Question:

24p3 (Neutrophil Gelatinase-associated Lipocalin/lipocalin-2) has recently emerged as a novel sensitive biomarker of kidney injury and has been implicated in tissue repair and regeneration. We have recently shown that its receptor, 24p3R, is expressed in rodent distal nephron, including collecting duct cells of the inner medulla (IMCD) where it contributes to protein endocytosis (Langelueddecke C. et al. J. Biol. Chem. 287:159-169, 2012). IMCD cells are exposed in vivo to osmotic stress, which requires an adaptive response for survival. Here we investigated expression of 24p3 and 24p3R in cultured mouse IMCD (msIMCD3) and rat primary IMCD cells, which were cultured in 300 - 900 mOsm/kg for 1-6 days.

Methods:

Hypertonicity was induced by NaCl + urea. Expression was measured by qRT-PCR, immunoblotting, ELISA and immunofluorescence microscopy, and cell proliferation by MTT assay.

Results:

Hypertonicity decreased both 24p3 mRNA and 24p3 protein secretion in cell supernatants, but increased 24p3R mRNA and protein expression as well as plasma membrane localization in msIMCD3 and primary cells. These changes were associated with increased Wnt5a and β-catenin mRNA in msIMCD3 cells, suggesting involvement of the canonical Wnt/β-catenin signalling pathway. However, hypertonicity decreased cell proliferation and was accompanied by suppression of the cell proliferation genes c-myc and cyclin-D1, which may reflect cellular damage.

Conclusions:

Osmotic stress decreases proliferation of IMCD cells and affects expression of 24p3 and its receptor inversely. The role of Wnt/β-catenin signaling and the significance of 24p3/24p3R in adaptation to osmotic stress in IMCD cells remain to be determined.

Funding: DFG TH345/11-1.