Evolution of hypoxia and hypoxia-inducible factor asparaginyl hydroxylase regulation in chronic kidney disease.

BACKGROUND: The roles of hypoxia and hypoxia inducible factor (HIF) during chronic kidney disease (CKD) are much debated. Interventional studies with HIF-α activation in rodents have yielded contradictory results. The HIF pathway is regulated by prolyl and asparaginyl hydroxylases. While prolyl hydroxylase inhibition is a well-known method to stabilize HIF-α, little is known about the effect asparaginyl hydroxylase factor inhibiting HIF (FIH). METHODS: We used a model of progressive proteinuric CKD and a model of obstructive nephropathy with unilateral fibrosis. In these models we assessed hypoxia with pimonidazole and vascularization with three-dimensional micro-computed tomography imaging. We analysed a database of 217 CKD biopsies from stage 1 to 5 and we randomly collected 15 CKD biopsies of various severity degrees to assess FIH expression. Finally, we modulated FIH activity in vitro and in vivo using a pharmacologic approach to assess its relevance in CKD. RESULTS: In our model of proteinuric CKD, we show that early CKD stages are not characterized by hypoxia or HIF activation. At late CKD stages, some areas of hypoxia are observed, but these are not colocalizing with fibrosis. In mice and in humans, we observed a downregulation of the HIF pathway, together with an increased FIH expression in CKD, according to its severity. Modulating FIH in vitro affects cellular metabolism, as described previously. In vivo, pharmacologic FIH inhibition increases the glomerular filtration rate of control and CKD animals and is associated with decreased development of fibrosis. CONCLUSIONS: The causative role of hypoxia and HIF activation in CKD progression is questioned. A pharmacological approach of FIH downregulation seems promising in proteinuric kidney disease.

Histology and synchrotron radiation-based microtomography of the inner ear in a molecularly confirmed case of CHARGE syndrome.

CHARGE (Coloboma of the iris or retina, heart defects, atresia of the choanae, retardation of growth and/or development, genital anomalies, ear anomalies) syndrome (OMIM #214800) affects about 1 in 10,000 children and is most often caused by chromodomain helicase DNA-binding protein-7 (CHD7) mutations. Inner ear defects and vestibular abnormalities are particularly common. Specifically, semicircular canal (SCC) hypoplasia/aplasia and the presence of a Mondini malformation can be considered pathognomonic in the context of congenital malformations of the CHARGE syndrome. We obtained a temporal bone (TB) of a patient with CHARGE syndrome who died from bacteremia at 3 months of age. The clinical diagnosis was confirmed in the patient by direct DNA sequencing and the detection of a de novo, truncating CHD7 mutation, c.6169dup (p.R2057fs). We assessed changes of the TB and the degree of neural preservation, which may influence the potential benefit of cochlear implantation. The TB was analyzed using synchrotron radiation-based micro computed tomography, and by light microscopy. The vestibular partition consisted of a rudimentary vestibule with agenesis of the SCCs. The cochlea was hypoplastic with poor or deficient interscaling and shortened (Mondini dysplasia). The organ of Corti had near normal structure and innervation. Modiolus and Rosenthal's canal were hypoplastic with perikarya displaced along the axon bundles into the internal acoustic meatus, which may be explained by the arrest or limited migration and translocation of the cell nuclei into the cochlear tube during development.