rescue” phenotypes caused by silencing the fly CoQ2 gene by providing nephrocytes with a normal human CoQ2 gene, as well as by providing flies with Q10, a popular supplement.

A new study led by Children’s National research scientists shows that coenzyme Q10 (CoQ10), a popular over-the-counter supplement sold for pennies a dose, could alleviate genetic problems that affect kidney function. The work, done in genetically modified fruit flies — a common model for human genetic diseases since people and fruit flies share a majority of genes — could give hope to human patients with problems in the same genetic pathway.

The new study, published April 20 by Journal of the American Society of Nephrology, focuses on genes the fly uses to create CoQ10.

“Transgenic Drosophila that carry mutations in this critical pathway are a clinically relevant model to shed light on the genetic mutations that underlie severe kidney disease in humans, and they could be instrumental for testing novel therapies for rare diseases, such as focal segmental glomerulosclerosis (FSGS), that currently lack treatment options,” says Zhe Han, Ph.D., principal investigator and associate professor in the Center for Cancer & Immunology Research at Children’s National and senior study author.

Nephrotic syndrome (NS) is a cluster of symptoms that signal kidney damage, including excess protein in the urine, low protein levels in blood, swelling and elevated cholesterol. The version of NS that is resistant to steroids is a major cause of end stage renal disease. Of the more than 40 genes that cause genetic kidney disease, the research team concentrated on mutations in genes involved in the biosynthesis of CoQ10, an important antioxidant that protects the cell against damage from reactive oxygen.

Drosophila pericardial nephrocytes perform renal cell functions including filtering of hemolymph (the fly’s version of blood), recycling of low molecular weight proteins and sequestration of filtered toxins. Nephrocytes closely resemble, in structure and function, the podocytes of the human kidney.  The research team tailor-made a Drosophila model to perform the first systematic in vivo study to assess the roles of CoQ10 pathway genes in renal cell health and kidney function.

One by one, they silenced the function of all CoQ genes in nephrocytes. If any individual gene’s function was silenced, fruit flies died prematurely. But silencing three specific genes in the pathway associated with NS in humans – Coq2, Coq6 and Coq8 – resulted in abnormal localization of slit diaphragm structures, the most important of the kidney’s three filtration layers; collapse of membrane channel networks surrounding the cell; and increased numbers of abnormal mitochondria with deformed inner membrane structure.

Journal of the American Society of Nephrology September 2017 cover

The flies also experienced a nearly three-fold increase in levels of reactive oxygen, which the study authors say is a sufficient degree of oxidative stress to cause cellular injury and to impair function – especially to the mitochondrial inner membrane. Cells rely on properly functioning mitochondria, the cell’s powerhouse, to convert energy from food into a useful form. Impaired mitochondrial structure is linked to pathogenic kidney disease.

The research team was able to “rescue” phenotypes caused by silencing the fly CoQ2 gene by providing nephrocytes with a normal human CoQ2 gene, as well as by providing flies with Q10, a readily available dietary supplement. Conversely, a mutant human CoQ2 gene from an patient with FSGS failed to rescue, providing evidence in support of that particular CoQ2 gene mutation causing the FSGS. The finding also indicated that the patient could benefit from Q10 supplementation.

“This represents a benchmark for precision medicine,” Han adds. “Our gene-replacement approach silenced the fly homolog in the tissue of interest – here, the kidney cells – and provided a human gene to supply the silenced function. When we use a human gene carrying a mutation from a patient for this assay, we can discover precisely how a specific mutation – in many cases only a single amino acid change – might lead to severe disease. We can then use this personalized fly model, carrying a patient-derived mutation, to perform drug testing and screening to find and test potential treatments. This is how I envision using the fruit fly to facilitate precision medicine.”

Related resources:
News release: Drosophila effectively models human genes responsible for genetic kidney diseases
Video: Using the Drosophila model to learn more about disease in humans