Burtey, S. | bioRxiv Science

bioRxiv2026

Identification of the Col4a3-/- mouse as a model of chronic kidney disease-associated cachexia

Background: Cachexia is a frequent complication of advanced chronic kidney disease (CKD), i.e. renal cachexia, particularly in patients undergoing hemodialysis in whom it represents one of the strongest predictors of morbidity and mortality. Yet, our understanding of the molecular mechanisms leading to body wasting in CKD and management of cachectic patients are still poorly defined. To date, a preclinical mouse model of robust and reproducible CKD-associated cachexia is missing. Here, we assessed in a systematic manner the cachectic phenotype of the genetic Col4a3-/- mouse model of CKD. Methods: 129/SvJ Col4a3-/- male and female animals were monitored longitudinally until they developed kidney failure. Measured glomerular filtration rate (mGFR), body composition and grip strength were recorded at baseline (6 weeks of age, before onset of kidney dysfunction) and at endpoint (CKD with weight loss or 12 weeks of age). The severity of CKD was confirmed by biochemical and histological analyses. Muscle atrophy was assessed via fiber cross-sectional area analysis, atrogene expression and transcriptomics. Adipose tissue wasting was assessed by measuring adipocyte area and proteins involved in lipid synthesis and breakdown. Liver acute phase response and systemic inflammation were evaluated by measuring circulating levels of key factors using ELISA. Results: Col4a3-/- animals developed CKD (decrease in mGFR: -85%, P<0.0001) and cachexia within 8-12 weeks of age. Cachexia was characterized by a progressive loss of body weight (-17.8% +/- 1.0, P<0.0001), lean (-8.2% +/- 2.0, P<0.0001) and fat mass (-66.5% +/- 4.7, P<0.0001) associated with reduced grip strength (-24.3% +/- 0.0, P=0.0002). At the tissue level, cachexia led to muscle atrophy and induction of atrogenes. Muscle transcriptomics further validated the cachectic phenotype of the Col4a3-/-, with 47% of genes altered in a similar manner with the well-established colon-C26 mouse model of cancer cachexia. It also revealed signatures that appeared more specific to renal cachexia. Adipose tissue wasting was characterized by a depletion in fat stores, consecutive to an imbalance between proteins involved in lipogenesis and lipolysis. Cachexia in this model was also associated with the induction of acute phase response in liver, elevated circulating levels of serum amyloid A and systemic inflammation, with the induction of established cachexia mediators (IL-6, GDF-15 P<0.0001). Both male and female mice developed cachexia. Conclusions: Our data highlight the potential of using the Col4a3-/- mouse model of CKD for the future study of renal cachexia, offering a more robust alternative to classically used models of partial nephrectomy or adenine-rich diet.

pathology↗

bioRxiv2021

mTOR-activating mutations in RRAGD cause kidney tubulopathy and cardiomyopathy (KICA) syndrome

BackgroundOver the last decaces, advances in genetic techniques have resulted in the identification of rare hereditary disorders of renal magnesium and salt handling. Nevertheless, {+/-}20% of all tubulopathy patients remain without genetic diagnosis. Here, we explore a large multicentric patient cohort with a novel inherited salt-losing tubulopathy, hypomagnesemia and dilated cardiomyopathy (DCM). MethodsWhole exome and genome sequencings were performed with various subsequent functional analyses of identified RRAGD variants in vitro. ResultsIn 8 children from unrelated families with a tubulopathy characterized by hypomagnesemia, hypokalemia, salt-wasting, and nephrocalcinosis, we identified heterozygous missense variants in RRAGD that mostly occurred de novo. Six of these patients additionally suffered from DCM requiring heart transplantation in 3 of them. An additional dominant variant in RRAGD was simultaneously identified in eight members of a large family with a similar renal phenotype. RRAGD encodes GTPase RagD mediating amino acid signaling to the mechanistic target of rapamycin complex 1 (mTORC1). RagD expression along the mammalian nephron include the thick ascending limb and the distal convoluted tubule. The identified RRAGD variants were shown to induce a constitutive activation of mTOR signaling in vitro, ConclusionsOur findings establish a novel disease phenotype combining kidney tubulopathy and cardiomyopathy (KICA) caused by an activation of mTOR signaling suggesting a critical role of Rag GTPase D for renal electrolyte handling and cardiac function. SIGNIFICANCE STATEMENTHere, we report on heterozygous variants in RRAGD in patients with profound hypomagnesemia, renal salt wasting, nephrocalcinosis, and dilated cardiomyopathy. The identified RagD variants induce a constitutive activation of mTOR signaling in vitro. These findings not only establish a novel monogenic disorder of the kidney tubule, but demonstrate the essential role of mTOR signaling for distal tubular electrolyte handling and cardiac function.

genetics↗