Prolonged K deficiency increases intracellular ATP, cell cycle arrest and cell death in renal tubular cells.

BACKGROUND

Chronic potassium (K) deficiency can cause renal damage namely hypokalemic nephropathy with unclear pathogenic mechanisms. In the present study, we investigated expression and functional alterations in renal tubular cells induced by prolonged K deficiency.

METHODS

MDCK cells were maintained in normal-K (CNK) (K=5.3mmol/L), low-K (CLK) (K=2.5mmol/L), or K-depleted (CKD) (K=0mmol/L) medium for 10days (n=5 independent cultures/condition). Differentially expressed proteins were identified by a proteomics approach followed by various functional assays.

RESULTS

Proteomic analysis revealed 46 proteins whose levels significantly differed among groups. The proteomic data were confirmed by Western blotting. Gene Ontology (GO) classification and protein network analysis revealed that majority of the altered proteins participated in metabolic process, whereas the rest involved in cellular component organization/biogenesis, cellular process (e.g., cell cycle, regulation of cell death), response to stress, and signal transduction. Interestingly, ATP measurement revealed that intracellular ATP production was increased in CLK and maximum in CKD. Flow cytometry showed cell cycle arrest at S-phase and G2/M-phase in CLK and CKD, respectively, consistent with cell proliferation and growth assays, which showed modest and marked degrees of delayed growth and prolonged doubling time in CLK and CKD, respectively. Cell death quantification also revealed modest and marked degrees of increased cell death in CLK and CKD, respectively.

CONCLUSIONS

In conclusion, prolonged K deficiency increased intracellular ATP, cell cycle arrest and cell death in renal tubular cells, which might be responsible for mechanisms underlying the development of hypokalemic nephropathy.