Protective Cellular Mechanism of Estrogen Against Kidney Stone Formation: A Proteomics Approach and Functional Validation.

Females have less incidence/prevalence of kidney stone disease than males. Estrogen thus may serve as the protective factor but with unclear mechanism. This study explores cellular mechanism underlying such stone preventive mechanism of estrogen. Madin darby canine kidney (MDCK) renal tubular cells are incubated with or without 20 nm 17β-estradiol for 7 days. Comparative proteomics reveals 58 differentially expressed proteins in estrogen-treated versus control cells that are successfully identified by nanoLC-ESI-Q-TOF-MS/MS. Interestingly, these altered proteins are involved mainly in "binding and receptor," "metabolic process," and "migration and healing" networks. Functional investigations demonstrate reduction of calcium oxalate (CaOx) crystal-binding capability of the estrogen-treated cells consistent with the decreased levels of annexin A1 and α-enolase (the known CaOx crystal-binding receptors) on the cell surface. High-calcium and high-oxalate challenge initially enhances surface expression of annexin A1 and α-enolase, respectively, both of which return to their basal levels by estrogen. Additionally, estrogen reduces intracellular ATP level and promotes cell migration and tissue healing. Taken together, estrogen causes changes in cellular proteome of renal tubular cells that lead to decreased surface expression of CaOx crystal receptors, reduced intracellular metabolism, and enhanced cell proliferation and tissue healing, all of which may contribute, at least in part, to stone prevention.