#2215 Early molecular and cellular features of aortic remodeling in a mild CKD-MBD model with low bone turnover

Abstract

Abstract Background and Aims Vascular calcification associated with a maladaptive bone response is common in CKD and is a major cause of mortality (up to 60% depending on CKD stage). Alterations in several intracellular signaling pathways have been reported during the cellular phenotype transition and vascular calcification, however the initial phases of vascular remodeling in early CKD-MBD remain poorly understood. The aim of this study was to investigate the early molecular and cellular features of aortic remodeling prior to calcification in a model of mild CKD-MBD with low bone turnover. Method We induced CKD-MBD by 3/4 nephrectomy (Nx, n = 8) in adult male spontaneously hypertensive rats (SHR) with normal phosphate (Pi) intake (0.6%). Controls were sham-operated Wistar rats (n = 8) and SHR (n = 8). Chronic kidney injury and Pi exchange parameters, serum levels of calciprotein particles (CPPs), intact PTH, intact FGF23, dickkopf-1 and sclerostin, static bone histomorphometry, aortic morphology (H&E, Masson's trichrome, calcein, von Kossa stain), CD31, aSMA, nestin, Col1a1, PDGFR-beta, PiT1, LGR4 and intracellular signaling molecules—phospho-ERK1/2, active (non-phospho) beta-catenin, Hes1, Gli1 were analyzed by IHC with quantitative morphometry and IF after 4 months. Confocal microscopy was performed at the Centre for Collective Use of the Pavlov Institute of Physiology, Russian Academy of Sciences (Zeiss LSM 710). Results The study found that Nx rats with chronic kidney injury comparable to human CKD S2 exhibited lower bone turnover (Fig. 1). The Nx group had higher serum levels of Pi and CPPs vs. control group, but there were no differences in Pi-regulatory factors (Figs 1, 2b). Additionally, the Nx group showed aorta remodeling, which was characterized by an increase in intima thickness, cellularity, and collagen accumulation in the medial layer (Figs 1, 2a). The histological parameters of intimal remodeling and perivascular fibrosis were found to be directly correlated with serum levels of Pi and CPPs. In Nx, there was a decrease in medial αSMA expression accompanied by an increase in phospho-ERK1/2, PiT1, nestin, Gli1, beta-catenin, dickkopf-1, and an decrease in Hes1 immunomorphological staining (Figs 1, 2a, c). αSMA-negative cells demonstrated the expression of osteogenesis-related molecules, such as phospho-ERK1/2 (Fig. 2a, c), and occasionally, RunX2 (Fig. 2a). Phospho-ERK1/2 and PiT1 were found to co-localize in Nx (Fig. 2c). Intimal remodeling was observed, characterized by increased beta-catenin and nestin expression (Fig. 2c). Conclusion In mild CKD-MBD with low bone turnover, early intimal and medial aortic remodeling was associated with higher serum Pi and CPPs levels, and upregulation of PiT1, ERK1/2. In addition, other signals likely related to osteogenesis (RunX2, LGR4) and regulation of vascular progenitor cells (Nestin, Wnt, Notch, Hedgehog) may be implicated.