A novel renal carbonic anhydrase type III plays a role in proximal tubule dysfunction

Abstract

Dysfunction of the proximal tubule (PT) is associated with variable degrees of solute wasting and low-molecular-weight proteinuria. We measured metabolic consequences and adaptation mechanisms in a model of inherited PT disorders using PT cells of ClC-5-deficient (Clcn5Y/-) mice, a well-established model of Dent's disease. Compared to cells taken from control mice, those from the mutant mice had increased expression of markers of proliferation (Ki67, proliferative cell nuclear antigen (PCNA), and cyclin E) and oxidative scavengers (superoxide dismutase I and thioredoxin). Transcriptome and protein analyses showed fourfold induction of type III carbonic anhydrase in a kidney-specific manner in the knockout mice located in scattered PT cells. Kidney-specific carbonic anhydrase type III (CAIII) upregulation was confirmed in other mice lacking the multiligand receptor megalin and in a patient with Dent's disease due to an inactivating CLCN5 mutation. The type III enzyme was specifically detected in the urine of mice lacking ClC-5 or megalin, patients with Dent's disease, and in PT cell lines exposed to oxidative stress. Our study shows that lack of PT ClC-5 in mice and men is associated with CAIII induction, increased cell proliferation, and oxidative stress.

Impaired Lysosomal Function Underlies Monoclonal Light Chain–Associated Renal Fanconi Syndrome

“…12,13 In addition to defective apical transport, abnormal proliferation is often observed in diseased PT cells. 13,24,33 Increased proliferation was consistently observed in kCH kidneys and mPTCs exposed to RFS-kLCs as indicated by the PCNA and cyclin-D1 markers and bromodeoxyuridine incorporation. Our data suggest the involvement of the Y-box transcription factor ZONAB, which is active during nephrogenesis and PT maturation.…”

“…Previous studies have shown that a delicate balance between factors involved in proliferation and others involved in differentiation operates in PT cells. 24 The balance can be defective, for instance, in cystinosis, where increased proliferation and dedifferentiation of PT cells are associated with abnormal activity of ZONAB caused by defective intercellular junctions. 13 This study does not provide a direct correlation between increased rate of proliferation and dedifferentiation of PT cells.…”

“…12 A defective expression of apical receptors may reflect imbalance between differentiation and proliferation. 13,24 Analyses of kCH kidneys revealed a marked increase in the expression of proliferative markers (proliferating cell nuclear antigen Pcna, Ccnd1, and Ybx3/ZONAB) ( Figure 2D) associated with nuclear translocation of PCNA and ZONAB ( Figure 2, E and F). Conversely, neither the expression nor the nuclear location of PCNA or ZONAB was consistently altered in kDE kidneys (Supplemental Figure 1, C and D).…”

In-depth phenotyping of a Donnai–Barrow patient helps clarify proximal tubule dysfunction

“…[3]), type 3 carbonic anhydrase (CAIII, from Ref. [8]) or Tamm-Horsfall protein (UMOD, from Ref. [15]).…”

“…Similarly to Dent's disease, genetic inactivation of Clcn5 in mouse induces a severe trafficking defect in PT cells, with loss of megalin and cubilin at the brush border and LMW proteinuria [7]. Furthermore, ClC-5 inactivation causes urinary excretion of type 3 carbonic anhydrase (CAIII) [8]. CAIII has been uniquely detected in the urine of ClC-5-or megalin-deficient mice and patients with Dent's disease.…”