Epigenetic Modification of Klotho Gene in Uremic Milieu – from Initial Insults, Progression to Ion Transport in Renal Epithelial Cells

Chronic kidney disease (CKD) is a major problem in Taiwan. The CKD is characterized with progressive nature, even the recovery of primary disease. The progressive nature mimics an accelerating premature aging. Epidemiological data showed that biological age was often older than chronological age in these patients. It is still unknown whether this biological aging process correlates with the alteration of interior environment in CKD patients a specific molecular mechanism. klotho gene is an anti-aging gene. Genetic mutation of klotho causes premature aging-like phenotypes and shortens lifespan. Overexpression of the klotho gene suppresses aging and extends lifespan. Human klotho is primarily expressed in distal tubular epithelial cells of kidney where klotho plays an important role in calcium and phosphate transport. Renal ischemia, hyperglycemia, and inflammatory processes are 3 major primary renal insults, which lead to CKD. It is likely that the initial events have a determined effect on the target gene, klotho, and press the “Go” button for the premature aging. Progression of renal failure is associated with the accumulation of many toxic metabolites and substances, which are normally secreted or metabolized by kidney. It is likely that these changes in interior milieu will modify specific gene expression via epigenetic mechanism. Growing evidence has shown the CKD patients have a decreasing expression of klotho gene and increase total DNAmethylation. The question arises whether the initial renal injury and/or alteration of interior milieu caused by CKD will modify the expression of the klotho, via an epigenetic modification. We hypothesize firstly that initial renal injury/uremic substances will modify the expression of klotho gene. Secondly, the modification may via the methylation of klotho gene. Thirdly, the methylation and alteration of klotho gene may affect the specific signaling pathway and calcium-phosphate transport activity, which may initiate a cascade of progression of renal failure. In the study, we will firstly establish 3 animal models of renal ischemia, hyperglycemia, and inflammation to demonstrate the alteration of klotho expression in renal injury animals. We then establish cultured cell models, which expresses klotho and major transport mechanisms. We will then test the effects of different groups of known uremic toxins, namely phosphorus as small water-soluble compound, p-cresol and indoxyl sulfate as protein-bound compounds, and parathyroid hormones and AGEs as middle molecular compounds, on the expression of klotho and transporter. We will further examine the effect of these known toxic substances on the methylation of klotho gene. The responding signal transduction pathway will be also examined. These mechanisms are important in understanding whether initial renal injury and subsequent uremic milieu may affect the function of renal epithelial cells and possibly lead to systemic effects. The fulfillment of the proposal will greatly enhance our knowledge of epigenetic related kidney injury and form a solid basis to develop possible measurement to stop the progression of clinical chronic kidney disease.

Project ID:PC10101-1476
External Project ID:NSC99-2314-B182-004-MY3