The SGLT2 inhibitor dapagliflozin improves kidney function in glycogen storage disease XI

Glycogen storage disease XI, also known as Fanconi-Bickel syndrome (FBS), is a rare autosomal recessive disorder caused by mutations in the SLC2A2 gene that encodes the glucose-facilitated transporter type 2 (GLUT2). Patients develop a life-threatening renal proximal tubule dysfunction for which no treatment is available apart from electrolyte replacement. To investigate the renal pathogenesis of FBS, SLC2A2 expression was ablated in mouse kidney and HK-2 proximal tubule cells. GLUT2Pax8Cre+ mice developed time-dependent glycogen accumulation in proximal tubule cells and recapitulated the renal Fanconi phenotype seen in patients. In vitro suppression of GLUT2 impaired lysosomal autophagy as shown by transcriptomic and biochemical analysis. However, this effect was reversed by exposure to a low glucose concentration, suggesting that GLUT2 facilitates the homeostasis of key cellular pathways in proximal tubule cells by preventing glucose toxicity. To investigate whether targeting proximal tubule glucose influx can limit glycogen accumulation and correct symptoms in vivo, we treated mice with the selective SGLT2 inhibitor dapagliflozin. Dapagliflozin reduced glycogen accumulation and improved metabolic acidosis and phosphaturia in the animals by normalizing the expression of Napi2a and NHE3 transporters. In addition, in a patient with FBS, dapagliflozin was safe, improved serum potassium and phosphate concentrations, and reduced glycogen content in urinary shed cells. Overall, this study provides proof of concept for dapagliflozin as a potentially suitable therapy for FBS.

Bardet-Biedl syndrome: The pleiotropic role of the chaperonin-like BBS6, 10, and 12 proteins

Bardet–Biedl syndrome (BBS) is a rare pleiotropic disorder known as a ciliopathy. Despite significant genetic heterogeneity, BBS1 and BBS10 are responsible for major diagnosis in western countries. It is well established that eight BBS proteins, namely BBS1, 2, 4, 5, 7, 8, 9, and 18, form the BBSome, a multiprotein complex serving as a regulator of ciliary membrane protein composition. Less information is available for BBS6, BBS10, and BBS12, three proteins showing sequence homology with the CCT/TRiC family of group II chaperonins. Even though their chaperonin function is debated, scientific evidence demonstrated that they are required for initial BBSome assembly in vitro. Recent studies suggest that genotype may partially predict clinical outcomes. Indeed, patients carrying truncating mutations in any gene show the most severe phenotype; moreover, mutations in chaperonin‐like BBS proteins correlated with severe kidney impairment. This study is a critical review of the literature on genetics, expression level, cellular localization and function of BBS proteins, focusing primarily on the chaperonin‐like BBS proteins, and aiming to provide some clues to understand the pathomechanisms of disease in this setting.

The SGLT2-inhibitor dapagliflozin improves neutropenia and neutrophil dysfunction in a mouse model of the inherited metabolic disorder GSDIb

Glycogen Storage Disease type 1b (GSDIb) is a genetic disorder with long term severe complications. Accumulation of the glucose analog 1,5-anhydroglucitol-6-phosphate (1,5AG6P) in neutrophils inhibits the phosphorylation of glucose in these cells, causing neutropenia and neutrophil dysfunctions. This condition leads to serious infections and inflammatory bowel disease (IBD) in GSDIb patients. We show here that dapagliflozin, an inhibitor of the renal sodium-glucose co-transporter-2 (SGLT2), improves neutrophil function in an inducible mouse model of GSDIb by reducing 1,5AG6P accumulation in myeloid cells.

MO036DAPAGLIFLOZIN RESCUES THE RENAL PHENOTYPE OF GLYCOGEN STORAGE DISEASE TYPE IB

Background and Aims

Glycogenosis I type b (GsdI-b) is a rare metabolic disease and immune disorder characterized by hepato-renal glycogen accumulation caused by a deficiency in the Glucose-6-phosphate transporter (G6PT). G6PT transports glucose-6-phosphate (G6P) from cytoplasm to endoplasmic reticulum (ER) where a G6Pase catalyses the hydrolysis of G6P in glucose and phosphate. G6PT deficiency lead to impaired glucose homeostasis, myeloid disfunction and long-term risk of hepatocellular adenomas. No causal therapy is so far available for GSDI-b patients besides a dietary approach to control glycemia and the use of Granulocyte Colony-Stimulating Factor (GCSF) to improve neutropenia. Over time, these supports increase the chronicity of GSDI-b with some complications. A mouse model recapitulating the GDSI-b has been recently generated by inducing G6PT suppression after tamoxifen injection. Here, we characterized the renal phenotype of TM-G6PT-/- mice model focusing on the molecular mechanisms that lead to renal dysfunction. Finally, we evaluated the efficiency of Dapagliflozin, a selective inhibitor of SGLT2, on kidney functions in terms of therapeutic effect.

