Osteopontin activity modulates sex‐specific calcification in engineered valve tissue mimics

Abstract

Patients with aortic valve stenosis (AVS) have sexually dimorphic phenotypes in their valve tissue, where male valvular tissue adopts a calcified phenotype and female tissue becomes more fibrotic. The molecular mechanisms that regulate sex‐specific calcification in valvular tissue remain poorly understood. Here, we explored the role of osteopontin (OPN), a pro‐fibrotic but anti‐calcific bone sialoprotein, in regulating the calcification of female aortic valve tissue. Recognizing that OPN mediates calcification processes, we hypothesized that aortic valvular interstitial cells (VICs) in female tissue have reduced expression of osteogenic markers in the presence of elevated OPN relative to male VICs. Human female valve leaflets displayed reduced and smaller microcalcifications, but increased OPN expression relative to male leaflets. To understand how OPN expression contributes to observed sex dimorphisms in valve tissue, we employed enzymatically degradable hydrogels as a 3D cell culture platform to recapitulate male or female VIC interactions with the extracellular matrix. Using this system, we recapitulated sex differences observed in human tissue, specifically demonstrating that female VICs exposed to calcifying medium have smaller mineral deposits within the hydrogel relative to male VICs. We identified a change in OPN dynamics in female VICs in the presence of calcification stimuli, where OPN deposition localized from the extracellular matrix to perinuclear regions. Additionally, exogenously delivered endothelin‐1 to encapsulated VICs increased OPN gene expression in male cells, which resulted in reduced calcification. Collectively, our results suggest that increased OPN in female valve tissue may play a sex‐specific role in mitigating mineralization during AVS progression.

Inflammatory serum factors from aortic valve stenosis patients modulate sex differences in valvular myofibroblast activation and osteoblast-like differentiation

“…6D †), corroborating previous work suggesting increased OPN expression may drive reduced osteoblast-like differentiation. 41 Cluster and pathway enrichment analyses of candidate proteins identify p38 MAPK signaling as a candidate pathway regulating myofibroblast activation…”

Sex as a Biological Variable in Tissue Engineering and Regenerative Medicine

“…As for valvular calcification, Gourgas et al (69) characterized mineral deposits of surgically excised calcified valves and found sex differences in mineral composition and morphology, suggesting that minerals formed more slowly in female valves and by a different mineralization pathway. Using a degradable hydrogel ECM mimic, Schroeder et al (73) showed that extracellular osteopontin mitigated calcification by female valvular interstitial cells and that elevated amounts of extracellular osteopontin could reduce calcification by male valvular interstitial cells. Elevated amounts of osteopontin in female valve tissues were suggested as a potential sex-specific mitigator of valvular calcification during disease progression (73).…”

“…Using a degradable hydrogel ECM mimic, Schroeder et al (73) showed that extracellular osteopontin mitigated calcification by female valvular interstitial cells and that elevated amounts of extracellular osteopontin could reduce calcification by male valvular interstitial cells. Elevated amounts of osteopontin in female valve tissues were suggested as a potential sex-specific mitigator of valvular calcification during disease progression (73). In vitro work has shown that matrix remodeling can also be sexually dimorphic, owing to differences in ECM and matrix metalloproteinase production (74,75).…”