2,8-Dihydroxyadenine-induced nephropathy causes hexosylceramide accumulation with increased mTOR signaling, reduced levels of protective SirT3 expression and impaired renal mitochondrial function

AIM

Chronic kidney disease (CKD) is accompanied by increased cardiovascular risk and heart failure (HF). In rodents, 2,8-dihydroxyadenine (DHA)-induced nephropathy is a frequently used CKD model. Cardiac and kidney tubular cells share high energy demand to guarantee constant contractive force of the heart or reabsorption/secretion of primary filtrated molecules and waste products by the kidney. Here we analyze time-dependent mechanisms of kidney damage and cardiac consequences under consideration of energetic pathways with the focus on mitochondrial function and lipid metabolism in mice.

METHODS AND RESULTS

CKD was induced by alternating dietary adenine supplementation (0.2 % or 0.05 % of adenine) in C57BL/6J mice for 9 weeks. Progressive kidney damage led to reduced creatinine clearance, kidney fibrosis and renal inflammation after 3, 6, and 9 weeks. No difference in cardiac function, mitochondrial respiration nor left ventricular fibrosis was observed at any time point. Investigating mechanisms of renal damage, protective SirT3 was decreased in CKD, which contrasted an increase in protein kinase B (AKT) expression, mechanistic target of rapamycin (mTOR) downstream signaling, induction of oxidative and endoplasmic reticulum (ER) stress. This occurred together with impaired renal mitochondrial function and accumulation of hexosylceramides (HexCer) as an established mediator of inflammation and mitochondrial dysfunction in the kidney.

CONCLUSIONS

2,8-DHA-induced CKD results in renal activation of the mTOR downstream signaling, endoplasmic reticulum stress, tubular injury, fibrosis, inflammation, oxidative stress and impaired kidney mitochondrial function in conjunction with renal hexosylceramide accumulation in C57BL/6J mice.

A Rare Genetic Mutation in a Stone Former

A 30-year-old woman with history of passage of stones since childhood presented with oliguria and pedal edema for 10 days. She had hypertension with a creatinine of 4.1 mg/dL. Evaluation showed presence of bilateral multiple renal calculi with features of chronicity of kidney disease. Metabolic work-up for nephrolithiasis turned out to be negative and eventually renal biopsy revealed features of chronic interstitial nephritis with greenish brown refractile crystals in the tubular lumen and interstitium. The possibility of dihydroxy adenine crystalline nephropathy was considered. Spectrophotometry of RBC lysates revealed decreased activity of Adenine phosphoribosyl-transferase enzyme. Gene amplification by PCR and sequential analysis identified a missense mutation in exon 3 region of APRT gene in the patient and her family members. This case report highlights the need to contemplate the diagnosis of DHA crystalline nephropathy in young patients with nephrolithiasis and the identification of a rare genetic mutation, which is being reported for the first time in India.

An Unusual Course of a 2,8-Dihydroxyadeninuria Crystalline Nephropathy Secondary to Adenine Phosphoribosyltransferase Deficiency

Adenine phosphoribosyltransferase (APRT) deficiency is a rare disorder caused by an autosomal recessive genetic disease leading to the deposition of 2,8-dihydroxyadenine (2,8-DHA) in the kidney. The disease remains under-recognized, oftentimes diagnosed in late stages of renal insufficiency or a failed kidney allograft with biopsy-proven disease recurrence. Here, we present the case of a 59-year-old middle eastern male patient diagnosed with 2,8-DHA nephropathy after a very unusual presentation, and we show how the initiation of an appropriate therapy slowed down his evolution toward kidney replacement therapies. His disease was found to be secondary to a specific APRT gene variant c.188G>A p (Gly63Asp) also described in 4 other patients, all from middle eastern origins.