Potential Role of H-Ferritin in Mitigating Valvular Mineralization

Abstract

Objective— Calcific aortic valve disease is a prominent finding in elderly and in patients with chronic kidney disease. We investigated the potential role of iron metabolism in the pathogenesis of calcific aortic valve disease. Approach and Results— Cultured valvular interstitial cells of stenotic aortic valve with calcification from patients undergoing valve replacement exhibited significant susceptibility to mineralization/osteoblastic transdifferentiation in response to phosphate. This process was abrogated by iron via induction of H-ferritin as reflected by lowering ALP and osteocalcin secretion and preventing extracellular calcium deposition. Cellular phosphate uptake and accumulation of lysosomal phosphate were decreased. Accordingly, expression of phosphate transporters Pit1 and Pit2 were repressed. Translocation of ferritin into lysosomes occurred with high phosphate-binding capacity. Importantly, ferritin reduced nuclear accumulation of RUNX2 (Runt-related transcription factor 2), and as a reciprocal effect, it enhanced nuclear localization of transcription factor Sox9 (SRY [sex-determining region Y]-box 9). Pyrophosphate generation was also increased via upregulation of ENPP2 (ectonucleotide pyrophosphatase/phosphodiesterase-2). 3 H-1, 2-dithiole-3-thione mimicked these beneficial effects in valvular interstitial cell via induction of H-ferritin. Ferroxidase activity of H-ferritin was essential for this function, as ceruloplasmin exhibited similar inhibitory functions. Histological analysis of stenotic aortic valve revealed high expression of H-ferritin without iron accumulation and its relative dominance over ALP in noncalcified regions. Increased expression of H-ferritin accompanied by elevation of TNF-α (tumor necrosis factor-α) and IL-1β (interleukin-1β) levels, inducers of H-ferritin, corroborates the essential role of ferritin/ferroxidase via attenuating inflammation in calcific aortic valve disease. Conclusions— Our results indicate that H-ferritin is a stratagem in mitigating valvular mineralization/osteoblastic differentiation. Utilization of 3H-1, 2-dithiole-3-thione to induce ferritin expression may prove a novel therapeutic potential in valvular mineralization.

Hydrogen sulfide inhibits aortic valve calcification in heart via regulating RUNX2 by NF-κB, a link between inflammation and mineralization

“…In apolipoprotein E deficient mice kept on high-fat diet valvular calcification appears [3] and that is accompanied by valvular inflammation ( Fig. 1 ) as it was earlier revealed in CAVD [30] . Since in our in vitro experiments H 2 S inhibited nuclear translocation of both NF-κB and Runx2, and translocation of Runx2 was shown to be dependent on NF-κB, we examined their localization in aortic valves of ApoE -/- mice kept on a high-fat diet with or without administration of AP72.…”

“…Upregulation of Runx2 was identified to be a maladaptive response during injury to the vasculature, in uremic milieu, and hyperglycemic conditions [42] and was suggested to be both a mediator and a potential therapeutic target in vascular mineralization [43] . In our previous studies [3] , [30] and others’ [3] , [14] , [30] , [41] , [42] Runx2 was found to be manifested in the nucleus of valvular tissue cells in CAVD indicating the presence of an early signal for transformation of valvular interstitial cells into osteoblast-like cells.…”

“…Increasing number of evidences indicates the key role of osteogenic transcription factor Runx2 in cardiovascular calcification including CAVD [3] , [14] , [30] , [40] , [41] . For instance, the increase in intracellular phosphate level promotes nuclear translocation of Runx2 resulting in transition of cells towards an osteoblast phenotype [14] .…”

Ferritin in Kidney and Vascular Related Diseases: Novel Roles for an Old Player

“…In this study we showed that the induction of FtH was associated with the decreased osteoblastic activity of valvular interstitial cells. This inhibitory effect was attributed to the reduced nuclear accumulation of cbfa-1, and as a reciprocal effect, its enhancement of the nuclear localization of transcription factor Sox9 (SRY [sex-determining region Y]-box 9) [127]. These findings provide additional support to previous observations that identified reduced Sox9 function as a potential culprit of calcific valvular disease [128] and further corroborate the “anti-osteoblastic activity” of FtH.…”

“…More recently, similar inhibitory effects in mitigating the calcification of valvular tissues were demonstrated [127]. Valvular calcification and stenosis (particularly aortic valve) is a common finding in patients undergoing dialysis and the elderly population.…”