#1515 Myocardial remodeling is associated with redistribution of phosphate, PIT1/ERK1/2 up-regulation and signaling pathways alterations in mild CKD model
Authors: Bogdanova Evdokia , Sadykov Airat , Beresneva Olga , Zubina Irina , Sharoyko Vladimir , Dobronravov Vladimir 
Published: May 2024

Abstract

Background and Aims
Patients with CKD have significantly increased cardiovascular risk, and heart failure is a leading cause of morbidity and mortality in these patients. Myocardial hypertrophy is a hallmark of cardiac remodeling and dysfunction in CKD and is known to be mediated by angiotensin II, catecholamines, hyperphosphatemia, hyperparathyroidism, increase in FGF23, decrease in Klotho and alterations in various signaling pathways including calcineurin, mitogen-activated protein kinase ERK1/2, calmodulin-dependent protein kinase II etc. Less well understood are the mechanisms of fibrosis and intramyocardial arterial remodeling in CKD, which may be related to hyperphosphatemia and decreased renal and systemic Klotho. The aim of this study was to evaluate the molecular and cellular features of myocardial remodeling in experimental mild CKD.

Method
We induced CKD by 3/4 nephrectomy (Nx) in adult male spontaneously hypertensive rats (SHR) with a follow-up period of 4 months. Animals were fed standard chow containing 0.6% phosphate. Sham-operated Wistar rats and SHR served as controls. We measured serum creatinine, renal interstitial fibrosis area, systolic blood pressure (BP), myocardial mass index (MMI), histological indices of myocardial hypertrophy, interstitial fibrosis and intramyocardial artery (IA) remodeling (H&E, Masson's trichrome, von Kossa stain), myocardial phosphorus content, serum levels of inorganic phosphate (Pi), PTH and FGF23. Myocardial expression of phosphate transporters PiT1, ERK1/2, WNT, BMP, Notch, Hedgehog signaling pathways and LRG4 molecules was evaluated by PCR-RT, IHC and IF (Zeiss LSM 710; study performed at the Centre for Collective Use “Confocal Microscopy” of the Pavlov Institute of Physiology, Russian Academy of Sciences).

Results
Chronic kidney injury and phosphate regulatory factors did not differ, whereas BP and MMI were higher in sham SHR vs. Wistar rats (Fig. 1). Nx rats showed features of mild chronic kidney injury before the elevation of serum PTH, FGF23 levels (Fig. 1). Myocardial P content and serum Pi were higher in Nx and in the combined SHR group and directly correlated with indices of IA remodeling. Cardiomyocyte diameter, myocardial interstitial and perivascular fibrosis were higher in Nx (Figs 1, 2a) and accompanied with upregulation in Ppp3ca mRNA (calcineurin A, Fig. 2b), Mapk1 mRNA (ERK2, Fig. 2b), phospho-ERK1/2 (Figs 1, 3), PiT1 (Figs 1, 2c), Lgr4 (Fig. 2c) and downregulation of Hes1 mRNA (Fig. 2b). PiT1 and pospho-ERK1/2 were co-expressed in IA media from SHR (Fig. 2c). In Nx, nestin and LGR4 were expressed by IA adventitia and media cells, myocardial interstitial cells, and occasionally co-localized (Fig. 2c). Hes1 expression was detected in IA and capillary endothelial cells and co-localised with Gli1 in IA media; Gli1 was also detected in cardiomyocyte nuclei (Fig. 2c). In SHR, beta-catenin expression in cardiomyocytes was more pronounced in Nx (Fig. 2c).

Conclusion
Mild CKD is associated with histological and molecular features of cardiomyocyte hypertrophy, myocardial fibrosis and intramyocardial arterial remodeling, which are probably modulated by phosphate redistribution and its tissue retention involving upregulation of PiT1 and ERK1/2, as well as alterations in signals related to progenitor regulation and myocyte hypertrophy.