Development and Diseases of the Collecting Duct System

Abstract

The collecting duct of the mammalian kidney is important for the regulation of extracellular volume, osmolarity, and pH. There are two major structurally and functionally distinct cell types: principal cells and intercalated cells. The former regulates Na⁺ and water homeostasis, while the latter participates in acid-base homeostasis. In vivo lineage tracing using Cre recombinase or its derivatives such as CreGFP and CreER^T2 is a powerful new technique to identify stem/progenitor cells in their native environment and to decipher the origins of the tissue that they give rise to. Recent studies using this technique in mice have revealed multiple renal progenitor cell populations that differentiate into various nephron segments and collecting duct. In particular, emerging evidence suggests that like principal cells, most of intercalated cells originate from the progenitor cells expressing water channel Aquaporin 2. Mutations or malfunctions of the channels, pumps, and transporters expressed in the collecting duct system cause various human diseases. For example, gain-of-function mutations in ENaC cause Liddle's syndrome, while loss-of-function mutations in ENaC lead to Pseudohypoaldosteronism type 1. Mutations in either AE1 or V-ATPase B1 result in distal renal tubular acidosis. Patients with disrupted AQP2 or AVPR2 develop nephrogenic diabetes insipidus. A better understanding of the function and development of the collecting duct system may facilitate the discovery of new therapeutic strategies for treating kidney disease.

Figure 1.. Loss of H3m2K79 is observed in the intercalated cells in Dot1l^AC mice.

Kidney sections from Dot1l^f/f and Dot1l^f/f Aqp2Cre (Dot1l^AC) were subjected to double immunofluorescence staining with a rabbit antibody specific for dimethyl histone H3 K79 (H3m2K79) to determine the functional status of Dot1l and a goat antibody recognizing V-ATPase subunits B1 and B2 to identify the intercalated cells. H3m2K79 was robustly detected in all intercalated cells in Dot1l^f/f mice, but undetectable in the most of intercalated cells in Dot1l^AC mice. Hence, Cre-mediated inactivation of Dot1l driven by Aqp2 promoter in the Aqp2Cre transgene occurs in the intercalated cells, indicating that Aqp2 promoter is activated in the intercalated cells during development. Arrow and arrowhead: Cells with abolished or intact H3m2K79, respectively. These cells were amplified in the inserts. Scale bar: 50 μM and 16.3 μM for insert.

Figure 2.. Loss of H3m2K79 in the intercalated cells of Dot1l^AC mice is not due to promiscuous expression of Cre expression.

Kidney sections from Dot1l^AC were subjected to double immunofluorescence staining with a rabbit antibody specific for Cre recombinase to detect constant and constitutive expression of Cre and the goat antibody recognizing V-ATPase subunits B1 and B2 to identify the intercalated cells. Cre is robustly detected in B1B2⁻ tubular cells, which are principal cells that have constant and constitutive Aqp2 expression. However, Cre is undetectable in the intercalated cells, suggesting that Aqp2 promoter is silenced after the Aqp2⁺ progenitor cells are differentiated into the intercalated cells during development. Arrow: B1B2⁺Cre⁻ (Intercalated cells). Arrowhead: B1B2⁻Cre⁺ (Principal cells). Boxed area is magnified and shown at the bottom. Scale bar: 50 μM (top) and 16.3 μM (bottom).