MO566THE BONE EXPRESSION OF WNT INHIBITORS IN THE EXPERIMENTAL MODEL OF EARLY CHRONIC KIDNEY DISEASE

Abstract

Abstract Background and Aims Molecular mechanisms implicated in the initial stages of inorganic phosphate (Pi) imbalance in chronic kidney disease (CKD) remain poorly understood.The aim of the study was to evaluate whether canonical Wnt pathway inhibitors (iWnt) involved in early response to Pi retention in CKD. Methods Mild CKD was induced by 3/4 nephrectomy (NE) in spontaneously hypertensive rats (SHR) fed rat chow diet containing 0.6 % phosphate. Controls were sham operated SHR (SO). Duration of experimental exposure (NE or SO) was 2 and 6 months. Serum levels of creatinine (Cr), inorganic phosphate (Pi), fractional Pi excretion (FEPi), intact parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), alfa-Klotho (KL), sclerostin (SOST) and Dickkopf-1 (DKK1) were measured. The following morphological characteristics by light microscopy of bone metaphysis and kidney tissues: the area of renal interstitial fibrosis (RF) (Masson's trichrome), bone matrix volume (MV), the active osteoblasts to trabecular cells number ratio (aOB/cells), eroded surface to bone surface ratio (ES/BS) (hematoxylin & eosin), and bone SOST and DKK1 proteins expression (by IHC) were analyzed and calculated quantitatively. Statistical comparisons among groups were performed using Mann–Whitney U-test and Kruskal-Wallis H-test. Results Serum Cr, RF and indices of Pi exchange in the experimental model corresponded to early CKD (Table). Pi elevated in NE6 suggestive for its renal retention. KL level decreased (Table) in all experimental groups vs control. No differences were observed in serum levels FGF23 (p=0.62) and PTH (p=0.63). Serum SOST and DKK1 levels were significantly higher in NE6 group compared to SO6 (Table). The bone SOST and DKK1 expression increased in NE6 compared to SO6 (Figure). aOB/cells were lower in NE2, SO6 and NE6 vs SO2 (all p-values<=0.041). ES/BS increased in NE2 (vs SO2) while being lowest in NE6 and SO6 animals (Table). SOST and DKK1 metaphyseal expression increased in NE6 compared to SO2, SO6, NE2 (Figure). Osteocyte SOST expression increased in SO6 compared to SO2 and NE2 without differences in later groups. Osteoblast SOST expression was also higher in SO6 vs SO2 (Figure). Conclusion Increased serum levels of sclerostin and Dickkopf-1 and their bone expression are apparent in early stages of experimental CKD associating with hyperphosphatemia. Alterations of bone resorption and osteoblast depopulation occurred before the increase of serum Pi likely reflecting incipient stages of renal Pi retention. These molecular and cellular events seem to be independent of systemic FGF23 and PTH response.