Kidney Week

Abstract: SA-PO634

Novel Models to Study Fanconi Syndrome and CKD Due to Heterozygous GATMP341L Mutations

Session Information

• Genetic Kidney Diseases: Models, Mechanisms, and Therapies
  October 26, 2024 | Location: Exhibit Hall, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Genetic Diseases of the Kidneys

• 1202 Genetic Diseases of the Kidneys: Non-Cystic

Authors

• Arroyo Ariza, Daniel Felipe, Washington University in St Louis, St Louis, Missouri, United States

Daniel Felipe Arroyo Ariza, MD

• Singal, Rhea, Washington University in St Louis, St Louis, Missouri, United States

Rhea Singal

• Allegretti, Andrew S., Massachusetts General Hospital, Boston, Massachusetts, United States

Andrew S. Allegretti, MD, MS

• Humphreys, Benjamin D., Washington University in St Louis, St Louis, Missouri, United States

Benjamin D. Humphreys, MD, PhD, FASN

• Jüppner, Harald, Massachusetts General Hospital, Boston, Massachusetts, United States

Harald Jüppner, MD

• Portales Castillo, Ignacio A., Washington University in St Louis, St Louis, Missouri, United States

Ignacio A. Portales Castillo, MD

Background

Autosomal dominant Fanconi syndrome due to GATM mutations (GATM-FS) presents during childhood with evidence of proximal tubular (PT) dysfunction and progresses to end stage kidney disease in adults. Kidney biopsies of patients with GATM-FS show PT injury and Arginine:glycine amidinotransferase (AGAT), the enzyme encoded by GATM, accumulates in PT mitochondria. Besides renal dysfunction, we found lower levels of guanidinoacetate (GAA) and creatine in patients with GATM P341L mutations. To further study the pathophysiology of this disease, we tested the enzymatic function of AGAT P341L using patient-derived cells, generated human kidney organoids and a novel Gatm^P341L mouse.

Methods

GAA synthesis by the AGAT mutant was measured in patient-derived immortalized lymphocytes using stable isotopes of arginine and glycine, and the effect of creatine on GATM expression was assessed in wild-type kidney organoids. We generated mice carrying the Gatm^P341L mutant^, using CRISPR/Cas9 methodologies.

Results

In comparison to wild-type cells, GAA synthesis by patient-derived GATM^P341L+/- LCL cells was reduced by ~50%, consistent with our findings of low GAA and creatine in plasma and urine of affected patients. Creatine supplementation (5 g daily) restored plasma creatine levels in a patient with GATM-FS, and in vitro creatine (10 mM) down-regulated AGAT expression in kidney organoids.
At 4 weeks of age, Gatm^P341L/+ mice showed higher phosphate excretion than wild-type littermates (median Pi/Cre: 0.97 vs 0.42, p<0.05). At 8 weeks, blood urea nitrogen also tended to be higher in plasma of Gatm^P341L/+ vs wild-type mice, 66.5 vs 21.8 mg/dl in males.

Conclusion

Our results support the hypothesis of deficient creatine metabolism in GATM-FS and the possible use of low levels of GAA as biomarker of this disease. We now developed several promising experimental models, kidney organoids, LCLs, and Gatm^P341L/+ mice for evaluating the role of abnormal creatine metabolism in renal disease and the potential therapeutic effect of creatine supplementation in GATM-FS.