Hydrogen sulfide as an anti-calcification stratagem in human aortic valve: Altered biogenesis and mitochondrial metabolism of H(2)S lead to H(2)S deficiency in calcific aortic valve disease

Hydrogen sulfide (H(2)S) was previously revealed to inhibit osteoblastic differentiation of valvular interstitial cells (VICs), a pathological feature in calcific aortic valve disease (CAVD). This study aimed to explore the metabolic control of H(2)S levels in human aortic valves. Lower levels of bioavailable H(2)S and higher levels of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) were detected in aortic valves of CAVD patients compared to healthy individuals, accompanied by higher expression of cystathionine γ-lyase (CSE) and same expression of cystathionine β-synthase (CBS). Increased biogenesis of H(2)S by CSE was found in the aortic valves of CAVD patients which is supported by increased production of lanthionine. In accordance, healthy human aortic VICs mimic human pathology under calcifying conditions, as elevated CSE expression is associated with low levels of H(2)S. The expression of mitochondrial enzymes involved in H(2)S catabolism including sulfide quinone oxidoreductase (SQR), the key enzyme in mitochondrial H(2)S oxidation, persulfide dioxygenase (ETHE1), sulfite oxidase (SO) and thiosulfate sulfurtransferase (TST) were up-regulated in calcific aortic valve tissues, and a similar expression pattern was observed in response to high phosphate levels in VICs. AP39, a mitochondria-targeting H(2)S donor, rescued VICs from an osteoblastic phenotype switch and reduced the expression of IL-1β and TNF-α in VICs. Both pro-inflammatory cytokines aggravated calcification and osteoblastic differentiation of VICs derived from the calcific aortic valves. In contrast, IL-1β and TNF-α provided an early and transient inhibition of VICs calcification and osteoblastic differentiation in healthy cells and that effect was lost as H(2)S levels decreased. The benefit was mediated via CSE induction and H(2)S generation. We conclude that decreased levels of bioavailable H(2)S in human calcific aortic valves result from an increased H(2)S metabolism that facilitates the development of CAVD. CSE/H(2)S represent a pathway that reverses the action of calcifying stimuli.