Method

Machine learning approach to computer based evaluation of renal morphology was used to analyze the renal sections from TM-G6PT-/- treated with or without dapagliflozin.

Results: G6PT is expressed in all renal zones and a severe downregulation of G6PT mRNA expression in whole kidney of TM-G6PT-/- mice can be observed. TM-G6PT-/- mice show tubular vacuolization and overall cellular dysfunction of PT due to a high glycogen accumulation. TM-G6PT-/- mice manifest glycosuria, phosphaturia and polyuria associated with a down regulation of main transporters of PT cells. The urine concentrating defect is due to a primarily role of G6PT in CNT/CD cells confirmed by a downregulation of AQP2, main water channel along CD segments. This mouse model recapitulates the human GSD-Ib renal phenotype characterized by a disfunction of PT but also CNT/CD cells. In order to evaluate whether targeting the glucose metabolism would improve the renal phenotype of these mice we limited glucose flux across the apical membrane of PT cells, applying the SGLT2-inhibitor dapagliflozin to reduce new glycogen formation. After one month of treatment, Dapagliflozin prevents glycogen accumulation in TM-G6PT-/- mice and ameliorates the main dysregulated markers of PT function. This finding was paralleled by an improvement of the histological features of kidney morphology in dapagliflozin treated TM-G6PT-/- mice.

Conclusion

Our data provide evidence that treatment with dapagliflozin ameliorates intracellular glycogen storage and improves the renal functions in TM-G6PT-/- mice.

Potassium depletion induces cellular conversion in the outer medullary collecting duct altering Notch signaling pathway

Potassium depletion affects AQP2 expression and the cellular composition of the kidney collecting duct. This, in turn, contributes to the development of a secondary form of nephrogenic diabetes insipidus and hypokalemic nephropathy. Here we show that after 14 days of potassium depletion, the cellular fraction of A-type intercalated cells increases while the fraction of principal cells decreases along the outer medullary collecting duct in rats. The intercalated cells acquired a novel distribution pattern forming rows of cells attached to each other. These morphological changes occur progressively and reverse after 7 days of recovery on normal rat chow diet. The cellular remodeling mainly occurred in the inner stripe of outer medulla similar to the previously seen effect of lithium on the collecting duct cellular profile. The cellular remodeling is associated with the appearance of cells double labelled with both specific markers of principal and type-A intercalated cells. The appearance of this cell type was associated with the downregulation of the Notch signaling via the Hes1 pathways. These results show that the epithelium of the collecting duct has a high degree of plasticity and that Notch signaling likely plays a key role during hypokalemia.

Label-free quantitative proteomics of the MCF-7 cellular response to a ferritin–metallodrug complex

Schematic summary of the experimental workflow based on label-free quantitative proteomics.

ERK1,2 Signalling Pathway along the Nephron and Its Role in Acid-base and Electrolytes Balance

Mitogen-activated protein kinases (MAPKs) are intracellular molecules regulating a wide range of cellular functions, including proliferation, differentiation, apoptosis, cytoskeleton remodeling and cytokine production. MAPK activity has been shown in normal kidney, and its over-activation has been demonstrated in several renal diseases. The extracellular signal-regulated protein kinases (ERK 1,2) signalling pathway is the first described MAPK signaling. Intensive investigations have demonstrated that it participates in the regulation of ureteric bud branching, a fundamental process in establishing final nephron number; in addition, it is also involved in the differentiation of the nephrogenic mesenchyme, indicating a key role in mammalian kidney embryonic development. In the present manuscript, we show that ERK1,2 signalling mediates several cellular functions also in mature kidney, describing its role along the nephron and demonstrating whether it contributes to the regulation of ion channels and transporters implicated in acid-base and electrolytes homeostasis.